Comparing Techniques for Predicting Spatially-Specific Larval Sea Lamprey Density in a Large River

The St. Marys River is one of the largest contributors of parasitic sea lampreys to Lake Huron and upper Lake Michigan.  Larval phase sea lampreys are controlled through the application of granular Bayluscide with the goal of reducing sea lamprey induced mortality on lake trout and other fish species.  Chemical control occurs in 71 treatment plots but not all plots are treated annually.  Decisions about which plots to treat are currently based on the most recent year’s data, although 19 years of spatially referenced deepwater electrofishing data are available.  This work focuses on developing three modeling approaches that incorporate the entire 19 year time series to inform larval lamprey treatment decisions.  A spatially-specific age-structured population model was developed, as well as generalized linear models and generalized additive models.  Simple current year density estimates were also calculated for comparison.  Two years of intensive deepwater electrofishing data (2010-2011) were used to evaluate the performance of the four methods based on plot rankings and the accuracy of the density estimates.  All of the approaches provided more precise predictions than just using the last year’s data. The age-structured model accurately ranked plots for treatment and successfully identified plots with the highest larval lamprey abundance.