Alewife age, growth and fecundity in Lake Michigan

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.