Regardless of their race, many people who behave like this, crowding you at a fishing hole, casting over your line, etc., do NOT have a fishing license just as you have suggested. One thing you can do is say something like, "Ummm, hey buddy. Do we need a fishing license to fish in this river? I don't have one, but that's okay, right? You won't tell, right?"
Half the time they will laugh and say, "No problem! I don't have a license either!" These people are not bright. And if they agree with you that it's okay not to have a fishing license/salmon tags, call Fish & Game on them ASAP. Get good clothing descriptions/vehicle descriptions, etc. Be sure to tell Fish & Game you are 100% willing to testify in court against these people, and give Fish & Game your name and contact info to let them know you are serious. Be willing to wait at the side of the road for Fish & Game to show up so you can guide them to the offenders. Give Fish & Game mile marker info, etc., to help them find your exact spot on the river.
Hopefully Fish & Game will confiscate their gear in addition to ticketing them.
These people are not bright. Half the time they will laugh and admit that they don't have a fishing license, too. Make them pay for it.
If they don't speak English, then pull out your fishing license/salmon tags and show it to them and say the word for "license" in Spanish or Vietnamese, etc. It's simple to learn one word from a foreign language. If they try to ignore you when you say the word "license" in their native language and you physically show them your license, then you know they don't have one. Or they may simply shake their head "no" and indicate they don't have one. Call Fish & Game on them.
The main thing is that if you have a strong hunch that these people are fishing without a license, you are probably right. Be able to articulate your reasons as to why you believe this, and Law Enforcement will come out. If you are wrong and it turns out these people have licenses and tags, oh well. Law Enforcement will not be angry with you. Much of the success of OSP, Fish & Game, etc., comes from people giving them tips, so they don't mind at all following up on tips that sometimes don't pan out. But odds are, you will be right at least 50% of the time anyway.