A 1600 Work I
1600 Work II
1600 Work III
Phylum Chordata II--The Sharks
Bill Long 5/9/07
Three Other "Dangerous-to-Humans" Sharks
In the previous essay I introduced the taxonomy of sharks and finished by writing about the "wastebasket of the sea," the tiger shark--Galeocerdo cuvier. I will conclude my treatment of sharks in this and the next essay by speaking about the great white, the oceanic white tip and the bull sharks. Pictures of each abound online. Before I get to a description of each, I want to introduce you to some "shark talk"--the vocabulary of selachology.
But even before we do that, I want to bring to your attention one arresting fact about the "man-eating" sharks. There is such a negative hype about them, fueled by stories such as the attack on a swimmer off the coast of Kihei in Maui yesterday, that one might get the impression that the human species is besieged by these killer sharks. But people who study these things assure us that the number of documented unprovoked shark attacks in the past five years averages about sixty per year throughout the world, with the number of deaths resulting from these attacks averaging around five per year.
Is that all? Yep. I checked my numbers hither and yon, and that was the figure I got. But let's put one figure next to it. Do you know the number of sharks that are killed by humans every year? Well, more than 25,000,000. Most of them are used for their skin or to make shark soup or are killed by mistake--while fishermen are after other catch. What, then, is wrong with this picture? We are terrified of the thing which we kill 5 million to 1 (of us). Just think what it is like to be a shark! If we are terrified of them when the numbers are so small, what must they feel when we are around?
The Vocabulary of the Study of Sharks
Well, you should know, that the word selachology appears in no modern dictionary. It does appear, however, in the Century. It only receives 58 Google "hits" when you type it in. I am sure this essay will then jump to the top of the selachology entrees. Whopee. Almost all of these Google "hits" are to a 17th century article. Thus, the word doesn't look too promising, does it? But it is derived from the Greek word selachos, which means a "sea fish," and is used to describe the study of sharks. The sharks belong to the Superorder Selachimorpha, and one of the genera of sharks is called the Selache, so we can see where the word comes from. Even today the word Selachii is used synonymously with Chondrichthyes.
But the more interesting vocabular of sharks has to do with terms like "heterocercal," "apex predator," "pelagic sharks," "synapomorphy," "spotted wobbegongs," "ampullae of Lorenzini" and "porbeagles." Some species of sharks, including the great white, live in the wide ocean. Indeed, the only species dangerous to humans which seems to live in shallow water is the bull shark, Carcharhinus leucas, which was portrayed as the feared predator in Steven Spielberg's blockbuster movie Jaws.
The Pelagic Environment
Let's begin with the place where many of them live--the pelagic zone. The pelagic zone is what we might call the "open sea," the sea which is neither coastal nor on the ocean/sea floor (if you live on the ocean floor you are called a "benthic" fish). This zone is further diveded into five regions, which are picturered here. Roughly speaking, the
1. Epipelagic zone is from the surface to 650' in depth;
2. Mesopelagic zone from 650'-3300' in depth;
3. Bathypelagic zone from 3300'-13,000' in depth;
4. Abyssopelagic zone from 13000'-THE BOTTOM;
5. Hadopelagic zone, when you have a thin slit in the floor of the ocean and it goes yet deeper. The 36,000 foot deep Marianas Trench, discovered only in 1960 by Piccard and Welsh, is the deepest place in the ocean.
Though deep-ocean biologists have found traces of life even in the deepest part of the oceans, I think these "abyssopelagic" parts offer far more to the fertile imagination than the few creatures that can be studied in those depths. After all, the Greek word abyss means "bottomless," as the Greeks thought the sea to be. Thinking about "bottomless" things can reall stir the imagination.
I also wanted to pause on a word that I hadn't heard previously-wobbegong. It is a brown carpet shark found off the coast of Australia. The name is aboriginal. Its scientific name, Orectolobus maculatus, which means "stretched out and rounded protuberance" and "spotted" signifies the "truth" about this shark, that it has brown or buff spotted markings. It also has "barbels" its head. This has nothing to do with things you lift at the gym; a "barbel," the Latin barba means "beard," is "a fleshy filament hanging from the corners of the mouth of some fish." So, now that we have learned a few words, we can study this slow-moving predator.
Speaking of the interesting sharks, however, one of the most fascinating is the very rare megamouth shark. There have only been about 38 documented sightings of this 15' long and 1600 pound shark, whose distinctive feature is a "large, distensible" mouth which it never seems to close. Seems to remind me of some people...One description of the megamouth (Megachasma pelagios) has this: "
"The Megamouth Shark has two unequal sized dorsal fins, a strongly heterocercal tail, and lacks any distinctive body markings. Its colour varies from grey to blueish-black above and is pale grey below. The tips of most of the fins are usually white."
So, we are introduced to a new word--a heterocercal tail. Such a tail is one where the two lobes are of different size--the upper one being long and the lower is short. A picture of a heterocercal tail is here. If the two lobes of the tail are approximately the same size, we say that the shark has a homocercal tail (the Greek word kerkos means "tail").
Well, sometimes you run into a shark, such as the great white, which is called an "apex predator." A predator is so-called because it is preyed on by no one or nothing. A partial list of apex predators in nature is here. You can really become fascinated just by studying the list, so I won't list it completely here. Here are a few, however: African wild dog, anaconda, bobcat, human, bald eagle, black bear, electric eel, giant otter, dhole, cheetah. Come to think of it, if you held a party and invited these various creatures to appear, I bet they would begin to prey on each other pretty quickly.
Wouldn't you know it? I am out of space in this essay and still have not yet told you about these three other dangerous sharks, as well as a few other "shark words." There is always tomorrow.