Stocked‐Fish Introgression into Wild Brook Trout Populations Depends on Habitat

Abstract

The genetic constitution of populations is affected by myriad factors, including both natural and anthropogenic habitat transformations. Previous work on the population structure of Brook Trout Salvelinus fontinalis has suggested that supplemental stocking for fishery enhancement has transformed natural genetic diversity. We utilized microsatellite analysis of 11 loci to examine the genetic structure of over 950 Brook Trout sampled across 50 locations, including hatcheries; holding ponds; wild, unstocked waters; and repeatedly stocked waterbodies across Adirondack lakes and ponds in New York State, USA. From these data, we estimated the degree of introgressive hybridization, tested for associations with landscape and stocking variables, and tested predicted patterns of genetic diversity, effective population size, and genetic population structure. Widespread repeated stocking of a single hybrid strain has led to the dramatic genetic homogenization of Brook Trout across the sampled lakes and ponds. Model selection indicated that environmental factors were more important than stocking intensity for determining the extent of stocked‐fish introgression, and certain environmental circumstances may make some populations relatively resilient to repeated stocking activities. Known, protected heritage strains were confirmed as mostly unadmixed, but holding ponds with heritage brood populations used for supplemental stocking had become differentiated from the natal strains in two of the three cases tested. In addition to the importance of these results for understanding the effects of stocking activities on the genetic integrity of Brook Trout populations, our findings illustrate how current genetic techniques can aid in the development of management practices that are related to the conservation of species supporting economically important freshwater fisheries.

A global synthesis of peer‐reviewed research on the effects of hatchery salmonids on wild salmonids

“…Next, we recorded the pathway of hatchery effect (i.e., genetic, ecological, fishing, disease) and VSP parameter(s) studied. Given the number of genetic publications on diversity, we further classified those studies according to the attribute that was analyzed, including diversity (e.g., Williamson & May, 2005), genetic population structure (e.g., Bruce et al, 2020), effective population size (e.g., Berejikian & Van Doornik, 2018), or a combination thereof such as both population structure and effective population size (e.g., Almodóvar et al, 2020).…”

“…In practice, scientists, managers, and policymakers may be familiar with studies in their region and on species they are tasked with managing and conserving but may be unaware of research outside their immediate scope of focus. For example, there have been numerous hatchery studies on Atlantic salmon ( Salmo salar ) and brown trout ( Salmo trutta ) that commonly reference one another (Horreo et al, 2014; Nilsson et al, 2008) and there are several publications on brook charr ( Salvelinus fontinalis ) (Bruce et al, 2020; Létourneau et al, 2018; Marie et al, 2010), yet those results are rarely cited or utilized in research on Pacific Salmon and vice‐versa (e.g., Tatara & Berejikian, 2012; Wang et al, 2002). Accordingly, while several studies have reviewed hatchery effects on wild salmonids (Fraser, 2008; Naish et al, 2007), few have covered both Oncorhynchus and Salmo spp.…”

The genic view of hybridization in the Anthropocene

“…My literature search uncovered 31 papers (out of 59 studies, 53%) that involved the introduction of non‐native species (Figure 2a ). Some of these cases involved intentional movement of organisms, such as the release of game‐farm birds for hunting purposes (Forcina et al, 2020 ), the stocking of fish populations with captive‐bred animals (Beheregaray et al, 2017 ; Bruce et al, 2020 ), or the translocation of large mammals between African game reserves (Grobler et al, 2018 ; Miller et al, 2020 ; van Wyk et al, 2019 ). Other human‐assisted translocations were unintentional, such as the transport of aquatic organisms in ship hulls (Oziolor et al, 2019 ) or plant seeds by cargo or passenger transport, sometimes resulting in cryptic invasions and hybridization events (Morais & Reichard, 2018 ).…”

Streamwide Evaluation of Survival and Reproduction of MYY and Wild Brook Trout Populations

“…Placer Creek had the highest population density of wild Brook Trout but the lowest reproductive potential. Third, environmental factors, including habitat and water chemistry, were correlated with varying levels of introgression of hatchery-reared Brook Trout (Marie et al 2012;Bruce et al 2020). Our study streams varied in stream morphology and habitat types.…”