Long-term trends in catch and effort of commercial linefish off South Africa's Cape Province: Snapshots of the 20(th) century

The Cape commercial linefishery, established during the first half of the 1 9(th) century, currently consists of about 2 500 vessels (+/- 20 000 crew), which land some 15 500 tons of fish each year. In spite of a long history, a lack of a long-term catch and effort data series has severely hindered t he management of the fishery. This paper provides commercial catch and effo rt data for three periods during the 20(th) century: 1897-1906, 1927-1931 a nd 1986-1998. Trends in catch per unit effort (cpue) were verified with add itional data from the inshore trawl-fishery, from fishery-independent surve ys and, where possible, stock assessment. According to a Linefish Managemen t Protocol developed for the linefishery, any stock demonstrating a histori cal reduction in cpue or catch contribution of more than 75% is to be regar ded as overexploited. Evaluations based on present datasets support this ar bitrarily determined reference point for cpue. but reveal that catch compos ition is a poor indicator of stock status and should be used with caution. In spire of technological advances such as the advent of combustion engines , nylon lines, echo-sounders, electronic navigational aids, onboard freezer facilities and larger vessels, declines in catch rare indicative of severe overexploitation (i.e. 75-99%) were observed for many important linefish s pecies during the 20th century. Most of these were higher-trophic-level spe cies from the warm/temperate East Coast. several of which are also endemic. Life-history characteristics of the vulnerable species (i.e those demonstr ating declines in cpue of > 75%) include predictable location in time and s pace (either coastal migrant or resident), longevity (> 15 years) and late maturity (relative to maximum age). Apart frorreduced productivity associat ed with stock depletion, other setbacks, such as ecosystem alteration, loss of genetic diversity and shortterm commercial extinction, are also anticip ated. In order to rebuild depleted linefish stocks it is deemed essential t o create additional marine reserves, dramatically improve enforcement, deve lop extensive public awareness programmes and substantially reduce commerci al effort.