Deep-sea Sharks: The Deep and Abyssal Shark

Los deep-sea sharks, also called deep-water sharks and in some cases abyssal sharks, are species of animals that inhabit areas of the ocean below 200 meters, where sunlight is scarce or nonexistent. These shark species have developed unique adaptations to survive in extreme conditions of pressure and darkness, such as the ghost shark (Hydrolagus trolli), sighted at depths of up to 2,600 meters in the Kermadec Trench in the Pacific Ocean.

However, although there are some types of sharks that live below 1,000 meters in depth, not all inhabit the same zone, and that's what you will discover in this article.

General characteristics of deep-sea sharks

Morphological adaptations

Deep-sea sharks usually have elongated and flattened bodies, large eyes or pits to detect light, and bioluminescent skin. These characteristics allow them to navigate and hunt in absolute darkness.

Physiological adaptations

These species have body pressure regulation systems and slow metabolisms to survive in high-pressure, low-temperature conditions. Some species also have specific adaptations in their circulatory system to improve oxygen absorption.

Behavioral adaptations

Deep-water sharks exhibit specific behaviors such as daily vertical migration, where they ascend to shallower waters to feed and descend again during the day.

Differences between deep-water, abyssal, marine, and freshwater sharks

Deep-water sharks and marine sharks have different adaptations for their respective habitats. Abyssal sharks, those living on the seabed, possess characteristics such as bioluminescence, large eyes to see in the dark, and slow metabolisms to survive in high-pressure, low-temperature conditions. In contrast, shallow-water marine sharks usually have more hydrodynamic bodies to swim quickly, brighter colors to camouflage with sunlight, and faster metabolisms to maintain their activity in warmer waters with more abundant food.

Marine sharks, inhabitants of oceans and seas, are adapted to a salty environment, while freshwater sharks, which live in rivers and lakes, prefer environments with lower salinity. Additionally, marine sharks are generally larger and more varied in species, while freshwater sharks tend to be smaller and less diverse in comparison.

In terms of size, there are no evident physical differences since each species has a different size from another, and these differences are relevant between species and not simply related to the depth at which they live.

Main species of deep-sea sharks

There are numerous species of sharks that inhabit deep waters, including the Greenland shark (Somniosus microcephalus), the megamouth shark (Megachasma pelagios), and the goblin shark (Mitsukurina owstoni).

Greenland shark (Somniosus microcephalus)

The Greenland shark is known for its extreme longevity, living over 400 years. It inhabits the cold waters of the Arctic and North Atlantic and is one of the most studied deep-sea sharks.

Megamouth shark (Megachasma pelagios)

Discovered in 1976, the megamouth shark is a rare and little-known species. It feeds on plankton through filtration and is famous for its enormous mouth and vertical migratory habits.

Goblin shark (Mitsukurina owstoni)

The goblin shark, known for its unique appearance with a long, flattened snout, inhabits depths of up to 1,300 meters. It is a fascinating example of the evolutionary adaptations of deep-sea sharks.

Pelagic thresher shark (Alopias pelagicus)

The pelagic thresher shark is distinguished by its long tail, which it uses to stun its prey. It inhabits deep waters of the Pacific and Indian Oceans and is known for its daily vertical migrations.

Frilled shark (Chlamydoselachus anguineus)

The frilled shark has a long, serpentine body, similar to an eel. It is found at depths of up to 1,500 meters and is one of the most primitive shark species that exist.

Cookiecutter shark (Isistius brasiliensis)

The cigar shark, also known as the cookiecutter shark, is famous for the circular bites it leaves on its prey. It lives in deep waters and is found in all tropical and subtropical oceans.

Blackmouth catshark (Galeus melastomus)

The blackmouth catshark inhabits the eastern Atlantic and the Mediterranean. It is characterized by its small size and its ability to live at depths of up to 1,200 meters.

Pacific sleeper shark (Somniosus pacificus)

Similar to the Greenland shark, the Pacific sleeper shark is known for its deep-water habitat and slow movement. It inhabits the North Pacific and can be found at depths of up to 2,000 meters.

Bluntnose sixgill shark (Hexanchus griseus)

The bluntnose sixgill shark is an ancient species with primitive characteristics, such as its six gills. It inhabits deep waters and is found in oceans worldwide. It is also known as the cow shark, differing from other species by having six gill slits instead of the typical five of most sharks. Its name derives from its appearance which, in many cases, resembles a cow due to its mottled skin and robust body.

Gulper shark (Centrophorus granulosus)

This shark is distinguished by its large eyes, which allow it to see in the dark depths of the ocean. It inhabits deep waters of the Atlantic and the Mediterranean.

Birdbeak dogfish (Deania calcea)

The birdbeak dogfish, also known as the arrowhead dogfish, inhabits depths of up to 1,450 meters. It is found in the Atlantic and Pacific Oceans and is known for its elongated, slender body.

Blackbelly lanternshark (Etmopterus spinax)

The blackbelly lanternshark, also known as the velvet belly lanternshark, is known for its bioluminescence. It inhabits depths of up to 1,500 meters and is found in the eastern Atlantic and the Mediterranean.

