Sharks are totally ocean-living so it really means the same as fish...
Sharks are indeed a type of fish but unlike "fish" which implies benevolence sharks imply a type of fish that "attacks" and inflicts damage upon people and other living things near the coastal waters just like landfalling hurricanes do.
So I think the fact that shark are fish also is the point - fish curve out to sea but the bad fish (shark) go for the coast to attack, feed, etc..
fish, shark, fish fish, SHARK!
