Yes, it's been an issue for a long time! I grew up on the Northern California coast and have fished the Pacific for salmon on small commercial boats. I have been following the removal of Benbow dam, which has been recently completed. It was built in 1931 on the Eel River in Humboldt County and the removal took a lot of time and resources.
Now that the project is done, it will be interesting to see how the numbers have changed. Check out this fish survey report in the Healdsburg Tribune on January 30, 1939 (80 years ago) about salmon migration through the Benbow dam:
Fish Survey Shows Thousands Going Upstream to Spawn
Though fishing is reported poor in coast rivers and streams due primarily to lack of rain, the fish in large quantities are scaling ladders where numerical count is kept.
A numerical summary of the combined census from both ladders at Benbow dam, for the period October 8, 1938, to January 15, 1939, inclusive, gives the following record:
Seasonal total: 17,359.
King salmon, (5993): grilse, 2135, males 1296, females 2562.
Silver salmon, (6689): grilse 1217, males 2933, females 2539.
While by January 15 the king salmon migration had begun to decline, seasonally, the migrations of both silver salmon and steelhead are only well underway.
Over the new Mad river ladder in Humboldt county from the time of its opening to January 17, a total of 2860 fish have scaled the ladder. Of this number 1151 were king salmon, 223 king grilse, 437 silver salmon, 55 silver grilse, and 1102 steelhead.
On January 17, 227 steelhead passed over the ladder in two hours. One steelhead caught in this area weighed 23 pounds.