Comparative migration ecology of striped bass and Atlantic sturgeon in the US Southern Mid-Atlantic Bight flyway

Seasonal migrations are key to the production and persistence of marine fish populations but movements within shelf movement corridors or, “flyways”, are poorly known. Atlantic sturgeon and striped bass, two anadromous species of concern, are known for their extensive migrations along the US Middle-Atlantic Bight. Seasonal patterns of habitat selection are well described within spawning rivers, estuaries, and shelf foraging habitats, but information on the location and timing of key coastal migrations is limited. Using a gradient-based array of acoustic telemetry receivers, we compared the seasonal incidence and movement behavior of these species in the near-shelf region of Maryland, USA. Atlantic sturgeon incidence was highest in the spring and fall and tended to be biased toward shallow regions, while striped bass had increased presence during spring and winter months and selected deeper waters. Incidence was transient (mean = ~2 d) for both species with a pattern of increased residency (> 2 d) during autumn and winter, particularly for striped bass, with many individuals exhibiting prolonged presence on the outer shelf during winter. Flyways also differed spatially between northern and southern migrations for both species and were related to temperature: striped bass were more likely to occur in cool conditions while Atlantic sturgeon preferred warmer temperatures. Observed timing and spatial distribution within the Middle-Atlantic flyway were dynamic between years and sensitive to climate variables. As shelf ecosystems come under increasing maritime development, gridded telemetry designs represent a feasible approach to provide impact responses within key marine flyways like those that occur within the US Middle-Atlantic Bight. 

Methods
All data were collected using VEMCO acoustic-release telemetry receivers deployed within the shelf region off the coast of Maryland and Delaware, USA from November 2016 to December 2018. All unique transmitter ID codes have been assigned reference numbers so that individual acoustically-tagged fish can be distinguished for analyses, but other identifiers have been removed to respect the data ownership rights of primary tagging organizations. These are the minimal required data to reproduce the results of "Comparative migration ecology of Striped Bass and Atlantic Sturgeon in the US Southern Mid-Atlantic Bight flyway". Additional details are available upon request to the author.

Residency and transit data were formulated by running original VEMCO detection data through the “RunResidenceExtraction” function in the R (R Development Core Team, 2015) V-Track software (c/o Franklin Ecolab, The University of Queensland, St Lucia, Qld, Australia). Residency events were only calculated using data collected in the focal acoustic receiver array of 24 receivers centered on the proposed Maryland Wind Energy Area (WEA). In the function, a residence event began when an acoustically-tagged fish was detected at least two times at a single receiver and was terminated when the tag was detected at a different receiver or if no new detections were recorded for 12 hours. Transit events were calculated using detections that occurred in both the Maryland acoustic receiver array and an adjacent array located of the coast of Delaware, in the proposed Delaware WEA. Only serial detections between the two arrays are reported; in the function, a transit event occurred any time an individual tag was detected sequentially between the Maryland and Delaware acoustic telemetry arrays within the span of a month.