Dusky Shark Facts & Worksheets

Carcharhinus obscurus, also known as the dusky shark, is a significant species of coastal shark that is found in both tropical and temperate oceans. Dusky sharks, often called bronze or black whalers, are recognized for their long-distance swimming abilities and seasonal, temperature-driven migrations. They have a sizable frame and are usually a muted shade of grey with smoky edges to their fins. 

See the fact file below for more information on Dusky Sharks, or you can download our 27-page Dusky Shark worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

DESCRIPTION

• The dusky shark is one of the largest in its genus, measuring 10 feet long and weighing between 350 and 400 pounds. 
• The giant dusky shark ever documented weighed 765 pounds and was estimated to be 14 feet in size. 
• They have a slim build, rounded nose, underdeveloped nostrils, and medium-sized eyes framed by third eyelids. They have 14-15 rows of teeth in each jaw, with the top set being broad and triangular and the lower group being narrower and more serrated. There are five long slits that these sharks use to breathe. 
• The shark’s pectoral fins, which are sickle-shaped, account for around a fifth of its total length. Their anal fin is enormous, whereas the second dorsal fin is considerably smaller and located on the other side of the body.

HABITAT

• The Atlantic, Pacific, and Indian Oceans aren’t the only places you’ll find dusky sharks; you’ll also find them in the Mediterranean Sea and the Caribbean. They inhabit the deep sea, the surf zone, and the shallow coastal seas of places like the Gulf of Mexico.
• From around 1,300 feet deep on the continental shelf, dusky sharks have been spotted cruising up to the shoreline. The Mediterranean and Australia are potential homes for these creatures.
• Dusky sharks inhabit shallow coastal regions and deeper oceanic waters along the continental shelf. They are most comfortable between 66 and 82 degrees Fahrenheit and steer clear of low-salt environments like estuaries.

BEHAVIOR

Diet

• They eat various marine organisms, from cephalopods and barnacles to cephalopods and tuna. Their diet also includes pelagic fish like anchovies and tuna, as well as demersal fish like eels and porgies, reef fish like barracudas and groupers, cartilaginous fish like thresher sharks and skates, and invertebrates like cephalopods.
• They have even been seen eating marine turtles, garbage, and dead animals on rare occasions. Dusky sharks are opportunistic predators that consume almost anything they can get their teeth on.

Migration

• They are a nomadic species that travel over 2,000 miles during their annual migration, with adults traveling further than youngsters of the same age. Adults tend to follow a seasonal migration pattern, moving northward during the warmer months of summer and then returning southward during the colder months of winter. 
• The juvenile sharks behave in an analogous manner, remaining in the surf zone during the spring and summer months and migrating to waters further out to sea during the fall and winter months. They finally catch up with the grownups when they are older via paths that have not yet been determined but will be determined in the future.

Reproduction

• Dusky sharks are viviparous, meaning the embryos develop inside the mother’s uterus and receive oxygen and food via an umbilical cord. During the spring mating season, the females collect sperm from multiple men to fertilize their eggs later. She gives birth to anywhere from 3 to 16 pups after a pregnancy that lasts roughly two years and typically occurs in areas with shallow water, such as lagoons. Pregnancy intervals average one year.
• Adolescents’ age of sexual maturity varies by region, although it typically occurs between 18 and 32 years old. Their typical lifespan is 40-50 years.
• Slow development and low reproductive rates render dusky sharks susceptible to overfishing. They take a long time to grow up; men don’t become sexually mature until around 10, and females don’t until approximately 18.

Gestation and Litters

• Compared to other shark species, the gestation period of a dusky shark is exceptionally long, at up to 22 months. The average mother can have two to eighteen puppies in a litter.
• Pups are born at a total length of about 70–100 cm and grow slowly from that point on. 
• Females have a gestation period of two to three years and give birth in the summer months in the shallow coastal waters.

