Biology of the Longfin Mako

(Isurus paucus)

Field Marks Body slender, spindle-shaped; snout conical, moderately long; teeth smooth-edged, without basal cusplets, tips of anterior teeth not reflexed; gill slits long, extending partially onto top of head; pectoral fins broad-tipped and as long or longer than head (straight-line distance from tip of snout to top of 5th gill slit); first dorsal fin origin behind free rear tip of pectorals; second dorsal and anal fins minute, with pivoting base; strong keels on caudal peduncle; caudal fin lunate. Color: dark blue to bluish black above, fading to bluish grey on the flanks; undersurface of snout and area around the mouth dusky or bluish black.
Size Pups are 38-49 in (97-125 cm) long and about 26.5 lb (12 kg) at birth; most specimens are about 7 ft (2.2 m) long and 150 lbs (70 kg) in weight; maximum known length is 14 ft (4.3 m), based on a female specimen taken 15 mi (24 km) off Pompano Beach, Florida, in February 1984.
Range Widely distributed in tropical to warm temperate seas, but records are spotty due in part to confusion with the Shortfin Mako (Isurus oxyrinchus); fairly common in the western Atlantic (Gulf Stream waters, northern Cuba to southeastern Florida) and possibly in the central Pacific (near Phoenix Island and north of Hawaii), but apparently rather rare elsewhere; recent records from off northwestern Africa and the Iberian Peninsula, from the northern Gulf of Mexico to the Grand Banks, and off New South Wales, Australia.
Habitat Primarily inhabiting the upper mesopelagic during the day, venturing into the epipelagic at night; in the Cuban longline fishery, most catches are off the continental shelf at depths of 360-720 ft (110-220 m), but rare from depths of 60-300 ft (18-91 m); off New South Wales, Australia, catches recorded from 164-623 ft (50-190 m), where surface temperatures were about 68-75F (20-24C). Between North Carolina and the Grand banks, longline catches are made from May-October; distribution in northern parts of the western North Atlantic is apparently limited to the Gulf Stream and outer edges of the continental shelf; species taken on the same longlines include Swordfish, Bluefin, Yellowfin and Bigeye tunas, and sharks such as the Shortfin Mako (Isurus oxyrinchus), Blue (Prionace glauca), Sandbar (Carcharhinus plumbeus), and hammerheads (Sphyrna spp.); in October 1972, an 11-ft (3.4-m) female specimen was caught in the northeast Indian Ocean with a Swordfish rostrum broken off in its abdomen.
Feeding Little data available; probably feeds on pelagic squids and schooling fishes; most specimens are caught on longlines in deep tropical waters, usually by swordfishermen, where chemical lights (Cylume lures) may attract the sharks to bait - suggesting that prey may be similar to that of the Swordfish (Xiphias gladius) at depth and that bioluminescent prey are sometimes taken. This species' often slimmer build and long, broad-tipped pectoral fins suggest that it is slower and less active than its better-known relative, the Shortfin Mako (Isurus oxyrinchus).
Reproduction Ovoviviparous, featuring oophagy at late stages of development; litter size 2-8 pups; a 10.8-ft (3.3-m) female with 8 well-formed, apparently late-term pups was caught in Mona Passage (between Hispaniola and Puerto Rico), in January 1983, another about 12 ft (3.7 m) long contained a 38-in (97-cm) long female embryo (with evidence that a second embryo had been spontaneously aborted during capture) was caught on a swordfish longline in the Florida Current off east-central Florida in December 1980 - suggesting that pups may be born during winter in relatively shallow coastal areas. No data available on a restricted mating season, if any.
Age & Growth Males mature at a length of about 6.5 ft (2.0 m), females at about 8 ft (2.5 m); no data on age at maturity or longevity for either sex.
Danger to Humans Has not been implicated in attacks on people or boats; regarded as potentially dangerous due to its large size, impressive dentition, and relationship to known dangerous species.
Utilization Often taken in the Cuban longline fishery off the north coast of Cuba; probably taken regularly in the tropical pelagic Japanese longline fisheries and apparently marketed in Tokyo; in addition to longlines, this species is also taken on hook-and-line and with anchored gillnets. Its flesh is utilized fresh, frozen, and dried salted for human consumption.
Remarks Remarks: not formally described until 1966, this species is often confused with the Shortfin Mako (Isurus oxyrinchus); considering that it is regularly caught in several commercial fisheries, it is remarkably poorly known; captures should be retained and reported.

