JULY 1884 

POTENTIAL IMPACT OF DEEP SEABED MINING 

ON THE LARVAE OF TUNAS AND BILLFISHES 

Walter M. Matsumoto 

NOAA-TM-NMFS-SWFC-44 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Memorandum NMFS 

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NOAA Technical Memorandum NMFS 

This TM Series 1s llsed lor documentation and timely communication of preliminary resulfs imfelim reports. 01 

special purpose information and have not received complete formal review. editorial control. or detailed editing 

JULY 1984 

POTENTIAL IMPACT OF DEEP SEABED MINING 

ON THE LARVAE OF TUNAS AND BILLFISHES 

Walter M. Matsumoto 

Southwest Fisheries Center Honolulu Laboratory 

National Marine Fisheries Service, NOAA 

Honolulu, Hawaii 968 12 

Prepared for 

NOAA Division of Ocean Minerals and Energy 

Washington, D.C. 20235 

NOAA-TM-NMFS-SWFC-44 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige. Secretary 

National Oceanic and Atmospheric Administration 

John V. Byrne. Administrator 

National Marine Fisheries Service 

William G. Gordon, Assistant Administrator for Fisheries 
TABLE OF CONTENTS 

Page 

Introduction ............................. 1 

in the Pacific Ocean ......................... 1 

Distribution .......................... 1 

.dults. .......................... 1 

Larvae.e ......................... 6 

Foodand feeding ........................ 9 

Adults ........................... 9 

Larvae and juvenile8 .................... 11 

Spawning ............................ 12 

Development and growth of 13 

15 

Environment ............................ 15 

Oceanographic feature8 ................... 15 

Biological features .................... 16 

Tunas and billfishes in the DOMES area ............. 18 

Movementoftunas ........................ 19 

Effects of mining .......................... 20 

Impact on environment ...................... 20 

Impact on primary production .................. 24 

Impact on microzooplankton ................... 25 

Impact onfish .......................... 25 

Adults ........................... 25 

Tuna and billfish larvae .................. 27 

Sedimentation ..................... 27 

Turbidity ....................... 28 

Environmental factors ................. 29 

Other poseible effects ..................... 32 

Effects on fisheries ...................... 34 

Summary and conclusions ....................... 35 

Acknowledgments ........................... 38 

Literature cited ........................... 39 

Distribution and biology of tunas and billfishee 

larvae ................. The Deep Ocean Mining Environmental Study (DOMES) Area ........ 
TABLE 

. 

1. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Fish species caught (in pounds) by pole-and-line fishing in 1978 during 

the Hawaiian fish aggregating device experiment (Matsumoto et al. 

1981) * 

LIST OF FIGURES 

Distribution and areas of abundance of yellowfin tuna in the Pacific 

Ocean. Hatched area represents range of distribution; dots represent 

catches of mare than 1 fish per 100 hooks ([Japan.] Fisheries Agency, 

Research Divi.sion 1970, 1972, 1973, 1981; Shingu et al. 1974; Calkins 

1975; [Korea.] Fisheries Research and Development Agency 1981). 

Distribution and areas of abundance of bigeye tuna in the Pacific 

Ocean. 

catches of more than 0.8 fish per 100 hooks ([Japan.] 

Research Division 1970, 1972, 1973, 1981; Shingu et al. 1974; [Korea.] 

Fisheries Research and Development Agency 1981). 

Hatched area repreeents range of distribution; dots represent 

Fisheries Agency, 

Skipjack tuna distribution (hatched areas) and fisheries (cross-hatch 

areas) in the major oceans. 

late summer poleward displacement (Matsumoto et al. 1984) . The mean 15°C isotherms represent maximum 

Distribution and areas of abundance of blue marlin in the Pacific 

Ocean. Hatched area represents range of distribution; dots represent 

catches of more than 0.3 fish per 100 hooks ([Japan.] 

Research Division 1970, 1972, 1973, 1981; Shingu et al. 1974). 

Fisheries Agency, 

Distribution and areas of abundance of striped marlin in the Pacific 

Ocean. Hatched area represents range of distribution; dots represent 

catches of more than 0.4 fish per 100 hooks ([Japan.] 

Research Division 1970, 1972, 1973, 1981; Shingu et al. 1974). 

Fisheries Agency, 

Ocean current systems in the Pacific Ocean. 

Distribution of yellowfin tuna larvae in the Pacific Ocean (Klawe 1963; 

Matsumoto 1966; Ueyanagi 1967, 1969; Hirota 1977; Nishikawa et al. 

1978). 

Distribution of bigeye tuna larvae in the Pacific Ocean (Matsumoto 

1966; Ueyanagi 1969; Nishikawa et al. 1978). 

Distribution of skipjack tuna larvae in the Pacific Ocean (Hirota 1977; 

Matsumoto et al. 1984). 

10. Distribution of blue and striped marlin larvae in the Pacific Ocean 

(Matsumoto and Kazama 1974; Ueyanagi 1974; Nishikawa et al. 1978). 

11. General surface circulation scheme in the eastern tropical Pacific with 

prim manganese nodule mining area (hatched) and DOMES stations A, B, 

and C. 
12. Assumed movement of the various stocks of skipjack tuna in the Pacific 

Ocean. The numerals along the migratory routes represent quarters and 

locations of high CPUE cells of skipjack tuna taken by the Japanese 

tuna longline fishery, 1964-67. Stock designations are shown in 

parentheses (Matsumoto 1975). 

13. Assumed routes followed by tagged skipjack tuna from the eastern to the 

central Pacific. The letters represent tagged fish and the numerals 

along the routes represent quarters of high catch rates of skipjack 

tuna taken by the Japanefie tuna longline fishery, 1964-67 (Matsumoto 

1975). 

14. Planar view of the plume reconstructed from nephelometer traces. 

Contour levels are nephelometer voltages. Background voltage is 

approximately 3.3 (Burns et al. 1980). 

15. Calculated surface plume of a commercial mining ship traversing a 

rectangular pattern oriented normal to the advection direction at 

advection velocity of 25 cm/s and mining ship speed of 1 m/s. 

Concentrati.ons of particulates in suspension are given in ug/R 

(Lavelle and Ozturgut 1981). 

iii 
ABSTRACT 

Assessment of the probable impact of deep seabed mining on the eggs 

and larvae of tusas and billfishes is made, based largely on studies of the 

effects of sedimentation on eggs, larvae, and adults of freshwater, 

estuarine, and a few marine fishes. Most of the changes to the environment 

resulting from mining, such aa increased suspended sediment particles, 

reduced illumination due to turbidity, mixing of cold bottom water with 

surface water, and changes in trace metals, salinity, and oxygen levels of 

the surface water, are not extensive enough to endanger tuna and billfish 

eggs and larvae. One probable effect, temperature of discharge, is 

acknowledged, but its effects are expected to be insignificant. Cold 

bottom water (4"-1OoC) discharged over the side of the mining ship and 

falling directly onto tuna eggs and larvae at the surface could cause 

thermal shock, resulting in the termination of embryonic development, 

development of abnormal larvae, and loss of equilibrium by,the larvae. 

Losses from thermal shock, estimated annually at 15.3 metric tons (MT) of 

skipjack tuna and 10.7 MT of yellowfin tuna, representing 0.16 and 0.04% of 

the total annual catches of the respective species in the eastern Pacific 

northern fishery (the fishery north of Mexico), are insignificant and are 

not likely to have any noticeable impact on the fishery. These losses 

could possibly be increased fourfold, if the mining ship were to act as 

fish aggregating devices, but even at these higher levels, the impact on 

the fishery would be negligible. 

iv 
INTRODUCTION 

In the Programmatic Environmental Impact Statement prepared by the 

National Oceanic and Atmospheric Administration (NOAA 1981) pursuant to the 

Deep Seabed Hard Mineral Resources Act and the National Environmental 

Policy Act, several unresolved impacts from seabed mining of manganese 

nodules in the eastern Pacific Ocean (lat. 5"-20"N, long. ll0"W-180") are 

identified as having the potential to cause adverse effect on the biota. 

One potential unresolved impact is the effect of particulates discharged at 

the surface on fish larvae. 

Recent studies on the alteration of the environment and the effects on 

phytoplankton, macrozooplankton, and certain fish species resulting from 

mining operations in the area have been completed (Ozturgut et al. 1988; 

Chan and Anderson 1981; Hirota 1981; Lavelle and Ozturgut 1981; Lavelle et 

al. 1982). These studies include data on the discharge characteristics, 

surface plume, and effects of suspended particulate matter on phytoplankton 

and macrozooplankton of the area. 

of tunas exposed to seawater containing suspended particulate matter in 

concentrations similar to that expected from mining operations have been 

done also (Barry 1978). 

adult tunas would not be affected significantly by discharges from mining 

operations. 

growth of the larvaeo however, have not been addressed adequately. 

Laboratory experiments with two species 

Based on these experiments, it was determined that 

The possible effects of particulates on the survival and 

This report describes the biology of tunas and billfishes in the 

Pacific Ocean, with emphasis on the prime mining areas, examines the 

probable effects of mining on eggs, larvae and adults, and discusses the 

significance of adverse effects on the fisheries. 

DISTRIBUTION AND BIOLOGY OF TUNAS AND BILLFISHES IN THE PACIFIC OCEAN 

Distribution 

Adults 

The distribution of the tunas in the Pacific Ocean has been described 

at length by Blackburn (1976) and Sund et al. (1981). Of those species of 

tunas and billfishes which occur more or less continuously across the 

ocean, the following, due to their commercial importance, are of concern in 

the area of prime interest for commercial deep seabed mining: yellowfin 

tuna, Thunnus albacares; bigeye tuna, r. obesus; skipjack tuna, Katsuwonus 

pelamis; blue marlin, Makaira ninricans; and striped marlin, TetraPturus 

audax. 

The areal distribution of the tunas does not vary much by species 

(Figs. 1-31, but there are differences in abundance within the distributional range. 

the western Pacific west of the 180th meridian, between lat. 40"N and 40"s 

in the central Pacific west of long. 14OoW, and from Central America to 

lat. 35"s in the eastern Pacific. The distribution is narrowed to lat. 

20"N and 30"s in the eastern central Pacific at long. 115"-120"W. 

abundance generally are restricted to within 20" of the Equator. 

tuna, a more temperate species, is found in cooler waters than the 

yellowfin tuna. 

Yellowfin tuna are distributed between lat. 45"N and 45"s in 

Areas of 

Bigeye 

It is distributed from let. 45"N to nearly 50"s in the 
2 

Figure 1.--Distribution and areas of abundance of yellowfin tuna in the Pacific 

Ocean. Hatched area represents range of distribution; dots represent catches 

of more than 1 fish per 100 hooks ([,Japan.] Fisheries Agency, Research 

Division 1970, 1972, 1973, 1981; Shingu et al. 1974; Calkins 1975; [Korea.] 

Fisheries Research and Development Agency 1981). 

western Pacific, from rat. 40"N to 45'5 in the central Pacific, and Ut. 

35'N to 40'5 in the eastern Pacific east of long. 130'W. Unlike that of 

yellowfin tuna, the distribution of bigeye tuna is not constricted in the 

eastern central Pacific. The areas of ,abundance are skewed further to the 

north in the central and eastern central Pacific (between long. 165'E and 

125'W) and to the south in the eastern central and eastern Pacific (east of 

long. 140"W). Skipjack tuna are distributed between lat. 45"N and 45'5 

west of the 180th meridian. The distribution narrows gradually to the east 

and is constricted off Baja California and offshore from the South American 

Continent. The areas of abundance are indicated by the extent of present 

fisheries. In the western Pacific, west of the 180th meridian, the area of 

abundance extends from lat. 45"N to about 20"s and narrows rapidly to the 

area slightly east of the Hawaiian Islands. In the eastern Pacific, the 

area of abundance extends from Baja California to central Chile along the 

coast and narrows seaward to about long. 14O"W. The apparent gap in the 

area of abundance between long. 140" and 160"W is due to the absence of 

fishing effort. 

The distribution of billfishes does not differ greatly from that of 

the tunas. Blue marlin occurs between lat. 45"N and 40"s in the western 

Pacific, lat. 40"N and 35"s in the central Pacific, and lat. 35"N and 35'5 

in the eastern Pacific (Fig. 4). The area of abundance lies between the 

Equator and lat. 25"N in the western half of the ocean and between lat. 5"N 

and 20"s in the eastern half. The distribution of striped marlin is nearly 
3 

Figure 2.--Distribution and areas of abundance of bigeye tuna in the Pacific 

Ocean. Hatched area represents range of distribution; dots represent catches 

of more than 0.8 fish per 100 hooks ([Japan.] Fisheries Agency, Research 

Division 1970, 1972, 1973, 1981; Shingu et al. 1974; [Korea.] Fisheries 

Research and Development Agency 1981). 

OF OCCURRENCE 

RARE OCCURREN 

Figure 3.--Skipjack tuna distribution (hatched areas) and fisheries (crosshatch areas) in the major oceans. 

late summer poleward displacement (Matsumoto et al. 1984). 

The mean 15°C isotherms represent maximum 
h 

Figure 4.--Distribution and areas of abundance of blue marlin in the Pacific 

Ocean. Hatched area represmts range of distribution; dots represent catches 

of more than 0.3 fish per 100 hooks ([Japan.] Fisheries Agency, Research 

Division 1970, 1972, 1973, 1981; Shingu et al. 1974). 

similar to that of blue marlin in the central and eastern Pacific. In the 

western side, however, the poleward limits are at lat. 50"N and 50"s (Fig. 

5). The area of abundance lies in a northwestward direction from the 

northwestern coast of South America to Japan, and is situated to the north 

of the center of blue marlin abundance. The southern edge of striped 

marlin abundance overlaps the northern edge of blue marlin abundance in the 

east ern Pacif ic. 

