NOAA Technical Report NMFS 81 September 1989

Catch-per-unit-effort and Biological

Parameters from the Massachusetts

Coastal Lobster (Homarus americanus)

Resource: Description and Trends

Bruce 1. Estrella

Daniel J. McKiernan

U.S. Department of Commerce
NOAA TECHNICAL REPORT NMFS

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34. Additions to a revision of the shark genus Carcharhinus: Synonymy of Aprionodon and Hypoprion, and description of a new species of Carcharhinus (Carcharhinidae),

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Columbia Rivers, by George A. Swan, Tommy G. Withrow, and Donn L. Park. April

1986,34 p.

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Edward P. Myers, Donald E. Hoss, Walter M. Matsumoto, David S. Peters, Michael

P. Seki, Richard N. Uchida, John D. Ditmars, and Robert A. Paddock. June 1986,

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42. Effects of temperature on the biology of the northern shrimp, Pandalus borealis,

in the Gulf of Maine, by Spencer Apollonio, David K. Stevenson, and Earl E. Dunton,

Jr. September 1986, 22 p.

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Uchida, Sigeiti Hayasi, and George W. Boehlert (editors). September 1986, 105 p.

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(Pisces: Sparidae), by George H. Darcy. September 1986, 19 p.

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association and bilateral pattern and their significance in species separation, by Lochai Chen. September 1986, 17 p.

46. Distribution and relative abundance of pelagic nonsalmonid nekton off Oregon

and Washington 1979-84, by Richard D. Brodeur and William G. Pearcy. December

1986, 85 p.

47. Reproduction, maturation, and seed production of cultured species: Proceedings

of the twelfth U.S.-Japan meeting on aquaculture, Baton Rouge, Louisiana, October

25-29, 1983, by Carl J. Sindermann (editor). February 1987,73 p.

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Mentici"hus americanus, in the northwestern Gulf of Mexico, by Stephen M. Harding

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for age determinations, by John W. Ropes. March 1987, 5 p.

51. Status, biology, and ecology of fur seals: Proceedings of an international

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L. Gentry (editors). June 1987,212 p.

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Huppert (editor). May 1987, 45 p.

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by Janet A. Gooch, Malcolm B. Hale, Thomas Brown, Jr., James C. Bonnet, Cheryl

G. Brand, and Lloyd W. Reiger. June 1987,23 p.

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finfish, shellfish, and their products, by Judith Krzynowek and Jenny Murphy. July

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NOAA Technical Report NMFS 81

Catch-per-unit-effort and Biological

Parameters from the Massachusetts

Coastal Lobster (Homarus americanus)

Resource: Description and Trends

Bruce T. Estrella

Daniel J. McKiernan

September 1989

u.s. DEPARTMENT OF COMMERCE

Robert Mosbacher, Secretary

National Oceanic and Atmospheric Administration

John A. Knauss, Under Secretary for Oceans and Atmosphere

National Marine Fisheries Service

James Brennan, Assistant Administrator for Fisheries
The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary product or proprietary material mentioned

in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales promotion which would

indicate or imply that NMFS approves, recommends or endorses any proprietary product or proprietary material mentioned herein, or which has as

its purpose an intent to cause directly or indirectly the advertised product to

be used or purchased because of this NMFS publication.

ii
CONTENTS

Acknowledgments iv

Abstract 1

Introduction 1

Methods 1

Study area 1

Sampling 2

Analytical procedure 3

Results 3

Relative abundance 3

Immersion-time standardization 3

Commercial landings 5

Mortality estimates 7

Exploitation rate 8

Carapace length 10

Weight-length relationship 12

Sex ratio 14

Maturity 15

Culls 17

Trap mortality 18

Summary 19

Citations 20

III
Acknowledgments _

We are indebted to the many commercial lobstermen and dealers who

assisted in this cooperative lobster-resource monitoring effort. Gratitude

is also extended to staff of the Massachusetts Division of Marine Fisheries

who endured many long hours at sea collecting data. Ann-Marie Schultz

and Steven Cadrin assisted with graphics programming. David Aiken and

Susan Waddy, Department of Fisheries and Oceans, St. Andrews, New

Brunswick, kindly fumished information regarding the cement-gland staging

technique. Automatic data processing was supported by the National Marine

Fisheries Service (NMFS) Northeast Fisheries Center, Woods Hole, MA.

Joseph Idoine and Michael J. Fogarty, NMFS, provided computer analytical

and statistical advice. We also thank Jay S. Krouse and two anonymous

reviewers for helpful suggestions with the manuscript. Robert Lawton and

Arnold Howe reviewed an earlier version of this paper.

IV
Catch-per-unit-effort

and Biological Parameters

from the Massachusetts

Coastal Lobster

(Homarus americanus)

Resource: Description

and Trends

BRUCE T. ESTRELLA

DANIEL J. McKIERNAN

Commonwealth of Massachusetts

Division of Marine Fisheries

18 Route 6A

Sandwich, MA 02563

ABSTRACT

A comprehensive description ofthe Massachusetts coastal lobster

(Homarus americanus) resou,rce was obtained by sampling commercial catches coastwide at sea and at dealerships between 1981

and 1986. A commercial lobster sea-sampling program, wherein

six coastal regions were sampled monthly, with an areal and

temporal data weighting design, was the primary source of data.

An improved index of catch per trap haul/set-over-day was

generated by modeling the relationship between catch and immersion time and standardizing effort. This 6-year time-series

of mean annual catch rates tracked closely the landings trend

for territorial waters.

During the study period there was a gradual increase in indices

of exploitation and total annual mortality which corresponded

to a gradual decline in mean carapace length of marketable

lobster. The frequency of culls escalated from 10.0% in 1981

to 20.9% in 1986, while the percentage of lobster found dead

in traps was consistently less than 1%. The sex ratio (%F:%M)

was significantly different from 50:50 and approximated a 60:40

relationship during the study period.

Male and female weight-length relationships were significantly

different. Females weighed more than males at smaller sizes and

less than males at larger sizes. A north-south clinal trend was

evident wherein lobster north ofCape Cod weighed less at length

than those from regions south of Cape Cod.

Functional size-maturity relationships were developed for

female lobster by staging cement gland development. Proportions mature at size represent more realistic values than those

obtained by analyses of percent of females ovigerous.

Regional variation occurred in most ofthe parameters studied.

Three lobster groups, differing in major population descriptors,

are defined by our data.

Introduction _

The American lobster (Homarus americanus) ranges over

the continental shelf of the western North Atlantic ocean from

Labrador to Cape Hatteras. Its biology and behavior have

been extensively studied (Anthony and Caddy 1980, Cobb

and Phillips 1980, Reinhart 1986). Specific information on

its population dynamics was gathered by governmental

researchers to formulate the American Lobster Fishery

Management Plan (NEFMC 1983). However, with the exception of Maine and New York the detailed collection of

long time-series of catch-effort and biological data was lacking among the lobster harvesting states.

Until rt;cently, historical trend data on the lobster resource

along the Massachusetts coast were limited to annual landings in number or pounds of lobster, total traps reported

fished, and licensing statistics. A crude catch-per-unit-effort

(CPUE) calculation (landings/traps reportedly fished) was

available from these data. Additional data describing the

fishery and resource were generated primarily through shortterm research efforts involving sampling of lobster catches

at dealerships or from commercial lobster traps at sea.

Since lobster supports the most economically important

single specics fishery in Massachusetts coastal waters, the

regular assessment ofthe status ofthis resource is warranted.

Accordingly, a long-term coastwide lobster monitoring program was devised and initiated by the Massachusetts Division of Marine Fisheries in May 1981. A structured, comprehensive sea sampling-survey design was chosen by which

both CPUE and biological data could be collected temporally

and areally with sufficient precision for stock assessment.

The overall objective was to assess variation in population

parameters due to environmental factors, fishing pressure,

and regulatory changes.

This sampling program provided the core of the data discussed in this description ofthe Massachusetts coastal lobster

resource. However, additional studies involved sampling and

procedures which were beyond the scope of the sea-sampling

effort and included special sampling at sea and at dealerships

in association with laboratory analyses.

Methods _

Study area

The study area is primarily defined by the Massachusetts

territorial sea, except where lobstering activities of cooperating commerciallobstermen exceeded territorial boundaries (Fig. 1). Territorial waters total 5,322 km2 (2,055

nmi2), of which an estimated 60% is considered major

lobster habitat. Six sampling regions-Cape Ann, BeverlySalem, Boston Harbor, Cape Cod Bay, outer Cape Cod, and

Buzzards Bay-were chosen for coverage of the major lobstering regions of the state. For convenience, these regions

are depicted as generalized hatch-marked areas in Figure 1

wherein lobster gear sampled may be discontinuously

distributed.
MA

1. CAPE ANN

2. BEVERLY-SALEM

3. BOSTON HARBOR

4. CAPE COD BAY

5. OUTER CAPE COD

6. BUZZARDS BAY

SCAI..£

6 NAUTICAL MILES

Figure 1

Map of Massachusetts coast showing hatch-marked sampling regions and territorial

boundary line.

Sampling

Sampling of coastal waters was accomplished by monitoring catches during normallobstering operations of volunteer

commerciallobstermen in each designated region. Multiple

lobstering operations were observed to reduce bias from

varying degrees of lobstering skill and to enhance areal

coverage. Five lobstermen were monitored in the southern

Gulf of Maine regions (Cape Ann south through Cape Cod

Bay), three in the outer Cape Cod region, and three in Buzzards Bay. Trap-sampling events were day trips, conducted

at least monthly per region (except when manpower limitations precluded effort or cooperating lobstermen were not

operating) during the major lobstering season, May-November. Sampling effort during the study period increased with

manpower availability. In 1981, 36 sampling trips were conducted during which 12,392 lobster were sampled from 5,736

trap hauls. In 1986, 82 sampling trips were made during

which 40, 114 lobster were sampled from 14,799 trap hauls.

