Abstract

Blue marlin, Makaira nigricans, occur seasonally in the northern Gulf of Mexico (nGOM), and are targeted by billfish tournaments during May through August throughout the region. There is little information on the biology of blue marlin in the nGOM; thus, marlin captured in tournaments provide a unique opportunity to gather data. We sampled 43 blue marlin from nGOM tournaments from 2000-2005 to determine reproductive patterns. All fish were females, and ranged from 254 to 351 cm lower jaw fork length and 119.1 to 478.8 kg. Gonadosomatic index (GSI) values were low in all fish, ranging from 0.39 to 1.05, and there was no difference in mean GSI values between May, June and July. However, histological inspection showed ovarian recrudescence was evident in all fish captured during May, 83% of the females captured in June, 55% of the females captured in July and 50% of the females captured in August. Females in the early maturation ovarian class were captured most frequently during all months; 17% of females were in the mid maturation ovarian class in June while females in the late maturation class were found only in July. Some females in July and August were in the regression ovarian class, indicating the cessation of spawning. Thus, the available data indicate blue marlin spawn in July and August in the nGOM. Plankton collections are being taken in the nGOM to confirm the presence of blue marlin larvae, which would verify the spawning season.

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