Commercial fishers and marine biologists along the U.S. West Coast are watching a familiar threat return. Sea surface temperatures are running roughly 3 to 4 degrees Fahrenheit above normal from southern California to the Gulf of Alaska, and the Northeast Pacific set a record average temperature of 20.6 degrees Celsius on September 9, 2025. The warm anomaly weakened briefly in late autumn but re-intensified after October and November, expanding again across a wide swath of open ocean. Species are already responding: market squid have pushed north into Oregon waters, forcing the state to adopt its first-ever squid-fishing regulations. For coastal economies that depend on predictable fish populations, the question is whether strong upwelling can keep the worst of the heat offshore or whether the pattern will mirror the devastating marine heatwave of 2014 to 2016.
Warm water, cold upwelling, and the shelf boundary
NOAA scientists have designated two concurrent heatwave events in the region, tracked under the labels NEP25A and NEP26A. Those names follow a standardized system that groups contiguous pixels of anomalously warm water and assigns them identifiers based on the year and sequence of formation. The system draws on NOAA’s National Centers for Environmental Information, which calculates marine heatwave data using the Optimum Interpolation Sea Surface Temperature dataset and applies the Hobday definition for event detection.
What makes the current episode distinct from the 2014 to 2016 “Blob” is the behavior of coastal upwelling. During that earlier event, weak upwelling allowed warm water to flood the continental shelf, collapsing productivity and triggering mass die-offs of seabirds, sea lions, and commercially valuable species. In 2025, upwelling has been strong enough to hold warm waters offshore, feeding nutrients into the nearshore zone and sustaining the base of the food web. That physical barrier matters because species displacement depends not just on how hot the open ocean gets but on whether the heat penetrates the shallow waters where most commercial and forage fish live.
If upwelling strength stays above the 2024 median through the end of this year, the share of heatwave area overlapping the continental shelf could remain limited, reducing nearshore species displacement compared with 2014 to 2016 even though sea surface temperature anomalies are similar in magnitude. That hypothesis is consistent with the pattern NOAA described in its California Current Ecosystem Status Report, but it carries a significant caveat: upwelling is seasonal and wind-dependent, and any shift in atmospheric circulation could let the warm mass push shoreward quickly.
The broader backdrop is a Northeast Pacific that has already been flagged by NOAA as experiencing another large marine heatwave. That assessment underscores how persistent the anomalies have become and how closely they are being tracked across the California Current, from Baja California to British Columbia. While the current pattern is not identical to the Blob, the spatial footprint and intensity are comparable enough that many managers now treat these warm phases as recurring features rather than rare shocks.
Species on the move and Oregon’s new squid rules
The biological signal is already measurable. Market squid, a species historically concentrated off southern and central California, have shifted their range northward as water temperatures climbed. Oregon had never needed to regulate a squid fishery before, but the influx of market squid into its waters prompted the state to write and adopt its first set of squid-fishing rules. That regulatory response is a concrete indicator of how quickly warming can redraw the map of marine resources and force management decisions in states that lack institutional experience with a given species.
Peer-reviewed research published in Nature has shown that marine heatwaves can produce “thermal displacement” at scale, relocating fish populations by hundreds of kilometers. The study provided a quantitative framework linking anomalous temperatures to shifts in species distributions across multiple ocean regions. Applied to the current West Coast situation, that framework suggests the displacement risk is real but unevenly distributed: species tied to the continental shelf face less pressure when upwelling keeps the nearshore cool, while pelagic species in the open ocean are more exposed.
For market squid, that distinction is critical. The species prefers relatively cool, productive waters and spawns nearshore, but adults can track favorable conditions along the coast. As warmer water extends northward yet remains buffered from the immediate shoreline by upwelling, squid can expand into new latitudes without necessarily abandoning traditional spawning grounds further south. The result is a patchwork of availability for fishers from California to Oregon, with landings increasingly reflecting where the temperature gradients and productivity lines intersect in a given season.
California’s Department of Fish and Wildlife has incorporated the heatwave’s extent and re-expansion into its 2025–2026 risk assessment, tying expected ocean conditions to ENSO transition probabilities. That document signals that state managers are already factoring the warm anomaly into harvest decisions, though specific quota adjustments tied to the current heatwave have not been publicly detailed. For now, the emphasis is on flexibility: maintaining the ability to tighten or loosen regulations rapidly as new survey data and temperature maps arrive.
Gaps in the data and what to watch through winter
Several pieces of the puzzle are still missing. No primary landings or survey datasets have yet quantified the exact northward displacement distance or biomass shift for market squid or other key species in 2025. Monthly heatwave extent percentages and regional probability outputs from NOAA’s experimental forecast product have not been published in a form that allows precise tracking of the offshore-versus-coastal penetration pattern. Without those numbers, the hypothesis that upwelling is keeping the shelf below a critical heatwave coverage threshold remains plausible but unconfirmed.
The NOAA Integrated Ecosystem Assessment program operates a California Current heatwave tracker that compares the evolving footprint of the present anomaly with the Blob and other past events. That tool offers one of the clearest visual summaries of how far the warm pool has advanced toward the coast and how its intensity has waxed and waned over time. Yet even there, the resolution is coarser than what many fishery managers would like when making port-by-port decisions about effort, season timing, and bycatch risk.
Through the coming winter, three indicators will matter most. The first is upwelling strength, particularly during late spring and early summer when winds typically drive the strongest vertical transport. A sustained drop in upwelling would likely allow the warm offshore mass to slide onto the shelf, compressing habitat for cold-affinity species such as salmon and Dungeness crab and amplifying the kind of ecosystem stress seen a decade ago.
The second is the behavior of the heatwave itself: whether the anomalies deepen and persist at the surface, or begin to relax under the influence of changing atmospheric patterns. Even modest cooling could ease thermal displacement pressures and slow the pace of range shifts, buying time for management responses. Conversely, a further intensification would increase the odds that new species assemblages become the “new normal” for at least several years.
The third is the management response. Oregon’s rapid move to regulate squid illustrates how quickly policy can adapt when signals are clear and stakeholders are engaged. Other states may face similar decisions if sardines, anchovies, or highly migratory species change their usual routes in response to the warm pool. Transparent use of heatwave forecasts, coupled with real-time monitoring of landings and surveys, will be essential to avoid both overreaction and complacency.
For coastal communities, the stakes are practical rather than abstract. Port economies that depend on a small number of target species are especially exposed to sudden shifts in availability, while processors and distributors must decide whether to invest in new gear and markets for species that may or may not remain abundant. The evolving marine heatwave in the Northeast Pacific is, in that sense, both an oceanographic event and a stress test for how flexibly the West Coast’s fisheries system can respond to a warmer, more variable sea.
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*This article was researched with the help of AI, with human editors creating the final content.
