The influence of the Columbia River plume on the survival of steelhead (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha): a numerical exploration

Abstract

Are smolt-to-adult return rates (SARs) for wild steelhead (i.e., sea-run rainbow trout, Oncorhynchus mykiss ) and wild Snake River spring–summer Chinook salmon ( Oncorhynchus tshawytscha ) related to changes in the Columbia River plume at the time that juvenile migrants enter the ocean? We used three-dimensional (3D) numerical models of the baroclinic circulation in the Columbia River estuary–plume–shelf system to simulate within-season variation in plume size and location, comparing the results with SARs for each day that juvenile salmon entered the ocean for 1999–2003. We found that steelhead benefited from the plume environment at a narrow window of time around their ocean entry. However, when large-scale ocean conditions turned unfavorable, the contribution of local plume conditions to the overall variability in steelhead survival became not significant. A similar evaluation revealed that the plume did not affect survival of Chinook salmon, at least at the fine scale of variability considered. The differential response between the two species is consistent with observed and previously reported behavioral characteristics they exhibit. We speculate that steelhead mainly use the plume to move quickly away from coastal habitats and the predation pressures associated with this environment, for a more direct migration than Chinook salmon to ocean habitats in the Gulf of Alaska.

Estuarine Habitats for Juvenile Salmon in the Tidally-Influenced Lower Columbia River and Estuary : Reporting Period September 15, 2008 through May 31, 2009.

“…• In a separate but related project, both DB11 and DB14 were used to address the question of whether the intraseasonal variability in smolt-to-adult survival rates (SARs) for steelhead (Oncorhynchis mykiss) and Snake River spring/summer chinook salmon (O. tshawytscha) are related to conditions in the Columbia River plume when the juvenile migrants enter the ocean [6]. Results suggest that steelhead (but not Chinook) salmon benefit from the plume environment at a narrow window of time around their ocean entry.…”

“…SATURN relies on 3D numerical models [2,3] to systematically simulate and understand baroclinic circulation in the Columbia River estuary-plume-shelf system [4][5][6][7] (Fig. 1).…”

Annual Report to the Bonneville Power Administration, Reporting Period: April 2008 - February 2009 [re: "Survival and Growth in the Columbia River Plume and north California Current"].

“…32). Existing multi-year simulation databases of circulation produced by SATURN have multiple applications in understanding plume variability [5] and the role of the plume on salmon survival [6].…”

Evidence for multiple navigational sensory capabilities of Chinook salmon

“…Yearling Chinook salmon from the Columbia River enter the ocean and quickly migrate north (Peterson et al 2010). Although general migration patterns are known (Weitkamp 2010, Tucker et al 2011) and environmental correlates have been proposed (Bi et al 2007, Burla et al 2010a, Peterson et al 2010), a comprehensive understanding of the early ocean ecology and migration behavior of these juvenile salmon is missing.…”

“…Burke et al (2013) found that the response to (unspecified) large-scale variables, such as the sun or Earth's magnetic field, was stronger than the response to local environmental cues, which suggests that salmon primarily use navigation in their migrations. However, orientation to local conditions is also suggested by the high correlation between yearling Chinook salmon catches and local environmental conditions (Bi et al 2007, Burla et al 2010a, Yu et al 2012.…”