Researchers are unsure about the causes for the behaviour, but theories include that it is a playful manifestation of the mammals’ curiosity, a social fad or the intentional targeting of what they perceive as competitors for their favourite prey, the local bluefin tuna.
Wasn't there a big thing about how they suspected these attacks might have started with a mother watching her baby get maimed and killed by a yacht? Like, I swear it was a thing, but I can't find any articles about it and Wikipedia says roughly the same thing as the quoted paragraph.
I will say though, that I found this bit from Wikipedia interesting:
Researchers have also suggested that the behaviour could be a "fad". Other such cultural phenomena among orcas have been short-lived, such as in 1987 when southern resident orcas from Puget Sound carried dead salmon around on their heads.
Fascinating.
