I also sent the Market an email, appealing to their business sense by saying:
1. Native steelhead are endangered, even if Indians and/ or commercials are allowed to net them in certain watersheds.
2. It's bad publicity to advertise and sell endangered species. You wouldn't do business with a butcher who had a sign in his window 'Fresh Panda steaks $4.99/ lb' would you? Well, the Market is in this position today by selling native steelhead.
3. Turn this to a public relations advantage by stopping the sale of native steelhead immediately. Instead, switch to a hatchery- or farm-raised only steelhead policy, and advertising this. (The fish will taste just as good.)
If I lived in the area, I might also have politely mentioned that this scenario would be preferable to a film on the 6 o'clock news of school kids carrying signs saying 'Stop killing our endangered steelhead'. A half dozen concerned citizens handing out leaflets explaining why native steelhead should not be purchased (but hatchery steelhead were OK), and urging a boycott of the Market would complete the picture. 
If this approach works, you can take the campaign to the next largest fish market and/ or the supermarket chains in sequence.
The three possible flaws in the above argument are: (a) there are certain times of the year when hatchery or farmed raised fish aren't available, only natives; and/ or (b) farm-raised steelhead (diploid rainbows) don't taste as good as native or hatchery steelhead (do they?); and/ or (the clincher) (c) it's cheaper for us to buy native steelhead than farm-raised steelhead and/ or we can sell natives at a higher profit margin.
If any of the above is true, a boycott with lots of negative publicity may be the only way to get retail sellers of native steelhead to see the light. After all, to a fish market steelhead are not a passion, they are a commodity to earn a profit from.