Not just Shark
Pictures: Elasmodiver contains photos of sharks, skates, rays, and
chimaera's from around the world. It began as a simple web based
field guide to help divers find the best places to encounter
different species of sharks and rays but it has slowly evolved into
a much larger project containing information on all aspects of shark
diving and photography. There are now more than a thousand shark
pictures and sections on shark evolution, biology, and
conservation. There is a large library of reviewed shark books, a
constantly outdated shark taxonomy page, a monster list of shark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 accessed here:
If you're looking
for a broader range of marine life pictures the following links
represent a new area of elasmodiver.com that contains pictures of
other marine organisms and of marine habitats. This expansion of
Elasmodiver is in its first stages but will eventually include pages
on all types of marine mammals, bony fishes and marine invertebrates
as well as coastal habitats, reefscapes and other imagess relating
to the ocean. Please return regularly to enjoy the progress.
For centuries, the Diamond Shoals off of North Carolina have been collecting
shipwrecks. Hundreds of crumpled merchant vessels swamped by Mother Nature’s
fury, and scores of battle scarred war machines torn apart by enemy shells,
loom above the otherwise featureless substrate.
Subjected to racing currents and pounded by relentless surge, each wreck
eventually erodes into an unidentifiable debris field. But in the interim,
while the doomed ships still hold their structure, they are magically
transformed into vibrant marine oases.
Initially, planktonic life forms looking for a permanent home, attach
themselves to every available inch of real estate. Larger invertebrates like
snails and small crabs soon follow and begin grazing on the newly seeded
decks.
Within a season or two, blennies, angelfish and other small tropicals have
arrived from who knows where and the ghostly corridors are filled with
swarms of silvery baitfish that morph from one shadowy corner to the next.
Bermuda chub peck away omnivorously at anything slow enough to constitute
lunch and amber jacks sweep down from the heavens to scoop up the weak and
injured.
Suspended in the water column, schools of shimmering Atlantic Spade fish
practice their synchronized swimming techniques, while motionless barracudas
hang in groups around the remaining masts like living sign posts pointing to
other distant oases.
Lording over the entire food web, enormous sandtiger sharks hover in the
choicest locations or patrol slowly back and forth with their unblinking
eyes and implacable, snaggletooth grins.
Sandtiger’s belong to the mackerel shark order but they share few
characteristics with their fast moving mako and white shark cousins.
There are three species of sandtigers: the smalltooth sandtiger which is
rarely encountered except at great depth around Malpelo Island, the bigeye
sandtiger which is extremely rare and inhabits even deeper water than its
smalltooth cousin, and the common sandtiger that many divers around the
world have come to know and love.
Even beyond the diving community, sandtigers are well known celebrities.
Their ability to gulp air in order to counteract their negative buoyancy
means that they do not have to swim continuously to avoid sinking. This
makes them popular sharks in public aquariums because they are less likely
to swim into the walls and inflict damage on themselves.
However, long-term incarceration in small aquarium tanks does have an
adverse effect on the sharks. After a few years in captivity, sandtigers
often show signs of abnormal growth patterns including stunted fins and
hunched backs.
Even in the wild, sandtigers have their problems. Many populations struggle
with parasitic growths in their mouths and I have seen sandtigers with spine
deformations and even one albino that had somehow managed to survive till
adulthood.
Sandtigers (called ragged-tooth sharks in Africa and grey nurse sharks in
Australia) are unique in more ways than one. They are livebearers that
produce two offspring (one in each uterus) per season. The developing
embryos indulge in inter-uterine cannibalism. Once they have devoured all of
their smaller siblings, they begin consuming a constant supply of
unfertilized eggs that are channeled into the oviducts – a feeding strategy
known as oophagy.
The sandtiger’s ability to mooch slowly along with a stomach full of air is
a fascinating adaptation but in some ways it may be a double-edged sword. It
allows the sharks to conserve energy, which means that they do not have to
feed as often as faster swimming species. That is a great advantage for
large predators that have to rely on a limited food supply like the
sandtigers on the wrecks of North Carolina. But, sandtigers are also ram
ventilators and their casual approach to swimming may in some ways limit
their oxygen uptake, making them more sluggish and possibly even slower
witted than other mackerel sharks.
Sandtigers are not picky eaters. They are known to consume bony fishes,
small sharks, rays, squids, crabs, and lobsters. Interestingly, the North
Atlantic population has not yet developed a taste for red lionfish.
A decade ago, lionfish from the tropical Pacific somehow managed to
establish themselves on the wrecks of the Diamond Shoals. Its possible that
the invaders were flushed from the bilges of passing ships or they could
have been released from home aquariums but however they got there, they
appear to be flourishing. As they have no natural enemies, it looks as
though the ecosystems that they have invaded may be changed forever by their
presence.
One of the best known wrecks off the North Carolina coastline is called the
Spar. It is a thriving 300ft long artificial reef that was sunk about a two
hour run from Morehead City. Because of its elevation and intact
superstructure, it is often packed with sandtigers.
In recent years it has been plagued by red lionfish but during a productive
weekend shooting sandtigers on the Spar this summer, I was unable to locate
a single invader. Could it be that the sharks have developed a taste for
spicy Asian cuisine? It’s a nice thought but it is more likely that the
lionfish have either migrated into cooler water for the summer or they are
hiding in the bowels of the wreck where sandtiger photographers seldom
venture.
It may seem like a catastrophic problem but before you lose too much sleep
over the lionfish invasion, consider this: marine environments are in a
constant state of change. Change can seem scary, especially when humanity is
involved in manipulating the natural order of things, but the wrecks of the
Diamond Shoals are a manipulation as well.
Five hundred years ago the biggest topographic anomalies on the sea floor
were probably a few small Viking ships. A thousand years ago there would
have been nothing on the Diamond Shoals except an occasional whale carcass.
Now that large vessels are equipped with 21st century navigational aids and
better marine safety protocols, North Carolina’s crumbling underwater
habitats are unlikely to be replenished. It’ll take a while, but in a
century or two there will be very few manmade structures left on the
seafloor. That means, no more colonies of invertebrates, no more levitating
sandtiger sharks and no more lionfish.
Mother Nature rolls with the punches. When conditions permit, she presents
us with jewels like the marine oases we have right now.
The lesson to be learned from her is to never waste an opportunity. So, dust
off your dive gear and enjoy the wondrous diversity of marine life on the
shipwrecks of North Carolina while you can.
