Tuesday, September 7, 2010
Photograph by Brian J. Skerry
According to an article at the National Geographic website, two of the World's
most dangerous sharks (to humans) have been found in the Potomac River near Washington, D.C.! The species of shark which have been found is known as the "Bull Shark". To read about this discovery click on the following link:
Source of image: http://animals.nationalgeographic.com/animals/enlarge/bull-shark-shallow-water.html
According to the website:
"the Potomac has two sources. The source of the North Branch is at the Fairfax Stone located at the junction of Grant, Tucker, Preston counties in West Virginia. The source of the South Branch is located near Hightown in northern Highland County, Virginia. The river's two branches converge just east of Green Spring in Hampshire County, West Virginia to form the Potomac."
I did some research about Bull sharks online and discovered that Bull Sharks can be found in most freshwater rivers that empty into the sea or saltwater bays. This is most unusal for a shark as most sharks cannot tolerate being in fresh water.The bull shark is the best known of 43 species of elasmobranch (cartilaginous fish), in ten genera and four families to have been reported in fresh water.Elasmobranchs' ability to enter fresh water is limited because their blood is normally at least as salty (in terms of osmotic strength) as seawater, through the accumulation of urea and trimethylamine oxide, but bull sharks living in fresh water reduce the concentration of these solutes by up to 50%." (source:http://en.wikipedia.org/wiki/Bull_shark ).
A possible answer to the question of why some sharks live in Fresh water is that:
"If a typical sharks were to swim its very 'salty' body into fresh water, so much fresh water would diffuse into its tissues that the kidneys would have to work overtime in order to get rid of it all. This is a very energy-demanding process, and explains why most sharks do not enter fresh water: it's simply too much effort to keep excreting all that freshwater. But some sharks, such as the Bull Shark (Carcharhinus leucas), are able to enter fresh water for prolonged periods. They achieve this neat trick by greatly reducing their bodily concentrations of urea and TMAO. (Trimethylamine N-oxide)."
"Human skin is relatively water-tight, but fish skin in rather leaky. As a result, the bodies of most marine fishes are constantly losing fresh water to the surrounding sea. But all living things need a supply of water inside their bodies in order to function properly. What most fishes must do to restore the water their bodies need is drink lots and lots of seawater You've heard the expression, "Drinks like a fish"? Well, it's true: marine fishes drink seawater almost constantly. In order to get rid of the excess salt contained in the seawater, many fishes have specialized salt-secreting structures in their gills called "chloride cells". But sharks have hit upon a different strategy. Instead of being less salty than the sea, sharks store certain metabolic wastes (namely, urea and trimethylamine oxide, or TMAO for short) so that their overall 'saltiness' is actually slightly greater than that of the sea. As a result, sharks do not continually lose their bodily supply of freshwater to the sea. Instead, any fresh water they need diffuses gently into their bodies through the mouth, gills, and other exposed membranes. Any excess water in a shark's body is filtered by the kidneys and excreted out an opening called the 'cloaca', located between the pelvic fins (the rearmost paired fins, behind the shark's belly). It's a very elegant solution to a significant environmental challenge."
"Even so, a Bull Shark in fresh water is slightly saltier than its surrounding environment, so that it must continually excrete excess water in the form of dilute urine." (source:http://www.elasmo-research.org/education/topics/p_sharks_in_fresh.htm)
Fascinating! Here is a video which talks about the fact that a fisherman caught a
bull shark in the Potomoc: the fisherman gives an explanation for why the bull shark was found in the Potomoc.
source of video:( http://www.youtube.com/watch?v=2rGug1-5BwY )
Here is a video about Bull Sharks:
Here is a map which shows where the Potomoc River flowing into
Chesapeake Bay and then the Atlantic Ocean
ocean: (source: http://www.virginiaplaces.org/boundaries/graphics/capes.gif
Wow, it never ceases to amaze me how something we thought could not happen can happen in our World!
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Thoughts worth thinking about
Laws alone can not secure freedom of expression; in order that every woman and man present their views without penalty, there must be spirit of tolerance in the entire population.- Albert Einstein Too often we underestimate the power of a touch, a smile, a kind word, a listening ear, an honest compliment, or the smallest act of caring, all of which have the potential to turn a life around. - Leo Buscaglia
A person's true wealth is the good he or she does in the world. - Mohammed
Our task must be to free ourselves... by widening our circle of compassion to embrace all living creatures and the whole of nature and its beauty. -Albert Einstein
The best way to find yourself, is to lose yourself in the service of others. - Ghandi
The unselfish effort to bring cheer to others will be the beginning of a happier life for ourselves. - Helen Keller
Aim for success, not perfection. Never give up your right to be wrong, because then you will lose the ability to learn new things and move forward with your life. Remember that fear always lurks behind perfectionism. Confronting your fears and allowing yourself the right to be human can, paradoxically, make yourself a happier and more productive person. - Dr. David M. Burns
Life is as dear to a mute creature as it is to man. Just as one wants happiness and fears pain, just as one wants to live and not die, so do other creatures. -His Holiness The Dalai Lama
Mankind's true moral test, its fundamental test (which lies deeply buried from view), consists of its attitude towards those who are at its mercy: animals. And in this respect mankind has suffered a fundamental debacle, a debacle so fundamental that all others stem from it. -
Milan Kundera, The Unbearable Lightness of Being
The worst sin towards our fellow creatures is not to hate them, but to be indifferent to them. That's the essence of inhumanity. -George Bernard Shaw
Ego's trick is to make us lose sight of our interdependence. That kind of ego-thought gives us a perfect justification to look out only for ourselves. But that is far from the truth. In reality we all depend on each other and we have to help each other. The husband has to help his wife, the wife has to help the husband, the mother has to help her children, and the children are supposed to help the parents too, whether they want to or not.-Gehlek Rinpoche Source: "The Best Buddhist Writing 2005 pg. 165
The hostile attitude of conquering nature ignores the basic interdependence of all things and events---that the world beyond the skin is actually an extension of our own bodies---and will end in destroying the very environment from which we emerge and upon which our whole life depends.