17 August 2011
Last updated at 15:26
Wolves in Sweden went extinct in the 1970s, but a few Finnish wolves have since re-established a small population.
The 250-strong Swedish wolf population is inbred and suffers from smaller litter sizes than other wolf populations and backbone deformities.
Inbreeding is not the wolves' only problem, they are often killed on roads and die of disease.
The wolves are also shot by poachers, who worry that they will kill their highly trained and expensive hunting dogs. The wolves see the dogs as competition for food.
Researchers at the Grimso Wildlife Research Station in Sweden use radio collars to tag wolves to monitor their numbers.
A research team on the ground locates the footprints of an animal and then a helicopter is called to dart the animal from the air.
Once the wolf is darted, it falls aleep and is loaded in the helicopter, which delivers it to a meeting point where the vets are waiting.
Researchers unload the wolf, carrying its body to a clearing where it is fitted with a GPS collar - about 10% of Swedish wolves are tagged.
Researchers monitor the tagged animals and use their survival to estimate the total number of wolves that survive each year.
Although researchers find some of their tagged wolves dead, many wolves and their collars disappear without trace.
The Swedish team suspects that poachers are shooting the animals and destroying the collars. Here researchers keep a wolf warm as it recovers from the anesthetic.
In a new study, published in Proceedings of the Royal Society B, the researchers estimate that over half of the dead wolves go unrecorded.
The research suggest that without the last decade of poaching, Sweden's wolf population would be four times larger.
The penalty for poaching the European wolf, Canis lupus, can be up to 4 years in jail; a sentence that seems to fail to act as a deterrent.