Researchers from the Russian Academy of Sciences' Institute of Ecology and Evolution who survey the migration of beluga whales in northern Russia have established that the satellite tracking device put on an Arctic beluga whale named Dasha one year ago went out of service last week due to an exhausted battery.

Vladimir Putin tagged Dasha with the transmitter in August 2009 so that researchers could then monitor her migration via the ARGOS satellite system.

Dasha was caught and released in the Sea of Okhotsk, and researchers say she still inhabits that area. Her tracking device stopped sending signals last week, as the device's battery lasts only 9 to 12 months.

The transmitter detaches itself from the carrier as soon as the battery dies. And the scars from its nylon fixings heal within two to five weeks' time, leaving no trace on the whale's body.

The Institute of Ecology and Evolution's survey of beluga whales in the Sea of Okhotsk is ongoing. During their summer expedition, they put tracking devices on several more beluga whales caught there. These transmitters will make it possible to continue surveying the population numbers and migratory patterns of beluga whales in Russia's territorial waters.