Report on the regional training course on fish stock assessment
Chambo is a species complex consisting of three tilapine cichlids (Oreochromis lidole, O. quamipinnis, O. karongae) endemic to Lake Malawi. Taxonomic identification is problematic at the young stages of the fishes. Chambo constitute the basis of an important commercial and artisanal fishery. Length frequency data were collected three times per month from a commercial midwater trawl. The von Bertalanffy growth parameters obtained by the Bhattacharya method and Gulland and Holt plot are cons idered not valid according to the authors knowledge of the species biology and fishery. Then a set of growth and natural mortality parameters was forced to proceed into the analysis. Catch curve method was applied to achieve an estimate of the total mortality. Virtual population analysis (Jones' length cohort analysis)- shows that only the large size fish are exposed to the fishing mortality. It was also stressed that there is need for more representative samples to get more meaningful res ults. Experimental bottom trawl-survey was carried out between 1981-1986 in the Ugandan side of Lake Victoria. Daily commercial catches from various fish landings were available. The individual length and weight data set used in the analysis was from Jana-Nsadzi area of the lake. Data have been collected in June, September, November and December 1981. Batthacharya method and Gulland and Holt plot were used to estimate the growth parameters. The catch curve analysis supplied the total morta lity value. Jones' length cohort analysis was applied to obtain the exploitation pattern. Finally long term prediction was carried out using the Thompson and Bell model. The total yield and the calculated Maximum Sustainable Yield (MSY) for the Ugandan side of the lake seem to suggest the overexploitation of Synodontis victoriae. This scenario is considered unrealistic.
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| Format: | Project biblioteca |
| Language: | English |
| Published: |
1991
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| Online Access: | https://openknowledge.fao.org/handle/20.500.14283/AM842E http://www.fao.org/3/a-am842e.pdf |
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