Publication Abstract

Improvements in the management of Bay of Biscay anchovy by incorporating environmental indices as recruitment predictors

J.A.A. de Oliveira, A. Uriarte and B.A. Roel

A short-lived species such as anchovy is particularly difficult to manage in the context of the ICES advisory system because the population and the fishery in the prediction year depend largely on incoming recruitment. In the absence of pre-recruit surveys, environmental indices can be used as predictors of recruitment and to provide management advice. Environment/recruitment relationships (ERR) have been established for the Bay of Biscay anchovy population, but their performance is still being tested. The purpose of this paper is to investigate under what circumstances incorporating environmental indices would lead to improvements in managing this anchovy stock in terms of reducing the risk of falling below B_lim and increasing yields. The assessment is made by stochastic simulation of the anchovy population and its management. Management actions resulting from advice based on geometric mean recruitment or on precautionarily low levels of recruitment are compared with those resulting from recruitment forecasts based on precise levels of use and knowledge of real environment/recruitment relationships. The uses considered were direct use (R estimated from the ERR) or indirect (expected R as a trigger of a precautionary approach). Linear models for ERR with a coefficient of determination (r²) of 0, 0.25, 0.5 and 1 are considered in the simulations for cases when such relationships are known perfectly or when the parameters are estimated and selected with measurement error. Results illustrate circumstances when the use of environmental indices to predict recruitment result in an improvement in TAC advice under the Precautionary Approach.

Reference:

J.A.A. de Oliveira, A. Uriarte and B.A. Roel, 2003. Improvements in the management of Bay of Biscay anchovy by incorporating environmental indices as recruitment predictors. ICES CM 2003/Y: 18. 13pp. ICES Copenhagen.