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Aqua-Predator-Sharks-1of2
J. Moore (j#d#.moore@canrem.com)
Tue, 27 Jun 95 12:36:00 -0500
This is a shortened version of the beginning I used in the first post on
crocodiles, "AquaticPredators-Sharks-1of4"; for quotes about the AAT
postulating a water environment as a haven from predators, refer to that
post:
Attempts to construct theories about early human evolution must contend
with, among other things, the problem of predation and how to avoid it.
Both crocodiles and sharks which are highly dangerous to humans even
today are to be found in both fresh and salt water in Africa.
In this post I am describing the habitats and habits of water-based
predators. This post will deal with sharks.
I must say, after reading
about both sharks and crocodiles, that I feel that predation by
crocodiles would have been a greater problem for the AAT's water-based
transitional hominids than predation by sharks. There are three main
reasons for this: first is that sharks, while they do often come into
quite shallow water, are more common in greater depths of water. Second
is that sharks seem to attack humans only partly for food; partly it's
out of an apparent defense of what it considers its territory. Third is
that attacks may only consist of one or two bites; but of course leaving
a hominid crippled might well be essentially the same as killing it
outright.
In contrast, crocodiles like to live in shoreside waters just where the
AAT-proposed hominids are postulated to have lived; crocodiles generally
stalk and kill mammals, including humans, as food; and crocodiles, once
they get hold of their victim, do not let go, even when being pelted
with rocks, stabbed with knives and spears, or when sticks are rammed
down their throats. Crocodiles are serious about their job.
The information quoted here regarding shark attack comes from chapters
about shark attack in many areas of the world, including the US,
Australia, and South Africa. This information is applicable to all
trpoical and sub-tropical areas in Africa (the area in question here) as
all three of the species of sharks which swim into and/or frequent
shallow waters (and which are consequently most dangerous to humans)
live in those tropical and sub-tropical African waters, as well as being
widespread throughout the world.
My additional notes will be in brackets [] and offset by *****s.
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[Like this.]
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The following quoted material is from:
1989 *Sharks in Question: The Smithsonian Answer Book*
Springer, Victor G. (curator in the Department of Vertebrate Zoology,
Division of Fishes, National Museum of Natural History, Washington,
D.C.), and Joy P. Gold (Technical Information Specialist at the
Department of Vertebrate Zoology, National Museum of Natural History,
Washington, D.C.)
Smithsonian Institution Press: Washington, D.C. and London.
***********************
[Some people say crocodiles don't live in salt water; we've already seen
that that is wrong. Some also say that sharks don't live in fresh
water; that is wrong as well. In fact, one of the most dangerous of
sharks (the Bull Shark, sometimes also called the Zambezi Shark) lives
in both fresh and salt water.]
***********************
pp. 66-67:
Icthyologists (scientists who study fishes) have been interested in the
sharks that occur in freshwater. Formerly, sharks found in Lake
Nicaragua, Lake Izabal in Guatemala, the Ogowe River in western Africa,
the Zambezi River in eastern Africa, the Tigris River near Baghdad, and
the Amazon River of South America, to name but a few, were each believed
to be a different species that was confined to freshwater. Recent
studies, however, demonstrate that in all these rivers and lakes there
is but one species: the bull shark, *Carcharhinus leucas*, which is also
commonly found in the warm, shallow waters of the oceans. In Lake
Nicaragua, which drains into the Caribbean Sea by the broad Rio San
Juan, the bull shark apparently moves freely between saltwater and
freshwater. Even the rapids along the river seem to present no barrier
to its passage. The bull shark has been implicated frequently in shark
attacks on bathers, especially in warm freshwaters such as Lake Nicaragua
and the Zambezi River, which have access to the sea.
***********************
[Is this shark dangerous to humans?]
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pp. 116-117:
Bull Shark
Of all the sharks swimming the continental coasts of tropical and
subtropical seas, the bull shark, *Carcharhinus leucas*, may be the most
dangerous. In number of attacks on humans, it is one of the three
species of sharks most often implicated. It may not have the white
shark's reputation, but its large, heavy body, huge jaws, and very large
teeth make it meter for meter just as formidable. Even though it
appears to move slowly when cruising the shallows inshore, it is capable
of fast, agile movements when it wants to attack prey. In Natal, South
Africa, the bull shark is particularly notorious as an aggressive
species, and it is caught four times more frequently than either the
white or tiger sharks in the protective antishark nets set off the
beaches.
pg. 117:
The species is relatively large, purportedly growing to a length of
3.4 m, but with an actual record of only 3.2 m (based on a report from
Brazil). Individuals over 3 m are rare.
pg. 160 (from Appendix Three: Lengths of Selected Sharks):
Bull Shark (*Carcharhinus leucas*)
at maturity: male 1.57-2.26 meters; female 1.8-2.3 meters;
maximum total length: recorded 3.2 meters, reported 3.4 meters.
smallest free-living 0.56-0.81 meters
pg. 117:
The bull is the only shark known to live in the saltwaters of the
oceans, the brackish water of estuaries and river mouths, and the far
upper reaches of freshwater rivers and lakes. Even its newborn young
and juveniles enter freshwater without difficulty. It travels from the
Caribbean 100 km up the Rio San Juan to Lake Nicaragua, where it was
long thought to represent a different land-locked, endemic species. It
has also been reported from Lake Ysabel in Guatemala, the Mississippi
and Atchafalya rivers in the southern United States, 3,700 km up the
Amazon to Peru, the Gambia River on the middle upper west African coast,
more than 550 km from the sea up the Zambezi River on the middle lower
east African coast, the Tigris River of Iraq, the Hooghly River of
northeastern India, and Lake Jamoer in New Guinea. These are but a few
of the bodies of freshwater frequented by bull sharks. As recently as
August 12, 1985, a large, 2.7 m bull shark weighing about 216 kg was
caught in the Chesapeake Bay along the western North Atlantic seaboard.
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[So they're fairly big, and they live virtually everywhere. What do
they eat?]
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pg. 118:
Bull sharks feed on a variety of prey and are almost as omnivorous as
the tiger shark, the ocean's junk food eater; however, the bull is less
likely to eat indigestible garbage. It favors bony fishes and other
sharks, particularly young ones in the nursery grounds. In the sea, it
will also kill and eat dolphins and sea turtles. In rivers, it has been
known to kill hippopatomuses. Even the remains of large land animals,
including antelope, cattle, dogs, and humans have been found among its
stomach contents.
Dr. Leonard Compagno, who was the ichthyological consultant to the
film *Jaws*, believes that the bull shark is quite possibly the most
dangerous of all sharks, and that many attacks attributed to other
species may actually have been committed by bull sharks. The famous,
closely spaced series of five attacks -- four fatal -- that occurred in
New Jersey in 1916, have been attributed to the white shark. At least
three of the attacks, however, occurred two miles up a narrow tidal
creek, a habitat type in which no white shark has ever been confirmed to
occur. A tidal creek is a likely place for bull sharks to be found, and
few other species of sharks have been reported from such a habitat. No
other western Atlantic shark species is known to enter tidal creeks.
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[They're big, they live virtually everywhere, and they attck and kill
humans even today. They're one of the main reasons South Africa and
Australia have erected expensive anti-shark nets on their beaches.]
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pg. 108:
How does the white shark attack its prey? Generally by surprise, and
from behind and below, sometimes in an accellerated headlong rush at 17
kph to 25 kph, sometime inverting on its back or rolling to its side,
according to the size and posture of its prey.
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Continued next message...
Jim Moore (j#d#.moore@canrem.com)
* Q-Blue 2.0 *
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