The fishery: This traditional fishery along the South African West Coast is more than 100 years old. Lobsters are caught by means of metal traps deployed from deck boats, and lighter ring nets deployed from small dingies. The 2003 TAC was set at 3206 tons whole weight and is worth about US$ 250-300 million. There were 745 private and corporate quota holders in 2002, most of whom are represented by the West Coast Rock Lobster Association. The fishery is managed by a TAC, individual quotas, a closed season, closed areas, a minimum size, gear regulations and a zonal breakdown of the annual TAC.A brief review of management issues and OLRAC's involvement: In 1989 OLRAC was contracted to investigate the feasibility of using SCUBA divers to harvest rock lobsters in a remote region along the South African west coast, and to simultaneously assess the status of the stock in this area. Although the harvesting component of the SCUBA diving operation did not yield commercially viable catches, the scientific survey component and the quantitative work by OLRAC laid the foundations for future quantitative scientific advice on the management of the resource. In 1990 the industry was affected by a sudden downturn in commercial catch rates.
Catch rates rapidly became uneconomical, bait usage increased by many times its normal levels, and the percentage of discards exceeded 80% by weight in many areas. OLRAC advised the industry to investigate the possibility of discard induced mortality in the industry, pointing out that this could be leading to a loss of 2000 tons of TAC per annum.
OLRAC used a size based population model to show that the reduction in catch rate, which reached critical proportions during the first part of the 1991/92 fishing season, was due to the reduced moult increment levels first detected by government research scientists from tagged lobsters.
These scientists ascribed this to a reduction in the availability of mussels, the main food source for lobsters. However, OLRAC argued that in additional to environmental factors, some of the problems in the fishery could be due to the strict adherence to the 89 mm minimum size. This could have resulted in genetic selection for slow growth, and caused widespread injuries in the undersized lobster stock, both factors in growth rate retardation. OLRAC investigated various options for eliminating discard mortality and for weathering a period of poor growth rates. On the strength of intense field work and computer based quantitative analyses, OLRAC proposed:
- A reduction in the minimum carapace size from 89 mm to 65 mm,
- A strictly controlled TAC and large mesh netting on traps as before.
- An immediate and sharp increase in catch rate following the reduction in the minimum size
- Although moult increments in the fishery have increased only gradually since 1991, there have been large increases in catch rate over the last two fishing seasons, and the resource is showing strong signs of recovery
- The virtual elimination of discarding, discard mortality and the incidence of injured lobsters.
OLRAC's philosophy with the West Coast Rock Lobster fishery, as with other fisheries, is that fisheries management must address the trade-off between economic risk and biological risk, it must be practical, and it must allow consideration of the logistics of fishing, targeting and market requirements to influence one's interpretation of basic catch statistics.