SURVIVAL AND METAMORPHOSIS OF SEA LAMPREYS IN LAKE ERIE TRIBUTARIES

Adult sea lamprey abundance in Lake Erie increased during the past decade, exceeding pre-control levels and causing extensive mortality on some strains of stocked lake trout (Markham 2015). Control agents speculate that this increase may be due to an uncontrolled larval sea lamprey population in the St. Clair River because other known sources of larval sea lampreys are regularly treated with lampricide. Chemical control options for the roughly 1 million larval sea lampreys in the St. Clair River have been developed and are quite costly, with kill of ~30% of the estimated population costing around $1.1 million. In general, the Great Lakes Fishery Commission and its agents prioritize chemical treatment options to execute across the basin by ranking the cost to kill a large larval sea lamprey (> 100 mm) with each treatment. ‘Cost to kill’ rankings assume that all large larvae, regardless of source, have the same probability of surviving to inflict damage to the fishery. However, emerging data suggests that survival of juvenile sea lampreys may vary across the Great Lakes basin as well as within an individual lake. Johnson et al. (2013, JGLR) determined survival and metamorphosis rates of sea lamprey in six tributaries of Lake Michigan/Huron by releasing coded wire tagged (CWT) larvae into those streams and recovering them as adults. Survival of sea lampreys from metamorphosis to the adult stage was estimated to be 42%. Barber et al. released recently metamorphosed sea lampreys in the St. Clair River delta and several other sea lamprey infested Lake Erie tributaries during 2012 and recovered them as adults during 2014. Survival from metamorphosis to the adult stage was nearly 10 times lower than in Lakes Michigan and Huron: estimated at 4% for sea lampreys released in the St. Clair River and 7% for sea lampreys released in other Lake Erie tributaries. We hypothesize that juvenile sea lamprey survival in Lake Erie is lower than in Lakes Michigan and Huron because of mortality inflicted by predators and differences in habitat. An alternative hypothesis is that the observed survival difference between studies conducted by Johnson and Barber was an artifact of differing mark-recapture methods: Johnson released larval sea lampreys and Barber released recently metamorphosed sea lampreys. We propose to replicate the Johnson study in Lake Erie because release of larval sea lampreys provides estimates of larval survival and metamorphosis rates, both of which are parameters necessary to model control scenarios in the St. Clair River. Specifically, our objectives are to (1) determine if survival and metamorphosis rates of larval sea lampreys in the St. Clair River differ from other major sea lamprey producing tributaries in Lake Erie and (2) determine if survival and metamorphosis rates of sea lampreys differ between Lake Erie and Lakes Michigan and Huron.