title: Into the deep: the functionality of mesopelagic excursions by an oceanic apex predator.
abstract: Comprehension of ecological processes in marine animals requires information regarding dynamic vertical habitat use. While many pelagic predators primarily associate with epipelagic waters, some species routinely dive beyond the deep scattering layer. Actuation for exploiting these aphotic habitats remains largely unknown. Recent telemetry data from oceanic whitetip sharks (Carcharhinus longimanus) in the Atlantic show a strong association with warm waters (>20°C) less than 200 m. Yet, individuals regularly exhibit excursions into the meso- and bathypelagic zone. In order to examine deep-diving behavior in oceanic whitetip sharks, we physically recovered 16 pop-up satellite archival tags and analyzed the high-resolution depth and temperature data. Diving behavior was evaluated in the context of plausible functional behavior hypotheses including interactive behaviors, energy conservation, thermoregulation, navigation, and foraging. Mesopelagic excursions (n = 610) occurred throughout the entire migratory circuit in all individuals, with no indication of site specificity. Six depth-versus-time descent and ascent profiles were identified. Descent profile shapes showed little association with examined environmental variables. Contrastingly, ascent profile shapes were related to environmental factors and appear to represent unique behavioral responses to abiotic conditions present at the dive apex. However, environmental conditions may not be the sole factors influencing ascents, as ascent mode may be linked to intentional behaviors. While dive functionality remains unconfirmed, our study suggests that mesopelagic excursions relate to active foraging behavior or navigation. Dive timing, prey constituents, and dive shape support foraging as the most viable hypothesis for mesopelagic excursions, indicating that the oceanic whitetip shark may regularly survey extreme environments (deep depths, low temperatures) as a foraging strategy. At the apex of these deep-water excursions, sharks exhibit a variable behavioral response, perhaps, indicating the presence or absence of prey.
authors.affiliation: Microwave Telemetry, Inc. Columbia Maryland USA.
authors.forename: Lucy A
authors.initials: LA
authors.lastname: Howey
authors.affiliation: Microwave Telemetry, Inc. Columbia Maryland USA.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Tolentino
authors.affiliation: Department of Biological Sciences Florida International University North Miami Florida USA.
authors.forename: Yannis P
authors.initials: YP
authors.lastname: Papastamatiou
authors.affiliation: Shark Research and Conservation Program Cape Eleuthera Institute Eleuthera The Bahamas.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Brooks
authors.affiliation: Abercrombie & Fish Miller Place New York USA.
authors.forename: Debra L
authors.initials: DL
authors.lastname: Abercrombie
authors.affiliation: National Institute of Polar Research Tachikawa Tokyo Japan; Department of Polar Science SOKENDAI (The Graduate University for Advanced Studies) Tachikawa Tokyo Japan.
authors.forename: Yuuki Y
authors.initials: YY
authors.lastname: Watanabe
authors.affiliation: Shark Research and Conservation Program Cape Eleuthera Institute Eleuthera The Bahamas.
authors.forename: Sean
authors.initials: S
authors.lastname: Williams
authors.affiliation: Shark Research and Conservation Program Cape Eleuthera Institute Eleuthera The Bahamas.
authors.forename: Annabelle
authors.initials: A
authors.lastname: Brooks
authors.affiliation: School of Marine and Atmospheric Science & Institute for Ocean Conservation Science Stony Brook University Stony Brook New York USA.
authors.forename: Demian D
authors.initials: DD
authors.lastname: Chapman
authors.affiliation: Microwave Telemetry, Inc. Columbia Maryland USA.
authors.forename: Lance K B
authors.initials: LK
authors.lastname: Jordan
keywords: Apex predator; deep‐diving behavior; foraging; k‐means cluster analysis; mesopelagic zone; satellite tagging