Ocean Ecosystem Indicators Show Less Than Ideal Conditions for Juvenile Steelhead
Photo: Nasa Earth Observatory
NOAA Fisheries reports dramatcally less productive nearshore ocean conditions off the Pacific coast in 2024. The results of the annual fisheries and oceanographic survey along the West Coast documented declines in both the abundance and in the compostition of key marine fish larvae (ichthyoplankton) that feed juvenile steelhead and salmon. The Index of coastal (ichthyoplankton) prey biomass was the lowest value observed in the time series, and the species composition of the winter Ichthyoplankton comprised lower proportions of coastal larval fish species resulting in the worst-ranked ichthyoplankton community scores related to steelhead and salmon survival in the last 27 years. Together, these results of impoverished prey forecast poor survival at a critical time for juvenile salmon and steelhead that out-migrated this past year.
These findings come from the Newport Hydrographic line (NHline) and the Juvenile Salmon & Ocean Ecosystem Survey (JSOES), conducted by the NOAA Fisheries Northwest Fisheries Science Center in cooperation with Oregon State University (CIMRS Program) out of Newport, OR. NHline and JSOES are the longest-running ocean and juvenile salmonid surveys on the West Coast and have clearly demonstrated reliable correlations between ocean conditions, including near-shore prey species, and the distribution, abundance, and survival of juvenile salmon and steelhead in the West Coast marine nearshore ecosystem. The research has established that in years when the winter ichthyoplankton biomass is high and the ichthyoplankton community is dominated by nearshore species, salmon and steelhead show better condition and later return as adults in higher numbers. Observed low abundance and a community dominated by less nutritious offshore prey species in 2015-2020 were likely key contributors to the period of poor salmon and steelhead returns seen coast-wide in subsequent years.
This news comes at a time when record runs of steelhead and various salmon species recently have been documented along many of the watersheds on the West Coast. These improved runs, beyond what many managers had predicted, were likely the combined result of slightly improved ocean conditions when these fish out-migrated to sea in 2021-2022 (reversing years of extremely poor productivity) and particularly in 2022 with the absence of competitive odd-year pink salmon. Scientists have long warned that record-high numbers of pink salmon in the North Pacific, principally from hatchery stocking by the State of Alaska, exacerbate the impacts of warming ocean waters on wild steelhead and other salmon and marine organisms. For example, the alternate-year life cycle of pink salmon in the distant waters of the North Pacific can explain the declined growth of steelhead returning to far inland Idaho.
Physical ocean conditions in 2024, a time of out-migration, were also concerning. The North Pacific Gyre Oscillation (NPGO), an oceanographic climate index linked to North Pacific temperature regimes, ranks 2024 as one of the warmest, and therefore least productive, in recent years. Fluctuations in the NPGO capture the array of oceanographic processes controlling ocean salinity and nutrient levels. Nutrient fluctuations drive changes in plankton production that cascade throughout the marine food web. In general, it is recognized that “a hot ocean is a hungry ocean.”
For steelhead, cooler (positive) index values are linked to better survival, and warmer (negative) index values are correspondingly related to lower survival. Accordingly, the NPGO has been an environmental variable found to help explain the changes seen in wild steelhead returns.
And a reminder, not all anadromous Pacific salmon and steelhead are as vulnerable to changes in ocean conditions. The least sensitive species to climate change spend the least time in freshwater. In contrast, the most sensitive species spend more time in freshwater, rely on extensive summer adult migrations, or depend heavily on estuaries and near-shore coastal rearing habitats. Salmon feeding ecology in the ocean is also a key factor. For example, with their shorter life cycle, including lack of a freshwater rearing phase and lower position on the marine food web, most pink salmon populations throughout the Pacific Northwest have not shown any real fluctuations in productivity. In contrast, wild steelhead and chinook salmon have exhibited more serious declines with their longer lifespans, greater dependence on freshwater habitat, and higher position on the marine food web.
Annual Ocean Indicators Point to Varied Conditions for Pacific Salmon | NOAA Fisheries