Preliminary status of Lake Ontario Alewife based on the 2019 spring trawl survey

Abstract

-The 2019 spring prey fish trawl survey was the most extensive fish survey ever conducted on Lake Ontario with 252 bottom trawls collecting 214,569 fish from 39 species, in main-lake and embayment habitats, at depths ranging from 5 to 225 meters (16.5 – 742.5 feet). -Alewife distribution was similar in U.S. (southern) and Canadian (northern) portions of the lake, which differs from the previous three years of whole-lake surveys when Alewife in April were more abundant in either U.S. (2017) or Canadian (2016, 2018) waters. -The 2019 lake-wide average biomass index for adult Alewife (Age2+) declined 29% relative to 2018. -The lake-wide biomass index for Age-1 Alewife in 2019 (2.2 kg/ha) declined relative to 2018 (2.6 kg/ha) and was the lowest Age-1 biomass observed since whole-lake sampling began in 2016. -The current biomass, size structure, and age structure of the adult Alewife population reflect the lower than-average Alewife reproductive success observed in the 2013- and 2014-year classes. -Reproductive success was also lower than average in 2017 and 2018, suggesting the adult Alewife biomass may continue to decline.