Science of salmon stocking: report

Executive summary

Atlantic salmon is an iconic species of significant cultural and economic importance in countries around the N. Atlantic Ocean basin. The species has been in long term decline and is becoming locally extinct or in poor conservation status across a growing sector of its historic range. The need to respond has focussed attention on the contentious management option of stocking populations with reared fish, which has been deployed in various contexts for over a century. This overview seeks to bring together the science behind the various considerations needed to be taken prior to and following stocking, with a view to aiding design of salmon management strategies that balance risks and benefits within a broad policy framework. Benefits are generally categorised within contexts of conservation and enhancement of salmon populations, and as mitigation for imposed pressures. Risks are generally categorised as potential genetic and ecological damage to populations, including transfer of parasites and pathogens. Supplementation of wild populations with salmon raised in hatcheries can play a part in securing benefits, but may also have potential to cause significant and long-lasting harm, depending on the situation. Understanding the available science is required by stakeholders constructing management plans, by policy makers setting the broad context for using stocking and by regulators assessing proposals. Development, assessment and application of stocking plans should follow a series of procedures to 1) consider whether stocking is required; 2) consider non-biological, ecological, general hatchery, implementation and operational factors; 3) consider detailed hatchery and broodstock issues; 4) evaluate fish release options; 5) consider monitoring strategies; 6) apply review and feedback as adaptive management. Here we review application of the available science for informing these processes.