ICES mar. Sei. Symp., 199: 61-72. 1995

Fecundity of the American lobster (.Homarus americanus) in Massachusetts coastal waters

Bruce T. Estrella and Steven X. Cadrin

Estrella, B. T ., and Cadrin, S. X. 1995. Fecundity of the American lobster (Homarus americanus) in Massachusetts coastal waters. - ICES mar. Sei. Symp., 199: 61-72.

Fecundity estimates were calculated for American lobster (Homarus americanus) from three Massachusetts coastal regions. Southern Gulf of Maine (Cape Ann to Cape Cod Bay) estimates were significantly lower than those observed in both Buzzards Bay and outer Cape Cod. No difference was found between fecundity estimates from the latter two areas. Egg diameter was largest off outer Cape Cod followed by southern Gulf of Maine, then Buzzards Bay. Buzzards Bay females had a greater abdominal width than those from the other sites. Lobster fecundity estimates from southern Massachusetts waters were almost identical to 100-year-old estimates from the same area. However, these historical fecundity data were significantly different from our southern Gulf of Maine estimates. An evaluation of the broad variability in published fecundity estimates for American lobster indicated that small sample sizes in some studies may have substantially affected the slopes and predictive reliability of the regression analyses. However, geographic variation is not discounted.

Bruce T. Estrella and Steven X . Cadrin: Massachusetts Department o f Fisheries, Wildlife, and Environmental Law Enforcement, Division o f Marine Fisheries, 18 Route 6A, Sandwich, M A 02563, USA [tel: ( +1) 508 8881155, fax: (+1) 508 888 6842],

Introduction

Studies of fecundity in American lobster (Homarus americanus) have been conducted from Newfoun­dland to southern New England, but results have var­ied (Herrick, 1896; Saila et al., 1969; Squires, 1970; Perkins, 1971; Squires et al., 1974; Ennis, 1981; Campbell and Robinson, 1983; A ttard and Hudon, 1987). There has been much speculation in the litera­ture about the cause of this variability.

Herrick (1896) reported volumetrically calculated fecundity estimates from the vicinity of Buzzards Bay and Vineyard Sound, Massachusetts. His sample size, 4645, was the largest of any published fecundity study. Saila et al. (1969) combined lobster samples from three different areas: Point Judith, Rhode Island; Magdalen Islands, Quebec; and Massachu­setts, and calculated fecundity estimates with an elec­tronic counter. They suggested that Herrick’s volu­metric technique overestimated egg counts at size and concluded that their curve was more realistic. Some authors disagreed. Squires (1970) suggested the possi­bility of geographic variation to explain variability in fecundity estimates. Subsequent studies found areal differences in fecundity within the Canadian mari­

times (Squires et al., 1974; Ennis, 1981; Campbell and Robinson, 1983); however, small sample sizes, large variability in egg counts at size, and disparate size compositions due to regional differences in size at maturity, raised questions about validity and com­parability of results. Aiken and Waddy (1980) dis­cussed the variability among published fecundity esti­mates and hypothesized that differences among them could be due to methodology, geography, or sample size.

Although the seasonal timing of fecundity studies is an important consideration, most studies were con­ducted near the end of the incubation period (M ay- June), which is after the time of greatest egg loss (Perkins, 1971). Furthermore, differences in counting methodology among these studies, for example elec­tronic counters and subsample count expansions based on measures of volume or dry weight, were discounted as a potential source of bias since count validation produced errors which were generally less than ±2% (Aiken and Waddy, 1980).

Small sample sizes and large variability in egg counts at size can bias regression analysis results. The acknowledgement of considerable individual variation in fecundity by several authors emphasizes the need

62 B. T. Estrella and S. X . Cadrin ICES m ar. Sei. Symp., 199 (1995)

LABRADOR

’ Northwest, C o a s t ' * /

QUEBEC

GULF OF

SAINT

LAWRENCE

loswarlos

NEWFOUNDLAND

^Northumberland A . St. / /

BRUNSWICK

CANADA

MAINE 'Cape Ann

GULF

OF

MAINEMASSACHUSETTS Cape

CodBay

NORTH

ATLANTIC

OCEAN OuterCapeC od

ElizabethIstands— 40'

Figure 1. Northeast coast of the United States and Canada with ovigerous American lobster sampling sites.

to sample adequately, but this is not a simple task today. The intense fishing effort on our coastal lobster resource has reduced the availability and size of egg-bearing females, since many females are sent to market before extruding eggs. This increases the difficulty of acquiring sufficient samples to assess fec­undity and geographic variation in it.

H ere, we provide fecundity estimates for Massa­chusetts coastal lobster, determine if significant regional differences in fecundity exist, and assess the validity of H errick’s estimates for lobster in Massa­chusetts waters.

