if any, warmer temperatures might actually be having on Alaska’s wild salmon.
We do know, from testing and experience elsewhere, that higher temperatures can have profound effects on salmon and other cold-water fish. Higher temperatures can reduce growth rates (when fish have to put more energy into respiration and metabolism), reduce the survival of eggs and fry, affect the timing of out-migration (reducing marine survival), increase disease, and make fish more vulnerable to pollution (since some chemicals and metals increase in toxicity with higher temperatures). Warmer waters can also influence food supplies, vulnerability to predators, and competition with other species including exotics that move into waters made more hospitable to them. And we do know that when fish (and living organisms generally) are stressed by any one process, they’re less able to deal with other stressors.
Along the West Coast of the United States, salmon runs have been in serious decline, with the collapse of California’s Sacramento River Chinook runs resulting in a complete closure of sport and commercial salmon fishing off the coast of California and most of Oregon. The reason for the collapse was not clear. Some biologists pointed to unusual weather patterns that disrupted the upwelling of nutrient-rich water in coastal waters that normally supported the marine food web. Other people pointed to water quality issues related to damaged habitat, agricultural pollution, and altered flows and temperatures related to development and water diversions. Greenhouse gas-induced climate change might be just one factor among a series of environmental insults.
In the Sacramento River, engineering efforts had already been made to try to keep temperatures from becoming overly warm; in 1996 a temperature control system was added to the Shasta Dam to release deep, cold water from the lake bottom. As early as 1976 and 1977, thousands of Sacramento River salmon died when water temperatures rose to sixty-two degrees Fahrenheit. (Recall that Alaska’s “do not exceed” temperature is sixty-eight degrees, and that in 2005 our Anchor River exceeded that on six days.)
Michael Healey, a professor emeritus at the University of British Columbia, is a nationally recognized expert in both the ecology of Pacific salmon and the design of resource management systems. He has noted that the effects of climate change on salmon are of major concern to resource managers and that the degree of warming expected in both freshwater and marine habitats over the next century “will have uncertain but potentially devastating effects on salmon and their ecosystems.”2 By focusing on the sockeye salmon of British Columbia’s Fraser River (the most valuable—commercially and ecologically—salmon river in Canada), he has developed a model for examining the cumulative effects of climate change on the many stages in the salmon life cycle and across generations. What he lays out is not pretty.
First, he notes that in recent years large numbers of adult salmon that enter the Fraser River have failed to make it to the spawning grounds and many that did died without spawning, and that a late run has been entering the river weeks earlier than in the past. Extremely poor survival in the Fraser in 2004 was linked to exceptionally high temperatures. Sockeye returning to the Fraser have been both smaller than in the past and with lower energy reserves, suggesting that “energetic exhaustion” may be one cause of the observed mortality, perhaps along with temperature stress and disease.
For his analysis, Healey recognized eight stages in the life of the sockeye and detailed the effects of increasing temperature (drawn from previously published scientific studies) on each stage, then looked at how the effects on each stage affected performance at later stages. He has shown that global warming has negative effects on productivity at every stage and that the effects at one stage carry through to the next and then generationally. He further considered how the effects of high temperatures at each stage might be mitigated or adapted to—biologically and by management and policy decisions. For example, management options might include releasing cool water from reservoirs upstream of spawners, fertilizing lakes to make up for nutrient deficits related to the mismatch of plankton bloom times, and preventing overfishing. Policies might include reserving adequate stream flows in salmon rivers, managing predators, and establishing “salmon first” for the use of estuarine habitats.
Healey wrote to me, “I had been stuck a bit trying to find anything positive to say, but I think I have a found a thread (melting Arctic is opening new habitat for salmon).” Given time, he says, salmon will naturally colonize the Arctic, but he fears that their rate of moving into new habitats might be too slow to keep ahead of global warming. It was his opinion that managers and policy makers should be thinking now about assisting salmon to colonize the Arctic (by transplanting them or developing freshwater nurseries), not only to keep salmon in the world but also to retain the option of eventually restoring populations to the south, when the climate there is favorable again.
Alaska has its own example of temperature-stressed salmon not making it back to their spawning beds. A five-year study of Yukon River salmon infested with Ichthyophonus linked the microscopic parasite (commonly called “ick”) to warmer stream temperatures.3 Before the mid-1980s, Ichthyophonus, which causes “white spot disease” in fish, had never been reported from the Yukon River. Today, it infects more than 40 percent of the river’s adult Chinook salmon.
This disease, which can be fatal to fish, doesn’t harm people but makes the salmon meat mealy, with an odd smell and unpleasant texture, fit only for feeding to dogs. Richard Kocan, a fish disease expert from the University of Washington, has linked the emergence of the disease to increased river temperatures. Average Yukon River temperatures have been rising for three decades. Since 1975 June water temperatures at the village of Emmonak, on the river’s delta, have increased from less than fifty-two degrees to fifty-nine degrees Fahrenheit with July temperatures even higher.
Kocan found that the number of infected fish, and severity of the disease, was highest in the study years with the highest temperatures and highest during the times of summer when the water was warmest. Laboratory studies have also shown that Ichthyophonus thrives as a host’s temperature increases (as would be the case of cold-blooded salmon in warming water). Kocan’s peer-reviewed study concluded, in the conservative manner of science, that water temperatures above fifty-nine degrees appeared to correlate with increases in Ichthyophonus infection, and that rising average water temperatures in the Yukon River in the last three decades may be an important cause of increased disease and mortality among Chinook salmon. He believed—but did not have good data to support—that as much as 20 percent of the Yukon’s Chinook were dying from the disease en route to their spawning grounds. Ichthyophonus has also been detected, in limited surveys, in salmon in other rivers, and in other fish species. Kocan considers it to be a classic emerging disease—defined as a disease that has either newly appeared in a population or has been known for some time but is rapidly increasing in incidence or geographic range. In this case, the triggering factor for its emergence appears to be warming waters.
To put it simply, Ichthyophonus may have always been with us, but a warming climate may be redistributing it, allowing it to flourish in parts of the north where cold temperatures once acted as a barrier to its spread and where species, themselves stressed by warmer temperatures, lack individual or evolutionary resistance.
And more of the same may be on the way.
In a spitting rain, Mauger and I headed back south on the highway, past an eagle’s nest in a bare cottonwood right next to the road, to our last stop, at Stariski Creek. Stariski is a smaller watercourse than Ninilchik but still an important salmon river, with spawning runs of king, silver, and pink salmon, along with steelhead and Dolly Varden trout. At Stariski, culverts running under the highway had been recently replaced with a bridge, and Inletkeeper was hired by the Alaska Department of Transportation to check turbidity around the project. The project included a fancy new boardwalk that led from the road to the river, so that even someone in a wheelchair could easily roll to streamside for fishing. The whole bridge project, including riverbank stabilization with rock and willow plantings, was necessitated by not one but two “hundred-year (that is, expected to occur only once in a century) floods”
