Dusky shark

Lore & Background

The dusky shark was first scientifically described by French naturalist Charles Alexandre Lesueur in an 1818 issue of Journal of the Academy of Natural Sciences of Philadelphia. He placed it in the genus Squalus and gave it the specific epithet obscurus, Latin for 'dark' or 'dim', referring to its coloration. Subsequent authors recognized it as belonging to the genus Carcharhinus. Lesueur did not designate a type specimen, though he was presumably working from a shark caught in North American waters. Many early sources gave the scientific name as Carcharias (later Carcharhinus) lamiella, but the type specimen for that name was later discovered to be a copper shark (C. brachyurus), so C. lamiella is not considered a synonym of C. obscurus.

The dusky shark has a slender, streamlined body with a short round snout, long sickle-shaped pectoral fins, and a ridge between the first and second dorsal fins. It can be identified by these features and its faintly marked fins. The species is nomadic and strongly migratory, with populations moving seasonally towards the poles in summer and towards the equator in winter, traveling hundreds to thousands of kilometers. One tracking study in the northern Gulf of Mexico found it spends most of its time at depths of 10–80 m (33–262 ft), with occasional forays below 200 m (660 ft), and it has been recorded from a depth of 400 m (1,300 ft). It prefers water temperatures of 19–28 °C (66–82 °F) and avoids low-salinity areas such as estuaries.

Adult dusky sharks have a broad and varied diet consisting mostly of bony fishes, sharks and rays, and cephalopods, but also occasionally crustaceans, sea stars, bryozoans, sea turtles, marine mammals, carrion, and humans. The species is viviparous with a three-year reproductive cycle: females bear litters of 3–14 young after a gestation period of 22–24 months, followed by a year of rest before becoming pregnant again. Females are capable of storing sperm for long periods due to their nomadic lifestyle and low overall abundance. Dusky sharks are one of the slowest-growing and latest-maturing sharks, not reaching adulthood until around 20 years of age.

Reader's Guide

The dusky shark is highly valued by commercial fisheries for its fins, used in shark fin soup, and for its meat, skin, and liver oil. It is also esteemed by recreational fishers. Because of its slow reproductive rate, the species is very vulnerable to human-caused population depletion. The International Union for Conservation of Nature (IUCN) has assessed this species as Endangered worldwide and Vulnerable off the eastern United States, where populations have dropped to 15–20% of 1970s levels. The dusky shark is regarded as potentially dangerous to humans due to its large size, but there are few attacks attributable to it. Its significance lies in its role as a widespread apex predator and in the conservation challenges posed by its slow life history, which makes recovery from overfishing extremely difficult. The species' long gestation period—tied with the spiny dogfish as the longest of any animal—underscores its unique biology and the need for careful management.

Did You Know?

• The species reaches adulthood at around 20 years of age, making it one of the slowest-maturing sharks.
• Populations off the eastern United States have dropped to 15–20% of 1970s levels.