Spatial and temporal variation in marking rates and severity of sea lamprey attacks on salmonines in Lakes Michigan and Huron

The United States and Canada have invested substantial effort to control sea lamprey Petromyzon marinus in the Laurentian Great Lakes and to estimate their effects on lake trout Salvelinus namaycush, a native salmonine undergoing rehabilitation. However, sea lamprey also attack Pacific salmon Oncorhynchus spp. and brown trout Salmo trutta, which contribute to a fishery worth nearly $7 billion USD annually. Marks on surviving hosts are used to assess damages caused by sea lamprey and success of control efforts. We examined spatial and temporal variation in marking rates, mark type, and stage of healing on lake trout, Chinook salmon O. tshawytscha, rainbow trout O. mykiss, coho salmon O. kisutch, and brown trout in Lakes Michigan and Huron. Mean marking rates were highest for lake trout, followed by brown trout, Chinook salmon, rainbow trout, and coho salmon in Lake Michigan, but were several times higher for Chinook salmon than for lake trout (all sizes) and small (533–635 mm) and medium (636–737 mm) rainbow trout in Lake Huron, particularly in summer. Chinook salmon had a lower proportion of healed marks relative to fresh marks compared to lake trout in both lakes, which may indicate differences in post-attack survival. Although lake trout may be the preferred sea lamprey host, Chinook salmon and other species are also suitable and available in Lake Michigan; and Chinook salmon may be a preferred host in Lake Huron. Accounting for alternate hosts could inform fisheries management and improve damage assessments of the sea lamprey control program.