Biology of the Shortfin Mako (Isurus oxyrinchus)
by Richard Martin 1999 -- All Rights Reserved

Just about every shark enthusiast has one species that is his or her absolute, hands-down favorite. Some favor the Great White. Others hold in particularly high regard the strange and wonderful hammerheads, Goblin, or thresher sharks. Still others - divers mostly - regard as deeply totemic whichever shark species they first encountered in the wild. The precise combination of favorite shark species and the reasons for choosing it are as many and varied as shark enthusiasts themselves. For what its worth, the Shortfin Mako is my all-time favorite shark.

Growing to a length of almost 13 feet (4 metres) and a weight of over 1 100 pounds (500 kilograms), the Shortfin Mako is, by any standard, an impressive fish. For me, however, there is something more. This species seems to exhibit the very finest attributes (real or projected by my admittedly romantic imagination) ever evolved by sharkdom. A symphony of liquid grace and finely controlled power, the Shortfin Mako is warm-bodied, free to roam the depths and breadths of the open ocean in away that evokes admiration and envy in my wanderlust heart. From stem to stern, the Shortfin Mako is an exquisitely streamlined, beautifully sculpted fish; inside and out, this species' form and function is spare and efficient, enabling it to utilize energy with elegant economy yet sprint as fast as the fastest fish in the sea. Its large, dark eyes suggest a degree of intelligence and sensitivity that it may not, in fact, possess. And - if I am to be completely honest - I must confess that there is another, psychologically revealing reason behind my fascination for this particular shark: it seems the quintessential embodiment of predatory lethality.

The Shortfin Mako is the fastest lamnid and the champion speedster among sharks. It is also a spectacular and much sought-after gamefish, often leaping repeatedly when hooked. Among sport anglers, this explosive activity combined with dazzling ultramarine flanks has earned the Shortfin Mako the dramatic honorific, "Blue Dynamite". Famed western author and big game angler Zane Grey held this species in particularly high regard, noting that hooked Shortfins typically leap in sets of three, with the third leap usually the highest - sometimes as much as 15 to 20 feet (5 to 6 metres) above the surface. Calculations show that for a mako to leap 20 feet (6 metres) into the air, a speed of 24.6 miles (39.6 kilometres) per hour is required - and this for a shark impeded by the drag of a fishing line trailing from its mouth.

Hooked mako leaps clear of the water's surface. Photo taken 42 km (26 miles) southeast
of Block Island, Rhode Island. Photo copyright 1996 Capt. Bill Brown.

Underwater and unimpeded by a fishing line, the Shortfin Mako has been reliably clocked at 31 miles (50 kilometres) per hour, and there is one claim that this species is capable of a burst speed of up to 46 miles (74 kilometres) per hour. But it is extremely difficult to get a fish in the wild to swim in a straight line over a measured course. Laboratory measurements of numerous kinds of fishes - representing a wide range of body sizes - swimming against an artificial current have revealed a surprisingly uniform maximum burst speed of about 10 times the body length per second. Thus, for an average-sized, 6.5-foot (2-metre) Shortfin, its theoretical maximum speed might be something on the order of 45 miles (72 kilometres) per hour. Some estimates of the top-speed of a Shortfin Mako are considerably higher.

In an effort to determine the maximum swimming speed of the Shortfin Mako, two New Zealand researchers undertook a simple experiment which yielded astonishing results. Off the coast of Auckland, aquarist Craig Thorburn and film-maker Mike Bhana videotaped a 3-foot (1-metre) juvenile Shortfin Mako - estimated to be about one year of age - chasing a baited camera trolled behind their boat. The shark seemed to have no trouble keeping up with the towed array at medium speeds, so the researchers decided to accelerate to see just how fast the little Mako could go. From this experiment, Thorburn and Bhana estimate that the shark accelerated from a dead stop to cover a distance to the bait of more than 100 feet (30 metres) in just two seconds. If, as Thorburn and Bhana attest, the shark did indeed start from a standstill - which seems behaviorally unlikely - to cover the stated distance in the stated time, the little Mako must have achieved an acceleration of at least 50 feet (15.24 metres) per second, per second. This acceleration rate rivals that of the very fastest sport cars and seems rather improbable. Nevertheless, using this figure as the constant rate of acceleration, calculations suggest that by the time this little Mako reached caught up with the bait, it reached a top speed of about 68 miles (110 kilometres) per hour! But it should be stressed that if any of Thorburn and Bhana's estimates (the shark's initial speed, the actual distance covered, the time required to reach the bait, etc.) is inaccurate, this startling figure could be 'off' by quite a bit.

Whatever its actual top speed, there is little doubt that the Shortfin Mako is able to catch and eat very speedy prey. It is primarily a piscivore, taking mackerels, tunas, bonitos and other scombrids, anchovies, herrings, Bluefish (Pomatomus saltatrix), grunts, lancetfishes, cod, ling, whiting and other gadids, Australian 'salmon' (Arripis), yellowtails and other carangids, sea basses, porgies, Swordfish (Xiphias gladius), and even other sharks (including Blue Sharks [Prionace glauca], whaler sharks [Carcharhinus], and hammerheads [Sphyrna]). Many of these fishes are particularly fast-swimming, yet they are apparently snapped-up 'on the fin': fishes taken from the stomachs of Shortfin Makos that are not in an advanced stage of digestion are often surprisingly "healthy-looking" - except for the deep stab wounds mid-body, where the shark apparently grasped each fish once before swallowing it whole.

