Genetic stock identification reveals greater use of an oceanic feeding ground around the Faroe Islands by multi-sea winter Atlantic salmon, with variation in use across reporting groups

Abstract

While it is known that the oceans around the Faroe Islands support an Atlantic salmon (Salmo salar) feeding ground, the relative use of this resource by different age classes and populations remains largely unexplored. Using genetic stock identification and run–reconstruction modelling, we observed a consistent pattern whereby the proportion of multi-sea winter salmon (MSW—fish that have spent multiple winters at sea) for a reporting group was substantially greater around the Faroes than the MSW proportion among that group’s corresponding pre-fisheries abundance. Surprisingly, MSW fish from Ireland and the United Kingdom were as likely to occur around the Faroes as were MSW fish from more north-eastern regions. While 1SW salmon (single sea-winter fish) from Ireland and the United Kingdom as well as Southern Norway occurred in similar proportions around the Faroes, 1SW fish from the north-eastern regions were virtually absent. Our results indicate that the oceans around the Faroes host a predominantly MSW feeding ground and use of this resource varies across age classes and reporting groups. Furthermore, these results suggest that MSW fish from some reporting groups preferentially migrate to the Faroes. Variation in spatial resource use may help buffer salmon populations against localized negative changes in marine conditions via portfolio effects.

Diet drives performance trade-offs along Atlantic salmon ontology

“…The sampling sites for this study are one of the major marine feeding grounds for the majority of European salmon populations, especially for older sea age groups such as 2SW and 3SW salmon (Jacobsen & Hansen 2001;O'Sullivan et al 2022). This region is a diverse habitat for both fish and crustacean prey (Jacobsen & Hansen 2001), the dynamics of which may be important for salmon maturation (Vollset et al 2022).…”

“…Samples were collected in autumn (November and December) and winter (February and March) seasons in 1992-93, 1993-94 fishing periods from 55 locations (see Figure 2). The fish were genetically assigned to large-scale regional groups (Ireland and the UK, Southern Norway, and Northern Norway; the latter encompassing fish assigned to Barents Sea drainages (O’Sullivan et al . 2022)).…”

Leveraging the genetic diversity of trout in the rivers of the British Isles and northern France to understand the movements of sea trout (Salmo truttaL.) around the English Channel

“…At present, however, evidence that MPAs are effective for the conservation of highly mobile species such as sea trout is limited (Breen et al, 2015). Nevertheless, to determine the efficacy of MPAs, to regulate fisheries and contribute to policy we require knowledge of where and when individuals are at sea (O’Sullivan et al, 2022). Genetic assignment studies, such as that presented here can help identify both fish movements and fisheries pressure on species, thereby providing evidence crucial to the designation and meaningful placement of MPAs (Jeffery et al, 2022).…”

“…Given the importance of anadromous individuals to the resilience of trout populations (Goodwin, King, Jones, Ibbotson, & Stevens, 2016), effective conservation and management of such populations requires extensive information on species biology, behaviour, life cycle and the challenges they face at different life history stages (Nevoux et al, 2019; Whelan et al, 2017), including knowledge of when and where sea trout go during their marine migrations (O’Sullivan et al, 2022; Thorstad et al, 2016). Of particular relevance is the incidence of individuals taken as by-catch in non-target marine fisheries; again, data on this specific to sea trout are very poor (Elliott et al, 2023).…”

Ontogenetic variation in the marine foraging of Atlantic salmon functionally links genomic diversity with a major life history polymorphism

“…Individuals were genotyped using a GTSeq approach (Campbell, Harmon, & Narum, 2015) with a panel of 167 SNPs as outlined in (Aykanat et al, 2020). This panel allowed individuals to be assigned to their reporting group of origin (O’Sullivan et al, 2022), as well as to score the genotypes at focal SNPs within our target loci. The focal SNPs were vgll3 TOP and six6 TOP.LD (hereafter, vgll3 and six6 ).…”