NOAA Technical Report NMFS 129 April 1997

The History, Present

Condition, and Future

of the Molluscan Fisheries

of North and Central

Atnerica and Europe

Volutne 3, Europe

Edited by

Clyde L. MacKenzie,Jr.

Victor G. Burrell,Jr.

. Aaron Rosenfield

Willis L. Hobart

u.s. Department of Commerce
U.S. DEPARTMENT

OF COMMERCE

WILLIAM M. DALEY

SECRETARY

National Oceanic and

Atmospheric Administration

D.James Baker

Under Secretary for

Oceans and Atmosphere

National Marine

Fisheries Service

Rolland A. Schmitten

Assistant Administrator

for Fisheries

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The NOAA Technical Report NMFS series of the Fishery Bulletin carries peer-reviewed, lengthy original research reports, taxonomic keys, species synopses, flora

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NOAA Technical Report NMFS 129

A Technical Report of the Fishery Bulletin

The History, Present Condition, and

Future of the Molluscan Fisheries of

North and Central A:m.erica and Europe

Volu:m.e 3, Europe

Clyde L. MacKenzie, Jr.

Victor G. Burrell, Jr.

Aaron Rosenfield

Willis L. Hobart (editors)

April 1997

u.s. Department of Commerce

Seattle, Washington
On the cover

An early etching of oysters of varying ages attached to a block of wood, circa

1880's, courtesy of W. L. Hobart.

Suggested reference

C. L. MacKenzie,jr., V. G. Burrell,jr., A Rosenfield, and W. L. Hobart

(eds.). 1997. The history, present condition, and future of the molluscan fisheries of North and Central America and Europe, Volume 3, Europe. U.S. Dep.

Commer., NOAA Tech. Rep. 129, 240 p.

Note

Volumes I and 2 are scheduled for publication later in 1997.

Purchasing additional copies

Additional copies of this report may be purchased from the Superintendent of

Documents, U.S. Government Printing Office, P.O. Box 371954, Pittsburgh,

PA 15250-7954; 202-512-1800. The report is also available for purchase in

paper copy or microfiche from the National Technical Information Service,

5285 Port Royal Road, Springvfield, VA 22161.

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used or purchased because of this NMFS publication.
CONTENTS _

J. HAMMER

O. STRAND

J. H. V0LSTAD

P. S. KRISTENSEN

H. EIRlKSSON

A NICOLAJSEN

M. N. L. SEAMAN

M.RUTH

E. EDWARDS

F. REDANT

R. DIJKEMA

P. GOULLETQUER

M.HERAL

CACERES-MARTINEZ,J.

A FIGUERAS

F. D. L. RUANO

N. MATTEI

M. PELLIZZATO

A BENOVIC

AALPBAZ

B. TEMELLI

Y. STAYKOV

The Mussel Industry of Sweden

The Molluscan Fisheries and Culture of Norway

Oyster and Mussel Fisheries in Denmark

The Molluscan Fisheries of Iceland

The History of the Queen Scallop Fishery of the Faroe Islands

The Molluscan Fisheries of Germany

Molluscan Fisheries in Britain

The Belgian Mollusk Fisheries

Molluscan Fisheries and Culture in the Netherlands

Marine Molluscan Production Trends in France:

From Fisheries to Aquaculture

The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain

Fisheries and Farming of Important Marine Bivalves in Portugal

Mollusk Fisheries and Aquaculture in Italy

The History, Present Condition, and

Future of the Molluscan Fisheries of Croatia

A Review of the Molluscan Fisheries of Turkey

Mollusk Fisheries in Bulgaria

7

25

39

49

57

101

115

137

165

191

201

217

227

233

III

The Mussel Industry of Sweden

JOELHAAMER

Fishery Board

Coastal Laboratory

Hus 31, S42671, Vastra

Frolunda, Sweden

ABSTRACT

Sweden farms blue mussels, Mytilus edulis, on a small scale. The Swedish system consists of

longlines supported by buoys and uses as mussel collectors 5 cm wide x 8 m long woven

strips of polypropylene with edges of terylene silk. The fishery and farming of other

mollusks are negligible.

Introduction Historical Use of Mussels

Sweden has a small mollusk fishery consisting of the

farming ofthe blue mussel, Mytilus edulis, on suspended

longlines. The industry began experimentally in 1971,

and through the 1970's and 1980's it produced commercial quantities of mussels (Fig. 1, Table 1). The

fishery and farming of other mollusks than mussels is

negligible, though several attempts have been made to

farm flat oysters, Ostrea edulis.

Mussel farming was not stimulated by demand for

mussels as either fish bait or for the canning industry,

but rather because of the discovery that mussels could

be farmed in Sweden. The mussel industry has developed slowly in Sweden because the home demand for

mussels is small, industry and investors have had little

interest in it, and diarrhetic shellfish poisoning (DSP)

has become frequent since 1984 and prevents mussel

harvests for long periods of the year.

Table 1

The mussel harvest in Sweden, 1983-1991, and export

data from 1988 onward in metric tons (wet weight).

Blue mussel shells have been found in kitchen middens at

Rottjarnslid located about 100 km north of Goteborg.

They are dated at about 5,000 B.C. The middens also

contained shells of flat oysters, Ostrea edulis, and cockles,

Cardium edule, fish bones, and fish hooks. It is impossible

to tell whether the mussels were used as bait or food.

Before World War II, mussels were used mostly as bait in

the longline fishery. People in fishing areas did not eat mussels, but they were eaten to a small extent by people in cities.

About 300 t/year were canned for human consumption.

During World War II, a shortage of fish led to an

increase in mussel consumption. People harvested mussels mostly by hand from small boats. In 1945, 973 t of

mussels were landed. Between then and 1970, mussel

landings stabilized at about 500 t/year. In 1970, Swedish production of canned mussels ceased due to competition from low-priced mussels imported from Denmark.

From 1937 to 1984, no interruptions in mussel harvests

were noticed due to toxic mussels being eaten.

Development of Mussel Fanning

Year Hal>'est

1983 1,498

1984 1,278

1985 415

1986 325

1987 2,566

1988 858

1989 241

1990 1,163

1991 1,643

Exports

387

81

1,016

1,288

The idea of growing mussels on longlines stemmed

from observations in 1966 that mussels set heavily and

then grew well from the sea surface down to a depth of

20 m on a mooring for hydrographic instruments. The

observations led to the establishment of experimental

farms in a sheltered coastal area at the island ofSmaget,

10 km south ofStromstad on the Swedish western coast.

The farming method used in Sweden involves

longlines supported by buoys (Fig. 2). An important

1
2 NOAA Technical Report NMFS 129

issue when the Swedish farms began was minimization

ofthe amount oflabor involved as workers in Sweden at

that time (1971) had much higher wages than competing mussel growers in southern Europe. Investment

costs also had to be small because Swedish industry and

investors had only a mild interest in mussel farming.

The Swedish longline farming unit usually has 10

parallel wires about 200 m long connected at both ends

to a 10 m perpendicular rail. The wires are 16 mm in

diameter, galvanized, and are surrounded by polypropylene rope. Plastic barrels, 200 I in size, are attached to

the wires as buoys. Woven strips of polypropylene with

edges of terylene silk are used as mussel collectors. The

strips are 5 cm wide and 8 m long.

Under natural conditions in the wild, mussel larvae

set mainly on algal filaments such as green algae and

diatoms (Bohle, 1971; Bayne, 1976). The terylene silk

on the edg-es of the strip collectors is a good substitute

for algal filaments and the mussels spat initially prefer

to attach to the edges. The spat later creep over the entire

surface of the strips where they settle permanently.

The strips can be deployed quickly in the spring ard

retrieved quickly at harvest. A rapid installation in the

spring enables farmers to install the strips at the right

time when mussel larvae are the dominant settling species in the water.

When the strips are deployed during the 2-3 weeks of

maximum setting of mussel larvae, about the only species

on the strips is mussels. One meter ofstrip can hold about

10 kg of harvestable mussels. With new mechanized harvesters available, two men can harvest about 30 t ofmussels/day.

Fanning Strategy

Mussels spawn on the Swedish coast when the water temperature reaches about 10°C in late May. By midJune, the

0----+---\---+----+--+----159oN

~---+--)-+---__+__--158°30'

r-~---t-+----158°

mussel larvae are ready to settle. Mussel farmers follow

development of the larvae, and when they are close to

settling the strips are deployed. The settling period lasts

about three weeks. One worker can deploy from 5,000 to

10,000 m ofstrips/day, provided the wires in the longline

system are anchored at the selected site in advance and

the strips are prepared with weights and fixing threads.

When the settlement (Fig. 3) is heavy with 20,000-

40,000 spat/m, most of the spat leave the strips by

Figure 2

The Swedish longline system with the dimensions 10 x 200 m. The longlines can carry

20.000 m of farming strips with a production capacity of about 200 t in 2 years. The

mussel operation consists of 10 wires about 200 m long, supported by buoys 200 I in size, and

polypropylene strips 5 cm wide and 8 m long. The mooring is made with two 10 m long rails

and four 200 kg anchors.
_____________________________ Haamer: The Mussel Industry of Sweden 3

Figure 3

Mussel strip, 5 cm wide, with recently set spat. Match shows relative size of the spat. Photograph byJ. Haamer.

themselves when they are small. Most of the small mussels fall to the bottom where they are eaten by starfish,

crabs, and fish, or are buried in mud that can be anoxic. In early tests, manual thinning and replanting of

small mussels was tried, but was found to be too costly.

About 600 adult mussels remain on each strip at the

end of the growing season.

The only work carried out between the deployment

of collectors and harvest is to add new buoys for increased buoyancy during the mussel growing period.

Farmers do not deploy all the buoys to the wires at the

beginning so as to reduce wearing of the equipment.

The average mussel farm has a production capacity of

150-200 t and occupies 2,000 m2.

Predators and Fouling

The main mussel predators are starfish, ASlerias rubens,

and eider ducks, Somaleria mollissima. Starfish larvae can

settle on the strips and feed on the mussels, and when

numerous, can clean the mussels off the strips. Locations with strong currents and wave action suffer less

starfish predation than calm areas, because starfish tend

to fall off the strips when agitated. The only method

thus far used to get rid of the starfish is to shake the

strips vigorously by a diver or by a boat using a crane.

Eider ducks are common on the west coast ofSweden

and number about 60,000 in the mussel farming area.

Individual eider ducks eat about 2.5 kg/day, mainly

mussels. Several methods have been used to prevent

the eiders from eating the farmed mussels which they

prefer over wild mussels, probably because they have thinner shells. Methods tried, such as hunting, automatic gas

guns, submarine sound buoys, and eagle sound, all failed.

Several farmers had to give up because of the eiders.

Underwater studies showed the eiders use their wings

to swim and stay down. To obstruct their swimming in

the farms, wires and strips were placed closer together.

The distance between wires did not exceed 1 m and

between strips, 0.5 m. In using this method, the eiclers

can eat only from the outer parts of a farm.

The main fouling organisms on the mussels are the

ascidian Ciona inleslinalis and the polychaete Pomaloceros

lriqueler. The ascidian can become clominant on the

strips because it grows faster than mussels. The problem is most severe in areas where currents are weak.

Pomaloceros larvae settle on the shells of older (>2 years
4 NOAA Technical Report NMFS 129

Figure 4

A simplified drawing of the Swedish mussel harvester and a ship-borne

cleaning system, designed for longline operations. The harvester is going

backward and the mussel strips are loosened by the man standing in the

box at the stern of the boat. The mussel clusters are brought up from the

water with a submerged conveyor. The farming strips are separated from

the mussels half way up the conveyor. On the upper end, the mussels

drop into the separator/cleaner. The separator/cleaner takes the mussels to storing sacks as well.

old) mussels and cause problems in the cleaning process if the mussels are packed for the fresh market. The

strategy to avoid fouling problems is to choose farming

areas where these organisms are less common.

Harvesting

A continuous harvesting method has been developed for

the longline system (Fig. 4). Several boats with harvesting

devices have been designed. At harvest, the longline wires

are lifted onto a power block at the edge of the stern 1 m

above the water surface. The wire runs parallel to the boat

and the boat runs backward. One man loosens the strips

from the wire at the same time as a conveyor catches the

strips with musselsjust under the water surface and brings

them to the cleaning machines. Another conveyor delivers the cleaned mussels into big sacks.

The mussel clusters are brushed off the strips, which

are used again. Cleaning equipment for the thin-shelled

farm mussels was developed in Sweden in 1983. Brushes

are attached to two parallel moving belts. The mussel

clusters are brushed from above, and breakage was less

than 5%. A harvester with a crew of two can harvest 15-

40 t of mussels/day.

Strategies and Life Story of a Mussel

Industry, 1979-1984

In 1979, when farming and harvesting equipment had

been developed, a new company, Mussellina AB1, was

established to exploit farmed mussels based on this new

1 Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA.
___________________________ Haamer: The Mussel Industry of Sweden 5

technique. The company was formed by people from

industry and from a university where mussel research

and development had been conducted since 1975.

The main objectives of the company were to:

1) Work with mussels year-round,

2) Develop new mussel products based on high quality

raw material and to create a market for the products,

3) Farm half of the mussels needed for the production

within the company and buy the other half from

contracted farmers,

4) Continue with research and development work and

follow the development abroad, and

5) Establish shellfish quality control in Sweden to obtain public confidence in the products.

The new mussel products were frozen. This was new

for the Swedish market. Three IQF (individually quick

frozen) mussel products were produced: boiled mussel

meat, breaded mussel meat, and mussels in the shell. A

smaller amount of fresh mussels, cleaned and packed

in 1 kg net bags was produced. The IQF mussel meat

was well received by restaurants, which previously had

access only to canned mussels.

The marketing strategy for all the products was initially to concentrate on the catering market. The intention was not to introduce the products on the consumer

market from the beginning. Without heavy marketing

efforts, there is always the risk that unknown frozen products will remain too long in shop freezers and deteriorate.

The company went bankrupt in 1984 because of 1)

costly trials trying to enter the consumer market and 2)

the absence of a shellfish toxicity control program in

Sweden at the time. When Musselina went bankrupt,

the farms were not harvested. Many mussel farms were

abandoned and became a nuisance to local governments.

Because ofthis, it is now more difficult to obtain a farming

permit, and there must be a bank guarantee for financing

the removal of the mussel farm if anything goes wrong.

When the company started after 8 years of experimental farming on the Swedish coast, there had been

no known observations of DSP or paralytic shellfish

poisoning (PSP) there. The management of the company was well aware of the risks of algal toxins, and for

this reason it tried to engage food control authorities in

toxic algal control. The local food control laboratory

made only mouse tests when the company needed export licenses. In September 1984, DSP was found in the

mussels and production stopped. After the company

went bankrupt and closed, its processing machinery

was sold to Ireland.

In 1983, DSP was observed among people consuming

mussels. For that reason, a surveillance system to detect

DSP toxins in mussels was begun in 1986. The DSP

toxin is the phycotoxin okadaic acid produced by

Dinophysis spp. (Edebo et aI., 1988). Higher DSP toxin

concentrations were found in mussels from the outer

archipelago than in mussels from more sheltered waters. The seasonal variation in the less sheltered waters

often showed a maximum of DSP toxins in the autumn

when toxic dinoflagellates were abundant. However,

during the spring blooms, normally dominated by diatoms, the toxin disappeared from the mussels.

The mussel harvests in Sweden declined afterward.

In 1987, it had a temporary recovery due to harvest of

old farms. But the prices for mussels >3 years old were

too low to motivate farmers to put out new collectors.

The main consequence of the bankruptcy was that

the first wave of enthusiasm for mussel farming faded,

and it became difficult to attract new people and capital to mussel farming and processing. The number of

farming enterprises declined rapidly from the year 1987

when there were 24 enterprises with a farming area of

294,000 m2, to 8 enterprises with an area of 112,600 m2

in 1992. In 1993, the mussel industry in Sweden employed about 10 people. Most mussels now produced in

Sweden are exported (Table 1).

The Future

There likely will be a future for the mussel industry in

Sweden. The technique for longline farming is functioning on an industrial scale, the control of shellfish

toxicity is established with scientific backing, and the

finding offarming areas without toxic alga problems all

suggest that the Swedish mussel farmers will survive.

Aclmowledgements

The drawings were made by Terrence FIorell. This chapter is abstracted from two previous papers by Joel

Haamer: 1) Strategies for mussel (Mytilus edulis) farming in Sweden including larvae catching, growing, predation control, shellfish toxicity control, harvesting and

marketing, 23 p., and 2) Presence of the phytotoxin

okadaic acid in mussels (Mytilus edulis) in relation to

nutrient composition in a Swedish coastal water, 23 p.

Both appeared in a bulletin edited by the author, entitled "Phycotoxin and oceanographic studies in the development ofthe Swedish mussel farming industry," Earth

Sciences Center, Goteborg University, Pub!. A4, 1995.

Literature Cited

Bayne, B. L. (ed.)

1976. Marine mussels, lheir ecology and physiology.1nl. BioI.

Programme 10, Cambridge Univ. Press, London.
6 NOAA Technical Report NMFS 129

Bohle, B.

1971. Settlement of mussel larvae Mytilus edulis on suspended

collectors in Nor>Vegian waters. In D.J. Crisp (ed.), Fourth

European Marine Biology Symposium, Cambridge Univ.

Press, London.

Edebo, L., S. Lange, X. P. Li, S. A11enmark, K. Lindgren, and

R. Thompson.

198H. Seasonal, geographic and individual variations of

okadaic acid content in cultivated mussels in Sweden. APMIS

96: 1,U36-I,042.
The Molluscan Fisheries and Culture of Norway

0IVI D STRAND*

Department ofFisheries and Marine Biology

University of Bergen

H~yteknologisenteret

N-5020 Bergen, Norway

JON HELGE V0LSTAD**

Institute ofMarine Research

p. O. 1870 Nordnes

N-5024 Bergen, Norway

ABSTRACT

In coastal Norway, mollusks important for food or bait include the northern horse mussel,

Modiolus modiolus; blue mussel, Mytilus edulis; Iceland scallop, Chlamys islandica; great scallop, Pecten maximus; ocean quahog, Arctica islandica; and to a lesser extent, Cardium sp., and

the softshell clam, Mya arenaria. The Pacific oyster, Crassostrea gigas, and Manila clam,

Ruditapes philippinarnm, were introduced in recent years. The iceland scallop also is harvested offshore. The first gear documented for harvesting mollusks may have been an iron

rake in 1773. Fishermen later used various types of grabs and dredges. In early times,

mussels were generally used as food, but they were, in more recent times, commonly used as

bait for fish. The flat oyster was used for food in southern Norway until the beds became

depleted in the mid-1800's. Oyster seed after that was grown in pools, but production always

was small. In the mid-1980's, the fishery for Iceland scallops in northern areas increased

rapidly and peaked in 1987 when 45,000 t (round weight) were landed. Landings fell

sharply and were only 2,500 t in 1992. Since the early 1980's, spat of several species have

been reared in hatcheries and nurseries, but the cultivation industry is small. The potential

for increased mollusk cultivation is good. Mollusks are not commonly eaten in Norway.

Introduction

Along the coasts of orway, inshore mollusks important in fishery and culture, for food or bait, include the

northern horse mussel, Modiolus modiolus; blue mussel,

Mytilus edulis; Iceland scallop, Chlamys islandica; great

scallop, Pecten maximus; flat oyster, Ostrea edulis; ocean

quahog, Arctica islandica; and to a lesser extent cockle,

Cardium sp., and softshell clam, Mya arenaria. Species

introduced in recent years are Pacific oyster, Crassostrea

gigas, and manila clam, Ruditapes philippinarum. The

Iceland scallop is also harvested in offshore waters.

Shell piles or middens, common at ancient living

sites in Norway, date from 6000 B.C. (Simonsen, 1988)

and show that mollusks were widely utilized and a common part of daily meals from the Stone Age to the

Middle Ages. The most frequent species found in them

were the ocean quahog, blue mussel, cockle, softshell

clam, common limpet, Patella vulgata; and periwinkle,

Littorina sp. Flat oyster shell was mainly limited to southern Norway. Scallop shells found in childrens' graves

from the Iron Age in northern Norway suggest they

were used as children's toys then,just as they are today

(Bratrein, 1988; Simonsen, 1988). This may explain

why scallop shells are seldom found in household wastes

from that time, although low accessibility due to their

depth distribution is a more likely explanation. In the

Stone Age, some shells were used asjewelry; ornaments

* Present address: Institute of Marine Research, Department of

Agriculture, P.O. Box 1870 Nordnes, N-5024 Bergen, Norway.

** Present address: University of Maryland, Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory,

Solomons, MD 20688.

7
8 NOAA Technical Report NMFS 129

made from scallop shells have been found in grave sites

dating from as early as 1500 B.C.

Probably the first mollusk harvesting gear documented was an iron rake in 1773 (Bratrein, 1988); later,

fishermen used various types of grabs (Fig. 1). In 1857,

a sledge was developed for catching mussels (Bratrein,

1988), a type of gear that eventually developed into the

modern dredges like those used in the offshore fishery

for Iceland scallop (Fig. 1).

In early times, mollusks were generally used as food.

In recent times, however, they have been commonly

used as bait in the coastallongline fishery. Using mollusks as bait was first alluded to around 1770, while the

first record of commercial exploitation of mollusks was

in 1869 (Bratrein, 1988). The dominant bait species for

the longline fishery was the northern horse mussel.

Others were the ocean quahog, Iceland scallop, blue

mussel, and to a lesser extent, the cockle and softshell

clam (Wiborg, 1946). Since other types of bait replaced

the horse mussel in the 1950's, its fishery declined rapidly.

Harvests of the flat oyster for food probably had

considerable commercial importance in some coastal

areas of southern Norway before the beds were depleted in the mid-1800's. After that, methods were developed for cultivating spat in heliothermic "polls," the

Norwegian name for land-locked fjords with sill depth

less than the depth of pycnocline (layer between brackish surface water and saline subsurface water). However, more than 100 years of experience has produced

only minimal commercial production. Apart from the

former oyster fishery, harvest of mollusks for human

consumption had little importance until the mid 1980's.

Then, the fishery for Iceland scallop in northern areas

increased rapidly, and it peaked in 1987 when 45,000 t

(round weight) were harvested through the use of advanced gear. However, subsequentlandings have decreased

dramatically, and in 1992 the total quota for the fishery in

offshore and coastal areas was only 2,500 t. Harvests of

natural stocks of mollusks, except Iceland scallops, have

not been regulated.

Since the early 1980's, spat of great scallop, flat oyster, Pacific oyster, Manila clam and carpet clam, Ruditapes

decussatus, have been produced in hatcheries and nurseries, while spat of blue mussel and Iceland scallop

have been produced by natural spat collection. So far,

the cultivation industry in Norway, including blue mussel, oysters and scallops, is small. Cultivation of mollusks is regulated through governmental license, based

on consideration of environmental impact, pollution

risks, disease contamination risks, etc. Today, mollusks

are not a common part of meals in Norway, but there is

increasing use of some mollusks as food.

Iceland Scallop _

Habitat Description

The main distribution of Iceland scallops is north of

the Lofoten islands, with extensive scallop beds at Jan

Figure I

Typical equipment showing the historical development of harvesting gears in Norwegian mollusk fisheries. (A) Iron rake

with a grab for harvesting horse mussels from shallow waters. (8) Dredge for harvesting mussels in deeper waters. The

dredge is 0.8 m wide, 0.3 m high, and I m long (the bag is not shown). (C) Double-action dredge used in the offshore

Iceland scallop fisheries. The dredge weighs 3.5 t and is about 5 m wide and 0.5 m high, and the bag which is made of iron

rings is up to 6 m long.
Strand & Vl!llstad: The Molluscan Fisheries and Culture of Norway 9

JAN

MAYENS

B

History of the Fishery

I Rubach, S. 1992. Finnmark Havbruksstasjon, P.O. Box 476, N-9601

Hammerfest, Norway. Personal commun.

Cirripedia spp., are abundant and foul the shells of live

scallops, but scientific surveys show that fouling does

not slow the scallops' growth!.

c NORTH CAPE 50 lQOkm

Figure 3

Scallop beds (shaded) formerly identified as beds with

commercial exploitable densities (Map A), and surveyed areas (encircled) (Map B) (from Rubach and

Sundet, 1989). Map C shows beds ofIceland scallops in

northern Norway. Open circles show areas with empty

shells and a few small living scallops (from Wiborg,

1963).

About a century ago, Iceland scallops were found in

substantial quantities in some fjords in northern Norway (Sars, 1878; Storm, 1878-80; Sparre Schneider,

1881; Kiaer, 1906; Soot-Ryen, 1924). Exploratory fishing by the Institute ofMarine Research (IMR) in Bergen

Figure 2

Areas of Iceland scallop, Chlamys islandica, fisheries:

Jan Mayen, Svalbard, Bear Island, and coastal waters in

north Norway.

Mayen, Bear Island, and Spitsbergen (Wiborg, 1963,

1970; Wiborg et aI., 1974; Sundet, 1988) (Fig. 2, 3).

Along the coast of Norway from Lofoten to the Russian

border, large beds occur mainly in fjords having one or

more shallow sills at their entrances (Sundet, 1988;

Wiborg, 1963). Iceland scallops are scarce farther south

because bottom temperatures are too high, but they do

occur as relict populations in the S0rgjerdfjord west of

Trondheim, along the island of Tautra in the

Trondheimfjord, at the entrance of Lysefjord near

Stavanger, and in the Lindaspolls and the Fauskangerpoll north of Bergen (Wiborg, 1963; Greve and

Samuelsen, 1970).

Along the coast of Norway the depth range of Iceland scallops is 15-60 m, atJan Mayen and Bear Island

it is 70-100 m, and at Spitsbergen it is usually 30-70 m.

Iceland scallops are most abundant in localities with

strong currents, and they prefer a bottom of sand,

shells, and stones. Bottom temperatures ofscallop banks

vary considerably, from about -1.5° to SoC in the Barents

Sea, and from 4° to 10°C in coastal areas. In the fjords

of Norway the salinity is usually less than 33.5%0, while

on the Banks in the Barents Sea or atJan Mayen it may

reach 34.7-34.9%0 (Wiborg, 1963).

Predation on Iceland scallops by starfish, Asterias sp.,

can be substantial. In shallow coastal areas, eider ducks,

Somateria sp., prey on them (Brun, 1971), and, north of

Spitsbergen, walruses, Odobenus rosmarus, also prey on

them. At Bear Island and Spitsbergen, barnacles,
Jan Mayen 1.192 9,085 1,621 0 1,500 500

Bear Island 0 4,042 12,227 195 0 3,269

Spitsbergen 0 1,372 30,250 13,994 4,598 2,981

Trams 0 124 849 688 760 548

Tutal J.l92 14,623 44,947 14,877 6,858 7,298

Table 1

Catches of Iceland scallops in metric tons (t) round

weight by area for 1985-90. Meat weight is 10% of

scallop weight for machine-processed scallops in the

offshore areas and 14% (including gonads) for the

manually shucked scallops from Troms.

10 NOAA Technical Report NMFS 129

in the 1960's and 1970's revealed that extensive scallop

beds occurred at Bear Island and Spitsbergen (Wiborg,

1963, 1970; Wiborg et aI., 1974). However, cost-efficient gear for harvesting scallops in offshore areas did

not exist at the time. Prompted by the onset of a fishery

for Iceland scallops at Jan Mayen in 1985, resource

surveys were conducted by the University of Troms0

and IMR from 1986 to 1989 to assess and monitor

stocks in the Barents Sea (Rubach and Sundet, 1989).

Substantial areas were surveyed, and several beds with

commercially-exploitable densities were mapped (Fig.

3A, B).

Beginning of the Commercial Fishery

Area 1985 1986

Catches (t)

]987 1988 1989 ]990

A commercial fishery in coastal areas ofTroms began in

1985 (Fig. 3C). The gear and techniques were adopted

from Canada, the United States, Iceland, and the Faroe

Islands. Fishermen shucked the scallops on-board manually. During the off-season from March to July, many of

the boats fished for cod and shrimp. An offshore fishery

also began in 1985, and it increased rapidly as oceangoing ships discovered large quantities of scallops at

Jan Mayen. During the first year only 3-4 vessels participated in the fishery, but effort quickly expanded, peaking at 27 vessels (one registered from abroad) during

1986 and 1987. Subsequent participation dropped to

13 vessels in 1988, 3-4 in 1989-90, and 2 vessels in 1991.

The numbers of fishermen varied from about 10 to 12

on the smaller vessels to 36 on the larger ones. During

1987, total fishing effort exceeded 2,1 00 ship-days, ranging from 14 to 266 fishing days for individual veSSEls.

The total annual catch in meat weight/vessel varied

from 3 to 884 metric tons (t), while the daily catch

exceeded 6 t for the most efficient vessels. The total

catch (round weight) reached about 45,000 t with a

landed value of 156,520,000 NOK (US$24,456,000) in

1987, but fell afterward and was 7,298 t with a landed

value of 37,769,000 NOK (US$5,901,000) in 1990

(Tables 1, 2).

A total of 11 vessels, 10-14 m in length, were licens~d

for fishing in the coastal areas of northern NOffiay

(Troms and Vesteralen) (Fig. 2), while 34 vessels participated in the offshore fishery between 1985 and 1992.

Ocean-going vessels, ranging in length from 29 to 69 m,

were mostly modified factory trawlers, fresh fish and

shrimp trawlers, purse seiners, and longline vessels. A

limited number were modified supply ships from the

oil industry, while 7 vessels were contracted and specifically designed for Iceland scallop dredging. The larger

of the specially designed ships cost about 100 million

NOK (US$15.6 million), and typically operated 3

dredges simultaneously (Fig. 4). State-of-the-art instrumentation included geographic positioning systems,

Table 2

Value of total landed catch (in thousands).

Value (x1,OOO)

1985 ]986 1987 1988 1989 1990

NOK 5,8l:l8 94,543 156,520 61,770 36,428 37,769

L'S$ 920 14,777 24,456 9,562 5,692 5,901

specially designed acoustic instruments and software

for determining bottom type, and a computerized system controlled the dredges which kept wire tension

and warp length within specified limits.

When the fishery began, the boats used a single-side

action dredge (2.5 m wide) from Iceland, that was

towed at 2 knots. Afterwards, catch efficiency was increased through use of a double-action dredge and

higher towing speed. The dredge was a modification of

U.S. and Canadian dredge types and was towed at 4-5

knots with equal efficiency on both sides (Fig. 1, 4).

Processing the Catch

At the beginning of the offshore fishery, little was known

about machine processing of scallops at sea. In other

countries, scallops were typically delivered to processing plants on land or shucked manually at sea. Traust

Ltd. developed a pioneer automatic system for processing scallops at sea in Iceland, and, in 1985-86, it was

fitted onboard the Norwegian F/V Holberg. The system

was reasonably efficient for smooth bottoms and clean

(i.e., barnacle free) scallops atJan Mayen, but substantial, costly modifications had to be made in other areas

of the Barents Sea where bottoms were rough and the
Strand & V~dstad: The Molluscan Fisheries and Culture of Norway II

Figure 4

The FIV Concordia, 67 m long with 3,300 hp, a scallop dredger especially designed for the

offshore Iceland scallop fishery. The vessel typically operates three dredges simultaneously.

scallops had extensive fouling. In these areas the discards of broken scallops were about 25-30% fur the

most efficient vessels and as high as 50% for others,

resulting in substantial profit losses.

The production process has improved steadily over

the years, and an efficient system, partly developed in

Denmark, for sorting scallops from stones and empty

shells has been installed on vessels. Processing systems

similar to that developed for the FlY Holberg in 1985-

86 were later employed by most Norwegian ocean-going scallop dredgers (Fig. 5).

Besides scallups, the catch typically consists of large

amoun ts ofstones, empty shells, and other debris which

has to be discarded. The catch first goes through a

rough sorting process to discard undersized scallops

«65 mm) and large stones, and then through a socalled "stone trap" where most of the trash is removed.

Wear and tear on the machinery frum stones, barnacles,

and scallops is substantial, and the transport bands

used in this part of the production line are the same

type as those used in the mining industry. After discarding most of the trash, the scallops are kept in a basin of

fresh water or warm (about 30°C) sea water, to relax the

muscles and open the shells before they are steamed

for roughly 20 seconds at 98°-100°C. The soft parts are

then shaken loose from the shells and separated from

them in a basin of saturated saltwater. Gonads and

other soft parts are subsequently removed from the

muscles. The scallops are then quick-frozen, graded by

size, and then packed, usually in 10 kg boxes for export.

The Iceland scallop was exported mainly to the United

States until 1987-88, but since then exports to France

have amounted to a substantial portion.

Production system refinements in recent years have

mainly improved the sorting of trash from the scallops.

In particular, a system using water under high pressure

to sort out scallops early in the production line has

increased productivity by effectively reducing the quantity ofscallop discards. The final product weight is now

10% of the weight of whole scallops compared with

14% when scallops were shucked manually and gonads

were retained.

Since 1989 the Norwegian vessel, FlY Concordia, a

former offshore scallop dredger, has been engaged in

the surf clam fishery in Canada. Norwegian and Canadian partners have transferred and adapted scallop

dredging technology to the surf clam fishery.

Regulations

Inside the straight protection line along the coast of

northern Norway, the government restricts fishing for

Iceland scallops to 1 August-l March. For 1985-91, the
12 NOAA Technical Report NMFS 129

CATCH

SORTED ROUGHLY

"STONE TRAP"

u v u

SHELL

.. #f ...

~"'~'~ ., SOFT PARTS ., .,

SHELL

FRAGMENTS , SOFT

PARTS

... '!It>

o 0

GRADING

,---__,-,#f ro-o-o-o--=O"" '!It> ...

o 0 0 0 0 I-P-A-CK-I-N-G---'I I-S-T-OR-A-G-E---'I

o 0 0 00

Figure 5

A typical production line on an offshore scallop dredger.

total catch quota was 600 t round weight. Since 1987, a

scallop bed, "Berg feltet," south of Tromso has been

closed. In 1986, bounded catch-reporting by logbooks

was implemented. Fishing has been prohibited inside a

protection zone extending 4 n.mi. from the coastline of

Svalbard (first established in 1812 and modified by the

government in 1935, 1952, and 1955). Outside this

zone, no regulations were in effect for the Barents Sea

scallop fishery in 1985; any registered vessel could participate. In 1986, restrictions preventing new boats from

entering the fishery were implemented. Beginning in

1987, other regulations were put into effect: A lower

size limit of 65 mm was introduced for all areas, and,

because stocks were depleted, scallop beds were closed

atJan Mayen on 15 October. In 1989, a limited area of

these beds was reopened for fishing. The total quota of

1,500 t round weight was taken by three vessels. In 1990,

one vessel was allowed to do exploratory fishing in an

area outside the two main scallop beds and catch a

maximum of 500 t round weight. In 1989, the scallop

beds at Bear Island and Moffen were closed.

Scallop Culture

Techniques for collecting Iceland scallop spat were

tested successfully in Balsfjord in the beginning of the

1980's (Wallace, 1982). Thin nylon monofilamentswere

used as a substrate for settling larvae. In 1986-88, the

University of Troms0 conducted research on artificial

spat production ofIceland scallops in a laboratory-scale

hatchery, but it was not successful (Wallace, 1989).

The collected spat were held in nets suspended from

longline systems at depths of 2-12 m, and they grew

faster and had a higher meat content than scallops held

at 40 m (Wallace and Reinsnes, 1985). The market size

of 60-70 mm was reached in 3-4 years, compared with

7-8 years for scallops growing in the wild. The first

commercial-sized farm for culturing scallops was established near Hamar0y (lat. 68°N) in 1985. Supported by

regional authorities, it was intended as a model for the

development of an industry based on cultivating Iceland scallops in northern Norway. Nets, sorting equipment, and transport gear adapted for cultivation were

developed to optimize production. Farms were subsequently established in coastal areas from Helgelandskysten (lat. 65°N) and northward. In 1987-89, a

total of 14,000 spat collectors were set out by the farm

near Hamar0Y, and as many as 20,000 spatlcollector

bag were harvested. The spat were supplied to farms in

the region. Mterward, spat production declined mainly

due to insufficient methods for handling the collectors

(Table 3), but higher productivity was obtained by removing spat from the collectors after 2 years instead of

1 year2. In 1990, the model farm was shut down due to

low productivity, and farming activities along the coast

declined.

l Aasjord, D. 1992. P.O. Box 71, N-8260 lnnhavet, Norway. Personal

commun.
Strand & V~lstad: The Molluscan Fisheries and Culture of Norway 13

Present Condition of the Fishery

During 1992, only one or two ocean-going ships were

fishing for scallops in the Barents Sea, while 11 were

licensed for scallop dredging within the Norwegian

basic line, where the fishery was open between 1 August

and 1 March. Its 1992 quota was 500 t round weight.

Scallop beds at Bear Island were reopened for fishing

from 1 September 1992 through the end of May 1993,

with a total catch quota of 2,000 t round weight. The

scallop bed at Moffen was reopened from 1 June 1992

to 1January 1993.

Prognosis of the Fishery and Culture

The most substantial scallop beds have been mapped

by surveys made by scientific and commercial vessels.

During the 1980's, the fishery was conducted on longestablished scallop beds with a large proportion of old

(>10 years) scallops. The fishery is not likely to support

more than 3-4 vessels on a long-term basis, due to high

exploitation rates in the late 1980's and slow growth

and resettlement rates of the scallops. Offshore vessels

are costly, and hence large catches, often more than 2-

3 t/day, are required merely to cover expenses. The

fishery is self-regulating, in part, since vessels usually

leave a scallop bed when the catches become marginal.

Since harvesting efficiency is typically low, this generally occurs long before the beds become depleted.

The development of methods to collect spat of the

Iceland scallop may lay the foundation for future commercial cultivation. The scallops would be suspended

from longline systems or seeded on the bottom.

GreatScallop __

Habitat Description

Great scallops occur at depths of 5-60 m In coastal

waters from the southeast to the Lofoten islands (lat.

68°N), the northern limi t of their natural distribution

(Wiborg and B0hle, 1974; H0isaeter, 1986). They favor

bottoms of sand or a mix of sand, mud, and gravel.

Densities as high as 2-3/m2 are fairly common in some

fjords along the western coast (Wiborg and B0hle, 1974)

and in coastal areas outside Trondheim3. In Skagerak

and Kattegat, scallops occur mainly at 25-50 m. Their

3 Monkan, A. 1992. Taro S~ell A/S, N-7190 BesSaker, Norway. Personal commun.

Table 3

Production of molluscan spat in millions. Ostrea edulis were produced in polls; Crassostrea gigas, Ruditapes philippinarum,

R. decussatus, and Pecten maximus in hatcheries; and Chlamys islandica by artificial seed collection.

Production (millions)

European flat oyster,

O. edulis

Pacific oyster,

C. gigas

Manila clam,

R. philippinarum

Carpet shell,

R. derussatus

Iceland scallop,

C. islandica

Great scallop,

P. maximus

1903-30

1931

1932

1933

1934

1935

1929-681

1984

1985

1986

1987

1988

1989

1990

1991

<0.5

1

1.5

2.1

4

5

2

6

12

13

3 18

5 8

5 40 5

3 170 5 006

70

I Production statistics are not available from this period, but annual production of up lO about 10 million spat in Vagstranda have been

alluded.

Production estimates for 1984-89 are from Vagstranda. In addition, minor quantities were produced in small breed-polls during the

1970's and 1980's.

3 Produced by semi-intensive method in Espevikpollen (see text).
14 NOAA Technical Report NMFS 129

distribution is believed to be limited by hydrographical

conditions, particularly variations in temperature and

salinity due to the cold brackish water coming from the

Baltic sea during late winter and early spring (Parsons

et aI., 1991).

In controlled laboratory experiments, juvenile scallops had substantially higher mortalities at low salinities

«29%0) at 5°C, a common temperature during winter,

than at lOoC (Strand et aI., 1993). In contrast, juveniles

grown in suspended culture in a fjord on the southwestern coast had high survival during winter, when salinity

dropped to as low as 25-29%0. The scallop's main predators are starfish and the edible crab, Cancer pagurus.

History of the Fishery

The great scallop has been of little commercial importance in Norway. Early dredging attempts yielded low

returns, due mainly to rough bottoms and an abundance of seaweed that filled the dredges in only short

tows (Wiborg and B0hle, 1974). Instead, since the 1960's,

scuba diving has been the most common harvesting

method. The harvest by leisure diver-fishermen has

probably been extensive in some areas along the cO".st,

and, around Bergen there are signs of over-exploitation. During 1987-91, in the coastal areas outside

Trondheim, divers harvested an estimated 50,000 scallops, while 100,000 (20 t round weight) were harvested

in 1992 by a commercial firm3. Several unconfirmed

reports suggest that similar quantities have been harvested along the western coast in recen t decades (Wiborg

and Bohle, 1974). The diver-fishermen sold them mainly

to local fresh markets (restaurants and hotels). In recent years, prices have ranged from 8 to 15 NOK

(US$1.20-2.00) Iscallop in domestic fresh markets.

Scallop Culture

Spurred by the increasing European scallop cultivation

interest in the early 1980's, the feasibility of commercial scallop culture in Norway was considered. Extensive areas along the coast might provide suitable habitat. Growth studies from western orway suggested that

scallops attain commercial size (l00 mm) in 4-5 years

after spawning (Strand, 1986). Collection of wild spat

has been only marginally successful, as <36 spatlcollector bag were collected in Sognefjorden (Hovgaa'd,

1983), with similarly low numbers, 30-40 spatlcollo-ctor bag, being harvested in coastal waters outside

Trondheim3.

A research program at the University of Bergen during 1985-88 focused on the development of hatchery

technology and cultivation methods appropriate for

Norwegian waters. After promising results of spat production in a laboratory-scale hatchery, a large-scale pilot commercial hatchery was built in 0ygarden, north

of Bergen, in 1987 (Magnesen, 1989). The hatchery,

operated by 4-5 persons, had low production during

the first 2 years, mainly due to technical problems with

scaling up ofthe laboratory production system. In 1990-

91, however, there appeared to be a breakthrough.

Factors crucial for producing spat, 1-3 mm long, were

identified in a controlled hatchery environment

(Magnesen, 1991). Large-scale production seemed feasible, but high mortality rates followed when spat were

transferred to the sea. During 1988-91, a total of60,000

spat (Table 3), 15 mm long, were produced in the

hatchery, with the peak number of 25,000 in 1991.

Efforts to grow spat in artificial nursery systems have

nut been successful (Magnesen, 1989), while use of a

shallow enriched sea basin, combined with a system for

manipulating salinity, fertilization, and circulation, has

proven successful for the growth of juveniles only for a

limited period during summer (Andersen and Naas, 1993).

The cultivation method termed "ear-hanging" involves

hanging of the scallop on a vertical suspended line by a

nylon string passed through a small hole drilled in the

ear of its shell. Growth was faster by hanging the scallop

from a nylon string cemented to the shell rather than

through a hole drilled in the ear (Strand, 1991). Cement stringing may be used on smaller scallops, 20-25

mm. than the size needed for drilling a hole through

the ear, 40-50 mm. The intermediate culture in nets

may then be shortened, giving a more cost-efficient

cultivation technique.

Present Condition of Fishery and Culture

Reliable statistics for the total harvest of great scallops

by diver-fishermen along the coast do not exist; this

harvest may be substantial. The commercial firms near

Trondheim have been earning their incomes by harvesting wild stocks, and undersized scallops, <l0 cm

long, are reseeded on the beds. They have also cultivated scallops suspended on longline systems, using

nets and ear-hanging. In 1993, a processing plant was

established for the production of dishes on the half-shell.

A national research and development program on

sca:Ilop cultivation was started in 1993. The program

deals with spat production in hatcheries, intermediate

culture in nets or cages, and extensive sea bed cultivation.

Outlook

Scallop abundances along the coast are too low to support a large commercial fishery. Nevertheless, regula-
Strand & V~lstad: The Molluscan Fisheries and Culture of Norway 15

tions are probably needed to protect certain scallop

beds from depletion. Substantial increases in production of the great scallop can be obtained only through

aquaculture. Many areas along the coast from Stavanger

to north of Trondheim appear to be highly suitable

habitats for scallop farming (Strand, 1991). However,

increased knowledge about environmental requirements

for cultivation are needed to assess the production

potential, and, since the bottom topography is generally rough, development of efficient harvest methods

are needed. Methods for reducing predation on seeded

spat, as well as interference with other activities in coastal

waters should be addressed.

Horse Mussel

Habitat Description

Horse mussels occur along the entire coast at depths of

5-90 m, while extensive beds are found from the western coast to Northcape (Fig. 6) (Wiborg and Bohle,

1974; H0isaeter, 1986). In some regions between Bergen

and Trondheim they are also abundant on tidal flats

(Wiborg, 1946). Mussels are commonly attached by a

byssus to hard bottom or gravel, or may be partly buried

in sand, sand mixed with mud, or clay bottom. Their

main predators are starfish; common whelks; dogwhelks,

Nualla lapillus; edible crabs; wolf-fish, Anarhichas lupus;

and eider ducks (Wiborg, 1946).

History of the Fishery

The horse mussel has been the main species in Norway's

bait fishery, probably since longline fisheries began in

about 1500-1600, although it was first alluded to as bait

in 1770 (Bratrein, 1988). Horse mussels as bait were

first mentioned in the Annual Report of Norwegian

Fisheries in 1869, when commercial quantities were

used in longline fisheries in Lofoten4 .

Fishermen harvested horse mussels from shallow waters using a stick with a grab which they could operate

with a line (Fig. 1). Different types of sticks were developed for various depths and bottom conditions. Sticks

up to 15 m long were operated from small rowboats,

and fishermen usually held a water-glass between their

teeth leaving their hands free to handle the stick. They

brought the mussels to the surface with the stick or

collected them in a net on the bottom and then hauled

them to the surface. The season began between October and January and continued until March or April

4 Anonymous. 1894-96. Aarsberetning vedkummende Nurges

Fiskerier, Lofotfiskeriet. Kristiania. Cited in Wiborg (1946).

,

,

,

",': -(~', ~, \_,,/'~~J

("'~<'

,/'••/ 68 0 N

\)

.r=-'-----66°N

/

'~

/1--'/ ----61.0N

,

, TRON{HEIM

--_62°N

')

Figure 6

Locations where commercial harvests of horse mussels,

Modiolus modiolus, have taken place (from Wiborg, 1946).

when spawning occurred or until the spring algal bloom

reduced visibility in the water (Wiborg, 1946).

The development of dredges for use in deeper waters

expanded the area where mussels could be harvested

and increased the use of mussels as bait for the longline

fisheries in the 1880's (Wiborg, 1946). Fishermen usually pulled the "modern" dredge (Fig. 1) by a hand

winch operated from an anchored boat. Mussels were

also harvested by divers, who could select preferred

market sizes. However, diving operations could be limited by visibility and depth and were in most cases not

profitable. Limited information is available on catch

and effort for the above harvesting methods. Many

mussel beds were extensively exploited and some have

been wiped out by fishing (Wiborg, 1946; Bratrein,

1988). As early as 1891, government regulations were

contemplated. In 1897, 1912, and 1933, various measures limiting the fishery were promoted but never

implemented. Cultivation of horse mussels was considered impractical because the mussels grow too slowly

(Wiborg,1946).

The earliest harvests of horse mussels for use as bait

in the longline fishery were in Lofoten and adjacent

areas (Fig. 6). The mussels were sold whole and in tubs
16 NOAA Technical Report NMFS 129

of about 60 I each. Preservation of horse mussels with

salt allowed harvests of beds at some distance from

Lofoten. This practice was first mentioned in 18834. In

subsequent decades, use of salted mollusks as bait increased in a market which had been traditionally dominated by herring and squid. In 1888, roughly 400 t meat

weight of mussels were used as bait, 9% of the total

weight of bait (Bratrein, 1988). Horse mussel fisheries

in the Bergen area (Fig. 6) became the most important

source of bait for the longline fisheries in Lofoten.

Other important bait fisheries took place in Trl'mdelag

and Nordland. The overall annual catch from 1914 to

1951 varied from about 70 to 600 t, with a value of

nearly 500,000 NOK (US$78,000) (Wiborg, 1946). The

use of horse mussel as bait declined substantially in the

1950's as new technology developed to favor other baits

like frozen herring and prawns, but a small harvest

supplying some local fisheries has continued.

Present Condition and Prognosis of the Fishery

Diver-fishermen harvest modest quantities of horse

mussels along the coast and sell them fresh or as shucked

mussels in brine. Dredges, similar to those used in the

former bait fishery, are used on some beds along the

coast. Currently, the market for horse mussels is limited. In the future, however, it may increase and their

seemingly extensive resources along the coast could be

used more. Stock management should take into account lessons learned from overfishing practices in the

former bait fishery along with existing biological knowledge of this species (Wiborg, 1946).

Blue Mussel .

Habitat Description

The blue mussel is distributed along the entire coastline. The most extensive beds are found northward to

Trondheim in sheltered areas, influenced by freshwater runoffwith salinities of20-30%0 (Wiborg and B0hle,

1974). In the Oslofjord, they are normally found in

depths down to 10 m, and along the southern coast

down to 3-4 m. In outer areas of the western coast,

larvae will settle on artificial substrates in the upper

0.2-0.3 m (Aase and Bjerknes, 1984). Settlement depth

of larvae increases towards the fjords, and in the inner

part of the Sognefjord it may reach 16 m (Hovgaard

and Joranger, 1981). In fjords with high freshwater

runoff, blue mussels may be absent in the upper meters,

as they do not thrive in salinities <15%0. Their main

predators are eider ducks, starfish, wolf-fish, dogwhelks,

and the edible crab.

History of the Fishery

The only recorded landings of dredged blue mussels

are from the period 1872-1912 (B0hle, 1974). As many

as 60 t/year were harvested in the Oslofjord for use as

bait in the longline fishery. Harvests of blue mussels for

human consumption was limited; during this period, a

maximum of 2.5 t/year from the inner Oslofjord were

sold in the fish market in Oslo.

Farming Mussels

In the 1960's and 1970's, interest in blue mussel cultivation increased, and toward the end of this period many

farms were established. The most common cultivation

method involved collecting spat in the wild on artificial

substrates and growing them on suspended longline

systems. A rough surface, such as ropes of polypropylene or stripped net-lines, was generally preferred as

substrate (Kleppe, 1986; Hovgaard andJoranger, 1981).

Mussels were grown to market size, 50-60 mm, on the

substrate on which they settled, or they were removed

and put in net bags for further growth (B0hle, 1972).

Mussels grown on their settling substrate usually require thinning to obtain good growth. A yield of 5-10

kg/m of line may be obtained after 1.5-2.5 years.

In recent years, an increasing portion of the mussel

supply for the fresh market has been harvested from a

bottom culture operation at Fosen outside Trondheim

(Fig. 6). In a bed about 0.5 hectare in size, 1-2 m deep,

and with strong currents, wild mussels settled or were

seeded. They are harvested from a boat, using a grab

operated with a stick, and pulled to the surface by a

boom. Mussels were harvested from this site in the

former bait fishery.

Statistics on the number of farmers involved in blue

mussel cultivation are not available from official records.

The number of shellfish-farms in business has been

considerably lower than the number of licenses. In

1987 about 100 farms (800 licenses) existed, but in

1990 the number fell to 20-30 farms (400 licenses).

Most mussel farming has been part-time work.

As a result of the optimistic prospects for mussel cultivation in the early 1980's, several processing plants were

built. A plant in Austevoll, built in 1981, had an annual

production capacity of 2,500 t round weight. The main

product was steamed mussels in brine. However, the mussel supply from farmers in western Norway never reached

quantities needed to support a profitable business.

In the past decade, various products from 3-5 processing plants have been introduced to the market.

Whole mussels, frozen in their naturaljuices, have been

sold in 0.6 kg or 1 kg packages to Scandinavian markets.

Production reached roughly 100 tin 1987, but stopped
_________________ Strand & V~lstad: The Molluscan Fisheries and Culture of Norway 17

because of an insufficient supply and the diarrhetic

shel1fish poisoning (DSP) problem. Whole mussels have

also been canned (600 g portions). Production ofsinglefrozen mussels has recently been started in mid Norway. In the last decade, the main problem for processing plants has been lack of a mussel supply.

Cultured mussels have also been considered as food

for farmed salmon and cod. They must cost fish farmers

<1 NOK (US$0.15)/kg to make them economical to

use. Such a low price can be obtained only through

large-scale production.

The former Fish Farmer Trade Organization (FOS)

had exclusive rights to trade in cultivated mol1usks in

Norway during 1985-91. According to statistics obtained

from FOS, mussel production increased in the early

1980's, peaking at 500 t in 1985, and subsequently

decreased (Table 4). However, actual production is

known to be considerably higher, and, for 1989-91,

estimated annual production was 300-500 t, mainly

from the districts north ofTrondheim. In recent years,

farmers have been paid 3-5.50 NOK (US$0.50-0.90)/

kg for fresh mussels and about 11 NOK (US$1.70)/kg

for iced and packed mussels.

Waters affected by runoffs from manufacturing industries are closed for harvesting and cultivation of

mol1usks. Current knowledge on contaminants in the

most affected areas are summarized in Naes et al. (1992)

(organochlorines and polycyclic aromatic hydrocarbons) and Ringdal and Julshamn (1994) (heavy metals). The Hardangerfjord appears to be an ideal habitat

for mussel cultivation (Kleppe, 1986). However, in 1984

mol1usk harvesting and cultivation were obstructed there

because quantities of heavy metals caused by runoffs

from the metal1urgy industry in Sorfjorden were high

(Slinning et aI., 1984).

Another problem is eider duck predation, which can be

substantial as they have invaded farms in large numbers in

many regions. Fouling of cultivated mussels byascidians,

bryozoans, hydrozoans, and seaweeds may also be immense, particularly in outer coastal areas (Kleppe, 1986).

Shellfish Poisoning

Cultivation of blue mussels in Norwegian fjords has

shown great potential, but for the presence of algal

toxins. Mter 1984-85, the decline in mussel production

(Table 4) was mainly a result ofstrict quality control to

protect the public from DSP and paralytic shel1fish

poisoning (PSP) (Tangen, 1983; Hovgaard and

Byrkjeland, 1987). The inability to control algal toxins

was a limiting factor, and, in later years, DSP, and in

some instances PSP, has severely hampered mussel production along the southern coast and in the fjords of

western Norway. In the Sognefjord, where the condiTable 4

Production of cultivated blue mussel, Mytilus edulis, in

metric tons (t) and oyster, Ostrea edulis and Crassostrea

gigas, in thousands for 1983-91. Data for 1983-84 from

Norwegian Shellfisheries Association; 1985-89 for Fish

Farmer Trade Organization. Numbers estimated by the

authors are given in brackets.

Blue mussel Oyster

Year (t) (x1,000)

1983 300 300

1984 400 [600] 100

1985 500 [800] 500

1986 170 95

1987

1988 87 96

1989 45 [500] 145

1990 [300)

1991 [300]

tions for mussel cultivation otherwise appeared ideal,

approximately 1,000 t were discarded due to DSP in

1984. The diarrhetic shellfish toxins (DST) in mussels

harvested from Sognefjorden are complex and different from DST usual1y found in European mussels, but

resemble the profile found in Japanese scal10ps (Lee et

aI., 1988). Algae toxins are less of a problem north of

Trondheim. In recent years, therefore, mussels have

been produced only in the northern areas, despite

slower growth (2.5 years to reach market size) compared with areas further south (1.5 years). A monitoring program on toxic phytoplankton along the coast

has been conducted since 1991. In some areas it includes phytoplankton analysis and mouse test when

toxic phytoplankton species are found. The Directorate of Fisheries is responsible for quality control relating to biotoxins (PSP, DSP) and chemical and bacteriological pollutants. The quantity of toxins to be tolerated, as well as methods in the use of mice for testing,

have been disputed for many years.

Present Culture Status

Blue mussel cultivation, currently hampered by algal

toxins, is limited to the coast outside Trondheim and

northward. About 10 farms are in business, producing

10-50 t/year each. In 1991, a total of 200-300 twas

produced; roughly 100 t from the bottom culture at

Fosen and the rest from cultivation on suspended

longlines. Two processing plants employ 4-6 persons.

Production was expected to increase in 1992. Farmers

have been paid about 4 NOK (US$0.60) /kg of fresh

mussels processed by the plant. Bottom-cultured mussels sell for 12 NOK (US$1.80) /kg iced and packed.
18 NOAA Technical Report NMFS 129

Future Culture

Mussel production in Norwegian fjords could be substantially increased. However, expansion will depend

on whether a system for limiting the effect of algal

toxins, primarily DSP, can be developed. Reliable methods for DSP analysis and comprehensive monitoring

programs need to be developed. More research on the

aspects of algal toxins and their relations to bivalves is

needed. Considering that 40-70% of total cost in a

mussel farm is in harvesting, more cost-efficient harvesting systems are also needed. Both those and methods for suspended culture would have to be adapted to

local conditions.

Adaption of the Norwegian control system on algal

toxins to new standards may give rise to substantial

increase in blue mussel cultivation. If a situation allows

harvesting for at least 6 months/year, an increase of

total production within 3-4 years to a few thousand

metric tons can result (Stav0strand, 1989). Production

might increase to 10,000-20,000 t in Norwegian fjords

in the next ten years.

European Flat Oyster _

Habitat Description

Depletion of the oyster beds along the coast during the

1870-80's induced people to develop methods for producing and cultivating spat in the heliothermic "polls"

(Matthews and Heimdal, 1980). The flat oyster now

occurs mainly in polls, where temperatures may reach

about 30°C during summer.

Polls are numerous along the southern and western

coasts (Fig. 7). The northernmost site where the flat

oyster occurs is at lat. 65°49'N (Soot-Ryen, 1951). Ancient shell piles show that oysters were abundant along

the southern coast in the Stone Age (B0hle, 1984).

Today, temperatures in open coastal waters are normally too low for oysters to exist, but there are exceptions along the southeastern coast.

The main predators offlat oysters are starfish and the

edible crab, as well as wolf-fish, wrass, Labrus bimaculatus;

common whelk, and dogwhelk (Gaarder and Bjerkan,

1934). The boring sponge, Cliona celata, often grows in

its shell. Gaarder and Bjerkan (1934) reported that

Polydora sp. and "shell disease" (probably the fungi,

Ostracoblabe implexa) 5 have also been observed in shells,

but only on imported oysters from Holland in the

1930's.

5 Mortensen, S. H. 1992. Institute of Marine Research, Department

of Aquaculture, P.O. Box 1870 Nordnes, N-5024 Bergen, Norway.

Personal commun.

::~:-,-----62 QN

\ , I \

7::/f/ -'OON

SOE 10 0 E

Figure 7

Locations of polls where commercial cultivation of European flat oyster, Ostrea edulis, has taken place (from

Wollebaek, 1901; Gaarder and Sparck, 1932; Gaarder

and Bjerkan, 1934; Bohle, 1984). Commercial bivalve

hatchery locations are shown by open triangles.

History of the Fishery

Oysters were highly valued, and their fishery probably has

had considerable commercial importance in some coastal

areas. The decline in use of oysters during the Middle Ages is

assumed to be attributed to a reduction of natural stocks

due to climatic changes. Stocks along the western and

southern coasts were harvested and exported to Denmark

(Danevig, 1932). They were also preserved in pickle and

exported to the Baltic area, Russia, and Belgium as late as

1750 (Helland-Hansen, 1908). Official economic reports

showed that all regions south ofTrondheim had oyster harvests in 1830-35, but exports were minimal (Danevig, 1932).

Little information is available on harvesting methods. A rake with a net behind was mentioned as suitable

for harvesting oysters from the bottom along shores

(Anonymous, 1900). A long nipper made of wood was

described as harvesting equipment for collecting oysters

fixed to hard bottom (Danevig, 1932), a method similar to

the one used for harvesting horse mussels (Fig. 1).
Strand & V0lstad: The Molluscan Fisheries and Culture of Norway 19

Figure 8

The Espevikpoll at Tysnes south from Bergen. The poll, 2.6 hectares in area with a maximum depth of 5 m, is seen in

the foreground, the fjord in the background, and the entrance to the fjord is seen along the landbased nursery

building. The hatchery is by the floating pier. (Photo: S. Mortensen).

The dramatic depletion of the stocks of oysters during the 1860-70's was believed to be due to climatic

changes, resulting in oyster stocks being increasingly

susceptible to exploitation and diseases (Friele, 1907;

Gaarder and Bjerkan, 1934).

History of Cultivation

In 1878 Rasch (1880), who was engaged to reestablish

the oyster fishery, found that several polls were inhabited by large numbers of oysters. This was attributed to

high water temperatures, and he proposed to introduce the pond-culture technique known from France,

Holland, and Denmark, but originally an ancient Italian method. Spat that could be produced in the coastal

polls were intended for seeding on the depleted oyster

beds to reestablish the commercial fishery. In 1879 the

"Society for Promotion of Fisheries" in Bergen became

engaged in oyster cultivation and initiated investigations of topography and hydrography in the polls, and,

early in the 1880's, a considerable number of oyster

companies were established with relatively high investments (Rasch, 1880; Gaarder and Sparck, 1932). Spat

were also imported from Holland. The optimistic effort

was temporary, however, and only two companies surRunoff

It HW

,w~/

Figure 9

A schematic represen tation of polls used for cultivation

of oyster. The breed-poll is for spat production where

tidal exchange and runoff are controlled by a gate in

the entrance to the outside fjord; the spat-poll is for

spat grow out, where poll water is influenced by tidal

exchange with the fjord.

vived, one in the Ostravigpol1 near Egersund (south of

Stavanger) and one in the Espevikpol1 on Tysnes (south

of Bergen) (Fig. 7). The Espevikpol1 has since been
20 NOAA Technical Report NMFS 129

used for mollusk cultivation almost continuously from

1882 until today (Fig. 8).

Polls used for cultivation are of two types (Gaarder

and Bjerkan, 1934). Relatively small polls, termed

"breed-polls," 5-10 m deep and about 1-5 hectares in

area, have been used for spawning and collecting spat

(Fig. 9). They have restricted water exchange over the

sill or barrier and retain freshwater runoffwhich results

in a strong salinity stratification. In polls prepared for

cultivation, tidal exchanges and outflows of runoff are

controlled by a gate in the entrance to the outside

fjord. The vertical haline density gradient retains warm

temperatures in the pools (termed heliothermic by

Kirkland et aI., 1983) by the "greenhouse" effect.

Spat are held for growth in relatively large polls,

termed "spat-polls," which are as much as 20 m deep

and 40 hectares in area and have an exchange of water

with the outside (Fig. 9). Along the southern coast, the

polls are smaller, more open than those along the

western coast (Fig. 7), and not as suitable for oyster

cultivation (B0hle, 1984).

Advice on cultivation methods in breed-polls was published by "Society for Promotion of Fisheries" (Anonymous, 1900; Wollebaek, 1901, 1903; Helland-Hansen,

1908). Following this advice, farmers closed the entrances to the outside fjords early in spring to attain

temperatures of about 20°C in May-June. They held

broodstock oysters on netting suspended at a depth of

1-2 m (where temperature was highest) [rom a wire

stretched over the polls. During June-July, when oysters spawned, farmers set out collectors made of bunched

birch on wires between the oysters. The birch was suitable since the spat were easy to remove from the loose

bark. In autumn the gate in the entrance was opened,

allowing fjord water to enter the poll. Total renewal

normally occurs during winter when the fjord water is

homogenous, i.e., heavy enough to replace the bottom

water in the poll. Farmers removed the spat on the

collectors in April-May, almost a year after spawning.

In the early years of cultivation, they grew spat at the

bottom and harvested them by rakes. Later on, they

cultivated them on nets suspended on a wire stretched

over sounds, bays, or in spat polls. This method protected the oysters from predators, harvests were more

efficient, and growth was faster.

In the early 1900's, 25-30 spat-polls were in operation, but the number declined due to a low spat supply

from the breed-polls (Gaarder and Sparck, 1932). In

most polls, spat production was unpredictable and commercial cultivation was difficul t after years with low spat

settlement. Spat production in Espevikpollen, however,

failed only in 2 years from 1885 to 1900 and the poll

normally produced 1 million spat/year (Anonymous,

1900). Hence, it seemed that spat production in

Espevikpollen was high and stable, but production later

declined and in the 1920's only minor quantities ofspat

were produced. According to the Annual Report of

orwegian Fisheries, published from 1879, annual oyster production never exceeded 30 t (S0mme, 1936).

In the middle 1920's, the potential of spat production in polls was again seriously considered because

farmers in Limfjorden (Denmark) needed more spat.

Based on intensive investigations in the Espevikpoll

during 1927-29, Gaarder and Sparck (1932) gave the

following advice on management of the polls. Besides

temperature, which until then was considered as the

main factor for successful spat production, supply of

nutrients (nitrate and phosphate) were needed in the

breed-polls. Light availability could be increased by

reducing the thickness of the brackish surface layer.

Competitors for oyster food should be reduced; benthic

competitors were killed by mixing the hydrogen-sulphide bottom layer into the poll water during winter.

By following the suggestions, farmers increased their

production in the early 1930's (Table 3), and, in 1934,

eight polls were producing spat. One was Vagstranda in

Romsdal (lat. 63°N) (Fig. 7), a poll with a depth of 10 m

and about 30 hectares in size. It had the characteristics

of a spat-poll. The tidal influence and the agriculture

surrounding the poll presumably provided a good nutrient supply and a high production capacity compared

with the small breed-polls. Cultivation of oysters began

in 1929, and, from then until 1968, spat were produced

from this poll and exported to Limfjorden. Annual

production has been as high as 10 million spat, and

total production including oysters for consumption has

been as high as 80-90 t.

A minor cultivation in the small breed-polls continued

until the end of the 1970's when interest in molluscan

cultivation increased. At the beginning of the 1980's, 5-8

breed-polls were in operation with up to 300,000 spat!

poll produced annually. Spat production was reestablished

in Vagstranda in 1984 (Table 3). In 1989, production

peaked at 12 million spat. In recent years, most of those

produced were exported to Spain. While birch was used as

spat collectors for oysters exported to Limfjorden; wood

shavings were used in later years. After 1989, production

was curtailed because spat failed to set and the demand

for spat was low. Farmers normally lease the polls from the

landowner, and since 1985 the government has required

each farmer to have a license to cultivate oysters.

In the 1980's, farmers grew oysters in trays or racks of

baskets suspended from longline systems in fjords. According to the former Norwegian Shellfish Farmers

Association, in 1983, 75 farms were cultivating oysters.

In 1986, about 12-16 million oysters (probably including imported oysters from Scotland) were being cultured (Stav0strand, 1989), and in 1985 annual production (probably including the Pacific oyster, Crassostrea

gigas) peaked with 500,000 oysters (Table 4).
Strand & V01stad: The Molluscan Fisheries and Culture of Norway 21

Hatchery Culture

In Espevik and on Fosen, two hatcheries were trying to

produce spat during the second half ofthe 1980's (Fig.

7), but commercial spat production has not succeeded.

A semi-intensive spat production method in mesocosmos

system, described by Naas (1991), has been shown to

have promising potential for commercial production

(0. Strand, personal commun.) (Table 3). Larvae were

cultivated in plastic enclosures (7-12 m3) placed in the

Espevikpoll, where temperatures of 20°-24°C could be

maintained during the summer. Natural algal blooms

in the polls were used as food and renewed if necessary.

Since 1988, postlarvae produced in the hatchery and

the mesocosmos system have been cultivated in pumped

upwelling nurseries using the Espevikpoll as a food

production system (Fig. 8). In 1990, the bivalve production capacity in this cultivation system was successfully

enhanced by manipulations of nutrients (total supply

and composition), light availability, and stratification.

Compared with the calculated natural bivalve production capacity of about 1 t live weight, 1990 production

was increased sixfold (Strand, in press).

Oysters have been sold only fresh in the shell. In

recent years, farmers have been paid 2-3 NOK

(US$0.30-0.50)/oyster. In 1987, a station for depurating oysters was established at Har0Y, western Norway.

This station, with complete packing plant, was certified

for oyster export to France.

Current Oyster Culture

Spat of the flat oyster is not produced commercially,

probably reflecting the poor market situation in Europe. The national demand for spat is low because the

possibilities for commercial oyster cultivation in Norway using existing methods are limited. A minor harvest of cultivated oysters does occur. Several farmers

have begun trials of cultivating oysters in bags on shallow bottoms or on racks in shallow waters.

Future Oyster Culture

Oysters from cultivation sites in Norway have been surveyed the last few years, and Bonamia ostreae and other

serious parasites have not been observed (Mortensen,

1992). Considering the history of the situation in Europe, where oyster production has been severely depleted by diseases, absence of serious parasites in Norwegian oyster stocks should give oyster cultivation considerable future possibilities.

Traditional methods ofspat production in polls have

low potential due to unpredictability and restricted

production capacity. An exception may be large polls

such as Vagstranda, but viable commercial production

requires development of efficient cultivation methods

and technology. The promising method ofspat production in mesocosmos systems in heliothermic polls has

great potential to produce spat at low cost. Emphasis

should be given to broodstock management, food value of

natural plankton during plankton succession in

mesocosmos water, and efficient methods for settlement.

Using polls as a food production system for bivalve nurseries has potential for future low-eost spat production.

Other Native Species

The ocean quahog is abundant in several locations on

the western coast and in northern Norway. It has been

commercially harvested as bait, and as many as 1,500

quahogs/day have been dredged for this use (Wiborg

and B0hle, 1974). Also, the periwinkle, common whelk,

and common limpet have been considered sufficiently

abundant to support small-scale fisheries (Wiborg and

B0hle, 1974). During the mid 1980's, attempts to harvest the common whelk using pots in outer Oslofjorden

were not commercially successful.

In the late 1980's, spat production of the introduced

Manila clam, Ruditapes philippinarum, encouraged cultivation trials with the carpet clam, Ruditapes decussatus. In

1990, the hatchery at Espevik produced spat of the carpet

clam (Table 3). The queen scallop, Chlamys opercularis, has

been considered as having potential for cultivation in

many areas along the western coast where good conditions exist for natural spat collection (Hovgaard, 1986).

Introduced Species

The Pacific oyster was introduced from Scotland to the

hatchery in Espevik in 19795, and from 1981 until 1986

farmers imported spat of this oyster from Scotland for

cultivation along the Norwegian coast. However, strong

restrictions were placed on the importation of mollusks

for cultivation purposes in 1986 when the total number

of Pacific oysters in culture was 2.5-3 million

(Stav0strand, 1989). The hatchery on Fosen produced

10 million spat in 1987-89 and an additional 6 million

eyed larvae were exported to Scotland, while the hatcheries in Espevik and 0ygarden produced 3 million spat

annually in 1989-90 (Table 3). Considerable quantities

of this production have been exported to Greece, Germany, and Ireland. The Pacific oyster grows considerably faster and survives better than the European flat

oyster, particularly in mid-Norway, and, despite lower

prices for it when sold, it has become the dominant

cultivated oyster in that area.
22 NOAA Technical Report NMFS 129

The Manila clam was introduced from Scotland to

Espevik and Fosen in 19875, and, in 1987-1988, minor

quantities were produced in hatcheries there. In 1989-

91, a total of 280 million spat, 1-3 mm long, were

produced by the hatcheries in Espevik and in 0ygarden

(Table 3). The spat were cultured in pumped upwelling

nurseries in Espevik and in Vagstranda, and then exported to Spain and Ireland. Production has since declined owing to low demand.

TheFuhrreofCwhrre _

Spat of the Pacific oyster and Manila clam, and probably also the carpet shell, can be produced in large

quantities in hatcheries and efficiently grown in nurseries using the polls as a food production system and

thermal source. Blue mussel production may substantially increase if algal toxins are controlled. Development of efficient methods and technology in culture

would probably provide possibilities for commercial

production also for the native great scallop, Iceland

scallop, flat oyster, and carpet shell. However, considerable market development will also be required. Great

scallop, blue mussel, and flat oyster are considered as

the best candidates.

The increase of salmon farming in coastal areas has

introduced conflicts regarding potential molluscan farming sites, and authorities are concerned about the possible effects of substances used in fish farming on mollusk survival and growth. Mattson et al. (1988) has

demonstrated the negative impact of the parasiticide,

Neguvon6, used frequently as treatment for sea-lice in

salmon farming, on blue mussels and the flat oystels.

Recently, the impact of antibiotics used in salmon [arming on the fauna around fish farms has received attention (Samuelsen et aI., 1992). Mollusks may be important

carriers of fish diseases (Mortensen et aI., 1992). A minimum distance of 1 krn from fish farming sites is normally

required for obtaining a license for mollusk cultivation.

Norwegian waters have high productivity, large sheltered areas, high water quality, and limited pollution,

and bivalves at culture sites are free from the pathogens

causing major culture problems in many parts of Europe5. The potential for increased mollusk cultivation

in Norwegian waters appears to be good.

Acknowledgments

We are much indebted to many persons associated with

Norwegian molluscan fisheries and aquaculture for con6 Mention of trade names or commercial firms does not imply e:1-

dorsement by the National Marine Fisheries Service, OAA.

tributing to this chapter. Special thanks to Bjarne Schultz

and Hild Ynnesdal (Directorate of Fisheries) for providing information on Iceland scallop fisheries and regulations, to Elin Holm for drawing the figures, and to

Stein H. Mortensen for valuable comments and suggestions on the manuscript. The financial support through

grants from the Norwegian Fisheries Research Council

(NFFR) is much appreciated.

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24 NOAA Technical Report NMFS 129

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Oyster and Mussel Fisheries in Denmark

PER SAND KRlSTENSEN

Danish Institute ofFisheries and Marine Research

Charlottenlund Castle

2920 Charlottenlund, Denmark

ABSTRACT

Oysters, Ostrea edulis, and blue mussels, Mytilus edulis, are the principal commercial mollusks

of Denmark. From around 4000-2800 B.C., coastal natives commonly ate oysters, mussels,

and cockles, Cerastoderma edule. Oysters later became scarcer and gastropods, mostly periwinkles, Littorina littorea, became important as food. For centuries, Danish kings enjoyed

oysters at royal banquets. From the 16th to the 19th centuries, oysters were harvested in the

Wadden Sea. During most of the last century, fishermen used a netlike tool, called a "brile"

to harvest them, but in the 1870's dredges were introduced. During 1948-49, 993,387

oysters were landed, and, in the 1950's, landings were relatively high, reaching 4,000,000

oysters in the 1953-54 season. They declined afterward, and the last harvest was in 1982. In

the 1970's and 1980's, Pacific oysters were imported on a small scale, and, in 1991, one

farmer produced about 100,000 oysters. Before World War II, mussels were used mostly as

bait for longline fishing. In the 1940's, many mussels were harvested for food. People

developed a taste for them and landings have been good ever since. In 1991, landings from

Limfjord alone were 109,000 t. The mussel fleet consists of 55 vessels that land mussels in 10

harbors. Most market mussels are used in the canning industry where they are boiled and

put into jars or tins. Canneries pay about US$77It for them. Fishing for cockles is new. The

largest landing was 3,400 tin 1989. The molluscan fishery will remain stable during the next

5-10 years.

Introduction

Edible oysters, Ostrea edulis, and blue mussels, Mytilus

edulis, are the two principal commercial shellfishes of

Denmark. The shellfishing areas are the Danish Wadden

Sea where salinities are about 34%0, the Limfjord where

they are 23-33%0, and the Little Belt and Isefjord where

they are about 17%0 (Fig. 1). Water temperatures there

are around 2°C in January and 18-19°C in August, and

the bottoms range from hard sand to stable silty substrates. A fishery for the cockles Cerastoderma edule and

C. larrnarki is relatively new.

Early Shellfishing Records

From excavations of prehistoric settlements in Denmark, we know that oysters and mussels have been on

Danish menus for about 6,000 years (Madsen, 1888;

Muller, 1897; Petersen, 1922; Andersen and Johansen,

1986; Petersen, 1986; Brock and Bourget, 1989;

Andersen, 1989). The natives who lived along the coasts,

creeks, and estuaries of Denmark (Erteb0lle) from

around 4000-2800 B.c. regularly ate oysters, mussels,

and cockles, Cerastoderma edule (Andersen andJohansen,

1986; Nielsen1). One of the largest Danish shell mounds

at Meilgaard, which is also one of the largest found in

Europe, contains about 2,000 m3 of anthropogenic

wastes consisting primarily of oyster shells. For almost

400 years, oysters constituted up to about 32% of the

food intake of the 40 or so natives living in Meilgaard

(Petersen, 1922; Bailey, 1978).

Later, in the early Iron Age, the number of oyster

shells decreased in the kitchen middens and shells of

mussels, cockles, and many species of gastropods (but

mostly periwinkles, Littorina littorea) , increased. This

was probably due to a change in the climate, as summers

became colder in 3000-2000 B.c. and fewer oysters were

available. From about 2400 B.C. until 1587 AD., there are

few or no records of oyster, mussel, and cockle shells.

ielsen, P. O. 1992. The lational Museum of Denmark. The OMAgroup. Personal commun.

25
26 NOAA Technical Report NMFS 129 _

The Oyster Fishery

Today, one company (in Frederiksund) mines 10,000

year-old oyster shells from deposits in the bottom of

Roskilde Fjord, a small fjord next to Isefjord. The shells

lie in layers several meters thick and are sold worldwide

as a calcium supplement for egg-laying hens.

" Mention of trade names or commercial firms does not imply endorsement by the ational Marine Fisheries Service, NOAA.

Frederik the Second, King of Denmark, announced

that all oyster fisheries in the Kingdom were henceforth to be regarded as a royal monopoly. Only persons

with royal permission were allowed to collect and sell

oysters. Permissions were given primarily to the local

feudal vassals (Krogh, 1870; Aaberg, 1926).

In the 16th and 17th centuries, fishermen received

severe penalties if they were caught with oysters or

oyster fishing gear. A third or fourth offense could

mean a death sentence. Later, in the 19th and 20th

centuries, local fishermen were forced to deliver all

oysters fished in the Limfjord or elsewhere to the concessionary companies.

From the 16th to the 19th centuries, oysters were

caught in the Wadden Sea (Fig. 1). Schleswig-Holstein

(today the northern part of Germany) then belonged

to the Kingdom of Denmark; thus, a greater part of the

Wadden Sea area was under Danish control during this

period. In the war of 1864 between Germany and Denmark, Denmark lost most of the Wadden Sea. In the

18th century, oysters caught in the Danish Wadden Sea

were sold as "Flensburg Oysters," primarily in Copenhagen, but, in periods with good catches, to other parts

of Europe as well. The last oysters caught in the German part of the Wadden Sea was in the 1950's (Seaman

and Ruth, 1996).

Besides the Wadden Sea, oysters also occurred naturally in the Kattegat, between Skagen and the small

islands known as "Hirsholmene," for nearly 200 years

from 1709 to 1900. Oysters in the "Fladstrand" (Fig. 1),

first harvested in 1756, occurred in deeper water (10-

20m), and were therefore difficult to harvest. They had

the best quality, however, and were worth fishing. Those

oysters were called "Fladstrand oysters" and were sold

primarily in Copenhagen. Their annual yield was small

compared with other Danish oyster fisheries; at most,

only about 200,000 oysters were harvested. At an auction

in 1777. the oyster banks at "Fladstrand" were leased by a

single concessionary company. Later, only one, or at most

only two companies leased the oyster fishery at "Fladstrand."

A contract between a concessionary company and

the Danish GovernmentdatedJune 1875 mentions that,

between the first of September and the first of May, the

King should have 30 barrels each of 500 "Fladstrand"

oysters of the best quality delivered to the court. The

last oysters, about 200,000, were caught at "Fladstrand"

in 1895 (Anonymous, 1896; Aaberg, 1926). The royal

(after 1849 the governmental) monopoly was annulled

in 1982, when the last concessionary company (Limfjord

Oyster Companl) (Fig. 1, no. 1) had to give up the

monopoly due to a total failure in oyster catches over a

number of years.

I

I

I

lOG' i

KATTEGAT

.

Schleswig

SKAGERAK

Figure I

The areas (hatched) for the Royal (governmental) monopoly of oyster catching. The main commercial centers for selling oysters during the last three centuries in

Denmark and the most important mussel fishing areas

and the locations of the most important Danish molluscan industries are numbered 1-7: 1. Glyng0re Limfjord

(now Abba Seafood); 2. R0m0 Seafood; 3. Vejle Mussel

Industry Ltd.; 4. L0gst0r Mussels Industry; 5. Vilsund

Mussels-Industry; 6. Dan-Shell Fish (cockle industry);

7. Jegind0 Mussels.

For centuries, Danish Kings considered oysters a treat

at royal banquets. Almost 900 years ago, King Knud the

Great brought oysters home from England and introduced them to the Wadden Sea. Later, in the Middle

Ages, oysters were found in Danish waters and mentioned in the royal archives. On 21 February 1587,
______________________ Kristensen: Oyster and Mussel Fisheries in Denmark 27

The Limfjord Fishery, 1851-1982

The Limfjord, 1,575 km2 (Fig. 1), is the largest fjord in

Denmark. Oysters were found there some years after

the dikes burst at Agger on 3 February 1825 allowing

saltwater from the North Sea to pour in and change the

salinity permanently. Before that, the Limfjord was

brackish, and for centuries it had supported freshwater

fisheries in its westernmost areas. In its more brackish

eastern part, a substantial herring fishery existed for

several centuries until it began to decline in 1825.

Oysters were discovered first at Lemvig in the western

part of the Limfjord in 1851 (Fig. 1). They probably

immigrated from the North Sea between 1825 and 1850.

Only a few thousand oysters were found there, however,

during the first 15 years after their discovery (Table 1).

In 1861, the oyster fishery was leased by the Danish

Government to five different interests at an annual

license fee of 885 Rd (about US$272; Rd 0.5 = ca. Dkrl

= ca. US$0.15 ) (Krogh, 1870) (Table 1). In 1865 the

catch was 1,147,350 oysters, and, during the oyster season of 1868-69, the catch was 3,868,500 oysters worth

about 67,622 Rd. (about US$20,000) (Tables 1,2)

(Krogh, 1870). The license fees fishermen paid for

fishing those oysters were only about 1.3% of the oysters' market price.

From 1871 to 1876, the license fee for the new concessionary company was raised to 42,000 Rd (about

US$13,000), which was about 32% of the sales value of

the oysters caught. Annual license fees ranged from

322 Rd in 1858-61 to Dkr 240,000 in 1878-79, while the

harvests of oysters ranged from only 30,000 in 1852-53

to 7,519,030 in 1871-72 (Table 1).

