Chapter 1: Aquarium Sharks and Rays
From Microcosm Aquarium Explorer
Contents |
Introduction
By Scott W. Michael
For centuries, the simple word “shark” has been synonymous with gut-wrenching fear because of the nature of the potential threat that some species pose to human beings. Of all the creatures that inhabit the oceans, none evokes a more emotional reflex.
For example, in 1558, Guillaume Rondelet, a prominent French biologist, wrote of the School Shark (Galeorhinus galeus), “This fish so longs to wound men in the thighs, the groin, the heels, or any exposed part, that it sometimes leaps onto dry land when it sees men with bare legs near the water . . .” This aggressive behavior, no doubt a product of Rondelet’s imagination, is amazing when one considers that this particular fish attains a length of only 1.8 m (5.9 ft.) and generally eats small fishes and squids. Over 300 years later, Henry David Thoreau penned, “I have no doubt that one shark in a dozen years is enough to keep up the reputation of a beach a hundred miles long.”
One long-standing misconception about sharks and rays is that they are primitive and dim-witted or lacking brainpower (except for overgrown olfactory lobes, which are in part responsible for their extremely keen sense of smell). In fact, studies on the central nervous systems of sharks and rays have shown that not only do many of the more “advanced” species have large brains relative to their body size (many fall within the range of birds and mammals), but that the development of the divisions of the elasmobranch brain is similar to that of mammals. Behavioral studies bear this out.
Many sharks and rays often surprise researchers with their intelligence, displaying complex behavioral repertoires and learning simple tasks at rates comparable to rats. As scientists continue to piece together the puzzle of shark behavior, human emotion has begun to shift from fear to fascination. Today, many appreciate even such feared species as the Tiger Shark (Galeocerdo cuvier), mako sharks (Isurus spp.), and Great White Shark (Carcharodon carcharias) for what they are: efficient, finely adapted super-predators.
Among the noteworthy characteristics shared by some sharks are:
- An exquisitely developed sense of smell. Some are able to detect substances dissolved in water in concentrations as low as 1 part per million.
- Phenomenal sensitivity to electromagnetic charges, unmatched by any other animal. They can pick up charges of one-millionth of a volt—enabling them to detect even the faint bioelectrical impulses produced by the nervous systems of their prey.
- Acoustic monitoring abilities that astonish scientists. A low-frequency disturbance, such as the thrashing of a wounded fish underwater, can attract sharks hundreds of yards away.
- A remarkably tough skin armored with minuscule toothlike scales called denticles. In one British report, pellets from a 12-gauge shotgun blast fired at a range of 61 cm (23.8 in.) bounced off the hide of a live Whale Shark (Rhincodon typus).
- Tremendous speed in some species. The Shortfin Mako, (Isurus oxyrinchus) has been clocked at 56 km/h (35 mph), and may even be able to attain bursts of speed in excess of 96 km/h (60 mph).
- Exceptionally strong jaw muscles. A powerful shark can exert some 3,069 kg of bite pressure per sq. cm (44,000 lbs. per sq. in.), compared to a bite pressure of about 10 kg per sq. cm (150 lbs. per sq. in.) in humans.
- A huge range of sizes, from the 15 m (49 ft.) Whale Shark (Rhincodon typus) to the Spined Pygmy Shark (Squaliolus laticaudus), a widespread deep-water dwarf species that reaches full adulthood at a length of only 15 cm (5.9 in.).
- Live birth in some species; in some noteworthy others, young survive as intrauterine cannibals, feeding on eggs produced by their mothers to spur their own growth before birth.
- A fascinating family tree—biologist John E. McCosker of the California Academy of Sciences’ Steinhart Aquarium calls it an “evolutionary bramble bush.” It includes the largest-known fish ever to swim Earth’s seas, Carcharodon megalodon, a 15 m (49 ft.) apex predator known by its 15 cm (5.9 in.) fossilized teeth, as well as the bizarre chimeras or “ghost sharks” that have been discovered at depths down to 2,432 m (7,977 ft.). The Order Myliobatiformes includes some of the most elegant and awesome creatures in the ocean, including the giant manta rays, which can have wingspans of 6 m (19.7 ft.) and weigh up to 1.36 metric tons (1.5 U.S. short tons).
An Aquarist’s Challenge
It is not surprising, therefore, that many marine aquarists—professionals and amateurs alike—are drawn to these animals. While the fierce reputation of sharks in the popular mind causes some people to recoil in fear, many others of us find them irresistibly interesting and worth knowing better. For anyone fascinated by aquariums, it doesn’t take much to spark a keen interest in keeping sharks and rays in captive systems where they can be observed close at hand and over long periods of time. Indeed, most marine aquarists, at one time or another, entertain the idea of purchasing a shark for their home saltwater systems.
