One of the sharks known to be one of the oldest species that exist in the world is the eel shark. Over time it has been called a living fossil. This is because this animal has lived since prehistoric times and is still living today. However, although this may be more normal in other species, this has hardly had any evolution throughout all this time.
Therefore, we're going to dedicate this article to the frilled shark. If you want to learn about their biology, way of life, diet and reproductionThis is your post
Key features
Normally, all species undergo environmental adaptations over time and evolve. Environmental conditions and interactions with other individuals in natural habitats and ecosystems are not always the same. Therefore, species tend to develop in their genes some of the strategies that serve them to better survive in these environments and to be more successful in both survival and reproduction.
However, the frilled shark has barely changed since prehistoric times. It remains an animal with almost the same characteristics as when it originated. This is why it is called a living fossil, as it is an animal species that has the characteristics of prehistory. Although it is an animal quite well known to people almost all over the world, not much information is known about it.
It is known by many names because it is such a popular species. The name frilled shark comes from its snake-like shape. It belongs to the Chlamydoselachidae family and is part of the main groups de peces and has other common names such as the ruff shark. Currently, We can see this in conservation assessments with a status that usually ranges between "least concern" and "near threatened". depending on the area and the source consulted. The reason it appears with some degree of concern is that it is caught incidentally in deep-sea fisheries (trawling and bottom longlining) and its life cycle is very slow.
When they arrive from the depths to the surface they arrive dead, since they cannot withstand sudden changes in pressure. Another factor for which they are almost threatened is the slow reproduction they have. If we add that they need many years to reproduce and increase their populations with which they are caught accidentally, it is normal that the number of individuals of the species is less and less.
Description
The body of the eel shark is very thin compared to other sharks. It is a body similar to that of an eel. Usually, They have an average length of about 2 metersThis does not mean that all individuals are this size. Some have been recorded with lengths of up to 4 meters.
The nose is in the central part of the front of the head with a rounded shape. Although it is not entirely clear, it handles about 300 teeth in total. It has them distributed in 25 transversal rows, which means that hardly any prey can escape from this deadly shark.
The strength it has in its jaw and the shape it has helps it swallow large prey without problems. The color of the shark is dark brown. It has dorsal, pelvic and anal fins in addition to 6 gill openings.
They are quite fast swimming. One of the curiosities that draws the attention of these sharks is that, when they swim at high speed, they do so with their mouths open. These are animals that cannot survive outside their habitat or in captivity, no matter how much care they receive..
Primitive anatomical features Features that distinguish it from other modern sharks include a terminal mouth (at the tip of the snout and not on the ventral surface), the presence of six pairs of gill openings whose first pair forms a “ruff” or frill around the throat, and a single dorsal fin very far back, located opposite the anal. The sideline channel is largely superficial and visible, and the axial axis retains a robust notochord with cartilaginous reinforcements, a trait considered ancestral among elasmobranchs.
The pectorals are small and roundedThe pelvic and anal ducts are relatively large and elongated, and the tail is knocked downwith a poorly defined terminal lobe. The eyes are oval, without a nictitating membrane, and their dentition consists of extremely sharp, backward-facing tricuspid teeth, perfect for retain slippery prey like squid. Although large specimens have been reported, the most frequently confirmed total length is below 2 meterswith females slightly larger than males. The young, at birth, typically measure between 40 and 60 cm.
Habitat and area of distribution
These animals live in quite great depths. Between this and the fact that they cannot be kept in captivity, it is normal that not much is known about this species. You can't just do studies on them. They usually live at a depth of 600 meters, with a minimum of 150 meters. It is the closest they have been seen to the surface.
The only way to do them rise to the surface They have to search for food desperately. However, they do so at night, since they don't want to be seen at all.
Its area of distribution is quite wide but with an irregular character. We can find them in Angola, Chile, New Zealand, Japan, Spain, and in the Atlantic and Pacific Oceans.
In more detail, it is a species bathydemersal and benthopelagic from the edge of continental shelves and slopes. Its documented global bathymetric range covers approximately from 50 to 1.600 m, more frequently among 120-1.250 m (in some areas, 270–1.280 m). It is rarely observed near the surface, and surface sightings are usually associated with dying or disoriented individuals due to pressure changes.
Present a patch distribution in cold to temperate waters of the Atlantic and Pacific Oceanswith records on continental margins in both hemispheres. In the Atlantic, it has been recorded from high latitudes in the northeast to temperate zones in the southwest, including oceanic archipelagos; in the Pacific, there are reports off Australia, New Zealand, Japan, Taiwan, the west coast of America and sectors of the central Pacific. This apparent fragmentation is due both to its deep ecology and to the low detectability by conventional sampling methods.
It is believed that he performs nighttime movementsDuring the night it rises to shallower strata in search of prey, and during the day it remains in deeper waters. When the water column warms up in the surface layers, it tends to avoid shallow waters, which reduces their incidental capture during those times.
