Reproduction of the Nassau grouper, Epinephelus striatus (Pisces: Serranidae) and its relationship to environmental conditions

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Spawning aggregations of the Nassau grouper, Epinephelus striatus, occurring at the southern end of Long Island were investigated during the winters of 1987–1988 and 1988–1989. Fish aggregate at two specific sites around the time of the full moon in December and January, possibly not during November and almost certainly not during February. At one site the fish aggregate well inside the shelf edge while at the other they are on the dropoff into deep water. Fish migrate, probably as distinct groups of up to about 500 individuals, to the sites on or before the full moon and remain for several days. There was no significant difference in the size of males and females caught from the aggregations between years or months. Female/male sex ratio was between 5 : 1 and 3 : 1. Courtship occurred in late afternoon with spawning commencing shortly before sunset. Most spawning occurred within 10 min of sunset. Water temperatures were 25.0–25.5°C during a period of gradual decrease towards the annual minimum in February and March. Two color patterns were important in courtship and spawning. The ‘bicolor’ pattern is a submissive coloration indicating a non-aggressive state acquired by both males and females near the time of spawning. The ‘dark’ phase is acquired by females who are followed by numerous bicolor fish during courtship and they lead spawning events in this pattern. Spawning occurred among subgroups of the aggregation numbering 3–25 fish; gamete release was well above the bottom. Drogues deployed with the gametes either moved inshore or did not move far away from the shelf edge over the course of several days. Nassau groupers may not strictly be protogynous hermaphrodites and other groupers which form spawning aggregations may not be so either. Latitudinal shifts in spawning time may be related to water temperatures. Currents at aggregation sites do not appear to favor offshore transport of eggs. Questions of whether spawning aggregations should be protected need to be answered.