Abstract

The Nassau grouper spawning aggregation off the west end of Little Cayman, Cayman Islands was monitored for five consecutive years (2002-2006). An aggregation of approximately 2,000 Nassau grouper (Epinephelus striatus) appears to be stable over the last three years of the study period. Over five years, times of peak numbers of Nassau groupers ranged from one to five days after the full moon (January or February). Nearly 300 spawning bursts were recorded over the study period. On average, spawning bursts were recorded 21 minutes before sunset to 11 minutes after sunset, but were observed as early as an hour before sunset to 20 minutes after sunset. The timing and number of spawning bursts were variable each year. All spawning bursts were observed in the months of January or February. Spawning periods ranged from three to six days in duration and ranged in moon phase from one day after the full moon to eight days after the full moon. The month for the major spawning event appeared to be influenced by the date of January’s full moon. Late January full moons (occurring 30 days or more after the winter solstice) resulted in major spawning events in January. Conversely, early January full moons resulted in major spawning events in February. Currents were slack or negligible during nights of spawning. Over a period of 24-48 hours and during sunset dives, prior to the first spawning night, the percentage of Nassau groupers in the bicolor phase increased to 80%, at which time spawning occurred. This shift in color phase may be used to predict when spawning will occur. The formation and the physical location of the Nassau grouper aggregation had low variability throughout the monitoring period. Aberrant colorations of individual Nassau groupers were observed at the study site. Subsequent sightings both on and off the spawning site suggests permanent anomalous pigmentation that was useful for tracking inter-year survivorship. Twenty-one other fish species displaying spawning coloration or behavior were recorded at the site

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