Which sharks have the longest known lifespan of all vertebrates on Earth?

Can you believe that there are sharks that can live for over 400 years? Greenland sharks have the longest known lifespan of all vertebrates on Earth. Scientists estimated the age of a Greenland shark to be about 400 years in 2016. It is said that they do not even reach sexual maturity until they are about 150 years old.

Greenland sharks are rarely encountered by humans. They are thought to prefer colder, deeper environments but may be found anywhere between the sea surface and depths of 2,200 meters (about 7,200 feet). Greenland sharks are slow-moving, typically swimming at rates of less than 3 km (about 1.9 miles) per hour. They are carnivorous, and their diet is often made up of several different types of fishes, including smaller sharks, eels, flounders, and sculpins. Crustaceans, seabirds, and carrion—as well as terrestrial mammals (such as horses and reindeer) that likely fell through the ice—have been found in stomach analyses of the species. Greenland sharks are not considered dangerous to humans, in part because they live in regions where people do not typically swim; the only known report of a possible attack by a Greenland shark on a person dates to 1859.

Greenland sharks are considered to be a near-threatened species by the International Union for Conservation of Nature. The species was valued for its liver oil; about 114 litres (30 gallons) of liver oil can be obtained from a large specimen (see also fish oil). (Although the flesh of the Greenland shark may be eaten, it is toxic unless properly cleaned and dried or repeatedly boiled prior to consumption.) Greenland sharks were fished commercially from the 19th century until 1960. Norway persecuted Greenland sharks during the 1970s, because they were considered to be a nuisance that threatened other fisheries. In the early 1900s as many as 30,000 Greenland sharks were caught a year. In the present day the annual take is far smaller; small-scale subsistence fisheries in the Arctic harvest fewer than 100 individuals annually, and roughly 1,200 are caught accidentally in fishing trawls.

Credit : Britannica 

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Why are nurdles a problem?

The world has woken up to the threats posed by plastic-especially the single-use ones - to the environment and marine life in particular. In the recent decades, scientists have also come to recognise the dangers of microplastics, which are extremely small pieces of plastic debris resulting from the breakdown of plastic products. Now, they have sounded alarm over another tiny, yet hazardous plastic items called nurdles. Depending on their density, nurdles can either float to the surface of the water or sink below the surface. In either case, they are a threat to animals and birds.

What are nurdles?

Nurdles are lentil-sized plastic pellets used as raw material for most of today's plastic products. Made of plastics including polyethylene, polypropylene, polyvinyl chloride, and polystyrene, the pellets are transported to factories around the globe where they are melted down and used to I create plastic bags, kitchenware, bottles, and more. Through leaks, spills, and other storage or transportation errors, nurdles end up in the environment, eventually making their way to the ocean. When the X-Press Pearl container ship caught fire and sank in the Indian Ocean in May 2021. 87 containers full of lentil-sized plastic pellets aboard were accidentally spilled into the ocean.

Since the disaster, nurdles have been washing up in their billions along hundreds of miles of Sri Lanka's coastline, according to reports.

Why nurdles are a concern

According to The Guardian, 250,000 tonnes of the pellets end up in oceans each year. Because of their size and colour, nurdles look a lot like fish eggs, which makes them particularly appealing to seabirds, and other marine animals. Accidental ingestion of nurdles can cause ulcerations, starvation and eventually deaths in marine animals. Further, nurdles absorb toxins and harmful chemicals like persistent organic pollutants (POP) found in the air, and water. POP come from pesticides, toxins and other harmful chemicals. After nurdles absorb these toxic chemicals, they are eaten by fish and get passed on in the food chain. The toxin may eventually end up on our plates.

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What is the difference between an octopus and a squid?

Squids and octopuses are cephalopods, members that fall under the molluscan class Cephalopoda. But these aquatic invertebrates do not have shells. Their blood is blue due to the presence of copper in it, and they also have three hearts each. But octopuses and squids differ in their physical characteristics, habitat, and behaviour.

An octopus has a round head, while a squid's head is triangular in shape. Octopuses do not have any bone in their body, while squids possess a stiff structure known as a pen that acts as a flexible backbone. Octopuses do not have fins, while squids have two on their heads. Both have eight arms, but squids have two specialized tentacles in addition which are used to catch prey.

While octopuses live in the ocean floor, squids live in the open sea at various depths depending on the species. Octopuses feed on crustaceans on the sea bottom, while squids feed on shrimps and fishes. Usually, squids are larger than octopuses.

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How can crocodiles use ocean currents to travel longer distances?

Saltwater crocodiles enjoy "catching a wave" and can travel hundreds of kilometres by surfing on ocean currents. This current riding behaviour allows for the conservation of energy. Estuarine or saltwater crocodiles (Crocodylus porosus), found in Southern Asia and Australia, are the world's largest reptiles and can grow up to 5.5 metres in length.

Working at the remote Kennedy River in northeastern Australia, the team of scientists — which included the late Steve Irwin, "The Crocodile Hunter" — tagged 27 adult seawater crocodiles with sonar transmitters, employing 20 underwater receivers deployed along a 39-mile-long stretch of the river (63 km) to track the reptiles' every move for more than 12 months. They found both male and female adult crocodiles undertook long-distance journeys, regularly traveling more than 30 miles (48 km) from their home area to the river mouth and beyond into open sea.

The scientists also discovered the "salties" always began long-distance travel within an hour of the tide changing, allowing them to go with the flow. They halted their journeys by hauling out onto the river bank or diving to the river bottom when the currents turned against them.

The researchers originally were just aiming to investigate the territorial habits of the crocodiles and how they divvied up land among themselves.

Credit : Live Science 

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How do baby turtles communicate with each other?

Baby turtles make sounds to communicate with each other while still in the egg, to help synchronize when they hatch. Being able to coordinate hatching times is an important survival technique. If they all hatch together, there is a better chance that more of them will make it across the beach and into the water.

Researchers from Brazil, Mexico and the US got together to study the nests of 12 leatherback sea turtle nests in Oaxaca, Mexico. Starting on day 51, the point at which the babies's ears should be developed enough to hear sounds, they monitored the nests for any signs of noise. They immediately began detecting sounds, recording more than 300 different noises in total. They classified the sounds into four categories, including chirps, grunts and "complex hybrid tones," or sounds composed of two parts that they classified as pulse characteristics and harmonic frequency bands. 

That latter sound - the most complex of the bunch - was only recorded in nests that contained just eggs, rather than eggs and hatchlings (most had begun hatching by day 55). The baby turtles, the researchers believe, may be coordinating their hatching timing by emitting the sounds. This phenomenon has been observed in other animals ranging from birds to crocodiles, likely as a survival mechanism. In the case of the turtles, hatching en masse brings a certain strength in numbers. While some babies will be picked off by predators, a bird can only eat so many sea turtles at a time, meaning at least a few will make it to the sea. 

This finding, the authors point out, means that light pollution might not be the only anthropogenic nuisance threatening baby sea turtle survival. Noise pollution could be affecting them, too. 

Credit : Smithsonian 

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