Disregard that PFBC study, it's more full of holes than Swiss cheese.
A great deal of harvest of brook trout goes on. Mostly in the early season, and particularly on opening weekend. And some after summer thunderstorms. Almost every brook trout stream's population is affected by this cropping.
There a very few streams that aren't affected much by angler harvest, for reasons I won't explain. I had the good fortune to fish a few of these, and it's like night and day compared to "regular" brook trout streams. There's just a whole lot more of the larger brookies in the streams that don't get hit.
If you are really interested in learning about harvest on brook trout streams, you have to actually go out to different brook trout streams on opening weekend. After you do that some years, you'll see that the brookie streams are getting hit.
You learn about this stuff by actually fishing brookie streams a lot, particularly on opening weekend. These studies are a joke. They send some college kid out there with a clipboard. But the hard-cores will see there's some kind of study going on, and just go to some other stream. As soon as they see the vehicle they'll go somewhere else. They're not out there to talk to somebody with a clipboard. They're out there to get some brookies for the pan.
The only anglers who will talk to the clipboard toters are people like us, the C&R flyfishers, who are proud to tell them that we fish C&R.
This is the Heisenberg Uncertainty Principle at work. You can't conduct a study without the study affecting the thing you are trying to measure. At least I think that's the Heisenberg Uncertainty Principle. I'm not completely certain, though.