“Dramatic increases in smolt survival are needed to overcome the negative impacts of climate change for this threatened species.”
So conclude salmon researchers about Snake River spring/summer Chinook in a paper published this week and who say that the “urgency is greater than ever to identify successful solutions at a large scale” that yield stronger young fish more capable of dealing with a warming North Pacific.
Their article, “Climate change threatens Chinook salmon throughout their life cycle,” published in Communications Biology, finds that while warmer conditions in the future present a mixed bag of positives and negatives for eight Idaho stocks during their freshwater phases in the streams of the state’s rugged interior mountains, it’s all bad news when those fish are out in the ocean.
“Climate impacts were most dramatic in the marine stage, where survival was reduced by 83 to 90 percent,” write Lisa G. Crozier, Brian J. Burke, Brandon E. Chasco and Richard W. Zabel with the National Marine Fisheries Service’s Northwest Fisheries Science Center in Seattle and Daniel L. Widene of Ocean Associates, Inc.
“This occurred despite the fact that smolts arrived at Bonneville Dam about 6.5 days earlier, indicating an earlier initiation of the marine stage, which generally improves marine survival,” they state.
Their “life-cycle modeling” shows that even the strongest of the individual stocks from tributaries of the mainstem Salmon and its South and Middle Forks face a strong risk of extinction by 2060.
“This is telling us that it’s going to become increasingly difficult for these species to make it back to the rivers,” said Zabel, in a NMFS story about the paper. “While salmon have proven themselves to be adaptable over time, we don’t know how they may respond to this relatively rapid change.”
It’s particularly worrying because, according to NMFS, these ESA-listed Snake springer/summers spawn and rear in what is considered to be the – as in the one – last Chinook stronghold, given its salmon-friendly water temperatures and pristine habitat.
From a fisheries perspective, they represent the largest wild component of the spring run up the Columbia and what the states’ managers guard for as they set seasons off Cathlamet, Longview, St. Helens, Portland, The Dalles, Clarkston and Lewiston for hatchery kings.
The five researchers acknowledge that their work comes with at least a strong pair of caveats.
The North Pacific and its rich pastures might not warm as fast as modeled, or it will but some “ecological surprise” will emerge “that will reverse the historical relationship between [sea-surface temperatures] and salmon survival.”
“Although warm conditions have been associated with lower-quality prey and more warm-water predators, it is possible that novel communities will arise with different responses to temperature, or that salmon will adapt to an altered food web in a positive manner,” they write.
On the flip side, that oceanic curveball could also yield new competitors and decrease Chinook survival.
Also troubling is how applicable their research may be to other West Coast Chinook runs, as well as coho, sockeye and other salmon species.
“Although we have focused on details for certain populations, there is strong synchrony across all populations within this Chinook ESU and more broadly across other salmon species throughout their southern distributions. Such synchrony suggests that the responses we found could represent a widespread phenomenon,” they write.
So what can be done?
“Throughout salmon watersheds, improving and expanding access to rearing habitat should increase smolt abundance and body condition, resulting in improved population viability,” write Crozier, Burke, Chasco, Zabel and Widene.
They add: “The urgency is greater than ever to identify successful solutions at a large scale and implement known methods for improving survival. Management actions that open new habitat, improve productivity within existing habitat, or reduce mortality through direct or indirect effects in the ocean are desperately needed.”
One of the quintet, Chasco, has also looked into the high toll that harbor seals and others have on Chinook, modeling that recovered populations of pinnipeds ate nine-plus times as many in 2015 as they did in 1970.
But the new paper also comes at the same time that a “large scale” fish fix was just unveiled – the comprehensive $33.5-billion plan of Rep. Mike Simpson (R-ID) to breach the lower four Snake River dams, which these particular Chinook that were studied must swim through twice.
Per a recent ODFW presentation, dams are the single largest source of freshwater mortality for wild Chinook smolts, accounting for over 42 percent of deaths.
“Everything else is, relatively speaking, such a tiny piece of the overall puzzle,” said Tucker Jones, the agency’s Columbia River manager, during a recent panel discussion on Snake River restoration.
Breaching the quartet plus spring spill of 120 to 125 percent total dissolved gas over Columbia dams could increase smolt-to-adult returns, or SAR, to 4 to 5 percent, per ODFW.
Rep. Simpson says that researchers advise him that the SAR for Idaho’s wild Chinook is around 1%, “which I am told is below replacement and on a trajectory towards extinction.”
Citing a 2016 paper, the NMFS researchers say that smolt survival through the Snake and Columbia dams “generally now meets recovery targets … and cumulative mortality over 500 km of in-river migrating fish is similar to that estimated for unregulated rivers of similar length.”
“However, slow travel time through slow-flowing reservoirs behind dams, combined with increased surface temperatures in these reservoirs, can potentially result in lower marine survival,” the five write. “Mitigation efforts to increase smolt body size and advance migration timing could increase marine survival. Restoration efforts in freshwater habitats, such as restoring floodplains, riparian planting to reduce stream temperature, reconnecting side-channel habitat, and supporting other natural processes in juvenile salmon rearing areas also enhance/restore freshwater salmon production.”