What Happens in the Ocean Does Not Necessarily Stay in the Ocean

“StopLight” chart showing the array of ocean condition indicators. Source: NOAA Fisheries.

Recent news of improving ocean conditions along the West Coast is a positive signal for wild steelhead and was met with widespread celebration. The early onset of strong upwelling during the most recent spring transition, in addition to other ocean indicators, signals a shift to cooler, more productive conditions associated with better survival of outmigrating juvenile steelhead and salmon. Guy Fleischer, WSC’s Science Advisor, offers insights on how this is definitely encouraging news, but cautions that we are far from being totally out of the woods. Fleischer draws a connection to recent research examining how pervasive poor ocean survival can trigger reduced freshwater productivity and how this has implications for our expectations of how quickly depleted wild steelhead populations can recover.

By Guy Fleischer, WSC Science Advisor

As described in my previous blog post, the changing conditions in the North Pacific are now widely recognized as an important factor in the overall fate of wild steelhead populations. Numerous scientific publications have clearly linked cycles of observed ocean warming and cooling to trends in steelhead abundance (as well as salmon and other marine species). This broadened awareness has helped us understand that the recent warm ocean cycle – in addition to the suite of other stressors these fish face in both fresh and salt water – can help explain the sustained downswing suffered recently by many wild steelhead populations along the West Coast.

We now understand that the recent warmer conditions produced a lack of seasonal upwelling in the North Pacific. This upwelling would normally lift colder, nutrient-rich waters to the ocean surface and stimulate increased nearshore productivity. However, the persistent warm water resulted in sustained, stagnant conditions - otherwise known as the well-documented “Blob” - and produced anoxia, harmful algal blooms, a lack of abundant food, and other circumstances which translated into poor survival conditions for out-migrating steelhead.

Shifting Conditions

However, according to a recent report by researchers at NOAA, this last year was marked by a much-heralded switch to more productive conditions in the North Pacific. Images of the zooplankton Neocalanus, a large, normally sub-arctic copepod (small crustacean zooplankton), found to be abundant in samples along the West Coast during May, signaled a welcome transition to cooler ocean conditions. These changes are fully reflected in the trends in the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). (Both of these oceanographic indices are an aggregation of oceanic and atmospheric processes driven largely by ocean temperature regimes).

The switch to a cooler ocean phase involves shifts in atmospheric and ocean current systems and transport between the Gulf of Alaska and the West Coast. In addition to upwelling, the cool waters of the Gulf of Alaska (via the Alaska Current) have begun to reposition to allow sharing with the California Current along the West Coast, bringing the more productive plankton into the waters off the West Coast.

For steelhead, the NPGO index values during winter and early spring, a key time during the first marine summer for steelhead and a predictor of survival, have flipped from past successive years of strongly negative (warmer low productivity) conditions towards more positive (cooler higher productivity) conditions. Similar trends are displayed by the PDO. From a steelhead productivity perspective, it is expected that these conditions will improve overall smolt-to-adult survival, particularly as there is strong scientific evidence that conditions early in a steelhead’s marine residence shape their overall survival in the ocean.

Trends in the winter NPGO index. Improved conditions for steelhead occur when positive, cooler phases occur (blue outline) and are declined when negative, warmer phases occur (red outline).

At face value the reappearance of big, fat juicy Neocalanus is a good reason to make the headlines in newspapers from Seattle to Wenatchee to Chehalis, as well as Oregon Public Broadcasting, not to mention numerous sportfishing websites and social media channels. This particular plankton species was also prevalent back in 2008 and that year ranked highest for favorable ocean conditions for juvenile salmon, and by extension, steelhead. To us passionate, ever-optimistic steelheaders, these changes were some of the best news in many years.

