Are they a group of elderly people? I was there today too from 2pm to 3:30pm, fishing at the southeast side.
If so, i think it's not worth getting upset at that, just let them know they are wrong, and if shiets persist, just call in. Don't worry about whether the DFO or CO etc would show up or not, just do our part and call them in.
Sometimes it's hard to change some people's values and behaviours, especially for the people that grew in a different society(regardless of the race). I speak both mandarin and cantonese, and i have approached some of the violators that speak the languages quite a few times. All I can say is that, if you talk to these people in a friendlier tone, MOST of them would usually change the way they are fishing, and some of them are even very willing to learn more because there is no language barrier. As well i think pointing out the race would not help diminishing stereotypes....
So, take it easy, dude. The next time you see this, just call in and walk away, don't let them ruin your day.