Oceans of Change: Recent Conditions in the North Pacific Are Dramatically Affecting Steelhead Survival
"The Times They Are A-Changin’ " – Bob Dylan
By Guy Fleischer, WSC Science Advisor
Steelhead populations on the West Coast are affected by what scientists often call the “Four H’s”: Habitat degradation, Hatchery influence, Harvest, and Hydropower dams. But there is another critical element to their survival: the High Seas. Historically, most of our attention has been drawn to those issues which are mostly within plain sight and, for many anglers and conservationists, this has meant an intense focus on the freshwater portion of steelhead life cycles. But now, because of recent dramatic declines in survival, we need to pay attention to this key component beyond our immediate gaze, beyond that deep pool or run we are planning to fish. We need to think ‘salt’, because, without the Pacific Ocean, steelhead are, well, not steelhead.
All of us understand that steelhead are amazing masters of their aquatic environment. Oncorhynchus mykiss has adapted to living in both freshwater and saltwater - with a life history much more diverse than their salmon cousins - where they can live comfortably as either a resident form or an anadromous form and both of which can coexist (and cross‐breed to produce progeny of both forms). At some time in the distant past, most likely during the late Oligocene Epoch (about 30 million years ago), the oceans began to cool - the cooler water, more productive of food organisms for fish, is believed to be a feature that allowed salmon and steelhead to adapt to anadromy to take advantage of this increased marine food productivity. About 8 million years ago, the Pacific Ocean began to look more like what it is today; by then, steelhead and salmon similar to those we know today had been living in coastal rivers for about 2 million years.
The North Pacific Ocean beckoned. The allure of better growth and survival undoubtedly drove these fish to partly abandon their freshwater habits and begin to include a salty, nutritious stint in the ocean. Quite a trick, metabolically, and one that then exposes these fish to the quirks of the ocean environment. An environment of dynamic complexity but opportunity – a briny yin and yang. Those complex oceanographic and weather patterns in the vast North Pacific can be described in simpler terms by the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). These are oceanographic indices that – much like the DOW Jones Industrial Average or the S&P 500 – integrate and aggregate complex and varied elements into a single index that can be used to track changes and show trends.
Instead of financial and economic performance, the PDO and NPGO describe changes in collective oceanographic environmental features including sea surface temperature, sea surface height, sea level pressure, salinity, chlorophyll-a (algae abundance), and upwelling of ocean nutrients. Recognizable patterns are seen in these indices - patterns that can inform us about the processes that drive the ocean’s physical condition. Importantly, these physical ocean conditions are valuable in understanding and predicting changes in the ecological fates of the ocean’s inhabitants ranging from the smallest plankton to fish to the largest whales.
Oscillations in these indices are well documented and expected. They document warming and cooling cycles and the coupled suite of other physical features. In fact, it has been well established that variations in marine survival of salmon and steelhead are linked to large-scale changes in North Pacific oceanic and atmospheric conditions.
But the ocean environment is changing. Increasingly, the Northeast Pacific has been experiencing large and long marine heatwaves. Some winter temperatures are starting to be greater and to persist longer than ever recorded in the instrumental record. Enter The Blob – that persistent, unyielding body of warm water that settles over the North Pacific. There it sits, right over the migratory corridor where steelhead (and salmon) are found during their years at sea.
Source: CMOS Bulletin SCMO Vol.42, No.2, April 2014
The Blob was first documented in 2014-2016. But it came back, and the new Blob looks warmer and larger than the infamous Blob of 2014-2016. Blobs are thought to form when the changing climate produces lighter-than-normal winds that don’t mix the accumulated warmed water properly, among other things. Without the mixing that produces colder, nutrient-rich upwelling, the Blob won’t disperse. It acts like a stubborn relative that won’t leave, just taking up most of the space on the couch.
The increasing persistence and magnitude of marine heatwaves have real implications for altering the entire marine food web - mainly through lower ocean productivity and in observed shifts in the ranges of different species. Tropical and subtropical fish are now being found off south-east Alaska. Not necessarily a good omen for some salmon species (Chinook and coho) but in particular steelhead.
