Dusky shark
From Wikipedia, the free encyclopedia
| Dusky shark | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 |
||||||||||||||||
| Conservation status | ||||||||||||||||
| Scientific classification | ||||||||||||||||
|
||||||||||||||||
| Binomial name | ||||||||||||||||
| Carcharhinus obscurus (Lesueur, 1818) |
||||||||||||||||
 Range of dusky shark
|
The dusky shark, Carcharhinus obscurus, is one of the larger species of shark, reaching 350 kg. The dusky shark is also known as the black whaler, bronze whaler, and dusky whaler. Less frequently used names include bay-shark, brown dusky shark, brown shark, common whaler, dusky ground shark.
Contents |
[edit] Physical description
The dusky shark has a long streamlined body that is brown or gray above and white below. The first dorsal fin originates over or near the free rear tips of the pectoral fins. There is a low ridge between the dorsal fins. On the side of the body a stripe can be seen from the pelvic fins to the head. They can reach 3.65 m. The average size is about 2.6 m (8 ft total length and about 180 kg (400 lb).
[edit] Diet
The diet of the dusky shark includes small schooling fish such as sardines and anchovies, as well as larger fish like tuna, mackerel, flatfish and eels. The dusky shark also eats dogfish, catsharks, skates and rays and sometimes bottlenose dolphins.
[edit] Reproduction
Females become sexually mature at about 3 m (10 ft), while males become sexually mature at 2.9 m (9.5 ft). Males attain sexual maturity at about 19 years; females mature at about 21 years of age. They are viviparous and females give birth to a litter of 6 to 14 pups. After 16 months gestation the pups are delivered at a size of approximately 95 cm (3 ft). They reproduce every 3 years, either between June and July or December and January.
[edit] Habitat and ecology
The dusky shark is found worldwide in warm temperate continental waters extending from the surface to a maximum depth of 400 m. Juveniles are often seen by scuba divers at Fairy Bower, near Shelly Beach, in the Sydney suburb of Manly.
The dusky shark undertakes long temperature-related migrations. On both coasts of the U.S., duskies migrate northward in summer as the waters warm and retreat southward in fall as water temperatures drop. Seasonal migrations (north in winter and south in summer) also occur off South Africa. In Western Australia, adolescents and adults move inshore during the summer and fall, with young-of-the-year occupying separate inshore areas.
[edit] Conservation
The main threats to dusky sharks are overharvesting and bycatch. In the U.S. they were declared overfished in 1993. In 2006, the U.S. National Marine Fisheries Service (NMFS) completed a stock assessment that found the species was at 20 percent of virgin biomass. Commercial and recreational fishing has been prohibited in the U.S. since 1998, but over 2,000 were caught recreationally in 2003. A time/area closure was implemented in North Carolina in 2005.
The dusky shark is a U.S. National Marine Fisheries Service Species of Concern. Species of Concern are those species about which the U.S. Government’s National Oceanic and Atmospheric Administration, National Marine Fisheries Service, has some concerns regarding status and threats, but for which insufficient information is available to indicate a need to list the species under the U.S. Endangered Species Act (ESA).
[edit] Similar species
Sandbar sharks, and bignose sharks have higher first dorsal fins originating farther forward. The dusky shark is hardest to distinguish from the sandbar shark which has a smaller maximum size. Bignose sharks have longer snouts. The silky shark has the second dorsal fin with free tip length usually more than twice fin height. The night shark has green eyes. Bull sharks and spinner sharks lack interdorsal ridges.
[edit] Danger to humans
The dusky shark has not been linked to any attacks although it is considered potentially harmful, and may cause surprise attacks. This is due in large part to its imposing size and propensity to dwell in shallow coastal waters.
[edit] References
- Shark Specialist Group (2000). Carcharhinus obscurus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 09 May 2006. Database entry includes justification for why this species is near threatened
- "Carcharhinus obscurus". FishBase. Ed. Ranier Froese and Daniel Pauly. November 2005 version. N.p.: FishBase, 2005.
- Carcharhinus obscurus (TSN 160268). Integrated Taxonomic Information System. Retrieved on 30 January 2006.
