Survival and movement patterns of central California coast native steelhead trout ( Oncorhynchus mykiss) in the Napa River.

Drawing on acoustic telemetry this study identifies and describes local and regional scale survival and movement patterns of Central California Coast steelhead ( Oncorhynchus mykiss), including their potential utilization of newly restored tidal marsh habitats in the Napa River system. Between April 8th and May 5th of 2010, 20 steelhead smolts ranging in fork length from 164 to 305 mm were collected, tagged with acoustic transmitters, and released in the upper Napa River (above tidal influence). We found no effect of release date ( P < 0.001) or size ( P < 0.005) on survival estimates based on model likelihoods. Cumulative survival from smolt release location to the Golden Gate Bridge over approximately 77 river kilometers (RKM) was 0.60 (SE = 0.16). Reach-specific survival was lowest in the initial 30 km reach (0.70 SE = 0.1). Survival was higher in San Pablo Bay (0.89 SE = 0.1) and San Francisco Bay (0.96 SE = 0.2). Sixty percent of the fish that entered the ocean were detected on a line of acoustic monitors at Point Reyes approximately 60 km north of the Golden Gate. Average movement rates of smolts were highest in San Pablo Bay (36.6 km∙d SE = 3.3) and San Francisco Bay (28.9 km∙d SE = 6.6). Smolts migrated more slowly in the river (9.0 km∙d SE = 0.9) and ocean (4.1 km∙d SE = 1.2). However, smolt movement rates in the river were dependent on location. Average movement rates of smolts were greatest shortly before their exit from the Napa River (83 km∙d SE = 13.2). Fish were not detected within the recently reconnected former salt production ponds (North, Central, and South units) adjacent to the Napa River. Based on the detection patterns of fish throughout the study area, it appears that most fish were moving at relatively high rates and were not exploring off-channel habitat. [ABSTRACT FROM AUTHOR]