Ocean Conditions and the Future of Wild Steelhead
Recent news coverage has brought renewed attention to the North Pacific's changing ocean conditions and what they mean for steelhead and salmon. NOAA scientists have been tracking how environmental shifts in the North Pacific are affecting survival rates for these iconic fish, and the picture isn't necessarily promising.
For juvenile steelhead, winter and early spring ocean conditions can make or break an entire year class. As these young fish enter the ocean for the first time, they encounter a gauntlet of biological and physical oceanographic factors, all tied to a single, increasingly dominant feature: Heat.
The North Pacific is warming at an alarming rate. Ocean heat content continues to climb, sea surface temperatures have hit record highs, and marine heat waves, those prolonged periods of dangerously elevated ocean temperatures, are becoming more frequent and severe. While the region has been warming rapidly for two decades, 2025 stands out as markedly hotter than even recent years.
The North Pacific Gyre Oscillation (NPGO), an established oceanographic index, helps explain the impacts of increasing temperature effects through the marine ecosystem. The NPGO correlates with shifts in salinity, nutrient availability, and chlorophyll-a concentrations, all driven by changes in upwelling patterns and water circulation. Together, these factors shape primary productivity and food web dynamics in ways that ultimately determine whether wild steelhead thrive or struggle.
The pattern is obvious: cooler, nutrient-rich oceanic conditions (shown in blue in the chart below) drive higher productivity and better steelhead survival. Warmer, less productive environments (shown in orange) correspond with reduced success for steelhead and many salmon species.
The correlation between steelhead productivity and the NPGO is clear and concerning. Ocean conditions have been consistently unfavorable since late 2013, aligning precisely with the recent diminished steelhead returns across the Pacific Northwest.
Greenhouse gas emissions are the primary cause of these changes. The world’s oceans have become a dumping ground for much of the excess heat trapped by rising levels of greenhouse gases, absorbing an estimated 90% of the extra heat. As atmospheric carbon traps more heat, the ocean's surface layer warms, reducing vertical mixing with colder deep water. This creates a thinner mixed layer where heat becomes concentrated, accelerating surface warming in a self-reinforcing cycle.
But the North Pacific isn't just warming, it's warming faster than any other ocean basin on Earth since 2013.
The region has experienced two major marine heat waves in just five years, with devastating consequences for marine mammals, seabirds, fisheries, and the coastal communities that depend on them. These events aren't anomalies, they're warnings.
What the future holds for wild steelhead, and for the broader North Pacific ecosystem, remains uncertain. But recent data from "the Blob," a massive patch of anomalously warm water that formed in the northeastern Pacific, offers troubling insights into what might become the new normal.
The impacts of recent warming have been extensive and significant. With global ocean temperatures expected to continue to rise, these developments may indicate fundamental ecological changes currently in progress—changes that could pose serious survival challenges for wild steelhead, which are already at risk due to a century of habitat degradation and overfishing.
Wild steelhead are resilient, much more so than hatchery origin fish, a well-established observation that demands a real focus on conserving natural-origin fish. The advantage of greater fitness of wild steelhead cannot be ignored given the more challenging environment stemming from the changing climate.