FERRARO; DAILY TIME OF SPAWNING 



data commonly obtained in ichthyoplankton re- 

 search and does not require a continuous field 

 sampling program. 



Factors influencing the accuracy of estimated 

 spawning times of fishes in this paper are intra- 

 specific and interspecific differences in develop- 

 ment rates offish embryos and temperature effects 

 on embryo stage (Table 1) duration. Intraspecific 

 differences in development rates are likely to intro- 

 duce only small and unbiased error in spawning 

 time estimates since incubation times from which 

 age estimates are made are short (<24 h) and 

 mean stages of development of all embryos of a 

 species (<24 h old) in a sample are used in the 

 embryo age calculation. Interspecific differences 

 in development rates of most species in this study 

 are also probably small ( see Results). A maximum 

 standard deviation of 2.3 h can be expected in 

 spawning time estimates due to the influence of 

 temperature on embryo stage duration because 

 most fish eggs were collected in water tempera- 

 tures above 15° C (Ferraro 1980). Surface water 

 temperatures at the time of field collection were 

 probably adequate indicators of natural incuba- 

 tion temperatures of recently spawned eggs since 

 there is little, if any, vertical thermal stratification 

 in the Peconic Bays and surface water tempera- 

 ture at a particular location generally fluctuates 

 by <1° C during a tidal cycle (Hardy 1976). 



Based on the occurrence of recently spawned 

 eggs in plankton collections at Beaufort, N.C., 

 Kuntz (1915) and Hildebrand and Cable (1930) 

 concluded that A. mitchilli spawned between 1800 

 and 2100 h ( 13-16 h after sunrise), and Hildebrand 

 and Cable (1938) concluded that Trinectes 

 maculatus spawned between 1800 and 2000 h 

 (13.5-15.5 h after sunrise). Those observations 

 coincide with the onset of spawning estimated for 

 A. mitchilli and T. maculatus in this paper. Reint- 

 jes' (1968) conclusion that B. tyrannus spawns at 

 night, Welsh and Breder's (1924) conclusion that 

 C. regalis spawns in the evening and at night, and 

 Sette's (1943) calculations showing Scomber 

 scombrus spawns throughout the day were con- 

 firmed in this research. Wicklund's (1970) obser- 

 vations on the spawning of cunner overlap but 

 have a much shorter duration than that indicated 

 for cunner in Figure 2D. Wicklund (1970) only 

 observed spawning by small (total length <125 

 mm) cunners between 1200 and 1700 h (7-12 h 

 after sunrise); he never observed larger cunners 

 spawning although they were present and de- 

 fended territories in his study area. 011a and 



Samet (1977) noted that tautog in laboratory 

 aquaria spawned almost exclusively between 1330 

 and 1600 h (7.5-10 h after sunrise). Their experi- 

 mental fish, however, had been exposed to un- 

 natural photoperiod and temperatures and 

 spawned about 2 mo earlier than tautog normally 

 spawn in nature. Recently spawned eggs in 

 plankton collections indicated that some tautog 

 spawn in the afternoon (8-10 h after sunrise) in the 

 Peconic Bays, but the bulk of tautog spawning 

 appears to take place later in the evening and at 

 night. 



A systematic division of fishes in the Peconic 

 Bays and a summary of their spawning times is 

 presented in Table 4. Only Atlantic mackerel 

 showed no indication of diel spawning periodicity, 

 and only scup spawned exclusively during day- 

 light hours. The remaining species spawned 

 primarily during the evening or at night. Nothing 

 exceptional is known about the adult habits or 

 embryos of Atlantic mackerel or scup to suggest 

 why their spawning times are different from the 

 other species. There appears to be no connection 

 between bathymetric distributions of embryos of 

 some of the species (Williams 1968) and spawning 

 time. There was no evidence of constancy in 

 spawning time above the family level. Solar 

 spawning times of most species, though, were con- 

 sistent throughout the spawning season and in 

 samples collected at different locations, indicating 

 seasonal and local differences in ecologic factors 

 (e.g., temperature, salinity, water depth, tide) had 

 no effect on daily spawning time. 



The tendency of marine teleosts with planktonic 

 eggs to spawn in the evening or at night is evident 

 in a listing (Table 5) of some species known or 

 suspected of diel spawning periodicity. There is 



Table 4. — Systematic division and summary of spawning times 

 (hours after sunrise) of fishes in the Peconic Bays, N.Y. Spawn- 

 ing is indicated by + . 



459 



