The potential use of predictions of recruitment success in the management of the South African anchovy resource

Abstract

In the existing management procedure for the South African anchovy Engraulis capensis resource, an initial Total Allowable Catch (TAC) is set at the start of the fishing season in January, before the year's recruitment of 0-year-old fish, an important component of the catch, is known. Recruitment is therefore assumed to be equal to the observed median. This TAC may be revised in May or June, after the actual recruitment has been estimated. This procedure incorporates a risk that, if recruitment is below the median, the stock could be adversely depleted before the mid-year recruitment survey. A simulation approach is used in this paper to assess the possible benefits, in terms of average annual catch and interannual fluctuations in catch, of three different methods of predicting recruitment earlier in the season, if such methods were available. The results show that the average annual catch could be increased theoretically by up to 48 per cent if a very precise prediction (CV = 0,1) could be made at the start of the fishing season. In practice, more modest improvements of 21 per cent by prerecruit surveys undertaken in March each year, or 16 per cent by means of a two-class ordinal prediction with 70 per cent success, may be attainable. However, these improvements would result in increased interannual fluctuations in catch, a situation which may be detrimental to the fishing industry.