Before the River: Revealing How Lamprey Migrate in Open Water and Coastal Environments

The phenology of lamprey spawning migrations in lentic systems is well understood for several species worldwide. By comparison, virtually nothing is known about lamprey behavior in large lacustrine and oceanic environments. We made an unprecedented attempt to understand how sea lamprey, Petromyzon marinus, return to coastal environments, locate river plumes and enter rivers of the Laurentian Great Lakes during their spawning migration. VEMCO acoustic arrays provided high resolution (30s intervals, <5m accuracy) 3D paths of sea lamprey movement  in an offshore array with 3 km² of coverage over 3 km from a coastline and on the coast in front of the Ocqueoc River (2 km² of coverage). The offshore array revealed that 81% of individuals arrived at the nearest coast within 72 hours and sea lamprey achieved arrival by following local bathymetric contours towards shallower water. The coastal array captured sea lamprey movement in front of a river under two conditions, (1) low larval sea lamprey population following removal (2010); and, (2) higher larval population following larval recruitment (2011). Although larval odor did not significantly influence river plume encounter or river mouth localization, the coastal array revealed that larval odor does influence the decision of sea lamprey to enter rivers.