The Role of Impoundments, Temperature, and Discharge on Colonization of the Columbia River Basin, USA, by Nonindigenous American Shad

Abstract

Ecologists have become increasingly aware of the combined effects of habitat disturbance and climate change on the establishment and proliferation of invasive species. Long‐term data on the population of the invasive American Shad Alosa sapidissima in the U.S. portion of the Columbia River basin provide an opportunity to examine how habitat disturbances affect the abundance and spatial distribution of an invasive species in a heavily modified environment. After the establishment of American Shad in the Columbia River in the late 1800s, the drainage was transformed from its natural lotic state to a series of reservoirs, with concomitant changes to discharge and temperature regimes, which are confounded by climate change. As the Columbia River was dammed, American Shad extended its range and increased in abundance. A large and rapid increase in spawning population abundance (recruits per spawner = 63) followed completion of The Dalles Dam in 1957, which inundated Celilo Falls, a natural barrier to upriver American Shad migration. Regressions revealed that the annual percentage of American Shad migrating upstream from McNary Dam varied with water temperature and discharge (R2 = 0.72), but not population density. When Atlantic coast rivers were dammed, however, American Shad lost spawning habitat and declined in abundance. Understanding the rapid colonization of the Columbia River by American Shad may reveal ways to help American Shad recolonize rivers where they are native. Understanding the roles of water temperature and discharge may allow us to project effects of climate change on the future distribution and abundance of American Shad in the Columbia River basin. Our results suggest that dam construction and alterations to the temperature and discharge regimes of the Columbia River have contributed to the increase in abundance and spatial distribution of American Shad. These changes might have improved the reproductive success of American Shad by providing access to additional spawning grounds and creating suitable juvenile rearing conditions.

From salmon to shad: Shifting sources of marine‐derived nutrients in the Columbia River Basin

“…Although spawning densities of shad in the CRB are unknown, Hinrichsen et al. () estimated that only 10% of John Day Reservoir had silt‐free gravel that was suitable for spawning and that cross sectional water velocity gradients could further restrict the spawning distribution of American shad. While shad are unlikely to have broad influence on biological productivity, they may have more pronounced localised effects on nutrient concentrations.…”

“…The decline of salmon runs in the Columbia River Basin has created a nutrient deficit (Gresh et al, 2000), but this deficit is probably restricted to headwater spawning areas and not the mainstem where shad presumably spawn. While large numbers of nonnative shad have the potential to offset nutrient deficits, shad spawn in the lower CRB and the estuary (Hinrichsen et al, 2013), while salmon historically spawned throughout the CRB. Today, most CRB salmon return to hatcheries; however, the majority of these carcasses are returned to the watershed for nutrient enhancement (Twining et al, 2016).…”

“…significantly increase dissolved N and P concentrations via excretion (Capps & Flecker, 2013). Although spawning densities of shad in the CRB are unknown, Hinrichsen et al (2013) to pre-and postspawner adults erroneously concluded that fish are unconditionally net P sources. However, with ontogenetic differences in % P applied, fish were unconditional P sinks (Ebel et al, 2015).…”

“…However, shad numbers increased sharply after closure of The Dalles Dam (river kilometre (rkm) 308) and subsequent inundation of Celilo Falls, a previously impassable barrier, in 1957. Numbers jumped again after fish ladder modifications alleviated congestion of upstream migrating salmon and shad at lower Columbia River dams in the early 1970s (Hinrichsen, Hasselman, Ebbesmeyer, & Shields, 2013;Monk, Weaver, Thompson, & Ossiander, 1989). The number of shad migrating upstream past each successive dam decreases with distance from the Pacific Ocean with only a few fish migrating past Lower Granite Dam on the Snake River and Priest Rapids Dam (rkm 639) on the Columbia River ( Figure 1).…”

A Synthesis of Findings from an Integrated Hatchery Program after Three Generations of Spawning in the Natural Environment

“…U.S. census data indicate that the human population increased by 11% in Yakima County and by 18% in Washington State between 2000 and 2013, the years for which we analyzed adult return performance for the CESRF. Human population growth and the development associated with it have had profound effects on salmon productivity throughout the Columbia River basin over the last several decades, including impoundment effects (Milbrink et al 2011;Harnish et al 2014;Tiffan et al 2014); increases in the abundance and spatial distribution of nonnative American Shad Alosa sapidissima (Hinrichsen et al 2013), which is altering food webs (Haskell et al 2013); urbanization effects (Hughes et al 2014); toxic and pollutant effects (Johnson et al 2013;Meador 2014;Nielsen and Morace 2014); and changes in the estuarine food supply (Breckenridge et al 2015). In addition, climate change is already affecting salmon in the Pacific Northwest, and these effects will increase in future years (Preikshot 2008;Dalton et al 2013).…”