Applying the diagnostic criteria of wound morphology and dental allometry on white shark (Carcharodon carcharias) (Lamnidae) predation on a Franciscana dolphin (Pontoporia blainvillei) (Pontoporiidae) in the Brazilian southern coast
Walter Nisa-Castro-Neto, Patricia Charvet, Paulo Guilherme Carniel WagnerContext
The presence of the white shark (Carcharodon carcharias) off the coast of Brazil is rare and without records of its feeding behaviour. The Franciscana dolphin (Pontoporia blainvillei) is an endangered species in the same area, with declining populations.
Aims
Provide the first forensic record of C. carcharias predating on P. blainvillei off the coast of the south-western Atlantic, documenting a new white shark occurrence off the Brazilian coast.
Methods
The white shark wounds were identified according to the dimensions of the teeth marks, bite morphology, tooth allometry and scars orientation. The total length and weight of the white shark were estimated by using the measurement of the upper jaw bite circumference (UJBC), by using bite marks and TPSdig software for calculations. The age estimation of the Franciscana dolphin was established through the use of the von Bertalanffy model. The Franciscana dolphin was found stranded on the beach, with death estimated between 3 and 5 days earlier according to skin peeling and decomposition state.
Key results
The Franciscana dolphin (~1.72-m total length, TL) was an adult specimen (estimated to be ≥4 years), unsexed because of two sharp bites (Bite III) in the ventral area and one in the dorsal area. An upper jaw average interdental distance between teeth A1 and A2 on the right side measured 0.5 cm and the Bite I UJBC measured 60.3 cm. The white shark bite measurements indicated an estimated TL between 3.6 and 3.8 m, and weight between 400 and 490 kg. Bite patterns suggest a subsurface attack strategy, consistent with white shark predation on small cetaceans documented globally. Bite I was the most recent bite on the Franciscana dolphin. Bite II caused haemorrhage on the dorsal fin, indicating that the cetacean was still alive when it was predated.
Conclusions
The predation of C. carcharias on P. blainvillei confirmed that the species is an active inhabitant of the Brazilian southern coast, on the basis of forensic evidence obtained from the stranded specimen.
Implications
Given the rare records of white shark on the coast and the systematic decline of both species, it is essential to elucidate their roles in the ecosystem.