SHARK!

[lady cop]

as a lifelong SCUBA diver and erstwhile underwater photographer, i am quite interested in sharks. and since we have Aussies here (any South Africans?) i would really enjoy discussing sharks, myths, attacks, conservation of species, legends, anything shark-related. why are they the stuff of nightmares? what about the proliferation of silly movies after "JAWS"? did it affect you? i like them, most species don't want to eat you, then again they touch a primitive chord in many of us. an involuntary shiver up the spine when encountering one. :shark: :shark: :shark: :shark:

[LadyShea]

I think that something in our primitive brains recognizes the perfect predator. A great white with its rows of triangular teeth and torpedo like body is just that.

In museums, you can see the jaws of prehistoric sharks large enough for a group of people to stand in...scary and fascinating.

[lady cop]

yes...megalodon...80 feet long according to the size of fossilized teeth found. sure would provoke a visceral response! i think it goes to the ancient fear of being EATEN. we are the top of the food chain with a few exceptions.

[viscousmemories]

JoeP and Farren are both in S. Africa. I don't know anything about sharks except what I've gleaned from movies like Jaws and the occassional shark attack report I've heard, like Bethany Hamilton (http://www.cbsnews.com/stories/2003/11/03/national/main581410.shtml), the 13 year old competitive surfer who got her arm bitten off two years ago. As a result I have a fear of sharks, but I've never really been in the ocean anyway, so it's not a fear that restricts me much. They are very cool fish, though.

[LadyShea]

I was addicted to Discovery channels shark week. Shark attacks are rare, but headline garnering when severe, which adds to the overall fear factor.

[godfry n. glad]

I understand sharks have to keep moving in order the breathe.

There are lots of different kinds of sharks, too. Most of them are of little risk to humans.

[lady cop]

I understand sharks have to keep moving in order the breathe.

There are lots of different kinds of sharks, too. Most of them are of little risk to humans.
it is my understanding that all sharks, like all fish, have to keep moving to keep oxygenated water flowing through their gills, one exception is the innocuous nurse shark who just lays there on the bottom. i see a lot of them in the keys. one thing we do get in caribbean waters is the grey reef shark...they are quite aggressive, you need to be smart enough not to keep speared bloody wriggling fish in your hand, i have known a few divers to lose a hand that way. :snorkel:

[Ymir's blood]

Shouldn't this be in the food forum? :chin:

[JoeP]

No South Africans here. Nope. :chicken2: :chicken2:

I'm hardly a "lifelong" scuba diver and have never encountered a shark underwater (only with thick plate glass between me and it). Many divers go specifically to meet ragged-tooth sharks (http://encarta.msn.com/media_461544307_761552860_-1_1/Ragged-Tooth_Shark.html) (raggies (http://www.wavescape.co.za/top_bar/tidings/Sharks/raggie.html)).

There are some attacks. A 78-year-old woman was killed (http://www.news24.com/News24/South_Africa/News/0,,2-7-1442_1621944,00.html) by a great white late last year in Cape Town, generally regarded as less of shark threat area because of the colder water than on the Natal coast.

Most Natal beach holidaymakers assume the beaches are protected by shark nets, but I think this is quite patchy. I've heard of an electric wire system for repelling sharks, but afaik it's only used in Australia. some details (http://news.nationalgeographic.com/news/2002/06/0603_020604_shark2.html)

Sharks have to keep swimming because they have no swim bladder (http://en.wikipedia.org/wiki/Swim_bladder), unlike most bony fish, and would otherwise sink. All fish have to keep water moving past their gills, but they do this by sucking water in through their mouths and expelling it past the gills.

As ever, wikipedia (http://en.wikipedia.org/wiki/Shark) is a good starting place: Until the late 16th century sharks were usually referred to in the English language as sea-dogs. The name "Shark" first came into use around the late 1560s to refer to the large sharks of the Caribbean Sea, and later to all sharks in general. The name may derive from the Maya language word for shark, xoc, pronounced "shock" or "shawk".

... What was the question again? :wink:

[Weaselboots]

I've only ever seen one while in the water. Spent some time camping on a island in the Barrier Reef, with a uni SCUBA Diving club. I was snorkling at the time, and it swam beneath me. I think it was only a Reef Shark, but it still gave me the heebies. We lured a few big guys with fish bits to the side of the Zodiac. They are amazing critters.
I've heaps of Wobbegongs and Port Jackson Sharks while diving in Sydney Harbour....no real danger, just don't stick ya hand in thier mouth.
Just before christmas a 18 year old and a 29 year old were killed in separate incidents.

In 200 years, there have been a total of 548 recorded attacks in Australia — 182 of them fatal.
http://www.deh.gov.au/coasts/species/sharks/

Not many considering the amount of time we spend in the water.

[ceptimus]

There are plenty of sharks all around the UK, but the water is so murky that you hardly ever see them.

I think the bull shark is especially pretty, though it is one of the more aggressive species.

[The Lone Ranger]

I don't know anything about sharks except what I've gleaned from movies like Jaws ...

Fortunately, there's nary a grain of truth in Jaws. (Peter Benchley once claimed that if he'd actually known anything at the time about shark behavior, he'd never have written Jaws.)



Sharks have to keep swimming because they have no swim bladder, unlike most bony fish, and would otherwise sink. All fish have to keep water moving past their gills, but they do this by sucking water in through their mouths and expelling it past the gills.


As JoeP points out, sharks lack a swim bladder to give them positive bouyancy. They partially compensate by having a large, oil-filled liver. Even so, sharks are (slightly) denser than water, so they'll sink if they stop swimming.

