Rapid Colonization of Upstream Habitats by Oncorhynchus Mykiss Following Culvert Modification

Abstract

Habitat fragmentation threatens the persistence of fish populations, and road crossings (e.g., culverts) are particularly problematic because they are globally ubiquitous and can block access to critical habitats. Barrier removal or modifications that allow upstream access can result in expanded distributions, increased abundances, and gene flow among historically isolated populations. Actions that promote connectivity, gene flow, and the potential expression of multiple life history forms (e.g., anadromy in Pacific salmon Oncorhynchus spp.) are thought to buffer against extinction and are increasingly important given the high rates of imperilment for many fish species. We collected genetic samples from juvenile O. mykiss (anadromous steelhead and resident Rainbow Trout) prior to and following the modification of a culvert that served as a historical barrier to upstream movement and tested for changes in genetic composition through time. Prior to culvert modification, levels of genetic diversity were low and genetic differentiation with reference collections of anadromous steelhead was high. After treatment, we observed increased levels of genetic diversity, larger estimates of effective population size, and decreased genetic differentiation with steelhead, indicating an influx of individuals from a downstream population. Using an inexpensive genetic‐based monitoring approach, we show that culvert modification can result in the rapid reestablishment of connectivity between historically isolated populations.

Genetic analysis reveals a complex mosaic of admixture in Brook Trout in a historically fragmented watershed

“…In turn, Rogers et al (2021) found that assessments of barriers using screening tools may underestimate the extent of fish movement through culverts, and they emphasized the importance of using multiple metrics to judge passability along with consideration of temporal and spatial variation in habitats. Overall, our results from the upstream reach of GR3 (one of the three tributaries that were historically fragmented) show the strongest pattern of genetic differentiation consistent with studies that have linked impassable culverts with high levels of genetic differentiation (e.g., Torterotot et al 2014; Wood et al 2018; Knoth et al 2022), and these results further substantiate the idea that the specific characteristics of the culverts play a role in shaping genetic structure.…”

Evaluating effectiveness of restoration to address current stressors to riverine fish

“…However, this pattern did not hold true for control/impact research designs, and may be to the result of inherent differences between sites that confound results in such control/impact comparisons (Christie et al., 2019; Michener, 1997). Richness and density increases can be ecological indicators resulting from improved connectivity which allowed fishes to expand their distributions, access habitats to facilitate a suite of life‐history stages, and promote gene flow to recover genetic diversity (Knoth et al., 2022). However, the identity and composition of species was an important consideration that was not necessarily captured by summary metrics such as species richness.…”

“…Richness and density increases can be ecological indicators resulting from improved connectivity which allowed fishes to expand their distributions, access habitats to facilitate a suite of life-history stages, and promote gene flow to recover genetic diversity (Knoth et al, 2022). However, the identity and composition of species was an important consideration that was not necessarily captured by summary metrics such as species richness.…”

The Genetic Composition of Wild Steelhead Based on Spatial Proximity to a Hatchery

“…In addition, reproduction occurring between anadromous and resident O. mykiss within these tributary systems may buffer population size FINE-SCALE STEELHEAD POPULATION GENETIC STRUCTURE estimates during depressed anadromous runs (Arden and Kapuscinski 2003). Genetic interactions between resident and anadromous O. mykiss have been documented in a variety of studies (Courter et al 2013), including work conducted in the Potlatch River drainage, a tributary to the lower Clearwater River (Bowersox et al 2016;Knoth et al 2022). Finally, low N e estimates in some of our study streams could be associated with smaller or marginal habitat tributaries, where mixing of wild and hatchery steelhead across tributaries may provide a mechanism for retention of high genetic diversity in the presence of low numbers of breeders (Heath et al 2002).…”

“…2016; Knoth et al. 2022). Finally, low N e estimates in some of our study streams could be associated with smaller or marginal habitat tributaries, where mixing of wild and hatchery steelhead across tributaries may provide a mechanism for retention of high genetic diversity in the presence of low numbers of breeders (Heath et al.…”