NAGOYA (Kyodo) -- Kyukichi Tsutsui, a former captain of a Japanese tuna fishing boat exposed to nuclear fallout from a 1954 U.S. hydrogen bomb test in the Pacific Ocean, died of natural causes earlier this year, his family said Friday. He was 92.

Tsutsui died at home in the central Japan city of Nagoya on June 4. He was one of 23 crew members aboard the Fukuryu Maru No. 5, also known as the Lucky Dragon No. 5, who were all exposed to radioactive particles released by the largest-ever U.S. nuclear weapon test at the Bikini Atoll in the Marshall Islands on March 1, 1954.

One crew member died about six months after the Castle Bravo test. Tsutsui took over duties leading the ship after the captain suddenly fell ill.