Pirate attacks dropped slightly in 2011 for the first time in five years thanks to increased security, but the situation off Somalia is a growing concern, a maritime watchdog said Thursday.

Around the globe there were 439 recorded incidents of piracy and armed robbery last year, compared with 445 in 2010, which was the fourth consecutive year of increased piracy.

In total 802 crew members were taken hostage in 2011, also down from the four-year high of 1,181 the year before.

Forty-five vessels were hijacked, 176 boarded and 113 fired upon, while there were 105 reported attempted attacks. Eight crew members were killed during the year, the same number as in 2010.

But Somali pirates remain the greatest threat, as more than half -- 237 -- of the incidents took place off the coast of Somalia in 2011, against 219 in 2010.

Pottengal Mukundan, director of the IMB Piracy Reporting Centre, said the overall figure for last year would have been higher without increased efforts by international naval forces to tackle the problem.

"These pre-emptive naval strikes, the hardening of vessels and the deterrent effect of privately contracted armed security personnel have all contributed to this decrease," he said in the report.

But the IMB report highlighted the first hijacking by Somali pirates of an anchored vessel from within the territorial waters of Oman, underlining the need for ports and vessels at anchorages to be vigilant.

Elsewhere, Nigeria and Benin continued to be "piracy hotspots", it said.

Although 10 attacks were reported in Nigeria, including two hijackings, the IMB warned that this number was not a true reflection of the real threat of Nigerian piracy.

Britain will hold an international conference in February on the instability in Somalia and focus on ways of protecting ships from pirates in the Gulf of Aden.