Review of Klamath River Chinook Spawner Floor Science

The Pacific Fishery Management Council is faced with an overfishing concern of Klamath chinook due to projected Klamath spawner escapement being under the Salmon FMP 35,000 floor for the third consecutive year. The Council has developed three options, one of which includes closing the fishery between Central Oregon and Point Sur for the remainder of the season. The SWFSC and the NWFSC were asked to comment on the effect of escapement levels below the 35,000 floor and whether they would jeopardize the capacity of the Klamath to produce maximum sustained yield on a continuing basis.

The resulting report reviews the Klamath situation and discusses the level of uncertainty in the abundance forecasts. The report investigates the Salmon Technical Team’s Ricker spawner recruit model 2 which includes early marine survival and found that the probability of a recruitment lower than previously observed ranged from 52 to 76 % assuming poor early marine survival conditions. However, if average survival conditions are assumed, the estimated probability ranges from 0.2 to 1.4 %. The report then goes on to discuss long-terms changes in stock productivity, which are highly variable but have a downward trend. The report reviews reasons for that downward trend, which include loss of diversity, local environmental degradation and reduced flows leading to higher temperatures and lower water quality. The report confirms that the 35,000 spawner floor is prudent to insure the capacity of the Klamath to maintain maximum sustained yield on a continuing basis. (April 3, 2006)