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

Abstract

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.

Stability of behavioral syndromes but plasticity in individual behavior: consequences for rockfish stock enhancement

“…However, the results of stock enhancement releases have been mixed (Molony et al 2003), largely due to several problematic issues (Brown and Day 2002;Salvanes and Braithwaite 2006). For example, the supplementation of wild stocks can be economically inefficient if the hatchery environment leads to genetic or environmental effects that cause fish to suffer reduced fitness after release (Reisenbichler and Rubin 1999;Fleming and Petersson 2001).…”

Intron polymorphism (EPIC-PCR) reveals phylogeographic structure of Zacco platypus in China: a possible target for aquaculture development

“…Overfishing has led to a decrease in fish size, mainly in lakes (Cao et al, 1991;Xie et al, 2001), and the biodiversity is thought to be decreasing (Fu et al, 2003). Faced with this danger, fish farming is a solution for biodiversity conservation (Brown and Day, 2002). For this strategy, the use of detailed methods for discriminating intraspecific geographic diversification is necessary.…”

Effects of habitat enrichment and food availability on the foraging behaviour of juvenile Atlantic Cod (Gadus morhua L)

“…Following a decline in several important fish-stocks, particularly marine species, extensive restocking programmes have been undertaken, but often these have had limited success because of the high post-release mortality (Olla et al 1994(Olla et al , 1998Brown and Day 2002;Chan et al 2003). For example, analysis of long-term data-sets from released larval cod along the Norwegian coast demonstrates little, or limited effect on populations, despite initial effects positively influencing the 0+ class (Salvanes et al 1994;Svasand et al 2000;Chan et al 2003).…”

“…While in some cases failure of these programmes may be because the ecosystem is unable to support the large numbers of fish released, it is generally assumed that hatchery-reared fish are less fit for survival compared to fish that develop in the wild environment (Brown and Day 2002;Salvanes and Braithwaite 2006). As brood fish used for restocking purposes are commonly taken from local stock (so that local genetic adaptations are conserved), it is reasonable to assume that the major differences between wild and artificially reared fish are caused by the hatchery rearing environment.…”

“…It is believed that a variable rearing environment may help with this by priming fish to behave in a more flexible and adaptive manner (Berejikian et al 2001;Brown and Day 2002;Salvanes and Braithwaite 2006;Lee and Berejikian 2008). Most of the research investigating the effects of enrichment in fish rearing environments has focused on the role of structural enrichment.…”