It may be "dirty" but not really a secret. Page 18 of the current regs pamphlet has a full page of consumption recommendations from the Dept. of Health (DOH). For Puget Sound the DOH provides a detailed break-out by WDFW marine areas and also specific "hot spots" within each of those areas. Here is the link: http://www.doh.wa.gov/CommunityandEnvironment/Food/Fish/Advisories/PugetSound.

While they do not cite the actual levels they do indicate that the two primary contaminants are PCBs and methyl mercury.

For all of the eastern strait, San Juans, Hood Canal and inner Puget Sound waters the general recommendation is for no more than one serving per week of (ocean) Chinook and no more than two servings per month of blackmouth (but, again, note any hot spots listed).

One anecdotal comment: Pinniped reproduction seems not to have been adversely affected from eating all of those blackmouth (they have to have gone somewhere.....).