Lake Ontario Alewife, Alosa pseudoharengus, maturation and reproduction dynamics

Abstract

Since their introduction in Lake Ontario, alewife (Alosa pseudoharengus) have dominated the forage fish community, making them the primary food source for the lake’s economically valuable sport fish populations. Therefore, alewife population dynamics can impact fishery success and management. Recently observed declines in alewife abundance and year class strength variability further increase the need to better understand alewife reproduction. The objectives of this study were to quantify maturation and reproductive dynamics of Lake Ontario alewife by 1) determining if alewife display determinate or indeterminate fecundity, 2) determining if age 2 alewife could be considered part of the spawning stock, and 3) assessing reproductive potential across alewife ages 2 to 6. We collected alewife from various locations in Lake Ontario from October 2017 to October 2018 and measured gonadosomatic index, condition factor, gonad development, spawning potential, batch fecundity, and embryo survival data. Evidence of a prolonged spawning season and the presence of multiple batches of advanced oocytes in the ovaries of alewife suggest this species display indeterminate fecundity (i.e., can spawn multiple batches of eggs in a single spawning season). Spawning potential (observed spawning and or the presence of mature gonads) was observed in 63.9% of age 2 females and 90.4% of age 2 males captured in June and July, indicating age 2 alewife should be considered part of the spawning stock. This was confirmed by the successful survival of embryos of age 2 parents. When comparing embryo survival data among all ages, older females displayed higher embryo survival, and our beta regression model suggested female age best explained observed. In addition, alewife older than age 2 appeared to have a higher proportion of indeterminate spawners, further suggesting older alewife have increased reproductive output vs younger fish. However, the lack of variation in relative batch fecundity among ages suggest other variables, such as size may better explain this variability.