Lowerre-Barbieri et al.: Age and growth of Cynoscion regalis 



647 



n=191 

 Pound net 



>4 , n ■j? i 



40-| /si, 634 

 Haul seine 



O 100 200 300 400 500 600 700 



4 °1 n=254 



Gill nel 



IVmiiI^hiiiiiiimiimmmimi 

 100 200 300 400 SOO 600 700 



Total length (mm) 



Figure 3 



Length frequencies of Chesapeake Bay weak- 

 fish, Cynoscion regalis, by gear in 1990. 



Bay — three age 6 and one age 10. In Delaware Bay 

 in 1992, seven fish were collected — one age 4, one 

 age 5, four age 6, and one age 8. An additional six 

 fish >3.6 kg were collected at the 1992 World Cham- 

 pionship Weakfish Tournament in Delaware, all age 

 6. In 1993, only four fish >3.6 kg were collected — one 

 age-12 fish from Chesapeake Bay, and three fish from 

 Delaware Bay, ages 6, 8, and 11. Maximum TL ob- 

 served in both regions was 875 mm. Maximum TGW 

 was 6.3 kg in Chesapeake Bay and 6.6 kg in Dela- 

 ware Bay. Ten fish collected from Delaware Bay >age 

 8 were similar in size to the two fish collected in 

 Chesapeake Bay (See Fig. 7 below). 



Growth 



Weakfish size (TL) was a poor predictor offish age. 

 Ages 1 and 2 were the only groups which did not 



have overlapping size distributions (Fig. 6). In con- 

 trast, TL's of fish (ages 2-5) collected in April and 

 May, showed broad ranges, much overlap, and mul- 

 tiple modes (Fig. 6). A fish 350 mm TL or 350 g TGW 

 (Table 2) could potentially be any of these ages (2-5). 



Observed size at age was used to estimate weak- 

 fish growth, because there was no evidence of size- 

 selective mortality. Mean size at first annulus showed 

 no consistent pattern with increasing age (Table 3), 

 and no significant differences were found between 

 sizes at first annulus by age («=540, F=1.75, P=0.06). 



Weakfish growth was well described by the von 

 Bertalanffy model (Fig. 7). The von Bertalanffy curve 

 was calculated for pooled sexes because weakfish 

 show no readily observed sexual dimorphism. Al- 

 though lengths at age were similar for both sexes, 

 mean TL's at age were usually larger for females than 

 for males, and significantly so for ages 2 and 3 (Table 

 4). Mean observed TL's of pooled male and female 

 Chesapeake Bay weakfish in April and May were 176, 

 311, 412, 510, 558, and 631 mm for ages 1-6, respec- 

 tively. Despite the high variability in size at age, 

 observed lengths at ages 1-12 showed a good fit 

 (r 2 =0.98) to the von Bertalanffy model (Fig. 7). The 

 model's estimated parameters, asymptotic standard 

 errors, and 95% confidence intervals fell within a 

 reasonable range, given the observed data (Table 5). 



Although the SW-TL relationship of weakfish col- 

 lected in Chesapeake Bay differed significantly by 

 sex (ANCOVA, P<0.05), the equations (male 

 SW=9.1xlO" 6 TL 31 and female SW=6.9xlO" 6 TL 305 ) 

 and coefficients of determination (r 2 =0.99) were simi- 

 lar for both sexes. Therefore, an equation for pooled 

 sexes was calculated (Fig. 8): 



SW = 6.0 x 10~ 6 TL 3 ° 4 (r 2 =0.99, n =3,742). 



The slope (b=3.04, SE=0.005) was not significantly 

 different from 3 U-test, £=0.002, P>0.05) indicating 



