2024 Summary of Ocean Ecosystem Indicators

2024 was a mix of average and poor ocean conditions for juvenile salmon in the northern California Current. The Ocean Niño Index (ONI) was strongly positive, indicating a moderate to strong El Niño that persisted from May 2023 to April 2024. During this period, at station NH-5—located on the Oregon shelf in 60-m water depth—local sea surface temperatures and near-bottom temperatures were warmer than average (>1.5°C). Similarly, at station NH-25—located on the slope in 300-m water depth—subsurface temperatures at 150-m depth were 0.5°C warmer than average. The lower trophic level response to this equatorial El Niño signal off Oregon was characterized by decreased biomass of northern copepods, increased biomass of southern copepods, and increased numbers of sub-tropical copepods, resulting in increased copepod species richness. The winter ichthyoplankton that are important forage for juvenile salmon also responded to these warm conditions. The Index of Coastal (ichthyoplankton) Prey Biomass was the lowest value we have observed in the time series, and the species composition of the winter Ichthyoplankton Community Composition had low proportions of coastal larval fish species and high proportions of offshore larval fish species, resulting in the worst-ranked ichthyoplankton community scores in our time series. Together, these results suggest a lipid-poor food chain; poor ichthyoplankton prey biomass and ichthyoplankton species composition (type of fish available as prey) for piscivorous juvenile salmon that out-migrated in 2024.   

The physical spring transition occurred earlier than usual this year, on March 29, due to pulses of upwelling-favorable winds. However, these winds were generally weak and sporadic, often interrupted by downwelling-favorable winds. By late May, upwelling intensified, and on June 7, the copepod community transitioned from a southern copepod dominated community to a northern community. The biomass of northern copepods rapidly increased and remained elevated from June – September, ranking 6^th in the 27-year time series.  

The ocean indicators in 2024 suggested moderate to poor conditions for juvenile salmon. The overall rank of the indicators was 18 out of 27. However, that rank was likely favorably skewed by very low ranks of the summer (ranked #1) and winter (ranked #7) Pacific Decadal Oscillation (PDO). In recent years, this basin-scale index has shown weaker correlations with regional and local sea surface temperatures compared to historical patterns. Indeed, this winter marked the first occurrence in the time series where two basin-scale indicators—the Oceanic Niño Index (ONI) and the Pacific Decadal Oscillation (PDO)—were strongly out of phase. This indicates that basin-scale indices such as the PDO should be interpreted cautiously, and are best placed into a broader ecological context with the other ocean ecosystem indicators.   

Pacific Decadal Oscillation and Ocean Niño Index

The PDO turned negative (cool phase) in January 2020 and has remained strongly negative through 2024. The most negative PDO values of the 27-year time series occurred during the summer of 2024, ranking the summer PDO #1. The Ocean Niño Index (ONI) was strongly positive, indicating El Niño conditions (values ≥ 0.5 °C) from the summer of 2023 through April of 2024. This was the first time in the time series that the ONI and PDO were strongly divergent. The ONI dropped below the El Niño conditions threshold in May 2024, and the National Weather Service Climate Prediction Center predicts the ONI will remain negative throughout the winter and into spring 2025.  

Upwelling Index at 45°N

Strong winter storms led to stronger-than-average downwelling during the winter of 2023-24. Pulses of upwelling-favorable winds started in March, and we estimated that the physical spring transition occurred on March 29. Following the physical spring transition, upwelling-favorable winds were weak and sporadic, with episodes of downwelling-favorable winds and cold (8°C), upwelled water was not observed on the shelf at station NH-5 until May 31 (hydrographic spring transition). Upwelling winds were average during the summer, though data have not been available since the beginning of September to determine the length of the upwelling season.

