HALES: ROUND SCAD IN THE SOUTH ATLANTIC BIGHT 



seasonal pattern. Catch differences indicative of a 

 southward migration in winter and northward in 

 summer (either N < S in winter and spring or N > 

 S in summer and fall) occurred only in winter 1975 

 and summer 1976. Distributions opposite to the 

 above patterns occurred in summer 1975. Similar- 

 ity in the numbers (Chi-square test, P = 0.50, 1 df) 

 of gill rakers, a variable character (Berry 1969), 

 from specimens collected off South Carolina in 

 winter (i = 37.2, s^ = 1.2, n = 33) and summer 

 (x = 36.9, s^ = 1.4, n = 38) also suggested that 

 discrete stocks were not migrating through the 

 South Atlantic Bight. 



Although adults and juveniles were caught at all 

 depths throughout the year, length-frequency dis- 

 tributions by depth (Fig. 2) showed a similar pat- 

 tern for nearly every cruise: fish size decreased from 

 9-18 m to 19-27 m depths, then increased with in- 

 creasing depth to 110 m. Catches in 9-18 m consisted 

 primarily of adults in fall and winter, whereas both 

 juveniles and adults were captured in spring and 

 summer. Juveniles predominated in 19-27 m, where- 

 as adults composed most of the catch in deeper 

 waters. 



Table 4.— Comparison of catches of Decapterus punctatus north 

 and south of lat. 31°30'N by cruise. If the Wilcoxon rank sum (Z) 

 is significantly different (*), the direction of the difference is in- 

 dicated. SCn = sum of the catches north (n^ = # trawls north), 

 ZCj = sum of the catches south (n^ = # trawls south). 



Reproductive Biology 



All stages of ovarian maturity had different fre- 

 quency distributions of oocyte diameters (Fig. 3). 

 Resting ovaries contained primary or first growth 

 phase oocytes approximately 25-115 /^m in diameter. 

 Few larger (>115 fxra) developing or atretic oocytes 

 occurred. Oocytes in developing ovaries ranged from 

 30 to 375 nm in diameter, and exhibited character- 

 istics of first or second growth phase. Either one 

 or two modes were present in the frequency distri- 



butions of the sizes of second growth phase oocytes, 

 100-375 ^m in diameter. Germ cells in ripe ovaries 

 ranged from 30 to 495 /im in diameter. Ripe ovaries 

 contained oocytes in both growth phases and matur- 

 ing ova. Two or three modes were present in the 

 frequency distibution of germ cells of ripe ovaries. 

 Spent ovaries contained small oocytes in primary 

 growth phase and occasionally larger oocytes under- 

 going atresia. Germ cells in these flaccid ovaries 

 were usually 30-255 /im in diameter, although larger 

 cells were observed. Gonadosomatic indices (Table 

 5) changed as expected: indices increased from rest- 

 ing through ripe stages, then decreased for spent 

 fish. 



Maturity stages of testes were more difficult to 

 distinguish because testes often contained all stages 

 of spermatogenesis; therefore, stage determination 

 was based upon subjective interpretation of the 

 relative quantities of spermatocytes, spermatids, 

 and sperm. Although more variable, gonadosomatic 

 indices of males (Table 5) were similar to those of 

 females. 



Table 5. — Gonadosomatic indices (gonad wt/(total body wt - 

 gonad wt)) of Decapterus punctatus by stage maturity, x = 

 mean, s = variance, n = sample size. 



Seasonal occurrence of maturity stages showed 

 good agreement between males and females (Fig. 

 4), and indicated a protracted spawning period. 

 Developing gonads were found from February 

 through August, and ripe individuals of both sexes 

 were collected from March through August. 



Examination of gonads indicated that both species 

 mature at approximately 110 mm FL. Frequency 

 distributions of length by sex (Fig. 5) indicate that 

 both sexes mature over a narrow size range. Speci- 

 mens <100 mm FL were immature, whereas more 

 than 90% offish 110-119 mm FL were mature. Both 

 ripe males and females were collected in the size 

 range at which gonadal development begins (100- 

 109 mm FL). 



Fecundity estimates (# ova female"^ yr"^) for 32 

 ripe females (119-174 mm FL) ranged from 6,200 

 to 51,000 per female and were highly variable for 

 specimens of similar sizes. The distribution of the 

 sizes of the oocytes in these ovaries was not deter- 



255 



