In respect to four vs two as the daily quota:
Difference in daily quotas between salt and freshwater is due to the coast wide recreational allocation quota, 5%. Fishing effort and catches are significantly higher in the non-tidal portion of the Fraser River than other areas. The daily quota therefore is kept at two so all fisheries can remain open for as long as you have been seeing.
Lets look at some numbers:
Assume 30 locations, 50 fishers per location, three shifts a day, two fish per person, 70% success rate, 40 days of fishing. Total river take is 252,000 fish.
Run is estimated at 34,000,000 fish. 5% is 1,700,000 fish. Since it is stated that catch is higher in the non-tidal assume 70% allocated to non-tidal or 1,190,000 fish.
Add 25% to the take by moving to the four fish limit for the last few days of the season and the take rises to be 315,000 fish.
The commercial boys and girls are worried sick that there will be too many spawners on the beds this year. So there is lots of room for a four fish limit for these last days of the season.