Learning about dolphins: curiosity and trepidation

Every year more is added to the body of knowledge about marine mammals. Knowledge is shared internationally through various fora and different media. Nevertheless, relatively little is known about these magnificent animals, and every opportunity is taken to study and research them. Thus, when a dead Bottlenose Dolphin washed ashore not far from Brest, it was a chance handed on a plate for the experts to do a necropsy. 

The cadaver, a few days old, was brought to the dissection chamber at the Oceanopolis. As one of our research topics is cetacean (whales and dolphins) research, this was an umissable chance for us too as, like the scientists, we  have to seize every opportunity. We were very pleased to be given permission to film and photograph the necropsy and to talk to Thierry Chambon, the officiating vet. Although very interested in the procedure and the findings that a necropsy can reveal, I have to admit to a certain amount of trepidation at the prospect of seeing a beautiful animal being cut open and its internal organs being examined. Luckily it all went well.
Stranded dead dolphins are common in Brittany. Strong currents and winds regularly bring the floating cadavers to shore. A couple of hundred Common Dolphins wash up every year, with a peak from the end of January to April. What is rare though is a Bottlenose Dolphin being washed up, and for this reason, Thierry Chambon needed to do a thorough investigation. He was assisted by Christine and Jean-Marc, who had been on the scene when Mignon was brought in.

After putting on sterile protective clothing, the first procedure was to establish some general data on the dolphin by an external visual check. It was an adult male, three metres in length, and clearly – even to our inexperienced eyes – very underweight. For the rest, there were no significant wounds or scarring to account for its death.

Getting to work
I had never thought about it, but a necropsy on a large animal is very physical work. Armed with scalpels, knives, saws, bolt croppers and other fearsome implements, Thierry and Jean-Marc set to work, soon building up a sweat. The dolphin was lying on his left side, and a ‘window’ was cut in the right side of the lower belly. The resulting large flap of skin and blubber was folded back to reveal the internal organs and allow access to them.

The kidneys were the first large organs to be removed, and they bore tell-tale signs of how the dolphin had died. The liver, stomach and lungs confirmed these signs: parasites and worms. The kidneys contained air, an abnormal phenomenon, while the stomach was crawling with worms, and the liver and lungs were covered in little round balls which were parasites. Unusually, no food was found either in the stomach nor in the intestines, meaning that the dolphin had not fed in a number of days. The upshot was that the dolphin had been unable to withstand the onslaught of the worms and parasites, and in a weakened state was unable to hunt. His very thin layer of blubber showed that he had lived off his fat reserves until they were simply used up. Basically, he got sick and starved to death. His corpse was then brought ashore by the stong winds and waves of the past days.

Identifying the dolphin
Other tests will be done later, in the laboratory. A number of samples such as skin, blubber, and blood were taken to check DNA and diseases. A piece of the melon (the special fat-filled sac in front of the brain through which cetaceans use echo location) was also taken. This seems to be a significant point to check for pollutants. The dorsal fin was removed and photographed. As each fin is unique, they, along with scarring patterns and very specific measurements such as between the nasal holes to the base of the fin, are used to identify individual animals. This fin will be checked in databases, including the Europhlukes database, to find out if this dolphin was a member of two known groups of Bottlenose Dolphins off the coast of Brittany. Or perhaps he was a passing visitor who unfortunately met his end here.