We had similar problems with the sharks in Far Cry 3—like the bears, they're beastly to take down. And you need shark skins for several high-level inventory upgrades, for some inexplicable reason.
Well, we found it difficult to take out sharks until we found a boat with a chain gun mounted on its stern. That makes sharks into chum faster than you can swallow your first mouthful of shark fin soup.
Okay, that was bad. Killing sharks for their fins is cruel. Thankfully, Far Cry 3's Rook Island seems to have an overpopulation problem in the shallows. And you can't actually take the fin anyway! You take the skin and throw the rest away. Better?