Sleeper Shark

The sleeper shark is a family of deep-sea predators found all over the world. The name of this shark comes from their reputation as slow-moving and sluggish animals, but some studies suggest they are in constant motion, traveling a few miles per day along a vertical route in the ocean.

Some smaller, more elongated species from this family are called dogfish. As the name suggests, they have a more traditionally fish-like appearance. Unfortunately, because of their reclusive nature, there is a lot we still don’t understand about their behavior.

Classification and Family

The sleeper shark family is classified as Somniosidae. This is derived from the Latin word “Somnus” for sleep.

Evolution and Origins

Due to their perceived sluggish behavior, sleeper sharks were historically believed to be sedentary creatures residing near the ocean floor, predominantly feeding on arrow-tooth flounder and octopus. Shortened Version: Early fishlike vertebrate fossils are too incomplete to trace the origins of modern fishes precisely.

Ancestral forms likely evolved in streams during the Ordovician Period. Placodermi, a diverse group of armored fishes, emerged during the Silurian and Devonian periods but declined by the end of the Devonian.

Some placoderms survived until the Early Carboniferous, but modern bony fishes (Osteichthyes) and cartilaginous fishes (Chondrichthyes) are thought to have evolved from a common ancestor among early jawed vertebrates. Chondrichthyes and Osteichthyes both appeared during the Devonian period.

Species

There are around 20 recognized species of sleeper sharks within the family, spread across six different genera. These are the most well-known species:

• Greenland Shark (Somniosus microcephalus): Found throughout the waters of the North Atlantic and Arctic, the Greenland shark has the longest known lifespan of any species of vertebrates. Based on the rate of growth, it’s thought to live between 250 and 500 years. It’s also one of the largest sharks in the world.
• Pacific Sleeper Shark (Somniosus pacificus): Native to the North Pacific, including Japan and California, this is another large and relatively well-known species. It is thought to be closely related to the Greenland shark. The sides of the body contain sharp, teeth-like structures that give it a kind of bristly feel.
• Portuguese Dogfish (Centroscymnus coelolepis): Despite the name, this species lives all over the globe, from the Atlantic coast of the United States to the southern waters of New Zealand. It has sharp eyesight to detect prey in deep water where sunlight does not penetrate.

Appearance

The sleeper shark exhibits considerable variation in size and appearance. The typical species is characterized by an elongated body ranging between blue-gray and brown in color, a rounded snout, and two small dorsal fins with or without spines at the base.

Many species are no more than a few feet in length, but the Pacific sleeper shark and the Greenland shark easily exceed this. Measuring up to 20 feet, these two species rank among the largest sharks in the world.

Distribution, Population, and Habitat

Sleeper sharks can be found in deep water seas near continental shelves and slopes all around the world, from the extreme north of Greenland to the southern fringes of South Africa. Most species prefer the cold Arctic or temperate waters, but some also live in deep tropical waters.

Because of their elusive nature, many species haven’t yet been evaluated for their conservation status, though numbers may be falling. The vulnerable Greenland shark has been traditionally targeted for its oil and meat in the Atlantic.

Predators and Prey

The sleeper shark is an apex predator in its natural environment. It has many interesting adaptations for feeding. The Pacific (and perhaps other species) has a mouth that functions as a kind of vacuum to suction up prey, while the lower teeth will cut up whatever food it cannot swallow whole.

What eats the sleeper shark?

On account of its size, the sleeper shark does not have many natural predators. It’s thought that the killer whale and some larger sharks may prey upon them.

What does the sleeper shark eat?

The sleeper shark is thought to consume a wide variety of different fish, squid, and mollusks, and possibly even seals as well. Stomach contents suggest it may also feed upon giant squid. Despite its slow speed, it may be capable of striking quickly at its prey from a close range in a surprise attack.

Reproduction and Lifespan

Scientists still don’t fully understand the reproductive habits of the sleeper shark. It is thought to reproduce by a method called ovoviviparity, in which the eggs develop and hatch inside the womb without the assistance of a placenta.

The length and timing of the breeding season vary by species, but once impregnated, females can carry each baby for more than a year, sometimes producing tens of baby sharks at a time.

These are exceptionally slow-maturing and long-lived sharks, many of them living for dozens of years, but the Greenland shark is exceptional even by these standards. Estimates suggest that the baby shark reaches full maturity at 150 years old and lives up to 500 years of age. Their extremely slow metabolism and swim speed may account for this extraordinary longevity.

Fishing and Cooking

The sleeper shark is not usually consumed by people, on account of its elusive nature and somewhat inedible flesh. However, the Greenland shark is hunted for food in Iceland and turned into a national dish called Hákarl.

While the shark’s flesh contains high levels of toxic compounds such as trimethylamine oxide (TMAO), people have found a way to ferment and dry the meat to make it safe for consumption. It has a very strong smell and fishy taste that has been known to repel people who consume it for the first time.