Results of a spiny lobster survey around Mahe Island during September and October 1991
Spiny lobster fishing in the Seychelles is an artisanal done essentially by skin divers operating at night in the shallow waters surrounding by the islands. Because of human population distribution lobster fishing grounds are concentrated on the inner granitic islands. In September 1992, a random stratified samoling program was set up to gather biological information from the entire granitic Mahe plateau. Direct census of fishery resources by Scuba divers swimming underwater transects was selected as the most feasible and expedient means by which to enact the Resource Survey. This report present partial result gathered for the survey around Mahe Island only and provides an estimate of the Maximum sustainable yield for the granitic plateau by extrapolation of the Mahe results. Around Mahe, three species were found in the catches, P penicillatus being the most abundant and caught mainly by skin divers between 2 and 8 meters. P. longipes and P. versicolor were more rare and often found in deeper water in the Scuba diving zone. Catch rates were much higher for skin divers than scuba divers (4.63 lobsters per man hour against 0.63 for Scuba divers) Mean carapace length of each species were respectively for males and females: (P.p.)=95.8, P.p.)=95.9; (P.1.)=86.6, (P.1.)=70.1, (P.v.) =106, and (P.v.P=78.5 mm. In total, during the two months survey, the percentage of mature females was found to be :) P.P.)=52.9, (P.1.)=55.5 and) P.v.)=25, Cephalothoracic length at first maturity for females was found to be 79.2 mm for P.penicillatus and 74.2 mm for females of P.longipes. The length-weight relationship per species for males and females respectively, were found to be :) P.p.): W=1.63*L2.66, (P.p.): W=2.25*L2.25. (P.1.): W=2.03*L2.64, (P.1.): W=1.45*L2.81; (P.v.): W=-0.688*L2.96, (P.v.): W=-0.715*L3.3 (W=gr, L=cm). The minimal size at first capture for P.penicillatus should be increased from 75mm to 80mm of cephalothoraicc length. Maximum sustainable yield (MSY) for Mahe Island was found to be 1.17 tonnes/year, and simple extrapolation of the Mahe data to the entire granitic plateau gives a MSY of 3.5 tonnes. This MSY is probably an underestimate based on standing stock rather than virgin biomass. Another estimate of the virgin biomass was done utilizing the maximum biomass found in a station for each biotype. This approach lead to an MSY in the Mahe waters off 4.7 tonnes, while for the whole plateau it gives a MSY of 15.5 tonnes. The fact that only 33.9_310= of the lobsters caught in the Mahe waters could be retained by a fishery, obliges one to adopt the conservative approach.
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| Format: | Report biblioteca |
| Language: | English |
| Published: |
Seychelles Fishing Authority
1992
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| Subjects: | Panulirus, Fishery surveys, Fishery biology, Population characteristics, |
| Online Access: | http://hdl.handle.net/1834/5118 |
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