The South African hake fishery (M. paradoxus and M.
capensis)
The fishery: The South African hake fishery
comprises capital intensive fishery and processing sectors. Turnover is between
US$ 250 million and US$ 300 million, on an annual TAC for both hake species of
166,000 tons (2002). Bycatch makes a significant impact to the value of the
industry. Quota holders are represented by the Deep Sea Trawling Industry
Association. The main management measures for the resource are a TAC, individual
quotas and gear regulations.
A brief review of management issues
and OLRAC's involvement: OLRAC has been involved in the scientific
management of the South African hake fishery since 1991. There are two pressing
scientific issues in the management of the resource. The first is the attempt
being made to introduce long lining as an important component of this trawl
fishery on the grounds that it is less capital intensive and biologically more
productive. It may therefore offer a defensive means of redistributing quota,
for which there is considerable political pressure.
OLRAC conducted a
quantitative evaluation of the relative biological merits of trawling and
long-lining, and concluded that:
- Sexual dimorphism in hake life history strategy has implications for yield-per-recruit calculations used for comparing the biological productivity of trawling versus long lining. Long liners catch an extremely high proportion of females which is only half of the stock; hence the biological productivity of long lining is not necessarily greater than trawling.
- Although in certain scenarios the biological productivity of long lining is larger than trawling, this is only true at high levels of long lining effort. Long term catch rates at this level of effort may not be economically viable.
- There is a very strong fishing down effect in a long line fishery. Long term catch rates are predicted to be in the order of one sixth of the initial catch rate. The only way to maintain catch rate will be to fish increasingly smaller hake.
A second and probably more important issue in the management of the fishery is a new interpretation of the commercial catch rate database produced by government scientists using a General Linear Modeling approach. These scientists recently produced a version of the GLM suggesting that the hake resource biomass has declined over the last 15 years. This is a complete turnaround from previous interpretations of the same data which showed an increase in resource abundance.
OLRAC has carried out a critical and wide ranging evaluation of the use of the GLM method. The results show that variable targeting for bycatch species in the hake fishery has impacted on hake catch rate in a complex way which GLM theory may be unable to address in a straightforward manner. In addition, it has emerged that separate GLM analyses for small, medium and large hake size classes produces sharply conflicting results. The only way of explaining this is to consider the possibility that the effective codend mesh size in the fishery has changed over the years. OLRAC's research shows that an increase in the minimum legal codend mesh size in 1976 reduced catch rates below the economic breakeven threshold. This destabilised the industry which was then faced with either going out of business (one company did), or getting around the mesh size regulations by the use of small mesh liners in codends and by exploiting weaknesses in mesh size regulations to make it possible to fish illegally with small mesh codends. Important implications for an interpretation of commercial catch rate data follows from this work. The results of OLRAC's research is being submitted at joint government-fishing industry meetings specially set-up to consider input by OLRAC. OLRAC's written submissions have therefore opened up the scientific debate, and scientists are modifying some of their earlier negative positions on the resource.
