This is according to the International Maritime Bureau said.
From July to September only one ship reported an attempted attack by pirates, compared with 36 attacks in the same three months last year.
Pottengal Mukundan, director of the bureau, said: "We welcome the successful robust targeting of pirate groups by international navies in the high-risk waters off Somalia, ensuring these criminals are removed before they can threaten ships.
"It's good news that hijackings are down, but there can be no room for complacency. These waters are still extremely high-risk and the naval presence must be maintained."
International navies have stepped up pre-emptive action against pirates, including strikes on their bases on the Somali coast. Shipping firms have bolstered their defences with armed guards, razor wire, water cannons and safe rooms. According to the bureau, no vessel with armed guards has ever been hijacked.
Last year, piracy in the busy shipping lanes of the Gulf of Aden and the northwestern Indian Ocean netted $160-million and cost the world economy about $7-billion, figures from the One Earth Future Foundation show.
Timo Lange, a spokesperson for the European Union Naval Force Somalia, attributed the decline in attacks to a number of factors, including monsoon season. He said the efforts of counterpiracy forces, including Nato, Russia and China, had contributed and there was better co-operation between the forces.
"Our operations are more and more intelligence-led," he said. "We react to events and we can get a report from a merchant vessel and close in on that region and actively look for those pirates."
There are also signs that Somalians are resenting the pirates and placing their hopes in a new central government. "The communities are getting fed up with the pirates and expel them from their communities so they have to look for other places to hide," he said. But he added that, without substantial change in Somalia, "the danger of piracy is always there".
The decline comes as a new president and Parliament attempt to bring stability to Somalia for the first time in 20 years.
Rory Lamrock, an intelligence analyst with security firm AKE, said piracy was a less attractive enterprise but this depended on security being maintained. "The gains are all reversible, because the main conditions on the land, such as poverty, insecurity, the distribution of firearms and a lack of institutional development, remain largely unchanged," he said.
"If security measures are rescinded, it would be easy for pirate syndicates to resume their activity to similar levels of recent years."
The Ifiso independent vetting coalition, a civil society group in Somalia, echoed his sentiment. The group's legal officer, Bashir Yusuf, said: "As long as these conditions are not addressed and as soon as security measures are relaxed, piracy will bounce back."
Pirates off Somalia are still holding 11 vessels for ransom with 167 crew members as hostages on board. Twenty-one more kidnapped crew members are being held on land. – © Guardian News & Media 2012