**ABSTRACT NOT FOR
CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for
this completion report are provided below. For a copy
of the full completion report, please contact the author via e-mail at michaelhansen@usgs.gov
or brook@usgs.gov. Questions? Contact the
GLFC via email at frp@glfc.org or via
telephone at 734-662-3018.**
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.
June 2019
ABSTRACT:
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.