But it is possibly too soon to count any steelhead ‘chickens’ before they hatch. First, these ocean indicators operate ecologically at the low end of the food web. How these recent changes will cascade further up the marine food web is not predictable. Near-shore conditions may have improved, but we still have that big body of unprecedented marine heat waves covering a large area of the North Pacific, covering the portion of the ocean occupied by growing steelhead (typically, steelhead do not linger nearshore but move quickly offshore to the open ocean). These warm conditions were not at all present in 2008, so their impacts on present-day steelhead survival remains to be seen.

The copepod Neocalanus, found in abundance in offshore samples during 2021. Photo source: NOAA Fisheries.

Not Quite Ready For Prime Time

But to the point here, some recent key published papers by researchers at Simon Fraser University in British Columbia are demonstrating how such pervasive unproductive ocean conditions and their effects on steelhead survival can trigger subsequent and equally pervasive changes in their freshwater productivity.

One recent published study found that steelhead in the Keogh River have declined by an order of magnitude because of a recent lengthy period of poor smolt-to-adult survival, at a level that would not be expected based on established stock and recruitment dynamics (see my blog on this topic).

The researchers found that the areas in the river used by steelhead juveniles shrank over time during the period of poor marine survival. The result is reduced smolt production at the watershed scale. The take-home is that as fewer areas get used for spawning and rearing in a river system during a period of poor marine survival, ecological population regulation re-adjusts, thus reducing overall steelhead smolt production.

When faced with these conditions of reduced watershed productivity, it should be clear to both anglers and fishery managers that every returning spawner really counts and we should expect highly constrained fishing or even closures. These are the fish that have survived the full gauntlet of freshwater and ocean challenges thrown at them - most definitely the spawners to protect!

Another complementary study in the Keogh River examining several migratory salmonids, including steelhead, found an alarming shift to both low marine and freshwater productivity starting around 2010 where large steelhead declines were observed. This followed a 15-year period of high freshwater productivity, despite low marine survival. Increased levels of predation from large seal populations and competition for food in the ocean (likely from extensive stocking of pink and chum salmon) were both associated with the initial lower adult marine survival in steelhead. This likely put in place changes in the river that then were met by additional impacts from land use practices (logging in particular), triggering a shift in recruitment productivity as carry-over from the poor ocean conditions.

Taken together, these results reveal how changes in marine and freshwater environments jointly shape wild steelhead productivity, with intertwined consequences to their resilience. These research results help explain how a shrinkage of areas used for spawning, which can alter the stock-recruit relationships that define steelhead productivity, recovery trajectories, and sustainable harvest levels, can be driven by seemingly distant ocean conditions.

They also point to the importance of watershed structure and connectivity between sections of habitat within the river system. Interestingly, the research predicted that greater amounts of higher-quality spawning habitat would not differ substantially in their typical level of smolt production during a period of high marine survival (think of the increases seen on the Skagit from 2009 to 2014 during favorable ocean conditions); however, these areas could produce some of the greater declines in smolt production during the poor marine-survival period (think of our current situation observed in the Skagit River system and others), as not all areas within the watershed are likely to sustain recruitment during periods of subsequent poor ocean survival. Using the research results to simulate other scenarios under poor ocean conditions in models, the researchers found watersheds with uniform habitat quality exhibited greater stability in shifts in habitat use during low marine survival, due to habitat patch connectivity.

These findings underscore how wild steelhead’s time-tested fidelity to natal spawning areas, while being the source of spatial contraction into more productive patches and delaying recovery, also contributes to population persistence across changing environmental conditions. Stream-rearing salmonids are well known for their propensity to return to the same spawning and nursery areas where they were born - a smart evolutionary strategy to cope with periods of poor environmental conditions. If you think about it, the surviving fish should return to proven river habitats first, and don't start to utilize the secondary, or restored, habitat sections until their populations are big enough to push fish into those additional places.

A graphical depiction of the phenomenon where depressed populations experience a shift in the stock-recruit relation that results in lower levels of productivity than expected.

Source: William Atlas, Wild Salmon Center.

