Evaluation of Larval Pacific Lamprey Occupancy of Habitat Restoration Sites in the Portland Harbor Superfund Area

Habitat restoration actions focused on the recovery of juvenile Chinook salmon Oncorhynchus tshawytscha are being implemented in the Portland Harbor Superfund area of the Willamette River. These actions may also have effects on co-occurring Pacific Lamprey Entosphenus tridentatus. Use of restored habitats by lampreys, particularly the larval life stage, has not been extensively studied. Therefore, there is a need to monitor the effectiveness of these efforts relative to larval Pacific Lamprey. Determining the effects of habitat restoration actions on Pacific Lamprey requires evaluation of lamprey occurrence before and after project implementation. This study is focused on the occupancy of larval Pacific Lamprey and Lampetra spp. in shoreline, confluence, and tributary habitats at five restoration sites. These restoration sites are being or have been constructed to provide compensation for injuries to natural resources as part of the Portland Harbor Natural Resource Damage Assessment (NRDA). These restoration sites include Alder Point, Harborton, Linnton, Triangle Park, and Rinearson. In addition, the study is evaluating the occupancy of lamprey at a non-NRDA site, PGE 13.1, located in a reach of the Willamette River that bisects the city of Portland. In 2022, we sampled four restoration sites, Harborton, Linnton, Rinearson, and PGE 13.1. We also evaluated whether larval Pacific Lamprey occupied corresponding habitats at six reference sites in the Portland Harbor Superfund area (McCarthy Creek, Columbia Slough, Ross Island, Cemetery Creek, Oswego Creek, Multnomah Channel, and Miller Creek). A generalized random tessellation-stratified approach was used to select random, spatially-balanced sample quadrats (30 m x 30 m square) across the lower Willamette River and Multnomah Channel, or sample reaches (50-m) in wadable tributaries. In 2022, no larval lamprey were detected at Harborton south confluence, north confluence, or tributary, however, one larval lamprey was captured at the Harborton delta confluence. No lamprey were detected in the confluence, shoreline, or tributary habitat at the Linnton restoration site. At the Rinearson Natural Area, larval lamprey were detected in two of the six tributary reaches (d = 0.33), but were not detected at the Rinearson confluence (d = 0.00). Two larval lampreys were detected at PGE 13.1 (d = 0.20), where larval lamprey have not been detected in previous years. At the six reference sites sampled in 2022, larvae were detected at McCarthy Creek, Columbia Slough, Ross Island, Cemetery Creek, Oswego Creek, and Miller Creek. A total of five larval lamprey were captured at restoration sites and 17 were captured at reference sites. This information is being used as part of a long-term evaluation of the effects of habitat restoration on occupancy and distribution of larval lamprey in the Portland Harbor Superfund area.