Defense Date

12-7-2021

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

David Kerstetter

Second Advisor

Gregory Skomal

Third Advisor

Rosanna Milligan

Keywords

White shark, Habitat utilization, Migration, Carcharodon carcharias, Diving behavior, HMMoce

Abstract

The ecology of white sharks Carcharodon carcharias in the western North Atlantic (WNA) is largely unknown. With a lack of essential fish habitat (EFH) identified by the National Oceanic and Atmospheric Administration (NOAA), understanding white shark behaviors is crucial to protect aggregation sites and other essential habitats (e.g., mating, parturition) for white sharks. To better understand the movements of these animals, data from 26 tagged white sharks are examined here. Data from the pop-up satellite archival transmitting (PSAT) tags from these sharks were analyzed using the HMMoce package for R (R Development and Core Team 2015) and tracks were generated for all 26 individuals. Additional environmental parameters from the PSAT data were used to generate improved tracks, which were cross referenced with oceanographic data from ocean observing system portals.

Vertical movements uncovered 3 main behavior clusters: ROD (rapid oscillatory dives), Travel, and Coastal. These behaviors occurred both on and off the continental shelf, but ROD did not occur in waters around Cape Cod. This behavior was also not present in juveniles (n = 3). There was no evidence of an offshore common foraging area, but Cape Cod was shown to be a large aggregation site, likely due to the increased seal population and warm waters in the summer months. Overall, this research provides a more comprehensive understanding of the temporal and spatial movements in white sharks in the WNA. It also helps establish the diving behaviors of this population. With large knowledge gaps regarding the white shark life history and ecology, these findings help pinpoint areas of importance for white sharks in the WNA, to better assist with management of this species and its habitat.

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