Dusky shark

Carcharhinus obscurus

Description

The dusky shark has a long streamlined body that is brown or gray above and white below. There is a faint lateral stripe that extends to the pelvic fin. Juveniles have a dark colouration on the tip of the caudal fin and the underside of the pectoral fins that is less pronounced in adults. The first dorsal fin is much larger than the second with a dermal ridge found between the two dorsal fins. The upper lobe of the caudal fin is larger than the lower lobe. The pectoral fins are long and curved on the trailing edge. The upper teeth of the dusky shark are broad and triangular with a serrated edge, but while the front teeth are virtually erect, the others are slightly oblique. The lower teeth differ since they have narrow, erect cusps with more finely serrated edges than the upper teeth.

Range

This shark is found in the Atlantic, Pacific and Indian Oceans. They continue to be found southward to the Caribbean Sea, the Gulf of Mexico and through to Brazil. It is rare in Canadian waters as its northernmost range is Georges Bank where it is occasionally caught by fishermen.

Habitat

The dusky shark is one of the larger species living in warm temperate continental waters. It is found from inshore waters out to the edge of the continental shelf. The specimens captured in Canadian waters were found at a water temperature of 19 degrees Celsius.

Life History

The dusky shark can grow to 364 cm in length. Average size is 305 cm and 160 to 180 kg. Studies have shown this shark is long lived and slow growing. They are believed to live more than 30 years.

Diet

The diet of this 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.

Reproduction

Females become sexually mature at about 3.0 meters (10 feet, 17-22 years), while males become sexually mature at 2.9 meters (9.5 feet, 20-23 years). 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 feet).

Interaction with People

This shark is exploited by commercial fisheries throughout much of its range, but is mainly exploited by longline fisheries for shark, tuna and swordfish. Population abundance has declined by 60-80%. It is considered dangerous to swimmers and divers due to its size and proximity to shore.

Distinguishing Characteristics

• Dermal ridge between the first and
  second dorsal fin
• Upper and lower teeth nearly erect
• Nictitating membrane over eye