Abstract

The exploitation of Nassau grouper spawning aggregations by fishermen over the last fifty years has caused many aggregations to disappear, and has been the primary cause of the dramatic decline of Nassau stocks Caribbean-wide. In the USVI, the major Nassau grouper aggregation site was fished to extinction the 1970’s, and although now federally protected, shows no sign of recovery. Five kilometers to the east however, Nassau grouper have been found aggregating to spawn on the Grammanik Bank, a reef traditionally fished for yellowfin grouper (Mycteroperca venenosa) during their spawning season. Although illegal to harvest, Nassau were caught as by-catch and poached from the site by fishermen fishing for yellowfin. In 2005, the Caribbean Fisheries Management Council closed the bank to all bottom fishing from February 1 to April 30 annually and to fish traps year-round. Since then we have documented increased numbers of Nassau grouper on the Grammanik Bank, as well as a greater mean size, greater maximum size, and smaller minimum size. Hydro-acoustic and external tag data indicate that the fish are coming from the west and north. The Nassau grouper are spatially and temporally mixed with yellowfin grouper during courtship, and we believe this behavior may be an artifact of decreased numbers of Nassau, now using the yellowfin as surrogate aggregation members. It is doubtful that any other large Nassau grouper spawning aggregation sites remain in the USVI, so the effectiveness of the Grammanik Bank fishing closure may play an important role in the recovery of local stocks.

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