2023 Summary of Ocean Ecosystem Indicators
Long-term monitoring of ocean conditions and their effect on juvenile Pacific salmon survival off Oregon and Washington.
Similar to the mixed signals that occurred during 2022, the ocean ecosystem indicators in 2023 also suggest average conditions for juvenile salmon in the Northern California Current (NCC). The overall mean rank of the 15 indicators in 2023 was 11th out of 26 years, with some indicators suggesting good conditions, some suggesting poor conditions, and some in between. For estimating salmon ocean survival, these inconsistent patterns among indicators decrease our confidence in any forecasts.
While the May – Sept PDO value was the most negative value in the time series, surpassing the coolest values in 2022, these strongly negative PDO values are more likely due to warmer sea surface temperatures in the western Pacific than to regional conditions in the eastern Pacific. The PDO values reflect the spatial pattern of SST across the entire North Pacific and, in recent years, have not indexed regional conditions in the NCC as well as in past years. Further, following three years of cool La Niña conditions, the equatorial SST anomalies became positive in April 2023, and have remained so for the past five months, signaling El Niño conditions. Together, the dissociation of NCC surface and sub-surface temperatures from the PDO values, and the transition from La Niña to El Niño conditions suggest a changing ocean environment in 2023 in the NCC.
Local spring and early summer sea surface and subsurface temperatures were cooler than average. However, strongly positive sea surface, and weakly positive sub-surface temperature anomalies occurred starting in July, and these positive anomalies have persisted through the fall. These positive anomalies coincide with the timing of an offshore marine heatwave moving onto the continental shelf. While upwelling favorable winds were weak and intermittent during the beginning of the upwelling season, the wind stress was stronger than average from mid-May through mid-September. These stronger-than-average upwelling conditions dampened the positive near-bottom water temperature anomalies on the shelf (+0.5 °C) compared to the much warmer (+2 °C) surface temperature anomalies. Together, these data demonstrate that regional temperature patterns were variable in 2023, and the temperature variation suggests that environmental conditions for juvenile salmon in the NCC were inconsistent throughout the summer.
The biological indicators also showed mixed signals in 2023. Likely due to the weak and intermittent upwelling at the beginning of the season, the biological spring transition occurred on May 28, almost one month later than the long-term mean. Despite this late transition, the northern and southern copepod biomass anomalies, and the copepod species richness showed signs of cool ocean conditions and a lipid-rich community throughout the spring and summer. However, these anomalies were not as strong as in previous years (2020–2022), resulting in average biomass anomalies for the May–Sept period. The winter ichthyoplankton indices in 2023 were mixed, with above-average biomass of prey for juvenile salmon, but the species composition was slightly more offshore taxa as opposed to coastal taxa. The juvenile salmon catches were also mixed, with relatively low Chinook salmon catches (ranked 19th out of 26) and relatively high juvenile coho salmon catches (ranked 8th).
Pacific Decadal Oscillation and Ocean Niño Index
The PDO turned negative (cool phase) in January 2020, and has remained strongly negative through 2023, ranking 2023 first as the most negative PDO in the 26-year time series. Despite this, the Ocean Niño Index (ONI), which is the three-month running mean of equatorial sea surface temperature (SST) anomalies, shifted from negative (cool) to positive (warm) in April. These equatorial SST anomalies have remained above the +0.5 °C threshold for five consecutive months, signaling El Niño conditions. The NOAA Climate Prediction Center predicts El Niño conditions will continue through at least spring 2024.
While these two basin scale indices are not always in phase, the strong separation of these two indices is the first occurrence in the past 26 years. Because the PDO is an index of the spatial SST pattern in the north Pacific, the strongly negative PDO values over the past few years likely reflect the increased SST gradient across the north Pacific, from warmer sea surface temperatures in the western Pacific compared to the eastern Pacific. As a result, this basin-scale index no longer reflects regional sea surface temperatures (which have been warmer than average since July) as well as in previous years.
Upwelling Index at 45°N
The upwelling season was one of the shortest in the 26-year time series, lasting 150 days. The physical spring transition, as indexed from the cumulative upwelling favorable winds, occurred on April 24, ten days later than the long-term average. Following the spring transition, upwelling favorable winds were intermittent and weak until mid-May. However, from mid-May until the fall transition on September 21, the upwelling favorable winds were stronger than the long-term average.
Sea Surface Temperatures from NOAA Buoys
Cooler than average sea surface temperatures occurred during March and April. Despite the physical spring transition on April 24, warmer-than-average sea surface temperatures occurred during mid-May, likely reflecting the weak and intermittent nature of the beginning of the upwelling season. However, temperatures were cooler than average from mid-May to mid-June coincident with the onset of persistent and strong upwelling winds. The temperature anomalies then became positive in mid-July, coincident with a marine heatwave that reached the continental shelf during that time, and they remained strongly positive through the fall.
Water Temperatures on the Shelf and Slope
Sub-surface temperature on the continental slope (150 m), and near-bottom temperature on the continental shelf (50 m), along the Newport Hydrographic Line, were colder than average in early 2023. However, warmer-than-average temperatures were observed on the slope starting in April, and on the shelf starting in July. The timing of the positive temperature anomalies on the shelf follows the SST anomalies, and satellite observations of a marine heatwave inhabiting the shelf. The near-bottom temperature anomalies (+0.5 °C) were not as strong as what was observed at the surface (+2 °C), likely due to the strong upwelling favorable winds delivering cool bottom water to the shelf.
Unlike recent years, hypoxic oxygen concentrations below 1.4 ml/L were not measured on the shelf (50-m depth) during any sampling occurrence from June through August in 2023. This was the first year hypoxic conditions were not observed since 2017, when the magnitude and duration of hypoxic water on the shelf began to increase.
Northern copepod biomass continues to be positive since 2018, however the biomass anomalies were not as strongly positive in the winter of 2022, and during 2023, as in the previous years. Southern copepod biomass was positive during the fall/winter of 2022 and was negative during all of 2023. The May-Sept average of the northern copepod biomass anomalies ranked 12th, and the average of the southern biomass anomalies ranked 11th in 2023 in the 26 year time series. Despite the presence of a marine heatwave, and the onset of El Niño conditions in 2023, the copepod species richness remained low (ranked 8th in the time series).
The biological transition from a warm-water lipid-deplete winter copepod community to a cold-water summer community occurred on May 28 2023, ranking below average at 16th in the time series’.
Pyrosomes and other gelatinous zooplankton
While colonial tunicates called pyrosomes were a common occurrence in our plankton nets from fall 2016 through midsummer 2018, they have been absent in large numbers over the past several years.
Of note, there were large abundances of chain-forming salps in our May and June surveys along the OR and WA coasts. While these gelatinous zooplankton can be common in offshore samples, in 2023 they were prevalent at nearshore stations.
The 2023 winter (January-March) ichthyoplankton Index of Coastal Prey Biomass (ICPB) was above the long-term mean, ranked the 7th highest biomass in the 26-yr time series. However, the community composition of the winter ichthyoplankton in 2023 included more warm water offshore taxa than cool water coastal taxa. These winter ichthyoplankton data suggest above-average prey biomass (ICPB), but a prey composition with more offshore taxa that are associated with warmer ocean conditions as indexed from the community composition of prey for piscivorous juvenile salmon that out-migrated in 2023.