Spatio-Temporal Variability in White Shark (Carcharodon carcharias) Movement Ecology During Residency and Migration Phases in the Western North Atlantic

Understanding how mobile, marine predators use three-dimensional space over time is central to inform management and conservation actions. Combining tracking technologies can yield powerful datasets over multiple spatio-temporal scales to provide critical information for these purposes. For the white shark (Carcharodon carcharias), detailed movement and migration information over ontogeny, including inter- and intra-annual variation in timing of movement phases, is largely unknown in the western North Atlantic (WNA), a relatively understudied area for this species. To address this need, we tracked 48 large juvenile to adult white sharks between 2012 and 2020, using a combination of satellite-linked and acoustic telemetry. Overall, WNA white sharks showed repeatable and predictable patterns in horizontal movements, although there was variation in these movements related to sex and size. While most sharks undertook an annual migratory cycle with the majority of time spent over the continental shelf, some individuals, particularly adult females, made extensive forays into the open ocean as far east as beyond the Mid-Atlantic Ridge. Moreover, increased off-shelf use occurred with body size even though migration and residency phases were conserved. Summer residency areas included coastal Massachusetts and portions of Atlantic Canada, with individuals showing fidelity to specific regions over multiple years. An autumn/winter migration occurred with sharks moving rapidly south to overwintering residency areas in the southeastern United States Atlantic and Gulf of Mexico, where they remained until the following spring/summer. While broad residency and migration periods were consistent, migratory timing varied among years and among individuals within years. White sharks monitored with pop-up satellite-linked archival tags made extensive use of the water column (0–872 m) and experienced a broad range of temperatures (−0.9 – 30.5°C), with evidence for differential vertical use based on migration and residency phases. Overall, results show dynamic inter- and intra-annual three-dimensional patterns of movements conserved within discrete phases. These results demonstrate the value of using multiple tag types to track long-term movements of large mobile species. Our findings expand knowledge of the movements and migration of the WNA white shark population and comprise critically important information to inform sound management strategies for the species.

Jumping the Shark: White Shark Representations in Great White Serial Killer Lives—The Fear and the (Pseudo-)Science

Sharks are among the most endangered nonhuman animals on the planet because of industrial fishing, the shark meat and fin trade, expanding recreational fishing, and other anthropogenic causes. White sharks (Carcharodon carcharias), the most visible in popular culture, remain vulnerable (VU, IUCN Red List) and understudied, although population recovery is having a measure of success in regions like the Eastern Pacific and the Northern Atlantic of the United States. As numbers rise, Jaws associations also remain in vogue in programming that emphasizes human–wildlife** conflict such as Shark Week’s Great White Serial Killer Lives. Network marketing typically promotes this content by hyping shark science. Textual analysis, however, suggests that exposure to pseudoscientific narratives and unethical fear-inducing images is counterproductive to wider support for conservation programs and public recognition for sharks’ rights to their habitats.

A shark's eye view: testing the ‘mistaken identity theory’ behind shark bites on humans

Shark bites on humans are rare but are sufficiently frequent to generate substantial public concern, which typically leads to measures to reduce their frequency. Unfortunately, we understand little about why sharks bite humans. One theory for bites occurring at the surface, e.g. on surfers, is that of mistaken identity, whereby sharks mistake humans for their typical prey (pinnipeds in the case of white sharks). This study tests the mistaken identity theory by comparing video footage of pinnipeds, humans swimming and humans paddling surfboards, from the perspective of a white shark viewing these objects from below. Videos were processed to reflect how a shark's retina would detect the visual motion and shape cues. Motion cues of humans swimming, humans paddling surfboards and pinnipeds swimming did not differ significantly. The shape of paddled surfboards and human swimmers was also similar to that of pinnipeds with their flippers abducted. The difference in shape between pinnipeds with abducted versus adducted flippers was bigger than between pinnipeds with flippers abducted and surfboards or human swimmers. From the perspective of a white shark, therefore, neither visual motion nor shape cues allow an unequivocal visual distinction between pinnipeds and humans, supporting the mistaken identity theory behind some bites.

Unique iris and pupil morphology in lamnid sharks

Documentation of the iris concentrating on color, pupillary shape, and orientation has been reported in a number of elasmobranch species, but has not been documented in lamnid sharks. This study examined the eyes of three lamnid sharks, white shark (Carcharodon carcharias), mako shark (Isurus oxyrinchus), and porbeagle shark (Lamna nasus) to characterize the iris color and pupil shape. All three species possess a brown color iris circling a horizontal slit pupil. A blue limbal ring of color circles the iris caused by the sclera and cartilage from the limbus which extends into the anterior chamber of the eye. The unique characteristics of the iris and pupil shape are described and implications of these findings on future research are discussed.