#sleeper sharks

Today's fish of the day is the Pacific sleeper shark! 

The Pacific sleeper shark, scientific name Somniosus pacificus, is known for their sluggish demeanor, and unique look. Named not only for their behavior, but for the small fins, making it harder for the to thrash when caught by humans. These sharks can be found around the continental shelf of the Pacific, spanning from the Southern coasts of Japan across the Northern Pacific down to the coasts of Baja Mexico. Although they can be found trapped in intertidal areas, as they are incapable of escaping strong tides. This may be why these sharks are often found in deeper waters as they age, from 2000 meters and below once they reach sexual maturity. 

Despite their pacific sleeper sharks' slow nature, they can reach a regular size of 3.7-4.3 meters, with a maximum size of around 7 meters. These sharks have lower teeth specialized for slicing, and upper teeth used for spearing and trapping prey. These teeth are used, as these sharks hunt via suction, before slicing into their caught prey. These sharks act as stealth predators, waiting until small prey crosses close. The sleeper shark preys on small surface and bottom dwelling animals, such as: seals, various fish, octopi, and whales. Pacific sleeper sharks in particular have the ability to roll the eye backward in its socket, lacking a nictitating membrane to do so, a relatively common adaptation in the genus of sleeper sharks. This is to protect against the thrashing of prey as the shark feeds. They are not often predated on, as their flesh is toxic to humans and incites symptoms of drunkenness. 

Like many other deep dwelling sharks, the Pacific sleeper shark's reproduction and lifecycle isn't very well known. Like most other sharks, they are ovoviviparous, having eggs inside the mother until they are ready to hatch. Mothers can be found with as many as 300 eggs per breeding season, although only a maximum of 10 will be born. These juvenile sharks come into the world at a size of 42cm or less. However, there is no knowledge on defined breeding season, time of gestation for fry, any possible courtship behaviors, or lifespan. This is likely due to their deep environment, and inability to be eaten. 

That's the Pacific sleeper shark, everybody! I hope you enjoyed getting to read about them, and have a wonderful Monday!

Pacific sleeper shark - Somniosus Pacificus. Shark Research Institute. (n.d.). https://www.sharks.org/pacific-sleeper-shark-somniosus-pacificus

Somniosus Pacificus summary page. Fishbase. (n.d.). https://www.fishbase.se/summary/Somniosus-pacificus.html

Matta, M. E., Tribuzio, C. A., Davidson, L. N. K., Fuller, K. R., Dunne, G. C., & Andrews, A. H. (1970, January 1). A review of the Pacific Sleeper Shark somniosus pacificus: Biology and fishery interactions. Welcome to the NOAA Institutional Repository. https://repository.library.noaa.gov/view/noaa/65736

Today's shark is the pacific sleeper shark!

The basics: a close relative of the more Internet-famous Greenland shark, the pacific sleeper shark (Somniosus pacificus) is another large species of deepwater sleeper shark found in the Northern hemisphere. They are rarely seen and still very poorly understood. Pacific sleeper sharks have lower teeth that overlap to make a single serrated edge, like the blade of a steak knife, used to saw bites off prey. Like Greenland sharks and others in their genus, Pacific sleeper sharks are often found with a parasitic copepod attached to their eyes.

Conservation status: near-threatened. Populations of sleeper sharks are still poorly understood. However, juvenile sharks especially are at risk of bycatch, which has the potential to degrade their populations.

Today's fun fact: initial research into this species suggests that Pacific sleeper sharks average around 12 feet long, with the largest verified individual being 14 feet long and weighing almost two tons. However, much larger individuals have been filmed and documented, but their sizes never verified, including sharks ranging between 25-30 feet long. If reports of such large Pacific sleeper sharks were ever verified, they could dethrone the great white as the largest extant macropredatory shark!

Spiny dogfish (Squalus acanthias), Greenland shark (Somniosus microcephalus)

Fishes of the World. Written by Hans Hvass. Illustrated by Wilhelm Eigener. Originally published in 1964.

Best Shark bracket Squaliformes

Round 1

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Viper dogfish vs. Lanternshark

Seal shark vs. Frog shark

Greenland shark vs. Pocket Shark

Taillight shark vs. Spiny dogfish

Velvet dogfish vs. Cookie cutter shark

Greenland Shark (Somniosus microcephalus)

Family: Sleeper Shark Family (Somniosidae)

IUCN Conservation Status: Vulnerable

Found in cold regions of the Arctic and northern Atlantic oceans, the Greenland Shark is best known for its extremely long lifespan: members of this species regularly live to be over 200 years old, with some individuals living for over 400 years. Sluggish and extremely slow when swimming, it is an opportunistic carnivore that will take any sufficiently large prey that comes near enough for it to catch: it feeds largely on squids and smaller fish such as herrings, halibuts and salmon, but on occasion may also eat animals as large as seals, sea lions and dolphins (although as Greenland Sharks have rarely been seen actively attacking marine mammals and are far too slow to catch a healthy dolphin or seal, it is suspected that most of the marine mammals found in their stomachs were already dead when they were eaten - this would also explain the occasional discovery of the remains of terrestrial animals such as Reindeer and Polar Bears in their digestive tracts.) While little is known about the Greenland Shark’s life cycle, it is believed that they reproduce rarely and take a considerable amount of time to do so - current estimates (based on the development and estimated age of various adult and juvenile Greenland Sharks caught by fishers) suggest that they take over 100 years to reach sexual maturity, and upon successful mating their eggs (which develop and hatch inside their mother’s body) take a further 8-18 years to hatch. Greenland Sharks are frequently caught by fishing vessels (both deliberately to be eaten or for their livers, the oils of which are sold as having medicinal properties, and accidentally as by-catch), and this practice combined with the very slow rate at which they repopulate due to their extremely long generation length has caused concerning declines in populations of this species in recent years. The high concentration of the compound Trimethylamine N-oxide in the organs, fat and muscles of the Greenland Shark (which aids the shark’s tissues in enduring intense cold) means that the flesh of this species is poisonous to most animals if not first dried or fermented. 

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Animal Advent Calendar - Day 5

Rare footage of a Greenland Shark (Somniosus microcephalus)

Greenland Sharks are the longest lived vertebrate, with lifespans of 400+ years, and are the largest arctic fish. The majority of Greenland Sharks are blind due to parasitic copepods that attach themselves to the eye. They are generalist scavengers, eating carcasses of animals that have fallen to the seafloor. They are rarely seen by humans due to their deep habitat.

Just like counting rings on a tree trunk, most sharks can be aged by the growth bands around their vertebrae. The greenland shark is a remarkable exception; as their soft vertebrae lack these bands, the age can only be determined by the layers on the lenses of their eyes. Some scientists also use radiocarbon dating, which can be useful as greenland sharks can easily live to be over 300 years old.

(Image: An ancient greenland shark (Somniosus microcephalus) by Franco Banfi)