The future of stock enhancements: lessons for hatchery practice from conservation biology

The world's fish species are under threat from habitat degradation and over-exploitation. In many instances, attempts to bolster stocks have been made by rearing fish in hatcheries and releasing them into the wild. Fisheries restocking programmes have primarily headed these attempts. However, a substantial number of endangered species recovery programmes also rely on the release of hatchery-reared individuals to ensure long-term population viability. Fisheries scientists have known about the behavioural deficits displayed by hatchery-reared fish and the resultant poor survival rates in the wild for over a century.Whilst there remain considerable gaps in our knowledge about the exact causes of post-release mortality, or their relative contributions, it is clear that significant improvements could be made by rethinking the ways in which hatchery fish are reared, prepared for release and eventually liberated. We emphasize that the focus of fisheries research must now shift from husbandry to improving post-release behavioural performance. In this paper we take a leaf out of the conservation biology literature, paying particular attention to the recent developments in reintroduction biology. Conservation reintroduction techniques including environmental enrichment, life-skills training, and soft release protocols are reviewed and we reflect on their application to fisheries restocking programmes. It emerges that many of the methods examined could be implemented by hatcheries with relative ease and could potentially provide large increases in the probability of survival of hatchery-reared fish. Several of the necessary measures need not be time-consuming or expensive and many could be applied at the hatchery level without any further experimentation.