Another way of safe tuna fishing would be to just fish for safejack tuna, it's the type of tuna that doesn't associate itself with dolphins.
There's also alot of it to so it could be substainably fished.
The reason we don't fish for it properly is because it's harder to find then over types if tuna, reason being with other types you spot the dolphins and odds are tuna is with it. With these there not. They eat it in japan alot though, it's very nice, bit lighter than normal tuna.