Not just a
huge collection of
Elasmodiver.com contains images of sharks, skates, rays, and a few
chimaera's from around the world. Elasmodiver began as a simple web
to help divers find the best places to encounter the different
species of sharks and rays that live in shallow water but it has
slowly evolved into a much larger project containing information on
all aspects of shark diving and shark photography.
now more than 10,000 shark pictures and sections on shark
evolution, biology, and conservation. There is a large library of
reviewed shark books, a constantly updated shark taxonomy page, a
monster list of shark links, and deeper in the site there are
numerous articles and stories about shark encounters. Elasmodiver is
now so difficult to check for updates, that new information and
pictures are listed on an Elasmodiver Updates Page that can be
isn’t easy to find a ghost shark. Most hide in the eternal darkness hundreds
of meters below the thin slice of ocean that we generally visit. But, along
the shorelines of Puget Sound and British Columbia, one species regularly
materializes out of the gloom to the delight of surprised scuba divers.
Ratfish (Hydrolagus colliei) are not really reef dwellers. They forage
for food in the sand and mud so the best way to get a close look at one is to
swim out onto the sand flats at night where they can be seen flapping around,
mouth slightly agape, sifting through the silt in search of clams and small
crustaceans. When caught in the beam from a diver’s flash light, their ghostly
silhouettes shimmer metallically, and their eyes glow a frosty emerald green.
Ratfish and other ghost sharks (subclass holocephali) only loosely resemble
true sharks (subclass elasmobranchi). They have the same cartilaginous
skeletons but unlike sharks, their upper jaws are fused to their brain cases.
They also have a flap of skin called an operculum, which covers their gill
arches. Another immediately obvious difference is in the way that they swim.
Ratfish achieve forward momentum by flapping their broad pectoral fins while
their skinny, whip-like tails undulate from side to side in a vaguely
think that their appearance is odd, wait until you hear about ratfish sex.
ratfish have claspers extending from their anal fins just like sharks. They
use them to transfer sperm to the female during copulation. Male sharks
usually bite the female’s flank or pectoral fin to maintain position while
they are coupled, but ratfish have a more unusual strategy. They have another
clasper in the middle of their foreheads – no, I’m not making this up. This
extra appendage has tiny barbs on its underside and can be used like a Velcro
covered arm to stop the male from falling away before he’s finished. Maybe
dating would be much simpler if we all displayed our sexual intentions in the
middle of our foreheads.
the female ratfish is impregnated, two embryonic offspring begin to grow
inside leathery egg cases that the female carries around until she is ready to
deposit them onto the reef. These cases resemble the rough shape of the adult
with a large oval for the body and a tapering, feathery extension for the
tail. Sometimes, discarded egg cases can be seen lodged between rocks or
rolling around on the seafloor.
sixgills, dogfish, and their other aggressive relatives, the newly hatched
ratfish immediately disappear into the depths. Where exactly they go, and the
perils they face in their lightless world, is anyone’s guess. Most young
ratfish probably end up in the bellies of ferocious looking deep sea fish.
Their only defense against this is a tall venomous spine on the leading edge
of their first dorsal fin. This painful weapon can be held high to inflict a
nasty puncture wound on any mouth snapping shut around it.
sharks have been lurking in the depths for the last 340 million years.
Initially they flourished alongside the true sharks, and the fossil record
contains evidence of many bizarre looking species, some of which may have
grown up to 3 meters in length but perhaps unable to compete for space with
their fiercer cousins, they eventually diminished both in size and numbers.
Today there are only three families left, containing around 34 species and
most of these are condemned to a life in the inhospitable depths.
sharks may be a rare site for divers, but if you drag yourself away from the
reef long enough to look, you could be rewarded by an encounter with one of
nature’s oddest creatures; a remnant from an evolutionary branch of fishes
almost eradicated from today’s shark dominated oceans.