MEPS 325:187-194 (2006)  -  doi:10.3354/meps325187

ABSTRACT: The dusky grouper Epinephelus marginatus pair spawns in summer in the NW Mediterranean. Only a few spawning sites have been identified, mostly in marine reserves. Because the dusky grouper is vulnerable to fishing, there is a need to identify and predict the occurrence of spawning for conservation purposes. To gain insight into the temporal patterns of dusky grouper spawning, we monitored a reproductive population in the Medes Islands Marine Reserve, Catalonia, from 1996 to 1999. We observed 44 successful spawning events. At a monthly scale, the highest reproductive activity occurred in August, when surface temperatures were at a maximum (monthly average of 24 to 25°C), and during days with 14 daylight hours, 2 mo after the summer solstice (21 to 22 June). At a daily scale, the greatest number of spawns occurred when the surface temperature was highest (25 to 26°C) and the temperature at 20 m was 17 to 19°C, during anticyclonic conditions, and when tidal amplitude and wave height were largest. Spawning occurred during all moon phases, although it was more frequent during the new moon and the first quarter. Reproductive males did not show sustained spawning activity during consecutive days and had an average spawning rate of 1.5 spawns d^–1. All spawning occurred at dusk, between 1 h before and 30 min after sunset. There was no population-wide synchronicity of spawning, since we never observed all monitored males spawning within the same day. These results should allow researchers to predict the temporal occurrence of dusky grouper spawning elsewhere in the Mediterranean.

KEY WORDS: Epinephelus marginatus · Spawning · Reproductive patterns · Environmental factors · Marine reserves