Evolutionary consequences of habitat loss for Pacific anadromous salmonids

Abstract

Large portions of anadromous salmonid habitat in the western United States has been lost because of dams and other blockages. This loss has the potential to affect salmonid evolution through natural selection if the loss is biased, affecting certain types of habitat differentially, and if phenotypic traits correlated with those habitat types are heritable. Habitat loss can also affect salmonid evolution indirectly, by reducing genetic variation and changing its distribution within and among populations. In this paper, we compare the characteristics of lost habitats with currently accessible habitats and review the heritability of traits which show correlations with habitat/environmental gradients. We find that although there is some regional variation, inaccessible habitats tend to be higher in elevation, wetter and both warmer in the summer and colder in the winter than habitats currently available to anadromous salmonids. We present several case studies that demonstrate either a change in phenotypic or life history expression or an apparent reduction in genetic variation associated with habitat blockages. These results suggest that loss of habitat will alter evolutionary trajectories in salmonid populations and Evolutionarily Significant Units. Changes in both selective regime and standing genetic diversity might affect the ability of these taxa to respond to subsequent environmental perturbations. Both natural and anthropogenic and should be considered seriously in developing management and conservation strategies.

Breeding site selection by coho salmon (Oncorhynchus kisutch) in relation to large wood additions and factors that influence reproductive success

“…Although this would seem to be a natural foundation for understanding breeding behavior of salmon (Cury 1994;McClure et al 2008), the bulk of research regarding reproductive requirements of salmon is dominated by studies of habitat use Kondolf and Wolman 1993;Sear and DeVries 2008). In Table 3.…”

Dispersal and productivity of Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon colonizing newly accessible habitat

“…In the US Pacific Northwest, dams and other structures have severely reduced the quantity and quality of spawning and rearing habitats accessible to Pacific salmon (Oncorhynchus spp. ), contributing to lost biodiversity, local extinctions, and threatened or endangered conservation status within regions occupied by extant populations (National Research Council 1996;Sheer and Steel 2006;Gustafson et al 2007;McClure et al 2008). Dam removal or circumvention projects intended to benefit Pacific salmon and steelhead (anadromous rainbow trout, Oncorhynchus mykiss) have increased markedly over the last decade, and research quantifying colonization patterns and processes is needed to provide a scientific foundation for management decisions confronting such projects (Anderson et al 2014).…”

Predation by Northern Pikeminnow and Tiger Muskellunge on Juvenile Salmonids in a High‐Head Reservoir: Implications for Anadromous Fish Reintroductions

“…many populations (Beechie et al 2006;Sheer and Steel 2006;McClure et al 2008). To combat salmon declines and reopen historically accessible habitats above dams that cannot be feasibly removed, reintroductions of anadromous salmonids using trap-and-haul methods are increasingly being proposed as part of relicensing agreements with regulating agencies.…”