FTA: “They target the orca, because they think there must be tuna under the pods,” says Jörn Selling, a marine biologist for Firmm whale watching and research foundation with 17 years’ experience in the Straits. “They go right through the pods, their hooks cutting the dorsal fins”.

[…]

But many conservationists suspect some fishermen retaliate violently”

I think it’s at least equally likely they learned that boats of a certain size in the neighborhood of tuna can attack their family, and do this to protect it.