Why such an early close date on the South Fork of the Salmon

I just read that the SF of the Salmon will close on the 9th. Only 2 1/2 weeks after the season has opened. This year there were 273,000 plus Salmon over Bonneville. 118,000 more that last year. There were 87,000 over Lower Granite. 47,000 more than last year. According to your catch numbers the catchable fish on the South Fork this year close to 750 fish. This is roughly 1.6% of the fish over Granite. Given the huge return numbers closing the South Fork this early seems to be a closure based on something other than numbers. I am wondering what the motivation is behind this decision.