Methods

Optimal sample sizes needed to assess geographic differ­ences in fecundity estimates were calculated according to Jessen (1978) with the formula:

n — d^ lfC V 2]) / D 2

where t = Student’s t value, CV = coefficient of vari­ation, and D = difference expressed as a percentage of mean fecundity.

Coefficients of variation used in this equation were derived from empirical fecundity data which were pro­vided by G. P. Ennis (pers. comm.) and summarized in Ennis (1981). We determined with these data that a minimum sample size of 24 per 5 mm carapace length (CL) grouping was necessary to detect a 10% difference between mean egg counts at an alpha level of 0.05.

During the periods 24 April to 16 July 1987 and 4 May to 22 June 1988 a total of 433 egg-bearing female lobster were collected from commercial lobster traps in three coastal Massachusetts regions: southern Gulf of Maine (Cape Ann south through Cape Cod Bay, n = 148), outer Cape Cod (n = 133), and Buzzards Bay (n = 152; Fig. 1). W henever possible, lobster were individually wrapped in newspaper to minimize egg loss during trans­port to the laboratory.

For each lobster sampled, CL and second segment

ICES m ar. Sei. Symp., 199 (1995) Fecundity o f the American lobster in Massachusetts coastal waters 63

SOUTHERN G ULF OF MAINE3 .5 8 0 2 2 0 )] 1.09886Y ■ 1 (0 .000919833 (X40

30 N - 148

20

, -!K l

I O UTER CAPE COD

6 0 Y • ((0.0127547221 (X3 .0 6 2 7 8 9 )] 1 .03034

50 N ■ 133

> 40

O 30

20

BU ZZARDS BAY

Y ■ [(0 .00 0 0 7 6 4 0 1 9 (X4 .1 7 5 0 6 0 )] 1.0967230

20 N ■ 152

120 130 14011010070 80 90

2.0

1.8

1.6

2.0

E E,

cnLU I—LU 1.8

_ OUTER CAPE COD

<QCD CDLU

1.6

2.0

1.8

1.6CARAPACE LENGTH (mm)

Figure 2. Size-fecundity relationships for American lobster from three Massachusetts coastal regions.

width were measured to the nearest mm and cull status (missing or regenerating claws) was recorded. CLs ranged from 72 to 137 mm in the southern Gulf of Maine, 83 to 143 mm in outer Cape Cod, and 71 to 102 mm in Buzzards Bay.

Tails with egg clutches were severed from their bodies, labelled, wrapped in cheesecloth to prevent egg loss, and preserved in containers with 10% formalin for a minimum of 2 weeks. Eggs were then removed from each tail and stored in bottles with 10% formalin until all samples were collected.

The eye spot index (Perkins, 1972) was calculated for 10 eggs from each clutch in order to establish the stage of embryonic development for each egg sample. Eye lengths and widths were measured to the nearest 0.1 mm. A mean eyespot index (eye length + width/2) was then generated for each egg mass. Egg clutches exhibiting evidence of hatching were excluded from analyses.

Egg diameter was also measured to the nearest 0.1 mm from each of the 10 egg samples per clutch. In order to account for deviations from sphericity, the shortest and longest diameters of each egg were measured and averaged.

Eggs were then air-dried on fine-mesh screens for 3 to 10 days and rubbed against the screens to remove

SOUTHERN GULF OF MAINE

— 71-80 mm CL (N=41)

'•••81-90 mm CL (N=61)

— 91-100 mm CL (N = 33)

“*■ >100 mm CL (N=9)— I---- 1------1--

1 1 1 1—

BUZZARDS BAY

81-90 mm CL (N=23)

— 91-100 mm CL (N=41)

101-110 mm CL (N=31 )

+ 111-120 mm CL (N=23)

— >120 mm CL (N=16)H 1---------1-------H-------

“ 71-80 mm CL (N=55)

81-90 mm CL (N=62)

‘ >90 mm CL (N=42)-I-

0.3 0.70.4 0.5 0.6

EYESPO TIN DEXFigure 3. Relationships between American lobster egg diam­eter and eyespot index by 10 mm carapace length groups for three Massachusetts coastal regions.

cementum, setae, and other debris. Samples were weighed to the nearest 0.0001 g. One gram subsamples were counted and total sample counts were calculated based on whole sample weight. E rror was assessed by comparing actual counts of six samples with their corres­ponding calculated totals from subsample counts. The error ranged from -1 .20% to 1.81% (x = 0.38%) and compares favorably with other studies.

Lobster fecundity data are heteroscedastic owing to the increasing variability of fecundity with increasing carapace length. A base 10 log transformation of the data was performed to correct this and to facilitate comparison with other published estimates which were similarly treated. The log transformation is also war­ranted because of the curvilinear relationship between fecundity and CL.

