Spatially Varying Population Demographics and Fishery Characteristics of Lake Erie Walleyes Inferred from a Long-Term Tag Recovery Study

Abstract

Although the Lake Erie population of Walleyes Sander vitreus exhibits complex spatial structuring, the extent to which population demographics also vary spatially is unknown. Using a spatial tag recovery model, we estimated region- and age-specific mortalities and regional movement probabilities by using recoveries from a jaw tagging study initiated in 1990. The best-performing model based on a comparison of quasi-likelihood Akaike's information criterion values had age-group-specific movement probabilities, age- and region-specific natural mortalities, and age-group- and region-specific annual fishing mortalities. Commercial fishing mortality varied considerably during the study, while recreational fishing mortality was more static. Natural mortality of age-5 and older Walleyes was lower than that of younger fish in all regions, with values ranging from 0.30 to 0.40 for age-4 and younger fish and from 0.13 to 0.27 for age-5 and older fish. In Lake Erie's western basin, natural mortality of age-4 fish was lower than that of age-3 fish. Sensitivity analyses indicated that some natural mortality estimates were sensitive to (1) prior probability distributions assigned to mortality components and (2) assumed movement probabilities in regions where no tagging was conducted. The decline in natural mortality with age in Lake Erie's western basin matches what has been found for other populations, suggesting that such patterns are perhaps common in exploited Walleye populations. Movement probabilities in the western basin were greater than those in the combined central and eastern basins. The mortality rates and movement probabilities estimated in this study should assist in the parameterization and scaling of a spatially explicit Lake Erie Walleye assessment model, the development of which has been recommended for the lake's quota management system. Our study is one of the first to apply a spatial tag recovery model to a freshwater fish population for estimating mortality components. We encourage wider use of this method to improve the understanding of how mortality components and movements vary regionally within freshwater systems.

Received March 26, 2013; accepted August 19, 2013

ACKNOWLEDGMENTS

We thank B. Haas, M. Turner, D. Einhouse, M. Thomas, A. Cook, and C. Murray for their efforts associated with the long-term jaw tagging study of Lake Erie Walleyes. Additionally, this study would not have been successful without the financial and logistic support of the OMNR, MDNR, ODNR, Pennsylvania Fish and Boat Commission, NYSDEC, and Great Lakes Fishery Commission. Support for T. Brenden was provided by contributing partners of the Michigan State University (MSU) Quantitative Fisheries Center, including the Council of Lake Committee Agencies, MDNR, Great Lakes Fishery Commission, MSU College of Agriculture and Natural Resources, MSU Extension, and MSU AgBioResearch. This article is contribution 2014-01 of the MSU Quantitative Fisheries Center.