Frilled Shark

The frilled shark is a “living fossil”, owing to its primitive physical features and lack of evolutionary changes over the years. Its common name comes from its gill slits which form a fleshy frill. 

German naturalist Ludwig Doderlein discovered the first frilled shark, but his findings were lost. So, the official documentation of this species fell to American zoologist Samuel Garman, who named it in 1884. The last part of its scientific name, anguineus, means snake-like or eel-like in Latin.

Description

Size: Length- Males: 5.6 ft (1.7 m) Females: 6.6 ft (2.0 m)

Teeth: The jaws hold over 300 teeth, shaped like miniature tridents. There are 19-28 rows of teeth in the upper jaw, while the lower jaw holds 21-29 rows.

Fins: Frilled sharks haveshort, round pectoral fins and a small dorsal fin with a rounded margin positioned opposite their anal fin.  The large broad anal, and pelvic fins, also appearing round like the other fins, lie at the tail end of their body. The caudal fin is huge, triangular in shape, and covered in scales.

Body and Coloration: They have a slender, elongated body giving them an eel-like appearance, alongside a broad, flat head and a short, round snout. Their eyes are relatively large without any protective membrane. These sharks have two slits close to their eyes, functioning as nostrils. There are six gill slits near the throat, with the first one forming a collar and the last five creating a fleshy frill.

They mostly have a chocolate brown appearance, lighter on their undersides.

Range and Distribution

Though seen worldwide, details of its exact distribution remain unrecorded. Specimens have been found in different locations, including southeast Japan, New Zealand, eastern Australia, Norway, western Ireland, northern Scotland, northern Namibia, northern Chile, South Africa, and southern California.

Habitat

Like most other deep-sea sharks, the frilled shark is found close to the continental shelf at around a depth of 1640 – 3280 ft but may also dwell at 4900 ft.

Diet

They primarily consume cephalopods (mainly squids) and smaller sharks that form 60% of their diet. Other forms of prey include bony fish and sea slugs.

Lifespan

Their estimated lifespan is 25 years.

Behavior

• They are amongst the slowest moving of all deep-sea sharks.
• Solitary in nature, the frilled sharks only interact when they mate.
• Scientists theorize that these sharks might hunt in different ways. They include curling themselves into a smaller size before propelling forward with momentum to strike or sucking their prey in by creating negative pressure with their gills. They may even attract fish towards them using their bright teeth.
• They don’t just look like eels but even swim similar to them in a serpentine manner.

Do They Attack Humans

They hardly come in contact with humans since they inhabit greater depths. Hence these sharks pose no threat to them.

Predators

There are few known predators of the frilled shark, but larger shark species most likely threaten them.

Adaptations

• They have adapted to life in the deep sea with the help of their cartilaginous skeleton and large liver filled with lipids of low-density, allowing them to stay buoyant.
• A lateral line present along the body increases the perception of these sharks, allowing them to detect changes in their environment.
• Their long, pointed teeth help them establish a firm grip on their prey’s soft bodies.

Mating and Reproduction

Like all other sharks, the frilled shark undergoes internal fertilization, meaning the male uses his claspers to inject his sperm into the female’s cloaca. There is no seasonal mating period as weather changes on the ocean’s surface do not affect the deep sea.

Life Cycle

A litter consists of 2-15 pups, born after a long gestation period of up to 3.5 years. Initially, at birth, the young sharks measure around 15-24 inches in length. Male juveniles reach sexual maturity at 3.3–3.9 ft (1.0–1.2 m), while for females, it’s 4.3–4.9 ft (1.3–1.5 m).

Conservation Status

The IUCN lists the frilled shark as “LC” or “Least Concern”. It was initially listed as “Near Threatened” due to the risk caused by overfishing done in their habitat as well its slow reproduction rate, but it was later re-classified to “LC”.

The New Zealand Threat Classification System classified this shark as “At Risk – Naturally Uncommon” in 2018. This is primarily due to the shark’s rarity, making it hard to detect their exact population in the wild.

Interesting Facts

• While not quite a sub-species, a variant of these sharks is found near the coast of South Africa with a shorter head and larger pectoral fins.
• It has several other names, including scaffold shark, frill shark, lizard shark, fringe shark, and silk shark, due to its unique appearance.
• Results of forensic studies have deduced that their stomachs hold little or no food at all. This indicates that these sharks may have a fast-acting digestive system or go hungry for long intervals between feedings.