Don't let them get away with it without at least saying something. They may not understand the language but you can make your displeasure abundantly clear.

A buddy and I came across a family of Asians on a dock when we pulled in who were crabbing. He looked in their bucket and proceeded to start tossing the crab out one at a time- "too small!, too small!, female!" etc. until there were none left. They gave us dirty wtf looks but oh well obey the law. Luckily everybody wasn't kung fu fighting on the dock.