Sea samplers used portable cassette tape recorders to record

the following parameters: 1 Carapace length (CL) to the

nearest mm (to the nearest 0.1 mm between 80.5 and 81.0

mm in order to establish minimum legal size which was 81

mm CL during the study period); 2 sex; and 3 condition,

including degree ofshell hardness, culls (lobster with missing or regenerating claws), mortality, and presence of

extruded ova on females (ovigerous). Catch in number of

lobster, number of trap hauls, and set-over-days were also

recorded. Studies of maturity, morphometrics, and weightlength relationship (g/mm CL) were accomplished with

samples collected at sea and at commercial lobster

dealerships.
Analytical procedure

Data were computer coded and keypunched for analysis on

the Woods Hole Oceanographic Institution's computer

system (Digital Equipment Corp. VAX-ll/780). A computer

auditmg process was used to detect keypunch and recording

errors, and statistical analyses were performed with SPSS

(Nie 1983) and SAS (SAS Inst. 1985) statistical subprograms.

An areal and temporal data-weighting scheme was incorporated into analytical software because parameter means

exhibit significant fP-gional and monthly variations. As a

result, each month's data contribute equally to regional

parameter means which are weighted by area in square

nautical miles when generating coastwide means.

Unless specified otherwise, the terms "legal" or "legalsized" lobster include all lobster in the carapace-length

category ~81 mm. The non-ovigerous segment of this

category is analyzed separately and referred to as "marketable lobster." The sublegal length category includes all

lobster <81 mm CL.

Data on lobster landings and effort (number oftraps fished)

are derived from lobstermen's catch reports compiled

annually by the Commercial Fisheries Statistics Project of

the Massachusetts Division of Marine Fisheries.

Since current management strategy stresses uniform coastwide regulations, all data are grouped for a coastwideanalysis. However, two factors mandate a regional data treatment as well: the uniqueness of the Massachusetts coastline

with its role in providing a temperature barrier at the southern

end of the Gulf of Maine which profoundly affects many

marine species (Colton 1964), and the influence of offshore

lobster stocks on the inshore resource.

Results _

Relative abundance

Immersion-time standardization Indices of relative abundance traditionally used to assess the lobster fishery include

catch per trap haul (CTHAUL) and catch per trap haul!

set-over-day (CTHSOD). Thomas (1973) reported CTHAUL

as unreliable due to its insensitivity to seasonal changes in

catchability and emphasized the importance of incorporating

immersion time (gauged by set-over-days) into the index,

since catch varies with fishing time. Consequently, CTHAUL

is useful only in assessing annual abundance trends if immersion time does not vary considerably. CTHSOD represents

an improvement over CTHAUL because of its temporal

weighting function; however, this index is unrealistic because

catch does not increase in direct prop0l1ion to immersion

time.

The relationship between catch and immersion time was

investigated for American lobster trap fisheries (Thomas

1973, Skud 1979, Fogarty and Borden 1980, Auster 1985).

These studies concluded that catch increased 'With immersion time at a decreasing rate toward an asymptote. This

declining fishing efficiency over time is a function of reduced

3

entry due to bait breakdown, trap saturation, escapement,

or progressive exploitation of available lobster. Miller (1983)

reviewed previous efforts to model this relationship in trap

fisheries for other species as well.

Gulland (1955) derived a nonlinear regression model to

describe the relationship between catch and immersion time:

where Cs is the catch on day S, Ceo is the asymptotic catch,

and R is the capture rate. Caddy (1977) recommended the

usc of this model to standardize effort to a comlnon immersion time. Miller (1983) regarded it as a widely accepted

model.

To establish a relationship between catch and immersion

time for use in our analyses, we used 1985-86 CPUE data

(no. lobster) collected from the Cape Ann region. These data

were advantageous because of the large sample size (observations from 6,167 trap hauls), which included a wide range

of immersion times, and because all data were collected from

a single ]obsterman, thereby eliminating variability attributable to fishing skill.

Only catch rates for marketable lobster were analyzed.

Sublegals were excluded in order to avoid excessive variation in catch rates resulting from escapement through vents,

variable vent number, and location. Data were partitioned

by season: Spring (May, June), summer (July, Aug.,

Sept.), and autumn (Oct., Nov.). The relationship between

CTHAUL and immersion time was expressed by Gulland's

(1955) non-linear regression model (Fig. 2). Generally, catch

increased over time at a decreasing rate toward an asymptote. The relationship for spring data showed a longer timeperiod before an asymptote was reached than for summer

and autumn data. The high catch rates and shorter time to

an asymptote observed during summer and autumn probably

reflect the shorter bait-attraction time due to bait breakdown

and the greater availability of legal lobster due to recruitment from the molt. The spring relationship probably resulted

from the effect of cold water temperature in extending bait

life and reducing lobster activity. These factors would be

expected to result in poorer catch rates. The reduced availability oflegal lobster due to fishing pressure is another factor

which may cause catch rates to decline.

In order to correct for variable immersion time, we adapted

Sinoda and Kobayasi's (1969) approach:

C's = Cs(l-e -Rs*/ l-e -Rs)

where C's is the adjusted catch at day s, Csis the empirical

catch/trap haul on day s, R is the capture rate, and s *is the

standard immersion time (modal or mean immersion time).

The ratio term is an estimate of fishing power and serves

as a correction factor for set-over-days.

Effort was standardized to our survey modal value of 3,

whereby catches of traps hauled following a 3-day immersion were assigned the immersion correction factor of 1.0.

Immersion times greater than or less than 3 days were
--

- ---

a: 1.2 SPRING I UJ I

t- 1.0

(j) T

a:l 0.8 I

0

+1

....J 0.6

UJ J- .-......,..•.....-

....J 0.4 I T

a:l I 0.2

UJ 0.0 -------'-------

1.2 t SUMMER -- a:

L--1

« 1.0

LL. 0.8 I

0 0.6 I

I - 0.4

J~ ....J

::> 0.2

«

:r: 0.0 , ,

1.2 --,

a.. AUTUMN T

« 1.0 l a: T

t- 0.8

a: I I ] UJ 0.6

a..

:r: 0.4 i

() 0.2

() 0.0

0 1 2 3 4 5 6 7 8

IMMERSION TIME (DAYS)

Figure 2

Relationship between predicted American lobster CTHAUL (catch/trap

haul) and immersion time (dotted line), with observed CTHAUL means

and 95% confidence intervals.

adjusted accordingly (Table 1). These corrected estimates

of immersion time were used to calculate an adjusted

CTHSOD index for marketable lobster which we labeled

CTH' 3 (CTHAUL standardized to 3 set-over-days, Table

2).

The new index reduces the variability in annual indices

(relative to annual changes in landings) which is evident in

the conventional CTHSOD time-series (Table 3) and tracks

the landings' trend for territorial waters very well (Fig. 3).

Its 6-year trend is similar to that of CTHAUL (Table 4)

only because the mean annual immersion times for the

1981-86 sampling period were similar, ranging from 3.3987

4

_._-------

Table 1

Seasonal estimates of regression model coefficients, predicted

CTHAUL (cateh/trap haul in numbers of lobster), and soak-time

correction factors for Massachusetts commercial lobster data. ----

Spring Summer Fall ------

Cro 0.54602 0.83002 0.73470

(SE) (0.05424) (0.04406) (0.04646)

R 0.60831 0.88977 1.\1799

(SE) (0.15038) (0.19040) (0.30781)

Predicted Corr. Predicted Corr. Predicted Corr.

Day CTHAUL factors CTHAUL factors CTHAUL factors --_.._.-

1 0.24883 0.54333 0.49809 0.63313 0.49450 0.69744

2 0.38427 0.83905 0.68998 0.89318 0.65617 0.92545

ooסס1.0 0.70903 1.00000 0.77250 ooסס1.0 0.45798 "

4 0.49810 1.08760 0.80639 1.04388 0.72630 1.02437

5 0.51994 1.13528 0.82032 1.06190 0.73196 1.03243

6 0.53182 1.16123 0.82603 1.06930 0.73380 1.03495

7 0.53829 1.17536 0.82838 1.07234 0.73441 1.03580

Table 2

CTH'3 (catch/trap haul in numbers of lobster standardized to 3 setover-days), statewide and by region, for all marketable American

lobster sampled during commercial lobster trap-catch survey,

Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 0.767 0.785 0.803 0.696 0.825 0.816

Cape Ann 0.732 0.808 0.624 0.663 0.634 0.699

Beverly-Salem 0.934 0.898 0.881 0.835 0.663 0.496

Boston Harbor 1.\08 1.254 1.096

Cape Cod Bay 0.710 0.776 0.680 0.479 0.716 0.822

Outer Cape Cod 0.808 0.824 0.765 0.598 0.856 0.811

Buzzards Bay 0.611 0.571 1.110 0_870 0.953 0.907

Table 3

CTHSOD (catch/trap haul per set-over-day in numbers oflobster),

statewide and by region, for all marketable American lobstersampled

during commercial lobster trap-catch survey, Massachusetts coastal

waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 0.249 0.309 0.302 0.238 0.284 0.263

Cape Ann 0.181 0.349 0.304 0_289 0.238 0.267

Beverly-Salem 0.305 0.368 0.397 0.291 0.197 0.146

Boston Harbor 0.362 0.467 0.367

Cape Cod Bay 0.287 0.364 0.285 0.178 0.280 0.275

Outer Cape Cod 0.125 0.146 0.138 0.113 0.180 0.130

Buzzards Bay 0.202 0.190 0.320 0.314 0.327 0.356
CD

o

r- 11 aO

X 10.0

9.0

...J 8.0

LANDINGS

0.9 CTH'3

0.8 T

0: 0.7 0

u. 0.6

u.

UJ CTHAUL 0.9

Z 0.8

::> 0.7

0: 0.6

UJ

a.. 0.4 CTHSOD

I

() 0.3

0.2

() 0.1

1981 1982 1983 1984 1985 1986

YEAR

Table 4

CTHAUL (catch/trap haul in numbers of lobster), statewide and

by region, for all marketable American lobster sampled during

commercial lobster trap-catch survey, Massachusetts coastal waters,

1981-86.

