From: "Saved by Windows Internet Explorer 8" Subject: Hammerhead sharks see the world in glorious 3D, sight tests reveal | Science | The Guardian Date: Tue, 9 Feb 2010 21:13:13 -0500 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0299_01CAA9CC.B0EA5450" X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18005 This is a multi-part message in MIME format. ------=_NextPart_000_0299_01CAA9CC.B0EA5450 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.guardian.co.uk/science/2009/nov/27/hammerhead-sharks-3d-sight-tests =EF=BB=BF
The wing-like heads of = hammerhead=20 sharks with their widely spaced eyes give the creatures excellent = binocular=20 vision
A scalloped hammerhead shark, one of the species = given sight=20 tests. Photograph: Stephen Frink/Corbis
The bizarre appearance of hammerhead sharks has led generations of = marine=20 biologists to ponder the same question: why the wide face?
Part of the answer may now be at hand. Eye tests on species caught = off the=20 coasts of Florida and Hawaii show that the wider the head the better the = shark's=20 binocular vision, and hence its perception of distance.
The fish are thought to have evolved their wide, wing-like skulls to = enhance=20 their sense of smell and ability to pick up electrical activity from = other marine = life, but=20 the latest study is the first to investigate the role eyesight may have=20 played.
"One of the things they say on TV shows is that hammerheads have = better=20 vision than other sharks, but no one had ever tested this," said = Michelle=20 McComb, a marine biologist at Florida Atlantic University.
Of the nine species of hammerhead shark, the aptly named "winghead" has = the most=20 pronounced cranial features, with a skull as wide as half its body = length. The=20 more inconspicuous bonnethead shark has the most narrow skull of all=20 hammerheads.
The scientists caught hammerheads and other shark species, such as = lemon=20 sharks and blacknose sharks, and transported them back to the laboratory = for eye=20 tests. During the examinations, a low-intensity light was swept = horizontally and=20 vertically across the eye of each shark, while electrodes picked up = electrical=20 activity from the fishes' retinas.
The researchers then worked out the size of the visual field for each = eye in=20 the different shark species. This revealed any blindspots, but also = highlighted=20 regions where the visual fields from each eye overlapped to produce = binocular or=20 3D vision.
The eye tests showed that the bonnethead shark had a modest 13 degree = overlap=20 in the visual fields of its eyes, while the winghead had an enormous 48 = degree=20 overlap, giving it a much broader field of 3D vision. The study appears = in the=20 Journal of Experimental = Biology.
"When we first started the project we didn't think that the = hammerhead would=20 have binocular vision at all," McComb said. "We were out there to dispel = the=20 myth."
You have 5000 characters left
Logged in as
=20
Loading...............
Closing this window without pressing "Report" will result in your =
words being=20
lost.
Are you sure?
Thank you
Sorry, something has gone wrong and this action cannot be completed.=20 Please try again later.
Very interesting report.
A few illustrations (particularly if they were interactive) would = have been=20 great to have.
Well, gosh, there's a surprise.
Now we need a report on why the sky is blue... or why policeman = wear pointy=20 hats.
@Thumper123
Obviously you did not read the article or you would have learnt = that there=20 are a number of, not necessarily mutually exclusive, theories on the = benefits=20 of those heads. Also thinking you know something and having the hard = data to=20 prove not only that you know it but how and to what degree of = confidence is an=20 entirely different thing.
Anyway, thankyou Guardian for that report. I have wondered about = what those=20 heads are for since I was small and used to get children's books on = marine=20 biology out of the library. I also knew someone who got slashed in the = leg by=20 a hammerhead while he was checking a set net in a muddy harbour in New = Zealand. Next we need to figure out why they congregate in huge = numbers* off=20 particular seamounts at particular times.
*but quickly before the shark fin fishers decimate them for a = tasteless=20 soup. I could cry with frustration.
I'm glad the tests finally confirmed what many believed. A = scientist -( LV=20 Compagno) based in Cape Town where I live hypothesised this in the = 80's if I=20 recall. I'm no physicist but I am curious as to why McComb wanted to = dispel=20 the binocular vision myth when it seemed pretty commonsense from an = angles /=20 field of vision point of view?
