HORSE MACKEREL ON THE AGULHAS-BANK - SUMMARY OF CURRENT KNOWLEDGE

Horse mackerel are ubiquitous in South African waters and even occur i n river estuaries. On the south coast, average size increases offshore and eastwards. Distribution patterns reflect trends in availability p roduced by migrational habits. The pear quality of the long-term data series for horse mackerel hinders stock assessment for this resource. Although catch and catch rare (CPUE) data are available for each of th e fleets involved in the fishery, each of the CPUE series has specific biases and none of them can be used as a reliable index of abundance. A surplus-production model was developed to allow for multiple CPUE s eries.(1,2) This model was used in the past with reservations because the data series were poor. Preliminary results from an acoustic survey of part of the stock indicate that the production model may have unde restimated the size of the resource. Consequently, it is felt that the Sea Fisheries Research Institute is not yet in a position to supply s cientifically defensible management advice for the horse mackerel reso urce. All South African horse mackerel south of the Orange River are c onsidered as one stock, although otolith dimensions and maturation pat terns differ between west- and south-coast specimens. Published growth constants (K) and 50%-maturation lengths vary considerably, ranging f rom 0.325 yr(-1) to 0.556 yr(-1) and from 32 to 43 cm TL, respectively . Two major spawning periods are identified, one lasting from May to A ugust and the other from October to January. Spawning does not seem fo be confined to specific areas. The diet consists mainly of planktonic crustacea, but horse mackerel are not specialist feeders. Retention l engths are available for horse mackerel but the results are largely ma sked by biases inherent in the methods used. Perspectives are given fo r future research directions.