Northwest Fisheries Science Center

Outlook of adult returns for coho and Chinook Salmon

The anomalous warm ocean conditions that had persisted since September of 2014 are dissipating. While ocean ecosystem indicators in 2015 and 2016 suggested some of the poorest outmigration years for juvenile salmon survival in the 21 year time series, some of the indicators in 2017 were fair, while the indicators in 2018 pointed towards neutral conditions, indicating that the ecosystem might be returning to normal.

PDO and ONI. The PDO turned positive (warm phase) in January 2014, remained strongly positive through June 2017, and has been weakly positive or neutral throughout 2018. La Niña conditions (negative Ocean Niño Index values less than or equal to -0.5) persisted during the fall/winter of 2017/2018 from October through March, then became neutral throughout most of 2018.

Upwelling Index at 45°N. The winter downwelling period was close to the climatological mean until the end of January (day 30) when upwelling favorable conditions persisted resulting in weaker than average downwelling for the remainder of the winter (Figure CU-04). The onset of upwelling on April 15, 2018 followed the long term mean as did the cumulative upwelling during the summer. However, the lack of winter storms prolonged the upwelling season 12 days longer than average.

Sea Surface Temperatures (SST) at NOAA Buoy 46050. Negative temperature anomalies occurred during the winter from mid-February through April from weakened winter storms and upwelling favorable winds. Although the Bakun upwelling index indicated average upwelling during the summer, positive SSTs occurred (+2.5°C) for much of the summer, with brief periods of negative surface temperatures during the end of May, July and the beginning of September (Figure TA-02).

Temperature and salinity properties on the continental shelf/slope. During the upwelling season, the deep water on the shelf was anomalously warm ranking the third warmest in the 21 year time series.

Hypoxia. Hypoxic oxygen concentrations below 1.4 ml/L were observed on the shelf from late June through September, with the 2nd lowest value in the 13 year time series recorded in late August of 2018 (Figure HYP-01).

Zooplankton. During the anomalously warm years in 2015 and 2016, the copepod community remained in a warm state and never transitioned to a cold water (upwelling) community during those years. During January through May of 2017, the copepod community was still anomalously warm, however the community did shift to a cold water community in July 2017, 3 months later than the climatology. In 2018, the community shift from winter to summer occurred on time compared to the climatology, however the fall transition (the shift from an upwelling to a downwelling copepod community) was delayed two months, presumably from the lack of the onset of winter storms and brief periods of equatorward (upwelling favorable) winds. Recent storms in November finally shifted the community to a winter community.

During the first half of 2018, the biomass of lipid rich northern copepods was neutral while the biomass of small southern copepods was positive (Figure NSC-01). After the onset of the upwelling season, the biomass of northern copepods became positive and the biomass of southern copepods became negative.

Pyrosomes. Colonial tunicates called Pyrosomes were a common occurrence in our plankton nets since 2016. We started seeing these rare organisms in the Fall of 2016 and they increased in density and size in the spring of 2017. Pyrosomes were collected in high densities again during our surveys between winter and midsummer of 2018. Similar to 2017, pyrosome density and size increased in the spring and early summer months. Pyrosomes were collected offshore in August 2018, but were not seen in surveys in fall and winter 2018.

Winter Ichthyoplankton. The winter biomass of larval stages of fish species common in salmon diets was above average this year (Figure WI-01), ranking the 4th highest over the 21 years of data. While this suggests a high abundance of food for juvenile salmon, the species composition of the wintertime larval fish community suggested that conditions for outmigrating juvenile salmon were poor.