Good article. Kinda intresting to find out
Still looks silly =
even=20
though it can see better than the the common killing machine we call a =
shark
It's not a wing-like shape. If it were a wing-like shape, they = might=20 perhaps call it the wing-head shark. It's a hammer-like shape, thus a=20 hammerhead shark.
@muscleguy
I also knew someone who got slashed in the leg by a hammerhead = while he=20 was checking a set net in a muddy harbour in New = Zealand.
This is unlikely in the extreme. Hammerheads are not aggressive (in = fact=20 very shy), tend to stay deep (40m+) and are warm water sharks. NZ is=20 sub-tropical and the water is colder than their usual habitat. You're = more=20 likely to get hit by lightning than to get attacked by any shark, let = alone a=20 hammerhead.
I can't find the source right now, but I have read that there is = not a=20 single recorded attack anywhere in the world by a = hammerhead.
lindapalermo
It's not a wing-like shape. If it were a wing-like shape, they = might=20 perhaps call it the wing-head shark.
Ian Sample
Of the nine species of hammerhead shark, the aptly named "winghead" has the most pronounced cranial = features, with a=20 skull as wide as half its body length. The more inconspicuous = bonnethead=20 shark has the most narrow skull of all hammerheads.
i'm happy to see articles like this concerning the natural world = and of an=20 educational nature.
if we had more of this and less intellectually backward tripe like = BB and=20 X-Factor and countless murder shows, i am sure the world would be a = nicer=20 place.
as far as hammerheads are concerned RooBear, i'm unsure of the = species you=20 talk about but here in Eastern Australia they are commonly found in = warm=20 shallow water feeding on baitfish.
but if you're in the wrong place/time surfing or swimming for = example, the=20 story goes that they may mistake you for whatever, but this appears to = scotch=20 that myth.
"Dec 29 - 2002, Dutch tourist suffers lacerations after being = attacked by a=20 hammerhead at Apollo Reef off the far north Queensland coast."
rare, but it happens.
@Roobear
I am afraid you are wrong. For a start the shark was not being = aggressive,=20 he was only slashed iow an open mouthed pass. It was likely the shark = was=20 availing itself of the contents of the set net and perceived the guy's = actions=20 in drawing it in to check it as a threat. So far from being aggressive = it was=20 likely being defensive.
Anyway hammerheads congregate in large numbers around the Poor = Nights=20 Islands just off the other coast of Auckland. Also other supposedly = 'tropical'=20 sharks are found in NZ waters. The same harbour is noted for the = visitations=20 of thresher sharks and tiger and mako have been sport fished off the = Northland=20 coast. I'm not claiming those species are year round residents, they = are all=20 pelagic wanderers and go where the food is. The Manukau harbour is = also full=20 of rays and lots of fish. I used to fish there regularly as a = teenager. I=20 fought a long battle with a stingray off the tip of the Cornwallis = Peninsula=20 once before it broke the line for eg. I was a bit relieved as there = isn't much=20 room there at high tide and I didn't much fancy the prospect of = sharing it=20 with an angry stingray.
According to the International Shark Attack File site;
Hammerheads are considered potentially dangerous sharks. = According to the=20 International Shark Attack File, there have been 21 unprovoked = attacks with=20 2 resulting in fatalities for all species of the genus Sphyrna. = However, few=20 if any attacks can be directly linked with this species due to the=20 difficulty distinguishing species of hammerheads involved in = attacks. Due to=20 its large size and variety of prey, this shark should be treated = with=20 respect and caution.
It's not a wing-like shape. If it were a wing-like shape, they = might=20 perhaps call it the wing-head shark. It's a hammer-like shape, thus = a=20 hammerhead shark.
I think Winghead might be a more suitable name, considering the = head is the=20 shape of a wing. The head is not the shape of a hammer, the hammer = shape is=20 only completed when you look at the whole shark and the body forms the = "handle".
Thumper123
27 Nov 2009, 9:20AM
Well, gosh, there's a surprise.
Now we need a report on why the sky is blue... or why policeman = wear=20 pointy hats.
Pointy heads?
Those who can't grasp "winghead" should think F1 car, not=20 aircraft.