From the beginning of the oyster fishery in the

Limfjord in the 1850's, the government asked different

officials and biologists to estimate the total standing

stock and the possible quantities of oysters that could

be fished in the fjord without much detrimental effect

on the standing stock. Thus, for almost 100 years, the

Danish Government has been advised of the stocks

(Petersen, 1907, 1908, 1925; Sparck, 1924, 1925, 1927,

1928,1929,1932,1949, 1950; Lund, 1942).

The first reports on investigations of the Danish oyster production, however, were written by nonbiologists.

Chamberlains (Royal officers) (Eschricht, 1860; Krogh,

1870; Tonning, 1893) wrote reports on the natural

oyster production in Denmark and on oyster culture

from countries all over the world.

Tonning (1893) was the director of an oyster company which had permission to harvest and sell oysters

from the Limfjord and the "Fladstrand" and was appointed oyster farmer by the Danish Government. Positive reports about culturing oysters in different parts of

Europe, mainly France, Italy, and Holland, led in 1860

to the imports of oyster seed to Denmark, especially to

the Limfjord. From 1864 to 1900, more than 12 million

seed oysters (0. edulis) primarily from France, England,

and Holland, were imported to the Limfjord (Krogh,

1870; Collin, 1884; Tonning, 1893).

In 1860 the Danish government issued a resolution

that any person who wanted to grow imported seed

oysters in Danish waters would need permission to do

so. This permission was granted so long as the culture

activity would not hinder the passage of ships and the

regular fisheries in the area. Permits were given for 10

years at a time and the grower had to pay fees to the

government. Six permits were issued from 1861 to 1866,

and five permits were issued from 1870 to 1880. No

experiments, with the exception ofthose in the Wadden

Sea, the "Fladstrand," and the Limfjord, however, were

successful.

The reason for the failure to grow oysters in Danish

waters outside of the traditional areas has never been

determined. Krogh (1870) believed that licensefees, which

the farmers had to pay the government whether or not

they produced oysters to sell, were one of the main reasons for the failures in the Little Belt and some fjords in

the 19th century. He wrote that it always took considerable time to produce oysters in Danish climatic conditions. Perhaps farmers should have paid fees only after

they were producing oysters. Lack of knowledge about

oysters' salinity requirements, food requirements, and suitable substrates for spat may also have caused the failures.

Dredging Oysters

Danish literature on the oyster fishery has little information on the fishing gear used. During the last century, oysters were caught with a netlike tool called a

"brile" or "bregl" (Fig. 2A). The catching part of the

"brile" was a net fastened on a wooden stick kept bent

by a rope tied to the shaft. When used for catching

oysters, the "brile" was without the iron sticks at the

lower end. The oyster fisherman sailed over the oyster

banks looking down to locate the oysters and then

lowered the "brile" to catch them.

In the 1870's, dredges were introduced in the oyster

fishery in the Limfjord. They consisted of a small ironframed box with iron net and iron teeth. The dredge

was more efficient than the "brile," but broke some of

the oyster seed. For this reason, dredging for oysters

was prohibited during some years in the late 1890's.

F1uctuation in Limfjord Yields

The number of native oysters in the Limfjord has fluctuated (Table 2) ever since the discovery of oysters

there in 1851. Mter low production in the 1850's and
28 NOAA Technical Report NMFS 129

early 1860's, it rose to 1,147,350 oysters in 1865-66 and

peaked at 7,519,030 oysters in 1871-72. In 1885-86,

however, the fishery was suspended for 5 years because

production fell to only 921,825 oysters. When it began

again in 1890-91, production did not increase but fell

further to only 586,648 oysters. Annual production remained low until the 1910-11 season, when 3,430,000

oysters were harvested.

Table I

The yearly yield, license fees, and names and numbers of concessionaries in the oyster fishery in the Limfjord from 1852 to

1906 (Petersen, 1907). (Dkr 1 = ca. RdO.5 in 1875; US$1 = ca. Dkr 6.5).

Harvest year Concessionaries Yearly license fees No. of oysters harvested

1852-53 Steenberg, Claudi, and Lykke (ca. US$l 24) Rd 400 ca. 30,000

1853-54

1854-55

1855-56 The same tenants (ca. US$100) Rd 325 ca. 86,000

1856-57

1857-58

1858-59 Steenberg (ca. US$100) Rd 322 ca. 150,000

1859-60

1860-61

1861-62 1. Brix (ca. US$272) Rd 885

1862-63 2. Steenberg & Co.

1863-64 3. Steenberg & Co.

1864-65 4.+5.j0rgensen, Kl0vberg, and Schibby

1865-66 1,147,350

1866-67 1,207,150

1867-68 1,727,100

1868-69 3,868,500

1869-70 4,620,967

1870-71 5,343,248

1871-72 The Danish Fishmonger, Inc. (ca. US$13,000) Rd 42,000 7,519,030

1872-73 (Paulsen and Kuhnert) 7,511,825

1873-74 7,364,765

1874-75 5,551,155

1875-76 5,933,130

1876-77 The Bank ofTrade (ca. US$37,000) Dkr 240,000 5,521,915

1877-78 (Paulsen, Kuhnert) 3,555,735

1878-79 Dkr 240,000 2,628,025

1879-80 110,000 2,875,130

1880-81 70,000 1,479,295

1881-82 111,747 2,075,990

1882-83 96,470 1,759,810

1883-84 84,000 1,319,465

1884-85 946,865

1885-86 921,825

1886-90 Preservation Int. customs duties No fishing

1890-91 Tonning and Teilmann-Friis Dkr 17,599 586,648

1891-92 34,855 774,570

1892-93 29,298 871,944

1893-94 26,632 765,299

1894-95 32,264 890,572

1895-96 Tonning Dkr 32,679 1,007,178

1896-97 33,845 1,053,828

1897-98 36,614 1,164,565

1898-99 34,709 1,088,391

1899-1900 32,349 993,968

1900-01 Brinck,jensen, Halse, and Spellerberg Dkr 63,591 1,009,547

1901-02 70,256 1,133,171

1902-03 63,540 1,024,840

1903-04 67,702 1,091,969

1904-05 66,257 1,068,673

1905-06 72,504 1,238,846
Kristensen: Oyster and Mussel Fisheries in Denmark 29

Table 2

The harvest of native 0. edulis in the Limfjord from 1852 to 1937. ative and cultured oysters harvested from 1937 to 1982

(Sparck, 1949; Poulsen, 1946; Anonymous, 1955-77).

No. of o.of o.of

oysters oysters oysters

Year harvested Year harvested Year harvested

1852-.:53 30,000 1897-98 1,164,565 1942-43 25,000

155,835

1853-54 o data 1898-99 1,088,391 1943-44 45,000

'44,142

1854-55 No data 1899-1900 993,968 1944-45 180,000

119,142

1855-56 86,000 1900-01 1,009,547 1945-46 525,000

'274,337

1856-57 No data 1901-02 1,133,171 1946-47 950,000

'162,450

1857-58 No data 1902-03 1,024,844 1947-48 1,100,000

'889,890

1858-59 No data 1903-04 1,091,969 1948-49 1,500,000

1993,387

1859-60 No data 1904-05 1,068,673 1949-50 2,400,000

1860-61 150,000 1905-06 1,238,846 1950-51 3,100,000

1861-62 o data 1906-10 annually 1,000,000 1951-52 2,600,000

1862-63 No data 1910-11 3,430,000 1952-53 3,400,000

1863-64 No data 1911-12 3,752,000 1953-54 4,000,000

1864-65 No data 1912-13 3,980,000 1954-55 3,800,000

1865-66 1,147,350 1913-14 3,950,000 1955-56 2,700,000

1866-67 1,207,150 1914-15 3,956,000 1956-57 2,300,000

1867-68 1,727,100 1915-16 5,621,737 1957-58 2,100,000

1868-69 3,868,500 1916-17 4,739,096 1958-59 1,500,000

1869-70 4,620,967 1917-18 2,465,132 1959-60 1,800,000

1870-71 5,343,248 1918-19 3,977,171 1960-61 1,100,000

1871-72 7,519,030 1919-20 4,721,972 1961-62 1,600,000

1872-73 7,511,825 1920-21 4,171,703 1962-63 1,400,000

1873-74 7,364,765 1921-22 3,372,656 1963-64 800,000

1874-75 5,551,155 1922-23 2,525,753 1964-65 200,000

1875-76 5,933,130 1923-24 1,142,177 1965-66 1,000,000

1876-77 5,521,915 1924-25 490,507 1966-67 500,000

1877-78 3,555,735 21925-26 1,000,000 1967-68 700,000

1878-79 2,628,025 21926-27 1,400,000 1968-69 600,000

1879-80 2,875,130 21927-28 2,000,000 1969-70 1100,000

1880-81 1,479,295 21928-29 1,600,000 1970-71 1400,000

1881-82 2,075,990 21929-30 2,900,000 1971-72 '300,000

1882-83 1,759,810 21930-31 4,000,000 1972-73 '300,000

1883-84 1,319,465 21931-32 3,200,000 1973-74 '400,000

1884-85 946,865 21932-33 1,800,000 1974-75 1600,000

1885-86 921,825 21933-34 1,000,000 1975-76 1600,000

1886-90 No harvest 21934-35 2,000,000 1976-77 '700,000

1890-91 586,648 21935-36 1,300,000 1977-78 '500,000

1891-92 774,570 21936-37 400,000 1978-81 No data

1892-93 871,944 1937-38 300,000 1981-82 11,000

'11,475 Annul. of monopoly

1893-94 765,299 1938-39 800,000 1982-91 No fishing

17,998

1894-95 890,572 1939-40 1,200,000 1992 One license

'24,053

1895-96 1,007,178 1940-41 100,000

17,915

1896-97 1,053,828 1941-42 100,000

122,672

I Number of oysters harvested from the native stock, 1938-82.

2 No fishing on the natural stock from 1925 to 1937.
30 NOAA Technical Report NMFS 129 _

A.

Figure 2

The different fishing gears used previously and toda}'

in the oyster and mussel fisheries in the Limfjord. A:

"brile" (after Rasmussen, 1968). B: Mussel dredges

"Limfjord" type; the upper one is the "old" dredge.

The first biological reports and estimates of the stocks

of oysters in the Limfjord were those by Petersen (1907,

1908, 1925) and by Sparck (1928). Sparck (1928) made

estimates ofoyster stocks in the Limfjord in 1924 and 1927

by having divers collect oysters from three areas (Table 3).

To cover larger areas than divers did, Sparck also sampled

oysters over 30,000-50,000 m2 of bottom by dredging

(Table 4). In 1924, the average density was one oyster per

9.0 m2, but by 1927 the stock density had decreased to an

average of only one oyster per 60 m2, showing a decline of

81-86% since 1924 (Table 5). Sparck (1949) estimated

the total number of native oysters in the Limfjord in 1914

at about 150 million, and in 1932 it was only 15 million.

The fishing of oysters had minor effect on stock sizes

(Petersen, 1925; Sparck, 1924). Sparck (1927) states

that in the 1920's only about 8% ofthe total stock in the

Limfjord was removed by fishing. At the same time, the

natural mortality was around 20%.

From 1925 until about 1970, native oyster production was poor. Despite conservation measures imposed

from 1925 to 1937 after the decline in catches in 1925 to

only 490,507 oysters (Table 2), production did not improve when the fishery resumed in 1937. The planting of

more than 15 million seed oysters from 1910 to 1925 had

not helped either. Production of native oysters after the

fishery resumed in 1937 was still low (i.e., between 8,000

and 55,000 oysters per year), remaining so until 1945.

To increase landings, the concessionary company

imported about 170 million seed oysters from France,

Holland, and Great Britain during 1924-56. Especially

from Norway a large number of seed oysters were imported by train (Strand, 1996). The number of oysters

produced from imported seed during 1925-37 is given in

Table 2 as the difference between the number of native

oysters and the total number of oysters harvested every

year. The resulting production for 1937-69 was around 16

million marketable oysters, and the gain was only around

10% (Anonymous, 1955-77). The last good production of

native oysters was in the middle 1970's, when about 700,000

oysters were landed. In the 1979-81 seasons, seed oysters

were imported from the Seasalter hatchery in England,

but subsequent harvests remained low.

The reason for fluctuations in the Limfjord oyster

stocks was probably due to a number of colder summers (Sparck, 1924, 1928, 1949). Studies of other Danish oyster stocks, as well as those elsewhere in Europe,

show that changes in summer water temperatures play

a crucial role in fluctuation~ of stock sizes and production of European oysters (Sparck, 1949).

After World War II, native oyster production increased

again. During 1948-49, 993,387 native oysters were

landed, and, in the 1950's, landings were relatively high

and reached 4,000,000 during the 1953--54 oyster season.

They declined afterward, and the last harvest of native

oysters in the Limfjord was in 1982 (about 1,000 oysters).

Information from fishermen on bycatches of oysters

in the mussel fishery in 1991 and 1992 suggest a new

good period for native oysters in the Limfjord. Although

summer temperatures have not been particularly high

during the last 5 years, the winters have been mild, with

no ice cover, and with water temperatures around 5°C

in January and February.

Predators and Competitors

In addition to low water temperatures, predators and food

competitors may also limit the stock size of oysters. Sea

stars, Astmas rubens, and crabs, Carcinus rna.enas, may destroy

many young oysters, while blue mussels and ascidians probably compete with oysters for food (Sparck, 1927, 1949).

Pacific Oysters in Denmark

In addition to the imports of O. edulis seed to the

Limfjord, Pacific oyster, Crassostrea gigas, seed was also
Kristensen: Oyster and Mussel Fisheries in Denmark 31

Table 3

Diver investigations of the oyster stocks at different localities in the Limfjord carried out in 1924 and 1927 (Sparck, 1928).

Number Number

of oysters of oysters

Size in 1924 in 1927

Local Area invest. distribution

Locality characteristics by diver (m2) (em) Live Dead Live Dead

Flovtrup (eastern part of Limfjord) Depth 5 m, gravel and stones 6-7 3 0 0 0

7-S S 3 1 0

900 1S-9 15 5 1 0

19-10 17 5 3 1

'10-11 6 4 3 1

'11+ 4 0 0 0

Hanbjerg (central western part Depth 4.S m, gravel and stones 4-5 I 0 I 0

of Limfjord) 5-6 3 0 0 0

700 6-7 15 6 2 0

7-S 37 10 9 0

18-9 55 14 S 1

19_10 51 10 12 2

110-11 27 0 6 0

111+ I 0 0 0

Oddesund (the most western part Depth 5 m, clay, gravel, 5-6 2 0 0 0

of Limfjord) and stones 6-7 IS 6 0 0

900 7-S 31 21 4 2

IS-9 40 19 5 5

'9-10 3S 14 7 5

']0-11 ]0 3 2 3

111+ 1 0 0 0

1 These sizes are marketable oysters.

Table 4

Dredged investigation of the native oyster stocks in Denmark's Limfjord in 1927. Number of predators and food

competitors mentioned (Sparck, 1928).

Area Total no. of No. of Food competitors

Locality dredged (m2) oysters caugh t predators caught (mussels) (t)

Livoe (central part of Limfjord) 725 A. rubens Several hundred

50,000 13 135 C. maenas

Riisgaard (central part of Limfjord) 35,000 30 300 A. rubens Several hundred

Thisted (central part of Limfjord) 30,000 17 500 A. rubens Several hundred

imported in the 19th century. However, the oysters did

not reproduce. In the 1970's and 1980's, Pacific oysters

were imported once more to compensate for the low

supply of European oysters. They were grown on suspended longlines in the Little Belt and the Isefjord, the

second largest Danish fjord, near Copenhagen (Fig. 1)

(Kristensen, 1989a). Oyster growing was successful, and

in 1985-86 more than 300,000 were sold in the

Copenhagen fish market at an average price to the

farmer of Dkr 3.90/oyster (about US$0.65). However,

C. gigas grown in France and exported to Denmark at a

price between Dkr 2-3/oyster competed strongly with the

Danish produced C. gigas. The competition was by price

and not quality. In 1991, one Danish farmer produced

about 100,000 Pacific oysters for the domestic market. In

the same year, a company imported about 500,000 French

oysters, mainly from Brittany, to sell in Copenhagen.

The Mussel Fishery

In the Danish Wadden Sea, mussels are found intertidally as well as subtidally. In the Limfjord, they are found

in 1-14 m of water and in the Little Belt and the

Isefjord they are in 1-10 m of water. All mussel populations build a muddy layer between their mussel carpet
32 NOAA Technical Report NMFS 129 _

Table 5

Diver investigations ofthe native oysters in the Limfjord

in 1924 and 1927 at the same localities and the same

area investigated as in Table 3 (Sparck, 1928).

and the bottom. In the Wadden Sea, the layer of mud

may be as thick as 50 em.

Asterias robens and Carcinus mamas are the most common associates on the mussel beds, and they are taken

as bycatch in the mussel fishery. Others are barnacles,

ascidians (particularly Slyela clava), and Crepidula spp.

which is common in some areas of the Limfjord.

Investigations on the predation and natural mortality

of mussels were conducted in 1991 in the Wadden Sea

(Hobo Deep) (Egerrup and Laursen, 1992). Predation

from crabs was insignificant but mortality from sea stars

and birds, particularly eider ducks, Somaleria mollisiMa,

can be high in winter. Mortality from other causes is

highest during summer.

Investigation

year Locality

Flovstrup

1924 Hanbjerg

Oddesund

Flovslrup

1927 Hanbjerg

Oddesund

Stock

densities:

m2/oysler

17

3.7

6.4

1I2.5

18.4

50.0

Percent

decline in

oyster densities,

1924 to 1927

85%

81%

86%

Figure 3

An old traditional Danish mussel vessel carrying around 30 t

of mussels.

ormally, each mussel vessel in the Wadden Sea has

a crew of two or three. In the Limfjord, each usually

had only two persons, but in the last 5 years, there has

been a tendency for skippers to dredge mussels alone.

Many skippers state, however, that their wives often

demand that they employ assistants.

Dredging Mussels

The Mussel Fleet

The Danish mussel fishing fleet consists of 55 vessels.

Of these, 46 fish in the Limfjord and are registered in

different harbors, such as Lemvig, Aalborg, and Thisted.

Four vessels are registered in Esbjerg and one in Havneby

on the island R0m0 in the Wadden Sea (Fig. 1); two

vessels are registered in Holbaek in the Isefjord, and

two vessels are registered in the Little Belt.

In 1991,4 vessels registered in Lemvig in the Limfjord

area fished mussels in the Little Belt, and in 1991, one

vessel registered in Esbjerg fished mussels in the

Limfjord (Fig. 1). The vessels land mussels in morc

than 10 different harbors. yk0bing Mors, the largest

city on the largest island in the Limfjord, is the most

important landing harbor (Fig. 1, no. 1).

Most Danish mussel fishing vessels are old rebuilt

fishing vessels (Fig. 3), usually with wooden hulls and a

hold in their center. They have a capacity of 15-30 t. In

the Wadden Sea, old Dutch mussel dredging vessels

with capacities of 60-80 t are used.

Before engines were used regularly in the fishing boats

in the Limfjord, mussel fishermen may have used gear

other than dredges to catch mussels. However, no information on the gears is available.

In the large mussel fishery in the 1940's, the mussel

fishing gear used was a Danish-constructed dredge with

a rectangular frame of OAx2 m (Fig. 2B). Today, this

dredge is used by only a few fishermen. Instead most

use the "Dutch" dredge, which causes less damage to

the sea bottom and the mussels. Two types of "Dutch"

dredges are used. In the Limfjord, fishermen normally

use only one dredge as was required in the regulation

of the mussel fishery. Therefore, the dredges are much

larger than dredges used in the Wadden Sea. The

"Limfjord" dredge can hold up to 1.5 t of mussels; the

"Wadden Sea" dredge holds only 0.5 t. The mussel

vessels in the Wadden Sea use 4 dredges at a time.

The "Limfjord" dredge is emptied like the codend of

a trawl. whereas the "Wadden Sea" dredge is emptied

by tilting. The dimensions of the catching frame of the

two different dredges are the same (about 0.7x1.8 m).
_______________________ Kristensen: Oyster and Mussel Fisheries in Denmark 33

Modern mussel vessels in the Limfjord (Fig. 4) use the

same fishing technique as used in the Wadden Sea and

use two dredges at a time.

In the Limfjord, fishermen set their one dredge over

the starboard side of their vessels, whereas those in the

Wadden Sea set two dredges on each side oftheir vessels.

The dredges are towed by wires, 14 mm in diameter,

which are let out 30-60 m, depending on the water depth

and the bottom type. On soft bottoms, the dredge is equiped

with an extra beam to prevent it from digging and catching

mud and to ensure that only mussels are taken.

The towing speed is usually around 3.5 knots. Over

dense mussel grounds, the hauling time is only about 2

minutes, whereas on sparse mussel grounds the hauling

time can be up to 20 minutes. The Wadden Sea is

shallow and boats can dredge mussels only about 2

hours before and after high tide.

Saving Seed Mussels

Successive generations of mussels settle on top of older

ones, and thus seed are dredged up with adult mussels;

seed are not separated on the vessels and are landed

ashore. The mussels are sorted on land, and the seed

mussels were used as fertilizer or simply discarded.

The mussel fishermen maintain that during the last

10 years more than 20,000 t ofsmall mussels have been

destroyed annually. Currently, investigations are being

conducted in Limfjord to determine whether it is practical to return small mussels to the beds, and, during 1990-

93, an experiment to relay the small mussels on selected

bottom culture plots was underway (Kristensen, 1991).

During the sorting process, it was found that 3-8% of

the mussels had their shells damaged and would probably die (Kristensen, 1991). About 98% of the small

mussels with unbroken shells survive when returned to

the beds during the colder periods of the year (water

temperature <12°C), whereas only about 50% survive

inJune-September (water temperature >12°C) plantings.

Preliminary results show that the returned mussels

grow to market size (i.e., >4.5 cm) within 2 years. The

planted mussels also have a higher meat content (+30%)

than those from the natural beds. By returning 20-

25,000 t of sorted small mussels annual, yields in the

Limfjord may increase by about 40,000 t. This would

amount to an increased annual production of around

40% of the present fishery (Kristensen, 1993).

Any environmental problems created by returning

the dead or dying mussels seem small when compared

with the benefits of returning 0.5-1 billion filtering

mussels to the fjord. Within a fortnight or so, the live

o

o

LCL ~~5

Figure 4

Technical drawing of a modern mussel vessel from the Limfjord. 1-5: Sorting system for mussels: 1.

Hollow for the caught mussels; 2. Conveyor for the caught mussels; 3. Washing and sorting roller; 4.

Outlet for mud and small mussels; 5. Conveyor for commercial sized mussels (Kristensen, 1991).
34 NOAA Technical Report NMFS 129

mussels will have ingested all the nutrients released from

the decomposing of the dead mussels (Kristensen, 1991).

Fishery Regulations

The mussel fishery is under the authority of the Ministry of Fisheries and is adminstered through the law for

fisheries in marine areas, "Saltvandsfiskeriloven." Those

who want to fish for mussels must apply to the Ministry.

The licenses are issued for 1 year and must be kept

onboard the vessel all times. After use, they have to be

returned to the Ministry. If a mussel fisherman wants to

fish mussels somewhere else, he must apply for a license that covers the new area and return the old one.

In the Limfjord, mussel fishing is allowed only between sunrise and sunset and is not allowed on Sundays

or during July. The minimum shell length for mussels

that may be landed in the Limfjord is 4.5 cm; a bycatch

of undersized mussels of 10% is allowed (in wet weight).

Landings per vessel must not exceed 30 t per day and

100 t per week. Currently, no annual quota is established for the mussel fishery in the Limfjord. However,

in the last 4 years, four areas have been closed for mmsel

fishing in the interest of environmental protection.

In the Limfjord, the vessel size is restricted to a CRT

below 8 t and engine power must not exceed 175 HP

(130 kW). Recently, legislation with respect to the number of dredges allowed in the mussel fishery in the

Limfjord has been liberalized. However, most fishermen have not changed the number of dredges they use,

but the newly built mussel vessels in the Limfjord use at

least two dredges of the "Wadden Sea" type.

In the Wadden Sea, mussels can be dredged only

between sunrise and sunset and dredging is not allowed

on Fridays and Saturdays. It is also prohibited from 1

May to 15 July. Only mussels with a shell length of at

least 5 cm can be landed. Again, bycatches of mussels

smaller than 5 em are, however, allowed up to an amount

of 10% (in wet weight) of the catch. Fishing is allowed

only in areas agreed upon with the Ministry of Environment. Each vessel is limited to a maximum of 40 t per

day and 100 t per week. Annual quotas are established

by the Ministry of Fisheries.

The engine power for the vessels in the Wadden Sea

is restricted to 300 HP (225 kW), but there is no CRT

limit. In the Isefjord and the Little Belt, engine power or

CRT for vessels are not limited and there are no quotas.

Historical Production

All mussels landed are from natural stocks and are

therefore limited. The Limfjord has always been the

most important mussel area. Areas of minor imporTable 6

Danish mussel landings from 1972 to 1991. The important mussel fishing areas outside the Limfjord are the

Isefjord, the Danish Wadden Sea, and the Little Belt

(Kristensen, 1989a, b).

Mussel landings (t)

Year Limfjord Other Danish waters Total

1972 24,958 5,410 30,368

]973 22,183 4,831 27,014

1974 23,571 5,165 28,736

1975 23,168 4,630 27,798

1976 30,192 7,678 37,871

1977 41,]36 6,416 47,552

1978 42,000 4,756 46,756

1979 41.507 5,726 47,233

1980 55,707 119,662 75,369

1981 38,207 133,555 71,762

1982 44,071 113,867 57,938

1983 48,879 t7,532 55,411

1984 49,255 318,639 67,894

1985 35,853 324,000 59,853

1986 63,335 326,999 90,334

1987 49,496 1.336,360 85,856

1988 61,766 210,757 72,523

1989 68,316 27,248 75,564

]990 84.955 28,380 93,335

1991 108,8]4 t,316,945 125,759

I Isefjord.

t l.ittle Belt.

3 Danish Wadden Sea.

tance are the Isefjord, the Wadden Sea, and the Little

Belt (Fig. 1; Table 6).

The first information on Danish mussel landings from

the Limfjord is from 1908 when 14 metric tons (t) of

mussels were landed at a value of Dkr 1,000 (about

CS$ll/t). Before World War II, the Danish mussel

fishery was small and mussels were used primarily as

bait for longline fishing in the North Sea.

In the 1940's, people in central Europe needed rich

protein food. Since the fjords of occupied Denmark

had large quantities of mussels rich in protein, many

mussels were harvested to meet the demand. During

1942-44, more than 160,000 t of mussels were landed

in the Limfjord alone (Fig. 5).

Immediately after World War II, landings fell to the

prewar level. However, Europeans had developed a

taste for Danish mussels, and, from 1948 to 1974, annuallandings rose to between 8,800 and 22,200 t (average 17,000 t). During 1972-78, mussel landings increased once more to average 29,600 t annually (range

22,183-42,000 t). During the late 1980's and the early

1990's, mussel landings increased to their highest since

World War II, and, in 1991, landings from the Limfjord
_______________________ Kristensen: Oyster and Mussel Fisheries in Denmark 35

120

100

-=-

8 80 0.

::::.

OIl

c:

'0 60 c:

]

::l 40

::E

20

ol-. "-.-t.~!!Ko.L-JIIW.....,;..lO!..!lC...:JIL-~-~-----l

1900 1910 1920 1930 1940 1950 1960 1970 \980 1990 2000

Years

Figure 5

Net musse1landings from the Limfjord and other Danish waters from 1908 to 1991. Note:. =Limfjord, =

Other waters (after Randl0v, 1982; Kristensen, 1989b).

alone were 109,000 t (Fig. 5, Table 6). The industry

credits the Ministry of Fisheries for the large increase

and uses the license system to place the vessels in different mussel fishing areas.

During the 1980's, the Isefjord and the Wadden Sea

had large landings. In 1980-82, landings from the

Isefjord were about 55,000 t, and in 1987 about 25,000

t. From 1983 to 1987, the landings from the Wadden

Sea totalled around 75,000 t. Currently, landings from

the Wadden Sea are much reduced, and in 1991 they

were only 5,539 1. Annual landings from the Isefjord

are normally about 3,000 t while those from the Little

Belt are 5,000-7,000 1.

Relative Landings and Incomes

In the 1920's and the 1930's, mussel landings constituted about 45% of the total landings of fish and mussels from the Limfjord. However, the landed value of

the mussels constituted only 1-4% of the total landings

(excluding oysters). Today, mussel landings constitute

more than 90% ofits total landings and more than 70%

of their value.

In 1991, the mussel fishery in the Wadden Sea rose to

a value of Dkr 15.8 million (Dkr 2.86/kg) (sold as live

mussels) which command a price four times as large as

those harvested in the Limfjord and marketed canned.

In 1991 the total first sale value of the Danish mussels

totalled about Dkr 81.8 million (US$12.6 million). Mussel

fishing earnings are better than some others within the

Danish fishing fleet. Danish mussel fishermen have an

annual income between Dkr 1-2 million (US$150,000-

300,000); this is from an annual mussel catch of between 2,000-4,000 t per vessel.

Mussel Culture Experiments

Denmark currently has few mussel culture projects. In

the 1960's and later in the 1980's, several experiments

were conducted. Experiments in the Wadden Sea in

the 1960's were designed to culture mussels on the

bottom. Local mussels and those from the Limfjord

were transplanted to selected plots. Due to high mortality rates, however, the experiments were abandoned

and did not lead to commercial mussel culture. The

mussels transplanted from the Limfjord were unable to

deal with the high densities of sand particles in the

water and died (Theisen, 1968).

The success in Sweden in growing mussels on

longlines led to a number of corresponding experiments in various Danish fjords (Isefjord, Mariager Fjord,

Randers Fjord, and South ofFunen; Fig. 1) (Kristensen,

1989a; Kristensen and Hoffmann, ]991). Municipalities, the Ministry of Fisheries, and the EEC supported

groups that conducted the experiments with longline

systems; later, some groups became commercial production companies (Kristensen, 1989a). Problems with

ice cover, which causes damage to longlines, forced

many growers to discontinue their operations

(Kristensen, 1989a; Kristensen and Hoffmann, 1991),

however, and only one company has "survived." The

company grows mussels on longlines in Mariager Fjord

for the domestic market.

Some experiments continue, for instance, in the

Limfjord. Longline-grown mussels will be successful

commercially, however, only ifsold alive. They will never

be able to compete with wild mussels that are to be

canned as canneries pay only about Dkr500/t (about

US$77It) for mussels. Most Danish mussels are used in

the canning industry where they are boiled and put

into jars or tins. Longline growers have to obtain firstsale prices at least as high as Dkr3-4,000/t (about

US$460-615/t) to realize a profit. The Danish live mussel market is limited and amounts to only a few hundred metric tons annually.

Public Health Aspects

Public health aspects for landing and sale of Danish

mollusks are established in the proclamation 717 of 26

October 1990 from the Ministry of Fisheries, on public

health terms for fishing, manufacture, and sale of mollusks in Denmark. Proclamation 104 of 22 March 1984

for distribution of oysters in Denmark was still in force

in 1992.
36 NOAA Technical Report NMFS 129

The rules for heavy metals in food for human consumption are established in the proclamation from the

Ministry of Environment no. 447 of 5 September 1985

and no. 612 ofl6 September 1986.

The proclamations from the Ministry of Fisheries

establish the number of fecal bacillus to be less than

300 cells/100 g of mussel meat or the number of E. coli

has to be less than 230 cells/ 100 g of mussels for direct

human consumption. The 1 January 1993 common

EEC rules (91/492/EOEF) were to be established for

fishing, manufacturing, and sale of mollusks in all 12

member countries.

In 1990 the voluntary supervision for toxic algae in

the Danish mussel fishery failed, and a number of people

got sick and got diarrhea. As a result, new and more

strict supervision rules were agreed upon by the Ministry of Fisheries, the industry, and among the fishermen.

The new proclamation established that mussel fishing

is not allowed unless water and mussel samples have

been taken the week before the beginning of the fishery. The water samples are sent for laboratory examination, where the number of potential toxic algae are

registered. Mussel samples are sent to be tested for

their toxic content. Mouse assay tests are used. The

mouse tests are difficult to interpret, however, as the

mice may die from various causes. Chemical methods

are being investigated. Such methods will be better

than mouse tests but are not yet refined enough to

establish whether the mussels are free of toxins and safe

to eat.

Supervision ofDSP (diaeretic shellfish poison) is carried out all year. PSP (paralytic shellfish poison) is

supervised during 1 April to 1 October, and if PSPproducing algae are observed in the water samples, the

Ministry of Fisheries has to approve the results ofsupervision before fishing is allowed. The Limfjord has been

divided into 22 subareas, and 1-2 samples from each

subarea have to be examined for toxic algae and approved upon before fishing can take place.

Oysters for the fresh fish market have to be depurated for at least 7 days in recirculating UV-sterilized

salt water at optimum salinity and temperatures that

allow them to cleanse themselves. Before the oysters

are released for sale they have to be tested for E. coli and

for algal toxins.

The Mussel Processing Industry

Six companies buy mussels from Danish fishermen.

One of these, Jegind0 Mussels, exports only live mussels (in 2-4 kg plastic bags or in 25 kgjute bags) (Fig. ],

no. 7). The other five companies boil the mussels for

sale. Two factories, R0m0 Seafood (Fig. 1, no. 2) and

Vejle Mussel Industry Ltd. (Fig. 1, no. 3), are located

some distance from the Limfjord and the mussels are

trucked to the factories. The industries on the Limfjord

are L0gst0r Mussels Industry (Fig. 1, no. 4), Vilsund

Mussels-Industry (which delivers live mussels for export

also) (Fig. 1, no. 5), and Abba Seafood (Fig. 1, no. 1).

In the last 3 years, Swedish capital (Abba Seafood) has

taken over two Danish mussel industries, Glyng0re

Limfjord (Fig. 1, no. 1) and Marina, at the Limfjord.

Mussel Commodities

Danish mussels are prepared several ways for consumers. Most boiled mussels are produced as single frozen

mussels for garnish in pizzas and salads. The industry

produces a wide variety of types of canned, nonperishable commodities such as mussels in butter, garlic butter, spicy sauce, tomato sauce, escabeche sauce, and

soya oil. Some mussels are smoked and packed in oil in

tins similar to kippers.

The industry also produces perishable commodities

such as mussels in water, mussels in vinegar, mussel

salad with different vegetables, mussels in tomato sauce,

and mussels in seafood sauce. These are sold in jars

(net weight 340 g or 12 oz), tins (net weight 113-850 g

or 4-30 oz), and buckets (2.4-2.7 kg or 85-95 oz).

Buckets are usually sold on the wholesale market. Mussels caught in the Wadden Sea are sold primarily as live

mussels and are exported.

Mussel Sales

More than 90% of the Danish mussel production is

exported onto the world market at an annual value of

Dkr 200-250 million (about US$30-40 million), or about

3% of the total annual Danish export of fish and fish

products. In the last 1-2 years, prices of mussel meat

have increased 10-30%. Thus, at present, the mussel

industry is satisfied with the market situation.

Frozen Danish mussels dominate the European market (by 70%) and Danish producers compete with each

other on the market. Danish canned mussels account

for less than 10% of the world market. In Denmark

most mussels (79%) are sold as nonperishable, perishable, or as single frozen mussels.

The Cockle Fishery

Fishing for cockles in Danish waters is relatively new. In

1980 The Danish Agency for Forest and Nature Conservation stopped the digging of lug worms, Arenicola marina, in the Danish Wadden Sea. In compensation, one

fisherman received a 10-year license (1982-92) to fish
________________________ Kristensen: Oyster and Mussel Fisheries in Denmark 37

cockles, Cerastoderma edule and C. larmarki, outside the

islands in the Wadden Sea. During those 10 years, landings have varied. The largest landing, 3,400 t, was in

1989. The first sale prices of the cockles, about Dkr 25

(about US$4) per kg of meat, have been rather high

during the last couple of years, while normal prices are

about Dkr 11 (about US$I. 70) per kg ofmeat. In 1992-

93, the cockle fishery was restricted to only four small

areas near Esbjerg, the largest city in the Danish Wadden

Sea. In addition, it was allowed only in one of the four

subareas for 1 year at any given time. The total permitted fishing area was restricted to only 7 km2 which

amounts to about 1% of the entire Wadden Sea.

During the last 1-2 years, fishermen have attempted

to find cockles elsewhere in Danish waters but with

poor results. The cockle fishery in Denmark will never

reach the same magnitude ofthose in Holland or Great

Britain. Probably, annual catches in Denmark will be

between 5,000 and 10,000 t wet weight (about 1,000-

2,000 t of meat).

Other Bivalve Fisheries _

Other commercial bivalves in Danish waters are Arctica

islandica, Clamys opercularis, and Spisula solida. They have

all been fished commercially for short periods. In 1992,

one fisherman in Esbjerg landed S. solida for the domestic market and export. His weekly landings

amounted to about 25 t, and he sold them for about

Dkr 5-10/kg (US$0.75-1.50/kg). The "mini clams," as

they are called, are sold at the fishmonger's at a price of

about Dkr 35/kg (about US$6/kg). Fishermen have

never dug Mya arenaria commercially, although the

clams are common in Danish waters.

Environmental Issues

Conflicts between the mussel fishery and the interests

of environmental protection have resulted in restrictions. Mussel fishing vessels must dredge in waters at

least 1.4 m deep to prevent damage to eelgrass, Zostera

marina, beds. The Ministry of Fisheries can make exemptions on the draft rule, however, for vessels already

approved for mussel fishing. In addition, large areas

(about one-third) of the Danish Wadden Sea will, in

the near future (1992 or 1993), be closed for human

activity including fishing for mussels and cockles. The

fishermen and the Ministry of Fishery have agreed to

carry out a controlled fishery for mussels in the Ho Bight

to investigate the role of the mussel fishery in stabilizing

the biomass and production of mussels in the area.

Currently, cockle fishing is prohibited in Ramsar and

bird protection areas. However, cockles may be more

common there than anywhere else. Permission to fish

cockles in protected areas is restricted as great consideration is given to the wildlife and birdlife in the area.

The Future of Molluscan Fisheries

The Danish mollusk fishery will likely remain stable at

the current level during the next 5-10 years. Perhaps

the number of vessels in the mussel fleet, particularly in

the Limfjord, may increase slightly. Declines in landings from other European countries, such as Holland

where mussel culture failed in 1990 and 1991, however,

may result in larger landings in Denmark. Meanwhile,

the industry is concerned that the demand for mussels

may decline in the future as the average mussel consumer is a middle-aged male, and few young people eat

mussels regularly.

Acknowledgments

I thank K. Richardson for critically reading the manuscript and the Museums of L0gst0r and Randers for

providing me with literature on the kitchen mounds

found in Denmark. I also thank L. Haumann and the

Ministry ofFisheries for providing old literature on oyster

culture in Denmark and the mussel industries for the

advertisement materials on their different commodities.

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Om den naturlige 0stersbestands st0rrelse. Ber.: fra Den

Danske BioI. Sta. XXXVII:59-64.

1949. Fluctuations in the stock of oyster (Oslrea edulis) in the

Limfjord in recent time. Rep. to ICES Spec. Sci. Meet. on

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Strand, 0., and]. H. Voistad.

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MacKenzie, Jr., V. G. Burrell, Jr., A. Rosenfield, and W. L.

Hobart (eds.), The history, present condition, and future of the

molluscan fisheries of North and Central America and Europe.

U.S. Dep. Commer., OAA Tech. Rep. 129, p. 7-24.

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1893. The oyster-culture. An attempt at short account of the

present state and condition of this culture. [In Fr., Engl.] A.

F. H0st & S0n, Copenhagen.
The Molluscan Fisheries of Iceland

HRAFNKELL EIRlKSSON

Marine Research Institute

Skulagata 4

P. O. Box 1390

121 Reykjavik, Iceland

ABSTRACT

The Iceland scallop, Chlamys islandica, is the only commercially important mollusk in

Iceland. Other shelled mollusks harvested for bait or food on a small scale during most of

this century include Arctica islandica, Buccinum undatum, Modiola modiolus, and Mytilus edulis.

Beds of Iceland scallops occur off all but the south coasts of Iceland. Most are in depths of

20-60 m. The fishery began in 1969. The total number of boats, which range in length from

10-33 m, increased from 21 to 60 during 1977 to 1985, then decreased to 31 in 1990. The

average number of trips/boat/year is 65-70. Scallops are landed daily for processing the

next day. The historical peak oflandings was 17,068 t of meats in 1985, but was 10,000-12,400 t

in 1988-91. Most scallop meats were exported to the U.S. until 1988, but since have been

increasingly exported to France. A roe-on French market recently has been developing for the

scallops. Minor changes are forecast in the future; landings probably will stabilize at 8-9,000 t.

Introduction

At present, the Iceland scallop, Chlamys islandica, is the

only commercially important mollusk in Iceland, with a

number of local fisheries. In 1987 an Arctica islandica

hydraulic dredge fishery was initiated but it ceased 2

years later. Apart from that, Arctica has been fished for

bait since around 1900, but only locally in small amounts.

There is also a long tradition of fishing the European

flying squid, Todarodes sagittatus, for bait, although

catches are very intermittent in connection with the

sporadic squid migrations in Icelandic waters.

Moreover, Buccinumundatum, Modiola modiolus, and Mytilus

edulis have been fished on a very small scale for export and

local consumption. In addition, mussels used to be collected for bait in a number oflocalities in the first half of

the century. While this paper discusses only the Iceland

scallop fishery, reported landings of all molluscan species

for 1969-91 are shown in Table 1 (Anonymous, 1978-92).

The Chlamys islandica Fishery _

Habitat Description

Beds of Iceland scallops are found along all but the

south coast of Iceland. However the main distribution

is rather discontinous and almost entirely limited to

infjord areas (Fig. 1).

The majority of beds are characterized by a sloping

topography with depths ranging from 15 to 75 m, although the greatest density ofscallops is normally found

in depths of 20-60 m. Substrates can vary from relatively fine sand to coarse shelly sand, often with gravel

and occasional boulders (Eiriksson, 1970, 1986).

Bottom temperatures varying from _0.30 to 9.6°C

have been recorded on sustainable scallop grounds. On

one occasion (August 1982) a temperature of >10°C

was recorded on scallop beds in Hvalfjordur, Iceland.

However, results of a survey in April 1983 indicated a

65% decrease in scallop biomass in the area compared

with that ofthe previous year, accompanied by an equivalent increase in percentage of empty shells called

"cluckers." Thus, nonfishery-related mass mortalities

had occurred, possibly in connection with the elevated

late summer or early fall bottom temperature in 1982

(Eiriksson, 1986).

The most common large epifauna living on scallop

shells are barnacles on the upper valve and tubiferous

polychaetes on the lower valve. Some notable animal

associates on scallop beds are various echinoderms,

Asterias rubens, Echinus esculentus, Strongylocentrotus

droebachiensis, and Cucumaria frondosa; the spider crab,

Hyas araneus; and the whelk, Buccinum undatum. One of

those, the starfish, A. rubens, is most likely the main

39
40 NOAA Technical Report NMFS 129 _

67" .-_~2=_r4'-o__,---_--'2=-r2'-o__,---_--'2=-j0'--o__-,----_-'-i 18'--o__-,----_-'-i16i'-°__-,--_---'-14r'-°__,--_-----, I I I I I I

-

I I I I

Figure 1

Scallop fishing grounds and ports in Iceland.

scallop predator, although an overall low rate of natural mortality is indicated by clucker:live-scallop ratios in

catches.

History

The C. islandica fishery dates back to 1969. When searching for a market sample of ocean quahogs in

Isafjardardjup in northwest Iceland in late 1968, a good

catch of scallops was obtained by accident. After favorable reception of market samples in the United States,

a fishery was initiated in the area in early 1969 with

landings for the first year amounting to some 400 metric tons (t) live weight.

The successful initiation of the scallop fishery in

Isafjardardjup was followed by nine dredge surveys in

the years 1969-73, ranging from Hvalfjordur northward to the east coast. The surveys were led by scientific

personnel from the Marine Research Institute in

Reykjavik, but funded by additional parties, including

grants from fisheries funds. Many beds with fishable

concentrations ofIceland scallops were charted in those

surveys, leading to a number of new localized fisheries,

with the one starting in Breidafjordur in 1970 being the

most important (Fig. 2) (Eiriksson, 1986). Thus annual

scallop landings increased rapidly from 400 tin 1969 to

over 7,300 t in 1972 (Fig. 3, Table 2).

The development of the fishery was halted in 1973 as

the American market for scallop meats declined, which

led to annual landings decreasing to only 2,800 t in

1974-75. However, during the next 10 years, landings

rose steadily from 3,700 t in 1976 to the historical

maximum of 17,068 tin 1985. This was largely related

to the increased landings in the Breidafjordur fishery

from 3,400 to 12,700 t during 1976-86.

From the peak in 1985-86, annual landings decreased

again to 10,000-12,000 t in 1988-91, of which 9,000-

10,000 t have been taken in the Breidafjordur area. This

is partly the result of decreasing area catch quotas, but
________________________ Eiriksson: The Molluscan Fisheries of Iceland 41

Table 1

Reported landings (t) of molluscan species in Iceland

from 1969 to 1991 (from Anonymous, 1978-92).

Iceland Ocean Flying

Year scallop quahog squid Whelk

1969 402

1970 2,432

1971 3,658

1972 7,349

1973 4,848

1974 2,851

1975 2,784

1976 3,669

1977 4,427

1978 8,719

1979 7,800 436

1980 9,079 16

1981 10,186 7

1982 12,076 13

1983 15,181 4

1984 15,583 1,634

1985 17,068 2 3

1986 16,429 12

1987 13,272 1,085

1988 10,059 4,724

1989 10,772

1990 12,416

1991 10,297

is also linked with deteriorating markets in the late

1980's (Eiriksson, 1986; Anonymous, 1978-92).

The majority of vessels fishing for scallops are involved in other fisheries, some for up to 9-10 months of

the year but others for only 4-6 months. The smaller

boats are mostly inshore shrimpers in winter, but they

fish for demersal species in spring to summer. The

larger boats, especially those of the Breidafjordur fishery, go gill netting for cod during March-May and

inshore and offshore shrimping in the summer.

Since the beginning of the scallop fisheries around

1970, the boats in the northwestern fjord fisheries have

been small, mostly shrimp trawlers, ranging in length

from 10 to 15 m. However, in recent years this fleet is

more typified by 10-20 m (15-50 GRT) boats, with a

crew of 2-4 and fishing with one dredge of 1.5-2.4 m

width. In the larger Breidafjordur fishery in West Iceland, the size of boats has ranged from 15-25 m (20-

100 GRT, averaging 58 GRT) in 1972 increasing to 15-

33 m (20-165 GRT, averaging 90 GRT) in 1990. The

Breidafjordur fleet is composed of multipurpose

trawlerI gill net boats with a crew of 4-7 and one 1.5-

2.7 m dredge, depending on size of boat. From 1977 to

1985 the total number of boats in the scallop fisheries

increased from 21 to 60 but decreased again to 31 in

1990. At the same time the average size ofscallop boats

increased from 53 CRT in 1977 to 70 CRT in 1990

(Anonymous, 1978-92).

Most vessels in the scallop fisheries have been

equipped with the wheelhouse aft, but rigged to tow

the dredge from the stern and haul it in on the side

(Fig. 4a, b). In the first years (1969-71) an Icelandic

box-type dredge was used, resembling in some ways

hydraulic clam dredges. It consisted of a rigid metal

frame, a steel blade and box-shaped container that was

emptied by opening the rear end. In 1972 two types of

overall more effective dredges were introduced from

Britain: The Manx Blake dredge and the Conolly roller

dredge. The use ofthe Blake-type dredge became widespread in 1972-73, although it has been greatly modified and strengthened over the years, especially in connection with the rapid expansion of the Breidafjordur

fishery (Eiriksson, 1986).

The present Breidafjordur dredge has similar ranges

in width as the British prototypes, but it is up to three

times heavier (800-1,000 kg). The frame is of heavygauge steel, and it has two runners connected horizontally, including a rigorous stone guard in the center.

Instead of a fishing blade that was used in the Icelandic

box-type dredge, the modern dredge has a relatively

heavy chain ground rope in front of a metal ring belly.

A heavy metal tail bar is attached to the rear of the ring

belly and netting which forms the bag of the dredge

(Fig. 5).

An additional Icelandic dredge has also become popular since around the mid 1980's, particularly in the

ISafjardardjup and Hunafloi area. It is equipped to fish

on both sides, and with its rolling bar and chain ground

rope this dredge slides more easily over larger stones

and boulders.

In all the fisheries, scallops are landed daily for processing the next day. Thus, in a typical week, the scallop

boats are making five daily trips from Sunday through

Thursday. Although some boats have been making 100-

150 trips annually, the average number has been 65-70

trips a year in 1985-90. The fisheries are mainly seasonal during August-February, and landings in AprilJuly are generally at a minimum. However in 1991-92

there was an increasing fishery in April-May in connection with a relatively recent scallop roe-on market in

France.

In the early years of the fishery, the catch was emptied on top oflarge sorting tables on deck and sorted by

hand. However, the hand-sorting process tended to be

time-consuming owing to many undersized animals being taken along with a lot of trash. Therefore, stainless

steel rotary sorterIwashers, introduced in the 1970's,

became widespread by the early 1980's.

Scallops are mostly landed in 300-500 kg containers

or sometimes bags for machine shucking and processing the next day. Most of the production is in the form
42 NOAA Technical Report NMFS 129

" u

j

'"

:J1J

Figure 2

Detailed chart of m~ur scallop beds in Breidafjordur.

of scallop muscles (meats) that have been separated

from the viscera by cleaning machines, whose mechanism is based on a series of counter-rotating rollers.

The scallop meats are fine-trimmed manually, mechanically size-graded, and individually quick-frozen in blast

freezers. The yield of Iceland scallop muscle averages

10-12%, but fluctuations are considerable by areas or

seasons or both. Scallop meats were mostly exported to

the United States until 1988, after which they were

increasingly exported to France. Recently, a roe-on

French market has developed for Iceland scallops which

involves increased manual handling following mechanical shucking. This production increases the yield up to

about 15-18%. Figure 6 gives the annual production of

scallop meats and the export value in U.S. dollars during 1969-91. The production reached a maximum of

1,840 t in 1985, and the value of exports peaked at

US$14.1 million in 1986. However, taking all Icelandic

marine exports, the proportion of scallops was highest

in 1983 and 1972 at 2.5% and 2.3%, respectively, but
Eiriksson: The Molluscan Fisheries of Iceland 43

Table 2

Nominal catch (t) by areas and overall, 1969-91, of Iceland scallops (from Anonymous, 1992).

Year Breidafj6rdur Hvalfj6rdur Patreksfj6rdur Arnarfj6rdur Dyrafj6rdur isafjardardjup Hunafl6i Skagafj6rdur Vopnafj6rdur Overall

1969 420 402

1970 2,216 199 17 2,432

1971 2,542 68 140 534 374 3,658

1972 4,564 78 295 19 2,087 306 7,349

1973 3,218 140 196 3 1,219 72 4,848

1974 2,851 2,851

1975 2,729 28 27 2,784

1976 3,420 148 101 3,669

1977 3,752 73 260 342 4,427

1978 7,575 17 126 128 603 270 8,719

1979 6,055 16 178 141 473 937 7,800

1980 7,133 42 279 155 615 855 9,079

1981 8,328 315 32 522 74 687 228 10,186

1982 10,034 521 27 670 123 634 67 12,076

1983 11,218 346 59 842 100 921 1,695 15,181

1984 11,880 82 67 550 28 867 1,733 376 15,583

1985 12,128 16 754 120 881 1,986 665 518 17,068

1986 12,708 619 121 707 1,232 513 529 16,429

1987 11,071 227 84 314 1,576 13,272

1988 9,810 30 219 10,059

1989 10,066 60 469 177 10,772

1990 10,090 299 124 704 1,199 12,416

1991 8,918 339 346 597 98 10,298

has decreased to around 1% in 1990-91 (Anonymous,

1978-92).

As a rule, scallop processing plants are located at

ports of landing. Stykkish6lmur, at the western bay of

Breidafjordur, is by far the most important scallop port,

with frozen scallop meats accounting for about 55% of

the value of marine products in 1990. Other important

scallop ports are Grundarfjordur and Brjansl<ekur (also

in the Breidafjordur area), Bildudalur (at Arnarfjordur),

Isafjordur (at Isafjardardjup), and Hvammstangi,

Blondu6s and Skagastrond in the Hunaf16i area.

Catch per unit of effort (CPUE = landings per hour

of fishing) has been monitored by logbook catch reports since late 1972. In Breidafjordur, where catch

rates have generally been high, dredge tows are often

limited to only 5-10 minutes, averaging 4 tows per

hour. However, tows of 20-30 minutes are quite regular, especially in the smaller fjord fisheries.

Due to improved gear efficiency and the introduction ofsorting machines, the average catch per hour in

the Breidafjordur fishery increased from 500-600 kg in

1972-74 to around 1,000 kg in 1981-83. Moreover, the

average catch per hour has since remained in or around

950 kg (Fig. 7). However, if adjustments are made according to some known changes in dredge efficiency,

20000

18000 0 OTl-lERAREAS

• BREIDAFJORDUR 16000 Vl

c:

2 14000

0

"C 12000 CD

E 10000

en

C) 8000 z

15 6000 Z

:5 4000

2000

a 970 1 2 3 4756 7 8 980 1 2 3 4856 7 8 990 1

YEAR

Figure 3

Landings of Iceland scallops from Breidafj6rdur and

other areas in 1969-91.

the CPUE has decreased from around 1,300 kg in 1981-

83 to some 950 kg during 1988-91. A similar trend has

been observed in the smaller fjord fisheries, although
44 NOAA Technical Report NMFS 129

Figure 4

Fishing for Iceland scallops in Breidafj6rdur. a. View from pilothouse ofvessel showing dredge being landed; three

other scallop dredge boats are in view. b. View from bow of vessel showing dredge about to be emptied. At right,

note rotary sorter/washer and three crewmen culling scallops.

a

b
_________________________ Eiriksson: The Molluscan Fisheries of Iceland 45

Figure 6

Annual production of scallop meats (xlOO t) and export value (millions of U.S. dollars) during 1969-91.

D TONS(MEATS)

- VALUE

9701234756789801234856789901

YEAR

20 -,-------------------,

18

(i;"

c

.Q

1200

---0-- BREIDAFJ.

- ISAFJ.

1000

Oi

c

:E

J@ BOO

:::>

BOO

w

::::>

Q.

u 400

Figure 5

A 500 kg catch of live scallops taken in a 1.5 m

Breidafjordur dredge during a research survey.

the catch rates are lower due to either less density of

scallops or smaller boats and gear (Anonymous, 1992).

200 +TO,......-,-.,..--....--T-...,..........-r....-,....-,-.........,.-.......--.--j

70 72 74 76 78 80 82 84 86 88 90 92

YEAR

Scallop Management _

Figure 7

CPUE (kg landed per hour fishing) in Breidafjordur,

Isafjordur, and Hunafl6i 1972-91.

The rapid expansion of the scallop fisheries following

the discovery ofwidespread beds in the early 1970'sled

to early catch limitations by late 1972. First, entry into

the fisheries was limited to local fishing boats, and log

books were made compulsory for monitoring the fisheries. By 1976 the number of processing plants was

limited by the Ministry of Fisheries, which allocated a

catch quota to each licensed plant in accordance with

the total allowable catch (TAC) of each local fishery.

Since 1984 a government management system has been

enforced based on individual boat quotas for all major

demersal, pelagic, and invertebrate species, including

the Iceland scallop.

The government management scheme became particularly effective during the rapid development of the

large Breidafjordur fishery in the late 1970's and early

1980's. At the same time, the scallop stock in the area

has been monitored by an annual dredge survey in

addition to the use of CPUE data from skipper's catch

reports. Moreover, those two data sets have formed the

basis of an annual TAC recommendation by the Marine

Research Institute. As a rule, this management plan has

been effective and maintained high enough catch rates

for a profitable fishery in this area. On the other hand,

the smaller fisheries have shown a much greater volatil-
46 NOAA Technical Report NMFS 129

ity, fluctuating or even discontinuing in phase with the

market situation each time.

Scallop meats are regularly inspected by the Icelandic Fisheries Laboratories. Over 100 batches were inspected in 1991, including 400 bacteriological samples

(personal commun.).

Current Scallop Status _

Scallop quotas were allocated to 38 boats in 1991. All

but two or three of these are multipurpose vessels fishing equally for scallops, demersal species (i.e. cod and

haddock), shrimps, and even herring. The boats range

in size from 10 to 20 m in the smaller fjord fisheries in

northwest Iceland to the considerably larger 15-33 m

vessels in the most important fishery at Breidafjordur.

Most of the fleet has been built within about the last 30

years, with the older boats having, as a rule, been well

maintained or even largely rebuilt in later years (Table

3) (Anonymous, 1990). Crew size varies according to

size of boat, from 2 to 7, but most often from 3 to 6.

The annual 1991 quota per boat varied from as little

as 45 t live weight and up to 750 t. However, the present

management system allows for an interchangeability or

transfer of quotas between boats. A typical daily catch

in Breidafjordur varies from 4 to 8 t, and catch per hour

from 600 to 1,200 kg, depending on size of boat, dredge,

and crew. In the smaller fisheries of northwestern Iceland, the catch per hour is more typically 300-500 kg

with daily landings of 3-4 t.

All the reported Icelandic scallop production is exported. In 1991, France was the largest market with

88% ofIceland's scallop exports followed by the United

States.

Present government management regulations are

based on total allowable catch (TAC) for each fishery.

Each area TAC is set annually for the quota year 1

Sept.-31 Aug., and allocated to a limited entry of local

boats, based on their average landings in a number of

years previous to the individual boat quota system. Other

Table 3

Length (m) and age of the Icelandic scallop fleet in

1991-92 (from Anonymous, 1990).

Length No. of Building No. of

(m) boats year boats

10-14 13 1945-54 2

15-19 4 1955-64 10

20-24 6 1965-74 16

25-29 12 1975-84 2

30-34 3 1985- 8

regulations include a minimum landing size of 6 cm

(shell diameter) in all fisheries and closed areas according size of boats in the Breidafjordur fishery.

Monitoring the stocks is made possible by compulsory catch reports, stating daily catch, fishing hours,

and size of boat, dredge, crew, fishing area, and subarea. The logbook data along with an annual dredge

survey of 120 standardized tows, are used for the annual

TAC recommendation by the Marine Research Institue

for the Breidafjordur area, but regular surveys are biennial or less often in the smaller fisheries.

In 1990, scallop landings amounted to 12,400 t at a

landed value of US$5.5 million. At the same time some

1,366 t ofmeats were exported, for a total value of$12.7

million. From 1990 to 1991, the price per kg oflanded

whole scallops rose from $0.44 to $0.51, which meant

that in spite of total landings dropping to 10,300 t in

1991, the overall landed value remained relatively stable

at $5.3 million. Moreover, although exported scallop

meat production in 1991 decreased to 1,160 tat $11.3

million, the price per kg of meats went up by some $0.40

over the previous year, to $9.69 (Anonymous, 1978-92).

The Future _

The TAC recommended by the Marine Research Institute for the Breidafjordur fishery in the quota year 1

Sept. 1992-31 Aug. 1993 amounts to 8,500 t. This is an

unchanged TAC from the previous quota year, but

considerably lower than the highest recommended

TAC's for this area of 1l,000 tin 1983-85 and 1987.

Although the abundance of larger scallops (over 8 cm)

decreased during the 1980's, the proportion of medium scallops (7-8 cm) has stabilized since about 1988.

Also, recruitment of5.5-6.5 cm individuals has appeared

well above average in 1991-92 (Anonymous, 1992).

However, major changes are not forecast in scallop

quotas in this area over the next 10 years and landings

will probably stabilize at 8,000-9,000 t.

The present TAC for the smaller fjord fisheries combined was set at 2,850 t for the quota year 1991-92,

whereas the recommended TAC for the quota year

1992-93 stood at 3,000 t (Anonymous, 1992). Thus, the

overall scope for increasing the scallop fishery appears

rather limited, and total annual scallop landings are

expected to remain at 10,000-12,000 t in the future.

At present, the possibility of unknown inshore scallop grounds is considered remote, although some

smaller beds may still be unknown or not utilized. Furthermore, no potential offshore stocks have been located in Icelandic waters. Therefore, the scope for increasing the fishery may lie in developing the scallop

fishing gear to improve its efficiency and reduce shell

breakage and indirect fishing mortality.
____________________________ Eiriksson: The Molluscan Fisheries of Iceland 47

Literature Cited

Anonymous.

1978-92. Utvegur 1977-91 [Fishery statistics 1977-91]. Fish.

Assoc. Iceland, Reykjavik.

1990. islenskt Sj6mannaalmanak 1991. 66:506-595. Fish.

Assoc. Iceland, Reykjavik.

1992. State of marine stocks and environmental conditions

in Icelandic waters 1992. Prospects for the quota year 1992-

93. Hafranns6knastofnun (Mar. Res. Inst.) Fj6lrit 29:63-66.

Eiriksson, H.

1970. Athuganir a horpudiski, Chlamys islandica Muller, ari6

1969. Hafrannsoknir 2:57-68.

1986. H6rpudiskurinn, Chlamys islandica Muller. Hafranns6knir 35:5-40.

The History of the Queen Scallop Fishery of the Faroe Islands

ARNI NICOLAJSEN

Fiskirannsoknarstovan

(Fisheries Laboratory ofthe Faroes)

Postrum 3051, Noatun

11 0 Thorshaven

Faroe Islands (Denmark)

ABSTRACT

The queen scallop, Chlamys opercularis, is the only commercially important mollusk around

the Faroe Islands. The scallop beds are close to shore, about 15 n.mi. from land. The fishery

for the scallops began in 1970 with older fishing vessels being modified for scalloping. At the

same time, a processing plant was constructed. The trend in catches has been increasing. In

1970-77,4-9 ships dredged for scallops, but as inshore beds were overfished several boats

left the fishery. In 1978-87, from 2 to 5 ships comprised the fleet, and in 1988-91 only one

ship was fishing on the scallop beds. Nearly all scallop production is exported. Its value

increased throughout the period to nearly US$6 million in 1990, but was US$3 million in

1991. In most of the period, nearly all the production went to the U.S., but since 1988

increasingly more has been exported to France.

Introduction

Situated between Scotland and Iceland, the Faroe Islands (Fig. 1) are surrounded by the relatively warm

waters of the Northeast Atlantic Current with a mean

water temperature ranging from 6°C in February to

lOoC in August. Though different bivalves and gastropods are fished for bait and limited local consumption,

these catches are small and not recorded. The exception is the queen scallop, Chlamys opercularis, which

remains the only commercially exploited species (Fig.

2). It is dredged on the Faroe Plateau which constitutes

the northwesternmost distribution of this species in

Europe. Some small-scale rearing of the blue mussel,

Mytilus edulis, has been attempted in sheltered areas

recently, but no serious production or sale has sprung

from it, and this enterprise has stopped now.

Queen Scallop Habitat and Fishing Areas _

The queen scallop beds are situated relatively close to

shore, about 1-15 n.mi. from land, on sandy, rocky, or

soft bottom in depths of 30-60 fathoms with a total area

of about 400 km2 (Fig. 1). The dominant cohabitants in

the main habitat of the scallop are different species of

whelks, Buccinum undatum, Neptunea despecta; mussels,

Astarte elliptica, Venusfaciata, Cardium echinatum, Modiola

modiolus, Artica islandica, Venerupis rhomboides; starfishes,

Asteria rubens, Henricia sp., Hippasteria phrygiana, Crossaster

papposus; brittlestars, Ophiopholis aculeata, Ophiotrix

fragilis; sea urchins, Strongylocentrotus droebachiensis, Echinus esculentus; sea anemones, Tealia felina; hydroids,

Abietinaria abietina, Hydrellinariafalcata; and hermit crabs,

Pagurus bernhardus. The main fishing grounds lie east of

the islands, but in 1988 a new area was discovered north

of the islands. The development of the fishery in the

two areas will be treated separately.

Fishery Development _

The queen scallop fishery was spurred by the development in the Scottish scallop fishery which, after a decline in catches of the great scallop, Pecten maximus, in

the late 1960's, turned to the somewhat smaller queen

scallop. Communications with Scottish fishermen and

information from Faroes fisheries biologists suggested

the possibilities for a future scallop fishery in the Faroes.

When fishing began in December 1970, older fishing

vessels were modified for the scallop fishery (Fig. 3). At

the same time, a processing plant was constructed. After the first year of fishing, it became obvious that the

adductor muscle of the scallop was largest in the au49
50 NOAA Technical Report NMFS 129 ........; _

tumn, and the fishing season was voluntarily set from

August to January. The scallops are shocked in a processing plant (Fig. 4), at first by hand but later theprocess has gradually become more automated.

\~-l.j \

Faroes , < L-/ t: r--- ... c: I

v '-./\

... , r--J

0,

.:. \I

--....... ...

\ I

" \

(

...

/ .... /

.... ....

/

" / c

" \

e'o ,

0' I

,J -.,~

.... I '=.:J~ \ ....

)/1 C)~ \ I

j_._- :)' c;G

._-_.__: "j < ._---- - I

\

(\'\ \ \ \ .... .... \

Figure I

Map of the Faroe Islands (shaded), distribution ofscallop beds (heavy outlines), and depth contour lines.
Nicolajsen: The History of the Queen Scallop Fishery of the Faroe Islands 5 I

The main trend in catches and catch per unit of

effort (CPUE) in units of catch (kg/foot/hour) per

dredge width in feet per hour the vessel spent on the

fishing grounds, has been increasing throughout the

more than two decades of scallop fishing (Fig. 5). The

increase in catches follows the slow but constant improvement in ships, gears, and fishing skills, as well as a

gradual extension ofthe fishing area from time to time.

The trend in catches can be described for three main

periods. During 1970-77 the catches were stable at

around 500 metric tons (t) of whole scallops per year.

In 1978-87 the catches stabilized at a new level of

Figure 2

The outside and inside of the queen scallop.

Figure 3

An older fishing vessel used for dredging scallops.
52 NOAA Technical Report NMFS 129

Figure 4

Top photo, the first processing plant for the queen scallop at Gvri on the island of Streymoy. Below is the present scallop

plant at the same site.
______________ Nicolajsen: The History of the Queen Scallop Fishery of the Faroe Islands 53

In 1970-77, the CPUE increased from the initial level

of about 27 kg/foot/hour to about 41 kg/foot/hour.

In this period, fishing was carried out by 4-9 ships (17-

80 BRT) with 3-6 crew members. The vessels used one

dredge 3-9 feet wide. The gear was light and wires thin.

Usual length of wire out when fishing has been 3-5

times the depth. The towing speed was 2-3 n.mi./hour.

At first, fishing went on mostly in a limited area close

to the islands, but as these beds were overfished several

boats left this fishery and the ones that stayed had to

search for new grounds. The series of maps (with year

number) show a circulation between the subareas as

some beds were depleted by fishing and others are

growing new stocks. The legend shows the percentage

of catch taken in each subarea (Fig. 6).

The scallop vessels usually remained at sea for a day

and had about 2 hours ofsailing time to the harbor and

used another few hours to unload. In this period, the

undersized shells (less than 55 mm high) that had to be

thrown back into the sea, had to be sorted by hand (Fig.

7). As piles of shells were sorted, the fishing operation

stopped for a while, and this delayed the actual fishing

somewhat. Around 1973 an automatic sorting machine

was installed in some boats and this increased the number of hauls per day. In 1975 some vessels shifted to

thicker wire and this increased the efficiency considerably. In 1978 the CPUE went up dramatically to about

69 kg/foot/hour.

6,000 120

100

80

<Il :; c: 0

.9 .c:

g 60 c50

:::;; '"

OJ

><:

40

20

a 1975 1980 1985 1990

Year

around 1,900 t. The period 1988-91 has been unstable,

with increasing catches from around 2,000 t to 4,000 t.

Most of the increase can be attributed to factors such as

learning skills and technological improvements, but,

especially for the third period, time spent on the fishing grounds has increased as well.

Figure 5

Catches and CPUE of the queen scallop, east of the

Faroe Islands, in the period 1970-1991.

(

,

1.-'1

79 ,.

Percent

of

catches

o

1 - 5

C]]

6 - 24

25- 49

50- 74

..

75 - 100

Figure 6

Development in distribution of catches of the queen scallop, Faroe Islands, in the period 1970-82. The number on the top

of each frame refers to the season, i.e. 70 = 1970/71. From Nicolajsen (1984).
54 NOAA Technical Report NMFS 129 _

Figure 7

Part of the catch of queen scallops on deck of a dredging

vessel.

The period 1978-87 started with a high CPUE of

about 64 kg/foot/hour mostly due to a shift of gear

from a light 12-foot Scottish type dredge to a heavier

Faroes-type 12-foot dredge (Fig. 8). The number of

vessels were 2-5, though two of them caught more than

95% of the catches, as they were the most efficient

vessels.

In 1980 a larger vessel (180 BRT) replaced an older

vessel (80 BRT) , and from 1982 it towed two dredges at

a time. thereby increasing its effort and catches

considerably (Fig. 9). But the two dredges were not

used fully as the hauling operation now took longer.

This meant a drop in the calculated CPUE which did

not take account of this fact.

In more recent years, 1988-91, only one ship has

been fishing the traditional beds, and CPUE and total

catches have continued to rise. This has been due to

the increase in towing speed and eagerness to exploit

more intensely, prompted by the prospect of harsh

competition from a large scallop factory trawler. This

new factory trawler was one of two originally built for

Faroes shipping companies for the Iceland scallop fishery in the Barents Sea in 1987 (Fig. 10, 11). As the

fishery for the Iceland scallop, Chlamys islandica, collapsed in 1988-89, one of these trawlers applied for

fishing permission at the Islands, and this was granted

provided that it was outside the traditional eastern scallop beds. It had been known from the ongoing fishery

and from fisheries investigations that some beds were

outside the traditional fishing grounds, but now a larger

Figure 8

A Faroe Islands 12-foot dredge for the queen scallop.

Figure 9

A 180-BRT vessel, Nordheim, which towed two dredges for the

queen scallop.
Nicolajsen: The History of the Queen Scallop Fishery of the Faroe Islands 55

Figure 10

The factory scallop dredger, Fame (in the middle of the

picture) .

Figure 11

View ofscallop factory trawler, Fame, showing part of raised

dredge.
56 NOAA Technical Report NMFS 129 _

5,000 ---------------1

1975 1990

6,000-,--------------------,r:.=--,

I Others

•

Germany

•UK

o

France

III

Denmark

•USA

o 4,000

1

3,000t--------1------j

3 '"+ -___ 1,0001

oi~... 1980 1985

Year

8,000 --------r16

7,000 -J14

US$=6.50 DKr Prices I

6,000 12

5,000 10 0

0 Cl

C!. x

U> 4,000 8 ;;;;

Cf) Cf) ::> ::>

3,000 6

2.000

1,000 I

o . 0 1975 1980 1985 1990

Year

Figure 12

Export value and prices of the queen scallop, 1972-91.

Figure 13

Export value and markets of the queen scallop, 1972-91.

ship was willing to search more effectively. It soon discovered a comparatively large area of about 100 km2

north of the Islands with high concentrations of scallops. This area was fished for several months each year

until the end of 1990 when the factory trawler was taken

over by foreign owners.

ated by the fishing industry and farming of Atlantic

salmon, Salmo salar, and rainbow trout, Oncorhynchus

mykiss. Being reared in areas exposed to organic waste,

blue mussels have occasional been affected by PSP, and

harvesting has been prohibited for the relevant periods.

Markets and Prices

The Future

Nearly all the queen scallop production is exported.

The export value has increased throughout the period

from a few hundred thousand dollars to almost US$6

million in 1990, but was only US$3 million in 1991. The

high values in 1989 and 1990 were due to increased

catches especially from the northern area.

Prices were stable at US$4/kg (of adductor muscles)

in the 1970's but went through a turbulent phase in the

1980's, peaking at over US$12/kg in 1983. In 1988 the

price dropped to US$6/kg when the scallops were sold

to France instead of the United States. During the last

two seasons, prices have been around US$8/kg (Fig.

12). In most of the period, almost all production went

to the U.S. market and the remainder to Europe. But

since 1988 more and more has been sold to France. In

1991 none went to the United States (Fig. 13).

Since the factory trawler stopped fishing in December

1990, about 10 vessels have applied for fishing rights in

the northern area. Due to protests from longline fishermen, however, the politicians have bowed to their demands and stopped any further exploitation of this

area. In the midst of rising unemployment this hardly

seems logical, but the traditional hook-and-line lobby is

much stronger than the more recent dredge lobby. As

fishing on the eastern area has reached its limit, it

might be wiser to spread the current capacity over the

two areas instead of allowing new ships into this fishery.

There have been talks of rearing or ocean ranching

the great scallop, Pecten maximus, which exists sparsely

on the Faroe Plateau. Also, resettling of young queen

scallops from deeper but less productive waters to shallower and more productive areas has been considered.

The Environment and Pollution _ Literature Cited

The environmental question has never been an issue in

the Faroes queen scallop fishery, as the beds are in

areas with strong currents and there is practically no

industrial waste apart from inshore eutrophication crcNicolajsen, A.

IYH4. Jomfru0sters (Chlamys aperculans) i f;er0esk farvand.

populationsdynamik og fiskeri. [The queen scallop (Chlamys

apercula'ris) in Faroese waters. population dynamics and fishery]. Univ. Roskilde, Denmark. Thesis, 83 p. In Dan.
Introduction

The Molluscan Fisheries of Germany*

MATTHIAS N. L. SEAMAN

Fisheries Biology Department

Institute for Marine Research

24105 Kiel, Germany

MAARTEN RUTH

Fisheries Agency

State ofSchleswig-Holstein

24148 Kiel, Germany

ABSTRACT

The German molluscan fishery has always concentrated on the North Sea. Mollusks occur in

the Baltic Sea, but are not as marketable. In prehistory and the Middle Ages, coastal

inhabitants gathered mussels, Mytilus edulis, cockles, Cerastoderma edule, and flat oysters,

Ostrea edulis, for food and also used mussels as agricultural fertilizer. An organized oyster

fishery developed in the 16th century and had considerable economic importance for 300

years. Oysters were dredged with sailing vessels near the coast, as well as far offshore.

Catches peaked in the second half of the 19th century at 3-5 million oysters per year. They

declined dramatically in the following decades due to permanent recruitment failures, and

the flat oyster finally disappeared from the German coast in the 1950's. An organized fishery

for freshwater pearl mussels, Margaritifera margaritifera, also developed at the end of the

Middle Ages, but mismanagement and environmental degradation since the late 19th

century have brought this species to the brink of extinction as well. Other mollusks

harvested on a smaller scale in the past have been softshell clams, Mya arenaria, and whelks,

Buccinum undatum. The modern mussel fishery for human food began in 1929 with the

introduction of novel dredging methods. Annual catches were in the order of a few

thousand tons during the first half of this century and have attained 20,000-60,000 tons

since the early 1980's; concomitan tly, prices have increased five-fold in recent decades. The

fishery is now based on 14 highly specialized vessels harvesting from 3,800 ha (9,500 acres)

of culture plots which are seeded with mussels from natural beds. Pacific oysters, Crassostrea

gigas, were first introduced in the 1970's, and a natural population has recently begun to

establish itself. They are cultured by one company which imports half-grown seed from the

British Isles. A nearshore hydraulic dredge fishery for cockles began in 1973, but was

banned for political reasons in 1992. It was replaced by a new offshore fishery for hard

clams, Spisula solida, which ended when the clam stock suffered total mortality in the 1995-

96 ice winter. The molluscan fisheries and aquaculture sector (production and processing)

in 1995 employed almost 100 people year-round and another 50-100 seasonally. The

annual product is about US$35 million.

fish and shellfish available throughout the country, and

per capita seafood consumption is slowly increasing. It has

Germany has about 2,000 km of coast (about half on

the North Sea and half on the Baltic); the German

molluscan fishery, however, has always been concentrated in the North Sea sector (Fig. 1). Shellfish consumption was of only local importance until the 20th

century. Modern processing and marketing now make

* This study was supported by the Federal Environmental Agency,

Environmental Research Plan of the Minister for the Environment,

Nature Conservation and Nuclear Safety ofthe Federal Republic of

Germany (Grant 108 02 085/01), and by the State of SchleswigHolstein. This is publication 50 of the project Ecosystem Research

Wadden Sea.

57
58 NOAA Technical Report NMFS 129 _

55

54

53

NORTH

N.

SEA

BALTIC SEA

MECKLENBURG - CISPOMMERANIA

"'0

o

i

»

Z

o

Figure I

The German coast: Molluscan fisheries have always been based on the North Sea sector.

attained 14 kg per year (twice as much as in the U.S., but

only one-tenth that ofJapan) , 20% ofwhich is shellfish.

The Wadden Sea

The German North Sea coast is characterized by 5,000

km2 of tidal flats and channels, which are largely protected by island chains and interrupted by the Weser

and Elbe estuaries. This shallow coastal area (Fig. 2),

termed the Wadden Sea, extends up to 30 km off the

mainland shore. There are two daily tides, with average

amplitudes between 1.7 m on the open coast and 3.5 m

in inlets; current speeds may surpass 3 m/second in the

tidal channels, and 1 m/second on the flats. Storms are

frequent. The turbidity of the water is very high, and

particulate inorganic matter levels may attain several

grams per liter. The grain size of the bottom sediments

varies from 2 mm (coarse sand) to 0.002 mm (clay),

depending on local current and wave action.

The Wadden Sea is subject to extreme environmental fluctuations. The average salinity is around 30%0,

but the effects of evaporation and precipitation are

often very important; annual fluctuations from 20° to

34%0 are common, and short-term variability is from 0

to 40%0. Water temperatures are around the freezing

point in winter and may be more than 20°C in the

summer; on the tidal flats, the daily temperature variation at the surface of the substrate may be more than

30°C, and more than 60°C in the course of the year.

Periodic winter ice conditions may almost wipe out the

macrofauna on the tidal flats. but the populations generally recover in the following spring and summer

(Wolff, 1983; Reise, 1985; Beukema, 1989).

The vegetation consists mainly of Spartina, Zostera,

Enteromorpha, Ulva, and Fucus species. The benthic

macrofauna consists ofrelativeIy few particularly adapted

species, but these may be present in enormous numbers. Bivalves account for more than two-thirds of the

Wadden Sea biomass. According to Wolff (1983), the

most important are blue mussels, Mytilus edulis (23% of

the biomass in ash-free dry weight); softshell clams, Mya

arenaria (17%); cockles, Cerastoderma edule (16%); and

Macoma balthica (8%). These biomass values are subject

to great fluctuations from one year to another (Asmus,

1987; Beukema, 1989; Obert and Michaelis, 1991).

Except in the case of blue mussels, there are no

recent large-scale surveys of the German bivalve stocks;

we estimate that the predominant species at present are

the Atlantic jackknife clam, Ensis directus (introduced

from America in the late 1970's; Essink, 1986); the hard

clam, Spisula solida (in deeper waters seaward of the

Wadden Sea); Mytilus edulis; and Cerastoderma edule, in

that order. The larvae of Ensis are by far the most

abundant in the plankton (Pulfrich, 1995). All of these

bivalves are burrowers, except for blue mussels, which

form dense natural beds in which the individuals attach

to each other by their byssus threads; although the

mussels make up 20-70% ofthe biomass in many areas,

they occupy only 1% of the space. The once very com-
Seaman & Ruth: The Molluscan Fisheries of Germany 59

ud flat •... :-

North

Sea

#

1# f)

##

Mixed

.. sediment

o

o

.-'::'Salt

.marsh

Dike

Mainland

Figure 2

Diagram of the Wadden Sea coastal area: # are mussel aggl'egations (1 = wild bed, high

intertidal; 2 = wild bed, low intertidal; 3 = culture plot; 4 = wild bed, subtidal). A "hallig" is a

small island not protected by a dike.

mon flat oyster, Ostrea edulis, vanished from the German coast in the 1950's. The most important gastropods are whelks, Buccinum undatum; periwinkles, Littorina

spp.; and Hydrobia spp.

The adult mollusks are preyed upon by large numbers of birds, mainly eider ducks, Somateria mollissima;

seagulls, Larus spp.; and oystercatchers, Haematopus

ostralegus. Mussels are also consumed by starfish, Asterias

rubens. Bivalve spat and juveniles are taken by shore

crabs, Carcinus maenas; brown shrimps, Crangon spp.;

and by fishes (mainly plaice, Pleuronectes platessa) (Wolff,

1983; Reise, 1985, 1992; Michaelis, 1992; Nehls and

Ruth, 1994a, b).

The Western Baltic Sea

In the Baltic Sea, tides and currents are negligible, and

the water attains depths of more than 10m very close to

shore. Bottom sediments are mainly fine sand and silt.

Environmental conditions are more stable than in the

Wadden Sea, except for marked seasonal fluctuations

in salinity, with surface values from 15 to 23%0 at

Flensburg Fjord, and 8-17%0 off the coast of Mecklenburg; bottom water salinities are about 10%0 higher.

Annual temperature fluctuations are between O·C and

20°C (Siedler and Hatje, 1974). Oxygen deficiency in

the bottom water has become an increasing problem in

recent years (Weigelt and Rumohr, 1986).

The brackish character of the Baltic Sea reduces the

number of species, and there is also a reduction in

benthic biomass with decreasing salinity. Bivalves generally account for 90% or more of the benthic biomass

off the German coast. The main bivalve is the quahog,

Arctica islandica, with local densities of 100-500 g/m2

fresh weight; other important bivalves are Abra alba,

Macoma balthica, Astarte borealis, Cerastoderma spp., and

M. edulis. The low salinities in the inner Baltic cause

stunted growth, sterility, and brittle shells in many species; on the other hand, many shallow-water species are

also found at greater depths where the salinity is higher

(e.g. mussels at 100 m). The main predators of bivalves

are fishes, such as cod, Gadus morrhua, and flatfishes

(Arntz, 1978; Theede, 1981).
60 NOAA Technical Report NMFS 129 _

History of the Gennan

Molluscan Fisheries _

Large piles of molluscan shells have been found associated with Stone and Iron Age and Viking settlements.