Predicted size-fecundity relationships were calcu­lated with least-squares linear regression, which was corrected for systematic bias (Sprugel, 1983) with the method of Saila et al. (1988). Equations reported here are in the form:

Y = (a[xb]) (correction factor)

6 4 B. T. Estrella and S. X . Cadrin i c e s m ar. sei. Symp., 199 (1995)

Table 1. Mean fecundity estimates and associated statistics calculated by 5 mm size groups for American lobster from Massachu­setts coastal regions 1987-1988.

CL range N Min Max Mean STD CV

Buzzards Bay 71-75 23 1093 9528 5087 1843 36.235

76-80 33 584 13360 6499 2775 42.696

81-85 35 1452 13243 8546 2717 31.792

86-90 27 3644 17006 10913 3199 29.311

91-95 22 8942 18720 13857 2977 21.48596-100 8 10564 17935 15370 2783 18.108

101-105 4 7167 24934 15502 9282 59.872

Southern Gulf of Maine71-75 8 4083 6963 5733 840 14.646

76-80 35 983 10038 5737 2338 40.74981-85 28 1476 12554 7201 2748 38.166

86-90 35 2974 16882 9734 3368 34.597

91-95 26 4343 17137 11046 3603 32.616

96-100 7 6362 20785 12066 5715 47.364

101-105 5 8629 18540 13368 3621 27.090

106-110 0111-115 2 16406 20830 18618 3128 16.802116-120 0121-125 1 35 857 35857 35857126-130 0131-135 0136-140 1 43115 43115 43115

O uter Cape Cod81-85 5 8574 13021 10841 1751 16.15586-90 18 5 835 14853 11931 2701 22.640

91-95 26 7636 20901 14365 3797 26.43196-100 16 8494 23057 16607 4529 27.273

101-105 18 11347 30901 18758 4172 22.242

106-110 13 15415 29357 21662 4658 21.503

111-115 13 14666 35978 25 261 6191 24.510116-120 10 18496 37043 26955 6384 23.684

121-125 9 22738 44359 33268 6161 18.518

126-130 2 32183 33936 33060 1240 3.750

131-135 1 52261 52261 52261136-140 1 47392 47392 47392141-145 1 64144 64144 64144

Table 2. Stepwise multiple linear regression results for American lobster from three Massachusetts coastal regions. Data represent percentages of variation in fecundity explained by each variable.

Gulf of Maine Buzzards Bay O uter Cape Cod

Carapace length 41.880 41.465 69.280

Abdominal width 1.827 5.048 1.727

Eyespot index 0.001 0.302 0.031Egg diameter 1.307 2.101 5.288Culls 0.066 0.116 0.031

Total 45.081 49.032 76.357

ICES m ar. Sei. Symp., 199 (1995) Fecundity o f the American lobster in Massachusetts coastal waters 65

2.0

1.9

?

trUJl~ÜJ 1.8

<QOOLU

1.7

1.6

0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

EYESPOT INDEX

Figure 4. Egg diam eter-eyespot index relationships for A m er­ican lobster from three Massachusetts coastal regions.

1.9

EEŒ.U JI—U J

<Q 1.8

00U J

1.7

80 85 90 95 100 105

CARAPACE LENGTH (mm)

Figure 5. Egg diam eter-carapace length relationships for American lobster from three Massachusetts coastal regions.

Results

1. Fecundity and morphometries

Scatterplots revealed large variability in egg counts at size within each region (Fig. 2, Table 1). Stepwise mul­tiple linear regression analysis was performed on the empirical data to determine the source of variation. CL and abdominal width were strongly correlated (r = 0.944386 for Buzzards Bay, 0.9327137 for southern Gulf of Maine, and 0.9573708 for outer Cape Cod) and

SOUTHERN GULF OF MAINE

OUTER CAPE COD

BUZZARDS BAY

/

SOUTHERN GULF OF MAINE

OUTER CAPE COD

BUZZARDS BAY

//

accounted for a large percentage of the variability (Table 2). Eyespot index accounted for <1% of the variability, while egg diameter, which increases as the egg develops and as CL increases (Fig. 3), may be, as a result, only incidentally implicated (<6% ). The effect of lost or regenerating claws on egg production was negli­gible.

Analysis of covariance was used to test for geographic variation in the size-fecundity relationship. The slopes of regression lines for any pair of regions tested were not significantly different (Table 3). However, tests of elev­ations of slopes indicated that southern Gulf of Maine fecundity estimates were significantly lower than those from both Buzzards Bay and outer Cape Cod. Estimates from outer Cape Cod and Buzzards Bay were not signifi­cantly different and were therefore combined to produce the corrected equation:

Y = (0.000497 [X3 7580]) 1.01522

Analyses of variance and Mann-Whitney U tests of mean fecundity estimates for 5 mm size groups with sample sizes >18 were also used to assess regional vari­ation. Results of analysis of covariance were partially supported by these tests (Table 4). Significant differ­ences were found between two of the four size groups tested in the comparison between southern Gulf of Maine and Buzzards Bay data; however, both southern Gulf of Maine size groups were significantly different from corresponding outer Cape Cod data, while Buz­zards Bay and outer Cape Cod fecundity estimates were not significantly different.

