|Shark of the Month - Frilled Shark
Thursday, 11 July 2013
Blog brought to you by Shark Guardian - Frilled Shark
Description - The little-known, deepwater-dwelling frilled shark (Chlamydoselachus anguineus) is one of the most primitive species of living shark. The species name anguineus, which derives from the Latin for snakelike, only partly conveys its bizarre appearance. The head is lizard-like and features a blunt-ended snout and a very large mouth armed with multiple rows of sharp, three-pronged teeth. While each tooth is relatively small, there are around 300 in total, providing almost a thousand sharp hooks on which to trap struggling prey. Behind the head, on both sides of the body, there are six gill slits, which each possess a distinctive frilly margin. The front slits on each side extend beneath the body, meeting under the throat, giving the appearance of a frilly collar. The body is dark brown or grey in color, with a large anal fin and small, paddle-shaped pectoral fins, while the dorsal fin is relatively small and set very far back on the body. The caudal fin has a small, vestigial lower lobe, while in contrast, the upper lobe is very elongated, and further extends the serpentine body.
Biology - Owing to its deepwater habitat, very few observations of the frilled shark have been made in its natural environment. Analysis of stomach contents of frilled sharks brought to the surface indicate that this species mostly preys on deep water squid and a variety of fish, including other sharks. While it is unclear exactly how the frilled shark feeds, its set of needle-sharp, inwardly-pointing teeth, and the fact that its jaws can open extremely wide, suggest that it may actively take prey over one and a half times its own length. Interestingly, this species has also been found higher in the water column at depths between 50 and 200 metres, where it feeds on faster-swimming squid, although these may be taken as carrion or when the squid are exhausted after reproducing.
The frilled shark, like many other sharks, is ovoviviparous, which means that after fertilisation, the embryos develop within the female’s uterus, receiving nourishment from a yolk sac. Once the yolk sac nutrients are exhausted the embryos absorb nutrients from secretions within the uterus until birth takes place. The litter is very small, numbering only two to ten offspring, which each measure between 40 and 60 centimetres in length. Studies of frilled shark embryos indicate that this species could have a gestation period of over 3.5 years, which, if accurate, would be the longest known amongst the vertebrates.
Range - Although the range of the frilled shark extends almost worldwide, it has a very patchy distribution. Populations occur on the outer continental shelves and upper continental slopes off Norway, northern Scotland and western Ireland, south as far as northern Namibia. Other populations occur in the eastern Pacific off southern California and northern Chile; in the west Pacific, off south-east Japan, eastern Australia and New Zealand; and also possibly in the western Indian Ocean, off South Africa.
Habitat - A predominantly deepwater species, the frilled shark typically lives close to the seabed or in the water column at depths between 500 and 1,000 metres, but may be found as deep as 1,500 meters. Individuals are, however, sometimes found higher in the water column at depths between 50 and 200 meters.
Status - The frilled shark is classified as Near Threatened (NT) on the IUCN Red List.
Threats - While the frilled shark is not an important target species for fisheries, individuals are regularly taken as bycatchin some localities by bottom and midwater trawls as well as deep-set longlines and gillnets. When accidently caught, the meat is used for human consumption, fishmeal or is discarded. With almost nothing known about this species’ global population size, it is not clear what effect bycatch may be having. Nevertheless, given this species’ apparent scarcity, long gestation period and low reproductive output, even small losses could have serious consequences for the frilled shark’s survival. Any expansion in deepwater fisheries effort is therefore a cause for concern.
Conservation - There are currently no known conservation measures in place for the frilled shark. While a small number of UN states are developing or have developed shark management plans for commercial fisheries, few, if any, of these employ for managing deepwater fisheries bycatch.