On Monday, Somali pirates captured a Greek-flagged bulk carrier transporting fertiliser, Mwangura said.
The 52,000-tonne Navios Apollon was hijacked "en route from Tampa, Florida, USA, to Rozy, India," with a crew consisting of a Greek captain and 18 Filipinos.
The ship was boarded by 10 men on speedboats in the Indian Ocean northeast of the Seychelles archipelago, the Greek coastguard said.
Speaking to Al Jazeera, Simon Jones from Trinton International, a maritime risk and security assessment company, said: "The problem is the area of sea they are trying to protect is so vast ... that [searching for] a few pirates sprinkled around the area ... is like trying to find a needle in a haystack.
"The only realistic way that piracy can be stopped at sea ... is for those vessels to be pratically prepared to prevent piracy occurring, preventing them getting on board and preventing them from getting close to the vessel ... the navies cannot be there all the time.
"You haven't got a blanket requirement by all shipping companies travelling through these dangerous regions or a regulation that requires them to adhere to security requirements."
Earlier, pirates seized a Yemeni freighter and 15 crew members.
The Al-Mahmoudia2 left the port of Aden, in Yemen, on December 18, the Yemeni authorities said on Monday, without revealing the nature of its cargo or destination.
The Yemeni freighter and the UK-flagged chemical tanker were intercepted by pirates in the Gulf of Aden, key maritime bottleneck near the entrance to the Red Sea.
The two attacks in the Gulf were the first since August and came as international naval missions were trumpeting the results of a year-long effort to secure the area.
Since the end of the summer monsoon season allowed pirate attacks to resume three months ago, Somali pirates had abandoned the Gulf of Aden for the wide open seas of the Indian Ocean, venturing as far as the Seychelles and beyond.
Despite the increased international presence off Somalia's coastline - the longest in Africa - pirates raked in huge ransoms.
On Sunday, pirates said they collected $3.5m for the release of the Chinese bulk carrier Dexinhai.
The Singapore-flagged MV Kota Wajar was also released nearly 10 weeks after being hijacked, the European Union naval task force said on Monday. The amount of the ransom is not yet known.
The latest captures and releases bring to at least 11 the number of ships currently held by pirates, together with close to 250 seamen, according to Ecoterra International, an environmentalist NGO monitoring maritime activity in the region.
Among those in captivity are a British couple captured on October 22 while sailing their yacht to Tanzania.
|The hijackings come despite a considerable naval presence in the region [AFP]
In a recent video, Paul and Rachel Chandler said that their captors were "losing patience" and could kill them within a week if no ransom was paid.
The pair were briefly held on board the recently released MV Kota Wajar.
Alongside the EU, the US, Nato and other national navies also deployed warships off the Somali coast in December 2008 to protect vessels and secure maritime routes in the Gulf of Aden and the Indian Ocean.
Thanks to state-of-the-art technology, huge budgets and ever-improving co-ordination, the foreign armada has thwarted many attacks.
They have also captured dozens of pirates, generally equipped with rudimentary skiffs, ladders and grapnels.
But one out of four ships sailing through the danger zone still does not comply with international recommendations for safe passage, the navies say.