My job for a while was to do ISU's for PS salmon stocks. We did ISUs for Chinook, coho, pink, chum, and sockeye for each of the management areas except the Straits unit. Updates were done weekly from July (LW sockeye) through January (Nisqually chum). Each week we also updated the allocations so that fisheries could be adjusted up or down depending on remaining harvest.

We further evaluated the ISU performance by looking at how well they predicted the run as compared to the forecast. In the vast majority of cases, the ISU was quite a bit more accurate.

The runs were generally updated based on commercial fisheries as we had almost immediate (>95% of a day's landings in 3 days) data. We used Indian, Non-Indian, gill net or purse seine depending on which one worked best.

Of course, this was in the 80s and technology has advanced so much that they must have better ways to come up with estimates.