How many sharks are there

The results were very exciting: 22 water samples collected over a few weeks detected more sharks than hundreds of baited underwater camera observations over two years, and thousands of scuba dives over a period of decades.

Nearly half of the species detected through environmental DNA could not be found at all using traditional methods.

And while eDNA could detect the presence of some sharks in about 90 percent of the samples, underwater cameras could only manage just over 50 percent, and scuba diving around 15 percent. Interestingly, eDNA outperformed the other methods in both pristine and impacted areas. A range of shark species were detected even in busy, noisy and depleted areas, where they were thought to be extirpated.

Similarly, eDNA can help by revealing the appearance of newly established, alien species that are expanding their range. All of this is good news for everyone, and this is why. Given the speed and efficiency of eDNA sampling, a much larger portion of the sea can be screened, in a shorter time, to gather an overview of the patterns of diversity across large areas and habitats, along various environmental gradients, and at different times.

Potentially, we could rapidly build maps of species diversity and use them to create predictive models and identify the factors that influence diversity, while methods are being developed to improve the quantitative aspect of eDNA detection, also in other charismatic species.

All of it will be of great help to those who must devise plans to protect crucial habitats and ecosystems. Environmental DNA science is still rapidly developing.

In , he discovered the RMS Titanic , and has succeeded in tracking down numerous other significant shipwrecks, including the German battleship Bismarck , the lost fleet of Guadalcanal, the U.

He is known for his research on the ecology and evolution of fauna in deep-ocean hydrothermal, seamount, canyon and deep trench systems. He has conducted more than 60 scientific expeditions in the Arctic, Atlantic, Pacific, and Indian Oceans.

Sunita L. Her research explores how the larvae of seafloor invertebrates such as anemones and sea stars disperse to isolated, island-like habitats, how larvae settle and colonize new sites, and how their communities change over time. Kirstin also has ongoing projects in the Arctic and on coral reefs in Palau. Her work frequently takes her underwater using remotely operated vehicles and SCUBA and carries her to the far corners of the world.

What are they? Sharks are elasmobranchs, a group of animals that includes rays and skates, whose members have a skeleton made of cartilage, rather than bone, and, unlike most other fish, lack a swim bladder. How many? There are more than species of sharks and at least one species is found in every ocean, including the Arctic Ocean. How big? The smallest shark is the deepwater dogfish Etmopterus perryi at only 8 inches and the largest is the whale shark Rhincodon typus , which, at 13 meters, 42 feet , is the largest fish in the ocean.

How long? The lifespan of a shark depends on the species, but is at least 70 years in white sharks Carcharodon carcharias. What color? Threats Tens of millions of sharks are killed by humans each year compared to 12 humans killed by sharks in Nearly all species of sharks in the North Atlantic have declined significantly over the past two decades.

Sharks are threatened primarily by overfishing, which has been largely driven in recent years by the rise in demand for sharkfin soup, as well as by fishing activities that do not target sharks, but that capture them as bycatch. Many shark species mature late, have a long gestation period up to two years , and give birth to less than a dozen pups.

All these factors contribute to low productivity rates among sharks, making many populations particularly vulnerable to fishing mortality. How much? Their ocean home is also in danger. From climate change warming the water - affecting both habitats, prey and shark population shifts - to plastic pollution, which could cause entanglement or be ingested, especially by filter feeders.

WWF is working around the world to better protect and manage our oceans — including vital shark habitats. We can all play our part to reduce our plastic use, increase recycling and clean up our plastic pollution.

And we can all work together to fight devastating climate change, which is affecting both people and wildlife. Fundraising Block. Adopt Please select an elephant a lion a panda a turtle an african rhino an orangutan a dolphin an amur leopard a gorilla a snow leopard a polar bear a penguin a jaguar.

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