Introgression from farmed escapees affects the full life cycle of wild Atlantic salmon

Abstract

Early and late life history and growth are affected by farmed salmon introgression across 105 wild populations of Atlantic salmon.

Introgression of domesticated salmon changes life history and phenology of a wild salmon population

“…Our results showed that the magnitude of change for most of the admixture‐influenced traits was modest. This observation is consistent with the results of similar previous studies (Bolstad et al, 2017, 2021; Skaala et al, 2019). The results of modeling the effect of admixture on life history traits of wild Atlantic salmon populations following introgression from domesticated and directionally selected conspecifics also indicate that under low to modest intrusion scenarios, the mean population change is likely to be weak and potentially undetectable (Castellani et al, 2015, 2018).…”

“…Two earlier studies based on 62 and 105 Atlantic populations, respectively (Bolstad et al, 2017, 2021) indicated a high variability of the effect of admixture on sea age, with results showing that admixture may lead to both increases and decreases in age at maturation of males and females, depending on the genetic background of the recipient wild population. Our observation of a male‐specific decrease in age at maturation in the river Etne raises two points for discussion.…”

“…Although not specifically tested here, it is possible that this, together with differences in underlying genomic architecture of domesticated salmon, may give rise to the sex‐dependent result. The hypothesis of a major‐effect locus being associated with the effect of introgression on life history and growth was, however, tested in a study based on 105 Norwegian rivers (Bolstad et al, 2021). This reported little or no evidence of locus effect on the effect of admixture.…”

“…These pioneering common garden experiments have more recently been complimented by a small but growing number of studies looking at the response of Atlantic salmon populations subjected to gene flow from domesticated fish escaping from fish farms, either from single events or cumulative introgression. Concurring with the results of common garden studies, these more recent studies of natural populations displaying admixture have also demonstrated poorer survival of domesticated, hybrid, or admixed fish (Sylvester et al, 2019; Wacker et al, 2021; Wringe et al, 2018), as well as changes in the life history traits age and size at adult maturation (Bolstad et al, 2017, 2021). Nevertheless, although this growing literature contributes to our understanding of the consequences of introgression of domesticated conspecifics in wild Atlantic salmon populations, there is still a need for further studies to elucidate and quantify the full magnitude of this challenge.…”

Decadal Trends in the Migration Phenology of Diadromous Fishes Native to the Burrishoole Catchment, Ireland

“…Increasing water temperature has been identified as being a principal driver of the phenomenon (Kovach et al, 2013;Arevalo et al, 2020;Teichert et al, 2020) and modeling experiments using future climate projections indicate that earlier runs of fish are increasingly likely (Hedger et al, 2013;Teichert et al, 2020). While it is tempting to attribute any significant changes in migration phenology to the direct effects of climate warming, these species are impacted by interacting multiple stressors, including fishing, land use change, introgression with captive-bred individuals, food web disruption, the presence of dams and the incidence of parasites (Palstra et al, 2007;Belletti et al, 2020;Bolstad et al, 2021;Sobocinski et al, 2021;Tillotson et al, 2021). Shifts in phenology are therefore likely to be context-dependent, but worth exploring as we strive to understand, mitigate and adapt to the interconnected impacts of climate change and biodiversity loss on ecosystems.…”