Mixed-Stock Analysis of Lake Michigan's Lake Whitefish (Coregonus Clupeaformis) Commercial Fishery
Andvik, Ryan T.
University of Wisconsin-Stevens Point, College of Natural Resources
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Six genetic stocks of lake whitefish have been described in Lake Michigan. Concerns exist about the mixed-stock characteristics of Lake Michigan’s lake whitefish commercial fishery. The genetic stock-structure model and microsatellite reference database for lake whitefish spawning aggregates in Lake Michigan provide a framework for addressing some key information gaps. These gaps include determining if a mixed-stock fishery exists and what level of exploitation each of the six stocks is experiencing. The objectives of this research were: (1) to determine if differential stock harvest occurs in the total commercial catch, (2) determine if spatial differences in genetic composition are present in the harvest, and (3) determine if seasonal differences are present in the commercial harvest. Mixed-stock analysis was conducted on 18 commercial harvest samples collected from spring 2009 to fall 2010. Results showed considerable variability in composition of genetic composition throughout the lake. The samples consisted of 2 to 4 genetic stocks contributing relatively large proportions. The predominant stocks observed in the samples of harvested fish were the North and Moonlight Bay stock (NMB), Big Bay de Noc stock (BBN), the Northern stock (NOR; Epoufette and Naubinway), and the Northeastern stock (NOE; Grand Traverse Bay and Hog Island). For most samples, significant admixture of stocks was present; however, the majority of the samples showed the dominant harvested stock represented <60% of the total sample. Samples from WFM-08 were the most homogeneous, with 80.3% of the sample comprised of the Southern stock (SOU; Saugatuk, Ludington, Muskegon, MI). Multiple samples from WI-2 and WFM-01 across spring, summer, and fall of both sample years showed seasonal differences within in some years, and between years. Interestingly, samples from zone WI-2 were consistently comprised of a majority of BBN fish as opposed to the geographically proximate, NMB stock. In many cases, the data showed ≤50% of the sampled fish were from the most geographically proximate stock. These findings have implications for stock-specific management and the allocation of fish to various quotas as geographic location of harvest does not correlate to genetic stock harvest.