The distribution of tunas and billfishes is influenced by surface currents and temperature. In the Pacific Ocean, warm currents (North and South 

Equatorial Currents) flow westward across the ocean (Fig. 6). At the western end, the currents are deflected poleward and carry warm water to higher 

latitudes. Cool currents flow eastward across the ocean at about lat. 45"N 

and 45"s. At the eastern end, the main body of both currents turn toward 

the Equator and carry cold water to lower latitudes. The current flow 

affects the climatic surface temperatures so that the western side of the 

ocean is characterized by a very broad belt of tropical water, a very 

narrow belt of temperate water, and a rapid transition to the cold waters 

of higher latitudes. The eastern side is characterized by a very broad 

belt of temperate water and a very narrow belt of tropical water (Brock 

1959). This results in the wider distribution of tunas and billfishes in 

the western side and the narrower distribution in the eastern side. 

Temperature ranges in the entire distributional area and in areas 

where abundance is high enough for commercial fishing have been published 
5 

N 

u 

u! 

'C 

IC 

C 

IC 

EC 

x 

K 

3 

- 

Figure 5.--Distribution and areas of abundance of striped marlin in the 

Pacific Ocean. Hatched area represents range of distribution; dots represent 

catches of more than 0.4 fish per 100 hooks ([Japan.] Fisheries Agency, 

Research Division 1970, 1972, 1973, 1981; Shingu et al. 1974). 

for the tunas on a worldwide basis (Laevastu and Rosa 1963). These are, 

respectively, 11"-28" and 18"-22°C for bigeye tuna, 18"-31" and 20"-28°C 

for yellowfin tuna, and 17"-28" and 19"-23°C for skipjack tuna. 

reports (Robins 1952; Uda 1957; Jones and Silas 1963; Broadhead and Barrett 

1964; Williams 1970; Sharp 1978) indicate an even wider temperature range 

for skipjack tuna: 14"-30" and 17"-30°C. At the northern and southern 

extremes of their distribution, the tunas almost certainly respond directly 

to temperature changes (Uda 1957; Schaefer 1961). The direct influence of 

surface temperature on distribution is less obvious in the tropics where 

temperature is relatively uniform throughout the year (Laevastu and Rosa 

1963). 

by the distribution and abundance of suitable food, such as in areas of 

upwelling and convergence (Blackburn 19651, by vertical thermal structure 

(Green 1967; Sharp 19781, and by oxygen levels (Hanamoto 1975; Sharp 1978). 

In the eastern Pacific yellowfin tuna fishery, Green showed that purse 

seining was more successful where the top of the thermocline did not exceed 

18 q and where the mean temperature gradient was sharp (>0.5S°C/m) within 

the thermocline. Sharp (1978) noted that the optimum fishing for this 

species appeared to occur where the 23°C isotherm was shoaler than 50 m and 

the 15°C isotherm was above 80 m. 

Other 

Here the distribution and abundance of tunas are controlled mainly 

Tunas and billfishes are distributed vertically to great depths. The 

vertical distribution of tunas and some billfishes has been estimated by 

various methods. 

depth of 380 m, based on experimental vertical longline catches (Saito 

Although bigeye and yellowfin tunas were distributed to a 
6 

Figure 6.--Ocean current systems in the Pacific Ocean. 

1973; Saito and Sasaki 19741, the depths of greatest concentrations were 

stratified with some overlap among species. 

mostly at 150-290 m, yellowfin tuna at 150-300 m, and bigeye tuna at 290- 

380 m. 

because they are largely taken by surface fishing gear, were observed at 

depths of 152 m from submarines (Strasburg et al. 1968). They have been 

detected at 235 q with echo sounders (Yamanaka et al. 19661, and at 263 

with ultrasonic devices (Dizon et al. 1978). 

Striped marlin were taken 

Skipjack tuna, which have been considered surface dwellers, mainly 

Larvae 

The distributional range of tuna larvae is less extensive than that of 

the adults. Yellowfin tuna larvae (Fig. 7) range from lat. 35"N to 25'5 in 

the western Pacific and from lat. 30"N to 25"s in the central Pacific. The 

range narrows to about lat. 10"N and 20"-25"s in the east central Pacific 

(long. 130" to 140"W) and to lat. 26"N and 10"s in the eastern Pacific. 

The north-south distribution of bigeye tuna larvae (Fig. 8) is less 

extensive than that of yellowfin tuna larvae. It ranges from lat. 35"N to 

25"s in the western Pacific, from lat. 25"N to 10" or 15"s in the central 

Pacific and lat. 20"N to 10"s in the eastern Pacific. The distribution 

constricts to about 10" north and south of the Equator at about long. 135"- 

155"W and lat. 15"N to the Equator at about long. 125"W. Skipjack tuaa 

larvae are distributed over the widest north-south range among tuna species 

in the western half of the ocean (Fig. 9). 

35"N to 40"s in the western sector, and lat. 30"N to 35"s in the central 

sector, but constricts sharply to lat. 10"-15"N and 20'5 east of long. 

145"W and lat. 15"N east of long. 1OO"W. 

limits coincide quite well with the 25°C surface isotherm. 

The range extends from lat. 

In all species the poleward 
7 

Figure i'.--Distri.bution of yellowfin tuna larvae in the Pacific Ocean 

(Klawe 1963; Matsumoto 1966; Ueyanagi 1967, 1969; Hirota 1977; 

Nishikawa et al. 1978). 

I 

N 

D 

D 

0 

IO 

0 

IO 

0 

K 

K 

S 

- 

Figure 8.--Distribution of bigeye tuna larvae in the Pacific Ocean 

(Matsumoto 1966; Ueyanagi 1969; Nishikawa et al. 1978). 
8 

Yet. I. 

Figure 9.--Distribution of skipjack tuna larvae in the Pacific Ocean 

(Hirota 1977; Matsumoto et al. 1984). 

Figure 10.--Distribution of blue and striped marlin larvae in the Pacific Ocean 

(Matsumoto and Kazama 1974; Ueyanagi 1974; Nishikawa et al. 1978). 
9 

The distribution of blue and striped marlin larvae (Fig. 10) somewhat 

resembles that of the bigeye tuna larvae in the western and central 

Pacific. With the exception of two capture sites shown in the figure, none 

has been reported east of long. 140"W. 

Information on the vertical distribution of tuna larvae has been 

obtained entirely from zooplankton and larval fish net tows. There is 

sufficient evidence to indicate that tuna larvae are distributed vertically 

to depths of 130 m or more (Strasburg 19601, 'but most are confined to the 

upper 50 or 60 m (Matsumoto 1958; Strasburg 1960; Klawe 1963; Ueyanagi 

1969; Hirota 1977). Strasburg found no difference in the catches of tuna 

larvae made at the surface (horizontal net tows) and at 0-60 m (oblique net 

tows). Ueyanagi also found no difference in the catch rates of larvae 

sampled in horizontal tows made at the surface (0-2 m) and in subsurface 

(20-30 m) layers. This was also true for larvae of albacore, skipjack, 

yellowfin and bigeye tunas. No difference was apparent in the catch rates 

of and yellowfin tuna larvae taken in neuston net tows at the surface 

and in 1-75 m oblique bongo net tows, but much higher catch rates were 

obtained for skipjack tuna larvae at the surface than'in the 1-75 m depth 

layer (Hirota 1977, tables 21-24). 

There is some evidence of vertical diurnal migration by skipjack tuna 

larvae, but this may not be true of yellowfin and bigeye tuna larvae. 

Ueyanagi (1969) reported that the mean surface catch rate of skipjack tuna 

larvae per successful night tow was five times greater than that of day 

tows; whereas the mean catch rates of yellowfin and bigeye tuna larvae were 

about equal for day and night tows. Part of the higher night catches of 

skipjack tuna larvae could have been due to net dodging during daylight, 

but this effect should be small in view of the absence of similar day-night 

differences in the catch rates of yellowfin tuna and bigeye tuna larvae. 

Food and Feeding 

Adults 

Tunas are broadly carnivorous, nonselective, opportunistic feeders, 

and will likely prey upon any forage organisms present in their vicinity. 

Studies of stomach contents of tunas in the eastern, central, and western 

Pacific (Reintjes and King 1953; Ronquillo 1953; King and Ikehara 1956; 

Watanabe 1958, 1960; Iversen 1962; Alverson 1963; Waldron and King 1963) 

all indicate that the diet of tunas is quite varied, but only a few kinds 

of the more abundant organisms present in a given area are taken in 

quantity . 

The food of tunas consists of three major categories: crustaceans, 

molluscs (almost entirely cephalopods), and fish in varying proportions, 

depending upon the tuna species and the area in which they occur. 

central Pacific, fish and cephalopods make up the bulk of the food 

consumed. The proportions of the major food categories range from 1 to 6% 

crustaceans, 20 to 39% cephalopods, and 62 to 75% fish. In the eastern 

Pacific, however, crustaceans and fish are the major source of food, and 

cephalopods are only of minor importance. 

592 crustaceans, 3 to 8X cephalopods, and 37 to 47% fish (King and Ikehara 

1956; Iversen 1962; Alverson 1963; Waldron and King 1963). 

In the 

The proportions range from 45 to 
10 

The diversity of food eaten by tunas is reflected in the large number 

of invertebrate orders and fish families represented in the stomach 

contents. Among the crustaceans, food items consumed by yellowfin and 

skipjack tunas in the central and eastern Pacific included organisms in the 

Orders Isopoda, Amphipoda, Euphausiacea, Decapoda, Mysidncea, and 

Stomatopoda. Copepods were consumed only by skipjack tuna in the central 

Pacific, and bigeye tuna utilized the fewest crustacean Orders: Isopoda, 

Amphipoda, Euphausiacea, and Decapoda. 

The greatest diversity in the food of tunas is in the large number of 

fish families represented. King and Ikehara (1956) list 47 fish families 

in the food eaten by yellowfin tuna and 35 fish families for bigeye tuna in 

the central Pacific, Alverson (1963) lists 22 fish families for skipjack 

tuna and 41 for yellowfin tuna in the eastern Pacific, and Waldron and King 

(1963) list 41 fish families for skipjack tuna in the central Pacific. Of 

the total fish families given for each tuna species, 14 were common to all 

four species, 22 were common to bigeye, yellowfin, and skipjack tunas in 

the central Pacific, 33 were common to bigeye and yellowfin tunas in the 

central Pacific, and 13 were common to yellowfin and skipjack tunas in the 

east ern Pacific. 

Despite the diversity of the fish species eaten by the tunas, fish of 

only a few families make up the bulk of the fish portion of the diet, and 

the major fish families differed for some species by area. In the central 

Pacific, the Families Scombridae, Gempylidae, and Bramidae were the most 

important fish food items of yellowfin and bigeye tunas and Scombridae, 

Carangidae, and Mullidae of skipjack tuna. In the eastern Pacific, the 

fishes of the Families Scombridae, Ostraciidae, Tetraodontidae, and 

Exocoetidae were important food items for the yellowfin tuna and those of 

Gonostomatidae, Exocoetidae, Trichiuridae, Myctophidae, and Engraulidae 

were important food items of skipjack tuna. Other studies by Ronquillo 

(1953) and Watanabe (1958) show similar diversity and similarities in fish 

families represented in the stomach contents of tunas from the western 

equatorial Pacific. 

Tunas feed primarily during the hours of daylight from the surface to 

depths of 380 m (Saito 1973; Saito and Sasaki 1974). 

surface usually occurs in compact schools, consisting of fish that are 

generally smaller than 100 cm. These schools are often composed of mixed 

species, such as skipjack tuna with small yellowfin tuna, small yellowfin 

tuna with small bigeye tuna, or all three species together, and are 

generally encountered in the vicinity of land masses, seamounts, banks, or 

around floating objects (Alverson and Peterson 1963). The larger yellowfin 

and bigeye tunas feed at great depths (135 m or more), but may ascend to 

shallower waters to feed at night (Watanabe 1958). 

Feeding at the 

The marlins also are carnivorous opportunistic feeders and feed on 

pelagic fish, squid, and crustaceans, Members of six orders of invertebrates (Decapoda, Amphipoda, Stomatopoda, Heteropoda, Pteropoda, and 

Cephalopoda) and 36 fish families have been reported from stomachs of 6 

species of billfishes from the western Pacific (Watanabe 1960). Although 

the list of food items may not be representative of any single species, 

(all items were listed under marlin), it does indicate that the variety of 

food items eaten by billfishes as a group is comparable to that of tunas. 

Strasburg (1970) indicated that the dietary habits of marlins varied 

between species and areas. He found that the striped marlin fed mostly on 
squids, sauries, and other fishes off New Zealand, sauries off California, 

squids off Peru and Chile, anchovies off northern Chile, snake mackerel and 

lancetfish off the Bonin Islands, and tunas in the central Pacific. The 

blue marlin fed mostly on squids in the Philippine Sea, tunalike fish off 

New Zealand and in the central Pacific, dolphin and tunalike fish off the 

Bahamas, and small tunas (young albacore; frigate tuna, Auxis thazard; and 

kawakawa, Euthynnus affinis) in Hawaii. Other fishes consumed by striped 

marlin include mackerels, carangids, sardines, herring, cornetfishes, and 

boxfishes (Ueyanagi and Wares 1975). 

Larvae and Juveniles 

There is only limited information on the food organisms consumed by 

tuna and billfish larvae. Studies of stomach contents provide only a 

partial list of the food eaten, since much of the delicate food items 

presumed to comprise the diet of the larvae quickly become unrecognizable 

due to digestion. Nishikawa (1975) noted only small numbers of copepods 

and residues of fish larvae and crustaceans in the stomachs of skipjack 

tuna larvae (3-9.5 mm standard length (SL)), and fish 'larvae, Euphausia, 

larval Decapoda, Amphipoda, and Octopoda in stomachs of skipjack tuna 

juveniles (17.5-26 .O mm SL). Lipskaya and Gorbunova (1977) recorded 4 

kinds of copepods and larvae of 2 kinds of flyingfish in stomachs of 

striped marlin larvae and juveniles (6.4-29.0 mm SL), and 7-9 different 

species of copepods and larvae of 12-15 fish species, including those of 

the Families Istiophoridae, Gempylidae, Scombridae, Coryphaenidae, 

Holocentridae, Mullidae, Myctophidae, Engraulidae, and Exocoetidae, in the 

stomachs of blue marlin larvae and juveniles (6.0-22.0 mm SL). 

