Forecasting Returns of Coho and Chinook Salmon in the Northern California Current in the Face of Climate Change: a Role for High-Frequency Long Term Observations

Successful weather forecasting is based on a basic understanding of the underlying physics and physical mechanisms that determine the weather.  Successful forecasting of fishery yields will require a basic knowledge on where in the ocean a given species lives during all parts of its life cycle, and of processes that determine the key recruitment bottlenecks.  Towards the goal of forecasting salmon returns to rivers of the Pacific Northwest, we have monitored hydrography, plankton and juvenile salmonid abundance in coastal waters off Washington and Oregon for 14 years. We have established that most coho and fall Chinook stocks live in shelf waters off the Pacific Northwest and that recruitment depends on processes in these waters.  Using our oceanographic data, we now provide forecasts of the returns of coho and Chinook salmon to the Columbia River and coastal streams of Oregon and SW Washington. Forecasts are posted to a website www.nwfsc.noaa.gov.  The rates at which these salmonids return to their natal streams are clearly a function of the phase of the Pacific Decadal Oscillation (negative phase results in good returns; positive phase, poor returns); however, although the phase of the PDO is a necessary condition, salmon returns are best predicted by local biological factors: date of biological spring transition, biomass anomalies of northern lipid-rich copepods, copepod and ichthyoplankton community structure, and catches of juvenile Chinooks during June surveys and juvenile coho in September surveys.   Our ability to forecast salmon in the future will depend in part on our ability to forecast the impact of global climate change on ocean conditions in coastal waters. Coupled biophysical ecosystem models along with continued long-term ecosystem observations will become a requirement for understanding how variations in physical climate forcing will affect fisheries and marine ecosystem productivity.