Towards sustainable exploitation of Nile perch consequential to regulated fisheries in Lake Victoria
Keywords:
Stock assessment, Fisheries independent and dependent data, fishing effort and co-managementAbstract
Understanding fluctuations in the abundance and distribution of fishery resources over space and time is fundamental in order to address concerns about their sustainability and the basis for their management. Stock assessment studies were conducted on Lake Victoria from 1997 to 2001, with the aim to assess the status of the stocks, in particular of Nile perch. This paper summarises the findings for the Tanzanian part of the lake and makes reference to the Kenyan and Ugandan national waters for comparison. Both fisheries independent data from bottom trawl surveys and fisheries dependent data from catch assessment and frame surveys were used. Current exploitation levels and practices are analysed and linked to growth, mortality and reproductive characteristics of the stock. Abundance estimates and distribution patterns are discussed in relation to the exploitation levels, and key threats to the sustainability of the resources highlighted. Options are provided for a sustainable management of the Nile perch fishery.
The 2000 frame survey revealed an intensive fishing effort. In addition, the Nile perch fishery was found to depend largely on juvenile fish. The size at first maturity was at 54.3 cm TL (1.6 yr) and 76.7 cm TL (2.5 yr), for males and females, respectively. Over 80% of the commercial catch was below the size at first maturity for males and 99% below that for females. Bottom trawl data (88% juveniles) suggest good recruitment to the stock, but yield per recruit modelling indicates unsustainable exploitation tendencies. The current annual yield (estimated at 138 324 ± 6 229 t) is well above the estimated sustainable level (109 000 t). It is recommended to reduce the exploitation rate by 50% and to increase the size at first capture. Co-management is considered to be the most effective option to implement monitoring, control and surveillance strategies.
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