French commandos stormed the yacht in an attempt to free skipper Florent Lemaçon, his wife, their three-year-old son and two crew members.
They killed two pirates and captured three but they also accidentally shot Lemaçon dead.
The three accused - Mohamed Mahamud, Abdelkader Osman Ali and Mahamud Abdi Mohamed, aged between 26 and 31 - claimed that extreme poverty had forced them to turn to piracy and expressed regret for their actions.
"We weren't arguing that poverty justifies piracy," said defence lawyer Fabian Lahaie. "But there are the facts. When the pirates they were in utter poverty. The people who went them out to sea to attack boats didn't provide enough petrol to get back to shore, so they had to get a result to survive."
Lawyer Arnaud Colon de Franciosi, representing the survivors, said they were not looking "for vengeance" but that the accused should be "held responsible" for their acts.
The families believe the French government of authorised the operation to try and frighten potential pirates and did not pay sufficient attention to the hostages's safety.
"I believe that Florent Lemaçon died for reasons of state," Colon de Franciosi. "This operation was meant as a powerful signal to the Somalis, the hostages were a secondary consideration."
The sentence came as British director Philip Greengrass's film Captain Phillips, which stars Tom Hanks and is about the hijacking of the MV Maersk Alabama off the Somali coast, hit screens around the world.