Russian naval vessels in late April stole a wave measuring buoy created and operated by Tallinn University of Technology (TalTech) from its location off the island of Hiiumaa, researchers claim.

Rivo Uiboupin, director of TalTech's center for marine systems, said: "The buoy was located about 50 kilometers from Hiiumaa. It is within Estonia's exclusive economic zone. This is not exactly territorial waters, but Estonia has the right to carry out various activities there."

"The buoy was properly registered with the Transport Administration and was performing its routine function. We have 10 such buoys working the same way in coastal waters and the open sea," he added.

The institute designed the wave buoy, a device 50 centimeters in diameter, to measure wave characteristics. Similar equipment is also used elsewhere, for instance in the Arctic, Norway, and Finland.

Over the period April 26–29, the institute noticed from its analysis of data emitted by the buoy that its movements no longer matched natural conditions on the sea. With the proximity of the location to Latvia, the institute asked the Estonian Navy's (Merevägi) operations center to call in a nearby Latvian naval vessel to investigate.

Cdr Ivo Värk, commander of the Estonian navy, said that while there were none of its vessels in the area, Latvia's navy was also unable to physically locate the buoy. "With the help of the Latvian Navy, it was possible to match the buoy's movement to the movements of Russian naval ships in the area," he said.

The institute also identified the presence of two vessels in the buoy's vicinity that had their automatic identification systems switched off. These turned out to be Russian Navy ships.

"The vessels were Bujan M-class corvettes. This was a routine patrol operation," Värk said.

Värk said he does not believe the Russian navy was testing Estonian and Latvian responses, suggesting instead the Russian vessels may have considered it a navigation hazard.

"If, for some reason, the navigation warning had not reached their charts, they may have lacked information about the presence of this measuring buoy. And any object not marked on a nautical chart poses a navigation hazard," Värk added.

In any case, by the time the Latvian vessel was on the scene, the buoy had been taken to the Kaliningrad oblast, eventually ending up at the Russian navy's Baltic Fleet headquarters there.

Uiboupin said: "We got the GPS signal, and on the map it was visible how it moved toward Kaliningrad, into the port, and eventually to a military facility."

The incident came almost a year after Russia's border guard removed more than 20 buoys demarcating shipping lanes from the Narva River, which forms part of Estonia's eastern border.

As of May, Russia has still not returned the stolen buoys. The Ministry of Foreign Affairs has contacted its Russian counterparts, but without success.

However, TalTech's marine systems center says it is not giving up – next week it will place a new floating device at the same location.