Stingray spines: A potential cause of killer whale mortality in New Zealand

Abstract

Stingrays are a significant component of the diet of killer whales (Orsinus orca) in New Zealand waters. However, encounters between stingrays and several marine mammal species are known to have fatal consequences for the latter. Thus, it was speculated that similar injuries could be a mortality factor among killer whales in New Zealand. An autopsy examination of a sub-adult female killer whale found floating in the Hauraki Gulf, revealed deep body penetration by two stingray spines and superficial penetration by a third spine. One of the deeply-embedded spines appeared to be recently acquired as it was still covered by an intact integument. It was located posterior to the cranium in the region of the vascular cranial rete mirabile and in close proximity to three major arteries. Otherwise, the whale was in good body condition and there was no evidence of pre-existing disease or injury. It is likely that death occurred either as a result of blood loss, or as a result of an acute reaction to toxins released by the stingray spine. Predation on stingrays is probably a learned behavior among killer whales in New Zealand, and given its prevalence among the resident whales, it is generally a successful foraging strategy. However, this case indicates that the strategy is not without risk. Thus, stingray spine injury should be considered a potential cause of stranding or beaching among killer whales in New Zealand.