Estimating Trout Mortality Caused By Feeding of the Chestnut Lamprey in the Manistee River, Michigan

During a study of the life history of the chestnut lamprey Ichthyomyzon castaneus in the Manistee River, I devised a method of estimating the trout mortality caused by feeding of the lamprey in the river. The method was based on aquarium studies of trout killed by feeding lampreys and an estimate of total growth (net production sensu Ricker) of the lamprey population in the river. Estimates of lamprey abundance in the river were based on marking individually 1,911 adult lampreys between May and November 1961. Of 11,066 captures during this period, 2,785 were recaptures of marked lampreys. Unfortunately, extensive movement of the marked lampreys (maximum of 25 miles in 6 days) made estimates of population size difficult. But in the intervening years, development of Program MARK has provided tools for improved estimates of population size and mortality rate under these conditions. I will report estimates of trout mortality based on these new methods.