Skip to main content

Record returns of sockeye salmon in northwestern U.S.

Thumbnail
Adult sockeye salmon have to travel upstream, and often over waterfalls like those pictured, in order to spawn. (Photo: U.S. Fish and Wildlife Service)

This summer is shaping up to be a record-breaking one for sockeye salmon. Record numbers of the salmon have been returning to the Northwest's Columbia Basin this summer, with a run of more than 400,000 now expected. Two days in the end of June saw thousands more crossing the river's dams in a single day than the total numbers seen in some previous years.

What do these numbers mean for the once-waning population of sockeye salmon? I recently talked to AAAS member David Welch, the CEO of Kintama Research Services. Kintama is a world leader in the design and use of underwater acoustic telemetry to answer questions about the survival, migration, and behavior of marine animals, including salmon.

AAAS MC: What is a salmon's life cycle? What do we currently know about how and why they travel to spawn?
David Welch, CEO of Kintama Research: In the southern end of the sockeye's range, almost all sockeye salmon have a four year life cycle. Adults return from sea, spawn in the autumn, and die. The fertilized eggs overwinter in the gravel before the fry emerge the following spring. In most populations the fry then migrate to a nearby lake, where they grow and feed for one year and then migrate to sea as smolts, after spending approximately 1.5 years in freshwater. The sockeye then migrate downriver and up the Pacific coast as juveniles before migrating offshore (at some point that is unclear) and spend the majority of their marine life in the offshore North Pacific and Bering Sea. During their last, fourth, year of life they then migrate several thousand kilometers back to the mainland and upstream to their natal rivers to spawn and complete the cycle.

AAAS MC: What factors do you think are contributing to the record numbers of sockeye salmon returning to the Columbia Basin this summer?
Welch: There have been a number of correlated climate-related changes that occurred that are contributing to the astonishing runs. The sockeye now returning to the Columbia River in large numbers in 2012 went to sea in 2010. This is a continuation of several years of dramatically improved runs. Starting in 2008, the west coast switched to colder, wetter weather. This led to more precipitation on land, affecting freshwater, and also led on the marine side to a colder coastal ocean with a switch to a cold water plankton community. Cold water plankton have substantially higher fat reserves than warm water species. Our own work (on Chinook salmon in the Columbia River) saw a large improvement in coastal ocean survival following the switch to colder conditions in 2008, which has continued. This is likely due to the changed ocean conditions.

AAAS MC: There are a number of dams in that area. Do dam constructions and operations affect these salmon?
Welch:
Dams certainly cause some mortality. However, new dam construction (or removal) hasn't occurred in the Columbia since 1977 so this cannot be the cause of the spectacular ups and downs over the last 20 years. Recent changes in dam operations have decreased the number of smolts that die during their downstream migration; however, the improvements in adult return rates are confounded with the ocean changes, so unfortunately no one has a clear idea of how much of the greatly improved adult returns are due to the incremental freshwater changes and how much is due to changes in ocean conditions. In 2009, sockeye runs returning to the Fraser River in British Columbia collapsed (sparking a judicial inquiry); the following year, when the inquiry was just getting up to full steam, there were record breaking returns. Sockeye returning to the Fraser River do not encounter dams along their migration route, thus demonstrating that other factors besides dams have large impacts. There are also other sockeye populations in both the U.S. (Ozette Lake) and Canada (Sakinaw Lake) that are listed as being of extreme conservation concern, yet they have very short free-flowing rivers and apparently excellent freshwater habitat, so marine factors are apparently controlling these populations.

One of the scientific reviews commissioned by the judicial inquiry in Canada has just been published (http://www.nrcresearchpress.com/doi/pdf/10.1139/f2012-063) and documents a very widespread decline over two decades in sockeye populations stretching from Washington State north to Alaska. This type of work strongly suggests that a common effect due to changes in the ocean environment is at work and probably plays the major role in determining salmon returns.

I think that the "dams versus ocean effects on salmon" is a key question for science to answer, because we need to clearly understand which of the recent changes in freshwater and the ocean environments is contributing most to the improved returns. Lacking data, there is much speculation; we need to have a clear quantitative understanding of what is happening if we are to get cause and effect properly sorted out for policy makers... the stakes are huge.

AAAS MC: Almost all of the salmon returning to the Columbia Basin this summer are wild fish bred in rivers, instead of the hatcheries that produce most Northwest salmon. What is the significance of this for wild salmon, other aquatic animals and the ecosystem in which they live? Are there larger implications of this year's glut of salmon, or are this particular summer's numbers an aberration?
Welch:
Hatcheries are important for supporting the ability of people to catch salmon. Unfortunately, they also cause a lot of problems (e.g., overfishing of wild salmon stocks and diluting the wild salmon gene pool; there is growing evidence that the offspring of hatchery-reared adults spawning in the wild survive poorly, so interbreeding of hatchery and wild fish may also be reducing the fitness of the wild populations).

Another major question concerns how much of the recent jump in salmon numbers is actually due to freshwater actions. Right now most salmon managers are sitting back and are pretty happy because adult returns are way up coast-wide. However, if this is mainly due to cooler ocean conditions and the climate suddenly swings to a warm phase—on top of the general trend to warmer temperatures we are already seeing due to global warming—all hell is likely to break loose as the finger pointing that characterized the 1990s (when ocean conditions were much warmer than they are now) comes back with a vengeance. I worry that we are losing the opportunity to find out what the real balance of effects between freshwater and marine influences is on salmon now, before it again becomes an urgent priority under the Endangered Species Act; science needs time to answer these questions, whereas in the political and legal arenas people want answers yesterday. We need to prepare now for the questions legislators will ask us within a very few years.

AAASMC: At a recent AAAS meeting, you talked about biologging salmon in British Columbia. What is biologging, and what can scientists use it for?
Welch:
Biologging is the use of modern electronic tags to follow individual fish for months or years at a time. Properly designed, these telemetry systems work in both in both freshwater and the coastal ocean. This technology is just starting to transform fisheries science. For the first time we have a tool for directly measuring survival, even for astonishingly small animals such as salmon smolts. More importantly, with these new measurement tools comes the opportunity to do explicit experimental tests of scientific theories, directly in the ocean. Historically, this ability transformed other areas of science, such as chemistry and physics, by allowing rapid testing and rejection of scientific theories, and led to a radical increase in the speed of scientific progress. We think that can happen in fisheries research too.

Related Links: