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Published:
Apr 14, 2004Keywords:
Portunid crabs production species diversity habitat preference
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The Fishery of Portunus pelagicus and Species Diversity of Portunid Crabs along the Coast of Dar es Salaam, Tanzania
Abstract
Keywords: Portunid crabs, production, species diversity, habitat preference
Production, habitat preference and distribution of the blue swimming crab, Portunus pelagicus and the diversity of portunid crabs were studied along the Dar es Salaam coastline, Tanzania. Samples were obtained from beach seine nettings and basket traps. The samples from basket traps were used in habitat preference studies only. The production of Portunus pelagicus was assessed in terms of catch rate and biomass, and the biomass and contribution of recruits to the stock estimated using the Leslie method. Seasonal variations in catch rate were found, with peaks between December and May. The highest catch rate was recorded at Msasani Bay (2.24 kg/haul/100-m net), and the lowest at Mzinga Creek (1.08 kg/haul/100-m net). The harvestable biomass for Dar es Salaam coast on average was 34.5 tonnes/year, while the contribution of recruitment to the biomass was about 20.2 tonnes/year. Portunus pelagicus was the most abundant portunid in all the sites, comprising between 39.1 and 81.5% of the catches at Mzinga Creek and Kunduchi respectively. Charybdis anisodon, Scylla serrata and Portunus sanguinolentus were also found in various proportions at the sites. Generally there was a significant difference in species diversity between sites, with P. pelagicus showing a high preference for the sub-littoral shallow waters. For rational exploitation of this crab, management measures based on the estimated harvestable biomass and the size at first maturity are recommended.
Western Indian Ocean Journal of Marine Science Vol.2(1) 2003: 75-84
Production, habitat preference and distribution of the blue swimming crab, Portunus pelagicus and the diversity of portunid crabs were studied along the Dar es Salaam coastline, Tanzania. Samples were obtained from beach seine nettings and basket traps. The samples from basket traps were used in habitat preference studies only. The production of Portunus pelagicus was assessed in terms of catch rate and biomass, and the biomass and contribution of recruits to the stock estimated using the Leslie method. Seasonal variations in catch rate were found, with peaks between December and May. The highest catch rate was recorded at Msasani Bay (2.24 kg/haul/100-m net), and the lowest at Mzinga Creek (1.08 kg/haul/100-m net). The harvestable biomass for Dar es Salaam coast on average was 34.5 tonnes/year, while the contribution of recruitment to the biomass was about 20.2 tonnes/year. Portunus pelagicus was the most abundant portunid in all the sites, comprising between 39.1 and 81.5% of the catches at Mzinga Creek and Kunduchi respectively. Charybdis anisodon, Scylla serrata and Portunus sanguinolentus were also found in various proportions at the sites. Generally there was a significant difference in species diversity between sites, with P. pelagicus showing a high preference for the sub-littoral shallow waters. For rational exploitation of this crab, management measures based on the estimated harvestable biomass and the size at first maturity are recommended.
Western Indian Ocean Journal of Marine Science Vol.2(1) 2003: 75-84
