The Biology of Sharks and Raysby A. Peter Klimley, Steven Oerding (Illustrator)
The Biology of Sharks and Rays is a comprehensive resource on the biological and physiological characteristics of the cartilaginous fishes: sharks, rays, and chimaeras. In sixteen chapters, organized by theme, A. Peter Klimley covers a broad spectrum of topics, including taxonomy, morphology, ecology, and physiology. For example, he explains the body/i>
The Biology of Sharks and Rays is a comprehensive resource on the biological and physiological characteristics of the cartilaginous fishes: sharks, rays, and chimaeras. In sixteen chapters, organized by theme, A. Peter Klimley covers a broad spectrum of topics, including taxonomy, morphology, ecology, and physiology. For example, he explains the body design of sharks and why the ridged, toothlike denticles that cover their entire bodies are present on only part of the rays’ bodies and are absent from those of chimaeras. Another chapter explores the anatomy of the jaws and the role of the muscles and teeth in jaw extension, seizure, and handling of prey. The chapters are richly illustrated with pictures of sharks, diagrams of sensory organs, drawings of the body postures of sharks during threat and reproductive displays, and maps showing the extent of the species’ foraging range and long-distance migrations. Each chapter commences with an anecdote from the author about his own personal experience with the topic, followed by thought-provoking questions and a list of recommended readings in the scientific literature.
The book will be a useful textbook for advanced ichthyology students as well as an encyclopedic source for those seeking a greater understanding of these fascinating creatures.
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The Biology of Sharks and Rays
By A. PETER KLIMLEY, STEVEN OERDING
THE UNIVERSITY OF CHICAGO PRESSCopyright © 2013 The University of Chicago
All rights reserved.
An Introduction to the Cartilaginous Fishes
The cartilaginous fishes, in particular the sharks, inspire both awe and fascination. Why is this? The answer to this question may lie in the role of some, such as the white and tiger sharks, as apex predators in an alien world. In comparison to all of these species, humans are ill adapted for life in the seas. We swim awkwardly with clumsy arm strokes and kicking leg movements. We can dive underwater only for at most a few minutes before we must rush to the surface to breathe, often suffering panic due to our inability to see far in this dimly lit, blue-green world. Humans do not smell underwater or hear well in this eerily silent world. The cartilaginous fishes are masters of this alien environment. They swim effortlessly in this viscous medium and possess senses that enable them to find their prey in total darkness at great distances. Humans feel insecure in the presence of these fishes, of which a few of the largest feed on marine turtles, seals, sea lions, and dolphins. We hold these predatory species in awe and are keen to learn more about why they are masters of the sea. However, you will learn in this book that other cartilaginous fishes such as the whale shark, basking shark, and many rays are lower on the food chain, the former being filter feeders of plankton and the latter swallowing buried clams and worms.
This chapter is a brief introduction to this very diverse group. The emphasis will be on describing the benchmark studies on each particular subject. It is impossible here to cover the enormous scientific literature on the biology of the cartilaginous fishes, which is reviewed in over a dozen compendiums on specific topics. The results of these key studies will be presented in diagrams and graphs in order to introduce you to authentic scientific data so that you can read them critically. "Spotlights" are included in each chapter to focus your attention on the sophisticated methods used by pioneer scientists to make important scientific discoveries. These features will help you understand the scientific method and learn to appreciate the adventure of being a scientist. Finally, each chapter ends with intellectually stimulating questions; you are encouraged to delve into the scientific literature to answer them. Also included are lists of keynote articles for your further reading. The purpose here is to provide you with a "road map" with which to pique your interest and motivate you to learn more about the biology of the cartilaginous fishes.
There are currently 503 species of sharks, 699 species of rays, and 49 species of chimaeras in the class Chondrichthyes according to FishBase, a web-based portal of information on fishes maintained by an international consortium of scientists. The name Chondrichthyes is formed from the Greek prefix khondros meaning "cartilage" and suffix ikhthus for "fish." These species are referred to as the cartilaginous fishes. They have a skeleton composed of cartilage, a substance less calcium-impregnated than bone. This class is in the subphylum Craniata, which includes all animals having a brain enclosed within a solid case. The cartilaginous fishes are separated into two subclasses, the Holocephali and Elasmobranchii. The species in the first subclass have a single gill opening on either side of the head whereas members of the second have multiple openings on either side. The name Holocephali is derived from holos meaning "whole" and kephale meaning "head." It refers to a large, rounded head. These species are called chimaeras based on their appearance. Their large head with large eyes and protruding teeth, flexible body, and long tail make them vaguely resemble the fire-breathing Greek monster of that name. The monster had a lion's head, goat's body, and serpent's tail. The name of the second subclass, Elasmobranchii, is formed from elasmo meaning "plate" and suffix branch for "gill." This large taxonomic group is composed of the sharks, which have cylindrical bodies, and the rays, which have flattened bodies. Unlike the chimaeras, these species have multiple gill openings—the latter numbering from five to seven.
