The piracy-powered boom is apparently continuing despite a sharp drop in the number of successful ship seizures. The presence in the Indian Ocean, Gulf of Aden and Arabian Sea of warships from more than 30 nations is apparently beginning to reduce the rate of hijacking.

Successful Somali pirate attacks fell to 24 last year from 45 in 2010, according to Nato’s count. The total number of attempted ship takeovers remained constant: 129 last year and 132 in 2010.

More difficult conditions for the pirates have led them to try to maximise the returns from each ship they capture, Dr Shortland notes.

“Ransom negotiations now drag on for longer and result in record payments,” she writes. The largest reported payment for a single hijacking was $3 million in 2008 and $9 million in 2010.