Northwest Fisheries Science Center


Ocean Indicators and Salmon Forecasting

Since 1996, the Center has been monitoring the ocean environment off the Washington and Oregon coasts, its interaction with the California Current, and how ocean conditions affect salmon. This ongoing research is helping us better understand some key relationships between climate, oceanography, and biology that largely determine the fate of salmon entering the ocean during specific years.

What is the ocean index?

NWFSC scientists have developed a novel ocean index tool that combines a suite of oceanographic data, such as sea surface temperature, with biological indicators, such as the amount of salmon prey. Together, these indicators can capture the dynamics of a changing ecosystem and allow us to predict the relative abundance of Chinook and coho harvests far enough in advance for decision makers to plan for good, average, or poor-yield years. The accuracy of such predictions is invaluable to state and federal fishery managers in setting harvest limits and allocations and for tracking recovery of endangered or threatened salmon runs.

Recent salmon forecasts

In 2008, scientists tracked one of the highest levels of ocean productivity observed on record, with a negative Pacific Decadal Oscillation (PDO) index that hadn't been observed in over 50 years, the coldest sea surface temperatures in Pacific Northwest waters in over 35 years, and the highest copepod biomass measured in 6 years. These indicators lead scientists to predict good adult salmon returns, a number confirmed by precocious jack returns that year.

In 2009, scientists noted that ocean conditions took a turn for the worst, with a positive PDO index, warmer sea surface temperatures, reduced copepod biomass, and a massive infusion of a sub-tropical predator, the Humboldt squid. The ability of the suite of indicators to capture the transition of the California Current large marine ecosystem from a productive to a less productive ecosystem allowed managers to more quickly adjust harvest rates of important living marine resources and ensure their sustainability for future use.

In 2010, the trend of cold ocean conditions was interrupted in mid–2009 by the emergence of an El Niño event at the equator that continued into spring 2010 before dissipating. Because of this, the ocean began to warm and remained warm through April 2010. However, a cooling trend resumed in May, and by July 2010, the ocean was the coldest observed in recent years. These extremely mixed signals produced both the "best of times" and "the worst of times" in terms of ocean conditions for salmon, making it difficult to predict returns of coho in 2011 and Chinook in 2012. Scientists said their best guess was to expect near–average returns of coho in 2011 and Chinook in 2012.

In 2011, the ocean indicators sent a mixed message, with certain indicators suggesting the potential for above average salmon returns (i.e., persistence of strong La Niña conditions, a negative PDO, positive copepod anomalies from May-September) balanced by negative indicators (i.e., relatively warm surface waters on the continental shelf, weak upwelling in spring, a short upwelling season, and low abundances of ichthyoplankton during January-March). Considering the previous two years were characterized by below-average ocean conditions, scientists predicted that that 2011 would be an intermediate year with the foundation to support a rich biological community if the ocean conditions remain positive in 2012. However, given the mixed signals, scientists were less certain about the prediction for coho in 2012 and Chinook in 2013.

In 2012, scientists forecast above-average returns of coho in 2013 and Chinook in 2014. Similar to the past several years, individual indicators have sent a mixed message. Certain indicators suggest the potential for above average returns (the persistence of strong La Niña conditions, a negative PDO, positive copepod indicators from May-September, and high catches of spring Chinook salmon in the June survey). However, negative indicators include a late start to the upwelling season, a very warm sea surface temperatures in June and July and a short upwelling season. Given these mixed signals, scientists were less certain of the prediction for coho salmon in 2013 and Chinook salmon in 2014.

In 2013, the recent trend of mixed ocean conditions continued. The physical indicators such as PDO and El Niño were both "neutral", sea surface temperatures were warmer than usual, and upwelling was weak (except for July). However, all biological indicators pointed to good ocean conditions - large lipid-rich zooplankton were present in high numbers, winter fish larvae which become salmon prey in spring were moderately abundant, and catches of spring Chinook during the June survey off Washington and Oregon were second highest in 16 years. Given these mixed signals (and by assigning greater weight to the 'biological indicators'), scientists see potential for good returns of coho salmon in 2014 and both types of Chinook salmon in 2015.