An improved method to estimate sea lamprey wounding rate on hosts with application to lake trout in Lake Huron

To better estimate wounding rates on hosts of sea lamprey (Petromyzon marinus) in the Great Lakes, methods were developed to fit a logistic model for the mean number of wounds per host as a function of host length. These methods were applied to the number of wounds (the sum of type A-I to A-III marks on hosts collected in spring) on individual lake trout (Salvelinus namaycush) collected by surveys and by a commercial fishery in three regions of U.S. waters of Lake Huron from 1984 to 2000. Wounds per fish were assumed to follow a Poisson distribution, and a number of models were examined using maximum likelihood techniques. Parameters were allowed to vary spatially and temporally, and Markov Chain Monte Carlo techniques were used to evaluate uncertainty in parameter values. By using data for individual hosts and modeling the effect of host length as a continuous function, this method makes more complete use of available data, increases precision, and removes biases in comparison with widely used approaches for estimating wounding rates. In this application, the asymptote, or wounding rate on the largest lake trout, varied over years and among lake regions. In addition, the inflection point (where wounding rates increased most rapidly toward the asymptote) varied among regions, shifting toward smaller lake trout lengths further north in Lake Huron. This change in shape suggests some complexity in the sea lamprey-lake trout interaction. For a 500-mm lake trout, a host size observed in all areas, estimated wounding rates were highest in the north.