The most common shells found in Iron Age kitchen

middens are those of blue mussels, Mytilus edulis, and

cockles, Cerastoderma edule; other bivalves (mostly flat

oysters, Ostrea edulis) , and gastropods (mostly periwinkles, Littorina littorea) were consumed less often

(Harck, 1973). Canute the Great, King of England,

Denmark and Norway, reportedly had oysters brought

from England to the West Coast ofSchleswig in the first

half of the 11th century A.D.; artificial oyster beds are

also said to have been established during his reign

(Muller, 1938; Amold, 1939). Since the 13th century, the

North Frisians brought their produce, fish, and oysters by

boat to the market in Hamburg (Hansen, 1877).

Reliable descriptions of the prehistoric and medieval

fisheries, however, are lacking. Coastal inhabitants gathered mussels and oysters for private consumption, and

mussels and brown algae were also used as agricultural

fertilizer. The mollusks were presumably collected by

hand, rake, or fork on the extensive tidal flats at low

tide and transported to the shore, either on small boats

or with mud sledges drawn across the flats. There were

attempts to reserve oyster consumption for noblemen,

but poaching was common. There are no indications of

trade or transport inland, and molluscan consumption

was probably limited to the coastal zone.

Traditional Flat Oyster Fishery

A systematically organized German oyster fishery first

developed off the islands of SyIt and F6hr on the west

coast of Schleswig-Holstein in the 16th century. The

region was still under Danish overlordship at the time,

and the first historical record is a decree by the Danish

King Frederick II, dated 4 February 1587, in which the

harvesting of oysters without permission is placed under punishment in order to protect the stocks from

overfishing. The oyster fishery, reviewed by Schnakenbeck (1928, 1953), Muller (1938), and Neudecker

(1990), became an important economic activity in the

17th century, even leading to military skirmishes between German and Danish, and between German and

Dutch fishermen, as well as among German fishermen

from different islands. Swedish merchant ships repeatedly robbed North Frisian fishermen of their catch in

the Elbe estuary, as they were sailing to market in Hamburg, temporarily bringing the oyster fishery to a halt in

the 17th century (Hansen, 1877). In the 18th century

the stock off the shore ofWangerooge in Lower Saxony

was protected against poachers by the installation on

the dike of four cannon and a gallows (Linke and

Ruthning, 1937).

The oysters were fished with single-masted sailing

vessels and iron dredges (Fig. 3, 4); this method had

probably been used since the 13th century, but it was

not until the 17th century that priests began to teach

mathematics and navigation to the fishermen. Considering the frequently gusty winds and choppy seas, as

well as shifting shoals and treacherous tidal currents in

the Wadden Sea, the oyster fishery must have demanded

extraordinary skill. According to parish chronicles, it

also claimed many a fisherman's life. Conditions on the

coast were generally harsh, and storm floods often killed

thousands of people, sometimes depopulating entire

islands.

Figure 3

Early 19th century iron dredges used in the oyster

fishery (after Kroyer, ] 837; from Neudecker, 1990).
Seaman & Ruth: The Molluscan Fisheries of Germany 61

The Schleswig-Holstein oyster fishery was economically more important than that off Lower Saxony, and

has consequently been described in better detail. The

King of Denmark began leasing the beds of SchleswigHolstein in 1627; the entire lease was held by one

person (generally a wealthy merchant or a company)

for several years. More than 100 fishermen from the

islands of R0m0, Sylt, and Amrum, working on about

30 boats, were employed by the leaseholders, but due to

natural constraints (such as tides and weather conditions), the oyster fishery probably offered employment

for no more than 40 days per year; at other times, the

men would engage in other seagoing activities (ranging, for instance, from acts of piracy to whaling in the

Arctic Ocean), or they might tend to their land plots.

Crisis and Management of the Fishery-The price for

the lease of the oyster beds in Schleswig-Holstein increased continuously from 60 Reichsthaler (Rtr.) in

1627 to 6,000 Rtr. in 1728 (at the time, 1 Rtr. probably

corresponded to the weekly income ofa worker, so that

the 18th century price ofthe lease would be more than

US$3 million in present terms); in addition, the leaseholders had to deliver several tons of oysters free of

charge to the royal court in Copenhagen and to local

noblemen every year. This created a financial pressure

on the leaseholders that led to overexploitation.

Destruction of oyster beds by overfishing and ice

winters was a constant problem since the end of the

17th century, and systematic management began in

1703 with the closure ofthe beds for 3 years. From 1709

on, overfishing, fishing during the reproductive season

(May-August), and the sale of undersized oysters (less

than 7 cm in diameter) were forbidden. Regular inspections of the oyster beds by government officials

became the rule, and in the 18th century the position

of royal superintendent of the oyster fishery became a

highly respected and lucrative office (Muller, 1938).

As in Roman times, the oysters were eaten raw on the

half-shell; they were reputed to have medicinal properties, but the ill effects of consuming raw oysters which

had been stored out ofwater for too long were also well

known (Anonymous, 1731). Most of the catch was marketed in Hamburg, and oysters were sometimes shipped

Figure 4

19th century oyster cutter from Sylt Island. The boat is towing two dredges; the inset (upper right) shows a typical

dredge (Engraving by R. Weix; copyright by AJtonaer Museum, Hamburg).
62 NOAA Technical Report NMFS 129 _

as far as Hungary and Russia. The increasing market

demand was met by the import of cheaper oysters from

England and the Netherlands; when landings from the

Wadden Sea were high, the market price in Hamburg

would drop by 75% in the course of one day, and the

leaseholders often lost money on the venture.

Mter a severe ice winter nearly wiped out the stock in

1829-30, the fishery took 25 years to recover. Fishermen from Hamburg and the Netherlands attempted to

exploit deep-water stocks off the coast of SchleswigHolstein, but the activity proved too difficult at the

time, and the oysters were too poor in quality, to be

economically feasible. There were attempts to introduce oysters to Mecklenburg and Pomerania in the

Baltic in 1753, 1830, and 1843, but the oysters quickly

died in the low salinity (Mobius, 1887). The difficulties

of the Schleswig-Holstein fishery also led to increased

exploitation of the oyster stocks in Lower Saxony, and

the fishery offJuist and Borkum yielded almost 200,000

oysters yearly from 1841 to 1846; it collapsed in the

1850's because of overfishing and silt deposition on the

oyster beds (Linke and Ruthning, 1937).

From 1859 on, 40,000 oysters were relayed every year

to repopulate the beds in Schleswig-Holstein. The market price in Hamburg tripled between 1860 and 1875

from M35 to MI05/100 kg (at that time, M4 equaled

US$I; Dean, 1893). This provided an incentive for

overexploitation again, and production peaked in the

1860's at 4-5 million oysters per year. Mter SchleswigHolstein came under Prussian control, the new authorities conducted a survey of the fishery in 1868

(Muller, 1938). The oyster fishery employed 60 fishermen from Sylt and Amrum, working on 23 boats, plus

several artisans and the crew of a transport steamer.

Harvested oysters were taken directly to the market in

Hamburg or stocked in the port of Husum in four

saltwater ponds with a storage capacity of 150,000-

400,000 oysters. In 1878-80, 52 oyster beds were known

(more than twice as many as in 1724), varying from I to

242 ha (2.5-598 acres) in size, and their total surface

was 1,785 ha (4.410 acres).

Decline of the Wadden Sea Oyster Stock and Fishery on

Deep-water Stocks-In the 1870's the annual catch from

the Wadden Sea fluctuated between 1.2 and 3.2 million

oysters, but the stocks suffered increasing recruitment

problems, forcing a closure of the beds from 1882 to

1891. The stock, however, did not recover, and landings in Schleswig-Holstein decreased from I million

oysters per year in the early 1890's to about 300,000 in

1910 (Muller, 1938), with consequent price increases.

The fishery in Lower Saxony no longer existed and a

deep-water stock off Heligoland Island collapsed in 1882.

The market supply was maintained by a wintertime

fishery on the oyster stocks of the outer German Bight,

located 100-150 n.mi. offshore in 40 m of water. This

fishery lasted from 1885 until 1914 and was based on

the port of Finkenwerder near Hamburg (Schnakenbeck, 1928; Broelmann and Weski, 1992). The initial landings were 3 or 4 million oysters per year, and

roughly I million per year from the mid-1890's until

the beginning of World War I (estimated after

Ehrenbaum, 1892, and Anonymous, 1913). The overall

annual catch, however, must have been much higher

(possibly close to 10 million oysters), because the same

stocks were sometimes exploited by other German,

Dutch and English fishermen, including motorized vessels catching demersal fishes (with oysters as bycatch).

The boats from Finkenwerder were two-masted ketchrigged smacks and cutters (Fig. 5) 20 m in length, with

crews ofthree. The oysters were caught with 26-ft (8 m)

beam trawls (and with British-type otter trawls after

1903) whose netting was reinforced with coconut fiber.

The fishing season was from November to March; a

single trip generally lasted 2 weeks, but under adverse

conditions the men were sometimes forced to stay at

sea as long as 4 weeks. The oysters were landed at

Cuxhaven, where they sold for M4 (US$I) per hundred. When winds were foul, however, the men might

sail to the Netherlands, Denmark or England to sell the

catch, and then return directly to the oyster grounds.

Until the 1880's the fishermen of Finkenwerder, a

port with 100-200 boats at the time, had been content

catching flatfish near the coast from March to November. laying up the boats in winter. At the end ofthe 19th

century, however, the increasing competition from capitalist fishing steamers, the ensuing decline in fish stocks,

and the loss of other sources of income in the Elbe

estuary due to the competition from steam-powered

tugboats and ferries made the upkeep of a smack unprofitable unless the fishery continued year-round. Most

of the fishermen fished in the estuary during the winter, but the young captains. often desperately in debt after

purchasing boat.s, were forced into the profitable oyster

fishery, regardless ofthe risk and hardship it meant.

Because the gear had to be hauled aboard every few

hours and the catch was immediately cleaned on board,

the men were always wet and never able t.o sleep more

than two hours at a time; rheumat.ism and arthritis

often forced them to give up at an early age. The boats

were not designed t.o sail in open seas, nor did they

have the maneuverability required in t.he German Bight,

with permanent lee shores to the sout.h and east. The

men never survived if their boats sank; t.he annual mortality rat.e of fishermen was 5%, and there were hardly

any pensions for the widows and orphans (Broelmann

and Weski, 1992).

The deep-wat.er fishery had to be discont.inued during World War I; it did not resume after t.he war because the oysters rapidly disappeared.
Seaman &: Ruth: The Molluscan Fisheries of Germany 63

B ~o'

-1:1-"--0'

1m

-------------------------- ------------------------- ---------------------------------------------------_.

Figure 5

A (top)=Fishing smack from Finkenwerder, Hamburg (copyright by Museum

of Transportation and Technology, Berlin). For centuries this type of boat was

used in shallow-water finfisheries. It had a flooded hold (the "Bunn") under

the water line (B, afterJ. Broelmann, modified), enabling the fishermen to

bring the catch (mostly flatfish) alive into the port. In the oyster fishery on the

open sea, however, the Bunn might cause the boat to capsize in heavy weather;

if it listed by more than 20°, air could enter into the hold through the

perforations below and leave the boat without ballast (Reproductions from

Broelmann and Weski, 1992).

Disappearance of the Flat Oyster-In the late 19th and

early 20th century there were repeated attempts at oyster culture, spat collection, and artificial breeding by

French and Dutch methods (initiated by Mobius, 1877;

see also Dean, 1893), as well as various management

efforts (Hagmeier, 1916; Hagmeier and Kandler, 1927),
64 NOAA Technical Report NMFS 129

but they all failed. From 1894 to the 1930's, hundreds

of thousands and sometimes millions of spat and halfgrown oysters from the Netherlands, France, and Norway were relayed on the Schleswig-Holstein beds almost

every year. This allowed the shallow-water fishery to

resume, and a fishing steamer (Fig. 6) was put into

service in 1911. The continuous introduction of foreign oysters, however, also introduced various diseases

and fouling organisms. Moreover, the imported oysters

were not as resistant to the harsh environmental conditions as the native oysters, and they apparently failed to

reproduce (Hagmeier, 1941); in Lower Saxony, the

introduction of Dutch and British oysters met with outright failure (Sarrazin, 1987).

By 1925, about one-fourth of the coastal oyster beds

had disappeared under sand banks, and almost half

had given way to mussel beds and Sabellaria (tube-dwelling polychaete) reefs, or they had been colonized by

various other organisms; most of the remaining oyster

beds were depleted, and the oysters and oyster shells

were so strongly fouled that they could hardly provide

settlement surfaces for oyster larvae (Hagmeier and

Kandler, 1927). The fishery continued on Sylt and Fohr

with Dutch seed into the 1930's, but annual production

ultimately declined to a few thousand oysters. By then,

Hagmeier (1941) had already concluded that the oysters had been outcompeted by mussels (and also by

slipper shells, Crepidula fomicata), and he predicted that a

return to the traditional fishery would not be possible.

The last living oysters were sighted in the early 1950's.

The deep-water oyster stocks were almost certainly

destroyed by the heavy gear of motorized fish trawlers

(Anonymous, 1913), but the reasons for the prolonged

recruitment failures which resulted in the extinction of

the Wadden Sea stocks are unknown. Habitat changes,

such as the secular rise of the sea level and the increase

in tidal amplitude (Fuhrboter, 1989) may have favored

some species over others, but there have also been

various speculations regarding anthropogenic effects.

The same phenomena as described by Hagmeier and

Kandler (1927) have been made responsible for the

disappearance of the Wangerooge oyster stock in 1806

and for the downfall of the oyster fishery of Lower

Saxony in the mid-19th century (Linke and Ruthning,

1937).

Since the 17th century, the continuous building of

dikes for land reclamation and for connecting various

islands to the mainland caused changes in the Wadden

Sea hydrography; the topography of the bottom always

needs a few decades to adjust (Gerritsen, 1992; Hock

and Runte, 1992), and there may have been a perpetual

mismatch between hydrographic conditions and the

Figure 6

Oyster steamer "Gelbstern" from List (Sylt) in 1927. This vessel was about 25 m long and was

propelled by two paddlewheels located amidships on either side of the hull. It could tow six

dredges simultaneously (Photograph by R. Kandler; courtesy of Heye Rumohr).
______________________ Seaman & Ruth: The Molluscan Fisheries of Germany 65

substrate for larval settlement. This may also explain

why existing oyster beds constantly suffered from siltation or disappeared under sandbanks. In the 1920's,

finally, the recruitment problems may have been compounded by the destruction ofthe offshore stocks, which

were probably ten times greater than the Wadden Sea

stock and which may have been an important source of

larvae.

Evolution of the Fishery for Blue Mussels

The German mussel fishery is a relatively recent activity. Before the 19th century, mussels were mentioned in

documents only in relation to the necessity for their

removal from oyster beds. The first written records on

mussel consumption are from the Napoleonic Wars; in

1812, the East Frisian Islands were occupied by French

troops, and in the following severe winter the mussels

saved the soldiers from starving. As is still the case

today, the mussels were eaten after being boiled in

water. Nineteenth century documents show that the

coastal population regularly consumed mussels in times

of famine, and in the Western Baltic mussels were cultured on "stakes" (trees with the smallest branches removed). In Kiel Fjord during the second half of the 19th

century about 1,000 such stakes were driven into the

bottom in 4-5 m depths every year. The mussels were

harvested after 2-5 years for an annual yield of about 80

metric tons (t) (over 3 million mussels; Meyer and Mobius,

1865). Mussel cultivation in the Baltic was given up during

the 20th century for unknown reasons.

Heins (1868) urged North Sea fishermen to attempt

the cultivation as well, but mussels were regarded as a

poor man's food, and on the North Sea coast they were

mainly fished for use as fertilizer until the beginning of

the 20th century. The mussels were caught at low tide

with rakes and forks and brought in small boats to

sailing cutters waiting in deeper water, from which the

catch was landed in the harbors at high tide. The fishing season was from September to April, avoiding warm

weather. Landings have been recorded by fisheries authorities since 1887 in Lower Saxony and since 1914 in

Schleswig-Holstein1.

The first motor-powered vessel was put into use in

1909, but until 1914 only a few hundred tons were

landed annually, and only a dozen fishermen and vessels participated in the fishery. Increased demand during World War I resulted in a record catch of almost

I In Lower Saxony: Staatliches Fischereiamt, 27534 Bremerhaven. In

Schleswig-Holstein: Fischereiamt des Landes Schleswig-Holstein,

24148 Kiel. Data on landings and prices are also regularly published as part of the annual reports of the state fisheries agencies in

Das Fischerblatt, Schleswig-Holstein Chamber of Agriculture, Kiel.

10,000 t in 1916-17, and almost all German fishing

vessels with a sufficiently shallow draft were involved.

The strong fishing pressure and the effects ofice winters

led to a collapse of the fishery in Schleswig-Holstein in

1919. In Lower Saxony, annual landings were about 1,100

t throughout the 1920's (Schnakenbeck, 1928, 1953; Nolte,

1976; Sarrazin, 1987; Kleinsteuber et al., 1988).

Development of a Mixed Fishery in Lower SaxonyThe mussel fishery in Lower Saxony recovered with the

beginning of mechanization in 1929. The rake-andfork method was abandoned in favor of dredges developed by Dutch fishermen, leading to higher daily catches

and to the exploitation ofsubtidal stocks. Annual landings more than doubled, and a marketing company was

formed in 1933 to stabilize prices. The use of mussels as

animal feed was banned in 1934. By 1937, the fishery

employed more than 60 fishermen on 26 vessels; these

were motor-powered (15-60 hp) and 10-15 m long

(Fig. 7). Mussels were loaded on deck. Extensive cultivation on reserved plots around the low-water line was

reintroduced (first attempts in the 1920's had failed),

and more than 31 licensed plots existed by 1939. After

the outbreak of World War II, catches peaked at more

than 5,000 t in 1939-40, but the fishery subsequently

collapsed due to overfishing and ice winters.

In the post-war period, mussel catches remained low,

again owing to winter ice mortalities, and to the infestation of the mussels with Mytilicola intestinalis. These

parasitic copepods initially caused high mortalities or

rendered the mussels unmarketable because of the reduction in meat content; the mussel populations seem

to have adapted in the following 20 years, and Mytilicola

infestation no longer causes mortality or weight loss

(Dethlefsen, 1975; Nolte, 1976). In the 1950's, however, many fishermen had to abandon their culture

plots and use their multipurpose boats to catch mainly

finfish and shrimp. In 1965, there were 10 fishermen

involved in the mussel fishery in Lower Saxony using

vessels 15-20 m in length with an average of 80 m3 hold

capacity and 130 hp engines. They managed 25 culture

plots with 180 ha (450 acres), but most of them also

engaged in other fisheries.

A Specialized Fishery in ScWeswig-HoIstein-The mussel fishery in Schleswig-Holstein resumed in 1934 with

the introduction ofthe first specialized Dutch-type mussel dredging vessel. These low-draft boats were 15-21 m

long and had engines of75-100 hp; they could simultaneously operate 2 or 4 dredges which were emptied

into a hold. Most of the landings were from natural

beds; the catch could attain 40 t in one day, and total

landings increased to 2,000 tin 1939. More than 9 such

boats (some of them confiscated from Dutch owners)

were in operation during World War II, leading to a
66 NOAA Technical Report NMFS 129

Figure 7

Boat used in the mussel fishery off Lower Saxony around 1930. Two dredges can be

seen hanging from the booms. This type of boat could also be used to catch finfish

and shrimp (Photograph by Willy Nolte; from ?'<olte. 1976).

record yield of 15,000 t in 1942-43. The fishery lost

most of its Dutch vessels in 1945, but catches remained

stable at 2,000-4,000 t in the post-war period; Mytilicola

infestation of mussels in the Netherlands and Lower

Saxony gave the fishermen from Schleswig-Holstein the

opportunity to supply the Dutch market. On the other

hand, the market demand also motivated shrimpers

and Dutch fishermen to exploit the stocks of SchleswigHolstein, thus increasing the fishing pressure.

In 1950 and 1953, the state legislature passed laws to

protect the first post-war culture plots and prevent overfishing of natural mussel beds. The size ofthe boat hold

was limited to 50 m3, and the number of dredges to two

(in addition, engines were limited to 35 hp for mussel

boats in the Baltic sector). It was forbidden to transport

mussels from other regions into or through the coastal

waters of Schleswig-Holstein; culture plots were made

subject to licensing, and their borders were defined by

decree. These regulations are still in effect. but exemptions concerning the boats' performance are the rule.

In 1965 there were 8 companies in Schleswig-Holstein

devoted exclusively to mussel fishery, with specialized

vessels (about 20 m length, 110 m3 hold capacity, and

90-hp engines), leasing 35 mostly subtidal culture plots

with 380 ha (950 acres).

Other Marine Molluscan Fisheries

Whelks-These gastropods (Buccinum undatum) were

caught from 1951 to 1974 in Lower Saxony, initially by

one boat using special dredges (Fig. 8). The total catch

for the 24-year period was 3,000 t (Table 1), mostly

originating from the Ems estuary, and all of it was

exported to the Netherlands. A consumer demand never

developed in Germany. Catches continuously increased

at first, inducing other fishermen to join the fishery.

Landings peaked at 450 t in 1971, and two specialized

vessels (19 m long, 220-hp engines) were built for the

whelk fishery in that year. Landings, however, subsequently declined dramatically, and the fishery was given

up 3 years later (Nolte, 1976), as the Netherlands began to buy from English producers. According to Lozan

(1994), the downfall was due to the fact that 90% ofthe

catch was undersized, making on-board sorting too tedious; on the other hand, the refusal of the German
______________________ Seaman & Ruth: The Molluscan Fisheries of Germany 67

Figure 8

Buccinum dredge. The chain mesh in front ofthe opening is designed to repel stones, but may also inflict

damage on benthic fauna (from von Brandt, 1984).

fishermen to supply the Dutch industry on a regular basis

also contributed to the termination of the relationship2.

Softshell Clams-These clams (Mya arenaria) , are never

found in prehistoric and medieval kitchen middens,

nor in recent geological records, and it is presumed

that they were introduced accidentally from orth

America, either around the year 1600 (Hessland, 1946;

cited after Berghahn, 1990), or by the Vikings in medieval times (Petersen et aI., 1992). They have been fished

in the Wadden Sea for use as pig fodder (and for

human consumption in times of famine). A regular

fishery has never existed, however, and data are scarce,

except for the last post-war period.

From 1945 to the early 1950's more than 14,000 t

were collected by the coastal population, mainly by

digging the clams out of the sand with pitchforks and

shovels at low tide (Kuhl, 1955). Sometimes, they would

be washed out of the sediment by the action ofa boat's

propeller going full throttle against a dragging anchor

in shallow water; the boat would be beached, and the

clams loaded aboard at low tide. The most important

source of clams was the area north of the Elbe estuary.

A clam sausage was produced in the late 1940's, but

attempts to initiate a commercial fishery were given up

due to the lack of market demand ( eudecker, 1990).

Cockles-According to older fishermen3, Dutch boats

used to land on sand banks off the German coast into

2 Wolfgang Hagena, State Fisheries Agency for Lower Saxony and

Bremen, 27534 Bremerhaven, Germany. Personal commun., 1992.

3 Jurgen Petersen, retired fisherman from Wittdun, Amrum Island,

and others. Personal commun., 1992.

Table I

Landings and prices of the whelk fishery (5-year averages, after Hagena, 1992a).

Catch Price

Period (t/year) (OMit)

1951-1954 4 430

1955-1959 26 940

1960-1964 89 810

1965-1969 173 980

1970-1974 304 1,220

the 1960's to collect cockles, Cerastoderma edule, by rake;

a large-scale fishery, however, did not begin in Germany until 1973. Annual catches fluctuated greatly,

because of nearly total ice mortalities in some winters;

in Schleswig-Holstein, for instance, landings were nil

from 1978 to 1983, and the record catch of 12,500 t

(1,600 t cooked meat) in 1983 was all from Lower Saxony.

Catches and prices! are summarized in Table 2. The

landings were almost exclusively exported to the etherlands for processing and reexport to southern Europe.

There were three companies in Schleswig-Holstein

and two in Lower Saxony engaged in the fishery. In

each state, one company fished cockles exclusively,

whereas the others also held mussel licenses. The fishery was open from July to February, and the cockles

were caught by the Dutch method of hydraulic dredging (discussed later). The boats were 30-35 m long, 8 m

wide, and had a particularly shallow draft; they were

equipped with motors of up to 300 hp and special

pumps, as well as with culling and cooking facilities.

The catch was usually cooked on board; the empty

shells had to be either deposited on land, or ground to

a fragment size of less than 6 mm before being thrown

overboard at assigned dumping areas. As a minimum

size regulation, 600 cockles had to yield at least 1 kg of

meat (Hagena, 1992a).

The inception of three national parks covering the

entire German Wadden Sea in 1985, 1986, and 1990.

drastically reduced the area available to the fishery. In

addition, the fishery became increasingly hampered by

protests against the hydraulic dredging method, which

may remove up to 5 cm off the surface of the sediment.

Environmental concern focused on the resulting mortality of benthic organisms, as well as on the dredge

marks, which may remain visible on the tidal flats for

months. Although scientific studies have demonstrated

that the cockle fishery does not seriously harm the

environment (de Vlas, 1982, 1987), the fishery was

banned for political reasons (1989 in Schleswig-Holstein and 1992 in Lower Saxony; Hagena, 1992b:50).
68 NOAA Technical Report NMFS 129

Table 2

Landings and prices of the German cockle fishery (calculated from official data in the annual reports of the

state fisheries agencies; some of the landings were raw

cockles, and these have been converted to cooked meat

by multiplying by 0.13).

Catch] Price

Year (t/year) (DM/t)

1973 150 1,720

1974 R33 1,970

1975 583 1,900

L976 156 1,110

1977 594 1,200

1978 790 2,040

1979 5R8 1,960

1980 190 1,180

1981 532 1, L50

1982 2i\1 970

1983 1,627 1,220

1984 1,319 1,450

1985 459 2,270

1986 194 4,160

1987 757 3,910

1988 191 2,160

1989 431 1,950

1990 744 2,800

1991 5~8 6,400

1992 14 3,IRO

1 Cooked meat.

Extraction of Shell Deposits-Bivalve shells have been

burned for the production of lime at least since the

16th century on the North Sea coast (Hansen, 1877).

Marine deposits of mollusk shell fragments (so-called

"Schill") attain a thickness of several meters in some

tidal channels. They were strongly exploited off Lower

Saxony by hydraulic dredging with boats in the 1930's

and 1940's to meet the high demand resulting from

military construction on the East Frisian islands. Mter

World War II, the Schill fishery provided calcium for

animal feeds (Michaelis, 1993). It ended in 1967 when

the last dredging vessel was shipwrecked4.

4 Hermann Michaelis, Coastal Research Station, 26548 Norderney,

Germany. Personal commun., 1992.

The Freshwater Pearl Mussel Fishery

Pearl mussels, Margaritifera margaritifera, were once extremely abundant throughout Europe, including Germany. Their biology and fishery have been reviewed by

Wachtler (1986) and Bischoff et al. (1986). Pearl mussels inhabit cold, fast-flowing oligotrophic waters and

are very slow growing; their life span ranges from 60 to

>100 years, for a final size of about 15 em. Although

their ability to produce pearls has been known since

ancient times, a systematic fishery did not develop in

Germany until the 15th century.

Judging by the number of pearls found in 16th and

17th century treasures and relics, the German pearl

mussel stocks must have numbered in the tens or even

hundreds of millions of mussels. The church and the

princes attempted to enforce their exclusive rights with

harsh punitive measures (Fig. 9) and strict controls. For

the fishermen, as well as for the government inspectors,

the pearl fishery was only a part-time occupation, but it

was very profitable and well managed in many areas.

One rule, for example, was that a given brook or river

would only be fished once every 10 years. Mussels with

certain shell malformations (so-called "Perlzeichen,"

which had resulted from earlier damage and indicated

that the mussel might carry a pearl) were pried open with

a special tool (Fig. lOB), and the pearl was removed

without serious injury to the mussel, which was returned

to its site.

In some regions, however, it was not known that by

the study of Perlzeichen and use of special tools the

mussels need not be destroyed to ascertain whether

they carried pearls (only one in several hundred actually does), and pearl mussels were broken and thrown

on land by the millions. When German unification in

1866 put an end to local and regional management, the

exploitation of pearl mussels became a free-for-all and

caused a quick downfall of the fishery. Moreover, the

species' complex life cycle (its larvae are obligatory

parasites on the gills of brown trout, Salmo trutta) and

its stringent ecological requirements were obscure at

the time, and no major attempts were made to save its

habitat, which was increasingly suffering the effects of

industrial pollution, intensified agriculture, and stream

regulation. By the early 20th century, the total number

of pearl mussels in Germany had declined to about 5

million, and environmental degradation has since

brought them nearly to extinction (Wachtler, 1986;

Bischoff et aI., 1986).
Seaman & Ruth: The Molluscan Fisheries of Germany 69

Figure 9

Warning to pearl mussel poachers (1736). The inscription reads: "Don't get yourself hurt."

Poaching was generally punished by amputation of a hand (except in Bavaria, where

poachers were executed by hanging), and similar signs were usually posted on river banks

near pearl mussel stocks. For more than two centuries the sign shown here (a painted oak

panel) kept guard over a stock in Schwienau Creek belonging to Ebstorf Monastery in

northern Germany; it was finally removed in the 1950's (Original at Ebstorf Monastery;

photograph courtesy of State Natural History Museum, Braunschweig).

ft,akm A!"tu- T,~.J... "VnUfU. ADFOL'4 C

~'

Ie D D D

Figure 10

Instruments for the removal of pearls from live pearl mussels, developed in the 1630's by Malachias Geiger, physician

to the Duke of Bavaria (after Geiger, 1637; reproduction courtesy of State Natural History Museum, Braunschweig).
70 NOAA Technical Report NMFS 129

Figure 11

Intertidal oyster culture at List/Sylt. The oysters are in bags of plastic netting

which are strapped to tables made of iron rods. Oysters and tables must be stored

on land during the winter to avoid ice damage (Photograph courtesy ofDittmeyer's

Austern-Compagnie, List/Sylt).

Current Molluscan Production

The German molluscan fisheries and aquaculture sector (production and processing) now employs nearly

100 people year-round and another 50-100 seasonally.

It creates additional jobs in the marketing and transportation sector, but the actual number of jobs is

impossible to estimate. The annual value generated

is about DM 50 million (US$30 million); in exceptionally good years, this figure may be more than twice as

high.

Culture of Pacific Oysters

Cupped oysters, Crassostrea virginica and C. angula'a,

were introduced to the German Baltic Sea and Wadden

Sea in the late 19th (Mobius, 1887) and early 20th centuries, and again between 1954 and 1964; the experiments

were discontinued, however, mostly for economic reasons

(Neudecker, 1990). Pacific oysters, C. gigas, were introduced in the early 1970's, and an experimental hatchery

ofthe Federal Fisheries Research Agency was in operation

in Langballigau (Flensburg Fjord) from 1978 to 1984.

The salinity in Flensburg Fjord proved too low for succesful

growout (Seaman, 1985), butseveral fishermen and small

companies attempted commercial production off various

Wadden Sea islands in the 1980's.

Only one company survived by 1992; it is located in

List (Sylt), and its production is based on the import of

half-grown oysters from the British Isles. The oysters

are imported in spring and grown in sacks made of

plastic netting, which are strapped to iron tables on the

tidal flats (French "poche and table" method, Fig. 11);

they attain marketable size (70-90 g) in 1-2 years. The

standing stock is almost 2 million oysters, and annual

sales total 1.2 million (company information). More than

1 million oysters are overwintered in land-based tanks to

avoid the risk of total loss during ice winters. The company has 5-10 employees year-round; it uses additional

labor at the time the stock is brought out to the flats in

spring, and at harvest time. The enterprise began with an

original investment of DM3 million (US$2 million), and

its annual sales now total DM1.5 million (US$1 million).

The oysters sell in restaurants for DM6 (US$4) apiece.

The company conducts monthly sampling for algal

toxins (DSP and PSP), as well as for bacteria, both in

the oysters and in the ambient seawater; tests for heavy

metals and for organic pollutants such as PCB's are

done twice a year. In addition, there are further standards to be met for a government quality certificate.

The oysters are shipped in baskets made of plywood,

which are packed with moist reeds, Fragmites comunis,

and sold to restaurants and wholesalers throughout the

country; they are usually eaten raw on the half-shell.

Although they have a very high quality, the production
Seaman &: Ruth: The Molluscan Fisheries of Germany 71

method (the overwintering procedure, in particular) is

also more expensive than elsewhere, and market competition with cheaper French imports is the main constraint.

Oyster consumption in Germany more than doubled

during the 1980's, but is now stagnating at 700 t yearly.

The German market is supplied mainly from France

(400 t); imports from the British Isles and from the

Netherlands, as well as German production itself, account for another 100 t each (Neudecker, 1991;

Neudecker5). The oysters from Sylt are often preferred

over the French during the summer, because they have

a lower spawning activity, and the company has now

recovered the original investment and is making a profit.

Blue Mussel Fishery

In the past two decades, the North Sea blue mussel

fishery, reviewed by Ruth and Asmus (1994), has undergone further sophistication, whereas mussel production in the Baltic sector has ceased altogether. Evolution of the fishery has been stimulated by international

developments, but it was also encouraged by a concerted management effort in the 1970's and 1980's,

focusing on sanitation, marketing, and environmental

aspects (Kleinsteuber and Will, 1976-86). The mussel

5 Thomas Neudecker, Federal Fisheries Research Agency, Palmaille,

22767 Hamburg, Germany. Personal commun., 1992.

fishermen in Lower Saxony have given up their mixed

fishery in favor of a highly specialized mussel fishery.

The surface area of the culture plots and the landings

have risen steadily; boats have been modernized and

new vessels (Fig. 12) have been built and, although the

number of boats has decreased, the power and capacity

of the fleet have become greater.

Coinciding with the trend toward specialization and

modernization, the German mussel fishery has increasingly come under foreign control in recent years, even

though the various companies are all based in Germany. At present, there are 14 boats in the fishery (6 in

Lower Saxony and 8 in Schleswig-Holstein), but one is

subject to restrictions. The six licenses (boats) in Lower

Saxony are owned by three German fishermen (one

license each) and one German-Dutch company, which

holds the remaining three; in Schleswig-Holstein there

are two German companies with one license each, as

well as one Dutch-controlled and one British-controlled

company with three licenses each.

The German mussel culture is an extensive bottom

culture. The fishermen must submit an application specifYing location and size of the culture plots; state authorities will grant the plot (at a nominal fee) if there is

no conflict with other user groups. There are now more

than 80 culture plots off the German North Sea coast;

the size of a plot is between a few dozen and more than

100 ha (about 100-300 acres). Since 1990 the total

culture area has remained at 2850 ha (7,000 acres) in

Figure 12

Mussel dredger Ex Mare Gratia from Schliittsiel (Schleswig-Holstein), built 1987 in

Husum. The boat is carrying a full load (Photograph by Maanen Ruth).
72 NOAA Technical Report NMFS 129

Schleswig-Holstein and 1012 ha (2,500 acres) in Lower

Saxony.

Equipment-Significant technical improvements in the

procedures used to spread small mussels from the boats

onto the subtidal culture plots have contributed to the

growth of the mussel fishery in recent years. Initially,

the seed mussels had been shoveled overboard by hand,

and later by mechanical grabs. The development of

seeding procedures using conveyor belts reduced the

manpower required, but maintenance costs were high

due to wear and corrosion, and a high proportion of

mussels were damaged during seeding. Today, the

method used exclusively involves flooding holds to flush

out the mussels through hatches below the water line

by means of strong injector pumps (Fig.13); the seeding density is regulated by pump pressure and sailing

speed of the vessel. The system requires little maintenance, and hardly any mussels are damaged in the

process. On the other hand, it has led to an increase in

the vessels' total displacement for a hold of equal size.

The typical boat today is about 35 m long, up to 9 m

wide, has a hold capacity of about 100 m3, and has a

draft of 0.7-1.3 m unloaded and 1.5-2.3 m at full load.

The vessels are powered by one or two diesel engines

(total of 300-600 hp) and driven by one or two screws

which are enclosed in a broad ring and sometimes

protected additionally by steel screens on both sides.

There are two holds (fore and midships), each equipped

with an injector pump and mechanically operated

hatches on both sides of the hull. The mast (frequently

an A-shaped frame) is located in front ofthe holds. The

vessels have four booms (one for each dredge) and the

dredges are operated by six (frequently hydraulic)

winches, one to operate the warp of each dredge and

the other two to pull two dredges simultaneously over

the hold and empty them. The central hydraulic pump

is generally driven by a separate diesel engine.

A mussel boat is usually operated by a captain and a

crew oftwo. The pilot bridge and (nowadays luxurious)

accomodations are located astern. The pilot bridge is

equipped with custom electronic navigation aids such

as radar, CPS or Decca6, navigation plotter, FM radio

set, and cordless telephone. Color echo sounders are

used to find subtidal beds and to examine possible

locations for new culture plots. A dory is used for shallow-water operations, such as landing on tidal flats to

search for intertidal beds.

Method of Extensive Culture-The fishermen seed their

culture plots with mussels fished from natural beds

(Fig. 14). The fishery typically removes only half of the

6 Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA.

Figure 13

Mussel dredger: view of the dredges and holds. The pipe seen in the hold is used

during the seeding procedure to pump water into the hold and flush out the mussels

through lateral hatches beluw the water line (Photograph by Maarten Ruth).
Seaman & Ruth: The Molluscan Fisheries of Germany 73

actual mussel biomass of a mature natural bed with a

mixed age distribution (Schirm, 1991); a higher proportion may be captured on dense beds ofjuveniles or

in years when the standing stock is small and market

demand is high. Daily catches are normally about 100-

150 t, including so-called "tara" (i.e. empty shells, stones,

mud, and bycatch), which represents a full hold. On

dense subtidal beds or culture plots with sufficient water depth at low tide, the boat hold can be filled in 5

hours and, if the wild bed or culture plot is located

close to the landing site (which is the exception), the

daily catch can be doubled. Although subtidal stocks

are generally preferred, they hardly exist in Lower

Saxony; the reasons are unclear.

In the case of intertidal stocks and on low density

natural subtidal beds the catch per unit effort is much

smaller; the economic limit depends on market prices

and on the amount of stock on the culture plots. The

situation during the spring of 1990 provides a good

example. At that time, there were no subtidal beds in

Schleswig-Holstein, most ofthe culture plots were empty,

and dense intertidal beds were missing due to recruitment failures in previous years; prices promised to hit

record highs, and the fishermen fished on the remaining intertidal beds until the catches per flood tide fell

below 30 t (including up to 50% tara).

The mussels from wild stocks seldom have the meat

content required for immediate marketing. After being

fished from a natural bed, the mussels are often kept in

the hold for a few hours, sometimes in fresh water or

with added salt, to kill noxious organisms such as starfish. Half-grown mussels (20-50 mm shell height) are

seeded at densities of 100 t/ha; so-called seed mussels

(5-20 mm shell height) are relayed at densities of 30-

40 t/ha (these weights include tara, i.e. bycatch organisms, shells, mud, and stones). The success of a culture

strongly depends on careful seeding; it may take up to 5

hours to spread 100 t ofseed evenly across a plot.

Adequate culture sites must have good growing conditions, low storm risk (shelter ofislands or sand banks),

low ice risk (sufficient depth), stable bottom without

moving sands, and a low probability of massive impact

by predators (e.g. starfish, eider ducks) or other detrimental organisms (e.g. barnacles). Tidal currents should

not exceed 1 m/second. Most ofthese factors are highly

variable, and the fishermen try to offset the risk of

unfavorable conditions in one particular subarea by

distributing their plots as widely as possible. In SchleswigLanding size > 50 mm

intertidal

Subtidal

MTHW

MTLW

Figure 14

Diagram of the mussel cultivation procedure. Mussels are fished from wild beds, relayed on culture plots, and later fished

again for landing.
74 NOAA Technical Report NMFS 129

Holstein all plots are subtidal, at depths of up to 10 m

below the high-water mark; they are located in the

region north ofthe Eiderstedt Peninsula. In Lower Saxony

most of the culture plots are just above the low-water line,

in the sheltered sector west of the Weser Estuary.

At good locations small mussels attain the meat content

and size (well over 50 mm) required for marketing within

1-2 years. After harvest the plots are cleaned ofremaining

empty shells, starfish, mud, and pseudofeces deposits before reseeding. A good plot will return more than 100 t of

mussels per ha (1,500 bushels/acre) including tara, and

the yield is generally higher than the quantity seeded

originally (in the Netherlands the yield-to-seed ratio is <1,

because Dutch regulations until recently forced the fishermen to seed with haste, and because the large number of

licenses that have been granted leads to the use of many

less desirable sites, and to frequent relaying ofstock).

Management and Regulations-The fishing licenses are

the prime tool for managing the German mussel fishery. They are granted by the state governments for a

period of 1-3 years, but the fishermen have no legal

rights to be awarded licenses or to have them renewed.

Any new regulations can be introduced and enforced

by the state governments at will, particularly because

the license conditions can be changed and the licenses

can be revoked at any time. Laws and regulations are

reviewed in CWSS (1991).

In Lower Saxony, the state reserves the right to impose restrictions on the fishing season, allowable catch,

and fishing sites. The fishermen must inform the authorities about the natural beds on which they intend

to fish; the beds between the polluted Elbe and Weser

estuaries are closed to the fishery, and the other beds

are opened only after the authorities have confirmed

their safety. Although the size of the culture plots has

been frozen at present levels, there are no catch limitations. Minimum size of mussels for the consumer market is 50 mm (10% undersized mussels, calculated by

live weight, are permitted), and maximum size for seed

is 40 mm (10% oversized permitted); relaying may only

occur within the boundaries of the state. Mussels from

culture plots may be landed year-round; wild beds rr,ay

be fished only from 1 October to the end of February,

but exceptions for the seed fishery are possible between

1 March and 15 June. Controls of minimum sizes, fishing areas, and fishermen's catch records are relatively

frequent.

In Schleswig-Holstein, new regulations took effect in

January 1996, and the State Fisheries Agency now employs a biologist concerned exclusively with monitoring

the mussel fishery. There are no geographical restrictions or catch quotas, but the landing of mussels is

forbidden from 15 April to early July (the precise date

being set to coincide with the beginning of the fishing

season In the Netherlands). The boats are operated

under exemptions from the laws decreed in 1950-53;

the number oflicenses has now been definitely limited

to eight. The fishermen have voluntarily relinquished

the cultures located in "Zone 1" (the most protected

area) of the National Park, and traded them in for sites

in "Zone 2" (Fig. 15). Culture sites are granted by the

State Ministry ofAgriculture after consideration ofother

interests (shrimp fishery, navigation), and the overall

surface has now been limited to 2,800 ha (7,000 acres).

Minimum landing size is 50 mm (20-40% undersized

mussels, calculated by live weight, will be permitted;

this is subject to ongoing negotiations). Mussels from

wild beds may no longer be sold on the market; they

may be fished year-round, but exclusively to seed culture plots in Schleswig-Holstein, where they must remain for the duration of at least one growing season.

The fishery on intertidal beds has been banned altogether, and the fishery in subtidal areas of "Zone 1" is

permitted only when seed mussels are not to be found

elsewhere.

Until 1996 the fishermen worked almost without government supervision, and only their adherence to the

size regulations was checked a few times a year. There

are no reliable economic and production data, because

the catch statistics are derived from the fishermen's

records and estimates, and because profits and losses of

the international companies can be easily manipulated

between the German daughter firm and the foreign

parent. To better oversee the companies' activities, the

State of Schleswig-Holstein has also introduced new

reporting regulations in 1996, including an electronic

surveillance system (see "Outlook" section).

Shellfish sanitation was rarely an issue in Germany in

recent decades until the first massive outbreak of

diarrhetic shellfish poisoning (DSP) in 1986 (Meixner

and Luckas, 1988), which had a strong (but temporary)

market effect; paralytic shellfish poisoning (PSP) has

never been recorded in German waters. Health and

quality tests are now conducted before and during the

fishing season by various government laboratories. Before the season opens, both states analyze the mussels

for bacteria, algal toxins (PSP and DSP), heavy metals

(lead, cadmium, and mercury), and radioactive nuclides; in Lower Saxony, the mussels' gross chemical

composition and their hydrocarbon (HCH and PCB)

content are also analyzed and, in Schleswig-Holstein,

bacterial concentrations in the seawater are determined.

During the mussel fishing season, Lower Saxony measures algal toxins biweekly, and controls following the

"European Community Regulations for Shellfish Water

Quality" are conducted every 3 months. In SchleswigHolstein, algal toxins and bacteria in the mussels are

determined weekly during the fishing season. Both states

have routine monitoring programs for noxious algae in
Seaman & Ruth: The Molluscan Fisheries of Germany 75

NORTH

SEA

r

rza

Boundary of the Wadden

Sea National Park

Zone 1 (areas with

highest protection)

Intertidal mudflats

Sandflats and sandbanks

Figure 15

The Schleswig-Holstein Wadden Sea National Park. The isolated areas enclosed

by solid lines represent "Zone 1" with the

highest protection status. The structure

ofthe Wadden Sea and ofthe corresponding national park in Lower Saxony are

similar. Original map by the National Park

Agency for the Schleswig-Holstein Wadden

Sea, Tanning.
76 NOAA Technical Report NMFS 129

800-

700-

g. 600-

Q)

u 500 'L:

C.

Q) 400

f·AJ OJ

Q)

> 300

<i

200 .-.A+-

100

1965 1970 1975 1980 1985 1990 1995

70

60

0 50 0

0, • Schleswig-Holstein 40 <J) [ZI Lower Saxony OJ

c 30 - '6

c

Cll 20 - ---J

10

o~~~'!JlIf1'llJ4I!!'l1~

1910 1920 1930 1940 1950 1960 1970 1980 1990

Figure 17

Average prices for blue mussels from 1965 to 1995 as

calculated from official data in the annual reports of

the State Fisheries Agencies. Auction prices in Yerseke

(Netherlands) are better indicators of the market situation; e.g., auction prices of fresh mussels for the consumer market doubled from 1991 to 1992, but this is not

reflected in the German data, which consisted mostly of

half-grown mussels for reseeding on Dutch beds.

Figure 16

German blue mussel landings (in thousands of tons

fresh weight) from 1910 to 1995. Official data from

annual reports of the State Fisheries Agencies. The

figures include 20-40% "tara" (bycatch, empty shells,

mud, and stones) until the late 1980's; figures for recent years represent net weight of the sold catch (clean

product). In general, the catch consists predominantly

of large mussels for the consumer market; in 1991 and

1992, however, the landings were largely composed of

seed for export to the Netherlands.

dishes. or added to deep-freeze menus sold in supermarkets; cooked meats are sold in glasses, with or without spices, and often used for salads.

Germany has two processing plants with 40-100 employees each (depending on the season), both situated

Marketing-When it is landed, the catch is loaded with

a mechanical grab directly from the ship's hold onto

trucks (about 5% of the mussels are destroyed in the

process); this procedure precludes the use of refrigerator trucks, because they cannot be loaded from above.

The trucks reach the most distant market, Italy, within

36 hours; shorter distances (e.g. to the Netherlands)

are covered overnight. Most German mussels are sold

fresh to wholesalers from the Dutch mussel center in

Yerseke, who depurate them in large saltwater ponds

and then process or resell them. The remaining landings are sold on the German market, as well as to

wholesalers in Belgium, France, and Italy. Half-grown

mussels may be sold directly to Dutch fishing companies (often the parent companies of German firms) as

seed for their plots. Seed exports to the Netherlands

were particularly important in the 1991-92 season, attaining 40,000 t (tara excluded). Landings and average

pricesl are shown in Figures 16 and 17.

When the wholesale price in Yerseke is very high the

German catch goes almost exclusively to the Netherlands, and most of the fresh mussels sold on the German market are then imported from the Danish

Limfjord (for various reasons, the Limfjord mussels are

considered low in quality by the Dutch industry). On

the other hand, some of the German fishermen traditionally sell their mussels in the population centers of

western Germany (Rhine/Ruhr area), and one fisherman has an extensive marketing organization with up

to 40 seasonal employees here. In years when the Dutch

catches are high, however, the Germans may suffer

intensive competition on the Rhineland market from

the aggressive and well-organized Yerseke traders.

Consumer preference is for large mussels (>20-25 g

live weight) with clean shells (even mussels with mechanically removed barnacles are difficult to sell to

Belgian and French consumers), and high meat content (ratio of cooked meat weight to live weight >30%)

with "white" meat (indicating low spawning activity);

the French market will also accept smaller mussels.

Other quality criteria are general appearance, taste,

and smell. Insufficient market supply reduces the standards for acceptability, besides increasing the price.

High quality mussels are generally sold fresh, mostly to

restaurants, where they are boiled in water with spices,

and eaten from the shell; except on the coast, mussels

are rarely cooked by private households. Lower quality

mussels are processed, which involves removal of sand,

freezing or cooking, and packaging. Frozen mussels are

sold to restaurants, which use them for a variety of

coastal waters. To prevent the introduction of diseases,

Schleswig-Holstein enacted a new regulation in 1996,

prohibiting mussel boats from entering or leaving the

state's waters without prior official permission.
Seaman & Ruth: The Molluscan Fisheries of Germany 77

in Schleswig-Holstein. They are run by a British and a

Dutch-controlled company. To promote the local

economy, the state government has linked the mussel

licenses granted to foreign-controlled companies to the

operation of these plants, but both process mostly imported Danish mussels, because the German catch commands a better price in the Netherlands.

Economics-German retail price to consumers is about

DM5.00/kg (US$1.50/lb), but prices vary widely during the year. At the Dutch mussel auction center of

Yerseke, wholesale prices are highest at the beginning

of the season in July, due to the high demand from

Belgium at the beginning of the Belgian vacation season. Because of seasonal restrictions in Germany (particularly in Schleswig-Holstein), most of the German

catch has not really reached the retail market until

September, when prices were already declining; the

new seasonal regulations enacted in 1996 should improve the profitability of the German fishery.

Price fluctuations are additionally affected by peculiarities of the market (Gibbs et aI., 1994). In July 1992, for

example, wholesale prices for top quality fresh mussels at

Yerseke attained DM5.80/kg (US$1.70/lb), but the consumers did not accept the price increase. The dealers

were unable to sell the merchandise and a lot of highquality mussels had to be processed at a loss. Dutch wholesale prices consequently plunged at the beginning of the

season and then stabilized below DM1.50/kg (US$0.40/

lb); seed prices in 1991-92 were about half as high, attaining about DM800 (US$500) per ton (all wholesale prices

are only estimates, because the transactions involve a lot of

deal-making and exchanges of nonpecuniary favors).

The price of a new mussel boat exceeds DM3 million

(US$2 million), and the operation costs for the vessel

(including salaries for the crew, equipment repairs,

depreciation, etc.) are about DM1.5 million (US$1 million) per year. A profitable operation requires annual

landings of nearly 2,000 t per boat, but the catch fluctuates greatly from one year to the next. The combined

landings of the Netherlands, Germany, and from the

Danish Wadden Sea have been relatively stable during

the past several decades, as low catches by one country

were compensated by high landings of another, and

rather than reflecting the state of the stocks on culture

plots and natural beds, German mussel production is

largely determined by the market situation in the Netherlands (which depends on the Dutch catch).

New Offshore Fishery for Hard Clams

In 1992 a large stock of hard clams, Spisula salida, was

discovered about 10 n.mi. west of Amrum Island, and

the fishermen have since found a series of hard clam

beds all along the German North Sea coast. A 1975

study of the benthic macrofauna of the German Bight

(Salzwedel et aI., 1985) found only isolated beds of

Spisula salida, and Meixner (1993) roughly estimates

that the entire hard clam population had a biomass of

100,000-150,000 tons at that time. In 1992-93 the stock

off Amrum, which is spread over several km2, was estimated at about 100,000 t, and all the Spisula stocks

probably added up to far more than 200,000 t (Ruth,

unpubl. data). This implies a significant increase in

biomass, and it would also mean that the hard clam

population is superior in size to the stocks of blue

mussels, which presently provide the mainstay of the

German molluscan fishery.

The Spisula stocks are located partly within and partly

beyond the Wadden Sea boundaries. The former fall

under the jurisdiction of state authorities, which have

granted six licenses to different companies. The latter

fall under the jurisdiction ofthe European Union (EU),

and are not subject to any regulation whatsoever; thus

any fishing boat from a EU member country is allowed

to catch offshore clams without restriction. The clam

beds, which are also frequented by shrimp fishermen,

are situated on banks of coarse sand at depths of about

10 m. The clams attain a maximum size of 45 mm at 7

years of age; in commercial catches they are 2-5 years

old and have a size of 35-43 mm. Their flavor is excellent, and their meat content (20% cooked weight) is

intermediate between cockles (13%) and mussels (30%).

The clams disappear from the fishery from November

to May, but this also is a common phenomenon in the

Spisula fishery off the U.S. Atlantic coast. Presumably,

the clams are out ofreach of the dredges, because they

dig in deeper and the soil hardens7; this assumption is

supported by the fact that the catch per unit of effort

decreases progressively during OctoLer while, at the

same time, the number of broken clams in the dredge

increases. Despite the temporary disappearance, there

does not seem to be any serious winter mortality.

The boats employed are regular cockle dredgers;

they use one modified hydraulic dredge (Fig. 18) that

has pressure and suction pipes almost 40 m long. The

dredge is set for maximum penetration into the sediment (6-7 cm). Bycatch organisms (mostly sandeels,

flatfishes, and other bottom-dwelling fishes, as well as

various crustaceans and bivalves) represent less than

1% of the weight of the catch. The fishing trips normally last 1 day. Due to the exposed locations, wave

action at wind speeds higher than 4-5 Beaufort leads to

damaged pipes and dredges, and the fishery can only

take place 30-40 days per year. The catch (5-8 t/hour)

passes directly from the exit of the suction pipe through

7 Clyde L. MacKenzie.Jr., NMFSJamesJ. Howard Laboratory. Highlands, NJ 07732. Personal commun., 1992.
78 NOAA Technical Report NMFS 129

a rotating drum for sieving and culling, and then proceeds onto a conveyor belt which empties into the hold.

Clams for the frozen market are watered on board in

tanks of2-3 m3 to allow them to eliminate the sand; the

watering process is omitted when the catch is destined

to be cooked, because the sand can be eliminated by

thorough rinsing of the cooked meats.

The catch was initially shoveled by hand into wooden

boxes and later transferred to refrigerated trucks. This

was too time consuming and labor intensive, however,

and the procedure followed now is the same as in the

mussel fishery, i.e., the contents of the hold are loaded

onto trucks with mechanical grabs, despite the fact that

a higher proportion of clams is damaged by the procedure. The clams are landed at the ports of Harlingen

(Netherlands), Havneby (Denmark), or Dagebiill (Germany), processed in the Netherlands, and sold to Spain

and Italy. The official landings' from Germany (Table

3) are underestimates. The total landings of clams from

the German coast were probably about 5,000 tin 1993

(Meixner, 1994), and well over 10,000 t in 1995 (including Dutch vessels fishing in ED waters). The price

data are similarly unreliable, e.g., the clams are two

orders of magnitude more expensive on the Spanish

retail market, and the price to producers must therefore be much higher than given in Table 3.

Outlook _

Most shellfishery activities are subject to substantial legal

constraints and environmental pressures, such as those

which led to the ban ofthe cockle fishery. Any new fishery

or expansion of an existing fishery in the Wadden Sea will

probably be blocked by pressure from environmental

groups, and further growth of the molluscan fishery appears possible only in offshore areas situated beyond the

limits ofthe National Parks. The following gives an estimation of the German production potential, and of the

possible evolution of the German molluscan fisheries,

although we must admit that developments are often too

sudden and surprising to allow reliable prognostication.

Figure 18

Hydraulic suction dredge used in the large-scale fishery for burrowing bivalves such as

cockles and hard clams. On top of the opening of the dredge (left) is the pressure pipe,

from which water is ejected at high pressure through a slot-shaped nOLZle in order to

disperse the sediment. The knife underneath (between the rails) lifts remaining sediment and clams into the cage; the penetration depth of the knife is adjustable. The

catch is sucked into the suction pipe (top), is carried upward through the impeller of

the vacuum pump, and is emptied aboard the ship into a rotating drum sieve (Photograph by Maarten Ruth).
Seaman & Ruth: The Molluscan Fisheries of Germany 79

Table 3

Landings and prices of hard clams, Spisula solida, in

Germany (official data of the state fisheries agencies;

some of the landings were cooked meat, and these

have been converted to raw catch by multiplying by 5).

Catch Price

Year (t/year) (DM/t)

1992 426 690

1993 1,301 370

1994 1,463 230

1995 7,314 230

Oyster Culture

Culture of Pacific oysters, Crassostrea gigas, has proven

economically feasible in Germany, as long as it is conducted on a large-scale professional basis. Although the

more expensive production method (land-based overwintering) is largely compensated for by the German

oyster's high meat content, a reduction in production

costs will still be necessary to make the German oyster

truly competitive. There are some excellent potential

sites along the German North Sea coast, and the annual

oyster production could theoretically be expanded to several thousand tons ifGerman consumer demand increased

further or if the French market became accessible.

Present statutes forbid the introduction of exotic

species into the Wadden Sea, whereas the culture depends exclusively on foreign imports of half-grown oysters. The authorities have, in practice, been treating

Japanese oysters as an endemic species, because they

were first introduced before the new regulations came

into effect. Any proposed expansion of culture activities, however, would have to overcome resistance from

other interest groups, such as environmentalists. On

the other hand, a natural population of C. gigas has now

finally established itselfin the southeastern North Seatwo decades after the species' first introduction-ultimately leading in 1994 to widespread recruitment in

the northern part of the Wadden Sea (Reise and Ruth,

manuscr. in prep.). This second stock spawned in 1995,

and its development should open a long-range perspective for Pacific oyster culture in Germany.

Blue Mussel Fishery

Annual catches have always undergone strong fluctuations, and this will remain so in the future. The latest

decline in German landings resulted from a paucity of

seed mussels, but it does not represent any fundamental change in the fishery itself. Environmental regulations and objections by the shrimp fishery will prevent

any further expansion (number of licenses and total

surface of culture plots). There are demands to further

extend "Zone 1" (Fig. 15) and these may lead to the

closure of considerable parts of the Wadden Sea to the

fishery, with a subsequent reduction of landings. In

addition, the diminishing eutrophication of the North

Sea (due to the expected reduction of nutrient inputs)

may also result in a decrease in productivity (Boddeke

and Hagel, 1991). The present National Park statutes,

however, do offer a secure perspective, and they will

force the fishery to become more efficient in the long

run (Ruth, 1991, 1992, 1993a, b).

The regulations introduced in Schleswig-Holstein in

1996 (such as the ban of the fishery in intertidal areas

and in "Zone 1") completely fulfill the demands of

environmental organizations. In addition, the SchleswigHolstein fishermen are now required to report to the

Fisheries Agency on a daily basis (geographic location

and time of day of their fishing trips, weight and quality

of the catch, seeding activities, etc.), and they will also

have to install electronic devices to allow the authorities

to monitor their ships' activities in detail, thus providing a solid basis for management and control of the

fishery.

Environmentalists continue to criticize the mussel

fishery, however, and some ofthem would probably like

to see it banned altogether. Their demands for quotas

and catch limitations must be rejected; stifflimits would

cause enormous economic losses to the fishery in good

years, and flexible limits are impractical because stock

size fluctuates too strongly and too abruptly (Nehls and

Ruth, 1994a,b). For example, in the case of an exceptionally strong local recruitment, a prolonged intensive

seed fishery at the site of the spatfall greatly improves

growth and survival of the remaining unfished juveniles

by spreading them over a larger area and by reducing

the local population density; this immensely increases

the total biomass of seed mussels and enables the fishermen to stock their cultures with maximum economic

profit and minimum use of ecologically sensitive intertidal beds.

Hard Clam Fishery

The new fishery at first merely provided some compensation to boats which had been grounded by the ban on

cockles. By 1995, the fishermen succeeded in overcoming initial difficulties in processing and marketing, and

the clam fishery was beginning to surpass the mussel

fishery in economic importance. The stocks, however,

were wiped out completely in the first months of 1996,

when the most severe winter conditions in 33 years (-1°C

and 36%0 salinity in the bottom water) persisted until
80 NOAA Technical Report NMFS 129

April. The size of the Spisula stocks was probably the

result of a succession ofstrong recruitment events during the past several years. The clam population had an

evenly mixed age distribution, opening prospects fur a

prolonged sustainable fishery. Considering that the officiallandings for 1995 represent the catch of only two

vessels within the 12 mile zone (the other four boats did

not exercise their licenses), the hard clam fishery is

potentially much more profitable than that for blue

mussels.

It is impossible to predict whether the hard clam

stocks will recover, as has been the case with blue mussels, which frequently suffer high winter mortalities and

always offset them by strong recruitment a few months

later. In addition, the clam fishery faces various other

constraints. It has now begun to attract the attention of

environmentalists. Judicious management of the fishery will remain an impossibility for years to come, because the Federal government has relinquished its authority over the stocks, which now fall partly under

regional and partly under European jurisdiction. A scientific assessment is long overdue, but proposals for a

study of the stocks and the fishery have fallen prey to

budget limitations on the part of the responsible government authorities. Germany is the only country with

a hard clam fishery which has not conducted a survey,

and we do not expect one to be carried out in the

foreseeable future. Despite its enormous potential, the

German Spisula fishery's future can only be characterized as completely uncertain.

Unexploited Stocks

Squids, Alloteuthis subulata and Loligo vulgaris, constitute part of the bycatch of the finfisheries in the German Bight. The annual catch is in the order of 10 t, but

most of it is either discarded overboard or goes into

fishmeal production, and only a few hundred kg per

year are landed8. The stocks seem to have been increasing in recent years (Steimer, 1993), but an increase in

landings is not expected.

Whelks, Buccinum undatum, are abundant locally, but

the stock has never been studied. The toxic effects of

tributyl tin (TBT) on whelk reproduction may have led

to a decline of the population in recent decades. Past

experience, and the fact that whelks are also K-strategists which reproduce slowly (Gendron, 1992), suggest

that even a small-scale fishery (e.g. for export to southern Europe) could not be sustained.

Softshell clams, Mya arenaria, continue to be abl:.ndant in the Wadden Sea, but an exploitation of the

stocks is not to be expected, due to the absence of a

8 Silke Steimer and Uwe Piatkowski, Institut fiir Meereskunde. 241 Oei

Kiel, Germany. Personal commun., 1992.

market, as well as environmental constraints (the stocks

are within the limits of the National Parks, and a modern fishery would have to employ hydraulic dredges

with deep penetration in to the sediment).

Cockle. Cerastoderma edule, stocks would easily support a highly profitable fishery, but the present ban will

remain in effect in the foreseeable future.

Atlantic jackknife clams, Ensis directus, have become

extremely common in the Wadden Sea since their appearance in the late 1970's. They were presumably introduced accidentally with the ballast water of tankers

(Essink, 1986). The clams have an excellent meat content and their retail market price is DM28/kg (US$7.50/

lb). The stock has not been studied until now. Part of it

is located outside of the Wadden Sea proper, and is

therefore not subject to the restrictive National Park

regulations. A fishery with methods used elsewhere (e.g.

Scottish mechanical dredges9) may well be feasible,

and the companies engaged in the hard clam fishery

have also applied for Atlanticjackknife clam licenses. A

fishery on Ensis, however, might well lead to new conflicts between environmental and economic interests.

The next developments will probably depend on the

immediate market situation.

Ocean quahog, Arctica islandica, and horse mussel,

Modiolus modiolus, stocks in the North Sea are not very

important and undergo continuous destruction by the

beam and bottom trawls of the finfisheries (de Groot

and Lindeboom, 1994). A fishery of either stock is

unfeasiblelO. In the Baltic Sea, natural production of

ocean quahogs probably far exceeds 100,000 t/year,

but the quahogs grow and reproduce slowly, and they

are subject to intensive predation by fishes as well as

destruction by trawls (Brey et aI., 1990; Rumohr and

Krost, 1991). An attempt at a fishery by one fisherman

in Schleswig-Holstein in the early 1980's was quickly

given upll. The feasibility of quahog aquaculture (e.g.

Kraus et aI., 1992) has not been studied in Germany.

In the Baltic Sea, various attempts in recent years to

use the mussel and cockle stocks off the coast of

Mecklenburg have been abandoned. Mussels, for instance, may attain densities of 10 kg/m2, but less than

10% of the natural population reaches market size (40

mm); in culture on ropes, less than half of the mussel

biomass attains market size within 2 years (Bottcher

and Mohr, 1991). On the east coast of Schleswig-Holstein (where salinities are higher), between 400 and

500 t were landed in 1986 and 1987, but this fishery was

9Eric Edwards, Shellfish Association of Great Britain, Fishmonger's

Hall, London, England. Personal commun., 1Y92.

10 Heye Rumohr, Institut hir Meereskunde, 24105 Kiel, Germany.

Personal commun., 1992.

IIThomas Neudecker, Federal Fisheries Research Agency, Palmaille,

22767 Hamburg, Germany. Personal commun., 1992.
Seaman & Ruth: The Molluscan Fisheries of Germany 81

abandoned in 1989. Fishery and culture activities could

only become economically attractive again here if the

Wadden Sea mussel fishery has a major crisis, which

appears unlikely at present.

Concluding Remarks

The historical record shows that user conflicts are nothing new to the molluscan fishery (and they were definitely more dreadful in the old days), and management

of these fisheries has a tradition spanning at least three

centuries. Today, political controls on the shellfisheries

may often appear excessive. It should be kept in mind,

however, that at the turn of the century the pearl mussel fishery was destroyed by the lifting of management

regulations and by environmental degradation, and that

the traditional oyster fishery in the Wadden Sea failed

despite all regulation, stock enhancement, cultivation,

and biological research efforts. This experience should

be a stern warning to those involved in present-day

molluscan fisheries and in the management of this

valuable resource.

Acknowledgments _

Important information, technical assistance, and reproductions for this paper have been provided by

Rudiger Berghahn, Institute of Hydrobiology and Fisheries Science, Hamburg; Hans-Otto Boysen, State Fisheries Agency of Schleswig-Holstein, Kiel; Wolfgang

Hagena, State Fisheries Agency for Lower Saxony and

Bremen, Bremerhaven; Jurgen Hevers, State Natural

History Museum, Braunschweig; Adriaan Leuschel, fisherman from Wyk/Fohr; Hermann Michaelis, Coastal

Research Station, Norderney; Ilona Oelrichs and Heye

Rumohr, Institute for Marine Research, Kiel; Brigitte

Scharsack, Veterinary College of Hannover; Frank

Schlichting, Altonaer Museum, Hamburg; and Raga

Schumer, Dittmeyer's Austern-Compagnie, List/Sylt.

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2,078 p.
Molluscan Fisheries in Britain

ERIC EDWARDS

The Shelljish Association of Great Britain

Fishmongers' Hall, London Bridge

London, EC4R 9EL, United Kingdom

ABSTRACT

Mollusks, particularly oysters, Ostrea edulis, were an important source of food and employment for British fishermen as far back as the Roman occupation, and oysters were once a

staple part of diets in poorer sections of the coast. In the early 19th century, oyster dredging

from sailing smacks expanded and oystering became one of Britain's largest fisheries;

production peaked in the mid-1800's. Blue mussels, Mytilus edulis, also have had a long

history of use. Other species, such as cockles, Cerastoderma edule, and scallops, Pecten maximus

and Chlamys apercularis, are harvested from wild stocks along with the periwinkle, Littorina

littorea, and whelk, Buccinum undatum, that are often harvested in remote areas. Molluscan

fisheries are distributed all around the British coastline. Harvesting methods range from

hand gathering of periwinkles, raking of cockles, and potting whelks, to dredging for oysters

and scallops and suction dredging for cockles. In England, mussel farming is growing; seed

mussels are transplanted from natural beds to "lays" in sheltered areas for growth. In

Scotland, mussels are being farmed, using rafts and longlines, and Pacific oyster, Crassostrea

gigas, production is expanding. Hatchery production of Pacific oysters was developed at

Conwy, North Wales. Commercial hatcheries now produce up to 100 million juvenile Pacific

oysters/year. The most important mollusks landed by weight are cockles (20,000 t), scallops

(17,000 t), and mussels (10,000 t), with scallops being the most valuable. Cockles and

mussels are eaten locally, but most scallops are sold on the continent, mainly France. The

interest in mollusk farming is growing, including nonindigenous species, such as the Pacific

oyster; Manila clam, Tapes philippinarum; and northern quahog, Mercenaria mercenaria, but

management of wild stocks to control exploitation will have vital importance in the future.

Introduction

For generations fishermen have exploited Britain's large

molluscan resources to gain a livelihood. Records going back as far as the Roman occupation prove that mollusks, particularly oysters, were a valuable source offood.

Around British coasts a wide variety of molluscan

shellfish (bivalves and gastropods) have been harvested

from estuaries and shorelines to deep water. Some bivalve mollusks, such as the native oyster, Ostrea edulis,

and the common mussel, Mytilus edulis, have a long

history of cultivation. Other species, such as cockles,

Cerastorderma edulis, and two species of scallops, Pecten

maximus and Chlamys opercularis, have been taken from

wild stocks and their fisheries have suffered wide catch

fluctuations. Gastropods, such as the periwinkle, Littorina

littorea, and the common whelk, Buccinum undatum,

form the basis of local fisheries, often undertaken in

remote areas, but valuable to the local population.

In an industry distributed all around the British coastline a wide variety of traditional methods have been

used to harvest mollusks. These range from hand-gathering of winkles and raking of cockles on the shores to

dredging for oysters and scallops in deep water and

suction dredging for cockles in shallow estuaries.

Nowadays in Britain there is a growing emphasis on

farming mollusks rather than just exploiting wild stocks.

The growers are concentrating on oysters and mussels,

and there is both experimental and commercial production of clams and scallops, including the use of

nonindigenous species such as the Pacific oyster,

Crassostrea gigas; Japanese littleneck or Manila clam,

Tapes philippinarum; and the American hard clam or

northern quahog, Mercenaria mercenaria.

Extensive research on mollusks after 1950 by the

government's Fisheries Departments has led to a greater

emphasis on the management of stocks to ensure a

better yield. Research on mariculture and disease con85
86 NOAA Technical Report NMFS 129 _

trol has added to our knowledge of the biology and

artificial production of these valuable species.

Mollusks are widely eaten in Britain; some species

like oysters, scallops, and queens are expensive luxury

foods, while cockles, mussels, and whelks are much

cheaper. This paper outlines the history of Britain's

most important mollusk fisheries, explains the changes

which have taken place, and provides an up-to-date

description of the current fisheries.

Geographical Distribution and Size

The British Isles (England, Scotland, Wales, and Northern Ireland) has an extensive coastline of about 5,000

km. In general, oysters, mussels, cockles, and clams are

harvested or grown in various shallow estuaries, and the

scallops are caughtfurther out in deeper waters. Winkles

are collected by hand from rocky shores, and whelks

are widely distributed in many coastal areas, where they

are caught in baited pots. The distribution of the main

molluscan resources are shown in Figure 1 and briefly

described by region below.

England and Wales

The northeast coast of England is too rocky to support

any important bivalve mollusk fisheries, although scallops are caught farther out in the North Sea. Winkles

are collected from the rocky shores, and whelks are

present in some places and are heavily exploited.

An area of the east coast known as "The Wash" supports a major cockle and mussel fishery, and there are

important whelk grounds off the Norfolk coast. Pacific

oysters are also grown in this area.

Oyster beds have traditionally been important in the

shallow estuaries of Essex and both native and Pacific

oysters are cultivated. Large beds of cockles in the

outer Thames Estuary support a valuable fishery.

The Solent, on the south coast near the Isle ofWight,

is a major "native" oyster fishery, and Southampton

Water has the largest natural stock of American hard

clams (accidentally introduced from the United States

in the early 1900's) (Utting and Spencer, 1992).

Various estuaries along the south and southwest coasts

have small mussel beds, and there are an increasing

number of Pacific oyster culture ventures. The River

Fal estuary in Cornwall has a large native oyster fishery,

but production has been hit by the disease Bonamia.

In the northwest of England, large cockle and mussel

beds are located in Morecambe Bay and the Ribble

Estuary. The Welsh coastline has commercial cockle

fisheries in the Burry Inlet, and mussels and Pacific

oysters are grown in the Menai Strait.

Scotland

Scottish waters, particularly on the west coast, are well

suited to mollusk production. In recent years, along

with the valuable fisheries for wild scallops, there has

been considerable investment in mussel farming, using

rafts and longlines, and an expansion in Pacific oyster

production. A native oyster fishery in Loch Ryan exploits one of the few natural stocks left in Scotland.

On the east coast, the Dornoch Firth holds the Tain

Mussel Fishery, which has a large wild mussel stock.

Other Scottish estuaries have dense mussel beds, but

the quality is poor due to overcrowding.

Mussels arc also cultivated along the west coast, where

numerous mussel farms produce small quantities by

hanging culture. The quality of these mussels is excellent, and there is a growing demand, mainly in the

United Kingdom, for Scottish farmed mussels.

The scallop, Pecten maximus, and the queen scallop,

Chlamys opercularis, are both present in sufficient quantities to support important fisheries in a number of

areas off Scotland.

There is growing fishing pressure on the wild scallop

stocks using trawls and dredges. Attempts are being

made to cultivate both species of scallops in Scotland,

using modified Japanese methods for spat collection

and growth. Although four or five farms are in commercial production on the west coast, the annual output is

less than 200 metric tons (t), mainly queen scallops.

Northern Ireland

In recent years, the bivalve industry in this area has

been dominated by one Pacific oyster culture and export business based at Strangford Lough. There is a

native oyster fishery in the River Foyle and wild mussels

are taken from Belfast and Carlingford Loughs.

Importance of Mollusk Fisheries

In 1994, the total production ofshellfish in Britain was

111,080 t with a first-sale value of£128 million (US$192

million). This catch included crustaceans, cephalopods,

and mollusks.

Table 1 shows the main mollusk species, which made

up a catch of 55,795 t worth £31.7 million (US$47.5

million) in 1994. The weight represented 50% of the

country's total shellfish catch but only 25% ofthe value.

The scallops and queens are the most valuable species landed (£23 million or US$34.5 million combined)

whereas the cockle, mussel, and winkle catches are

each worth around £1 million (US$1.5 million). For

record purposes, the landings of mollusks during
____________________________ Edwards: Molluscan Fisheries in Britain 87

...___--"T""-___r--~-.....,..--r_-....,...-___r--~-_r--...___-...,.-__y--_r_-__r--r_-, 610

20

19

18

Shetland oysters

Islands ~~::~:scaIlOPS

17

16

Orkney 'fht7

Islands ~omussels

<t>lllJ pacific oysters

59°

Figure 1

General distribution of mollusks around Britain.

55°

56°

49°

54°

500

53°

58°

570

52"

51°

1° 2° 3° 4°

queen

scallops

5° 4° 3° 2° 0°

pacific

F IE oystars a sluary scallops

~":.\' natiVII (jy.~ oysters ~\sy.

":.~G

scallops

8° go 12° 11 ° 10°

3

4

5

6

9

8

7

2 .'

11

13

10

14

15

12

53

51

54

51

55
88 NOAA Technical Report NMFS 129

8 selected years between 1947 and 1994 have been

tabulated in Table 2.

Landings of the different mollusk species fluctuated

considerably during these 40 years, and many factors

will have contributed to increases and decreases in

production.

In bivalves, the level of recruitment is a major factor

controlling any expansion ofthe fishery. The growth in

artificial production using hatchery stock (e.g. Pacific

oysters) will help to increase production ofsome species,

but proper management ofthe stocks to control exploitation will be of vital importance in the coming years.

While the government statistics for mollusks are underestimated (probably tenfold) it is obvious that U.K

mollusk production is low compared to other western

countries. The future for mollusks is considered separately for each species but, in general, we expect better

market opportunities in Europe and improved producTable 1

Landings of mollusks by British fishing vessels in 1994. 1

Weight First-sale value

Species (t) (£ thousands)

Clams 8 13

Cockles 22,329 3,069

Mussels 10,037 1,985

Oysters 2538 1,180

Periwinkles 2,264 1,554

Queens 2,977 1,788

Scallops 14,020 21,209

Whelks 3,312 894

Totals 55,795 31,692

I Source: HMSO Sea Fisheries Statistical Tables.

2 Underestimated.

tion methods to help develop the U.K mollusk industry

in the 1990's.

Oysters

The Flat Oyster

The native flat oyster, Ostrea edulis, has provided a long

established fishery in England, Scotland, and Wales.

Ample evidence from old discarded shells shows that

the ancients used oysters as an important source of

nutritious food. Records show that the Romans exploited Britain's natural oyster beds and even sent supplies back to Rome.

At one time oysters formed a staple part of the diet of

the poorer sections of certain coastal communities.

However, the onset of industrialization in the early

19th century initiated an expansion in oyster dredging,

which turned it into one of Britain's largest fisheries.

According to Key (1991), stocks in the early 19th

century were large and lightly fished. As industries began to expand inland and the railway systems developed, transport became easier and markets for oysters

boomed. By 1824, important and valuable oyster fisheries had been established on the east coast ofEngland in

the larger estuaries in Essex and Kent.

The peak production period in the history of the

fishery was in the mid-1800's. Philpots (1890) records

that 700 million oysters were consumed in London in

1864, as well as many more in the provinces. So immense was the oyster industry that 120,000 men around

the coasts of Britain were engaged in dredging oysters

in the 1880's.

Most of the catch was taken by small sailing smacks

with a few crew, who worked dredges by hand. Very

quickly local stocks were worked out, and the east coast

Table 2

Quantities (t) of mollusks landed in U.K. during selected years and their value (£).1

Quantity (t)

Scallops and Oysters Total value

Year queens Winkles (native) Whelks Mussels Cockles (£)

1994 17,000 2,264 528 3,312 10,347 22,329 £32,000,000

1990 14,015 1,766 161 755 6,610 19,593 £20,000,000

1985 12,617 2,294 477 1.630 5,825 7,826 £19,000,000

1983 16,543 2,765 290 1,336 5,856 5,837 £11,000,000

1975 14,060 2,761 488 3,148 6,913 16,385 £ 3,500,000

1965 550 550 250 1,700 2,850 7,050 £ 400,000

1955 1,158 330 903 ~,247 3,826 7,584

1947 3,379 362 424 1,730 5,539 8,792

J Source: Sea Fisheries Statistical Tables.
____________________________ Edwards: Molluscan Fisheries in Britain 89

250

40

1970

1970

1960

1960

1950

1950

1940

1940

1930

1930

o ,LLLLJ. LLLl.!.f-L.LL.L.LL.L.LLt-LLL-LLL-LLL-t-'-'-'-U-LU-'--Y-LULLWLLLy.'-'

1920

O-Y-J...Ll.Ju.Ll..l...l,LLl.LLl..l..Ll-Y-J..LLl..LLl...L.1,JULULLU..J.,Ll-.l..Ll.l..Ll.LY..u

1920

Cultivation Techniques and Species

Cole (1956) and Davidson (1976) both described

Britain's oyster fisheries and cultivation techniques. Four

species have been cultivated during this century: the

European flat oyster, Oslrea edulis; the Portuguese oyster, Crassoslrea angulala; the American oyster, Crassoslrea

virginica; and more recently the Pacific or Japanese

oyster, Crassoslrea gigas.

Large imports of native oysters came from Holland

and France for relaying from 1901 until 1962, when the

practice diminished. Importations peaked in 1937, when

it is reported that 40 million oysters were relaid on

English grounds (Fig. 3).

The American and Portuguese oysters were brought in

to supplement the supply of native oysters. The trade in

American oysters started in about 1876 but there have been

no importsfrom the Un~ted Statessince 1940, and the Portuguese trade, started in 1926, was stopped in the 1970's

because of viral gill disease (Utting and Spencer, 1992).

Figure 2

Landings and value of native flat oysters in England

and Wales (1920-72). Source: Davidson, 1976.

en 200

-0

c:

CIl

en

:::J 150 o

.r:

len 100

-0

c:

:::J

f1.. 50

Total Catch

lilao

c:

.2

~20

en

'-

OJ

en

>. 0 10-

Total Value

boats started to explore sources ofsupply further afield.

They worked every available oyster stock, some in deep

water, around the English, Scottish, and Irish coasts;

catches were sent direct by well-boat to London or

exported to the Continent.

By the middle of the 19th cen tury most oyster fisheries were becoming severely depleted and pressure was

put on the government to remedy the situation. Parliamentary Select Committees were set up and, as a result

of their reports, legislation was passed in 1877 to ban

the sales of oysters in the summer, from 14 May to 4

August each year, to conserve the breeding stocks. This

closed season is enforced to this day for Oslrea edulis

under the Sea Fisheries (Shellfish) Act of 1967.

Provisions were also made for public fishing rights to

be removed by the granting ofregulated fisheries, where

minimum landing sizes and other restrictions could be

introduced by law. Meanwhile, the industry was seeking

new supplies for a hungry market, but the prosperity of

the oyster industry did not carry on into the 20th century (Orton, 1937).

French (1989), who provides an excellent account of

the Essex oyster fisheries, reports that by 1902 the 500

million oysters reputedly sold in Billingsgate Fish Market, London, had dwindled to a total catch of28 million

for the entire country. Almost without exception, commentators have blamed overfishing for the decline.

French, who has been an oyster grower all his life, believes

that this is an over-simplification of the problem.

According to him, the decline started as the Industrial Revolution accelerated. Oysters disappeared first

close to centers ofindustry and population as pollution

increased. Imports of the American oyster or "blue

points," Crassoslrea virginica, from bays in the northeastern United States, which began in the 1870's, brought

in pests and competitors such as the drill, Urosalpinx

sp., and slipper limpet, Crepidula. The imports were to

fill the gap in the trade during the summer months.

The first half of the 20th century therefore saw the

British oyster fisheries in a rather depleted condition,

striving to maintain momentum with additional burdens

of pests. Spatfalls got smaller and less frequent, and cold

winters and floods further reduced the stock levels.

