02 September 2008
Wolves are not quite the red-blooded hunters we thought they were. It appears they prefer to dine on a nice piece of salmon rather than deer. Ecological studies into predator-prey relations have traditionally shown that wolves feed on hoofed animals like deer, elk and moose, particularly during the spring and summer.
However, ecologists have recently noticed that the fanged animals can capture and eat salmon in the autumn when the fish swim upriver.
The suggestion has been that wolves fall back on salmon as an alternative food source when deer are scarce. But Chris Darimont and colleagues at University of Victoria and Raincoast Conservation Foundation, British Columbia, Canada, have shown that wolves actually prefer salmon, whether or not deer are on the menu.
Darimont and colleagues spent four years studying the feeding habits of eight packs of wolves in the Great Bear Rainforest region of British Columbia.
Spawning salmon are unavailable for most of the year. They leave rivers at the start of spring the size of a human finger and spend up to five years growing in the ocean. When they return to their native streams in the autumn, often the size of a five-year-old child, they offer a huge pulse of nutrients to predators that can harvest the creeks.
Salmon is rich in fat compared to deer, containing four times the amount of caloric energy per bite. Combined with the fact that they are predictable, spatially constrained in creeks and don’t fight back like deer do, salmon is an ideal food resource.
Darimont and his team used genetic tests to analyse over 2000 droppings and 60 hair samples to determine their wolves’ dietary habits.
“Hair is metabolically inert, so it records what that wolf was eating during that time of hair growth,” explains Darimont.
The results show a seasonal shift in diet from deer in spring and summer to salmon in the autumn, even when deer is readily available – suggesting the availability of salmon is driving the change in feeding.
This means, says Darimont, if commercial salmon fishing continues at the rate it is now, the implications for wolves and other species could be disastrous.
Although wolves have deer as a fallback, other species like mink and grizzly bears rely heavily on salmon. The ability of female grizzlies to bear young is completely dependent on salmon availability, as is breeding and lactation in mink.
For these reasons, human exploitation of salmon must be scaled down, says Darimont. He supports the Canadian government’s Wild Salmon Policy, which aims to put the needs of the ecosystem ahead of those of the fishing industry when managing salmon stocks.
Journal reference: BMC Ecology, DOI: 10.1186/1472-6785-8-14