GEOGHEGAN and CHITTENDEN: REPRODUCTION, MOVEMENTS OF LONGSPINE PORGY 



approximately normally distributed. Hatching 

 dates of 15 February and 15 March were assigned 

 to the 1978 and 1979 year classes, respectively, to 

 estimate their growth and ages. Descriptions of 

 spawning periodicity and growth assume that S. 

 caprinus reach 20-30 mm TL 1-2 mo after hatch- 

 ing. This assumption and assigned hatching 

 dates seem reasonable because: 1) Stenotomus 

 caprin us average 13-14 mm TL/30d growth dur- 

 ing their first 8 mo of life (Fig. 3); 2) the slope and 

 elevation of the regression of ovary weight on 

 total length for the 1979 year class was greatest 

 in mid-March (Fig. 4, Table 3) and back calcu- 

 lated length of this year class was —5.26 mm TL 

 at d of age (Fig. 5). A hatching date of 15 Febru- 

 ary was assigned to the 1978 year class because 

 this year class recruited about 1 mo earlier in 

 1978, although gonad data are lacking for this 

 period. There appears to be no published data on 

 size at early age other than our findings. 



Our interpretations of the life history of S. 

 caprinus obviously apply best to the area off 

 Freeport, Tex., but they probably apply to much 

 broader areas in the Gulf, judging from the 

 agreement of our findings with the general pub- 

 lished data on this species. 



MATURATION AND SPAWNING 

 SEASONALITY 



Results 



Stenotomus caprinus mature at 90-125 mm TL 

 as they approach age I. Sex could be determined 

 by eye at 90 mm TL as many fish entered the 

 Early Developing stage ( Fig. 6). Fish entered the 

 Late Developing, Ripe, and Gravid stages at 100- 

 125 mm TL. These data are supported by the 

 extrapolated .r-intercepts of ovary weight on 

 total length which were 80-100 mm TL during 

 the January-April spawning period (Fig. 4, 

 Table 3). Our estimates of size at maturity agree 

 with the mean sizes at age I given later. 



Little somatic growth occurs after S. caprinus 

 enters the later stages of gonad maturation (Fig. 

 6). Mean sizes of fish approaching age I were 1 10 

 mm TL in the Early Developing, 113 mm in the 

 Late Developing, 115 mm in the Gravid and 

 Ripe, and 118 mm in the Spent/Resting stages. 



Stenotomus caprinus spawn once a year in a 

 discrete period from January through April. 

 This period is indicated by collections off Texas 

 of fish that were 30-40 mm TL in April 1978. 20- 

 50 mm in May 1979, and 20-40 mm in February- 



March 1980 (Fig. 2), and by the capture of fish 

 20-80 mm TL in late April 1980 in the north cen- 

 tral Gulf (Fig. 7). No spawning occurs from May 

 through December, because the smallest fish 

 collected in that period belong to year classes 

 hatched before May. Peak spawning occurred in 

 March and early April in 1979 and from Janu- 

 ary through March 1980 as indicated by the in- 

 creased slopes and elevated ovary weight-total 

 length regression lines in those periods (Fig. 4, 

 Table 3). The sharply defined and readily fol- 

 lowed length-frequency modes for each year 

 class indicate that spawning occurs in one dis- 

 crete period each year. 



Gonad maturity data support a January-April 

 spawning period and indicate that virtually all 

 S. caprinus spawn at 12 mo of age. Fish in Gravid 

 or Ripe stages occurred only in the period Janu- 

 ary-April, and Spent/Resting stage fish ap- 

 peared immediately thereafter (Fig. 8). Virtually 

 all spawning occurs in the period January-April 

 and few fish delay spawning until age II because 

 extremely few fish were in the Immature, Matur- 

 ing Virgin, or Early Developing stages in that period. 



The spawning period probably spans about 50- 

 80 d within the January-April interval, assum- 

 ing larger fish were spawned before smaller 

 ones, and all fish grew at the same rate as noted 

 later. The spawning period duration was ap- 

 proximated from growth increments and size 

 ranges (expressed as 99% confidence limits for 

 observations) of the 1978 and 1979 year classes in 

 June and July (Table 2), their first months of full 

 recruitment. The mean 99% confidence limit for 

 observations in the June-July period was 22.19 

 mm in 1978 and 40.27 mm in 1979, and respec- 

 tive mean daily growth was 0.45 mm/d and 0.50 

 mm/d. Calculated lengths of spawning periods 

 were 49 din 1978 (22. 19 mm ^0.45 mm/d) and 82 

 d in 1979 (40.85 mm -s- 0.50 mm/d). These esti- 

 mates suggest that the successful spawning pe- 

 riod is much shorter than the January-April 

 interval indicated by length compositions and 

 gonad data. 



Stenotomus caprinus exhibited a sex ratio of 

 1.00 male to 1.21 females. This ratio was ob- 

 served in 1 ,506 fish examined during the spawn- 

 ing period and differs significantly from Ll(x 2 

 = 13.01, a =0.05, df = 1). 



Discussion 



Our findings agree with the limited literature 

 on Stenotomus reproduction. Previous workers 



525 



