Finding appropriate harvest policies for admixed fisheries to ensure long term population sustainability of native Great Lake fishes

Grant: # 1250

Grant Amount: $151,204.81

Board Decision Year: 2012

Michigan State University - Department of Fisheries and Wildlife (East Lansing)

Department of Fisheries and Wildlife

Brenden, Travis O. ([email protected]) 517-355-0003

GLFT - Ecosystem Health and Sustainable Fish Populations-C - Ecological and biological fisheries research to inform management

Project Details

Many Great Lakes fisheries exploit intermixed fish stocks in which individuals from several different spawning populations overlap in habitat occupancy during periods of harvest by commercial and recreational fisheries. With intermixed fisheries, there often is a danger that less-productive populations may be overharvested if harvest limits do not take intermixing into consideration. Despite recognition that many fisheries in the Great Lakes exploit mixtures of populations, stocks continue to be largely treated as discrete, independent units for management purposes. For example, most of the statistical catch-at-age (SCA) assessment models that are used to estimate abundances and mortality rates for lake whitefish and lake trout in the 1836 Treaty waters of Lakes Huron, Michigan, and Superior make no accommodations for fish movement. This unaccounted movement could be impacting the accuracy of the SCA model predictions as well as the appropriateness of harvest limits that are set based on the different harvest control rules used to manage the respective fisheries.

In this project, the researchers’ goal was to provide fishery managers insight into pragmatic techniques for dealing with admixture fisheries that exploit multiple spawning populations, both from the stock assessment and harvest policy perspectives. They found that a pooled assessment approach was the most consistent method for assessing intermixed fish stocks. A total annual mortality control rule based on 50 percent of the fishing mortality that resulted in the maximum sustainable yield for the least productive population did the best job of protecting spawning populations across the range of explored simulation scenarios. When modeled, little to no benefit came from establishing fishing harvest policies for individual regions based on catch data from mixture fisheries. If such an approach was attempted, conservative control rules would still be necessary to have a low risk of overharvesting spawning populations. For single populations, relative yields were reduced and risk of stock depletion and interannual variability in yield increased when assessments were multiannual. Conversely, for intermixed populations, interannual variability in yield actually decreased when assessments became multiannual, which may be related to assessment model data quality issues.


Final Report
View - Final_Report_narrative_1250.pdf