Prevalence of the Nematode Hysterothylacium aduncum in the Amphipod Americorophium salmonis Consumed by Juvenile Chinook Salmon (Oncorhynchus tshawytscha) in the Columbia River Estuary

From March 1982 to December 1983, juvenile chinook salmon (Oncorhynchus tshawytscha) were sampled by beach-seine in the Campbell River estuary and adjacent waters of Discovery Passage in order to examine estuarine use by wild and hatchery stocks. Wild juvenile chinook entered the estuary as migrant fry and were present in the estuarine zone mainly in late April to June, in the transition zone in mid-May to July, and in the marine zone in July. Hatchery fish were released from early May to early July. Maximum catches of wild stocks were similar in the estuarine and transition zones, while the maximum catches of most hatchery stocks were higher in the transition zone. For both wild and hatchery chinook, catches in the marine zone were much lower than in the estuarine and transition zones. Wild fry resided in the estuary for 40–60 d, while most hatchery fish used the estuary for about one-half this period. Wild stocks showed a relatively constant rate of increase in mean size from May to September. Higher rates of increase in the mean size of hatchery fish were shown by groups with earlier release dates and smaller mean sizes. Residency time and growth rates for wild fish were comparable with those observed in an estuary without hatchery fish. Potential for interaction between wild and hatchery stocks was greatest in the transition zone, where hatchery fish were most abundant and because hatchery releases occurred when catches of wild fish were highest in this foreshore area.

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

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f10-083 ◽

2010 ◽

Vol 67 (10) ◽

pp. 1671-1684 ◽

Cited By ~ 20

Author(s):

Michela Burla ◽

António M. Baptista ◽

Edmundo Casillas ◽

John G. Williams ◽

Douglas M. Marsh

Keyword(s):

Oncorhynchus Mykiss ◽

Chinook Salmon ◽

Large Scale ◽

Oncorhynchus Tshawytscha ◽

Numerical Models ◽

River Estuary ◽

Columbia River ◽

River Plume ◽

Columbia River Estuary ◽

Columbia River Plume

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.

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