Abstract
In North America, impassable, man-made barriers block access to salmonid spawning habitat and require costly restoration efforts in the remaining habitats. Evaluating restored spawning habitat quality requires information on salmon water velocity and depth preferences, which may vary in relation to other variables (e.g., water temperature). We demonstrate a generalizable, low-cost method to gather and analyze these data by combining aerial redd surveys of winter-run Chinook salmon (Oncorhynchus tshawytscha), 2D hydraulic modeling, and generalized linear models to calculate spawning resource selection functions (RSFs). Our method permits the examination of interactions between environmental variables and habitat selection, which are frequently treated as independent. Our methods resulted in an RSF that shows interactions between both velocity and depth preference with changing temperature. Preferred depth increased and preferred velocity decreased with increasing temperature. Spawning RSFs for environmental variables may change as other environmental conditions (i.e., water temperature) change; thus, it is important to account for potential interactions when using or producing RSFs.
Highlights
Decisions species make about habitat selection are crucial for their fitness, and understanding these decisions is critical for management
The resource selection functions (RSFs) depth value peaked at 4.1 m, which is deeper than the average depth of presence points (2.7 m, SD 1.4 m; Fig. 3A)
Our RSFs indicate that the winter-run salmon prefer spawning in water that is 4.0 m deep with a velocity of 1.17 m·s–1, which is deeper but with a similar average velocity as the presence data on the Sacramento River, and that these depth and velocity preferences change with increasing temperature
Summary
Decisions species make about habitat selection are crucial for their fitness, and understanding these decisions is critical for management. One of the most important, and often final, decisions a female salmonid makes is where to deposit her eggs. This is a complex decision, as her eggs must survive numerous threats throughout the incubation period for her genes to enter the generation. Her eggs and alevins (young fry) must avoid oxygen depletion, de-watering, overheating, freezing, predation, pathogens, scouring, and superimposition. To reduce the risk of these threats when selecting a spawning location, spawners must consider a variety of environmental characteristics that affect reproductive success, such as gravel size, geomorphology, hydraulics, and aquatic vegetation (Crisp and Carling 1989; Merz et al 2008; Moir and Pasternack 2008). Two key characteristics that greatly affect the risks posed by these threats are water velocity and depth (Groves and Chandler 1999)
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