One of the biggest problems in Jefferson Parish is drinking and driving. So one would think the main responsibility of the police department would be to stop those DUIs. Not if there are rats in the canal that need shootin'!
In the middle of his patrol, Seagal decided it would be more entertaining if they stopped trying to pull over drunk drivers (booooring) and joined up with the SWAT team to shoot nutria (fun!). Steven makes it known that his Buddhist beliefs don't allow him to kill something if he doesn't have to, but that doesn't mean he can't watch his buddies shot the shit out of those vermin!
In all fairness, they were hunting the nutria because they chew through the canals, and they tried trapping them. But trapping didn't work, so the only way to get rid of those suckers is to shoot the shit out of 'em. And that's how those cheap Elmer Fudd hats you buy on the street for eight dollars are made.