Changes in the biomass of chambo in the southeast arm of Lake Malawi: A stock assessment of Oreochromis spp

摘要

Lake Malawi has one of the most diverse fish faunas in the world (500-650 species) and is a major source of protein for the people of Malawi. Chambo {Oreochromis spp.) is one of the most important food fishes; its abundance has declined sharply over the last twenty-years. Surveys by the Malawi Department of Fisheries have shown a decrease in chambo density in the southeast arm of the lake and the annual harvest has dropped substantially since 1985. We conducted a dynamic stock assessment of Oreochromis spp. which included all vessel and gear types and covered the entire southeast arm of Lake Malawi. Chambo biomass peaked in 1982 and then declined continuously through the early 2000s. The biomass is highly correlated with the mean lake height two years prior suggesting that recruitment may be linked to increased nutrient input, and spawning and nursery habitat associated with the flooding of low lying areas. The main driver of chambo biomass, however, was fishing pressure which was above the level that would achieve maximum sustainable yield during the entire time series. This study provides a baseline from which to measure changes due to future management actions or climate variations.