Native Americans of the Great Plains thought the light display came from northern tribes who were cooking their dead enemies in huge pots over blazing fires. They carried knives to protect themselves from it. In Estonia, one legend said the lights appeared when whales were playing games. Another said they were sleighs taking guests to a spectacular wedding feast. Fishermen in northern Sweden took the lights as a good prophecy, believing they were reflecting large schools of herring in nearby seas. If you whistled at the aurora , some Native Americans believed it would sweep down and take you away.
Clapping your hands, however, caused the lights to retreat, keeping you safe. Meanwhile, in northern Scandinavia, the Sami people hid indoors during the light show. Call Repeater Layout : vertical-2up. Northern Lights Photography Tour. New Itinerary! Northern Lights Photography Tour Photograph the northern lights from one of the most aurora-active spots on Earth on this small-group winter encounter with the Canadian North.
Travel Stories. Get Weekly Updates Our weekly eNewsletter highlights new adventures, exclusive offers, webinars, nature news, travel ideas, photography tips and more. Get Weekly Updates. All elasmobranchs have a rectal gland which functions in the excretion of excess salts accumulated as a consequence of living in seawater.
Bull sharks in freshwater environments decrease the salt-excretory activity of the rectal gland, thereby conserving sodium and chloride. Bull sharks caught in freshwater have subsequently been shown to have lower liver densities than sharks living in marine waters. This may reduce the added cost of greater negative buoyancy. Bull sharks are able to regulate themselves to live in either fresh or salt water.
It can live in fresh water for its entire life, but this does not happen, mostly due to the reproductive needs of the shark. Young bull sharks leave the brackish water in which they are born and move out into the sea to breed. Whilst it is theoretically possible for bull sharks to live purely in fresh water, experiments conducted on bull sharks found that they died within four years. The stomach was opened and all that was found were two small, unidentifiable fishes.
The cause of death could have been starvation since the primary food source for bull sharks resides in salt water. In a research experiment, the bull sharks were found to be at the mouth of an estuary for the majority of the time. The driving factor for a bull shark to be in fresh or salt water, however, is its age; as the bull shark ages, its tolerance for very low or high salinity increases.
Initially, scientists thought the sharks in Lake Nicaragua belonged to an endemic species, the Lake Nicaragua shark Carcharhinus nicaraguensis. In , following specimen comparisons, taxonomists synonymized them.
The bull shark's diet consists mainly of bony fish and small sharks, including other bull sharks,  and stingrays. Their diet can also include turtles, birds, dolphins, terrestrial mammals, crustaceans , and echinoderms. They hunt in murky waters where it is harder for the prey to see the shark coming.
After the first initial contact, they continue to bite and tackle prey until they are unable to flee. The bull shark is a solitary hunter, though may briefly pair with another bull shark to make hunting and tricking prey easier. Sharks are opportunistic feeders,  and the bull shark is no exception to this, as it is part of the Carcharhinus family of sharks.
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Normally, sharks eat in short bursts, and when food is scarce, sharks digest for a much longer period of time in order to avoid starvation. This is a distraction tactic; if the predator moves to eat the regurgitated food the bull shark can use the opportunity to escape. Bull sharks mate during late summer and early autumn,  often in freshwater  or in the brackish water of river mouths.
After gestating for 12 months, a bull shark may give birth to 1 to 13 live young. They are viviparous , born live and free-swimming. The bull shark does not rear its young; the young bull sharks are born into flat, protected areas. The male bull shark is able to begin reproducing around the age of 15 years while the female cannot begin reproducing until the age of 18 years.
The courting routine between bull sharks has not been observed in detail as of yet.
Researchers, who surveyed the aquifer with electromagnetic waves, say the deposits are more or less continuous, starting at the shoreline and extending far into the continental shelf. Normally, sharks eat in short bursts, and when food is scarce, sharks digest for a much longer period of time in order to avoid starvation. This Gulf sturgean weighed 85 pounds, but they can reach hundreds of pounds and possibly 1, CW: It seems like young adult books are much more popular now than they were when I was younger. Think the iPhone 11 is too pricey? The bull shark's diet consists mainly of bony fish and small sharks, including other bull sharks,  and stingrays.
The male likely bites the female on the tail until she can turn upside down and the male can copulate at that point. At some points, the harassment of the male can become violent. Seeing scratches and other marks on a mature female which may be from the mating ritual is not uncommon.
Bull sharks have an unusual migratory pattern in comparison to other sharks. They are found in rivers all over the world. They give birth in the fresh water of rivers. The young bull sharks are free from predators while they grow up in the river before they go out to the sea to find mates. The ability to be able to survive in both fresh and salt water also gives another benefit that has been driven by evolution.
Because the majority of sharks are only able to survive in salt water, the bull shark has evolved to have their offspring in the fresh water where other sharks cannot enter.
Since bull sharks often dwell in very shallow waters, are found in many types of habitats, are territorial by nature, and have no tolerance for provocation, they may be more dangerous to humans than any other species of shark. One or several bull sharks may have been responsible for the Jersey Shore shark attacks of , which were the inspiration for Peter Benchley 's novel Jaws. Bull sharks have attacked swimmers around the Sydney Harbour inlets.
Many of these bite incidents were attributed to the Ganges shark , Glyphis gangeticus , a critically endangered river shark species, although the sand tiger shark was also blamed during the s and s. The bull shark prefers coastal water, which is less than feet in depth. This is mostly due to their feeding patterns, since they prefer murky waters.
This is also a problem, since this gives them the most interaction with humans. It is known that bull sharks inhabit areas off the coast of Florida, and there have been reports of bull sharks getting close enough to the coast to bite humans, since the bull shark is a territorial animal, which encourages aggressive behavior.
Behavioral studies have confirmed that sharks can take visual cues in order to discriminate between different objects. Bright yellow mesh netting was found to be easily avoided when it was placed in the path of the bull shark. This was found to be the reason that sharks are attracted to bright yellow survival gear rather than ones that were painted black. In , researchers tagged and recorded the movements of young bull sharks in the Caloosahatchee River estuary.
They were testing to find out what determined the movement of the young bull sharks. The movement was found to be directly related to the bull shark conserving energy for itself. One way the bull shark is able to conserve energy is that when the tidal flow changes, the bull shark uses the tidal flow in order to conserve energy as it moves downriver. Bull sharks have no natural predators in the wild, in fact humans are their biggest threat. Larger sharks, such as the tiger shark and great white shark , may attack them, typically only targeting juveniles however.
Saltwater crocodiles have been observed preying on bull sharks in the rivers and estuaries of Northern Australia ,  and a Nile crocodile was reported as consuming a bull shark in South Africa. From Wikipedia, the free encyclopedia. Species of fish.
Conservation status. Play media. Sharks portal. Retrieved 23 December In-Fisherman 16 July Retrieved on 30 November Florida Museum of Natural History. Retrieved 8 September National Geographic. Retrieved 3 April ReefQuest Centre for Shark Research. Retrieved 19 August Australian Museum. The Shark Almanac. New York: The Lyons Press.
Marine and Freshwater Research. The proportion of mature males with running spermatozoa increased from 7.
Elasmobranch biodiversity, conservation, and management: Proceedings of the international seminar and workshop. Shark Diver Magazine. Archived from the original on 15 February Retrieved 10 November Total Pro Sports. BBC News.