Each year, during May and the first week of June (the second quarter in the charts identified above), adult blue marlin, white marlin, sailfish and swordfish concentrate to spawn at about 12 Caribbean area locations, which glow red in the charts listed above. I believe that the adults return year-after-year to the same spawning sites where they began life, just as salmon return to their exact stream of origin. For the western North Atlantic, these spawning area “hot spots“ are located in the deepwater gaps between the largest of the Caribbean islands (i.e., the Yucatan Straits between Mexico and Cuba, the Florida Straits between Cuba and Florida for swordfish, the Windward Passage between Cuba and Haiti, the Mona Passage between the Dominican Republic and Puerto Rico, the gap between Puerto Rico and the Virgin Islands, the Anegada Passage between the Virgin Islands and St. Maarten), and two large areas, one about 550 miles east of St. Maarten and the other, 350 miles east of Trinidad. The latter two spawning sites appear to be the most important. They are positioned on or near the two major surface currents, the North Equatorial and the South Equatorial (see chart below), which flow from West Africa toward the Caribbean. North Atlantic hurricanes originating over West Africa track westward along and are powered by the northern of these two warm water currents.
While the billfish all spawn at the same location at the same time, swordfish spawn at greater depth than do the others. Since all their young eat anything they can catch including other young billfish, such a separation by depth has distinct survival advantages.
Additional evidence of the timing and location of marlin spawning is provided in published scientific studies. Marlin ovary maturation peaks in May and larval blue and white marlin have been collected in plankton nets in Exuma Sound (in the Bahamas) and the Mona Passage. If you want to see what a half inch blue marlin looks like, go here: www.BigMarineFish.com/photos_blue_marlin_pg5.html
Over the years, I have paid close attention to published reports in both the Atlantic and Pacific Oceans by the sport fishing community on where and when marlin (blue, white, black and striped), sailfish, swordfish, bluefin, bigeye and yellowfin tuna were caught, especially where fish large enough to be considered adults were caught during the period when they ought to be spawning. The location and timing of IGFA all tackle world record catches is also very instructive. Based on recently reported catches by sport fishermen, I think there is a very good chance that spawning also occurs during May and early June on the eastern side of the North Atlantic at about the same latitude as the Caribbean (15 to 20 degrees N.), the area of the Cape Verdes Islands (e.g., see Capt. Les Gallagher’s article in Marlin, December/January 2008).
Why do marlin and swordfish spawn in these locations? Probably to position their young where they will have the best chance of survival – sufficient food, moderate temperatures and fewer predators. Over thousands of years of their evolution, those adults that chose these areas to spawn were more successful in terms of the young’s survival than those which spawned elsewhere – survival of the fittest in action. As you would expect, their nursery areas are located down-current from the spawning sites. Major nursery areas include the coast of Venezuela (down-current from the spawning site on the South Equatorial Current), the northern Caribbean Sea (down-current from all the gaps between the Caribbean islands), the northern Gulf of Mexico (down-current from the Yucatan Straits spawning site), and the east coast of Florida (down-current from the spawning site in the Florida Straits between Florida and Cuba). Since longlining is prohibited in the Bahamas and Cuban waters, we have no data from U.S. longliners from these areas. If we did, I would expect we would find spawning areas and nursery grounds in both. Juvenile marlin and swordfish remain in their general nursery areas, perhaps venturing further and further north along the U.S. East Coast as they grow larger, until they become adults capable of spawning. As adults, the migratory pattern of both marlins and swordfish expands considerably.