Production figures for the period of 1920-72 (Fig. 2)

show that the catch fell from 40 million oysters in 1920

to about 8 million during the 1950's. Good spatfalls in

1957-59 revived hopes for improved stock levels, but

the severe winter of 1962-63 virtually destroyed the east

coast beds. By the end of that decade, landings had

fallen to a low of 3 million and production has not since

grown.

In 1982, tests revealed that the disease Bonamia had

been inadvertently introduced into several important

English fisheries, causing large-scale mortalities. This

further reduced the level of production in the 1980's.
90 NOAA Technical Report NMFS 129

Portuguese oysters spawned only to a very limited

extent in this country, as they require a rather higher

water temperature than is normally experienced even

o

g 5

- 4 en

C

o 3 ....

U

·S 2

Q)

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970

Figure 3

Landings of oysters of mixed species in the U.K. (open

histograms) and imports, for direct consumption, of

European flat oysters (hatched histograms) and American oysters (closed histograms). Source: Utting and

Spencer, 1992.

in the southern part of England. American oysters did

not reproduce at all and both species could therefore

be sold during the summer months, when native oysters

could not be sold by law because they were spawning.

Oyster Fishing

The European flat oyster fishery continues to use traditional techlliques and gear which are often peculiar to

a specific locality. Harvesting methods range from small

dredges (Fig. 4) towed by rowing boats to the use of

large (6-foot) dredges on 40-foot powered vessels.

Most of the oysters reaching market have been relaid

from a spatting ground. A large supplier ofthese "brood"

oysters is the Solent Oyster Fishery, on the south coast

of England (Key, 1981). Its development followed the

location of a large natural resource of flat oysters in

1971 and t.he utilizat.ion of t.his valuable st.ock to replenish beds on the east coast. and for direct. export t.o t.he

cont.inent up to t.he present day.

Cole (1956) and Ort.on (1937) describe t.he cycle of

cultural operat.ions on a t.raditional English oyst.er bed.

Work begins in the spring, at t.he close ofthe market.ing

season (September-April inclusive) with t.he laying of

Figure 4

Dredging oysters by hand in Galway Bay, Ireland. Photograph by the author.
____________________________ Edwards: Molluscan Fisheries in Britain 91

fresh breeding stock. During May and June attention is

concentrated upon the elimination of pests, particularly

the drills, Urosalpinx and Ocenebra, which breed then.

In areas which benefit from a natural spatfall, additional settling surfaces must be provided. The bottom

may be dredged and harrowed to drag up fresh cultch

from the mud, and the natural supply may also be

supplemented by laying cockle, oyster, or mussel shell

from elsewhere. At this season (June-July) oysters approaching maturity may be dredged up and relaid in

localities known to give rapid growth and fattening.

June-August is usually a quiet time on most oyster

fisheries, but intense activity is resumed in September,

when the dredging of oysters for market begins. While

dredging, the oysterman removes all pests and competitors such as shore crabs, starfish, drills, and slipper

limpets. The collection of market oysters continues

throughout the winter, although certain fisheries (e.g.

Solent) now have a shortened fishing season to conserve the stocks. Most native oyster fishing ends in

March, but the cultivation of Pacific oysters, described

later, provides a source of oysters for the trade during

the summer months.

Pacific Oysters

The era of massive commercial importations of oyster

seed from abroad ended in the 1960's with a growing

awareness of the risks involved in introducing alien

pests, parasites, and diseases. The 1960's were notable

for two reasons: Implementation ofthe Molluscan Shellfish (Control of Deposit) Order 1965, whieh controlled

mollusk imports to prevent the introduction of diseases, and the development of hatchery culture seed.

Walne (1974) describes how the hatchery production of the Pacific oyster was developed at the Ministry

of Agriculture, Fisheries and Food Fisheries Laboratory, Conwy, N. Wales, to a level where it could be

applied on a commercial scale. Under strict quarantine

conditions, C. gigas broodstock was brought to Conwy

from the U.S. Pacific coast and induced to spawn in the

hatchery. In 1979, sufficient trials had been undertaken by MAFF to assess the culture characteristics of

Pacific oysters in British waters.

The research at Conwy in the 1960's, under the late

Peter Walne, identified the Pacific oyster as having

considerable potential to revitalize the U.K. oyster industry. The species does not spawn regularly in our

cool waters, but it is robust and grows to saleable size

(80-100 g) in 36 months.

Years of patient work by Walne and his team paid off.

Commercial hatcheries now produce up to 100 million

juvenile Pacific oysters each year. Many of these are

exported abroad, but Pacific oysters are grown at some

300 sites in England, Scotland, Wales, and Northern

Ireland, and this introduced oyster now makes a significant contribution to the U.K. oyster industry.

Spencer (1990) describes in detail how Pacific oyster

seed should be handled and provides culture methods.

Both Spencer (1990) and Drinkwater (1987) recommend tray or bag culture low down the shore (Fig. 5).

Most U.K. growers have now adopted tray or bag

culture using trestles to raise the oysters offthe seabed.

U.K. production, based on seed supplied by a hatchery,

is currently about 750 t per year and is slowly rising.

Development of the new Pacific oyster industry was

hit during the 1970's and early 1980's when tributyl tin

(TBT) was used as a small boat antifoulant. The presence of this toxic chemical, even at trace levels, caused

severe thickening of the shells of Pacific oysters and

stunted their growth.

Since July 1987, the use ofTBT-based paints on small

inshore vessels has been banned, and the toxic levels of

TBT in most estuaries have fallen below the dangerous

level. Consequently, the shell thickening which caused

problems to many Pacific oyster growers has disappeared, and production is steadily increasing.

At present most growers sell their Pacific oysters to

outlets such as shellfish bars, restaurants, hotels, and bars.

Since they are cheaper than the native oyster, and available year-round, their popularity is increasing, and present

trends indicate both an increase in production and market opportunity, including sales on the Continent.

Mussels _

Mussels have been harvested from early times, either as

a cheap source of food or as fish bait. Calderwood

(1895) describes how many large natural mussel beds

in England, Scotland, and Wales provided bait for the

important line fisheries.

A Mussel Commission set up in 1889 reported that

"... 50,000 fishermen of Scotland use mussels as their

bait for part or all the year." So great was the demand

for mussels for bait to supply the line fisheries that

many beds were overfished and supplies were imported

from Holland to boost the available stocks. The decline

in this type of fishing in the 1950's ended this trade in

bait.

Old records also describe how mussels were eaten by

poor people, but the amounts seem to be small and

there was a preference for oysters. Even so, the records

of the Worshipful Company of Fishmongers show a

trade in live mussels at London's Billingsgate Fish Market since the 1800's.

According to Cole (1974), mussel consumption suffered from an association with typhoid because they

were often taken from sewage-polluted waters and eaten
92 NOAA Technical Report NMFS 129 _

Figure 5

Pacific oyster culture using mesh bags laid on steel trestles in Essex. Photograph by the author.

raw. This situation changed in 1920, when the first

reliable cleansing technique was evolved by Dodgson

(1928) at Conwy (Fig. 6). Since then, purification techniques have been further developed (Wood, 1969), mussel consumption has steadily increased, and nowadays

mussels are growing in popularity as a safe seafood.

British mussel production is relatively small (Table

2), at around 10,000 t/year, and comprises less than 5%

of the total European Community (EC) catch.

Large areas of tidal flats, including The Wash,

Morecambe Bay, Solway and Dornoch Firths in Scotland, and other river estuaries, such as those of the

Conwy in North Wales and the Teign and Taw in Devon, produce most of the wild U.K. mussel harvt>st.

These are all areas of natural production, but the commercial development of these natural beds, however

abundant they might seem, is hindered by the unpredictable nature of the stock caused by varying recruitmen t levels.

Mason (1972) describes in detail the cultivation of

the European mussel. In Britain, there has been a

gradual move from just exploiting wild beds by dredging or handpicking to mussel farming. Mason (1972)

and Dare (1980) describe the bottom cultivation of

mussels when small (seed) mussels are transplanted

from natural beds onto "lays" in more favorable sheltered sites, where growth and survival is improved.

This technique, widely used in Holland, can be highly

productive, and a properly managed ground will yield

100-125 t live weight of mussels per hectare, or 20-25 t

of cooked meat, every 2 years. Mussels are suitable for sale

at a minimum length of50 mm; local bylaws in some areas

prevent smaller mussels from being dredged for sale.

Mussels are also grown attached to coil' and various

synthetic ropes suspended from rafts and buoyed

longline systems. Net tubes are also used to hold seed in

this type of suspended culture (Fig. 7,8).

Trials in western Scotland (Mason, 1969) and North

Wales (Dare and Davies, 1975) showed the biological

potential of floating culture even in cold temperate

C.K. waters. Mussel crops reached minimum market

size in 1-1 1/2 years and possessed high meat contents

(30-35% cooked meat yields).

Since those 1970's trials, a valuable mussel industry

has been developed along the west coast of Scotland,

where there are many suitable deep and sheltered inlets.

In 1991, Scottish growers produced over 1,000 t of

top-quality farmed mussels for which there is an in-
____________________________ Edwards: Molluscan Fisheries in Britain 93

Figure 6

A mussel depuration plant at Conwy, N. Wales. Photograph by the author.

creasing demand. This method is more expensive and,

at present, less productive than bottom culture. But it is

more suitable for these Scottish waters rather than the

shallow estuaries of England and Wales.

Despite improved prospects for mussels, the main

problems faced by the grower are continuity of seed

supplies and the effects of predation by crabs and starfish. In Britain, the shore crab, Cancinus maenas, causes

widespread and sometimes severe losses ofsmall mussel

seed on intertidal and deep-water lays in many estuaries. Mussels below 40 mm in length are particularly

vulnerable to crab predation.

Mussel beds near sewage discharge points are a particular problem, and in many areas the health authorities control or prohibit the sale of mussels from these

areas unless they have been cooked or undergone an

approved purification process to cleanse them (Fig. 6).

In January 1993 a new EC Directive coveri~g the hygienic production of mussels and other bivalves further

reduced the risks of contaminated mussels reaching

the market.

Edwards (1984) describes how many shellfish growers in Britain consider the mussel as potentially the

most important mollusk in their waters. Market demand continues to improve, and exports to France and

Holland are steadily increasing. Investment in new

equipment such as mussel dredgers and Spanish-type

raft systems will see mussel production double in the

next decade.

The Common Cockle _

More cockles are landed in Britain than any other

mollusk (Table 1); they occur all around our coasts,

living mainly between mid-tide and low-water levels.

Common on sandy beaches, cockles also inhabit a wide

variety ofsubstrates ranging from soft mud to gravel.

Cockles have been exploited by generations of coastal

inhabitants. But nowadays, the traditional hand-raking

methods of harvesting have been replaced by hydraulic

dredges and there is a huge demand for this tasty shelI-
94 NOAA Technical Report NMFS 129

---~------~

A

B

Figure 7

Types of cultivation: A) longlines, B) raft (adapted

from Drinkwater, 1987).

fish. The main cockle beds in Britain are situated in the

outer Thames Estuary, The Wash, the Dee estuary, Solway

Firth in Scotland, and the Burry Inlet in South Wales.

Cockle landings have fluctuated considerably during

the past 50 years; between 1930 and 1960 they oscillated around 7,500 t live weight, but have increased

threefold today because of improved harvesting methods and better markets. Landings during 1960-90 demonstrated the variability of the fishery which relies on

natural recruitment. Landings were fairly high in the

1960's, but the severe winter of 1962-63 wiped out

much of the British stocks and catches fell. There was,

however, an exceptionally good spatfall in the summer

of 1963, and landings increased un til the presen t day

when between 30,000-40,000 t of cockles are landed

annually.

Franklin et al. (1980) describe the cockle fisheries of

England and Wales and the regulations which control

them. Edwards (1992) describes the growing demand

for cockle meats in Holland and Spain and how this

overseas market has provided a "bonanza" for U.K.

producers.

Nearly all the cockles sold in the United Kingdom

are heat-processed and then sold freshly cooked or

preserved in some way (IQF or vinegar/brine). Heat

treatment, by boiling or steaming, cooks the meats and

all.::>ws easy separation from the shells. Nowadays, there

are strict cooking guidelines, and all processing factories must be approved by the public health authorities.

Figure 8

Mussel farming using hanging rope culture in the west

of Scotland. Photograph by the author.

Particular care must be taken with cockles harvested

from estuaries where the beds may be pol1uted by sewage. Health authorities now insist that sufficient heat

treatment be provided to raise the core temperature of

the cockle meat to 90°C for 90 seconds. At this level of

cooking, all pathogenic bacteria and viruses are destroyed and cockles now have a much improved hygiene record.

Harvest methods vary around the country. In the

Burry Inlet, South Wales, regulations restrict the use of

mechanical harvesting methods and the licensed gatherers used only horses and carts for transportation until

the late 1970's. Nowadays, tractors can be used but the

cockles are still hand-raked out of the sand into piles,

which are then sieved to allow the small cockles to return

to the beds (Fig. 9). The commercial-sized cockles are

then put into sacks and loaded onto the carts or tractors

for transport to boiling sheds for washing and cooking.

In the Thames Estuary, The Wash and the Solway

Firth, Scotland, boats fitted with modern hydraulic suction dredges exploit the stocks (Fig. 10). These dredges,

developed in the 1960's, continuously remove cockles

from the seabed by simply pumping seawater, sand, and

cockles all up onto the deck of the vessel for sieving and

packing the cockles. Catch rates can reach 2-3 t/hour,

but there is no evidence yet that beds are destroyed by

this efficient method.

For example, these dredges have been used in the

Thames Estuary since 1971, and there is no evidence

that the beds have been over-exploited with the present

level of effort (7-12 boats). Even so, many cockle beds

in Britain are potentially under threat from heavy fishing due to the high demand for this bivalve.

Sea Fisheries Committees, which manage the cockle

fisheries in England and Wales, have local regulations
____________________________ Edwards: Molluscan Fisheries in Britain 95

Figure 9

Hand raking for cockles in Wales. Photograph by the

author.

Figure 10

A cockle dredger fitted with hydraulic suction gear.

Photograph by the author.

Figure 11

Scallops landed in the C.K.: A) king scallop, Pecten

maximus, 100 mm width; B) queen scallop, Chlamys operulans, 50 mm width.

A B

similar culinary place to the local "bay scallop," ArgffjJecten

irradians. Since the queen fishery developed in the early

1970's, many boats have alternated between the two species, although the larger scallop fetches a better price.

The U.K. scallop fisheries are very valuable, and in

1994 the catch of both species was recorded as 17,000 t

worth £23 million (US$35 million). Of that, Scottish

fishermen alone produced 11,400 t (67%).

Mason (1983) describes the development ofthe Scottish scallop fishery; the west coast is the main fishing

area, but new beds have recently (1992) been exploited

such as restrictions on the kind of fishing gear used, a

minimum landing size, and quotas. Arrangements are

now in hand to restrict the level of fishing effort, especially for large hydraulic cockle dredgers.

Future prospects for the U.K. cockle industry depend

both on supply and demand. There are fears that catches

in many fisheries are unlikely to be sustainable at recent levels unless recruitment improves. In the meantime, even small beds of cockles are being exploited to

meet the current high demand.

Exploitation ofthe scallop Pecten maximusand its smaller

cousin the "queen" forms an important fishery with

landings now reaching 17,000 t (Fig. 11). Britain has

had important scallop fisheries for a number of years.

Mason (1985) writes that fishing for scallops was recorded in England and Ireland as early as the 16th

century, but it did not spread to Scotland, where scallops were often called "clams" until the early 1930's.

The big increase in fishing did not come until the early

1960's and, prior to that, most of the scallops were sold

alive at Billingsgate Fish Market, London.

Until World War II, the smaller queen scallop was

used in Scotland as cod and haddock bait by line fishermen. With the decline of line fishing after the World

War II, there was no further need for the queens, and

the fishery stopped. However, in about 1967 developments in processing equipment made it possible to

handle and prepare queens more easily and economically. At about the same time a market was found for

them in the United States, where the meats filled a

Scallops and Queens _
96 NOAA Technical Report NMFS 129 _

in the Moray Firth, on the eastern side of Scotland, and

around Orkney and Shetland.

Despite 20 years of exploitation, the yield from

Scotland's scallop resources remains high. Experience

has shown that as the catch rate on one bed declines,

fishermen tend to move to other scallop beds or change

to an alternative fishery (e.g. trawling for fish). In England and Wales, the main fishing areas are in the English

Channel and in the Irish Sea, but catches have fallen

recently because of heavy fishing and poor recruitment.

Fishing Methods

Scallops are caught in heavy dredges towed over the

seabed. On some inshore grounds the scallop populations are exploited by skin divers, but many beds are

too deep for this method.

The history of scallop dredging is of interest. The

traditional scallop gear is the dredge, fitted with a

toothed bar. In the late 1950's and early 1960's, the

boats fished from two to four dredges, 4 feet in width.

In the early 1960's, bigger boats came into the fishery

and used larger 6-foot dredges, towed by separate warps.

Later the dredges became standardized at the 4-foot

width, and they were fixed to a towing bar with 2 to 5

dredges attached (Fig. 12). The latest developmentwas

the spring-loaded toothed bar which allows the gear to

pass over various hazards on the seabed without hanging up. Beam trawls are also used to take queen scallops. Indeed, since they can swim quite actively, queens

can avoid the toothed dredge, which is more effective

for the slower scallop.

Markets

Scallops have long been considered a luxury shellfish.

Demand varies, but scallops generally find ready markets at home and abroad. At present, scallop markets

are very good; there is a growing U.K. demand, but

most of the catch is still exported to the continent,

mainly to France.

Supplies are exported either fresh (in the shell or

shucked) or frozen. Traditionally, scallops are sold with

the gonads (roe-on) as this adds to the appearance of

Figure 12

Scallop dredges fitted to a towing bar. Photograph by the author.
____________________________ Edwards: Molluscan Fisheries in Britain 97

the product. However, in the U.S. trade only the white

adductor muscle was exported. A growing number of

countries now recognize scallops as a high-value seafood, and the 1990's are expected to see the strong

demand for scallop meat continue to rise. This increased demand will encourage fishermen to search for

new beds, and there is a growing interest in farming

scallops using methods developed in Japan.

Mason (1983) describes the development of scallop

culture in Scotland, where both species are farmed,

using collectors made ofmonofilament netting in mesh

bags laid out along the coast to collect the "spat" during

the times of natural spatfall. The scallops are then

grown in lantern nets (Fig. 13). This culture system,

now used on the west coast of Scotland, allows growers

to obtain a cheap supply of natural spat collected from

the sea, though only small quantities offarmed scallops

have so far been marketed.

In Scottish waters, scallops reach a commercial size

of 100 mm (at 20 meats/pound, roe-on) in 3-4 years.

Figure 13

Scallops are grown to salable sizes in lantern nets.

Photograph by the author.

Queens reach a saleable size of 60 mm in 21/2 years and

give a yield of 60-70 meats/pound. There are 26 registered scallop and queen farms in Scotland, and production is about 80 t.

According to the Food and Agricultural Organization of the United Nations, the international demand

for scallops will come from the United States and France,

but new markets are expected to develop in Spain,

Italy, and Portugal where seafoods are popular. Scallops are seen as an easy-to-use product which fits well

into the requirements of the seafood processing industry and modern consumption habits. The future for the

U.K. scallop industry in the 1990's looks bright.

Other Species

The whelk and the periwinkle are gastropods which are

commercially exploited in parts of Britain. These "sea

snails" have been eaten as a cheap source of food for

centuries but, in recent years, valuable export industries have developed around them (Table 1).

The common whelk, called the "buckie" in Scotland,

is a carnivorous animal which is easily caught in pots

baited with dead fish. Various types of pots are used

around our coasts. Types with an iron frame were favored because of their weight, but concrete-based plastic pots are now common. Whelks can be caught yearround, but catches do decline in hot summers, when

the warming of the water tends to make this animal

sluggish, and at extremely low temperatures.

The traditional market for whelks is at the seaside

holiday centers, where they are sold at shellfish bars.

Since whelk meat can be tough and rather indigestible,

this seafood is not favored by the modern gourmet, and

home sales have declined. In 1990 the fishery was

boosted by large exports of the extracted meats to

Korea and Japan. How long this trade will last is not

known but, in 1996, supplies were still being sent frozen to the Far East in 20 t container loads.

In Scotland, and to a much lesser extent in England

and Wales, the collection of "winkles" is an important

part of the local economy. Production data in the

Government's fisheries statistics (Table 2) are completely underestimated because winkle pickers include

school children, the unemployed, and the retired, and

their catches are mainly unrecorded. Furthermore, 95%

of the catch is exported alive to the continent, where

this small gastropod is considered a delicacy.

Clams are not an important shellfish in Britain. The

native clam or "palourde," Tapes decussatus, is highly

valued in Europe, but natural U.K. stocks are small.

The Manila clam is a more recent introduction to Britain, with broodstock being imported by MAFF from the

U.S. State of Washington in 1980. Trials by staff at the
98 NOAA Technical Report NMFS 129

Fisheries Laboratory, Conwy, N. Wales, have proved the

Manila clam to be a hardy, fast-growing species, with

substantial potential for commercial production (Utting,

1987) .

Similar in appearance to the native species and easy

to rear in the hatchery, Manila clams are now being

cultivated in Britain, but production is still below 100 t.

Spencer et al. (1991) describe the culture techniques

of Manila clams using trays or plots on the shore, protected with netting.

The American hard-shelled clam, Mercenaria

mercenaria, was brought to England in the early 1900's

and has become established as a self-sustaining population on the south coast of England, in Southampton

Water. Whether its introduction was deliberate or accidental is subject to speculation. It may have been brought

over by American servicemen during World War I or in

ballast in sailing ships from New York City, or it may

have been discarded from transatlantic liners sailing to

Southampton (Utting and Spencer, 1992).

These clams have been a valuable resource for local

fishermen who harvested them by hand before 1970

but later dredged the stock. The fishery is now in decline, due to the lack of any substantial spatfall, after

the closure of a nearby power station, which helped to

raise water temperatures in the confines ofSouthampton

Water.

Future Prospects _

Turning first to production, it must be stressed that

most wild U.K. stocks of native oysters, mussels. scallops,

and queens have been exploited for decades and most

populations are already being exploited at varying levels. The cultivation of Pacific oysters and clams is still a

small part of our industry, but there are signs of slow

growth. There are still opportunities to increase home

demand; the need is to persuade existing customers to

eat more mollusks and also to persuade nonconsumers

to start eating these shellfish.

Ifsupplies can be increased by better management of

the wild stocks and by increased farming, there are

opportunities for British producers to export to the

continent, where mollusks are widely eaten. The U.K.'s

strengthening links with the EC and the formation of a

"Single Market" in 1993 should help develop markets,

especially in France and Spain.

However, the British industry faces many problems

in taking advantage of these opportunities. Tougher

EC health regulations will raise standards, but some

small growers may have inadequate capital to meet the

upgraded depuration and hygiene standards. The U.K.

shellfish industry faces increasing opposition from the

environmental lobby and the designation of British

estuaries as areas for nature conservation may result in

shellfish developments being hindered. Conflict with

other water users, such as industrial and recreational

interests, is also affecting investment and confidence in

the future.

There is also a need to promote our shellfish. The

Sea Fish Industry Authority is the organization which

develops and helps to promote U.K. fisheries. Efforts to

raise product awareness of U.K. mollusks, both fresh

and frozen, must be increased. Quality is of particular

importance, but there are still opportunities which could

lead to exciting and profitable development ofBritain's

mollusk industry.

Literature Cited

Calderwood, W. L.

1895. Mussel culture and bait supply. MacMillan & Co., Lond.,

121 p.

Cole. H. A.

1956. Oyster cultivation in Britain. HMSO, Lond., 43 p.

1974. Marine pollution and the United Kingdom fisheries. In

H. Jones (ed.), Sea fisheries research, p. 277-303. Elsevier

Sci. Pub!., Lond.

Dare, P.

1980. Mussel cultivation in England and Wales. Minist. Agric.,

Fish. Food, Lowestoft, Lab. Leaf]. 50:18.

Dare, P., and G. Davies.

1975. Experimental suspended culture of mussels (Mytilus

fdulis) in Wales using spat transported from a distant settlement ground. Aquaculture 6:257-274.

Davidson, P. E.

1976. Oyster fisheries of England and Wales. Minist. Agric.,

Fish. Food, Lowestoft, Lab. Leaf]. 31:15.

Dodgson, R. W.

1928. Report on mussel purification. HMSO, Lond., 498 p.

Drinkwater,].

1987. Shellfish cultivation in Scotland. Dep. Agric. Fish. Scotl.,

Scott. Fish. Inf. Pamphl. 13:20.

Edwards, E.

1984. Mussels-the bountiful marine resource. World Fishing

33(1l):45.

1992. Heavy fishing threatens cockle stocks. Fish Farm. Int.

19(10):1.

Franklin, A., G. D. Pickett, and P. M. Connor.

1980. The scallop and its fishery in England and Wales. Minist.

Agric., Fish. Food, Lowestoft, Lab. Leafl. 51:19.

French, P.

1989. Oyster fishing in Essex. In Proceedings of 20th Annual

Conference Shellfish Association, Lond., p. 88-96.

Kev, D.

1981. A review of development of the Solent Oyster Fishery,

1972-80. Minist. Agric., Fish. Food, Lowestoft, Lab. Leafl.

5:!:36.

1991. The native oyster fisheries of England and Wales. In

Proceedings of 22nd Annual Conference Shellfish Association, Lond., p. 5-18.

'vlason, ].

1969. Mussel raft trials succeed in Scotland. World Fishing

18(4) :22-24.

1972. The cultivation of the European mussel, Mytilus edulis L.

Oceanogr. Mar. BioI. 10:437-60.
________________________________ Edwards: Molluscan Fisheries in Britain 99

1983. Scallop and queen fisheries in the British Isles. Fish.

News (Books) Ltd., Lond., 144 p.

1985. Scallops and their fisheries. Proceedings of the 16th

Annual Conference Shellfish Association, Lond., p. 32-37.

Orton,]. H.

1937. Oyster biology and oyster culture. Buckland Lectures for

1935. Edward Arnold, Lond., 211 p.

Philpots,]. R.

1890. Oysters and all about them.John Richardson, Lond., 241 p.

Spencer, B. E.

1990. Cultivation of Pacific oysters. Minis!. A~ric., Fish. Food,

Lowestoft, Lab. Leaf]. 63:47.

Spencer, B. E., D. B. Edwards, and P. F. Millican.

1991. Cultivation of Manila clams. Minis!. Agric., Fish. Food,

Lowestoft, Lab. Leaf]. 65:29.

Utting, S. D.

1987. The potential of clams. Aquacul!. Ireland 31:16-17.

Utting, S. D., and B. E. Spencer.

1992. Introductions of marine bivalve molluscs into the United

Kjngdom for commercial culture - case histories. ICES Mar.

Sci. Symp. 194:84-9l.

Walne, P. R.

1974. Culture of bivalve molluscs. 50 years' experience at Conwy.

Fish. News (Books) Ltd., Lond., 173 p.

Wood, P. C.

1969. The production of clean shellfish. Minis!. Agric., Fish.

Food, Burnham, Lab. Leaf]. 20:16.

The Belgian Mollusk Fisheries*

FRANK REDANT

Fisheries Research Station

Ankerstraat 1

B-8400 Ostend, Belgium

ABSTRACT

Bivalves and gastropods landed in Belgium are taken as a by-catch of fisheries targeting

finfish or crustaceans, and the nation has never had specialized molluscan fisheries. Species

landed consist mainly of whelk, Buccinum undatum; and scallops, Pecten maximus and Chlamys

spp. Long-term trends in the landings of mollusks are closely related to long-term changes in

fleet and vessel size, gear types used, fishing grounds and targetspecies, and demand on the local

market. In the 1950's, the annual landings ofwhelk fluctuated between 80 and 200 t, while those

ofscallop were insubstantial. Since then, the landings gradually rose to record figures of 678 t for

whelk and 762 t for scallop in the mid-1970's. Most recently, there has, however, been a

substantial drop in the landings of both species. Provisional figures for 1991 and 1992 revealed

an almost 50% decrease in landings for whelk, and 80% decrease for scallop. Documented

history on mollusk trade and consumption in the area nowadays called Belgium goes back to the

early days of the Roman occupation. A regional seafood specialty in Belgium is "moules frites"

(blue mussels, steam boiled with a mixture ofvegetables, and served with French fries). In 1990,

over 30,000 t of mussels were consumed, all of which were imported, mostly from the Netherlands. Whelk is eaten locally, but other mollusk species, such as scallops, venerids, and cardiids,

were not eaten to any extent until recent decades. Mollusks, as a whole, contribute about onefifth to the nation's per capita consumption offinfish and shellfish.

Introduction

When, around 55 B.C., the Roman emperor GaiusJulius

Caesar conquered the lands west of the lower Rhine

River, he met such a fierce resistance that in his written

comments he called the Belgians the bravest of all

Gauls: "Homm omnium fortissimi sunt Belgae, ...."

Since then, the Roman empire has faded away, and so

has the Belgians' fame. Nowadays Belgians have the

reputation, not so much of being the bravest, but certainly of being the most burgundian of all Germanic

peoples-a race that does not despise a delicate meal

and a hearty drink. In gastronomic terms this is translated into a broad choice oflocal dishes and beverages.

When it comes to mollusks, however, the inventory of

regional specialties is limited tojust one: "Moules frites"

(blue mussels, Mytilus edulis, steam-boiled with a mixture of vegetables and served with French fries). Its

popularity can easily be measured from the quantities

of mussels consumed: In 1990 these amoun ted to over

30,000 metric tons (t) (1.1 million bushels), by a total

population ofjust under 10 million people. Most unfortunately for the local fisheries, however, all mussels are

imported.

This roughly sets the tone for the Belgian mollusk

fisheries; Belgium never had any specialized molluscan

fisheries, and for various reasons probably none will

ever develop. Bivalves and gastropods landed in Belgium are taken as a by-catch of fisheries targeting finfish or crustaceans, and the number of species marketed is small-mostly whelk, Buccinum undatum, and

"scallop," the common denominator for a mixture of

mainly great scallop, Pecten maximus, with much smaller

quantities of queen scallop, Chlamys spp.

For many years research priorities in the Belgian

fisheries have been on much more economically important species or species groups: Herring (in the years

immediately before and after World War II), gadoids,

flatfishes, shrimp, and Norway lobster, Nephrops

norvegicus. As a matter of fact, this is the first attempt

ever"made to comprehensively review the Belgian mollusk "fisheries." For practical reasons, the review is limited to the period between 1950 and 1990. All fishing

areas mentioned in the text are shown in Figure 1.

• This study was subsidized by the Institute for Scientific Research in

Industry and Agriculture (ISRIA), Brussels, Belgium.

101
102 NOAA Technical Report NMFS 129 _

Development of the Mollusk Fisheries _

The 1950's

In the early 1950's the Belgian trawler fleet comprised

about 460 vessels, with an overall fishing capacity of

roughly 60,000 HP (Fig. 2, 3). The vast majority (about

290 vessels or almost two-thirds of the fleet) were small

cutters and shrimp trawlers of <50 CRT, with engines of

<120 HP. The fleet also counted about 150 mid-class

motor trawlers (50-150 CRT and 120-350 HP) and a

small number of large motor and steam trawlers (>150

o~ g;go Fladen

IJ Grounds

o

Celtic Sea

North Sea

Botney Gut

France

Figure 1

l\Iajor fishing grounds of the Belgian trawler fleet in the North Sea and adjacent waters.
______________________________ Redant: The Belgian Mollusk Fisheries 103

'950 1955 1960 1965 '970 1975 1980 1985 1990

o 0

150

-+- Number or vessels

---*" Fleet GAT

-a- Fleet HP 120

i

c

0-

r

60 <>

c

m

0:

'" 30

m

D

5 200 z

5001 ----------;:======::::;-1

Figure 3

Number of vessels, overall gross tonnage (CRT in thousands), and nominal fishing power (1,000 HP) of the

Belgian trawler fleet, 1950-90.

be much more efficient to catch shrimp and flatfish,

was introduced in the shrimp fishery in the early 1950's

(Desnerck and Desnerck, 1976), but it took almost 10

years before this technique was largely adopted by the

flatfish-directed trawlers.

Otter trawling is not the most efficient way to catch

strictly benthic organisms, such as whelk or scallop.

Thus, the whelk and scallop landings remained small to

insubstantial throughout the 1950's. Annual landings

ofwhelk fluctuated between 80 and 200 t, with the highest

figures being recorded in the early 1950's (Fig. 6). Great

scallop and queen scallop were only considered as a

GRT and >350 HP). The latter included some older

vessels, built in British shipyards in the mid-1920's.

Shrimp trawlers, cutters, and the smaller motor trawlers

were concentrated mainly in the coastal waters, the Southern Bight, and the easternmost part of the English Channel, where they fished for brown shrimp, Crangon crangon;

gadoids (cod, Gadus mtYrhua; and whiting, Merlangius merlangus); flatfish (especially plaice, Pleuronectes platessa; and

sole, Solea solea), various species ofrays, Raja spp.; herring,

Clupea harengus; and sprat, Sprattus sprattus (Fig. 4, 5).

Most mid-class and some of the larger trawlers fished

in the northern North Sea (particularly in the Moray

Firth and on the Fladen Grounds) and the central and

the southern North Sea. Their landings consisted mainly

of gadoids (haddock, Melanogrammus aeglefinus; cod;

and whiting), flatfish (plaice and sole) and, locally and

seasonally, herring (Fig. 4, 5).

The largest vessels successfully fished for gadoids

(haddock; cod; saithe, Pollachius virens; and whiting),

ling, Molva spp.; and redfish, Sebastes spp.; on the southern and western coast of Iceland. In 1950, their landings accounted for about one-fifth of the Belgian finfish and shellfish production; 5 years later they scored

the highest ever landings of20,850 t,just under one-third

of all finfish and shellfish landed in Belgium (Fig. 4).

In the early 1950's, the fisheries on the so-called

western grounds (English Channel, Celtic Sea, and Irish

Sea) were not particularly important. Together they

yielded between 3,000 and 5,500 t of finfish and shellfish annually, or <10% of the Belgian landings (Fig. 4).

In the immediate post-war period, otter trawling was

the most popular fishing method: Demersal for

roundfish, flatfish, and shrimp; pelagic or semipelagic

for herring and sprat. Beam trawling, which proved to

600 1 -------------;=====::;1 801----------~=====;1

_ Others

_ Ceilic Sea

[lIIll) English Channel

D IrIsh Sea

Iceland

o C~S North Sea

N North Sea

1950 1955 '960 1965 1970 1975 1980 1985 1990

70

60

HP class

_ ) lOaD HP

751-1000

EJ 501-750

401-500

El 301-400

m 201-300

0101-200

100 HP

500

E

200

1950 1955 1960 1965 1970 1975 1980 1985 1990

Figure 2

Numbers of vessels in the Belgian trawler fleet by horsepower class, 1950-90.

Figure 4

Quantities of finfish and shellfish landed by the Belgian trawler fleet (thousands of metric tons) by ICES

Subarea, 1950-90.
104 NOAA Technical Report NMFS 129

1950 1955 '960 1965 1970 1975 1980 1985 1990

Ii!I Other areas

o Irish Sea

Celtic Sea

ED Channel

North Sea

100

400

300

500

600

o

1950 '955 1960 '965 '970 1975 1980 1985 1990

700 Ir=====:::::;-------;;;;------~

_ Mollusks

o Crustaceans

_ Other pelagic

IlllIIJ Herring

o Other demersal

___ Cartilaginous

c:J Flatfish

G6dlforms

70 .

801--·-·--·-----····-· ---

S 60

<;

.

0>

30

Figure 5

Quantities of finfish and shellfish landed by the Belgian trawler fleet (thousands of metric tons) by species

or species group, 1950-90.

Figure 6

Belgian landings of whelk, Buccinum undatum, all fishing gears combined, by ICES Subarea, 1950-90.

separate item in the official landings statistics from

1972 onward. Until then they were included under the

heading "Other shellfish," i.e., all shellfish except brown

shrimp; Norway lobster; lobster, Homarus gammarus;

brown crab; Cancer pagurus; cephalopods; and whelk.

Judging from the quantities of "Other shellfish" landed

in the 1950's «25 t and most often even <5 t/year), the

landings of great scallop and queen scallop must ha\'e

been extremely low at that time.

During the 1950's only minor changes occurred in

terms of fleet composition and fishing capacity; fleet

size slightly decreased to 432 vessels in 1960; average

gross tonnage remained fairly constant; and average

engine power rose slightly from 142 HP in 1950 to 167

HP in 1960. Despite the decrease in fleet size, the overall

fishing capacity increased by 20% from about 60,000 HP

in the early 1950's to just over 72,000 HP in 1960 (Fig. 3).

The changes in terms of catch composition, on the

other hand, were much more pronounced. The distant

fishery in the Icelandic waters peaked in 1955, then

slowly declined to about 16,000 t in the early 1960's

(Fig. 4). Overfishing of the herring stocks in the North

Sea resulted in a sharp drop in landings, from 19,800 t

in 1955 to merely 3,700 t in 1960. As a consequence,

gadiforms became by far the most important species

group, representing >40% of the Belgian finfish and

shellfish landings (Fig. 5).

Early 1960's to the Mid-1970's

In the early 1960's, several trends began to develop

within the Belgian fishing industry which would have a

m~or impact on whelk and scallop landings. Throughout the 1960's, many small cutters and shrimp trawlers

were decommissioned (Fig. 2). Simultaneously, new

and much larger vessels entered the fleet (albeit in

smaller numbers), while the engines in many existing

vessels were replaced by more powerful ones. Up to the

early 1970's, the nominal decrease in fleet size was

largely matched by the net increase in average engine

power. As a result, total fishing capacity gradually rose

from about 72,000 HP in 1960 to just over 100,000 HP

in the early 1970's, after which it slightly decreased

again to about 92,000 HP in 1975 (Fig. 3).

In the 1960's the Belgian finfish-directed trawler fleet

also started to switch from otter trawling to beam trawling. The beam trawl had already been introduced in

the shrimp fishery in the early 1950's (see previous

section) and, since then, it had become increasingly

popular. Beam trawling for flatfish started in the mid1960's, and because of its obvious merits of yielding

much higher catch rates, it quickly superseded otter

trawling. Many vessels were adapted or even reconstructed to allow beam trawling. Most of the newly built

units were from the very beginning conceived as beam

trawlers, or as multifunctional trawlers which could use

either a beam or an otter trawl.

Beam trawls owe their effectiveness to the much

heavier groundrope and the fact that they can be easily

rigged with so-called tickler chains. Tickler chains sweep

the seabed in front of the groundrope and raise flatfish

from the seabed into the trawl's mouth. Heavy

groundropes and tickler chains also contribute to increase catches of epibenthic animals, such as large gastropods, scallops, and starfish.
____________________________ Redant: The Belgian Mollusk Fisheries 105

Figure 7

Nephroprdirected otter trawler (27 ill length over all, 98 GRT, 375 HP) fishing in the Botney Gut-Silver Pit

area, central North Sea. Photograph by E. Coucke.

Later on, the development of chain mats and

groundropes with wooden or rubber "bobbins," enabled the beam trawlers to fish for flatfish even on

rough grounds with scattered boulders and stones, which

were not accessible to otter trawlers.

The overall increase in nominal fishing power

throughout the 1960's, combined with the introduction of the much more efficient beam trawl in the mid1960's, resulted in a considerable increase in effective

fishing capacity of the Belgian trawler fleet, especially

with respect to bentho-demersal finfish and shellfish.

This had an immediate effect on the whelk landings,

which quickly rose from about 100 tin 1965 to a record

of 678 t in 1975. Over 90% of these were caught in the

North Sea (Fig. 6). This is not surprising because at that

time most of the flatfish-directed effort was confined to

the North Sea. Precise data on the areal distribution of

the fishing effort are not available for this particular

period but, judging from the proportions of plaice and

sole taken (the prime target species ofthe beam trawlers),

it can be assumed that some 65-90% of the beam trawl

effort must have been concentrated in the North Sea.

Another feature which undoubtedly contributed to

the increase in the whelk landings was the expansion of

the Nephrops (Norway lobster) fishery in the central

North Sea (particularly in the Botney Gut-Silver Pit

area) from the late 1960's onward (Fig. 7).

Throughout the 1950's and most of the 1960's, the

larger part (60-90%) of the Nephrops landed by Belgian

trawlers was taken in Icelandic waters. In the late 1960's

and early 1970's, however, the landings of Icelandic

Nephrops fell sharply, and in 1974 they came to a definite end. The latter was an immediate consequence of

the September 1972 agreement between Iceland and

Belgium which laid down the conditions under which

Belgian trawlers were allowed to fish in the Icelandic

EEZ. This agreement included, amongst others, an explicit ban on Nephrops trawling.

The gap in the market, created by the "loss" of the

Icelandic Nephrops grounds, was quickly filled by the

expansion of the Nephrops-directed otter trawl fishery in

the central North Sea. Nephrops landings from this area

almost doubled from the late 1960's to the late 1970's,

from 295 tin 1968 to 575 tin 1978.
106 NOAA Technical Report NMFS 129

Mid-1970's to the Mid-1980's

In the late 1970's and throughout the 1980's, modernization of the Belgian trawler fleet continued (Fig. 2,

3). Fleet size decreased further, from 268 vessels in

1975 to 205 in 1980, then roughly stabilized. Between

1975 and 1985 the average gross tonnage rose from 90

to 110 CRT, and the average engine power from 343 to

468 HP. These trends continued during the late 1980's,

raising the average gross tonnage to 124 CRT in 1990,

and the average engine power to 520 HP. Over the

same period the overall fishing capacity ofthe fleet first

decreased from about 92,000 HP in 1975 to just below

80,500 HP in 1980, then steadily increased again to its

present level of about 107,000 HP (Fig. 3).

Changes in landings composition were most striking

with regard to both areas fished and species landed. By

the end of the 1960's, the herring fisheries had completely collapsed and, except for a short upsurge in the

mid-1970's and another one in the mid-1980's, annual

landings hardly exceeded 1,000 t or even 500 t. Because

of the "facing out" agreement with Iceland, the landings from that area (mainly gadoids and redfish) fell off

rapidly from about 12,500 t in the early 1970's to <1,500

t in the mid-1980's. On top of that, several important

gadoid stocks, especially in the orth Sea, started to

suffer from overexploitation, causing an extra drop in

the gadoid landings (Fig. 4, 5).

Consequently, the Belgian trawler fleet was increasingly geared to flatfish (Fig. 9, 10). In 1982, flatfish

became the most important species group in the landings. By 1990, their part in the Belgian finfish and

shellfish production had reached record levels of61.5%

and almost 70%, respectively, of quantities landed and

gross return to the fishermen (Fig. 5 and 11).

The search for plaice and sole led to a further overall

increase in beam trawl effort and to a further diversion

of effort to the western fishing grounds (English Channel, Celtic Sea, Irish Sea, and Bay of Biscay). Soledirected beam trawl effort (which may be considered as

a fairly reliable index of the overall fishing effort toward flatfish) rose sharply from the mid-1970's to the

scallop had little or no "culinary tradition" in Belgium.

Cooked or steam-boiled whelk was a well-known dish,

especially to the coastal population, but for some reason scallop was not widely appreciated. This started to

change in the early 1970's. The revival of tourism and

gastronomy, both induced by the economic boom of

the "Colden Sixties," helped to familiarize the Belgian

consumer with more "exotic" seafoods, such as scallop,

squid, and cuttlefish. A market was established, and

from the mid-1970's onwards, the national demand for

scallop quickly rose.

No records available

Other areas

o Irish Sea

Ceillc Ssa

o Channel

rn NOrth Ssa

200

I 700 r

800

g 400

-.l 300

1

500

Figure 8

Belgian landings ofscallops, Pecten rnaxirnus and Chlarnys

spp., all fishing gears combined, by ICES Subarea, 1950-

90.

In the 1980's (the only period for which accurate

landings data by statistical rectangle, gear type, and

vessel class are available) the Nephrops-directed otter

trawlers landed between 35 and 65 t of whelk annually,

i.e., 10-20% of all whelk caught in the North Sea by

Belgian trawlers. Similar vessel class or gear statistics are

not available for the 1960's or the 1970's, but it seems

likely that the increase in the Nephraps-directed effort in

the late 1960's and in the 1970's contributed to the increase in landings ofwhelk from the orth Sea as well.

Scallop was not dragged along by the same stream of

events which pushed up the whelk landings from the

mid-1960's onwards. For several reasons it took almost

another decade before the scallop landings started to

rise (Fig. 8).

First of all, the offshore fishing grounds in the North

Sea never have been extremely rich in scallops. According to ICES statistics, the North Sea as a whole never

yielded >10% of the European scallop landings, mostof

which were taken in inshore waters on the British east

coast. This explains, at least in part, why the Belgian

scallop landings remained at a low level throughout the

1960's and the early 1970's. At that time, most of the

Belgian beam trawl effort was concentrated on the more

or less offshore fishing grounds in the orth Sea, which

are even poorer in scallop than the coastal waters.

However, judging from the quantities of scallop

landed from the North Sea in the 1980's, it is almost

certain that the quantities caught in the 1960's and

early 1970's must have been large, as compared with

the few tons actually landed. Discarding must have been

substantial, and this was closely related to the small

sales potential for scallop at that time. Unlike whelk,

800 r;::::=====,----------=:-----i

a lj-1-L.l..-'-t-'--L.L--Y--L.l--L-L-j--L.L...L.L-j-J1950 1955 1960 1965 1970 1975 1980 '985 1990
_______________________________ Redant: The Belgian Mollusk Fisheries 107

Figure 9

Flatfish-directed beam trawler (30 m length over all, 182 CRT, 900 HP) ofthe type currently

fishing in the North Sea and on the western grounds. Photograph by R. Fonteyne.

Figure 10

Beam trawl with chain mats, used to fish for flatfish on rough grounds. Photograph by R.

Fonteyne.
108 NOAA Technical Report NMFS 129

3500 r-;:::=====:::;-------.----I

Figure 11

Gross return of the Belgian finfish and shellfish landings by species or species group, 1950-90.

'950 '955 1980 1965 '970 1975 1980 '985 1990

are stabilizing at between 230 and 265 t, while scallop

landings continued to decline to a mere 90 t in both 1991

and 1992 (a decrease of about 80% from the mid-1980's).

For scallop, sufficient evidence exists to conclude

that the alarming decrease in landings is due to a depletion of the stocks, especially on the western grounds

(see the section on seasonal fluctuations in the landings). Contrary to scallop, the state of exploitation of

the whelk stocks has never been studied in detail, at

least not in the North Sea. Therefore, it is difficult to

identify the precise reason for the decline in the landings. The recent drop in whelk landings per unit effort

(discussed later), and the dwindling auction prices,

which fell roughly 25% despite an almost 50% decrease

in landings (see next section), suggest that both biological and economic factors may have contributed to

the decline in whelk landings.

..__.. _ ..- ..__ _._ _+

_ Mollusks

o Crustaceans

III Other pelagic

[[[[] Herring

o Other demersal

Cartilaginous

[IJ Flatfish

GadlfOffT'lS

3000

E 2000

o

c

1500

1000 z

u::

W

1Il 2500

Trends in Gross Returns and Auction Prices

early-1980's in all western areas. Trends varied from

one area to another, from a roughly 50% increase in

the Celtic Sea and the Irish Sea, to a steep fivefold

increase in the English Channel.

The overall increase in flatfish-directed fishing effort

in areas with high scallop densities (such as the English

Channel and, to a lesser extent, the Celtic Sea and the

Irish Sea), together with the increasing demand for

scallop on the national market, brought about a real

boom in the scallop landings, from <50 t in the late

1960's and early 1970's to a record 762 tin 1976. The

next year, the landings dropped by nearly 45% to about

430 t. From then onward until about 1987, they fluctuated between 350 and 600 t. More than half of the

scallop landings were taken in the English Channel.

The Celtic Sea yielded 15-25% of the landings, the

North Sea 10-20%, and the Irish Sea 5-15% (Fig. 8).

Over the same period, whelk landings were at a similar level, fluctuating between 350 and 500 t. Until 1982,

>90% of these were landed from the North Sea. Together with scallop, however, the landings of whelk

from the western grounds (especially from the English

Channel) rose sharply during the middle and late 1970's,

and by 1983 their part in the Belgian whelk landings

had reached 20-25% (Fig. 6).

The Late 1980's

Most recently the landings of both whelk and scallop

dropped substantially, from 430 t in 1988 to just over

230 tin 1990 for whelk (Fig. 6), and from 480 tin 1987 to

also about 230 t in 1990 for scallop (Fig. 8). Provisional

figures for 1991 and 1992 suggest that the whelk landings

Ever since the early 1950's, the Belgian mollusk "fisheries" have been of minor importance in terms of both

quantities landed and financial returns to the fishermen. In the 1950's and early 1960's, whelk and scallop

represented <0.4% of the overall yield ofthe Belgian sea

fisheries (all finfish and shellfish landed by Belgian trawlers in Belgian ports) (Fig. 5), and <0.3% of the sales

figures in the auctions (Fig. 11).

This situation changed, at first in the late 1960's with

the rise of the whelk landings, and again in the mid1970's with the rise of the scallop landings. Since then,

the contribution of whelk and scallop to the total sea

fisheries yield has fluctuated between 2.0 and 3.5%,

and their share in the sales figures has fluctuated between 1.0 and 1.5%.

The gross returns of whelk increased from BEFO.3-

1.0 million (BEFl = US$0.03) in the 1950's and the

early 1960's to BEF7.Q-I0.0 million in the late 1970's and

the 1980's. Record sales figures were reached in 1983 and

1984, with almost BEFl3.0 million (0.6% of the total sales

figure for all finfish and shellfish landed in Belgium).

ominal auction prices of whelk (not adjusted for

annual inflation) varied considerably throughout the

1950's and the 1960's from BEF3.5 to 9.5/kg. From the

early 1970's to the early 1980's they almost tripled, to

over BEF28.0/kg, then fel1 again to between BEFI7.0

and 22.5/kg (Fig. 12).

Deflated auction prices (adjusted to 1950 prices, using a compound pluri-annual inflation index), show

little or no long-term trends. Even the sharp rise in

whelk landings from the mid-1960's to the mid-1970's

had no major impact on prices. Rather surprisingly, the

recent drop in landings was not accompanied by an

increase in the auction prices. Since 1984, deflated
______________________________ Redant: The Belgian Mollusk Fisheries 109

40

20

60

No records avaIlable

of-L-L...L.J--+-,-'--'--Y--L.L-'--'--t-'--'-'---4-LL'---'--If-'-'-'--'+-'--L.L--,-+-'--'--L.L..j

1950 1955 '960 1965 1970 1975 1980 1985 1990

o f-L-LLJ'--t-'LLJ-Y-'--'-'--'-P-L.L--'-+-'--'---'--'--t-'--'-'---4-LLLLj--L-L.LY

1950 1955 1960 1965 '970 '975 '980 1985 1990

Figure 12

Nominal and deflated auction prices (REF/kg) ofwhelk,

Buccinum undatum, 1950-90.

Figure 13

Nominal and deflated auction prices (REF/kg) ofscallops, Pecten maximus and Chlamys spp., 1950-90.

prices have been far below the average for the preceding 15 years, and in 1988 they almost reached a historical minimum (Fig. 12). Whether this is due to market

saturation is unclear, but it almost certainly enhanced

discarding by the fishermen which, in turn, may have

put some pressure on the landings.

Whelk always has been among the cheapest offisheries products, outvalued by almost all other finfish and

shellfish, except for some ill-reputed species such as

horse mackerel, Trachurus trachurus, and flounder,

Platichthys Jlesus.

Data on gross returns and prices per kilogram of

scallop are available from the early 1970's onwards. At

that time the demand for scallop on the local market

was poor and the auction price low, at about BEFl5.0-

18.0/kg. Since then, nominal auction prices increased

almost continuously, to a peak value of BEF91.5/kg in

1990. Deflated auction prices also showed an upward

trend, from BEF6.5-10.0/kg in the 1970's and early

1980's to over BEFI7.0/kg in the late 1980's, a doubling of their market value in <10 years (Fig. 13).

Nowadays, scallop ranks in the top ten of the most

expensive fisheries products, behind turbot, Psetta

maxima; anglerfish, Lophius piscatorius; halibut,

Hippoglossus hippoglossus; sole; brill, Scophthalmus rhombus; brown shrimp; lobster; Norway lobster; and lemon

sole, Microstomus kitt, but ahead ofsome "renowned" fisheries products such as haddock, cod, plaice, and ray.

Increasing landings combined with increasing prices

made the gross returns of scallop rise quickly, from

<BEF5.0 million in the mid-1970's to >BEF20.0 million

in the 1980's. Scallop had an outstanding year in 1986,

with a sales figure of BEF37.5 million (1.2% of all

finfish and shellfish auctioned).

Over short periods and under relatively stable market

conditions, there appears to be a close inverse relationship between landings and auction prices, for both whelk

and scallop. In the long term, however, this relationship is

overshadowed by the major changes in the market situation, which occurred over the past decades. The increase

in demand for scallop in the mid-1970's, for example,

created a much larger sales potential for this species and,

as a result, the market was able to absorb much larger quantities, without any drop in the auction prices (Fig. 13).

Present Status of the Fisheries

Seasonal Fluctuations in Landings and LPUE's

Seasonal fluctuations in landings and landings per unit

offishing effort (LPUEI) are well documented for whelk

and scallop for the years 1981-90. The available database includes total and species-directed effort (in numbers of voyages, hours fished, and HP corrected fishing

hours) as well as quantities landed by area, month, gear

type, and vessel class. Discussing or even summarizing

all the data would be beyond the scope of this publication. The focus, therefore, will be on two representative

examples, beam trawl landings ofwhelk from the North

Sea and scallop from the English Channel, with some

side comments on the other fisheries.

North Sea whelk landings by flatfish-directed beam

trawlers show a clear seasonal pattern, with peak values

I The LPUE's in this paper were calculated from effort data for

vessels actually landing whelk or scallop, and not from effort data

for the fleet as a whole. Unless stated otherwise, LPUE's are given

in kg/hour trawling.
110 NOAA Technical Report NMFS 129

o '--------j----+---+----t-----+---'

Figure 15

Relationships between beam trawler CRT and peak

season LPUE's of whelk, Buccinum undatum, landed

from the North Sea.

) 200

/

a/

51-100 101-150 151-200

GRT Vessal class

50

lOr--------------------,

9 ~e8s0n -+- 1981-82 '*" 1982-83

a; -B- '983 -84

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Irish Sea, albeit slightly shifted in time. Peak landings

usually occur between January-February and April-May

in the Celtic Sea, and between March-April and MayJune in the Irish Sea. Beam trawling in the Irish Sea is a

strictly seasonal activity, with 55-85% of the fishing

effort concentrated in the period March-June. The

seasonal pattern of the North Sea scallop landings is

irregular, with respect to both rhythm and range of the

fluctuations.

Before the decline of the scallop landings in 1988,

peak season LPUE's in the English Channel ranged

in autumn and early winter, usually between September-October and January-February (Fig. 14). In most

years there is a second, much lower and much narrower

peak in the landings aroundJune. Roughly similar fluctuations appear from the data series for the Nephropsdirected otter trawlers operating in the central North

Sea and for the flatfish-directed beam trawlers in the

English Channel.

The whelk LPlJE's of North Sea beam trawlers displaya seasonal pattern similar to that in the landings.

In the early and mid-1980's (i.e., before the decline of

the whelk landings), the average LPUE's during the

peak season varied from 0.6 to 2.8 kg/hour trawling for

the 51-100 CRT vessels, from 1.7 to 3.6 kg for the 101-

150 CRT vessels, from 3.5 to 6.5 kg for the 151-200

CRT vessels, and from 4.5 to 7.9 kg for the largest

vessels. The data available for vessels ::::50 CRT were too

erratic to be included in this comparison. Data for

individual seasons show a clear, almost linear relationship between CRT and LPUE (Fig. 15). In recent years,

however, the peak LPUE's dropped by about 50% as

compared with the figures for the early 1980's. This

may be due to a decline of the stocks or to an increase

in discarding by the fishermen in response to the relatively low auction prices of whelk (see previous section

on trends in gross returns).

Scallop landings by beam trawlers fishing in the English Channel show marked seasonal fluctuations, with

sharp peaks between December-January and April-May

(when, from a gastronomical point of view, the scallops

are at their best, because of the fully developed gonads

or "coral"), and marked lows during summer (Fig. 16).

Similar patterns are recorded for the Celtic Sea and the

90r-------------------,

80

70

30

20

10

o

Jan Jan Jar. Jan Jan Jan Jan Jan Jen Jan

I IMlni~lulul~IMI~lool

90

80

70

60

I 50 m

0

c

40

30 - --- - -_..__......-

20

10

o

Jan Jan Jan Jan Jen Jan Jan Jan Jan Jan

I 81 I 82 I 83 I 84 i 85 I 86 I 87 I 88 I 89 I 90 I

Figure 14

Monthly landings of whelk, Buceinum undatum. trom

the North Sea by flatfish-directed beam trawlers, aU

vessel classes combined, 1950-90.

Figure 16

Monthly landings ofscallops, Pecten maximusand Chlamys

spp.. from the English Channel by flatfish-directed beam

trawlers, all vessel classes combined, 1950-90.
____________________________ Redant: The Belgian Mollusk Fisheries III

from 3.9 to 6.3 kg/hour trawling for the ~50 GRT

vessels, from 3.2 to 8.3 kg for the 51-100 GRT vessels,

from 2.6 to 6.7 kg for the 101-150 GRT vessels, and

from 3.5 to 17.8 kg for the 151-200 GRT vessels. Data

for the vessels >200 GRT were too few to allow any

comparison. The data series for individual seasons show

a broad and hardly conclusive array of relationships

between GRT and LPUE.

Since 1988, the peak season LPUE's ofscallop in the

English Channel fell by >70% as compared with the

early 1980's. Similar drops occurred in the North Sea

and the Celtic Sea but not in the Irish Sea. The severe

drop in the LPUE's in scallop-rich areas such as the

English Channel and the Celtic Sea gives reason for

concern since it may be symptomatic of an alarming

depletion of the scallop stocks.

Management Regulations

Except for the regulations set by the Commission of the

European Union (which are legally binding to all EU

member countries), national or local management regulations that specifically apply to the Belgian mollusk

fisheries do not exist. For great scallop there is a minimum landing size of 110 mm (ICES Sub-area VIId -

English Channel East) or 100 mm (all other areas),

measured across the largest width of the shell (EU

Regulation 3094/86, Section 5). No minimum landing

size regulations exist for queen scallop or whelk.

For the time being, there are no catch or effort

restrictions for any of these species (at least not in the

areas accessible to the Belgian trawler fleet). This may

change, even in the near future, especially if the depletion of the scallop stocks continues along the trend set

during the most recent years.

Management regulations not directly aimed at mollusks, such as the temporary closing of fishing areas for

plaice or sole to avoid overshooting the TAC's, may,

however, have an immediate impact on the landings of

other species as well, including whelk and scallop.

Mollusk Trade and Consumption _

The First Traces of Mollusk Consumption

The documented history on mollusk consumption in

the area nowadays called Belgium, goes back to the

early days of the Roman occupation (1st century A.D.).

Excavations on inland Gallo-Roman sites revealed fragments and complete shells of several marine mollusk

species (Gautier, 1972, 1983; Cordy, 1981; Peuchot,

1981; Van Neer, 1988, 1990), amongst which oysters

were by far the most abundant. Oysters were highly

prized by the Romans, and the presence of a variety of

oyster that is typical for the English Channel and the

British Isles, suggests they were sometimes traded over

long distances.

Strong evidence on the methods used to transport

the oysters is lacking, but they most probably were

firmly tied up to avoid loss of liquid, and then covered

with seaweed to keep them cool and moist (Peuchot,

1986). Even under these conditions, the shelflife of

oysters is relatively short, which led to the hypothesis

that they were brought quickly to destinations, possibly

by mounted couriers (Peuchot, 1981).

Mussels and cockles, Cerastoderma edule, were first

found in remains from the 1st to 3rd centuries (Gautier,

1972, 1983; Peuchot, 1981), and whelks in funeral tombs

and rubbish dumps from the 2nd to 4th centuries

(Gautier, 1972). Mollusks probably were consumed even

earlier by prehistoric populations living along the coast,

but, as yet, no faunal remains from such sites are available.

Archeozoological investigations on medieval and early

post-medieval sites, covering a time span of>I,OOO years

between the 6th and the 17th century, yielded numerous fish and shellfish remains, including oysters, mussels, cockles, whelks, and periwinkles, Littorina littorea

(Gautier, 1983; Gautier and Van der Plaetsen, 1986;

Van der Plaetsen, 1985a). The finds confirm that,

throughout the ages, there has been an active trade in

fisheries products, including mollusks, between the

coastal areas and the inner parts of the country; Van

der Plaetsen (l985b) provides a comprehensive review.

Rise and Fall of the Oyster Growing Industry

The local history of oyster growing dates back to the

end of the 18th century, when the first oyster growing

farm was established near Ostend (Halewyck and Hostyn,

1978). Young oysters were imported from the United

Kingdom and grown to a commercial size in man-made

ponds. The industry flourished during the "Belle Epoque"

period, from about 1865 to 1914, with annual exports of

up to 30 million of the internationally renowned

"Ostendaises" or "Royal d'Ostende" to France, Russia, the

Balkans, Germany, and Austria. On the eve ofWorld War

I, the oyster industry counted 26 growing farms and employed >270 people (Halewyck and Hostyn, 1978).

After World War I, the oyster growing industry started

to subside. Many oyster parks had been severely damaged during the war, and the supply of young oysters

was badly affected by a disease outbreak in the English

rearing farms (Halewyck and Hostyn, 1978). First attempts to revive the industry and to actually rear oysters

in the Ostend Sluice-dock (an inland seawater basin,

originally designed to "blowout" the harbor) were fairly

successful, but they were thwarted by World War II.
112 NOAA Technical Report NMFS 129

New trials, especially in the 1960's, largely failed because of increasing problems with water quality and

with competitors (barnacles and Crepidula) of the seedling oysters (Halewyck and Hostyn, 1978). The last oyster

growing company ceased its activities in the early 1980's.

Trends in Mollusk Consumption Since the 1950's

In 1990 (the most recen t year for which exhaustive

trade and consumption statistics were available), Belgium imported about 34,200 t of live, fresh, frozen, or

dried marine bivalves and gastropods (product weight,

not converted to live weight), and 2,600 t of canned or

likewise preserved mollusks (including cephalopods).

The total live weight of the bivalve and gastropod imports (all commodity groups combined) was estimated

at about 37,500 t, a figure that exceeded the grand total

of the Belgian finfish and shellfish landings by roughly

6,500 t. The overall value ofthe imports (all commodity

groups, cephalopods excluded) amounted to BEF2.6

billion, i.e., 11.5% of the grand total for all finfish and

shellfish imports for human consumption in 1990.

The 1990 imports of bivalves and gastropods (excluding canned products) comprised. amongst others,

30,630 t product weight of live or fresh blue mussels;

1,590 t of oysters (European flat oyster, Ostrea edulis;

and various species of cupped oysters, Crassostrea spp.);

and 900 t of fresh or frozen pectinids, mainly from the

Netherlands (92.0%) and France (4.5%). Imports from

non-EU countries represented <0.5% of the total.

Compared with the imports, the 1990 exports were

small: 280 t of marine bivalves and gastropods (product

weight) and 700 t of canned mollusks (including cephalopods). The exports (all commodity groups. cephalopods excluded) had an overall value of about BEF120

million Uust over 1.5% of the total export sales figure

for fisheries products). Part of the exports consisted of

canned mollusks, imported as raw products and processed by the local food industry.

The availability of import and export statistics varies

widely among species in both detail and time span covered. For mussels, the data series goes back to the immediate post-war years, but the imports and exports of many

otherspecies, such as pectinids, venerids, and most cephalopods, were not recorded as separate items in the trade

statistics until 1988. Long-term trends in the national

consumption ofindividual species orspecies groups, therefore, can be given for only a limited number of them.

The total consumption2 of blue mussels fluctuated

between roughly 19,000 and 25,000 t/year from the

2 Consumption figures were calculated as Imports + Landings -

Exports, and unless stated otherwise, are given in metric tons live

weight per annum.

early 1950's until 1980. In 1981 it increased in one

stroke by 5,400 t, and since then it has balanced between roughly 25,000 and 32,000 t/year, with a peak of

31,800 t in 1982. The annual per capita consumption of

mussels followed a similar trend (Fig. 17). Most blue

mussels were, and still are, imported from the Netherlands. In 1990 Belgium took 30,320 t or almost onethird of the Dutch mussel production, together with

much smaller quantities (usually <3% of the imports)

from Denmark, France, Germany, Ireland, and occasionally the United Kingdom.

The annual consumption of flat and cupped oysters

has fluctuated widely over the past decades, from 560 t

to just over 2,900 t. Since 1986 it has remained fairly

stable at about 1,600 t/year. In 1990 the oyster imports

comprised 53 t of live flat oysters and 1,530 t of "Other

oysters," mainly supplied by the Netherlands (54%)

and France (43%).

The total consumption of "Other mollusks" (a wide

variety of bivalves, gastropods, and cephalopods including, amongst many others, whelk and scallop) increased

almost linearly from 830 t (live weight) in 1965 to 4,250

tin 1990.

The data series on canned mollusks (including cephalopods) shows considerable variations. Consumption

figures fluctuated between 1,000 and 1,600 t/year (product weight) from the mid-1960's to the mid-1970's

and, after a sharp increase to almost 2,100 t in 1977,

between 1,400 and 2,200 t/year in the late 1970's and

throughout the 1980's.

The annual per capita consumption of mollusks (including cephalopods) ranged from 2.5 to 3.1 kg live

weight from the mid-1960's to the mid-1970's, then

5.0 II -8- Tot.' mollusks I'

40 r1_:-r~'U.:USB.'S - ..

0-

5 3.0 -

!t---.···········..--···· 0.0 f-W-LJ.+'--'--'--Y--'--'-'-Y-LJ....!-L-t-'--'-'-Y-L.J...J-Lf...LL-'--'-f-l--'--'-Lj

1950 1955 1960 ~965 1970 1 975 1980 1985 1990

Figure 17

Annual per capita consumption (kg live weight) of

mollusks (including cephalopods), and blue mussel,

Mylitus edulis, 1950-90.
______________________________ Redant: The Belgian Mollusk Fisheries 113

The Future _

Figure 18

Tentative breakdown of the 1990 per capita consumption of mollusks (kg live weight) by species or species

group.

Against the cheerless background of declining scallop

stocks and a dwindling whelk market, the immediate

future of the Belgian mollusk "fisheries" does not look

promising. If the current overexploitation of the scallop stocks continues, the EU may be compelled to set Anonymous.

1950-90. De evolutie van de Belgische visserijsector. [Trends

in the Belgian fisheries industry.] Advis. Comm. Sea Fish ..

Ostend, val'. pagin.

1950-90. Officiele lijst del' Belgische vissersvaartuigen. [Checklist of the Belgian fishing vessels.] Minist. Transport, Dep.

Shipping, Bur. Shipping Camm., Ostend, var. pagin.

1950-80. Sea fisheries: Monthly and annual landing statistics.

Natl. Inst. Stat., Brussels, var. pagin.

1950-90. Fisheries products: Import and export statistics. Natl.

Inst. Stat., Brussels, var. pagin.

1980-90. De Belgische zeevisserij: Aanvoer en besomming.

[The Belgian sea fisheries: Landings and gross returns.J

Minist. Agric., Dep. Econ. Affairs, Sea Fish. Serv., Ostend,

var. pagin.

1980-90. Uitkomsten van de Belgische zeevisserij. [Results of

the Belgian sea fisheries. I Minist. Agric., Dep. Econ. Affairs,

Sea Fish. Serv., Ostend, var. pagin.

1986. Verslag van de proefnemingen "Schelpenvisserij" -

Technisch verslag van het Beheerscomite 'Visserij projecten."

[Progress report on scallop dredging experiments - TechniThe author wishes to thank the following persons for

their help and assistance: Ms. Van Sieleghem, for extracting the landings and effort statistics from our national databases; Dr. Van Neer, for providing extensive

information on the archeozoological studies on finfish

and shellfish; and Dr. Jaspers and Mr. Fonteyne, for

critically reviewing the manuscript of this paper.

precautionary TAC's to protect them. In that case, the

Belgian fisheries may well be pinned down to very low

or even zero TAC's in a number offishing areas, which

would put a serious constraint on the development of

any specialized scallop fisheries.

Attempts to develop such a fishery were undertaken

by the Fisheries Research Station (Ostend, Belgium) in

the mid-1980's (Anonymous, 1986). The experiments

consisted of rigging a series of scallop dredges to the

beam of a beam trawl, and to fish for scallop on the

offshore scallop grounds in the English Channel. Although the results were promising, with catches of up

to 22.5 t ofscallop in 16 days at sea (i.e., an average of

1.4 t/day), the technique was never used on a commercial

scale, mainly because fishermen lacked interest in it.

The traditional, almost conservative, attitude ofmany

fishermen and shipowners with respect to target species and fishing techniques has been a major impediment to the diversification of the Belgian sea fisheries.

Beam trawling for plaice and sole currently pays well. In

the long term, however, focusing on a small number of

species may well prove not to have been the best way to

guarantee the future of the Belgian fishing industry.

Literature Cited

Acknowledgments _

Others 0139

Oyster s 0156

Whelks 0024

Pectlnlds 008

Bivalves and

gastreDods

All species and

cemmedi t y greups

Mussels

3075

quickly rose to just over 4.1 kg in 1982. Within the next

5 years it declined to about 3.5 kg, but most recently it

increased again to 4.1 kg (Fig. 17). The exact share of

bivalves and gastropods therein is difficult to establish,

except for the years 1988-90, when they represented

91-93% of the annual mollusk consumption. A tentative breakdown by species or species group of the 1990

per capita mollusk consumption is given in Figure 18.

Mollusks, as a whole, contribute about one-fifth to

the total consumption of finfish and shellfish in Belgium, a figure that has hardly changed over the past 25

years. Flat and cupped oysters are usually eaten raw

from the shell, with a dash of pepper and a few drops of

lemon juice; mussels and whelk are most often steamboiled with a mixture of onions, leek, celery, and parsley. The domestic consumption of other bivalves and

gastropods is low and, strictly speaking, there are no

traditional, regional preparationsfor these species. Restaurants throughout the country, however, may offer a

wide choice of dishes, most often inspired by French,

Spanish, or Italian gastronomy, of which mollusks are

an essential ingredient.

Mussels, scallops, queen scallops, cockles, and sometimes carpet shells, Venerupis spp., are also used in salads, and in sauces accompanying, for example, cooked

or fried whitefish. Worth mentioning, and typically Belgian, is the so-called "sauce aI'Ostendaise," a creamy

dressing with brown shrimps and mussels, which goes

particularly well with sole.
114 NOAA Technical Report NMFS 129

cal report management committee "Fisheries Projects".] Intern. Rep. Minist. Agric., p. 1-22.

Cordy,]. M.

1981. Archeozoologie. In R. Brulet (ed.), Braives gallo-romaine,

p. 197-200. Pub!. d'Hist. de l'Art. et d'Archeo!. Univ. Catho!.

Louvain 26.

Desnerck, G., and R. Desnerck.

1976. Vlaamse visserij en vissersvaartuigen - Deel II: De

vaartuigen. [Flemish fisheries and fishing vessels - Part II:

Vessels.] Desnerck and Desnerck, Pub!., 542 p.

Gautier, A.

1972. Dierenresten van het Laat-Romeins grafveld te Oudenburg

(Prov. West-Vlaanderen, Belgie). [Animal remains from the

Late-Roman burial field in Oudenburg, Province of WestFlanders, Belgium.] Helinium, 12(2):162-175.

1983. Les vestiges animaux du village Gallo-Romain de

Ploegsteert (1978-1982). Mem. Soc. d'Hist. de CominesWarneton 13:520-524.

Gautier, A., and P. Van der Plaetsen.

1986. Beenderen uit de Boudelo-Abdij: Een eerste kennismaking. [Animal remains from the Boudelo abbey: An introduction.] VOBOV-Info 21:5-11.

Halewyck, R., and N. Hostyn.

1978. Oostends oesterboek - Historiek van de Oostendse

oesterteelt vanaf de 18e eeuw tot op heden. [History of the

Ostend oyster growing industry since the 18th century.] "De

Plate" Pub!., Ostend, 68 p.

ICES.

1960-85. Bulletin statistique. Int. Counc. Explor. Sea,

Copenhagen, var. pagin.

Peuchot, R.

1981. Rapport preliminaire sur l'analyse des coquilles de

Mollusques recoltes dans les fouilles de Treignes (1980).

Amphora 26:41-44.

1986. Proposition pour une interpretation plausible du transport des huitres a l'epoque romaine. In La region du Virion

du temps des cavernes au temps des chateaux, p. 35-36.

Pub!. Cent. d'Etudes Docum. Archeo!. Virionva!.

Van der Plaetsen, P.

1985a. Beestig Gent - Archeozo6logie in een stad. [Arch eozoological investigations in the city of Ghent.] Stadsarcheologie, 9 (3): 12-26.

1985b. Import van dieren in onze gewesten in archeozo61ogisch

perspektief. [Animal imports in Flanders and their

archeozoological context.] VOBOV-lnfo 18-19, p. 31-39.

Van Neer, W.

1988. Archeozo61ogische vondsten uit de La Tene- en de

Romeinse periode te Broekom (Limburg). [Archeozoological finds from the La Tene and the Roman periods

in Broekom, Province of Limburg.] In W. Vanvinckenroye

(ed.), De Romeinse villa op de Sassenbroekberg te Broekom.

[The Roman villa ofSassenbroekberg, Broekom.] Pub!. Provo

Gallo-Romeins Mus. Tongeren 38:37-42.

1990. De archeozo61ogische resten. [Archeozoological remains.]

In W. Vanvinckenroye (ed.), De Romeinse villa's van Piringen

en Vechmaa!. [The Roman villas of Piringen and Vechmaa!.],

Pub!. Provo Gallo-Romeins Mus. Tongeren 42:31-33.
Molluscan Fisheries and Culture in the Netherlands

RENGER DIJKEMA

Netherlands Institute for Fisheries Research (RIVO-DLO)

P.O. Box 77

4400 AB Yerseke

The Netherlands

ABSTRACT

Trade in mollusks in the Netherlands dates from the 1st century and the Middle Ages. In the

late 18th century, 145 vessels harvested oysters, Ostrea edulis, in the Zuiderzee; landings were

about 14 million oysters/season. After 1850, landings began to decline sharply. Blue

mussels, Mytilus edulis, had been fished mainly for local and regional consumption, but by

1870 an export market for fresh mussels developed. Much of molluscan production has

since been exported to Belgium and France. Mussel culture began to develop after 1865.

Mussel growers dredged seed on wild banks and sowed it on their culture plots in Zeeland

and the Wadden Sea. There now are 77 mussel firms; their fleet consists of 82 vessels. After

harvest, the mussels are transported to Yerseke and sold by an auction. A small-scale fishery

for cockles, Cerastoderma edule, existed in which fishermen raked the cockles in knee-deep

water. In the early 1960's, the hydraulic dredge was developed for harvesting cockles and

production increased thereafter. There currently are 43 cockle dredge boats; most cook the

cockles at sea. Fisheries for periwinkles, Littonna littorea; whelks, Buccinum undatum; and

softshells, Mya arenana, became substantial in the second half of the 19th century. The

whelks were harvested with dredges. Whelks now are harvested only in the North Sea as a bycatch of flatfish beam trawlers. Softshells were dug commercially with forks and spades on

tidal flats until about 1952, but now only small quantities are dug. Each year, from 700-1,500

t of Crassostrea gigas are produced. During the past 5 years, average annual production of

mollusks was about 80,000 t of blue mussels, 50,000 t of cockles, and 5 million oysters, with

an average landed value ofDFLl20 million (US$70 million). In 1989, the molluscan fishery

employed 1,520 people directly and 1,940 indirectly. As the demand for mussels is increasing, mussel prices probably will increase. The molluscan industry feels increasingly threatened by government measures aimed at reducing the impact of the fishery on the environment and wildlife.

Introduction

The first indications of molluscan trade in the Netherlands date from the first century and the Middle Ages.

Mussel and oyster shells have been found in Roman

settlements (Lauwerier, 1988) and in 7th and 8th century excavation sites (Groenman-van Waateringe and

Van Wijngaarden-Baker, 1990). The locations were 80

and 200 km from the coast. For centuries, the production was low and mainly destined for local markets.

A relatively low domestic consumption ofseafood, at

present (1993) about 12.5 kg/person/year, has been

below the production capacity of the coastal waters,

and has left considerable scope for export. Beginning

in the last century, an export market for bivalves was

developed and it has since expanded to its present

scale. Export and transit oflive shellfish is facilitated by

the favorable conditions for storage of live mollusks

and crustaceans offered by the Oosterschelde estuary

and the proximity of a large market in Belgium and

France, both countries with a tradition of seafood consumption. The average production of mollusks during

the last 5 years was about 80,000 t of blue mussels,

Mytilus edulis (2,900,000 bushels), 50,000 t of cockles,

Cerastoderma edule (1,375,000 bushels), and 5 million

oysters Ostrea edulis (25,000 bushels), with an average

landing value around DFL 120 million (US$70 million). In 1990, the total turnover of the mollusk sector

was about DFL 300 million (US$165 million). In 1989,

the molluscan fishery employed 1,520 people directly

115
116 NOAA Technical Report NMFS 129

and 1,940 indirectly. Imports of mussels, cockles, and

oysters make up for bad harvests and allow a stable

supply of the export market. Additionally, other live

shellfish are imported, stored, and exported.

Production Areas _

The Wadden Sea (Fig. lA) is a shallow, inshore sea in

the north of the country separated from the North Sea

by a row of islands. It extends from the Netherlands to

Denmark. The Dutch section covers 2,500 km2, 67% of

which are intertidal sandflats, separated by tidal channels. In the western part, the area ofintertidal sandflats

is small (about 37%) compared with the eastern part

(73%). Due to its large area, its shallowness, and the

occurrence of drifting ice in cold winters, the wild and

cultured mollusk populations are regularly decimated

by ice scouring and exposure to waves and currents.

The water is relatively turbid; under normal (no storm)

conditions the suspended solids concentration is 15-50

mg/1. The salinity is 30-32%0. The mean tidal amplitude is 1.5 m in the western part and 3.0 m in the east.

Until 1932, the Zuiderzee was an inland sea with an

estuarine character. That year the fresh lake Ijsselmeer

was created by the construction of an enclosure dike

for safety and land reclamation (Fig. lA). Mollusk culture and fisheries were thereafter restricted to the marine Wadden Sea.

In the Province of Zeeland, in the southwest of the

country, three estuaries (from north to south), the

Grevelingen, Oosterschelde (Eastern Scheidt), and

Westerschelde (Western Scheidt) were initially fed by

the Rivers Rhine, Meuse, and ScheIdt (Fig. IB). In the

last decades, these estuaries have been modified considerably during a flood protection scheme (Dijkema,

1988). Only the Westerschelde has retained its estuarine character. In 1971, the Grevelingen estuary was

dammed off on two sides. It is now named Lake

Grevelingen, a rather shallow (2-10 m) stagnant marine lake, covering about 100 km2, with a stable and

artificially maintained salinity. The Oosterschelde (310

km2, 54% of which are intertidal sandflats) was closed

in 1986 with a permeable flood barrier. The resulting

reduction of the tidal exchange lowered the current

speed by 30%, but did not depress the bivalve production capacity (Van Stralen and Dijkema, 1994). The

tidal amplitude now lies between 2.00 and 3.00 m. The

water temperature varies between 0° and 22°C and the

salinity between 28 and 30%0. The Westerschelde used

to be an important area for mussel culture and fisheries. Land reclamation has caused the mussel plots and

wild mussel banks to disappear. Only cockles are now

fished on the sandflats. Populations of edible mollusks

are also found in the shallow part of the North Sea

coast to a depth of about 20 m. The area is exposed to

strong wave action during gales. A few locations are

sheltered by sandflats. When bivalve beds survive the

winter storms there, they are fished. Plans exist to create mussel culture plots in this area.

Oyster, Mussel, and Cockle Fisheries,

and Early Culture Trials

Oysters

In the early 18th century, the European flat oyster,

Ostrea edulis, was collected and dredged in the eastern

Wadden Sea between Schiermonnikoog Island and the

mainland and in the western Zuiderzee between Texel

and Wieringen (Fig. lA). As early as 1714, imports of

seed oysters from Denmark were reported (Hoek, 1911),

illustrating that recruitment was unable to keep up with

exploitation of the beds. The variable stock size must be

attributed mainly to losses due to freezing and ice,

shifting sandflats, and the capricious reproductive success of the flat oyster in the Zuiderzee, where in many

summers the water temperature does not exceed 16°C.

This minimum temperature is necessary during a couple

of weeks for successful spawning and settlement.

In the last quarter of the 18th century, 145 vessels

were reported fishing in the Zuiderzee: 60 from Texel,

25 from Zoutkamp, and 60 from Schiermonnikoog

(Hoek, 1911). According to Paludanus (1776), the fishermen collected oysters on foot at low tide, dressed in

leather waders and often using wooden boards attached

to their feet to prevent sinking in the mud. The catch

was collected in wooden troughs which were dragged

over the flats. In this manner up to 2,000 oysters could

be collected per day. Use of long-toothed iron rakes is

also mentioned. Iron dredges, first reported in 1740,

were initially used only in the eastern part of the

Zuiderzee. The dredges were similar to those used in

the German Wadden Sea and probably also to those later

described by Moebius (1877). They were 4 feet wide and

had bags with undersides made of2" iron rings (Fig. 2). A

small ship towed 2 or 3 dredges, a larger ship 4 dredges. As

the ships had no winches, the dredges were often emptied

into small boats towed behind the ships.

To be profitable, dredger landings had to be at least

100,000 oysters per season. This means that in the

second half of the 18th century, landings in the

Zuiderzee must have amounted to roughly 14 million

oysters or more per season. The fishermen mostly held

their catch for shorter or longer periods on private

"oyster banks" demarcated with wooden poles.

Paludamus (1776) describes 60 such beds off Texel,

each measuring 25 ha. Undersized oysters were fattened, and marketable oysters were kept there until the
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 117

--" _. \

(

----.r"

\

\

Rhine River /' /" ..... j_.

