Researchers at UVic have found humans kill fish at rates 14 times higher than they evolved to endure. Photo by Ivonne Wierink – Fotolia
Our behaviour is unique — and uniquely harmful — compared to other animals
Humans have emerged as a unique class of “super-predators,” exploiting other animals in ways seldom seen in the natural world, according to a new report by researchers at the University of Victoria.
And the combination of “wickedly efficient killing technology” and short-sighted resource management is particularly bad news for nearly every species on Earth, said lead author Chris Darimont, Hakai-Raincoast conservation scholar at UVic.
In short, we don’t hunt like other hunters, we don’t consume like other animals and we tend to kill at rates many times higher than other top predators.
A number of events in our development as a species have changed our place in the animal kingdom, said Darimont, who is also science director for the Raincoast Conservation Foundation.
The development of projectile weapons vastly reduced the risk associated with hunting, allowing us to kill from a relatively safe distance.
“Being a predator is a very dangerous lifestyle,” he said. “Large mammalian prey fight back and you may be injured. So that was an early game-changer.”
Advances in weaponry played a large role in the extinction of the woolly mammoth, sabre-tooth cats and flightless birds.
In fact, humans still kill other predators at roughly nine times the rate that large land carnivores such as wolves, lions and bears typically kill each other in the wild, according to the report, titled The Unique Ecology of Human Predators published in the journal Science.
“In B.C., there is good evidence with grizzly bears for example that the populations cannot withstand the extra mortality of trophy hunting,” said Darimont.
Humans are also the only predators capable of exploiting fossil fuels to travel large distances at terrific speeds on land, at sea and in the air.
“Predators spend a lot of energy searching for prey, roaming large areas,” he said. “We are the only predator that has an external energy source to help us hunt more efficiently.”
Finally, technology has allowed us to kill prey previously beyond our reach in huge quantities.
After the Second World War, fishing fleets began to range out of coastal waters, with large amounts of fuel, sonar fish finders and freeze-at-sea technology that allowed us to exploit fish populations far from the coastal waters plied by our ancestors.
“We began to fish in places we had never been and at depths we had never been,” Darimont said.
Many of the world’s fisheries exploit more than 10 per cent of the target species biomass available annually — the total weight of all the fish in a population — while natural predators usually take around one per cent or less, the report states.
Using catch estimates of 282 fish species, the researchers found that humans kill fish at rates 14 times higher than our prey evolved to endure.
And while most predators hunt the young, the old and the sick, we do things differently.
Humans have a preference for larger prey, which selectively targets adults of reproductive age and damages the ability of prey populations to procreate and sustain their numbers, according to co-author UVic biologist Tom Reimchen.
B.C’s herring roe fishery — in which adult fish are scooped up by the thousands in order to harvest eggs from the females — is particularly wasteful of the herring’s “reproductive capital,” said Darimont. Coastal First Nations have traditionally harvested roe from kelp beds or rafts of branches, taking a small fraction of the “reproductive interest” of the population and leaving the adult fish to reproduce for many more years.
What fisheries scientists call sustainable exploitation has more to do with sustaining the annual yield for industry than it does the ability of fish populations to thrive, he said. Even so-called managed fisheries harvest at several times the rate of natural predator consumption, the report states.