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A study to assess the status of the large scale commercial fisheries operating in southern Lake Malawi was conducted using generalised linear modelling and Principles of Precautionary Approach. The generalised linear modelling analysis was used to standardise catch per unit of effort data from 1976 to 2009 and to determine the effects of fishing vessel characteristics such as engine size and hydro-acoustic devices on fish catch rates. The Precautionary Approach, through reference points like Bmax (reference point corresponding to period of relatively high fish catch rate), Bpa (reference point at which precautionary management action should be undertaken), Blim (limit reference point beyond which a fishery is considered seriously depleted) and Bcur (reference point corresponding to current fish catch rate), was used to assess the status of fish stocks using standardised fish catch rate which approximated fish biomass or stock size. Results of the assessment indicated that the current fish biomass level in all three categories, bottom pair trawl, stern bottom trawl and stern mid-water trawl fisheries, is well above Blim, but is 9–12% above Bpa, which is very close suggesting that the fishery is fully exploited and precautionary management measures are required. Suggested measures included introduction of fishing closed season for the large scale commercial fisheries which will be dependent on the biology of the most important target fish stocks, relocation or reduction of fishing effort in the current fishing grounds and intensification of patrols to reduce incidences of illegal, unreported and unregulated fishing activities.

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Diplotaxodon limnothrissa is a widely distributed species occurring throughout Lake Malawi from the surface to a depth of at least 220m. It is probably the most abundant cichlid in the lake, with biomass estimates of around 87 000t in the pelagic zone alone. The species is exploited commercially in the southern part of the lake but, since its inception, this fishery has never been assessed. Analysis of sectioned sagittal otoliths revealed that D. limnothrissa is a slow-growing and relatively long-lived species, attaining ages in excess of 10 years. Length-at-age was described using the von Bertalanffy growth model, with combined-sex growth described as L t = 211.21(1 -exp(-0.24(t + 1.36)))mm TL. Females matured at 139mm TL at an estimated age of 3.18 years. Total, natural and fishing mortalities were estimated at 0.63yr -1 , 0.38yr -1 and 0.25yr -1 respectively.

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