Hot eats and cool creeks: juvenile Pacific salmonids use mainstem prey while in thermal refuges

Thermal refuges form important habitat for cold-water fishes in the face of rising temperatures. As fish become concentrated in refuges, food resources may become depleted. In this study, we used invertebrate drift sampling and fish density surveys to quantify potential in-refuge food limitation, te...

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Bibliographic Details
Published in:Canadian journal of fisheries and aquatic sciences 2017-10, Vol.74 (10), p.1588-1602
Main Authors: Brewitt, Kimberly S, Danner, Eric M, Moore, Jonathan W
Format: Article
Language:English
Subjects:
Analysis
Animal behavior
Animal feeding behavior
Animal populations
Behavior
Body temperature
Body temperature regulation
Creeks
Diet
Environmental aspects
Fish
Food resources
Foraging habitats
Freshwater
Habitat utilization
Habitats
Heterogeneity
Oncorhynchus mykiss
Population density
Prey
Radio-tagging
Rivers
Salmon
Salmonidae
Salmonids
Studies
Temperature
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Summary:Thermal refuges form important habitat for cold-water fishes in the face of rising temperatures. As fish become concentrated in refuges, food resources may become depleted. In this study, we used invertebrate drift sampling and fish density surveys to quantify potential in-refuge food limitation, temperature-sensitive radio-tagging studies to quantify thermal habitat use, and isotopic analyses to determine diet sources for juvenile Pacific salmonids using thermal refuges in California’s Klamath River. Juvenile salmonids using refuges formed by tributary junctions with the mainstem river obtained the majority (range = 47%–97%) of their diet from mainstem prey sources. Mean steelhead (Oncorhynchus mykiss) body temperatures were significantly cooler (∼3.5 °C) than diet-inferred foraging temperatures. Thus, while fish seek cooler habitat for physiological benefits, they rely primarily on mainstem prey. Moreover, consistently high densities of fish in refuges (mean = 3.5 fish·m −2 ) could lead to density-dependent food limitation. Thus, mobile consumers like fish can exploit existing heterogeneity associated with cold-water refuges by gaining thermal benefits from a food-limited cold-water habitat while deriving the majority of their prey from the warm mainstem river.
ISSN:0706-652X
1205-7533
DOI:10.1139/cjfas-2016-0395