They are very shy, and very easily scared by humans. But I do know = someone=20 who was knocked off a surfboard by one, and saw the scar it left in = his=20 leg.
Thank you Guardian for posting an article of interest about sharks =
rather=20
than the usual "surfer bitten by shark" nonsense that only serves to=20
perpetuate the false "Jaws" stereotype. If you swim/ surf/ dive near =
sharks,=20
then you should know that you are potentially taking a risk if you =
don't=20
understand sharks. The ocean is not a swimming pool - respect it and =
respect=20
the animals that live there and you are less likely to get hurt.=20
http://www.stopsharkfinning.net
I'd be interested to know whether the 'wings' contribute anything = to the=20 shark's manoeuverability. As the eyes/electric sensors were moved = further and=20 further apart, the "stalks" presumably had to evolve to a low-drag = shape to=20 avoid impeding it through the water, but once it got to a certain = size, it=20 would have possibly enhanced the shark's ability to turn quickly, just = like=20 the canard planes on some aircraft. That advantage would have led to = even more=20 evolutionary pressure towards larger and wider wings, and maybe the = vision=20 advantage is actually secondary to this. I wonder if any studies have = been=20 done?
headfish
Spot on about Compagno, he did indeed theorize about hammerheads = and=20 binocular vision - but as I recall he had no experimental evidence. = This tends=20 to be the way science progresses, its pretty hard to prove things, but = you can=20 try to disprove them and if you can't, they're probably true. I = presume that=20 was what these guys did.
As for hammerheads being shy and avoiding people, I've always found = them to=20 be quite curious, but not very aggresive - they'll usually leave if = shooed=20 away. Like most sharks (and unlike most other fish) they're pretty = inteligent.=20 They probably can bite if it suits them, but I suspect that most of = the=20 injuries reported here were caused buy their skin, which is pretty = rough, and=20 covered in scales that are modified teeth.
Remember evolution goes in bursts. If the skull expands and conveys = predatory advantage probably though the detection of electrical = fields, where=20 would the eyes evolve to. Advantage to those with eyes with a clear = field of=20 vision ie at the end of the skull. Anywhere else and the eyes would be = not be=20 as useful and possibly redundant
The fish are thought to have evolved their wide, wing-like skulls = to=20 enhance their sense of smell and ability to pick up electrical = activity from=20 other marine life, but the latest study is the first to investigate = the role=20 eyesight may have played.
They haven't evolved that on purpose. I think evolution just =
changes=20
anything and
then the individuals won't die if it isn't too bad. =
But there=20
was surely no shark who said "I want to improve my eyesight by getting =
a wide=20
head."
So what is different about hammerheads that makes this head shape = an=20 advantage? Why would they, as opposed to other species need really = good=20 binocular vision? Is it their favoured prey? Habitat type? Is = binocular vision=20 to do with some social context rather than hunting? Lots of=20 questions...
Sorry, commenting is not available at this time. Please try = again=20 later.
Apologies, something has gone wrong and this action cannot be = completed.=20 Please try again later.
Please read our community = standards.
Loading...............
Closing this window without pressing "Post your comment" will result =
in your=20
words being lost.
Are you sure? =20
Thank you for your comment. This has been submitted for moderation. = =
Your comment has been successfully posted.
Sorry, something has gone wrong and this action cannot be completed.=20 Please try again later.
You have 5000 characters left
Logged in as
=20
Loading...............
Closing this window without pressing "Report" will result in your =
words being=20
lost.
Are you sure?
Thank you
Sorry, something has gone wrong and this action cannot be completed.=20 Please try again later.
Last 24 hours
Last 24 hours
Avoid excess baggage fees with this simple and accurate digital = luggage=20 scale by Salter.
From: =C2=A319.99
camfed international.
camfed is a fast-paced and award-winning=20 organisat=E2=80=A6.
Up to =C2=A330K + benefits.
womankind worldwide.
womankind worldwide are seeking two = programme=20 mana=E2=80=A6.
=C2=A331,260.
oxfam gb.
oxfam has extremely ambitious plans to grow = its=20 in=E2=80=A6.
=C2=A318,736 - =C2=A325,260 = pa.
Comments in chronological order (Total comment)