Lake sturgeon (Acipenser fulvescens) of the upper St. Lawrence River – Resurgence, distribution, and habitat associations

From 2011 to 2015, a resident lake sturgeon population, listed as “Threatened”, was studied in the 1,000 Islands section of the upper St. Lawrence River. Index short-term coarse-mesh gillnetting, hook-lining, and intensive acoustic telemetry examined distribution and microhabitat association precisely where a historic commercial fishery, closed in the late 1980s, was conducted. Sturgeon were caught consistently (105) in a core population area in an 8-km middle section of the 23-km study area. Acoustic telemetry of 33 individuals confirms strong fidelity of this resident population to the core area, highest in fall and winter (87%). Intense manual locating sessions (229) during both daytime and nighttime throughout the year yielded 1,172 precise locations along with transmitter pressure (depth) and temperature. In summer, sturgeon occupied deeper waters in daytime (17.6 m) than at night (16.7 m) and were significantly deeper in the water column (P<0.0001; 14.2% off bottom daytime, 20.4% nighttime). Seasonal assemblages were documented. Sturgeon were suspended in the water column, selectively using current velocities of 0.12–0.18 m/s. Spring dispersal and migrations to a spawning tributary 33 km downstream were confirmed. Current velocity and soft-bottom benthic productivity are particularly important to this commercially historic and now resurging resident large-river sturgeon population.