Spawning Patterns of Pacific Lamprey in Tributaries to the Willamette River, Oregon

Abstract

Addressing the ongoing decline of Pacific Lamprey Entosphenus tridentatus across its range along the west coast of North America requires an understanding of all life history phases. Currently, spawning surveys (redd counts) are a common tool used to monitor returning adult salmonids, but the methods are in their infancy for Pacific Lamprey. To better understand the spawning phase, our objective was to assess temporal spawning trends, redd abundance, habitat use, and spatial patterns of spawning at multiple spatial scales for Pacific Lamprey in the Willamette River basin, Oregon. Although redd density varied considerably across surveyed reaches, the observed temporal patterns of spawning were related to physical habitat and hydrologic conditions. As has been documented in studies in other basins in the Pacific Northwest, we found that redds were often constructed in pool tailouts dominated by gravel, similar to habitat used by spawning salmonids. Across the entire Willamette Basin, Pacific Lampreys appeared to select reaches with alluvial geology, likely because this is where gravel suitable for spawning accumulated. At the tributary scale, spawning patterns were not as strong, and in reaches with nonalluvial geology redds were more spatially clumped than in reaches with alluvial geology. These results can be used to help identify and conserve Pacific Lamprey spawning habitat across the Pacific Northwest.

Received May 16, 2014; accepted July 16, 2014

ACKNOWLEDGMENTS

Funding for this study was provided by the Columbia River Inter-Tribal Fish Commission through the Columbia Basin Fish Accords partnership with the Bonneville Power Administration under project 2008-524-00 (Brian McIlraith, project manager). We thank several landowners that provided survey access as well as logistical support for our project. Additional fieldwork assistance was generously provided by K. McDonnell and C. Christianson. M. Colvin, B. McIlraith, B. Heinith, J. Peterson, B. Gerth, G. Giannico, J. Jolley, G. Silver, and R. Wildman provided sampling and analyses advice as well as lending field equipment to our project. A critical review by A. Brumo, S. Whitlock, and three anonymous reviewers greatly improved the quality of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.