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.

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