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

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 (lt) with the von Bertalanffy model as lt = 140.0 (1 − e−1.0t) mm TL. Age-at-50%-recruitment into the fishery (tr) 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(lt)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.