Warm gulf bodes poor steelhead survival
August 14, 2014
Menacing “El Nino” signs have eased though not disappeared.
But another potential salmon nemesis – an apparent warm phase Pacific Decadal Oscillation – has made an appearance with warmer than average sea surface water conditions from the Gulf of Alaska and the eastern Bering Sea down to the so-called California Current off the coast of Oregon and Washington.
“It should be noted that those Columbia/Snake River spring chinook and steelhead stocks that entered the ocean this spring and traveled to the Gulf of Alaska to feed may experience very poor survival this year due to the exceptionally warm conditions (and likely associated low productivity) in the Gulf of Alaska,” according to information provide by NOAA Fisheries’ Bill Peterson, a senior scientist and oceanographer with the agency’s Northwest Fisheries Science Center.
Peterson and Phil Mote on August 5 provided the Northwest Power and Conservation Council with an update on patterns of climate variability, such as the El Nino-Southern Oscillation (ENSO) that could affect Northwest weather, the region’s precipitation and snowpack accumulation and the ocean food web. Mote is director of the Climate Change Research Center at Oregon State University.
Those environmental conditions within the Northwest and in the Pacific can affect the survival of Columbia River basin salmon stocks, including imperiled species that are listed under the Endangered Species Act.
Water temperatures in the Gulf of Alaska “have never, ever, ever” been as high as they are right now, according to Peterson. The surface water is 2 degrees centigrade higher than the previous recorded high, he told the Council. That temperature data goes back to 1900.
“Neither of these conditions are good for salmon, perhaps especially for the types that migrate to the Gulf of Alaska to feed (spring chinook and steelhead; fall chinook and coho to a much lesser extent),” Peterson said of the existence of the warm phase PDO and uncharacteristically warm water temperatures in the Gulf of Alaska.
Phe warm phase has been in evidence since the first of the year. Research has shown that when warm phase PDO settles in “the zooplankton community structure in the northern California Currrent becomes more sub-tropical in nature and becomes dominated by lipid-poor species. This bodes ill for West Coast salmon…,” according to a memo prepared for Tuesday’s meeting.
More lipid-rich species are available to provide fatty nourishment for salmon when water temperatures are cooler.
These warm and cool phases result from the direction of winter winds in the North Pacific: winter winds blowing chiefly from the southwest “result in warmer conditions in the northern California Current,” according to information posted on the NWFSC web page.
“The CC warms at such times due to onshore transport of warm waters that normally lie offshore. Conversely, when winds blow chiefly from the north, upwelling occurs both in the open ocean and at the coast, leading to cooler conditions in the northern CC,” according to the science center.
Either phase can persist for a decade or two according to records, but those cycles seem to have shortened in recent times to about five years, Peterson told the Council.
“The listing of several salmon stocks as threatened or endangered under the U.S. Endangered Species Act coincides with a prolonged period of poor ocean conditions that began in the early 1990s,” according to the science center.
The return of El Nino conditions after several years’ absence seemed likely according to ocean, wind and rain signals monitored this late spring and early in the western Pacific east of Australia. Warmer than normal sea surface temperatures that persist and spread eastward across the Pacific eventually (after averaging certain levels of divergence for the norm for at least three months in a row) warrant an El Nino declaration.
“In April and May it really looked like this was going to be a humdinger,” Mote said of rising sea surface temperatures and other climatic signals being observed in the equatorial Pacific.
But cooling has been witnessed in recent times.
“Right now it looks like nature has backed off a little bit on El Nino,” Mote said. “All of our indices are trending back toward normal territory.”
“Temperatures are actually cooling at the equator, Peterson said, including off the coast of southern Peru and to some degree in the California Current. The California Current moves south along the western coast of North America, beginning off southern British Columbia, flowing southward past Washington, Oregon and California, and ending off southern Baja California.
According to the Aug. 7 Climate Prediction Center’s ENSO alert system update, the chance of El Niño during the Northern Hemisphere fall and early winter has decreased to about 65 percent. That’s down from an 80 percent assessment made a month earlier by the CPC.
“Over the last month, model forecasts have slightly delayed the El Niño onset, with most models now indicating the onset during July-September, with the event continuing into early 2015,” the CPC discussion says.
According to the July 29 Council memo, “even if there is only a weak to moderate El Niño event in 2014/15, juvenile salmon entering the California Current Ecosystem in 2015 are likely to experience very low survival due in part to the ‘warm blob’ that occupies the entire Gulf of Alaska as well as waters of the offshore California Current off Washington and Oregon. Other fished species are likely to be affected in a similar manner because the food chain upon which they depend will have lower bioenergetics content.”