1981 1982 1983 1984 1985 1986

State 0.747 0.740 0.753 0.668 0.796 0.795

Cape Ann 0.759 0.723 0.504 0.578 0.596 0.660

Beverly-Salem 0.884 0.857 0.793 0.780 0.661 0.494

Boston Harbor 1.107 1.181 1.071

Cape Cod Bay 0.658 0.677 0.617 0.446 0.666 0.797

Outer Cape Cod 0.887 0.896 0.811 0.650 0.896 0.859

Buzzards Bay 0.610 0.578 1.116 0.821 0.938 0.835

to 3.7489. Greater benefits of enhanced data comparability

and accuracy oftrends were realized in the smaller regional

data sets where annual mean immersion times sometimes

differed substantially. Consequently, this analysis is an important adjunct to small-scale commercial trap-sampling programs in which the mean immersion time sampled is likely

to exhibit annual variability.

An analysis of the CTH'3 index for marketable lobster

during the 6-year study period did not indicate significant

differences (based on presence or absence of overlap of 95 %

confidence intervals) in the 1981-83 indices, but a statistically

5

Figure 3

Commercial American lobster landings and CPUE indices from

Massachusetts territorial waters, 1981-86. CTHAUL =catch/

trap haul; CTHSOD = catch/trap haul per set-over-dayj CTH'3

= CTHAUL standardized to 3 set-over-days.

significant decline occurred in 1984. This was followed by

a significant increase in 1985, with no statistical difference

in 1986.

Catches ofsublegallobster are affected by both soak time

and escapement through vents; consequently, soak-time

standardization modeling for this size group would require

different assumptions. Sublegal lobster catch rates were

therefore limited to conventional CTHSOD (Table 5) and

CTHAUL (Table 6) indices which generally increased

through 1983, significantly declined in 1984, then increased

again through 1986.

Commercial landings Historical landings data provide a

perspective on the current condition of the fishery and support recent catch-rate trends. Annual Massachusetts coastal

landings (excludes data from offshore fishery), available only

in number of lobster, generally declined between 1888

(1,740,850) and 1917 (402,469), then gradually increased

through 1921 (1,618,988', Fig. 4). Subsequent landings,

available only in pounds, increased through 1947 (2,341,882

to 3,663,363 lbs), but were relatively stable thereafter

through 1974. Major increases occurred between 1975

(5,172,545 lbs) and 1986 (12,580,793 lbs).

These trends in landings were primarily a reflection of

nominal fishing effort (total traps fished). Reported effort

averaged below 20,000 traps through 1918; 30,000-40,000

traps throullh 1929; 60,000 traps during 1930-40; then
Table 5 Table 6

CTHSOD (catch/trap haul per set-oyer-day in numbers oflobster), CTHAUL (catch/trap haul in numbers of lobster), statewide and

statewide and by region, for all American lobster <81 nun CL, by region, for all American lobster <81 mm CL, sampled during

sampled during conunerciallobster trap-catch survey, Massachusetts commercial lobster trap-catch survey, MassachlL'.etts coastal waters,

coastal waters, 1981-86. 1981-86. _._--- .-------

1981 1982 1983 1984 1985 1986 1981 1982 1983 1984 1985 1986 ----------

State 0.580 0.672 0.718 0.521 0.647 0.700 State 1.473 1.40] 1.624 1.389 1.705 1.899

Cape Ann 0.067 0.109 0.586 0.450 0.395 0.474 Cape Ann 0.256 0.199 1.044 0.909 1.031 1.126

Beverly-Salem 0.708 0.711 1.263 0.948 0.833 0.801 Beverly-Salem 1.855 1.713 2.526 2.504 2.567 2.435

Boston Harbor 0.901 1.162 1.138 Boston Harbor 2.773 3.038 3.314

Cape Cod Bay 0.710 1.013 0.639 0.322 0.594 0.551 Cape Cod Bay 1.544 1.680 1.345 0.825 1.337 1.512

Outer Cape Cod 0.037 0.024 O.Q3S 0.033 0.035 0.027 Outer Cape Cod 0.233 0.145 0.210 0.189 0.160 0.161

Buzzards Bay 0.787 0.620 0.638 0.785 0.848 1.312 Buzzards Bay 2.381 1.916 2.316 1.965 2.452 3.118

14 500

Num ber of lobster

12 Pounds of lobster

400

Number of traps -l

CD 10 ::0

0

» T"" "l)

X 300 en

8 -n

Cf) en (!)

z :::I:

6 m

Cl 200 0

z X <t:

-l ..... 4 0

VJ

100

2

0

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

YEAR

Figure 4

Historical American lobster landings and effort data for Massachusetts, 1888-1986.

100,000 traps through 1964. From 1965 to 1986 the number

of traps increased from 100,000 to "-'400,000 traps.

Although increased fishing effort has resulted in steadily

increasing landings, the average annual pounds per trap (annual landings/total traps fished) declined between the

rnid-1960s and rnid-1970s (Fig. 5). It is conceivable that this

may have resulted from a saturation of easily accessible,

coastal lobster habitat with traps. Nevertheless, the annual

average pounds/trap increased between the late 1970s and

1986. This trend is consistent with CTH'3 data for the

1981-86 period.

Increases in CPUE between 1976 and 1986 may have been

caused by several factors acting in concert:

6

1 Expansion of lobstermen's territories to deeper,

relatively less-exploited habitat to avoid competition.

2 Improved fishing efficiency due to the advent of

LORAN C and color depth finders and their increased use

on lobster boats. These assist in relocating prime lobstering

grounds in deeper, more offshore waters where landmark

relocation is not possible.

3 Enhanced lobster larval survival due to favorable environmental conditions (Le., warming trend through late

1970s) may have increased population size. Temperature is

also an important factor controlling molting (Campbell 1983).

Optimal water temperature will enhance the proportion of

lobster molting and maximize legal catch.
500

!

Number per trap

Pounds per trap

80 400

Num ber of traps -i

J)

a.. » « "I::J

0:: 300 (f)

I- 60 'TI

0:: (f) W :x: a.. m

I 200 0

0 40

!;.t X

.... 0 0

'" 20 100

o 0

1880 1890 -1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

YEAR

Figure 5

Historical American lobster landings and catch/trap data for Massachusetts, 1888-1986.

4 Juvenile lobster survival may have been aided by the

installation of escape vents in traps mandated by a 1977

Massachusetts regulation. Escape vents also enhance the

catch of legal-sized lobster, presumably due to an inverse

relationship between crowding and probability of entry

(Krouse and Thomas 1975, Fair and Estrella 1976, Krouse

1978, Nulk 1978, Pecci et al. 1978, Fogarty and Borden

1980).

Total lobster landings from all lobster harvesting states also

increased between the late 1970s and 1986 (Anonymous

1988). These increases cannot be attributed to greater fishing

effort alone. In the Canadian Maritimes, where trap limits

and a license moratorium (including a license buy-back

system) have been enforced for years, landings have also increased. Landings there have doubled, and in some areas

have increased five-fold, since 1981 (D.S. Pezzack, Dep.

Fish. Oceans, Halifax, Nova Scotia, Canada B3J 2S7, pers.

commun., June 1988).

Mortality estimates

Estimates of total instantaneous mortality (Z) and total annual

mortality (A = 1-e -z) were computed by two methods

(which produce extremes in the possible range of estimates).

The method of Gulland (1969) requires computing the slope

ofthe regression line of numbers at estimated age-15 % molt

groups calculated from mean carapace-length increases

attained from molting (Fair 1977), 14% for Buzzards Bay

(Estrella, unpubl. data)-plotted in the natural log. Beverton and Holt's (1956) process employs von Bertalanffy

7

growth equation parameters (K =0.0634, Loo =253 nun;

Fair 1977) and mean and minimum length of exploitable

sizes:

where K = growth rate constant,

Loo = asymptotic length,

I = mean length of exploitable sizes, and

Ie = minimum exploitable size.

Total annual mortality estimates (A), when computed by

the method of Gulland (1969), were generally high. Six-year

means ranged from 85 % (Cape Ann) to 94 % (Boston

Harbor) in Gulf of Maine regions, with 97% in Buzzards

Bay and 36% off outer Cape Cod (Table 7). Estimates computed by the method ofBeverton and Holt (1956) ranged from

74% (Cape Ann) to 84% (all others) in Gulf of Maine

regions, with 91 % in Buzzards Bay and 42 % off outer Cape

Cod.

Results of Gulland's method tend to be slightly higher than

those of Beverton and Holt's for all regions except outer Cape

Cod. Considering the high level of effort in most of the

inshore area, the higher estimates seem more realistic. Mortality estimates have increased over time in response to

escalated fishing effort. The 1981-86 mean Cape Cod Bay

estimates of total instantaneous mortality and total annual

mortality were Z =2.55 and A =92 %, respectively, when

calculated by Gulland's procedure. These values were

slightly higher than 1970-76 means calculated from length-
Table 7

Total instantaneous (Z) and total annual percent (A) mortality estimates of American lobster statewide and by region, Massachusetts coastal

waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean ------

Beyerlon Beyerlon Beyerlon Beyerlon Beyerlon Beyerlon Beyerlon

Gulland and Holt Gulland and Holt Gulland and Holt Gulland and Holt Gulland and Holt Gulland and Holt Gulland and Holt

(1969) (1956) (1969) (1956) (1969) (1956) (1969) (1956) (1969) (1956) (1969) (1956) (1969) (1956)

State 1.58 1.35 1.72 1.45 1.66 1.39 1.66 1.41 1.76 1.47 1.80 1.49 1.70 1.43

79% 74% 82% 77% 81% 75% 81% 76% 83% 77% 84% 78% 82% 76%

Cape Ann 1.65 1.32 2.18 1.39 1.72 1.35 1.92 1.52 1.94 1.33 2.03 1.32 1.91 1.37

81 % 73% 89% 75% 82% 74% 85% 78% 86% 74% 87% 73% 85% 75%

BeYerly-Salem 1.97 1.59 2.15 1.70 2.41 1.85 2.71 1.78 3.64 1.96 3.60 1.99 2.75 1.81

86% 80% 88% 82% 91% 84% 93% 83% 97% 86% 97% 86% 94% 84%

Boston Harbor 2.52 1.82 3.59 1.75 2.60 1.92 2.90 1.83

92% 84% 97% 83% 93% 85% 94% 84%

Cape Cod Bay 2.53 1.64 2.69 1.92 2.42 1.72 2.52 2.07 2.31 1.88 2.83 1.92 2.55 1.86

92% 81% 93% 85% 91% 82% 92% 87% 90% 85% 94% 85% 92% 84%

Outer Cape Cod 0.43 0.54 0.46 0.55 0.42 0.53 0.33 0.52 0.52 0.57 0.51 0.55 0.44 0.54

35% 42% 37% 42% 34% 41% 28% 41% 41% 43% 40% 42% 36% 42%

Buzzards Bay 3.02 2.97 3.00 2.53 8.64 2.26 3.14 2.21 3.55 2.36 3.71 2.41 4.18 2.46

95% 95% 95% 92% 99% 90% 96% 89% 97% 91% 98% 91% 98% 91%

frequency data by Fair (1977) for the same region and by

the same method, Z = 2.15 and A = 88 %. Coastwide annual

mean estimates ofZ gradually increased during the 1981-86

study period.