Rome Wasn’t Rebuilt In A Day

So what should we anglers expect whenever ocean conditions finally start to improve? As offered by the research, with all other things equal, given the persistence of the recent stint of poor ocean conditions coupled with the high level of spawning site fidelity exhibited by returning wild steelhead (low stray rates), we should not necessarily expect an immediate recovery of smolt production.

As part of the analysis on the Keogh, even allowing a greater stray rate in exploratory model simulations, the typical mean return time for smolt production to return to previous levels of productivity was 3.5 generations. I’ll repeat that: 3.5 generations (with 4-5 years considered typical for a steelhead generation).

The researchers understood that this rate may be pessimistic, as it did not factor in life history diversity attributes such as varying age at smolting or spawning, and iteroparity (repeat spawning). But the message is clear: the response by wild steelhead populations will likely not be immediate given their life history, so there needs to be an expectation that managers allow sufficient time for the population to rebound. Decisions to continue harvest or even prematurely relax protections may hamper the potential for population growth and expansion into habitat areas that are under-seeded or entirely unused.

When steelhead populations reach low numbers, driven by intensive harvest or environment conditions (or both), the downtick in areas used for spawning can naturally exacerbate the effects of fish density limits on productivity. This is because newly emerged offspring (fry and parr) do not have the mobility to access other vacant habitats (as shown in these studies).

“The phenomenon of spatial contraction when populations are low provides a compelling argument for protecting habitat and places an increasing emphasis on the need for restoring riparian habitats in degraded watersheds, particularly in the face of anthropogenic pressures such as mixed-stock fisheries and as a hedge against the full range of effects of ever-present climate change.”

Obviously, in those watersheds where low abundance forces smolt production to become totally driven by the number of spawners (what scientists call exacerbated density dependence), all efforts to restore habitat, such as reconnecting floodplain habitats and improving riparian functioning, will go a long way to benefit recovery of steelhead populations - and set the stage to allow wild steelhead to persevere during future periods of poor ocean conditions.

Buffering the effects of cyclical poor marine survival has particular importance to wild steelhead populations. Mechanisms and patterns underlying these kinds of productivity bottlenecks are different among anadromous species with diverse life histories. For example, with their shorter life cycle and lack of a freshwater rearing phase, most pink salmon populations throughout the Pacific Northwest have not shown any real fluctuations in productivity, while wild steelhead (and chinook salmon), with their longer lifespans and greater dependence on freshwater habitat, suffered serious declines.

These recent studies, along with other research, highlight the critical importance of monitoring and documenting the trends in adult-to-smolt recruitment and any changes in the in-stream rearing spatial structure (the pattern in habitats used by juveniles) for successful management and conservation of steelhead populations. The phenomenon of spatial contraction when populations are low provides a compelling argument for protecting habitat and places an increasing emphasis on the need for restoring riparian habitats in degraded watersheds, particularly in the face of anthropogenic pressures such as mixed-stock fisheries and as a hedge against the full range of effects of ever-present climate change.

As 21st Century steelheaders, we must acknowledge our passion and be clear-eyed about their state. We need to be focused on more than just fishing. As articulated in our Now or Never essay, we need to be “prioritizing ecological restoration, sacrificing for long-term recovery, and rebuilding by giving back more than we take.” Sage advice supported by science.

Referenced Research Publications

Atlas, W. I., Buehrens, T. W., McCubbing, D. J. F., Bison, R., & Moore, J. W. (2015). Implications of spatial contraction for density dependence and conservation in a depressed population of anadromous fish. Canadian Journal of Fisheries and Aquatic Sciences, 72, 1682–1693. https://doi.org/10.1139/cjfas -2014-0532

Wilson, K. L., Bailey, C. J., Davies, T. D., & Moore, J. W. (2021). Marine and freshwater regime changes impact a community of migratory Pacific salmonids in decline. Global Change Biology, 28, 72– 85. https://doi.org/10.1111/gcb.15895