Dennis W. Lee

An examination of sexual dimorphism in Atlantic and Pacific blue marlin using body weight, sagittae weight, and age estimates☆

Abstract Length, weight and otoliths of Atlantic and Pacific blue marlin ( n = 436) were sampled between 1979 and 1983 in the Atlantic and Pacific Oceans from recreational landings. Otolith weight was highly variable within size classes, but the range of otolith weights was the same for males and females from both oceans. Although age estimates for Atlantic and Pacific blue marlin were not validated, males and females were estimated to be equally long-lived, reaching estimated ages of >20 yr, yet females achieve much larger somatic sizes than males. Length was not useful in predicting estimated age. The sex-related size differences in Atlantic and Pacific blue marlin can be attributed to differential growth between sexes. Although males can grow to a maximum size of ∼ 160 kg and females grow to at least 540 kg, longevity was similar for both sexes. The sex-related size differences in blue marlin are related to differential growth between sexes and are not due to differential mortality. Otolith weight was linearly related to estimated age and r 2 ranged from 0.70 to 0.91 for Atlantic and Pacific blue marlin. This relationship demonstrates potential for estimating the age structure of the landings, if validation of the aging method can be achieved.