Geographic variation in the relationship between egg diameter and eyespot index was evident (Fig. 4, Table 5). Analysis of covariance results indicated that the outer Cape Cod egg diam eter-eyespot relationship was consistently larger than the southern Gulf of Maine relationship, which in turn was generally larger than that from Buzzards Bay. Egg diameter also increased with carapace length and exhibited the same geographic differences as that for the egg diam eter-eyespot index relationship (Fig. 5, Table 6).

There was also geographic variation in the abdominal w idth-CL relationship. Abdominal width of egg- bearing females from Buzzards Bay was larger at CL than those from southern Gulf of Maine and outer Cape Cod (Fig. 6, Table 7).

2. Historical fecundity data

Herrick (1896) described egg counts from a total 4645 ovigerous female lobster collected off southern Massa­chusetts. Approximately two-thirds of these (2967) were captured in Vineyard Sound and around the Elizabeth Islands in southern Buzzards Bay between April and

66 B. T. Estrella and S. X . Cadrin ICES m ar. Sei. Symp., 199 (1995)

Table 3. Results of analysis of covariance of American lobster size-fecundity relationships from southern Gulf of Maine (SG O M ),outer Cape Cod (OCC), and Buzzards Bay (BB).

Slopes Means

CL range tested F P F P n

SGOM vs BB 72-102 0.7847 0.376 7.6623 0.006 290OCC vs BB 83-102 0.8055 0.371 2.7302 0.100 158SGOM vs OCC 83-105 0.0054 0.941 25.8957 <0.001 175

Table 4. Results of analysis of variance tests on regional American lobster fecundity estimates by 5 mm size groups.

F tests forSample sizes equality of variances Equality of means tests

CL range N1,N2 Fs Critical value of F A N OVA Mann-Whitney

SGOM vs BB 76-80 35,33 1.261 1.76 0.428 0.28381-85 28,35 1.063 1.69 0.136 0.038*86-90 35,27 1.227 1.86 0.187 0.08391-95 26,22 2.968 2.00* 0.006* 0.011*

BB vs OCC 86-90 27,18 1.641 2.13 0.274 0.15191-95 22,26 1.755 2.00 0.794 0.469

SGOM vs OCC 86-90 35,18 2.014 2.09 0.026* 0.011*91-95 26,26 1.691 2.01 0.004* 0.003*

* = significant difference at °c SO.05 level.

Table 5. Results of analysis of covariance of regional egg diam eter-eyespot index relationships for American lobster fromsouthern Gulf of Maine (SGOM), outer Cape Cod (OCC), and Buzzards Bay (BB).

Slopes MeansEyespot

Range tested F P F P n

SGOM vs BB 0.30-0.58 0.30 0.585 8.69 0.003 271OCC vs BB 0.30-0.69 7.03 0.008 72.58 <0.001 296SGOM vs OCC 0.30-0.58 1.00 0.317 35.74 <0.001 292

Table 6. Result of analysis o f covariance of regional egg diam eter-carapace length relationships for southern Gulf of Maine(SGOM ), outer Cape Cod (OCC), and Buzzards Bay (BB).

Slopes Means

CL Range tested F P F P n

SGOM vs BB 72-102 1.0935 0.297 7.3199 0.007 293OCC vs BB 83-102 5.7959 0.017 25.9704 <0.001 165SGOM vs OCC 83-105 1.5627 0.213 5.5370 0.020 173

June 1889-1894. The remaining 1678 were taken 15 miles southwest of No Man’s Land Island from 20 April to 16 June 1894. These observations were given to Herrick by Vinal Edwards of the US Fish Commission, Woods Hole, Massachusetts, who calculated fecundity- at-size after determining a count of 6090 eggs per fluid ounce. Since Herrick (1896) presented Edwards’ data in summary form, formal comparative analyses of his data with ours were not possible. Consequently, we acquired

Vinal Edwards’ original data logs from the archives of the National Marine Fisheries Service (the successor agency of the US Fish Commission), Woods Hole, and computerized the data. Difficulty was encountered in matching the sample size to that reported by Herrick (1896), despite numerous data checks. A total 6176 records from the time period and sampling sites in question were found and keypunched; 1681 from No Man’s Land Island and 4495 from Vineyard Sound and

ICES mar. Sei. Symp., 199 (1995) Fecundity o f the American lobster in Massachusetts coastal waters 67

75

SOUTHERN GULF OF MAINE .