Uotani et al. (1981) examined stomach contents of numerous (>4,000) 

larvae of albacore, yellowfin, bigeye, southern bluefin, Thu_n_nu_g mgno_pii, 

skipjack, and frigate tunas, ranging from 2.21 to 22.5 mm total length 

(TL), from the area northwest of Australia. 

copepods, copepod nauplius and eggs, Ostracoda, 1 species of Cladocera, and 

other Crustacea; polychaete larvae; fish larvae; arrow-worm; and Appendicularia. The stomach contents of four species of tunas (albacore, 

yellowfin, bigeye, and southern bluefin) consisted mainly of small itans 

0.21-0.80 mm body length, but that of skipjack and frigate tunas contained 

numerous items exceeding 0.81 mm body length. Feeding studies of larval 

fish such as herring (Blaxter 1965; Bjoerke 1978; Uotani et 81. 1978) and 

anchovy (Ciechomski 1967b; Lasker 19751, show that the diet at initial 

feeding consists largely of mollusc larvae, and copepod eggs and nauplii. 

Other crustacean larvae such as the nauplii of barnacles, mollusc larvae 

that generally hatch as trochophores, trochophores of sabellid polychaete 

and larvae of echinoderms all may serve as initial food of fish larvae (May 

1970). It is conceivable that larvae of tunas and billfishes also utilize 

similar food items at first feeding, as evidenced by the copepod nauplii 

found by Uotani et 01. (1981) and by the successful experimental rearing in 

tanks of various tuna larvae that had been initially fed rotifers or oyster 

larvae (Hnrada et al. 1971; Harada, Murata, and Furutani 1973; Harada, 

Murata, and Miyashita 1973; Harada et al. 1980). 

They recorded 10 species of 

Although larvae of tunas and billfishes may require delicate food 

items at initial feeding, their dependence on such food may be for a brief 

period only. The unusually large mouth of these larvae, which is 

approximately 20 to 32% of body length in larvae larger than about 4.0 nu 

(Gorbunova 1975, figures from Ueyanagi 1963) permits thun to feed on fish 

larvae and other larger orgnnisnls much sooner than larvae of other fishes. 
12 

Vision is the most important sensory function used in feeding by 

marine fishes. For successful feeding and survival, the larvae must 

perceive the prey. 

first-feeding larvae of herring, plaice, pilchard, and anchovy, which all 

have rather small eyes, react to prey at distances of 0.2-1.0 body length, 

and that the perceptive range increases with growth (Hunter 1980). 

observations have not been made for tuna or billfish larvae, but their 

proportionately larger eyes, which range from 10 to 15% of body length in 

larvae 3.2-16.5 mm SL (Gorbunova 1975), should enable them to perceive prey 

at greater distances. Other tests measuring thresholds of light intensity 

for larvae and juveniles of several species of salmon, whitefish, pike, 

herring, and plaice indicate a falloff in the rate of feeding corresponding 

with light condit.ions at dusk and dawn (Blaxter 1969). 

period thus must vary considerably with season, latitude, clarity of water, 

and cloud cover for these fish, and this should apply to tuna and billfish 

larvae as well. 

Studies on visual perception by larvae indicate that 

Similar 

The daily feeding 

Spawning 

Spawning by tunas and bil If ishes have been determined from examination of gonads and from the capture of larvae. Figures 7-10 show the 

maximum area in which spawning has occurred in the Pacific Ocean, based on 

the capture of larvae. 

throughout the year in tropical waters and during the summer at higher 

latitudes. Consequently, seasonal variations are evident mainly at the 

northern and southern extremeties of the spawning area. 

Spawning by tunas and billfishes generally occur 

In the western Pacific, spawning by yellowfin and bigeye tunas occurs 

between lat. 20"N and the Equator in the first quarter of the year, between 

lat. 30"N and 10"s in the second quarter, between lat. 35" and 15"N in the 

third quarter, and between lat. 15"N and 20"s in the fourth quarter 

(Nishikawa et al. 1978). In the central Pacific (long. 140"W to 180">, 

yellowfin tuna spawn throughout the year between 1st. 14"N and 5"s and in 

the first quarter between lat. 6" and 14"s (Matsumoto 1958). 

eastern Pacific yellowfin tuna spawn throughout the year between lat. 25" 

and 7"N (Klawe 1963). The annual spawning potential of yellowfin tuna has 

been estimated, on the basis of gonad indices (Kikawa 19661, as being 

slightly greater in the central and eastern equatorial Pacific than in the 

western Pacific, and that of bigeye tuna between long. 100" and 140"W as 

being double that in the western Pacific west of the 180th meridian. 

In the 

Skipjack tuna also spawn across the entire Pacific but spawning 

intensity is sharply reduced in the eastern equatorial Pacific east of 

long. 12O"W (Klawe 1963). Most of the spawning by skipjack tuna occurs in 

equatorial waters between lat. 1O"N and 1O"S, and long. 130" to 145"W, and 

between lat. 20"N and 10"s from long. 145"W to the Asian Continent. The 

center of highest spawning lies between long. 140"W and 160"E (Matsumoto 

1975). Other spawning areas north of lat. 20"N include the waters around 

the Hawaiian Islands (Seckel 1972) and south of Japan between lat. 25" and 

30"N (Ueyanagi 1969). As in yellowfin and bigeye tunas, spawning occurs 

throughout the year in equatorial waters and during summer at higher 

latitudes. 

Tunas spawn in a fairly wide range of temperatures, varying by species 

and locality. In the western Pacific, yellowfin tuna spawn in temperatures 

between 24" and 29°C; bigeye tuna, between 27" and 29°C; and skipjack tuna, 

between 23.5" and 30°C (Ueyanagi 1969). In the eastern Pacific, the 
13 

temperature range of yellowfin tuna spawning is between 24" and 32"C, with 

a marked increase in spawning as the temperature increases above 26" or 

27°C (Klawe et al. 1970). The spawning temperatures in the central Pacific 

around the Hawaiian Islands range from 21.7" to 27°C for yellowfin tuna 

(unpublished data, Southwest Fisheries Center Honolulu Laboratory, National 

Marine Fisheries Service) and 22" to 27°C for skipjack tuna (Matsumoto et 

al. 1984). 

Hawaiian waters appears to be close to the minimum spawning temperature for 

this species. 

larvae hatched at temperatures of 17.2"-20.8"C during laboratory rearing 

experiments . 

The lower end of the temperature range for yellowfin tuna in 

Harada et ale (1978) reported that no normal yellowfin tuna 

The known spawning areas for striped and blue marlins are indicated in 

Figure 10. 

waters east of long. 130"W may be due to the absence of larval studies of 

these fishes from that area. A report on the sexual maturity of billfish 

caught in this area (Kume and Joseph 1969) shows that females of both 

striped and blue marlins in spawning condition were present in the area 

bounded by lat. 20"N and 3OoS, and long. 1100 and 130"W, with the southern 

distribution limited to the lower latitudes (10"s) east of 'long. 110"W. 

in the tunas, spawning presumably occurs throughout the year along the 

Equator and during summer, north and south of the Equator. 

The nearly complete absence of billfish larvae in equatorial 

As 

In all the species mentioned above, the mature female releases large 

numbers of eggs in a single spawning. The estimates for bigeye tuna ranged 

from 2.9 to 6.3 million eggs (Yuen 1955); for yellowfin tuna, 2 to 8 

million eggs (June 1953); for skipjack tuna, 0.1 to 2 million eggs (Yoshida 

1966); and for striped marlin, 11 to 29 million eggs (Eldridge and Wares 

1974). No information is available on the fecundity of blue. marlin. 

Spawning by tuna in captivity has been reported by Kaya et al. (1982). 

Female skipjack tuna weighing between 1.4 and 2.2 kg spawned in a tank 

within 8 h after capture. The spawned ova measured 1.0 mm, the same as a 

ripe ova, as compared with ovarian ova of 0.59-0.74 mm in fish taken from 

the same school. The rapid development of the ova--normal development is 

estimated at 2-3 months (Matsumoto et al. 1984)--was believed to have been 

induced by stresses experienced by the fish during the capture, transport, 

and confinement processes. The viability of the ova was demonstrated by 

artificial fertilization and successful hatching of the larvae. The rapid 

maturation and spawning of skipjack tuna in captivity is currently being 

exploited to produce larval skipjack tuna for experimental studies. 

Development and Growth of Larvae 

A number of tuna species have been reared successfully from artificially fertilized eggs. 

1980), and skipjack tuna (Inoue et al. 1974; Ueyanagi et al. 19741, and 

also bullet tuna, &cjt~ ggchgi (= 4. &~&sg=a; Harada, Murata, and 

Furutani 1973) , frigate tuna, 4. ~l~gggiid (Harada, Murata, and Miyashita 

19731, and striped bonito, Sgxdg gr_ie_r~&_a&ig (Harada et al. 19741, which are 

of minor commercial importance . 

These include yellowfin tuna (Harada et al. 1971, 

Yellowfin and skipjack tuna embryos developed and hatched in 23 to 35 

h after fertilization in water temperaturea of 24.5O-29"C; whereas those of 

bullet and frigate tunas and striped bonito developed and hatched in 34 to 

72 h in water temperatures of 20°-24"C. Yellowfin and skipjack tuna larvae 
14 

were 2.6-2.7 mm TL at hatching, bullet and frigate tunas 3.3-3.6 mm TL, and 

striped bonito 4.1-4.3 mm TL. As in other fishes (Ciechomski 1967a; Fonds 

et al. 19741, the rate of embryonic development increased with temperature. 

The yolk was absorbed 2 days after hatching in striped bonito and skipjack 

tuna, in 3 days in yellowfin tuna, and from 2 to 4 days in mackerel tuna. 

The eyes were completely pigmented, the mouth was fully formed, and feeding 

began at the time of yolk absorption. 

Feeding by tuna larvae reared in tank8 started 2-3 days after 

hatching, at about the time of yolk absorption. The initial food of 

yellowfin tuna larvae consisted of rotifers, _Bganc_h_ipu_g ~hgg&lib, and 

oyster larvae, Q_aspg&~g_eg gipp5la_ (Harada et al. 1971). The larvae were 

fed several kinds of marine copepods (unspecified species) 8 days after 

hatching when they were 5-6 mm TL. In one feeding study (Harada et al. 

19801, yellowfin tuna larvae were fed a diet of rotifers, copepods, and 

larvae of parrotfish, QElegngghgg fggc_iggug, 2.5-4.0 mm TL. Due largely to 

feeding on fish larvae, larval growth was found to be especially rapid 

after the 10th day. In examining stomach contents of larval and juvenile 

skipjack tuna taken in plankton nets, Nishikawa (1975) noted that of 15 

larvae with identifiable food remains, 5 larvae (3.0 to 9.2 mm TL) had 

consumed copepods and 1 larva (7.0 mm TL) had eaten a fish larva; that most 

(73%) of the juveniles (17.5-26.0 mm TL) had consumed fish larvae, whereas 

others had consumed euphausiids, copepods, decapods, amphipods, and 

octopods; and that juveniles, 48.0-120 mm, fed almost entirely on fish 

larvae. Based on these studies, it appears that larval tunas begin feeding 

on copepods at about 3.7 mm body length and continue to do so until they 

are at least 26 mm in body length; larval fish appear in their diet at 

about 6 or 7 mm TL or approximately 10 days after hatching; and fish larvae 

and euphausiids are the dominant food items in juveniles 17 to 26 mm in TL. 

Similarly, stomach content analyses by Lipskaya and Gorbunova (1977) and 

Gorbunova and Lipskaya (1975) indicate that billfish larvae initially feed 

on copepods and feed on fish larvae when they are about 6 mm TL. 

Growth was extremely rapid for larvae of all species from about the 

10th day. 

days (indicating a linear growth rate of 1.6 mm/day), in water temperatures 

declining from 28.6' to 25.6'C. The total growth was from 2.7 mm at 

hatching to 51 mm in 38 days. Bullet and frigate tunas grew even faster, 

3.2-3.5 mm/day in temperatures rising from 25.4' to 28.3'C. Frigate tuna 

grew from 3.3 mm at hatching to 120 mm in 33 days, and bullet tuna from 3.3 

to 157 mm in 52 days. Striped bonito showed the fastest growth rate, 6.4 

mm/day from the 10th to 42d day, in temperatures increasing from about 20" 

to 28°C. 

days. Fonds et al. (1974) indicated that the growth rate of garfish, 

B_g&gg bglogg, larvae was linearly correlated with temperature. If this 

holds for tuna larvae as well, the growth rate of yellowfin tuna larvae 

should have been greater than reported above. 

larvae is not known since larvae of this species have not been reared 

beyond 5 days. 

A 10-day-old yellowfin tuna larva grew from 5.8 to 51 mm in 28 

The total growth was from 4.1 mm at hatching to 290 mm in 99 

Growth of skipjack tuna 
15 

THE DEEP OCEAN MINING ENVIRONMENTAL STUDY (DOMES) AREA 

Env i ro nme n t 

Oceanographic Features 

The premining environmental conditions in the DOMES area have been 

summarized by Ozturgut et al. (1978). Some oceanographic features that 

affect the tuna and billfish, particularly the eggs and larvae, are worth 

noting. Several surface currents prevail in the area: the westward 

flowing North Equatorial Current (NEC) between about lat. 20" and 10"N, an 

eastward flowing North Equatorial Countercurrent (NECC) between lat. 10" 

and 4"N, and a westward flowing South Equatorial Current (SEC) between lat. 

