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Can Contemporary Cisco Stocks Support Historical Levels of Yield in Lake Superior?
*Principal Investigator. 1U.S. Geological Survey, Great Lakes Science Center, Hammond Bay Biological Station, 11188 Ray Road, Millersburg, MI 49759. 2U.S. Fish and Wildlife Service, Green Bay Fish and Wildlife Conservation Office, 2661 Scott Tower Drive, New Franken, WI 54229.
Historically, the cisco Coregonus artedi was the predominant prey fish and target of commercial fisheries throughout Lake Superior, but most populations collapsed by the mid-1900s. Populations in western U.S. waters partially recovered by the early-1990s, but contemporary abundance is thought to be below historical levels, and driven by highly variable and sporadic recruitment, with few year-classes sustaining adult stocks and fisheries. We used stochastic, age-structured simulation models based on the Ricker stock-recruit relationship and observed combinations of life-history parameters to determine whether historical (pre-1955) cisco yield in Lake Superior could be explained by contemporary (1992–2015) abundance, life-history characteristics, and recruitment dynamics. In Minnesota and Wisconsin waters, historical density-independent recruitment rates ranged 1.1–1.4-fold greater than contemporary rates, whereas contemporary density-dependent recruitment rates ranged 5.5–9.0-fold greater than historical rates. The contemporary error term was similar to that historically in Minnesota waters (1.0-fold variability) and 3.9-fold greater than that historically in Wisconsin waters. Historical estimates of adult abundance and age-1 recruitment ranged 3.6–6.0-fold and 6.5–8.8-fold greater than contemporary estimates. When compared to contemporary stocks, our results suggest that historical stocks had (1) similar ability to reproduce at low spawning stock sizes, (2) lower rates of compensatory density-dependence at high spawning stock sizes, (3) lower recruitment variation across all spawning stock sizes, (4) higher average adult abundance and age-1 recruitment, and (5) were more resilient to commercial fishing. Our findings provide context for managing cisco fisheries in Lake Superior and information to inform management strategies and expectations for coregonine reintroduction and restoration in Lake Superior and other Great Lakes.