Sharks are feared and admired by people of all ages. These creatures fill media and popular culture in the Western world with their impressive teeth and carnivorous diets. However, many people might not realize that there are over 400 known species of sharks- and although they maybe aren’t as iconic as the Great White in the film Jaws, they are unique in their own right. The bluntnose sixgill shark is an interesting species to explore as much is still unknown about its behavior and reproduction. Here’s the information that is known about the bluntnose sixgill shark.
Before you learn about specific sharks, it’s important to know some general information about them. You probably think of sharks and think about the ones you see in movies but there are so many more complex and fascinating shark species than the ones that are depicted.
Species in the subclass of sharks have skeletons made of cartilage which is much different from the fish in the ocean that have skeletons made from bone in it. Sharks have five to seven gill slits on the sides of their heads While most other fish only have one Gill on each side of their head. Sharks filter oxygen through these gills so that they can breathe in the water. Sharks come in a wide variety of sizes. The whale shark is the largest fish species on Earth and they can grow more than 55 feet long while the dwarf lantern sharks are much smaller and can only reach around 8 inches in length.
Sharks can be found throughout the world and both deep and shallow Waters. They migrate vast distances to feed and breed. Some sharks are solitary while there’s like to be a part of groups. Scientists are still trying to figure out how long sharks live and they’ve only studied a fraction of the shark species found on Earth. Most notably the Greenland shark is the Earth’s longest living vertebrate. It has lived to be 272 years old.
Even though sharks have a reputation for being scary, they’re not a significant threat to humans. People aren’t sharks’ preferred food. Shark attacks have increased at a steady rate since 1900 but this is a result of better recording of attacks and a rising population of humans. Even though shark attacks are seen all over in horror movies, shark bite people out of curiosity, defense, or confusion. A beach goer has a 1 in 11.5 million chance of being bitten by a shark which means they have a greater chance of being struck by lightning.
In general, humans are a greater threat to sharks than they are to us. Humans are responsible for a large decrease in shark populations all over the world. The biggest threat is overfishing. 100 million sharks are killed each year to supply the demand for expensive culinary dishes. Also, humans are responsible for climate change and rising water temperatures in coastal developments are contributing to the decrease in shark populations.
Bluntnose Sixgill Shark
The bluntnose sixgill shark boasts 6 rows of teeth in its broad, flat head. There are six saw-like teeth on each side of its bottom jaw and nine smaller teeth on either side of the upper portion of its mouth. It has teardrop-shaped fluorescent green eyes with black pupils, a lateral line down its side, and one dorsal fin. The pectoral fins are rounded at the tip and have broad bases. Its pelvic fins have rounded tips and the anal fin is smaller than the dorsal fin. The shark’s body rounds out to a blunt and wide snout.
This shark also shows dentition and denticles on his body. Dentition is a distinguishing character of the bluntnose sixgill shark and it has six broad, saw- like teeth on each side of the lower jaw. The upper jaw has nine smaller serrated single cusped teeth on each side of it. This is a great way for scientists and researchers to distinguish the bluntnose sixgill shark from some of the others. The denticles of the bluntnose sixgill shark have three teeth with a defined axial crest and lower crest. These two are loosely to moderately closely arranged with very little overlapping. These denticles on the posterior of the caudal fins upper margin are larger and smoother ones. You also might recognize that they are more oval in shape.
The bluntnose sixgill shark is either gray, olive green or brown on the upper side. These colors usually fade to a paler underside. It has a distinct like colored stripe along each flank close to the lateral line of the shark. Their fins also appear to have pale edges. There are some living individuals of the shark that have fluorescent green eyes.
This large-bodied shark can grow up to 26 ft (8 m) in length but on average, full grown adults measure in at 16 feet (4.8 m). When the bluntnose sixgill shark reaches maturation, males weigh around 440 pounds (200 kg) and females are approximately 880 pounds (400 kg) in weight. The males reach maturity around 11-14 years old and females mature between 18-35 years. This species is thought to live to around 80 years.
Typically, sharks have only five gill slits but this shark is distinguished from other species by its six gill slits, which give it its name. There are some species that are easily confused with this shark. One species that is sometimes confused with the bluntnose sixgill shark is the big eyed sixgill shark. The bluntnose sixgill shark is much larger and it has a blunt snout while the big eyed sixgill shark is smaller and it has a more pointed snout. Another species that is confused with the bluntnose sixgill shark is the frill shark. This shark has fang-like teeth and 6 gill slits with gill covers that extend across the throat but the coloration and size is a little different.
