FERRARO: DAILY TIME OF SPAWNING 



stages were completely absent. Spring spawners 

 typically had polymodal embryonic stage fre- 

 quency distributions with one or more embryonic 

 stages absent between adjacent modes. As water 

 in the Peconic Bays warmed, the number of modes 

 in the embryo stage frequency distribution de- 

 creased such that by midsummer the distribution 

 was unimodal. Also, as water temperature in- 

 creased the most recently spawned eggs of most 

 fishes were found at consistently later stages of 

 development. 



Indirect evidence from field data indicated that 

 embryonic development rates of most species in 

 this study were similar. Tests of differences be- 

 tween modes of embryo development stages repre- 

 senting two consecutive day classes from field 

 samples at 17° C by a posteriori sums of squares 

 simultaneous testing procedure 'Sokal and Rohlf 

 1969) indicated no significant difference (P>0.05) 

 in embryonic growi:h per day of 5. tyrannus; bay 

 anchovy, Anchoa mitchilli; tautog, Tautoga onitis; 

 Tautogolabrus adspersus; and searobins, 

 Prionotus spp. Also, age differences between day 

 classes offish embryos in field samples at tempera- 

 tures between 15.0° and 17.5° C were calculated 

 using the B. tyrannus embryo age prediction 

 Equations ( 1) and (2). The results (Table 2) showed 

 that the B. tyrannus equations gave good predic- 

 tions of the expected age difference between em- 

 bryo day classes for most of the species in this 

 study. 



With the exceptions of scup, Stenotomus 

 chrysops; Atlantic mackerel, Scomber scombrus; 

 and to a lesser extent Tautoga onitis and 

 Tautogolabrus adspersus very few early -cleavage 

 stage eggs were collected in our daytime sampling 

 program. 



Table 2. — Mean age differences (x, in hours) of fish embryos 

 representing two consecutive day classes in field samples at 

 temperatures' between 15.0° and 17.5° C determined by devel- 

 opment stage differences between day classes and embryo age 

 prediction equations for Brevoortia tyrannus. The expected age 

 difference is 24 h. 



Species 



Number of samples 



tSE 



25.6: 



21.8: 

 20.5i 

 25.4: 

 24.9: 

 23. 6i 

 24.2 = 

 22.0: 

 22.0: 



0.40 

 0.31 

 0.48 

 1.21 

 0.43 

 0.77 

 1.57 

 0.39 

 3.16 



Mean daily spawning times of fishes were calcu- 

 lated from hourly time of spawning frequency dis- 

 tributions of sample estimates of spawning time 

 (Table 3). The 1974 data were used to compute 

 estimated spawning times of Stenotomus 

 chrysops; weakfish, Cynoscion regalis; window- 

 pane flounder, Scophthalmus aquosus; and but- 

 terfish, Peprilus triacanthus, and only 1973 data 

 were used to compute the spawning time of the 

 hogchoker, Trinectes maculatus. Time of spawning 

 estimates were similar for species where data were 

 available for 2 yr. Histograms of relative fre- 

 quency distributions of sample estimates of 

 spavining time are presented for 1973 data on An- 

 choa mitchilli; Brevoortia tyrannus; Tautoga 

 onitis; Tautogolabrus adspersus; northern and 

 striped searobins, Prionotus carolinus and P. evo- 

 lans (note: the searobins are considered together 

 because their embryos can not be reliably distin- 

 guished); and Trinectes maculatus in Figure 2. In 

 summary, the results show that A. mitchilli, B. 

 tyrannus, P. carolinus , P. evolans, T. maculatus , C. 

 regalis, S. aquosus, and Peprilus triacanthus 

 spawn primarily in the evening or at night; 

 Tautoga onitis and Tautogolabrus adspersus 

 spawn in the afternoon and at night; and 

 Stenotomus chrysops spawns in the morning. 



There was no evidence of diel spawning 

 periodicity by Atlantic mackerel. Typically, all de- 

 velopmental stages (Table 1) were present in sam- 

 ples containing Atlantic mackerel eggs. The only 

 general trend in the Atlantic mackerel egg data 

 was a decrease in numbers of later developmental 

 stages, presumably due to dispersion or egg mor- 

 tality. 



Table 3. — Mean daily spawning times [DST, in hours after 

 sunrise) of fishes calculated from hourly frequency distributions 

 of sample estimates of spawning time. Estimated ages of fish 

 eggs <24 h old in field samples were subtracted from their time of 

 collection to obtain sample estimates of spawning time. 



Species 



Year 



DSr=SE 



'Range of temperatures cfiosen were temperatures at whiicfi at least two fish 

 embryo day classes would be present. 



Brevoortia tyrannus 



Anchoa mitchilli 



Stenotomus chrysops 

 Cynoscion regalis 

 Tautoga onitis 



Tautogolabrus adspersus 



Peprilus triacanthus 

 Prionotus spp. 



Scophthalmus aquosus 

 Trinectes maculatus 



457 



