SHEPHERD and GRIMES: REPRODUCTION OF WEAKFISH 



which were captured during May 1981 in Dela- 

 ware and Gardiners Bays. An oocyte diameter of 

 0.20 mm was determined from diameter frequency 

 distributions and the degree of yolk accumulation 

 as the size between oogonia and developing ova, 

 and was used as the lower size limit of ova in the 

 fecundity estimates. Each sample was diluted 

 with distilled water, stirred, then several aliquots 

 removed from the solution to provide a density of 

 about 10,000 ova in a 6 x 6 cm gridded petri dish. 

 About 800-1,000 ova were counted from six ran- 

 domly selected squares, then adjusted for a total 

 subsample count. Two subsamples were counted 

 per sample and three if the ova sample was from a 

 large fish (>60 cm). The sample and subsample 

 were oven dried at 40°C for a minimum of 24 h 

 then weighed to the nearest 0.001 g on a Mettler 3 

 balance. Total fecundity was calculated as 



Total fecundity = [number in subsample x 

 (sample wt/subsample wt)] + number in 

 subsample. 



Predictive equations of fecundity from length and 

 weight were fit to a geometric mean (GM) func- 

 tional regression (Ricker 1975) following log-log 

 transformation. 



RESULTS 



Seasonality 



The changes in maturity stages during the year 

 indicate spawning takes place from May to mid- 

 July for weakfish in Delaware Bay and north to 

 Long Island (Fig. 2). In May, all 122 mature fish 

 examined of both sexes were in the developing or 

 ripe stage of gonad development. The 50 fish that 

 were inspected in June included 100% of the males 

 and 70% of the females in a developing or ripe 

 stage. Several of the ovaries examined in a June 

 sample from Gardiners Bay had the appearance of 

 being partially spent. The ovary was flaccid, 

 slightly hemorrhaged and the lumen filled with 

 fluid, but a few transparent ova were still visible. 

 Spawning weakfish in Delaware Bay were cap- 

 tured as late as 12 July, when 11% of the females 

 and 76% of the males were classified as ripe. In the 

 same month, 84% of the females were in spent 

 condition. By August, all of the fish examined at 

 all locations were in postspawning condition. 



MAY JUNE JULY AUG SEPT OCT NOV DEC 

 FEMALE 



30 



17 



2U 



U 



MAY JUNE JULY AUG SEPT OCT NOV DEC 

 RECOVERING [ IMMATURE ^DEVELOPING | | RIPE 



SPENT 



3 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



FIGURE 2. — Changes in visual maturity stage of weakfish, 

 Cynoscion regalis, in 1980-81 for the New York Bight. TV indi- 

 cated for each month. 



Weakfish from Sandy Hook Bay were not available 

 until June and all the samples examined from this 

 area were in postspawning condition, either spent 

 or recovering. 



This seasonality of spawning at each of the sam- 

 ple locations was suggested by seasonal changes in 

 the GSI. Mean GSI values (percent gonad weight 

 relative to somatic weight) ± 95% C.I. (Confidence 

 Interval) of all females rose from 5.75 ± 1.29 in 

 May to a peak value of 6.04 ± 1.43 in June, then 

 declined to 1.76 ± 0.40 by July (Fig. 3). Male GSI 

 were at a yearly high of 4.88 ± 1.45 in May but 

 declined to only 2.51 ± 0.85 by July. The mean GSI 

 values for females were consistently higher in all 

 months except July. Gonad size reached the lowest 

 levels for both sexes in August with mean GSI 

 values of 0.71 ± 0.07 and 0.19 ± 0.02 for females 

 and males, respectively. The GSI values remained 

 low until the last samples were collected in 

 November. 



Specific spawning time, as reflected in GSI, was 

 dependent on the size of the individual fish (Fig. 4). 



503 