4"N and 9"s (Fig. 11). The position and velocity of these currents vary 

seasonally. Measurements of the currents at Sites A, B, and C (Halpern 

1976, 1977) indicate an eastward flow at Site A with a mean velocity of 

almost 20 cm/s (9.4 nmi/day) at a depth of 20 m in the fall, an eastward 

flow at Site B with a mean velocity of 3 cm/s (1.3 nmi/day) in the spring, 

and a westward flow at Site C with a mean velocity of almost 17 cm/s (7.9 

nmi/day) at 20 m in the fall. Seasonally the NECC fluctuates in velocity 

from 5 to 30 cm/s (2.4 to 14.1 nmi/day) in the spring to 5 to 15 cm/s (2.4 

to 7.1 nmi/day) in the fall (NOAA 1981). The effects of these currents on 

tuna are discussed under Movement of Tunas. 

Surface temperatures (LaViolette and Seim 1969) vary noticeably in the 

DOMES area. 

at lat. 20"N varies from 21" to 24°C during the year. At the longitude 

through Site B, the temperature during the year varies from 23" to 25°C and 

from 22" to 26"C, at Site C. 

At the longitude through Site C, the mean surface temperature 

The 25°C isotherm, which roughly defines the 

.9-- I ~CHRISTMAS,l ~~ ~ 

I 

I 

SOUTH EQUATORIAL i- CURRENT I +-+. 0"- ~ 

1800 w I 70° 150° 140° 130' 130' I100 

Figure 11.--General surface circulation scheme in the eastern tropical Pacific 

with prime manganese nodule mining area (hatched) and DOMES stations A, B, and 

C. 
16 

limit of larval capture, lies to the north of Sites A and B during the 

entire year, but only for 6 months at Site C. The thermal structure in the 

DOMES area is typical of the tropical Pacific with a well-defined.surface 

mixed layer overlying a strong thermocline (Fig. 12). The mean depth of the 

mixed layer was 35532 m during summer and 55218 during winter (Ozturgut 

et al. 1978). 

Measurements of suspended particulate matter (SPM) in the DOMES region 

made during the summer of 1975 indicate that SPM is most abundant in 

surface waters (mean concentration of 42220 ~.lg/R), and uniformly low, 

1053 w/R, below 200 m (Baker et al. 1979). The concentration in 

surface waters is considered low but typical of open ocean waters. The 

general features of SPM concentrations change very little between 

summer and winter. Most of the particles (9122.9%) are smaller than 

4 pn with mean medium diameters of 2.020.4 pm. 

RTHWEST (NW 1 NORTHEAST (NE 1 

__________-----_--- 

SOUTHEAST (SE 1 

- 

N 

10 

IC 

!C 

IC 

C 

IC 

?( 

x 

K 

- 

Figure 12.--Assumed movement of the various stocks of skipjack tuna in the Pacific 

Ocean. The numerals along the migratory routes represent quarters and locations 

of high CPUE cells of skipjack tuna taken by the Japanese tuna longline fishery, 

1964-67. Stock designations are shown in parentheses (Matsumoto 1975). 

Biological Features 

Zooplankton research in the DOMES area at Sites A, B, and C was done 

in the summer of 1975 and winter of 1976 (Hirota 1977). Information on 

microzooplankton was limited to vertical distribution. The major features 

of distribution of microzooplankton (0.183-0.035 mm diameter) were: 

nauplii, tintinnids, and Micgggktgllg (copepod) tended to have maxima 

shallower than 40-60 m; (2) gpcgag (copepod) tended to have a much deeper 

(1) 
17 

maximum, often at 100 m or more; and (3) radiolaria and foraminifera showed 

relatively smaller depth variation than (1) or (2) above. 

tintinnids, and M.cgegg&glJg were the most likely to be associated with the 

chlorophyll maximum, which occurred at depths of 69224 m in summer and 

54230 m in winter. The approximate ranges of numerical abundance of each 

of the five taxa were 3,000-15,000/m3 for nauplii, 1,000-15,000/m3 for 

tintinnids, 1 ,000-10,000/m3 for radiolarians and foraminifers, 500-5,000/m3 

for Qgcggg, and 100-500/m3 for l$cg~ggtgllg. 

about a third of those in the eastern Pacific (EASTROPAC) area (Beers and 

Stewart 1971) and overlapped those in Hawaiian waters (Gundersen et al. 

1976). 

the upper 160 m was 145/11 of ciliates and 5/R of copepod nauplii and 

foraminifers. The microplankton standing stock as "tissue volumes'' 

integrated over the 0-150 m layer showed a range of 423-852 mm3/m2. 

volumes were approximately one-half of the volumes reported for Hawaiian 

waters (Gundersen et al. 1976) and one-third of those for the EASTROPAC 

area along long. 105"W (Beers and Stewart 1971). 

The nauplii, 

The abundance estimates were 

The average abundance of microzooplankton smaller than 0.035 mm in 

These 

The average macrozooplankton standing stocks (dry weight) integrated 2 over the 0-200 m depth layer ranged from 1,048 to 2,900 mg/m at the three 

site stations (Hirota 1977). The highest concentrations of macrozooplankton were in the upper 150 m and moderate concentrations between 200 and 900 

m. The areal distribution of the standing stocks (neuston net catches) 

showed a gradient from southeast to northwest, approximately normal to the 

DOMES station sites. 

B and C and the lowest along Site A and the top half of Site C. 

The highest stocks were at the southern half of Sites 

The major taxa of macrozooplankton were copepods, euphausiids, 

chaetognaths, larvaceans, ostracods, pteropods, and larval fishes (Hirota 

1977). The mean abundance of copepods in the upper 100 m ranged from 

152,000/1,000 m3 at Site A to 296,000/1,000 m3 at Site B in 1975, and 

171,000/1,000 m3 at Site A to 205,000/1,000 m3 at Site C in 1976. The most 

common species were the small (ca. 1 mm TL) cyclopoids (Qgcggg and _O&Bpng> 

and calanoids (Egggcglgggg, cglecglg~gg, and Clausocalanus), whose 

abundance8 ranged from 1,000 to 59,000/1,000 m . euphausiids in the neuston layer ranged from 1,400/1,000 m3 at Site A to 

2,900/1,000 m3 at Site 8. 

at Site B; whereas copepods were nearly equally abundant at Sites A and C, 

and euphausiids least abundant at Site A. 

in the neuston layer and 20,000 to 33,000/1,000 m3 in the 0- to 200-01 depth 

layer (Hirota 1977). 

18,000/1,000 m3 for ostracods in the two depth layers. 

of chaetognaths ranged from 2,000 to 9,000/1,000 m3. 

abundance were noted between sites and years. 

-3----------- 

Both copepods and euphausiids were most abundant 

The main abundance of 

The mean abundance of larvaceans ranged from 18,000 to 250,000/1,000 m3 

Corresponding values for pteropods were 3 000- 

16,000/1,000 m3 and 2,000-5,000/1,000 m3, and 200-1,500/1,000 m 3 and 5,000- 

The mean abundance 

Large differences in 

Fish larvae from the neuston layer were predominantly Hemiramphidae 

and Exocoetidae with a few midwater forms, mainly Gonostomatidae, and a 

number of nearsurface fish (Carangidae, Scombridae, Bramidae, and 

Scomberesocidae). 

midwater forms (Gonostomatidae and Myctophidae) and low concentrations of 

nearsurface fish (Scombridae, Coryphaenidae, Hemiramphidae, and 

Exocoetidae). Three taxa, Hemiramphidae, Exocoetidae, and Gonostomatidae, 

were abundant at all sites whereas Scombridae were well represented at Site 

Larvae from the 0- to 100-m depth layer included mainly 
18 

A, Carangidae and Bramidae at Site B, and Scomberesocidae at Site C. The 

mean abundance of all fish larvae in the 0- to 100-m depth layer ranged 

from 700 to 900/1,000 m3 in 1975 and from 300 to 400/1,000 m3 in 1976. 

The families of commercial interest included the Scombridae (tunas and 

mackerels) and Istiophoridae (billfishes), the latter represented by a 

single specimen taken at Site A (Hirota 1977). 

Tuna8 and Billfishes in the DOMES Area 

Information on fishes in the DOMES area has been reviewed by Blackburn 

(1976). 

skipjack tunas and striped and blue marlins. 

small quantities include the sailfish, Istiophorus platypterus, shortbill 

spearfish, Tetrapturus angustirostris, and black marlin, Makaira indica. 

There are five commercial fisheries for tunas or billfishes in the area: 

(1) the Japanese longline fishery, which fishes throughout the area with the 

exception of the northeastern corner (lat. 10"-15"N, long. 115"-130"W); (2) 

the Japanese live-bait and purse seine fisheries for skipjack and small 

yellowfin tunas in the South Pacific, which in recent years (particularly 

the purse seinere) have extended eastward along the Equatorial Countercurrent to long. 169"W (Tanaka 1978); (3) the United States live-bait and 

purse seine fisheries for skipjack and small yellowfin tunas, which in 

recent years (particularly by the seiners) have expanded westward to long. 

150"W between lat. 15"N and 5"s (Matsumoto et al. 1984); (4) the Hawaiian 

live-bait fishery for skipjack tuna, which fishes at or just outside the 

northern edge of the DOMES area; and (5) the Hawaiian longline fishery for 

yellowfin and bigeye tunas and billfishes. 

catches in metric tons (MT) in 1973 (Blackburn 1976) were approximately: 

Commercial fisheries in the area exist for yellowfin, bigeye, and 

Other billfishes taken in 

The DOMES area commercial 

Yellowfin tuna 62,700 MT (57,400 MT United States 

purse seine and longline; 

5,300 MT Japanese longline) 

Bigeye tuna 16,600 MT (Japanese longfine) 

Bil If ishes 5,500 MT (Japanese longline) 

Bigeye tuna and billfishes 300 MT (Hawaiian longline) 

Skipjack tuna 6,700 MT (United States purse seine 

and live bait) 

Total 91,800 MT 

The total catch would be much greater today if the Japanese skipjack 

tuna catch east of the 180th meridian--the eastward expansion to long. 

160"-165"W began in 1977 (Tanaka 1978)--and the catch of the Hawaiian 

recreational fishery were included. 

tuna fishery and the Hawaiian recreational fishery in the DOMES area are 

not readily available; however, it was estimated (Honolulu Laboratory 

staff) that the latter caught 996 MT of billfishes and 2,501 MT of tunas, 

mostly yellowfin and skipjack, in 1976. 

Catches of both the Japanese skipjack 

Larvae of yellowfin, bigeye, and skipjack tunas and striped and blue 

marlins are generally present in the DOMES area (Figs. 7-10). 

are larvae of species of fish taken in smaller quantities, i.e., frigate 

tuna, sailfish, and shortbill spearfish. Larvae of yellowfin and skipjack 

Also present 
19 

tunas are most abundant around Hawaii in summer and absent in winter, In 

other sectors of the DOMES area north of lat. 15"N, larval abundance is also 

seasonal. In the sector west of long. 150"W between lat. 14" and. 5"N, 

larvae are abundant throughout the year and their abundance peaks during 

winter (Matsumoto 1958). Between long. 150" and 130"W, larvae of yellowfin 

tuna are generally restricted to south of lat. 10"N. This is more 

pronounced for skipjack tuna larvae (Fig. 9). As mentioned previously, the 

dip in the distribution to lat. 10°N in this sector may be due to a similar 

southward shift of the surface isotherms, but it is a180 due partly to the 

low level of sampling north of lat. 10"N. East of long. 130°W, larvae of 

yellowfin tuna are taken as far north as lat. 20"N during summer (Matsumoto 

1958; Strasburg 1960; Klawe 19631, but larvae of skipjack tuna occur only 

occaeionally and in small numbers (Klawe 1963). 

in a similar manner as those of yellowfin tuna but at lower levels of 

abundance. 

skipjack tuna larvae are the most abundant: the catches are twofold to 

threefold greater than that of yellowfin tuna larvae (Matsumoto 1958; 

Higgins 1970). 

Larvae of bigeye tuna occur 

In Hawaii and the equatorial Pacific, including the DOMES area, 

Larvae of striped and blue marlins are found throughout the northsouth range of the DOMES area west of long. 145"W (Fig. 10). The apparent 

absence of larvae east of long. 145"W may be the result of low priority 

given to studies of billfish larvae in that region. 

studies of larval fish in the EASTROPAC area have been made (Ahlstrom 1971, 

19721, the studies were based solely on collections obtained from oblique 

hauls to 200 m. Collections obtained from surface hauls, which produce the 

most larval billfish, have not been analyzed. Thus far, larvae of only one 

species of lesser commercial importance, shortbill spearfish, have been 

taken at one station in the DOMES area at approximately lat. 19"N, long. 

137"W (Howard and Ueyanagi 1965). 

Although detailed 

Movement of Tunas 

Hypotheses and observations on tuna movement in this region include 

those of Rothschild (19651, Blackburn and Laurs (19721, Seckel (1972) , Williams (19721, and Matsumoto (1975). These authors variously stressed the 

probable importance of food sources, ocean currents, and temperature in the 

migratory behavior of skipjack tuna. 

It is generally accepted that tunas, mainly skipjack, migrate eastward 

from the eastern half of the DOMES area along the NECC. These fish enter 

the eastern Pacific northern fishery off central Mexico in the spring, 

proceed northward along Baja California as the season progresses, and return 

south along the coast in the fall. 

the equatorial central Pacific to spawn (Fink and Bayliff 1970). 

The major portion of the fish return to 

Williams (1972) proposed three migration models involving the movement 

of larvae, young and adult skipjack tuna from the equatorial Pacific west of 

long. 130"W to the eastern Pacific northern fishery in spring and their 

return to the central Pacific at the end of the season. According to the 

model, the NECC provides the eastward transport of larvae and young, and the 

California Current Extension provides transport for their return as adults 

to the equatorial spawning grounds west of long. 130"W. 

proposed the existence of a number of semi-independent skipjack tuna stocks 

in the Pacific Ocean by following the quarterly movement of the areae of 

high catch rates in the Japanese longline fishery over a period of 4 years 

Matsumoto (1975) 
20 

(1964-67). 