A 1982 study by fisheries biologists Chuck Stillwell and Nancy Kohler examined the diet and feeding habits of the Shortfin Makos in the western North Atlantic. Stillwell and Kohler examined the stomach contents of 399 Shortfin Makos of both sexes, ranging in length from 2.2 to 10.8 feet (0.7 to 3.3 metres). Samples were obtained from specimens landed during shark fishing tournaments held in New Jersey, New York, and Rhode Island, and others from individuals taken as bycatch on offshore longlines set between Cape Hatteras, North Carolina, and the Grand Banks. Teleost remains were found in 67% of the stomachs examined, while cephalopods were found in 15% of stomachs. Cephalopods consumed by the Shortfin Mako were primarily ommastrephiid squids - especially the Short-Finned Squid (Illex illecebrosus), a species which is abundant throughout the study area from spring through fall - and were taken mostly in offshore waters.

Perhaps the most startling revelation of Stillwell and Kohler's study is the enormous importance of Bluefish in the diet of the Shortfin Mako off the US Atlantic seaboard. Bluefish occurred in 43.8% of Shortfin Mako stomachs examined and, by volume, constituted 77.5% of this species' diet; consumption and diet were found to be the same for both sexes. Stillwell and Kohler found that the average stomach capacity of a Shortfin Mako is about 10% of its body weight and estimated the average daily ration at about 4.5 pounds (2 kilograms). From this, Stillwell and Kohler calculated that, each year, Shortfin Makos may consume 4.3 to 14.5% of the available Bluefish resource in the area between Cape Hatteras and Georges Bank.

Stomach contents of Shortfin Makos have also been reported to included sea turtle heads, a 'porpoise' (probably a pelagic dolphin, family Delphinidae), squids, salps, and - occasionally - detritus. Surprisingly, pelagic dolphins are rarely reported in the diet of the Shortfin Mako, but have been found among the stomach contents of very large individuals. The Shortfin Mako's teeth are highly distinctive: smooth-edged and - at the front of the jaw, at least - gracefully recurved: the efficient grasping teeth of a fish-eater. But, like those of the White Shark (Carcharodon carcharias), the upper anterior teeth of the Shortfin Mako broaden with increasing size. Shortfins over 10 feet (3 metres) long have relatively broad, flat, and triangular upper anteriors, which are perhaps more suitable for dismembering large prey than the awl-shaped upper teeth of smaller Makos. Thus, unlike smaller Shortfin Makos, large individuals may be able to feed on prey too big to be swallowed whole.

Fortunately for us, in the vast majority of cases shark attack do not seem to be feeding related. Yet - because of its large size, awesome speed, power, and dentition, and aggressive nature - the Shortfin Mako is definitely a dangerous shark. Although authenticated reports of attacks by this species against humans are very rare, it has been known to attack divers and even the occasional swimmer. I have dived with solitary subadult Shortfin Makos on several occasions, and they still unnerve me ... perhaps even more than the much larger but slower and more 'controlled' White Shark. In baited contexts, at least, I have found that a Shortfin generally moves and changes direction relatively quickly, buzzing past a diver only to circle and repeat the twitchy, high-speed visual inspection. In short, a Shortfin Mako often seems a bundle of pent-up nervous energy. This species' combination of rapid, jittery movements and a mouth bristling with wicked-looking teeth always reminds me of an archetypal neophyte armed robber: jangling nerves and a lethal weapon with a hair-trigger - potentially a very explosive situation! Fortunately, the generally offshore habitat of the Shortfin Mako prevents it from coming into contact with most swimmers. Most, but not all.

At about 5 p.m. on 7 September 1974 at the northeastern extreme of the Red Sea, a 20-year-old woman - identified in the technical report only as "Ms. B.A." - was swimming with her boyfriend about 1 650 feet (500 metres) offshore when she was savagely and repeatedly attacked by a 6-foot (2-metre) shark, later positively identified as a Shortfin Mako. Before being rescued, B.A. was bitten approximately 12 times, mostly on her forearms and thighs. She barely survived the attack; ultimately, her lower left arm had to be amputated.

It is quite possible, perhaps likely, that the Shortfin Mako would be something less than my favorite shark if one mangled me in the same manner as the unfortunate Ms. B.A. If I am ever attacked by a Shortfin Mako, it would remain a fast, beautiful, and superbly efficient creature. But some forms of appreciation are best at a distance.

Richard Martin is a former shark fisheries biologist turned marine educator. He frequently gives humourous talks on marine biological subjects at aquaria, museums, and dive trade shows, and has written and illustrated over 90 articles and columns for various national magazines as well as two books, Shark Smart: the Divers' Guide to Understanding Shark Behaviour and Do Whales Fart? And Other Questions. Martin's current research focuses on the behavioural ecology of tropical reef sharks and the biology of deep-sea sharks. He is the the founding director of ReefQuest Expeditions (an eco-tourism company which conducts credit and non-credit courses in marine natural history at select locations throughout the tropical Pacific), as well as a member of the American Elasmobranch Society and the National Marine Educators Society. Martin lives in Vancouver, Canada, and is busily working on several new books.

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