Evolution and Classification
The bluntnose sixgill shark, scientific name Hexanchus griseus, is a primitive species belonging to the Hexanchidae family. Its appearance is similar to fossil shark forms that date back to the Triassic period, nearly 200 million years ago. Living species that are related to the bluntnose sixgill shark include the Greenland shark and the dogfish.
This shark also goes by common names including brown shark, cow shark, bull shark, grey shark, mud shark, sixgilled shark, Atlantic mud shark, and brown shark.
The bluntnose sixgill shark is distributed widely throughout the globe as it is a highly migratory species. They live in a wide range of seas around the world, in temperate and tropical areas. This shark has been found off the coasts of many countries such as Argentina, Iceland, Madagascar, Japan, and Mexico.
This species resides in deep water and makes its home over the outer continental, insular shelves, and upper slopes. During the day, it rests near the ocean floor and at night it moves closer to the surface in order to feed. This is because adults become distressed by light exposure. Young sharks will swim close to shorelines to search for food, but only during the nighttime. Adults typically swim around depths of 100 m (330 ft) or more.
The female sharks reach sexual maturity when they are 4.5 m (15 ft) long and the male sharks mature when they hit 3.15 m (10.3 ft) in length. Around May to the end of November, male and female bluntnose sixgill sharks meet to breed. Although actual mating behaviors have not been observed, it is hypothesized that the male uses his specially adapted teeth for courtship in which he nips at the female’s gills, pectoral fins, and flanks in order to entice her into mating. This is evidenced by the seasonal scars the females have around the gill slits.
The bluntnose sixgill shark is ovoviviparous. This means that the eggs hatch inside the body of the female with the embryos staying in her body until the end of the gestation period. The shark embryos are nourished via a yolk sac in the female shark. The gestation period is likely around 2 years, but the exact timing is unknown.
Before giving birth, the female moves to shallower nursing areas in order to give birth on the outer continental shelves and upper slopes. Each litter can have 22 to 108 pups. The shark pups have lighter belly coloring than the adults do. The pups are 60 to 75 cm (24 to 30 in) when they are born.
The bluntnose sixgill shark is a nocturnal feeder. It feeds on large bony and cartilaginous prey including lampreys, hagfish, flounder, billfish, dolphinfish, cod, rays, and chimaeras. Other prey include spiny dogfish, longnose dogfish, prickly sharks, and shortnose dogfish. Small fishes, crabs, squid, snails, and shrimp are also consumed by the bluntnose sixgill shark. The shark scavenges on carcasses of whales, sea lions, and seals.
Hunting happens from a close range. The shark is generally sluggish and nature but when it is searching for prey, it can use its powerful tail to hit high speeds while chasing its food source. The specialized saw-like teeth on its bottom jaws help the shark tear apart prey that it can’t swallow. Smaller prey are captured in the corner of its jaw using a sideways movement of its head.
This shark needs to watch out for its own predators. Sea lions, white sharks, and killer whales are all potential threats to the bluntnose sixgill shark.
Bluntnose Sixgill Shark and Humans
The bluntnose sixgill shark is an important species for humans as it is fished commercially and by game-hunters for its meat which comes fresh, frozen, and dried salted. Fishermen use traps, trawls, gillnets, and line gear to catch this shark. Sometimes it is captured by accident in fisheries for other species. The remnants of this animal are also utilized and sold for oil, pet food, and fishmeal.
In the presence of humans, the shark does not attack without being provoked. In fact, no attacks on humans by the bluntnose sixgill shark have been reported since the 16th century. For the most part, members of the species tolerate being around people. The shark reacts to physical contact by snapping and swimming off into deeper waters to get away from being surrounded by humans.
Regional populations of the species have been depleted due to pressures and exploitation from the fishing industry and its popularity as a sport fish. The exact effect of targeted fishing on worldwide population levels of the bluntnose sixgill shark is unknown however, because of the lack of population and fisheries data. As a result, the International Union for the Conservation of Nature listed this shark as “Near Threatened”.
Learning about threatened sharks is the first step to saving them. If you want to help save sharks, then volunteering with organizations that help them is a good way to start. If sharks are your passion, then you can help save the oceans by helping them.