Exotic Animals

I saw a news articles on Yahoo News about a Georgia aquarium that keeps whale
sharks.  Well, actually, the article was about how they failed to keep whale
sharks… They’ve had two die in the last few months.  You can read the link
here:  http://news.yahoo.com/s/ap/20070613/ap_on_sc/whale_shark_dies;_ylt=AvwkMwHazr_wOWMp7Hh_pjXMWM0F

After I read this, I was wondering: Just what is a whale shark, and why are
they so hard to keep in captivity?

As the fish’s name suggests, whale sharks are the shark equivalent of baleen
whales.  They are big (growing up to 40 feet long), and they are plankton-eating
filter feeders.  They are found in tropical seas, worldwide, usually near the
surface.  They are harmless to humans.

Like all filter feeders, whale sharks have an enormous mouth for their body
size; their mouths can be over 4 feet wide.  Unusually for sharks, their mouths
are also at the very front of the head, instead of on the underside; this allows
the shark to simply open its mouth while swimming to suck in the huge volume of
water they need in order to filter out enough food.  Remember, these are 15 ton
animals, which eat some of the very smallest prey available.

Whale sharks have an ingenious adaptation for filter feeding.  Like all fish,
they have gills.  The external features of gills are obvious to humans: the
slits along the sides of the animal, just behind the head. Internally, however,
gills have a very complex, comb-like structure, designed to get the maximum
water flow over tiny blood vessels, so that the animal can extract oxygen from
that water.  This structure is a good pre-adaptation for filter feeding.  (I may
talk about pre-adaptation in a future post; it is a fascinating subject in
evolutionary biology.)  The whale shark will eat anything which the internal
gill structure traps in the mouth.

While I was looking up information about whale sharks, I came across several
references to Thor Heyerdahl’s famous Kon Tiki expedition, when he sailed a
primitive raft across the South Pacific, and proved that human colonization of
the Polynesian islands was technically feasible for Stone-Age people.  During
the trip, he had an encounter with a whale shark, which he described as the
biggest and ugliest face any of us had ever seen in the whole of our
lives.

Whale sharks might not be pretty, but they are fascinating.

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I found this story the other day, while I was looking through some back news
articles, and it struck my fancy…  It’s about a fisherman in Indonesia, and
the unusual fish he caught…

http://news.yahoo.com/s/nm/20070521/od_uk_nm/oukoe_uk_indonesia_fish

He caught what may be the world’s rarest fish: the ceolacanth.  This fish is
only known to live in deep waters of the Indian Ocean, near the Comoro Islands,
or in deep waters of the Indonesian archipelago.  It is a unique animal in many
respects.

First, and most famously, it was thought to be exctinct since the time of the
dinosaurs.  In 1938, however, one was caught of the southeastern coast of
Africa, and when it was identified, by the South African ichthyologist Marjorie
Courtenay-Latimer, the hunt began to find it’s natural habitat.  This was later
discovered hundreds of miles north of the original find, around the Comoro
Islands.  Later, in the 1980’s, another population of ceolacanths was discovered
in Indonesia.

The fish is also famous, though, for its position on the evolutionary tree. 
The ceolacanth is that most rare of beasts: a true missing link.  In this case,
it’s a link between early fish, and early terrestrial animals.

The ceolacanth has very unusual fins.  Instead of a fin supported by numerous
rays, a ceolacanth’s fins are supported as a fring around a stout, limb-like
appendage.  The fish has four of these appendages, two pectoral and two pelvic. 
The analogy to fore- and hind-limbs is obvious, and scientists believe that all
modern land dwelling animals arose from a fish in the ceolacanth family.

This is an exciting find; as the article notes, ceolacanths cannot live in
surface waters; the temperatures, pressures, and light levels are all wrong for
them.  Their natural habitat is at least 60 meters (almost 200 feet) below the
waves, and they have never been successfully kept in captivity.  In their own
habitat, ceolacanths are dangerous predators; at the surface, they prove to be
surprisingly fragile.  This could explain how these fish stayed hidden from
human eyes for so long.

And that’s all I have to say about this.  Animals don’t get much more exotic
than the ceolacanth.

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You’ve probably heard about this already; it’s been in the news on and off for the last few weeks.  Two humpback whales swam up the Sacremento River, and hung out for a while.  Here is a news article about them:

http://news.yahoo.com/s/ap/20070521/ap_on_re_us/delta_whales

It’s not really unusual for large whales to come close inshore; it is unual for them to swim upriver so far. The last tiem a humpback spent so much time in the Sacremento River was in 1985.  The two whales this time are apparently a mother and calf, and made it more than 20 miles upstream before they turned back to head for the ocean.

As the article notes, they both have wounds which may have come from boat propellers.  This is a common hazard for inshore aquatic mammals.  In south Florida, where a lot of people have boats, and a lot of boat channels are inhabited by manatees, propeller injuries are common.  Even dolphins, cetacean relatives of humpback whales, are sometimes hit by boats.

Whales like these, however, are less frequently injured by boats.  For starters, humpbacks are big, up to 60 feet long, making them easy to see.  Also, these large whales can dive deeper, and stay down longer, allowing them to avoid surface craft.

It’s not likely that the propeller wounds will prove life-threatening to either whale.  Whales in general, and large whales in particular, possess thick layers of blubber directly under their skin, which serves the dual purpose of insulating the animal in cold water and armoring the animal against injuries.  Blubber injuries to whales usually heal and leave the animal with no lasting problems.  The main problem with such injuries is infection.  This is more of a problem for these whales, since the river they’re in now is not as clean as the open ocean.

I’ll post more about these whales later, if they ever decide to leave leave the river…