Is handling and transport stress limiting post-stocking survival of yearling bloater C. hoyi in Lake Ontario?

Contributing Authors

Executive Summary

Experimental stocking of bloater (Coregonus hoyi) in Lake Ontario has been ongoing since 2012. In total, only 31 hatchery-origin bloater have been recaptured between 2015-2026, suggesting low post-stocking survival. Acoustic telemetry studies in Lake Ontario indicate post-release survival of bloater may be as low as 12% in the first three weeks at large and environmental conditioning studies suggest most bloater mortality is occurring in the first two days post-stocking. Scientists at USGS Great Lakes Science Center and USFWS Lamar National Fish Hatchery evaluated the effect of transport/handling stress as a mechanism limiting post-stocking survival. Three experimental studies were conducted to test the effect of 1) stocking time of day (AM/PM), 2) transport hauling water temperatures (5°C/10°C), and 3) handling type (netting/fish pumps) on the physiological stress response and post-stocking survival of bloater. Blood cortisol concentration was used to quantify the stress response of transported bloater and mortality counts were used to quantify post-release survival in the days following transport. Although bloater exhibited a measurable stress response to transport and handling, post-stocking survival was >95% across EXP 2 and 3. When isolated from other environmental stressors, our experiments suggest transport and handling are not a significant source of mortality. It is important to mention, however, that bloater in EXP 2 and 3 were transported to and from a laboratory and not Lake Ontario. Stressors in Lake Ontario (e.g., changes in temperature and pressure (depth), natural forage, and predation) may compound the elevated stress response in transported bloater, which may lead to changes in post-stocking survival.