SURVEYS AS A RESEARCH TOOL FOR MANAGING DYNAMIC STOCKS

It is often assumed that assessments based on commercial catch and eff ort data, such as a virtual population analysis, will track trends in abundance more accurately than assessments produced by research survey s. Catch and effort data from a fishery provide information on the fis h that were caught. For many fisheries, assessments based on catch dat a, even those incorporating survey data, are quite variable and may gi ve a misleading picture of the health of the entire stock. Though abun dance estimates generated by marine surveys are also variable, they of ten appear to track abundance trends more accurately than techniques t hat use catch data. Some statistical methods for analyzing survey data are briefly reviewed and comparative case studies of the assessments of the Newfoundland northern cod stock, the Namibian hake stocks, and Barents Sea cod and haddock are presented. Given the uncertainties inh erent in a catch based assessment, it is concluded that surveys should be used to generate an assessment independent of catch statistics as a check of the catch based estimates. (C) 1998 Elsevier Science B.V. A ll rights reserved.