Growth in Makaira nigricans diverges sharply by sex. Males slow early and seldom exceed roughly 160 kilograms; females continue growing and account for all the very large individuals reported. The largest documented Atlantic blue marlin have exceeded 800 kilograms.
The difference is not merely a curiosity for record books. Because egg production rises steeply with female size, the largest fish are also the most productive spawners, and a fishery that selects for the biggest animals removes exactly the individuals contributing most to reproduction. This is one reason billfish assessments pay attention to size composition rather than tonnage alone.
Tagging has shown blue marlin crossing the Atlantic and moving between the northern and southern hemispheres, which complicates management further, since a fish caught off one coast may have spawned near another. Stock structure in the Atlantic is treated as a single unit for assessment, an assumption that continues to be examined.