The attack is the most recent sign of a fresh bout of Somali piracy in the Indian Ocean, coinciding with a slew of attacks on merchant shipping in the Gulf of Aden and the Red Sea.
David Appleton, head of professional and technical at Nautilus, which represents more than 20,000 maritime workers, said the utmost priority should be the safeguarding of the lives of seafarers.
The territorial waters affected extend halfway into the 12-mile-wide Bab al-Mandab Strait, through which around 15% of the world's shipping traffic passes.