Warm water in Pacific could cook Idaho’s salmon and steelhead

By Rocky Barker
Idaho Statesman
December 2, 2014

History says the situation could be disastrous for Idaho’s salmon and steelhead.

A mass of warm water thousands of square miles in size that reached 74 degrees Fahrenheit on the surface last summer is being called “the blob.” But scientists say it’s too early to tell if it’s short-term phenomena or a sign of a longer trend. Surface temperatures are 3 degrees higher than normal.

“Since it’s outside of anybody’s experience, we don’t know what to expect,” said Bill Peterson, an oceanographer with the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center in Newport, Ore.

The warm-water “blob” stretches from New Guinea to the Gulf of Alaska, where the warming is most apparent. Fishermen and researchers are seeing southern species such as sunfish, thresher sharks and skipjack tuna as far north as off the Copper River in Alaska.

Bad For Salmon

A lot of factors affect the health of Idaho’s sea-going salmon and steelhead: habitat and water flows and conditions in the Snake and Columbia tributaries; dams and the passage devices that fish must use to navigate the dams; fishing techniques and seasons; and predators such as seals. But ocean conditions are among the most critical, because the fish spend much of their time maturing in the ocean and the shape of the ocean is largely beyond human tinkering. The remarkable improvement in salmon and steelhead runs in recent years is at least partly due to the favorable ocean cycle.

Peterson has documented that when the north Pacific is warmer, the Columbia and Snake rivers’ salmon and steelhead productivity drops dramatically. More predators such as mackerel and even Humboldt squid show up, voraciously eating the salmon as they expand their territory.

Food that young salmon eat, such as the small crustaceans known as krill, also disappears in warmer waters. Idaho fishery biologists are watching the ocean conditions closely, but still expect a good adult return in 2015.

“It’s the effects on the juveniles we’re really going to have to watch over the next few years,” said Pete Hassemer, Idaho Department of Fish and Game’s manager for salmon and steelhead.

From the mid-1970s to 1996, the Pacific was in a long warm stretch.

This warm phase of what scientists now call the Pacific cecadal oscillation – PDO for short – was the period when Idaho’s salmon nearly went extinct. Nate Mantua, leader of the Southwest Fisheries Science Center Landscape Ecology Team in California, is one of the scientists who has tracked these cycles in ocean temperatures.

“The 1990s were a terrible time for Northwest salmon,” Mantua said.

Uncertain Future

Since then, the north Pacific has seen a few, but shorter, warming patterns. Today, however, “the PDO pattern is very strong,” Mantua said.

“I don’t think we know if this is going to be a long pattern or a short one,” he said.

El Nino is another of these oscillations. Scientists give that name to a warm band of Pacific surface temperatures that develops off the western coast of South America and causes climatic changes across the globe. We’re also seeing an El Nino setting up this year, Mantua said.

A strong El Nino hurts Idaho’s salmon and steelhead by reducing flows in the rivers and ocean conditions.

Climate Change or Not?

Mantua is doubtful “the blob” is the result of human-caused climate change.

He recently published results of a study with Jim Johnstone that said the average coastal temperature increase of 1 degree Celsius since 1900 appears to be the result of shifts in winds and air circulation over the eastern Pacific Ocean, not human-caused climate change. But the influence of global warming from increased greenhouse gases is growing, he said.

“Thirty to 40 years from now, (global warming) will be dominant,” Mantua said.

Axel Timmermann sees it differently. The climate scientist and professor studying variability of the global climate system at the International Pacific Research Center at the University of Hawaii at Manoa does tie “the blob” to global warming.

“Record-breaking greenhouse gas concentrations and anomalously weak north Pacific summer trade winds, which usually cool the ocean surface, have contributed further to the rise in sea surface temperatures,” Timmerman told Science Daily.

It’ll take decades to know whether this is the ocean’s natural cycle or something more at work.