My Science School

Blue whales are the largest animals ever to live on our planet. They feed almost exclusively on krill, straining huge volumes of ocean water through their baleen plates (which hang from the roof of the mouth and work like a sieve). Some of the biggest individuals may eat up to 6 tons of krill a day.

Blue whales are found in all oceans except the Arctic Ocean. There are five currently recognized subspecies of blue whales.

The number of blue whales today is only a small fraction of what it was before modern commercial whaling significantly reduced their numbers during the early 1900s, but populations are increasing globally. The primary threats blue whales currently face are vessel strikes and entanglements in fishing gear.

Blue whales sometimes swim in small groups but are more often found alone or in pairs. They generally spend summers feeding in polar waters and undertake lengthy migrations towards the equatorial waters as winter arrives.

Blue whales typically swim at about 5 miles an hour while they are feeding and traveling, but can accelerate to more than 20 miles an hour for short bursts. They are among the loudest animals on the planet, emitting a series of pulses, groans, and moans, and it is thought that in the right oceanographic conditions, sounds emitted by blue whales can be heard by other whales up to 1,000 miles away. Scientists think they use these vocalizations to communicate and—along with their excellent hearing—perhaps to sonar-navigate the dark ocean depths.

The primary diet of blue whales is krill—tiny shrimp-like animals, but fish and copepods (tiny crustaceans) may occasionally be part of the blue whale’s diet. When blue whales hunt for food, they filter feed by swimming toward large schools of krill with their mouth open and closing their mouths around the krill while inflating their throat pleats. Once closed, blue whales then push the trapped water out of their mouth with their tongue and use their baleen plates to keep the krill trapped inside.

Credit : NOAA Fisheries 

Picture Credit : Google

Blue whales are the largest animals ever to have lived on Earth. They can grow to a length of 30 metres and weigh 173 tonnes. Also among the loudest animals on the planet, the blue whale can make a range of sounds to communicate with others of the species hundred miles away and to navigate.

Now, scientists have determined how much energy species of different sizes invest to capture their prey and which of these species reap the greatest rewards for their efforts. To do so, they gathered data from hundreds of feeding whales.

The results demonstrated that the availability of their prey limits that body size in all whales, but only filter-feeding whales have evolved a feeding strategy that helps them to achieve the largest body sizes to have ever evolved on Earth.

Scientists obtained the data for their study after seeking and tagging whales, porpoises, and dolphins of various sizes—from 5-foot-long harbor porpoises to gigantic blue whales. They also tracked animals’ underwater activities using multi-sensor tags, which were temporarily affixed on animals’ backs via suction cups, reaching from their boats with long poles to stick.

Credit :  Tech Explorist 

Picture Credit : Google

The tench is a large, hardy olive green-coloured fish native to Europe. Found in lakes and rivers, its skin secretes a lot of slime. Also known as doctor fish, its slime is believed to have healing properties. The slime was once used on humans to treat wounds.

Tench prefer shallow lakes, rivers, and backwaters with a great deal of vegetation. In some parts of the world, they spend the winter buried in mud.

To find food, the tench uses short sensory organs that protrude from each side of its mouth, called barbels, to search the river or lake bottom for snails, mosquito larvae, and other small creatures. Tench also eat detritus, algae, and plant matter.

Male tench reach maturity at around two to three years old, females about a year later. That happens in late spring or summer when the female releases her eggs every 15 days or so until the temperature cools. She does this near plants so that the sticky eggs attach to the vegetation. One or two males will swim by and release sperm. Once the eggs hatch, the larvae stay attached to the plants for several days before swimming off.

In Europe, tench are threatened by the alteration of waterways and other kinds of river engineering.

Credit : National Geographic

Picture Credit : Google