Evaluation of Larval Pacific Lamprey Occupancy of Habitat Restoration Sites in the Portland Harbor Superfund Area 2023 Annual Report

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 benefit from monitoring 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 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 2023, we sampled three restoration sites, Harborton, Linnton, and Rinearson. We also evaluated whether larval Pacific Lamprey occupied corresponding habitats at five reference sites in the Portland Harbor Superfund area (McCarthy Creek, Columbia Slough, Cemetery Creek, Oswego Creek, and Multnomah Channel). 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 2023, no larval lamprey were detected at Harborton south confluence, delta confluence, or tributary, however, one larval lamprey was captured at the Harborton north confluence. This was the first detection in the north confluence post restoration. 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 one of the seven tributary reaches (d = 0.33), and eight larval lamprey were detected in five of the ten Rinearson confluence sites (d = 0.50). At the five reference sites sampled in 2023, lamprey were detected at Columbia Slough, Cemetery Creek, and Oswego Creek. A total of 10 larval lamprey were captured at restoration sites and 13 larval lamprey and one transforming Lampetra spp. 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.