The long evolutionary history of the cartilaginous fishes is described in chapter 2. You will learn that the holocephalans were very diverse and abundant in the Paleozoic Era that ended roughly 250 million years ago (mya) and became far less so by the end of the Mesozoic Era 60 mya. Although sharks existed in the ancient seas with the early chimaeras, the species of sharks and rays radiated in the Mesozoic Era to occupy many new niches and become dominant fishes in the modern oceans. You will be introduced to species in the modern orders of sharks at the end of that chapter. Chapter 3 provides a description of the swimming styles of the sharks, rays, and chimaeras, their skeletons and fins, muscles, and external dermal denticles, and finally of how their caudal and pectoral fins propel them through the water with great agility. Ridged, tooth-like denticles are distributed over the entire body of sharks. However, they cover only part of the body of the less rapidly swimming rays and are absent on the bodies of the even slower-swimming chimaeras. The denticles serve to reduce drag, or the resistance to forward movement, as the viscous medium of water passes close to the body during forward movement. Competitive swimmers now wear suits covered with ridges similar to the rows of denticles on the skin of a shark or ray to increase hydrodynamic efficiency. Chapter 4 explains how the cartilaginous fishes balance the water and electrolyte content of their body fluids with that of the ocean. They are able to control the influx of the ions of sodium and chloride and the efflux of water using their rectal gland, kidney, and gills. They remain nearly isosmotic with saltwater because in addition to sodium and chloride ions, their tissues contain two other solutes in large concentrations, urea and trimethylamine oxide. Some species, such as the bull shark and freshwater stingray, enter fresh water environments. These species need instead to counteract the osmotic gain of water; they do this by producing copious urine. As water is drawn through the mouth, past the gills, and out the gill slits, heat from the body diff uses outward across the gills to warm the passing water, and oxygen diff uses inward from the water during the process of respiration. Furthermore, heat is lost from the muscles through the skin to a colder environment. Thus, it is not surprising that most chondrichthyans are ectothermic, or cold-blooded—their body temperature conforms to the temperature of the external environment. Despite these challenging obstacles to heat retention, the mackerel and thresher sharks and manta and mobula rays have evolved anatomical adaptations that enable them to warm their body in cold water. Specialized retes consisting of bundles of blood vessels in muscles, stomach, brain, and eyes enable these endothermic, or warm-blooded, species to maintain warm bodies. This important capability of mackerel sharks from the family Lamnidae and manta ray from the family Mobulidae will be discussed in chapter 5.
The cartilaginous fishes have a diversity of senses with varying ranges of detection that will be described in chapters 6 through 9. These fishes rely on their different senses to provide them with information that enables them to seek out their prey or mate or to flee from a predator. Chemicals are transported by currents in an odor corridor. These species detect chemicals as they pass through their nares (fig. 1.1f) and can follow a chemical gradient to its source. For example, a white shark can find a decaying whale carcass over a distance of several kilometers. Rays use this sense to locate living species buried within the substrate such as clams. They excrete chemicals into the water exiting their burrows. The anatomy of the olfactory receptor, how it differs among different species, the receptor's sensitivity to a myriad of chemicals, and the ability to localize the source of an odor source will be explained in chapter 6. Cartilaginous fishes can perceive with their inner ears (fig. 1.1c) the low-frequency pressure waves emitted by a struggling fish as far as half a kilometer away. At a closer distance, the tiny particle displacements propagated by the struggling fish can be detected with tiny cilia in lateral line and cranial canals and small neuromasts scattered over the body (figs. 1.1g & 1.1d). The structure of these sound pressure and water displacement organs, their spectral sensitivities, and the anatomical diversity among species will be described in chapter 7. The shark or ray sees its prey or mate upon approaching even closer—under the best conditions at a distance of 20 meters or so from it. The eyes of cartilaginous fishes have a tapetum lucidum (fig. 1.1b). This thin layer of reflective crystals located at the back of the retina reflects light back through it so that the light passes twice by the sensitive receptors providing two opportunities to absorb the photons. This increases the predator's ability to distinguish shapes in the low light levels present at twilight and nighttime. During daytime, dark tissue migrates over the exposed surface of the crystals and absorbs the impinging light so that it is not reflected backwards through the retina. In chapter 8, you will learn about the underwater photic environment, the anatomy of the eye, the spectral sensitivities of visual pigments, and the visual capabilities of the different cartilaginous fishes. All of the sharks, rays, and chimaeras have small pores on the underside of their heads connected to gel-filled tubules that lead to the nervous system, called the ampullae of Lorenzini (fig. 1.1e). These sense minute electrical fields, which are produced by fish, clams, and crabs while out of sight buried in the sand. This electromagnetic sense, described in chapter 9, enables sharks, rays, and chimaeras to find their way in the apparently featureless ocean by following the subtle patterns of magnetization on the sea floor or the earth's dipolar magnetic field.
The cartilaginous fishes are often described as "mindless feeding machines" in film documentaries. This is not really true. The size of their brains and various lobes will be described in chapter 10 along with their learning capabilities. The ratios of brain to body mass of more advanced sharks such as the scalloped hammerhead and bat eagle ray are comparable to those of birds and even mammals. Consistent with this is the ability of sharks to learn to discriminate between targets on the basis of their degree of illumination at a rate comparable to that of a mouse. The more advanced species of cartilaginous fishes have large and well-developed foliated forebrains, consistent with their possessing a diverse behavioral repertoire and complex social system comparable to those exhibited by birds and mammals.
