Abstract:
Alewife Alosa pseudoharengus are an integral part of the Lake Michigan ecosystem, but have
been showing signs of declining health and reduced abundance in the past decade. A similar decline was
shown in Lake Huron a decade before the collapse of the Alewife population in the early 2000s. Hence,
there is concern the Lake Michigan Alewife, and to a larger extent, the Lake Michigan fish assemblage
may be threatened. The objective of this study was to identify temporal changes in Alewife demographics
in an effort to predict future trends. Specifically, we will evaluate length frequency, Fulton’s condition
factor K, annual growth rates, fecundity and age at maturity. Fulton’s Condition Factor for Alewife
declined from a mean of 0.83 in 1979-1994 to 0.74 in 1994-2012. Von Bertalanffy growth curves from
the last decade show an overall decrease in growth rate, maximum length, and maximum age, compared
to growth rates in the 1960s, 1970s, 1980s, and 1990s. Further, Alewife fecundity has decline in recent
years. The shift in Alewife abundance and size structure in Lake Michigan in 2014-2015 suggested
altered predator/prey ratios, ultimately resulting in a change in the fish assemblage, specifically, reduced
salmonid abundance. These composite results identified a scenario in Lake Michigan similar to Lake
Huron in the early 2000s.