(Northern and Southern), with the migratory paths of the stocks following a 

clockwise direction in the central and western North Pacific and a 

counterclockwise direction in the eastern North Pacific and Southern 

Hemisphere, corresponding with the surface current flow of the major water 

masses (Fig. 12). 

taken by skipjack tuna tagged in the eastern Pacific and captured in Hawaii 

and Christmas Island by projecting the duration of liberty of these fish to 

the time scale and direction of movement indicated in the proposed model 

(Fig. 13, primary and assumed secondary routes). The most likely paths all 

pass through the DOMES area. 

He recognized approximately seven stocks in each hemisphere 

Matsumoto further attempted to fit the assumed routes 

EFFECTS OF MINING 

Impa c t on Environment 

Most of the concern on seabed mining relates to the surface and benthic 

discharges and their possible effects on the biota. 

discharge and surf ace plume resulting from test mining operations indicated 

that the discharge consisted of sediment, bottom water, nodule fragments, 

and benthic biota. Sediment was the major component of the particulates 

discharged, of which 68-87% by weight was pelagic clay, and the residual was 

primarily calcium carbonate, sea salt, and silicon dioxide (Bischoff et al. 

1979; Ozturgut, Lavelle, and Erickson 1981). Measurements of the discharge 

were made during mining tests conducted by Ocean Mining Associates (OMA) and 

Ocean Management, Inc. (OMI). In the OMA tests, the total particulate 

concentration in the shipboard discharge averaged 5.8 g/R. The discharge 

passed over the side, fell to the sea, and mixed rapidly with the surface 

water. A large percentage of the sediment particulates were found to settle 

out of the euphotic zone within a few hours, but the fine fraction of the 

discharge was presumed to be long-lived in the mixed layer. 

near surface concentration of particulates at the transect closest to the 

mining ship (15 min after initial mixing or 75 m behind the ship) was 

900 %/R (Ozturgut et al. 1980). 

mixed layer averaged 443 pg/R after 1 h, 177 w/R after 2 h, and 69 yg/R 

after 3 h, with ambient concentration being 28.5 pg/R. In the OM1 tests, 

the particulate concentrations were 598 w/R after 1 h, 55 ~.lg/R after 5 h, 

45 pg/R after 28 h, and 34 pg/k after 37 h, and the ambient concentration 

was 37 pg/t (Lavelle et al. 1982). The surface plume measured during the 

OM1 tests (Burns et al. 1980), had traveled about 4.5 km from the mining 

ship in <5 h and was 1 km wide at that point (Fig. 14). 

Investigations on the 

The maximum 

The particulate concentrations in the 

During full-scale commercial mining, the miner will discharge three 

times the volume of the test miner and at higher bulk densities, but the 

mining ship speed (estimated at 1 m/s) will be four times that of the 

average test miner speed, so that discharge volumes per unit ocean area will 

be slightly decreased over that of the mining tests (Lavelle and Ozturgut 

1981 1. 

The pattern that commercial mining ships make across a mining area will 

be one that maximizes the sea floor recovery of nodules. Thus Lavelle and 

Ozturgut (1981) envision that 30- by 30-km mining tracts will be 

successfully and intensively mined, and that within this area, the mining 

ship will traverse a rectangular pattern 30 km on the long side and 3.6 km 

on the shorter side, with such rectangular patterns offset by 40 m. Taking 
21 

I 150. Ib I200 I io- I 

41 

Ds,' 

4) 3'.. 

--/*I*----' /- 

- \4 

77- -6- --t 

cFigure 13.--Assumed routes followed by tagged skipjack tuna from the eastern 

to the central Pacific. 

along the routes represent quarters of high catch rates of skipjack tuna 

taken by the Japanese tuna longline fishery, 1964-67 (Matsumoto 1975). 

The letters represent tagged fish and the numerals 
22 

North 

t Plume 

Axis \ 

H 

I krn 

/*-3Okn 

winds 

6.8 

Figure 14.--Planar view of the plume reconstructed from 

nephelometer traces. 

voltages. Background voltage is approximately 3.3 (Burns 

et al. 1980). 

Contour levels are nephelometer 

the tong axis to be normal to the advection stream and 1 m/s as the speed of 

the mining ship, the authors envision traverses resulting in a serpentine 

surface plume approximately 70 km long (Fig. 15). 

describing the dispersion of particulates, concentrations higher than 

100 

and concentrations of 50 pg/% (near ambient) at distances of about 14 km. 

Eased on their models 

would be found at distances <6 km downstream of the mining ship 

Suspended particulates were found to significantly reduce light 

penetration. At depths between 10 and 20 m in l-h-old plume water, the 

attenuation coefficient of photosynthetically active radiation (PAR) wa8 

0.13/m, more than three times the average ambient value, and the attenuation 

coefficient of blue light in the plume (0.105/m) was more than twice the 

ambient value. Below 25 m, the attenuation coefficients of PAR and blue 

light in the plume were about the saute as in ambient water, and the 1% light 

depth was 20 IU shallower in the plume (70 m) than in ambient water (Ozturgut 

et al. 1980; Ozturgut, Lavelle, and Burns 1981). 
23 

ol I I 1 1 

0 20 40 60 80 

DISTANCE (km) 

Figure 15.--@alculated surface plume of a commercial mining ship 

traversing a rectangular pattern oriented normal to the advection 

direction at advection velocity of 25 cm/s and mining ship speed of 

1 m/s. 

(EavelPe and Ozturgut 1981). 

Concentrations of particulates in suspension are given in pg/t 

During test mining, cold bottom water of 4" to 10°C (mean = 7°C) was 

discharged over the ship's side through a 30-cm pipe. 

to fall onto the sea surface 3 m below the pipe at a rate of 120 fils 

(Ozturgut, Lavelle, and Erickson 1981). The discharge water mixed rapidly 

with the surface water and was undetectable in CTD casts after 1 h 

(E. Ozturgut, Ozturgut Bceanographics, Inc., Seattle, Washington, persb 

commun., October 12, 1982). Under commercial mining operations, the volume 

of discharge would be three times that of the test miner, but since the 

mining ship's speed would be four times greater, the discharge volume per 

unit ocean area would be slightly decreased over that of test mining 

(Lavelle and Ozturgut 1981). Thus, the dissipation of cold water would not 

be much different from test mining. 

The water was allowed 

Trace metals could be introduced into the water column from bottom 

water or released from sediments and nodule fragments in the discharge. 

Since dissolved trace-metal content of bottom and surface layers are not too 

different, there should be no detectable trace-metal increases at the 

surface due to the discharge of bottom water. Deep-sea clays, however, are 

particularly enriched in many heavy metals, and along with nodule fragments, could release trace metals directly to the water column and be taken 

up by plankton (Ozturgut, Lavelle, and Burns 1981). 

Based on estimates of commercial mining discharge rates of selected 

laanson, P. J., A. J. Chester, and F. A. Cross. 

particulate trace metals, Hanson et al.1 showed that A1 and Fe principally 

1982. Potential 

assimilation by and effects on oceanic zooplankton of trace metals from 

manganese nodule fragments discharged from planned ocean mining operations. 

Southeast Fisheries Center, National Marine Fisheries Service, NOM, 

Beaufort. NC 28516. Manuscript prepared for NOAA, Division of Ocean 

Minerals and Energy, Rockville, MD 20852. 
24 

from sediments and Mn from nodule fragments were the most abundant 

(discharge rates of 1,100-1,700 g/s); followed by Ba, Ni, Cu, and Co (12-77 

g/s>; and Zn, Pb, Ma, V, and Cr (1.4-9.5 g/s). By integrating the discharge 

rates over the mining year and by comparing them with the annual atmospheric 

deposition rates, which were the principal steady state inputs of trace 

metals to the mixed layer, the author8 demonstrated that the discharge rates 

exceeded the deposition rates by several orders of magnitude and concluded 

that the mining discharge could significantly increase the levels of some 

metals and alter the trace metal concentrations. 

Experiments with resuspended bottom sediments by Rosenbauer and 

Bigchoff (19781, however, indicated that all concentrations of Ni, Zn, Cr, 

Fe, Cu, Mn, and A1 were below detection limits in oxygenated seawater and 

only Mn and Ni were released in insignificantly small quantities (0.03 ppm 

Ni, 0.03-2 ppm Mn) in deoxygenated seawater. 

assess the amount and direction of metal exchange between artificial 

seawater and crushed Mn nodules (Benjamin and Felmy 1981) indicated that in 

the pH range of seawater, the amounts of Co, Cu, and Cd released were below 

the analytically detectable limit, even in the most concentrated slurry 

tested (20 g/R). 

Other experiments conducted to 

Impact on Primary Product ion 

Impact of mining on phytoplankton photosynthesis and primary production 

was examined by Chan and Anderson (1981) in terms of light reduction, 

nutrient enrichment, and toxic chemical effeets. The study indicated that 

local reduction in primary production due to light attenuation inside the 

plume was significant; however, because of rapid settling of a large 

percentage of the sediment particulates, the shading effect on phytoplankton 

wae expected to be only temporary, on the order of several hours. Since the 

adaptation of phytoplankton to a new light regime takes 1 to 2 days, shortterm shading in the discharge plume was not expected to appreciably affect 

phy t op lankt on phot osyn thee is. 

Chan and Anderson (1981) assessed the effect of mining on nutrient 

enrichment from information in the literature. Based on the average 

discharge rate and the rate of mixing between discharge and ambient water in 

test mining, the authors calculated that nitrate enrichment would be no more 

than 0.03 pg-atm/J?, within the first few minutes and 0.003 yg-atrnlg within 

the first hour, These increases were expected to be below analytical 

detectability and not to have any appreciable immediate effect on the 

nitrate-uptake rates and primary production. 

nutrients introduced into the euphotic zone were expected eventually to be 

incorporated into primary production, but even at full-scale mining rates 

the increase in primary production due to one or even a dozen mining 

vessel8 was not expected to create any significant change in the marine 

food chain, 

In the long tern the 

Experiments conducted by Chan and Anderson (1981) to study the effects 

of heavy metals and other toxic substances indicated that the mining 

discharge had no effect on the short-term photosynthetic rate, even when 

these substances were present at a fairly high concentration. Due to the 

insignificant amount of heavy metal8 from bottom sediment and the rapid 

mixing and dispersal of the mining discharge, any long-term toxic effect was 

considered negligible. 
25 

Impact on Hicrozooplankton 

. 

The effects of mining discharge on microzooplankton have not been 

investigated. Any effect on these organisms could be catastrophic since 

they are essential for first-feeding fish larvae. Although fish larvae are 

dependent on these food items for a brief period only, they represent an 

essential first step in ensuring the survival of the larvae. 

The potential effects of mining on macrozooplankton have been examined 

by Hirota (1981) from limited field data (three replicate neuston net tows 

each in ambient water and discharge plume at two test mining sites) and in 

laboratory experiments. The standing stocks of macrozooplankton, based on 

neuston net tows, were significantly higher in ambient water at one mining 

site and in plume water at the other. 

macrozooplankton taxa in ambient and plume localities were equally high at 

both mining sites. 

were apparently unaffected by the mining plume, at least over a short-term 

period b 

The similarity of occurrences of 

Stock abundance and taxonomic composition at the surface 

Laboratory experiments with 12 species of copepods exposed to low-tomedim particulate concentrations, including the range of concentrations 

observed during test mining, have been made to determine mortality rates 

(Hirota 1981). 

was (5% for most species after 24 h and only slightly higher (within 10%) 

after 48 h. The results indicated that mining discharge at the 

concentrations used in the experiments and observed in test mining plumes 

did not cause unusually high mortality. 

The difference in mortality between treatments and controls 

The study by Hirota (1981) also included the examination of fecal 

pellets from copepods and measurements of rates of fecal pellet production, 

pellet size, and sinking speeds. On the basis of this study as well as 

studies by other workers, Hanson et al. (see footnote 1) suggested that 

zooplankton will ingest significant quantities of particulate matter 

injected into surface waters, which could lead to assimilation of trace 

metals. From results of feeding experiments in the literature, they 

concluded that assimilation of trace metals from food through the gut walls 

of zooplankton was not particularly efficient and that normal processes of 

elimination, such as excretion (both soluble release and fecal pellet 

production), molting, and egg laying, appeared to rapidly reduce the levels 

of trace metals that were initially incorporated into tissue. 

Impact on Fish 

Adults 

There have been relatively few studies on the effects of suspnded 

particulates and turbidity on pelagic marine fishes. 

have focused on the physiological and pathological effects of high turbidity 

on freshwater and estuarine species. Many of these fishes that are normally 

exposed to high turbidities in nature are not bothered by high test 

turbidities (Wallen 1951; Herbert and Merkens 1961; Alabaster 1972, 1977; 

Sherk 1972; Neumann et al. 1975). Wallen (1951) and Alabaster (1972, 1977) 

reported that particulate concentrations below 60 mg/R were not harmful to 

trout, B&Q g4if;dng~i and 8. &u,&&g; however, physiological effects have 

been observed in some fishes at much higher turbidities. Prolonged exposure 

to excessively high turbidities have produced clogged gill cavitiee 

Most of the qtudies 
26 

resulting in suffocation (Everhart and Duchrow 1970, cited by Swenson and 

Matson 1976) and abnormal changes in the gills (Herbert and Merkens 1961; 

Alabaster 1972). Alabaster (1972) found thickening and fusion of. the 

epithelial cells of the secondary lamellae in some 5. trgttg taken from 

rivers carrying particulate concentrations of 1,000 and 5,000 mg/R. 

and Merkens (19611 observed that survival of rainbow trout, S. gghrdgggi, 

was adversely affected in laboratory tests at concentrations of 270-810 mg/k 

Herbert 

The turbidity caused by suspended particulates affect fish in other 

ways, most importantly in their feeding behavior, by making it more 

difficult for the fish to see their prey. 

observed that at constant light intensity the reactive distances of 

bluegills, &gg@g mcgpcoiggg, to h$n_~g diminished as turbidity 

approached 30 Jackson Turbidity Units (JTU) (ca. 44 mg/R). 

noted a significant reduction in the feeding rates of these fish a8 

turbidity was increased from 60 to 120 and 190 Nephelometric Turbidity Units 

("TU) (ca. 88, 177, and 280 ug/R, respectively). Reduction in feeding rate 

due to turbidity could ultimately lead to a reduction in growth (Sykora et 

al. 1972). Heimstra et al. (1969) found a general decrease in activity of 

juvenile largemouth bass, kf4cge~rgggg sglgg_idgg, exposed to turbidities of 

14-16 JTU (ca. 21-24 pg/t) and Shiraishi and Shimada (1972) reported that 

activity of downstream migrating salmonid fish was reduced by increased 

turbidity. 