\'

L.

'-.

\

"

(

.I

/

(

'/'

/'

I .J'

I 1._.

) \.

(' )

\ ( .-'_O-J

Meuse River

BELGIUM

S h

' 0.9

c lermonnikoog

Terschellin~ ~. '.': ;.

. .:·Zou~amp

d?' n1> .,.- • r_'U", . -J""

. 00~ Texet)..: flj.~ '...

. .

....

.......') ./~ /"., '-...... (._./ \

"

.....,

'---._./''\.\,

..... .~

Zeeland

NORTH SEA

Scheidt River

A

.',

\

I

50 km "'- ,

Figure lA

The Netherlands' major mollusk fishing and production areas: Wadden Sea and Zeeland.
118 NOAA Technical Report NMFS 129 _

season opened. The oysters were shipped mainly to

Amsterdam and to the German cities Bremen and HamB

o 5 10km :'-=~J

burg and even as far as the Baltic cities Riga and St.

Petersburg.

Figure IB

The Zeeland mollusk production and fishing areas: Lake Grevelingen, Oosterschelde, and Westerschelde. Culture plots for

mussels are shown in black. Culture plots for oysters are marked as are the mussel rewater plots.
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 119

Figure 2

Typical 19th century oyster dredge, used in the Dutch and German Wadden Sea. The iron rings on the

underside were 6-7 cm in diameter (after Moebius, 1877).

Mter 1850, landings began to decline sharply, probably due to a combination of high fishing pressure,

mortality, and failing recruitment (Hoek, 1879). Mter

1856, rarely more than 300,000 oysters were landed per

season at Texel, which caused poverty among the fishermen. Initially, attempts were made to restore the

oyster production by sowing on sheltered beds the undersized specimens from the large imports of consumption oysters from Denmark, England, and Scotland.

Between 1859 and 1884, other unsuccessful restocking

trials were made on different locations in the Zuiderzee,

this time with specially imported seed oysters weighing

about 40 g. In 1884, considerable investments were

made in seed oysters that were relaid in an area off the

island ofWieringen where the public fishery was banned.

The trial failed due to natural causes and also poaching, as supervision was insufficient. The plots were eventually restored to the public fishery (Hoek, 1901).

A culture experiment off Texel in 1930, with 6 million seed oysters, likewise failed. Mter a few more vain

attempts, the flat oyster disappeared from the Wadden

Sea between 1940 and 1950. It is supposed that, in

addition to stock depletion, hydrographic changes

caused by the closure of the southern Zuiderzee in

1932 may have played a role.

In the estuaries in Zeeland, exploitation of the wild

oyster banks also dates from the early 18th century.

Also here, overexploitation occurred, and chronicles

mention imports of seed oysters from the British Isles

(Baster, 1762). The principal fisheries were found in

the Oosterschelde off Zierikzee and in the Grevelingen

off Bruinisse. Later, in the 19th century, the eastern

part of the Oosterschelde and the Westerschelde also

made lucrative oyster grounds for fishermen from

Yerseke and Tholen. Oysters were fished mainly with

long-toothed iron rakes. Natural fluctuations in stock

size were less pronounced than in the Zuiderzee, which

can be attributed to higher water temperatures and

more sheltered beds. Nevertheless, the oyster beds were

gradually overexploited and the industry became increasingly dependant on imports.

In 1825, a Fisheries Authority for the Zeeland waters

was installed by the Government to regulate the rapidly

deteriorating fisheries (Fokker, 1926). Fishing for spat

and seed oysters was forbidden, and a fishing season

was introduced, starting in October. Despite these regulations, that were hardly complied with, the stocks remained small, and massive imports had to supplement

the landings. Around 1850, 200 ships were only exceptionally able to land more than 1 million oysters/year

among them. Increasingly, pleas were heard in favor of

a switch to oyster cultivation (Hoek, 1902). By 1886, all

public oyster fisheries had been closed and culture

plots were rented. Since 1971, a wild oyster fishery has

again existed in Lake Grevelingen. Until the oyster

disease bonamiasis broke out in this lake in 1988, between 5 and 7 million oysters were harvested there each

year. At present, the landings have fallen to about 1-2

million flat oysters per year. Wild banks of Pacific oysters in the Oosterschelde are fished for seed oysters

and, to a lesser extent, for market size oysters.

Mussels

Until the middle of the 19th century, blue mussels,

Mytilus edulis, were fished mainly for local and regional

consumption, with mussels from the Zuiderzee being

peddled in Amsterdam and from the Westerschelde

sold in Antwerpen. In the second half of that century,
120 NOAA Technical Report NMFS 129

when the population of the big cities grew rapidly due

to industrial development, the demand for inexpensive

protein-rich nutrition increased and mussels appeared

to be an attractive food. By 1870, an export market for

fresh mussels also developed. The principal destinations were Belgium and England. From 1913 to 1929,

those two countries imported 25,000-38,000 tand 2,700-

4,500 t, respectively, per year. Between 1924 and 1929,

from 1,000 to 3,100 t were also exported annually to

France, and 2,400-3,000 t went to Germany. Apart from

this, an unknown quantity of mussels was taken every

year in the Westerschelde by Belgian fishermen, after

an 1839 treaty with Belgium had granted equal fishing

rights in that estuary to citizens of both countries. In

the 19th century, mussels from the Zuiderzee were

fished mainly from Wieringen, Harlingen, and Zoutkamp

and shipped to northern Great Britain and the cities of

Bremen and Hamburg. Mussels from Zeeland were sold

in Antwerpen by the fishermen themselves and were also

shipped to London from Vlissingen, Zierikzee, or

Rotterdam. The development of steam-powered vessels

after 1860 further enhanced the fresh mussel exports.

In the first half of this century, the mussel fishery in

the Zuiderzee was mainly in the hands of fishermen

from Wieringen with 30 ships and from Texel with 12

ships (in 1910). They used small sailing craft, equipped

with one or two iron dredges. Hand rakes were also used.

The development of mussel culture in Zeeland after

1865 created a strong demand for small seedling mussels. As mussel seed is usually scanty in the southern

estuaries and abundant in the Zuiderzee, a large mussel

seed fishery developed each year in the latter area.

Around 1880, about 80 ships from Zeeland fished the

banks of mussel seed in the Zuiderzee. This met with

protests from the local fishermen, who saw themselves

outnumbered by their southern colleagues.

In 1910, the first steam-powered dredger appeared

from Zeeland; it harvested ten times as much as the

traditional sailing ships (Hoek, 1911). In the following

years, protests increased and the number oflicenses for

steam dredgers was limited. The increasing trend in

mussel consumption culminated during World War I

(1914-18), when navigation at sea was limited and seafood was scarce. Between 1897 and 1930, the total national mussel production was around 40,000 t, with

5,000 t coming from the Zuiderzee. A large share of

these mussels were exported to Germany. In 1918, the

production was 120,000 t of wild-captured and 4,500 t

of cultured mussels (Havinga, 1932).

Motorization steadily increased and, during 1926-

28, 20 steamships landed mussels. By 1932, almost all

the fleet was motorized.

Through time, fishermen from Wieringen also harvested mussels to be sold as fodder to duck farms at the

borders of the Zuiderzee and, as with starfish, mussels

were also used as manure on farmland. Furthermore,

mussel shells still serve as spat collectors in oyster culture, and farmers use them to stabilize marshy soils.

Currently, the only existing wild fishery is that on

seed and half-grown mussels. It is restricted to about 6

weeks in the spring and 2 weeks in the autumn. Between 50,000 and 150,000 t of seed and half-grown

mussels are fished in most years on subtidal and intertidal wild banks by the mussel growers, to be sown on

their culture plots in Zeeland and the Wadden Sea.

Cockles

A small-scale fishery for cockles, Cerastoderma edule, has

existed since the second half of the 19th century. Cockles were fished in knee-deep water (0.1-1 m) with gear

that is still in use: The "beugel" or "klauw," a longstemmed rake with teeth of 5-6 cm and a net bag, about

equal to that described by Von Brandt (1972). The rake

is dragged through the sand by a belt around the waist

of the fisherman, while he holds the stem over his

shoulder and slowly works backward with a to-and-fro

movement. Around 1870, cockles were fished offTexel

and Terschelling, and shipped to England after being

cooked and preserved with salt or vinegar, or both (Van

der Viis, 1975).

Around 1930, cockles worth DFLlO,OOO were landed

per year. Most of the fishery took place between

Harlingen and Terschelling (Ypma, 1962). Production

declined after closure of the Zuiderzee in 1932. The

cockle fishery in the estuaries in Zeeland was smaller

than that in the Wadden Sea. The sandflats in the

Westerschelde were also worked by a number of Belgian fishermen who sailed their catch upstream and

sold it directly in Belgium. Practically the entire Dutch

production was exported fresh to France and Belgium

and, before 1965, as conserves to England. The exported quantities in both areas were small and variable

initially but increased substantially in the 1950's, when

up to 20 ships fished in the Wadden Sea. Some had

adopted the British method to flush the cockles out of

the sand with the aid of the ship propeller.

In the early 1960's, the hydraulic dredge was developed, using a water jet to dislodge the cockles from the

sediment in front of a steel blade that cut about 4 cm

deep and scooped the cockles into the cage of the

dredge. The full cage was hauled aboard and was emptied through a lid at the back. The investments to

develop this system were possible because the ships

could also be deployed successfully in the seed mussel

fishery, and a substantial market for cooked deep-frozen cockles had been developed in Spain. After 1970,

th is type ofdredge was gradually replaced by the presen t

version that, apart from the pressure pipe for the water
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 121

jet, is equipped with a suction pipe connected to the

top of the cage of the dredge, through which the catch

is continuously pumped aboard (Fig. 3). On deck, the

catch passes rotating sieves in which sand, undersized

cockles, and other small by-catch are separated from

the catch and washed overboard. This development,

which started in the Wadden Sea, has considerably

increased the efficiency of the fishery, as the dredges

need no longer to be hauled aboard.

Thanks to a growing demand for deep-frozen cockles

on the Spanish market, the fishery has developed explosively: In 1960,3 ships were fishing for cockles with

suction dredges in the Wadden Sea and 2 in the

Oosterschelde; in 1974, 24 dredgers, mostly adapted

inshore barges, were active. In 1974, the government

started to regulate the fishery, restricting the number

of cockle fishing licenses to 35. In 1981, the cockle fleet

numbered 32 ships, several ofwhich had been designed

especially for this fishery.

The Present Fishery

Currently, there are 36 cockle dredgers licensed to fish

in inshore waters and 7 more to fish in the offshore

area. The 36 licenses are owned by 15 companies.

Since the end of the 1980's until the 1993 season,

almost all ships were equipped with two suction dredges

1 m wide, one at each side. As a reaction to drastic

reductions of the fishing area by the government, the

industry in 1993 voluntarily reduced the fishing capacity ofthe fleet by halving the width ofthe dredges. Most

dredges can operate to a water depth of 10-13 m, but

fishing depths of 20-25 m are possible. As cooking

cockles is cheaper at sea than on land, most dredgers

are equipped with continuous, conveyor-belt cookers.

The cockles are cooked during low tide, when the tidal

flats cannot be fished. Cooking is permitted only in

designated areas where the microbiological water quality is checked regularly by the government and where

piles of empty shells on the bottom cannot pose problems for shrimp beam trawlers.

Before cooking, the cockles are spread out on deck

and immersed in seawater for a few hours to de-sand. A

part ofthe catch is landed fresh and cooked in conserve

factories. There are two specialized cooking ships with

deep-freezing capacity. The cooked cockles are shucked

on vibrating screens; the empty shells are dumped overboard. After the fishing season, they are removed by

commercial shell dredgers and are ground to fabricate

grit used on poultry farms. The cooked meat, about 12-

20% ofthe fresh weight ofthe cockles, is brought to the

processing plants, where it is mainly canned (70%), or

block-frozen or individually quick frozen (IQF) for export. There are 8 processing plants using continuous

pressure cookers. The plants, most of them located in

Figure 3

Hydraulic dredge (1 m wide) for harvesting cockles. It is attached to double

6-IO"-suction and pressure pipes at both sides of the ship. On board, the

catch is separated from the water in a washing mill, through which undersized cockles and bycatch are washed back to sea.
122 NOAA Technical Report NMFS 129 _

Zeeland, are owned by the same fishing companies.

They also process mussels and, during the off-season.

fish and vegetables.

The government has taken a number of restrictive

measures to regulate this rapidly expanding fishery,

such as the maximum number of36 licenses, maximum

of 2 dredges of 1 m width per ship or one dredge of 1.2

m width, a minimum mesh width of 15 mm of the sieves

and the cage of the dredge and, before every fishing

season, decisions on closed areas and periods. Nevertheless, the fishing effort of the fleet has increased

considerably during the last 10 years. This is a result of

a series of technical developments. The ships have become larger, to about 40xl0 m and a draft of only 45-

50 em, enabling them to fish cockle beds high in the

tidal range. But the most important development has

been an increase ofthe engine capacity ofthe ships a.nd

of the dredge pumps. This has permitted an increase in

fishing speed from 2.5 to 4 knots with a proportional

rise in fishing efficiency. The average catch of a cockle

dredger is 130 t (3,575 bushels) offresh cockles (20 t of

meats) per fishing day during the first and most productive weeks of the fishing season.

In typical years, 10-20% of the cockles are captured

in the southern estuaries, 0-20% on the North Sea

coast in the south, and 50-80% in the Wadden Sea.

Vnti11991, the average landed value ofthe cockle meat

was DFL25 million (US$13.37 million) per year. The

annual value of the exported canned and deep-frozen

product was about DFLlOO million (US$53 million).

Cockle landings fluctuate considerably due to yearly

differences in recruitment and mortality. Since 1991,

closure of fishing areas by the government has also

affected landings. Figure 4 shows cockle landings in

fresh weight since 1946. They clearly demonstrate the

increase in fishing effort of the last two decades. The

reduced stocks after 1990 forced the cockle fishing

industry to reduce its effort, so that in 1991 and 1992 a

part of the cockle fleet was not used. To keep the

exports going in 1992, cockles were imported from the

United Kingdom, Ireland, France, and Denmark.

The manual cockle fishery, which had declined in

the 1960's, revived after 1986, when conserve factories

started to pay attractive prices. Fresh cockles are also

exported to Belgium and France. In 1988, 352 licenses

for the manual cockle fishery were issued to professionals and amateurs. In 1989, the maximal number of

licenses was restricted to 90, only for professionals.

Hand-cockling is practiced as a part-time occupation.

The same gear as described above is used. Usually a

1965 1970 1975 1980 1985 1990

Year

o -4-...---rl~m~m~~

1945 1950 1955 1960

E30

-rn0)

.S 20

"'0

c

....J 10

80,-----------------------------,

-rn 70

E

...

0)60

o

_50

o

rn

C40 o

Figure 4

Cockle landings in fresh weight for 1946-92. No data are available for 1968-70 and

1974-75. Note the strong increase after 1960 following development of mechanical

dredging and other technical improvements.
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 123

boat is used to reach the sandflats and to transport the

catch. The landings vary with the size of the cockle

stocks and, until 1993, amounted to between 2 and

10% of the national landings. In contrast with the mechanical cockle fishery, hand-cockling is permitted yearround. A hand-cockIer has about 1.5-2 hours to dig on

a tidal flat per tide. He removes cockles from about 100

m2 and gets about 800 kg (22 bushels), that adds up to a

catch ofroughly 100 t (2,500 bushels)/man/year. In 1991,

1 kg offresh cockles yielded aboutDFLO.80 (US$0.43). By

1993, the price had gone up to DFL2.00 (US$1.14).

The Future

The mollusk industry feels increasingly threatened by

government measures that are aimed at reducing the

impact of the fishery on the environment and wildlife.

The main fishing areas, the Wadden Sea and the

Oosterschelde, have been declared natural reserves.

Fisheries on seed mussels and cockles arouse protests

from nature preservationists, who claim that wild mussel and cockle beds are damaged. In years with small

mussel and cockle stocks, the industry is accused of

depleting food for bivalve-eating birds, such as eider

ducks, Somateria mollissima, and oystercatchers,

Haematopus ostralegus. Substantial sections of the intertidal flats in both areas are closed to the fishery. Additionally, a certain percentage of the wild mussel and

cockle biomass must be reserved for birds. In years with

small stocks, this will bring along serious restrictions

and, in extreme cases, even complete suspension of

these fisheries. The predominantly intertidal cockle

fishery will suffer most from these measures. Fortunately for the mussel industry, 70-80% of the seed

mussels are captured subtidally. The mussel growers,

however, prefer intertidal seed for its hardiness.

Miscellaneous Mollusk Fisheries

Fisheries on periwinkles, Littorina littorea; whelks,

Buccinum undatum; and softshells, Mya arenaria; became

substantial after the general rise in seafood consumption in Europe in the second half of the 19th century.

In 1900, the combined landed value of these species in

the Zuiderzee amounted to DFLlOO,OOO (Hoek, 1901).

Between 1935 and 1950, a small fishery on the common

Atlantic slippersnail, Crepidula fornicata, existed in the

Oosterschelde. In 1941, during the war, this species was

used to make a protein concentrate and later for shell

grit production. This fishery was subsidized to help

oyster growers control this pest.

In 1909, 140 ships from Wieringen fished periwinkles

in the Zuiderzee, that abounded in vast eelgrass, Zostera

marina, fields and on mussel banks around that island.

The total yearly landings from dredging, bag-netting,

and hand-collecting periwinkles were around 2,100 t.

The fishery was so intensive that the size of the animals

declined and regulation was considered. Periwinkles

were exported live to Belgium, France, and England.

This fishery nearly disappeared after the wholesale decline of the eelgrass in the early 1930's.

In Zeeland, where the tidal difference is much larger

than in the Zuiderzee, periwinkles were collected mainly

on tidal flats and dike slopes during low tide. Between

1892 and 1895, 60-98 t of periwinkles were landed per

year. In some instances, plots were leased from the

government for collecting. After 1950, the periwinkle

stocks began to decline, labor costs became too high,

and the fishery eventually disappeared in the 1960's.

Now, all periwinkles are imported, mainly from Ireland, by four firms in Yerseke. They are stocked in

basins (Fig. 5), where they are selected, packed, and

exported mainly to Belgium and France.

The fishery on whelks, which were sold fresh and

cooked, developed to an appreciable scale in the second half of the 19th century. In years when mussel and

oyster fisheries were low, it served as a supplemental

source of income for mussel and oyster growers who

dredged them on their culture plots. Between 1920 and

1935, about 35 sailing ships were dredging whelks in

the Zuiderzee, using traditional mussel and oyster

dredges. They caught between 180 and 500 t per year,

which in 1925 commanded DFLO.16/kg. In 1950,94 t

were landed, worth DFL1.42/kg. After 1950, 30-50 t/

year were landed in the Wadden Sea area. In the 1960's,

the whelk populations declined, and the fishery came

to an end around 1970. At present, whelks are fished on

only a small scale in the North Sea, mostly as a bycatch

of flatfish beam trawlers. Fishing with pots or creels, as

in Great Britain and France, is not practiced in this

country. Since the mid-1980's, whelks are shucked,

deep-frozen, and exported, mainly to Japan. In 1991,

about 200 t of meat were exported. The 1991 landing

price was DFL 1-1.5/kg (US$0.53-0.80) fresh weight.

Softshells were dug commercially with forks and

spades on the tidal flats in Zeeland until about 1952. In

1926 and 1930, respectively, 279 and 50 t (10,200 and

1,800 bushels) of this species were landed in Zeeland,

yielding about DFLO.05/kg. They were consumed mainly

in France. In 1952, the landings were only 1.8 t (66

bushels), fetching DFLO.15/kg. After 1952, the species

was still collected in the Westerschelde by Belgian fishermen who sold their catches directly in Belgium. There

were no fishery records for this species in the Dutch

Wadden Sea. At present, only tiny lots of softshells are

collected incidentally and sold on special request.

When mollusks on the European market are scarce,

even undersized cockles, with meats weighing <1 g,
124 NOAA Technical Report NMFS 129

Figure 5

Storage of flat oysters in tidal basins in Yerseke. These brick basins were

constructed at the end of tr,e 19th century when oyster culture in the

Nelherlands began.

become attractive for the fishing industry. Also, the cut

trough shell, Spisula subtruncata, which occurs in dense

banks off the North Sea coast, is then fished. This

happened on a modest scale in 1989, but in 1992 and

1993, when there was a general scarcity of cockles,

several thousand tons of this species were fished with

cockle dredges, then cooked, shucked. and exported to

Spain and Italy. Also, a small fishery on Spisula solida

now exists. Since about 1990, scallops, Pecten maximus,

have been fished by 3-5 fishermen who had stopped

beam trawling for flatfish because prospects were uncertain. Scallops hardly occur on the Dutch coast, but

they are fished off the Scottish coast and the French

and British coasts of the Channel. Multiple scallop

dredges of the British type are used.

Fishery Regulations _

In 1707, the first governmental measures were taken in

Zeeland to regulate the mussel and oyster fisheries. In

this case, the aim was to reserve the fisheries for the

local fishermen. The first measures on a national scale

to protect oyster stocks were probably taken by the

French occupants at the end of the 18th century.

In 1925, national legislation became more concrete.

Fishing in Zeeland was, in principle, available for all

Dutch citizens. The regional fisheries authority was installed to deal with repeated complaints about

overexploitation of the fish and shellfish populations.

It imposed minimum sizes and closed seasons for most

fishes and shellfishes and regulated the fishing gear.

Mussels had to be captured with the so-called "slagrijf,"

a long-toothed rake. The use of dredges needed special

permission and toothed dredges were forbidden. Mussels <3 years old were protected, oysters had to be larger

than 7.5 inches and could only be fished between 1

October and 31 February. Each fisherman had to pay

for his fishing license and had to paint a registration

number on his ship. Inspectors were employed to enforce the regulations.

At present, molluscan fisheries and cultivation are

regulated by the Fishery Law, which is implemented by

the Ministry of Agriculture, Nature Management, and

Fisheries. Management policy was, until recently, aimed

at stock conservation but, increasingly, nature protection is being taken into account. Fisheries for mussel

seed and cockles are regulated by season and area.

Before each fishing season, the Netherlands Institute

for Fisheries Research (RIVO-DLO) makes stock assessments that form the basis for the regulations. Since

1991, the mussel industry has applied its own quotation

system to distribute the catch among the growers and to

avoid excessive dredging on the seed beds. In 1993, for

the first time, the mussel growers abstained from fishing for seed mussels in autumn to spare the natural

banks.
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 125

Oyster and Mussel Culture

Flat Oyster Culture

Mter 1865, Zeeland oyster stocks and banks became

increasingly overexploited, and the supply of seed oysters from Scotland decreased. A change from a wild

fishery to cultivation seemed the only way to maintain a

fishery. In 1866, a group of well-to-do potential private

investors in oyster culture had made a vain appeal to

the government to rent them oyster banks that they

wanted to convert to culture plots. Mter a visit to a

French governmental oyster culture project in the Bay

of Arcachon, this group invited the director of this

project to come and assess the possibilities for a cultivation project in the Oosterschelde. He judged commercial culture to be an economically feasible activity.

Finally, the government was convinced, and decided

to suspend the fishery and to rent out suitable grounds

in a shallow area east ofYerseke, the Yerseke Bank (Fig.

1B). On 6 May 1870, the first public rental of culture

plots took place. The 260 plots, with a total area of

3,085 ha, were rented for around DFL 7.00/ha/year

(Havinga, 1932). In 1886, the last public fishing grounds

became culture plots.

Local fishermen, who could not afford to rent culture plots, to their dismay saw their fishing grounds

disappear into the hands of wealthy outsiders. In the

decade to follow, many of them became employees in

the oyster growing firms; others managed to rent small

plots where they produced seed oysters from spat, which

they sold to the growers. The new oyster growing firms

invested large sums in buildings, ships, tidal storage

basins, and further equipment. The first motorized ships

appeared in 1885, and motorization was common by

1910. Culture techniques and design of equipment were

largely derived from existing operations in France and

England (Buch, 1886). The new industry boomed, causing explosive economical and demographical development in the small village ofYerseke (Van Ginkel, 1988).

Its population grew from 770 inhabitants in 1849 to

4,469 in 1885.

In 1882, the rent sum for culture plots, which was

established by public bidding, started to rise from DFL7

to DFLl10/ha/year. This was so high that it affected

the profit. Meanwhile, oyster production in Europe

increased. By 1889, the market became saturated and

prices dropped, forcing growers to increase their production. Mter 1885, the growth rate and meat quality of

the oysters in the Oosterschelde began to decline. P. P.

C. Hoek (1902) who, as the governmental adviser in

fishery affairs, was asked to investigate the decline,

blamed overstocking ofthe plots. He estimated that the

annual production after 1895 was around 50 million

oysters. To reduce food competition, he concluded,

the oyster stocks on the plots had to be reduced drastically. In later years, biologists have believed that the

carrying capacity of the production area is sufficient to

sustain an annual maximum production of 25 million

oysters of satisfactory meat quality.

More problems followed in 1902 after contaminated

oysters were consumed in England. It caused an outbreak of typhoid fever, with some people dying. This

created an "oyster scare" in all of Europe, and oyster

consumption collapsed. In 1906, the Dutch government imposed sanitary control measures on mollusks

and the coastal waters and certification, but oyster exports did not recover before 1911. The national production then rose to 20-40 million oysters/year, and

remained about stable until 1962.

In 1926, the introduction of the slipper snail created

a serious problem for the oyster industry in Zeeland.

The numbers of this gastropod, which had been introduced into Great Britain in 1880 with a shipment of

oysters from the United States, increased explosively in

Europe and thrived on oyster beds in the Oosterschelde.

In the colder Wadden Sea, it did not form a stable

population, despite massive introductions with seed oysters from Zeeland in 1930-34. Large numbers of slipper snail spat, settling on the shells sown out for oyster

spat collection in summer, overgrew and killed the

oyster spat. Additionally, the large amount of slipper

snails on the culture plots competed with oysters for

food and depressed their growth and meat quality.

In 1935, measures were taken to combat the slipper

snails. A premium was given for dredging and landing

them. In 1937, the use of shells for spat collecting was

temporarily forbidden, and the oyster growers reverted

to spat collection on limed rooftiles, which made a less

attractive settling substrate for slipper snail larvae. Steady

dredging appeared the most successful way to reduce

slipper snail numbers. Its numbers stabilized after 1950,

and the gastropod is now a nuisance only on a number

of oyster and mussel plots in the Oosterschelde and

Lake Grevelingen after consecutive warm summers. In

the Wadden Sea, slipper snails are rarely encountered.

The extremely cold winter of 1962-63 killed most of

the oyster stock, and ice destroyed the holding facilities

in the Oosterschelde. Recovery ofthese facilities and of

a new oyster stock were postponed, as the government

had decided to dam off the Oosterschelde and convert

it to a freshwater lake to reduce the risk of flooding

(Dijkema, 1988). Most of the about 160 oyster growers

quit the industry and were indemnified by the government. Only 10 larger and more diversified growing

firms, that could afford to do so, remained in business

for the time being. As the stock of parent oysters was

destroyed, they had to import seed oysters from France

and other countries. Originating in the Atlantic Ocean,

these oysters are not hardy enough for the Dutch win-
126 NOAA Technical Report NMFS 129

ter climate. Culture was therefore limited to fattening

between April and December.

0. edulis culture techniques did not change essentially between 1880 and 1962. The most obvious developments occurred in spat collection. Initially, roof tiles

coated with a mixture of lime and fine sand were used.

They were placed in the tidal zone in June and July at

locations with reputed good spatfall. In 1885, as many

as 30 million roof tiles were placed. Mter 1904, cockle

shells, which required far less labor and could be sown

in deep water, were increasingly used as collectors.

Between 1924 and 1930, 40,000-50,000 m3 of cockle

shells were sown each summer.

The hardy and slowly disintegrating cockle shells,

that persisted and accumulated on the oyster beds for

several years, however, appeared to host the survival

stages of the fungus Ostracoblabe implexa that causes the

feared "shell disease." During warm summers, the fungus causes black malformations on the inside of shells

oflive oysters and eventually kills them. For this reason,

and also because enormous amounts of slipper snails

settled on the cockle shells, their use was banned in

1936. Mter 1939, only the use of mussel shells, which

degrade much faster, and limed roof tiles was allowed.

Owing to high labor costs, roof tile use ended after

1963. Since then, only mussel shells have been used.

Spat was removed from the roof tiles by hand, mostly by

women, in April ofthe year following spatfal\. Spat were

then reared on trays in the tidal zone for another season before being relaid on shallow culture plots. Around

1960, oysters were relaid 2-3 times per growth-cycle of

4-5 years. In 1955, there were 152 oyster culture firms.

A more detailed description of oyster culture in the

1950's is given by Korringa (1976a).

In 1976, the government changed its policy and decided to conserve the tidal exchange in the Oosterschelde with a permeable flood barrier (Dijkema, 1988).

As adjacent waters had already been dammed off for

safety reasons or had been reclaimed, mollusk culture

had disappeared there, except in Lake Grevelingen.

For the remaining oyster growers, who all resided in

Yerseke, there was again a perspective that now the

Oosterschelde would remain open. Unfortunately, the

recovery of the flat oyster culture was prevented by

another cold winter in 1978-79 that killed part of the

oyster stock, and by an outbreak of the disease

bonamiasis in 1980 after the protozoan Bonamia ostreae

was introduced from France (Grizel, 1985). The government placed a ban on oyster farming in the

Oosterschelde and forbade direct transport to nearby

Lake Grevelingen, where a population of winter-hardy

native oysters had survived the damming. Thanks to

this measure, the oyster population and with it the 16

existing oyster growers and fishermen, were temporarily spared the consequences of the disease. In 1988,

bonamiasis was finally brought into the lake with infected oysters, after the ban on relaying in the

Oosterschelde had been lifted. Until that moment, the

lake had produced 10-15 million consumption oysters/year, half of which were cultured.

Present Status

Flat oysters are reared on bottom plots in the inland

section of the Oosterschelde (1,700 ha) and in Lake

Grevelingen (380). On special plots, spat are collected

on mussel shells, sown mostly in densities of 30-60 m3/

ha (345-690 bushels/acre). The shells are sown inJuneJuly as soon as water temperatures above 18°C have

prevailed for several days and sufficient numbers of

eyed larvae are counted in the water. Mter settlement,

the mussel shells, with attached spat, are kept on the

plots for 1 year. Then they are dredged up and relayed,

usually to deeper plots with better conditionsfor growth.

Market size is reached in 4-5 years from settlement at a

weight of 70-100 g. Labor and fishing costs are considered too high for the old-fashioned intensive culture

with 2-3 relayings. Also, the cleaning of the bottom of

the plots by dredging to remove shell debris, formerly a

duty to minimize the risk of shell disease, is now often

neglected. At present, only a few million flat oysters are

produced per year in the Grevelingen and the

Oosterschelde. Annual mortality due to bonamiasis varies between 30 and 90%. The sharp decline of flat

oyster production is partly offset by substantial imports

from countries like Ireland, Greece, Turkey, Canada,

and even Chile, which allows exports to continue. Prices

have risen sharply. The oysters, which are mostly small

(60-80 g) because bonamiasis affects oysters of 70 g

and heavier, fetch a wholesale price of DFLO.7-1.0

(US$0.37-0.53) apiece (1993). This high price considerably reduces the sales volume, as many consumers

change to the much cheaper Pacific oyster, Crassostrea

gigas, that costs only DFLO.30 (US$0.16) apiece on the

wholesale market.

Culture and Fishery of the Pacific Oyster

Mter the outbreak of bonamiasis, oyster growers in the

Oosterschelde were forced to change to the culture of

the Pacific oyster. In Yerseke, it is usually called by its

French name, "creuse," which means hollow. This species has been cultivated and fished in the Oosterschelde

on a small scale since the late 1970's. It was deliberately

introduced after imports of the related Portuguese oyster, C. angulata, had been severely reduced owing to an

outbreak of iridiovirus, causing gill disease (Comps,

1983). In 1964, small amounts of 10 mm spat of the
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 127

Kumamato and the Myagi strains, imported from Japan, were stocked on a shallow plot in the Oosterschelde.

The growth rate appeared excellent, and in the following year the weight of the oysters increased from 25 to

100 g. The decision to introduce C. gigas had been

based on the assumption that the summer water temperatures in the area would not be warm enough for

successful recruitment, as had been the case for C. angulata.

The contrary proved true. Probably due to local heating of the seawater in shallow places on the tidal flats at

low tide during sunny weather, spawning and spatfall of

C. gigas can be profuse in the shallow eastern section of

the Oosterschelde, where water temperatures can reach

24°C during warm summers. About 10 years after the

introduction, wild, reef-like Pacific oyster banks developed on sandflats in the intertidal zone and on dike

slopes. Natural recruitment is sufficient to maintain

this population, which is probably the northernmost in

Europe. Wild spat is dredged and seeded on the culture

plots, and there is also a small commercial nursery

using imported spat. Most of the spat, however, is collected on mussel shells, that are usually broken to avoid

floating and are sown in the tidal area. The grow-out

plots lie just below the mean low water mark, but increasingly deeper plots are used.

Each year, about 700-1,500 t (19,250-41,250 bushels) of C. gigas are cultured, fished, and collected by

hand. Most oysters are exported to Belgium and Germany and, thanks to good meat quality, even to France,

which itself produces around 130,000 t of "creuses" per

year. Mter successive warm summers, C. gigas has expanded strongly in the Oosterschelde and is considered a pest by mussel growers, as it settles on the mussels and lowers their market value. To prevent expansion of this species into the Wadden Sea, transfer of

mussels from the Oosterschelde to that area has been

forbidden. Since 1986, C. gigas is also found in the

Westerschelde and, increasingly, in Lake Grevelingen.

The Future

Bonamiasis is now endemic to the entire southern area

and probably will remain flat, causing heavy losses. This

will be almost prohibitive for flat oyster culture and

fisheries as a sole occupation. A production of a few

million oysters per year, from fisheries and cultivation,

as a sideline for diversified shellfish firms, will probably

be the most that is feasible unless research, underway in

the Netherlands and France, is able to develop a strain

of flat oysters resistant to bonamia. Use of genetically

improved seed oysters would also require adoption of

more intensive, suspended culture methods, now applied by only two firms. The industry, however, does not

seem to be much inclined to innovate or to invest in

future development. Import, storage, and subsequent

export of flat oysters are expected to dominate the

Dutch oyster industry. As things stand, 0. edulis will

remain a scarce and expensive product, destined for

the luxury market. Prospects for the Dutch Pacific oyster culture depends largely on the development of demand on the European markets. As its culture in France

appears to have about reached its limits and European

demand is expected to increase further, there will probably be room for some expansion in the future.

History of Mussel Culture

Harvested mussels have been stored and rewatered on

the sea-bottom since the early 18th century, but official

records mention rental of mussel culture plots by the

southern regional fisheries authority since 1827 in the

Westerschelde and since 1865 in the Oosterschelde

(Fokker, 1926). In 1930, the first culture plots were

created in the northern Zuiderzee. Earlier, rentings

had only incidentally taken place, for instance in the

fertile and sheltered southern part of the Zuiderzee off

Enkhuizen. This area was lost to mollusk culture and

fishing, however, after its closure in 1932.

Large-scale development of Dutch mussel culture

was not at first stimulated by market developments.

Mter 1950, a disastrous outbreak of the "mussel parasite" Mytilicola intestinalis occurred following its introduction in 1948 in Zeeland with a shipment of mussel

seed from Germany. This crustacean, living in the intestine of the mussel, developed explosively on culture

plots in the Oosterschelde and caused large losses by

weakening the mussels until they died. Production plummeted from 50,000 t (1.8 million bushels) in 1949 to

just over 10,000 t (367,000 bushels) in 1953. To decrease the infection rate, lowering of the stocking density of mussels on the plots appeared a successful remedy (Korringa, 1957).

To maintain the total production, it was decided to

expand mussel culture to the Wadden Sea. Analogous

to the situation in the Oosterschelde in 1870, this operation required the closure of areas for the wild fishery, affecting about 20 mussel and shrimp fishermen from

Wieringen and Harlingen. Some of them were indemnified by the mussel growers, while others were permitted to

rent culture plots. In 1951, after trials by selected groups

of growers from Yerseke and Bruinisse, a number of culture plots were made off Terschelling and Wieringen. By

1955, 55,000 t of mussels were produced in the Wadden

Sea, and the production stabilized at around 60,000 t/

year (2.2 million bushels) in the 1960's.

New culture plots in the Wadden Sea also became

necessary because a number of growers, mainly from

Bruinisse, had lost plots after the closure of sea arms
128 NOAA Technical Report NMFS 129 _

with dams for flood protection. In 1966, some 19!'J

mussel growers were active, 105 of whom were fulltime.

Of these, 96 were based in Zeeland and about 15 in the

Wadden Sea. By 1991, the total number of growers had

decreased to 79, mainly by disappearance offirms without a ship and of small part-time growers. By 1990, the

number of growers based in the Wadden Sea had decreased to four, and in 1992 only two were left. Mter 1955,

the Mytilicola infection rate and mortality in Zeeland gradually decreased, a result of the lower seeding densities

combined with the development of an equilibrium between host and parasite. Mytilicola is now occasionally

found in low numbers in mussels without causing any

harm.

Mussel seed has been traditionally fished in the

Wadden Sea, as little spatfall takes place in Zeeland.

During 1954-56 and 1990-92, mussel spat recruitment

failed, causing great problems for the industry. The

growers were then forced to buy hand-collected seed

mussels from dikes or to import seed from Germany,

Belgium, and even France. In the past century, mmsel

seed had also been imported repeatedly from Great

Britain in years of bad recruitment (Drinkwaard, 1967).

Short periods without mussel seed can usually be bridged

by stocks on the culture plots, but when these had

become exhausted by storms and bird predation, the

shortage in 1991-93 became urgent for a number of

growers who had no prime material. In spring 1992, a

good recruitment occurred again.

The growth rate and meat yield of mussels in the

Wadden Sea is higher than in the estuaries of Zeeland,

especially on plots in the sea inlets, close to the North

Sea. A drawback of the Wadden Sea as a culture area is

the relative shallowness of most of its plots (1-4 m

below low tide) and thus high vulnerability to wave

action during storms. This allows considerable portions

of the cultured mussels and the wild mussel banks in

the tidal zone to be swept away during westerly storms

in winter. This may happen once in several years, but

sometimes, and especially in the last half decade, also

in successive years. This is reflected by the highly variable mussel production of this area (Fig. 6). For this

reason, the mussel growers prefer to rent a combination of productive but risky plots in the Wadden Sea

and more stable, but less productive plots in the

Oosterschelde. The European demand for mussels

shows a steadily increasing trend and the Dutch mussel

industry has benefitted for more than two decades from

good prices. Figure 7 shows some economical aspects of

the development of mussel culture-sinc€ 1960. The

180 --,---------------------------------,

1965 1970 1975 1980 1985 1990

Year

1960

Total

Wadden

Netherlands

Sea -J Zeeland

c 60

.2..

0 40 ::J

"0

0

.... \ 20 a.. -'\

0

1955

a> 160

c

o..

..... 140

o

120

c

ro

100

o

.. 80

c

Figure 6

Mussel production in the Netherland~.and in the production areas of Zeeland and the

Wadden Sea, 1951-91. Note the difference in the variability of production in the two

areas, a result of different susceptibility to storm mortality.
Dijkema: Molluscan Fisheries and Culture in the Netherlands 129

Year season began

plots in the Wadden Sea cover 6,000 ha, but only 3,700

ha ofthis area have adequate current speed and bottom

condition to allow production. In the Oosterschelde, 345

plots cover 4,000 ha, of which 2,250 are productive.

The average area rented per grower is 125 ha. The size

of the plots is 7-25 ha, their water depth is mostly 3-10

m and ranges to 15 m. Wild seedling mussels of 2-3 cm

or older and half-grown mussels of 3-4 cm length are

dredged in May and September, mainly in the Wadden

Sea. They are then relaid and reach market size within

1.5-3 years, depending on the productivity of the plot

used. On the best plots, a meat yield of 30-35% of the

fresh weight can be reached in August-September. The

meat yield peaks in August-October and reaches 20-

35% in the Wadden Sea and 17-30% in the Oosterschelde.

The plots are rented from the government. The growers pay a total rent sum of DFL4.3 million (US$2.3

million)/year for all plots. Their contribution is proportional to the culture performance of their plots and

to their share in the landings. Five governmental fishery inspectors supervise matters like the demarcation of

plots, the seed mussel fishery, mussel harvest and transport, and determination of the culture value of plots.

The construction of the flood barrier in the

Oosterschelde in 1986 reduced the current velocity

and reduced production on a number of plots. On the

other hand, the current reduction has made large areas

suitable for mussel culture that had been useless before, due to excessive current speeds, i.e., above the

upper limit of 60-80 cm/second at the bottom (Dijkema

and Van Stralen, 1989; Van Stralen and Dijkema, 1994).

Causes of mortality in mussel culture are storm damage, which makes reseeding necessary on plots stripped

of mussels by storms, and predation: 20,000-30,000 t

(730,000-1,100,000 bushels) of mussels are consumed

annually by a wintering population of 100,000-200,000

eider ducks in the Dutch Wadden Sea. Seagulls, Larus

argentatus, and oyster catchers prey on spat and halfgrown mussels on intertidal plots. Predation by shore

crabs, Carcinus meanas, can affect thin-shelled small

mussels, while mortality caused by starfish, Asterias rubens,

can be dramatic, especially on deeper plots close to the

tidal inlets. Like eiders, starfish can strip a culture plot

ofmussels in a couple ofdays, especially when these are

thin-shelled. Eider ducks are protected and can only be

scared away with noise in areas where this is permitted.

Starfish are combatted with special rollers, after which

they are killed with salt, freshwater, or by leaving them

in the ship overnight. Mussel seed fished from intertidal

plots is considered more resistant to predators.

Storm hazards and predation reduce overall culture

efficiency. An average of 1 t of consumption mussels is

harvested from 1 t of seed. It must be taken into account, however, that fished mussel seed contains 40-

60% of tare. Silt, sand, and shell debris are not in-

/

i

'975 1980 1985 1990

.0

.../1{

/,ci

::0

.s

.p'

,l!I•• ri'o-.o'

....

......5

•••..r:i

ill'

•.ci

1970

Engine power (HP)

Labor and profit In million DFL

Price allandmg In CIs/kg

Price Index 1969

1965

·······4····················

....•......0···

o +-~---r-~~-.---,~~~,......~~-.-~-.--,--~~-.---,~

1960

250

150

50

100

300

350

200

400

500

450

Figure 7

Economic and fleet development in the Dutch mussel

growing industry, reflected in the average engine power,

value at landing, the price (in cents/kg auctioned: 1

DFL = 100 cents), and the "Return to Labor" (total of

wages plus net profits) since 1960. The low return to

labor in 1991 is due to high expenses necessary to

purchase mussel seed in Germany. The price index

(1969 = 100%) shows the inflation during this period.

Source of statistics: Netherlands Agricultural Economics Research Institute (LEl-DLO), Division of Fishery

Economics.

Present Status of Mussel Culture

There are now (1993) 77 mussel growing firms. Although 60-70% of the production comes from the

Wadden Sea, all but two growers are native to and

based in Zeeland. Originally, all growers were family

enterprises, but this structure is declining. Increasingly

more firms have their capital spread out over shareholders, and individual companies are taken over by

other growers, mussel processing and trading firms, or

multinational food companies. Currently, 460 culture

increase in prices and returns until 1986 can be ascribed to inflation. Thereafter, the price increased

sharply due to shortages of mussels.
130 NOAA Technical Report NMFS 129

eluded in the statistics, whereas mussel production is

registered without tare. This makes the real efficiency

about twice as high. The low efficiency is partly caused

by increased storm damage and bird predation during

the last decade, in addition to increased fishing power

of the ships. Efficiency can be improved by decreasing

the storm risk. A number of the most exposed plots in

the western Wadden Sea will be moved to more sheltered and deeper areas.

A typical mussel growing firm owns one ship. Only a

small number of larger firms have two ships. The total

mussel fleet consists of 82 "cutters" (Fig. 8). For the

mussel seed fishery, cockle dredgers are also leased.

Two mussel ships are convertible to the cockle fishery.

The size ofships has increased markedly during the last

15 years. A modern cutter measures overall 35-40 m,

has a width of 8-9 m, and draws 50-90 em when empty.

This enables the growers to catch mussels on plots and

wild banks high in the tide zone. A cutter can carry

140-180 t (5,100-6,100 bushels). (The mussel industry

always measures in "mussel tons" of 100 kg, based on

barrels, used in the early days.) The ships have crews of

3, are driven by twin engines of 300-600 hp, and are

equipped with bow-propellers, ship-to-shore telephones,

and computerized positioning, echo-sounding, and .;atellite navigation equipment. The graph in Figure 6

gives an impression ofthe development of engine power

during recent decades.

Mussels are harvested with four steel dredges about

1.9 m wide, operated by a hydraulic or pneumatic 8-

drum winch (Fig. 9). When used on hard and sandy

bottoms, the round steel ground bars of the dredges

are provided with bolted-on 2x2 em steel blades, the socalled "knives." To save labor and time and to decrease

mortality by shell breakage, the system for unloading

the mussels and simultaneously sowing them on the

bottom has developed in the course of years from

manual shoveling (in the 1950's) to conveyor belts with

holes in the sides ofthe ship above the waterline (in the

1970's), and finally to a system by which water is pumped

into the hold and the mussels are washed out through

holes below the waterline. This system requires a double

bottom and sides of the ship (Fig. 10). Under favorable

conditions, a ship can be loaded with mussels within 4

hours and emptied in half an hour. The investment

costs in a new ship are DFL 1.5-2 million (US$0.8-1.07

million). More detailed descriptions of the mussel industry are given by Havinga (1932), Korringa (1976b)

for the 1950's, and Dijkema and Van Stralen (1989) for

more recent years.

After harvest, the mussels are transported to Yerseke

(Fig. 11), where the only mussel auction in the country

(and probably the world) is operated by the Commodity Board for Fish and Fish Products (Fig. 12). The

cargo of each ship is sold to the highest bidder among

about 27 accredited mussel traders, ofwhom all but two

are located in Yerseke. The purchased mussels are relaid

on special rewatering plots rented by the traders. Situated directly south of Yerseke, this shallow, sheltered

area has a firm, stable bottom and good, well-monitored water quality. There are 75 rewater plots of 5 ha.

The mussels remain on the plots for 2 weeks, during

Figure 8

Mussel "cutter" dredging for mussel seed in the western Wadden Sea.
Dijkema: Molluscan Fisheries and Culture in the Netherlands 131

which they excrete ingested sand and mud and recover

from stress caused by dredging and transport. Rewatering increases the shelflife of the mussels, while

dead and broken specimens are eliminated by crabs,

fishes, and seagulls. Additionally, the plots serve as "wet

warehouses" for the traders. Finally, the mussels are

dredged up carefully, in many cases placed directly into

containers on deck, and are sailed to the processing

plants. To allow the mussels to get rid of the last ingested sand, they are kept in the same containers in a

vertical flow of UV-sterilized seawater for 4-7 hours

(Fig. 13). Subsequently, they are de-clumped, rinsed,

de-byssused, in summer chilled to 7-10°C, graded, and

packed. About 70% of the production is sold fresh, and

Figure 9

View of mussel dredges. They are emptied by raising the bar at their end.

Figure 10

A 1980 generation ship used for dredging and transplanting seed mussels.

The mussels are washed out through holes below the waterline.
132 NOAA Technical Report NMFS 129

I ..

Figure 11

A ship with full load of mussels ready for unloading. Most ships have their

wheelhouses aft.

Figure 12

The mussel auction in Yerseke.

the rest is processed. About 10 processors cook, can,

and freeze mussels and cockles, and fabricate a variety

of composed mussel and cockle commodities.

The traders and processors market the mussels themselves. The "mussel office" of the Commodity Board for

Fish and Fish Products and a cooperative producers'

organization of which all growers and traders are members, are responsible for product quality. Quality standards and a minimum price are agreed on before each

season. In 1992, these were comprised of a minimum

size (35% ofthe mussels must have a shell length greater

than 50 mm), a minimum meat yield of 16%, and an

intervention price ofDFLO.27 (US$0.14) /kg. Mussels that

are landed for auctioning and do not meet these stan-
___________________ Dijkema: Molluscan Fisheries and Culture in the Netherlands 133

Figure 13

De-sanding containers for mussels at the plant of a mussel processor in

Yerseke.

dards are not auctioned but fetch the fixed intervention

price, after which they are kept separate on special plots,

to be sold back to the growers at the end of the season.

The starting date of the season, which runs from July

to April, is collectively agreed upon, mainly depending

on market demand. Product promotion, auctioning,

the intervention fund for unsold and substandard mussels, and a fund for research are financed with levies

paid by growers and traders per ton of product landed

or sold. Regulatory tasks, such as supervision of the

purity of the product and the water in the production

areas, and prevention of introductions of toxic algal

species, are delegated by the government to the "Commodity Board," and are eventually controlled by government, which also monitors the national shellfish

waters. The industry and the government both pay for

the monitoring program.

Between 1991 and 1993, the situation in the mussel

industry was dominated by the general lack of mussel

seed and market size mussels, a combined result of

storm mortality, failing recruitment, and predation by

birds. The shortage of mussel seed forced the growers

to import about 40,000 t (1.47 million bushels) of mussel seed and half-grown mussels from Germany in 1991-

92, for prices between DFLO.80 and 1.20 (US$0.43 and

0.64) /kg. Figure 7 shows how this depressed the profits

of growers and how the shortage of market-size mussels

raised prices dramatically. In 1991, the auction price

reached values between DFL1.50 and 3.00 (US$0.80

and 1.60)/kg and, at the start of the 1992-93 season,

even over DFL4.00 (US$2.14)/kg. The average price

was between DFLl.OO and 2.00 (US$0.53 and 1.07)/kg.

Imports of consumption mussels increased and in 1991-

92 amounted to 28,000 t (1.03 million bushels). The

high prices on the European market caused increased

competition by other mussel exporting countries like

Ireland and even Canada and New Zealand. Also, the

attractive prices stimulated about seven growers to begin suspended mussel culture, mostly on longlines, that

is labor-intensive. Spatfall of mussels and cockles occurred again in 1991 and 1992. A high growth rate of

the spat provided reasonable landings again in the

1993-94 season, with prices returning to values between DFLO.8 and 1.5 (US$0.45 and 0.85) /kg.

The Future of Mussel Culture

The mussel and cockle fisheries have grown to a large

scale as a result ofa high degree of mechanization. This

trend, generally in the form of concentration and internalization of the mussel growing, trading, and processing industry, is expected to continue in the coming

years. Also, the cockle industry and oyster industry took

part in this development. Eventually, this will probably

lead to an increase of large, horizontally (all species)

and vertically (from primary production to export of

commodities) integrated molluscan shellfish firms. A

number of specialized family enterprises will, however,

be able to maintain themselves.
134 NOAA Technical Report NMFS 129

As the demand for mussels is steadily rising, mussel

prices will probably increase. For a number of growers,

this will compensate their low productivity. For traders

of fresh mussels and the processing industry, however,

high prices affect their ability to compete with mussels

from other countries on foreign markets. Imports will

remain an important means to keep on supplying the

export markets.

On 1January 1993, sanitary and product quality regulations within the European Community were harmonized, and the economical borders between member

states disappeared. The microbiological purity of all

Dutch mollusk shellfish growing and fishing waters is

monitored more intensively and meets the "A" level,

which means that no purification is necessary. The

equipment of the processing industry is modern and

also up to the new standards. The Dutch molluscan

shellfish industry feels well-prepared for a new era of

free trade and generalized legislation within the European Community.

Literature Cited and Selected Citations

Baster,J.

1762. Natuurkundige uitspanningen, behelzende waarnemingen over eenige zeeplanten en zee-insecten. Haarlem,J.

Bosch, p. 71-81. [In Dutch.]

Buch, S. A.

1886. Oyster culture as seen at the London Fisheries Exhibition. U.S. Comm. Fish Fish., Rep. Comm. 1884, Pt. Xll:913-

923.

Comps, H.

1983. Les infections virales associees aux epizooties des huitres

du genre Crassostrea. [Viral infections, associated with diseases of oysters of the genus Crassostrea.J Rapp. P.V. Int.

Counc. Explor. Sea 182(1983):137-139. [In Fr.]

Dean, B.

1893. Report on European methods of oyster 'culture. Bull.

U.S. Comm. Fish Fish. 1891, XI:381-406.

Dijkema, R.

1988. Shellfish cultivation and fishery before and after a major

flood barrier construction project in the southwestern Netherlands. J. Shellfish. Res. 7(2) :241-2!'i2.

Dijkema, R., and M. R. van Stralen.

1989. Mussel cultivation in the Netherlands. World Aquacult.

20(4):56-62.

Drinkwaard, A. C.

1967. Beschouwing over de Zeeuwse visserij in de geboorteperiode van het Nederlandse visserijonderzoek. [Dissertation on the fisheries in Zeeland during the birth period of

Dutch fisheries research.] Zeeuws Tijdschrift 17 (2): 149-

155. [In Dutch.]

Fokker.

1926. Speech by the president of the Administration of the

Fisheries on the Zeeland Streams on the occasion of its

100th anniversary, 26 ofJanuary 1926. 36 p. [In Dutch.]

Grizel, H.

1985. Etude des recentes epiLOoties de l'huitre plate Us:"ea

edulis L. et de leur impact sur l'ostreiculture Bretonne (Study

of recent diseases of the flat oyster (u. edulis) and their

impact on oyster culture in Brittany). Ph.D. thesis, Univ. Sci.

Techn. Languedoc, Acad. Montpellier.

Groenman-van Waateringe, W., and L. H. van Wijngaarden-Bakker.

1990. Medieval archaeology and environmental research in

the Netherlands. In Besteman et aI., (eds.), Medieval archaeology in the Netherlands, studies presented to H. H.

van Regteren-AJtena, p. 283-297. Van Gorcum, Assen.

Havinga, B.

1932. Austern und muschelkultur. In Handbuch der seefischerei

Nordeuropas Band VII, Heft 5. Stuttgart, 61 p. [In Ger.]

Hoek, P. P. C.

1879. Ueber Austernzucht in den Niederlaenden. Deutsche

Fisschherei Verband. Circ. 2. [Engl. transl. by Herman

Jacobson.]

1901. Rapport over de schelpdierteelt in het Noordelijk deeI

van de Zuiderzee [Report on the molluscan culture in the

northern part of the Zuiderzee.] In Verslag van den staat

der Zeevisserijen over 1910, p. 72-91. [Report on the state

of the sea fisheries.] The Hague. [In Dutch.]

1902. Rapport over de oorzaken van de achteruitgang in

hoedanigheid van de Zeeuwse oester [Report concerning

the decline in quality of the Zeeland oyster.] Ed. Minist.

Waterways, Trade Ind., The Hague. 175 p. [In Dutch.]

1911. Rapport over de schelpdiervisscherij en schelpdierteelt

in de Noordelijke Zuiderzee. Verslag van den Staat der

Nederlandsche Zeevisserijen over 1910. [Report on the mollusk fishery and mollusk culture in the Northern Zuiderzee.

Report on the status of the Dutch sea fisheries in 1910.] The

Hague, 162 p. [In Dutch.]

Korringa, P.

1Y41. De slipper-limpet in Nederland. Econ. Voorlichting No.

50.

1949. Crepidula fornicata as an oyster pest. Int. Coune. Explor.

Sea, Spee. Meet. on Shellfish, 1949.

1957. Epidemiological observations on the mussel parasite

Mytilicola intestinalis Steuer, undertaken from the Netherlands, 1955. Ann. BioI., Copenhagen, 12 p.

1976a. Farming the flat oysters of the genus Ostrea-a

multidisciplinary treatise. Elsevier Sci. Publ., Arnst., 238 p.

1976b. Mussel farming in the Netherlands. In Farming marine

organisms low in the food chain. Elsevier Sci. Pub!., Arnst., 264 p.

Lauwerier, R. C. G. M.

1988. Animals in Roman times in the Dutch eastern river area.

Nederlandse Oudheden 12, Rob Amersfoort, 1 p.

Moebius, K.

1877. Die Auster und die Austernwirthschaft. Berl., p. 1-49.

[In Ger.]

Paludanus, R.

1776. Bericht omtrent het zoeken, korren, bewaren en

verzenden del' zogenaamde Texelsche Oesteren [Report on

searching, dredging, stocking and shipping of the so-called

Texel oysters.] In Oudheid-en natuurkundige verhandelingen, meestal betrekking hebbende tot West Vriesland

of het Noorderkwartier, p. 231-276 [Archaeological and

physical treatises, generally concerning West-Friesland or

the Noorderkwartier.] Van der Eyk en Vijgh, Leyden. [In

Dutch.]

Van der Vlis,J. A.

1975. t'lant van Texsel, een geschledschrijving [The land of

Texel, a historiography.] Langeveld and De Rooy, Den BurgTexel, 528 p. [In Dutch.]

van Ginkel, R.

1988. Limited entry: Panacea or palliative? Oystermen, state

intervention and resource management in a Dutch maritime community. J. Shellfish Res. 7(2) :309-317.

1YY I. Elk vist op zijn tij. A hislOrical-anthropologic study of a
Dijkema: Molluscan Fisheries and Culture in the Netherlands 135

maritime community in Zeeland, Yerseke, 1870-19I4.1SBN

9060ll.716.6, 143 p. [In Dutch.]

van Stralen, M. R., and R. Dijkema.

1994. Mussel culture in a changing environment: the effects of

a coastal engineering project on mussel culture (Mytilus

edulis L.) in the Oosterschelde estuary (S.W. Netherlands).

Hydrobiologia 282/283: 359-379.

von Brandt, A.

1972. Fish catching methods of the world. Fish. ews Books,

Lond., 240 p.

Ypma, Y. N.

1962. Geschiedenis van de Zuiderzeevisserij. [History of the

Zuiderzee fisheries.] Pub!. Found. Population Res. in Reclaimed Zuiderzee Polders, Den Haag, 224 p. [In Dutch.]

Introduction

Marine Molluscan Production Trends in France:

From Fisheries to Aquaculture

PHILIPPE GOULLETQUER

IFREJ'vlER

Aquaculture Research Laboratory

Avenue du General de Gaulle

B.P. 32. Port en Bessin, 14520

France

MAURICE HERAL*

IFREMER

Research Unit Shellfish Culture F:cosystems

Mus de Loup

B.P. 133, La Tremblade, 17390

France

ABSTRACT

The main activity in French shellfishing is culturing. Most culture involves oysters, Crassostrea

gigas, and Ostrea edulis; mussels, Mytilus edulis and M. galloprovincialis; and to a lesser extent

the scallop, Pecten maximus, and the exotic Manila clam, Tapes philippinarum. Wild species

harvested include the whelk, Buccinum undatum; abalone, Haliotis tuberculata; and bivalves,

such as the cockle, Cerastoderma edule; pectin ids, Chlamys varia and Aequipecten opercularis; and

several clams, e.g., Mercenaria mercenaria and Venerupis rhomboides. Recreational landings are

substantial. The flat oyster, O. edulis, has been part of human diets for centuries. Natural

beds were exploited through the Middle Ages until the last century by handpicking at low

tide and by boat dredging. The effort led to overfishing, and between 1853 and 1859, a

repletion program was initiated, mainly based on using wooden spat collectors, which

marked the beginning of French oyster culture. In 1860, a shortage of flat oysters led to the

introduction of C. angulata. Oyster production increased to a record high of 85,000 t of C.

angulata and 28,000 t of 0. edulisin 1960, but diseases hit C. angulata and led to its disappearance.

In 1972, C. gigas was introduced, spread rapidly by natural spatfall, and facilitated a fast industry

recovery. Oyster production now is 150.000 t of C. gigas and 2,000 t of O. edulis a year. Oysters

often are deployed in ponds for fattening before marketing. M. edulisis produced on the Atlantic

coast, while M. galtoprovincialis is mainly produced on the Mediterranean coast. Currently, 1,613

km of bouchots are used to grow mussels, yielding 58,000 t/year; longlines yield 30,000 t; onbottom culture, 2,000--3,000 t, and the public fishery, 20,000 to 30,000 t. The native clams, Tapes

decussatus and T. pullustra have been harvested. T. philippinarum was introduced and hatchery

cultured; production peaked at 500 t, but the clam has colonized natural areas. The common

scallop, P. maximus, and Mediterranean scallop, P. jacobaeus, are harvested by dredging. The

whelk is fished with pots; landings are about 15,000 tjyear. Abalones are harvested by hand at

low tide or by diving. Cockle harvests total about 10,00 t/year. The entire shellfishing industry

employs more than 20,000 permanent people and 30,000 part-time workers. Most shellfish are

marketed fresh in the shell, but some species, e.g., clams and scallops, are marketed frozen.

less than 10 bivalve species are cultured. However, molluscan culture, usually concentrated in highly producThe French consume around 60 species of mollusks,

including bivalves, gastropods, and cephalopods. Most

mollusks are harvested along the coasts ofFrance, while * Present address: IFREMER DRYIRA, URAPe, B.P. 133 La

Tremblade, 17390, France.

137
138 NOAA Technical Report NMFS 129

tive estuaries and bays, represents the most important

economic activity.

Most molluscan culture concerns oysters (including the

introduced Pacific oyster, Crassostrea gigas, and the native

flat oyster, Ostrea edulis); native mussels, Mytilus edulis and

Mytilus galloprovincialis; and, to a lesser extent, the scallop,

Pecten maximus, and the exotic clam, Tapes philippinardm.

In addition, French Polynesia is the focus of a highly

valuable pearl oyster, Pinctada margaritifera, culture.

Mollusks currently are cultivated over 20,000 ha (1

hectare = 0.4 acre): 14,000 ha in estuaries and 6,000 ha

in tidal areas, and distributed among 60,140 leasing

grounds. C. gigas production takes >72% of the total

leased grounds. The entire molluscan industry (including mussel culture) employs at least 20,000 permanent

and 30,000 part-time people.

Regarding the coastal and intertidal fisheries, most

of the species are harvested by boat or at low tide by

local fishermen. Although not evaluated, recreational

shellfish landings are substantial, particularly on the

Atlantic seaside and the English Channel. Species include the squids, Sepia officinalis and Loligo forbesi; gastropods, particularly the waved whelk, Buccinum

undatum, and the abalone, Raliotis tuberculata; and numerous bivalves such the cockle, Cerastoderma edule; the

pectinids, Chlamys varia and Aequipecten opercularis; and

several clam species (e.g., Mercenaria mercenaria and

Venerupis rhomboides).

Habitats

France's 5,500 km coastline is divided among three

frontages: The north and west on the Atlantic ocean

and English Channel totals 3,800 km, and south on the

Mediterranean Sea totals 1,700 km (Fig. 1). About 51 %

44

43

45

46

47

48

49

50'N

6'E

I

Bay ofSomme

Distribution of mean

mussel and oyster

landings (t) in France

(1993)

Thaulagoon

.30,000 /A"~

8,000

NORMANDY

Vendee

Bay

of

Biscay

Bay of Bourgneuf

.20,000

I!I 12,000

'I!J L'Aiguillon Bay Relsland l>;:,

\', Marennes

.35,000 ,'\l Oh~ron

2,500 Bay

Gironde estuary

c:

co

'"

o

o

.~

;:

co

Bay of

Brest

rp15,000

7,500

Figure I

Oyster and mussel culture in France: distribution of the rearing areas with average production (1,000 t) in each area.
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 139

of the coasts are urbanized, 960 km intensively so. Of

the 5,500 km, 800 km are located in highly productive

estuaries, and 580 km are island coastlines.

The coast of France is highly diverse. On the northern and western coast, 30% are rocky shores, 40% are

sandy beaches, and 30% are salt marshes, while on the

southern part, 65% are mostly rocky shores, 25% are

sandy bottoms, and 10% are salt marshes. France's temperate climate is affected by the Gulf Stream, with a

biogeographic barrier around Brittany, which limits

the spread of northern and southern marine species

originating from colder and warmer areas, respectively.

In northern Brittany, sea temperatures vary between 6"

and 10"C in February and 15" and 1TC in summer,

while summer temperatures rise above 20"C on the

Atlantic coast. Salinities range from 5%0 in the oyster

ponds to 20%0 on the coast in winter to 30 to 35%0 on

the coast in summer. Abnormal climatic patterns caused

by such variability may drastically affect shellfish population dynamics, affecting local landings (e.g., scallops).

In contrast, cultured species may be particularly well

adapted to the ecosystem variability, and thus be able to

limit abnormal events like recruitment failure (e.g., C.

gigas spatfall), and result in stabilized production. The

main difference between the northern-western and

southern frontages is the tide effect, which has determined species diversity and distribution and, therefore,

molluscan culture and fishing practices. The English

Channel and Atlantic coast are characterized by two

cycles a day (i.e., 12 h per cycle), while neap tides

alternate with spring tides every week, resulting in highly

favorable trophic conditions for molluscan culture. For

example, a 15.5 m record high tide range was observed

in the Gulf of St. Malo, while averaging 10m during

spring tides. Moreover, the tide varies around 8 m and

4 m on the western part of the northern Brittany and

Atlantic sides, respectively. In contrast, tides are almost

nonexistent on the French Mediterranean seaside,

prompting the farmers to develop subtidal techniques.

The salinity in the Mediterranean Sea is about 35%0.

The Oyster Industry _

History

The flat oyster, 0. edulis, a native of Europe, has been

part of the human diet for many centuries. The Romans built ponds to stock and sort oysters before exporting them to Rome (Grelon, 1978). Oysters were

distributed in shallow bays and estuaries along the

French coast.

Natural beds were extensively exploited through the

Middle Ages until the last century, by handpicking at

low tide or by boat dredging in deeper areas representing a large fishery (e.g., Cancale) (Pichot-Louvet, 1982).

Oyster shell piles, reaching 500,000 m3, equivalent to 5

trillion shells, were observed in the southwest of France

near I'Aiguillon and BourgneufBays. Originating from

the 10th century, they demonstrate the large oyster

fishery activity (Gruet and Prigent, 1986). In the 17th

century, oyster culture was initiated using ponds in salt

marshes on the Atlantic coast. Oyster spat were collected on rocks and separated from each other after

two years, then deployed in oyster ponds for 4-5 more

years. Oyster culture increased with a concurrent

decline in activity in salt marshes (Heral, 1990). In

those early days, oyster spat were obtained only from

fishing.

During the 18th century, fishing effort led to overfishing and destruction of natural beds. In 1750, regulations were enforced to restrict fishing during the breeding season (Heral, 1990). In Arcachon Bay and Brittany, several moratoria were enforced for a number of

years. During the 19th century, landings became irregular in spite of increased regulations. But an increased demand for fattening young oysters and market demands resulted in boosting fishing effort. From

1857 to 1872, fishing effort on Cancale oyster beds

increased by a factor of 13. Moreover, extremely cold

winters and predation pressure affected natural spat

recruitment. Coste (1861) described Cancale and

Arcachon oyster stocks as drastically reduced and those

from the Marennes-Oleron areas as totally exhausted.

Between 1853 and 1859, DeBon and Coste initiated a

repletion and reseeding program based mainly on using wooden spat collectors similar to those used in Italy.

This project marked the beginning of French oyster

culture with the control ofseed supply. In 1865, Michelet

developed the liming tile technique for collecting spat

and the oyster box for growing spat in Arcachon Bay

(Roche, 1897). But the main change facilitating culture

development occurred in 1852, when the French government took over the entire coastal management and

established rules of ground exploitation, therefore facilitating rational exploitation (Roche, 1897).

In 1860, a shortage of 0. edulis seed prompted oyster

farmers to import cupped oysters, Crassotrea angulata,

from Portugal to Arcachon Bay. A natural population

settled in the Gironde estuary when a shipment had to

be jettisoned during a storm in 1868. This species spread

naturally along the Atlantic coast up to Marennes-Oleron

in 1874, Re Island in 1878, then Vendee, and finally to

southern Brittany. In spite ofthis northern limit impeding natural reproduction, oysters were cultured in northern beds (e.g., Cancale) by transplanting seed. Both

species then were cultured simultaneously, particularly

in Arcachon Bay (Hinard and Lambert, 1928).

Around 1910, oyster production was equally divided

between both species (Fig. 2), but then a massive mor-
140 NOAA Technical Report NMFS 129

140

120

0 100 0

o.

:=. 80 co

.2

(j 60 :J

"C

40 Do

20

Year

Figure 2

Historical trends in French oyster production, 1900-93.

tality, perhaps caused by a disease, struck the flat oyster,

favoring an increase in the culture of the cupped oyster. The flat oyster population later recovered, but only

in the southern part of Brittany, with heavy spatfalls in

1925 and 1928. Hinard and Lambert (1928) reported

that C. angulata had replaced 0.. edulis on the spat

collectors in Arcachon Bay.

Spat collecting techniques, meanwhile, became systematic in the southwest of France, using oyster shell

strings and slates as well as chestnut and hazel stakes.

On the Mediterranean coast, off-bottom culture was

initiated around 1900 using 0. edulis cemented onto

steel ropes. Growout facilities were developed in shallow waters (3-4 m) at Seyne and Marseille. Oyster spat

came from the Thau Lagoon, but in 1932 this practice

was limited to one leasing ground in the lagoon. Oyster

production then increased substantially by using spat

imported from Brittany. Spat were cemented individually onto poles which were then hung from frameworks

deployed over mussel leasing grounds. This species was

cultured until 1950-51 , when stocks were depleted and

replaced by C. angulata.

On the Atlantic coast and the English Channel, oyster

production increased consistently to a record high of

85,000 metric tonsl (t) of C angulataand 28,000 tof 0. eduli.s,

in 1960. Concomitant to the production increase, rearing

areas were concentrated in highly favorable sites, usually

semiclosed bays protected from storms (e.g., MarennesOleron and Arcachon Bays). This resulted in higher stocking densities but poorer growth and increased mortality

rates (Heral, 1990; Heral and Deslous-Paoli, 1991). From

1966 to 1969, gill and viral diseases spread over several

major rearing areas, leading to massive mortalities between

1970 and 1973, and the final disappearance of C. angulata.

I At 32 U.S. standard bushels in 1 metric ton.

Seed and adults of the Pacific oyster, Crassostrea gigas,

were introduced in 1972 to reverse the ailing production and revitalize the oyster industry (Grizel and Heral,

1991). Imports ofseed were to sustain farmers' production; imports of adults were to restore natural broodstock

beds in several areas along the southwestern Atlantic

coast. The introduction was so successful that natural

spatfall in the following years in Arcachon and

Marennes-Oleron Bays facilitated a fast industry recovery. Then, two diseases, Marteilia refringens and Bonamia

ostreae, spread in the late 1970's and drastically reduced

production of O. edulis in almost all rearing areas. Despite

new management practices and an intensive repletion

program, O. edulis production has remained low.

Current Status

The annual production of oysters currently supplies

the French market and reaches 150,000 t of C. gigas and

2,000 t of 0. edulis (whole weight), with an exchange

value ofFl,500 million ($254.3 million) and F120 million ($20.34 million), respectively (Fig. 1, 2). Oyster

production represents more than 25% of the entire

French marine seafood production.

Oyster Culture

Several methods are used to produce oysters, depending

on the area. From a biological point of view, C. gigas'

natural distribution is more restricted than that of C.

angulata. Natural spatfall occurs regularly on the southwest Atlantic coast, mainly in the Gironde estuary and

Arcachon and Marennes-Oleron Bays, affecting the traditional oyster farming practices. Similarly to C. angulata,

seed transplanting from those bays to Mediterranean oyster culture areas (e.g., Thau Lagoon) and to Brittany and

Normandy is done on a large scale. Oyster farmers benefit

from dividing their production among several regions.

The seed supply is based mainly on natural spatfall,

using artificial spat collectors. The spat supply is reliable and regular. C. gigas larvae do not require a specific substrate (assuming it is clean, without fouling and

silt) many types of spat collectors are used (Fig. 3, 4).

Limed tiles usually are employed in Arcachon Bay and

are of particular interest for early spat removal. Plastic

PVC tubes with roughened surfaces recently became

the favorite, because their weight reduces field labor

while maximizing the spat collecting area; automatic

equipment facilitates the removal of spat.

Farmers currently are progressively and systematically shifting their spat production from using old spat

collectors to PVC tubes. The tubes are immersed in

seawater for several weeks, and then sun dried before
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 141

Figure 3

Several types of oyster spat collectors in use and the

rack culture in France (from Berthome et a!., 1984).

Hatcheries recently have begun to produce cultchless

spat and larvae for remote setting techniques. The latter is of particular interest to oyster farmers located far

from natural spatfall areas (e.g., Normandy). The choice

of spat collector for O. edulis settlement is more specific, and usually is tiles coated with lime and sand. The

lime composition varies among breeding areas (Marteil,

1976). Spat are removed after 6-10 months. More recently, use of tubular nets filled with mussel shell and

deployed off-bottom has been proven more cost-effective than tiles in southern Brittany (Grizel et a!., 1979).

Several techniques are used for the pregrowing and

growing stages, depending on peculiarities of each rearing area. The duration of each stage depends on local

stocking densities and ecosystem carrying capacity. Oysters are produced using on-bottom and off-bottom techniques, as well as in subtidal or intertidal leasing grounds.

On-bottom culture, intertidally or in deep water, is

carried out by first hardening the bottom and then

sowing seed directly with or without their spat collectors. In intertidal areas, a plastic fence defines the rearing area and effectively reduces green crab, Carcinus

maenas, predation. Following 1-2 years of pregrowing,

spat are scraped from the cultch, sorted by weight, and

t)1e!"1 put back on the bottoms for further growth.

The mean density for C. gigas is 5 and 7 kg/m2 during

the pregrowing and growing stages, respectively (Bacher,

1984). Marteil (1976) reported 0. edulisdensities ranging from 0.5 kg/m2 the first year, 1 kg/m2 the second

year, and 3-5 kg/m2 the third and four years.

On-bottom culture requires oyster farmers to harrow

or fork the oyster beds to limit siltation. One ton of C.

gigas and 0. edulis spat yields 20 t and 12-15 t (whole

weight) of marketable oysters, respectively. In subtidal

areas in southern Brittany, the density of 0. edulis has

been reduced from 0.5 to 0.1 kg/m2 to maximize the

growth rate since bonamia disease drastically reduces the

survival rate of the 3- to 4-year-old oysters. Disease effects

also prompted several oyster farmers to switch to C. gigas

culture in subtidal and intertidal rearing areas. Subtidal

culture is considered as more cost-effective than intertidal

culture, but requires higher investment. The availability

of grounds, however, has not as yet been assessed.

Rack culture on iron tables currently is the most

common technique used in intertidal areas on the Atlantic coast and English Channel (Fig. 3). Spat collectors or oyster bags are attached to tables 3 m long and

located at 0.5 m off-bottom. From 50 to 100 collectors/

m is the usual initial density; it is decreased to 8-10/m a

year later. Mter removal from the collectors, the seed is

sorted and deployed in bags that are 1 m long and 0.5

m wide and whose mesh size depends on the oyster size.

Although more efficient than on-bottom culture, this

method can lead to overcrowding of oysters in bags and

siltation underneath the tables by biodeposition. It there-

"- : -: ~. ~- .. -~:

Pole measurement in em: 70x10x2

Number 01 poles by meter 01 inslallation: 20

Actual capting surtace: 3.44 m'/m

Average number 01 shells by spear: 60

Maximum number ot spears by meter ot installation: 90

Maximum capting surtace: 60 m'/m

Real capling surtace: 42 m'/m

Number of tubes per packels: 7

Maximum number of packets by meter 01 installation: 50

Maximum capting surtace: 31 m'/m

Real capting surtace: 21.7 m'/m

MAIN CHARACTERISTICS

MAIN CHARACTERISTICS

MAIN CHARACTERISTICS

MAIN CHARACTERISTICS

Average number of slate by spear: 12

Maximum number of spears by meter of installation: 50

Maximum capting surface: 22 m2/m

Real capling surtace: 15.4 m'/m

MAIN CHARACTERISTICS

Average number 01 shells by spear: 12

Maximum number of spears by meter of installation: 100

Maximum captiog surface: 30 m2/m

Real capting surtace: 21 m'/m

Measures of the pockets: l00x50

Number ot oyster shells by pockets: about 650

Maximum number ot pockets by meter 01 installation: 10

Maximum captiog surface: 55 m2/m

Notice: these are never used alone; one single layer is

laid upon other types 01 collectors

MAIN CHARACTERISTICS

On the leh, seen trom the bohom. On the right,

seen in the oblique. The installations are built with

wood poles joined together w~h iron tubes or w~h

iron tables 3 meters long. The height above the

sediment varies between 0.5 and 1 m.

Oyster

shells

spear

111111 /I /I

LA SEUORE

111111"110

Slate pole

n~

~l~'Ei?i!fj Oyster-shell

net pockets

Slate spear

~~ Scallop ~<!- shells Tf spear

1ft

ft Plastic tubes

field deployment, to release any potential hazardous

chemicals. Monitoring larval abundance and environmental conditions are the key factors in deploying the

spat collectors and maximizing spat recruitment in the

two main bays, i.e., Marennes-Oleron and Arcachon.

Each year, nearly 5 trillion spat settle in Arcachon Bay

on 20 million spat collectors, and 10 trillion spat settle

in Marennes Oleron Bay (Berthome et aI., 1984). This

technique still is the major one for supplying a reliable

and regular seed supply in France and is responsible for

the oyster production success.
142 NOAA Technical Report NMFS 129 _

Figure 4

Detail of iron pipe spat collector covered with 8-month-old oysters, Crassostrea gigas.

fore requires stricter managemen t regulations. Oyster bags

weigh around 5 kg initially and 15-20 kg when the oysters

reach commercial size (Bacher, 1984). Rows of tables, 30-

100 m long, are placed parallel to each other, depending

on the tidal current pattern and direction (Fig. 5).

At the end of the rearing cycle on the Atlantic coast,

oysters are often deployed in oyster ponds for fattening

(Fig. 6). Old salt marshes were converted specifically to

ponds for oyster culture. Oysters are deployed at low

density (<10/m2) in the shallow (0.4 m) earthen ponds

which are filled by gravity with seawater at high tide.

During 10 days of neap tide, no water exchange occcrs,

and the phytoplankton blooms since the turbidity is low

and the nutrient load is high.

The phytoplanktonic species, Haslea (Navicula)

ostrearia, is of particular interest. Following this species'

bloom, its green pigment diffusing in the water is absorbed by oyster gills. This process leads to green colored oysters which are particularly tasty and expensive

in the market. Two brands are defined, "fines de claires"

for oysters spending a month in the oyster ponds at a

density of 201m2, and "speciales de claire," for oysters

fattened 2 months at a stocking density of 10/m~.

Farmers in Marennes-Oleron Bay have developed a

special quality brand called "Label Rouge," which has

stricter definitions than the previous ones and is based

on a 17 June 1983 State Decree (Ministry of Agriculture). This brand requires the fulfillment of high standards for oysters (e.g., shape, >9% meat condition index, salinity >20ppt, color, size), rearing conditions

(such as a 201m2 density), at least a month in oyster

ponds for fattening, tasting standards, as well as packaging and conditioning (e.g., storage temperature). The

oysters should be consumed within 10 days after being

packaged. This brand is a consumer guarantee for a

top-rated quality product. About 25% of the French

production is marketed as "fines de claires," while the

"speciales de claires" and "label rouge" (red label) oysters together constitute <10% of the yearly production.

In the Mediterranean lagoons, where the tidal range

is less than 1 m and the depth around 10 m, permanent

growout facilities are deployed from the sea surface.

The structures are 50 m long and 10-12 m wide and

support about 1,000 suspensions (Hamon and Tournier,

1981). Spat collectors covered by spat coming from the

Atlantic coast are hung directly under the structures;

the oysters are marketed 12-18 mon ths later. Some of

the oysters are cemented individually on wooden poles

and hung for one additional year to yield large fat

oysters aimed at a special market (Raimbault, 1984).

The average yield is 5-7 t of oysters per structure.

The Public Fishery

Fishermen harvest oysters on natural beds on the Atlantic coast every year. The beds resulted from the building of oyster bars for broodstock in the 1970's. A quota,
___ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 143

Figure 5

Harvesting oysters, Crassostrea gigas, grown in bags off-botlom on iron tables.

based on a yearly stock assessment, is given to authorized licensees for harvesting oysters in bacteriologically polluted areas. Landings have to be declared to

the Administration, and the oysters are grown in certified areas for at least 6 months before marketing. In

unpolluted areas, the public fishery is totally open during a specified harvesting season. This public fishery

aims to keep a sustainable wild broodstock similar to a

reserve system and to limit oyster proliferation that may

interfere with culture. However, the "natural" spatfall

relies mostly on the large cultured stock (e.g., >120,000 t

in Marennes-Oleron Bay on 3,200 leased hectares) rather

than on the wild stock (e.g., 22,000 t) (Prou et a!., 1994).

Regarding 0. edulis, a moratorium was enforced early

in the century on dredging the natural beds of Cancale

and the western coast of Normandy that once yielded

10,000-15,000 t yearly. Although a slight rebound occurred in 1970 with 1,600 t, landings have declined

steadily to the present time with 10-20 t during the

harvesting season in November 1993.

Harvesting Methods

In intertidal areas, harvesting usually is carried out

manually. Oysters from bottom culture are harvested

using oyster forks, stored in baskets, and then loaded

onto flat boats. Around 1.5 t is harvested by each farmer

during one low tide. New vehicles are being tested for

culturing and harvesting oysters on hard bottoms (Fig.

7). Although not mechanized, harvesting oyster bags is

an easier task and yields twice as much weight as before

(i.e., 200 bags during one low-tide period) (Fig. 5).

Experiments currently are in progress to mechanize

this process. In the Normandy area, tractors currently

are in use instead of flatboats to work on oyster fields,

since the tidal range is>10m, the intertidal area is large

(e.g., several km), and the bottom is hard. In subtidal

areas, dredging boats commonly are used; each harvests about 15 t/day (Marteil, 1976).

Processing and Marketing

Once harvested, oysters are brought to a processing

plant where they are washed with automatic equipment

and sorted by weight manually or mechanically (Fig. 8).

Electronic computerized equipment recently has been

developed to sort at least 8.5 t/day in up to 8 oysterweight sizes. Oysters then are packed and marketed.

