Good Lord. Don't know how they did it in GH but for PS the escapement goals were based on specific spawner survey arrays. In reality, the escapement number is really only an index of the actual number of spawners but if you do the same surveys every year the relationship between years would be similar.

Here is what an old WDFW scientist told me, regarding chum. The agency was finally recognizing that the escapement number used was actually a third to a hlaf of the real number. So, if we actually get the total escapement number we will have more fish to catch as the goal will stay the same. I asked him if he knew where the goals came from. He didn't. They were developed based on the spawner surveys that were giving the underestimates of the actual number. So, if the estimate is a half to a third of the real number, so is the goal as it was based on the estimate. Conclusion, a more accurate estimate does not give you a single additional fish to kill.

Obviously, by asking that question they don't understand how the numbers they are managing by were developed.