It is thought that man knows more about the moon’s surface than what lurks in the deep sea. Take a plunge into the inky depths, and an incredible diversity of weird and wonderful lifeforms exist. One group of these alien oddities are the deep-water sharks.
It is estimated that over 50% of the 500 recorded shark species live at depths of 700 meters or below.
Due to the harsh environmental pressures of living at such depth, shark species have evolved some pretty nifty adaptations to help them survive.
Behavioral adaptations, such as a slow metabolism and growth rate, have enabled certain species to reach ages of up to 400!
Even their physical appearance, somewhat alien-looking, has allowed deep-water sharks to roam these oceans for millions of years.
Why do sharks dive deep?
The ocean is divided into distinct sections, often distinguished by the level of light received. Species of deep-water sharks inhabit a part of the ocean known as the twilight zone.
The twilight zone ranges from approximately 200 meters to 1000 meters. Barely any light reaches this part of the ocean. Couple this with extreme pressure and frigid water temperatures; it would be a fair assumption to assume not much life could survive here.
However, ongoing studies have suggested that there may be ten times more life than we once thought at this depth.
With a large diversity of prey animals to be found at these depths, food availability could be the answer to why sharks dive deep.
The Vertical Migration
So, we’ve established that sharks dive deep to find food.
Granted, this isn’t a problem for deep-water species that have adapted to life here. But what about species of sharks found in shallower water?
The deep oceanic harbor a lot of life. Many shallow-water sharks undertake what’s known as “vertical migrations” to deep water to hunt.
Vertical migration is the movement pattern of some animals living within the marine environment.
Considering the high risks of increased pressure and colder temperatures associated with the deep, the pros must outweigh the cons.
Certain studies have discovered that some sharks follow their prey through the water column – spending time in the deep during the day and surfacing around night hours to forage and hunt.
One such species that display this behavior is the bigeye thresher shark. Typically a temperate water species, it was observed in a recent study that individuals spend daylight hours in cooler waters and migrate to shallower waters at night.
What sharks live in the deep?
There are many species of shark that thrive in waters deeper still.
The species below are found in some of the deepest parts of the ocean. Often referred to as the midnight zone, this ocean region ranges from 1000 meters to 4000 meters in depth!
- Frilled sharks – A real deep-water oddity, they get their name from the frilly appendages extending from the crown. Found throughout the Atlantic and Pacific Oceans, they have been recorded at depths of a whopping 1600 meters. Examinations have revealed that they have a large liver to help resist the overwhelmingly high pressure at this depth.
- Bluntnose sixgill shark – The third-largest predatory shark species. Individuals have been recorded hunting at a staggering depth of 1800 meters. Also known as the cow shark, they are sluggish animals, an adaptation for living in the deep.
- Portuguese Dogfish – Part of the sleeper shark family, this slender fish prefers to remain close to the seafloor, where it actively hunts for cephalopods and fish species. This shark species is thought to be the deepest diver of all sharks. They were found at depths of 3600 meters.
Sharks that occasionally dive in deep water
Many species of shark do not simply stay in one place. As species migrate across the globe, they fluctuate their diving to cater to the animal’s needs.
Some species can dive to incredible depths – despite not being a deep-water species.
Below are just some of the species of sharks that occasionally dive into deep water:
- Whale sharks – They are often thought to stay around the sunlit surface water, where most of their prey can be found. Marine studies, using tags on the pectoral fins of individuals, have recorded that some dived to a depth of 1800 meters.
- Tiger sharks – To help conservation projects, the migration routes of tiger sharks were recorded. Typically a surface-going shark, scientists were stunned to learn that tiger sharks frequently made dives to over 200 meters in depth. Scientists hypothesized this was either to help the sharks orient themselves better or a foraging tactic.
- Great white sharks – During daylight hours, they have been recorded as deep as 500 meters, well into the twilight zone. At night, they were observed hunting squid. The deepest ever recorded great white was found at depths of 1200 meters.
Over half of all recorded shark species have the capability of diving to great depths.
Some, such as the frilled shark and Portuguese dogfish, have made their home in the crushing depths of the deep.
Others, such as great whites and tiger sharks, occasionally venture down to deeper water to aid in survival techniques, such as foraging or orientation.
Some species, such as the Mako shark, undergo vertical migrations. Following the movement of prey species, these species remain in deep water during daylight hours and migrate to surface water at night.