OUTER CAPE COD

BUZZARDS BAY70

65

60

55

50

80 85 90 95 100 105

CARAPACE LENGTH (mm)

Figure 6. Abdominal width-carapace length relationships for ovigerous female American lobster from three Massachusetts coastal regions.

the Elizabeth Islands. Since we had no means of deter­mining which of Vinal Edwards’ records Herrick accessed and/or intentionally or inadvertently excluded, we compared the two data sets. Mean fecundity-at-size from Herrick (1896) was nearly identical to that which we generated from Vinal Edwards’ archived records (Fig. 7). Consequently, we decided to use the complete historical data set in subsequent analyses.

The historical size information was in total length (TL), which required conversion to CL for direct com­parison to contemporary data. However, we obtained substantially different results when we used available conversion equations (Saila et al., 1969; Squires, 1970; Squires et al., 1974) to plot Herrick’s size-fecundity relationship. This prompted us to generate a conversion equation specific to Massachusetts coastal lobster. A total 431 female lobster (62-174 mm CL, 184-495 mm TL) from Buzzards Bay, Vineyard Sound, and offshore southern New England were measured. Large offshore lobster were sampled in order to match the broad size range that was available to Herrick inshore in the late 1800s. The T L -C L relationships for inshore (n = 246) and offshore (n = 185) samples were compared with covariance analysis, and no significant difference was found between slopes (F = 0.037, p = 0.545) or elev­ations (F = 0.06, p = 0.805); consequently we combined samples. The resulting T L -C L conversion equation, CL = 0.351819 TL = 1.545255 (R2 = 0.9906; Fig. 8), was similar to that of Saila et al. (1969).

The following regression equation was generated from Herrick’s converted empirical fecundity data:

Y = (0.000564 [X3 7227]) 1.07266

A scattergram of the data (Fig. 9) depicts the large variability in fecundity-at-size which we observed in Massachusetts coastal waters. Descriptive statistics cal­culated from these data confirm this observation (Table8).

Analysis of covariance was used to test for differences between the size-fecundity relationship of the com­bined Buzzards Bay-outer Cape Cod data set and that from Herrick (1896). There were no differences in either the slopes (F = 0.0781, p = 0.780) or elevations (F = 0.1589, p = 0.690) of these regressions (Fig. 10). Neither was there any difference between the slopes of the his­torical data and our southern Gulf of Maine data (F = 0.0054, p = 0.942), but the elevation of the latter was significantly lower (F = 20.7899, p < 0.001).

3. Geographic variation in fecundity

Empirical fecundity data for five sites in Newfoundland waters and three sites off Nova Scotia, published by Ennis (1981) and Campbell and Robinson (1983), respectively, were acquired from the authors for com­parison with Massachusetts fecundity data. Analysis of covariance was used to test for regional differences in regression slopes and elevations. Size ranges tested in group comparisons were deliberately chosen to maxi­mize the sample sizes of the paired data sets.

Results indicated that the slopes for 54 of 66 com­parisons were homogeneous; however, only 22 of 66 pairs of groups exhibited both homogeneous slopes and means (Table 9). Outer Cape Cod fecundity data were statistically equal to fecundity data from Boswarlos and the northwest coast of Newfoundland and to Northum­berland Strait, Bay of Fundy, and eastern Nova Scotian regions. Also, no difference was found among Buzzards Bay, Herrick’s (southern Massachusetts, 1889-1894), and Bay of Fundy estimates.

Size-fecundity relationships were also described with nonlinear regression. In nearly all cases (except Ship H arbor and eastern Nova Scotian sites) nonlinear re­gression produced the higher R2 values (Table 10).

A graphical overlay of Massachusetts size-fecundity relationships with those published by Ennis (1981) and Campbell and Robinson (1983) revealed that nonlinear regression analysis produced curves which differed less than those generated by log-transformed linear re­gression (Fig. 11).

Using the assumption that sample size was an import­ant factor controlling analysis of covariance results, we combined fecundity data from sites within each study which exhibited homogeneity of either slopes or means. The following groups were created for comparison with Massachusetts data: Boswarlos and northwest coast of

68 B. T. Estrella and S. X . Cadrin ICES mar. Sei. Symp., 199 (1995)

Table 7. Results of analysis of covariance of regional abdominal w idth-carapace length relationships for American lobster from southern Gulf of Maine (SGOM), outer Cape Cod (OCC), and Buzzards Bay (BB).

