A Fine-scale Assessment of Using Barriers to Conserve Native Stream Salmonids: A Case Study in Akokala Creek, Glacier National Park, USA

Abstract

Abstract:Biologists are often faced with the difficult decision in managing native salmonids of where and when to install barriers as a conservation action to prevent upstream invasion of nonnative fishes. However, fine-scale approaches to assess long-term persistence of populations within streams and watersheds chosen for isolation management are often lacking. We employed a spatially-explicit approach to evaluate stream habitat conditions, relative abundance, and genetic diversity of native westslope cutthroat trout (Oncorhynchus clarkii lewisi) within the Akokala Creek watershed in Glacier National Park a population threatened by introgressive hybridization with nonnative rainbow trout (O. mykiss) from nearby sources. The systematic survey of 24 stream reaches showed broad overlap in fish population and suitable habitat characteristics among reaches and no natural barriers to fish migration were found. Analysis of population structure using 16 microsatellite loci showed modest amounts of genetic diversity among reaches, and that fish from Long Bow Creek were the only moderately distinct genetic group. We then used this information to assess the potential impacts of three barrier placement scenarios on long-term population persistence and genetic diversity. The two barrier placement scenarios in headwater areas generally failed to meet general persistence criteria for minimum population size (2,500 individuals, N e = 500), maintenance of long-term genetic diversity (H e ), and no population subdivision. Conversely, placing a barrier near the stream mouth and selectively passing non-hybridized, migratory spawners entering Akokala Creek met all persistence criteria and may offer the best option to conserve native trout populations and life history diversity. Systematic, fine-scale stream habitat, fish distribution, and genetic assessments in streams chosen for barrier installation are needed in conjunction with broader scale assessments to understand the potential impacts of using barriers for conservation of native salmonid populations threatened by nonnative fish invasions.

Legacy introductions and climatic variation explain spatiotemporal patterns of invasive hybridization in a native trout

“…Results show that climatic changes are interacting with legacies of species introduction and habitat degradation to threaten native cutthroat trout, as invasive rainbow trout continue to expand their range. Remaining nonhybridized populations represent only a fraction of the historic distribution and genetic diversity of cutthroat trout (Allendorf & Leary, ; Shepard et al., ), underscoring the urgency of addressing invasive hybridization through proven conservation strategies (e.g., suppression of non‐natives, installation of barriers, habitat restoration and protection) that prevent genomic extinction of additional populations and eventually entire lineages (Al‐Chokhachy et al., ; Muhlfeld et al., ; Pierce, Podner, & Carim, ). More broadly, our results suggest that mitigation of chronic human stressors—translocation of species and habitat modification—that interact with climate to promote the expansion of invasive species will be crucial for conserving biodiversity (Hauer et al., ).…”

Suppression of invasive lake trout in an isolated backcountry lake in Glacier National Park

“…; Muhlfeld et al . ). The introduction of lake trout into Flathead Lake in 1905 and the establishment of the opossum shrimp, Mysis diluviana (Audzijonytë & Väinölä), in 1981 (Spencer et al .…”

“…Glacier National Park (GNP) supports approximately one-third of the remaining natural lake core areas for bull trout in the United States (Fredenberg et al 2007). However, the majority of adfluvial bull trout populations in western GNP have declined in the last 25-30 years, owing to the invasion and establishment of non-native lake trout from Flathead Lake (Fredenberg 2002;Meeuwig et al 2008;Muhlfeld et al 2012). The introduction of lake trout into Flathead Lake in 1905 and the establishment of the opossum shrimp, Mysis diluviana (Audzi-jonyt€ e & V€ ain€ ol€ a), in 1981 (Spencer et al 1991) led to the proliferation and subsequent replacement of the bull trout as the dominant top-level piscivore (Fredenberg 2002;Ellis et al 2011).…”

Contrasting habitat associations of imperilled endemic stream fishes from a global biodiversity hot spot

“…Conservation strategies in many data deficient regions has had to rely almost exclusively on expert knowledge, but apart from the implications of cryptic diversity, lack of detailed knowledge of species ecology may misdirect conservation prioritisation, and can potentially lead to loss of biodiversity. For example, the building of weirs to prevent upstream migration of alien species has been considered to be one of the best conservation strategies to secure the remaining populations of threatened fish species [51,52]. Given the species-specific habitat associations of stream fishes, it is clear that careful selection of the location of such barriers is required so that the protected river sections will encompass optimal habitats for all the target species.…”