CK: Escapement is NOT an "impact", rather it's a "metric" - one used along with estimates of total catch in order to determine TAC and various fisheries management benchmarks.
"Escapement" is the number of fish that make it back to their spawning grounds that "escaped" the various capture fisheries, and predators, and diseases from fish farms (threw that one in especially for you CK).
"TAC" is Total Allowable Catch.
TAC is determined by looking at total return estimates (add escapement and total catch together), and then allowing for a certain percentage of "take" within all fisheries on the return estimate for that stock. Certain "weak stocks" are subject to a lowered exploitation rate (from 0-20%) where more robust stocks are allowed to be harvested at higher rates (20-50%). It's all about "risk adverse" managent, using the precautionary approach, WSP benchmarks and in-season management.
I could have done that - so let's do that now. Total in-river run size is calculated by adding together escapement AND in-river capture fisheries. In this case, it would be 2,657,000 PLUS 277,00 which equals 2,933,000. The in-river exploitation rate would be 277,000 divided by 2,933,000 or only 9.4%.
For the more robust stocks - this is a small in-river exploitation rate. For the more "at risk" stocks - this may or may not allow full conservation needs to be met as each species/stock has certain conservation targets that relate to numbers of spawners released to the spawning areas.
Here's some of the problems inherent in fisheries management:
1/ Each stock has a definate spawning and migration timing that is reasonably predictable, but may shift by a few weeks in any year,
2/ Sometimes weaker stocks intermingle with stronger stocks when migrating,
3/ Accurately determining exact timing of both robust and weaker stocks requires in-season management informed by DNA analysis and test fishing,
4/ Most fisheries take some portion of both weak and robust stocks, but the intent is to close those fisheries during the passage of weak stocks,
5/ You won't really know what came-in for the year until the run is over,
6/ Gill nets are made-up ahead of time to target a certain species, and have a certain mesh size, colour, hanging ratio and depth that might not fish appropriately for other species and sizes,
7/ fish species come into a river and migrate upstream in a certain dependable order, but larger rivers may have an assortment of species and runs that co-migrate in the mainstem fisheries but branch off to the tribs, and
8/ Capture numbers in the marine and in-river sports, sports-commercial, commercial, economic, and FSC fisheries may be inaccurate, unknown, or late in arriving. The idea is to add all of these numbers together in-season, and manage for a total TAC.
This list is far from exclusive or complete.
As far as the Fraser River goes - fisheries managers lump sockeye stocks wrt run timing, and mange each set of run timings as a single management unit with their own conservation targets and exploitation rates.
It's complicated. Just saying the run is "depressed" (which it may be or not) and claiming 276K is too big a number really doesn't give you the tools to assess anything. What stocks comprised that 276K is really the key to understanding potential impacts. Seeing what landed-up on the spawning grounds is the key to seeing any realized impact.
Trendsetter: if you have more accurate numbers - then lets use them. Don't forget FN have big extended families that often live off reserve, but are on the books of that FN; and the catch is processed, saved, and doled-out to them too - no matter where they currently live.