In France, oysters are sold on the fresh market without shucking, therefore explaining cultural and marketing practices. Oysters usually are eaten raw but a

small market involving restaurants requires large oysters for cooking and stuffing. Half of the production is

marketed for Christmas and for New Year's Eve, requiring a well organized marketing system. Oyster farmers

sell about 20% of their production directly to local
144 NOAA Technical Report NMFS 129

Figure 6

Aerial view of oyster ponds or c1aires.

markets (SECODIP, 1983) (Fig. 9). Supermarkets have

been increasing their market share, which currently is

estimated at about 30%. Few oysters are imported or

exported since the French supply and demand is balanced. Prices average FlO or $1.69/kg, but they fluctuate widely and depend on product quality and stock

availabi-lity. Extensive trade occurs between the various

rearing areas; they are characterized by a large variation in operating costs.

The Mother of Pearl and

Pearl Oyster Industries

History

During the 19th and early 20th centuries, the blacklipped pearl oyster, Pinctada margaritifera (L.) val'.

cumingui, was harvested for mother of pearl shell and

used for button manufacture as well as the fancy goods

industry (Intes, 1982; Coeroli, 1985). This species is

distributed among five archipelagos in French Polynesia

including Tuamotu and Gambier. This fishery began in

1802 at Gambier archipelagos and reached a yearly

production of about 500 t from 1889 to 1940. Fishermen dove to depths of 20-30 m and tore away pearl

oysters from coral pinnacles.

The first regulations to protect the resource, enacted

in 1904, sought to limit fishing effort. Lagoons were

spatially divided into three parts and opened for fishing

one after another. Despite the regulations, a record

high production was reached in 1919 with 1,000 t and

later 1,924 t in 1928. From 1940 to 1960, the average

yearly landings declined to 700 t, demonstrating the

fishery decline despite additional 1954 regulations limiting fishing effort (i.e., quotas and broodstock sanctuaries). Since then, consistent overfishing led to shrinking landings and a 50 t record low. For example, the

landings in the Takapoto Lagoon declined from 400 t

to less than lOt in 1984.

From 1962 to 1964, pearl culture was successfully

tested, with 1,095 black pearls being produced. Since

1972, pearl oysters have been harvested mainly to supply the pearl culture industry.
___ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 145

Figure 7

Recent shellfish culture equipment. Top figure shows oyster (on-bottom) harvesting

machine. Bottom figure shows this machine geared with a trailer which can float or be

used on soft bottom (slipping movement) and on hard bottom (wheels) (from Priour,

1986).

The first trials of mother of pearl culture were made

in 1875; spat were collected in the Tuamotu and Gambier archipelagos (Coeroli, 1985). Unfortunately, the

most common species collected, Pinctada maculata, had

limited commercial value. The spat collecting method,

technically under control by 1976, resulted in boosting

pearl oyster culture; it was carried out by family businesses and cooperatives. About 80% ofspat currently is

obtained by using spat collectors, while the remainder

is from collections on natural beds. Pearl culture is one

of the most important industries in French Polynesia

(Coeroli, 1985, Coeroli et aI., 1984, Buestel et aI., 1993).

As early as 1976, the American Institute of Gemology

(GIA) officially recognized the Tahiti pearl as "Cultured pearl of natural color." Later on, the In temational Confederation ofJewelery (ClBJHO) recognized

the label of "Pearl from Tahiti."
146 NOAA Technical Report NMFS 129

Figure 8

Sorting equipment for grading oysters by weight. The

equipment consists of a rotating turret with calibrated

coun terweigh ts.

Current Status

Pearl culture currently ranks third behind oyster and

mussel culture in commercial value. In 1976, the first

black pearl exports weighed 6 kg, worth $82,000. In

1983, production reached 139 kg, worth $4,182,000

(Coeroli, 1985). Since 1980, exports of black pearls

have increased by a factor of 40, and 600,000 black

pearls were exported in 1992, yielding F234 million

($39.66 million) (BuesteI2).

Culture

Pearl oyster culture is based on a 4-year rearing cyde

including spat gathering (12 months), rearing O~

2 D. Buestel, IFREMER, Tahiti Center, Vairao, French Polynesia,

19~3. Personal commun.

months), and then grafting and harvesting (18 months).

Spatial management of cultured areas is similar to that

currently used in culturing oysters on leased grounds in

the mainland of France. Spat collectors are hung

3-10 m deep from anchored buoys. They are deployed

regularly throughout the year since settlement may

occur year-round. However, two settlement peaks occur: from July to August and from October to December (Coeroli, 1985; Buestel et aI., 1993). Polyethylene

strips and branches of trees commonly are used as spat

collectors.

One year after settlement, the oysters, 6-10 em long,

are removed from the spat collectors. Each collector

yields up to 50 spat. In 1985, Takapoto Island alone

produced 500,000 spat in 1985. Oysters then are heel

pierced, attached to strings at a density of 10 oysters per

unit, and then deployed on subsurface long-lines at a

7-10 m depth range. The growout facilities are protected from fish predators (Tetrodon sp. and Balistoides

sp.) with wire netting. Every 3 months, fouling organisms are removed from the oysters. Once they attain

adult size, II em long, the oysters are grafted by introducing into their gonads a piece ofyoung oyster mantle

(2x2 mm size) and a nucleus (6-8 mm) originating

from the freshwater bivalve, Pleurobema cordatum. Commercial pearls are obtained in 15% of the grafted oysters 18 months later. But top-rated pearls usually are

limited in number. Oysters used to be sacrificed when

pearls were removed, but now a second grafting is being tested.

Marketing

Since the pearl culture industry began recently in French

Polynesia, marketing of the pearls is only partly organized. Market instability has resulted from the boosting

of supply and the limited professional structure in the

face ofwell organized traders.Japanese companies control 85% of the market.

The Mussel Industry _

History

Mussel production in France involves two common species, i.e., My.tilus fdulis, which is widely distributed along

the English Channel to the southwest coast of France,

and Mytilus galloprnvincialis, which is distributed mainly

on Mediterranean shores. Genetic crosses of the two

species are also present in several locations along the

French coast (Coustau, 1991). This wide distribution

has favored extensive fishing activity through the centuries, until the 19th century. However, as early as 1681, a
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 147

Figure 9

Direct marketing of oysters by farmers at a small market.

royal decree was enacted to control the public mussel

fishery in the Cancale area. At that time, several natural

beds were already described as overfished, well before

the oyster beds were overharvested (Pichot-Louvet,

1982).

Several natural beds along the French coast were

reported as exhausted in 1933, but fishing effort was

still high in the remaining productive areas (Lambert,

1933). Explanations for the decline included overfishing, dredging effects, recruitment variability, and destruction of the juveniles during fishing. Mussel populations meanwhile colonized ancient overfished oyster

beds in several places, particularly around Noirmoutier

which became an intensively fished area.

Mussel culture methods were developed as early as

the 13th century, but only in L'Aiguillon Bay in southwestern France (Dardignac-Corbeil, 1979). A historical

sketch describes the development of the wooden pole

or "bouchot" culture by a shipwrecked sailor in 1235.

\iVhile using nets to catch birds in the intertidal area of

the Bay ofL'Aiguillon, he noted that mussels settled on

the poles and yielded a better product than did wild

mussels. He then started mussel culture using wooden

poles sunk in muddy bottoms. The wooden poles were

deployed into two merging lines, 200-300 m long, with

a 45° V shape. The poles were linked to each other with

boughs. The resulting growout facility was also used as a

local finfish (pound) net. A net was deployed at the V

head to catch finfish at ebb tide. However, space was

not rationally used by this technique, which also maximized siltation.

Following an 1852 State Decree regarding government management, laws were enacted in 1853 and 1859

forbidding the V-shaped bouchol. After that, the two

lines of poles were set parallel to each other and deployed perpendicularly to the coast. This technique

spread widely along the French coast during the late

1800's. In 1855, L'Aiguillon Bay was still the only area

using the "bouchot" technique (Coste, 1861), but the

rearing area extended quickly northward with concomitant production increases and later (1860) to the La

Rochelle and Marennes-Oleron areas. More recently,

the rearing areas were extended to northern Brittany

(1954) and the western coast of Normandy (1965). At

the turn of the century, bottom culture was developed

where bouchot culture failed, for example in Le Croisic

and Isigny (Lambert, 1934).

Current Status

Currently, 1,613 km of bouchots are distributed along

the French coast. They yield 58,000 t

3 a year (Fig. 1,

10). Bottom culture is located mainly in the Bay of

Brest, and annual harvests run from 2,000 to 3,000 t

(FlOM, 1982). Harvests from longline culture were

30,000 tin 1993 (CNC, 1993). Annual landings from

the public fishery show a large variability resulting from
148 NOAA Technical Report NMFS 129

Figure 10

Historical trends of French mussel production (1,000

t). including culture and wild fishery. 1900-90.

irregular spat recruitment and usually range between

20,000 and 30,000 t. The main natural beds are located

in Normandy and yielded 25,000 ton 1,000 ha in 1980

and a record high of 50,000 t in 1993. The overall

production represents an exchange value reaching F650

million ($110.2 million).

1970 1980 1990 2000

Year

1910 1920 1930 1940

90

80

70

-

0

0 60 q

:=. 50 l:

:8 40 0

::J

'C 30 0

...

Q. 20

10

Mussel Culture

Bouchot Culture-The bouchot culture technique has

not changed drastically since its origin. Each pole is 4-7

m long, 15-25 em diameter, and protrudes 2-3 m above

the bed. Several wood types currently are used including pine, oak, and more recently, squared Brazili.ln

hardwood. The bouchot structure depends on the rearing area. In southwest France, the structures are 50-60

m long with 120-129 poles in single or double lines for

spatsettlement and 80-90 poles for growing (DardignacCorbeil, 1990). Bouchots should also be spaced at least

25 m apart. In northern Brittany, bouchots are 100 m

long, with 130-180 poles, and in Normandy they have

<200-250 poles. Bouchots are deployed during the first

trimester, and those for spat gathering, 3 mon ths before settlement.

In the spring (May-June), spat settlement occurs

intensively in several locations in southwestern France.

The spat are sold to mussel farmers in the remaining

rearing areas where this activity is not cost-effective

(e.g., northern Brittany and Normandy). Spat are gathered by using wooden poles set in the deepest areas or

horizontal coconut fiber ropes strung on the polesjust

before settlement (Fig. 11). The structures remain in

place untilJuly. Seed from the poles then is transferred

Figure 11

Spat-collecting ropes (coconut fibers) covered with blue

mussel, Mytilus edulis, seed.

to tubular nets that are reattached around the growing

poles (Fig. 12). Mesh size depends on mussel size. The

mesh tubes (3-5 m long) are placed around the poles

and nailed at each end. Through August, the mussel

seed spread and eventually cover the entire pole. Each

pole produces between 25 and 60 kg live weight of

mussels per rearing cycle (Boromthanarat and DeslousPaoli, 1988; Cerla, 1993).

On Bottom-On-bottom culturing is based on transferring mussels from natural beds with high densities to

culture plots where the density is reduced to improve

growth and fattening, and to control predation. On-bottom culture is located mostlv in the Boulogne area, Bay of

Brest, and southern Brittany. One-year-Dld mussels usually

are dredged in the Bay of Bourgneuf (Noirmoutier) and

the Loire estuary, then taken to the culture plots where

they are deployed at densities ranging from 25 to 30 t/ha.

This process is carried out in spring and early summer.

The rearing cycle lasts 14-24 months.
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 149

The Public Fishery

Figure 12

"Bouchot" mussel culture: Deployment of socks filled

with blue mussel, Mytilus edulis, seed on wooden poles.

Longline Culture and Suspended Culture-In the Thau

lagoon, off-bottom culture is based on fixed suspended

structures similar to those used for oyster culture. Mussel reproduction occurs almost year-round, but is most

intense during fall and winter. Seed is transplanted in

plastic mesh tubes and hung vertically from fixed tables.

On the Atlantic coast, a reduced availability of intertidal areas for developing mussel culture led to the

development of longline methods. The first trials were

conducted in Pertuis Breton using raft techniques during the 1960's (Dardignac-Corbeil, 1990). New subsurface longlines recently have been developed to resist

storm and wave effects along the Atlantic coast and

offshore along the Mediterranean seaside (i.e.,

Languedoc Roussillon region) (Barnabe, 1990) (Fig.

13). Several longlines are particularly adapted to areas

showing high tidal cycles on the Atlantic coast. Floats

are connected together by horizontal lines that support

a large number of vertical ropes where mussels are

grown. Production rates reach 18-20 t/ha/year.

In the Normandy area, around 100 fishermen working

on 40 boats are licensed in the public fishery, while in

the Bay of Bourgneuf, around 20 fishermen are so

licensed. Boat sizes run between 12 and 16 m. The

fishermen also harvest scallops, lobsters, and coastal

finfish. The decline of the finfisheries prompted additional entries and increased effort in the mussel fishery.

In the early days (19th century), natural beds were

harvested once every 3 years (Lambert, 1933), but now

fishing is done every year and all year long except

February, when the quality of mussel meat is reduced

by spawning. (Earlier, fishing was allowed only from

June to the following February.) A fishing quota now

allows 500 kg of mussels/day/fisherman. No fishing

activity is authorized during weekends, holidays, or

nights.

Harvesting Methods

Harvesting begins as soon as the mussels reach the 40

mm marketable length after a 12-15 month rearing

period. A 60-80 mm length is most common. Several

techniques are used depending on areas and cultural

practices. Mussels grown on wooden poles (bouchots)

are harvested by hand or more often by using hydraulic

fishing equipment that removes all the mussels at once

(Fig. 14). A cylinder is lowered to the bottom of the

pole, closed, pulled up, and the mussels are dumped

onto a trailer or into containers on boats. Amphibious

vehicles currently are used in intertidal areas to maximize

working time. Hydraulic forks are also used for unloading.

Mussels are harvested from on-bottom culture plots

and public beds by dredging with boats of 7-16 m

length and engines of 40-300 hp. In unpolluted areas,

mussels are dredged, cleaned, and sorted by size directly on the decks of the boats. Legal-sized mussels are

packed in 25 kg bags. Undersized mussels are thrown

back on the beds. In contrast, harvesting with longlines

requires especially designed vessels that are 10-15 m

long and are equipped with heavy lifting gear.

Processing and Marketing

In processing plants, automatic equipment facilitates

washing, declumping, debyssing, and grading. Marketable mussels are packed in 15-25 kg bags and sold for

the fresh market. Undersized mussels are transferred to

mesh tubes that are reattached in the field around the

growing poles.

Marketing is based on species peculiarities. Since M.

edulis spawn in spring, their condition index and the
150 NOAA Technical Report NMFS 129

Figure 13

Various types of long-line techniques: surface, subsurface, boltom lines, surface,

subsurface tubes, and ballast tank with suspended ropes (from Muller et a\., 191:!7,

IFREMER/DITI, cited in Heral and Deslous-Paoli, 1991).

meat quality are low between March and May, facilit:Hing the marketing of M. galloprovincialis. The commercial season for mussels harvested on the Atlantic coast

and along the English Channel lasts from June to November-December. Mediterranean production is commercialized all year since no major seasonal spawning

event occurs. Imports, mostly from Holland, fulfill the

French demand from September to March-April of the

following year. Prices for the "bouchot" mussels average F7-8 ($1.19-1.36)/kg, but fluctuate widely and

depend on product quality and stock availability. In

contrast, the ex-vessel value for mussels harvested on

IJublic beds peaks at F2-3 ($O.34-0.51)/kg and depends exclusively on stock availability.

The Clam Industry _

History

The native clams Tapes decussalus and, to a lesser extent, Tapes pullaslra have been fished extensively along
___ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 151

Figure 14

Hydraulic harvesting gear scraping mussels from bouchots (wooden poles).

the Atlantic coast and in Mediterranean lagoons (Vilela,

1950; Partridge, 1977). Guerin and Ganivet (\907) reported the distribution of natural beds along the French

coast. Brittany and the Thau Lagoon were the main

productive areas, but overfishing and irregular landings, leading to extensive imports, prompted shellfish

farmers and scientists to develop clam culture.

The first experiments were based on transfers of

natural spat to culture plots in Rouqueyrol in 1863,

then in 1878 in the Gulf of Gien and Bay of Toulon

(Mediterranean), where a broodstock sanctuary was

established (LeVailiant, 1953). Trials in southern Brittany early in the century similarly relied on erratic

natural spat supplies (Nicol, 1910, cited in LeVailiant,

1953). In 1955,750 leasing grounds, mostly in southern

Brittany, were seeded with clam spat (LeVailiant, 1953).

More recently, hatchery techniques provided a basis

for extensive culture development by controlling the

reproduction cycle. In 1972, the commercial hatchery

SATMAR experimented with the Manila clam, Tapes

philippinarum, and introduced a broodstock of 150 individuals from Seattle, Wash., to develop breeding techniques. On the basis of growth and survival rate comparisons, the Manila clam was selected for culture

(Latrouite and Perodou, 1979). Early in 1980, spat production was under control in hatcheries and was sufficient to sustain a large clam production.

In 1985, clam culture practices were fully operational

in several ecosystems, including tidal and intertidal areas and oyster ponds, and were proposed as a way to

diversify oyster as well as mussel culture. However, in

1986, an abnormal shell calcification called "brown

ring," resulting from a viral infection (Paillard and

Maes, 1994), appeared in the clams in several rearing

areas and reduced the landings (Goulletquer et aI.,

1989). Later on, in 1987 and 1988, this species extensively colonized natural beds in southern Brittany, leading to a new public fishery 2 years later. Annual production ranged from 1,000-1,500 t (whole weight) (Bachelet

et aI., 1993). Landings of cultured clams peaked at 500

t. Since then, large landings by the public fishery has

drastically slowed the development of clam culture.

Current Status

In 1993, clam culture yielded 1,000 t distributed

among ormandy (50 t), southwest Atlantic (200 t),

and Brittany (700 t)4. Halfofthe production in Brittany

is based on a rearing cycle including natural spat gathering and deployment in culture plots. Public beds

yield around 3,000 t/year with two-thirds coming from

the Gulf of Morbihan (1,000 t of Tapes philippinarum)

and the Thau Lagoon (l,000 t of T. decussalus and

T. pullaslra).

4 Al 26 U.S. standard bushels in 1 metric tun.
152 NOAA Technical Report NMFS 129

Clam Culture

Cultural practices and methods were extensively reported in the guide to Manila clam culture (IFREMER,

1988). Clam spat is produced in hatcheries, then

pregrowing is carried out by nursery techniques or by

seeding in semiclosed ponds or in intertidal areas using

mesh nets to control predation. The latter process is

fully automated, using tractors equipped with specific

gear to seed the clams and deploy mesh screening over

them. Additional gear allows automatic net brushing to

control fouling. Grow-out facilities also include protected culture plots and semiclosed ponds. In the ponds,

clams are grown in the bottom with mesh nets placed

over them; appropriate mesh sizes are used with different sizes of clams (Goulletquer et aI., 1988; DeValence

and Peyre, 1989). The usual rearing density in intertidal culture areas is about 250 clams/m2.

More recently, new intensive techniques were developed to counteract a food limitation that occurs in

semiclosed ponds in summer. Farm fertilizer and mineral nutrients are used on an experimental scale to

maximize primary production (Hussenot et aI., 1992).

A recent discovery of underground fossil seawater in

several locations along the Atlantic coast facilitates mass

production of microalgae (Baud, 1988). Standard conditions for intensive rearing (i.e., >2kg/m2) of Manila clams

were established successfully in the nursery and growing

stages (Baud and Haure, 1989; Baud and Bacher, 1990).

Harvesting Methods

Hand picking and hand raking are the traditional methods for harvesting clams in intertidal areas (Partridge,

1977). In the Thau Lagoon, in shallow waters <10 m

deep, clams are harvested also by skin divers using

forks, and by fishermen using hand rakes from boats. For

clam culture to be cost-effective, it was essential to have

mechanized harvesting techniques. In intertidal areas,

harrowing machines and specially-equipped tractors harvest 300 and 600 kg of clams per hour, respectively (Fig.

15, 16). A dredge was specifically developed to harvest

clams in semiclosed ponds (DeValence and Peyre, 1989).

Processing and Marketing

In the processing plants, automatic sorting machines

facilitate washing and size grading. Clams are marketed

mostly for the fresh market; the larger ones are sold to

restaurants. Clam prices have decreased from F60 or

$1O.17/kg (30 clams/kg) in 1983 to F50 or $8.47/kg in

1987, and to F30 or $5.08/kg in 1993, because the

Figure 15

Motorized equipment for harvesting cultured clams in soft bottom and small-acreage

leases.
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 153

Figure 16

Harvesting equipment for cultured clams in intertidal hard-bottom areas.

supply has been increasing from the public fisheries in

France and Italy.

The Scallop Industry _

History

The common scallop, Pecten maximus, and the great

Mediterranean scallop, P. jacobaeus, distributed in the

English Channel and Atlantic Ocean, and Mediterranean Sea, respectively, are the most common scallop

species harvested in France. Scallops used to be more

extensively distributed in shallow bays and estuaries

along the French coast. They were distributed near the

natural oyster beds and represented a bycatch of the

oyster dredging fishery (LeDantec, 1947). Fleets ofsmall

vessels designed for coastal fisheries originated from

this commercial activity and dredged for scallops in

winter in the relatively protected bays.

Irregular recruitment and overfishing resulted in cyclic production in several areas. At the turn of the 20th

century and concomitant with railway development,

the size ofthe dredging fleet was increasing in Normandy

to supply fresh markets. But in 1906, a survey of shellfish beds described the scallop populations as overfished in this region. In 1927, a fishery rebound occurred, and 200 fishing boats dredged the beds. In

1935, the resource disappeared again (CNEXO, 1977).

Before 1960, the main productive areas were located on

the Atlantic coast in southern Brittany (i.e., Yeu Island)

and the Bay of Brest, where production peaked at 35-

45% of the total French landings (Rieucau, 1980). Scallops were marketed canned or fresh.

The cold winter in 1963, combined with overfishing

during the previous years, affected the entire scallop

population. Scallops in the Bay of Brest disappeared,

but those in northern Brittany (e.g., St. Brieuc) were

discovered following the decline of the fishery for the

venerid, Venus verrucosa.

Fishing effort, meanwhile, increased in the eastern

part of the English Channel. Landings increased progressively from 5,000-6,000 t (whole weight)5 in 1963

to 20,000 t in 1972. Eastern Channel areas yielded 48%

of the total catch; 46% were harvested in northern

Brittany, mostly from St. Brieuc; and the remaining 6%

came from the Bay of Brest and southern Brittany.

Since a record high of 25,000 t during the 1970's, the

scallop fishery has declined progressively to 6,000-10,000

t. The decline was attributed to a decreasing broodstock

leading to irregular spat settlement (Dao et aI., 1992).

For example, Bay of St. Brieuc production shrank from

12,000 t in 1973 to 5,000 tin 1980, and the Bay of Brest

from 1,000 t before 1963 to <100 t during the 1980's.

j At 36.7 U.S. standard bushels in 1 metric ton
154 NOAA Technical Report NMFS 129

The semiclosed Bay of Brest was chosen to experiment with a large-scale restocking program based on

hatchery spat production. In 1978, the first trials based

on the spat repletion program yielded 40% adult sc.allops. They were followed by a large-scale program carried out between 1983 and 1988; the broodstock was

estimated to be 300 tin 1990. Although efficient (i.e.,

30% survival rate at 5 years old), concomitant research

demonstrated that 80% ofthe larval settlement variability resulted from climatic conditions, therefore limiting

the broodstock effect. Instead of producing broodstock,

the management strategy for the Bay ofBrest and Northern Brittany shifted to hatchery production of spat (2

mm length), a pregrowing phase in cages to a 30 mm

length, bed seeding for growing, and fishing for the

scallops when they were 3 years old (10.2-11 em length).

Current Status

The main productive natural beds of scallops are located in the eastern part of the English Channel, namely

Bay of Seine, offshore in the Mid-Channel, and in the

Bay of St. Brieuc (150,000 ha) in northern Brittany

(Fig. 17). Yearly landings reach 10,000 t, well below the

total French consumption of about 50,000-60,000 t,

divided equally among fresh, frozen, and processed

products (Dao et aI., 1992). Scallops with the roe attached, namely "coraillee," are considered a delicacy

and reach F25-35 or $4.24-5.93/kg while nonmature

scallops peak at F15-25 or $2.54-4.24/kg. Prices are

highly variable and depend upon season, as well as

supply and demand. Landed prices represent a total

F250 million ($42.37 million).

-44

- 45

- 46

-47

- 48

-49

2 4

I

Total Landings = 10,900 t

Distribution of mean

scallop landings in France

(1981-85)

o

NORMANDY

Charentes' Straits

4 2

o

Bay

of

Biscay

/'---,

Mediterranean

Sea

C

ell

Q)

u

o

u

Eell

vvester4·, English [)

Channel

Morlaix • 130 r

St.Brieuc

4000

Bayof Brest BRITIANY

Iroise Sea )_~

75 ~Groix Island

50'~B

21~~land

1600 'Y'"Yeu Island

CD

Figure 17

Distribution of mean landings (t) of the common scallup, Pecten maximus, between 1981 and

1985 in France.
___ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 155

The Scallop Fishery

The main feature of the 10 principal populations of

Pecten maximus is highly variable recruitment, since this

species is very sensitive to thermal fluctuations. A cohort abundance may vary from 1 to 10; it usually is

harvested within 3 years (Dao et aI., 1992). This high

resource variability led to a complex management system based on administrative and professional regulations. The administrative management frame concerns

legal marketable size, fishing gear, and season openings.

For the classified beds distributed within the 12-mile

limit, additional regulations are proposed by professional organizations; they will then be ratified by decision makers. The regional fisheries committee, namely

"Comite Regional des Peches," and its scallop subcommittee, enacts regulations specific to each natural bed

including licensee number; boat characteristics; fishing

time and daily hours; dredge number and mesh size;

annual, daily, and boat quotas; unloading harbors; and

minimum legal size (e.g., from 10.2 to 11 cm). This

committee also has the responsibility to specify the

opening of the fishing season per area and eventually

the closing ofthe fishery when the demand collapses. A

minimum price limit is established by the producer

organization, "Organisation de Producteurs," a special

European status to optimize seafood markets.

During the 1980's, more than 3,500 fishermen and

1,000 boats were involved in the scallop fishery. In just

the eastern part of the English Channel, 300 boats were

harvesting scallops. Around 600-700 fishermen and

200 boats currently are involved in this fishery. Most

scallop boats are 12-16 m long, and the crew size varies

from 3 to 5. The current fishing season is between

October and 15 May.

Although variable, the resource is predictable by stock

assessments. The management system therefore aims to

sustain the scallop population and secure the supply by

limiting yearly landing variability instead of maximizing

landings.

On the Mediterranean seaside, the scallop fishery

has always been a bycatch for a fleet of bottom trawl and

dredging boats. The minimum legal size for the great

Mediterranean scallop is 7 cm. Landings peaked at

around 100 t during the 1970's (Contat, 1983), but

shrank to 33 t in 1982, to 15 t in 1988, and to a 5 t

record low since 1990.

Scallop Culture

Based on the current fishery status, a cooperative program of scallop culture has been developed between

scientists, professionals, and managers since 1988. Its

originality is linked to the strong association of aquaculture and the fishery. The rearing cycle is characterized

by:

1) Hatchery production of post-larvae (2 mm), using

conditioned broodstock. Survival rate oflarvae is around

40% in the hatchery and then 20% ofsettled spat survive

in the nursery. At this stage, spat are set in flow-through

systems at an initial density of 100,000 post larvae per unit;

2) A pre-growing phase is the second stage using

rigid racks deployed on leased grounds in open sea.

One container can be loaded with 250,000 spat in 27

racks and be easily moved from the surface. At 10-15 mm,

scallops are sorted and density is halved; they reach 30

mm after 6 months. The survival rate reaches 35%.

3) Scallops finally are deployed directly on the bottom, at a 5-20 m depth, and at an average density of 10

individuals/m2. Scallops are dredged 2-3 years later

when the marketable size of 10 cm is reached (125-150

g total weight). The capture rate varies between 20 and

50% in the most productive areas (Dao et aI., 1992;

Fleury and Dao, 1992). The overall survival rate from

the larval to adult size is about 1%.

From a technical viewpoint, the rearing cycle is under control, but it requires further optimization since

its cost-effectiveness depends primarily on the products' exchange value. For example, with a 30% yield and

150 g scallops, production costs reach around Fl5-25 or

$2.54-4.24/kg above the 1994 fishery ex-vessel value.

Harvesting Methods

Dredges are the only gear used to harvest scallops.

Several types currently are in use in France (Fig. 18a, b,

19) (Dupouy, 1978; Duval and Portier, In press). Their

use depends primarily on regional peculiarities and

regulations. For example, the dredge specifically used

in the Bay of St. Brieuc is characterized by a diving

board, a 200 kg maximum weight, a width of2 m, with 7

cm tines spaced at 10 cm intervals, and an iron bag with

72 mm meshes. In northern Brittany as well as in the

eastern part of the English Channel, the use ofa springloaded dredge (80 cm wide) is increasing. On board,

the crew usually operates two to four dredges (1.5 m

wide). Scallopers can gear from 6 to 24 units when

using spring-loaded dredges that are on bars, 6 units

(dredges) to a bar. A boat towing 24 units would have 4

bars, 6 units on each.

Since scallops should be marketed alive, fishing activity lasts less than a day and the natural beds are near the

main harbors (e.g., Port en Bessin, St. Brieuc, Dieppe).

The largest boats in the eastern Channel, however, may

spend 2-3 days offshore. The farthest natural beds are

less than 80 miles from any harbor. The quota of250 kg

per fisherman is reached at the season opening; the

daily catch ranges mostly between 0.7 and 1 t per boat.
156 NOAA Technical Report NMFS 129 _

dredges

rubber B bobbin

J details cf pawl and

sp,ingassembly

A

/'

chain belly

Figure 18 A, B

Various types of shellfish dredges (from Duval and

Pourtier, In press, 18A; and Dupouy, 1978, 18B).

Processing and Marketing

Most scallops are marketed in the shell for the expensive fresh market. Landings of freshly shucked scallop

meats, another part of the market, compete with imports from Scotland and England. French scallops are

calibrated in the 10/30 and 10/20 meats per pound

categories for the fishery and culture, respectively (Dao

et aI., 1992). The French market requires a high quality

standard with less than 5% water loss during shuckir..g.

Most scallops for the frozen market as well as for processing plants are imported, except when the fishery

supply is so high that a bottom price is reached. Frozen

products usually are marketed by 2-5 kg packs or I.Q.F.

(Individual Quick Frozen).

Other Mollusks

Among other important mollusks harvested in France,

the squids, namely the common cuttlefish, Sepia

officinalis; and the European squid, Loligo vulgaris, and

veined squid, Loligo forbesi, combined; rank fifth and

sixth in landings with 10,000 and 5,000 t, respectively

(Chaussade and Corlay, 1988). They are caught using

several types of fishing gear including squid jiggers,

plastic pots, lures, seines, trammels, pelagic gillnets,

bottom set gillnets, and bottom trawls (Boletzky, 1992).

The fisheries areas are located mainly in the English

Channel and from southern Brittany to the Vendee

region for the coastal fisheries, and the Bays of Biscay,

Seine, and the Iroise Sea for the offshore fishery (Fig.

~O). Squids are marketed as whole for the fresh market

or frozen, as well as processed for the mantles, skinned

fins, and skinned tubes. Ex-vessel values reach flO or

$1.69/kg for Sepia and F22 or $3.73/kg for Loligo sp.

Several other species are also the focus of important

but local fisheries; statistical data regarding their landings are underestimated. The waved whelk, B. undatum,

with 15,000 t (whole weight) landed (F45 million or

$7.63 million landed value) is one. This species is mainly

fished using plastic pots with cement bottoms weighing

12-15 kg and baited with fish and crab. In 1992, 60

boats were potting them in the Gulf of St. Malo where

90% of the catch was landed. Each boat is <10 m long

and has a crew of 2-3. Since the development of the
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 157

Figure 19

Crew taking in a scallop, Pecten maximus, dredge.

hydraulic pot hauler during the 1980's, the fishing

effort has increased substantially and a boat can lift 500

pots a day (Veron, 1992). Pots are distributed every 5-

10 m along trot (boltch) lines (50-60 m long). Most of

the catch is sold to the French fresh market, but some is

exported to Belgium.

On the Mediterranean seaside, the purple dye murex,

Murex brandaris, is a bycatch of the bottom trawler fleet

in the Gulf of Lion. The trawlers use a special fishing

gear, named "radasse," which is built like a beam trawl,

using pieces of fishing net 8 m long. The murex have

spines that become caught in the net. The "radasse" is

trawled at 1-2 knots for 2.5 hours/tow on the fishing

grounds. The murex are removed from it when the

vessel returns to its harbor (Veron and Raimbault, 1992).

This fishery lands around 100 t (whole weight) /year for

an ex-vessel value of F3 million ($ 0.5 million).

Abalones, Haliotis tuberculata var. tuberculata on the

Atlantic coast and Haliotis tuberculata var. lamellosa on

Mediterranean coast, usually are harvested by local fishermen at low tide or by divers. On the Atlantic coast,

where abalones have been overfished, regulations restrict the harvesting to intertidal areas. In contrast,

large subtidal populations recen tly were reported mainly

in the Gulf of St. Malo, and a limited fishery based on a

license and quota system was initiated during the 1990's.

Abalones (8 em minimum legal size) are harvested

year-round, except during theirJuly and August reproductive period. The fishery is carried out by scuba divers

who use knives to remove the abalones from rocks.

Landings are about 20 t (whole weight) a year. All

landings must be reported to the Administration. Illegal fishing is often reported despite the regulations and

enforcement and is thought to run at least 100 t a year.

Abalone is the most expensive mollusk on the French

market and costs around FI00 or $17/kg. Most of the

catch (90%), however, is processed for export toJapan.

During the 1970's, culture experiments were carried

out to control the rearing cycle. Although hatchery

rearing was under control, the growout stages were too

long (i.e. 3-4 years) and not cost-effective. In 1994, new

techniques using underground seawater were being

tested to improve the efficacy of the rearing cycle.

Two additional pectinids, the queen scallop, Aequipecten opercularis, and the variegated scallop, Chlamys

varia, are the targets of dredgers and trawlers in the

English Channel and the Bay of Brest (Fig. 17). The

queen scallop is the only authorized bivalve caught by

bottom trawlers (Dao and Decamps, 1992). This species is fragile, which limits its commercial interest, and

is marketed only fresh. Around 2,000-3,000 t are harvested each year mainly in the western English Channel

(>1,000 t by 15 trawlers) and the eastern English Channel

(>1,000 t by 30--40 dredgers and trawlers).

Instability of the natural scallop beds results largely

from irregular recruitment and patchy distribution. The

variegated scallop used to be harvested in the Charentes'

straits, i.e., "Pertuis charentais," yielding a record high

of 2,000 t during the 1960's. Harvesting ended in the

1970's when heavy fishing decimated the populations.

The remaining dredging activity now is located in the

Bay of Brest where yearly landings are between 200 and

400 t. This species reaches the minimum legal size of 40

mm at 2 years old. Strict regulations limit harvesting to

licensees from November to the following February

(Dao and Decamps, 1992). Culture experiments were

done using natural and hatchery spat from 1989 to

1991, particularly by reseeding spat in oyster ponds.

Although growth rates were faster than in natural populations and market size was reached in less than a year,

survival rates were still too low to expect a full implementation of this rearing cycle.

The cockle, Cerastoderma edule, fishery yields around

10,000 t (F33 million or $5.59 million landed value) a

year (the landed quantity is underestimated). Cockles

(minimum legal size 30 mm) usually are harvested at
158 NOAA Technical Report NMFS 129 _

48

45

49

46

47

44

43

4

Thaulagoon

Sepia officinalis

fishing grounds

o coastalfisheries EEl offshore fisheries

o

NORMANDY

Bay

of

Biscay

l:

co

III

U

o

.!:!

E

co

Bayof

I·~Q

Figure 20

The offshore and coastal fishing grounds for squid, Sepia rifficinalis, along the French coast.

low tide by hand picking or using hand rakes along the

Atlantic and English Channel coasts. A commercial

reseeding activity is also carried out in southern Brittany (Le Croisic) where spat are deployed in culture

plots at a density of 1,000 individuals/m2; landings are

2,000-3,000 t a year.

Several venerid clam species are also the focus of

extensive fisheries. In 1861 and 1863, Coste introduced

the northern quahog, Mercenaria mercenaria, to France

in Arcachon Bay (Ruckebusch, 1949; Lambert, 1949).

The first clam batch reached 2 cm 2 years later, but the

quahogs failed to reproduce. Later on, from 1936 to

1939, other trials were carried out in southern Brittc.ny

(Belon River), but the quahogs again failed to reproduce. Meanwhile, at the turn of the century (1910), an

oyster farmer named Prunier introduced several quahogs to the upper Seudre estuary (Marennes-Oleron

Bay) where they successfully reproduced. Since then,

natural, but sparse, quahog beds have been reported in

several places including southern Brittany; their presence demonstrates successful reproduction (Lambert,

1949).

During the 1940's, the northern quahog was the focus of culture in the Seudre estuary. Small quahogs

were reseeded in oyster ponds as a byproduct of the

oyster industry. Since then, quahogs have been harvested by hand raking and hand picking in this estuary.

Dredges currently are used for harvesting quahogs in

sandy-muddy bottoms in southern Brittany (Morbihan).

Additional trials using hatchery spat were made during

the 1970's, but a slow growth rate and the quahog

distribution deep in mud bottoms limited the costeffectiveness ofthe culture, particularly when compared

with the Manila clam. The current activity centers on a

small fishery limited to the Seudre estuary and southern Brittany, and a bycatch elsewhere.

The warty venus, Venus verrucosa, is dredged for the

fresh market from September to April mostly in the
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 159

Gulf of St. Malo (95%); the remaining landings are in

northern and southern Brittany (Berthou, 1992). The

fishery, initiated during the 1950's, yielded a record

high of 5,000 t in 1962 and 1975, declined afterward to

4,400 t in the early 1980's, and to 1,400 tin 1988. In

1986,183 dredging boats were operating in this fishery,

with 75 working more than 6 months a year. Despite the

decline in landings, the fishery has remained attractive

since the ex-vessel value, although variable, has increased

to F20-50 or $3.40-8.50/kg. The dredge in use is specific for bivalves, rigid, with a 60 cm opening and an 8-

25 cm flat board. The metallic frame has 21-25 mm

grid spacing to retain only legal size clams (40 mm).

The banded carpet shell, Venerupis rhomboides, is also

harvested exclusively by dredging in the Gulf of St.

Malo and southern Brittany (Berthou, 1992). The minimum legal size is 38 mm. In 1988,800 t were dredged

for the fresh, processed, and frozen markets as well as

for export.

The dredging fishery of the common European bittersweet, Glycymeris glycymeris, yields 2,000-2,500 t a year

in the Gulf of St. Malo, southern Brittany, and Iroise

Sea for the fresh market. This underexploited population

would present a large potential for processing if meat

tenderizing techniques were developed (Berthou, 1992).

In the same areas, dredging boats harvest around

5,000 t/year of thick trough shells, Spisula ovalis, and S.

solida. The clams average about 35 mm long (range,

28-45 mm); the minimum legal size is 28 mm. Most are

sold for the fresh market, and the remainder are processed and frozen for southern European countries.

Only one year class usually is found in the natural beds,

leading ~o nearly complete harvesting oflocal subpopulations. The populations are characterized by good sets

every year and rapid growth of the clams. When fishermen shift their activity to other species or other natural

beds, the Spisula populations recover quickly (Berthou,

1992).

Bycatches ofthe previously cited fisheries include the

golden carpet shell, Venerupis aurea; chamber venus,

Circumphalus casina and C. rosalina; smooth callista,

Callista chione; sand gaper, Myasp.; mature dosinia, Dosinia

sp.; tellins, Tellina spp.; and otter shells, Lutraria sp.

In addition, there are small fisheries that involve

digging by hand and with rakes. The mollusks harvested

include the peppery furrow, Scormcularia plana; several

donaxes, Donax spp.; razor shells, Solen sp.; rayed trough

shell, Mactra corallina; and grey trough shell, M. glauca.

Shellfish Preparation for Consumption __

Most of the French molluscan production is marketed

fresh in the shell. The mollusks are washed and graded

by size. Some species (e.g., clams and scallops) can be

marketed frozen. Freshness is the main criterion for

French consumers, and, when required, preparation

and cooking are carried out on their own. Therefore,

any breading operation before marketing is rare and

concerns only clams. Battered processing for shellfish

does not exist in France. Canning is developed to a very

limited extent and concerns only the species of low

exchange values such as mussels, clams, and bycatch

species from the dredging fisheries on natural beds. A

small market has been initi:lted for smoked mussels,

but the demand is low since they do not yet fit French

consumption habits.

Mollusks are eaten several ways in France, including

raw, cooked using various recipes, boiled, and steamed.

Oysters and most of the clam species are eaten raw,

and, to a limited extent, the new French cuisine has

developed consumption of raw scallop, P. maximus, adductor muscles. Recipes are available for all shellfish

species previously cited, including oysters. However,

with oysters, this represents a very limited consumption

and is mostly proposed by restaurants. When cooked,

clams are often prepared using butter and culinary

herb stuffings. Since abalone muscle is very tough, it

must be tenderized with a mallet. The waved whelk, B.

undatum, and the periwinkle, Littorina littorea, are the

only species usually boiled in salty water and culinary

herbs. Species that are steamed include mussels, cockles, clams, and sometimes scallops. The steaming process requires added ingredients such as white wine and

culinary herbs.

Aquaculture and Fishery Management

Since the coastal area is the focus of mUltipurpose use,

state regulations are required to facilitate various and

simultaneous activities. For example, the 1986 state law,

"Loi du Littoral," specifies the legal framework regarding coastal managemen t. Two types of spatial management, namely "Schema d'Amenagement et de Mise en

Valeur de la Mer (SAUM)" and "Schema de Mise en

Valeur de la Mer (SMVM)" usually are proposed to

organize the coastal area by specifying priority uses.

The management plans are proposed by the state managers in agreement with local representatives, scientists, and administrators. A public survey meanwhile is

carried out to debate the proposals.

Regarding the marine-related activities, fishermen

benefit from a professional organization developed at

local, regional, and national levels, and funded by taxes

on business dealings. At each level, representatives of

each profession are elected on an equal basis of employers and employees. Forty-eight local fishery committees, namely "Comite Local des Peches," are distributed along the French coast. At the second level, four
160 NOAA Technical Report NMFS 129

regional committees (i.e.. Normandy, Brittany, Souhwest, and Mediterranean Regions) represent th('

fishermen's interests in relation to the regional adrr,inistration. Moreover, 18 interprofessional national committees are specialized in problems dealing with one

species or a species group, i.e., "Tuna committee," "Scallop committee," to organize the fisheries.

Besides the fishery, shellfish culture has a national

and nine regional committees to organize the industry.

Like the fishery organization, funds are provided from

taxes on commercial activities. The regional committee

involves state managers, scientists. and professional organizations, and it enacts the global rules and authorizations for use of the leasing grounds that remain inalienable and under state management. For example,

in the Marennes-Oleron Bay, the surface area of tables

used in oyster culture should not total more than onethird of the leased acreage, and no more than 6,000-

7,000 oyster bags should be placed in a hectare. In

Normandy, the upper threshold is 5,000 and 6,000

oyster bags/ha on the eastern and western coasts of

Cotentin, respectively. The committee debate to allot

each leasing ground to applicants is based on a regional

management plan, i.e., "Schema des structures," which

lists priority rules. A public survey meanwhile allows a

debate over the use of each leasing ground, and recommendations are considered by the committee.

The national council of fisheries and mariculture,

"Comite Central des Peches et Cultures Marines" overviews all committees, the entire organization, and aims

to provide information and improve relationships between sea-related activities and the Administration.

Public Health

Since the French shellfish market is based mainly on

raw and fresh products, it is particularly important to

protect the public from eating polluted or unhealthy

products. Several regulations are enforced to avoid public health problems. The main framework relies on

several national monitoring networks managed by

IFREMER, the French Research Institute for Sea Exploitation. They include 1) the monitoring network of

the coastal environment or "RNa," 2) the Phytoplanktonic monitoring network or "REPHY," and 3) the Microbiological monitoring network or "REMI" (for reviews, see Belin et al. (1993) and Berthome (1992)).

However, public health is only one ofseveral objectives

of the networks; others are marine life and environmental protection, trends, and risk assessments of environmental variables and contaminants. The networks

are funded by the Ministry of Environment, Ministry of

Research and Technology, and by shellfish farmers

through professional taxes.

Coastal Environment Monitoring Network,

"RNO"

The Coastal Environment Monitoring Network, "RNa,"

was started in 1974 for the water quality survey and

marine life and sediment surveys that began in 1978. It

resulted from the international treaty enforcements of

London and Oslo (1972), Paris (1974), and Barcelona

(1976). The main objectives are the monitoring ofyearly

trends and thresholds of seawater variables (e.g., temperature, salinity, oxygen, nutrients). Contaminant concentrations are determined four times a year in fish,

oysters, and mussels at 43 sites along the French coast

representing more than 100 experimental stations.

Heavy metals (i.e., mercury, cadmium, lead, zinc, and

copper), PCB, PAH, and organochlorines (i.e., DDT, DDD,

DDE, HCH, and Lindane) are systematically analyzed.

Phytoplanktonic Monitoring Network, "REPHY"

The toxic (DSP) phytoplanktonic blooms of Dinophysis

sp. that occurred in 1983 and resulted in hundreds of

gastroenteritis cases prompted managers to establish a

monitoring network to 1) protect public health, 2)

protect shellfish beds, and 3) develop a long-term data

base. This survey, called the Phytoplanktonic Monitoring Network, "REPHY," and initiated in 1984, has facilitated the systematic sampling of phytoplanktonic population trends and associated phenomena, as well as

early detection of abnormal phenomena along the

French coast. As soon as the latter is detected, an intensive survey assesses spatiotemporal fluctuations to provide insights for decision makers. Thirty-seven sectors

currently are systematically surveyed monthly from September to April and weekly from May to August. When

an abnormal event (e.g.. gastroenteritis) or a toxic

algal bloom is detected at an early stage, 73 additional

sites are added to the regular monitoring. When DSP

or PSP toxins are detected by scientific tests, the'area is

closed by state officials to impede any shellfish sales

until two negative tests (i.e., two consecutive weeks) are

reported.

Microbiological Monitoring Network, "REMI"

Early in the century, bacteriological control of oysters

was established by private funds to guarantee shellfish

quality. The state agency, Office Scientifique et Techniques des Peches Maritimes, OSTPM, took over this

bacteriological control in 1919 and organized a national network, now called the Microbiological Monitoring l'ietwork, "REM!." In 1989, the monitoring network was reorganized to include environmental quality
____ Goulletquer & Heral: Marine Molluscan Production Trends in France: From Fisheries to Aquaculture 161

concerns. The global approach focusing on trends and

thresholds is based on fecal coliform concentration

(i.e., number per 100 ml of meat) and, to a lesser

extent, on Salmonella occurrence as contamination indicators. In 1992, 345 stations were monitored monthly

along the entire French coast (5,500 km). More specifically in the mollusk farming areas and for the public

health concern, the monitoring effort is increased to a

weekly survey as soon as abnormal environmental conditions occur (e.g., heavy rains, agricultural practices in

the watershed, tourism activity). In addition to the increased frequency, the sampling incorporates additional

stations that total 278 nationally. Fecal coliforms and

Salmonella are systematically surveyed. The fecal contamination concentration is particularly important with

regards to the French and European regulations that

allow only direct commercialization without further

treatment below a 300 coli./l00 ml meat threshold. No

Salmonella is tolerated before marketing.

The Future _

In the past, the molluscan fisheries sector has shown

irregular landings due to abnormal recruitment and

excessive fishing effort. Improved stock assessments and

specific knowledge offactors affecting recruitment therefore are likely to improve the fishing industry economy.

Although successful in several areas (e.g., scallop fishery in the Bay of St. Brieuc), comprehensive management plans, including regulation enforcement based

on statistical stocks assessmen ts, appear necessary for

the natural shellfish beds showing high potential production (e.g., abalone). Fishing effort on current bycatch

species (e.g., dredged clams) is particularly likely to

increase and provide landings for the processors and

markets. In contrast, it seerps difficult to implement

management plans for species showing a short life cycle

and fast population recovery (e.g., mussel, cockle, and

Spisula sp.). In other respects, it is unknown to what

extent the current crisis affecting European finfisheries

will affect molluscan landings.

The culture of mollusks has been a large success in

France for several reasons including the extent of the

natural spatfall, high ecosystem carrying capacity, good

management, and good adaptation of the mollusks to

cultural practices. Past events have shown that the industry can be harmed, however, by epizootic diseases or

abnormal events such as dinoflagellate blooms. Markets and production can be affected. Scientific research

is critical to protect public health and optimize current

production.

One key element is to improve the balance between

the ecosystem carrying capacity and the mollusk stocking density. For example, Heral et al. (1986) have demonstrated that oyster production in the Bay ofMarennesOleron cannot be higher than 40,000 t for a stocking

density between 90,000 and 200,000 t. Increased stocking density resulted in increased mortality rates and

growth rate decline. This is a critical issue, since optimum stocking densities should be defined specifically

for each rearing area, to maintain quality products as

well as healthy shellfish populations, therefore limiting

a risk of disease occurrence. The second key element

for a sustainable industry is to prevent water quality

degradation, as a guarantee for quality products (e.g.,

bacteriological quality). The intensive monitoring networks already developed will facilitate early reports to

address the issues of abnormal events. For example, the

networks will likely lead to additional improved watershed management as well as plant equipment with regard to recent EU sanitary regulations that rate the

rearing areas according to water quality criteria.

Further industry advancements will be achieved by

developing automatic equipment and longline techniques, which should result in improved labor conditions, reduced labor costs, and development of offshore culture in unexploited areas. Other ways to improve the shellfish industry are anticipated in the near

future by implementing current research programs.

For example, disease resistant strains (e.g., O. edulis

against Bonamia sp.) and genetically manipulated animals currently are under review. Hatchery-produced

spat from such strains would be a way to improve shellfish production.

From a marketing viewpoint, the EU development

will obviously expand shellfish market possibilities within

European countries and could result in increased production. Official recognition of local labels, appellations, and brand names is likely to occur in the next few

years, facilitating product sales. However, new development should be considered concomitant with bioeconomic analysis of the shellfish industry. Coupling

models of production dynamics with marketing systems

will improve overall cost-effectiveness. It seems important also to take into account social and political approaches to facilitate sustainable development, since

they are key elements in industry dynamics. New conflicts in watershed, freshwater, and coastal space uses

are already anticipated, requiring insights and specific

knowledge for the decision making process.

Acknowledgments _

We thank P. Bertholl,J. P. Joly, J. Prau, J. Vigneau, J.

Morin, P. Duval, and D. Coatanea for providing valuable comments and advice to improve the manuscript

and also C. L. MacKenzie, Jr., and other reviewers for

their helpful suggestions.
162 NOAA Technical Report NMFS 129

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The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain

CACERES-MARTINEZ,j.* and A. FIGUERAS**

Instituto de Investigaciones Marinas CSIC

Vigo, Edwardo Cabello 6, 36208

Vigo, Spain

ABSTRACT

Spain produces several molluscan species, including mussels, oysters, cockles, clams, and

scallops. Nearly all grow in the Galician region in the northwest. Spain's production of

200,000 t of blue mussels, Mytilus galloprovincialis, per year, makes it the second largest

producer of cultured mussels in the world. Historically, mussels were consumed in Roman

villages and later by coastal peoples. They became important when farmers began culturing

them in the early 1900's. In 1946, raft culture was introduced and production increased

sharply. A sheltered environment is provided by flooded river valleys ("rias") for culturing

the mussels on ropes suspended from floating rafts. Farmers collect mussel seed from local

shores, attach the seed to the ropes, and grow them to market size in 13 to 16 months. In 1984,

there were 3,347 mussel rafts. Each produces an average of 47 t/year. About 7,000 people farm

mussels and 3,000 more are engaged in related industries. Production of the flat oyster, Ostrea

edulis, is limited with about 500 t/year. The cockle, Cerastoderma edule, is harvested mainly from

natural beds and also is cultured in protected parks; production is about 1,300 t/year. The clam

fishery targets Tapes decussata, Venerupis pullastra, and V. rhomboideus. Total production of clams is

about 2,000 t, all from natural areas. Three scallop species have commercial importance: Pecten

maximus, Chlamys varia, and C. opercularis. P. maximus is cultured on a small scale by attaching to

ropes 10-em seed collected from natural beds and suspending them from rafts for growth. All

bivalves from natural beds and rafts must be treated in one of 54 depuration stations.

Introduction

The waters of Spain have several species of mollusks

which have been gathered and farmed commercially

for many years. They include mussels, oysters, cockles,

clams, and scallops. Nearly all grow in the Galician

region of northwestern Spain.

Mussel Fishery

Spain, producing about 200,000 metric tons (t) of blue

mussels, Mytilus galloprovinciallis, per year, is the second

largest producer of cultured mussels in the world. Mussels also comprise more than 95% of Spain's total mollusk production; they are mainly cultured in the Galician

Region in northwestern Spain (Figueras, 1989).

Habitat Description

The Galician coast (Fig. 1), about 1,309 km long, is

characterized by flooded river valleys called "rias," where

farmers culture the mussels. Rias are up to 25 km long,

between 2 and 25 km wide, and from 40 to 60 m deep;

their bottoms are muddy, and they are bordered by

hills (Andreu, 1958). Annual productivity in the rias

averages 10.5 mg carbon/liter/hour. The temperature

ranges from 10° to 20°C, the salinity is around 34 %0,

and the tidal range averages 4 m. Tidal currents are

strong. There is a continuous upwelling of cold water

rich in nutrients, and these along with nutrients which

wash in from the hills during heavy rains (mean annual

precipitation is 1,250 mm) probably stimulate an abundance of phytoplankton. This, in turn, favors the growth

of mussels (Andreu, 1976; Iglesias et aI., 1984; Figueras,

1989). The sheltered rias provide an ideal environment

for culturing mussels on ropes suspended from floating

rafts (Lutz et a!., 1991). The most important culture

area is the ria de Arosa which is responsible for 60% of

Spain's mussels; it is followed by ria de Vigo and ria de

Pontevedra (Fig. 1).

* Present address: CICESE, Aquaculture Department, Av. Espinoza

#843, Col. Centro, c.P. 22830, Ensenada Baja California, Mexico.

** Address correspondence regarding paper to A. Figueras.

165
166 NOAA Technical Report NMFS 129

Natural populations of mussels are present in large

areas in mouths of the rias and islands on intertidal

rocky shores, where the mean density in the most

crowded beds is around 24,000 mussels/m2• They also

grow along the rias mainly on rocky areas, cliffs, and

boulders. Farmers collect mussel seed from these areas

to suspend from their rafts. Recruitment of seed mussels occurs throughout the year with the major settlement.season from May to September.

Associated Species and Predators

The associated species that occur in the natural mussel

beds are those found on rocky intertidal shores, such as

barnacles, Balanus sp., and algae, Enteromorpha sp. Mussel predators include crabs, Carcinus maenas; starfish,

Asteri.as rubens; and sea birds. The associated species

that colonize the mussels on ropes suspended from

rafts, by means of planktonic larvae or crawling, are

Finisterre

Old natural oyster beds

GALICIA

SPAIN

Santiago de Compostela

•

,/

,/

,

I

I

I ,~ , I

\ ' '.......- - .. , '- .......-- ,

I ....... \

'... ,' '.

Portugal

Ria de Ortigueira

..... -, --- --- I

---,

Ria de Muros y Noya

Pectinid beds

The mussel beds are distributed

along all the Galician coast

o Cockle and clam beds

Figure 1

The Galician region of Spain, showing the rias, old natural oyster beds, and the actual

mussel, cockle, clam and pectinid beds.
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 167

crustaceans such as the decapod Pisidia longicornis; amphipods, Phtisica marina and Eurystheus maculatus; ascidians, Ascidiella aspersa and Ciona intestinalis; and encrusting species such as balanids and polychaete worms,

Pomatoceros sp. and Elminius modestus. They compete

with each other for space and food and some can invade the mussel shells. Damage from crabs and starfish

is slight, but occasionally A. rubens and Nucella lapillus, a

gastropod, occur on the ropes. In addition, some fishes,

such as the sparid, Diplodus sargus, and golden mackerel, Sparus aurata, occasionally damage adult mussels

by crushing their shells; they also eat seed mussels. The

parasitic copepod, Mytilicola intestinalis, which has been

associated with damage to cultured mussels in other

countries, does not cause serious harm. Recently, the

parasite Marteilia sp. was found in mussels, but it did

not cause any serious harm. Farmers eliminate the associates and predators on the ropes by hand when they

thin the mussels (Andreu, 1976; Perez and Roman, 1979;

Gonzalez, 1982; Figueras, 1982; and Figueras et aI., 1991).

History of the Fishery

The earliest evidences of mussel consumption in the

Galician Region has been dated in the fourth century

B.C., when the natives left large deposits of bivalve

mollusks shells including mussels. These deposits, denominated "Concheiros," have also been found near

the Romanic villages of the first century A.D.

(DEMARSA, 1965; De La Penal). In the 16th century,

people from Portugal came to the ria of Arosa, in

I De La Pena, A. Archaeologist, Museo de Pontevedra, Pasanteria

#10, Pontevedra, Espana. Personal commun., Aug. 1992.

Cambados, to gather mussels, clams, and cockles

(Ferreira, 1988). Mussels became important in Spain

when farmers began culturing them at the beginning of

the 20th century. The first mussel culture was practiced

in Tarragona and Barcelona (northeast of the Iberian

peninsula) in 1901 and 1909, respectively, using poles

similar to those used in France. After the first trials, this

system was abandoned and use of floating structures

began. At this time, the natural populations of mussels

in the Galician rias were used mainly as manure on

farms and, on a limited scale, as a source of mussel seed

to be cultured. There were a few parks where farmers

practiced bottom culture of mussels; the mussels were

sold along the Mediterranean coast. In 1946 raft culture of mussels was introduced in the Galician region

and in a few years production increased sharply (Andreu,

1958,1962,1963,1968; Bardach et aI., 1972).

The early rafts consisted of square wooden frameworks suported by a central float and restored old ships

that supported wooden frameworks, from which farmers hung ropes of spart grass (Spartium junceum) (Fig.

2). Farmers attached mussel seed to the ropes, and

when the seed reached commercial size, they collected

them by hand or with a special pin wheel (Andreu,

1958; Canel, 1968; Nunez and Castro, 1990). Subsequently, the old ships were replaced by square or rectangular wooden frameworks supporting small houses.

Flotation consisted of wooden floats wrapped in wire

mesh and coated with concrete.

Today, a few old rafts remain, but most of the new

ones are constructed of a framework ofeucalyptus wood.

Their size varies considerably from less than 100 m2 to

more than 500 m2 (Perez Camacho et aI., 1991). These

structures are supported by from one to six floats constructed of wood or steel, covered with fiberglass or

Figure 2

An old mussel culture raft in the ria de Vigo.
168 NOAA Technical Report NMFS 129

Figure 3

A current mussel-culture raft in a shipyard of the ria de Vigo.

polyester, or filled with expanded polyester (Fig. 3).

Depending on the number of floats, the usable culture

area can be from 80%, when a central float is used, to

90%, when from four to six floats are used (Perez

Camacho et aI., 1991). Farmers secure the rafts with

one or two iron chains and a 20 t concrete anchor. In

protected areas with little boat traffic, they use only one

mooring chain. Two chains are better in exposed areas

or when the rafts are near the shore or heavy boat

traffic (Bardach et aI., 1972). The rafts are located

together, separated about 80-100 m from each other,

in groups called parks (Fig. 4). These vary in number of

rafts, and their locations are regulated by marine authorities. From the beginning ofmussel culture in 1946,

the number of rafts increased moderately to 400 in

1956, but after that, it increased rapidly (Table 1). The

average size of the rafts increased from 297 m2 in 1977

to 369 m2 in 1984 (Perez Camacho et aI., 1991). The

actual standard size of the rafts is 500 m2. Currently,

farmers work from shallow-draft, wide-beam boats (9 t in

weight), powered by diesel engines of about 24 hp. Each

has a basket and crane to raise the ropes and machines to

separate and thin the mussels (Nunez and Castro, 1990).

Culture Methods

Mussel culture is divided into five stages: I) seeding or

procuring the seed, 2) attaching seed to the ropes, 3)

thinning, 4) growing, and 5) harvesting.

Figure 4

Aerial view of the mussel culture rafts in the ria de Arosa.
_________ Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 169

Table I

Number of rafts and production of mussels from 1956

to 1995, modified from lUEDG (1989) and MAR (1991).

Year Rafts Production (t)

1946 10

1956 410 22,460

1958 707 39,700

1959 909 50,900

1960 1,099 61,550

1962 1,327 74,300

1963 1,424 79,750

1965 1,684 94,300

1966 2,050 114,800

1967 2,615 146,450

1968 2,786 156,000

1972 2,996 167,800

1975 3,134 175,500

1976 3,095

1987 3,242 200,000

1989 3,347

1995 3,386 230,000

Seeding or Procuring Seed-Culture begins when farmers collect mussel seed mainly from the natural beds

(60-70%) and the remainder from the collector ropes

hung from their rafts. Farmers can collect up to 1,500

kg of seed per low tide in about 4 hours from the

exposed rocky shores on the ocean side of the rias and

islands (Fig. 5) (Figueras, 1989). They use a special

steel shovel, called a "rasqueta," which has a blade

about 10 cm2 attached to a wooden handle. Farmers

suspend the mussels from their own rafts or sell them to

other farmers. The price is about 60 pesetas/kg (125

pesetas = US$l). Farmers gather around 4,500 t of

mussel seed (mean length = 2 em) from these areas

every culture cycle. They take the seed to the rafts,

keeping it moist, and attach it to ropes within 24 hours

after collection. To collect seed from the rafts, farmers

use special collectors made from old fish nets and suspend them during March and April (Andreu, 1958;

Nunez and Castro, 1990).

Attaching Seed to the Ropes-Farmers attach the seed

to the ropes by hand or with a machine which secures it

with a special cotton or rayon mesh; this mesh disintegrates within a few days (Fig. 6). By then, the mussels

have secreted new byssuses and have attached themselves to the ropes. Farmers attach from 1.5 to 1.75 kg

of seed per meter of rope, and the average weight of

seed for a rope is 14 kg (Figueras, 1989). The ropes,

usually 3 em thick and made of nylon, polyethylene,

and sometimes spart grass, vary in length from 6 to 10

m. Their rough surfaces facilitate the attachment ofthe

mussels. Each rope with attached mussels has a loop at

one end, which is fastened to a thinner polyester rope

called a "rabiza" (12-14 mm thick), which in turn is

lashed to the girders ofthe rafts. The rabiza usually lasts

only 3-4 years because it is exposed to air and sunlight

(Figueras, 1989), while the m;oyor rope lasts an average

of 6 years (Perez Camacho et aI., 1991). Each raft has

from 200 to 700 ropes. Every 30-40 em, wooden or

plastic pegs 20-30 em long are inserted between strands

Figure 5

A mussel bed on the oceanic side of the ria de Vigo.
170 NOAA Technical Report NMFS 129

a

Figure 6

a. Wrapping the mussels with a rayon net. b. Filling

sacks with mussels.

b

of the ropes to prevent the clumps of mussels from

sliding down (Fig. 7) (Figueras, 1989; Nunez and Castro,

1990; Perez Camacho et al., 1991). Farmers attach from

1 to 3 ropes/m2 of raft. This distribution allows an

adequate flow ofwater rich in food for the mussels and

prevents the mussel ropes from touching each other

(Figueras, 1989). Farmers install the ropes mainly frmn

November to March (Perez Camacho et al., 1991).

Thinning-The third step is thinning, which has to be

done to prevent the mussels from falling off in rough

weather; thinning also favors their fast and uniform

growth (Figueras, 1989; Nunez and Castro, 1990). Farmers do this when the mussels are half grown (shell

length 4-5 em) after 5-6 months of growth, usually

from June to October (Figueras, 1989; Nunez and

Castro, 1990). They bring the ropes into their boats

using a crane and rub off the clusters of mussels by

hand into a steel screen which separates them into

different sizes. A mechanic cylindrical screen can also

be used (Fig. 8). The mussels from each original rope

are attached to two to four new ropes (SOMEGA, 1975;

Figueras, 1989) with cotton or rayon netting. The average weight of the ropes is 46 kg (Perez Camacho et al.,

1991). Those farmers who automate this operation

spend 5-15 seconds per m of rope, or less than 14

hours for 500 ropes of 10 m length (Figueras, 1989).

This work is repeated once again before harvesting, if

the mussels grow rapidly and their weight and density

increases the risk that the mussel clusters will fall off. It

is also necessary when farmers have to ensure that all

mussels reach similar size at harvest time (Bardach et

al., 1972; Figueras, 1989).

Growing-The growth of mussels constitutes the fourth

culture step. In the Galician region, where this growth

is fast, mussels can attain market size (8-10 em) in 13-

16 months, especially in the areas closest to the ocean

side of the rias. The usual time required in some bays is

around 14 months. However, a high density of rafts in

the bays can slow the mussel growth (Figueras, 1989).

Growth ofmussels is minimal in summer and highest in

winter. Slow summer growth is related to the relative

paucity of plankton in the stratified water then, and it is
________ Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 171

Figure 7

A rope with settlement of mussels, showing wooden

pegs between the strands ofthe rope to keep the clumps

of mussels from sliding down.

more important than high temperature effects that

cause the seed collected on the ropes in the spring and

the fall and transplanted to the ropes, to reach the

same size at the end of the first winter (Bardach et al.,

1972; Figueras, 1989).

Harvesting-Mussels of commercial size are available

throughout the year and can be harvested at any time,

but the main harvest is from October to March when

their market demand is high and their condition is the

best. Meat weights can approach 50% oftotal wet weight

when the mussels are in the best condition. When a

large percentage ofmussels is close to spawning or have

just done so, harvesting should wait until they are in

better condition (Figueras, 1989). The mean production per m2 of raft area averages 130 kg and for an

entire raft 20 to 100 t, with a mean value of around 47 t.

Such values are highly variable and depend on size of

the rafts (Perez Camacho et al., 1991). Production is

also about 10 kg ofmussels per meter ofrope (Figueras,

1989). Annual losses (natural mortality and handling)

have been estimated at 15% (SOMEGA, 1975). Recent

results show that the natural mortality in mussel experimentally cultured is around 5% (Robled02).

To harvest mussels, farmers use cranes to raise the

ropes to their boats, where the mussels are separated and

graded by rubbing them over grids of iron bars. They

are then washed to clean off small mussels, silt, empty

shells, ascidians, and other unwanted organisms. Any

mussels too small for market are wrapped on new ropes

for further growing. The marketable mussels are then

packed in nylon bags and taken to depuration stations

(Fig. 9). Women usually do this work. Each handles

about 200 kg of mussels every 8 hours. Mussel production has increased sharply from 1956 to 1987 (Table 1).

2 Robledo, J. A. F. Biologist, Instituro de Investigaciones Marinas

CSIC, Vigo, Eduardo Cabello, 6, 36208, Vigo, Spain. Persona)

commun., Aug. 1992.
172 NOAA Technical Report NMFS 129

Figure 8

Mussel cluster disintegration with a cylindrical machine. and hand rubbing in a steel screen

for size sorting (for market or further growth).

Figure 9

Net bags with mussels destined for the depuration station.
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 173

Maintenance-Each raft normally holds three types of

ropes: Those for collecting seed, those with growing

mussels, and those with marketable mussels. Thus growers maintain continuous production from their rafts

(Figueras, 1989). Since the mussels grow faster near the

water surface, some growers periodically invert the ropes

to produce mussels of about equal size (Lutz et aI.,

1991). In rafts with only one central float, the equilibrium of the raft is altered when farmers raise ropes for

thinning or harvesting, and they have to put containers

filled with water on the appropriate area of the framework to avoid tilting it. A large number of mussel seed

and fouling organisms attach to the floats and, as they

grow, the weight of the raft increases. So, occasionally,

farmers have to clean the floats. It is easiest when the

raft is nearly empty and floats higher, leaving many

mussels and fouling organisms exposed to air where

they die and are easy to remove. For m~or repairs of

the framework or floats, farmers take the rafts to shipyards or factories. A medium-sized wooden raft has a

life span of 10-15 years, while modern fiberglass rafts

last considerably longer (Lutz et aI., 1991). Rafts range

in age from 0 to 30 years, with an average of about 8

years (Perez Camacho et aI., 1991).

Numbers of Fishennen in

Different Time Periods

The mussel industry in the Galician region is mainly

composed of family businesses. In 1975, SOMEGA estimated an average of 3.4 rafts per owner; only a few had

more than 10 units. Currently, the mean number of

rafts per owner is 1.5 and their operation is still by

families (MAR, 1991). A few big companies have more

than 12 rafts with permanent or temporary employees;

their operation is similar to any capitalist enterprise.

Some have their own depuration stations or work closely

with depuration stations and canning factories (Nunez

and Castro, 1990). Another middle-sized group has

from 5 to 12 rafts. These owners work on the rafts but

also hire extra help. Finally, the last and most numerous group is comprised offamilies who have from 1 to 5

rafts. They do all the work themselves and alternate the

operation of their rafts with fin fishing or land farming

(Nunez and Castro, 1990).

All members of the family work at culturing the mussels. Andreu (1976) stated that, with the exception of

the heavy work, women do all the work. One man and

three women are needed for the operation of a typical

raft. The size of the Spanish mussel industry in terms of

manpower is not easy to estimate because there are

many connected activities, and several companies that

work with mussels also deal with other species of mollusks. In 1958, 450 people worked directly in the raft

operation. By 1985, in the Galician region. about 7,000

people farmed mussels and 3,000 more engaged in

related industries such as depuration plants, cooking

and freezing factories, canneries, transport, and shipyards constructing mussel rafts and machinery.

With the growth of the industry, mussel farming associations have appeared. The largest one, called OPMAR,

has 80% of the proprietaries and has 1,664 members.

Currently, there are about 2,000 proprietaries with working families (MAR, 1991).

Government Regulations for Mussel Fanning

The first regulation regarding mussel culture in rafts

was approved in 1961 and, in 1974, the first plan for the

installation of rafts in the rias was implemented. A

regulation for collecting mussels from the natural beds

was established in 1969 and 1970. It prevents farmers

from gathering mussels fromJanuary toJuly, and establishes a minimum size of 50 mm. The regulation on the

gathering of mussel seed to supply the rafts is minimal:

Mussel farmers must notify the marine authorities about

the quantities and loc~lities of the mussel seed they

gather (SOMEGA, 1975).

The raft areas for culturing mussels are owned and

controlled by the government and leased to operators

for a small fee. The lease is for 10 years and is renewable. but it may be terminated by the government without notice. To obtain permission to put a raft in the

bay, the grower has to apply to the Ministry of Agriculture, Fisheries, and Food. Until 1988, the most important aspects related to the installation of rafts were

navigation, public works, national defense, and recreation. It was also important that the site chosen was not

subject to gross sewage pollution and that the planned

increase in production would not saturate the market.

The operator does not have to pay anything for the

concession, but does have to pay anchorage dues to the

Ministry of Public Works, and the industrial contribution is similar to all other factories and shops.

Legally, there is no limitation to the number of rafts

that a single owner can have moored, but recently the

number of rafts has been limited by new regulations

that consider the water quality and carrying capacity in

the area. In 1989 a water quality regulation for the

culture of bivalve mollusks was established and, during

1990, a regulation for the location of rafts was approved. Then in 1991 the regulation for the reorganization of the culture areas in the Galician region was

established (Tecnologia Ambiental, S. A., 1991). With

the integration of Spain into the European Economic

Community (EEC), the regulations for water quality for

mollusk culture have been made consistent with the

EEC directives.
174 NOAA Technical Report NMFS 129

Government Regulations for Selling Mussels

In 1964 the first law for mollusk quality and healthiness

was approved. This law established that inspection, water quality control, and healthiness of the mollusk has

to be coordinated by an official team of inspectors

consisting of representatives from governmental institutions denominated: General Direction of Salubrity,

General Direction of Marine Fishing, and the Instituto

Espanol de Oceanografia. Water and sanitary laboratories were constructed and the classification of littoral

areas, based on their water quality, was established. The

law states that all fishermen and fish farmers need a

license to market mollusks, and that all bivalve mollusks

taken from natural beds and those reared in rafts or

hatcheries must be purified in an authorized depuration station before their sale. The law for molluscan

depuration was modified in 1970, adding specifications

on the type, size, and color of package, and the use of

an official sanitary procedure was also included to obtain a better control for the national and export markets (SOMEGA, 1975). The last modification was made

in 1985.

For export, the first regulations and those from the

Commerce Ministry (Ministerio de Gobernacior. y

Comercio) are applicable dispositions that were approved in 1956. Other regulations to preven t the sale of

mollusks contaminated with biotoxins were approved

in 1986 and 1987, and the areas for the location ofrafts

to avoid the effects of biotoxins in the Galician region

were established in 1990. Finally, the regulations for

the exchange of mollusks were established in 1986.

Depuration

In 1964 the first depuration station with a daily capacity

of 15 t of mussels was opened in the Galician region

(DEMARSA, 1965). By 1975, 20 depuration stations

were registered in that region, and at present there are

54. The depuration stations obtain water from submarine collectors located at a depth of about 3 m beneath

the surface at low tide, or from coastal wells. The water

usually is treated with sodium hypochlorite (1-3%0) or

is i~ected with chlorine gas. The chlorinated water is

allowed to cascade down a series of three or more large

concrete tanks to remove the excess chlorine before

being pumped into indoor or outdoor storage basins

used for depurating the mussels. The use of ozonation

is not extensive, and there is no ultraviolet sterilization.

The mussels are held in trays or baskets placed on

raised concrete platforms in the basins at a density of 30

kg/m. Each basket contains 17 kg of mussels. For bacteriological safety, it is sufficient to keep the mussels 24

hours in the basins, but to have a wide safety margin

they are kept there for at least 48 hours. Mterward, the

mussels are packed in bags manually or automatically

in quantities ofl, 2, 5,10, and 15 kg; the bags are closed

with a metal wire turned tightly with a special spiralshafted hook. Depurated mussels are then packed in

yellow net bags provided with the authorized health

certification. The mussels without depuration are packaged in red bags. The colors are officially mandated, as

is their use.

Red Tides

Considering the high fertility of the rias, one wonders

whether excessive blooms of certain dinoflagellates

would not, once in a while, render the mussels dangerous to consumers. However, such phenomena are rare.

Nevertheless, Spanish biologists watch continuously to

determine if a dinoflagellate bloom is present in the

rias. The Department of Health also constantly screens

mussels from different rias to determine whether they

have PSP (paralytic shellfish poison) or DSP (diarrhetic

shellfish poison). If either condition is detected, the

entire ria or section of it is immediately closed to harvesting of all mollusks that grow there.

Distribution and Marketing

The growers take the mussels in their boats directly to

the depuration plants or to canning factories. There

are two mussel markets in the region: The fresh market

before depuration and the processed market. Larger

quantities of mussels are marketed fresh, but the canning market has grown since 1984 (Tables 2, 3). The

mechanization of handling is minimal, to reduce damage to mussel shells and thereby enhance the shelf life

of the mussels during transportation. In the warm season, refrigerated trucks are used to transport the musTable 2

Marketing of fresh mussels from 1984 to 1989 (MAR,

1991).

Amount marketed (t)

Year National Export Totals

1984 70,000 22,000 92,000

1985 75,000 21,000 96,000

1986 76,500 19,000 95,500

1987 85,000 24,000 109,000

1988 70,000 28,000 98,000

1989 68,000 27,000 95,000
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 175

Table 3

Marketing of mussels in the canning industry from

1984 to 1989 (MAR, 1991).

Amount marketed (t)

Year National Export Totals

]984 28,000 3,800 31.800

]985 36,200 4,600 40,800

1986 47,000 4,200 51,200

]987 56,500 4,300 60,800

1988 63,000 5,100 68,100

1989 69,000 6,000 75,000

sels. Ice bars are held with the mussels on the longer

trips to maintain a high humidity. Sometimes, mussels

for the Spanish market are transported by train. The

farmer sells the mussels to the depuration station. The

station sells the mussels to central markets, from which

they are sold to restaurants and consumers. The remaining mussels are sent to markets outside Spain

(Nunez and Castro, 1990).

The processed market deals with mussel meat, which

can be processed for cannery, demiconserve, and freezing. The mussels that go directly to the canneries are

those having the poorest quality and size (Nunez and

Castro, 1990). They are prepared by frying or boiling

and then covered with various sauces. They can be

served in many ways. The cans (about 115 g) are sealed,

cooked (sterilized) in an autoclave, labeled, and packed

in shipping cases for worldwide distribution. The marketing of canned mussels more than doubled from

1984 to 1989 (Table 3).

Mussel markets have been changing. At the beginning of mussel farming in Spain, mussel consumption

was limited, but today national consumption is more

than 100,000 t, mainly as fresh mussels (MAR, 1991). In

1984 the distribution of mussels was 40% for the fresh

market (76% of these for the local market and 24% for

export), 50% for canning (the quantity of canned mussels consumed in the home market was 89% and the

remaining 11 % was exported), and 10% for freezing.

In recent years, about 60% of mussels have been for the

fresh market and 40% for canning. The frozen portion

has been increasing and is estimated at 15,000 t per

year (MAR, 1991). Exports are mainly to Italy, France,

and Germany.

Costs and Prices

According to Andreu (1976), the cost of a floating raft

is governed by its size and the materials used. In 1948 a

single raft with all the equipment including 800 ropes

cost around 83,000 pesetas (P125 = US$I). In 1958 its

cost reached P250,000; of this, P150,000 were for carpentry, P21,000 for the chain and anchorage, P65,000

for the spart grass ropes, and P14,000 for the boat and

incidentals. In 1976 the cost was from Pl,500,000 to

P2,000,000 (Figueras, 1976), and currently their cost,

considering the equipment, is about PI5,000,000.

The price of the fresh mussels in 1951 was P2.0-2.5/

kg and, in 1958, P3.5-3.75/kg (Veiga, 1958). In 1976

the price directly from the rafts was from 7.5 to 9.1

pesetas per kg, and in the first sale the price reached

15-20 pesetas per kg. The price for the consumer was

about P30/kg (Andreu, 1976). Currently, the price for

the consumer is around PI80/kg. These prices are very

low when compared with prices for other kinds ofshellfish or meat. The profits for a family has been calculated at about 25% oftheir total production sold (MAR,

1991) .

Future of the Fishery

During the past 45 years, Spain's mussel production has

become the second highest in the world. However,

several biological, technological, and socioeconomic

factors must be considered and studied to maintain

and increase the production.

In the past few years, there has not been a substantial

increase in the number of rafts and, while the sizes of

rafts and rope size have grown, total production of

mussels has not grown. Thus a production limit is approaching and probably the number ofrafts should be

controlled (Porta, 1984). To increase production, new

suitable areas must be found. The loss occurring from

predation by starfish, crabs, and fishes is not substantial, and the parasites, Mytilicola intestinalis (copepod)

and Marteilia sp. (protozoa), have not really affected

mussel production. Nevertheless, a permanent program

is needed to study mussel mortalities, prevalences and

incidences of parasites, and condition index. Transplants of mussels without assurance that they are healthy

should not be made. A special program is needed for

the maintenance of the water quality, because an increase in pollution of the water could not only increase

the prevalence of parasites but also the levels of toxic

substances such as heavy metals. In this sense, the control program of red tides must go on, and it is important to evaluate the impact of mussel culture on the

environment and on other commercial species.

To regulate and control the use of seed for culture,

information is needed on distribution and collection of

mussel larvae, availability of seed, and such related

information as places where larvae set, amount ofseed

available, and effect of the gathering on the natural
176 NOAA Technical Report NMFS 129

populations and their recuperative capacities. Mussel

production can be affected by low salinity, which kills

mussels on the upper 0.5-1 m of the ropes, and by

winter storms which can damage and even sink the rafts

(Lutz et al., 1991). These problems can be reduced by

continuous monitoring of water salinity and with the

use of better rafts.

Mussel culture could be improved with the use of

new materials for raft construction including floats and

ropes, design of sinkable rafts that will permit the culture in rough waters while increasing the culture surface (Figueras and Figueras, 1990), improving the system which prevents mussel clusters from sliding down

the ropes, and better machinery for harvesting, transporting, and processing. However, any technological

improvement must take into account the total value to

the fishermen in the region, because one ofthe reascns

mussel culture is successful is the low operational cost

due to use of many family members. With high mechanization, much employment will be lost. On the other

hand, Spanish participation in the EEC will promote an

additional pressure for changes in socioeconomic structure. Heretofore, the marketing structure has not allowed

families to set prices. Only through a better group organization would it be possible to change this marketstructure

and give families more control of market prices.

Oyster Fishery

Production of the flat oyster, Ostrea eduiis, in Spain is

limited. Fishermen land only about 500 t a year (Xunta

de Galicia, 1990a). They obtain oysters mainly from rias

in the Galician region through the culture or maintenance of imported stocks in rafts (Gabin et al., 1990).

The old natural oyster beds have been depleted. Some

residual natural populations occur in some parts of the

rias of Arosa, Vigo, Pontevedra, Ortigueira. and near

San Cibran in the North of Galicia (Fig. 1).

Habitat Description

The natural habitat of flat oysters is subtidal; few gww

intertidally. They prefer clean waters that are rich in

oxygen and have weak currents. Their larvae require

hard substrata such as shells for settlement. Optimum

temperatures are from 15° to 20°C and salinities above

26%0 (Bardach et al., 1972; Xunta de Galicia. 1990a).

Natural conditions in the rias were ideal for large oyster

populations, but the massive mining of shells to supply

the animal food industry degraded the beds (Andreu

and Figueras, 1966). In addition, reduction in water

quality in coastal areas due to urban, seaport, and industrial developmen t adversely affected the natural oysreT habitats (Paw, 1987). On the other hand, water

quality and conditions for suspended culture is adequate, and today the culture or growing of oysters is

c<lrried out on floating rafts.

