SHEPHERD AND GRIMES: GROWTH VARIATIONS IN WEAKFISH 



paxameters. No statistical comparisons of growth 

 curves were made between regions because of the 

 large variance around parameters in Regions II and 

 HI. 



Historic Growth 



Weakfish in the New York Bight showed a general 

 increase in length at age between 1929, 1952, and 

 1980-81. Back- calculated lengths at age were com- 

 pared using a Student's t-test with variances of the 

 1980-81 data applied to the historic data (Table 6). 

 The application of the 1980-81 variances to the his- 

 toric data provided a more sensitive test of differ- 

 ences than would have been otherwise possible. 

 Literature values (Perlmutter et aL 1956) were 

 significantly smaller (P < 0.001) than present mean 

 lengths at age, with the exceptions that age 1 females 

 and age 6 males of 1952 and age 1 males of 1929 were 

 not significantly different from our values. After age 

 1, lengths at age of weakfish in 1980-81 were greater 

 than in 1952, which were greater than in 1929. Max- 

 imum size was greatest in 1 980-8 1 at 80 cm, followed 

 by 64 cm in 1952 and 52 cm in 1929. Longevity was 

 not consistent with maximum mean length at age. 

 Weakfish in 1952 were not >6 yr old (male) while an 

 8-yr-old male was captured in 1929 and an 11-yr-old 

 in 1980. Thus, larger but younger fish were caught in 

 1952 than in 1929, whereas 1980-81 fish were larger 

 and older than those caught in 1929 or 1952. 



fishery varied substantially with gear type and 

 season. An age- length key was applied to randomly 

 collected length frequencies to determine age struc- 

 ture of the fisheries in the Delaware Bay area. Spring 

 (May- July) landings from midwater trawls consisted 

 of fish from ages 1-10, with 85% of the catch being 

 >55 cm and age 5. Fall catches (August-November) 

 by otter trawls were primarily 1-yr-olds, 25-35 cm, 

 with occasional fish as old as 7 yr (Fig. 5). Young-of- 

 the-year fish (<20 cm) were removed from the otter 

 trawl catches by culling. Size-frequency data of 

 juvenile weakfish from NMFS groundfish surveys 

 were compared with commercial fisheries data. 

 Collections were made with otter trawls similar to 

 those used in the commercial fisheries. The analysis 

 of available NMFS length- frequency data was limited 

 to areas north of Chesapeake Bay (Fig. 5). In July and 

 August 1979, the data were primarily 1-yr-old weak- 

 fish, 20-30 cm. In September-October samples of 

 1978 and 1979, young-of-the-year weakfish pre- 

 dominated. Two length modes of young-of-the-year 

 weakfish < 20 cm were evident, undoubtedly because 

 the juveniles were composed of individuals resulting 

 from several spawning waves of adults (Daiber 1957; 

 Shepherd 1982). This bimodality of juvenile lengths 

 is reduced to a single mode by age 1, because of 

 growth convergence or high mortality of the smaller 

 juveniles during migration. 



DISCUSSION 



Fishery Age Structure 



Age-size composition of the commercial trawl 



Table 6. — Comparison of 1929 and 1952 growth of weakfish, 

 Cynoscion regalis, in the New York Bight to 1980-81 values for each 

 sex. Historic mean values weighted by N. 



Geographic variation in growth with a general ten- 

 dency toward larger sizes in cooler latitudes is a com- 

 mon occurrence among many marine organisms 

 (Wimpenny 1941). This phenomenon is particularly 

 well illustrated in some marine invertebrates such as 

 the Pacific cockle, Clinocardium nuttalli (Conrad) (= 

 Cardium corbis) (Weymouth and Thompson 1930). 

 Clinal variations in size have also been described for 

 fishes such as Atlantic menhaden, Breuoortia tyran- 

 nus (June and Reintjes 1959), American shad,/l/osa 

 sapidissima (Leggett and Carscadden 1978), and 

 croaker, Micropogonias undulatus (White and Chit- 

 tenden 1977). 



Weakfish follow a similar pattern of increasing size 

 toward the northern end of the range. Weakfish in 

 Region I (Cape Cod, Mass., to Ocean City, Md.) were 

 largest at each age, and attained a greater maximum 

 size and longevity. Growth of weakfish in Region III 

 (Virginia Beach, Va., to Cape Fear, N.C.) was lowest, 

 and fish from Chesapeake Bay, Region II (Ocean 

 City, Md., to Virginia Beach, Va.), had intermediate 

 growth. There was a discrepancy of 49 cm and 7 yr 

 between the largest northern and southern fishes. 



809 



