An evaluation of the use of triploid Atlantic salmon ž / Salmo salar L. in minimising the impact of escaped farmed salmon on wild populations

The impact of escaped farmed salmon on wild populations may have potentially negative genetic and ecological effects. There is widespread evidence that farmed salmon interact with wild salmon. The use of sterile fish in culture has been proposed as a means of eliminating genetic interaction and minimising the ecological effect of farmed salmon. In this study, the migration behaviour of groups of triploid salmon were investigated through the controlled release of microtagged triploid and diploid stocks on the western coast of Ireland. Mixed-sex and all-female stocks of ranched grilse origin were triploidised using hydrostatic pressure. Smolts were ranched from the hatchery of origin and two groups of post-smolts were released from cages in a marine site. The return of adult salmon from these experimental release groups to coastal and freshwater capture sites was monitored as part of the Irish national coded wire tag recovery programme. The return of triploid salmon from each of the release groups, both to the coast and to fresh water, was significantly reduced compared to diploid salmon. The highest percentage return to fresh water Ž . 2.25% was in the ranched mixed-sex diploid group. In contrast, no salmon from the cage release groups returned to the hatchery location on the Burrishoole river system and recoveries in other Ž . freshwater systems were low -0.01% . The return of a small number of hormonally deficient, sterile triploid female fish suggests that migration to fresh water is not inextricably linked with reproduction. The substantially reduced return of hormonally competent triploid males to the coast and to fresh water, indicates that other factors may have an effect on their marine survival. The ) Corresponding author. Tel.: q353-98-41112; fax: q353-98-41112. Ž . E-mail address: [email protected] D. Cotter . 0044-8486r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00367-1 ( ) D. Cotter et al.rAquaculture 186 2000 61–75 62 reduced return of triploid salmon to the coast and to fresh water, together with their inability to produce viable offspring, demonstrates the potential for triploidy as a means of eliminating genetic interactions between cultured and wild populations, and of reducing the ecological impact of escaped farmed fish. q 2000 Elsevier Science B.V. All rights reserved.