A UBC fisheries expert's warning from the 1990s now sounds prophetic with this summer's poor returns of Fraser River sockeye. UBC professor Scott Hinch predicted 15 years ago that warming sea-surface temperatures due to climate change would result in smaller and less abundant sockeye.
“It was some of the first work ever of that kind, and nobody's really followed up,” Hinch told the Georgia Straight.
More than 80 percent of the 10.6 million fish predicted by Fisheries and Oceans Canada are nowhere to be found in the Fraser, raising doubts about the future of this iconic species.
In a paper published in the Canadian Journal of Fisheries and Aquatic Sciences in 1995, Hinch and his colleagues stated that warm sea temperatures could impair production of plankton—organisms that start the food chain in the ocean—triggering a series of consequences.
“Assuming that growth rate is related to survivorship in the ocean, and it should be, then, yeah, it suggested that fewer adults may come back and they would be smaller,” Hinch said. “And it also carried the logic further out of the ocean into the river and said that smaller adults, those with lower energy, should have a more difficult time completing the river migration.”
Some 3.3 million Fraser sockeye reached their spawning grounds in 2005. According to the Pacific Salmon Commission, surveys in the Quesnel and Chilko tributaries indicated that about 130 million sockeye smolts moved out to the sea in 2007 for their two-year ocean migration.
What happened to these juveniles?
Jeff Grout, FOC's salmon resource manager, said he suspects that the fish didn't survive at expected rates. He rejected any suggestion that fish farms are responsible for poor returns.
“We have some information for juveniles that out-migrate from one of our big lakes in the Interior, the Chilko run. We did have a lot of juveniles—well above average—leave that system in fairly good size, which usually bodes well for their survival,” Grout told the Straight earlier this month. “So”¦we're thinking that marine survival is likely a factor in the poor returns we're seeing—especially in that we're seeing poor returns across all of these different lake systems.”
Hinch said that in the mid-1990s, coastal and northeast Pacific Ocean temperatures increased by half a degree and one degree Celsius, respectively, compared to the 1960s and 1970s. “So we're expecting, as climates continue to warm, another degree or two warmer in the next several decades,” he added.
River temperature is as important as sea-surface temperatures for sockeye, according to another paper coauthored by Hinch that was recently accepted by the Canadian Journal of Fisheries and Aquatic Sciences. It noted that about 1.3 million adult sockeye entered the Fraser River in 2004 but didn't reach their spawning grounds. The paper stated that the record high temperatures in 2004 were a “significant factor” behind the 57-percent spawning mortality.