Sea Surface Temperatures from NOAA Buoys 

Strong downwelling in the winter of 2023-24 led to persistent, warmer-than-average (>1.5°C) sea surface temperatures (SSTs) from October 2023 until May 2024. In May 2024, one month after the physical spring transition, SST anomalies became negative, as upwelling winds increased from weak and sporadic in the spring to more persistent in the summer. SSTs throughout the summer, from May – July, were mostly cooler than average, with a couple of warm events occurring towards the end of May and the end of June. SSTs became warmer than average (+1.5°C) in early August and trended strongly positive through September.

Water Temperatures on the Shelf and Slope 

Along the Newport Hydrographic Line, near-bottom water temperature anomalies at stations on both the continental slope (150-m; top panel) and the continental shelf (50-m; bottom panel) were warmer than average during the winter of 2023-24 and turned weakly negative (cooler than average) in May of 2024. Negative anomalies continued throughout the summer at both stations through September.

Hypoxia

Strong, persistent hypoxic conditions (oxygen concentrations below 1.4 ml/L) had been observed on the shelf (50-m depth) for six years from 2017–22. In 2023, hypoxic conditions were not observed during any sampling date, and in 2024, hypoxic conditions were observed during two sampling dates in August and September.  

Zooplankton

After a 5-year (2018-23) period of higher-than-average northern copepod biomass, there was a strong transition to negative biomass anomalies in the winter and spring of 2024, coinciding with El Niño conditions. Following the onset of upwelling, northern copepod biomass increased during May – September and ranked 6^th in the time series. Over the past five years, southern copepod biomass has oscillated more frequently than northern copepods. However, during the 2023-24 winter, their biomass remained consistently above average, also aligning with typical El Niño conditions. The summer southern copepod biomass and copepod species richness ranked higher (15th and 16th, respectively) than the northern copepod biomass, signaling the presence of a mixed copepod community during the summer months following the relatively strong El Niño. 

The transition from a warm-water, lipid-deplete, winter copepod community to a cold-water, summer community (biological spring transition) occurred on June 7, 2024, approximately one month later than the May 3 long-term mean.  

Winter Ichthyoplankton

The winter Index of Coastal (ichthyoplankton) Prey Biomass (ICPB) in 2024 was the lowest value we have observed in the 27-year time series. Additionally, the winter Ichthyoplankton Community Composition (ICC) in 2024 had low proportions of coastal larval fish species and high proportions of offshore larval fish species, resulting in the most positive ICC value observed in our time series. Together, these results suggest poor prey biomass and species composition (type of fish available as prey) for piscivorous juvenile salmon that out-migrated in 2024.    

The anomaly of the ICPB has typically been positive during colder ocean conditions—with a higher biomass of coastal fish taxa that salmon consume—and negative during warmer ocean conditions. Alternatively, the ICC anomaly is typically negative during colder ocean conditions—with a higher composition of coastal taxa such as larval Pacific sand lance, smelts, and sculpins—and positive during warmer ocean conditions, when the community composition shifts to more offshore taxa such as larval rockfish, northern anchovies, and Pacific sardines. In 2024, the indices were inversely related, suggesting poor prey biomass and species composition (type of fish available as prey) for piscivorous juvenile salmon that out-migrated in 2024. 

Pyrosomes and other gelatinous zooplankton

While colonial tunicates called pyrosomes were common in our plankton nets from fall 2016 through mid-summer 2018, they have been absent in large numbers over the past several years. However, pyrosomes were present in low numbers during our May and September 2024 Northern California Current Broadscale Ecosystem surveys. These surveys sample from northern California to northern Washington, and much farther offshore (200 nm) than our regular monthly sampling along the Newport Hydrographic Line (25 nm). The pyrosomes collected during these surveys were generally found further than 35 nm offshore of Newport and to the south. Pyrosome size consisted primarily of individuals less than 5 cm in length. 

Interestingly, large swaths of Velella velella, a neustonic hydrozoan, washed up on beaches throughout the winter and early spring of 2024. While Velella are not uncommon, these mass strandings are more prevalent in years with warmer-than-average winter sea surface temperatures. In the summer and fall, Pacific sea nettles were washing up in large numbers on Oregon beaches, and large swarms were also noted nearshore.