Vinyard and O'Brien (1976) 

Gardner (1981) 

Information on purely marine species is limited. Ritchie (1970) 

detected no ill effects of overboard dredge disposal on 44 species of fish 

in upper Chesapeake Bay. 

flora and fauna, including albacore and salmonids, flourish offshore from 

the mouth of the Columbia River in water containing particulate concentrations of 10-100 mg/R. Moore and Moore (1976) showed that turbidity reduced 

the ability of European flounder, Platichthvs flesus, to see epibenthic 

prey and increased the time required to capture pursued prey. 

Connor (1976) found that whitebait (immature clupeoids) avoided the edge of 

advancing "white water" mass polluted with china clay, whereas mackerel, 

Scomber scombrus, did not. It seemed that small numbers of mackerel 

entered the polluted water and, although being visual feeders, were able to 

locate prey (fishing lure). 

Pruter and Alverson (1972) indicated that abundant 

Wilson and 

The only study of turbidity and tuna was done by Barry (19781, who 

observed the reaction of captive yellowfin tuna and kawakawa to a turbidity 

cloud of suspended particulates of deep-sea mud from the DOMES area. No ill 

effects were observed as a result of short exposure to turbidities ranging 

from 6 to 40 NTU (ca. 9-59 mg/R). Behavioral responses were mixed. Although 

tunas were sometimes observed to avoid the turbid cloud, they readily passed 

through it, as the cloud circled the tank. Maximum turbidities at the point 

where tunas passed through the cloud ranged from 1.6 to 3.0 NTU (2.7-4.7 

mg/R) for yellowfin tuna and 1.7 to 4.43 NTU (2.28-6.8 rng/R) for kawakawa, 

and feeding occurred in turbidities to 7.4 NTU (11.2 mg/R). 

experiments by Barry indicated also that in DOMES mud turbidities greater 

than 2.5 NTU (4 mg/R), the test tunas sometimes became sufficiently upset 

to stop feeding and exhibited coughing behavior. Barry pointed out that it 

would be difficult to extend these findings to tunas in the wild, since (1) 

the captive tunas may have developed a higher tolerance to turbidity 

because of their exposure to algae-produced turbidity in the tank, and (2) 

the ability of tunas to detect turbidity clouds in the wild might be 

different from that of captive tunas. 

The preliminary 
27 

Reduction in the feeding rate of adult tunas in the mining plume need 

not be a large concern, however, because of the low concentration of 

particulates, the transitory nature of the plume, the ability of tunas to 

feed in turbid waters, and most importantly, the capability of the tunas to 

swim through and out of plume waters. The only possible effect to tunas 

could be the reduction of food organisms in plume waters as a result of a 

reduction in primary productivity. 

production (Chan and Anderson 19811, however, have been shown to be little 

affected by the discharge plume. 

of adult billfishes to turbid waters. Based on the similarity of their 

feeding habits (types of food eaten) with that of adult tunas and on their 

great mobility, they too should be unaffected by the discharge plume. 

Food organisms (Hirota 1981) and primary 

No studies have been done on the behavior 

Tuna and Billfish Larvae 

There have been some studies on the effects of suspended solids and 

turbidity on fish larvae, but hardly any on larvae of tunas and billfishes. 

The effects of plume water on larvae of tunas and billfishes must, 

therefore, be inferred from studies made of other fish larvae. The normal 

development of embryos, larvae, and postlarvae of fishes in the mining area 

could be affected by sedimentation, loss of illumination due to turbidity, 

and changes in the properties of water, such as temperature. 

------------- Sedimentation.--There have been only limited studies on the direct 

effects of sediment on the early developmental stages of fishes. Rosenthal 

(1971) observed that there were major decreases in egg hatching success and 

survival of herring larvae, Clg~e_a h_a_ggn_ggg, at high concentrations of "red 

mud" (600-7,000 mg/R), and that the development of the embryos were 

retarded. 

increased with increasing concentrations, due to the adherence of mud 

particles to the eggshells and thereby possibly interfering with gaseous and 

other exchanges between the eggs and surrounding medium. He further noted 

that the ingestion of red mud particles by the larvae eventually resulted in 

blocked food intake. Sherk et al. (1975) noted that exposure of estuarine 

fishes to sublethal concentrations of suspended solids significantly 

increased hematocrit value, hemoglobin concentration, and erythrocite 

number, indicating respiratory stress, and that the early life stages of 

these fishes were more sensitive to suspended solids than the adults. They 

reported also that 18-h exposure to fuller's earth in concentrations of 0.8 

g/R resulted in 100% mortality of juvenile bluefish, Pomatomidae. Swenson 

and Matson (1976) reported that growth and survival of lake herring, 

CQ~_~~QINI~ gr_&gd_i, larvae held for up to 62 days in experimental tanks were 

not affected by red clay concentrations ranging from 0 to 48 Formazon 

Turbidity Units ca. 1-28 mg/R). No differences were found in mortality nor 

average weekly growth rates over the observed range of red clay 

concentrations. 

He reported also that the number of embryonic malformations 

Direct effects of sediment on estuarine and freshwater fishes, such as 

While these fishes 

those mentioned above, generally occurred after prolonged exposure to high 

sediment concentrations ranging from 270 to 7,000 mg/t. 

have greater tolerance than ocean species to suspended particulates, the 

lower levels of concentrations and the rapid dissipation of sediments at the 

mining sites should lessen the impact on eggs and larvae of the latter 

species. In the test mining area, the maximum concentration of particulates 

15 min after initial mixing was (ca. 900 ug/R) Ozturgut, Lavelle, and Burns 

1981) and the concentration of particulates was found to dissipate rapidly 
28 

to- near ambient in (5 h (Burns et al. 1980). 

sediment concentration and the rapid development of tuna embryos (hatching 

occurs in about 1 day after fertilization) would allow the eggs minimal 

exposure time to sedimentation and thus reduce or negate embryonic 

malformation. 

2 to 3 days after hatching. By this time, of course, the concentration of 

sediment particulates should be at or near ambient and thus not pose any 

danger to the larvae in causing blocked food intake or in affecting their 

growth. The only likely effect of sediment would be to those larvae 

already in the feeding stages. However, in view of the rapid dissipation 

of the discharge, the exposure time would be confined to a matter of hours 

and, therefore, should not noticeably affect the growth of the larvae. 

Under commercial mining conditions, where discharge volumes per unit ocean 

area are expected to be slightly less than that of mining tests (Lavelle 

and Ozturgut 19811, the chances of sediment particulates directly affecting 

tuna eggs and larvae should be negligible. 

The rapid dissipation of 

As for the newly hatched larvae, feeding generally begins in 

'&gh&!&y.--Feeding is the prime activity of all fish larvae for 

survival. 

searching power and reactive distance of the larvae, their feeding 

efficiency, and the abundance of suitable food organisms present (Blaxter 

19651, but also on illumination. Blaxter (19801, in his review of vision 

and feeding of fishes, reported that the ability of fish to feed fell 

progressively during dusk or as the illumination was artificially reduced. 

The threshold illumination for feeding by more than 20 species of fish 

averaged about 0.1 lux. 

and to feed successfully fell progressively for larvae of some species 

(herring, plaice, and northern pike, _Esgx hc_iu_g) during dusk or as 

illumination was reduced. Kawamura and Hara (1980) noted that milkfish, 

C_h_ag_og &nos, larvae also could not take food in the dark, but that the 

juveniles were able to do so. For these larvae, feeding thus would be 

limited to daylight hours, and any reduction in illumination due to 

turbidity will in effect decrease the hour6 available for feeding or limit 

feeding activity to less than optimum levels. 

The success or failure in feeding will depend not only upon the 

He reported also that the ability to perceive prey 

To compensate for reduced illumination, the larvae will be required 

to depend even more greatly upon their swimming power to ensure sufficient 

prey contacts and upon their reactive distance and feeding efficiency. 

Bishai (1960) found that herring larvae 6-8 mm long could sustain a water 

current of 0.57-1.03 cm/s for at least 1 h, giving them the possibility of 

swimming 20-30 m in 1 h. Presumably larger and stronger larvae will have 

greater swimming capabilities and enable them to cover greater distances 

within daylight hours. For larvae smaller than 6 mm, however, distance 

covered and reactive distance, as well as feeding efficiency, would be 

greatly reduced in most species. In most fish larvae, the distance at 

which they react to prey is quite short. Herring larvae were found to 

react to prey at distances of 0.7-10 body lengths when they first started 

feeding (Rosenthal and Hempel 1970). Blaxter and Staines (1971) reported 

reactive distances of 0.4 body length for herring, 0.5 body length for 

plaice, P&gggggcQg ~lgpgsg, and sole, soleg wlgg, and 0.2 body length 

for pilchard, _Sg:di.g ~ilcqggd~g. Hunter (1972) found the reactive 

distance of northern anchovy, _Eggggg_lig umgugx, to be 0.4 body length. The 

larvae of all species, except plaice, were reported as having low feeding 

success (2-10%) at initial feeding. Plaice had high success rates (32-62%) 

due to their increased maneuverability and ability to swim backward. The 

short reactive distance and low feeding efficiency at first feeding would 
29 

be lessened even more by reduced illumination, which in effect would reduce 

the availability of food. Thus, growth and survival would be affected, as 

it has been observed in feeding studies of larvae of plaice (Riley 1966; 

Wyatt 19721, sea bream, kcmsgggug ghkmhsiPglig (Houde 19751, bay anchovy, 

Ag$_hg_a gi&$billi (Saksena and Houde 1972; Houde 1977), sardine, Hgggngulg 

~egggc~llg (Saksena and Houde 19721, and lined sole, &_hjggs lin_egtge 

(Houde 1977). To compensate for reduced reactive distance resulting from 

lower illumination, it will be necefisary for the larvae to increase prey 

contacts. Hunter and Thomas (1974) observed such an adjustment in larvae 

of anchovy, which increased their swimming speed and area of search at low 

prey densities. 

Although light intensity is important for the survival of larvae, 

light intensity alone may not directly influence embryonic development. 

Ciechomski (1967a) observed that eggs of anchovy, E. mi_ho.&g, kept in 

complete darkness developed and hatched in a normal way. In other tank 

experiments, Houde and Palko (1970) noted that mortality of sardine larvae 

was higher in a tank with poor lighting (one 75-W incandescent bulb) than 

in one with better lighting (two 40-W fluorescent bulbs). 

Thacker (1963) also reported high mortalities for larvae of plaice reared 

under poor light conditions (total light at the surface was below 30-ft 

candles). 

Riley and 

Undoubtedly, the feeding of tuna and billfish larvae will be affected 

by reduced illumination. 

however, by their greater swimming power, feeding efficiency, and better 

vision because of their larger eyes and mouth, and earlier development of 

fins than most other fish larvae. The rapid growth exhibited by these 

larvae should further aid them to survive and pass througn the critical 

early life stages. 

They should be able to compensate for this, 

Turbidity also affects larvae in other ways. Swenson and Matson 

(1976) noted that herring larvae had a tendency to concentrate closer to 

the surface when subjected to high turbidity. 

reaction to reduced light levels at the bottom of the turbid water 

chambers and suggested that such a reaction in the wild could indirectly 

influence survival by exposing the larvae to greater predation. Miller 

(1974), in his survey of larval fish in waters off sugar mills, sewer 

outfalls, oil refineries, thermal outfalls, urbanized areas with associated 

runoffs, and in harbors in the Hawaiian Islands, noted that species of fish 

larvae, including tunas, in turbid water were lower in density by 75% and 

in number by 55%, and that turbidity, whether natural or artificial, was 

negatively correlated with larval fish abundance. This study implies that 

fish larvae in the wild avoided turbid waters. If this is so, it does not 

seem likely that mortality by predation would be significantly increased in 

plume waters, as suggested by Swenson and Matson (1976). 

They attributed this 

E~vig~ggggtgl fgctpyg.--Salinity, oxygen, and temperature also affect 

the early development of fishes, particularly in the embryonic and larval 

stages. 

occurred normally at salinities of 25.8-50'/00, but salinities above or 

below this range produced pronounced abnormalities in the embryos. Fonds 

et al. (1974) found that survival of garfish, _Bgl~ge b_&gg, eggs was 

influenced predominantly by temperature, but the survival of larvae from 

hatching to 30-40 mm TL was influenced by both salinity and temperature. 

Survival of eggs and larvae was found to be maximized at salinities of 

Ciechomski (1967a) noted that the embryonic development of anchovy 
30 

31.4-37.1"/00 and temperatures of 17.4'-19.4"C, and the limits for survival 

of eggs were estimated at salinities of <lo to >45'/00, and temperatures of 

12O-24"C. 

salinity of 5"/o0. 

oxygen on striped bass, &_r_ogg ggxg&_ilig, eggs and larvae, Turner and 

Farley (1971) observed that reductions in dissolved oxygen from saturation 

(7.3-8.8 mg/R) to 4 and 5 mg/R adversely affected hatching success and 

survival of the larvae. Egg survival was found to decrease with an 

increase in temperature (from 18.3' to 22.2'C) or exposure time (from 6 to 

56 h), or a decrease in oxygen level. At an oxygen level of 4 mg/&, 

survival was consistently reduced for all exposure times, the length of 

time for hatching was longer, and a number of larvae hatched with various 

abnormalities. 

