Before you read further, a reminder: There is no “good” or “bad” in Nature. There is only perfection. Animals do what they do for a reason. We humans may not understand their behaviour but to impose judgement is ridiculous. There is always a net gain for some of the animals involved.
Yes, this is me making very clear that to either typify dolphins as “good” (the Flipper phenomena) or “bad” is sheer anthropomorphism and does nothing to enhance the understanding of animal behaviour.
Dolphins are dolphins and they do what dolphins need to do.
Dall's porpoise calf hit from below by Pacific white-sided dolphin.
Okay, now that I have made that very clear, I dare share the exceptional encounter I stumbled upon today. I found two adult (likely male) Pacific white-sided dolphins negatively interacting with a Dall’s porpoise calf.
I know there were only two dolphins as they had distinct dorsal fins allowing me to track them as individuals. I think they were adult males since the fins of adult males tend to be chunkier. I perceive that it was a negative interaction since the two dolphins were corralling the Dall’s porpoise calf; hitting it with their tails at the surface; pushing down on the calf’s head and hitting it from below. It was an encounter that I witnessed for 10 minutes and was very persistent and intense.
I also saw what I think were only two adult Dall’s porpoises repeatedly surfacing some 30 to 40 metres away from the interaction between the calf and the two Pacific white-sided dolphins.
In years past, I have seen this species of dolpin kill a harbour porpoise and a seal pup. It is quite a regular occurrence for these dolphins to interact with fish-eating (“resident”) killer whales in such a way that the killer whales dive longer, go silent and group up. Their interactions with humpback whales most often lead to the humpbacks “trumpeting”, rolling on the surface and slapping with their long pectoral fins.
Dolphins are smart. Very smart.
I put forward that interactions like this allow them to learn, to feed their hungry brains. If this does not sound plausible to you then you don’t have a younger sibling! Any of us who do know how “provoking” also allows young humans to learn. It allows them to find out “What happens when I do this?” “How about this?” “And when I do this?”
Dolphins are extremely social animals too. I believe such interactions allow the dolphins to exercise social bonds and strategize. The males of some well-studied dolphin species (e.g. spotted dolphins and bottlenose dolphins) have been found to have “coalitions” / “alliances”; social units that allow them to group defend, group feed and group mate. The Pacific white-sided dolphins are only beginning to be studied as individuals so science has yet to confirm what sort of social structures they might have. My hypothesis is that the two Pacific white-sided dolphins from today’s interaction have an alliance.
I cannot give you a conclusion to the interaction I witnessed today. When I last saw the porpoise calf, it was alive. However, as fate would have it, I had boat engine difficulty and therefore “lost” the animals as I dealt with my boat woes.
I have annotated the photos at the following link, leaving them in chronological order so that you can see how the interaction developed. I have also provided notes that will help you discern the two dolphins as individuals. Photography was challenging due to wind and the speed of the action.
Remember, no judging Nature for what wild animals do is Natural.
Click here for the photos.
Click here for a study documenting “porpicide” of harbour porpoise by bottlenose dolphins.