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  Topic: Sharks, and why some of us are interested in them.< Next Oldest | Next Newest >  
Renier



Posts: 276
Joined: Jan. 2006

(Permalink) Posted: June 21 2007,04:13   

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... most of the attacks in fresh water suggest they really are hunting for food.  Could be a case of mistaken identity, but again, a lot of those attacks involve multiple bites.  Some have suggested they are more aggressive in fresh water, but I also don't buy that, as it just seems more likely to me that where these attacks occur in freshwater, there is simply a lot higher concentration of people actually in the water, so you get a higher frequency of attack.


I agree. Rural Africa, for instance, has a lot of villages next to the big rivers. These people don't have access to fresh water and thus bath and swim in the rivers very often. I don't know what the ratio is to say holiday makers (swim, surf etc.) along the warm water coasts.

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yeah, again, they didn't know where the shark was.  I've seen many videotapes of dives where when the divers could see where the shark was, and turned to face it, the shark would go into circling behavior instead of attack behavior, and often would move off.


I'll keep that in mind if ever I encounter one of the big Whites on a dive. All brave now, but I reckon I'll just crap myself an island and go sit on top of it :-) I do however carry a power head just in case. I suppose it wonít really help if a shark is bent on munching me, but it does at least give one a greater sense of ability to defend oneself.

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sharks aren't invulnerable; especially ones that feed on large prey items like elephant seals.  We've seen whites with missing eyes and huge numbers of scars on occasion.  Even one missing eye can put a serious damper on prey location.  of course nothing is absolute, and while we often see whites hit once (hard) and then circle to allow for ensanguination, we also infrequently see them just going all out and chomping the prey to bits in rapid fashion.


I noted that many sharks close their "eyelids" when they start to bite a pray. Obviously to protect the eyes from injury. Whites however don't close their eyes, but rolls them back. This seems a less effective way of protecting the eyes? Another fascinating thing. If you have bait in the water and a White closes in to munch it then it rolls it's eyes back just before it bites the bait. However, at the last moment before contact with the bait, the Whites often turn their heads away and bites a metal part of the boat. The conclusion was that at the last moment, when the eyes are rolled back, the White uses those electric sensors on the nose to guide it towards the prey, and thus confuses the metal parts of the boat as prey/bait. Is this correct?

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Mako's typically feed on large pelagic fishes, but again, sharks being typically opportunistic, I've seen video of them feeding on marine mammals as large as full-grown bottlenose dolphins.  Amazing stuff - they would hit the tail of the dolphin full-speed to immobilize it and cause severe ensanguination, then come back to feed on it.


My grandfather was a fulltime fisherman (boat) at an early stage of his life. One day they were catching fish when all of a sudden a big shark jumped out of the water and landed in the boat. It knocked two people clean out of the boat and got its head stuck under one of the wooden benches. Of course, the crew got a helluva fright and promptly proceeded to calm the shark down... with nice big wooden batons and some spicy fisherman words. It worked. They killed it thinking the shark tried to grab one of them clean out of the air. I had a newspaper clip that showed the jaw. From left to right it was about 40-50cm. The newspaper had it down as a "Blue shark" but it was clearly the jaw of a mako. They had strange names for different sharks and fish in those days. Why do makos do that? Why do they jump out of the water and often attack boats? I think Whites are also known for such behavior?

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We know even less about mako behavior than we do about whites, mostly because they're pelagic, and large ones might be almost as rare these days as whites (they are a great food and sport fish, and so many have been taken by the longline and gill net fisheries that large ones have become quite rare).


Itís a sad thing. This whole shark fin soup stuff just makes me really angry and sad. To cut off a beautiful creature like that's fins and just leave the innocent dying animal. For friggen soup! Wonder who the REAL "murder" machines are. Don't think it's the sharks.

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A friend of mine has been studying a close relative, the Salmon Shark (Lamna ditropis) for some time now.


Never heard of it, but thanks for the tip. I'll trace down some info on distribution, behavior etc.

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yes, there has been some work on this area, and I have those references, but not ready to hand.  give me a couple of days to dig them up for you.  They do belong to the same family:  Lamnidae.  However, I recall a tremendous amount of controversy surrounding whether the linneages are actually based on a common ancestor.  also a lot of controversy around whether megalodon is actually an ancestor of carcharias or not, which is related to the same issue.


I would appreciate any info on this. It freaks me out. Makos look like Great Whites, but have teeth just like Raggies. Their type of teeth (grabbing teeth) forces them to catch smaller prey, yes? I assume that cutting teeth, like Whites, are useful when you are hungry and there is a nice juicy, pickled whale carcass floating around.

I don't believe them, but there were rumors about Megalodon not being extinct but alive and well in certain (human isolated) spots on Earth. Do you know anything about this and if there is any substance to these claims?

Did you ever encounter one of those "cookie-cutter" sharks? We don't have any over here, as far as I know. I saw a documentary that showed some seals with weird bite marks (think it might have sparked the Megalodon theory). Apparently, these cookie-cutter sharks swim up to a seal, bites a chunk out and then swims away (Drive-thru style). I would hate meeting one of those under water - wet suits are expensive!

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personally, i think the data from the long term studies of the sharks based on the satellite tagging and behavioral ecology programs will yield better results for long-term conservation than cage dives ever would.


You made some valid points. I'll read up on it, thanks for the info. "satellite/gps tags". Geez, I never knew that type of technology was being used. It's awesome. I should tag my kids with some...

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I suppose I can relate my tiny shark experience here, just FYI. Even in the UK we get sharks, where I am from originally (Dorset coast) we get two species: Porbeagle sharks and Basking sharks.


The basking sharks scare the surfers over here. What, they grow up to 12 meters I think?

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I'm not sure of the distance comparison, not brushed up on my metric system sad to say, but bulls have traveled up the Mississippi in the US as far as Illinios and I remember swimming in the Miss. and the Ohio many times during my younger days with never a thought that a shark may be cruising by.


Never even imagined the Mississippi had Zambezi/Bull sharks. Interesting.

Ichthyic, another question. Just to check up on a rumor. I heard that there are records of Whale Sharks hunting tuna somewhere in, I think, The Gulf of Mexico. Do you know anything about this offhand? I was under the impression that they are strictly filter feeders. Did any of you ever read Thor Heyrdahl's Kontiki expedition? There is some really freaky stuff in there, like the thing that munched the one bloke's sleeping bag.

  
  102 replies since June 11 2007,16:55 < Next Oldest | Next Newest >  

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