Estimates of fishing mortality (F) were calculated by

Cohort Analysis (Pope 1972) which assumes a von Bertalanffy growth curve. Resulting estimates of F plus an assumed natural mortality (M) of 0.15 (Fair 1977) approximate

estimates ofZ calculated by the Beverton and Holt technique.

Weighted average estimates of F (weighted by 5-mm size

frequencies) from Cohort Analysis were:

Survey size-frequency data (all lobster ~81 mm CL) were

expanded on the basis of total landings from commercial

lobstermen's catch reports. The population of legal-sized

lobster in the territorial sea during the 1986 season was then

calculated by Cohort Analysis and estimated to be 15,400,000

(Table 8).

Total mortality rates increased only slightly during the

6-year study period; however, significant changes in F can

affect yield. These yield changes can be predicted using F!J.T

values obtained from Cohort Analysis (Jones 1974). Results

indicate that the current exploitation rates in our coastal

regions are so high that only minimal changes in landings

Statewide

Cape Ann

Beverly-Salem

Boston Harbor

Cape Cod Bay

Outer Cape Cod

Buzzards Bay

1.27

1.22

1.93

1.80

1.70

0.47

2.11

8

would result from substantial changes in F (Table 9). The

exception is the relatively less-exploited outer Cape Cod

region.

Exploitation rate

Rates of exploitation (u =FA/Z, the fraction of the population removed by fishing) and exploitation ratios (E =F/Z,

the proportion of fishing deaths to all deaths) were calculated

with 1986 data. These statistics were estimated in two ways.

First, they were computed with A and Z values from the

Beverton and Holt (1956) methodology and F values derived

from Cohort Analysis (because all incorporate von Bertalanffy parameters); and, second, with A and Z values from

Gulland (1969) and Fvalues derived by assuming M =0.15:

Beverton and Holt Gulland

(1956) (1969)

u E u E

Statewide 0.66 0.85 0.77 0.92

Cape Ann 0.67 0.92 0.81 0.93

Beverly-Salem 0.83 0.97 0.93 0.96

Boston Harbor 0.80 0.94 0.88 0.94

Cape Cod Bay 0.75 0.89 0.89 0.95

Outer Cape Cod 0.36 0.85 0.28 0.71

Buzzard Bay 0.80 0.88 0.94 0.96

These indices reflect the substantial impact of fishing on

the lobster resource. Intense fishing effort removes the opportunity for individual lobster to grow to large sizes. This

effect on size can be described with an additional index which
Table 8

Cohort analysis of 1986 American lobster size-frequency data expanded to total Massachusetts landings.

No. No. Mean

Length group landed in sea no. F/Z ZI>.T FI>.T Z I>.T F

166.0---171.0 0.503E+03 0.640E+03

161.0---166.0 0.545E+03 0.131E+04 0.937E+03 0.810 0.718 0.582 0.790 0.909 0.640

156.0---161.0 0.152E+04 0.3IOE+04 0.208E+04 0.847 0.859 0.728 0.982 0.875 0.832

151.0---156.0 0.124E+04 0.481E+04 0.389E+04 0.727 0.439 0.319 0.549 0.801 0.399

146.0---151.0 0.223E+04 0.775E+04 0.617E+04 0.760 0.477 0.362 0.624 0.764 0.474

141.0---146.0 0.299E+04 0.118E+05 0.963E+04 0.740 0.419 0.310 0.577 0.727 0.427

136.0---141.0 0.642E+04 0.198E+05 0.155E+05 0.798 0.520 0.415 0.743 0.700 0.593

131.0---136.0 0.108E+05 0.333E+05 0.260E+05 0.806 0.518 0.417 0.772 0.671 0.622

126.0---131.0 0.274E+05 0.653E+05 0.475E+05 0.855 0.674 0.576 1.032 0.652 0.882

121.0---126.0 0.303E+05 0.103E+06 0.828E+05 0.798 0.458 0.366 0.743 0.617 0.593

116.0---121.0 0.468E+05 0.162E+06 0.130E+06 0.801 0.448 0.359 0.755 0.594 0.605

111.0---116.0 0.778E+05 0.257E+06 0.206E+06 0.815 0.464 0.378 0.810 0.573 0.660

106.0---111.0 0.139E+06 0.424E+06 0.334E+06 0.834 0.500 0.417 0.902 0.555 0.752

101.0---106.0 0.244E+06 0.713E+06 0.556E+06 0.845 0.520 0.439 0.969 0.537 0.819

96.0---101.0 0.254E+06 0.103E+07 0.864E+06 0.792 0.371 0.294 0.722 0.515 0.572

91.0--- 96.0 0.1I8E+07 0.233E+07 0.I60E+07 0.905 0.814 0.736 1.572 0.518 1.422

86.0--- 91.0 0.309E+07 0.571E+07 0.377E+07 0.915 0.895 0.819 1.764 0.507 1.614

81.0--- 86.0 0.40IE+07 0.103E+08 0.777E+07 0.878 0.587 0.516 1.233 0.476 1.083

Total 0.912E+07 0.154E+08 Wtd. avg. F: 1.271

Table 9

Prediction of the percent change in landings of American lobster at various percent changes in fishing mortality (F), Massachusetts coastal

waters, 1986.

Percent change in F

-50 -40 -30 -20 -10 +10 +20 +30 +40 +50

Cape Ann 7.24 7.20 4.58 2.91 1.38 -1.31 -2.44 -3.53 -4.40 -5.45

Beverly-Salem 8.27 7.10 5.43 3.58 1.79 -1.60 -3.33 -4.69 -5.99 -7.22

Boston Harbor 3.88 4.63 4.09 2.95 1.48 -LSI -2.99 -4.36 -5.70 -6.83

Cape Cod Bay 9.86 7.87 5.69 3.61 1.71 -1.56 -2.99 -4.39 -5.60 -6.75

Outer Cape Cod 21.87 17.06 12.11 7.51 3.45 -3.04 -5.42 -7.40 -9.04 -10.54

Buzzards Bay 7.62 7.00 5.55 3.78 1.92 -1.81 -3.64 -5.18 -6.73 -8.29

is easily computed by expressing the number of lobster in

the recruit molt group, 81-93 rom CL, as a percentage of

the total number oflegal-sized lobster. This "fishing pressure

index" was high during the 6-year study period (Table 10).

Approximately 87-98% of the lobster landed in all inshore

regions, except one, were captured shortly after molting

beyond the legal size limit of 81 rom CL. Fishing-pressure

indices varied from 38 to 48 % between 1981 and 1986 for

the outer Cape Cod region, where a large offshore migrant

group dominates catches. Buzzards Bay exhibited the highest

indices, which varied from 94 to 98% during the study

period.

A slight increasing trend in the 6-year time-series of

coastwide fishing-pressure indices was discernible (Table

10). Furthermore, a comparison of recent and 30-year-old

size-frequency data revealed the effect of escalated fishing

effort. Length-frequency data collected July-September 1957

9

Table 10

Fishing-pressure indices (% of all legal-sized American lobster in

recruit molt group), statewide and by region, commercial lobster

trap-catch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean

State 86 87 86 86 88 88 87

Cape Ann 91 92 87 89 87 87 89

Beverly-Salem 89 92 94 88 96 96 92

Boston Harbor 93 94 96 95

Cape Cod Bay 90 93 92 94 93 94 93

Outer Cape Cod 46 43 42 38 48 46 44

Buzzards Bay 98 96 96 94 96 97 96
CAPE COD BAY

BEVERLYISALEM

OUTER CAPE COD

Carapace length

Annual mean carapace lengths were calculated by region and

regions combined (Tables 11-14). Lobster from Buzzards

Bay averaged smaller in size than lobster from all other

regions sampled, while those from the outer Cape Cod region

averaged largest (Duncans Multiple Range Test, P =0.05).

Means from southern Gulf of Maine regions (Cape Ann,

Beverly-Salem, Boston Harbor, and Cape Cod Bay) were

intermediate and similar to one another. Buzzards Bay is

comparable to western Long Island Sound in warm average

water temperature and constricted access to outer coastal

waters. Its lobster size-distribution is similar to that described

by Briggs and Mushacke (1979) for the Sound. The Buzzards Bay lobster fishery is almost entirely dependent on new

recruits. Recruits from the late spring-early summer molt

period are generally depleted by August, particularly in

northern Buzzards Bay. At this time, most northern Bay

lobstermen undertake alternative fisheries until the autumn

molt produces another limited supply oflegal-sized lobster.

_ 1986

o 1957

100-r----------

80

60

40

20

o

I- 100

Z 80 W

() 60

a:

W 40

a.. 20

o

100

80

60

40

20

o

II III IV V VI

MOLT GROUP

Figure 6

Comparison of 1957 and 1986 marketable American lobster sizefrequency data from three coastal Massachusetts regions by 15% molt

groups: I 81-93 mm, II 94-108 mm, III 109-125 mm, IV 126-145 mm,

V 146-168 mm, VI 169-194 mm.

by sea-sampling commercial traps from three coastal Massachusetts regions were compared with similarly collected 1986

data from the same months and approximate locations (Fig.

6). Size frequencies from Beverly-Salem, Cape Cod Bay,

and outer Cape Cod regions were analyzed by 15 % increments. A 2-year comparison of group frequencies with the

chi-square test demonstrated that annual size frequencies

were significantly different for each of these regions

(P<O.Ol). This analysis by molt group clearly demonstrates

that larger lobster comprised a greater percentage of the catch

in 1957 than in 1986.

