Victoria researcher gains fame for big-shrink theory

By Judith Lavoie, Victoria Times Colonist

Predatory behaviour of humans is causing some species to shrink at an unprecedented rate, says a Victoria research scientist whose study has been deemed one of the top science stories of last year.Chris Darimont, a research scientist with Raincoast Conservation Society and postdoctoral researcher in environmental studies at the University of California, Santa Cruz, has found fishing and hunting are causing the planet’s most rapid evolutionary changes.

The research paper, first published in the Proceedings of the National Academy of Sciences, has been slotted at No. 30 in Discover Magazine’s Top 100 Science Stories of 2009. The list, which includes only a handful of Canadian stories, is being revealed throughout January on the magazine’s website.

While most predators take smaller and weaker prey, humans target the largest animals — whether salmon or grizzly bears. Combined with large harvests,that means species are getting smaller and breeding earlier, so they can have offspring before they’re large enough to be targeted, Darimont’s study found.

“If you consider things like fishing, this is of huge importance,” Darimont said in an interview.

“It means we are harvesting away our future bounty by causing fish to shrink in size and breed at an earlier age. From a human perspective, we are essentially whittling away future opportunities to have a sustainable industry.”

From the ecosystem perspective, humans taking the biggest and strongest can have ripple effects that reverberate up and down the food chain, he said.

“The public knows we’re taking away too many fish, but the threat goes above and beyond numbers,” he said. Trophy hunters who prize the big horns on bighorn sheep have caused average horn length and body mass to drop by about 20 per cent over 30 years, the researchers discovered.

“We’re changing the very essence of what remains, sometimes within the span of only two decades. In not only an ecological, but also an evolutionary context, we are the planet’s super-predator,” Darimont said.

The research seems to be creating a stir, he said, because it compares humans with other predators, which take juveniles or weaker animals, usually resulting in prey species becoming bigger and stronger.

The findings should be a wakeup call to resource managers, policy makers and commercial harvesting industries, said Darimont, who is hoping the exposure will result in changes in hunting and fishing regulations. “We should be harvesting at far, far lower rates so that, even if we choose the largest,it would have less of an impact,” he said. “And, if we think this is important, we should forego our preference for these trophy specimens.”

Darimont said he is thrilled the paper is attracting so much attention. “At Raincoast, we try to do good science and get that science to reach the public and decision-makers, so this has been a spectacular success,” he said.

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Coastal wolf with a salmon in its month.
Photo by Dene Rossouw.