Longlining in the northeastern Indian Ocean during October 1972, the Russian research vessel Chernomor hauled up a Longfin Mako that had narrowly escaped another fate. Caught at a depth of 260 to 300 feet (80 to 90 metres), the shark - an 11-foot (3.4-metre), 400-pound, (180-kilogram) female - had the broken-off bill of a Swordfish (Xiphias gladius) protruding from its abdomen. What made this case particularly curious is that the 5-inch (13-centimetre) protruding part was the tip, indicating that the bill had passed through the Mako's body and broken off on the other side. There was also another stab-wound on the shark's caudal peduncle near the anal fin, apparently also made by a Swordfish, perhaps even the same individual. These wounds strongly suggest that the Longfin had recently tussled with a Swordfish. But the question remains: who attacked whom? To examine this mystery, we must gather clues from what is known about the Longfin Mako, the Swordfish, and even draw on some Newtonian physics.

Formally described only in 1966, the Longfin Mako is one of the least known lamnids. It is also the second-largest member of its family, after the White Shark (Carcharodon carcharias) the largest recorded measured 14 feet (4.2 metres) in length, caught 15 miles (24 kilometres) off Pompano Beach, Florida in Februray 1984. Its sheer size and wicked-looking teeth proclaim that the Longfin Mako is a formidable predator, able to tackle the largest and most powerful of fishes. But can it really? The long, broad pectoral fins of the Longfin suggest that this species is slower and less active than its better-known relative, the Shortfin Mako (Isurus oxyrinchus). This inference is further supported by the curious fact that, although it has the same heat-retaining modifications to the circulatory system as other lamnids, the Longfin Mako is unique among members of its family in that it does not seem to be warm-bodied. The Longfin Mako's large eyes indicate that it is a deep-dwelling species and suggest that it may be a visual hunter. The former is supported by longline catches from off northern Cuba, as many Longfins are hooked at depths of 360 to 720 feet (110 to 220 metres) but few at 60 to 295 feet (18 to 90 metres); the latter is supported by reports of higher catch rates on longlines with Cylume sticks (chemical lights) attached near the baits. The Longfin Mako's diet probably consists of schooling fishes and pelagic squids, some of which may be bioluminescent (hence the increased catches on Cylume-equipped lines). Unfortunately, no one knows for certain what Longfin Makos eat.

Longfin Mako (Isurus paucus)The diet of the Shortfin Mako is relatively well known, including a wide variety of teleosts and cephalopods. Due to their similar size, shape, and dentition, it has long been assumed that the Longfin Mako eats more-or-less the same things as its short-finned congener, including large pelagic fishes such as Swordfish. A 730-pound (330-kilogram) Shortfin Mako harpooned near Bimini, Bahamas, was found to contain a whole 120-pound (55-kilogram) Swordfish. Off Montauk, New York, another Shortfin Mako of about 800 pounds (365 kilograms) was observed biting the tail off a Swordfish of undetermined size; when the shark was landed, it was found to contain about 150 pounds (68 kilograms) of Swordfish flesh*. Small individual Swordfish have also turned up as stomach contents in tunas, billfishes, and Blue Sharks (Prionace glauca). Other large fishes, Killer (Orcinus orca) and Sperm (Physeter macrocephalus) Whales may also eat them. But few predators are equipped to prey upon a full-grown swordfish.

