Almost all fish in the longline fishery under 180kg are males and almost all of those over 180kg are females. Detailed studies have proved that black marlin do not change sex. Detailed information on the sex structure of black marlin caught around the Coral Sea Rim, particularly in the areas influenced by the New Guinea Coastal Undercurrent, could greatly help to solve the possibility of sex-dependent migration patterns. Black marlin females grow in excess of 700kg, whereas males rarely exceed 200kg. Available information on age indicates that fish may reach 15kg in their first year, 30kg in their second year, and a 450kg female is over 10 years old.
Males probably reach similar ages as females, but with a slower growth rate.