Genetic Integrity of Lake Trout in Cold Lake, Alberta, Despite Decades of Supplemental Stocking

Abstract

Supplemental stocking is a widely used management tool to support recreational fisheries but is not always successful and can have consequences for the genetic composition of recipient wild populations. Introgressive admixture between native populations and genetically divergent stocking sources may lead to outbreeding depression and/or homogenization of genetic diversity, which could potentially decrease the fitness of the native populations. We assessed the genetic ancestry of Lake Trout Salvelinus namaycush in Cold Lake, Alberta, which received supplemental stocking from several sources after the closure of a historical commercial fishery. Recent demographic studies of Lake Trout in Cold Lake estimated increased natural mortality in the contemporary population relative to the period before the commercial fishery. Population-and individual-based analyses of microsatellite loci were used to compare samples from Cold Lake collected over multiple time periods against hatchery stocking sources and a native population connected to Cold Lake via the Cold River (Pierce Lake). Despite extensive stocking over several decades and evidence of historical introgression, evidence suggests that the contemporary Lake Trout population in Cold Lake has primarily native ancestry, with little admixture from hatchery source populations. The cause of the increased mortality remains unresolved, but ecological factors should perhaps be the focus of future studies.Supplemental stocking is a widely practiced management tool to provide fishing opportunities and to augment wild fish populations. Enhancing or maintaining self-sustainable wild populations is carried out by rearing fish in hatcheries and stocking their progeny into the wild (Araki and Schmid 2010). Despite the value and widespread use of stocking, numerous studies have shown that hatchery rearing can have behavioral and ecological consequences for both hatchery-reared fish and wild recipient populations when those fish are stocked (for reviews, see NRC 1995;Weber and Fausch 2003). In several species, hatchery-reared individuals have been shown to *Corresponding

Optimization of an amplicon sequencing‐based microsatellite panel and protocol for stock identification and kinship inference of lake trout (Salvelinus namaycush)

“…Genetic markers have been used for several decades to assess stock composition, survival, and recruitment in lake trout ( Salvelinus namaycush ), a long‐lived piscivore native to Canada and parts of the northern United States (Goetz et al, 2010 ; Grewe et al, 1993 ; Krueger et al, 1989 ; McDermid et al, 2020 ; Page et al, 2003 , 2004 ). A major focus of these efforts has been population management in the Laurentian Great Lakes (hereafter, Great Lakes), where a combination of intensive commercial fishing, spawning habitat degradation, and invasion by sea lamprey ( Petromyzon marinus ) eradicated or severely reduced the native stocks by the 1950s (Christie, 1973 ; Coble et al, 1990 ; Cornelius et al, 1995 ).…”

“…Standardization of microsatellite scoring among labs has historically posed multiple challenges which take significant effort to overcome (Ellis et al, 2011 ; Moran et al, 2006 ; Seeb et al, 2007 ; Welsh & May, 2006 ). Studies using electrophoresis‐based microsatellites have adapted markers from other species (Guinand et al, 2003 ; Northrup et al, 2010 ; Page et al, 2003 ), developed new markers (Rollins et al, 2009 ), or used some combination of the two (Baillie et al, 2016 ; Larson et al, 2020 ; Markham et al, 2022 ; McCracken et al, 2013 ; McDermid et al, 2020 ; Scribner et al, 2018 ). With the advent of next‐generation sequencing, studies have also employed restriction site‐associated DNA sequencing (RADseq), again with widely differing sets of loci (Bernatchez et al, 2016 ; Euclide et al, 2022 ; Morissette et al, 2019 ).…”

“…Genetic markers have been used for several decades to assess stock composition, survival, and recruitment in lake trout (Salvelinus namaycush), a long-lived piscivore native to Canada and parts of the northern United States (Goetz et al, 2010;Grewe et al, 1993;Krueger et al, 1989;McDermid et al, 2020;Page et al, 2003Page et al, , 2004.…”