Slopes Means

CL Range tested F P F P n

SGOM vs BB 72-102 8.2626 0.004 4.9761 0.026 296OCC vs BB 83-102 0.0003 0.986 10.5206 0.001 166SGOM vs OCC 83-105 0.6657 0.416 0.0778 0.781 178

80

— EDWARDS’ LOGS 1 8 8 9 -1 8 9 4

HERRICK (1896)

60

20

7 8 9 10 11 12 13 14 15 16 17 18 19 20

TOTAL LENGTH (in)Figure 7. Comparison of mean egg counts from American lobster by carapace length from Herrick (1896) and Vinal Edwards’ logs, 1889-1894.

180TL - 2 .8 4 2 4 CL ♦ 4 .3922 R 2 - 0 .9906 N ■ 431

160

140

_ j 120

CC 100

80

60430 480380230 280 330180

TOTAL LENGTH (mm)

Figure 8. Relationship between female American lobster cara­pace length and total length from Buzzards Bay, Vineyard Sound, and offshore southern New England.

Newfoundland = West Coast, NF; A rnold’s Cove, Para­dise, and Ship H arbor = Placentia Bay, NF; Northum­berland Strait, eastern Nova Scotia, and Bay of Fundy = Nova Scotia. The size-fecundity relationships from these groups showed greater similarities than were orig­inally apparent (Fig. 12A). However, analysis of covari­ance results indicated that the slopes and means were heterogeneous. Nonlinear regression lines of all but Placentia Bay, NF were almost superimposed on one another (Fig. 12B).

Discussion

The increase in egg diameter with lobster size parallels the findings of Attard and Hudon (1987), who observed

that the eggs of large lobster weighed more than those of small lobster. They concluded that the higher energy content may enhance larval growth and survival. How­ever, they found no correlation between egg dry weight and eyespot index. Egg diameter in the present study increased with eyespot index.

The larger egg size in outer Cape Cod lobster could be advantageous in sustaining larval development in the colder water environment east of Cape Cod and the potentially longer pelagic period there. O uter Cape Cod lobster are primarily offshore migrants which move shoreward seasonally.

The large variability observed in egg counts at size is an important consideration in American lobster fec­undity analyses. Stepwise multiple linear regression

ICES m ar. Sei. Symp., 199 (1995) Fecundity o f the American lobster in Massachusetts coastal waters 69

120

■ HUGHES (1965)

■ EDWARDS' LOGS 1 8 8 9 -1 8 9 4

100

80

t 60

40

20

60 70 80 90 100 110 120130140150160170180190200

CARAPACE LENGTH (mm)

Figure 9. Comparison of American lobster egg counts from Hughes (1965) and Herrick’s (1896) empirical data acquired from Vinal Edwards’ logs, 1889-1894.

60 80 100 120 140 160CARAPACE LENGTH (mm)

60 80 100 120 140 160CARAPACE LENGTH (mm)

Figure 11. Comparison of log-transformed linear (A) and non­linear (B) regressions of American lobster size-fecundity data from Newfoundland (Ennis, 1981), Nova Scotia (Campbell and Robinson, 1983), and two Massachusetts sites: southern Gulf of Maine and southern Massachusetts.

mo

>

ozDoUJ

40 60 80 100 120 140 160 180

CARAPACE LENGTH (mm)

Figure 10. Size-fecundity relationships from southern Massa­chusetts waters, 1889-1894 (Edwards’ logs), southern Massa­chusetts, 1987-1988, and southern Gulf of Maine, 1987-1988.

analysis verified that there was only a small contribution to variation in fecundity from the sampling period, as tested with the effect of the eyespot index (Table 2).

The extent to which egg inflation during development may dislodge eggs by breaching the cementum bonds is unknown. Although, we have observed that well- developed eggs appear to “ shake loose” more easily than eggs with minimal development.

The effect of claw loss or regeneration on egg produc­tion appeared negligible. However, such a relationship, if any, would depend upon energy partitioning away from ovarian development and toward claw regener­ation . There was no way to determine whether the cull lobsters which we observed lost their claws at a critical time relative to ovarian development.

The larger abdominal w idth-CL relationship exhibited by Buzzards Bay lobster did not fully explain the regional fecundity trend observed. A broader ab­dominal width could accommodate more eggs, but it had only a minor effect on egg counts in that region.

