Sharks, wolves and uninspected assumptions

Anecdotal assumptions are so often wrong.

In the Islands, do sharks attack surfers because the surfers look like turtles or seals? Are big sharks attracted to shore because the small sharks have been fished out? Is that always the same shark cruising the surf zone, or are they constantly moving around?

The answers to some of these questions are known, partially known, or unknown, and occasionally they are correctly known for the wrong reasons.

We were struck by an article this month on sharks' culture cousins, wolves. The piece was in the journal Frontiers in Ecology and the Environment.

This goes to the question of whether wolves are major predators on cattle. Ranchers have long said so, and have launched wolf kills to respond.

The conservation community has argued that wolves, if they come near cattle, are doing ranchers a favor, culling the weak. And that since they perform the same service for wild herds of elk and deer, they ought not be slaughtered.

The new study confirms that cattle are indeed a big piece of wolf diet, seasonally. The study was done by Canadian researchers from the University of Alberta, who used GPS tracking equipment to follow wolf travels in 2008 and 2009, during grazing seasons near the Rocky Mountains.

But the wolves, for the most part, weren't preying on the herds. They were feeding on dead cattle at “boneyards,” places where ranchers dumped cattle carcasses. The four wolves researchers tracked switched from wild prey to eating cattle during the grazing season, but in 85 percent of the cases, they were scavenging on already-dead cattle.

Ranchers were dumping the carcasses near their grazing cattle. The boneyards also attracted grizzly bears and cougars. For the wolves, the cattle made up almost half of their summer diet.

The message from the researchers was that ranchers' management practices are actually attracting predators to their herds. Thus, changes in management practices could reduce wolves' opportunities to feed on the herds.

The message for the rest of us is to be real careful about uninspected assumptions.

© 2011 Jan TenBruggencate