Diel distribution, behaviour and consumption of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a Wilderness stream
2011
Cromwell, Kara J. | Kennedy, Brian P.
- Understanding population regulation in juvenile salmonids requires distinguishing the effects of intrinsic (size, behaviour) and extrinsic (food, competition) factors. To examine the relative influence of these variables on juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Salmon River drainage (ID, USA), we examined diel differences in foraging microhabitats, behaviour and consumption in two areas with consistent differences in parr-to-smolt survival. In lower Big Creek (LBC, high-survival area) and upper Big Creek (UBC, low-survival area), we observed fish by snorkelling, recording length, behaviour (foraging rate and aggression) and physical (depth, velocity, cover, temperature) and biotic (density, size and species of neighbouring fish) microhabitat features. Stomach contents were extracted to estimate consumption. Depth and temperature were greater in LBC, where Chinook salmon were significantly larger and present at lower densities. Fish in LBC exhibited higher foraging activity during the day than night, but there were no size differences between day and night foragers. In UBC, a higher density area, foraging behaviour did not change between day and night, although the smallest size classes did not forage nocturnally. Regression models that integrated physical and biotic variables suggested that physical factors influenced foraging in both areas, but competition also affected foraging in UBC. Our results demonstrate that fish from low- and high-survival populations in Big Creek are exposed to different physical and biological influences during their first growth season, which are reflected in different diel foraging behaviours.
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