Marine Mammals of the World: A Comprehensive Guide to Their Identification

Thomas Allen Jefferson, Marc A. Webber, Robert L. Pitman, Brett Jarrett

• Verlag: Academic Press
• Jahr: 2011
• ISBN:
  9780080557847
• Thema: Biological Sciences
• Thema: Marine Biology

With coverage on all the marine mammals of the world, authors Jefferson, Webber, and Pitman have created a user-friendly guide to identify marine mammals alive in nature (at sea or on the beach), dead specimens "in hand", and also to identify marine mammals based on features of the skull. This handy guide provides marine biologists and interested lay people with detailed descriptions of diagnostic features, illustrations of external appearance, beautiful photographs, dichotomous keys, and more. Full color illustrations and vivid photographs of every living marine mammal species are incorporated, as well as comprehendible maps showing a range of information. For readers who desire further consultation, authors have included a list of literature references at the end of each species account. For an enhanced understanding of habitation, this guide also includes recognizable geographic forms described separately with colorful paintings and photographs. All of these essential tools provided make Marine Mammals of the World the most detailed and authoritative guide available!* Contains superb photographs of every species of marine mammal for accurate identification
* Authors' collective experience adds up to 80 years, and have seen nearly all of the species and distinctive geographic forms described in the guide
* Provides the most detailed and anatomically accurate illustrations currently available
* Special emphasis is placed on the identification of species in "problem groups, " such as the beaked whales, long-beaked oceanic dolphin, and southern fur seals
* Includes a detailed list of sources for more information at the back of the book.

1.

Introduction

The Need for This Guide

Interest in wildlife in general, and marine mammals in particular, has increased significantly in recent years, both in the general public and in the scientific and management communities. More people than ever are including wildlife watching in their activities, and this includes educational and adventure expeditions to see wild marine mammals up close. At the same time, there is increasing awareness of the integral importance of marine mammals to healthy aquatic ecosystems, and of the growing threats that a variety of human activities pose to these animals and their environments. Research and education programs are seeking to better understand and more clearly communicate the nature of these threats and appropriate steps to reduce or eliminate their impacts.

Good identification guides are integral to all these activities. Although there are many guides to limited geographical areas and some subsets of the world’s marine mammal fauna, there are few comprehensive guides that cover all the world’s whales, dolphins, porpoises, seals, sea lions, walruses, manatees, dugongs, marine and sea otters, and polar bears. Additionally, few of the existing guides provide special aids to identifying live animals, in-hand specimens, and skulls. This identification guide, compiled after several years of work by the authors and illustrators, is intended as a significant step toward filling that need.

We have attempted to make this volume as complete, comprehensive, and up-to-date as possible. However, we are aware that it is limited by the differences in the amount and quality of information available on the various groups, as well as by the inadequacies of our approach towards representing what is available. Therefore, we prefer to think of this as somewhat of a starting point, to be improved by input from those who use it in the field and lab. Future editions (assuming that there will be future editions, which is mainly determined by how well this one sells) will be modified to correct errors and deficiencies revealed by extensive use. In the mean time, we hope this book helps both amateurs and professionals with the sometimes-difficult task of positively identifying species of marine mammals they see alive or encounter dead.

Most biologists use the term ‘marine mammal’ to include members of five different mammalian groups: cetaceans (whales, dolphins, and porpoises), pinnipeds (seals, sea lions, and walruses), sirenians (manatees, dugongs, and sea cows), marine and sea otters, and the polar bear. These diverse groups are currently thought to represent five or six different recolonizations of the water by land-dwelling ancestors. The term marine mammal, therefore, implies no systematic or taxonomic relationship. In fact, the cetaceans are more closely related to camels and hippos than they are to other marine mammals, the pinnipeds have more in common with bears and weasels, and the sirenians are more closely allied to elephants and hyraxes. These differences not withstanding, however, all marine mammals have one thing in common—they derive all (or most) of their food from marine (or sometimes fresh) water.

All marine mammals have undergone major adaptations, which permit them to live in the water. The cetaceans and sirenians spend their entire lives in the water, while other marine mammals come ashore for various reasons, at particular times in their life cycle (most commonly to reproduce, molt, or rest). Major structural modifications to the bodies of cetaceans, sirenians, and pinnipeds involve the loss of hind limbs (e.g., cetaceans and sirenians), the adaptation of limbs for propulsion through water (e.g., pinnipeds), and the general streamlining of the body for hydrodynamic efficiency (all three groups). Structural modifications to the marine and sea otters and the polar bear by a marine existence are less apparent in body form; these animals in most ways still closely resemble their terrestrial counterparts.

