**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Evaluation of modification to improve fishway performance

M. Rutter ^1, and J. R. Bence¹

 ¹ Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824

 

Project overview

Assessment of how damages caused by sea lamprey are altered by sea lamprey management are central to the Great Lakes Fishery Commission's efforts toward assessing economically efficient approaches to sea lamprey control. A goal expressed by the Commission is to provide significant reductions in parasitic sea lamprey abundance and at the same time reduce the amount of chemical treatments. These combined goals require a highly efficient program. Our research was directed to provide an improved means to assess the consequences of sea lamprey management strategies and aid in moving the program closer to its goal of optimal sea lamprey management. More specifically our goal was to refine approaches used to assess and predict damage by sea lamprey to lake trout populations of the Great Lakes. We noted that application of a functional response model for sea lamprey feeding within the IMSL protocol is one method for assessing and projecting of future sea lamprey damages that takes into account changing lake trout and sea lamprey populations. However, the parameterized functional response model within the documented IMSL protocol had not been thoroughly ground-truthed against available wounding and lake trout mortality information in the upper Great Lakes and we had noted that its predictions did not match how wounding changed with lake trout size on Lake Huron. Furthermore, we noted that existing lake trout stock assessments on the upper Great Lakes assumed known sea lamprey-induced mortality based on the presumption of direct proportionality between this mortality and marking rates observed on the lake trout. Thus, simply using these estimates of lake trout abundance within a sea lamprey functional response risks an internal inconsistency problem, where the sea lamprey functional response model might imply substantially different mortality rates on lake trout than those assumed to derive the lake trout abundance estimates. However, without a sea lamprey functional response, the method of basing estimates of sea lamprey-induced mortality on marking data provides no forecasting ability, which is essential to the IMSL approach. We therefore undertook to parameterize and evaluate a sea lamprey functional response model. Our approach was to integrate the functional response parameter estimation into lake trout stock assessment models. We began with a review of information related to sea lamprey parasite-host interactions and development of an improved method for summarizing sea lamprey marking data. The review of knowns and unknowns regarding sea lamprey parasite-host interactions was an essential first step for moving forward and informing our modeling work. In large part the results of this review are reported in: Bence, J.R., M.A. Rutter, R. Bergstedt, W. Swink, G. Christie, P. Cochran, M.A. Ebener, J. Koonce. In press. Sea Lamprey parasite-host interactions in the Great Lakes. Journal of Great Lakes Research. This review also contributed substantially to the following publications: Stewart, T.J. Bence, R. Bergstedt, M. Ebener, F. Lupi, and M. Rutter. In press. Recommendations for assessing sea lamprey damages: toward optimizing the control program in the Great Lakes. Journal of Great Lakes Research. Ebener, M.P., J.R. Bence, R.A. Bergstedt, and K.M. Mullett. In press. Classifying sea lamprey marks on Great Lakes lake trout: observer agreement, evidence on healing times between classes and recommendations for reporting of marking statistics. Journal of Great Lakes Research. We worked to develop an improved method of summarizing marking data because we viewed this as an essential data source for fitting a functional response, yet estimated marking rates varied greatly and were often based on small sample sizes within a defined lake trout size category, year, and region. Our method uses maximum likelihood techniques to fit wounding rates (wounds per fish) as a logistic function of fish length. The logistic model makes use of data on individual fish and is capable of predicting the probability that an individual fish will have a specific number of wounds, based on the year and general region of collection and the length of the fish. The method remedies several severe limitations inherent in pre-existing methods for summarizing marking and we demonstrates the method through application to spring wounding data for lake trout collected in Lake Huron. The results of this work were reported in: Rutter, M.A. and J.R. Bence. In press. An improved method to estimate sea lamprey wounding rate on hosts with application to lake trout in Lake Huron. Journal of Great Lakes Research. Pre-publication versions of each of the manuscripts mentioned above are available electronically at: http://www.msu.edu/user/bence/reprints.html The core of our work on this project was the actual integration of a sea lamprey functional response model into lake trout assessment models and development of a way to use the results in stochastic projections. We did this for the main basin of Lake Huron, and provide example simulations of changes in sea lamprey and their corresponding impact on lake trout stocks. This work is reported on in detail in the following section titled: "Parameterization of a lake trout population model and a sea lamprey functional response," which constitutes a pre-submission draft of a manuscript intended for journal publication. The body of paper describes development and fitting of the model, and an appendix provides example forecasts.