Associated Species and Predators

Several species are associated with oysters, including

algae. Viva sp. and Enteromorpha sp.; ascidians, Phallusia

rnamillata and Ascidiella aspersa; other bivalves such as

Anomia ephippium, and the tube worms, Pomatoceros

lriqueter and Poiydora sp., that produce extensive damage to oyster shells. The most important predators are

the starfish, Marthasterias glacialis, A. rubens, and Asterina

gibbosa, and the gastropod Nassa sp. (Garcia del Cid,

1954). The blue mussel is another associate, and its

culture has had a negative influence on oyster production. According to Andreu (1973), mussel culture negatively affects oysters by 1) softening the bottom, 2)

filtering great quantities of oyster larvae, and 3) reducing the water circulation in rias that helps to cleanse

the bottom. Heretofore, the most important enemies

for oyster culture have been the protozoan parasites

Marteilia refrigens and Bonamia ostreae. They have been

associated with the largest mortalities that have occurred in cultured populations in Spain and the rest of

Europe (Figueras, 1991).

History of the Fishery

The first evidence of eating oysters in Spain comes

from the earliest natives of the Galician region called

"Castrenos," who left large deposits of oyster shells, or

"concheiros," in the fourth century B.C. (De La Penal).

These "concheiros" also appeared in the first century

A.D. near the Roman villages (DEMARSA, 1965). According to Ferreira (1988), in the 10th century, it was

documented that a noble family donated properties,

which included "ostrarias" (name of the oyster beds in

those times), to the ecclesiastical authorities. The same

author noted that in the 13th century, oysters were

consumed fresh in cities and monasteries, and the oyster fishermen or "farmers" were called "ostreiros." In

the 16th century, oysters were consumed in sauces.

According to Gondar (1983), in that century, the miter

of Compostela, in the Galician region, regulated oyster

harvests to obtain a continuous supply of them for his

court. By this time. some villages of the Galician rias

exported oysters and other shellfish to the Kingdom of

Castilla in the cen ter ofthe peninsula and to Asturias in

the north of Spain. Through the 18th century, in the

ria de Vigo. the natural oyster populations were heavily

fished to supply the monarchy. In 1706, near Carril in
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 177

the ria de Arosa, ships were chartered to take oysters to

other areas of Spain (Ferreira, 1988). According to

Andreu and Arte (1955), the ordinances of the

Pontevedra Province in 1768 referenced the existence

of abundant natural oyster beds in the rias of Arosa,

Pontevedra, and Vigo. By this time, Cornide (1778)

stated the heavy fishing on the natural oyster populations could deplete them. However, the exploitation

continued without controls. Labrada (1804), in his economic description ofthe Galician Kingdom, mentioned

that the Carril village women sold shellfish collected by

the men in the city ofSantiago and the village ofPadron.

According to Andreu (1962), the fishing in the middle

of the 19th century became more intense, and from

1869 to 1870, Paz Graells, an oyster specialist, first reviewed the oyster fishery in the north and northeast of

Spain, where the most important natural oyster production areas were. He reported a large decline in the

natural beds. The situation was associated with the supplying of oyster stocks to restore the French oyster

industry in the middle of the 19th century (Andreu,

1962; Madariaga de la Campa, 1969). The view by Graells

led to the Central Commission of Fishing establishing

two oyster parks in 1874, importing oysters from France,

and using French technology. The results were negative, however, in part because the localities selected for

the culture installations were poor and, as a result, both

parks were closed in 1884 (Andreu, 1962).

The success of oyster culture in France and the adequate natural conditions for oyster culture in Spain

encouraged private investors to try oyster culture

(Andreu, 1962). Dean (1893) related that oyster culture in Santander (north of the Iberian Peninsula)

used cages, which were arranged in rows in a sheltered

part ofthe harbor. These cages were elevated about 1 m

above the bottom and were rarely exposed even at low

tide. These early trials were abandoned because the salinity was too high and there were no natural oyster beds.

Fishing the existing natural beds continued, and they

further declined. For example, near San Simon in the

ria de Vigo, around 30 million oysters were harvested in

1935, while only 10 years later only 7 million were

harvested, and after 1952 the bed had been practically

depleted (Andreu, 1962). According to Madariaga de

la Campa (1969), in 1922, nearly 3.5 million oyster seed

were imported from France for grow out. However,

interruptions in oyster seed importation, the Spanish

civil war, and the subsequent prohibition of oyster seed

exports from France preven ted success. From 1953 to

1959, Sanchez (1936,1944,1951, 1952,1954) conducted

trials to obtain oyster spat on artificial collectors, and

the Instituto de Investigaciones Pesqueras (CSIC) also

carried out studies from 1953 to 1959 to protect and

reestablish natural oyster beds in the Galician Region.

However, the difficulty of obtaining oyster seed from

the natural beds, and problems with local shellfishermen

led to the failure of these projects (Andreu, 1962).

By the 1960's, natural populations of oysters were so

small that oyster fishing was unprofitable (Pazo, 1987).

At that time, several attempts were made to restore the

remaining natural oyster beds. They featured installing

several collectors similar to those used in Britanny,

France, in an experimental park near Villajuan in the

ria de Arosa (roofing tiles were secured by a central

pole) (Andreu, 1960, 1965a,b; Andreu and Figueras,

1968; Figueras and Andreu, 1968).

At the beginning of the 1970's, one park for oyster

culture was established in the ria of Ortigueira. The

oysters were maintained in cases (Fig. 10), and tile roof

collectors (Fig. 11) were used to collect oyster spat. In

1980 the park had about 20 t as brood stock, but afterward only around 8 t (Guerra, 1985). The reduction

was caused by high mortalities attributed to the parasite

Bonamia ostrae. In 1979 a hatchery for the semi-indusrial

production of oyster and clams seed was constructed.

In 1981 oysters from this hatchery were distributed to

various localities in the Galician rias, and their growth

was monitored (Guerra, 1985). Currently, the operation continues, and the results are promising but the

supply ofseed is small, and the parasites Mortellia refrigens

and B. ostreae are present. By the end of the 1970's and

beginning of the 1980's, about 300 rafts were used for

oyster culture; they held from 70 to 100 million oysters

which came as seed mainly from French Britanny. However, high mortalities were observed, and, between 1975

and 1976, about 70% of the oysters in the Galician

region were lost (Pardellas, 1982). Consequently, in

1981, the importation of seed from France was prohibited (Perez Camacho and Roman, 1985). By 1987 the

number ofrafts for oyster culture had decreased to 137.

Now the culture activities have been reduced to growing imported oysters from medium size or temporarily

storing commercial sized imported oysters for immediate marketing. Research continues on the natural collection of oyster seed and its production in hatcheries.

Several authors have tried to explain the failure in

the growth of oyster culture in the region during the

past century. One was Dean (1893), who stated that

Spain's long coastline permitted the local demand to

be satisfied without need of artificial methods. In addition, the difficulty of transporting oysters into the interior of the country discouraged the development of

regions where culture could otherwise have become

profitable. On the other hand, Figueras (1970) stated

that one possible explanation for the failure of oyster

culture in Spain was that the flat oyster had never been

a popular food in Spain and he pointed out that "in the

Louvre Museum can be seen only one picture by the

Spanish painter Nunez de Villavicencio (1600-1700)

"Los comedores de mejillon" (,mussel eaters'), but there
178 NOAA Technical Report NMFS 129

are many paintings of the French school in which oysters appear."

Culture

As noted, the establishment and growth of oyster culture

has been minimal. The first trials consisted ofthe adaptation of French culture technology without success. Afterward, floating rafts like those used for mussel culture,

were used for oyster culture. The method consisted of the

manual attachment of medium-sized oysters (around 5

cm) to ropes (1 cm diameter) with cement (Fig. 12).

Women workers attached two or three oysters every 10-15

cm (Figueras. 1970; Perez Camacho and Roman, 1985).

During an 8-hour day, 12 women could handle 800- 1,000

kg of oysters (20-30 units depending on their size). Workers hung the ropes from rafts and periodically raised them

Figure 10

Oyster culture cases in a Galician intertidal area in the 1970's.

Figure 11

Roof tile collectors for oyster seed in the Galician intertidal area in the 1970's.
_________ Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 179

to clean the oysters of seaweeds and mussel seed. They

harvested the oysters when they attained commercial size

of 8 cm after 9 or 10 months (Figueras, 1970).

Currently, relatively few oysters are hung from ropes.

Instead most are grown in plastic baskets hung from

the rafts. As they grow, the oysters are thinned out.

Farmers harvest them when they attain commercial size

and take them to depuration stations. All the seed and

the medium-sized oysters used are imported from Italy,

Greece, Egypt, England, and other countries.

Seed Collection

Government institutions (Conselleria de Agricultura

Pesca y Alimentacion), such as the Ribadeo station,

locally called "park" in the ria ofthe same name, collect

natural oyster seed. They use the French method of

roof tiles covered with a layer of lime. The lime layer

makes it easy to remove oysters when 2-4 cm long

(about 6-8 months after setting). Each collector usually

consists of 8 roof tiles held together with a cen tral wood

pole. Its height is about 1.25 m, and, to avoid predators

of seed oysters and the accumulation of sediment, the

first tile is about 20 cm above the bottom. The collectors are distributed over an intertidal area covering

about 4,000 m2 in straight lines. This institution also

conducts trials, using plastic materials for seed collection. Imported seed stocks from Italy, Greece, and other

parts of the world have been used. The larvae are fed

until they reach metamorphosis and then are placed

with plastic collectors (PVC) on which they settle. When

the oysters reach 5-10 mm in length, they are taken to the

rafts to grow (Guerra, 1985, Xunta de Galicia, 1990a).

Harvesting

Fishermen used to gather oysters from natural beds by

hand and with hand dredges. Some years ago, a special

dredge made ofsteel was designed. Locally called a "rastro,"

it was shaped like a rectangle (1.25 x 0.3 m) and provided

with teeth on its lower bar. The dredge scraped across the

bottom surface and had a net bag (2.0 x 1.25m) to hold

the oysters. It was towed from a boat powered by a motor

at least 50 hp in size (Arnaiz and De Coo, 1977). Currently, all the oysters are obtained from the rafts as oystering on the remaining natural beds is prohibited.

Regulations

As noted above, the first records describing regulations

for harvesting oysters are from the 16th century

(Gondar, 1983). Around 1923 and in 1935 other regulations appeared, but without success (Navaz y Sanz,

Figure 12

Ropes with attached oysters for the Galician area floating rafts in the 1970's.
180 NOAA Technical Report NMFS 129

1942). In 1981, oyster imports from France were prohibited because of the diseases there. The modern regulation of the oyster fishery was not approved un til 1964.

It established that all fishermen and fish farmers needed

a license to market mollusks, and that all bivalve mollusks gathered from natural beds and those reared in

rafts or hatcheries must be purified in an authorized

depuration station before sale. The regulation for molluscan depuration was modified in 1970 and 1985, adding specifications on the use of an official sanitary label

to obtain a better control for the market (SOMEGA,

1975; Tecnologia Ambiental, 1991). In 1984 a regional

regulation about inspection of fishing, collection of

shellfishes, and aquaculture were approved. In 1989 the

regulation on water quality for molluscan culture was

established. Other regulations to prevent the sale of mollusks contaminated with biotoxins were approved in 1986

and 1987, and in 1990 areas to place rafts in the Galician

region were established to control the effects ofbiotoxins.

Socioeconomic Aspects

One of the main factors causing the disappearance of

natural oyster beds was continuous harvesting without

any action to enhance abundance or to protect the

environment. This situation has been associated with

poor education of fishermen, called "mariscadores,"

who gather oysters (PalO, 1987). A related problem is

the diversity of types of people who gather oysters.

These include people who usually fish for sardines,

cephalopods, crustaceans, and other fishes; farmers and

fishermen's wives or family, and industrial workers. They

work only part time gathering bivalves. As this activity is

considered only a sideline, they are less concerned

about conserving the resource. Intermediaries, who are

unrelated to fishing or marine farming, control the

market prices. Both situations favor negative actions or

responses in the fishery, such as taking mollusks during

the closed season, taking undersized mollusks, and keeping the shellfishermen poor (Gonzalez, 1980).

Depuration

Oysters, like other bivalve mollusks destined for the

fresh market, must be depurated. They are put in cases

in depuration tanks that are filled with chlorinated

water. The maximum weight/m2 authorized is 30 kg,

and the depuration period is at least 42 hours. The

oysters are then packed in wood or plastic cases in

quantities of 12,25,50, and 100 individuals. Each package has an authorized label, on which the depuration

date and the shelflife of 5 days are printed. The oysters,

chilled on ice, are trucked to market.

Market

All the oysters are shipped to local markets and large

Spanish cities, mainly Madrid and Barcelona, where

they are distributed to supermarkets, hotels, and restaurants. The oysters are maintained in temperatures

from 3° to lO°e. They are usually consumed fresh and

eaten on the half-shell (Pardelias, 1982)

Future of Fishery

The protozoan parasites M. refrigens and B. ostreae constitute a major problem for European flat oyster culture

(Montes, 1991; Figueras, 1991). France, the largest oyster producer, has introduced culture of the Japanese

oyster, Crassostrea gigas, which is not susceptible to these

parasites. Currently, their oyster production is mainly

of this species, and production of flat oysters is small.

Spain has tried to prevent the introduction of these

parasites by limiting the culture of imported stocks.

Any projection of the future of oystering in Spain must

address the following points:

1) Protection of the remaining natural oysters and

oyster beds and the quality of their environment (bottom and water),

2) Improvement of techniques for collecting natural

seed and growing it in protected areas,

3) Improvement of hatchery and nursery techniques

to obtain native oysters for repopulation of the natural

oyster beds,

4) Culturing of oysters in areas free of M. refrigens

and B. ostreae,

5) Continued studies of adaptation ofimported stocks

(free of parasites) in favorable areas in the Galician

region,

6) Research studies to control B. ostreaeand M. refrigens

present in flat oysters,

7) Prevention of introduction of oysters or any other

mollusks unless they are guaranteed to be free of parasites,

8) Establishment of a genetic improvement program

for oysters,

9) Establishment of training programs for oyster fishermen and culturists, and

10) Improved culture technology through use of new

materials and modalities in areas where the incidence

of parasites is minimal.

Currently,Japanese oyster stocks have been imported,

and their adaptation to the natural conditions in the

Galician region is under study. These studies must go

on, but with special care in all aspects related to the

introduction of parasites and diseases. Finally, a balance should be established between the collection and

culture ofmollusks in the Galicia region, which permits

their protection, restoration, and use.
_________ Caceres-Martinez &: Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 181

Cockle Fishery

The cockle, Cerastoderma edule, is harvested mainly from

natural beds; there is little culture of them. Current

production is about 1,300 t per year (Xunta de Galicia,

1990b), about 90% of which is from the Galician bays

(Aguirre, 1973). The cockle is locally known as

"berberecho" or "croque" and is valued for its fast

growth, capacity to survive in changing environments,

and its economic value.

Habitat Description

The natural habitat of the cockle is sandy beaches or

sandy and muddy bottoms (Figueras, 1956), at depths

up to 10m (Ramonell, 1985). The euryhaline character

of cockles permits their distribution in river mouths

and estuaries (Fig. 1).

Associated Species and Predators

Several species of bivalve mollusks occur in cockle beds,

especially Scrobicularia plana, Venerupis pullastra, V.

decussata, and Loripes lacteus. The main predators of

cockles are the crab, C. maenas; starfish, Asteria rubens;

and flatfish, Solea sp.

History of the Fishery

The first records describing cockle fishing also describe

associated fishing for oysters. In the 16th century, people

from Portugal and other areas came to the ria de Arosa

near Cambados to gather oysters, mussels, clams, and

cockles (Ferreira, 1988). Since then, mollusk fishing in

the Galician region has been mainly for flat oysters, but

possibly, during the years of heavy fishing for oysters,

cockles and other bivalves may have been gathered.

Until the beginning of the present century, no specific

references on the abundant cockle and clam beds in

the rias of Galicia appeared (Gutierrez de Velasco,

1964). Since then, some quantitative data about cockles

have been published. In the ria de Pontevedra their

density reached 7,500 individuals per m2 (Lozano, 1948),

while in the ria de Muros y Noya their density reached

2,250 (Gutierrez de Velasco, 1964). Fishermen sold the

cockles to canneries. In 1949, in the ria de Vigo, cockle

production was around 3,200 t, but it declined after

that (Figueras, 1956). During 1955, a substantial mortality of bivalve mollusks, including cockles, was associated with heavy rains (Figueras, 1957). Until this year,

most cockle production was from the rias de Vigo, Arosa,

and Muros y Noya. From 1962 to 1964, the highest production was from the rias de Muros y Noya and totalled

about 3,800 tin 1963 (Gutierrez de Velasco, 1964).

Commercial cockle production obtained in the rias

and processed by the cannery factories of Arosa and

Muros y Noya from 1945 to 1963 ranged from 200 to

5,307 t (Table 4) (Gutierrez de Velasco, 1964). Cockle

production in the ria de Muros y Noya was around

2,500 t in the 1970's but, by the beginning of the 1980's,

production decreased to less than 1,000 t (Quiroga et aI.,

1980). These data show that cockles can be overfished if

their resource is not managed. Production from 1985 to

1988 in all the Galician region increased from 359 to

1,687 t (IUEDG, 1990), but if one looks at only production in the ria de Muros y Noya in the 1970's, production

actually declined (Xunta de Galicia, 1990b). Thus the

history ofthe cockle fishery has followed the same pattern

of other mollusks in the region, i.e., a large reduction in

supply from heavy fishing and an uncertain future.

Harvesting

Fishermen collect cockles in two ways: By boat or by

walking on the beaches at low tide and feeling for them

with their hands or with rudimentary shovels, which are

modified agriculture implements (Gutierrez de Velasco,

1964) .

Shovel types include the "sacho," a short curved triangular shovel which has a blade 16 x 24 em and a

handle about 90 em long; the "legon," which is similar

to the first but flat for more efficiency; the "sacha," a

rectangular flat shovel 20 x 15 em, with 35 em handle;

the "rastrillo," a typical rake (usually for agricultural

use), 20 em wide, and with a large handle; the "rastro,"

one of the common tools, a triangular structure of 1 m

x 75 em wide, with teeth on its bottom edge that support a net bag, to hold the cockles; "gancha," a metal

rake with short teeth; and, finally, the "rano," a rake

with large teeth. The walking collection of cockles has

been done mainly by women. Around 1964, each harTable 4

Commercial production ofcockles from rias, processed

by the canneries of Arosa, Muros, and Noya from 1945

to 1963 (Gutierrez, 1964).

Year Production (t) Year Production (t)

1945 200 1958 4,058

1953 499 1959 1,697

1954 1,887 1960 1,492

1955 282 1961 2,983

1956 909 1962 5,307

1957 1,614 1963 2,940
182 NOAA Technical Report NMFS 129 _

vester or "mariscador" obtained about 50 kg of cockles

of commercial size in a day.

The other collection method, using a boat with or

without a motor, is done at high tide or in subtidal

areas (Fig. 13). "Rastros," "ranos," and "ganchas" are

towed from the boats (Arnaiz and De Coo, 1977). Each

boat fisherman can gather 100-150 kg of cockles a day

(Gutierrez de Velasco, 1964). Currently, cockle fishing is

still done mainly by women, and the tools used are the

same as in early times (Figs. 14, 15, and 16).

Culture Methods

The first culturing of cockles was carried out in protected areas with clean, fine sand, which were called

"parks." The seed was collected from natural beds, taken

to the parks, and distributed at densities up to 400

individuals/m2. Periodically, it was necessary to clean

the parks of crabs and mud. The seed, growing individuals, and adults are distributed in different areas of

the park. Average cockle production is about 2 kg/m2•

Social Aspects and Regulation

The great increase in mollusk harvests which intensified at the beginning of this century, led to exhaustion

of the oyster beds, the improvement of collection tools,

the rise in the demand for other bivalve mollusks as

foods, and growth of the cannery industry (IUEDG,

1989). The composition ofthe fishermen was diverse as

it included temporary workers from farming, fishermen's

wives ur family, and industry. This favored unmanaged

exploitation, and the cannery industry, depuration stations, and intermediaries controlled the market, favoring

dependence of fishermen on them and limiting their

profits. According to Gutierrez de Velasco (1964), the

uncontrolled collection of cockles occasionally saturated

the market, which limited harvests and lowered prices. In

1959 a glutted market forced the fishermen to return

cockles to the beds. In addition, confrontations between

walking harvesters and boat harvesters were frequent, because boat harvests were more efficient and larger, producing larger incomes for boat fishermen.

To organize the fishery, fishermen's associations,

called "Cofradias de Pescadores," were established in

the 1940's in an attempt to regulate fishing by limiting

the quantities of cockles collected by each fisherman.

However, many new harvesters increased the problems

of distributing the resource equally. Finally, a harvester

license, called a "camet de mariscador," was required.

It was issued only to fisherman and their families, and

to poor people designated by the local government

(Gutierrez de Velasco, 1964). In 1964 the regulation

defining mollusk quality and purity was approved. It

Figure 13

Cockle harvest boats at the pier in the ria de Vigo in the 1970·s.
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 183

Figure 14

A woman collecting cockles with the "rastrillo" in a park culture of cockles and clams in

Carril (ria de Arosa).

Figure 15

A man with a "legon" that will be used to remove the sand and to collect cockles and clams

in Carril (ria de Arosa).
184 NOAA Technical Report NMFS 129

Figure 16

"Gancha" implement used to collect cockles from the boats. Rianxo, ria de Arosa.

also controls the distribution of harvester licenses. Other

regulations were approved later, as mentioned in the

sections on mussel and oyster fisheries. Currently, the

open season for cockle fishing is from March to October, and the minimum size allowed is 25 mm.

Market

As with all the bivalve mollusks consumed raw in Spain,

it is necessary to depurate cockles before they are sold

(Fig. 17). After a depuration period of 42 hours, cockles are packed in plastic net bags and sold to local

supermarkets, popular markets, restaurants, and hotels. Some are also sent to markets in the large cities,

such as Madrid and Barcelona (Fig. 18). However, most

cockles are canned. Around 1942, the cockle was exported to South America, and was called "oyster B"

(Navaz y Sanz, 1942).

Future of the Fishery

Since the increase in fishing for cockles at the beginning of this century, the harvesting gear, methods, and

social structure of the harvesters (mariscadores) has

scarcely changed. However, the decline in abundance

of the cockles and the integration of Spain into the

European Economic Community (EEC) will require

modernization of the fishery. Improvements in the

fishermen's association and fishing regulations will help

to train the fishermen and control prices. Fishing gear

and resource conservation must also improve. Aquaculture technology must improve through the creation of

large production parks and the development of new

technologies and tools. In the future, the construction

of hatcheries and nurseries will be necessary. In addition, maintenance of clean water is imperative, so the

cockles are not threatened by pathogens and contaminants. The European tendency is to control water quality for all the fishing and aquaculture activities, more

than to create and operate depuration stations. Studies

are also needed on cockle biology including reproduction, genetic improvement, population dynamics, and

pathology.

Clam Fishery

The clam fishery in Spain targets three main species:

Tapes decussata, locally known as "almeja fina"; Venerupis

pullastra, called "almeja babosa"; and V. rhomboideus,

called "almeja rubia." Their total production has been

estimated at 2,000 t (Xunta de Galicia, 1990c). All

come from harvests of natural beds in the Galician bays.

Other production areas are Cadiz and Huelva in the
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 185

Figure 17

Cockles, loose and in bags, before transportation to a depuration station.

Figure 18

Trucks used to transport cockles and clams in the 1970's.
186 NOAA Technical Report NMFS 129 _

Culture Methods

Harvesting

Some Galician areas have protected bottoms called

"parks" for the extensive culture of clams (Fig. 19).

Table 5

Production of clams in the ria de Vigo from 1927 to

1953 (Alvarez, 1960).

386

653

81

Year Production (t)

1943

1948

1953

153

29

87

Year Production (t)

1927

1933

1938

In the Galician region, fishermen harvest clams either

by walking the intertidal areas and using special hand

shovels or from boats. The capacity of the small boats is

about 1 t, while the large boats range up to 12 t. Some

are propelled with oars or outboard motors (Quiroga

et aI., 1980). Various collection tools are used, including the "rastro" and the "rano" (Arnaiz and De Coo,

1977). The closed season is from March to October,

and the minimum size allowed for T. decussata and V.

rhomboideus is 30 mm, while for V pullastra it is 25 mm.

Vigo ranged from 28,719 to 652,890 kg (Table 5).

Around 1956, clam production in the Galician region

was about 60% of national production (Alvarez, 1960).

At that time, 250 boats fished for bivalves near San

Simon in the ria de Vigo; each harvested from 10 to 12

kg of V pullastra per day (2,500 kg in all). The season

was from October to March. In areas nearest to the

mouth of the bay about 60 boats obtained 3,000 kg per

day. These differences were associated with the great

mortality that occurred in the inner part of the ria de

Vigo, due to heavy rains that produced a rapid drop in

salinity (Figueras, 1956). In the ensuing years, clam production has been variable, and statistical data on total

production is sparse. In the ria de Noya, production rose

from 1965 to 1969, later declined, and increased again in

1974, 1979, and 1980. However, the steady fishing of the

natural populations led to a reduction in natural populations, a diversification of the species collected to include

V rhomboideus, and a search of new collecting areas. From

1985 to 1986, production of the clams V pullastra and V

rhomboideus was around 1,700 t. Production of T. deccusata

was reduced, showing the effect of the intensive exploitation (Fernandez and Pardellas, 1986). Currently, production is about 2,000 t.

The 16th century records of mollusk fishing and consumption are mainly about the flat oyster and only

rarely about clams, but they do mention the marketing

of clams in Portugal and other places (Ferreira, 1988).

According to Navaz y Sanz (1942), the beginning of the

intensive fishing for clams was in 1926 and 1927. Digging was indiscriminate as fishermen used prohibited

tools and took clams of all sizes. Near San Simon, in the

ria de Vigo, fishermen found one natural clam population and depleted it in a short time. The fishermen sold

cases of clams weighing 54 kg for only 5 pesetas. Later,

when competition increased, the price was 30 pesetas.

In 1935 clam fishing was regulated and the quantity of

clams each fisherman was allowed to take during each

low tide was 14 kg, and the season was closed from May

to October. Then, near San Simon, there were 6,130

walking harvesters and 1,480 others using boats.

Despite the large clam harvests, their repopulation is

rapid. Lozano (1948) pointed out that populations of

T. decussata and V pullastra in the ria del Burgo recovered in less than a year from 1-5 to 30-50 clams per m2•

Production of clams from 1927 to 1953 in the ria de

History of the Fishery

Other bivalves growing with the three clams are Venerupis

aurea, Diosinia exoleta, and Tellina incarnata. Their main

predators are the crab, C. maenas; the starfishes A. rubens

and M. glacialis; gastropods, Natica sp.; and birds, Larus

sp. (Vilela, 1950; Aguirre, 1973; Campos and Saavedra,

1990). An individual C. maenas (6.5 cm width) can

consume 5-6 clams per day (Campos and Saavedra,

1990). Recently, protozoan Perkinsus-like infections

have been found in T. decussata in the ria de Vigo

(Robledo et aI., 1992).

Habitat

south ofSpain. T. semidecussatais produced in Andalucia.

Currently, there are few aquaculture activities of any

size. All the clams are valued in the region, and V

pullastra is considered as a traditional food.

Clams live on the sandy beaches of the rias. T. decussata

is buried in the sand from 15-20 cm from the middle of

the intertidal zone to a depth of a few meters. V. pullastra

lives in sand, gravel, or mud bottoms, usually from the

low tide mark to a depth of 40 m. V. rhomboideus is found

from the intertidal zone to a depth of 200 m (Navaz y

Sanz, 1942; Vilela, 1950; Ramonell, 1985).

Associated Species and Predators
Caceres-Martinez & Figueras: The Mussel, Oyster, Clam, and Pectinid Fisheries of Spain 187

Figure 19

A park for culturing clams in Carril (ria de Arosa) in the 1970's.

Farmers obtain seed from their own parks or from the

natural clam populations in the spring. They dig the

clam seed with sand using a small shovel, pass it through

a sieve to retain the seed, take it to their parks, and

spread it in densities of about 800 clams per m2. They

can also dig adult clams from seaport areas and spread

them in their parks. Periodically, they have to clean

their parks of predators and mud. In 1987 the Japanese

clam, Venerupis semidecussata, was introduced, and several trials have been made growing them in plastic

baskets hung on floating rafts and burying the clams in

the sand of protected parks, to study their adaptation to

the environmental conditions in the rias (Guerra et al.,

1990). Near Ribadeo, there is one hatchery for the

semi-industrial production of T. decussata. It produces

seed which is transferred to protected parks for growth.

Depuration and Marketing

Fishermen bring their clams to the depuration stations

where they are held in pools for at least 42 hours. The

clams are then packed in net bags of 0.5, 1, and 2 kg,

and are destined to be canned or eaten fresh. They are

sold in local supermarkets, popular markets, hotels,

and restaurants, including those in Madrid and

Barcelona. They are transported by refrigerated trucks

that maintain temperatures of 3°-10°C; the clams have

a shelf life of 5 days. Prices vary according to their

abundance in the market. However, as an approximation, in 1985 the price was about P99/kg. Currently, the

price for fresh clams is about P2,OOO/kg for T. decussata,

P1,200/kg for V. pullastra, and P900 kg for V. rhomboideus. Canned clams are prepared with vinegar and various sauces. In the Galician region, the most popular

meal with clams is "ameixas a marineira" (clams in

mariner sauce). The clams are open in salted water and

cooked with a special sauce (onions, garlic, parsley,

bread rind, and white wine).

Future of the Fishery

The history ofshellfishing in the Galician region shows

that the mollusks were improperly managed. First one

species was depleted and then another. First to be depleted was the oyster; after that the digging of cockles

and clams began, and as T. decussata became scarcer,

the digging of V. rhomboideus began. Currently, the populations of the other commercial bivalves are declining.

Besides heavy fishing, clams declined because pollution

increased and the seaports and urban areas grew, degrading the clams' habitat. The future ofthe molluscan fisheries in the Galician bays must be planned as an integral

reorganization program to include the following aspects:

1) Reorganization of the harvesters and the market

structure to improve the responsibility and profits of

the fishermen,
188 NOAA Technical Report NMFS 129

2) Creation of protected areas for the recovery and

growth of the natural populations,

3) Creation of a general program for treatment of

wastewater from the urban and industrial areas,

4) Establishmentofa permanent project on the population dynamics of the clams, and biological studies,

especially, to improve genetics,

5) Development of new aquaculture technology for

the hatchery, nursery, and grow-out phases,

6) Diffusion of a popular program for the protection

and consumption of bivalve mollusks,

7) Incorporation of the European technology for

these fisheries, and

8) Creation of a special research program on clam

pathology.

Pectinid Fishery

Three major species are of commercial importance in

Spain: Pecten maximus, called "vieira"; Chlamys varia,

called "zamburina"; and Chlamys opercularis, called

"volandeira." Historically, P. maximus has represented

the Christian symbol of the travel of the apostle St.

James through Spain, and this symbol is in all the

churches of the Galician region. When oyster production at the beginning of the 20th century declined, the

pectinids were gathered as an oyster substitute, and

their populations were substantially reduced (Navaz y

Sanz, 1942). The pectinids are fished in the mouth of

the rias where the main natural beds are (Fig. 1). Currently, harvests are regulated; the closed season is from

March to October and the minimum sizes allowed for

P. maximus is 10 em, and 4 em for both Chlamys species.

Their production is relatively small; during 1986 production of P. maximus was 44,497 kg (IUEDG, 1989).

Fishermen use the same implements to gather them as

they use for clams and cockles.

Currently, P. maximus is cultured on a small scale in

the Galician region by attaching small ones (10 em) to

ropes in floating rafts. Farmers obtain the small scallops

from the natural beds and attach about 150 scallops to

each rope.

The future of this fishery will depend on the growth

of new aquaculture technology and application of the

protective measures noted for the other bivalve fisheries in the region.

Acknowledgments

The authors wish to thank Antonio Figueras Montfort

for providing his bibliography and photographs for this

review. The participation ofJ. Caceres Martinez in this

work was generously supported by the Consejo Nacional

de Ciencia yTecnologia (CONACYT) from Mexico and

by the Consejo Superior de Investigacion Cientifica

(CSIC) from Spain, through a scholarship for his doctoral studies.

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Fisheries and Farming of Important Marine Bivalves in Portugal

FRANCISCO D'ASSIS LOPES RUANO

Instituto Portuguis De Investigariio Maritima (IPIMAR)

Departmento De Aquacultura

Avenida Brasilia

1400 Lisboa, Portugal

ABSTRACT

Oysters and other bivalves have been used as food since the earliest eras in Portugal. The

two most important commercial oysters are the flat oyster, Ostrea edulis, and Portuguese

oyster, Crassostrea angulata. The flat oyster declined after 1900 and was replaced in importance by the Portuguese oyster and more recently by clams. Pollution was the main reason

for decline ofthe oyster industry. Oyster culture began in the 1950's, and production rose to

10,000 t in 1964. About 2,000 people full-time and 10,000 others, for 8-9 months of the year,

cultured oysters. Production fell afterward and now is 150 t/year. The most important clam

cultured is Ruditapes decussatus. Fishermen gather seed, 5-10 mm long, from natural beds

and plant them in private plots. In 1.5-2 years, the clams attain marketsize of at least 25 mm.

Fishermen gather some other bivalves along the shores at low tide for sale. Bivalves have to

be depurated in areas where the quality is below Portuguese law or EEC regulations. Off the

north coast, a fleet of boats harvests bivalves found at depths from 10-50 m. The most

important are white clams, Spisula sp.; golden carpet clam, Venerupis aurea; razor clams, Ensis

sp.; and striped venus, Venus gallina. In 1989, fishermen landed 1,800 t of clams. At least 80%

of R decussatus and white clams are exported to Spain and France. Bivalves in Portugal are

sold fresh, refrigerated, frozen, and in many preprepared and precooked ways.

Introduction History of the Fisheries

The harvesting of bivalve mollusks has been an important component of Portugal's fisheries since ancient

times. A multipurpose fleet of boats in all the fishing

harbors of the 850 km Portuguese coast (Fig. I) has

harvested several species of bivalves, mainly the flat

oyster, Ostrea edulis (until the first decade of this century), and nowadays several species of clams, cockles,

and mussels. Fishermen have also harvested bivalves by

raking and by hand along the shores.

Most bivalves have been gathered and cultured in

estuaries, lagoons, and "rias" (deltaic complexes). However, manufacturing industries, agriculture, tourist facilities, and other activities are now intruding into them,

and the capacity to produce bivalves is being lost entirely in the Tejo estuary and partially in some others.

In areas that have good environments, induding good

water quality, bivalve production is good.

Oysters and other bivalves have been used as food since

the earliest eras in Portugal. Many shell deposits composed of different bivalves (but mostly oysters), bones,

ceramics, and charcoal have been found in prehistoric

sites along the Portuguese coast. The deposits, called

"concheiros" and located near the Tejo estuary

("Muge"), the Sado estuary ("Herdade do Portancho"),

and in Algarve ("Ponte de Marcil") (Fig. I), date from

the last Bronze Era, about the 9th century B.C. l

During the Roman occupation of Portugal, from

about 140 B.C. to 400 A.D., oysters were an important

food. Eating oysters was probably common in the Middle

I Information was collected from manuscripts provided by Rui

Monteiro, a former senior researcher ofInstituto de Biologia Maritima, and from a booklet published by the Centro Historico das

Universidades de Lisboa/Museu Arqueologico de Setubal.

191
192 NOAA Technical Report NMFS 129

42

41

z

<l:

W

U <l:

0 ll.

39' U Vl

tZ

<l:

...J

t-

<l:

38

37"

*_WHlfE CLAM BEOS

Figure 1

The principal areas where bivalves are produced in

Portugal.

East and spread to other provinces of the Roman Empire, including Portugal. The Romans harvested oysters

from natural beds in the two main estuaries, the Tejo

and the Sado. In the Sado estuary, ruins of a Roman

city, named "Cetobriga," still exist. They include tanks

for salting fish, which shows that the Sado estuary was a

big center for fisheries, salt production, fish processing,

and probably oyster production. The products were

sent to other provinces of the Empire.

Oysters and other bivalves always have had great importance in coastal communities. For example, in 1682,

responding to a request of local fishermen from the

north, a special law for the protection of bivalve beds

was passed as bivalves were a main food and providEd

employment for people. The nutritive value of oysters

was also recognized centuries ago and, in 1731, Francisco F. Henriques, a Portuguese physician, described

the advantages of eating oysters which included the

treatment ofseveral diseases.

In the 19th century, oysters continued to be an important food and were sold in several coastal markets.

In 1867, a private company signed a contract with the

government to lease a large area of public oyster beds

on the south shore of the Tejo estuary. The company

made commitments to: 1) Preserve and enlarge the

oyster beds, 2) create new oyster beds in the most

appropriate sites, and 3) develop methods for fattening

and improving the quality of oysters for export.

During a visit to Portugal in 1891, Bashford Dean,

biology instructor at Columbia College in New York

City, described the oyster near Lisbon: ''The harbor of

Lisbon is a miniature sea, a mile or more in width and

half a dozen miles long. The southern shore of this sea,

opposite the city, is the home of the oyster .... Those

oyster beds have not merely furnished the Lisbon market, but have been the center of active export" (Dean,

1893). Oyster culture did not then exist in the Tejo

estuary. In addition, the quality of oysters was poor, and

almost the entire production was exported to France

and England where they had to be rebedded for a while

to improve their quality before being eaten.

Although some measures were taken after the 1860's

to improve oyster quality in the natural beds, oyster

culture has been practiced only since the middle of the

20th century. In 1868 the first law was passed to regulate fishing in the natural oyster beds. It specified that

1) Oysters could not be harvested from 1 April to 31

September, covering the spawning season, 2) the minimum size of oyster that could be harvested was 5 cm,

and 3) oysters in intertidal zones could be gathered

only by hand.

After that, several measures were passed covering

special situations to protect human health. In 1895 the

first "Regulation law for the oyster industry, oyster parks,

and oyster culture" appeared. In 1923 the first "Sanitary

regulation law for oyster industry" was passed. In 1953

the government built the first depuration plant for

oysters in the Tejo estuary, and in 1972 it published the

new "Regulation law for oyster industry."

Despite those measures, the Portuguese oyster industry remained undeveloped and was limited to the gathering of available oysters. Nevertheless, this was a substantial fishery and, throughout history, thousands of

families have gathered thousands of tons of oysters

from hundreds of hectares of beds in the Tejo and

Sado estuaries and the Algarve lagoons, nearly all for

export.

In 1890 the flat oyster, which constituted 85% of

landings, was the most important bivalve landed, but by

1910 its share had fallen to only 40%. Its decline was

caused by overharvesting and silting ofthe beds in river

mouths and lagoons. To prevent further declines, the
_______________ Ruano: Fisheries and Farming of important Marine Bivalves in Portugal 193

Figure 2

Production of wild oysters by value and weight, 1896-

1978 (weights were not available until 1927).

Currently, its natural beds have declined to 200-300 ha

in the upper part of the Sado estuary and a few deepwater beds in the other locations.

-80

- VALUE + WEIGHT

----------.----,100

1900 10 20 30 40 50 60 70 78

YEARS

10000

100000

Harvesting-Before the modernization of the oyster

industry, fishermen gathered all oysters by dredging

from boats or by hand while walking. They harvested

flat oysters on the Algarve coast and Portuguese oysters

in estuaries and lagoons by towing small dredges from

sailor row boats. The old type of oyster dredge consisted of a semi-arched iron rod and a tooth bar with a

single row of 10-20 teeth, each 10 em long. Its net bag

was made ofleather. Fishermen towed it with a cable or

a long-handled pole (Silva, 1893). They dredged mainly

for flat oysters until 1910 or 1915 and then switched to

Portuguese oysters. Harvesting and culturing oysters

was important economically for 60-70 years until the

early 1970's; 80-90% were exported. Mterward, production declined sharply (Fig. 2).

Factors Causing Industry Decline-Pollution was the

main reason for decline of the oyster industry, particularly in the most productive areas (Vilela, 1975). Even

in olden times, the consumption of oysters caused periodic outbreaks of human diseases in coastal communities. For example, in 1887 several such outbreaks in

Lisbon were linked to oyster consumption (Monteiro,

1986). The oysters came from the north shore of the

Tejo estuary which had many sewage outfalls from

Lisbon. Since then, oyster harvesting along the entire

shore of the Lisbon estuary has been forbidden.

government, in October 1895, banned any harvesting

for 3 years in "rivers, rias, ports, lagoons, and bays ofthe

kingdom." The rule was included in Article 5 of the law

that established rules for "oyster beds exploitation, oyster

culture, and oyster deposits in public property waters."

Oysters

According to Nobre (1940) and Vilela (1975), there are

four oyster species along the Portuguese coast: flat oyster; Portuguese oyster, Crassostrea angulata; stone oyster, Ostrea stentina; and O. cochlear. Only the first two

species are economically important. The importance of

the flat oyster declined after 1900 and was gradually

replaced in the next decades by the Portuguese oyster

and more recently by clams. Nowadays, the flat oyster is

relatively rare along the coast except for a few small

natural beds in such lagoons as Lagoa de Albufeira,

located between the Tejo and Sado estuaries (Leal,

1984), or those on the south coast of Portugal. Its

production is limited to a few longline system units on

the south coast.

Abundance ofthe Portuguese oyster has increased in

almost all brackish water estuaries, lagoons, and rias. It

can occupy areas from intertidal and subtidal zones to

the deepest parts of canals, 10 m, and from river mouths

to several kilometers upstream. It occurs on substrates

of sand, sandy mud, silt, and shells. It tolerates a wide

salinity range, even as low as 2-6%0 in winter and after

heavy rains. Mter 1-2 months of rains, a large number

of oysters in the upper parts of estuaries become affected by so-called "fresh water edema" due to osmoregulatory dysfunction. In contrast, during summer,

in beds close to river mouths or inside lagoons, salinities can rise to 35-38%0 without any apparent stressing

of the oyster. The temperature range in its habitat

varies from a minimum of 8°-10°C in northern waters

during winter to 20°-30°C in southern lagoons during

summer.

During the rainy season, the water in large estuaries

carries a large quantity of silt. It flocculates and settles

on oyster beds, causing mud blisters in the shells of

oysters as well as heavy mortalities of oyster spat.

The main oyster predators are several species of crabs

(especially the green crab, Carcinus maenas) , gastropods,

sea stars, and sea birds. Oyster larvae are eaten byjellyfish.

The Portuguese oyster was formerly abundant, especially in the Tejo, Sado, Mondego, Mira, and Guadiana

estuaries, as well as in the Albufeira, Obidos, and Ria de

Aveiro lagoons on the west coast, and the coastal lagoons of Alvor and Faro-Olhao in the south (Fig. 1).

The best habitat for producing it was the Tejo estuary.

Shellfish Harvesting and Culture
194 NOAA Technical Report NMFS 129

Beginning in the middle of this century, large-scale

manufacturing industries have developed in Portugal.

A major site has been the large Setubal Peninsula,

between the Tejo and Sado estuaries which have the

large commercial harbors of Lisbon and Setubal, respectively. Several heavy industries, such as shipyards,

steel works, chemical complexes, oil refineries, cement

facilities, and paper mills have been constructed, first

on the south shore of the Tejo estuary and later on the

north shore of the Sado estuary. Sewage treatment facilities were inadequate or absent.

At the same time, agriculture and animal husbandry

intensified, and agroindustrial facilities were built in

the basins of the two estuaries. Use of fertilizers and

pesticides increased. In addition, the populations of

Lisbon and Setubal grew, and sewage outflows increased.

As a consequence, the quality and production ofoysters

declined in the Tejo estuary in the early 1960's. Now the

oyster fishery has ended and the old beds of Portuguese

oysters have been colonized by the noncommercial 0.

stentina (Ruano, 1984). The colonization could be linked

with degradation of the genetic patrimony of the intensively exploited Portuguese oyster, compared with an untouched genetic heritage of O. stentina, which gave it the

capacity to adapt and survive in a poor environment.

The same thing happened 10 years later in the Sado

estuary, where only a few natural beds remain. They

cover an area of about 200 ha in its upper parts.

Additional factors besides pollution were responsible

for the decline of the oyster industry:

1) The occurrence of several epizootics, namely the

"oyster gill disease" (Comps et al., 1976) caused by an

iridovirus, a severe disease causing extensive lesions in

the gill epithelium which sharply reduced filtering capacity and killed some young and stressed animals;

2) "Foot disease." a shell disease related to the fungus

Oystracomblabe implexa (Alderman, 1971), which is probably associated with a secondary bacterial infection. It

destroys the adductor muscle. Valve movements, tight

closure of the valves, water pumping, and blood circulation are reduced;

3) Several protozoan diseases, mainly caused by Hexamita sp., Ansistrum sp., and Trichodina sp., also affected

oysters by increasing their morbidity when they were

stressed by factors such as high temperatures;

4) An ineffective or absent management strategy to

protect the natural beds;

5) Overharvesting and depletion of the beds by fishermen who tried to meet a strong market demand; and

6) Nonexistence of hatcheries which could have provided farmers withjuvenile oysters when natural spatfalls

were declining.

Culturing Oysters-In the middle of the 20th century,

the Navy Ministry, which was the predecessor of the

current National Institute for Fisheries Research (INIP),

established the "Estacao de Biologia Maritima" (Marine

Biological Station). It was there that Herculano Vilela,

one of the most distinguished marine scientists of Portugal, and a few collaborators began modern oyster

culture in the country. Studies were conducted on the

biology, spacial and temporal distribution, reproduction, nutrition, and pathology of oysters. Rearing methods were adapted from France, first in the Tejo estuary,

1954-56, and later in the Sado estuary and Algarve

lagoons, and the industry improved. According to Vilela

(1951 b), the methodology involved three steps: Larval

attachment, spat collection, and growth.

Larval Attachment-Several types of collectors, including ceramic tiles covered by a cement mixture, chains

of shells, and plastic tubes, are put in selected sites

when government technicians predict that oyster larvae

will set in abundance. The technicians sample the water

for larvae every day.

Spat Collection-When the spat are 6-8 months old

and 2-4 cm long, workers remove them from the collectors as single oysters ("destruncagem" in Portuguese)

and place them in growing parks. The workers prepare

the parks ahead of time by cleaning them, compacting

theirsoil, and destroying predators and competitors. They

then grade the spat by size. If the spat are large enough,

they are placed directly on the ground; otherwise, they are

held in .wood trays ("casiers") which have net bottoms.

The trays, held 20-30 cm above the bottom by wood or

iron stockades, are cleaned periodically by workers.

Growth-The oysters remain in the parks until they

attain commercial size, at least 5 cm long. However, if

the water quality is poor and food is sparse, sometimes

it is necessary to transfer them to cleaner sites with

richer water to improve quality and growth. The operation, called "afinacao" (improvement), is carried out in

earthern ponds with inlet and outlet water control sluices

or at other appropriate sites.

As a consequence of improvements in culture methods, oyster production rose from 2,064 metric tons (t)

in 1956 to a peak of 10,000 t (1 t of oysters = 33 U.S.

bushels) in 1964 (Fig. 3). The overall area devoted to

culturing oysters, 950 ha, was controlled by 45 concessions employing about 2,000 people full time and 10,000

others for 8-9 months/year.

In 1968, when workers produced 8,496 t of oysters,

90% were exported to France. The net profit was 85

million PTE (Portuguese escudos) (US$3 million).

Present Situation-Methods and technologies for producing natural and cultured stocks of oysters are the

same as in the past. Most oyster production has been
_______________ Ruano: Fisheries and Farming of important Marine Bivalves in Portugal 195

1 0

192530 35 40 45 50 55 60 65 70 75

YEARS

·2

100000 14

\ 12

10000

10

=- 1000 8 § w :::.

6 E .. 100 Cll

:> .~

lij :i: > 4

10

- VALUE -+- WEIGHT

Figure 3

Production of cultivated oysters by value and weight,

1925-76.

transferred, however, from the Tejo and Sado estuaries

(Fig. 4) to Algarve. In the Tejo estuary, production

ended in 1972, while in the Sado estuary, production

has been stable at the limit set by the government of

150 t/year during the past 3 years, but it had declined

from 9,000 t/year in 1972. Fishermen rarely dredge for

oysters now, as the deep-water beds are depleted. In

addition, the government forbids any harvesting with

dredge boats in estuaries and lagoons. In coastal waters,

dredging is mainly for other bivalves and is tightly controlled to prevent conflicts between fin fishermen and

shellfishermen.

Fishermen have always gathered oysters in shallow

water and intertidal zones with different types of rakes,

forks, or other tools, and by hand. The methods are still

used by a small number offishermen and their families.

In the Sado estuary, a person can gather 80-100 kg (27

kg of oysters = 1 U.S. bushel) on a low tide. The season

lasts from September to April. The oysters must be

transplanted to other growing sites for 6-12 months to

improve their quality before being marketed.

Grooved Shell Clam

The most important clam species for culture is the

grooved shell clam, Ruditapes decussatus. Other common names for it are "Christian clam," "fine clam," and

"good clam." Farmers culture it in the Algarve lagoon

systems of Ria de Faro and Ria do Alvor (Fig. 1). The

lagoon's waters, which average 4 m deep, cover an area

of about 20,000 ha and are protected from the sea by

Figure 4

Small anchoring ground in the Sado estuary, showing

grading trays, rakes, and bags full of oysters.

several sandy islands. It is connected to the sea by four

main entrances or "barras." The margins of hundreds

of twisted canals and small islands inside the lagoon are

covered by extensive marshes. Sediment grain sizes vary

from sand/mud to coarse sand. The water temperature

ranges from 10° to 25°C, salinity from 33.8%0 in winter

to 38%0 in summer, pH from 7.7 to 8.3, and dissolved

oxygen from 140% during high tides to 60% during low

tides. This is an important ecosystem, acting as a nursery for many species which stock nearby coastal shores.

It is a good habitat for bivalves, especially clams, owing

to high primary productivity, and they grow rapidly

there.

The main predators ofthe grooved shell clam are the

green crab; fiddler crab, Uca tangeri; several species of

gastropods; sea stars; sparid fishes; and aquatic birds.

Its main competitors are bivalves, such as the blue mussel, Mytilus edulis; flat and Portuguese oysters; clams,

such as Venerupis pullastra and V. rhomboides; and the

cockle, Cerastoderma edule.

Culture-Farmers collect seed at a length of 5-10 mm

from natural beds. (The lack of hatcheries has been an

important factor limiting a good and stable production

during the past 6 years.) The seed is planted in manmade culture beds, called "viveiros," which are located

in intertidal zones where clams grow best. Grooved

shell clams burrow 5-15 cm in sediments. Clams <25

mm long grow 9-10 mm from March to August, the

period of most rapid growth, in the culture beds. They

grow slowly from September to March (GEA, 1987).

Farmers prepare the culture beds ahead of time by

adding sand and gravel to the sediment to permit the

transfer of food and oxygen between the water-sediment interface and the clams. This common practice
196 NOAA Technical Report NMFS 129

promotes growth of clams especially when they are

small.

The two main seasons for planting seed are March to

May (usingjuveniles which set during the previous fall)

and October to December (using juveniles which set

during the previous spring). Farmers also stock their

culture beds between those times ifseed is available at a

reasonable price.

Mter the seed is planted, farmers keep beds clean of

macroalgae and debris and try to control predation by

sea birds, green crabs, fiddler crabs, gastropods, and

fish. They use gravel to hide the small clams from sea birds

which seek them during low tides, and they cover the seed

with nets to protect them from the other predators.

Farmers plant the seed at a density of about I kg/m2.

Clam growth is variable, and soon after planting their

lengths vary from 5-20 mm and their densities from

200-400 clams/m2. Clams in the upper layers of culture

beds, especially in sloping areas, can be moved with the

sediments as much as several meters by strong tidal

currents during storms.

In 11/2-2 years at most, depending on the seed size

used, almost all the clams have reached the legal market

size, a minimum of25 mm. However, in the best areas, the

clams can reach an average length of 35 mm and sometimes 50 mm in the same period. Their final density varies

from 2 to 6 kg/m2, depending on conditions.

Farmers harvest the clams by digging in the sediment

with a special knife having a large blade (Fig. 5) and

then picking up the clams by hand. Mterward, the

clams are washed, graded, packed in mesh bags that

hold 25-35 kg each (Fig. 6), and then sent to markets

or depuration plants. Bivalves have to be depurated if

produced in areas where the quality does not reach the

values imposed by Portuguese law or EEC regulations

(MPN [most probable number] <300 fecal coliforms/

100 ml of meat and intervalvar liquid). Currently, all

production from the two main estuaries, the Tejo and

Sado, as well as Aveiro, Obidos, and Faro-Olhao lagoons must be depurated. Before the clams leave the

plants for market, government technicians check their

sanitary condition. If clams meet the standard, the technicians then attach a sanitary certificate to the batches of

clams. The bivalves that fishermen gather from wild beds,

usually in smaller quantities, are handled the same way.

Clam Mortalities-During the summer (hot) season of

1983, several farmers had substantial losses of clams

that were nearly market size. Such losses have continued. Several research teams found that a protozooan

parasite killed the clams. It was diagnosed first in 1984

as "Dermo" (Chagot et aI., 1986b; Ruano and Cachola,

1986), later as Perkinsus marinus, and finally as a new

species, Perkinsus atlanticus (Azevedo, 1989).

The high prevalence of this pathogen in clam populations may be attributed to several factors, such as

degraded muddy sediments, high clam densities, absence of any physical barriers between differen t culture

beds, and animal transfers between them. In addition,

year-round temperatures above 12°C and salinities above

15%0 contribute to its development.

: ! J ~llltlltt1~t. ~J.'

em

"- t ,I' I 1 I r t I' I t • • • • rJ II • .. "

Figure 5

Knife with special shape for harvesting clams by hand.

Figure 6

Fishermen washing and grading grooved shell clams.
_______________ Ruano: Fisheries and Farming of important Marine Bivalves in Portugal 197

Other pathogens have also been observed. For instance, Vilela (l951a) described several agents, specifically a new Haplosporidium species, which he identified

as Haplosporidium tapetis. Later, Chagot et al. (1986b)

classified it as Minchinia tapetis. The prevalence of the

diseases in the grooved shell clam in 1986 and 1987 are

summarized in Figure 7.

Production of the grooved shell clam (Fig. 8) has

varied in this century, but its economic and social importance to local communities has always remained

high. Currently, the total area used for producing the

clams is about 1,000 ha, which the government leased

to farmers. The number of culture beds is about 1,500,

total production of clams is about 4,000 t/year (1 t of

clams = about 25 U.S. bushels), and the number of

people directly involved with the culture beds is about

1,500.

Deep-water Clams

80

60

MONTHS

Along the northern coast, north of Aveiro, a fleet of

boats having capacities of477 GTRand 1,116 hp dredges

for clams (Fig. 9). Their targets are typical thalassic

bivalves, found at depths from 10-50 m. Currently, the

most important are the white clams, Spisula solida and S.

solidissima; golden carpet clam, Venerupis aurea; razor

clams, Ensis sp.; and striped venus, Venus gallina. Some

minor species are also taken. The catch rate of the

boats is 2,000 g ofwhite clams in a 5-minute tow (Sobral

and Jorge, 1989). However, for the same species and

same effort on the Algarve coast, the catch rate is only

10-700 g (Monteiro, 1985). In 1989 they landed about

1,800 t of clams, worth PTE214 million (US$1.4

million)(Sobral, 1990) (Fig. 10).

Figure 7

Prevalence of the most important pathogens of the

groove shell clam at Faro-Olhao lagoon in 1987 (Ruano,

1989).

Other Bivalves

Fishermen gather several other bivalve species, such as

mussels, cockles, and the wedge clam, Donax sp., along

the shores at low tide. It is an old and common activity

called "Marisqueio" (shellfish gathering) (Fig. 11, 12,

13) and takes place in the shallow waters of estuaries,

1 0

1901 10 20 30 40 50 60 70 80 88

YEARS

1000000 10

100000 8

10000 ;:-

- 8

[ 1000 - 4 i iii

> 100

10 2

VALUE -I- WEIGHT

Figure 8

Production of grooved shell clams by value and weight,

1900-87.

Figure 9

Dredges used for gathering white clams, razor clams,

and other bivalves in deep waters (10-30 m).
198 NOAA Technical Report NMFS 129

lagoons, and rias. Prime areas are on the south coast,

mainly in the Faro-Olhao and Alvor lagoons. Additional

centers are Ria de Aveiro. a deltaic complex of the

Vouga River 60 km south of Porto City, Obidos and

Albufeira lagoons, and the Mondego, Tejo, Sado, Mira,

and Guadiana estuaries.

Pulling dredges while walking in 0.8-1.2 m of waler

during low tides is another common way of harvesting

species, such as the wedge clam, on sandy grounds. I: is

done in lagoons and along the coast.

Another method uses a small dredge from a boat.

Crews of two anchor the boats and dredge the sur1000000

100000

5' 10000 °

o.

w

I- 1000

'"::J

0; 100 >

10

~---------------'--10

<="

6 °

0

q

E

4 Ol

'iii

2

rounding area. To retrieve the dredges, they use manual

winches or long-handled poles. During a single tide, a

crew can harvest 400-500 kg of clams, cockles, or musFigure 12

A fisherman carries his rake and basket of bivalves.

1 0

1896 6 16 26 36 46 56 66 76 1986

YEARS

-VALUE -t-WEIGHT

Figure 10

Production of the cockle, mussel, and minor species of

clams by value and weight, 1886-1988.

Figure 11

Fishermen gathering bivalves during low tide from the

shore of a lagoon.

'..-

Figure 13

A drag or rake for gathering cockles and mussels.
_______________ Ruano: Fisheries and Farming of important Marine Bivalves in Portugal 199

sels (36 kg of clams or cockles or 27 kg of mussels = 1

U.S. bushel).

Environmental Issues

The gathering of clams and especially the dredging of

grounds alters the upper layers of sediments where

several crustacean and finfish species obtain food and

shelter during phases of their life cycles. As a consequence, shellfishing is closely regulated by specific Administrative Rules issued by the government. They cover

the harvesting season, location of grounds, minimum

size for each species, size and power ofthe boats, as well

as characteristics of the dredges for the different species (Governmental Laws 438/72,11/80, and 43/87).

Public Health

For protection of human health, the government has

published several laws and Administrative Rules since

the middle of the 1800's regarding oyster production.

The same procedure has been followed more recently

for the other bivalves because several people had gastrointestinal infections after eating them. Consumption of cockles from Mondego estuary in October of

1975 is one example. Under law 11/80 and others such

as EEC Directives 923/79 and 432/91, Governmental

Law 261/89, Administrative Rule 980-A/89, and the

"Water Quality Act" 74/90, the government has legal

tools to control the entire production ofshellfish, from

the beds to consumers, to protect human health. A

special program for permanent control and monitoring of Portuguese coastal waters is conducted by the

INIP for early detection and quantification of toxic

microalgae to avoid human intoxications.

Mter harvesting bivalves, workers grade and wash

them to remove sand, mud, algae, and other detritus.

Mter that, while in boats or ashore, they pack the bivalves

in mesh bags and sell them to local dealers who resell

them to local markets or export them after certificaton

of their quality. Bivalves gathered locally from wild

stocks, usually in smaller quantities, are handled the

same way.

Landings Statistics

Bivalve landings have been reported as an independent

sector of fisheries statistics for nearly a century. However, their real importance has been neglected, and

part of the production was not and still is not mentioned in official statistics. This is because fishermen

harvest the clams from many small, widely distributed I

sites along the coast, and the people also pursue other

activities, mainly finfishing and farming. All data presented are official data collected from Estatisticas das

Pescas Maritimas/Estatisticas das Pescas 1886-1986.

Sales and Uses of Bivalves

At least 80% of the production of reared grooved shell

clams and the white clams are exported to Spain and

France. However, the national market has become increasingly important, especially in large population centers and seashore tourist areas where the clams are in

demand during the summer season.

Nowadays, bivalves in Portugal are sold fresh, refrigerated, frozen, and in many preprepared or precooked

ways. Other than oysters, eating raw bivalves is not

popular in Portugal. The traditional recipes for cooking bivalves in shells are: 1) Slightly steamed with no

condiments and 2) boiled in different sauces, mostly

consisting of aromatic herbs, often with garlic, onion,

and tomato, and usually with wine and olive oil. Shucked

bivalves, cooked with rice or mixed with other ingredients to make the stuffing for fried or roast cakes, are

also popular Portuguese cuisine.

The Future

We must restore and preserve bivalve environments

that have been degraded by pollution. Public and private organizations need to be shown that bivalves require good environments so their habitats can be protected. To restore the oyster industry in the Tejo estuary and especially in the Sado estuary, the following

steps must be taken: 1) All sewage must be treated; 2)

the remaining beds must be restocked and protected,

using some natural seed, but mainly hatchery seed; 3)

oyster production must be increased in the unused

areas of earthen fish ponds such as inlet and outlet

canals, certain areas of water reservoirs, and even in

other parts offish ponds; and 4) oyster culture technology should be diversified, using sticks, stakes, racks, or

combined methods as well as suspended devices using

trays or "casiers."

Nontraditional culture systems for the flat oyster,

such as long lines and suspended trays, have been tested

successfully on the southern seashore and in some lagoons. In 1991, production was 15 t by one unit; six

more units of similar design are projected for several

sites along the Portuguese coast. Two bivalve hatcheries

are under construction, and substantial quantities of

oyster seed have been imported every year from

France and Spain. Thus, the oyster industry seems to be

improving.
200 NOAA Technical Report NMFS 129

The absence of bivalve hatcheries has been a great

obstacle to the implementation of a sound epidemiological program to control diseases of the grooved shell

clam. The open culture system used and the strong

influence of environmental conditions make it difficult

to control them.

Acknowledgments

I thank my colleagues Rui Monteiro for helping with

the history and for allowing me to consult his manuscripts andJaime Menezes for reviewing the manuscript.

Literature Cited

Alderman, D.].

1971. Shell disease of oysters. Minist. Agric. Fish Food, Fish.

Invest. 26(8):1-14.

Azevedo, C.

1989. Fine structure of Perkinsus at/anticus n.sp. (Apicomplexa,

Perkinsea) parasite of the clam Ruditapes decussatus from

Portugal.]. Parasitol. 75(4):627-635.

Chagot, D., E. Bachere, F. Ruano, M. Comps, and H. Grizel.

1986a. Ultrastruture des stades sporules d'une haplosporidie

parasite de la palourde Ruditapes decussatus. Proc. 2nd. Int.

Colloq. Pathol. Mar. Aquacult. Porto. 2:37-38.

Chagot, D., M. Comps, V. Boulo, F. Ruano, and H. Grizel.

1986b. Etude histopathologique d'une reaction cellulaire chez

Ruditapes decussatus infecte par un protozoaire. Proe. 2nd.

Int. Colloq. Pathol. Mar. Aquacult. Porto. 2:39-40.

Comps, M.,]. R. Bonami, C. Vago, and A. Campillo.

1976. Une virose de l'huitre portugaise (Crassostrea angulata

Lmk.) C.R. Acad. Sci. Paris 282, D:1991-1993.

Dean, B.

1893. Report on the European methods of oyster-culture. B:.IIl.

U.S. Fish Comm. XI:357-406.

GEA.

1987. Mortalidade da ameijoa boa-Que causas? 52 Congr. do

Algarve, Montechoro 1:491-497.

Leal, A. M.

1984. Estado actual das ostreiras dos estuarios do Tejo, Sado,

Mira e do Algarve. In Seminario sobre aquacultura, p. 71-

86. Ed. INIP/ APRH, Lisboa.

Monteiro, C. L.

1985. Prospeq:ao preliminar dos bivalves de interesse comercial

do litoral algarvio--area de sotavento. Relatorios INIP, Lisboa

44, 110 p.

Monteiro, R.

1986. Salubridade e depuracao de moluscos bivalves-O

problema no Algarve. 4th Congr. Algarve, Montechoro 1:511-

518.

Nobre, A.

1940. Moluscos marinhos e das Aguas Salobras. Ed. Compo

Edit. do Minho, Barcelos, 808 p.

Ruano, F.

1984. A patologia na problematica da cultura de espeCles

invertebradas. In Seminario sobre aquacultura, p. 403-420.

Ed. INIP/ APRH, Lisboa.

1989. Agentes patogenicos da Ameijoa boa Ruditapes decussata

em populacoes cultivadas no litoral algarvio. In Seminario

Aquacult. Univ. Algarve, Faro, 10 p.

Ruano, F., and R. Cachola.

1986. Outbreak of a severe epizootic of Perkinsus marinus at Ria

de Faro clam's culture beds. Proc. 2nd. Int. Colloq. Pathol.

Mar. Aquacult. Porto.

Silva, A. A. B. da.

1893. Estado actual das pescas em Portugal. Ed. Imprensa

Nacional, Lisboa.

Sobral, M. P.

1990. Aspectos preliminares da caracteriza~ao da ameijoa

branca (Spisula solida L.) do litoral none. INIP/CRIP

Matosinhos.

Sobral, M. P., and I.Jorge.

1989. Prospec~ao de amelJoa branca (Spisula solida L.) no

litoral norte da costa Portuguesa nos meses de Maio/Junho

e Outubro de 1986. Relatorios Teen. Cient., lNIP,

Lisboa, 17.

Vilela, H.

1951a. Sporozoaires parasites de la palourde, Tapes decussatus

(L.). Rev. Fae. Cienc. Lisboa C,l (2) :379-393.

1951b. Os moluscos na economia do mar. Bol. Pesca 31:3-42.

1975. A respeito de Ostras. Biologia-expJora~ao-salubridade.

Notas Estudos. See. Estado Pescas, 1-Lisboa, 220 p.
Mollusk Fisheries and Aquaculture in Italy

NICCOLO MATTEI

Dipartimento di Biologia Ambientale

University ofSiena

Via delle Cerchia 3

53100 Siena, Italy

MICHELE PELLIZZATO

S. Croce 1860/B

30135 Venice, Italy

ABSTRACT

Molluscan farming in Italy dates back at least 2,000 years to when the ancient Romans

reared oysters, mussels, and fish. Italy was a leader in marine farming until the last century,

when, except for culture of the mussel Mytilus galloprovincialis, its molluscan culture waned.

For other species, culture techniques are recent and are limited mostly to nonindigenous

species introduced in the 1980's. In southern Italy, oyster spat once were caught on bundles

of branches and mussel seed on wooden panels deployed from rafts. The largest beds of

scallops, Pecten jacobaeus, Aequipecten opercularis, and Proteopecten glaber, and clams, Tapes

decussatus, T. philippinarum, T. aureus, and Chamelea (Venus) gallina, are found in the central

and northern Adriatic Sea. Culturists grow most ofltaly's mussels and clams in lagoons from

the Po estuary to Trieste. Mussels now are grown in suspended mesh socks and constitute

the highest landings of any mollusk, i.e., 175,000 t in 1992. The main species of clams

harvested are T. philippinarum and T. decussatus, both produced by culture, and C. gallina

and Callista chione, both landed from natural stocks. In many areas, T. philippinarum has

colonized natural bottoms where it is harvested. Fishermen introduced the Pacific oyster,

Crassostrea gigas, in the early 1960's, and grew them along with the native oyster, Ostrea edulis,

but have since nearly abandoned culturing them. In the 1960's, fishermen adopted the

"rapido" dredge from France which permitted the harvesting of P. jacobaeus in the Adriatic

Sea. In the early 1980's, scallops became scarcer and culturists began to grow them on

longlines. In 1989, 45,000 people were directly involved in shellfishing, 8,500 others in

processing, and 16,500 in distribution and marketing. Mollusks are eaten in various ways in

Italy. Molluscan production still relies heavily on fishing of natural stocks, but aquaculture

will be important in the future.

Introduction

Molluscan farming in Italy dates back at least 2,000

years, to when the ancient Romans farmed oysters

(Bouchon-Brande1y, 1890; Dean, 1893) and fish, as can

be seen in mural art of the time. Oysters, Ostrea edulis,

from the Adriatic Sea (Fig. 1) were eaten in European

capitals in the late 18th century (Fig. 2) and probably

long before.

Italy was the European leader in advanced marine

farming methods until the last century (Coste, 1861),

and for a long time the town of Taranto was at the

forefront ofItalian oyster culture. During the 1870's, in

the northern Adriatic Sea near Trieste, a series of 21

growing parks (10 acres each) was producing a total of

10 million European flat oysters, Ostrea edulis, annually.

The industry did not keep abreast of foreign technological improvements and its methods became obsolete

or inappropriate, except for culture ofthe mussel Mytilus

galioprovincialis (Mattei and Pellizzato, 1989).

Apart from mussel culture, aquaculture techniques

are recent and currently are limited mostly to nonin201
202 NOAA Technical Report NMFS 129

1 - Trieste: mussels

2 - Marano lagoon: clams, oysters, scallops

3 - Venice: mussels, oysters, clams

4 - River Po delta: clams, oysters

5 - Lesina: Exp. clams

6 - Taranto: mussels, oysters clams

7 - Naples: mussels, clams

8 - Sabaudia: Exp. clams

9 - Orbetello: Exp. clams

10 - La Spezia: mussels

11 - Sardinia lagoons:c1ams

12 - Sicilian lagoons: mussels

Figure 1

Italy, the surrounding seas, and the main molluscan culture areas.

digenous species introduced in the 1980's. Important

areas, other than Taranto, for culture include: The

Gulf of Naples (mussels, oysters, and clams); the lake

areas of Sabaudia and Orbetello (experimental culture

by fishermen of mussels and clams); the Gulfs of La

Spezia and Trieste (mussel hanging culture); the central and northern Adriatic Sea (mussels, clams, and

oysters); and Sardinia where molluscan culture is developing in lagoons around Cagliari (Fig. 1).

Most mollusks now landed, except mussels, are from

natural populations which are being depleted. Current

government policy is to restrict the harvesting of natural populations and to encourage the development of

aquaculture enterprises.

Ancient Shellfish Culture

Mussel and oyster culture, though somewhat artisanal

and empirical in its development, has been practiced in

Italy from antiquity. The Romans were among the first

European molluscan culturists. Their techniques are

represented in detail on funeral urns from the first

century B.C. that have been recovered in Puglia and

the Roman countryside (Fig. 3). Over the centuries, the

techniques were developed further, especially at Baia,

in the embayments of Fusaro (Fig. 4) and Lucrino. The

methodology has been preserved through the ages.

The antique culture methods, though adopted and

maintained by groups of fishermen at Naples and

Taranto, have changed little over the years.

The custom of using marine organisms as food had

an early origin, probably related to the maritime mercantile activities of the Phoenicians (l,200 to 64 B.C.),

and it was later amplified by Hellenic colonists in the

period of expansion to the islands and the peninsula to

the west of their homeland (323 to 30 B.C.). It thence

was transferred to the culture of imperial Rome (250

B.C.). Roman technologists perfected the methods and

equipment used for harvesting from natural populations in the estuaries and sea and developed land-based

systems, especially as regards culture and maintenance of

mollusks, as witnessed by the remains of sophisticated

facilities at Baia and Pozzuoli (cf. Gaius Plinius Secundus,

Natualis Historia, 1st century B.C.). Here the landed gentry constructed the complex systems referred to as

"ostrearia" for the hanging culture of oysters and possibly

mussels as figured in engravings on small vitreous bottles

now found in several archaeological collections. The apparent common use of mollusks and other marine animals in the diet of the residents of the Italian peninsula

and the Roman colonies is documented in numerous

mosaics dating from the end of the second century B.G

through the early Christian era (Solinari, 1987).

In the southern areas ofItaly, oyster spat traditionally

was caught on bundles of branches suspended from

horizontal lines in the culture parks. The spatted

branches subsequently were broken into smaller pieces

and inserted into lengths of coarse grass rope that were

hung vertically for oyster growout to market size. This

practice continues today on a limited scale (Fig. 5).

D'Erco (1862, 1863, 1864) described in detail the

culture of oysters and mussels in the northern Adriatic

Sea. Oysters were cultured in shallow impoundments

(claires) at Noghera near Trieste in the early and mid1800's. Mussel seed was collected and cultured on small

wooden panels deployed on rafts moored in the Laguna

Veneta near Venice. D'Erco also described the traditional

oyster culture methods that were still being practiced

widely in the southern part of the Italian peninsula.
___________________ Mattei & PeUizzato: Mollusk Fisheries and Aquaculture in Italy 203

Ecosystems and Mollusk Fisheries

Italy has one of the highest ratios of coastline to surface

area (I :43.4 km/km2) in Europe and on this basis might

be a major producer of fish and mollusks. But much of

the shoreline is unsuited for molluscan culture, and

production has never been able to meet domestic demand. In 1980, Italy had to import 42% of mollusks it

consumed, and by 1988 this figure had risen to 56%.

The west, south, and east coasts vary substantially in

shoreline types, sea bottoms, and hydrographic features.

The northern Tyrrhenian coast has rocky shores with

littoral bottoms alternately sandy, muddy, and stony. The

southern Tyrrhenian coasts are more rocky and irregular

with mostly stony bottoms. The habitat is similar along the

coasts ofthe Ionian Sea and the southeastern Adriatic Sea.

The range of tides on the coasts is about 10 em.

The central and northern Adriatic Sea have sandy

bottoms as far as the Gulf of Trieste, where they again

become rocky. Extensive flat bars in the sea range in

depth from 15 to 20 m, while the maximum depth in

sloughs is 70 m. The Adriatic Sea receives large inputs

of nutrients from the Po, Italy's longest river, and other

rivers draining the south face of the Alps, and since the

Figure 2

Painting of gentry in Vienna or Budapest feasting on oysters, Ostrea edulis,

harvested in the Adriatic Sea, 18th century.
204 NOAA Technical Report NMFS 129

Figure 3

The culture of oysters was a practice known to the ancient Romans, as is documented by two designs on urns

from the first century B.C. The upper design is from an urn from an unknown location. The lower design is

from an urn recovered at Piombino on the west coast; shape ufthe urn is shown at its right. Realizing the high

nutritive value of oysters, the Romans fed them to the sick and convalescents (Graioni, 1975).

exchange of water is slow, its waters are more productive than other zones in the Mediterranean Sea. Fish

and molluscan production are high. The largest beds of

scallops, Pecten jacobaeus, Aequipecten opercularis, and

Proteopecten glaber, and clams, Tapes decussatus, Tapes

philippinarum, Tapes aureus, and Chamelea (Venus) gallina;

in Italy are found there, and they produce at least 60%

of Italy's mollusks. Culturists grow most of Italy's mussels and clams in lagoon areas such as Marano and

Venice, from the Po estuary to Trieste. The tidal range

is about 1 m.

Numbers of Fishermen and Boats

In 1989, 45,000 people were directly involved in

shellfishing in Italy, with an additional 8,500 people in

processing and 16,500 people in distribution and marketing. The annual economic productivity per employee

was almost three times that in agriculture (54 vs. 20

million lira (L) (Ll ,400 = $USI in December 1992))

and productivity was higher than in the industrial and

service sectors. The total comprehensive value of this

sector of the domestic economy was US$4.944 billion.

Italy now has 527 dredge boats, of which 411 work in

the northern Adriatic Sea, and about 800 boats using

rakes (Table 1). The sizes of boats equipped with dredges

for catching mollusks such as scallops has been increasing; their mean displacement increased about 16% from

12.35 tin 1972 to 14.28 t in 1989 (Table 2). Fishermen

have been modifying their boat equipment to permit

them to use multifishing techniques, because fluctuations

in certain Italian marine resources have been frequent

and widespread. Italy now has about 7,000 boats which

have combined gears for finfish and mollusks.

Fishing Equipment and Regulations

Mollusks are sought by commercial and sport fishermen who use a wide range of equipment. In intertidal

and shallow zones, they harvest mollusks with rakes and

knives, while in deeper water they use dredges and

diving equipment.
_____________________ Mattei & Pellizzato: Mollusk Fisheries and Aquaculture in Italy 205

Figure 4

General view of Lake Fusaro, showing here and there the circular stake arrangements that appear to be parts of fish traps;

the single and double rows of stakes, by means of which the fagots were suspended; and at one of the extremities, the

labyrinths, in front of which there is a canal 2.5-3 m wide and 1.5 m deep, excavated in part in the sides ofa promontory,

and connecting the lake with the sea. A small lake, believed to be the ancient Cocyte, connects with this canal. In a pond or

reservation, the oysters destined for sale are placed temporarily (Coste, 1861).

Table I

Distribution of the number and gross net tonnage of

Italian shellfish harvest vessels in 1989.

Table 2

Italian fishing vessel characteristics, illustrating changes

in horsepower and size that have occurred from 1972

to 1989.

Fishermen use a hand scrape (a blade with net behind

it) to harvest mussels from rocks and wooden poles

No. of Displacement

vessels (t) Item 1972 1989

55 367 No. of fishing boats 18,155 18,433

Mean horsepower 50.81 102.77

Mean displacement (t) 12.35 14.28

Area

West coast (Tyrrhenian Sea)

South and southeast coasts

(South Tyrrhenian Sea,

Ionian Sea, southern

Adriatic Sea)

Central and north Adriatic coast

Shallow Areas

61

411

516

4,337 (used extensively to mark navigation channels in lagoons) and sometimes for harvesting clams, Tapes spp.,

from sediments. Its blade is 60-70 em wide, and its

handle is 3 m long. Fishermen use these hand scrapes

from a small boat.

Fishermen also use a toothed rake, which ranges

from 0.5 to 1.5 m wide and has a handle 1-2 m long,

from a boat. They attach a rope to the rake and lash it
206 NOAA Technical Report NMFS 129

Figure 5

Traditional method for culturing oysters, Ostrea edulis, in southern Italy in earlier times: A) preparing bundles of branches,

B) placing bundles in water (they are held down by stones), C) bundles are suspended on ropes strung between dolphins,

D) oyster spat on branches, E) in both scenes, the worker at left is removing fully grown oysters from ropes, and the worker

at right is breaking up clusters and putting individual oysters into baskets.

to the handle. The fishermen let out their boat anchor

line perhaps 200 m, lower the rake, and then pull it

along the bottom by winding in the anchor line. They

retrieve the rake by hand, empty it, and then run the

boat back to the previous location and repeat the operation. They often rake around an entire circle from a
____________________ Mattei Be Pellizzato: Mollusk Fisheries and Aquaculture in Italy 207

single anchor point. Regulations controlling the rake

are: 1) The width of its mouth cannot exceed 1.5 m, 2)

the mesh of the bag cannot be smaller than 20 mm, 3)

the length of the bag cannot exceed 2 m, and 4) the

boat must not be driven by a motor >100 hp or have a

displacement of>10 t.

Open Sea Harvests

Fishermen use two principal vessel!gear types to harvest mollusks in the open sea:

1) Vessels equipped with simple hydraulic dredges,

rakes, and other trawling equipment for mollusks have

the following characteristics and regulatory limits. The

propulsion engine can have a maximum of 150 hp for

dredging; the maximum boat displacement can be no

more than 10 t; and no auxiliary engines are allowed

for the pumps, the power takeoff winch. or the steel

cable for hauling the dredge or rake and anchor.

2) Vessels equipped with highly advanced, heavy hydraulic dredges which are capable of penetrating several centimeters into the bottom (Fig. 6, 7). This equipment has a cage frame constructed of steel bars. Its

Figure 6

The front of a hydraulic dredge. Photograph by N. Mattei.

3Ld~ = ~.l~JJ1~fY ~~_ ~.~. / --~,= ',- \ Direction of trawling )/

/

\ wipe rope Flexible

£~-~~~c'=~'~'H;:;;-~i·,,~J Figure 7

Example oftrawling system for hydraulic dredge (left) and its

hydraulic apparatus (right).
208 NOAA Technical Report NMFS 129

rectangular mouth is fitted with an adjustable blade

and a manifold ofjets running the full width ofits lower

leading edge. The sand and mud are fluidized by the

jets and expelled through the grilled sides of the box; the

mollusks are retained by the bars. Seawater is supplied, via

a large hose, from a pump aboard the vessel. The general

characteristics and regulatory limits on hydraulic dredges

are: 1) Maximum dredge mouth width (blade length) is 3

m, 2) a rigid cage for retaining the catch must be used, 3)

maximum pressure from the jets is 1.8 atmospheres, 4)

dredge weight cannot exceed 600 kg, 5) the lower part of

the cage must have a mesh or bar spacing which permits

passage of undersized and undesired organisms, 6) the

dredge must be hauled over the bottom only by warping

on a set anchor, and 7) the warping must be a steel cable

that is hauled in with a power winch.

In the 1960's, fishermen imported the "rapido" dredge

(also termed rampone) dredge (Fig. 8) from France,

which permitted the harvesting of hitherto untapped

benthic resources, mainly the scallop, Pecten jacobaeus,

below depths of 10 m in the Adriatic Sea. The scallop

densities are too low for harvesting elsewhere. The

rapido was originally designed for catching flatfish. It is

light, has short teeth, a fixed mouth, and its name

reflects the speed at which it can be towed. Its mouth

opening consists of a rigid frame, 20-40 cm high, and

its dredge bar has curved teeth and four skids to prevent the teeth from penetrating too deeply. A depression plate (diving plane) on the upper frame bar keeps

the rapido on the bottom. The mesh size of its bag is

variable and an apron of coarse plastic netting protects

its bottom from wear. By law, the rapido used for harvesting scallops can have a mouth between 1.6 and 3.2

m wide and a bag with a minimum 50 mm mesh size.

The sizes and numbers ofrapidos worked simultaneously

from a boat vary according to its power.

To harvest jacknife clams, Solen spp. and Ensis spp.,

fishermen tow hydraulic dredges with water jets on

their blades. By law, the distance between the bars on the

lower part of the cage must be at least 7 mm, and metal

meshes must not be used. In addition, the clams must be

culled by hand, the undersized animals must be returned

to the sea, and sieves must not be used or kept on board.

By law, dredges for clams, Chamelea gallina, Tapes aureus,

and Callista chione, must have cages that allow seed clams

to pass through. Minimum spacing in cages must be at

least 12 mm for bars, 17 mm for square metal meshes, 25 x

12 mm for rectangular meshes, and a 21 mm diameter for

perforated plates with round holes. The meshes and sieves

must be of approved construction and be easy to inspect.

