The control of mesh sizes in fishing gears and the introduction of other selective devices (for example, grids) is a widely used management technique for reducing levels of discarding, by allowing the smallest fish to escape the net before being landed on deck. This strategy assumes that these escaping fish survive the experience unharmed. If they do not survive, there is no justification for mesh size regulations.
Do Fish Survive After They Have Escaped?
Marine Scotland scientists have been developing methods to measure the levels of survival and since 1988, and have contributed greatly to the development of techniques for investigating this interesting subject.
Much of this work has focused on the key Scottish species: the gadoids, haddock, whiting, cod and nephrops.
Improving our Understanding
Work continues to improve our understanding of this difficult problem and in the development of improved techniques. Recently a theoretical study has shown that just a small escape mortality (approximately 25%) could undermine the potential benefits to the target fish stock of an increase in mesh size. This demonstrates the importance of measuring and accounting for this potential mortality in fisheries management. To this end, Marine Scotland Science is currently participating in an international project to investigate escape mortality of haddock, whiting and cod.
Watch a film about codend design and the escape of juvenile fish