Prédation du requin-tigre sur le dugong dans le lagon de la Nouvelle-Calédonie | Predation by a tiger shark on a dugong in the lagoon of New Caledonia

We report the recent sighting of a dugong from a small outboard motorboat by flat sea and completely clear sky on August 08, 2021, at around 09:00, in the southwestern lagoon of New Caledonia off La Tontouta (22°06.50'S 166°07'E). The dugong was lying horizontally below the surface when approached by the motorboat. The left lobe of its caudal fin was almost completely severed, which necessarily diminished its swimming capacity. The dugong was unable to dive, either because its injured caudal fin lacked the power to provide enough momentum, or because of general physiological distress. The main gash on the left lobe, clearly delineated along its entire length, was attributed to a single, powerful bite made by a large shark with homodont sharp teeth. The characteristics of this injury designate its perpetrator as a tiger shark, the only large predatory shark of New Caledonia to present this type of dentition. The bottom of the lagoon, at a depth of 11 m, was clearly visible from the surface. It consisted of gray sandy mud sediment with a sparse seagrass bed. A tiger shark estimated to be 3-4 m in length, recognizable by its blunt snout, its slender silhouette posteriorly and its asymmetrical caudal fin, passed back and forth near the bottom. The latter was possibly responsible for the quasi-severing of the dugong’s caudal lobe. The observations made here are reminiscent of a hunting technique observed previously on other large mammals including dolphins and humans, where the tiger shark cautiously approaches its prey from the rear, to promptly inflict a powerful bite intended to immobilize it and then waits for it to become weak enough to no longer represent a danger to the shark before devouring it. To our knowledge, this is the first case to document predation by a tiger shark on a dugong in New Caledonia.

Un dugong blessé a été rencontré en surface dans le lagon sud-ouest de la Nouvelle-Calédonie. Celui-ci, incapable de fuir, présentait une quasi-section d’un des deux lobes de la nageoire caudale, blessure attribuée à une morsure unique par un requin-tigre de grande taille. Sous le dugong blessé allait et venait l’agresseur potentiel. Cette observation documente pour la première fois la prédation du dugong par le requin-tigre dans les eaux côtières de la Nouvelle-Calédonie.