Salmon fishing is a huge business in Alaska so it shouldn't surprise anyone that its heavily managed and monitored by the Alaska Department of Fish and Game (ADFG). Of course photographers are far more interested in seeing those fish in streams, especially if there are bears trying to make a meal out of those salmon.
Although its pretty dry reading, here is the forecast for salmon returns in various parts of the state with break outs for the various species. There is also data on the accuracy of forecasts in previous years. Nailing down accurate forecasts for ADFG is much like catching those same salmon for a bear- elusive and slippery. ADFG's accuracy is about +/- 20% according to this report.
http://www.adfg.alaska.gov/FedAidPDFs/SP19-07.pdf