Genetic Risks Associated with Sablefish Aquaculture in British Columbia, Canada

Abstract

Sablefish (Anoplopoma fimbria) aquaculture is currently limited to three marine facilities in British Columbia (BC) with six-year licences that were issued on July 1st, 2024. As for any cultured species, removal of wild Sablefish individuals from a population for broodstock and inadvertent release of aquaculture individuals back into a population have the potential to pose genetic risks to the long-term sustainability of the species. For instance, captive and wild fish may be genetically or epigenetically differentiated, such that gene flow from captive-bred or captive-reared populations into natural populations may adversely affect fitness in the wild. The magnitudes of these potential genetic risks are often context- and species-specific, and genetic risks have yet to be formally evaluated for Sablefish aquaculture in BC. Understanding the genetic risks associated with marine Sablefish aquaculture is an important precursor to the continuation of this practice in a scientifically defensible manner within the province. Current aquaculture activities for Sablefish in BC involve collecting wild-sourced individuals for broodstock and producing either first- or second-generation captive-reared offspring with no intentional release of captive individuals back into the wild. In captive environments, natural selection that is typically experienced in the wild is relaxed, and artificial or domestication selection may cause traits to shift in a manner that would be sub-optimal in the natural environment. As a result, these differences can be harmful to wild populations if inadvertent escapees introduce disadvantageous genetic variation into natural habitats. The size of the genetic risks associated with the collection of broodstock and domestication are dependent on both the specific aquaculture practices and the biology of the cultured species. Numerous studies have demonstrated that gene flow from captive to wild populations is often to the detriment of fitness in the wild. However, the majority of this work in finfish has focused on salmonids, particularly Atlantic Salmon (Salmo salar), which have populations that are highly genetically structured. Unlike salmonids, Sablefish populations are widespread and relatively unstructured, suggesting that the genetic risks associated with aquaculture of this species may be comparatively low. In 2022, the stock status for Sablefish in BC, was found to be in the healthy zone (DFO 2009; DFO 2023). Fisheries and Oceans Canada (DFO) Aquaculture Management Division has requested that Science Branch provide advice on the genetic risks associated with marine aquaculture of Sablefish under both current practices and a possible future scenario in which broodstock are no longer wild-sourced. The assessment and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR) process will be used to support future decision-making related to Sablefish aquaculture. The specific objectives of this review are to: 1. Review the current understanding of wild Sablefish population genetics in British Columbia. 2. Document the potential genetic risks posed to wild Sablefish due to captive-rearing of individuals for aquaculture harvest. 3. Evaluate these potential genetic risks to wild populations in the context of current Sablefish aquaculture practices in British Columbia. 4. Assess how genetic risks may change if current practices for Sablefish aquaculture transition from the use of wild-sourced broodstock to captive broodstock. The intent of this report is not to provide a risk assessment of Sablefish aquaculture. Instead, this report serves to summarize the current understanding of Sablefish genetics and population structure in British Columbia, to identify the direct genetic risks of aquaculture activities to wild populations of the species, and to compare those genetic risks to those associated with the culture of other finfish species (e.g., Atlantic salmon). Finally, this report highlights data deficiencies that limit the certainty to which genetic risks of aquaculture can be assessed for this species. This Science Response Report results from the regional peer review of October 30, 2024, on the Genetic Risks to Wild Sablefish from the Escape of Farmed Sablefish.