The South African horse mackerel assessment using an age-structured production model, with future biomass projections

Johnston, Susan J; Butterworth, Doug S

The South African horse mackerel assessment using an age-structured production model, with future biomass projections

Working Paper

2004

Publisher

University of Cape Town

Department

Marine Resource Assessment and Management Group

Faculty

Faculty of Science

Abstract

The South African horse mackerel (Trachurus trachurus capensis) fishery began in 1950. It currently consists of a demersal/midwater trawl fleet (concentrated on the South coast) and a pelagic purse-seine fishery (concentrated on the West Coast). Adult horse mackerel are taken as a by-catch by the demersal trawl fleet and as a targeted catch by the midwater trawl fleet. Juvenile horse mackerel are taken as a by-catch by the pelagic purseseine fleet. Previous stock assessments for this fishery include a surplus production model (Punt 1989, 1992), and a Beverton-Holt yield-per-recruit approach (Butterworth and Raubenheimer 1992; Butterworth and Clarke 1996). For convenience, the rest of this paper uses “demersal” to imply both midwater and demersal operations.