The prevalence of larger lobster in 1957 is indicative of

a lower level of fishing pressure than in recent years, with

95,209 traps reportedly fished and 3,679,953 lbs of lobster

landed. By contrast, in 1981 licensed lobstermen reported

fishing 299,368 traps and landing 9,282,695 lbs (landward

of long. 69°W. and lat. 41 ON.). In 1986, a total of 399,808

traps reportedly captured 12,580,793 lbs. The mean

pounds/pot index declined from 39 in 1957 to 31 during

1981-86. The pounds/pot/fishermen also declined from

0.0227 in 1957 to 0.0215 in 1981 and 0.0208 in 1986.

Table 11

Mean carapace length (mm), statewide and by region, for all

American lobster sampled during commercial lobster trap-catch

survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean

State 81.7 82.1 81.7 81.7 81.6 81.2 81.7

Cape Ann 86.2 86.2 82.1 81.7 82.1 81.8 83.4

Beverly-Salem 78.2 80.0 77.9 78.3 78.2 76.8 78.2

Boston Harbor 79.8 79.2 79.1 79.4

Cape Cod Bay 80.0 79.5 80.0 79.3 79.6 79.7 79.7

Outer Cape Cod 95.5 96.0 95.9 96.5 95.1 95.0 95.7

Buzzards Bay 77.8 78.1 80.1 79.6 78.9 78.4 78.8

Table 12

Mean carapace length (mm), statewide and by region, for all

American lobster ~81 rnm sampled during cornmerciallobster trapcatch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean

State 88.7 88.2 88.5 88.4 88.1 88.0 90.3

Cape Ann 88.9 88.5 88.7 88.2 88.8 88.9 88.7

Beverly-Salem 87.6 87.2 86.7 86.9 86.4 86.3 86.8

Boston Harbor 86.9 87.0 86.5 86.8

Cape Cod Bay 87.4 86.5 87.1 86.2 86.6 86.5 86.7

Outer Cape Cod 99.1 98.9 99.5 101.1 98.2 98.7 99.2

Buzzards Bay 84.6 85.2 85.7 85.9 85.5 85.4 85.4

10
Table 13

f

Mean carapace length (mm), statewide and by region, for all CAPE ANN

marketable American lobster sampled during commercial lobster 10 N = 15065

trap-catch survey, Massachusetts coastal waters, 1981-86.

0

1981 1982 1983 1984 1985 1986 Mean BEVERLY ISALEM

88.5 87.9 88.1 88.2 87.8 87.6 89.4 10 N = 21509

State

Cape Ann 88.6 88.3 88.3 87.9 88.4 88.3 86.8 0

Beverly-Salem 87.6 87.0 86.6 86.9 86.2 86.2 86.7 BOSTON HARBOR

Boston Harbor 86.8 86.9 86.4 86.7 f- 10 N =24366

Cape Cod Bay 87.2 86.4 86.9 86.1 86.4 86.3 86.6 Z

Outer Cape Cod 98.2 97.5 97.4 99.7 97.0 96.3 97.7 W

() 0

Buzzards Bay 84.7 85.2 85.7 85.8 85.2 85.3 85.3 a:

w CAPE COD BAY

0... 10 N = 42042

0

Table 14 OUTER CAPE COD

10 N = 9818

Mean carapace length (mm), statewide and by region, for all

American lobster <81 mm sampled during commercial lobster trap- 0

catch survey, Massachusetts coastal waters, 1981-86. BUZZARDS BAY

1983 1984 1985 1986 Mean 10 N = 22234 1981 1982

76.1 76.3 76.1 76.1 0 State 75.8 76.3 76.2

Cape Ann 78.0 77.7 77.5 77.3 77.6 77.1 77.5 60 80 100 120 140 160

Beverly-Salem 74.3 76.5 74.9 76.1 75.9 74.7 75.4 CARAPACE LENGTH (mm)

Boston Harbor 77.1 76.9 76.9 77.0

Cape Cod Bay 76.6 76.4 76.7 75.6 76.1 76.2 76.3

Outer Cape Cod 75.9 76.2 77.1 75.1 76.6 75.9 76.1 Figure 7

Buzzards Bay 75.8 75.5 76.8 76.4 76.1 76.0 76.1 Comparison of 1981-86 summaries of American lobster size-frequency

data from six coastal Massachusetts regions.

It is noteworthy that Buzzards Bay exhibited the highest

fishing pressure (6-year mean fishing-pressure index of 96%;

Table 10) and was also characterized by the smallest mean

carapace length of legal-sized lobster (6-year mean 85.4

mm). Few lobster larger than 90 mm were found in this

embayment. Krouse (1973) and Fogarty and Borden (1980)

observed the same relationship between fishing pressure and

size.

The size characteristics of the lobster group off outer Cape

Cod were significantly different. Catches in this fishery are

seasonally augmented by the shoalward migration of large

offshore lobster which exhibit extensive migratory behavior

(Morrissey 1971). In addition, numerous tagged lobster from

recent Maine and Canadian tagging studies (Campbell 1982)

were recaptured in this region. A south-to-southwesterly

movement pattern of large mature lobster from Maine into

Massachusetts waters was described by Dow (1974).

Inshore-offshore movement of lobster probably occurs in

response to changes in water temperature. Cooper and Uzmann (1971) elaborated on the seasonal mixing of inshore

and offshore stocks all along the range of the American

lobster. Briggs and Mushacke (1980) encountered the greatest

number and widest size range of lobster in July and August

off the south shore of Long Island and classified this as an

offshore size distribution. The offshore influence on Cape

Ann lobster is discernible through size-frequency analysis.

11

Of all regions sampled, the percentage of lobster 100 mm

CL was greatest off Cape Ann (5.5 %) and outer Cape Cod

(40.1 %; Fig. 7).

There is additional evidence of infiltration of migrating

lobster from outside Massachusetts territorial waters. Numerous observations of lobster marked with V-shaped

notches in their uropods have been made during the study

period off Cape Ann and outer Cape Cod. These lobster are

presumed to have migrated from Maine waters where a

V-notched female protection program is enforced. This is

an industry-sponsored program intended to protect a segment

of the brood stock off the coast of Maine.

During commercial lobster-trap sampling off Cape Ann,

3.4%, 3.3%, and 2.2% of the legal-sized females were

observed with V- notches during the years 1984-86, respectively. Observations in the outer Cape Cod region totaled

3.1 %, 5.8 %, and 6.2 % for the same time period. All other

Massachusetts inshore regions sampled exhibited low percentages (0-0.8). V-notched females were generally large,

averaging greater than 100 mm CL.

Geography may be a factor in concentrating migrants off

Cape Ann and outer Cape Cod. These regions are adjacent

to steeply sloping gradients which lead to a much greater

depth range than is available to other, more "sheltered,"

inshore regions.
Figure 8

American lobster weight-length relationships by sex and region, from six

coastal Massachusetts regions.

100 110 120

FEMALES

FEMALES

MALES

90

BUZZARDS BAY

CAPE COD BAY

BEVERLYISALEM

100 110 120 80

FEMALES

MALES

90

OUTER CAPE COD

CARAPACE LENGTH (mm)

1800

CAPE ANN 1600

1400

1200

1000

800

600

400

1800 BOSTON HARBOR

1600

I- 1400

I 1200

CJ 1000

UJ 800

600

400

1800

1600

1400

1200

1000

800

600

400

80

-Ol

-

Mean carapace lengths for legal and sublegal size groups

off Massachusetts were remarkably consistent during the

6-year study period (Tables 12-14). The mean sizes oflobster

~81 mm calculated during 1981-86 for Beverly-Salem (86.3

mm), Cape Cod Bay (86.5 mm), and Buzzards Bay (85.4

mm) were similar to those calculated in 1976 by Fair and

Estrella (1976) for the same regions (86.9,87.3,85.1 mm,

respectively). This minimal size variation in recent years is

likely due to the recruitment dependency of this intensiv~ly

exploited fishery. Nearly all lobster landed are those which

molted into legal size during their last molt. Consequently,

potential variation in mean size from ~ariable y~ar-c.lass

strength, and/or magnitude of seasonal mshore migratIOns

of large offshore lobster, is likely to be mitigated by fishing

pressure.

Weight-length relationship

In order to determine the weight-length relationship, lobster

carapace lengths (mm) and corresponding body weights (g)

were collected at dealerships in the six designated coastal

regions between 1980 and 1988. Weight and length data were

collected throughout the seasons so expected weights-atlength are annual means. Body weight varies seasonally

relative to the molt and is usually lower during summer and

autumn, following molting, than during winter and spring.

Since lobster larger than 120 mm were rare, only those

in the 81-120 mm CL size range, excluding culls, were

analyzed, yielding a sample size of 4933 (M 2411, F2522).

A logarithmic transformation of the data was fitted to ~he

equation W = aLb by the method of least-squares, generatmg

the following relationships:

12
1600

1400

1200

O'l

-.-

I

<.':l 1000

W

800

600

NEW YORK (From: Briggs and MJshacke 1979)

MASSACHUSETTS

MAINE (From: 1h:>nas 1973)

40 0 LLLLJ---L.l---L.J.---L.J.--L.L--L.L...L.L-'--L-'--LLLL..LLLJ---L.l---L.l---'---J.---'--J......l....l.....l....l.--LJ

81 85 90 95 100 105 110 115 120

CARAPACE LENGTH (mm)

Figure 9

Comparison of American lobster weight-length relationships from New York, Massachusetts, and Maine.

W=0.0006920 [3.0374 (sexes combined),

W=0.0004692 [3.1221 (males),

W = 0.0009490 L2.9687 (females).

Analysis of covariance of regression coefficients revealed

a highly significant difference between the slopes and/or

intercepts of the male and female regression lines for each

region and regions combined (P<O.OOl). Covariance analyses of regional regression coefficients produced significant

differences among regions for male (P =0.001) and female

(P =0.001) data.

