West Africa: SENEGAL

First reported grouper spawning aggregation in Senegal

The information in this article was provided to the author by Cyril Calendini, a charter boat captain and fisherman in Dakar, Senegal. It is based largely on personal interviews of divers and fishermen who participated in the harvesting of groupers at the reported aggregation site.

A putative spawning aggregation of groupers was discovered by divers off the coast of Senegal in April 2008, several days after the full moon. Fishermen had observed the migration of several species of grouper southwards along the coast to this site. They saw groupers in water as shallow as 3 m and large numbers on the bottom in deeper water. Although there were no estimates of the numbers of groupers present at the possible aggregation site, it was described by divers as being like a “carpet of fish” covering the bottom. The groupers could apparently be approached by divers and pushed by hand with little reaction.

There were three different species of grouper identified at the site: dusky grouper (Epinephelus marginatus), white grouper (E. aeneus) and mottled grouper (Mycteroperca rubra). The divers estimated that dusky groupers were the most abundant and white groupers were abundant. The depth at the site was approximately 28 m and the water on the bottom was clear and cold (temp.16° C), apparently below a thermocline.; water visibility above the thermocline was poor. The estimated size of the area where the groupers were aggregated was approximately 400 m long and 100 m wide. On the day that the divers discovered the aggregation, they speared a number of groupers at the site and noted that the aggregated fish did not move away. The following day, more boats went to the site and many more groupers were shot. Fishing effort reportedly escalated dramatically at the aggregation site over just a few days. It was estimated that spearfishermen killed over 1,200 fish in 5 days. It is believed that all of the fish speared were dusky grouper. A conservative estimate of the number of spearfishermen diving at the site was 150. The groupers apparently remained in the same area for this entire period. During this same period, the market price for grouper dropped dramatically as the market became flooded over a few days.

Estimates of the numbers of white and mottled groupers taken were not available. The mottled grouper apparently migrated after the other two species had arrived at the site. Mottled grouper were taken mostly by handlining with live bait rather than by spearfishing. A traditional “panga fishing” boat reportedly caught 300 mottled grouper in one day and there may have been up to 100 boats fishing at the peak of this aggregation. Although landings figures are not available, a simple extrapolation from the above information leads to the conclusion that the potential impact of uncontrolled fishing could quickly decimate the numbers at this site with unknown but, certainly deleterious, longer term impacts.

Brian E. Luckhurst, fishery officer, retired. Umbria, Italy.
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Note from Editor: on the 2008 IUCN Red List E. aeneus is considered Near Threatened (http://www.iucnredlist.org/details/132722) and E. marginatus Endangered (http://www.iucnredlist.org/details/7859), in both cases due to overfishing.