White sharks (Carcharodon carcharias) along Cape Cod and Nantucket exploit steep sandbar drop-offs (the "rip"). They cruise in 4–10 meter depths, scanning the surface above for silhouette contrast created by gray seals commuting between coastal haul-out sandbars and offshore foraging shoals.
Researchers deploy stationary submerged hydrophones (Vemco VR2W receivers) listening for 69 kHz high-frequency ultrasonic acoustic tags surgically implanted or dart-tagged on apex sharks. Each ping carries an encoded transmitter ID, acoustic depth, and sensor temperature.
Following a predation strike, blood and lipid oils form an expansive surface slick. Vigorous semidiurnal tidal currents (frequently exceeding 2.5 knots through Nantucket Sound) stretch these scent plumes into elongated advective plumes, attracting scavenging or competing predators from kilometers away.
Seal foraging patterns tightly correlate with tidal currents. During high ebb tide, shallow sandbars at Great Point and Monomoy become exposed, compressing swimming seals into narrow tidal channels where high-speed water currents degrade seal evasive maneuverability while enabling lurking sharks to loiter beneath current eddies.
The export provides structured JSON containing receiver timestamp logs, transmitter code frequencies, calculated water depth, estimated shark swim velocity vectors, coordinates of predation events, and instantaneous plume advection area measurements for field analysis.
Nearshore wave action and longshore drift create a recirculation cell inside the surf break. In addition to tidal flushing, surf waves trap particulate organic matter and hemoglobin close to shore, generating the reddish, bloodied ocean conditions documented in recent Nantucket coastal observations.