IDENTIFICATION

• The dusky shark is distinguished by its long pectoral fins, pointed head, and flat back without a ridge between the dorsal fins. It has a long first dorsal fin and a heterocercal tail. It has serrated teeth, with those of the upper jaw typically large and triangular and thinner teeth in the lower jaw.
• Its upper body is grey or brown, while its underside is white and runs along the side as a blurry stripe. Above the pelvic fins, it curves forward. Juveniles have dark coloring on the pectoral fin underside and the lower lobe of the caudal fin. As fish age, the patterns on their fins fade.

JUVENILE AND ADULT LIFE STAGES

• Juvenile dusky sharks live in coastal areas near shore and graze on crustaceans and other small fish. As they grow, they enter deeper water and eat squid, octopus, and other sharks for sustenance. 
• Apex predatory adult dusky sharks can be found in various environments, including the shore, the outer continental shelf, and the nearby oceanic regions. They were recorded at a depth of 400 meters. Overfishing and unintentional bycatch are reducing their numbers, which is bad news because they reproduce slowly. 
• The great value of dusky shark fins has led to their protection being prioritized as an endangered species in the Northwest Atlantic.

THREATS TO SURVIVAL

• As a result of its development, this hazard now poses a significant risk to the western Atlantic and Gulf of Mexico. According to studies, population estimates for this area are only about 15% to 20% of what they were in the mid-1970s. 
• Even though commercial and recreational fishing for these sharks was forbidden in the western Atlantic and Gulf in 2000, they are nevertheless frequently captured inadvertently on longlines and other fishing gear, with tragic results. 
• Despite efforts to end it, the international traffic in shark fin soup continues to threaten the dusky shark population. Recent studies have shown that as many as 750,000 dusky sharks may be taken annually for the shark fin trade.

Dusky Shark Worksheets

This fantastic bundle includes everything you need to know about Dusky Sharks across 27 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about Dusky Sharks. Dusky Sharks, often called bronze or black whalers, are recognized for their long-distance swimming abilities and seasonal, temperature-driven migrations.

Complete List of Included Worksheets

Below is a list of all the worksheets included in this document.

1. Dusky Shark Facts
2. Carcharhinus Obscurus
3. Search in the Ocean
4. Tic-Tac-Toe
5. Dusky Shark Facts
6. Pop it!
7. Coastal Creatures
8. Natural Territory
9. Dangerous or Not?
10. Physical Features
11. Protected Not Feared

Frequently Asked Questions

What is a dusky shark, and where is it commonly found?

A dusky shark (Carcharhinus obscurus) is a species of requiem shark known for its dusky-gray to bronze-colored body. They are commonly found in warm-temperate and tropical waters worldwide. They prefer offshore habitats but can also be seen closer to the coast.

How large can dusky sharks grow, and what is their typical lifespan?

Dusky sharks are large and can grow up to around 12 feet (3.7 meters) or more in length. They have a relatively long lifespan for sharks, with some individuals living up to 40 years or more, depending on environmental conditions and fishing pressures.

What do dusky sharks primarily feed on?

Dusky sharks are opportunistic predators, and their diet includes a variety of prey such as small bony fishes, squid, crabs, and other smaller sharks. They are known to feed near the ocean’s surface as well as in deeper waters.

Are dusky sharks considered a threatened or endangered species?

Yes, dusky sharks are considered a vulnerable species according to the International Union for Conservation of Nature (IUCN) Red List. They face significant threats from overfishing, bycatch in commercial fisheries, and habitat degradation. Conservation efforts are in place to protect and manage their populations.

What is the reproductive behavior of dusky sharks?

Dusky sharks are ovoviviparous, meaning they give birth to live young after the embryos develop internally within the mother’s body. The gestation period for dusky sharks is approximately 22-24 months, one of the longest known gestation periods for sharks. They typically give birth to a relatively small number of pups, ranging from 3 to 14, depending on the shark’s size and age. This reproductive strategy makes them particularly vulnerable to population declines when subjected to overfishing.

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