Fishes that have an operculum covering the external gill openings can create negative pressure and draw water in through their mouths and over their gills to breathe. (They close the operculum and open the mouth -- this draws water into the mouth and throat -- then they close the mouth, open the operculum, and compress the throat cavity -- this forces the water through the gills.)

The vast majority of sharks lack opercula covering their external gill openings, and so must indeed move forward in the water with their mouths open, so that water flows into their mouths and through their gills. (This is sometimes called "ramjet breathing.") Some sharks have been found lying on the ocean floor and facing into currents with their mouths open -- in this way, they can breathe without having to constantly swim.

A handful of shark species, including the nurse shark, are capable of actively pumping water through their gills as bony fishes* do, and so don't need to swim (or find a convenient current) in order to breathe.


*As I'm sure most people know, sharks' skeletons are made of cartilage, not bone, so they're classified as "cartilaginous fishes" (Chondrichthyes). Fishes such as tuna, bass, etc. have bony skeletons and so they're classified as "bony fishes" (Osteichthyes).

By the way, contrary to myth, sharks do indeed get cancer. (So if someone tries to sell you "shark cartilage" as a means of warding off cancer, s/he is a huckster.)


Cheers,

Michael

[Goliath]

Boy, the sharks that I've seen! Lemme tell ya, the sharks of the Dakotas are some of the most vicious, fierce creatures you've ever seen! :D

Okay, in reality, the only shark that I ever saw was a nurse shark in an aquarium at a pet shop many years ago, and I caught my first actual glimpses of an ocean less than a year ago.

[godfry n. glad]

mathshark

[Sycophant]

I encountered a 4-5ft reef shark last year while I was snorkling in Fiji (serves me right, I was supposed to be working) -- I was somewhat freaked, but it seemed completely uninterested in me.

Also I used to jump of a wharf when I was a kid that was reputed to be a breading ground for sharks. Never saw any there. But I did see one swim past once when I was one a pontoon near the wharf,

Also, for good measure, here is a story from today's NZ Herald:
A golden day that not even sharks could spoil (http://www.nzherald.co.nz/index.cfm?c_id=1&ObjectID=10007815)

[Desert Dweller]

Just before christmas a 18 year old and a 29 year old were killed in separate incidents.
From memory these were both great white sharks...the archetypal predator. The question is however why were great whites so close to shore? The answer lies in the diminuition of food in the oceans. The real predators are the long line tuna fishing boats which let out miles (literally ) of baited line. Also incursions from SthAmerica inter alia into the southern oceans.
Closer to shore the coastal shark is in danger of extinction due to over fishing by amateur fishermen... they are now a protected species in Australian waters.
As Weaselboots correctly pointed out the deaths from shark attacks are greatly over-rated.
Some attacks have been known to occur during burling (throwing food scraps and blood into the water to attract sharks).
A new species recently discovered here...but like the wobbegong...lives deeper in the ocean though.

[The Lone Ranger]

I've always liked thresher sharks (http://www.worldshark.com/species/thresher/images/thresher1.jpg) myself. They've been observed using the very long dorsal half of the caudal fin to stun potential prey. They're also one of several shark species (great whites are another) that can maintain a body temperature significantly higher than that of the surrounding water.

Cheers,

Michael

[lady cop]

god i love this topic and have about 37 stories... but for now, as an aside, i watched DVD "open water" today", two divers stranded in shark-infested waters. it was not only a crashing bore, but do you remember hand-held camera in "blair witch" and how nauseating it was to watch? this thing was at water level and it made me SEASICK from the constant rollers! *BARF*

[viscousmemories]

Oh thanks for warning me. I was wondering if that movie was any good.

I can imagine the Blair Witch effect you describe, but I never saw that either...

[lady cop]

remind me to talk about the USS iNDIANAPOLIS, matawan creek in new jersey incident , and schooling hammerheads in the keys and how a northern kid ran all the way home after a hammerhead drove him up on a sandbar on his jetski , snapping at his ankles and blew his mind. hey, anything to get rid of the jetskis. i was lobbying for shooting them . :D

[Shake]

Just don't jump the shark (http://www.jumptheshark.com/)! :D

[godfry n. glad]

hey, anything to get rid of the jetskis. i was lobbying for shooting them . :D

Jetskis? I would stand in the way of passage of any such legislation. At least until snowmobiles are included.

Open season!!!

[Weaselboots]

i watched DVD "open water" today", two divers stranded in shark-infested waters.

I haven't seen the movie, but it was based to true life events up in Queensland in 1998. Two American divers were left behind on the Barrier Reef by the boat. I can't imagine anything worse.

http://www.michaelmcfadyenscuba.info/articles/lonergan.htm

http://www.cdnn.info/industry/i040523/i040523.html

[lady cop]

Weaselboots, thanks for links! i was curious about the real story. i was interested also in the suspicion that the whole scenario was staged. not credible on several levels. where could they find a dive operation complicit in such a plot? but...a few years ago in the keys we had a 'disappearance' of a diver with a chewed-up wetsuit later being found. and the DAY AFTER the wetsuit was found the 'victim's' mother was at key west courthouse trying to have him declared legally dead! there has NEVER been a fatal shark attack in keys waters. i think that guy did perpetuate a hoax for insurance monies. and is in the bahamas somewhere.

[Desert Dweller]

i think that guy did perpetuate a hoax for insurance monies. and is in the bahamas somewhere. I suspect that's right...remember that story at the time; there were oddities then. More danger from box jellyfish there than sharks.