Fast-swimming, well-armed, and growing to a length of up to 15 feet (4.5 metres) and a weight of more than 1 200 pounds (540 kilograms), an adult Swordfish is definitely not to be trifled with. This species is widely regarded as being extremely aggressive, known to use its bill to pierce large sharks such as the big Longfin Mako with which this essay began other Swordfishes, Blue (Balaenoptera musculus) and Fin (Balaenoptera physalus) Whales, floating wooden barrels, and the hulls of wooden boats. Swordfish have even been known to 'attack' deep-sea submersibles: in July 1967, at a depth of 2,000 feet (600 metres) off the coast of Georgia, a pugilistic individual rammed the research submersible Alvin, wedging its bill firmly in the sub's superstructure; thus attached, the Swordfish was brought to the surface, where it was eaten by Woods Hole Oceanographic Institution scientists that evening. Swordfish flesh is firm and delicious, but as we have seen few non-human predators ever have opportunity to taste it.*

Why would a Swordfish 'attack' a submersible or a Longfin Mako? Predation seems unlikely although a 45-inch- (114- centimetre-) long shark of the genus Carcharhinus (possibly a Silky, C. falciformis, or perhaps an Oceanic Whitetip, C. longimanus) was found in the stomach of a 12-foot (3.7-metre), 376-pound (171-kilogram) Swordfish captured in the Gulf of Guinea during December 1965; the shark was swallowed whole, apparently head-first, it's body showing no sign of a blow from the bill (suggesting that the shark may have been scavenged off the bottom). Self-defense is a possibility, although the Swordfish could out-sprint any submersible and probably the Longfin Mako as well. Besides, defensive attack presupposes that the punctured Longfin that began this essay was pursuing the Swordfish in a threatening manner. If that were the case, would not defensive slashes made with the Swordfish's bill have been concentrated around the shark's head rather than its abdomen and tail?

Why would a Longfin Mako and a Swordfish be in the same vicinity? The most likely answer is, of course, food. Swordfish - like many oceanic sharks - are opportunistic feeders and forage over a wide range of depths. Large Swordfishes are known to make frequent feeding trips to the bottom, where they feed on hakes (Merlucciidae), pomfrets (Bramidae), cutlass and scabbardfishes (Trichiuridae), snake mackerels (Gempylidae), redfish (Sebastes), lanternfishes (Myctophidae), bristlemouths (Gonostomatidae), and hatchetfishes (Sternoptychidae). Other known Swordfish prey includes pelagic creatures such as tunas (Thunnus), dolphinfish (Coryphaena), lancetfish (Alepisaurus), snake mackerels (Gempylus), flyingfishes (Exocedidae), barracudas (Sphyraenidae), pelagic squids (Ommastrephes, Loligo, Illex, and others), mackerels (Scombridae), herrings and sardines (Clupeidae), anchovies (Engraulididae), sauries (Scomberosocidae), and needlefishes (Belonidae). All of these creatures seem far more likely prey species of the toothy but probably languid Longfin Mako than the large, hyperactive, and well-armed Swordfish.

Therefore, I propose the following scenario for what happened to our hapless Longfin Mako. The shark and a large Swordfish were feeding in the same vicinity drawn by the same concentration of prey the Longfin Mako in its low-energy way, the Swordfish in its characteristic high-speed manner. Circling, either slowly or rapidly, is one of the simplest ways for a swimming predator to remain in an area offering rich feeding, and it may only be a matter of time before two predators feeding on the same patch of prey crossed paths. Since a Swordfish at speed is constrained by titanic inertial forces (powerful resistance to changes in velocity or direction imposed when any mass is propelled energetically), it resembles a piscine arrow: having tremendous kinetic energy but extremely limited agility. Thus, it is my suspicion that our perforated Longfin was simply the victim of an unlucky accident, a high-speed collision between it and a hyperkinetic Swordfish feeding on the same oceanic patch of prey animals.


* = Due to intense fishing pressure, especially in the North Atlantic, Swordfish are becoming quite scarce and it may be that soon even human gastronomes will be denied this delicacy. [Return to text]

 

ReefQuest Centre for Shark Research
Text and illustrations R. Aidan Martin
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