Death on the Fraser

Story by Mark Hume with Photography by Nick Didlick

Sockeye salmon in the Fraser River are dying from exhaustion and…cardiac collapse as they struggle to deal with water temperatures that are steadily rising because of climate change.

Two Sockeye salmon pair up on the Adams River spawning grounds

A federal judicial inquiry, appointed by Prime Minister Stephen Harper to look into the 20-year decline of sockeye stocks in Canada’s greatest salmon river, heard about the impact of global warming in testimony from two University of British Columbia scientists.

Two Sockeye salmon pair up on the Adams River spawning grounds
Dr. Scott Hinch, an expert on aquatic ecology, and Dr. Eduardo Martins, who studies population ecology, presented a research paper that was done at the request of Bruce Cohen, a Supreme Court of B.C. judge who is heading the Commission of Inquiry Into the Decline of Sockeye Salmon in the Fraser River.

The Commission, which is holding public, evidentiary hearings in the Federal Court, in Vancouver, has ordered 12 scientific papers covering everything from diseases and parasites, to the impacts of salmon farms and the effects of climate change.

The paper by Hinch and Martins states that in some years hundreds of thousands of sockeye die in the river from exhaustion, as they try to make their way upstream to spawn.

The Fraser rises in the Canadian Rocky Mountains and flows into the Pacific Ocean near Vancouver. It has runs of pink, chum, sockeye, Coho, Chinook and steelhead. The focus of the hearings is on sockeye, but it is expected the findings will have implications for other stocks as well, and for salmon in other salmon rivers from California to Alaska.

The Adams River

The paper by Hinch and Martins did not estimate how many Fraser salmon might have died in total, en route to spawning, but it states that sometimes 50 % or more of returning sockeye die before reaching the spawning grounds. The Fraser often has runs of several million sockeye. In 2010 around 30 million sockeye returned. That was the highest run in a century, and it marked a stunning turn around from the total collapse of stocks that occurred the year prior. In 2009 only about one million sockeye came back, when a run of more than 10 million had been forecast. That collapse spurred Prime Minister Harper to appoint the Cohen Commission, which has a two-year time table and a $25 million budget.

Dr. Hinch testified that the problem of en route loss was first identified in 1992, in three distinctly timed stocks of sockeye, the Early Stuart, which come back in the spring, the Early summer, and Summer-runs. A fourth stock, known as Late-runs, didn’t experience en route deaths until 1996. Dr. Hinch’s paper states that since 1996, en route loss of at least 30% has been observed for at least one run-timing group in each year.

And it states that most stocks, in most years, had losses of more than 50 %. He said the Fraser has increased in temperature by about two degrees C in the past two decades and it is projected to climb by between two and four degrees C over the next 60 to 80 years. Sockeye begin to struggle with temperatures over 18 C, and the Fraser often hits 20 C for several weeks each summer.
In the warmer water fish have to work harder to swim and obtain oxygen, and they can simply drop dead from exhaustion. Many fish make it to the spawning beds, but the females don’t have enough energy to lay their eggs.
Dr. Hinch said the warm water doesn’t directly kill fish, but it exposes them to multiple stresses, which opens them to disease infections, or can cause cardiac failure.

He said the dead fish usually sink quickly to the bottom and do not float to the surface, belly up, which explains why rafts of dead salmon aren’t seen floating down the Fraser in the fall.
Dr. Hinch said sockeye salmon in the Fraser and in the Columbia, and Atlantic salmon on the East Coast, have been changing the timing of their migrations apparently in an effort to avoid warmer water in their home rivers. Some Fraser runs are entering the river up to six weeks earlier than normal, while others are delaying.

Sockeye Eggs settle in the gravel on the Adams River

Dr. Hinch’s paper says Fraser sockeye have also been seen seeking cool-water refugia, sometimes going sinking into the depths of lakes, or schooling at the mouths of cold-water streams.

The paper says warmer water decreases the survivability of sockeye at almost all life stages. While eggs appear to have benefited from increased temperatures, alevins, fry, smolts and immature salmon in the ocean all appear to be negatively impacted by increased temperatures.
Dr. Hinch told the Cohen Commission, however, that there is shockingly little information available about salmon in the early stages of life. This information gap has led us to why we’re here today, he said.

Dr. Hinch noted that one run of sockeye in the Fraser, which spawns in the glacially-fed Chilko River, has adapted to a wide range of temperatures. The fish seem unaffected by the warm summer temperatures in the Fraser, and adjust quickly to the cold Chilko.

He said because we can’t know which stocks will be able to adapt to the warmer temperatures of the future, it’s paramount to be able to protect as many of these populations as possible.

Dr. Hinch said more fish will die en route in the future and fisheries managers will have to take the phenomenon into consideration when deciding the total allowable catch for any year.
Certainly we’re going to see higher en route mortality. . .we’re going to have to forsake more harvest on these fish, he said.

The Cohen Commission was established on November 5, 2009 and it has until June 30, 2012 to submit a final report.

Warmer water temperatures mean an uncertain future for some Sockeye runs

Warmer water temperatures mean an uncertain future for some Sockeye runs