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US Fish & Wildlife Service FieldNotes

Ashland FWCO Provides Support with Wisconsin’s Lake Trout Catch-At-Age Model

Region 3, June 26, 2013

Throughout the winter 2012 and spring of 2013, Ashland Fish and Wildlife Conservation Office fishery biologist Mike Seider provided technical assistance with the statistical catch-at-age (SCAA) model developed for wild lake trout in the Apostle Islands region of Lake Superior.

Working closely with biologists from the Wisconsin Department of Natural Resources, Red Cliff and Bad River Bands of Lake Superior Chippewa, and Great Lakes Indian Fish and Wildlife Commission, Mike helped to update data inputs and improve the model’s performance. The entire Wisconsin portion of Lake Superior lies within 1842 Treaty waters, and safe harvest limits have been set cooperatively by the Wisconsin State-Tribal Biological Committee since 1985. Since 2001, SCAA model outputs have been used to monitor the lake trout population and set safe harvest limits.

The SCAA model incorporates data from a variety of sources including the sport and commercial fisheries and agency gill net surveys. Although the commercial fishery targets lake whitefish, lake trout are also harvested in commercial gill nets and trap nets. Commercial statistics are summarized from mandatory reporting and on-board monitoring by state and tribal agencies. A popular sport fishery for lake trout also persists in the Apostle Islands too. The State conducts creel surveys at the major ports and estimates harvest and effort for inclusion in the model.

Spring and summer gill net surveys are also conducted to collect biological samples from the lake trout population. Age data and relative abundance, independent of the fishery, are important for ground-truthing the model. Annual samples of the fisheries and surveys age compositions are critical to these model, thus countless hours are spent by biologists each year, carefully ageing lake trout which may only grow an inch per year and live to be over 40 years old. Sea lamprey attack rates on lake trout are also measured each year during the spring survey. Annual attack/ wounding rates are used to estimate mortality attributed to lamprey predation on lake trout (another important input to the model).

Collection of important data via surveys and monitoring has been an important part of the management of lake trout in Wisconsin and throughout Lake Superior. The use of SCAA models has fostered opportunities for data sharing and greater collaboration among agencies. Maintaining and updating the data needed for most SCAA models is a large task and could not be accomplished effectively without successful cooperation between the partner agencies.

Contact Info: Larry Dean, 612-713-5312, Larry_Dean@fws.gov