Like its predecessor (Jefferson et al. 1993), since this is an identification guide, we include mainly information useful for identifying marine mammal species. For good introductions to the biology of mammals in general, see Gould and McKay (1990) and Macdonald (1984). More detail specifically on the biology of marine mammals can be found for cetaceans in Leatherwood and Reeves (1983), Evans (1987), Harrison and Bryden (1988), and Martin (1990); for pinnipeds in King (1983), Bonner (1990), Riedman (1990a), and Reeves et al. (1992); for sirenians in Reynolds and Odell (1991) and Reeves et al. (1992); for marine and sea otters in Riedman (1990b) and Reeves et al. (1992); and for polar bears in Stirling (1988) and Reeves et al. (1992). The best sources for basic information on the biology and phylogeny of marine mammals are Reynolds and Rommel (1999), Twiss and Reeves (1999), Berta et al. (2006), Hoelzel (2002), and Perrin et al. (2002).

Marine Mammal Identification and How to Use This Guide

Most available marine mammal identification guides do not provide the most appropriate information for accurate identification, have limited geographic or taxonomic scope, or are badly out-of-date. Two very good recent ones are Reeves et al. (2002) and Shirihai (2006). Marine mammals can be difficult to identify at sea. Even under ideal conditions, an observer often gets little more than a brief view of a splash, blow, dorsal fin, or back, and this is often at a great distance. Rough weather, glare, fog, or other poor sighting conditions only compound the problem. The effects of lighting, in particular, must be kept in mind. Many diagnostic characters may only be visible under good lighting or at close range. One must always acknowledge the limitations of the particular set of conditions that they are exposed to when making a marine mammal identification.

Sexual dimorphism is common in many pinnipeds and cetaceans. Northern elephant seals show an extreme form, which involves both size and body shape differences. The large individual in the background is an adult male, and the smaller one in the foreground is a fully-grown adult female. PHOTO: T.A. JEFFERSON

Many species appear similar to another, especially in the brief glimpses typical at sea. Animals of some poorly-known groups (most notably, beaked whales and Southern Hemisphere fur seals) are especially difficult to identify to species, even with a good look at a live animal or an “in hand” specimen (and even to most marine mammal specialists). For all these reasons, even experts often must log a sighting as “unidentified.” In all cases, this designation, accompanied by a detailed description is preferable to recording an incorrect identification. This point cannot be overemphasized!

In addition to the diagnostic variation among species, marine mammals often exhibit other types of variation in morphology and coloration. These are important to keep in mind when making identifications, as such variation can mask diagnostic species characters and cause confusion and even misidentifications. The most common types of such variation in external appearance are discussed briefly below.

Intraspecific geographic variation

Marine mammal species generally occur in populations that are (more-or-less) reproductively isolated from each other. If these populations have been separated for a long enough period of time, they may have evolved noticeable differences in their external morphology. Virtually every marine mammal species (with the possible exception of those that only occur as a single population, like the vaquita and possibly the baiji), shows some geographic variation. Much of this variation is subtle and not very noticeable, and therefore will not significantly affect field identification, but sometimes distinct geographic forms may have evolved. These may differ quite strongly in overall size, body shape, coloration, etc. Some such variants have been formally described as subspecies (which, in many cases, are incipient species), and have been given trinomials (subspecific names), but most have not been formally recognized. This book attempts to provide descriptions and illustrations/photos of geographic forms that are well-described and may be recognizable in the field, regardless of whether they have been described as subspecies.

Sexual dimorphism

Most marine mammal species show some sexual dimorphism, with one sex being somewhat larger than the other. In addition, many toothed whales and pinnipeds have males and females showing distinct differences in body shape and coloration. These differences usually remain insignificant until near the age of sexual maturity, but can become quite pronounced in adults. One must keep this dimorphism in mind when making identifications, especially in cases where only a single individual is involved. In the species accounts, we make every attempt to describe significant sexual dimorphism as it relates to marine mammal species identification.

Developmental variation

Obviously, young marine mammals do not look exactly like adults. Clearly, they are smaller than adults, but they may also have very different body proportions and color patterns. The head and appendages of most newborn marine mammals are typically proportionately larger than they are in adults. It is not uncommon for cetacean calves and pinniped pups to show very different pigmentation than adults. For instance, most dolphins have a muted version of the adult color pattern when first born. Size and other external differences of young animals are described in this book, when adequately documented.

Seasonal variation

Seasonal variation in external appearance is not nearly as important in...