Are Reflex Indicators Useful for Measuring Vitality and Predicting Delayed Mortality of White Sturgeon Released from a Simulated Fisheries Encounter?

White sturgeon Acipenser transmontanus are the largest freshwater fish in North America and a species exposed to widespread and relatively unregulated fishing stressors. Despite the growing interest in the recreational fishery for white sturgeon, little work has focused on the potential sublethal impacts angling has on their biology. In summer (July 2014, mean T = 19.0°C) and winter (February 2015, mean T = 6.6°C), 48 captive white sturgeon were exposed to fishing-related stressors and their physiological stress responses and reflex impairments were assessed to determine overall fish vitality. Reflex action mortality predictors (RAMP) have successfully predicted post-release mortality for a number of free-swimming fishes but have not been previously examined for use on sturgeon. Sturgeon reflex impairment increased significantly with treatment time (0 - 15 minutes). Reflex impairment was also significantly correlated with higher levels of circulating lactate and increases in glucose and hematocrit, as well as longer recovery times. Higher reflex impairments were associated with subsequent mortality, but only at the warmer temperatures in the summer (July). Overall, our study demonstrates that RAMP scores can be used to measure post-release vitality and predict mortality of white sturgeon exposed to acute stressors, such as an angling encounter.