[paul.fr]

if yes, how? If not, what a stupid name.

[another_someone]

We all produce electricity, but too small an amount to normally be noticeable - electric eels merely make more of it.

EEGs and ECS are sensitive sensitive enough to detect electric fields generated in the human body, and sharks (I think the great white, but not exactly sure which other species) are capable of detecting the electric fields generated by muscle activity of its prey.

[DoctorBeaver]

The hammerhead is the shark with the most sensitivity to electrical currents. Their cephalofoil (the actual hammer) gives a wider field of reception. Thus, they are more easily able to home in on prey buried in the sea bed.

A hammerhead can detect an electrical current 50% farther away than a similar sized sandbar shark can.

A hammerhead can detect the electric field from a 1.5v battery at about ten yards. Their prey, however, produces a much lower current than an AA battery.

The sharks hunt by sensing two kinds of electric fields: the DC field that results from the osmotic potential between the prey's body tissue and seawater, and the AC fields generated by the contraction of the prey's muscles.

But back to electric eels. Here's some info...
http://hypertextbook.com/facts/BarryLajnwand.shtml

I hate to even hazard a guess as to how far away a shark could detect those!

[Alandriel]

Your facts about hammerheads abilities to detect electrical currents astonish me, Doc.

You'll laugh, but I've had several 'near miss' encounters with just such sharks (btw, wonderful creatures!) while diving where they nearly have run me over - no kidding. I believe in all cases they were just as 'astonished' as me when the incidents happened, not having noticed me until it was almost too late. Perhaps they were preoccupied with other matters as I was, looking for nudibranchs and other small creatures in the reef.

Makes me wonder..... also, just exactly how much of an electrical field does a human create?

[DoctorBeaver]

Your facts about hammerheads abilities to detect electrical currents astonish me, Doc.

You'll laugh, but I've had several 'near miss' encounters with just such sharks (btw, wonderful creatures!) while diving where they nearly have run me over - no kidding. I believe in all cases they were just as 'astonished' as me when the incidents happened, not having noticed me until it was almost too late. Perhaps they were preoccupied with other matters as I was, looking for nudibranchs and other small creatures in the reef.

Makes me wonder..... also, just exactly how much of an electrical field does a human create?

Sharks are amazing creatures. I've been fascinated by them for years. Did you realise that there are more than 360 different types of shark?

Wow... that must have been something, in the water with hammerheads! You're lucky to be in 1 piece as they are 1 of the most dangerous sharks to man (the tiger shark being the most dangerous).

[Alandriel]

Yeah.... never DID like tiger sharks, especially once they're doing their figure 8 thing (attack pattern) One once made me nearly run out of air - you never say a diver JUMP out of the water the way I did that day. Phew....!!!!!

More than 360 different species?!?! That's awesome but yes, I can immagine that such a successful species would adapt to many different environments whith many different 'modifications'.
The most awe inspiring sight I've personally ever seen was an oceanic white, a group of about 5 actually.
One feels very...... erm... fishfoody! LOL

But as to hammerheads being dangerous I must contradict you somewhat. I think their 'dangerousness' is in direct relationship of their enviroment. In the Red Sea and Baha California I've encountered many times and they were anything but 'dangerous' per se. They barely took notice of me e.g. as also in the example above. I'm sure however that during certain times of the year with changing cycles (e.g. mating, changing water temps etc) their behavior will alter considerably.

I've always been fascinated by them - any shark pretty much that is and unfortunately it was mostly me running after them with a camera and them running away (except that one tiger shark.... not pretty to see those teeth up close....)

[DoctorBeaver]

Unfortunately I have to contradict you in return. I think the hammerhead is about No6 in the ranking of sharks most dangerous to humans. I know the white is No1. I think the others are tiger, bull, sand tiger & blacktip. I'll check it out.

[DoctorBeaver]

Of course, the white & tiger are cousins - as is the mako (mackerel) shark. All 3 have jaws that move forward as they bite so that the teeth protrude. That means they are biting in front of themselves rather than underneath, as is the case with most sharks.

[DoctorBeaver]

hmmm, I'm puzzled. According to The International Shark Attack File the hammerhead is No7. It gives No6 as the requiem shark - and that's what puzzles me. I always thought requiem was a grouping, not a specific species. I've always known lemon sharks, white tips, tigers,  Caribbean reef, Galapagos & grey reef (among others) to be requiem sharks.

I need to investigate this  []

[Alandriel]

I've had a look at the International Shark Attack File website.

Did you knolw that they have no data about any attacks in the Red Sea?

Hammerheads and other species might be 'dangerous' in other waters. I personally think that overall sharks have an undeserved 'bad reputation'. It's human stupidness / unawareness that's to blame.
Sharks only become 'dangerous' to man when environmental / seasonal conditions are condusive for attacks ~ those rarely exist in the Red Sea (or Baha California) and hence divers can swim quite happily with them. When conditions however are condusive and humans do get in the way (knowingly or not) then they're obviously in for trouble. Better public awareness and less hype would be nice.

I'm going to go trawling to find some facts and figures to back my opinion up - hopefully   []

[DoctorBeaver]

I would imagine that if there is a plentiful supply of reasonably-sized prey then hammers would be less hungry &, hence, less likely to attack humans. I don't know about the marine fauna in the Red Sea or Baja (although I believe there are some interesting Humboldt squids around Baja - maybe the sharks eat them.).

Then again, that's probably rubbish because hammers & threshers are just about the biggest danger in the Pacific, Indian Ocean, China Sea and other places in that area, and there's plenty of large prey there.

Where's our resident marine biologist when we need her!?  [!]

[Alandriel]

We have a resident marine biologist?  [8D] Hope to meet her / him.  []

Meanwhile......

Why do Scalloped Hammerheads school?

No one is sure why Scalloped Hammerheads school. We know that many sharks school at the youngest and most vulnerable stage of their lives. But Scalloped Hammerheads in the Sea of Cortez also school as adolescents and adults, when they have few predators. In the Sudanese Red Sea, however, Scalloped Hammerhead schools feature juveniles at the core with adults cruising the periphery like a protective wagon train in a Western movie.

Some researchers suspect that Scalloped Hammerheads may school as a prelude to mating, but in the Sea of Cortez the schools are composed mostly of adolescent females. However, an underwater cinematographer once filmed a pair of Scalloped Hammerheads copulating in the Sea of Cortez, the sharks locked together and falling to the seabed in graceful slow-motion.

The most likely reason Scalloped Hammerheads school in the Sea of Cortez is "refuging": the seamounts serve as meeting places conveniently near a rich food supply. It is likely that the schooling Scalloped Hammerheads use the seamounts as a conspicuous undersea landmark, taking advantage of opportunities to interact socially until nightfall, when the schools break up to feed.

Are Scalloped Hammerheads dangerous to humans?

Scalloped Hammerheads are not particularly dangerous to humans unless they are provoked in some way, such as by chasing, spearing, or touching them.

ReefQuest Centre for Shark Research

That's the only ref of hammers in Red Sea / Baha I've come up with so far.

There is This study that talks about increased hammerhead acitivites during seasonal 'upwellings' in the Gulf of California

.... more digging later.....

[edited to fix tags]

[DoctorBeaver]

Interesting. Thanks for that.