Modeling fitness changes in wild Atlantic salmon populations faced by spawning intrusion of domesticated escapees

Abstract

Genetic interaction between domesticated escapees and wild conspecifics represents a persistent challenge to an environmentally sustainable Atlantic salmon aquaculture industry. We used a recently developed eco‐genetic model (IBSEM) to investigate potential changes in a wild salmon population subject to spawning intrusion from domesticated escapees. At low intrusion levels (5%–10% escapees), phenotypic and demographic characteristics of the recipient wild population only displayed weak changes over 50 years and only at high intrusion levels (30%–50% escapees) were clear changes visible in this period. Our modeling also revealed that genetic changes in phenotypic and demographic characteristics were greater in situations where strayers originating from a neighboring wild population were domestication‐admixed and changed in parallel with the focal wild population, as opposed to nonadmixed. While recovery in the phenotypic and demographic characteristics was observed in many instances after domesticated salmon intrusion was halted, in the most extreme intrusion scenario, the population went extinct. Based upon results from these simulations, together with existing knowledge, we suggest that a combination of reduced spawning success of domesticated escapees, natural selection purging maladapted phenotypes/genotypes from the wild population, and phenotypic plasticity, buffer the rate and magnitude of change in phenotypic and demographic characteristics of wild populations subject to spawning intrusion of domesticated escapees. The results of our simulations also suggest that under specific conditions, natural straying among wild populations may buffer genetic changes in phenotypic and demographic characteristics resulting from introgression of domesticated escapees and that variation in straying in time and space may contribute to observed differences in domestication‐driven introgression among native populations.

Model-based evaluation of the genetic impacts of farm-escaped Atlantic salmon on wild populations

“…Detailed modeling methods using IBSEM are described in Castellani et al (2015Castellani et al ( , 2018 and Sylvester et al (2019). IBSEM models wild population changes in abundance, genotype, and individual size in response to the introduction of domesticated individuals.…”

“…Of these, IBSEM, an individual-based eco-genetic Atlantic salmon life history model, has been most extensively used. Applications include understanding how the proportion of escapees scales with demographic and genetic impacts in Norway (Castellani et al 2015(Castellani et al , 2018, how natural straying may mitigate these impacts (Castellani et al 2018), and how varying the strength of selection against offspring of aquaculture escapees in the wild influences population outcomes (Sylvester et al 2019). In addition to these modeling efforts, a recent study has modeled the escape, dispersal, and survival of escapees from release sites to wild rivers in Iceland (e.g.…”

“…Specifically, the population impacts (i.e. demographic and genetic) of farm escapees were examined using IBSEM, parameterized for southern Newfoundland populations (Castellani et al 2015(Castellani et al , 2018. To further illustrate potential applications to siting and risk assessment, we modeled the distribution of escapees in the wild prior to and following an aquaculture expansion scenario in southern Newfoundland using a spatial model of dispersal and survival recently implemented in Iceland (Johannsson et al 2017).…”

Swimming with the fishes: validating drift diving to identify farmed Atlantic salmon escapees in the wild

“…While consequences arising from escaped salmon are likely to be population-dependent (Fraser et al 2010, Glover et al 2013, Heino et al 2015, Wringe et al 2018, the offspring of domesticated salmon, and their hybrids with wild salmon, display reduced survival in the wild (McGinnity et al 1997, Fleming et al 2000, Skaala et al 2012. Therefore, introgression of domesticated escapees in native S. salar populations, if extensive enough, may ultimately lead to the extirpation of vulnerable populations (McGinnity et al 2003, Castellani et al 2018. It is therefore imperative to be able to quantify escaped salmon in relation to specific populations so that management strategies (e.g.…”

Epistatic regulation of growth in Atlantic salmon revealed: a QTL study performed on the domesticated-wild interface

“…5a) where we also documented epistasis. Individual-based eco-genetic models developed to study and quantify responses in wild populations to challenges such as genetic introgression, e.g., IBSEM: an individual-based Atlantic salmon population model [61,62], are based on additive inheritance of traits. Although this approach is defendable given that additive genetic variation explains most of the genetic differences in survival in the wild between domesticated and wild salmon [31,[63][64][65][66][67], as well as growth under controlled conditions [20,21,44], the demonstrated possibility of epistasis, as revealed here, suggests that non-additive variation should not be overlooked.…”