Those Predatory Sharks...
Predatory animals inspire a sense of awe, respect and fear among
humans. On land, big cats, wolves, and bears are some of the
quintessential predators. Dip beneath the waves, however, and
sharks take the stage, alongside orcas, sperm whales, and large
squids and fishes. Although there are many marine predators, it is the
sharks that have been most stereotyped as the "killers from the deep".
There's no denying the fact that sharks are carnivorous
and predatory. Generally, however, sharks have a more
diverse diet than usually credited by the general public. The giant
filter-feeding
basking shark (Cetorhinus maximus) is inclined to
consume copepods of
the genus Calanus. The whale shark (Rhincodon typus),
another very large filter-feeder (see link on this species below), also
feeds on
zooplankton, although it is not averse to taking small- to medium-sized
fishes
swept up in its enormous maw. Some sharks concentrate mainly on certain
types of prey, such as cephalopods (squids and octopuses); crustaceans
(lobsters, shrimps, etc.); shellfish, or small fishes, whereas others
will take prey from any of these groups. Many sharks
are oppurtunistic, meaning they will feed on most edible items they
encounter.
Whatever their dietary preference, sharks are well-adapted to deal with
their prey type. Many bottom-dwelling sharks, such as the orectolobiformes
(including the nurse sharks) and heterodontiformes (such as the Port Jackson
shark [Heterodontus portjacksoni]) have flattened molar-like
teeth and strong jaw muscles, all the better to crush the shells of
their common prey, molluscs and crustaceans. Another, better
known, example of dietary adaptation is the infamous white shark...
The white shark is an apex predator, with a varied diet including fishes
and pinnipeds. It is also notorious for having attacked (and in some cases
killed) more than a couple of humans. This reputation, and its unforgettable
visage, have made it the world's most famous shark. Beyond the sensational
attacks, however, is a spectacular creature which deserves a reputation
not as a mindless man-eater but as a true predatory masterpiece.
Here is a rare first-hand account of a white
shark attack on a diver. Thanks to Marco Flagg for the report.
One of the more potentially dangerous
sharks is the oceanic whitetip. Read more about this fascinating open-sea predator. (An Italian
version is available through www.squali.com.)
About 15 million years ago, a huge
shark known as Carcharodon (or Carcharocles)
megalodon appeared in the warm Miocene seas. This 15 m super
predator, related to the extant white shark, probably fed on large fishes,
small whales, and everything in between. Luckily for us, it appears to
have died out at the beginning of the Pleistocene era, around 1.5 million
years ago. Some researchers (mainly cryptozoologists), however, believe
there is evidence that suggests that megalodon is still alive. Like most shark
specialists and paleontologists, I do not subscribe to this theory, which
is based on scant, poor evidence and requires an ignoration of accepted
ecological and paleontological facts. I wrote a paper, published in The
Cryptozoology Review, criticizing the theory of megalodon
survival: "A Critical Evaluation of the Supposed
Contemporary Existence of Carcharodon megalodon".
In a recent issue of Wild About
Animals (vol. 12, no 2), a British magazine about pets, Karl Shuker (a
prominent cryptozoologist) reiterated his claims that Megalodon may still
be around, dismissing my research linked above. I wrote a
response to the article, but Wild About Animals felt it would be
inappropriate for publication as it was too long and not of great import to
them (this is unfortunate, but understandable as they are a popular
magazine about pets, not a journal). So, I have instead posted it here.
For an interesting article on
megalodon, with photographs, visit John Bruner's Home Page and
choose one of the links at the bottom of the page.
The white shark was recently
protected under a new law in Malta, along with the basking shark and manta
ray. Alex Buttigieg and the Marine Life Care Group spearheaded the effort,
and details can be found on Alex's shark news site.
Biology of
the Mako (Isurus oxyrinchus) by Rick Martin. Find out more
about this high-speed shark.
ReefQuest
South Africa Great White Shark Expedition Have you ever wanted to
assist in research on great white sharks and see these magnificent animals
in their element? This expedition, led by marine biologist Rick Martin, is
just such an oppurtunity! (You can also check out the results of the 2000
expedition, of which I was lucky enough to be a member).
Weird and Wonderful Sharks
Sharks are not particularly speciose animals, but they are still diverse
in form and function. There are over 400 species
and 8 distinct orders (not including the skates and rays, which are
basically flattened sharks). The origin of elasmobranchs has been traced
back to about
400 million years ago, and since then they have evolved many different
morphotypes, experimenting with many of the concievable
forms and shapes of an aquatic animal. Here are some highlights of some of
the weird and wonderful elasmobranchs.
Investigate the
several species of planktivorous
elasmobranchs in an article by marine biologist and author Rick
Martin entitled "The Big Shift."
The goblin
shark fully deserves its name, as Rick Martin explains. With
colour photos.
Travel back in time and take a look at some veryweird
fossil sharks (electrical, spiny and otherwise).
Do giant cookiecutter sharks exist? Click here
to find out.
One thing's for sure,
very large nurse sharks do exist!
Several specimens of megamouth shark have been caught or stranded since
the species was discovered in 1976. Here is a list of
these specimens courtesy of the Florida Museum of Natural History.
Also check out the FLMNH's megamouth
page.
New specimens of megamouth have been caught in recent years in the Phillipines. Check out Elson Elizaga's reports on a megamouth from 1998 and a megamouth from 2005.
A rare incident occurred
in 1998 when a megamouth was observed being attack by several sperm
whales off Sulawesi, Indonesia. Go here to find out more.
Coming in this section!: Weird
predatory behaviour, more Megamouth, and more!
Blue shark
(Prionace glauca)
Photo copyright Jim Knowlton/JimKnowlton.com
