Troops from a Spanish warship stormed a pirate skiff in the Gulf of Aden and rescued a French hostage missing from her yacht but found no trace of her husband, the EU anti-piracy mission said.

As a helicopter kept watch overhead, naval commandos in a fast launch fired on the skiff to disable its engine. The boat sank, but the hostage was rescued and seven pirates were arrested unharmed, the Spanish defence ministry said.

"She was the only hostage on board the skiff. Her husband was not on board," EU naval spokesman Captain Paul Gelly said, confirming the rescued hostage was Evelyne Colombo, wife and crewmate of missing sailor Christian Colombo.

"She is safe and sound," he said, explaining that Ms Colombo and the detained pirates are now on board the Spanish ship.

A German warship, the FGS Bayern, found the couple's catamaran the Tribal Kat, adrift in waters off Yemen on Thursday. There was no-one on board and the EU Atalanta naval command launched an air and sea search for the attackers.

French officials said there were signs of a struggle on board the yacht, which was towed to Djibouti to be studied by agents from the DGSE spy agency.

"It was like searching for a needle in a haystack," Captain Gelly said.

"Our priority was to search for any vessel that might have been leaving the area and heading for the coast of Somalia," he said.

The French frigate Surcouf detected a suspect vessel and on Saturday the Spanish warship SPS Galicia chased it down.

The Spanish defence ministry said when the skiff ignored an order to stop, the commander of the Galicia ordered his men to open fire.

"At that time, it was discovered that they had a hostage on board, who was a woman," it said.

"The amphibious ship proceeded to intercept the pirate vessel. The operation involved a helicopter and naval warfare team, who fired on the engine of the boat, to disable it."

'Taking a risk'

Christian Colombo is a former French navy crewman and the couple were experienced sailors who wanted to see the world and were passing through the Gulf of Aden en route for the Indian Ocean and eventually Thailand.

"They knew they were taking a risk and everyone advised them not to go," a relative said.

One of the couple's daughters, Emilie, posted a message of concern on the blog they were keeping of their high seas adventure.

"The last I heard from Christian was around a month ago. He was south of Egypt and heading for Malaysia," said the skipper's friend Gerard Navarin, who once helped him set a catamaran speed record off Toulon.

The waters between Yemen and Somalia are notorious for attacks by pirate gangs, and French yachts have been among the vessels seized in the past. A second yacht went missing at around the same time as the Tribal Kat.

Somali pirates frequently seize crew from merchant ships and pleasure craft in the dangerous waters off the conflict-ravaged Horn of Africa and have taken millions of dollars in ransom for their release.

According to the watchdog Ecoterra, at least 50 vessels and at least 528 hostages are being held by Somali pirates, despite constant patrols by warships from several world powers.

A French couple was kidnapped from a yacht in September 2008 as it headed through the Gulf of Aden.

A ransom was paid, but French commandos later ambushed the pirates, killed one, captured six more and recovered the cash.

In April 2009, another French yacht was seized. This time special forces troops intervened when the boat was still at sea.

In the ensuing gun battle a French bullet accidentally killed the hostage skipper.

In addition, a French DGSE agent is thought to have been held hostage by Islamist militants in the Somali capital since July 2009.

AFP