Lamna nasus, Porbeagle Shark [+]
Kingdom Animalia
Phylum Chordata
Class Elasmobranchii
Order Lamniformes
Family Lamnidae
Genus Lamna
species: Lamna nasus [+ITIS +WoRMS]
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Description & Behavior
The porbeagle shark, Lamna nasus (Bonnaterre, 1788), aka blue dog, beaumaris shark (UK), and mackerel shark, is closely related to the salmon shark, Lamna ditropis, measuring up to 3.7 m in length and weighing up to 230 kg. The life span of this species is 30 years. The porbeagle is a stout large shark with large black eyes, a pointed snout (slightly longer and more pointed than salmon shark's), and small, smooth, narrow teeth. They are dark blue to gray on the dorsal side, white on the ventral side and on the lower rear edge of the first dorsal fin.
As with all sharks in the Family Lamnidae, the porbeagle maintains its body temperature above ambient water temperature through thermoregulation. Few other fishes have this ability other than fast swimmers such as tuna. Body temperature is regulated by vascular counter-current heat exchangers (retia mirabilia) found in the muscle and viscera along with vascular shunts that route blood flow. These allow the sharks to retain heat produced by metabolic processes. Porbeagles can increase their body temperature up to 7-10°C above the temperature of the surrounding water. This helps the porbeagle adapt to the cold waters it prefers and facilitates fast swimming.
World Range & Habitat
The porbeagle shark, Lamna nasus, is found in the western Atlantic from Newfoundland, Canada to New Jersey, USA, and possibly southern Brazil to Argentina. In the eastern Atlantic, the porbeagle shark is found in Iceland and in the western Barents Sea to South Africa, as well as the Mediterranean. In the southwest Pacific the porbeagle is found in Australia and New Zealand, and in the southeast Pacific off Chile. In the Southern Ocean this species is found off South Georgia and the Kerguelen Islands.
The porbeagle inhabits the continental shelf as well as open water ocean basins. The porbeagle is also seen on occasion in inshore waters. They 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 m.
Feeding Behavior (Ecology)
The porbeagle shark, Lamna nasus, feeds 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.
Life History
The porbeagle shark, Lamna nasus, is ovoviviparous. Like other shark species, the mating ritual begins with the male shark grasps the female by biting her while he inserts the clasper into the cloaca to fertilize the female. 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 cm in length.
Females in the northern hemisphere reach sexual maturity at about 2.32-2.59 m in length, and females in the southern hemisphere at about 1.85-2.02 m. Males in the northern hemisphere mature at around 1.65-2.07 m 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, porbeagles mate between autumn and winter and give birth between spring and summer. It is thought that southern hemisphere populations in New Zealand and Australia give birth during winter.
Ovoviviparous: 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. Also known as aplacental viviparous.
Scientists solve porbeagle birth mystery
Conservation Status/Additional Comments
The porbeagle shark, Lamna nasus, is potentially dangerous to humans because of its large size, however human-shark conflicts with this species are extremely rare. Only two unprovoked bites have been reported. The porbeagle is hunted commercially and caught as bycatch by commercial fisheries, and consequently, populations in the North Atlantic have significantly declined.
Porbeagles are hunted commercially in Norway and Canada where fisheries are regulated. They are also caught there as bycatch, and are the second most common bycatch species in Norway. They are also frequently caught as bycatch by Japanese longliners. They are hunted for their meat, fins, oil and fishmeal. The porbeagle is also hunted recreationally to some extent in the United Kingdom, Ireland, the United States, and Canada.
Porbeagles have been observed making fast passes at divers on oil platforms in the North Sea, but they did not attack. This is likely agonistic (defensive) or exploratory behavior.
Overall, the porbeagle is listed as Vulnerable (VU A2bd+3d+4bd) on the IUCN Red List of Threatened Species but three subpopulations of porbeagles are Critically Endangered and Endangered:
Porbeagle Mediterranean subpopulation: Critically Endangered A2bd;
Porbeagle Northeast Atlantic subpopulation: Critically Endangered A2bcd+3d+4bd; and
Porbeagle Northwest Atlantic subpopulation: Endangered A1abd.
VULNERABLE (VU)
A taxon is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable (see Section V), and it is therefore considered to be facing a high risk of extinction in the wild.
Critically Endangered (CR)
A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see see Section V), and it is therefore considered to be facing an extremely high risk of extinction in the wild.
Endangered (EN)
A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered (see Section V), and it is therefore considered to be facing a very high risk of extinction in the wild.
References & Further Research
BioOne ~ CITES ~ Discover Life ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList ~ MarineBio Network ~ NCBI ~ SCIRIS ~ SIRIS ~ Tree of Life Web Project ~ Wikipedia
University of Florida/Florida Museum of Natural History Division of Ichthyology
Biology of the Porbeagle (Lamna nasus) - ReefQuest Centre for Shark Research
Porbeagle Shark - Canadian Shark Research Laboratory
Search the Web for Porbeagle Shark » ARKive ~ Ask.com ~ Ask Jeeves ~ bing ~ deviantART ~ dmoz ~ Dogpile ~ Google Images ~ MySpace Images ~ OceanFootage ~ Picsearch ~ StumbleUpon ~ Yahoo! Images ~ YouTube
