Spawning Drivers and Frequency of Endangered Atlantic Sturgeon in the York River System

Despite over 100 years of commercial exploitation for their eggs, there is limited information about the spawning behavior of Atlantic SturgeonAcipenser oxyrinchus oxyrinchus. Spawning return intervals for males and females have been estimated in the most general of time spans, and researchers have established only in the last 25 years that Atlantic Sturgeon eggs and larvae are freshwater obligates, dispelling the notion that spawning occurred in estuaries. In this study, capture data from 2013 to 2019 for Atlantic Sturgeon were analyzed to estimate spawning return intervals to the York River system, a tributary to the Chesapeake Bay in Virginia. Then, using the data for female capture, we examined the abiotic influences that appear to drive egg deposition. Both males and females return to spawn at more frequent intervals than has been reported in the literature, with males returning once every 1.13 years and females returning once every 2.19 years. Three females were documented returning to spawn in consecutive years-one of them returning 5 out of 6 years. All of the females that were captured on the spawning grounds were gravid, with eggs at stage 5 or further progressed. In all of the years, 105 fall adult females were caught: 73 were at stage 5, 26 at stage 6, and 6 at stage 7. Of the 26 stage-6 females, 13 were actively releasing eggs when they were captured. Egg deposition was correlated with photoperiod, water temperature, and a drop in barometric pressure in the 24 h prior to capture. Ten of 13 females that were releasing eggs were caught during day lengths that were within 30 min of the autumn equinox. Females that were releasing eggs were only captured at water temperatures that were between 21.5 degrees C and 25.1 degrees C. This information should provide the foundation of predictive models that allow researchers and managers to understand how this endangered species is likely to respond to climate change.