Two European-owned chemical tankers have been captured by pirates off the coast of Somalia over the past 24 hours, according to the Maritime Security Centre-Horn of Africa [1].

The first vessel—a 9,000-ton, Greek-owned and Panamanian-registered tanker, Nipayia—was boarded by pirates 450 miles east of Kismaayo yesterday afternoon. Nineteen crew members were on board. 

This morning, another tanker, the Bow Asir, was taken 250 miles east of Kismaayo. The 23,000-ton, Norwegian-owned and Bahamian-registered vessel had 27 crew members on board. The U.S. Navy's 5th Fleet, however, reports that there are 23 crew members on board, according to the Associated Press [2]. 

The AP also provides more information on how the Norwegian tanker fell into pirates' hands:

The owner of the Bow Asir, Salhus Shipping AS said it received a security alert message from the Bow Asir at 0729GMT saying the ship was being chased by two small boats with suspected pirates on board.

At 0745GMT, the captain reported that the pirates had boarded the vessel, the company said. Three hours later, Salhus Shipping received an e-mail from the ship confirming that 16 to 18 pirates carrying machine guns had gained control of the vessel, managing director Per H. Hansen said in a statement.

There have been no reports of ransom demands yet.

Piracy off of Somalia skyrocketed by 200 percent in 2008 over 2007, according to Agence France Press [4]. This year, however, piracy rates have declined due to harsh seas and a multinational effort to patrol pirate-infested seas off the Somali coast.

The navies of the United States, China, the European Union, NATO, and India have provided more than 20 ships to patrol the Gulf of Aden and the Indian Ocean following requests from the United Nations, the AP reports.