What really bothers me: why does it have only 6 legs?!

To be fair, since the city isn’t really fit for modern ship trading, it would be abandoned if not for tourism. Or be an exclusive hideout for rich people? You can’t really preserve a city in a bubble.

How does that say “killing tuna is good for the environment”?

Isn’t it kinda obvious it’s a comparison to other tuna? Best for the environment would be to kill yourself and not eat anything.

Was there any extra compensation offered for the added duty?