The military personnel were aboard an amphibious vehicle that sank Thursday in deep water off the coast of California during a training exercise.

"It is with a heavy heart that I decided to conclude the search and rescue effort," said Colonel Christopher Bronzi, commander of the 15th Marine Expeditionary Unit.

During the 40-hour search, Marine, Navy and Coast Guard helicopters, ships, and watercraft searched more than 1,000 square nautical miles, the marines said in a statement.

A total of 16 service members were on the amphibious vehicle -- until now eight were rescued but one later died, and two others are in critical condition.

The search and rescue operation now shifts to one aimed at finding the bodies of the missing service members, Bronzi said.