The Blob is obvious and well known. But there are also some more subtle changes happening at sea. For much of the 20th century, the PDO accurately described the climate patterns in the north and the NPGO described the patterns in more south areas of the North Pacific (generally separated at about the 38 degrees latitude). But all of that changed beginning around 1988-89.
In the late 80’s, a shift in the North Pacific climate changed the way the atmosphere affected ocean conditions. Specifically, the Aleutian Low, a prevalent low-pressure system that is one of the main drivers of the PDO pattern, became less active. This weather pattern had a major influence on ocean temperature, wind mixing of the water column, and ocean currents that were related to the PDO. Oceanographers refer to these changes as regime shifts.
It was also at this time, perhaps not so coincidentally, when the most recent declines in local steelhead returns were detected – measured as lower smolt-to-adult returns. This recent downturn in marine survival has, unfortunately, persisted for steelhead, even for coastal populations not impacted by additional pinniped-induced mortality (feeding seals and sea lions) as seen in Puget Sound. These same patterns are seen in British Columbia as well as Southeast Alaska. Basically, we are faced with the additional challenge from this reduced ocean productivity in managing steelhead .
Ocean Survival Trends for Puget Sound (left) and Coastal (right) Steelhead Populations. Source: Salish Sea Marine Survival Project.
And let’s not forget those other fish – salmon in particular – that spend their time living in the North Pacific.
Steelhead share these waters with fellow salmon and the total abundance of Pacific salmon have been rising to the highest they have been during the past 25 years. One striking statistic is that currently 40% of salmon biomass in the North Pacific is from hatchery origin by intensive stocking from Russian, Japan, and Alaska. Lots of mouths to feed out there.
Not surprisingly, the recent increased abundance of salmon across the North Pacific, and in particular pink and chum salmon, have raised concerns because of the link to fewer zooplankton and to overall reduced growth, survival, and delayed maturation of all salmon. While at sea, Steelhead do not rely directly on the types of plankton and other forage these salmon are depleting. However, we need to be concerned because the prey fish that steelhead use as food do.
Considering what’s currently happening in the North Pacific Ocean*, at least from a steelhead productivity perspective, we appear to be in, and probably will continue to endure, a period of lower smolt-to-adult survival for some time. Our current runs have plummeted to levels to trigger angling closures and ESA listings. There is understandable frustration by passionate anglers and those who make an honest living from the bounty of these fish. But looking at the larger picture, common sense dictates that it is time to temper our expectations and restrain ourselves, especially in the one aspect we can control immediately: angler effect.
To ensure a future that doesn’t involve writing the obituary for wild steelhead, we must acknowledge and immediately act in accord given the effects from the changes in the ocean environment.
The signs are all there: The Blob, the persistent poor returns of wild steelhead, even the shutdown of local ocean razor clamming and Dungeness crab seasons due to the predominance of Domoic acid, a marine neurotoxin that is a product of algae blooms resulting from warming ocean waters. The worn saying “Think Globally, Act Locally”, does now pertain to our steelhead in 2021 and beyond.
It is time for anglers to not just heed the rules, but also embrace the spirit of the conservation measures for these fish - bringing not only a fuller awareness to our choices of how we fish for steelhead during this and coming years, but in other daily choices that culminate in the broader impacts we are witnessing. And we definitely cannot use uncertainty or selfish disregard to justify indecision or paralysis in supporting corrective management, particularly when wild steelhead and salmon populations are sliding toward extinction throughout much of their native range.
*Oceanographic changes showing up in temperature and ocean currents aren’t just limited to the North Pacific. The number of Atlantic cod in the Gulf of Maine has hit an all-time low in recent years and scientists now attribute it to rapidly rising water temperatures. The key to saving the cod, researchers say, is for fishery managers to take such temperature changes into account when setting seasons and harvest quotas.
Further reading:
A New ‘Blob’ Menaces Pacific Ecosystems | Science (sciencemag.org)
Record-setting Salmon Abundance in North Pacific Ocean
Pacific Salmon and Steelhead Production in a Changing Climate: Past, Present, and Future
Understanding Ocean Changes and Climate Just Got Harder