Adult Life History of Pacific Lamprey in Freshwater Creek, a Tributary to Humboldt Bay, California

Very little published information on Pacific lamprey adult migration timing and movement patterns is available for small coastal streams or tributaries to large estuarine habitats such as Humboldt Bay. In recent years, California Department of Fish and Wildlife has collected various data (primarily incidental to salmonid monitoring) informing migration timing, spawning timing, and relative abundance in Freshwater Creek, a tributary to Humboldt Bay in Northern California. From 2012–2014, a weir and trap located near the tidal boundary were used to capture and PIT tag adults—both those migrating from the bay into freshwater and those moving downstream past the weir. Six Paired PIT tag antennas located throughout the mainstem at tributary junctures were used to detect directional movement of tagged fish. We used capture and tag detection records, along with data incidental to recent salmonid outmigrant trapping in tributaries, to describe adult movement timing and holding locations in the watershed, from time-of-entry into freshwater through the post-spawn period. Redd counts were also conducted from 2011–2015 across approximately 8 km of channel. We used these data to describe timing and relative abundance of spawning. Finally, we discuss these results in the context of other studies throughout the species’ range.