BLUE MARLIN ARE ONE OF THE MOST MAGNIFICENTLY ENGINEERED FISH ON THE BLUE PLANET
The everyday capabilities and evolutionary adaptations of this apex predator stagger the imagination. By SCOTT BANNEROT
Our most life-changing moments often involve exposure to something magnificent, electrifying, wonderful and mind-boggling: a musical performance, an athletic feat, a finely engineered example of quickness and beauty. Encounters with blue marlin — the frantic wail of the drag, the greyhounding behemoth bounding for the horizon — are all of the above. The evolutionary adaptations and everyday capabilities of these apex predators defy imagination.
Slots and grooves for neatly folding the dorsal, pectoral and pelvic fins into the elongated, fusiform body help this fish attain speeds of 72 mph, swim thousands of ocean miles and plunge to great depths. Twin caudal peduncle keels accelerate water flow during the tail sweeps, inducing leading-edge suction. The efficiency of countercurrent mechanisms that heat the brain and eyes, and extract oxygen from seawater, are unequaled in the animal kingdom. Blue marlin possess the largest eyes in the billfish family and process a high rate of frames per second, allowing them to detect, track and chase fast, maneuverable prey. Tiny otolith bones in the inner ear and a complementary lateral line system let them detect sound waves, gravitational forces, body motion, prey and low-frequency sounds in close proximity. Blue marlin also exert astonishing control over skin color changes that likely assist feeding.
Despite their ability to catch fast prey such as skipjack tuna and mahi-mahi, blue marlin are versatile, opportunistic feeders. Stomach content studies find individuals packed with squid, tiny filefish, triggerfish or puffers. Recent observations using sophisticated sonar and underwater video cameras indicate habitual methods for choosing, tracking and engulfing prey, as well as coordinated group feeding. Individuals position themselves below and to the side of a selected lure in a trolled spread, then lunge up and across in a sweeping take, from inside to outside the boat wake. Groups of about six blue marlin also herd tuna schools to specific sections of near-vertical walls. Using three deep “pushers” and three shallow “suppressors,” the marlin take turns flashing into the school to feed. If the tuna break up and over the top of the wall, the blues never spend energy wasting chase; they head back out to find another tuna school.
The more I learn about this species, the more amazed I am. No tool has done more to illuminate the sheer wonder of blue marlin than the Pop-up Satellite Archival Tag. It’s a mini-computer that records and archives depth, temperature and ambient light for a set number of days. After that, the computer orders the electro-corrosion of the wire attachment cable, which allows the device to float to the surface. The tag’s mini-antenna then transmits data to scientists via satellites. PSAT data show that although some blue marlin stay in relatively restricted areas, and some cross and even change oceans, by and large these fish follow ritualized long-distance movements coordinated with migrating prey and timed arrivals to optimal spawning areas. On a day-to-day basis, blue marlin cruise at slow, energy-efficient speeds of 1 to 3 knots, and make frequent daytime dives as deep as 2,625 feet. At night they curtail diving and stay well above the thermocline (a depth of about 600 feet).
Blue marlin can spawn about four times a season. Blues are the largest member of the billfish family, with evidence suggesting they can exceed 2,000 pounds. They are estimated to live as long as 27 years, with males living to about 18.
Commercial fishing dating from the 1950s has reduced the world’s standing crop of blue marlin by an estimated 80 percent, mostly as by-catch of longliners and purse seiners targeting tuna and other pelagics. The population is thought to be sustaining itself, but one need only look at photos from the 1930s and ’60s in Florida and the Bahamas to realize there is a huge difference between those times and now.
Sharp increases in high-seas fishing fleets, particularly by China in the Indo-pacific, do not help matters. We can make a significant contribution by reviving and releasing each blue marlin we catch, and it’s fair to say that anyone who sponsors PSAT is making an epic contribution to the future of this magnificent species.
Capable of zooming up to 72 mph, blue marlin on a day-to-day basis cruise at an efficient 1 to 3 knots and make frequent daytime dives as deep as 2,600 feet.
The right stuff: An apex predator built for speed, plunging to great depths and oceanic travel.