Ocean destratification and fish evacuation caused by a Mid-Atlantic tropical storm

Tropical and extratropical storms commonly occur in the Northwest Atlantic Ocean, sometimes causing catastrophic losses to coastal fisheries. Still, their influence on fish movements and range shifts is poorly known. We coupled biotelemetry observations of black sea bass in the U.S. Mid-Atlantic Bight with numerical modelling of the coastal ocean to evaluate the influence of Hermine (3-8 September 2016) on cold pool thermal destratification and fish evacuation. Spring through fall, black sea bass is a sedentary species, with movements focused on structure where they support important commercial and recreational fisheries. During summer 2016, we characterized the movements of 45 acoustically tagged black sea bass at three sites deploying acoustic receivers moored in shelf waters 18-31 km east of Ocean City, Maryland, and at depths 20-32 m in the southern Mid-Atlantic Bight. On 3 September 2016, cyclonic winds of Hermine caused rapid destratification of the water column. At experimental sites, bottom temperatures rose from 13 to 23°C in 10 h. An oceanographic model and observing data showed that the effects of this destratification dominated large portions of the Mid-Atlantic Bight and had long term effects on seasonal evolution of the shelf temperature. Nearly half of remaining black sea bass on 3 September (40%) permanently evacuated the experimental sites. Those that remained showed long-term depressed activity levels. Although the cause of this incomplete evacuation is unknown, it exemplifies partial migration, which may buffer black sea bass to regional impacts of changed timing or increased incidence of tropical storms.