In other experiments, garfish eggs failed to develop at a 

In laboratory experiments on the effects of dissolved 

Based on these studies, it seems that detrimental effects occur at 

either extremely high or low salinity levels--normal development takes 

place over a fairly wide salinity range--and after some hours of exposure 

to reduced dissolved oxygen levels. Although the levels at which these 

effects occur in eggs and larvae of billfishes and tunas could differ from 

the species noted above, the overall effects may be similar. 

area, however, ill effects from salinity and dissolved oxygen in the 

discharge water should be minimal because of the absence of extreme 

concentrations, such as those used in experimental tests, and because of 

the rapid mixing of the discharge water. 

of the water at depths greater than 5,000 m was 34.72 ~O.Olo/o~ (Burns et 

ill, 19801, which was well within the seasonal range of 33-35"/00 in the 

surface mixed layer (Ozturgut et al. 1978). From monitoring tests 

(Ozretich 19811, the mean oxygen concentration in 1-, 2-, and 3-h-old plume 

was reported as 4.68850.035 ml/&, nearly the same as the ambient mean 

concentration of 4.69520.05 ml/R, and the maximum dilution of the 

discharge water was reported to occur within the first few minutes of 

mixing with surface water. 

In the mining 

During test mining, the salinity 

Temperature appears to have a predominant influence in the development of embryos and larvae. Most fish eggs and larvae were found to 

survive a wide range of temperatures: 

al. 19811, 10"-17°C by anchovy (Ciechomski 1967a), ll"-2OoC by tiulka, 

Clupeonella delicatula delicatula (Pinus 1974) and 23 "-30°C by yellowfin 

tuna (Harada et al. 19781, to mention a few. At temperatures below or 

above the normal ranges, however, the development of embryos and larvae 

could be affected drastically. Ciechomski (1967a) observed that a 

temperature of 4°C water in the early blastula stage showed a complete halt 

in their development, death occurred in 5 to 6 days, and eggs which had 

been kept for 1 to 2 days at 4°C and transferred to normal temperature 

(14°C) died more quickly, suggesting that lower temperature may cause 

irreversible damages. At low temperatures (1Oo-12"C1, larvae of striped 

bass were found to hatch with a depressed cephalic region (Morgan et al. 

1981) and the larvae of yellowfin tuna were found to be deformed when 

hatched in temperatures below 20°C (Harada et al. 1978). Larvae of Pacific 

cod became so inactive at very low temperatures that they were unable to 

catch and consume food (Alderdice and Forrester 1971). 

higher than the normal range, hatched larvae of striped bass showed 

pugheaded features, small yolk sacs, and deformed internal organs (Morgan 

et al. 19811, and larvae of anchovy exhibited an increase in heartbeat from 

65-70 beats/min to about 100 (Ciechomski 1967a). 

14"-22"C by striped bass (Morgan et 

At temperatures 
31 

. 

Fish larvae can be affected also by thermal shock when subjected to 

sudden changes in temperature. Hoss et al. (1974) noted that larvae of 

Atlantic menhaden, Brgy~~gtig tygpgggg; spot, &gio_sto_g~g IK~Q~~Q~IJ~; 

pinfish, Egg_o&q ghhmqipclg; and three species of flounders, &rgdjcc&_hyg 

&g&g&ug, e. lg&hpgtigma, and 1). db_6gu_t&_a, acclimatized at 5", lo", and 

15°C and subjected to 15"-18°C increases in temperature showed immediate 

reactions, such as loss of equilibrium, erratic swimming, violent jumping, 

and convulsions. This initial period of reaction was often followed by a 

return to relatively normal behavior. These fish also received a thermal 

shock when they were returned to the original temperature. This second 

shock was often more violent than the first and was more pronounced at the 

lower acclimatization temperatures. According to the authors, the second 

shock may be a direct cause of mortality, or if the fish are not killed, 

they may be more vulnerable to predation. Griffith (1978) noted that 

threadfin shad, Qo_g~gega pxz&gggggg, acclimatized at 15°C and exposed to 

sudden cooling (2"-5"C decreases in 4 h) lost equilibrium in proportion to 

the magnitude of temperature decrease, as the temperature approached 4"- 

6"C, and that as much as 32% of the cold-shocked fish that had lost 

equilibrium for as short a time as 12 s before being returned to warmer 

wacer could not recover and experienced mortality. 

Eggs and larvae of tunas also could be affected by temperature as 

noted above. Because of rapid dissipation of the cold discharge water soon 

after initial mixing, such effects would be limited to the area immediately 

beneath the outfall. With the ambient surface temperature ranging from 21" 

to 26°C in the mining area and that of the discharge ranging from 4" to 

1O"C, the difference in the temperatures (17°C) would be similar in 

magnitude to that tested by Hoss et al. (1974) for other fish species. With 

thermal shock likely to produce an immediate reaction, there is reason to 

believe that eggs and larvae coming into direct contact with the cold 

discharge water would be affected adversely. 

Assuming that all tuna eggs and larvae coming into direct contact 

with the cold discharge water were to suffer mortality, a rough estimate of 

the total number of larvae that could be killed can be made and the losses 

evaluated in terms of the magnitude of the annual catches (see section on 

Effects on Fisheries). 

Under full-scale mining operation, bottom water will be discharged at 

the surface through a 30-cm pipe. The discharged water will f a l l t o the 

surface from a height of approximately 5 m and impact a swath of surface 

water approximately 1-m wide, l-m deep, and 89.4-km long (mining ship speed 

of 1 m/s per day. Thus, the volume of water affected per day would be 

within the planned mining area (Matsumoto 1958; Strasburg 1960; and 

unpublished data, Honolulu Laboratory files), the concentrations of tuna 

larvae were approximately 0.89 skipjack and 0.30 yellowfin tunas per 1,000 

m3. 

concentration times 86,400/1,000), could be affected by the discharge water 

each day. These numbers, however, represent only larvae past the initial 

feeding stage and do not include eggs and yolk sac larvae which, although 

present, were not analyzed in the larval studies. Size-frequency data from 

Strasburg (1960) indicate that about 33% of the skipjack tuna larvae and 

29% of the yellowfin tuna larvae taken in plankton net tows were at the 

initial feeding stage (3.0-3.9 mm TL). Assuming that eggs and 1- and 2- 

day-old yolk sac larvae were present at the time net tows were made and 

86,400 m 4 . Based on surface day and night plankton net catch data from 

Hence, 77 skipjack tuna and 26 yellowfin tuna larvae (larval 
32 

each stage survived to the first feeding stage in 1 to 3 days in like 

numbers, then an additional 76 skipjack tuna (77 x 0.33 X 3) and 23 

yellowfin tuna (26 X 0.29 X 3) larvae would be affected, bringing. the total 

eggs and larvae affected per day to 153 skipjack tuna and 49 yellowfin 

tuna. 

annual production of 1.5 million tons of ore (Ozturgut, Lavelle and 

Erickson 19811, ca. 45,900 skipjack tuna larvae and 14,700 yellowfin tuna 

larvae could be susceptible to thermal shock each year. 

In 300 mining days, the effort required to achieve the estimated 

These estimates represent the maximum number of larvae that could be 

affected if mining were done entirely in areas where spawning by both 

species occur. 

quarter (north of lat. 10"N and east of long. f40"W) of the projected 

mining area. 

affected by mining will be reduced in proportion to the time (days) mining 

is done in this sector. 

Skipjack tuna, however, do not spawn in the northeastern 

Consequently, the number of skipjack tuna larvae likely to be 

Other Possible Effects 

Tunas, as well as other pelagic fishes, have been known to congregate 

under drifting objects, such as logs, seaweed, rafts, and other flotsam. 

Fishermen have utilized this behavior of fishes by seeking and fishing 

around such objects, often with huge success (Uda 1933; Kimura 1954; 

McNeeley 1961; Inoue et al. 1963, 1968). In recent years manmade fish 

aggregating devices (FAD's) have been devised and anchored in coastal and 

deep open ocean waters in the Philippines (Murdy 1980; Aprieto 1981, de 

Jesus 1982, Matsumoto2), Hawaii (Matsumoto et al. 19811, many central and 

South Pacific Islands, New Zealand, Australia, and in the Indian Ocean 

(Shomura and Matsumoto 1982), and in the eastern Pacific (Guillen and 

Bratten3) (Fig. 16). 

in sufficiently large concentrations to entice commercial tuna purse 

seiners and pole-and-line vessels to fish around them. In Hawaii, poleand-line fishing vessels caught over 471 MT (1 million lb) of skipjack tuna 

and 45.4 MT (100,000 lb) of yellowfin tuna off four FAD's in 1978 (Table 

1). 

tunas, including skipjack, yellowfin, bigeye, kawakawa, frigate, and 

bullet, have been taken in a single purse seine set (see footnote 2). 

These FAD's have attracted fish, predominantly tunas, 

In the Philippines estimates of up to 200 MT of various species of 

Tunas of varied sizes ranging from (1 to >45 kg have been reported 

from beneath and around FAD's (Matsumoto et al. 1981). Small tunas ((1 or 

2 kg) generally rmained close to the FAD's during the day and night, but 

larger tunas (>3 kg), particularly the skipjack tuna, roamed over distances 

of 5 km or more away from the FAD's during daylight. The latter departed 

from the FAD's at sunrise and returned to it at sunset. The ability of the 

skipjack tuna to depart and return to a reference point has been 

demonstrated by Yuen (1970). By tracking bank-associated small (40-44 cm) 

2Matsumoto, W. M. Manuscr. in prep. Payao fishing in the 

Philippines. Southwest Fisheries Center, National Marine Fisheries 

Service, NOAA, P. 0. Box 3830, Honolulu, HI 96812. 

3Guillen, R., and D. A. Bratten. 1981. Anchored raft experiment to 

aggregate tunas in the eastern Pacific Ocean. Inter-Am. Trop. Tuna Comm., 

Internal Rep. 14, 10 p. Inter-American Tropical Tuna Commission, c/o 

Scripps Institution of Oceanography, P. 0. Box 1529, La Jolla, CA 92093. 
33 

Figure 16.--Locations where fish aggregating devices have been deployed, 

1979-81, or where deployment is planned in the Pacific and Indian Oceans 

(Shomura and Matsumoto 1982). 

Table I.--Fiah species caught (in pounrm/ uy pole-and-line Eiahing in 1978 during the Hawaiian 

fieh aggregating device experiment (Matnumot6 et at. 1981). 

L 

Skipjack tuna Yellowfin tuna Rawakawa Dolphin Tot81 

Catch per Catch per Catch per Catch per Catch per 

Buoy Viaits Catch visit Catch visit Catch viait Catch visit. Catch visit 

A 92 357,044 3,880.3 22,682 246.5 1,479 16.0 854 9.3 382,031 4,152.5 

B 1 5,110 5,110.0 0 0 .o 0 0 .o 0 0 .o 5,110 5,110.0 

C 14 103,037 7,359.8 1,475 105.4 4,218 301.3 0 0.0 108,730 7,766.4 

D 139 573,106 4,k23.1 80,183 576.9 1,706 12.3 3,034 22.6 658,029 4,734.0 

Total 246 1,038,297 4,220.7 104,340 424.1 7,403 30.0 3,888 15.8 1,153,900 4,690.6 

Percent of 

tot81 Catch 89.73 9.28 0.64 0.34 99.99 

skipjack tuna tagged with an ultrasonic device, Yuen showed that the fish 

was capable of making nightly journeys of 25-106 km (maximum straight line 

distances of up to 35 km from the bank). The tagged fish was observed to 

leave the bank at nightfall, returning to it at sunrise, and remaining over 

the bank throughout the day as a member of a school. This pattern of daily 

movement was observed for 3 days and again for 3 more days after an 

interruption of 2 days, when the vessel was required to return to port. The 

repeated daily pattern from and return to the bank led Yuen to conclude 

that the skipjack tuna was able to navigate and was aware of time. 

The ability of the skipjack tuna to depart and return to a FAD can 

significantly alter the normal distributional pattern of schools within an 

area. After having made initial contact with a FAD, a school may prolong 

its 8tay.h the area. 

schools around the FAD, as observed by Matsumoto et al. (1981). 

In due time this would result in a buildup of 

During the 
34 

peak fishing season, the FAD's attracted more tuna schools than normally 

would have been found in the area. The schools attracted to the FAD's 

remained in the vicinity or were replaced by other schools on a continuing 

basis, allowing the pole-and-line fishing vessels to fish around the FAD's 

for periods of up to 18 consecutive days. 

In the Hawaiian FAD's study, Matsumoto et al. (1981) reported that two 

or more schools were present around a FAD at the same time during April and 

May. The long-term (1950-61) sightings of skipjack tuna schools in 

Hawaiian waters for a comparable period (March-May) is given as 0.87 

schools per 10 h of scouting (Waldron 1964). Based on these sightings, 

FAD's could increase the number of schools within its vicinity by a factor 

of three or four. In nodule mining, the ship, moving slowly at a speed of 

1 m/s, could act as a FAD and accumulate tuna schools. Should spawning 

occur at this time, the concentration of spawned eggs around and in the 

path of the mining ship would be higher than usual, and the number of eggs 

that would eventually be exposed to direct contact with the cold discharge 

water also would be increased. A threefold or fourfold increase, as noted 

above, may not be unreasonable. 

Effects on Fisheries 

Mortality of tuna eggs and larvae caused by mining is bound to have 

some effect on the catches in the eastern Pacific surface fishery and the 

Hawaiian skipjack tuna fishery. The eastern Pacific fishery is a major 

fishery: The catch of skipjack tuna reached a high of 170,000 MT in 1978 

and averaged 128,300 MT annually in the 5-year period prior to 1980 

(Forsbergh 1980). 

in 1976 and averaged 201,000 MT annually over the same period (Cole 1980). 

