The biology and distribution of the monkfish Lophius vomerinus off South Africa

Abstract

The monkfish Lophius vomerinus is economically the most important bycatch species in the South African demersal hake fishery. To assist in the development of a bycatch management plan for the species, age and growth characteristics, reproductive and feeding biology, and distribution patterns were investigated. Age was estimated from sectioned illicia and growth parameters were modelled using the Schnute and von Bertalanffy growth models. The error sum of squares was similar between the two models, so the latter was used to model growth. The oldest recorded fish were 17 years and 16 years for males and females respectively on the West Coast and 17 years for sexes combined on the South Coast. Growth differed significantly between West Coast males and females. Length-at-maturity ogives indicate that L₅₀ for males and females was 376mm TL (total length) and 369mm TL respectively, corresponding to ages of approximately six years for each. Gonadosomatic indices for females suggested that spawning occurs in September. L. vomerinus is highly piscivorous, feeding mainly on demersal teleosts. Prey size increases with increase in predator length. Distribution data indicate that L. vomerinus move into deeper water as they grow, and that on the South Coast, this offshore movement is accompanied by eastward migration.