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We tend to think of sharks as being ocean dwellers, although there are a handful of species that live in freshwater. But bull sharks can live in both ocean waters and also in fresh water rivers, estuaries, and lakes for some time. They can do this because of their own special ability to adapt the process of 'osmoregulation'. Osmoregulation is the ability of an organism to maintain a constant concentration of water in its body even when its outside environment would normally cause it to loose or gain water. Freshwater and saltwater fish both osmoregulate. But bull sharks can adapt their osmoregulatory processes to survive in a broad range of water salinities, from the salt water of the ocean to the fresh water of a lake.
In sharks, the normal mechanism of osmoregulation in a marine (salt) environment is the high concentration of urea and other biological solvents in their blood and the removal of excess salt from their bloodstream through urine. The former allows them to absorb water from their marine surroundings, while the latter rids them of the salt they continually absorb. These tasks are primarily controlled by the kidneys.
In most sharks, these adaptations cannot be changed. If they are put into a freshwater environment, they will absorb too much water relative to their concentration of bodily solvents and loose too much salt to stay alive. In other words, most sharks cannot survive in fresh water because they are not capable of adapting to it.
Bull sharks are unusual because they can adapt readily to fresh water because they can adapt their process of osmogregulation.with The kidneys of bull sharks, (and to a lesser extent several other types of sharks) can be gradually adjusted to suit the salinity of the water they are in. When moved gradually into freshwater (perhaps by migrating from the ocean, to an estuary, and then upriver), bull sharks' kidney's remove less salt and more urea from the bloodstream through urination, essentially reversing the normal marine shark method of osmoregulation. This adaptation allows bull sharks to live entirely in estuaries or freshwater.
Originally posted by iceblue20-12
Yep get bullsharks in the river here,not uncommon.
I surf a lot,live on the coast, this time last year i was attacked from underneath,knocked me off my board and put a big hole in the bottom,worst part was it was a brand new board.
When i took the board back to the shop they new what it was straight away!
A week earlier a bullshark came out of the water on top of a surfers board just near us,he punched it in the nose a few times,it left him alone long enough for him to get out,and all of us too!
Sharks here are just part of life for a surfer.
Originally posted by Silver Star
reply to post by KIZZZY
In the event of the polar icecaps melting, and us being up to our knees in water, then I would imagine that these versatile predators would make mincemeat out of us.
Adaptability really is the key for the survival of any species. The Bull shark has a lot of potential.
Originally posted by iceblue20-12
reply to post by KIZZZY
LOL,most surfers are prepared for come what may.The search for the perfect ride,the perfect wave out weighs being eaten!!
On the other hand i have also surfed with whales only a few meters away,Dolphins and very playful seals,a gift from mother nature that money cant buy.
Originally posted by SNAFU38
Originally posted by cloudbreak
reply to post by KIZZZY
Yep - fresh water doesn't mean safety unfortunately...bull sharks have also been a major problem in Brisbane, Aus. over the years. There are estimated to be more than 500 of them in the Brisbane river...periodically people's dogs get taken from the edge of the river, which is the middle of a metropolitan area
Not just Brisbane.
They have been found deep inland in NSW waters over the years also. Bull sharks just dont care, if theres food, they chase it. If there isnt food, they look for it.
People just have to remember, THEY own the water, we just visit. If someone is unlucky enough (or their dog) to be taken, dont blame the shark, we entered their territory.
I know some take it as surprising sharks arent just in the oceans, but they are everywhere. Aussies know that fact well, we love the water, but we know who owns it.
"It's hard to tell from the photos and video, but the initial reports estimate it to be 20 to 30 feet in length, but it's hard to confirm," said Dittmar. While Humpback whales are normally found in much deeper waters, this one was reported a quarter mile east of the shipping channel in 20- to 25-feet-deep waters.