Precision in recruitment estimates and its implications on management of demersal fish stocks

Abstract

Errors in abundance indices of recruiting year-classes will affect stock predictions. The contribution of recruiting year-classes to the predictions of catch and spawning stock biomass for the stocks of Northeast Arctic cod, haddock and saithe is investigated. The effect various levels of error in the recruitment indices would have had on the predictions during the last two decades is calculated. The error in the index has frequently gone in the same direction for consecutive year-classes and errors of less than 30% have been relatively rare. Longer time series and new methodology will probably reduce the errors in the future, but substantial errors in the stock predictions must therefore be anticipated, even in the short term. Management aimed at moderate exploitation and stability can minimize the problem and the use of risk-analyses is desirable. Medium-term predictions rely to a large extent on assumptions of average recruitment and must be used with great caution.