Digital photo of a thin-sectioned lake trout otolith. Photo taken by Dale Hanson.

Within the 1836 Consent Decree waters, statistical catch at age models are used to estimate lake trout mortality rates and other population dynamics (e.g. stock size, growth rates, egg deposition, etc).  The models incorporate age specific catch and effort data from the commercial catches (bycatch from the lake whitefish fishery) and spring\summer agency fishery assessment surveys.  However, the largest, and oldest, lake trout are often not captured in either the commercial fishery or fishery surveys and therefore the mortality estimates in the statistical catch at age models do not have any “data source” to account for the presence of larger unsampled lake trout within the population.  Most agencies also perform lake trout spawn surveys to characterize spawner densities and these surveys more effectively target older fish.  However these surveys are not currently used in the models because it is difficult to sample spawning lake trout over the duration of spawning and catches vary depending on whether the survey occurred at the peak of spawning.     

The Modeling Sub-Committee (MSC) has recently begun work to assess whether mortality estimates can be improved by including fall spawner survey data.  The first step in this process involves ageing the fall survey catches.   Recently, Dale Hanson and Kevin Corcoran of the Green Bay NFWCO, created thin sections (Figure 1) from over three hundred lake trout otoliths to obtain age estimates for these fish.  As more lake trout become available, Hanson will develop a time-series of fall spawner survey ages and work with the MSC to develop a method to integrate this data source into the models.  This work demonstrates Green Bay NFWCO’s commitment to management assistance and the Consent Decree of 2000.