Marine predation injuries in yellow-eyed penguins (Megadyptes antipodes) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science in Wildlife Health at Massey University, Manawatū, New Zealand. EMBARGOED until 28 February 2025.
Yellow-eyed penguins (Megadyptes antipodes), endemic to New Zealand and its subantarctic islands, are one of the rarest penguin species in the world, with many factors threatening their survival. Marine predation is one such threat to this species, affecting a large proportion of adult and juvenile yellow-eyed penguins each year across their mainland range. New Zealand sea lions (Phocarctos hookeri) have been witnessed attacking yellow-eyed penguins, however other predators have not been definitively determined. Sharks are suspected based on the characteristics of some wounds. Barracouta (Thyrsites atun) have been implicated in some of the attacks, but evidence supporting this hypothesis is lacking. A broken fragment of tooth found in a yellow-eyed penguin leg laceration, provides evidence of a shortfin mako (Isurus oxyrinchus) or porbeagle shark (Lamna nasus) attack, but with the tooth incomplete and molecular testing inconclusive, an exact identification could not be determined. An increasing frequency of yellow-eyed penguins admitted to veterinary hospitals for treatment of marine predator injuries has been observed in the last decade. Necropsy data shows a similar trend. Assessment of individuals admitted to wildlife hospitals revealed that 84% had moderate to severe injuries. Two thirds (66%) of treated individuals survived to release, and of these 49.1% were not resighted after release, 22.4% were resighted as non-breeders and 28.4% subsequently made breeding attempts post release. Injury recrudescence occurred in 5% of cases. More than 15% of yellow-eyed penguins were hospitalised for multiple predation attacks during the study. Prognosis was largely attributed to the presence of severe injury complications. Hospital survival was reduced by nine times with the presence of a tendon or ligament injury, seven times with nerve damage and three times with osteomyelitis. Complications secondary to captivity were observed in 51.5% of necropsied yellow-eyed penguins which died or were euthanised in veterinary or rehabilitation centres, with fungal and bacterial pneumonia and air sacculitis, and tracheal stenosis, identified as the most common diseases.