The Hawaiian skipjack tuna fishery is a minor fishery, with annual catches 

for the same period averaging 3,100 MT (unpublished data, Honolulu 

Laboratory files 1. 

The catch of yellowfin tuna reached a high of 236,400 MT 

A crude estimate of the probable impact mining will have on the 

recruitment of 1-year-old fish can be made from available length-frequency 

and catch data. The eastern Pacific fishery can be separated at lat. 15"- 

16"N off the coast of Mexico into a northern and southern fishery. Nearly 

all of the fish entering the northern fishery originate in equatorial 

waters from an area west of long. 13OoW, within and north of the NECC 

(Rothschild 1965; Fink and Bayliff 1970; Williams 1972). In the period 

1971-74, the mean annual catch in the northern fishery was 9,747 MT of 

skipjack tuna and 24,833 MT of yellowfin tuna (Calkins 1975). Based on 

earlier published data (Davidoff 1963; Broadhead and Barrett 19641, 1-yearold (below 50 cm) skipjack tuna averaged 24.0% by weight of the catch in 

the northern fishery and 1-year-old (below 60 cm) yellowfin tuna averaged 

0.9% of the yellowfin tuna catch. Assuming that the proportion of 1-yearold fish remained the same in the 1971-74 period, the average annual catch 

of this age group would represent approximately 2,336 MT for skipjack tuna 

and 2,235 MT for yellowfin tuna. 

From earlier estimates, roughly 49,500 skipjack tuna and 14,700 

yellowfin tuna larvae were expected to be affected by mining each year. 

a nonmining situation, these larvae would be expected to suffer a natural 

mortality of 80% (Murphy and Sakagawa 1977) during the year. 

natural mortality, 9,900 skipjack tuna and 2,940 yellowfin tuna larvae 

should survive and enter the fishery as 1-year-old fish. 

In 

Adjusting for 

These numbers 
34 

represent approximately 15.3 MT of skipjack tuna and 10.7 MT of yellowfin 

tuna, based on an average weight of 1.85 kg for 40-50 cm skipjack tuna and 

3.17 kg for 50-60 cm yellowfin tuna (length-weight relationship tables, 

Honolulu Laboratory files). Adjusting for possible FAD-like effects of the 

mining ship would increase the totals to 65.2 and 42.8 W. for skipjack tuna 

and yellowfin tuna, respectively. These totals represent only an 

insignificant amount (0.64 and 0.16%, respectively) of the annual catches 

of the two species in the eastern Pacific northern fishery. The actual 

impact on the annual catches would be far less, if the efficiency of the 

gear, which is well below loo%, were considered. 

In the Hawaiian fishery, the skipjack tuna catch consists of fish 

migrating from the Japanese offshore and the eastern Pacific fisheries, as 

indicated from recaptures of tagged fish (Matsumoto et al. 1984) and very 

likely from the central equatorial waters to the south of the islands 

(Matsumoto 1975). 

area to the south. The effect of mining on eggs and larvae could affect 

the eventual recruitment of 1-year-olds, but unlike the sector east of 

long. 130°W, where tuna spawning does not occur north of lat. 10"-15"N, 

heavy spawning by skipjack and yellowfin tunas occur in Hawaiian waters 

north of the mining area. The larvae spawned could remain in the area and 

enter the fishery as 1-year-old fish a year later or migrate south into the 

mining area as juveniles during winter, at sizes large enough to be 

unaffected by mining discharge waters, and return as 1-year-old recruits. 

This should lessen the effects of mining insofar as the recruitment of 1- 

year-olds into the IIawaiian fishery is concerned. 

Recruitment of 1-year-olds may be mostly from the mining 

SUMMARY AND CONCLUSIONS 

Of the many changes to the environment resulting from nodule mining, 

increased sediment and turbidity in surface water and the discharge of cold 

bottom water at the surface were considered most likely to affect tuna and 

billfish eggs and larvae. The potential effects on the biota were examined 

in terms of small-scale test mining results and projections to full-scale 

mining effects were attempted whenever such information was available. 

In test mining studies, the maximum concentration of sediment 

particulates soon after mixing of the discharge and surface waters was 

given as 900 1lg/2 (Ozturgut et al. 1980). 

from mining extended downstream with the concentration of particulates 

dissipating rapidly to near ambient (55pg/R) in 5 h at a distance of 

approximately 5 km from the ship and to ambient (34 1ig/2) in about 37 h. 

Light attenuation in 1-h-old plume at depths of 10-20 m was 0.13/m, more 

than three times the average ambient value. 

(mean - 7"C), was found to mix rapidly with surface water and was 

undetectable in chlorinity-temperature-depth casts after 1 h. 

The surface plume that resulted 

Cold discharge water, 4"-10"C 

Under commercial mining conditions, with the ship traversing the 

mining area in a rectangular pattern 30 km on the long side and 3.6 km on 

the short side, particulate concentration of 100 ygl9, was expected at 

distances of (6 km downstream of the mining ship and concentration of 50 

vg/R (near ambient) at distances of about 14 km. 

WBR expected to be reached in about 15 h. 

was expected to be three times that of the test miner, but because the 

ship's speed would be four times greater, the discharge volume per unit of 

ocean was expected to be slightly less than that of test mining (Lavelle 

The latter concentration 

The volume of discharged water 
and Ozturgut 1981). Consequently, the dissipation of cold water was 

expected to be not much different from that of the test mining. 

Past studies on the effects of suspended solids and turbidity on fish 

eggs and larvae have dealt mainly with freshwater and estuarine species. 

Direct effects of suspended solids on the early developmental stages of 

fishes included such things as retarded embryonic development, development 

of malformed larvae, blocked food intake leading to undernourishment and 

reduced growth, and clogged gills resulting in respiratory stress and 

mortality. These effects generally occurred at relatively high turbidities 

of 270 to 7,000 mg/R and after prolonged exposures of 8 or 9 weeks 

(Rosenthal 1971; Sherk et al. 1975; Swenson and Matson 1976). The combined 

effects of low concentration and rapid dissipation of particulates in test 

mining and the extremely rapid development of the eggs and larvae of tunas 

(embryonic development and hatching of yellowfin tuna in about 1 day in 

tropical temperatures, yolk absorption in 2-3 days, and growth of larvae 

from 2.6 mm at hatching to 51 mm in 38 days) were expected to reduce the 

risk of prolonged exposure and thus prevent any ill effects. 

Reduced illumination caused by turbidity has been reported to affect 

These effects have been overcome by some species (e.g., herring) 

feeding by reducing the reactive distance and feeding efficiency of fish 

larvae. 

which increase their swimming speed and area of search for prey (Hunter and 

Thomas 1974). Because of the exceptionally large eyes and mouth and the 

rapid development of the fins in larvae of tunas and billfishes, it was 

expected that these larvae could compensate for reduced illumination better 

than most fish larvae. Thus, it was concluded that increased turbidity 

resulting from mining would not affect the survival of these larvae. 

Other properties of seawater, such as salinity, oxygen, and 

temperature, also were found to affect the development and survival of fish 

eggs and larvae, but only at extremely low or high levels and after 

prolonged exposures. 111 effects on tuna eggs and larvae in the mining 

site should be minimal, however, because of insignificant differences in 

the salinity of bottom and surface water and the rapid dilution of the low 

oxygen bottom water after mixing with surface water. 

The most likely, and perhaps the only, effect of temperature on the 

eggs and larvae of tunas will occur at the discharge point of bottom water. 

In nodule mining, the cold discharge water (4°-100C, average 7°C) falling 

onto the sea surface can come into direct contact with the developing eggs 

and newly hatched larvae drifting at the surface. Such contacts could 

cause the cessation of- embryonic development, the development of deformed 

larvae, or result in thermal shock to the larvae, causing them to lose 

equilibrium and become easy targets to predators or even result in death. 

Supersaturation of atmospheric gases could be a problem, but in the 

discharge of an airlift mining operation, supersaturation lasts only 

minutes due to rapid dilution. Exposure of fish to supersaturated gases, 

thus, is not expected to be a concern (Ozretich 1981). 

Based on the premining concentration of tuna larvae in the surface 

layer (1 m deep) within the mining area and on the estimated volume of 

surface water that would be affected by the discharge water in 300 days of 

mining each year, it was estimated that approximately 45,900 skipjack tuna 

and 14,700 yellowfin tuna larvae could be lost annually due to mining. 
37 

These figures would be about four times larger if the mining ship were to 

act as a FAD by concentrating tuna schools in the immediate vicinity of the 

mining ship. Spawning activities by these schools could increase.the 

concentration of eggs near the mining ship. 

threefold or fourfold greater than the concentration in nonmining 

situations. 

Such increases can easily be 

The impact of the mortality estimated above on the eastern Pacific 

northern fishery (north of lat. 15"N) and on the Hawaiian skipjack tuna 

fishery can be estimated. In the eastern Pacific, practically all of the 

fish entering the northern fishery originate in equatorial waters west of 

long. 13O"W. Larvae from this region are transported eastward in the NECC 

and enter the fishery as 1-year-old fish. Fish of this age group comprise 

24% by weight (2,336 MT) of the skipjack tuna and 0.9% (2,235 MT) of the 

yellowfin tuna taken annually in the northern fishery (average annual 

catches estimated for the period 1971-74). Of the estimated number of 

larvae that would likely be killed by mining (45,700 skipjack tuna and 

14,700 yellowfin tuna), 80% are expected to die of natural causes, leaving 

9,900 skipjack tuna and 2,940 yellowfin tuna (equivalent to 15.3 and 10.7 

MT, respectively) to survive and enter the fishery as 1-year-old fish. 

Adjusting for possible FAD-like effects of the mining ship would increase 

the totals to 65.2 and 42.8 MT for skipjack and yellowfin tunas, 

respectively. These totals, representing approximat.ely 0.64 and 0.16% of 

the annual catches of skipjack and yellowfin tunas, respectively, should 

have no noticeable effect on the total annual catches of both species taken 

in the eastern Pacific northern fishery. 

In the Hawaiian fishery, the impact of mining on the skipjack tuna 

fishery would be even less, since the species also spawns in the fishing 

grounds, outside of the projected mining area (i.e., n0rt.h of lat. 20"N). 

Larvae from these spawnings could remain in the area and be subjected to 

fishing a year later (as 1-year-olds) or migrate south into the mining area 

in winter as juveniles, at sizes large enough to withstand the impact of 

mining, and return as 1-year-old fish in the summer, together with fish 

spawned within the mining area. 

Based on this study, the probable effects of mining on tuna and 

billfish eggs and larvae appear to be negligible; however, the premises on 

which certain deductions have been made, require verification. Laboratory 

studies to accurately describe the effects of sediment and temperature on 

tuna eggs and larvae and on the spawning behavior of adult tunas need to be 

made. In the field, more detailed observations on the temperature of the 

water at the point of discharge are needed and the effect of the discharge 

water on tuna eggs and larvae at the point of mixing need to be determined. 

The abundance of tuna and billfish eggs and larvae along the path of the 

mining ship needs to be determined routinely, so that the extent of the 

damage to these life stages can be monitored. If damage to the eggs and 

larvae by the discharge is found to be excessive, then alteration of the 

discharge point, perhaps to subsurface levels, may be necessary. 

Aside from these studies concerning direct effects on eggs and larvae, 

additional studies are needed on the pelagic food web. It is recommended 

that the effects of sediment and temperature on all components in the food 

web be studied, particularly those organisms which are consumed during 

initial feeding by the larvae. 
38 

ACKNOWLEDGMENTS 

The author wishes to thank William F. Hettler and Jean Snider for 

their helpful suggestions and critical reviews. 

NOAA's Deep Ocean Mining Environmental Study conducted by the National 

Ocean Service, Division of Ocean Minerala and Energy. 

This work ie part of 
39 

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RECENT TECHNICAL MEMORANDUMS 

1 

k 

4 

Copies of this and other NOAA Technical Memorandums are available from the National 

Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167. Paper copies vary In 

price. Mlcrofishe copies cost $3.50. Recent issues of NOAA Technical memorandums from the 

NMFS Southwest Fisheries Center are listed below: 

NOAA TM-NMFS SWFC 34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

“Some data on dolphin mortality In the eastern tropical 

Pacific tuna purse seine fishery prior to 1970.” 

T. D. SMITH and N. C. H. LO 

(July 1983) 

“Precision of age determination of northern offshore spotted 

dolphins.” 

S. B. REILLY, A. A. HOHN, and A. C. MYRICK, JR. 

(August 1983) 

“Recovery of adult green turtles observed or originally tagged 

at French Frigate Shoals, Northwestern Hawaiian Islands.” 

G. BALAZS 

(August 1983) 

“Report of the workshop on long-range planning for the 

North Pacific albacore fishery.” 

D. J. MACKETT, Editor 

(November 1983) 

Distribution of four dolphins (Stenella spp. and Delphhus 

delphls) In the eastern tropical Pacific, with an annotated 

catalog of data sources. 

W. F. PERRIN, M. D. SCOll, G. J. WALKER, F. M. RALSTON 

and D. W. K. AU 

(Qecember 1983) 

Annotated references to techniques capable of assessing the 

roles of cephalopods in the eastern tropical Pacific Ocean, 

with emphasis on pelagic squids. 

J. B. HEDGEPETH 

(December 1983) 

Summary of environmental and fishing information on Guam 

and the commonwealth of the Northern Mariana Islands: 

Historical background, description of the islands, and review 

of the climate, oceanography, and submarine topography. 

L. G. ELDREDGE 

(December 1983) 

Diving patterns of the Hawaiian Monk Seal, Lisianski Island, 

1982. 

F. V. SCHLEXER 

(February 1984) 

“The Hawaiian Monk Seal of Laysan Island: 1982” 

D. J. ALCORN 

(April 1984) 

Atlas of airborne sea surface temperature observations In 

nearshore California waters, 1980-1983. 

P.N. SUND 

(July 1984)