Another type of dredge used specifically for harvesting oysters and mussels in shallow water is the

"ostreghero." It is heavily framed, ranging from 11 0 x

30 cm to 200 x 50 cm, with a toothed bar which scrapes

the bottom and a heavy cord bag with metal meshwork

having openings no smaller than 50 mm.

Other Management Measures

In an attempt to control the fishing fleet and improve

management of fisheries resources, the Italian government recently has tried to decrease or at least stabilize

the number of boats working. In 1989, the government

Figure 8

A rapido dredge for harvesting scallops. Photograph by N. Mattei.
___________________ Mattei & Pellizzato: Mollusk Fisheries and Aquaculture in Italy 209

promulgated severe restrictions on new entries to certain

fisheries. In addition, regulations for harvesting mollusks

now stipulate a maximum daily catch per boat of 600 kg

(1,325 pounds), 4-5 working days/week, and a limit on

the number ofboats working; a moratorium also exists on

issuing of new licenses. Recent legislation also reduced

the annual fishing period for C. gallina from 11 to 10

months, though it was so heavily fished in the past 10 years

that it now is impossible to obtain commercial quantities.

In 1990 the establishmen t of molluscan sanctuaries

in inshore littoral zones (from the beach to 1.5 n.mi.)

was also proposed. As yet, they have not been definitively established. At the same time, installation of new

propulsion engines or upgrading ofold ones and rebuilding of processing plants for the mollusk fishery were excluded from federal financial assistance. Daily quotas on

mollusk catches were reduced further, and the number of

operating days were reduced from 5 to 4 days per week.

Finally, special financial assistance was made available as

an incentive to develop new aquaculture enterprises.

Condition of Molluscan Fisheries

Mussels

Mussels have the highest annual landings of any mollusk,

and in 1989, Italy was second in Europe to Spain in mussel

production (Fig. 9). Statistics in Figure 9, listing 100,500 t

for Italy, are official government data for mussels passing

through established markets, but we estimate that mussel

production passing through both the officially recognized

outlets and the many smaller local markets was actually

about 175,000 t (5.8 million bushels) in 1992.

300

250

Z'

0

0

q 200

-

c

0 150 :u::l

'C

e 100 lL

50 .

0 E ITALY NL F D JU DN

Figure 9

Comparison of mussel production among the main

producers of Europe in 1989 (official quantities). E =

Spain, NL = Holland, F = France, D = Germany, JU =

Yugoslavia, DN = Denmark.

Culture methods are mostly traditional, but they are

highly developed and give good results. Near Trieste,

culturists have long-line installations for mussel culture

in open sea environments. Culturists put mussels, 10-

25 mm long, in mesh socks, and suspend the socks in

estuarine and marine areas until the mussels have

reached marketable size, 45-70 mm long, in 14-20

months (Pellizzato and Renzoni, 1989). They rework

the socks as often as 4-5 times to remove the larger

mussels and place them in socks with larger meshes.

A major breakthrough in the hanging culture of

mussels occurred in the mid-1960's with the introduction of polypropylene mesh tubing to form the mussel

cords. This material was introduced first at La Spezia and

quickly spread to the northern Adriatic. This change in

methodology greatly reduced the labor in preparing the

cords and permitted a substantial increase in the volumes

handled. Before the introduction ofmesh socks, the cords

were prepared by inserting small clusters of mussel seed

into twisted grass rope, a slow and tedious operation.

In the shallow lagoons of Venice-Chioggia, the Po

delta, Taranto, aples, and La Spezia, culturists use two

methods, known as the Venetian and the Taranto methods. They are different mainly in the configuration of

the support structures of the poles or racks.

In the Venetian system (Fig. 10), the racks are permanent structures, composed of two massive end-frames

which are supported by two or more dolphins of heavy

pilings to which is bolted a horizontal timber. Heavy

galvanized cables (12-14 mm in diameter) are stretched,

with about 50 em spacing, from the transverse member

of one end-frame to the opposite member; the distance

between end frames may be 100 m or more. At intermediate positions (about 5-10 m), horizontal supports composed of 15 x 15 em timbers run perpendicularly to the

cables and are supported by two or three light pilings.

In the Taranto system (Fig. 11), upright (corner)

support members are constructed of considerably lighter

stakes, cinched at their apex with cord or wire. The

clusters of poles are arranged in a quadric pattern with

spacing of 8-10 m. A heavy line is strung from corner to

corner to form square cells; often diagonal runs of line

are also used between corners.

In both systems, culturists hang the net socks with a

short length of light cord from the cables or lines so

that the tops of the socks are at or slightly above mean

low water. The length of socks is a function of water

depth, but a space of 0.5-1 m is left between the bottom

of the socks and the sediment surface.

In the past, mussel culturists in the northern areas

collected wild mussel seed from rocks and other shoreline structures, including the pilings of the culture

system. In the 1980's, they tested artificial collectors

made of netting and could obtain seed within their

parks. The traditional method at Taranto, however, has
210 NOAA Technical Report NMFS 129 _

Figure 10

Venetian mussel culture method. Photograph by M.

PellizzaLO.

always used collectors made of natural fiber cords. In

the past, small mussels were sometimes purchased from

third parties who gathered them for sale to the culturists.

Clams

The principal species of clams harvested in Italy are T.

philippinarum and T. decussatus, both produced by culture, and C. gallina and C. chione, both landed from

natural stocks (Mattei and Pellizzato, I989-E.S.A.V.,

1990) (Fig. 12). Before 1983, clam production was based

almost exclusively on natural stocks of T. decussatus and

C. gallina. But fishermen overharvested the wild stocks

and production fell. To meet the demand for clams,

culturists imported T. philippinarurn for sowing in estuarine areas beginning in 1983. This species, which grows

faster than native clams (Pellizzato and Mattei, 1986,

1988; Pellizzato et al., 1989) but is morphologically

similar except for its siphons, colonized Italian waters

in dense numbers and restored clam production

(Fig. 13).

Culturists raise T. philippinarum principally in lagoons

and saltwater impoundments in Marano, Venice, and

the River Po delta. Culture involves producing juvenile

clams in hatcheries and then sowing them on the bottom. At first, the seed is held in trays to preven t predation by crabs and the gilthead bream, Sparus aurata,

(Fig. 14). When the clams have reached 15-20 mm,

culturists transfer them to firm bottoms at a density of

200-400 clams/m2 and cover them with plastic nets to

limit predation (Fig. 15, 16). In 16-18 months, the

clams have grown to a commercial size of 35-40 mm.

Figure II

Taranto mussel culture method. Photograph by M. Pellizzalo.
____________________ Mattei &: PeUizzato: Mollusk Fisheries and Aquaculture in Italy 211

Oysters

Figure 13

Production trend of the carpet clam, Tapes philippinarum, from 1985 to 1991, for the northeastern coast,

the principal area in Italy for producing this species.

Until this century, the only oyster species cultured was

Ostrea edulis, which is indigenous to Italy (Korringa,

1976). In the early 1900's, fishermen introduced and

grew the Pacific oyster, Crassostrea gigas, but have since

nearly abandoned oyster culturing because consumers

have become cautious about eating them. C. gigas and

0. edulis are cultured only in traditional areas such as

the lagoons of Venice and Taranto. Culture consists

simply ofrestocking quantities harvested from prepared

and controlled environments. On a small scale, culturists

also collect seed on natural and artificial substrates.

They place the seed in vertically-stacked, multistory

baskets that are suspended subtidally until the oysters

grow to commercial size (Fig. 17).

1985 1986 1987 1988 1989 1990 1991

Year

/ lopo area DVenetian area I ~5

176

"4

..:; H

5.3 """ I""""

1..

/-= .= 003.=5 [ L;;:; A ~;, D

16

14

0 12

& 10 :s.

c

0 8

U:J 6 -c

e 4 0..

2

0

Figure 12

Five species offamily Veneridae clams harvested in the

Mediterranean Sea: Upper left, Venus verrucosa; upper

right, Callista chione; lower left, Chamelea gallina; lower

center, Dosina exoleta; and lower right, Tapes decussatus.

Photograph by E. Rufert from collect. of Mus. Civ. St.

Nat., Venezia.

Scallops

Culturists have been establishing parks or managing

natural beds with great commercial success. In many

areas, the species has also colonized natural bottoms

and is subject to controlled harvesting as for any wild

stock (E.SAV., 1990).

The best yields and growth rates of T. philippinarum

have been obtained by seeding areas having a good

circulation, which provides a good food supply and

usually better water quality. Some areas, such as fishfarming lakes, often show less favorable conditions since

they can be affected by hypoxia and extensive macroalgal

blooms, with consequent weakening and even death of

the clams during summer. Production of this species

has risen steadily from about 15 t (about 375 bushels)

in 1985 to 27,000 t live weight (about 700,000 bushels)

in 1991.

In the 1980's, after 30 years of intense exploitation of

naturally occurring scallops, the first signs of dwindling

populations were noticed. At the beginning of the

1980's, the beds of the two most important species,

Pecten jacobaeus and Aequipecten opercularis (Piccinetti et

aI., 1986), became smaller and production fell. The

situation deteriorated further in the mid 1980's to the

detriment of workers who shucked and packed the

scallops for market. The fishing fleet weathered the crisis

slightly better with relatively inexpensive diversification to

otherspecies. As a consequence ofthe lack of appropriate

harvest controls, the scallop resource now is on the brink

of extinction. Research has begun, therefore, into the

controlled production and growout ofscallops.

The first attempts at culturing P. jacobaeus began in

1991. Culturists grow them on long-lines in the open

sea (Fig. 18). The culture techniques being tried in the
212 NOAA Technical Report NMFS 129

Figure 14

Growing small seed of the carpet clam, Tapes philippinarum, in trays.

Photograph by M. Pellizzato.

Figure 15

Culturists free-seeding carpet clams, Taprs philippinarum, about I em in

size. Photograph by M. Pellizzato.
____________________ Mattei & Pellizzato: Mollusk Fisheries and Aquaculture in Italy 213

Figure 16

Culturists laying down netting mechanically to protect beds seeded with

clams. Photograph by M. Pellizzato.

Figure 17

Growing oysters in a basket as used in a lagoon. Photograph by M.

Pellizzato.
214 NOAA Technical Report NMFS 129

Figure 18

Italian scallop culture using the longline system. Photograph by M. Pellizzato.

northern Adriatic Sea are the same as those used in

Japan and the northeast Atlantic Ocean (Mattei et aI.,

1992). Culturists collect wildjuvenile scallops on masses

of artificial filaments (Fig. 19) and suspend them by a

line through a hole in a corner (ear) of their shells or

by holding them in multistory lantern-net baskets. Hatcheries for clam and scallop production are also being

constructed, especially in the northern Adriatic Sea. In

1991, landings (whole weight) of natural and cultured

P. jacobaeus were about 2,500 t (estimated), and of A.

opercularis, about 50-100 t (Fig. 20).

Snails

Fishermen, mostly in the southern Adriatic Sea, gather

snails for sale by scraping rocks and diving for them

using scuba gear. The snails are ofthe genera Cerithium,

Murex, Natica, Sphaeronassa, and Patella.

Mollusk Preparation For Eating

In Italy, mollusks are eaten several ways. Mussels are

steamed with vegetables and also cooked in tomato

sauce. The clam, C. gallina, is shucked mechanically

and cooked. Small scallops are eaten whole after being

fried, or cooked and served with wine or a sauce. Large

scallops are first prepared by cutting out the mantle

and then the muscle, gonad, and visceral mass are

broiled and eaten. The snails are boiled, with the large

ones pulled from their shells and marinated, while the

small ones are pulled from their shells and eaten directly by the diner.

The Future

Molluscan production still relies heavily on fishing natural

stocks. But increasingly sophisticated equipment, inad-
____________________ Mattei & Pellizzato: Mollusk Fisheries and Aquaculture in Italy 215

Figure 19

Examples of experimental artificial collectors ofscallop spat used in the

north Adriatic Sea. Photograph by N. Mattei.

800

200

c

o

U::>

"C

e

Cl.

°

°

0.

1,400,------------,------------,

Z" 1,000

1,200 r--------------'

"* P. jacobaeu5

oL- ~~~~~=:::::::::...~_ _.J

80 81 82 83 84 85 86 87 88 89 90 91

Year

Figure 20

Scallop production trends in the principal Italian scallop port, 1980 to 1991.

equate regulations (often ignored), and a marine ecosystem damaged by pollution have depleted natural stocks.

The reasons for the decline in certain resources are often

multiple, and they are not always easily identified.

Aquaculture will be important in the future. The

coastal lagoons are ideal for growing mollusks, but they

have limits as far as production and expansion are

concerned. The Adriatic Sea, with good conditions for

aquaculture, also must be used. The Adriatic's elevated

primary productivity would make it possible to farm

mollusks in high concentrations. A secondary benefit

from growing cultured mollusks is that their larvae

would disperse and might reestablish or enhance populations in natural grounds.

Literature Cited and Selected References _

Baud,J. P., andJ. Haure.

)989. Elevage intensif en marais de la palourde japonaise
216 NOAA Technical Report NMFS 129

(Ruditapes philippinarum) [Intensive culture of the Japanese

carpet shell clam in coastal impoundments.] Int. Aquacult.

Conf. 2-4 Oct. 1989, Bordeaux, p. 25-26.

Bouchon-Brandely, G.

1890. Oyster-culture in Italy. In]. R. Philpots, Oysters and all

about them, p. 662-692.

Bussani, M.

1983. Guida pratica di mitilicoltura. [Practical guide for mussel culture.] Edagricola Bologna, 231 p.

Cesari, P. and M. Pellizzato.

1985. Molluschi pervenuti in laguna di Venezia per apporLi

antropici volontari 0 casuali. Acclimazione di Saccostrea

commercialis (Iredale and Roughlely, 1933) e Tapes philippinarum (Adams and Reeve, 1850). [Mollusks introduced

intentionally or accidentally into the Lagoon of Venice by

human activities. Acclimation of Saccostrea commercialis and

Tapes philippinarum.] Boll. Malaco!., 21 (10-12):237-274

Coste, P.

1861. Voyage d'exploration sur Ie littoral de la France et de

l'ltalie. [Exploratory travel along the coasts of France and

Italy.] Paris, Deuxieme ed., 292 p.

Dean, B.

1893. Report on the European methods of oyster-culture. Bul!.

U.S. Fish Comm. XI:357-406.

D'Erco, R.

1862. Sulla coltura delle ostriche e sulle asterie 0 stelle di mare.

[On the culture of the oysters and on the asteroids or sea

stars.] Pub!. Coen, Trieste, 148 p.

1863. Sulla coltura dei pidocchi. [On the culture of blue mussels.] Pub!. Tipografia Lloyd-Austriaco, Trieste, 28 p.

1864. Sulla coltura dei pidocchi:opuscola secondo. [On the

culture of Blue mussels: Second Volume.] Pub!. Tipografia

Demorchi-Rougier, Zara, 15 p.

E.SAV.

1990. Tapes phillippinarurn-Biologia e sperimentazione. [Tapes

philippinarum-Biology and experimentation.] E.S.A.V.-

Regione Veneto, 299 p.

FAO.

1987. Mediterranee et Mer Noire, Zone de Peche. [Mediterranean and Black Sea, Fishery Zone.] Food Agric. Organ.,

U.N. 37, Rev. I, p. 1-760.

Froglia, C., and G. Ore!.

1971. Possibilita di determinazione di biocenosi bentoniche in

base agli organismi catturati con reti a strascico. [Possibility of

characterizing benthic biocoenoses based on the organisms

collected by otter trawls.) Quad. Lab. Tecno!. Pesca 1(2):37-41.

GUDRl.

1991. Adozione del terzo piano nazionale della pesca e

dell'acquacoltura nelle acque marine e salmastre (1991-

93). [Adoption of the third phase of the national plan for

fisheries and aquaculture in marine and brackish waters

(1991-93).] Gaz. Ufficale Della Repubblica Ita!. 12:1-60.

Graioni, U.

1975. Acquacoltura-dalla rivoluzione verde a quella b:u.

[Aquaculture-from the green revolution to the blue.] Min.

Agric. For., Roma, p. 20-21.

Korringa, P.

1976. Farming the flat oysters of the genus Ostrea. A

multidisciplinary treatise. Elsevier Sci. Pub!., Amst., 224 p.

Manzi,].]., and M. Castagna.

1989. Nursery culture of clams in North America. In].]. Manzi

and M. Castagna (eds.), Clam mariculture in orth America,

p. 127-147. Elsevier Sci. Pub!., Dev. Aquacult. Fish. Sci. 19,

Amst.

Mattei, N., and M. Pellizzato.

1989. Mollusc aquaculture in Italy. E.A.S. Q. News!. 53/53:

51-53.

Mattei, N., C. Piccinetti, and A. Renzoni.

1992. Sperimentazione di collettori artificiali per il reclutamento

di giovani individui di Pectinidae nel Nord. [Experimentation with artificial collectors for the setting of early sessile

stages ofbenthonic organisms in the northern Adratic Sea.]

Bol!. Mus. Storia lat. Venezia, 42(1991)1993:23-30.

Pellizzato, M., and N. Mattei.

1986. Allevamento di Tapes (Ruditapes) philippinarum (Adams

and Reeve, 1850) in alcuni biotopi lagunari veneti. [Culture

of Tapes (Ruditapes) philippinarum in some Venetian lagoon

biotopes.] Nova Thalassia 8:393-402.

1988. Aspetti economici dell'allevamento di Tapes philippinarum

(Adams and Reeve, 1850) nelle lagune venete. [Economic

aspects of the culture of Tapes philippinarum in Venetian

lagoons.] II Pesce 1:23-27.

Pellizzato, M., and A. Renzoni.

1989. Raccolta di seme di Mytilus galloprovincialis Lmk, Ostrea

edulis L., Crassostrea gigas (Thunberg) e loro allevamento in

laguna di Venezia. [ColleCl:ion of seed of Mytilus

galloprovincialis, Ostrea edulis, and Crassostrea gigas and their

culture in the Lagoon of Venice.] Nova Thalassia 8(Supp!.

3):381-392.

Pellizzato, M., N. Mattei, and A. Renzoni.

1989. Allevamento su scala commerciale di Tapes philippinarum

(Adams and Reeve, 1850) in alcune valli Venete. [Commercial scale culture of Tapes philippinarum in some fish culture

impoundments of the Veneto Region.] Oebalia 15:735-744.

Piccinetti, C., A. Simunovic, and S.Jukic.

1986. Distribution and abundance of Chlamys opercularis (L.)

and Pecten jacobaeus L. in the Adriatic Sea. Food Agric. Organ. U.N., Fish. Rec. 345/86:99-105.

Plinio, C.

1539. Plini secundi, HisLOriae Mundi libri XXXVII. [Plinius

Caecilius Secundus, World History, Book 37.] Officina

Frobeniana, Basilae.

1562. Historia naturale di C. Plinio Secondo, trad. di Domenichi

L. [Natural History of Plinius Caecilius Secundus. Trans!. of

L. Domenichi.] Giolito De Ferrari, Vinegia.

Scalfati, G.

1Y70. La mitilicoltura, il suo ambiente, l'organizzazione tecnicoeconomica e la disciplina. [Mussel culture, its environment,

technico-economic structure and its regulation.) Min. Mar.

Mercantile, Dir. Generale Pesca Marit., Mem. 29:1-272.

Solinari, V. S.-M.

1987. II pesce nel commercio e nelle mense dell'antichita.

[Fish in commerce and on the tables of ancient cultures.]

Padova, E.N.E.A.-A.E.1. 4:90-95.

Shumway, S. E. (ed.).

1991. Scallops: biology, ecology and aquaculture. Elsevier Sci.

Pub!., Amst., 1,095 p.

Valli, G., and D. Dovier.

1977. Observations preliminaires sur la reproduction et la

biometrie de Pecten jacobaeus L. [Preliminary observations

on the reproduction and biometry of Pecten jacobaeus L.]

Rapp. Comm. Int. Mer Mediterr., 24:4.
The History, Present Condition, and

Future of the Molluscan Fisheries of Croatia

ADAM BENOVIC

Biological Institute

20000 Dubrovnik

Croatia

ABSTRACT

For many years, European oysters, Os/rea edulis, and black mussels, Mytilus galloprovincialis,

have been cultivated in Croatia. About 16 additional mollusks, mainly the European date

mussel, Litophaga litophaga; Noah's are, Arca noae; bearded horse mussel, Modiolus barba/us;

and banded murex, Phyllono/us /runculus, have been gathered from natural beds for food

and other uses. From the 16th to the 18th century, the main oyster cultivation technique was

placing tree branches in the water to collect and grow spat to market size. Use of bundles of

branches of the mastic tree, Pis/acea len/iscus, continues today. After 1945, fishermen also

began to cultivate mussels. They collected small mussels along the shore, intertwined them

into ropes, and hung them. After 1965, fishermen switched to plastic mesh socks to hold the

mussels. Molluscan farms consist of lines of ropes suspended off-bottom by buoys and

anchored at their ends. Socks containing mussels or oysters hang from the ropes. Mussel

production is about 3,000 t/year. About one-third are sold fresh, either exported or to local

markets. The remainder are processed. Oyster production is about 2 million pieces/year.

About 60 people cultivate mollusks, and about 100 families produce small quantities of

mussels and oysters for local markets. During the past 20 years, the mussel, followed by the

oyster, are the only mollusks landed in quantity. Targeted fishing for mollusks from natural

beds is rare and is associated with finfishing, but some high-priced mollusks, such as the

European date mussel and banded murex, are sought and sold in local markets. Legal,

research, and the environmental issues will affect shellfisheries in the future.

Introduction Habitat Description

European flat oysters, Os/rea edulis, and black mussels,

Mytilus galioprovincialis, have been cultivated for many

years along the Croatian coast (Fig. 1). About 16 additional mollusks, mainly the European date mussel,

Litophaga litophaga; Noah's ark, Area noae; bearded horse

mussel, Modiolus barbatus; and banded murex, Phyilonotus

truneulus, have been gathered from natural beds for

food and other uses.

Oysters and mussels were once cultivated in at least

30 sites in Croatia, but for various reasons most sites

were abandoned. In the last 30 years, Limski Bay and

the Bay of Mali Ston have ~aintained production, and

a few years ago Zadar and Sibenik were brought back

into production. During the past 20 years, the black

mussel, followed by the oyster, are the only mollusks

landed in quantity.

The Adriatic Sea (surface area, 138,595 km2; average

depth, 173 m), the northernmost bay in the Mediterranean Sea, can be divided into northern, middle, and

southern regions according to physical, chemical, and

biological properties. The northern region is shallow.

rarely exceeding 50 m, and has wide temperature fluctuations of 6°-27°C, and a salinity of 34-37%0 due to

considerable inflow ofwater from the Po River. Biological production is higher than in other areas, primarily

owing to considerable nutrients coming from the land.

Its richness is portrayed through the larger quantities

ofrelatively few species, especially pelagic communities

(Revelante and Gilmartin, 1977).

The middle region extends from the 100 m isobath

to the Palagruza threshold, with its greatest depth atJabuka

pit (over 200 m); it has a temperature range of 10°-25°C

217
218 NOAA Technical Report NMFS 129

®

,~ '" '('.:\.

~\

Figure 1

The Adriatic Sea and historical sites of mollusk production (closed circles) along the coast of Croatia.

and salinities of 36-38%0. The land influence here is

weaker, and oscillations in ecological factors are less.

The southern region extends from the Palagruza

threshold to the sea's entrance off southeastern Italy,

and being directly influenced by Ionian Sea currents, is

somewhat similar to the open regions of the Mediterranean Sea. It has a great depth (maximum ofl,334 m), a

temperature range of 11°-23°C, and salinities of 37-

39%0. The influence from the land is minimal.

The ecological characteristics are somewhat different along the Croatian coast where river mouths, closed

and partly closed bays, and underwater springs strongly

influence local habitats. The coast of Croatia is mainly

rocky (limestone). The only areas where shellfish can

grow abundantly are sand and clay bottoms near the

river mouths and in a few sheltered bays ( Milisic, 1991).

Most mollusk cultivation sites were in the north where

ecological conditions are favorable (Buljan and ZoreArmanda, 1966), but during the last 30 years, only two,

Limski Bay and the Bay of Mali Ston, maintai~ed production, and an additional two, Zadar and Sibenik,

were activated a few years ago (Fig. 1).

Limski Bay, a northern Adriatic fjord, has an average

depth of 15 m and sand and clay substrates. The temperature range is 9°-26°C and salinities run 26-37%0.

Zadar, in the middle Adriatic, is sheltered, has an

average depth of 12 m, a temperature range of 10°_

23°C. salinities of 35-37%0, and a sandy bottom. In

1986, mussel cultivation was introduced near a culture

operation of European sea bass, Dicentrarchus labrax.

The bass culturists placed "pergolars" (plastic mesh

socks) with mussels near the sea bass cages with the idea

that the mussels might use phytoplankton grown on

nutrients excreted by the fish.

Sibenik, also in the middle Adriatic, has an average

depth of 15 m. temperatures of 8°-25°C, salinities of

18-37%0, and sand-clay bottom sediments. In 1987,

mussel cultivation was introduced near the mouth of

the Krka River.

The main shellfish production area in Croatia is the

Bay of Mali Ston near the City of Dubrovnik in the

southern Adriatic. The bay is especially productive because it is sheltered and has many underground springs.

Its depth ranges from 10-26 m, temperatures from

10°-25°C, and salinities from 24-37%0. Its sediments

are clay and sand.

Shellfisheries History

Prehistoric humans used shellfish for food along the

eastern Adriatic coast. Prehistoric oyster and mussel

shell piles were found in caves on the island of Hvar

(Novak, 1955), and ancient shell piles have been found

along the coast ofthe Istrian Peninsula, in the region of

Zadar and Sibenik, and in the area of the Bay of Mali

Ston (Fig. 1) (Glavina, 1976). From the times of the

Roman Empire, oyster cultivation was noted in the Bay

of Mali Ston, where some petrified oak branches with

oyster shells were found (Skaramuca and Gjukic, 1982).

The cultivation method used was the same in other

regions ofthe Roman Empire (Heral and Deslous-Paoli,

1991). Oyster cultivation in the Bay of Mali Ston was

noted in the sixteenth century (Basioli, 1982), but no

information is available on methods other than the

placing of oak, Quercus pubescens and Q ilex, branches in

the water and collecting them at suitable times.

More details are known only for the Bay of Mali Ston

from the sixteenth century onward. The main cultivation technique until the eighteenth century was to place

oak; olive. Olea europea; and cherry, Prunus avium,

branches in the water and collect the marketable oysters that had set and grown on them about 3 years later

(Skaramuca and Gjukic, 1982). Parallel to this, during

the seventeenth century and onward, the techniques

improved when oysters were grown on square wooden

frames which were placed in the water during the spawning season to collect spat and retrieved after the oysters

had grown (Basioli, 1982).

A ·'faschio." a bundle ofthin 2 m-Iong branches about

of the mastic tree, Pistacea lentiscus, was later invented

and proved to be the best tool for collectors, and it
________ Benovic: The History, Present Condition, and Future of the Molluscan Fisheries of Croatia 219

remains in use today (Fig. 2). In the nineteenth century, faschios were removed from the bottom after a

year, cut into smaller pieces, and hung on wooden

"tarantine" frames (Fig. 3). Mter 1930, methods improved with the construction of a squared park (Fig. 4)

fixed on the bottom and with the introduction of cementing small oysters onto wooden sticks. The sticks

are intertwined in the rope and hung on suspended

horizontal lines of the park (Basioli, 1968).

From the eighteen century until the abolition of the

Republic of Dubrovnik in 1808, oyster cultivation in the

bay was regulated by strict governmental rules. The

Government of the Republic of Dubrovnik issued licenses to local families for oyster cultivation and levied

a tax on the oysters. Notes in the Historical Archives of

Dubrovnik1 from 1641 describe the Order of the Government for obligatory checking of oysters for sale.

Controls for quality and size were established in the

Office for Measures and Standards. Mter 1711, production fell because prices declined and taxes increased2.

In 1786 the Senate of Dubrovnik recognized the

need to revive cultivation. Six families were chosen to

place 1,000 oak branches each in the sea, and then 500

new ones each year. The price of oysters was 10 dinars

per basket, the families and their mules were freed

1 Notes in the Historical Archive of Dubrovnik "Diversi di Stagna,"

18.02.1641.

2 Notes in the Historical Archive of Dubrovnik "Diversi di Stagna,"

24.03.1711.

Figure 2

A "fashio" (bundle of branches) taken from

the water after 7 months.

Figure 3

The oldest type of mollusk park (all wooden frames) still in use.
220 NOAA Technical Report NMFS 129

Figure 4

A wooden frame on vertical iron piles from a mollusk

park set up in about 1947. It is now almost abandoned.

from public duties, and the families were given loans3.

In 1899 the "First Dalmatian rational cultivation of

shellfish" company was founded. The company produced at least 800,000 oysters per year. Besides selling

oysters locally, it exported some to Rijeka (Fiume) (Fig.

1), Berlin, and Paris. At the peak of production in 1930,

the Bay of Mali Ston produced more than 1 million

individual oysters (pieces). They were transported by

train daily to markets in Zagreb, the capital of Croatia.

Other sites along the Adriatic coast did not maintain

cultivation, but many fishermen tried to follow the example of the Bay of Mali Ston. In Limski Bay, the

introduction of the tarantine method of collection and

cultivation was attempted from 1888 onward (Basioli,

1968).

After 1945, some fishermen also began to cultivate

mussels. They collected small mussels along the shore~,

intertwined clusters ofthem into ropes, and hung them

from suspended ropes. After 1965, the fishermen

switched from the ropes to plastic mesh "pergolars" to

hold the mussels. The socks were also hung on horizontal ropes.

Though the consumption of oysters, and to a certain

extent mussels, has a long tradition along the Croatian

coast, the local population always ate a number ofother

mollusks. The species eaten only raw has been the

oyster. The others have been served mostly in stews or

grilled. A discussion of the current molluscan fisheries

of Croatia can be separated into aquaculture and harvesting from natural beds.

Notes in the Historical Archive of Dubrovnik "Diversi di Stagno,"

27.04.1786.

Figure 5

The new type of mollusk park now in use. Lines of

plastic buoys are connected by ropes and anchored at

each end.

Cultivated Species

The black mussel and European flat oyster are the only

mollusks being cultivated. Mollusk farms, which vary in

size, consist of lines of ropes suspended off-bottom by

buoys and anchored at their ends. Socks containing

mussels or oysters are hung from the ropes (Fig. 5).

The fouling organisms that collect on the mussels and

oysters do not interfere with rearing them. In the Bay of

Mali Ston, they consist of sponges, polyzoans, and tunicates; barnacles are almost absent (Igic, 1981). The offbottom cultivation eliminates all benthic predators. The main

predator ofboth species is the sea bream, sparus aurata.

Black Mussel

In the past 20 years, this mussel has had the highest

production of any mollusk in Croatia. After 1945 it was

introduced into farms for trials, and mussel production

rose sharply because the market for it was strong and it

was e:tsy to cultivate. Mussels are cultivated in four

farms. i.e., in Limski Bay, in the Zadar and Sibenik

regions, and in the Bay of Mali Ston, the latter farm

produces more than 50% of the total (Fig. 6, 7).

Large ropes, primarily used for collecting mussel

spat, are placed in the water where the larvae concentrate. In the Bay of Mali Ston, larvae set near the surface. If this seed supply is insufficient, workers collect

additional quantities from natural beds along the shores,

and a few times in the past 20 years, a limited quantity

had to be imported from Italy.

After about 6 months, workers remove the small mussels from the ropes, put them in "pergolars" about 4 m
________ Benovic: The History, Present Condition, and Future of the Molluscan Fisheries of Croatia 221

Figure 6

North-south view of the most productive subarea of the Bay of Mali Ston (Bistrina). It

produces about 600 t of mussels (20,000 bushels) /year.

long, and hang them on the lines (Fig. 8,9). Mter 6-8

months, the mussel socks are harvested. The large mussels are delivered to markets, and the small ones are put

back in the socks for further growth. The entire growth

period from spat to market size is about 18-20 months.

Mussels have their highest quality in the summer.

Mussel production in Croatia was about 3,000 metric

tons (t) (100,000 bushels)/year in 1990. About onethird of the mussels are sold fresh, either exported or

to local markets where they sell for US$l/kg. The remainder are processed, principally by steaming them in

funnels, separating the meats from the shells, and deep

freezing the meat. Frozen mussel meat is packed in

quantities of 0.25, 0.5, and 1 kg. Mussels are exported

mainly to Italy. The Italian buyers visit the Croatian

farms and purchase the mussels directly from them.

European Flat Oyster

The oyster is now grown only in Limski Bay and the Bay

of Mali Ston. The main type ofspat collector is still the

"fashio," as in the past, but plastic plates of various sizes

(small, 20x20 cm; large, 50x50 cm), "Chinese hats,"

and some other types have been tested, and their use is

slowly growing (Fig. 10, 11, 12). Workers place collectors in traditionally known spat beds and, after about 6

months, remove them from the water. They cement the

small oysters onto pieces of wood or thin ropes. These

are then intertwined into thick ropes about 4 m long.

Figure 7

A view of the "Dalmacijabilje" Company in the Bay of

Mali Ston.

The thick ropes are then suspended from the ropes in

the farms and left there until the oysters attain market

size. Workers put any oysters that are too small for

market in baskets and suspend them again in the farms

for further growth.

The entire growth period from spat to market size is

about 18-20 months as with mussels. Oysters are of

highest quality during the winter. Traditionally, St. Joseph Day (19 March) is known as the day for judging

the annual harvest. In the Bay of Mali Ston (Town of
222 NOAA Technical Report NMFS 129

Figure 8

Experimental "pergolar" with l2-momh-old mussels

from 6 m depth.

Ston), it is a day of local celebration, including church

processions, barbecues, and sales of souvenirs.

Oyster production in Croatia was about 2 millicn

pieces in 1990, of which the Bay of Mali Ston produces

about 60%. The entire production is sold fresh, mostly

at local markets, where oysters sell for $0.10 apiece.

Somewhat less than 30% of the production is exported

to Italy.

Companies and Workers

In Croatia, only three companies4 are involved in mollusk production. They are Marimirna in Limski Bay,

Cenmar in Zadar, and Dalmacijabilje in Dubrovnik (Bay

of Mali Ston). Though the companies produce fish

also, an estimated 60 people work in mollusk cultivation. In addition, about 100 families produce small

quantities of mussels and oysters for local markets.

4 Mention of trade names or commercial firms does not imply endorsement by the National Marine Fisheries Service, NOAA.

Figure 9

Researcher from the Biological Institute, Dubravnik, holding experimental "pergolars" with 8-

month-old mussels from 6 and 8 m depth.

Sanitary Control

The government has regulations for the control of water quality and meat quality, which are checked by

veterinary authorities. With regard to new investments

in aquaculture projects. site selection and the capability

of the investor to cultivate mollusks have to be checked

by authorized institutions. A license is issued after government approval of the necessary documents.

Harvesting Natural Mollusks

Targeted fishing for mollusks from natural beds has

been rare and is associated with finfishing, such as

trawl-netting, gill-netting, and drag-netting. But some

precious or high-priced mollusks, such as the European

date mussel, or traditionally fished species, such as the

banded murex, have been sought by fishermen and

sold occasionally in local markets. The other mollusks

have been caught mainly for home use or for bait

by sportfishermen. No statistics on numbers of fishermen or landings are available for these species. The

following are mollusks, other than European oysters
________ Benovic: The History, Present Condition, and Future of the Molluscan Fisheries of Croatia 223

Figure 10

Plastic plates, a new type of oyster spat collector.

The oysters are about 3 cm in diameter and 8

months old.

and black mussels, with distributions, collection methods, and uses.

European Date Mussel

Called "prstac" in Croatia, this species is found along all

rocky coasts, preferring dolomites. The better known

beds are on the western coast of the Istria Peninsula,

the Velebit channel, the Split area, and the Bay of Mali

Ston. Date mussels bore into rocks and inhabit the

perforations. They are harvested year-round..'> Fishermen dive for them without tanks, use a chisel and

hammer to smash the surface of the stones, and then

pick out the mussels with forceps. In the past, solitary

stones and parts of stones used to be taken ashore and

carefully smashed to get the mussels, but now taking

the stones out of water is forbidden.

The species' meat is excellent and is a specialty in

restaurants. It is eaten steamed, with the addition of

5 In 1995 (after this article was written) the Croatian government

banned further harvesting of the European date mussel.

Figure 11

Researcher from Biological Institute, Dubrovnik,

examines a new type of oyster spat collector.

some spices. These mussels are rarely found in local

markets, as they are mainly sold directly to restaurants.

They are an excellent bait for the sea bream and other

fishes of the same family.

Noah's Ark

Called "kunjka" in Croatia, this species is distributed

along all rocky coasts. The best known beds are in the

Istria Peninsula, the Zadar area, and the Bay of Mali Ston.

Noah's ark is harvested year-round by boats using

modified rakes (kunjkara), or by diving and hand collection. The meat is tasty and eaten raw, steamed, or

grilled without spices or other additions. It is occasionally

found in local markets, and sport fishermen use it for bait.

Bearded Horse Mussel

Called "runjava dagnja" in Croatia, this species is rather

scarce, but is found along rocky shores, mainly at depths

below 2 m. It is most abundant in the Bay of Mali Ston,

B~y of Kastela (Split region), and Murter Island

(Sibenik region).
224 NOAA Technical Report NMFS 129 _

Figure 12

Detail of the new type of oyster spat collector. Diameter ofthe year-old oysters in front is about 5 em.

The bearded mussel is collected year-round with modified rakes or by diving and hand collection. The meat

is served raw or steamed, but only rarely sold in local

markets.

Noble Pen Shell

Called "periska" in Croatia, the noble pen shell, Pinna

nobilis, is common in the coastal zone of the Adriatic

Sea on sandy bottoms in 2-20 m depths. This is the

largest shellfish of the Adriatic Sea, and some reach 1.2

m in length. It was once collected year-round by diving

or by using special pincers called "Iosnar."

The meat can be prepared by steaming, but the species

was caught mainly for its decorative shell. However, the

noble pen shell has become rare, and since 1976 it has been a

protected species: it is unlawful to catch and sell them.

Great Mediterranean Scallop

Called 'Jakopska kapica" in Croatia, the great Mediterranean scallop, Pecten jacobeus, is common in the coastal

zone ofAdriatic Sea on sandy bottoms at 8-30 m depths.

It is common in the Zadar area and the Hvar channel

and is collected year-round by diving or using trawl

nets. The meat is edible and is prepared by steaming. It

is caught for its meat and decorative shells.

European Thorny Oyster

Called ''kopito'' in Croatia, the European thorny oyster, 5pondyIus gaedempus, is uncommon, but occurs along all rocky

shores to a depth of 30 m, usually attached to stones

covered with algae. It is collected year-round by diving or

using a special rake, the ''kopitar.'' The meat is edible and is

served raw with a few drops oflemon. It has no market value.

Tuberculate Cockle

The tuberculate cockle, Acanthocardia tuberculata, called

"kapica prugasta" by Croatians, is found along the entire Adriatic shore on sandy bottoms at 2-15 m depths. It

is most common near river mouths near the west coast of

the Istria Peninsula and in the Zadar and Split regions. It

is cal1ected year-round by diving or using rakes or dredges.

The meat is edible, but has no market value. The cackle is

used more for bait and for its decorative shells.

Poorly Ribbed Cockle

Called "obicni vaganj" in Croatia, the poorly ribbed cackle,

Aranthocardia paucicostatum, is common in the Adriatic Sea

and found on sand and clay bottoms at depths of between

5-200 m. Randomly taken in trawl catches, the meat is

edible but rarely available in local markets.

Olive Green Cockle

Called "kapica srcanka" in Croatia, the olive green

cockle, Cerastoderma glaucum, is common in the Adriatic

Sea, occurring on sand-clay bottoms mostly between 4

and 10 m. It is taken by dredging, raking, and diving.

The meat is edible, often served raw with lemon or

steamed, and is occasionally sold in local markets. It is

also used as bait for the sea bream.

Grooved Razor Shell

Called "cjevasti sljanak" in Croatia, the grooved razor

shell, Solen marginatus, occurs close to shore near river

mouths, on sandy and sand-clay bottoms of 0.3-3 m

depths. It is taken year-round by a special tool made of
________ Benovic: The History, Present Condition, and Future of the Molluscan Fisheries of Croatia 225

wire or by modified spoons for collection of sea sand.

Usage is the same as for the European date mussel, but

it is scarce because its spatial distribution is narrow.

Warty Venus

Called "prnjavica" in Croatia, the warty venus, Venus

verucosa, is common in the Adriatic Sea on sand and

gravel bottoms at 1-15 m depths. It is collected mostly

during the warm months by rake or by hand. It is rarely

sold in local markets, though the meat is edible. It is

prepared by steaming.

Grooved Carpet Shell

Called "kucica" in Croatia, the grooved carpet shell,

Ruditapes decussatus, is common in the Adriatic Sea,

mostly near river mouths. It occurs on clay-sand bottoms close to shore in shallow areas. It is gathered by

hand at low tide mostly during the winter. The grooved

carpet shell has excellent meat, is considered a specialty,

and is usually eaten at home. Occasionally it is sold in local

markets, and sport fishermen use it for bait.

Rayed Mediterranean Limpet

Called "plavi priljepak" by Croatians, the rayed Mediterranean limpet, Patella caerulea, a common Adriatic

snail, is found in tidal zones on rocky shores. It is

collected year-round, but is of best quality during the

winter. Fishermen harvest it with knives at low tide. The

meat is edible but rather hard when eaten raw. It is

steamed and served with some spices as an appetizer,

mostly at home. It is rarely sold in markets.

Turbinate Monodont

Called "ugrc" in Croatia, the turbinate monodont, Monodonta turbinata, another common Adriatic snail, is found

in intertidal zones on rocky shores. It is collected during

low tide by hand, mostly at night. Turbinate monodonts

are cooked in saltwater and must be removed when the

water boils. The meat is especially tasty and is taken from

the shell with a needle. Finfishermen eat it while waiting

for a catch with longlines. It is rarely sold in markets.

Common Pelicanfoot

Called "pelikanovo stopake" by Croatians, the common pelicanfoot, ApoOThais pespelicani, is found on sandy

and clay Adriatic bottoms at depths of 10-55 m. It is

collected by diving, by hand, or in trawl net catches.

The meat is edible, but it is collected mainly for its

decorative shell; it is rare in local markets.

Helmet Ton

Called" pUl bacVlls" in Croatia, the helmet ton, Tonna

galea, is the largest Adriatic Sea snail. It is common in

the middle and southern parts, mostly among the islands in the middle of the Adriatic coast, on sand and

sand-clay bottoms, at depths of 20-150 m. This species

was once taken year-round, mostly at night in trawl net

catches. It is protected by the government.

The meat is edible but rarely so used. It is usually

collected for its decorative shell. In the past, the shells

were used as containers and tools for decanting olive

oil.

Banded Murex

Called "kvrgavi volak" by Croatians, the banded murex,

Murex trunculus, a common Adriatic Sea snail, is found

on hard bottoms at depths of 2-50 m. It is most common in the Zadar and Split regions on bottoms fouled

by algae and near concentrations of organic matter.

These snails are scavengers, and fishermen gather

them using a trap baited with meat or collect them

from gill nets year-round, but mostly in summer. The

meat is edible and served steamed, mainly at home.

They are rarely sold in local fish markets, but they make

good bait for sport fishing.

Zoned Miter

Called by its scientific name Mitra zonata in Croatia, this

snail is rare and occurs on clay and coral bottoms at

depths of20-100 m. It is caught in trawl nets, but rarely.

This is the most precious and valuable snail ofthe Adriatic

Sea and is highly appreciated by malacologists, but its

collection and sale is forbidden by the government.

The Future

Important factors that will affect Croatian shellfisheries

include 1) legal issues, 2) research, and 3) environmental issues. First are new regulations that should favor

aquaculture projects. Governmental steps toward new

fishery laws include one relating to aquaculture, and

particular articles will encompass shellfish cultivation.

There are two problems to be solved: 1) Rules for site
226 NOAA Technical Report NMFS 129

selection and licenses and 2) monitoring the environment and production. In this regard, one of the future

obstacles that could arise is strict regulation of the European Community, which is the potential export market,

and the inability ofCroatia to follow these rules because of

the lack of specialized experts and sophisticated equipment. Croatia will need to seek help from more developed countries to establish acceptable monitoring.

Second are needs to expand research to develop aquaculture, including mollusk cultivation. Research is needed

for new species to be cultured. Current research is aimed

at developing new culture methods, and some, especially

for testing for presence of oyster larvae, are already being

given to fishermen for use. A principal goal is to reduce

the labor needed to collectseed oysters and cement them

onto wood and ropes. Research is aimed at having collectors that would remain in the water until the oysters attain

commercial size. A new species to be introduced is the

great Mediterranean scallop. To expand mollusk culture

methods, an exchange of knowledge \-"ith experts from

other shellfish regions will be needed.

Third is maintaining the present quality of the marine habitat and preventing future pollution. Designated areas for future investmen ts in aquaculture

projects need protection. This is closely followed by the

necessity for coastal zone planning, which should separate incompatible human activities, i.e., industrial vs.

aquaculture development. This should be reflected by

legislation, as well as efficient governmental services

that will enable an increase in aquaculture projects.

Taking into account the present increased interest

for new investments in aquaculture, total mollusk production, mainly that ofmussels, could increase to about

20,000 t in the next 10 years. Prerequisites are new

management, research, effective pollution control, and

expanded European markets.

Acknowledgments

I thank Biserka Simatovic for her help with the English

manuscript and Vlado Onofri for the photographs of

mollusk culture in the Bay of Mali Ston.

Literature Cited

Basioli,j.

1968. Shell-breeding on the eastern shores of the Adriatic.

Pomorski Zbornik 6: 179-218. [In Croatian with Eng!. summ.]

1982. Growth of shellfish in the eastern Adriatic, with reference to Maloston Bay. Tn Zbornik Radova Savjetovanja

"Malostonski Zaljev"-Prirodna Podloga i Drustveno

Valoriziranje. Dubrovnik, 12-14.11. 1981, p. 268-281.

Yugoslav Acad. Sci. Arts, Zagreb. [In Croatian with Eng!.

summ.]

Buljan, M., and M. Zore-Armanda.

1966. Hydrographic data on the Adriatic Sea collected in the

period from 1952 through 1964. Acta Adriatica XU: 1-438.

Glavina, F.

1976. Historical account on fisheries ofthe Peninsula Peljesac.

Peljeski Zbornik 1:93-166. [In Croatian with Span. summ.]

Heral, M., and]. M. Deslous-Paoli.

1991. Oyster culture in European countries. in W. Menzel

(ed.), Estuarine and marine bivalve mollusc culture, p. 153-

191. CRC Press Inc., Boca Raton, Fla.

Igic, L.

1981. The fouling of edible shellfish in Maloston Bay Zbornik

Radova Sa\jetovanja "Malostonski Zaljev"-Prirodna Podloga

i Drustveno Valoriziranje. Dubrovnik, 12-14.11.1981, p. 235-

251. Yugoslav Acad. Sci. Arts, Zagreb. [In Croatian with

Eng!. summ.]

Milisic, N.

1991. Skoljke i puzeviJadrana. in P. Pozar (ed.), Logos, Split,

302 p.

Novak, G.

1955. Prehistorijski Hvar, Grapceva Spilja. Yugoslav Acad. Sci.

Arts, Zagreb, 185 p.

Revelante, N., and M. Gilmartin.

1977. The effects of northern Italian rivers and eastern Mediterranean ingressions on the phytoplan kton of the Adriatic

Sea. Hydrobiologia 56(3) :229-240.

Skaramuca, B., and M. Gjukic.

1982. Present production and prospective cultivation of shellfish (mussels and oysters) in Maloston Bay. Tn Zbornik Radova

Savjetovanja "Malostonski zaljev"-Prirodna Podloga i

Drustvel10 Valoriziranje. Dubrovnik, 12-14.11.1981, p. 300-

308. Yugoslav Acad. Sci. Arts, Zagreb. [In Croatian with

Eng!. summ.]
A Review of the Molluscan Fisheries of Turkey

ATILLA ALPBAZ and BELGIN TEMELLI

Fisheries College

Aegean University

35 I00 Bornova

lzmir, Turkey

ABSTRACT

Large quantities of mollusks grow in Turkish waters, but Turks usually eat only the black

mussel, Mytilus galloprovincialis. Fishermen have gathered the mussel for many years. Other

species never were gathered until about 1970 when markets for them were found in Europe

and Japan. Since then, fishermen have gathered at least eight species. The striped venus,

Venus gallina, is gathered (30,000 t/year) by 1,000 boats and 2,500 fishermen using dry

dredges and hydraulic dredges. When a market for the sea snail, Rapana venosa, developed

in Japan, a fishery for them was established in the Black Sea. Fishermen harvest 550 t of

meats/year by dredging or diving. The flat oyster, Oslrea edulis, is harvested by diving or

dredging (1,500 t/year). The short-necked clam, Tapes decussatus, is harvested with shovels,

rakes, or by diving (250 t/year). The black mussel occurs along every coast, and about 200

fishermen harvest it by diving or dredging (1,000 t/year). About 100-150 fishermen in

Ayvalik Bay harvest 200-600 t/year of horse mussels, Modiolus barbatus. The future of the

molluscan fisheries will depend on the strength of foreign demand, because the local

demand is negligible. Some farmers are becoming interested in culturing the oyster, shortnecked clam, and black mussel.

Introduction

Turkey is surrounded by water on three sides: the Black

Sea on the north, the Aegean Sea on the west, and the

Mediterranean Sea on the south (Fig. 1). Its coastline is

about 8,000 km long. Large quantities of mollusks grow

in Turkish waters, but the people ofTurkey eat only the

black mussel, Mytilus galloprovincialis. Fishermen have

gathered the mussel for many years for sale to people in

shore towns and in large cities, such as Istanbul and

Izmir, but only about 1% of the population eats them.

Other species were not gathered until about 1970 when

markets were found for some of them in Europe and

Japan. Since then Turkish fishermen have gathered at

least eight species; all except the black mussel are exported. Estimates of mollusk production are difficult to

make because statistics are incomplete, showing only

that annual production is variable.

Species, Methods, and Quantities Produced _

The mollusks produced in Turkey in order of their

importance (Fig. 2) are: 1) striped venus, Venus gallina;

2) sea snail, Rapana venosa; 3) oyster, Ostrea edulis; 4)

short-necked clam, Tapes decussatus; 5) black mussel,

Mytilus galloprovineialis; 6) horse mussel, Modiolus

barbatus; 7) kidonya, Venus verrueosa; and 8) Area sp.

Striped Venus

This clam is the smallest shellfish that has commercial

importance in Turkey. Its shell is cloudy white outside

and bright white inside. Weights and sizes of the clams

are listed in Table 1.

The striped venus occurs abundantly in sand bottoms in the north Aegean Sea, the Sea of Marmara, and

the Black Sea near Istanbul, in depths up to 15 m (Fig.

1). Commercial fishing for them began in 1985. The

number of boats and fishermen gathering them in 1990

was 779 and 2,153, respectively, in the Sea of Marmara

and Aegean Sea (Table 2).

Besides those, about 200 boats and 350 fishermen

gathered them in the Black Sea. Thus, the total number of

boats is about 1,000; the number of fishermen is about

2,500. The boats are from 5 to 10 m long, and fishermen use two collecting methods. The principal one is

227
228 NOAA Technical Report NMFS 129

towing a dredge which measures 80 cm wide and 20 cm

high (Fig. 3). The second method is a hydraulic dredge,

which consists of a jet head, a knife blade, and a cage

(Fig. 4). The bottom is jetted in front of a knife blade

and the largest striped venus collect in the cage. The

dredge is retrieved and emptied on deck. In 1990,

there were four boats using hydraulic dredges, two at

Istanbul and two at Canakkale on the Dardenelle

(Fig. 5).

Some of the striped venus are canned in factories.

These, as well as live striped venus, are exported to

European countries. Production of the striped venus

was estimated at 4,169 metric tons (t) in 1988, 12,700 t

in 1990, and 30,000 tin 1991.

BLACKSEA

0.0. 0

TURKEY

MEDITERRANEAN SEA

o Mytilus galloprovincialis

.t::.. Venus gal/ina

• Rapana venosa

• Tapes decussatus

A Ostrea edulis

SYRIA

GEORGIA

IRAQ

Figure I

Main areas of molluscan shelifish production along the coasts of Turkey.

Figure 2

Principal molluscan shellfishes gathered in waters ofTurkey: 1) Ostrea edulis, 2)

Area sp., 3) Mytilus galloprovincialis, 4) Modiolus barbatus, 5) Venus verrucosa, 6)

Venus gallina, 7) Tapes decussatus, and 8) Tapes aureus.
___________________ Alpbaz & Temilli: A Review of the Molluscan Fisheries of Turkey 229

Sea Snail

Sizes and weights of the sea snail are given in Table 3.

Until recent years, the sea snail (Fig. 6) was not an

important commercial species, but when a market for it

developed in Japan, a fishery was founded in the Black

Sea and it has now become important. The snails occur

at depths up to 100 m, but most are gathered from

Table I

Morphological values (number =134) for striped venus

(Alpbaz et al. 1990).

Table 2

Number of fishermen and boats fishing for striped

venus in 1990.

No. of No. of

Location boats fishermen

Istanbul 86 264

Tekirtag 71 307

Bursa 30:l 892

Balikesir 120 140

Canakkale 200 550

Total 779 2,153

Category

Total weight (g)

Shell weight (g)

Meat weight (g)

Body length (mm)

Body width (mm)

Body thickness (mm)

x + Sx

9.76 ±0.07

6.70 ±0.06

2.82 ± 0.05

27.6 ± 0.01

29.1 ±0.02

16.5 ±0.01

%V

27.69

26.12

32.17

8.70

11.00

10.30

Min.

4.0

3.13

0.87

21.00

22.00

12.00

Max.

15.15

11.28

5.04

33.00

36.00

23.00

Figure 4

A dredge used for gathering Venus gallina. The

dredge works with water pressure.

Figure 3

A dredge used for gathering Venus gallina.

Figure 5

Boats dredging for Venus gallina.
230 NOAA Technical Report NMFS 129

depths of 30-40 m. The most common gear is the

dredge, but some fishermen gather them by diving.

Landing sea snails below a length of 45 mm is prohibited. to conserve the stocks. Fishermen, who use dredges,

gather undersize as wel1 as legal size snails and return

the small ones.

The meats are first prepared in factories and then

exported. In 1987 the quantity of meats exported was

500-600 t.

Oyster

Ostrea edulis is the only oyster species in Turkish waters.

No research has been done on it, except for the meristic measurements of oysters from Izmir Bay (Table 4).

Fishermen use two methods for gathering oysters.

One is by divers, who pick them up by hand. Each

gathers from 30 to 100 kg per day, depending on abundance of the oysters. The divers use air supplied from a

surface boat. The principal oystering area is Izmir Bay,

where divers from 10-15 boats gather them (Fig. 7).

Oysters are also gathered using dredges in Izmir Bay

and Dardenel1e, although this method is unlawful. Each

fisherman can dredge up 100-200 kg per day.

Oysters from Izmir Bay are superior to those in

Dardenelle, because their shells remain more tightly

Table 3

Average morphological values ofthe sea snail by collection area (Duzgunes et aI., 1988).

Collection area

Muddy Sandy Grassy Grassy and

Categury bottom bottom bottom sandy bottom

Body length (mm) 56.0 53.0 66.0 65.0

Weight (g) 35.0 30.0 70.0 70.0

Shell weight (g) 24.4 ~2.6 50.0 53.3

Meat weight (g) 8.t! 6.9 17.3 17.6

Table 4

Meristic values (110 oysters) of Os/rea edutis (Alpbaz et

al. 1990).

Category X±Sx %V Min. Max.

Body weight (g) 148 ±5.0 38 46 361

Meat weight (g) 17 ±0.6 38 2.2 34

Percent meal 12 ± 0.1

Shell length (mm) 90 ± l.~ 15 57 160

Shell width (mm) 72 ±0.9 14 53 97

Shell thickness (mm) 37 ±0.7 2u 21 60

closed and retain liquid better. Dardenelle oysters that

lose their shell liquor are sometimes dead before they

reach markets mainly in Italy and Spain. In 1991, production was about 1,500 t.

Short-necked Clam

This clam has the highest value per unit volume of the

shel1fish landed. The reason for the high price is the

difficulty in meeting the demand for them, because the

fishing season is from October to April when the water

is rough and cold. Fishing is forbidden in summer

because that is their spawning season.

The short-necked clam is gathered principal1y in Izmir

Bay (Fig. 1). Fishing for them began in 1970, and three

methods are used. The most common is using a shovel

Figure 6

Shells of the sea snail, Rapana venosa.

Figure 7

Boat equipped with an air pump for gathering of oysters by diving.
__________________ Alpbaz & Temilli: A Review of the Molluscan Fisheries of Turkey 231

in wading depths. The clams are emptied into a wire

screen box which retains the clams but not the sand

(Fig. 8). They are then put in a sorting box ashore to

separate large from small clams (Fig. 9). The small

clams are the ones that are sold.

Another method is to use rakes from boats 4-4.5 m

long. The handle of the metal rake, locally termed a

"sara," is 3-4 m long.

The third method is by divers gathering the clams by

hand. The collection sites are in 1 m ofwater where the

bottom is muddy. Such sites are difficult to find, so individual fishermen keep the locations of the sites a secret.

The quantities landed from 1976 to 1980 were 201,

149,254,618, and 416 t, respectively. Some pollution

problems in Izmir Bay have kept production lower than

it could have been.

Figure 8

Fishermen gathering the short-necked clam using

shovels.

Figure 9

Selecting small short-necked clams by using a sieve.

The landed value of the short-necked clam is

US$5.00/kg. Its exported value is about US$9.00/kg.

Tapes aureus also occurs in Turkish waters, but because its flesh is not highly desired it is not gathered

commercially. Some farmers, whose numbers were as

high as 200-300, used to come to the shores in the

cooler time of the year when things were slow on their

farms and gather Tapes aureus from October to May.

Each collected from 10 to 80 kg of Tapes per day. They

did need to obtain permission from authorities to collect them. They used to sell them for US$2-3/kg. The

export market paid US$5-6/kg for them. Production has

been declining, because pollution is increasing in Izmir

Bay. We believe that there is a need to do research on

pollution problems and their effects on production of

shellfish.

Black Mussel

The black mussel occurs almost everywhere along the

coast starting from Izmir in the Aegean Sea northward

to Istanbul and from there eastward along the Black

Sea to its eastern border at Hopa (Fig. 1). Large quantities could easily be exported, but countries such as Spain,

France, and the Netherlands produce such large quantities that the market is nearly glutted. The export price is

low. An expansion ofthe fishery in Turkey will depend on

whether the foreign demand for mussels increases.

About 200 fishermen gather black mussels by diving

or dredging. In a day, a diver can gather from 300 to 400

kg ofmussels, and a boat using a dredge gathers from 1 to

5 t of mussels, depending on the size of dredge.

People in Turkey eat the black mussel usually stuffed

with rice (Fig. 10), but also fried. Annual consumption

in Turkey is about 1,000 t.

Horse Mussel

This mussel is smaller than the black mussel, its ventral

shell is more convex, and its meat is more pinkish. It

occurs from about Istanbul to two-thirds down the eastern coast at Kusadasi (Fig. 1). It is especially abundant

with fat meats in Ayvalik Bay, about one-third the distance down the eastern coast, because waste water from

some olive oil factories enrich the water, producing

large quantities of phytoplankton.

Horse mussels mostly attach to stones composed of

CaC03, MgC03 FeO, and Si02. They are soft and easily

broken, and in Turkey are termed "Atilgana."

About 100-150 fishermen in Ayvalik Bay gather horse

mussels during the season from October to March. Fishermen gather them using dredges and by diving. The dredge

boats are about 6 m long, and have 9-10 hp engines. The
232 NOAA Technical Report NMFS 129

Figure 10

Mussels are usually stuffed with rice when eaten in Turkey.

dredges are 1 m wide, 0.5 m high, and the ring bag is 3-4

m deep. Two men work in each boat and pull the dredges

for 5-8 minutes. The catch includes kidonya, sea urchins,

starfish, and oysters, besides horse mussels. Diving is a less

prominent method because it is more difficult.

The demand for horse mussels in Greece is high, and

there is no trouble exporting the entire catch. From

200-600 t/year are landed from Ayvalik Bay.

The horse mussel is often smoked and preserved. After

cooking, the meatsfall away from the shells and are washed.

The meats are then soaked in vinegar for 5 minutes,

removed, dipped in olive oil, and placed on a grill where

they are smoked for half an hour at 80°C. They are then

stored in jars to which olive oil is added. They keep well.

Kidonya

The meat of this species is very palatable, but the species is too scarce for commercial production. Sometimes its meat is sold as the short-necked clam as the

two are similar.

Arcasp.

This species also has high quality meat, but it is too

scarce for much commercial production. It is sometimes exported with the horse mussel and short-necked

clam from Ayvalik (Fig. 1).

The Future of Molluscan Shellfisheries __

The future of the molluscan fisheries in Turkey will

depend partly on the strength of foreign demand, because local demand is negligible. The black mussel is

abundant, but the foreign demand has remained low.

The demand for other species produced in Turkey,

however, is strong. The striped venus could also become a more important species, because finfishing is

declining in the Sea of Marmara as fish are becoming

scarcer. The fishermen there may switch to gathering

the striped venus as a means of employment. The

shortnecked clam brings the best price, but there are

pollution problems in the fishing areas in Izmir Bay.

The landings of oysters are limited by lack ofsupply.

Hatchery rearing ofseafood is going to be important

in the future. There were no fish farms in Turkey in

1970, but since then fish farming has grown and now

there are at least 300 trout and marine fish farmers.

Some farmers are becoming interested in rearing the

black mussel, oyster, and short-necked clam.

Literature Cited and Selected References

A.lpbaz, A. G., and H. Hossucu.

1980. A study on the short-necked clam (Tapes decussatus)

collected from .lzmir Bay. E.U. Zir. Fak. Derg.

Alpbaz, A. G., and M. O. Balaban.

1991. An overview of molluscan shellfish industry in Turkiye.

Molluscan shellfish depuration. In W. Sotwell, G. E. Rodrich,

R. E. Montin (eds.), p. 365-368. CRC Press, Boca Raton, Fla.

Alpbaz, A. G., and M. Onen.

19i19. An investigation on the striped venus (Venus gallina)

exported from Turkiye. E.U. Su Urun. Derg. Cilt: 6, Sayi:

21-24(61-77).

Alpba/, A. G., M. Onen, and 1. Corus.

1990. An investigation about oysters (Os/rea edulis) collected

from Urla region. E.U. Su Urun. Derg. Cilt: 7, Sayi: 24-28,

Syf. 116.

Anonymous.

1990. A report on the Venus gallina. Agric. Minist. Turkiye, 45 p.

Duzgunes, E., H. Karagam, and K. Seyhan.

1988. A study on the growth and the meat yield of seasnail

(Rapana venosa, Val. 1846). Su .ljrunleri Derpisi Erijnuenti,

Bornova, Izmir 5(19-20):88-100.
Mollusk Fisheries in Bulgaria

YORDANSTAYKOV

Extension Service

Thracian University

6000 Stara Zagora, Bulgaria

ABSTRACT

The two principal mollusk species harvested along the coast of Bulgaria in the Black Sea are

the black mussel, Mytilus galloprovincialis, and the snail, Rapana thomassiana. Small quantities

of oysters, Ostrea sublamellosa and O. taurica also are harvested. From 100 to 120 boats harvest

the mussels from wild beds. In addition, some mussel farming occurs. The harvesting of

snails began in 1989 when export markets were found. From 250 to 300 boats harvest the

snails in deep water, while divers harvest them at depths of 4-5 m. In 1994, at least 7,000

people in Bulgaria were engaged in harvesting, transporting, processing, and marketing

mollusks.

Introduction

The Black Sea is situated between lat. 46°32' and 400 56'N

and long. 27°27' and 41 °42'E. The sea is 1,149 km long,

611 km wide, its average depth is 1,197 m, while its area

is 413,480 km2• Its coastline is fairly smooth with few

gulfs; a few tiny islands are located near the shores.

The black mussel, Mytilus galloprovincialis, and the

snail, Rapana thomassiana, are the main mollusks harvested along Bulgaria's Black Sea coast (Fig. 1). Two

species of oysters, Ostrea sublamellosa and 0. taurica, are

present, but they are relatively unimportant for food or

trade.

Mter 1989, statistical services in Bulgaria disintegrated.

The source of data presented here for years after 1988

is from interviews of people at state-owned and private

farms, harvesting firms, and firms that buy and process

mollusks.

Habitat

The Black Sea has currents as fast as about 9 em/sec.

They are generated by winds and the influx of large

quantities of freshwater along its northern coast. Currents in each half of the sea form two closed counterclockwise circles. A western current starts from the

mouths of the Danube and Dnieper Rivers and passes

the Bulgarian coast where its name is the Devil's Current. The water salinity at the surface is about 16-18%0

and, in deep water, about 22.5%0. The low salinity is

due to influxes of freshwater from the rivers and rainfall. The water temperature on the surface ranges from

24°C to 28°C in summer, while in winter it is about 6°C

in the open sea and O°C along the coast. The water

temperature at a depth of 75 m is about constant at

7.5°C. The color of the water is blue-green, while its

transparency near the coast decreases and is from 10 to 15

m from the surface. The dissolved oxygen concentration

in the water is 124-133% (Kaneva-Abadjieva, 1960).

Description of Mollusks

Black Mussel

The black mussel is the most common bottom species

of the Black Sea and comprises 63.6% of the total

biomass in its beds (Kaneva-Abadjieva and Marinov,

1960). It inhabits depths from 4 to 70 m, but the largest

concentrations are at depths from 15 to 30 m. In the

coastal zone, the mussels are attached by their byssal

threads to rocks, and in the deeper places ofthe muddy

bottom they are attached to shells of live and dead

mussels, forming large congregations (Kaneva-Abadjieva

and Marinov, 1963). Adult mussels have a length 30-80

mm. Mussels from the deepest areas have relatively thin

shells. Severe storms can kill all mussels along shallow

coasts, but new generations set and form congregations

on the rocks within 6-8 months (Trayanov, 1983).

233
234 NOAA Technical Report NMFS 129

Figure 1

Distribution of mussels along the Bulgarian Black Sea coast.

The total biomass of black mussels along the Bulgarian coast is about 300,000 t, but only about 100,000 tare

harvestable. The mussel beds near the Kaliakra Cape are

difficult to harvest because the bottom there is rough and

rocky and rough seas are common. The best locations for

harvesting mussels are near Balchick and Kavarna where

the mussel beds are located at depths averaging about 15

m; the yield is as much as 2.7 kg/m2. Large concentrations

of mussels occur in coastal zones near Varna, Emine

Cape, Byala, Nessebar, Pomorie, and Sozopol.

Snail

The snail, R thomassiana, is an exotic species. native to

the Sea ofJapan. It was introduced to the Black Sea b;/

attached snail eggs on the bottoms ofships. Found first

in the Black Sea in 1946, and along the Bulgarian coast

in the region of Varna Bay on rocky bottom at a depth

of 4-5 m in 1956, the snails afterward spread in large

numbers along the entire Bulgarian coast. The reasorfor the snail's rapid spread in the Black Sea was a lack of

natural enemies (Marinov, 1978). The snails inhabit

rocky and stony zones in coastal areas as well as mussel

beds on the muddy sea bottom at depths of 20-30 m.

In the past 40 years. the snails have caused substantial

changes in the bottom biocenosis of the Black Sea

(Konsulova. 1989). They have had a negative affect on

mussels living in coastal areas as well as those on muddy

bottoms at greater depths.

A campaign to exterminate the snails was begun in

1975, and special places for collecting harvested snails

were set aside (Konsulov, 1978). This activity was not

successful and the snails increased in numbers.

Mter 1989. during the transitional period to a market economy in Bulgaria, opportunities for exporting

the snails to various countries increased. Snail harvests

increased and exports to Turkey and later to Japan and

Korea increased. The harvests have led to a decrease in

the snail population.

Oysters

O. sublamellosa inhabits coastal rocks whereas 0. taunca

inhabits depths of around 20 m on hard substrate. Both

oysters are sparse in Bulgaria; the largest beds are off

Nessebar, Pomorie, and Sozopol. The oysters range

from 40 to 55 mm in length. They have little importance

as a market product, though their meat is delicious.

Mussel Harvesting

Most mussels are harvested with dredges from natural

beds at depths ofl5-20 m (Fig. 2). The remainder are

harvested at shallower depths along rocky coasts. The

fishing season lasts from March to October. Mussel

dredges have metal frames and nets and are towed

from boats. In coastal rocky areas at depths of 4-8 m,

divers harvest the mussels.

Between 1959 and 1977, the maximum mussel harvest was 872 t in 1961. The quantity harvested from

natural beds has since fallen and now ranges from 30-

40 to 100-110 t/year. Variations in annual landings are

not due to great changes in mussel supplies but to

variations in domestic and foreign demand (Ivanov,

1979). Opportunities recently available for fishermen

to harvest snails also contribute to decreased mussel

catches. The population of mussels has not fallen as a

result of harvesting or water pollution (Rojdestvenski,

1989; ZlatanovaI).

Each year, from 100 to 120 boats are active, harvesting mussels during the peak harvest period. Two fishermen work in each boat. The mussels are sold at open

I S. Zlatanuva. 1YY3. Mariculture in the integral management plan

for development of the Bulgarian Black Sea coast. Unpub!. rep.
____________________________ Staykov: Mollusk Fisheries in Bulgaria 235

Figure 2

Mussel fisherman, boat, and dredge.

markets or to processing factories. Retail prices of live

mussels in open markets are US$0.40/kg. The wholesale price of mussels in the factories is US$0.27/kg.

From 300 to 916 kg are caught by each boat during a

fishing season. If this quantity is sold by the fisherman's

family at retail prices, the incomes for one fishing season range from US$120-366/boat. The incomes from

mussels sold to the factories at wholesale prices range

from US$81-247/boat. The fishermen's incomes from

mussel catches are smaller than those from snail catches.

Mussel Culture

Bulgarian coastal aquaculture is still in its infancy. Biotechnologies for cultivating and processing mussels at

sea and ashore have been developed and implemented.

Two state-owned mussel farms were built in Bulgaria.

The farm in Sozopol was built in 1979-80 to have an

annual production capacity of 200-300 t, while the

farm in essebar was built in 1983-84 to have an annual production capacity of 300-400 t. When they operated, both produced much less. Production of cultured

mussels from the farm in Sozopol was 57 tin 1986, 150

tin 1987, and 100 tin 1988 (FAO, 1991). and the farm

in Nessebar now is closed. After the changes in Eastern

European countries as a result of general economic

decline, mussel culture also decreased, and now production is about 60 t/year from the Sozopol mussel

farm (Staykov, 1994).

In the transitional period to a market economy, many

private companies have become interested in commercial mussel culture in the Black Sea. Two private mussel

farms were built, and each now produces about 20-25

t/year.

Two systems of mussel cultivation are used in Bulgaria: A storm-proof floating system (Fig. 3) and a

longline system. The center of the storm-proof system

has a large float and an anchor, and 16 additional

anchors are located around the periphery'at a distance

of 80 m from the center. This system consists of thick

ropes, 80 m long and buoyed by suitable floats, from

which thinner vertical ropes 1.5 m long are hung. Mussels are attached to the vertical ropes (Konsulov, 1980).

On a structure ofthis type, about 30-40 t of mussels can

be reared in a period of 15-16 months (Konsulova,

1974, 1988).

The longline system consists of a series of long horizontal thick ropes which are buoyed by a number of

suitable floats. The system is anchored in place by concrete blocks. Thin vertical ropes to which the mussels

are attached are hung from the horizontal lines

(Konsulova, 1979). About 10 t of mussels are produced

from 10 longlines in the 15-18 months it takes for

cultivated mussels to attain market size. In contrast,

mussels attain market size on wild beds in 35-40 mon ths

(Konsulova, 1978; Konsulov and Konsulova, 1989). The

cultivation density depends on conditions ofthe region

and varies from 250-1,200 mussels/m ofrope (Velchev,

1983) .
236 NOAA Technical Report NMFS 129

Snail Harvesting

Snail harvests began in 1989 when opportunities for

export increased. Most snails are harvested at depths of

15-20 m using dredges similar to mussel dredges (Fig.

4). Each year, from 250 to 300 boats, each with three

fishermen, dredge for the snails (Fig. 5, 6, 7). Divers

harvest the remainder from rocky areas along the coast

at depths of 4-5 m. Snails harvested by both methods

range from 80 to 110 mm in length. The period for

Figure 3

Storm proofsystem for cultivation of mussels.

250 em

Figure 4

A dredging method for harvesting snails.
____________________________ Staykov: Mollusk Fisheries in Bulgaria 237

harvesting snails lasts from March to September and

sometimes to November. Catches are largest in June

and July. The government bans harvests during the

snail reproduction period of 1-20 August.

Snail landings have increased every year. Landings

were 1,500 t in 1989, 1,900 t in 1990, 2,600 t in 1991,

3, I00 t in 1992, 3,900 t in 1993, and 4,500 t in 1994.

About 5,000 t ofsnails were expected to be caught and

exported in 1995. At the beginning of this fishery, the

snail beds were not fully harvested. Harvests have increased as the international market demand has expanded. In the first years ofsnail harvesting, only Turkish firms were involved, exporting live snails. The entire

snail harvest now is processed (frozen and canned) by

Bulgarian firms.

In 1994, the price oflive snails was US$0.41 /kg. Each

boat lands 15,000-18,000 kg of snails worth US$6,150-

7,380 during a fishing season. A fisherman's income for

a season ranges from US$2,050-2,460.

Mollusk Processing and Marketing _

Mollusks in Bulgaria are either canned or frozen and

are sold as culinary products. Live mollusks also are

sold in markets. They are stored in polyethylene bags

Figure 7

Fishermen loading bags of snails onto a truck.

Figure 6

Divers with harvest of snails.

Figure 5

Boat and divers preparing to go after snails.
238 NOAA Technical Report NMFS 129

Figure 9

Machine for freezing mussel meats.

Figure 8

A retort for steaming mussels.

and arranged in wooden cases at lODe (Velchev, 1984).

Mollusk shells are processed into flour and used as a

mineral additive in poultry feed.

Mussels have high nutritive value (Korobkina et a!.,

1966). The percentage of meat weight in mussels ranges

from 19.9 to 28.1%, depending on the season, the

highest values being in February and March. The protein content of the meat ranges from 15.99 to 17.05%,

and the fat content from 1.58 to 2.31 %; both vary with

the season (Konsulova and Dobrovolova, 1989). Mussels are sold live, frozen, and processed.

The mussels are cleaned, steamed (Fig. 8), and then

the meat is separated from the shells by special machines. The freezing of meats is done in a freezing

channel at a temperature of -50oe (Fig. 9). Frozen

mussels are packed in bags holding 8 kg each. Frozen

mussel meat sells for US$5.1 /kg. About 25% is sold in

Bulgarian markets and the remainder is exported.

Annual production of canned mussels ranges from

10 to 25 t (Nikolov, 1965, 1966). The mussels are packed

in metal cans (550 g/ can which sells for US$3.00) and

in glass jars (300 g/jar which sells for US$2.43) (Fig.

10). The mussels are canned with a special sauce, with

rice, mashed potatoes, or their own shell liquor.

In shops, mussels are sold fried in flour and eggs, at a

price of US$O.88/0.1 kg, and as mussel salad for

US$0.73/0.1 kg. The price ofmussels in restaurants ranges

from US$5.50-9.50 when offered as a main course.

Snails are sold in markets as frozen or canned meat.

The primary processing includes washing, steaming,

and separating meat from the shells manually. The freezing of the snail meat is done the same way as with mussels.

The price offrozen snail meat is US$4.50-5.20/kg. About

10-15 t offrozen snail meat is sold in Bulgaria and the rest

is exported. Annual production of canned snail meat is

15-20 t (140 g/can which sells for US$0.95).

Bulgaria has 21 firms that buy mollusks. Three are

state- owned and the rest are private. Mollusks are processed in 18 factories, 15 of which are private. During

the fishing season of 1994, at least 7,000 people living

along the Black Sea were involved in harvesting, transporting, processing, and marketing live mollusks and

their products.

The Future

In the future, mollusk harvests and culture will likely

increase along the Bulgarian coast because the international demand for mollusks is large. Though mussel

harvests from natural beds could be increased, new

private companies are interested in mussel culture.
_______________________________ Staykov: Mollusk Fisheries in Bulgaria 239

Figure 10

Jars of canned mussel meat.

Mussels remain the principal species of interest for new

private farmers. Mussel culture is profitable and promising for increasing production because there are

enough spat and because primary phytoplankton is

high enough to promote rapid growth of mussels.

Traditional Recipes for Mollusks _

Bulgarians often consume mussels as a salad. The meat

from the boiled mussels is separated from the shells,

and then salt, cooking oil, and lemon juice are added

and, according to personal tastes, boiled potatoes and

carrots may be included. Mussels are also served with rice

or with carrots, onions, and mushrooms as a main course.

Oysters usually are opened, their shell liquor collected, and the meats are washed; they are then put

back into their shells. Various sauces are added along

with the shell liquor, and then the oysters are roasted.

Literature Cited

FAO.

1994. Aquaculture Production. Food Agric. Organ. U.N., Fish.

Circ. 815, Rev. 6, p. 148.

Ivanov, G.

1979. Statistical material about the Bulgarian catches of fish

and other aquatic animals in the Black Sea during the 1959-

1977 period. In L. Ivanov (ed.), Proc. Inst. Fish., Varna,

XVII, p. 75-84. Inst. Fish., Varna.

Kaneva-Abadjieva, V.

1960. Black Sea molluscs. State Publish. House, Varna, 58 p.

Kaneva-Abadjieva, V., and T. Marinov.

1960. Distribution of zoobenthos in Bulgarian Black Sea coast.

In A. Valkanov (ed.). Proc. Central Sci. Invest. Inst. Fish

Resour., Varna, 3, p. 117-161.

1963. Inhabitants of Black Sea bottom. State Publish. House,

Varna, 86 p.

Konsulov, A.

1978. Is it necessary to exterminate the snail in order for the

Black Sea to be saved? Fish Farming (Sofia) 7:11-12.

1980. Storm proof structure for mussel and oyster farming. In

L. Ivanov (ed.), Proc. Inst. Fish., Varna, XVIII, p. 113-Il9.

Inst. Fish., Varna.

Konsulov, A., and T. Konsulova.

1989. The ecological effect of cultivating of mussels in Black

Sea. Sci.-Popular Almanac "FAR," Varna, p. 77-87.

Konsulova, T.

1974. Preliminary results from experiments on artificial culture of mussels on the Bulgarian Black Sea Coast. In L.

Ivanov (ed.), Proc. Res. Inst. Fish. Oceanogr., Varna, XIII,

p. 93-105. Inst. Fish Oceanogr., Varna.

1978. Attempts for breeding Mytilus galloprovincialis Lam. in

the aquatory of the Bulgarian Black Sea coast by the method

"long lines." Fish Farming (Sofia) 8:2-4.

1979. Experimental rearing of Mytilus galloprovincialis Lam. in

the Bulgarian Black Sea coastal waters by "long lines" method.

In L. Ivanov (ed.), Proc. Inst. Fish., Varna, XVII, p. 55-65.

Inst. Fish., Varna.

1984. Studies on the growth of mussels Mytilus galloprovincialis

Lam. in culture condition on storm floating system in Cape

Kaliakra zone. In L. Ivanov (ed.), Proc. Inst. Fish., Varna,

XXI, p. 119-142. Inst. Fish., Varna.

1988. Biotechnique for Mytilus galloprovincialis Lam. cultivation on the Bulgarian Black Sea coast. Oceanology 17:

29-37.

1989. Distribution and quantity characteristic of the black mussel, Mytilus galloprovincialis Lam., and snail, Rapana

thomassiana crosse, in the sublittoral zone of Varna region.

Proc. Sci. Conf., Varna, October 30, p. 151-177. Sci. Res.

Worker's Union, Varna.

Konsulova, T., and S. Dobrovolova.

1989. Dynamics of yield and chemical composition of the meat

of Mytilus galloprovincialis Lam. naturally grown and cultivated on the Bulgarian Black Sea coast. Oceanology 18:

40-51.

Korobkina, G., E. Danileva, N. Kalinina, and T. Leonova.

1966. Nutritive value of the Black Sea mussels. Fish Farming

(Sofia) 6:11-12.

Marinov, T.

1978. Natural reserves of black mussel in the Bulgarian shelf of

the Black Sea. Fish Farming (Sofia) 5:4-5.

Nikolov, B.

1965. Output in clam processing. Fish Farming (Sofia) 6:

24-25.

1966. Quality and assortment of mussel products. Fish Farming

(Sofia) 2:20.

Rojdestvenski, A.

1989. The chemical quality of the Black Sea water in Varna

region. Proc. Sci. Conf., Varna, October 30, p. 102-109. Sci.

Res. Worker's Union, Varna.
240 NOAA Technical Report NMFS 129

Staykov, Y.

1994. Development of aquaculture in Bulgaria. Fisheries 19,

2:28-29.

Trayanov, T.

1983. Would artificial reefs be built. Fish Farming (Sofia)

5:7-8.

Velchev, V.

1983. Breeding of mussels in our country. Fish Farming (Sofia)

6:21-23.

1984. Cultivation of the black mussel without netlike bags. Fish

Farming (Sofia) 7:21-23.
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distribution of fishes and marine mammals, ionospheric

conditions, etc.

TECHNICAL SERVICE PUBLICATIONS-Reports

containing data, observations, instructions, etc. A partiallisting includes data serials; predictions and outlook

periodicals; technical manuals, training papers, planning reports} and information serials; and miscellaneous

technical publications.

TECHNICAL REPORTS-Journal quality with extensive details, mathematical developments, or data listings.

TECHNICAL MEMORANDUMS-Reports of

preliminary, partial, or negative research or technology

results, interim instructions, and the like.

Information on availability of NOAA publications can be obtained from:

u.s. Department of Commerce

National'Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

-« U.S. GOVERNMENT PRINTING OFFICE: 1997 589-233140005