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Beaver bank lodge use, distribution and influence on salmonid rearing habitats in the Smith River, California
Anthropogenic activities in the coastal plain of the Smith River have reduced the quality and quantity of productive salmonid rearing habitat. Consequently, restoration is needed to aid in the recovery of the threatened Smith River coho salmon (Oncorhynchus kisutch) population. The ecological engineering activities of the North American beaver (Castor canadensis) have been shown to provide beneficial salmonid habitat. However, data showing beaver importance in coastal rivers where they are unable to create dams is lacking. A substantial beaver population resides in and utilizes bank lodges in the mainstem and coastal tributaries of the Smith River basin in Northern California. This distribution overlaps almost entirely with the current coho salmon distribution in the Smith River. I conducted surveys during the summer 2014 and winter 2014-15 with two objectives: (1) to assess the influence of hydraulic control structures and bank height on beaver bank lodge site selection, and (2) to evaluate multi-season occupancy parameters of juvenile coho salmon at non-natal rearing habitats with and without beaver activity. Presence of a hydraulic control feature and increased bank height were found to have a significant positive influence on beaver bank lodge site selection. Volume of fish cover created by beavers was found to have a positive influence on juvenile coho salmon occupancy during summer rearing. Volume of cover created by beavers was a better predictor of coho salmon occupancy than other habitat variables commonly used in restoration, such as large woody debris. These data suggest that beaver enhance juvenile coho salmon non-natal rearing habitat in a large river system, even where beavers are unable to create channel spanning dams. Management and restoration decisions should consider beaver distribution and abundance in large river systems to better assess where and how beavers can be utilized to provide and enhance rearing habitat for juvenile salmonids in coastal rivers and streams, as well as how to improve habitat to support a robust beaver population.