GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE PORGY 



raw data were 99% for late September 1973 (S = 

 5/435) and 83% for January 1974(5 = 395/2,468). 

 Pooled cohort-specific estimates of 1 - S were 

 99.23% for the 1977 year class and 83.36% for the 



1978 year class using Heincke's procedure. The 

 different mortality rates for these year classes 

 are consistent with theoretical mortality rates 

 given later, and the greater postspawning survi- 

 val of the 1978 year class. 



Postspawning survival of S. caprinus, total 

 annual mortality rates, and maximum lifespan 

 varies greatly between years and year classes. 

 The 1977 and apparently 1976 year classes 

 rarely appeared after they spawned at age I (Fig. 

 2). In contrast, many members of the 1978 year 

 class survived after spawning at age I and 

 spawned again at age II. White and Chittenden 

 (1977) suggested somatic weight variation as a 

 factor in the survival of the Atlantic croaker, 

 Micropogonias undulatus. Somatic weight of fe- 

 male S. caprinus did not change in a regular 

 monthly pattern, and regression elevations dif- 

 fered widely in consecutive months (Fig. 12, 

 Table 4). 



Discussion 



Both time-specific and cohort-specific esti- 

 mates indicate that the total annual mortality 

 rate of S. caprinus is about 83-99%, depending on 

 postspawning survival. Lower values in this 

 range agree with theory (Royce 1972:238) that 

 total annual mortality is 78-84% if the maximum 

 age is 2.5-3 yr as observed. Higher values are 

 consistent with theoretical annual rates of 90- 

 100% given the 1-2 yr lifespan observed for some 

 year classes. 



Variation in postspawning survival might not- 

 be due to somatic weight changes because of the 

 lack of a regular monthly pattern and the wide 

 variation in regression elevations between adja- 

 cent months, although our somatic weight re- 

 gressions are based primarily on the 1978 and 



1979 year classes which did not disappear after 

 spawning. 



TOTAL WEIGHT-TOTAL LENGTH, 



GIRTH-TOTAL LENGTH, AND 

 LENGTH-LENGTH RELATIONSHIPS 



Regression and related analyses for total 

 weight-total length, girth-total length, and 

 length-length relationships are presented in 

 Table 5. 



Table 4.— Analyses for the monthly regressions of somatic 

 weight (V) in grams on total length (X) in millimeters for fe 

 male Stenotomus caprinus, October 1978-March 1980. All re- 

 gressions were significant at a = 0.05. 



Total length-total weight regressions for adult 

 males and females were not significantly differ- 

 ent in slope (F = 0.029, df = 1,657, a = 0.05) or in 

 adjusted means (F= 1.63, df = 1,658, a =0.05) so 

 that one pooled regression equation was pre- 

 sented for them. Calculated slopes varied signifi- 

 cantly from = 3.0 (t = 13.2, df = 1,682, a = 0.05) 

 except when data for immatures, males, and fe- 

 males were pooled (t = 0.197, df = 2,792, a = 

 0.05). 



GENERAL DISCUSSION 



Stenotomus caprinus, which inhabits the 

 warm temperate Gulf, exhibits markedly differ- 

 ent population dynamics from Stenotomus chry- 

 sops, which primarily inhabits the cold temper- 

 ate Atlantic north of Cape Hatteras, N.C. Our 

 data and the literature agree that for S. capri- 

 nus: 1) spawning occurs in one discrete period a 

 year with peak spawning in February or March; 

 2) all individuals reach maturity and spawn at 

 90-125 mm TL as they approach age I; 3) maxi- 

 mum size typically is about 200 mm TL, but most 

 fish are much smaller; 4) maximum lifespan is 

 2.5-3 yr; 5) total annual mortality rate is 83-99%, 

 but postspawning survival, total annual mortal- 

 ity rates, and lifespan vary between year classes; 

 and 6) average sizes are 110-135 mm TL at age I, 

 130-155 mm at age II, and 160 mm at age III. In 

 contrast, S. chrysops north of Cape Hatteras 1) 



537 