Aiken and Waddy (1980) reviewed possible causes of egg loss including disease, parasitism, and commercial handling. O ther factors may be variability in cement gland production, egg enlargement during develop-

120 n rS. MASSACHUSETTS 1889-1894

S. GULF OF MAINE 1987-1988

S. MASSACHUSETTS 1987-1988

30

CORRECTED LOG-LOG REGRESSIONS S. MASSACHUSETTS, 1987-1988 SOUTHERN GULF OF MAINE

CAMPBELL AND ROBINSON (1983)ENNIS (1981)

ÈQZDoLU

: 40

NONLINEAR REGRESSIONS S. MASSACHUSETTS, 1987-1988

SOUTHERN GULF OF MAINE CAMPBELL AND ROBINSON (1983)

ENNIS (1981)

70 B. T. Estrella and S. X . Cadrin ICES m ar. Sei. Symp., 199 (1995)

CORRECTED LOG-LOG REGRESSIONS WEST COAST, NF; R2= .396032, N=138 PLACENTIA BAY, NF; R2=.900558, N=183 / NOVA SCOTIA; R 2= .863435, N=166 S. MASS.; R2- . 60190, N-285

/ ' / ' / ’

/ / ' '

60 80 100 120 140 160CARAPACE LENGTH (mm)

£ 60

QZ 40DOLL 20

NONLINEAR REGRESSIONS- WEST COAST, NF; R2= .49772, N=138- PLACENTIA BAY, NF; R2=.89239, N=163- NOVASCOTIA; R2= .86372, N=166 -S . MASS.; R 2= .81878, N-285

B

60 80 100 120 140 160CARAPACE LENGTH (mm)

Figure 12. Comparison of log-transformed linear (A) and non­linear (B ) regressions of grouped American lobster size- fecundity data from Canadian and Massachusetts studies.

S, MASS. 1889-1894

— - S. GULF OF MAINE

100 ....... S. MASS. 1987-1988

OFFSHORE U.S.

CANADA

COo

80

x

^ 60 O

40

20

80 100 120 140 160 180

CARAPACE LENGTH (mm)

Figure 13. Comparison of previously published American lobster size-fecundity relationships from the Canadian Mari­times, offshore US, and Massachusetts.

ment, habitat abrasion, ingestion of eggs by predators (particularly while lobster are in traps). In 1896, Vinal Edwards recorded his observations of eels and cunners tearing the eggs from egg-bearing lobster in the shoals of Vineyard Sound, Massachusetts.

The contribution of commercial fishing activity to egg loss is uncertain; however, Buzzards Bay and southern Gulf of Maine regions have exploitation rates which are among the highest in the state. O uter Cape Cod has the lowest exploitation rate and CVs, but it is likely that factors other than exploitation rate are responsible. Exploitation in the late 1800s could not have been as intense as it is today, yet the CVs of Herrick’s data (Table 8) are as high as those from our Buzzards Bay and southern Gulf of Maine data when similar carapace length ranges are compared. This lack of change in southern Massachusetts fecundity data over a 100-year period does not support the argument that sustained fishing pressure may lower the size-at-maturity and, in turn, affect fecundity at size.

Nevertheless, we believe that the question of the validity of Herrick’s data was resolved. Our lobster fecundity estimates from southern Massachusetts waters were almost identical to the volumetrically-calculated estimates which Herrick (1896) summarized nearly 100 years earlier. The suggestion by Saila et al. (1969) that Herrick’s volumetric technique overestimated egg counts was initially based on a limited number of total counts from Hughes (1965). However, most of the egg counts from Hughes (1965) are well within the range of dispersion of Herrick’s data (Fig. 9). This is not surpris­ing, since Hughes' samples came from offshore Massa­chusetts, as did 52% of the samples used by Saila et al. (also provided by Hughes). The generally lower egg counts observed by Saila et al. may have been due to small sample size (n = 79) or to geographic differences, since they grouped Massachusetts samples with those from Canada and Rhode Island; however, their esti­mates were the lowest of all published studies (Fig. 13). It is only assumed that egg loss between time of capture and counting was minimized, but capture method, which was not identified, could have been a factor. Perkins' (1971) fecundity estimates, the second lowest of all pub­lished studies, were derived from samples taken by otter trawl which can enhance egg loss.

Massachusetts ovigerous female size-frequencies dif­fered among all three regions relative to differences in size-at-maturity and exploitation rate (Estrella and McKiernan, 1989). This complicated regional fecundity comparisons.

The significantly lower fecundity estimates which we obtained from lobster north of the peninsula of Cape Cod (southern Gulf of Maine region) may have been due to the lack of samples at larger carapace lengths. How­ever, these lower estimates may reflect environmental

ICES m ar. Sei. Symp., 199 (1995) Fecundity o f the American lobster in Massachusetts coastal waters 71

Table 8. Mean fecundity estimates and associated statistics calculated by 5 mm size groups for southern Massachusetts waters, 1889-1894 (derived from Vinal Edwards’ logs).