The reproductive mode of the cartilaginous fishes promotes early feeding success. The male inserts one of its two claspers (fig. 1.2f), scrolled outside portions of their pelvic fins, into the female's cloaca to inseminate her in a manner analogous to human reproduction. Unlike most bony fishes, the embryos of cartilaginous fishes incubate for longer periods of up to two years. Some sharks, many rays, and all chimaeras produce embryos that develop within large leathery cases, yet the majority of sharks give birth to fully developed young. The newborn is almost a miniature replica of an adult and able to chase and capture small fishes immediately upon birth. Courtship behavior and reproductive biology are described in chapter 11. Live bearing has both advantages and disadvantages relative to egg laying. The fully developed juvenile has a greater chance of surviving than a tiny larval fish, which will perish if it does not find food quickly after absorbing the nutrients within its yolk sac. However, fewer well-developed embryos can be produced by a live-bearing shark than the thousands of larvae produced by an egg-bearing fish, and the juvenile sharks are easily caught by hook and line or in the nets of fishermen.
In chapter 12, the anatomy of the jaws and teeth of the cartilaginous fishes will be described, as well as the role of the muscles and teeth in jaw extension, seizure, and handling of prey. Shark and ray jaws are particularly well-suited for handling their prey. Their upper jaw is attached to the cranium by a pair of ligaments; the lower jaw is attached to cartilaginous elements that support the gills (fig. 1.2d). The jaw's elastic connections enable a shark to open its jaws wider and swallow large prey items as well as to remove large chunks of meat from prey too large to swallow. There are multiple rows of serrated teeth in the upper and lower jaws (fig. 1.2e). Embedded in one jaw are pointed teeth for holding struggling prey in place whereas in the other serrated teeth are moved back and forth laterally to saw off a chunk of meat. With sharpness and thinness of the teeth comes a tradeoff—brittleness. Either fragments or whole teeth become dislodged from the shark's jaw when feeding. Embryonic teeth continuously develop in the back of the tooth fold along the forward edge of the jaw and move forward to take their place in a new row. The diminutive members of this row grow larger while moving forward to form the next outer row of teeth. The chimaeras possess jaws better suited to feeding upon crustaceans and mollusks by crushing their hard external skeletons with their multiple rows of hard, flattened teeth arranged within the jaws.
Chapter 13 will discuss what cartilaginous fishes feed upon, their frequency of feeding, their rates of digestion and growth, and to what age they live. The composition of the diet of the cartilaginous fishes often changes as they grow larger and migrate from one geographical region to another. A species must digest its prey efficiently. Most cartilaginous fishes have spiraling folds in their intestines that increase the digestive surface within a small space to maximize the rate of digestion (fig. 1.2c). Some scientists have suggested that cartilaginous fishes grow slower than bony fishes because the coiled stomach of the former is smaller than the straight stomach of the latter. The diminutive size of the intestine makes room for a large liver, needed to maintain buoyancy, and a large uterus, needed for the prolonged development of their young.
You will learn about types of movement patterns exhibited by sharks and rays in chapter 14. Little is known about the movements of the chimaeras. Some elasmobranchs are ambushers, and their movements are restricted to a confined area. These sharks and rays lie in wait on the bottom to ambush crabs and shrimps or fishes that walk or swim over them close to the bottom. Members of other species of sharks actively search for their prey over intermediate distances yet return to a single location either to rest or interact socially with other members of the species. Such is the case of the reef and hammerhead sharks. The planktivorous sharks are more nomadic, moving over large distances in the oceans and searching for areas where plankton is abundant such as at the mouths of rivers and seamounts and at the boundaries between currents. Generally, swimming is sustained and directional between resting and foraging locations and slow and nondirectional when at feeding grounds. During their migrations elasmobranchs display two characteristic swimming behaviors, oscillatory diving and surface swimming, whose functions are not yet known with certainty.
Excerpted from The Biology of Sharks and Rays by A. PETER KLIMLEY. Copyright © 2013 by The University of Chicago. Excerpted by permission of THE UNIVERSITY OF CHICAGO PRESS.
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Meet the Author
A. Peter Klimley is adjunct professor in the Department of Wildlife, Fish, and Conservation and director of the Biotelemetry Laboratory at the University of California, Davis. He is the author of The Secret Life of Sharks.
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Finally just what the Doctor (Hammerhead) ordered for anyone! As a shark scientist and educator, I'm overjoyed to finally have a book like this at my disposal and so grateful that someone put in all the time, effort, and patience with a publisher to put together all the information and references contained herein in one organized and easy to use book. It has already made my own writing and citing go much quicker! The information in the book cites real journal articles in a very smooth format that professionals can use, but doesn't get too technical for someone just starting to learn about sharks. There are some pretty exciting tales included too. It is "the standard" for shark biology and even good enough to use as the textbook to teach ichthyology (my students thought so) and also as the main book for marine biology classes. It is that useful! THE essential book for all interested in sharks.