Relationship between survey indices of recruitment and VPA abundance estimates for North-East Arctic cod

Precision and relevance of pre-recruit studies for fishery management related to fish stocks in the Barents Sea and adjacent waters. Proceeding of the sixth IMR-PINRO Symposium Bergen, 14-17 June 1994Survey estimates of abundance of recruiting and partially recruited age groups are important elements for tuning the VPA of north-east Arctic cod, both for estimating the present state of the stock and for future exploitation. The reliability of the assessment and prognosis is therefore dependent on the validity of the survey indices. In this paper, year-class abundances based on surveys are compared to estimated year-class abundances from a VPA. I The variability of the survey estimates, both within and between year-classes, is discussed in I relation to observed changes in cod density and vertical distribution. It appeared that the catch- I ability of recruiting age groups is density dependent. Specifically, catchability increases with 1 increasing stock abundance. Furthermore, cod appear to be distributed more pelagically at high I densities as compared with at low densities. The increase in catchability with density is found to override the expected negative effect on catchability of low availability at high density. As a consequence, a positive relation between catchability and reduced availability was found. Alternatives to a simple linear relation between survey and VPA abundance estimates are proposed