RIPARIAN PONDS AS SOCKEYE SALMON SPAWNING HABITAT IN THE CEDAR RIVER, WASHINGTON

摘要

River ecosystems which support salmon in urbanizing regions have been greatly impacted by past and current human developments. The Cedar River, near Seattle, Washington, has experienced loss of habitats and declines in salmon populations. The rehabilitation of the Cedar River requires information about how channels and floodplains function ecologically and their use by salmon. We examined differences in sockeye salmon spawning times in the river and riparian ponds and pond habitat preferences. Spawning peaked later in both ponds than in the river. Salmon spawning in Wetland 79 showed a higher correlation with the number of fish in the river than Cavanaugh Pond. Locations of fish in different river reaches appeared influenced by river discharge. Later spawning in Cavanaugh Pond suggested fish used the pond as refuge during high flows in the river. Habitat electivity indices indicated that spawning salmon preferred upwelling areas in ponds. Placements of redds in upwelling areas could benefit egg to fry survival by providing more stable interstitial flow, incubation conditions, and temperature regimes during egg development. Upwelling habitats should be an important consideration for protecting and restoring off-channel areas.