Increasing Certainty in Uncertain Times: Improving Estimates of Fall Chinook Salmon in the Nestucca River, Oregon

In 2009, the Oregon Department of Fish and Wildlife estimated 468 Chinook Salmon spawned in the Nestucca River basin, compared to a 20-year average of 10,942. The forecasted return for the following year was also very low, 639; however, there was a high degree of uncertainty around these estimates making fisheries management decisions challenging.  From 2010 through 2014, we conducted mark-recapture experiments in the Nestucca basin to assess the current status of the spawning population and to attempt to develop a better estimator of abundance. We conducted creel analysis concurrently during four of the five years to assess in-river harvest and to allow for an adjustment of the mark-recapture estimate for fish harvested above the marking site. Over those five years, we identified a visual index in a suite of six spawning surveys that demonstrated a consistent relationship to the mark-recapture abundance estimate over the range of population sizes and flow regimes experienced. From these data, we were able to generate a cost-effective method to estimate the spawning population more accurately in years in which we do not conduct mark-recapture. The estimates will also have precision measures to better inform management decisions.