Fatal tiger shark, Galeocerdo cuvier attack in New Caledonia erroneously ascribed to great white shark, Carcharodon carcharias

Tiger Shark Attack on a Scuba Diver in New Caledonia

Herein we report an unprovoked shark attack on a scuba diver in New Caledonia. The species responsible for the attack was identified as a tiger shark (Galeocerdo cuvier), based on both the victim's testimony and forensic examination. The victim suffered significant loss of soft tissues from one thigh, which resulted in hemorrhagic shock. Even though the event occurred at a remote location, miles away from the nearest hospital, appropriate first aid, immediate deployment of an alert system, and prompt helicopter transfer by an emergency rescue team allowed the victim to be transferred to an intensive care unit in stable condition and to undergo surgery within 4 h of being bitten. Early coverage of exposed bone was performed, followed up with negative pressure dressing, antibiotic treatment, hyperbaric oxygen therapy, and a split skin graft. In spite of the massive muscular loss incurred, the victim was able to regain her ability to walk within 6 wk of the incident. Shark attacks on scuba divers are rare and seldom reported, especially in New Caledonia.

[Shark attacks in New Caledonia from 1958 to 2020: a review of cases]

Background and objectives

Recent shark attacks in New Caledonia have prompted local authorities to elaborate a risk-management plan. The objective of the present paper is to produce detailed data on shark attacks that occurred in New Caledonian waters for the last few decades, as well as on the injuries of the victims, in order to inform rescue and medical services as well as authorities in charge of educating the public and providing security.

Methods

Incidents involving sharks and humans in New Caledonia for the last six decades were included into a database. Sharks were tentatively identified to species according to the shape, size and other external characteristics of injuries to the victims, together with witness accounts. The severity of shark bites was evaluated against the scale proposed by A.K. Lentz and co-authors (Am Surg. 2010;76:101-6).

Results

Sixty-seven shark-attack cases were recorded in New Caledonia from 1958 to 2020, of which 13 were lethal. The majority of the attacks concerned spearfishers and freedivers collecting invertebrates (58.5% of total). In the last decades, shark attacks may have increased towards bathers, swimmers and snorkelers (18.5%), and people taking part in water sports including surf, kitesurf, windsurf and SUP foil (14%). One scuba diver was also attacked (1.5%). Twenty attacks including 8 lethal ones were ascribed to the tiger shark Galeocerdo cuvier; 14 attacks including 2 lethal ones to the bull shark Carcharhinus leucas; 2 attacks including 1 lethal to the great white shark Carcharodon carcharías. The lethality of attacks was almost one in five, above the global average.

Conclusions

Feeding incentive appeared to be a frequent factor triggering attacks. The education of the public should be promoted as a preventive measure aiming to reduce the risk of such accidents.

Development and successful real-world use of a transfer DNA technique to identify species involved in shark bite incidents

Identifying the species involved in shark bite incidents is an ongoing challenge but is important to mitigate risk. We developed a sampling protocol to identify shark species from DNA transferred to inanimate objects during bite incidents. To develop and refine the technique, we swabbed shark bite impressions on surfboards and wetsuit neoprene collected under semicontrolled conditions. Methods were tested experimentally and then successfully used to identify the species involved in a real-world shark bite incident. Thirty-two of 33 bite impressions yielded sufficient DNA sequences for species identification, producing barcodes from five test species, including dusky, Galapagos, bull, tiger, and white shark. The latter three species collectively account for a majority of shark bites worldwide. Our method successfully identified the species (Galeocerdo cuvier) responsible for a fatal shark bite on December 8th, 2020 on the island of Maui, from swab samples collected from the victim's surfboard 49 h after the bite incident. Our experimental results demonstrate that shark species can be accurately identified from transfer DNA recovered from bite impressions on surfboards and wetsuit neoprene. The successful use of our method in the real-world incident shows great potential for the practicality of this tool. We recommend DNA swabbing as a routine part of the forensic analysis of shark bites to help identify the species involved in human-shark interactions.

Forensic genetic identification of sharks involved in human attacks

Each year, 75-100 unprovoked shark attacks on humans are recorded, most of them resulting in no or minor injuries, while a few are fatal. Often, shark identification responsible for attacks relies on visual observations or bite wound characteristics, which limits species determination and preclude individual identification. Here, we provide two genetic approaches to reliably identify species and/or individuals involved in shark attacks on humans based on a non-invasive DNA sampling (i.e. DNA traces present on bite wounds on victims), depending on the knowledge of previous attack history at the site. The first approach uses barcoding techniques allowing species identification without any a priori, while the second relies on microsatellite genotyping, allowing species identification confirmation and individual identification, but requiring an a priori of the potential species involved in the attack. Both approaches were validated by investigating two shark attacks that occurred in Reunion Island (southwestern Indian Ocean). According to both methods, each incident was attributed to a bull shark (Carcharhinus leucas), in agreement with suggestions derived from bite wound characteristics. Both approaches appear thus suitable for the reliable identification of species involved in shark attacks on humans. Moreover, microsatellite genotyping reveals, in the studied cases, that two distinct individuals were responsible of the bites. Applying these genetic identification methods will resolve ambiguities on shark species involved in attacks and allow the collection of individual data to better understand and mitigate shark risk.