Do Blue Marlin Spawn in the Northern Gulf of Mexico

Blue marlin, Makaira nigricans, are seasonal residents in pelagic waters of the northern Gulf of Mexico (nGOM) where they support an active catch-and-release and trophy recreational fishery. However, little is known about the biology of the species in the nGOM. We collected ovaries from 62 blue marlin (size range 253.4 – 351.3 cm LJFL) captured during fishing tournaments in the nGOM from 1999-2007 to examine their reproductive condition during the May through September resident period. Gonadosomatic Index was low during all months; mean values never exceeded 0.59 ± 0.07. Histological analysis found no females captured in the nGOM that were spawning capable, although several females captured in July 2006 and September 2007 had regressing ovaries with vitellogenic and/or hydrated oocytes undergoing atresia. Furthermore, a fish captured in June 2007 with early developing ovaries had a mass of hardened, hydrated oocytes interspersed throughout the ovary, suggesting a failed or incomplete spawning event during the 2006 season. While histological evidence suggests blue marlin do not spawn in the nGOM, we have collected blue marlin larvae < 7 d old along the western edge the Loop Current in the nGOM in July/August but not in other regions of the nGOM during the same months. Possibly, the larvae were spawned in the southern GOM or Caribbean Sea and transported to the nGOM by the Loop Current. The status of blue marlin spawning in the nGOM remains uncertain pending additional data collection.