So it is a cultural thing in the end?
I really do think so, a dog or a cow, a whale or a dolphin.
Some countries have the cow as a sacred animal and you can go to prison for killiing one, while others....Bratwurst :)
It's the last-link-of-the-food-chain effect. They cumulate all toxic elements.
Dolpins are not the last link in a food chain.
I found something Human health risks
The chief of the NIMD, Koji Okamoto, said, "We presume that the high mercury concentrations are due to the intake of dolphin and whale meat...
I'm not trying to convince you.
I mean that I don't think you are correct about dolphins, it appears to be an environmental issue effecting fish and whales in the area not just dolphins.