I'll have to disagree with Archman, although I agree with his point in general. Often it is the biologist studying species and ecosystems that recognize the problem in the first place, and that lobby or use their research to make the case before legislators (often in conjunction with environmental groups). Legislators are reactive and usually not aware of problems in the biological realm unless brought to their attention.
This is not to say that biologists do the captive breeding or other programs necessary to ensure the survival of a threatened species, although in our case here on Catalina they often do.
I agree that Ducks Unlimited has done a great job enhancing habitat for their "target" species. Salmon fishermen in northern California also helped capture fish to ensure eggs and milt for the CDF&G salmon recovery programs. It is good to see many billfishers encouraging scientists to study and help protect their "targets" and the trend away from kill tournaments to catch-and-release (despite fairly high mortality in some of those tournies). One could also look at the role of spearfishers who identified the decline in black or giant sea bass populations (Stereolepis gigas) in southern California (although biologist C. F. Holder first requested protection back in 1910).
Unfortunately the majority of fishers (at least in SoCal) seem to thwart efforts to preserve species as seen in the serious resistance through political pressure in what was supposed to be a strictly scientific approach to designating marine reserves in Calif., the pressure from commercial abalone harvesters to re-open seriously depleted red abalone stocks, and even the underhanded targeting of already protected species (including the black sea bass) by fishers.
And as for PETA, in my experience they often focus their efforts on domesticated animals including pets. I'm not sure if many of them have much grounding in natural ecosystems. Let's protect cats so they can eat more and more of the ocean fish stocks via canned pet food!