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.