By Rebecca Morelle
Science reporter, BBC News
Tracking walruses is harder than you might think
At first it sounds like a pretty simple task - find some walruses, stick satellite tags on a lucky few, sit back, relax, and track their migration from the comfort of your office.
But as a recent expedition to try and do just this has shown, the reality can be very different.
In April, a Greenlandic-Danish team of researchers set out to attach satellite tags to some of west Greenland's walruses so they could follow the animals during their migration.
They wanted to uncover the Arctic animals' secret summer location, as well as to find out how factors such as hunting, climate change and oil exploration were affecting their movements.
But over the last few months, the walrus tagging experiment has highlighted some of the highs and lows that wildlife biologists face in their endeavours.
"Working with animals - particularly walruses - in the Arctic is tough and you have to get used to disappointment," says Erik Born, lead scientist on the walrus tagging project and a biologist at the Greenland Institute of Natural Resources.
"Even getting to the animals can be a problem. Walruses are unpredictable, but the greatest challenge can be the weather and the ice - it can change so much from year-to-year and day-to-day."
Not a whisker
While the recent satellite tagging mission, although threatened by some extremly cold and icy conditions, was successful in making contact with some of the tusked beasts, it is not unusual to travel out to the Arctic and not even encounter a whisker of a walrus.
Getting stuck in ice is a common hazard in Greenland
Dr Born says: "One year, we were in west Greenland trying to find walruses. We were amongst the ice-packs when the wind suddenly changed and we got stuck in the ice.
"We sat there for two weeks until the wind changed back, by which time we had to return back to port."
Even if you do manage to brave the tough environment and find some walruses, deploying a matchbox-sized satellite tag with a crossbow or CO2-powered gun on to an animal that is the size and weight of a car isn't as easy as it sounds.
It is easy to lose satellite tags
Walruses are lumbering on land but they become infinitely more graceful - and evasive - once they hit the water.
With great skill and precision eight satellite tags were successfully attached to walruses' hides during the recent expedition. But it was also easy to see how a transmitter, which costs hundreds of pounds, could be lost in a split second to the sea by a rogue gust of wind or a slightly off-target shot, as happened with two other tags.
At this point, when your walruses are equipped with their new transmitting accessories, you would imagine all of the difficulties have been dealt with. But, as Dr Born points out, these research projects can be hit with yet more complications.
A quick look at the BBC News website's Walrus Watch map reveals how short-lived the signalling power of some tags can be - two of the tags attached to a mother and son failed to signal at all, probably because the electronics broke on impact with the walruses.
Even when the tag is attached, things can still go wrong
"Each time you go out in the field, you refine the tags so they are likely to stay on as long as possible," says Dr Born.
But, he says, despite tag improvements, it is still possible for the antenna and tag to be crushed under the weight of the walrus or scraped off by the ice.
Even if the tags are working, the Arctic elements can yet again cause more problems.
For walruses to begin their migration, the thick ice that they love sleeping and resting on needs to begin to retreat.
Dr Born explains: "Because the tags do not stay on for long, we have a very short window for detecting walrus migration.
"This year there was a lot of very thick ice and it was very disappointing to see most of the tags stop working before the walruses had really begun to move."
On the move
But while six of the deployed tags only revealed local - although still important - information on walrus movement, two tags told another story, and seeing results emerge out of the raft of uncertainties is incredibly rewarding, says Dr Born.
In particular, one tagged walrus - a 10-to-12-year-old female who has a calf in tow - has been of much interest to the researchers.
Her tag, which after almost three months is still beaming up signals to the overhead Argos satellite system, has shown that she has recently travelled hundred of kilometres to the south west of Baffin island, where it appears she has settled for the summer.
"It is very satisfying when you get a result like this," explains Dr Born, "and we will keep on watching the tag while it is still signalling to see where it goes."
And although the migration path of just one walrus might not necessarily apply to the rest of the population, it does give the team a starting point for more research.
The trick will be, says Dr Born, to go out again with more tags and put them on more walruses in the following years - and to prepare yourself for the inevitable disappointments that will be scattered amongst the successes.
"With walruses, and with other Arctic marine mammals, there is always some sort risk," he says.
"But while you could sit there getting grumpy about it, you need to think of the wonderful place you are working, the wonderful people you are working with - and you have to remember that if the animals were straightforward to study, you wouldn't be out there doing it in the first place."
Walrus 1: Male, 4-5 years
Walrus 2: Female, 10-12 years - has yearling calf in tow
Walrus 3: Anomalous data point
Walrus 4: Male, 5-6 years
Walrus 5: Male, 18-20 years
Walrus 6: Female, 5-6 years
Walrus 7: Male, 5-7 years
(No data received from a tagged female and her son)