Abstract

Most large groupers (Serranidae) form annual spawning aggregations (FSA) at predictable times and locations, which makes them extremely vulnerable to over-fishing. Seasonal or permanent fishery area closures can provide effective protection, but defining biologically relevant boundaries is difficult due to limited knowledge of the area occupied or the movement and migration patterns associated with spawning. The aim of this study was to determine the spatial and temporal pattern of movement and migration associated with spawning aggregations of Nassau (Epinephelus striatus) and yellowfin (Mycteroperca venenosa) grouper within the Grammanik Bank, a small (1.5 km2) seasonal closure on the southern shelf edge of the US Virgin Islands. Five male and 5 female groupers of each species were acoustically tagged and released on the aggregation site. An array of acoustic receivers was strategically placed in an overlapping curtain around the FSA. Data indicate that both species commonly moved 1 to 3 km in a few hours and could cover 20 km in a 24 hr period. Movements of tagged groupers at the spawning site carried them outside the existing closure boundaries and exposed them to fishing mortality on a daily basis. Moreover, we identified migratory pathways of both species which linked the Grammanik Bank closure and another large marine protected area (MCD) 3 km west. These results indicate that the existing Grammanik Bank boundaries are too small and should be increased to at least 10 km2 and include primary migration pathways.

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