Species Composition of Fisheries Resources of the Tana and Sabaki Estuaries in the Malindi-Ungwana Bay, Kenya

Abstract

For over 30 decades, the Sabaki and Tana estuaries of the Malindi-Ungwana Bay, Kenya have supported both the artisanal fishery and semi-industrial bottom trawl sectors. Currently these estuaries in the bay support over 3 000 artisanal fishers and a maximum acceptable fleet of four medium-sized trawlers. These sectors have exerted pressure on the fisheries resources of the bay and will continue to do so due to the increasing artisanal fishing effort. We describe the present status of the fisheries resources of the estuaries in the bay following shore-based catch assessments between 2009 and 2011, and shallow-water bottom trawl surveys in early 2011. These aimed to determine species composition, relative abundance and distribution patterns of the penaeid shrimps and associated trawl fish bycatches, and fish catches from the artisanal fishers. Five shrimp species: Fenneropenaeus indicus, Penaeus monodon, Metapenaeus monoceros, Penaeus semisulcatus and Penaeus japonicus were recorded. Distinct shrimp species composition existed between the two estuaries characterised by more abundant F. indicus in the Tana estuary, and more abundant P. semisulcatus in the Sabaki estuary. Bottom trawl fish bycatch species diversity was higher than for artisanal fish catches with a total of 223 and 177 species respectively. Shrimp total biomass and catch rates were significantly higher during the wet Southeast Monsoon (SEM) season than the dry Northeast Monsoon (NEM) season, and decreased as depth increased. On the other hand, trawl bycatch rates were significantly higher in inshore than offshore areas and distinct in composition but less differing between the seasons. Similarity in catch composition was evident between the artisanal catches and bottom trawl bycatches in the inshore areas. This similarity was attributed mainly to seven common and most abundant fish species targeted in artisanal fishery as well as these species made the highest bycatch proportion in the shrimp bottom trawls. Significantly smaller-sized individuals of these seven species occurred in trawl bycatches than in artisanal catches attributed to differences in gear selectivity. Implementation of the present shrimp fishery management plan, and continued monitoring of fish trawl bycatches will be crucial for the effective management of fisheries resources of the estuaries in the bay.