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Assessing Sustainable Fishing Yields Using Length-based Analytical Models: A Case Study with Nile Tilapia in Lake Hawassa (Ethiopia)

Alemu Y, Snoeks J, Teklegiorgis Y, Nyssen J and Brendonck L

Nile Tilapia, Oreochromis niloticus, is one of important commercial fish in Africa and other tropical regions. In Ethiopia, it accounts for more than 60% of the total annual landings. In Lake Hawassa, one of the rift valley lakes in Ethiopia, it even mounts to more than 85%. However, recently, the yield in the lake dropped to about 50% of its historical maximum, indicative of a dwindling population size resulting from overfishing. This research aimed at assessing the sustainable potential yield of tilapia in Lake Hawassa. Data were collected for one year, on a daily basis, from the commercial fishery. The growth parameters (L∞ and K), the total population (N) and the fishing mortality (F) were estimated using FiSAT II. The maximum sustainable and economic yields (MSY & MEY) and the corresponding fishing effort were determined using the length-based Thompson & Bell bio-economic model. Accordingly, the MSY was estimated at 466.3 tonnes per year. Our findings will be instrumental to prepare a fishery management plan for the lake. The procedure can also be applied to assess the fish stock of the other rift valley lakes.