Lake trout rehabilitation in Lake Ontario, 2020

Abstract

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout (Salvelinus namaycush) population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from standard surveys performed by USGS and NYSDEC. Response to the COVID-19 pandemic limited survey effort such that spring and summer bottom trawl surveys and the creel survey were not completed in 2020, and sites sampled during the fall gillnet survey were limited to those east of Rochester, NY. The catch per unit effort of adult lake trout in gill nets increased each year from 2008-2014, recovering from historic lows recorded during 2005-2007. Adult abundances declined each year from 2015 to 2017; and in 2017 were about 35% below the 2014 peak and 17% below the 1999-2004 mean. Adult abundance increased in 2018 by 51% over the 2017 value and remained nearly stable between 2018 and 2020. The 2020 rate of wounding by sea lamprey (Petromyzon marinus) on lake trout caught in gill nets was 2.27 A1 wounds (fresh wound) per 100 lake trout and was near target (2 wounds per 100 lake trout). Condition values for adult lake trout, indexed in September from the predicted weight for a 700 mm lake trout from annual length-weight regressions and Fulton’s K for age-6 males, were among the highest levels observed for the 1983-2020 time series. Reproductive potential for the adult stock indexed from the CPUE of mature females ≥ 4000 g was again above the target in 2020 continuing a trend observed in nine of the last ten years. The 2020 catch of young wild lake trout marked the 26th observation in the last 27 years, however the low numbers of native adults observed during that time period continues to indicate substantial restoration impediments still exist.