Occurrence, Detection, and Habitat Use of Larval Lamprey in Columbia River Mainstem Environments: The Dalles Pool and Deschutes River Mouth 2012

Pacific lamprey Entosphenus tridentatus are declining in the Columbia River Basin and larval lamprey use of large, mainstem river habitats is unknown. Their use of shallow depositional areas associated with tributary inputs is equally unknown. We used a deepwater electrofisher to explore occupancy, detection, and habitat use of larval Pacific lamprey and Lampetra spp. in The Dalles Pool and Deschutes River mouth of the Columbia River. We used a generalized randomized tessellation stratified (GRTS) approach to select sampling quadrats in a random, spatially-balanced order and used a deepwater electrofisher to collect larval lamprey. We did not detect any lamprey in our sampling and larval lampreys are likely at a density too low to detect. Substrates in The Dalles Pool were unsuitable for larval lamprey burrowing at many sites. Substrates appeared suitable for larval lamprey burrowing in The Deschutes River mouth and the lack of detection in this area was unexpected. We also conducted capture efficiency experiments with a deepwater electrofisher and found high capture efficiency (>70%) and survival after 96-h (nearly 100%). A deepwater electrofisher is effective for capturing larval lamprey and poses little risk to bodily injury.