Spatial Distribution of Sea Lampreys During Spawning Migration Through Great Lakes Tributaries

The sea lamprey (Petromyzon marinus) is an invasive parasite in the Laurentian Great Lakes that has devastated native fish communities.  Control efforts (e.g., removal via trapping, pesticide application, and sterilization) have substantially reduced their negative effects on the ecosystem.  However, sea lamprey populations remain above target levels in Lake Huron.  The St. Marys River is Lake Huron’s largest tributary and greatest source of parasitic sea lamprey.  All trapping occurs at upstream barriers to migration, yet some spawning may occur in the lower river or tributaries without traps.  Population assessment and control may be improved in this system by collecting, tagging, and releasing fish at downstream locations closer to Lake Huron.  However, no fine-scale spatial information exists to guide development of downstream trapping efforts.  We used acoustic telemetry to obtain fine-scale 3-dimensional positions for migrating adult sea lamprey at six locations in the St. Marys River in 2010.  Our objective was to determine if lampreys use distinct pathways during upstream migration and to determine if pathways can be predicted from bathymetry or water velocity data.   Of 300 tagged sea lampreys released in the lower river, 95% (284/300) entered the study area.   Most lampreys travelled within 1 m of the river bottom or near the shoreline, possibly showing preference for lower water velocities during upstream migration.  These fine-scale movement data may inform the development of new capture strategies in the lower river, where a larger fraction of the population is available for capture.