Development of a continental shelf acoustic telemetry array to support behavioral research of fish in a high energy ocean environment

Abstract

Acoustic tracking technology supports the study of behavioral patterns of finfish species over long periods and for long distances across coastal and marine environments. Our research program on elasmobranch movements required deployment of an acoustic array in a high-energy, continental shelf environment off Cape Hatteras, North Carolina. A meta-analysis of elasmobranch and teleost acoustic telemetry literature assisted in developing the anchoring and deployment system for the array. But at that time (2008–2014) the literature did not provide suggestions for cost-effective deployment in a remote, high-energy, offshore environment. Using best available information, we designed and deployed an array known as the “Cape Hatteras Acoustic Array” in Raleigh Bay just south of Cape Hatteras, North Carolina, 0–12 kilometers offshore in waters ranging from 10.6 to 36.5 m deep. At the time, retrieving and redeploying the entire anchoring system was critical to reduce expenditure and minimize structure left on the seafloor in this key commercial fishing area. We describe considerations for the anchoring system design and its deployment and retrieval in this high energy environment affected by alongshore currents, large ocean currents (i.e., Labrador Current and the Gulf Stream), and several storms. While Danforth anchors and heavy chain worked for routinely tended moorings, much heavier anchors and large concrete blocks were necessary for long-term deployments through hurricane seasons. Regular maintenance reduced biofouling of surface lines and equipment deployed on the seafloor with a highflier and surface buoy system marking location of the vertically suspended equipment to minimize interactions with commercial and recreational vessels. Our experience shows that both mooring design and regular retrieval are crucial in maintaining acoustic arrays in challenging marine environments.