Epimeletic behaviour observed in Algoa BaySaturday, 26th September 2020
By Lloyd Edwards
Epimeletic refers to behaviour exhibited by an adult, sometimes together with other adults, where they consistently stay near a dead, entangled, injured or stressed animal. In the case of cetaceans the animal is often a calf. They may help carry it along, keeping it afloat, protecting it from danger and in the case of an entangled animal trying to set it free. When directed towards a young animal by its mother it is known as nurturant behaviour, while if used by adults towards other adults it is known as succorant behaviour.
The first two photos show the recent example we came across in Algoa Bay just near St Croix Island. The female dolphin had her dead calf perfectly balanced on her rostrum / beak / forehead. The head of the calf had been damaged, but the rest of the body looked unharmed. Jake had seen this same pair two days earlier in the same place. They are part of a school of 400 Indo-Pacific bottlenose dolphins that we know as the “heavy breather” pod, because one of the members has a deformed blowhole and makes a weird blowing sound. Another member of this pod is a female known as “Holy” as she has a perfect hole through her dorsal fin. The last time we observed this behaviour was on 20th October 2018 within the same pod as can be seen in the third photo.
This behaviour between members of the same species has positive survival and evolutionary adaptive consequences. It cannot be ruled out that infanticide may take place which then leads to this epimeletic behaviour. Scientists recovered two dead calves where the female had displayed epimeletic behaviour. During the post-mortem it came to light that the calves died as a result of blunt trauma. This means that they were probably killed by an adult. This aggressive display is often observed in cetaceans. Although several cetacean species exhibit epimeletic behaviour it is more frequently observed in wild or captive bottlenose dolphins. Of the 78 records examined in all cetaceans between 1970 and 2016, dolphins were responsible for 92, 3% of the incidents.
It is very sad to see, as the mother may carry it around for a few weeks. She is either mourning her loss or helping it to stay afloat in the hope that it revives itself. Some animals have been known to carry a rotting carcass around, so it is more likely mourning. Scientists just do not know what is going on in its brain.
A female killer whale in the Salish Sea off Canada and the USA made news in 2018 when she carried her dead calf on her head for 17 days while the pod travelled 1600km. She was part of the Southern resident killer whales which feed mainly on salmon. On the 4th September 2020 she gave birth to another calf, which will hopefully fare better than the last one. The salmon on which they feed have become scarce and when the mothers start using up their fat reserves, toxins stored in the blubber may be taken up in the breast milk and so passed onto the calf resulting in death. As crazy as it seems, we had scientists on our boat recently who were studying toxins in penguin eggs. Some of these toxins found in penguin eggs here in Algoa Bay originated from pesticides used in Tzaneen in the Limpopo Province. These toxins enter the rivers, the Indian Ocean and get carried along in the Agulhas current to Algoa Bay where they are taken up by plant then animal plankton. This is in turn consumed by bait fish and adult penguins and passed onto their eggs. Next time think carefully before you use pesticides!
The head of the calf is the white section while the dorsal fin can be seen clearly. The tip of the females rostrum is quite worn and scarred but probably caused by digging for prey in the sand.
The adult also shows some scars on the tip of the dorsal which is caused by the teeth of another adult.
The scars on the flanks are from an unknown origin.
This photo was from our last observation in 2018. Here the skin has almost entirely peeled off the dead calf which makes me think it had been carried around for a lot longer than the one in the recent sighting.