Critical Habitat of Blue Marlin
blue marlin by Ron Pittard
SPAWNING AREAS - These two charts (1994 above and 1995 below) show where U.S. longline vessels reported catching the greatest numbers of blue marlin during the second quarter.  (Color code:  red >16, magenta 8-16, dark blue 4-8, pale blue 2-4, and yellow 1-2)   The "spring" quarter includes the peak period of spawning activity.  From these longline catch records we can see that adult blue marlin are being caught in the greatest concentrations, during the period of the year when they should be spawning, at a number of specific sites throughout the Caribbean region.  Blue marlin spawn primarily from March through June with the peak in April-May.  The primary spawning locations include the gaps or "passages" between the largest Caribbean islands (such as at each end of Cuba), a spot SSE of St. Croix, and two large "hot spots" located in the Atlantic well east of the Caribbean chain of islands.  These two open ocean areas are positioned on two major current systems - the North Equatorial and the South Equatorial.  A map showing generalized surface currents of the North Atlantic is available here.  It is important to recognize that these same, relatively small areas are also primary spawning areas for white marlin and for swordfish. 

The scientific community already accepts the fact that there is both a North Atlantic and a South Atlantic population of swordfish, which do not interbreed.  We believe there is also a northern hemisphere population of blue marlin (and white marlin).  It spawns at these "hot spots" during the northern hemisphere's spring.  The southern hemisphere population of blue marlin (and white marlin) spawns in the Royal Charlotte Bank area off Cabo Frio Brazil (site of many world record blue and white marlin catches) during the southern hemisphere's spring (thus phased 6 months behind the northern hemisphere).  For larger scale maps, see our Bycatch Maps section: (
white marlin) (blue marlin).  The catch of blue marlin to the north of the primary spawning areas during the second quarters reflects the return of some fish to their summer and fall feeding grounds following spawning.
Blue Marlin Catch 1994, 2nd Q
Blue Marlin Catch 1995, 2nd Q
Feeding Grounds- The chart on the right shows where adult blue marlin concentrate from summer through late fall every year.  The third quarter of 1994 is pictured here.  Specifically, blue marlin concentrate in a narrow band along the upper edge of the continental shelf (roughly between the 100 fathom and 1,000 fathom depth contours) which also lie along the "inshore" edges of the major surface currents (the Loop Current in the Gulf of Mexico and the Gulf Stream along the Atlantic coast).  Several "hot spots" appear each year at predictable locations.  These include the area of the Flower Garden Banks off Texas, the de Soto Canyon area off Pensacola, FL, the Charleston Bump area off Charleston, SC, and the edge of the continental shelf from just below Cape Hatteras, NC, to the eastern tip of Georges Bank off Massachusetts.  In previous years (when blue marlin were more numerous) such areas would produce much higher catch concentrations.  As can be seen, some blue marlin, probably the largest individuals, are also taken by longline vessels fishing for swordfish on the Grand Banks and beyond.  While not "sampled" by U.S. longline vessels, the extension of the Gulf Stream east of the Grand Banks brings these enormous females (over 1,400 lbs.) to the Azores, to Madeira and to the Canary Islands following the Azores Current and its extension, the Canary Current (see map of North Atlantic Currents here).  Adult blue marlin (and white marlin) will remain in these northern primary feeding area "hot spots" until cold temperatures drive them back south for the winter.  By spring, they all find their way back along the edges of these major surface currents to their Caribbean area "hot spots" for spawning.
Blue Marlin Catch 1994, 3rd Q
"Hot Spots" Are Not Just the Longliners' Favorite Fishing Sites

The longline fleet follows swordfish and the larger tunas over very broad expanses of ocean throughout their annual migrations, concentrating fishing effort where catches of the target species is highest.  The extent of the area fished each year is depicted here (
1995, 1996 and 1997).  "Hot spots" where blue marlin (and white marlin) are caught in the greatest number are very small in relation to the total area "sampled" annually by the U.S. longline fleet, and such areas do not necessarily coincide with the areas where longliners' effort and catch per unit effort of their target species is the greatest.  However, longliners do exert much effort in these species' prime spawning and feeding areas (the "hot spots"), which of course is the problem.
The Same "Hot Spots" Are Important to White Marlin, Swordfish and Sailfish as well as to Blue Marlin

By examining the charts presented on this website showing where U.S. longline vessels catch the greatest quantities of blue marlin, white marlin, sailfish and swordfish, one can easily see that all these populations depend on the same "hot spots" throughout their annual migratory cycle.  Just like salmon, they predictably return to very specific (and relatively quite small) sites for spawning during the spring of each year and to their primary fall feeding areas.  We would expect that a distinct race returns each year to each of their spawning area "hot spots."  (For example, we suspect there is a "Yucatan Channel race" of blue marlin that spawn annually between Cuba and Mexico's Yucatan peninsula.  We expect there are also "Yucatan Channel races" of white marlin, sailfish and swordfish just as there are likely "Florida Straits races" and "Mona Passage races" of all four, etc.) 

Some Make the "Big Circuit" Around the Entire Sargasso Sea

Over the course of their annual migratory cycle, some of the largest individuals of the larger species (blue marlin, swordfish, bluefin tuna and probably white marlin) may circumnavigate the North Atlantic Ocean following the major
surface current gyre.  However, from tag returns it is apparent that most adult blue marlin, swordfish, white marlin and sailfish migrate up and back down the east coast of the United States (following the western side of the Gulf Stream and along the edge of the continental shelf).
Related Sections

Swordfish,  Billfish,  Tunas  and  Sharks

Critical Habitat Maps for White Marlin
Facts about Atlantic Population Declines

White Marlin ESA Listing Petition

Articles about Big Game Fish and Fishing

Photos of Big Game Species


List of All Pages on this Website

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Live Moon Phase Display

Daily "Kill-o-Meter"

Longliners fish most heavily during the periods when the moon is brightest. So, this real-time image of the moon phase shows when the kill of swordfish is greatest and least. It also shows when the kill of blue marlin, white marlin, sailfish, sharks, tunas, sea turtles, marine mammals and a host of other marine life is also greatest - even though they are not even targeted. For more, see link above.



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