When regional data sets were combined, females weighed

slightly more than males at each millimeter increment between 81 and 98 mm. At 99 mm and larger, a reversal

occurred which was evident at varying sizes in all regional

weight-length relationships (Fig. 8). This reversal was probably related to the gradual attainment of sexual dimorphic

characteristics with the onset of maturity. Females may gain

less weight per molt than males, due to maturity-related

changes in physiology and an expenditure of energy toward

ovarian development. Female abdomens may broaden at

maturity to accommodate egg masses, but it is not clear if

13

increased volume and abdominal surface area are achieved

without increased weight. In contrast, the weight gain from

increased cheliped size in males is significant.

There is conflicting evidence in the literature regarding

a differential weight-length relationship for males and

females. Thomas (1973) found no significant difference

between male (N = 336) and female (N = 391) regression

lines when investigating the weight-length relationship in

Maine lobster. His tests were run on the sublegal-Iegal size

range. Briggs and Mushacke (1979) also found no difference

between male (N =52) and female (N =52) lobster weightlength relationships in western Long Island Sound. Their

samples ranged from 17 to 118 mm CL. However, Campbell (1983) observed a significant difference (P<O.Ol)

between the slopes of male (N = 135) and female (N = 197)

regression lines for lobster (47-144 mm) from Port Maitland,

Nova Scotia. Males were heavier than females. Aiken (1980)

described a similar relationship for lobster from Lydonia

Canyon.

Weight-length relationships (sexes combined) from Maine,

Massachusetts, and New York reflect north-south clinal

variation (Fig. 9). Lobster weight-at-Iength increased from
Table 15 Table 16

Percent of male American lobster. statewide and by region, sampled Percent of male American lobster ~81 mm carapace length, statewide

during commercial lobster trap-catch survey, Massachusetts coastal and by region, sampled during commercial lobster trap-catch survey,

waters, 1981-86. Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean 1981 1982 1983 1<./84 1985 1986 Mean

State 42.0 41.0 41.0 38.0 41.9 40.2 40.7 State 44.0 47.0 45.0 41.0 45.6 42.8 44.2

Cape Ann 42.0 46.0 39.0 35.0 41.2 40.7 40.6 Cape Ann 47.0 51.0 42.0 36.0 44.8 43.6 44.1

Beverly-Salem 44.0 41.0 51.0 50.0 42.2 50.7 46.5 Beverly-Salem 47.0 49.0 62.0 59.0 44.3 57.4 53.1

Boston Harbor 40.0 48.2 40.8 43.0 Boston Harbor 45.0 57.6 48.2 50.3

Cape Cod Bay 39.0 36.0 36.0 36.0 40.6 40.3 38.0 Cape Cod Bay 43.0 45.0 45.0 43.0 47.2 48.6 45.3

Outer Cape Cod 44.0 46.0 44.0 41.0 45.9 38.1 43.2 Outer Cape Cod 43.0 44.0 41.0 41.0 45.3 36.8 41.8

Buzzards Bay 43.0 47.0 36.0 34.0 36.2 31.9 38.0 Buzzards Bay 44.0 48.0 35.0 31.0 32.7 25.9 36.1

north to south. This trend was also evident within Massachusetts coastal waters. Buzzards Bay lobster had greater

weights-at-length than those from regions north of Cape Cod

(P<O.OI). The equations from all other Massachusetts

regions were similar to one another.

Sex ratio

The coastwide annual percentage of males in the catch ranged

from 38 to 42 % during the 1981-86 period (Table 15). The

percentage of male lobster 81 mm ranged from 41 to 47% ,

while that for sublegal males ranged from 36 to 40 % (Tables

16 and 17).

Females outnumbered males in nearly all regions during

every year of the study period. Chi-square analysis of annual sex ratios indicated that in all cases the ratios differed

significantly from 1: 1 (P<O.OI).

A majority of females in the sublegal catch may ::>e attributed to the reduced growth rate of females after the onset

ofsexual maturity, while the protection of ovigerous females

from exploitation would enhance the proportion of females

in the legal catch. Saila and Flowers (1965) constructed a

model of lobster stock composition and demonstrated the

latter to contribute to a higher proportion of females in the

legal-size category.

Behavioral segregation by sex may also affect sex ratio.

Indications are that sex ratio may vary by depth, with females

frequenting deeper water than males (Skud and Perkins 1969,

Briggs and Zawacki 1974, Cooper et aI. 1975, Briggs and

Mushacke 1979). The sublegal sex ratio near Boothbay

Harbor, Maine, approximated 50:50 (Krouse 1973,Cooper

et aI. 1975) while females predominated (M:F = 24:76) in

deeper (30-60 m) Maine waters (Cooper et aI. 1975).

A sex ratio in favor of males was observed in a mainly

sublegal population in a shallow cove in Buzzards Bay (Jelle

Atema, Mar. BioI. Lab., Woods Hole, MA 02543, pers.

commun., March 1983). This was hypothesized to have been

due to mature male competition in deeper water for territory

and mating burrows, thereby concentrating sublegal males

in shoalwater areas.

14

Table 17

Percent of male American lobster <81 mm carapace length, statewide

and by region, sampled during commercial lobster trap-catch survey,

Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean

State 40.0 37.0 38.0 36.0 39.6 38.7 38.2

Cape Ann 24.0 30.0 36.0 35.0 38.8 38.8 33.8

Beverly-Salem 43.0 37.0 47.0 47.0 41.6 49.1 44.1

Boston Harbor 38.0 44.6 38.5 40.4

Cape Cod Bay 37.0 33.0 31.0 32.0 37.3 36.0 34.4

Outer Cape Cod 53.0 54.0 55.0 44.0 49.3 44.5 50.0

Buzzards Bay 42.0 47.0 37.0 35.0 37.8 33.9 38.8

Lower proportions of males in the catch ofsublegal lobster

may also be caused by differential escapement from traps

(Fogarty and Borden 1980). Sexual dimorphism in the

carapace length-width relationship may be responsible, since

carapace width is the critical factor affecting escapement

through vents. In order to test this hypothesis, carapace length

and corresponding widths were collected through dealer and

sea-sampling efforts from 1983 to 1987. A total of 7,417

lobster from six coastal regions were tested. Only lobster

with carapace lengths of 69-93 mm were analyzed. This

range includes the pre-recruit (69-80 mm) and recruit (81-93

mm) molt groups and encompasses the size range most often

encountered in the inshore trap fishery.

Analysis of covariance of regression coefficients indicated

no difference between the slopes of length-width relationships for legal-sized females from each of the six regions

(Table 18). Tests of elevations of slopes indicated that

expected carapace-width means-at-Iength (y-intercepts) were

significantly wider for females (P<O.OI). No significant difference was found between slopes of sublegal male and

female regression equations from all regions except Cape

Ann. Sublegal females exhibited a significantly wider carapace width than males (P<O.Ol) in all regions except outer

Cape Cod.
Slopes Means N Slopes Means N

Cape Ann NS ** 1,006 * 705

Beverly-Salem NS ** 1,254 NS ** 780

Boston Harbor NS ** 635 NS ** 1,280

Cape Cod Bay NS ** 80 NS ** 125

Outer Cape Cod NS ** 323 NS NS 86

Buzzards Bay NS ** 465 NS ** 678

Table 18

Results of analysis of covariance of regression coefficients of male

and female American lobster carapace length-width relationships,

showing significance of differences (*0.05, **0.01, NS = not significant) between slopes and between carapace-width means, and sample size (N) by region, Massachuseits coastal waters, 1983-87.

In Narragansett Bay and Rhode Island Sound, Fogarty and

Borden (1980) found that the sex ratio in vented traps was

biased toward females. This was attributed to differential

escapement by females because of their significantly broader

carapace width. However, no significant difference was

found between male and female carapace length-width relationships off the coast of Maine (Krouse and Thomas 1975).

bor, were similar to one another. Their Lso estimates were

87 mm, while their proportions mature at minimum size were

18 and 27 %, respectively. Size-at-maturity was slightly

higher in the more northern Gulf of Maine region of Cape

Ann, where the LSD was 90 mm, and the proportion mature

at minimum legal stze was estimated at 20 %. The largest

size-at-maturity was found in the outer Cape Cod region,

where the LSD was 97 mm and only 12% were mature at

minimum legal size. Predicted proportions mature at a proposed minimum size of 84 mm CL were rv33 % for inshore

Gulf of Maine regions, 17% off outer Cape Cod, and 89%

in Buzzards Bay.

Size-at-maturity is related to summer water temperature

(Templeman 1936); high summer temperatures enhance

maturation at small sizes. Lobster in Buzzards Bay are subject to the highest maximum summer water temperature of

any region sampled. Buzzards Bay is a shallow embayment

with an average depth of only 11 m (Anraku 1964) and maximum bottom temperatures of about 21°C (Colton and Stoddard 1973). Shallow waters prevent the development of a

thermocline; Anraku (1964) and Rosenfeld et al. (1984) noted

summer vertical temperature gradients of less than 3°C.

Conditions are quite different in relatively deeper areas

of the Gulf of Maine and east of Cape Cod, where substantial thermoclines exist during summer and bottom temperatures are inversely proportional to depth. Bigelow (1927)

reported that Cape Cod Bay temperatures were higher than

the other Gulf of Maine regions due to the shoal water and

partial enclosure created by the peninsula of Cape Cod.

Boston Harbor waters, which are relatively shallow and

sheltered by several islands, experience similar warming. The

common LSD values of these two regions reflect their comparable temperature regimes.

Finally, the waters off Cape Ann and east of Cape Cod

are considerably deeper and colder than other inshore

regions. This is reflected by the elevated sizes-at-maturity

observed there. Furthermore, the historical occurrence in

these regions of tagged lobster from Maine and Canadian

studies and V-notched females, presumably from Maine, suggest that migrant lobster are more abundant here than in other

regions sampled.

Despite a few exceptions, the annual proportions of females

ovigerous during the 1981-86 study period were very similar

within each region (Table 19). Lower-than-normal sampling

intensity during the height of egger availability off outer Cape

Cod in 1981 and in Buzzards Bay in 1981-82 may have

caused the indices for those years to be below the 6-year

average. However, the four Gulf of Maine regional indices

were consistently at or below 5%, with Cape Ann averaging higher than the others. Six-year means for outer Cape

Cod and Buzzards Bay were 24 %.

