“Lamna nasus”
Porbeagle Sharks are closely related to Salmon Sharks measuring up to 3.7 meters in length and weighing up to 230 kilograms. The word “porbeagle” is obscure. A common suggestion is that it combines “porpoise” and “beagle”, referencing this shark’s shape & tenacious hunting habits. The life span of this species is about 30 years. Porbeagles are stout large sharks with large black eyes, pointed snouts and small, smooth, narrow teeth. They are dark blue to gray on their dorsal (upper) sides, white on their ventral (under) sides and on the lower rear edges of their first dorsal fin. Porbeagle Sharks maintain their body temperature above their current ambient water temperature through thermoregulation. Few other fishes have this ability other than fast swimmers such as Tuna. Their body temperature is regulated by vascular counter-current heat exchangers found in the muscle & viscera along with vascular shunts that route blood flow. These allow the Porbeagle Shark to retain heat produced by metabolic processes. Porbeagle Sharks can increase their body temperature up to 7-10 °C above the temperature of the surrounding water. This helps them adapt to the cold waters they prefer and facilitates fast swimming.
Porbeagle Sharks are found in the western Atlantic Ocean from Newfoundland, Canada to New Jersey and possibly to southern Brazil and Argentina. In the eastern Atlantic, Porbeagle Sharks are found around Iceland and in the western Barents Sea to South Africa as well as in the Mediterranean. In the southwest Pacific Ocean, Porbeagle Sharks are found off Australia & New Zealand and in the southeast Pacific off Chile. In the southern ocean, this species is found off South Georgia and the Kerguelen Islands. Porbeagle Sharks prefer cold water between 1-18 °C, however sightings have been reported in waters up to 23 °C. The depth range for the Porbeagle Shark appears to be between 0-715 meters. They tend to feed on small pelagic schooling fishes such as lancetfish, herring, sauries, mackerels and groundfish such as sand lances, lumpsuckers, flounders, hakes and cod. They also prey on other sharks and squid. Like other shark species, the mating ritual begins with the male shark grasping the female by biting her while he inserts his clasper into her cloaca to fertilize her. Females often have scars as a result, which sometimes helps scientists determine whether or not females have recently mated. Gestation is thought to last 8-9 months after which litters of 1-6 pups are born. Four pups is the average with 2 pups per uterus. Pups are born at about 68-80 centimeters in length.
Females in the northern hemisphere reach sexual maturity at about 2.32-2.59 meters in length and females in the southern hemisphere at about 1.85-2.02 meters. Males in the northern hemisphere mature at around 1.65-2.07 meters in length. In the northwest Atlantic at least, these sizes are reached in females of about 13 years of age and males of about 8 years. In the northern hemisphere, Porbeagle Sharks mate between autumn & winter and give birth between spring & summer. It is thought that southern hemisphere populations in New Zealand and Australia give birth during winter. The eggs are retained within the body of the female in a brood chamber where the embryo develops, receiving nourishment from a yolk sac. This is the method of reproduction for the “live-bearing” fishes where pups hatch from egg capsules inside the mother’s uterus and are born soon afterward. Porbeagle Sharks are potentially dangerous to humans because of their large size, however human-shark conflicts with this species are extremely rare with only 2 unprovoked bites having been reported.