title: Fitness reduction and potential extinction of wild populations of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon.
abstract: The high level of escapes from Atlantic salmon farms, up to two million fishes per year in the North Atlantic, has raised concern about the potential impact on wild populations. We report on a two-generation experiment examining the estimated lifetime successes, relative to wild natives, of farm, F(1) and F(2) hybrids and BC(1) backcrosses to wild and farm salmon. Offspring of farm and "hybrids" (i.e. all F(1), F(2) and BC(1) groups) showed reduced survival compared with wild salmon but grew faster as juveniles and displaced wild parr, which as a group were significantly smaller. Where suitable habitat for these emigrant parr is absent, this competition would result in reduced wild smolt production. In the experimental conditions, where emigrants survived downstream, the relative estimated lifetime success ranged from 2% (farm) to 89% (BC(1) wild) of that of wild salmon, indicating additive genetic variation for survival. Wild salmon primarily returned to fresh water after one sea winter (1SW) but farm and 'hybrids' produced proportionately more 2SW salmon. However, lower overall survival means that this would result in reduced recruitment despite increased 2SW fecundity. We thus demonstrate that interaction of farm with wild salmon results in lowered fitness, with repeated escapes causing cumulative fitness depression and potentially an extinction vortex in vulnerable populations.
authors.affiliation: Aquaculture and Catchment Management Services, Marine Institute, Newport, County Mayo, Ireland.
authors.forename: Philip
authors.initials: P
authors.lastname: McGinnity
authors.forename: Paulo
authors.initials: P
authors.lastname: Prodöhl
authors.forename: Andy
authors.initials: A
authors.lastname: Ferguson
authors.forename: Rosaleen
authors.initials: R
authors.lastname: Hynes
authors.forename: Niall O
authors.initials: NO
authors.lastname: Maoiléidigh
authors.forename: Natalie
authors.initials: N
authors.lastname: Baker
authors.forename: Deirdre
authors.initials: D
authors.lastname: Cotter
authors.forename: Brendan
authors.initials: B
authors.lastname: O'Hea
authors.forename: Declan
authors.initials: D
authors.lastname: Cooke
authors.forename: Ger
authors.initials: G
authors.lastname: Rogan
authors.forename: John
authors.initials: J
authors.lastname: Taggart
authors.forename: Tom
authors.initials: T
authors.lastname: Cross
mesh_terms: D000818:Animals; D017756:Aquaculture; D017753:Ecosystem; D005298:Fertility / Q000502:physiology*; D005618:Fresh Water; D005828:Genetics, Population; D006824:Hybridization, Genetic / Q000502:physiology*; D007494:Ireland; D011157:Population Dynamics; D020317:Salmo salar / Q000502:physiology*; D012623:Seawater; D016019:Survival Analysis