Chinook Salmon Spawning Requires More Than Just Velocity, Depth, and Substrate
Abstract
Everyone knows that Chinook salmon spawn on porous coarse gravel and fine cobble where velocities are moderate and depths are low, and that these local conditions predominate in riffles in river reaches with a slope of 0.01-0.03. In any river network there can be vast areas meeting these multi-scalar criteria and yet spawners are not equally or randomly distributed throughout, but are commonly clustered in a small fraction of the total available physical microhabitat. The purpose of this study was to investigate numerous heterogeneous physical variables that can further explain Chinook spawner behavior. Tested variables included morphological unit size, flow-dependent optimal microhabitat patch size, distance from water's edge, local decadal topographic change magnitude, dominant decadal topographic change process, and spatial scale of statistically significant temporal persistence of returns to past spawning sites. For all but the last variable, the performance metric was the forage ratio (FR) comparing % occurrence to % availability for each test variable. When FR < 0.5 or > 2, then occurrence is half of and more than double the random expectation, respectively. The testbed for the study was the 37.5-km lower Yuba River in California for which there exists a 1-m resolution 2D model of the whole river at discharges ranging from 0.2-22 times bankfull, a morphological unit map, a substrate map, a 1.524-m resolution topographic change map (adjusted for uncertainty), a map of the spatial pattern of topographic change processes, bioverified habitat suitability curves for velocity, depth, and substrate, and two years of river-long observations of Chinook redds (>6700 redds total). Chinook spawners were found to prefer and avoid specific sizes of riffles, runs, and riffle transition as well as specific sizes of flow-dependent optimal mesohabitat patches. They also preferred areas that had eroded 0.3-0.6 m in the last decade. There was no association with distance from water's edge. The strongest temporal persistence of spawning clusters occurred for sites that were at least 128 m long. Overall, microhabitat analysis is insufficient to explain all of the important drivers governing Chinook spawning site selection and the new factors reported are important to apply in spawning habitat rehabilitation design.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMEP23C0835P
- Keywords:
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- 0439 BIOGEOSCIENCES / Ecosystems;
- structure and dynamics;
- 1825 HYDROLOGY / Geomorphology: fluvial;
- 1856 HYDROLOGY / River channels