EU and NATO naval forces freed a ship commandeered by Somali pirates in the Gulf of Aden this week, even as the number of such attacks has dropped sharply.

Counter-piracy forces from the EU Naval Force Somalia's Operation Atalanta and NATO said they acted on a tip from port authorities in the Somali territory of Puntland and, after a pursuit, freed the crew of a pirated sailing vessel in the Gulf of Aden Monday.

EU military officials said the operation began Aug. 8 when Puntland authorities reported a possible hijacking of a traditional sailing vessel, or dhow. It was spotted early Saturday by the EU naval vessel Lafayette, subsequently intercepted and boarded unopposed.

Armed forces, however, found the pirates had fled the vessel, leaving it and the crew in good condition. The crew said the pirates left on a second pirated dhow, the Bourhan Nour.

That ship was tracked down by another EU Naval Force unit, the German frigate Sachsen, which intercepted it late Sunday as it was heading south toward the Somali coast. Intelligence indicated the suspects were seeking to link up with other pirates there.

The Sachsen kept pressure on the ship and was joined by EU NAVFOR flagship ITS San Giusto as well as the NATO flagship HNLMS Rotterdam of the Netherlands, and it was decided to set a trap for them, Rotterdam commanding officer Capt. Huub Hulsker said in a statement.

"There was not really anywhere for them to go," he said. "The situation was clear and some strict orders and two warning shots later, the suspected pirates surrendered."

It took the EU-NATO boarding team 20 minutes to gain control of the dhow, separating the crew from the six suspected pirates.

The arrests came as figures from the International Maritime Bureau indicated pirate attacks perpetrated by Somalis have dropped sharply in the first half of 2012.

Somali piracy activity, it reported, fell from 163 incidents in the first six months of 2011 to 69 in this year, while the number of vessels hijacked also dropped from 21 to 13 during the period -- including a hijacking-free monthlong period in June-July.

As of June 30, Somali pirates were known to be holding 11 vessels and 218 crew members, 44 of whom were being held ashore in unknown locations and conditions.

Somali piracy "continues to remain a serious threat," IMB Director Pottengal Mukundan said.

"Somali pirate attacks cover a vast area, from the Southern Red Sea, Gulf of Aden, and Gulf of Oman to the Arabian Sea and Somali Basin, threatening all shipping routes in the northwest Indian Ocean," he said.

The EU-NATO arrests this week demonstrated pirates are facing significant pressure from armed forces in the Gulf of Aden, said Commodore Ben Bekkering, commander of NATO's counter-piracy mission.

"If they make it to the open sea, they find it increasingly difficult to stay undetected and find opportunities to attack merchant vessels," he said. "That can be credited to a broad international effort and the effective coordination between many participants. In this case, NATO and EU worked closely together."