Comparison of the effects of different linefishing methods on catch composition and capture mortality of South African temperate reef fish

Abstract

The effects of hook size, bait type, water depth and fishing effort on the selectivity and capture mortality of reef fish were investigated in a standardised fishing experiment on the temperate south coast of South Africa. A total of 2 406 fish was caught at 273 stations, distributed according to a random-stratified design. Generalised linear models separated the influences of environmental factors such as depth, temperature and season from the effects of fishing methods on catch rates and capture mortality. Dominant reef predators
and larger individuals within species were more frequently caught on large hooks and sardine Sardinops sagax bait. The main cause for capture mortality was gut-hooking, aggravated by increased capture depth. Large roman Chrysoblephus laticeps were more frequently gut-hooked than small individuals. More roman were caught early in the fishing session and the average size of captured roman increased slightly during fishing sessions. The selection of legal-sized target fish can be increased by about 23% and immediate capture mortality of undersized fish can be reduced by 50% by using large hooks and sardine bait and by fishing for less than one angler-hour per station in water shallower than 20m. The results are useful for planning fisheries independent catch per unit effort surveys and for developing rules for catch-and-release competitions.

African Journal of Marine Science 2007, 29(2): 177–185