When I was preparing to acquire my own first shark, there was a real paucity of information available on elasmobranchs suitable for larger home aquariums. The sharks were available, but the information was not. The purpose of this book is to give some insights into the biology and husbandry of these special animals and to help the aquarist in selecting a species that can be adequately cared for in a home system. Unfortunately, some readers will come away discouraged by the realities of potential shark ownership. Most sharks, including species that appear in the pet trade with some frequency, are very poor candidates for captivity. Some adapt poorly, while others simply grow too large to be contained in a home aquarium. However, a number of the inshore and coral reef sharks will thrive in good aquarium habitats, living—and even reproducing—for many years, providing the dedicated aquarist with an unforgettable experience.
In addition, we will also investigate the sharks’ spectacular relatives, the rays, which also offer a few species that are good candidates for the determined aquarist. (Again, a number of available rays ought to be avoided by the average aquarist, and the species catalog in Chapter 4 will steer the reader through all of the likely choices.)
The Ethics of Keeping Sharks and Rays
Having a live shark or ray is a great responsibility, and ownership brings with it the obligation to provide an adequate facility to house your specimen comfortably. If you do not have the resources available to keep an adult specimen, do not purchase a juvenile. While some species can be kept as adults in aquariums of 285 to 684 L (75 to 180 gal.), others we will discuss require systems in the 912 to 1520 L range (240 to 400 gal.). A rambunctious shark that has outgrown the usual hobbyist-size tanks can be very, very difficult to sell or even give away.
I once received a rather desperate telephone call from a young woman who was trying to maintain a “shark aquarium” in an Omaha sports bar. At the time, I was the owner of a tropical fish store in Omaha, Nebraska, and she had been told of my interest in sharks and wondered if I might be able to help her with a problem. Expecting the usual questions about parasitic infections, feeding problems, or troublesome tankmates, I was surprised to learn that she was trying to find a home for a 1.2 m (3.9 ft.) Nurse Shark (Ginglymostoma cirratum) living in a 1.8 m (5.9 ft.) tank.
She had called a number of public aquariums to see if they would take her oversized specimen, but none had room for a large and growing shark. It is a widely held misconception that public aquariums are eager to take these animals from aquarists when they become too large. In fact, the biologists and keepers who manage these institutions routinely turn down offers of overgrown animals due to lack of space. She had even called Aquarium Fish Magazine in California to see if they had any suggestions. The editor gave her my name. I wish that I could report that I was able to save the day, but in the end I had tell her that the only real option seemed to be for her to euthanize the animal.
Harsh Consequences
This may seem harsh, but consider what else you might do with a 1.2 m (3.9 ft.) shark that could easily reach more than 3 m (9.8 ft.) in length. She suggested that she could drive it to Florida and set it free. I warned her strongly that this was an idea she should put out of her mind. Releasing a captive shark into the wild after it outgrows its tank is always ill advised—a specimen exposed to species from other regions (for example, an Atlantic species kept in captivity with a Pacific species) may carry parasites or pathogens that are not native to the area where it originated, and freeing such an animal in the wild may introduce pests or diseases not indigenous to the area, with potentially catastrophic consequences. Also, you should never release a species into an area where it does not naturally occur, for it can disrupt the ecological balance of the region (witness the devastation of North America’s Great Lakes fisheries by the accidental introduction of sea lampreys).
A Puerto Rican aquarist once admitted to me that he had released a Blacktip Reef Shark (Carcharhinus melanopterus)—an Indo-Pacific species—into the waters off his Caribbean island. This is the sort of irresponsible act that biologists dread and that conscientious shark keepers ought to discourage as strongly as possible.
Because it is not easy to dispose of an overgrown shark or ray, it is critical for the aquarist considering ownership of one to investigate its needs thoroughly (especially its space requirements) before making the purchase and commitment. Under good conditions, most of the shark species we keep in our aquariums can live for more than 25 years. If you have any doubts about taking on this sort of responsibility, be sure to select one of the smaller species that is much more likely to find a new home if the aquarist’s circumstances happen to change.
One Final Caution
An interest in sharks and rays can be infectious and incurable. There is seemingly no end to the books, videos, research papers, and ongoing discoveries about living and prehistoric elasmobranchs—easily enough to feed an aquarist’s interests for a lifetime. I acquired my first shark while a teenager, a bouncing baby Epaulette Shark (Hemiscyllium ocellatum) that proved to be a magnificent aquarium specimen. It would clamber about the tank on its four paired fins, grub in the sand for food, and probe the nooks and crannies of a little coral head I had constructed looking for live grass shrimp. It learned to take food from my fingers and became a real “pet.” More importantly, the little Epaulette Shark gave me some valuable insights into shark husbandry and stimulated my desire to learn more about its natural history. Several years later, I found myself photographing and studying its wild relatives on the Great Barrier Reef and in Papua New Guinea.
Over the years, as a hobbyist, aquarium store owner, marine biology student, and underwater photographer, I have kept and observed many, many different species of sharks and rays. They are as appealing to me today as they were decades ago. These are truly fascinating animals, and I am pleased to share the information and advice presented here in hopes that others may better understand, select, and care for captive sharks and rays.
From: Aquarium Sharks and Rays by Scott W. Michael