Escapement of fish during bottom trawl sampling — implications for resource assessment

In recent years studies of escapement of groundfish species such as cod, haddock and flatfish underneath the net of survey trawls have indicated common problems in Norwegian and Canadian surveys. In this paper we compare Norwegian and Canadian data on size-dependent escapement of cod and long rough dab, species common to both areas of investigation. Although survey trawls and experimental designs differ between the two countries, the similarities in the results are striking. Trawl net efficiency estimates showed that bobbin-rigged trawls used by both countries contribute significantly to escapement, resulting in considerable variability in estimates of pre-recruits. This variability is discussed in terms of its implications for resource assessments.