Pacific salmonid populations have faced significant decline due to poor management and human disturbance. Habitat restoration and monitoring is essential to the ongoing survival of these fish. This study examines population abundance of juvenile Coho salmon (Oncorhynchus kisutch), Chinook salmon (O. tshawytscha) and steelhead trout (O. mykiss) in five tributaries of the Trinity River in Northern California to determine the success of recent restoration efforts. We used traditional snorkel survey methods paired with an occupancy model to compare populations of two restored streams and four unrestored streams. We found that despite Coho being detected in all six streams, restored sites were less likely to have Coho compared to the unrestored streams. When Coho are not detected there was a high probability that the undetected fish was in fact not present in the site. We attribute these findings to the complexity of the restored streams making detection less likely, lack of riparian cover, and a low surveyor detection probability. Despite these contrarian findings, it is likely that as riparian vegetation matures and increases cover and shading, salmonids will use these streams in greater numbers. Our findings will aid in informing managers of how restoration decisions will affect Coho salmon populations.
Environmental Science and Management