With climate change heating up British Columbia's rivers, there are growing concerns about the vulnerability of cold-water species such as salmon.
But a new study shows salmon may have the ability to adapt to a warming world because Chinook that lay larger eggs produce offspring that have greater heat tolerance.
"What jumped out [of the data] was that the mothers with big eggs tended to have indicators the offspring were more temperature tolerant," said Tony Farrell, who holds the Canadian Research Chair in fish physiology at the University of British Columbia.
Dr. Farrell's lab helped Nicolas Munoz, a master's student at the University of Western Ontario, in a research project that measured the heat tolerance of juvenile salmon by tracking their heart rates as they were exposed to increasingly warm water.
Mr. Munoz worked with the Department of Fisheries and Oceans to capture spawning Chinook salmon at the Big Qualicum River on Vancouver Island.
Some 25 different "families" of offspring were produced for testing by mixing the eggs and sperm of several salmon.
"When you warm a fish up it primarily responds by raising its heart rate to deliver more oxygen to its tissues … then it reaches a maximum and sometimes the heart can go into arrhythmia," Dr. Farrell said.
He said Mr. Munoz's research showed the offspring that were best at dealing with warmer water came from females that produced larger eggs.
"That was unexpected and quite exciting because what we do know from the [science] literature is that egg size can be genetically determined," Dr. Farrell said. "And so egg size is heritable. So what you've got is a kind of indirect genetic effect which is being manifest through the mother. That was a highly novel finding."
He said the study could point to ways in which fisheries managers could adapt to climate change by selecting fish for breeding that produce the largest eggs.
"It's a heritable trait," he said of heat tolerance. "We can breed it into the stocks as opposed to just taking whatever random assortment nature gives us."
Mr. Munoz, lead author on a paper about the study just published by the Royal Society, said he undertook the project because he wanted to know whether or not salmon could adapt to high temperatures. "We basically did cardiac performance measures, basically looking at when the heart starts to collapse," he said. "Mothers with the largest eggs had the most thermally tolerant offspring."
Mr. Munoz said the finding fits with a general principle that when the environment gets harsh, mothers can compensate by producing fewer, but more robust offspring.
"There's this classic tradeoff in evolutionary biology that mothers can basically have many offspring of a lower quality or fewer offspring of a higher quality," he said. "What our data suggests is that in higher temperatures the way these populations can adapt … would be for selection for mothers to have larger eggs."
High water temperatures in the Fraser River, which is currently running about 1.5 degrees higher than normal, have been blamed for large die-offs of salmon in recent years.