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New Jersey Endangered and Threatened Species Field Guide


Image of A dusky shark.Zoom+ A dusky shark. Photo by NOAA.

Dusky shark

Carcharhinus obscurus

Species Group: Fish

Conservation Status

State: Other Classification

 


IDENTIFICATION

Also known as the bronze whaler or black whaler, this species can be difficult to identify due to similarities with other species, such as the more common sandbar shark. It is a large, fairly slender shark with a low ridge along the back between the dorsal fins. The average size of adults is 11.8 feet and 400 pounds. Color ranges from grey to bronze above, with a white belly, and with most fin dips dusky in color.

The snout is broad and short. Upper teeth are broadly triangular and serrated while the lower teeth have narrow cusps and are also serrated. The first dorsal fin originates over or near the lower tips of the pectoral fins. The first dorsal fin is smaller in dusky sharks than sandbar sharks and the origin of the first dorsal is more forward on the sandbar shark.

Image of Range of the dusky shark in New Jersey.Zoom+ Range of the dusky shark in New Jersey.

DISTRIBUTION AND HABITAT

The dusky shark occurs within coastal temperate and tropical waters throughout the world. Within the western Atlantic Ocean, they occur as far north as Cape Cod and as far south as southern Brazil.

This species can be found from the surf zone to depths of up to 1300 feet. They are not typically found within estuaries since they avoid areas of low salinity.

DIET

This species feeds on bony fish, smaller sharks, rays, and squid. They are generally not considered to be dangerous to humans. However, they may bite if approached too closely.

LIFE CYCLE

Dusky sharks are known to live up to 40 years. Males of this species reach sexual maturity when they are approximately 9.2 feet in length and 19 years old while females reach sexual maturity at approximately 9.3 feet in length and 21 years old.

This species reproduces every three years, usually in June or July. It is viviparous, giving birth to between 6 and 14 young which are between 33-39 inches when born. The gestation period is believed to be about 12-16 months or longer. Females will briefly move inshore to give birth.

Dusky sharks migrate annually based on sea surface temperature. As the water warms during summer, they migrate further north. They then return south as waters cool during the winter. They have been known to feed in large groups, especially when young. The young may fall prey to other shark species.

CURRENT STATUS, THREATS, AND CONSERVATION

The dusky shark is classified by NOAA Fisheries as a Species of Concern throughout its range and the species has been prohibited in both commercial and recreational fisheries since 2000. Though it has no legal conservation status in New Jersey, it is still illegal to take, possess, land, purchase, or sell them.

Studies have found that the dusky shark population within the northwestern Atlantic Ocean and Gulf of Mexico are only 15-20% of the population which existed in the 1970’s. Reasons for the species decline include illegal landings in both commercial and recreational fisheries and as by-catch, especially from long-line gear. Its slow growth, late maturity, and low rate of reproduction further hamper its recovery. Habitat degradation in coastal waters and nursery areas may impact juveniles. Marine pollution, especially from plastics, also threatens this and many other marine species.


Text written by Michael J. Davenport in 2016.


REFERENCES

Scientific Classification

Kingdom: Animalia
    Phylum: Chordata
       Class: Chondrichthyes
          Order: Carcharhiniformes
             Family: Carcharhinidae
                Genus: Carcharhinus
                   Species: C. obscurus

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