First report of a common dolphin (Delphinus delphis) death following penetration of a biopsy dart

Abstract

The remote collection of skin and blubber biopsy samples from free-ranging cetaceans is a powerful technique which has been increasingly used by scientists in recent years in a wide range of applications, particularly with respect to genetic and contaminant studies. Biopsy sampling, if carried out responsibly, is known to cause low-level reactions, and is unlikely to produce long-term deleterious effects. However, this technique is not completely devoid of risk for the sampled animals, particularly for smaller odontocetes. This paper reports the death of a common dolphin in the central Mediterranean Sea, following penetration of a biopsy dart and subsequent handling. The dolphin was hit in the dorsal muscle mass below the dorsal fin by a lightweight pneumatic dart fired from a distance of 6m by a variable-power CO2 dart projector. The methods and equipment had been previously successfully used with minimal effect on common dolphins and other species under similar conditions; it was therefore considered to be relatively uninvasive and more likely to reduce disturbance while increasing sample retrieval. However, in the reported event, a dart stuck in the dorsal muscle mass instead of recoiling as expected. Less than 2min after the hit, the dolphin began catatonic head-up sinking, and was recovered by a team member at depth. Basic medical care was given to ensure haemostasis, but the animal died 16min later. Minimal overall bleeding and a small wound in the thick muscle mass were not among the suspected causes of death. This may have been the consequence of either indirect vertebral trauma or stress. Furthermore, the dolphin had a relatively thin (7mm) blubber layer, that may have contributed to the unwanted outcome of the biopsy attempt. The author stresses that scientists should only adopt even mildly intrusive research methods after careful review and risk assessment in the light of the precautionary principle, and that their decisions must be reviewed on a regular basis according to the best available evidence.