Feeding and reproduction of the eel shark
This shark has a fairly varied diet. Thanks to its body, which allows it to swallow prey whole, It can eat a wide variety of animalsIts diet consists mainly of squid, cephalopods, other fish, and even sharks.
He is considered a fairly skilled and feared hunter. It tends to hunt at night to avoid being seen and catch other species off guard. It can be well camouflaged thanks to the color of its skin and it uses it as a surprise factor to attack prey. Perhaps this success in its diet and these characteristics make it not have to evolve to adapt to different environments. Thanks to its color it is camouflaged, it swims at high speed and it has rows of teeth and a jaw that allows it to swallow whole prey. With all these characteristics, it does not need to evolve, so it is still a primitive species, but today.
Regarding its reproduction, it is of the ovoviviparous type. At each birth there are between 5 and 12 young. The young need a fairly long gestation period. They must be growing up between 2 and 3 years. This is what we talked about before about one of the reasons why the species is almost threatened. Between the accidental capture, the need for gestation periods of 2 to 3 years and, of all the offspring, not all of them become adults, it is normal for the populations to be detrimental.
Once the young have left the mother's body, they are usually between 40 and 60 cm long. They are victims of other predators when they cannot yet defend themselves.
Studies of stomach contents from various specimens indicate that their diet is highly specialized in cephalopods, Especially decapod squid (in some samples they exceed half of the recorded items). Species of the genera have been identified Onychoteuthis, Sthenoteuthis, Gonatus, Histioteuthis, Chiroteuthis y Mastigoteuthis, among others. It also consumes teleost fish varied (in smaller proportions) and, occasionally, other deep-sea sharksThey are frequently found in their stomachs. squid beaks and vertebraeThis suggests relatively rapid digestion of soft parts and/or a low feeding rate in resource-poor environments.
His hunting technique combines the motionless stalking with bursts of acceleration, propelling itself like a snake to to ambush on fast-moving prey. In captivity it has been seen swim with your mouth openIt has been suggested (speculatively) that the gleam of its whitish teeth might attract prey in low light, although direct hunting has never been clearly documented in the wild. Under the stress of capture, it may regurgitate the stomach contents, possibly to lighten the load and facilitate escape.
Regarding reproduction, in addition to being ovoviviparousIt exhibits unique characteristics among deep-sea sharks. Litters range from 2 to 15 pups (with averages close to six), and the Gestation is extraordinarily long, estimated between two and three and a half yearsThe embryos grow very slowly (approx. 1,4 cm per monthand can receive nutrients from the mother in advanced stages of development. It has been described that right uterus It is the main organ that functions during pregnancy, possibly due to the liver's position and size. oocytes They reach remarkable dimensions within the animal kingdom, an indication of the strong maternal investment of the species.
La sexual maturity It is usually reached in males below 1,1 m and in females between 1,4-1,5 mThere is no marked reproductive seasonality: both testicular activity in males and ovulation in females are documented throughout the year, and some is suspected segregation by size and maturity in the aggregates. Mechanisms have been proposed for pause in embryonic development depending on food availability and environmental conditions.
Behavior and customs
In addition to its behavior of ambush predator, have been observed common injuries to the caudal fin, some associated with copulation (bites to maintain position) and others to Interactions with predators or fishing gear. Its tolerance to pressure change is very lowso that most of the specimens brought to the surface they do not surviveIt is a cryptic species, with low detectability, that It does not adapt to captivity, which greatly limits experimental research.
Taxonomy and classification
- Kingdom: Animalia
- Division: Chordata
- Class: Chondrichthyes
- Subclass: elasmobranchii
- Order: Hexanchiformes
- Family: Chlamydoselachidae
- Gender: Chlamydoselachus
- Species: Chlamydoselachus anguineus
Within the genus there is another valid species, the African frilled shark (Chlamydoselachus africana), described for populations in southern Africa. Although they are closely related, They should not be confusedThis article focuses on C. anguineus, the frilled shark with a wide and irregular distribution in the Atlantic and Pacific.
Conservation status and threats
The frilled shark has no significant direct commercial interest and its capture is usually accidental in fisheries of bottom trawling and longliningSome of the individuals discard, and a small proportion is used for fish flour or local consumption. long gestationLow relative fertility and late maturity increase the vulnerability to exploitation. The monitoring of incidental catches And limiting deep-sea fishing is key to maintaining stable populations.
Assessments of its status on a global scale have ranged between “lesser concern” and more cautious categoriesThis is partly due to the scarcity of data and the fragmented nature of their populations. In regions with effective regulation on fishing depths And in the arts, the pressure on the species tends to be less. Even so, the geographical expansion and in-depth fishing could increase the incidence of catch, so it is advisable to maintain schemes of precautionary management.
I hope this information to help you learn more about the frilled shark.
Although it rarely appears on the surface, its unique biology—from the ancestral morphology to longer gestation among vertebrates— makes it a key player in deep ecosystems. Understanding its ecology, reducing the bycatch and improving data collection will help ensure that this true “living fossil” continues to navigate the planet’s underwater canyons.