The 6-year mean carapace lengths of "eggers" in the

Beverly-Salem, Boston Harbor, and Cape Cod Bay regions

were similar (84.0, 82.5, and 85.4 mm, respectively) compared with the relatively large means of 97.2 and 107.5 mm

for Cape Ann and outer Cape Cod, respectively (Table 20).

Buzzards Bay females averaged lowest at 80.3 mm.

Legal-sized Sublegal-sized

Maturity

Female lobster size-at-maturity from five Massachusetts

coastal locations was evaluated with the cement-gland staging technique (Aiken and Waddy 1982). Results were compared with ovigerous female size-frequency data from

1981-86 commercial sea-sampling.

From 16 May to 16 June 1986, cement gland development

on 2,536 female lobster was assessed in five coastal regions

of Massachusetts (Fig. 1): Cape Ann (n = 634 lobster),

Boston Harbor (n = 576), Cape Cod Bay (n = 656), outer

Cape Cod (n = 367), and Buzzards Bay (n = 303). Specimens

were obtained onboard commercial lobster vessels during our

ongoing commercial lobster-trap sampling program, as well

as in dealerships where we sampled local fishermen's

catches. Pleopods were removed and examined microscopically to stage glandular development; specimens with questionable development were dissected and ovary maturation

was assessed according to Aiken and Waddy (1982). Sampling was conducted prior to the spring-summer molt in order

to determine the proportion of nonovigerous females that

would extrude eggs during the current season.

The proportion mature by 3-mm size intervals was

calculated and modeled with the logistic equation Y = al

(1 + e b+cX ) using the SAS Non-Linear Regression Procedure (SAS Inst. 1985).

The maturity curves (Fig. 10) indicate considerable variation in size-at-maturity. In Buzzards Bay, the estimate of

LSD (carapace length at 50% maturity) was 76 mm, while

79 % were estimated to be mature at minimum legal size (81

mm when study was conducted). Results from the two southern Gulf of Maine regions, Cape Cod Bay and Boston Har15
Figure 10

Functional size-maturity relationships for female American lobster from five coastal Massachusetts regions,

1986 (*observed data in 3-mm groupings).

Table 19 Table 20

Percent of females ovigerous, statewide and by region, for all Mean carapace length (mm) of all ovigerous female American lobster,

American lobster sampled during commercial lobster trap-catch statewide and by region, sampled during commercial lobster trapsurvey, Massachusetts coastal waters, 1981-86. catch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 Mean 1981 1982 1983 1984 1985 1986

State 5.9 7.7 10.9 9.1 8.6 9.1 8.6 State 88.5 87.6 88.6 87.4 87.9 88.1

Cape Ann 1.7 3.1 4.4 3.2 4.6 5.0 3.7 Cape Ann 109.0 100.3 94.3 90.5 93.8 95.0

Beverly-Salem 1.7 2.8 1.2 0.4 \.9 \.1 1.5 Beverly-Salem 80.5 84.5 85.8 83.5 85.9 83.5

Boston Harbor \.4 \.2 2.0 \.5 Boston Harbor 82.1 84.0 81.3

Cape Cod Bay 3.9 3.1 3.7 3.1 3.2 2.1 3.2 Cape Cod Bay 86.4 83.8 85.5 84.4 85.2 86.8

Outer Cape Cod Il.l 23.0 30.3 26.8 22.3 28.9 23.7 Outer Cape Cod 109.8 106.1 108.0 107.1 106.9 107.3

Buzzards Bay 16.0 16.9 32.5 26.6 25.0 25.3 23.7 Buzzards Bay 78.1 79.6 8\.6 83.0 80.1 79.4

16
CARAPACE LENGTH (mm)

Figure 11

Comparison of 1981-86 sununaries of ovigerous female American lobster

size-frequency data from' six coastal Massachusetts regions.

The abundance and size of ovigerous females are functions of the size-at-maturity and fishing pressure. Regardless of maturity status, most legal-sized females (over 95 %

in inshore Gulf of Maine regions) reach the market before

extruding eggs. The highest fishing-pressure index was found

in Buzzards Bay where only a relatively small percentage

of eggers were legal-sized (6-year mean 34.4%; Fig. 11).

Sublegal eggers were abundant there because most females

mature before minimum legal size. Briggs and Mushacke

(1979) computed a similar average berried-female length of

80 mm (range 64-120 mm) in western Long Island Sound.

The southern Gulf of Maine regions also exhibit high

fishing-pressure indices (89-95 %); however, few lobster are

mature at minimum legal size due to elevated sizes at 50 %

maturity (87-90 mm). Eggers are far less numerous there

than in Buzzards Bay and tend to be of larger size (except

for the Boston Harbor region, Fig. 11). Six-year mean

percentages of all egg-bearing females larger than minimum

legal size were: Cape Ann 79.6%, Beverly-Salem 55.5%,

Boston Harbor 35.3%, and Cape Cod Bay 54.5%.

Outer Cape Cod exhibited a high frequency of large eggbearing females (99.5 % were legal-sized). The largest size

at 50% maturity (97 mm) was observed in this region. A very

low fishing-pressure index (6-year mean 44 %) contributes to

the survival ofthe numerous large-sized eggers there (Fig. 11).

17

Table 21

Cull rate (%), statewide and by region, for all American lobster

sampled during commercial lobster trap-catch survey, Massachusetts

coastal waters, 1981-86. --~--

1981 1982 1983 1984 1985 1986

State 10.0 10.8 iO.7 14.8 18.1 20.9

Cape Ann 10.0 9.8 10.5 11.5 23.9 25.3

Beverly-Salem 8.3 8.6 10.2 20.9 23.0 30.0

Boston Harbor 13.3 19.3 19.1

Cape Cod Bay ILl 10.7 10.9 15.6 18.3 21.6

Outer Cape Cod 5.7 11.3 8.9 13.0 13.4 16.1

Buzzards Bay 13.5 14.7 12.4 12.4 13.4 14.6

Both Cape Ann and Outer Cape Cod regions exhibited a

higher proportion of eggers 100 mm CL than other inshore

regions. This is consistent with our V-notched female sizefrequency observations. Sixty-six percent of the V-notched

lobster observed off Cape Ann and 80% of those observed

off outer Cape Cod were larger than 100 mm CL. The influx of large offshore lobster, as well as migrants from the

northern Gulf of Maine areas off Maine and Canada, apparently contribute to these wider size distributions.

Similar observations were reported by Briggs and

Mushacke (1980) on the south shore of Long Island, New

York. They noted an average berried-female carapace length

of 99 mm (range 78-135 mm) and found only nine sublegal

eggers. Size distribution in this area was thought to reflect

mixing oflarge offshore migrants. This relatively open area

"Yith a greater depth range is comparable to outer Cape Cod

and Cape Ann regions which exhibited similar large average

lengths of egg-bearing females with few ovigerous females

less than minimum length.

Culls

The percentage of culls (lobster with missing or regenerating

claws) among all lobster sampled in Massachusetts coastal

waters ranged from 10.0% in 1981 to 20.9% in 1986 (Table

21). Coastwide indices for 1981-83 were statistically equal,

but those for 1984, 1985, and 1986 were significantly greater

and different from one another (Duncan's Multiple Range

Test, P =0.05). Legal, marketable, and sublegal size

categories exhibited similar trends (Tables 22-24). Indices

were generally higher for sublegals than for legals, a bias

which is assumed related to multiple recaptures (and

handling) of sublegals. Similar sublegal trends have been

reported by Briggs and Mushacke (1979, 1980).

The 6-year trend depicted an escalated number of culls in

all regions except Buzzards Bay where the incidence remained relatively stable. Until 1984, Buzzards Bay exhibited

the highest cull rate which was possibly related to its high

fishing-pressure index (highest among coastal Massachusetts

regions) and consequently high "throw back" rate. However, during 1984 most regional cull rates increased substantially while the Buzzards Bay rate remained unchanged.
Table 22

Cull rate (%), statewide and by region, for American lobster

;;>81 mm carapace length, sampled during commercial lobster trapcatch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 8.1 9.7 9.2 12.7 14.8 17.0

Cape Ann 10.7 9.6 7.5 10.4 19.4 20.3

Beverly-Salem 4.3 7.7 7.4 15.5 19.3 22.1

Boston f!arbor 10.1 16.2 15.8

Cape Cod Bay 93 9.3 10.0 13.2 14.5 18.1

Outer Cape Cod 5.3 10.3 8.1 13.3 12.5 14.9

Buzzards Bay 16.1 13.2 12.7 12.3 13.8 13.6

Table 23

Cull rate (%), statewide and by region, for marketable American

lobster sampled during commercial lobster trap-catch survey,

Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986 .-_._--_. _._.

State 8.2 9.9 9.2 13.2 16.2 17.6

Cape Ann 10.8 9.8 7.3 10.5 20.9 20.7

Beverly-Salem 4.4 8.0 'Jet 15.6 18 S 22.2

Boston Harbor 10.2 16.2 15.7

Cape Cod Bay 9.3 9.3 10.0 13.2 15.9 18.2

Outer Cape Cod 5.3 10.9 8.6 14.8 12.9 16.8

Buzzards Bay 16.9 13.1 12.3 12.6 15.4 14.1

Table 24

Cull rate (%), statewide and by region, for American lobster

<81 mm carapace length, sampled during commercial lobster trapcatch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 11.2 11.5 11.6 16.1 20.2 23.2

Cape Ann 8.0 10.6 12.6 12.2 26.9 28.7

Beverly-Salem 10.0 9.0 11.2 22.3 24.0 31.8

Boston Harbor 14.5 20.5 20.0

Cape Cod Bay 11.9 11.3 11.4 17.0 20.2 23.4

Outer Cape Cod 7.8 17.9 13.5 11.7 18.6 22.8

Buzzards Bay 12.7 15.2 12.2 12.4 13.3 14.9

This escalating cull rate may have reflected increased

fishing effort throughout coastal waters by mobile and fixedgear fishermen (Buzzards Bay is closed to trawling). Commercial traps fished increased by 34% during the study

period, which certainly enhanced the handling of lobster.