CL range n Min Max Mean STD CV

66-70 15 3045 12180 5989 2603 43.47271-75 38 3045 12180 6811 2420 35.52976-80 314 1523 15 225 7455 2921 39.18781-85 435 1523 19793 8701 3168 36.41586-90 873 1523 30450 10075 3725 36.97091-95 974 1523 36540 12004 4234 35.27596-100 849 1523 48720 14855 5158 34.725

101-105 403 3045 42630 17637 6142 34.825106-110 510 3045 54810 20587 7322 35.565111-115 550 6090 48720 26713 8218 30.765116-120 162 6090 54810 32894 8586 26.104121-125 443 6090 85260 36856 9762 26.488126-130 98 21315 60900 42848 8379 19.556131-135 291 12180 97440 46 183 10426 22.575136-140 52 24360 97440 54371 12913 23.750141-145 111 24360 97440 57416 11612 20.225146-150 13 36540 85260 64179 14415 22.460151-155 33 12180 85260 62192 18632 29.958156-160 8 60900 91350 76125 10796 14.182161-165 0166-170 4 54810 91350 77648 16016 20.627

Table 9. Results of analysis of covariance of available American lobster size-fecundity relationships from Canada and US waters. Key: * = heterogeneous slopes; X = homogeneous slopes and heterogeneous elevations; O = homogeneous slopes and elevations.

NWC BOS AC p SH NS ENS BF SGOM OCC BB SM

Northwest Coast (NWC)Boswarlos (BOS) XArnold’s Cove (AC) * XParadise (P) * X OShip Harbor (SH) O O O oNorthumberland Strait (NS) * O X X *

E. Nova Scotia (ENS) * O X X o oBay of Fundy (BF) o O X X * o oS. Gulf of Maine (SGOM) * X X X X X X XOuter Cape Cod (OCC) 0 O X X * 0 o o XBuzzards Bay (BB) * X X X X X X O X OS. Mass. 1889-1894 (SM) * X X * * X X O X * O

influence on lobster anatomy and physiology. Environ­mentally induced regional differences in size-at- maturity and other biotic and behavioral factors have been documented in Massachusetts coastal waters (Estrella and McKiernan 1989); it is plausible that fec­undity is similarly affected. Yet, differential egg loss cannot be discounted since these lobster, unlike those from the other two regions, were kept in submerged holding cars for 1-3 days after capture.

Covariance analyses indicated that size-fecundity re­lationships from some Massachusetts regions were stat­istically equal to those from some Canadian regions. This weakens the hypothesis of clinal variation and ob­scures any obvious life history strategy. It is possible that regional differences in fecundity may have been caused

by local or annual differences in water temperature, but fecundity is apparently a highly variable entity which is subject to a number of effects. This makes it difficult to separate annual or local variation from that caused by other factors. It may be advantageous to investigate geographic variation in fecundity earlier in the incu­bation period, before variability in egg loss affects results.

Despite potential areal effects, we suggest from our evaluation of published fecundity estimates that the large variability in egg counts-at-size is a major factor affecting fecundity regression results. It creates the need to adequately sample throughout the range of available CLs. The range of fecundity values in most published size-fecundity relationships is narrow at small CLs,

72 B. T. Estrella and S. X . Cadrin ICES mar. Sei. Symp., 199 (1995)

Table 10. Coefficients of determination (R 2) for log-trans­formed linear and nonlinear regressions of size-fecundity re ­lationships for American lobster.

Log-transformedlinear Nonlinear

S. Gulf of Maine 0.40784 0.64677O uter Cape Cod 0.69303 0.76697Buzzards Bay 0.41904 0.55079

S. Massachusetts (1889-1894) 0.70859 0.78969

A rnold’s Cove 0.77639 0.78787Paradise 0.88630 0.89082Ship Harbor 0.79694 0.79413Boswarlos 0.33181 0.53346Northwest Coast 0.36280 0.41857

Bay of Fundy 0.71033 0.73060E. Nova Scotia 0.62429 0.57590Northumberland Strait 0.75111 0.88469

where sample sizes are generally adequate, and broad at large CLs, where sample sizes are less than optimal (Fig. 13). Log-transformed size-fecundity relationships de­rived from highly variable egg counts would benefit from the use of a correction factor (Sprugel, 1983); however, the nonlinear regression model provides a better fit to the data. Herrick (1896) aptly described our dilemma when he stated that “The average number of eggs of a lobster of a given length has little value unless obtained from a large number of individuals” .

Acknowledgements

We are indebted to Gerry P. Ennis and Alan Campbell, who provided us with their empirical fecundity data. Daniel J. McKiernan assisted in the design phase of the study and along with Thomas Hoopes, Peter Hoar, and Brian Kelly contributed in the collection of ovigerous females. We are grateful for the cooperation of commer­cial lobstermen Fred Hillier, John Karbot, Christopher Kyranos, Steven Smith, Anthony Pribash, John Sampson, and Thomas Vital in sample acquisition. Ann Marie Schultz and David D. Pichette expended con­siderable effort in processing eggs. Software used to generate the study area map was developed by Josef

Idoine. Ann Spires and Kim Trotto keypunched the majority of the historical data.

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