Hunting male polar bears a risk to species
Jeff Holubitsky, edmontonjournal.comPublished: 6:18 pm
EDMONTON - A decline in the number of male polar bears due to hunting could lead to the collapse of the reproduction rate among females of the Arctic's greatest predator, a new University of Alberta study suggests.
"We need to carefully monitor sex ratios because if you lose too many males from the population, eventually females will be unable to find mates," the study's lead author, Peter Molnar said today.
"That could lead to a decline in pregnancies and such a decline could happen very rapidly."
The study combined mathematics and biology to examine 1997 data on about 2,500 polar bears from Lancaster Sound in the central Arctic.
About 1,500 of the bears were females. However, when only mature males and mature females not caring for offspring were considered, the sex-ratio was about one to one.
In natural conditions, without the harvesting of males, Molnar said there would be two to three males for every female because the sows keep their cubs for two years.
"But because we have taken out males for so many years we are now one to one," the PhD student with the university's biological sciences department, said.
"It is certainly something we must take into consideration, but I wouldn't go that far with the information we have today that we need to change the hunting policies, because we have not seen the changes yet and have not evaluated the hunting strategies in this paper."
Molnar said further studies are needed to examine what effect a reproductive collapse might have on Canada's polar bear population, however, because other factors such as cub survival and the population density of the bears must be considered.
"With polar bears right now we have a policy to preferentially harvest males over females and the argument behind that is that the females are the ones doing the reproduction," he said.
As a result, he said all Canadian polar bear populations are quite biased towards females.
"People started worrying if we could reach a point where there are too few males so females are unable to find mates."
Polar bears typically mate from the beginning of April to the end of May, when males follow the trails of females in estrous. If they like each other, they will mate over a period of about 2 1/2 weeks after which the female is generally pregnant.
The male will then wander off in search of other females.
The study looked at number of males that searched for and found females, how long the pair stayed together, if the males found other mates, and how many females a male could fertilize in a breeding season.
He said there currently appears to be no problem with the pregnancy rate. In Lancaster Sound, for example, 99 per cent of females find partners.
The paper says, however, that if the number of males declined to a threshold of two males for every three females, it could lead to a dramatic and rapid reproductive collapse of the species.
Molnar said a similar scenario was faced by the saita antelope in Asia after years of the heavy poaching male animals.
"For 10 years nothing happened, then from one year to another a sudden collapse occurred where pregnancy rates fell from 90 per cent to 20 per cent," he said.
The study was published in today's edition of a British journal called Proceedings of the Royal Society and was conducted in conjunction with the government of Nunavut.