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Rough-toothed Dolphin

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by Kate C
Publish date
26 June 2012
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In late May, a Rough-toothed Dolphin (Steno bredanensis) was spotted circling in shallow water at Mallacoota in eastern Victoria. Despite efforts to lead it back out to sea, the dolphin died shortly afterwards. Staff from Museum Victoria and the Department of Sustainability and Environment brought the specimen back to Melbourne Museum to study why it died, and to preserve its tissues and skeleton for the state fauna collection and future research.

Dolphin in a trailer Rough-toothed Dolphin (Steno bredanensis) at Mallacoota, about to be transported to Melbourne Museum.
Source: Museum Victoria
 

This unusual dolphin species is usually found in tropical waters and is poorly known from this part of the Pacific Ocean. While we'd much prefer that this individual were still swimming around in warm northern oceans, its death gives us the opportunity to learn more about this individual, and the species in general. Documenting the natural history of the state is part of Museum Victoria's mandate: dolphins are difficult to study in the wild, so much of what we know comes from necropsies, or post-mortem examinations.

people with dolphin specimen Kate Charlton-Robb talking to MV staff about the dolphin that stranded at Mallacoota.
Image: Dylan Kelly
Source: Museum Victoria
 

Before the necropsy began, staff at Melbourne Museum were invited to see the dolphin. It's a strange but wonderful perk of working in this building that every now and then, we get the chance to view rare animals up-close. Dr Erich Fitzgerald, Senior Curator of Vertebrate Palaeontology, and Dr Kate Charlton-Robb, a researcher at Monash University and Research Associate at Museum Victoria who studies Bottlenose and the newly-described Burrunan Dolphins, talked to staff about the species before performing the necropsy.

 

Watch this video with a transcript

The results of the necropsy showed that the dolphin – a young, large adult male – was quite unwell. First up, Kate and Erich found two large plastic bags in its stomach. The nature of a dolphin's anatomy means that plastic bags do not pass through the digestive tract, but get stuck in the main compartment of the stomach. This doesn't kill the dolphin immediately but puts a lot of stress on the immune system, making the animal susceptible to other diseases. Kate found several signs of immunosuppression: the dolphin had a very high parasite load – lots and lots of worms – and the lesions on its skin, caused by viruses that are common in cetaceans, were more extensive than would be expected in a healthy animal. Furthermore, the walls of the dolphin's heart showed some abnormalities and there were large blood clots in the heart itself. Microscopic examination of the dolphin's tissue, or histopathology, may reveal more about this animal's diseases but additional funding is needed to analyse the tissue samples.

plastic bags found in dolphin stomach These two plastic bags found in the stomach of the dolphin most likely contributed to its death.
Image: Dylan Kelly
Source: Museum Victoria
 

This is only the second specimen of the Rough-toothed Dolphin that has been collected in Victoria. The first was collected in 1869, and until recently, was incorrectly identified as the more common Bottlenose Dolphin.

 

Watch this video with a transcript

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