Summer storm events are a significant source of disturbance in the Middle Atlantic Bight (MAB) that cause rapid destratification of the water column.  Storm-driven mixing can be considered as a summertime disturbance regime to demersal communities, characterized by the recurrence of large changes in bottom water temperatures.  Black sea bass are a model ubiquitous demersal species in the MAB, as their sedentary behavior exposes them to summer storm disturbances and the physiological stresses associated with thermal destratification.  To better understand the responsiveness of black sea bass to storm impacts, we coupled biotelemetry with a high resolution Finite Volume Community Ocean Model (FVCOM).  During the summers of 2016-2018, 8-15 black sea bass were released with acoustic transponders at each of three reef sites, which were surrounded by data-logging receivers.  Data were analyzed for activity levels, reef departures, and fluctuations in temperature, current velocity, and turbulent kinetic energy.  Movement rates were depressed with each consecutive passing storm, and late-season storms were associated with permanent evacuations. Consecutive, compounding increases in bottom temperature associated with repeated storm events were identified as the primary depressor of local movement. Storm-driven increases in turbulent kinetic energy and current velocity had comparatively smaller, albeit significant, effect. The need to better understand the effect of storms on fish populations in the MAB is relevant in understanding both coincident anthropogenic impacts as well as future fisheries management.

A total of nine VEMCO VR2AR (VEMCO Ltd.) acoustic-release receivers were deployed across study sites during June-October, 2016-2018. Three receivers were positioned to capture movement behaviors associated with each reef. Receivers were deployed 800 m away and at 0°, 120°, and 240° angles from capture and tagging locations at each reef. Receivers were moored to the seabed with two 20.4 kg weight plates and positioned in the water column with one 10.8 kg buoyant buoy each. Receivers continuously recorded data on unique transmitter detections, recorded bottom water temperature (°C), and ambient noise at 69 kHz (mV) every 600 seconds. During June 2016-2018 and at each site, 8-17 black sea bass were surgically implanted with VEMCO V9-2H acoustic transmitters. Animal collection, surgical, and release procedures were approved by the UMCES Institutional Animal Care and Use Committee (IACUC-Secor-F-CBL-160-10). Transmitters emitted a 69 kHz signal at randomized 90-second intervals. Fish were captured at reef sites using rod-and-reel on a chartered recreational fishing boat, and immediately placed in a 57-liter tank containing ambient seawater until surgery. Fish selected for surgery were transferred to a surgery tank containing a mixture of sea water and Aqui-S anesthetic (20 mg L^-1; active ingredient clove oil). Once anesthetized, individuals were transferred to a sling lined with synthetic foam to minimize damage to fins and epithelium, and, while the head and gills remained immersed, a 1-cm incision was made cranial to the vent, and lateral to the midline. The transmitter was inserted through the incision and was closed with 1-2 single surgical-knot sutures. Post-surgery fish were transferred back to the holding tank to monitor for recovery. Telemetry data were analyzed for changes in local and broad-scale movement behaviors relative to storm events. A movement index was estimated as the average number of movements detected by consecutive unique receivers per hr. Hourly movement indices were aggregated across tagged fish within each site to provide a site activity index.

Oceangraphic variables (current velocity, turbulent kinetic energy, and bottom water temperature) were estimated during storm periods using  a Finite Volume Community Ocean Model (FVCOM).  The model was configured for the MAB region, with the eastern boundary located approximately at 70° W, and the northern and southern boundaries located at approximately 42° N and 34° N, respectively. Initial conditions of salinity and temperature for the FVCOM were based on predictions from the Regional Ocean Modeling System (ROMS) Experimental System for Predicting Shelf and Slope Optics (ESPreSSO) model. The FVCOM was run from August 25 to December 31, 2016, and from January 1 to December 31 for 2017 and 2018.  Time series of model-predicted current velocity, turbulent kinetic energy, and bottom water temperature were averaged across receivers to yield averaged hourly predictions per site. Time series data on modeled wind speed and direction were extracted at 3 hr intervals.  A cross section of triangulated grid-point estimates of bottom water temperature, current velocity, and turbulent kinetic energy were also obtained to investigate the response of the cold pool presence to identified storms. Estimated lateral outputs extended across the shelf in the Delmarva region of the MAB; estimated cross-sectional measurements were taken along a 39 km transect that bisected the central study site.