Management recommendations for Copadichromis chrysonotus (Pisces: Cichlidae) in Lake Malombe, Malawi, based on per-recruit analysis

Abstract

Abstract In Malawi, Lake Malombe supports a large fishery that harvests ca. 4500 tonnes per annum. One important small cichlid species, Copadichromis chrysonotus , contributes 500 tonnes to this catch. This paper presents the first assessment of the C. chrysonotus resource using per-recruit analysis. Age-based growth, mortality and sexual maturity parameters necessary for the pre-recruit models are estimated. Length–frequency analysis described length-at-age ( l t ) with the von Bertalanffy model as l t = 140.0 (1 − e −1.0 t ) mm TL. Age-at-50%-recruitment into the fishery ( t r ) was estimated at 0.57 years. The instantaneous rate of total annual mortality ( Z ) was estimated as 2.67 year −1 , natural mortality ( M ) at 1.31 year −1 and fishing mortality ( F ) at 1.36 year −1 . The weight-at-age W ( t ), for C. chrysonotus was estimated as W ( t ) = 0.000083( l t ) 2.58 . Length and age-at-50% maturity was estimated at 72 mm TL and 0.73 years, respectively. It is shown that the C. chrysonotus resource is over-utilised with spawner biomass-per-recruit at 29% of pristine levels. Effort reductions are recommended such that fishing mortality is reduced by 20–50 % to rebuild spawner biomass to acceptable levels. Per-recruit analysis as a suitable stock assessment tool for data-limited African fisheries is discussed.