588 



Fishery Bulletin 100(3) 



Table 3 



Estimates of the von BertalanfTy growth parameters for 

 pinfish by sex and for all sexed and unsexed fish combined. 

 MSE is the mean square error, r'- is the coefficient of deter- 

 mination, and n is the sample size. Asymptotic standard 

 errors are shown in parentheses. 



Sex 



MSE 



Male 228.5 0.31 -1.21 517.926 0.57 285 



(19.733) (0.079) (0.331) 



Female 212.0 0.33 -1.16 551.020 0.51 330 



(16.504) (0.082) (0.309) 



All fish 219.9 0.33 -1.10 537.490 0.55 645 



(12.204) (0.055) (0.203) 



en 



J FMAMJ JASOND 



Gulf of Mexico 



J FMAMJ JASOND 



Month 



Figure 5 



Plots of monthly gonadosomatic indices (GSI) for male and 

 female pinfish from Tampa Bay and the Gulf of Mexico. The 

 solid line connects median values. 



P=0.77, max-rescaled r^^CGO). Parameter estimates (stan- 

 dard error) were a = -7.78 (1.745) and /3 = 0.06 (0.014) for 

 males, and a = -9.83 (1.721) and (i = 0.08 (0.013) for fe- 

 males. The estimates of length at 50% maturity ±95% C.I. 

 were similar for both sexes: 132 ±8 mm SL for males and 

 131 ±8 mm SL for females. The smallest mature male was 

 112 mm SL and the smallest mature female was 92 mm 

 SL. The largest immature male pinfish was 245 mm SL 

 and female pinfish was 173 mm SL. 



Chi-square tests indicated that sex ratios did not devi- 

 ate significantly (P>0.05) from unity in any season. 



Length-weight relationships 



No significant differences (P>0.10) in slopes or inter- 

 cepts of standard-length on body-weight relationships 

 were observed between sexes in any period; therefore all 

 data were pooled for the subsequent analyses. Seasonal 

 length-weight regressions for both sexes combined are 

 listed in Table 2 for total and gonad-free body weight. 

 Regression slopes were significantly different between 

 periods only for the standard-length on total-body-weight 

 relationship (P<0.01). The regression slope was highest in 

 fall-winter, which indicates that pinfish gain more weight 

 per unit increase in length during this period than in 

 spring-summer. Adjusted means for the standard-length 

 on gonad-free body-weight relationship were not signifi- 

 cantly different between periods (P>0.05). 



Mortality 



Based on frequency plots by age, age-at-full-recruitment 

 was age 1 for pinfish in Tampa Bay and age 2 for those in 

 the Gulf of Mexico. Estimates of Z were 1.08/yr for Tampa 

 Bay pinfish and 0.88/yr for the Gulf of Mexico pinfish 

 (Table 4). Estimates of Z for all areas combined, assuming 

 full recruitment at age 2, were intermediate to the Z esti- 

 mates made for each area separately (Table 4). 



The estimate of A/ was 0.78/yr from Pauly's ( 1980) mul- 

 tiple regression equation by using L^ = 30.1 cm, ^=0.31/yr, 

 and mean annual temperature of 24°C. 



Distribution 



In the Gulf of Mexico, pinfish were captured at 90% ( 55/6 1 ) 

 of sites where trawls were pulled in depths of 6 to 30 m 

 during the baitfish survey (Fig. 6). Catch rates of pinfish in 

 the Gulf of Mexico varied significantly between years and 

 were associated with depth, but the significant interaction 

 term indicated that the relationship between depth and 

 catches varied between years (Table 5). Plots of cumula- 

 tive proportions of total catches by year showed that most 

 trawl catches (95%) occurred in waters <15 m during the 

 1994, 1995, and 1997 surveys, but in 1996, 95%^ occurred 

 in waters <17 m (Fig. 7A). 



Length summary plots for pinfish caught during the 

 baitfish survey showed that pinfish became segregated by 

 size as depth increased. Median length increased from 109 

 mm SL in the 6-10-m depth range to 152 mm SL in the 

 26-30 m depth range (Fig. 7B). The smallest (80-mm-SL ) 



