Suspicious looking tuna
That's the joke.
In the late 80's, there was a huge consumer push for tuna fishers to change their techniques so that they didn't kill dolphins while catching tuna. Before then, tuna fishers used to actually track dolphins, because following the dolphins generally meant being able to find the tuna faster. Then, they'd surround the tuna with their nets, indifferent to the dozens of dolphins they were drowning as part of the process.
By the 90's, there was legislation on how tuna cans could be labeled as "dolphin safe," and stepped up enforcement of the existing laws that made it illegal to intentionally kill dolphins.
During the height of this debate in the popular consciousness, of course, this comic came out joking about that link between dolphin deaths and tuna canning.
There were also myths of dolphin meat in tuna cans as well.
classic pro-dolphin propaganda
Nothing to see here officers tuna around
Still seems fishy mama, just a few more porpoises-ful questions.