Also, this increased effort entrapped more lobster with other

aggressive predators (lobster and finfish). These aggressive

encounters may be enhanced in wire traps which appear to

reduce escapement ofsublegallobster. In addition, these traps

have a reputation for causing culls because lobster are more

difficult to remove when they grasp the wire strands;

18

however, culling may vary with the individual lobsterman

depending upon his level of patience and care. The increased

use of traps (wood or wire) is a plausible explanation for

much ofthe increased cull rate, especially in nearshore waters

where other fishing activities such as trawling or gillnetting

are limited. Krouse (1976) noted a positive correlation

between fishing intensity (trap density) and cull rate off the

coast of Maine.

We have detected extraordinarily high cull rates during

certain months in the Cape Ann region, which may be caused

by fishing activities other than pot fishing. The traps sampled in this region were moved east to deeper water (~120-ft

contour) in the autumn. Cull rates of 49% and 53% were

subsequently observed during October and November,

respectively, in contrast to rates of 9-25 % during MaySeptember in shoaler waters. The higher incidence appears

to be a function of the area fished rather than seasonality.

This deepwater area is open to trawling by special permit

only during 1 Feb-31 March and 15 June-30 SepI, while the

shallower area is closed to trawling all year.

Russell et a1. (1978) found a higher incidence of culls on

mud bottom near a trawlable area of Rhode Island Sound

than on ledges elsewhere (12.4% vs. 10.3%). They inferred

that trawl-induced damage was the cause. Other studies

documented enhanced shell damage and cull rate from

bottom-trawl activity particularly during the molt period

(Currier 1984, Estrella 1989, Ganz 1980, Smith and Howell

1987). Also, the effect of gillnetting on lobster cull rates

needs investigation.

It is also possible that lobster which are behaviorally subordinate due to culling are forced to congregate on less than

optimal habitat, i.e., relatively flat, open areas of sand or

mud which lack structure. However, this hypothesis has yet

to be proven.

Claw loss may also occur naturally as a result of environmental or molting conditions. Adverse weather, which

results in strong winds and heavy seas that jostle or damage

traps, may cause culls. Briggs and Mushacke (1980)

documented the effects of a hurricane in greatly increasing

the cull rate. This problem may be particularly acute if trap

movement occurs while claws extend through mesh or lathe

spacing. Autotomy (reflex amputation of an appendage) may

be induced by damage or overstimulation of the limb nerve

(Cobb and Phillips 1980). A molting lobster which encounters difficulty in withdrawing a claw through the narrow

segment at the base of the old claw will drop this claw in

order to complete the molt. The proportion of culls occurring in this manner is unknown.

Trap mortality

The incidence of dead lobster in traps coastwide was always

less than 1 percent annually (0.04-0.22 %; Table 25) during

the 6-year study period. Indices for legal and sublegal size

groups were also less than 1 percent (Tables 26-:27). This

parameter value may vary seasonally and can be enhanced

by environmental stresses, molting, intra- and interspecific
Table 25

Perceilt trap mortality, statewide and by region, for all American

lobster sampled during commercial lobster trap-catch survey,

Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 0.15 0.04 0.22 0.15 (U8 0.20

Cape Ann 0.00 0.00 0.00 0.27 0.03 0.16

Beverly-Salem 0.00 0.00 0.00 0.00 0.04 0.22

Boston Harbor 0.00 0.03 0.Q3

Cape Cod Bay 0.00 0.02 0.03 0.00 0.00 0.02

Outer Cape Cod ll.46 0.22 0.23 0.48 0.40 IJ.85

Buzzards Bay 0.62 0.00 1.13 0.43 0.76 0.25

Table 26

Percent trap mortality, statewide and by region, for American lobster

~81 mm carapace length, sampled during commercial lobster trapcatch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 0.16 0.04 0.26 0.20 0.23 0.29

Cape Ann 0.00 0.00 0.00 0.10 0.03 0.22

Beverly-Salem 0.00 0.00 0.00 0.00 0.00 0.49

Boston Harbor 0.00 0.04 0.04

Cape Cod Bay 0.00 0.00 0.00 0.00 0.00 0.00

Outer Cape Cod 0.39 0.16 0.18 0.51 0.36 0.71

Buzzards Bay 0.62 0.00 1.46 0.40 0.96 0.28

Table 27

Percent trap mortality, statewide and by region, for American lobster

<81 mm carapace length, sampled during commercial lobster trapcatch survey, Massachusetts coastal waters, 1981-86.

1981 1982 1983 1984 1985 1986

State 0.15 0.03 0.20 0.12 0.15 0.15

Cape Ann 0.00 0.00 0.14 0.39 0.02 0.12

Beverly-Salem 0.00 0.00 0.00 0.00 0.05 0.16

Boston Harbor 0.00 0.02 0.02

Cape Cod Bay 0.00 0.03 0.05 0.00 0.00 0.03

Outer Cape Cod 0.87 0.65 0.50 0.31 0.62 1.62

Buzzards Bay 0.62 0.00 0.94 0.45 0.68 0.24

aggression during entrapment, pollution, or the synergistic

effect of these factors.

Lobster mortality in the wild may be attributed to a number

of causes (Sindermann 1979). Gaffkemia, a naturally occurring disease ofthe blood, has received the greatest notoriety

as a potential lobster killer. It has claimed many crustaceans

in lobster impoundments; however, no one has been able to

assess its contribution to natural mortality. Young (1973)

related documented lobster mortality offthe New Jersey coast

to a possible synergistic effect of low dissolved oxygen, high

temperatures, and gill fouling due to copious suspended

19

flocculated material. McLeese and Wilder (1964) found

death ensued when the chitinous covering of the gills was

attacked by shell disease, subsequently interfering with

respiration.

High temperature, low dissolved oxygen and salinity,

pollution, predation, and intra- and interspecific agg,ession

during entrapment may be particularly detrimental during

stressful periods such as ecdysis. It is at this time that lobster

are most vulnerable, particularly to physical damage. The

crowded conditions that potentially can occur in a lobster

trap enhance aggressive behavior which is less frequently

displayed in the wild (Atema and Cobb 1980). Such behavior

may be particularly lethal torelatively defenseless, recently

molted, lobster. Nevertheless, the 6-year record indicates

that trap mortality is consistently low and does not represent a problem to this fishery.

Summary _

The Massachusetts coastal lobster (Homarus americanus)

resource was profiled and its condition assessed with CPUE

and biological data collected at sea and at dealerships. The

use of a commercial lobster sea-sampling program to provide valid assessment statistics was described. Between 1981

and 1986, six coastal regions were sampled monthly, with

an areal and temporal data weighting design.

An improved index of catch per trap haul/set-over-day was

generated by modeling the relationship between catch and

immersion time and standardizing effort to our survey modal

value of 3 set-over-days. The coastwide annual mean catch

rate ranged from 0.696 to 0.825 marketable lobster per trap

during the study period. No significant difference was found

among 1981-83 indices, but a significant decline occurred

in 1984 followed by a significant increase to the 1985-86

record levels. This 6-year time-series of mean annual catch

rates tracked closely the landings trend for territorial waters.

Analysis of historical landings and effort trends between

1888 and 1986 indicated that substantial increases in both

have occurred in recent years. However, CPUE increases

may be due to changes in climate, larval survival, fishing

habits and efficiency.

Six-year trends in biological parameters included a gradual

increase in rates of exploitation and total annual mortality

corresponding to a gradual decline in mean carapace length

of marketable lobster. The frequency of culls among all

lobster sampled ranged from 10.0% in 1981 to 20.9% in

1986. Escalation of cull frequencies occurred in all regions

except Buzzards Bay where they remained relatively stable

at about 14%. Causative factors are discussed, such as fishing

effort, predatory activity, and ecdysis. The percentage of

lobster found dead in traps was consistently less than 1%.

The sex ratio (%F: %M) differed significantly from 50:50

and approximated a 60:40 relationship during the study

period. The effect on sex ratios of differential escapement

by sexes through trap vents was investigated. A significant

difference was found between the carapace length-width rela-
tionships of male and female lobster. Females exhibited

significantly wider carapace widths than males in all regions

sampled. Other factors affecting sex ratios were discussed.

These include possible behavioral differences of sexes

relative to maturation which may cause sex ratios to vary

by depth. Also, ratios in favor of females may be a function

of reduced growth rate of females in sublegal lobster and

protection of egg-bearing females in legal-sized lobster.

A significant difference was found between the weightlength relationships of male and female lobster. This difference was evident in all six regions and was characterized

by females weighing more than males at smailer sizes and

less than males at larger sizes. A north-south clinal trend

was evident, wherein lobster north of Cape Cod weighed less

at length than those from regions south of Cape Cod.

A cement-gland staging technique was used to establish

functional size-maturity relationships for female lub~ter in

five coastal Massachusetts regions. Proportions mature at size

represent more realistic values than those obtained by

analyses of percent of females ovigerous, because the effect

of fishing pressure in lowering the proportion ovigerous is

cIrcumvented.

Three lobster groups, differing in major population

descriptors, are defined by our data. Lobster from the outer

Cape Cod region exhibited the largest 6-year average

carapace length of marketable lobster (96 mm), the lowest

fishing-pressure index (44%), lowest total annual mortality

(A = 36%), and the largest size at which 50% ofthe females

were mature (97 mm). The 1981-86 mean annual percent

of females observed with eggs was 24 %.

Buzzards Bay lobster exhibited the smallest 6-year average

size of marketable lobster (85 mm), the highest fishingpressure index (96 %), the highest total annual mortality

(A = 98 %), and smallest size at 50 % maturity (76 mm). The

6-year mean percentage offemales with eggs was also 24 %.

Southern Gulf of Maine regions (Cape Ann, BeverlySalem, Boston Harbor, and Cape Cod Bay) were intermediate

in mean carapace length (87 mm), fishing-pressure index

(92 %), total annual mortality (A = 92 %), and size at 50%

maturity (87-90 mm). The percentage of females with eggs

was ~5%.

Large migrant lobster (> 100 mm CL, many of which were

ovigerous females) from either offshore or Canadian and

Maine waters were more numerous off Cape Ann and outer

Cape Cod than in other Massachusetts coastal regions sampled. Geography may be a factor in concentrating these lobster,

since these two regions are adjacent to steeply sloping

gradients which lead to a much greater depth range than is

available to other coastal regions sampled.

20

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