Fishery managers from Oregon and Washington added four additional days, from Saturday through Tuesday, of recreational spring Chinook salmon fishing in the mainstem Columbia River downstream of Bonneville Dam.  The Oregon Department of Fish and Wildlife says through last Sunday, April 2, there have been about 23,500 angler trips, resulting in a harvest of approximately 1,000 adult spring Chinook, only about 14 percent of the upriver spring Chinook allocation available to it prior to an in-season run size update.  ODFW staff believe that could go up to 40 percent of its pre-update upriver spring Chinook allocation by today, when the fishery was originally scheduled to close, leaving room to add more days and remain confident that the fishery will be well within its conservation limits.  The season upstream of Bonneville Dam, from the Tower Island power lines upstream to the Oregon/Washington border, started Monday and is scheduled to continue through Thursday, May 2.