Portuguese dogfish (Centroscymnus coelolepis)

This shark is known for its deep-water life and its ability to live on the seabed. It is found at depths of up to 3,700 meters in the Atlantic and Pacific Oceans.

Speckled catshark (Halaelurus natalensis)

The speckled catshark inhabits deep waters of the western Indian Ocean. It is found at depths of up to 500 meters.

Marine habitats and geographical distribution of deep-sea sharks

Deep-sea sharks are found in all the world's oceans, from polar regions to the tropics. Most inhabit areas of submarine canyons, continental slopes, and underwater mountains.

These sharks prefer environments with low light and high pressure, such as ocean trenches and bathyal zones. Some even live in anoxic conditions, where oxygen is extremely low.

Sightings of oceanic sharks in great depths

Marine habitats

These sharks prefer environments with low light and high pressure, such as ocean trenches and bathyal zones. Some even live in anoxic conditions, where oxygen is extremely low. Below are some specific areas where different species of sharks have been observed at great ocean depths.

Ocean trenches

Ocean trenches are some of the deepest regions of the ocean. Notable examples include the Mariana Trench in the Western Pacific, where species such as the goblin shark (Mitsukurina owstoni) have been sighted.

Those inhabiting greater depths are also known as abyssal sharks, generally found in deep waters, but not necessarily in the most extreme abyssal zones. While some abyssal sharks may inhabit very deep waters, such as those found in ocean trenches, many of them are found in waters closer to the surface but still in areas of significant depth.

Bathyal zones

The bathyal zones, which are between 200 and 2,000 meters deep, are common habitats for many deep-water sharks and fish. The bathyal zone of the North Atlantic is known for the presence of the Greenland shark (Somniosus microcephalus).

Seamounts

Seamounts, such as those of the Central Pacific Ridge, offer an ideal habitat for species such as the megamouth shark (Megachasma pelagios), which feeds on plankton in these nutrient-rich areas.

Submarine canyons

Submarine canyons, such as the Monterey Canyon in California, are refuges for various species of sharks that prefer the seafloor, including the frilled shark (Chlamydoselachus anguineus).

Anoxic zones

Some sharks can survive in low-oxygen conditions, such as those found in the Gulf of Mexico, where the cigar shark (Isistius brasiliensis) has been observed.

Cold-water areas

In the cold waters of the Arctic and North Atlantic, the Greenland shark (Somniosus microcephalus) is found, known for its longevity and ability to live in extremely low temperatures.

Continental slopes

Continental slopes, such as those of the North Sea, are typical habitats for the blackmouth catshark (Galeus melastomus), which lives at depths of up to 1,200 meters.

Anatomy and physiology of deep-sea sharks

Body structure

Deep-sea sharks have specialized body structures, such as flexible cartilaginous skeletons and fins adapted for maneuvering in tight spaces. Their skin is thick and may have dermal denticles for protection.

Sensory systems

These sharks possess acute sensory systems, including electroreceptors to detect electric fields and chemoreceptors to identify chemical signals in the water. Their eyes may be adapted to maximize light capture.

Feeding and digestion

The diet of deep-sea sharks varies from small fish and squid to carrion. They have efficient digestive systems to maximize nutrient extraction from their scarce prey.

Behavior and ecology of deep-sea sharks

Hunting strategies

They use various hunting strategies, such as ambushes and bioluminescence to attract prey. Some of these sharks that inhabit deep ocean zones are scavengers, taking advantage of dead animals falling from surface waters.

Migration patterns

Many deep-sea sharks perform daily vertical migrations, ascending to the mesopelagic zone at night to feed and descending again at dawn.

Trophic relationships and ecosystem

They occupy important roles in the food chain, acting as predators and regulators of other marine species' populations. Their presence is crucial for the balance of deep-sea ecosystems.

Reproduction and life cycle of deep-sea sharks

Reproductive strategies

Deep-sea sharks exhibit various reproductive strategies, including ovoviviparity and viviparity. Some lay eggs protected by tough capsules known as "mermaid's purses."

Embryonic development

Embryonic development can be slow due to the low temperatures of their habitat. In some species, embryos are nourished by egg yolks or through intrauterine cannibalism.

Growth and longevity

These sharks tend to grow slowly and can have long lifespans, with some species living over 70 years. Their slow growth and late maturation make them vulnerable to overfishing.

Interaction with humans

Importance in fishing

Some deep-water shark species are caught for their meat, liver oil, and cartilage. However, excessive fishing can threaten their populations due to their low reproductive rate.

Anthropogenic threats

Major threats include commercial fishing, pollution, and climate change. Habitat alteration due to human activities also poses a significant risk.

How deep-sea sharks are researched

Methods include the use of manned submarines, underwater robots, and telemetry techniques. These tools allow for direct observation and long-term monitoring of sharks in their natural habitat.

Additionally, monitoring technologies such as remote cameras, pressure sensors, and satellite tags provide detailed data on the behavior and movements of deep-sea sharks.

Recent studies have revealed new species and surprising behaviors, such as the use of bioluminescence for communication and hunting. These discoveries underscore the importance of continued exploration of the deep oceans.