Focus Groups: Groups Focusing on Specific Issues in Stock Enhancement

Animal Fitness and Release Strategies:

    Following the "First International Symposium on Stock Enhancement and Sea Ranching", which was held in Bergen, Norway in September 1997, the International Scientific Committee for the symposium discussed the possibility of establishing two groups to focus on the following issues. The WAS Working Group on Stock Enhancement has agreed to help focus research on these issues and report on progress in both areas at the "Second International Symposium on Stock Enhancement and Sea Ranching," which is scheduled to be held in Japan in 2002.

• Fitness of reared individuals for release in the wild. The development of any particular type of behaviour is determined by both genetic and environmental factors. The selection pressure for some traits is often higher and differently directed in nature than in a laboratory tank. Reared individuals might therefore be less well adapted to life after release than their wild conspecifics, and several studies have in fact documented high mortality of stocked individuals. A critical phase in sea ranching programmes is the transition from the hatchery environment to the wild. In this period the reared individuals have to learn to capture wild prey and to avoid predators. An important question is whether the survival after release can be increased by predator training, acclimatisation, or by improvement in the hatchery. Laboratory experiments suggest this, although it has not been verified under field conditions.

• Release strategy. Survival after release will vary according to a set of factors including time and size at release, habitat, carrying capacity, species composition (prey and predators). To maximise the benefit from stock enhancement programmes, it is important to summarise the present knowledge on this field, and to write protocols that will optimise survival after release.