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Home , Bathyraja, Bathyraja maculata, Bathyraja mariposa, Big skate, Deepsea skate, Leopard skate

Field Guide to , Skates, and Ratfish of

Duane E. Stevenson James W. Orr Gerald R. Hoff John D. McEachran

$25

Published by Alaska Sea Grant College Program University of Alaska Fairbanks Alaska Elmer E. Rasmuson Library Cataloging in Publication Data Stevenson, Duane E. Field guide to sharks, skates, and ratfish of Alaska / Duane E. Stevenson … [et al.]. – Fairbanks, Alaska : Alaska Sea Grant College Program, University of Alaska Fairbanks, 2007. p. : ill. ; cm. (Alaska Sea Grant College Program, University of Alaska Fairbanks) Includes bibliographic references and index. 1. —Alaska—Handbooks, manuals, etc. 2. Sharks—Alaska—Handbooks, manuals, etc. 3. Skates ()—Alaska—Handbooks, manuals, etc. 4. —Alaska—Handbooks, manuals, etc. I. Title. II. Stevenson, Duane E. III. Series: Alaska Sea Grant College Program, University of Alaska Fairbanks. QL638.6.S74 2007 ISBN 1-56612-113-2

Credits This book is published by the Alaska Sea Grant College Program, supported by the U.S. Department of Commerce, NOAA National Sea Grant Office, grant NA06OAR4170013, project A/161-01; and by the University of Alaska Fairbanks with state funds. The University of Alaska is an affirmative action/equal opportunity employer and educational institution. Sea Grant is a unique partnership with public and private sectors combining research, education, and technology transfer for public service. This national network of universities meets changing environmental and economic needs of people in our coastal, ocean, and Great Lakes regions. Book design and layout by Jen Gunderson, project coordination and graphics research by Kurt Byers, and production management and copyediting by Sue Keller, of Alaska Sea Grant. Cover art © Ray Troll. Cover design by Phil Raymond, Archetype Graphics, Fairbanks, Alaska. University of Alaska Fairbanks P.O. Box 755040 Fairbanks, Alaska 99775-5040 Toll free (888) 789-0090 (907) 474-6707 • fax (907) 474-6285 www.alaskaseagrant.org Alaska Contents

iv Preface v About the Authors vi About the Cover vii Acknowledgments 1 Introduction 4 Using This Guide 6 General Anatomy of Sharks 7 General Anatomy of Skates 8 General Anatomy of Cases 9 Key to the Sharks, Skates, and Ratfish of Alaska 14 Key to Egg Cases of Alaska Chondrichthyans 18 Ratfish Description 20 Descriptions 38 Descriptions 68 Photos of Alaska Sharks 69 Illustrations of Teeth of Alaska Sharks 70 Photos of Alaska Skates 71 Glossary 74 Selected References 76 Photo Sources 77 Index to Common and Scientific Names Inside back cover Map of North Pacific region iii iv Preface The primary purpose of this guide is to encourage and Most of the specimens, photos, and distribution data used in simplify the identification of chondrichthyans—sharks, the production of this guide were obtained during bottom skates, and ratfish—found in Alaska waters. It is intended trawl surveys conducted by the Resource Assessment and for professional fishery biologists as well as nonprofessional Conservation Engineering (RACE) Division of the National audiences. The guide has an identification key, designed Marine Fisheries Service, Alaska Fisheries Science Center primarily for the identification of specimens in hand. In (NMFS AFSC). These surveys provide a wealth of data for addition, color photographs, maps, and diagrams, as well as scientists and fisheries managers throughout the region, and text features such as diagnoses and similar species synopses, represent an invaluable aid to the effective stewardship of are included to aid users interested in rapid identification of Alaska’s marine resources. specimens that cannot be examined closely. We hope this guide will be useful to a broad audience, This guide also includes a key to the egg cases of including professional fishery biologists and fishery observers, chondrichthyans found in Alaska. Because this life stage commercial and recreational fishers, divers, and all others is poorly known for some species, it may not always be interested in learning more about Alaska’s chondrichthyan possible to identify an egg case to the species level. We resources. We also hope that this guide will encourage hope that including this preliminary key will stimulate conservation by providing the basis for better management further investigation into the interspecific differences in this and future research, as well as a tool to promote public important and interesting life-history stage. awareness and understanding of these vulnerable and poorly known fishes. Species are arranged in the guide in the order that they appear in the key to adult fishes, with the ratfish first, followed Duane E. Stevenson by sharks and finally skates. In most cases, this means that the James W. Orr most similar species are grouped together. Gerald R. Hoff John D. McEachran About the Authors Duane Stevenson and James Orr are research fisheries Seattle. His research focuses on the biology and ecology of biologists at the National Marine Fisheries Service (NMFS), noncommercial deepwater fish species in the North Pacific. Alaska Fisheries Science Center’s Resource Assessment He has done extensive work on the ecology and reproduction and Conservation Engineering (RACE) Division in Seattle, of skates in Alaska with an emphasis on conservation of their . Their research interests include the marine habitats. and systematics of many groups of fishes. In addition to published research, they have worked extensively within John McEachran is a professor in the Department of Wildlife both the AFSC groundfish program and the North Pacific and Fisheries Sciences at Texas A&M University in College Groundfish Observer Program to provide training and Station, Texas. His research concerns the systematics and produce field guides to several groups of Alaska fishes and biogeography of skates and rays, and species diversity and . biogeography of fishes of the central western Atlantic. He has also made several contributions to the series FAO Species Gerald Hoff is also a research fisheries biologist at the Identification Guide for Fishery Purposes. NMFS Alaska Fisheries Science Center’s RACE Division in

v vi About the Cover Ray Troll is an artist and naturalist based in Ketchikan, Alaska. underappreciated fish. Troll even has a New Zealand species Troll is widely known for his accurate and often “offbeat” of ratfish named after him: trolli. Troll’s accolades renderings of sea life. His fish-centric art can be seen on include the Alaska Governor’s Award for Individual Artist, T-shirts, in numerous books, and in nationwide museum and an award from the Academy of Natural Sciences for displays. He is a lifelong “sharkophile” and promoter of achievement in natural history arts. See www.trollart.com.

1. Thresher Shark, Alopias vulpinis, to 6.4 m (20 ft). 2 2. Basking Shark, Cetorhinus maximus, to 10 m (35 ft). 1 6 3. Okhotsk Skate, violacea, to 73 cm (2.5 ft). 7 4. Spiny Dogfish, Squalus acanthias, to 2 m (6.5 ft). 4 5. Sleeper Shark, Somniosus pacificus to 4.4 m (14.5 ft). 6. “,” Bathyraja sp., to 139 cm (4.5 ft). 3 7. Whiteblotched Skate, , to 147 cm (5 ft). 5 8. , binoculata, to 204 cm (7 ft). 8 20 9. Commander Skate, Bathyraja lindbergi, to 102 cm (3.5 ft). 9 10. Butterfly Skate, , to 76 cm (2.5 ft). 11. Salmon Shark, Lamna ditropis, to 3.1 m (10 ft). 10 12. Mud Skate, Bathyraja taranetzi, to 77 cm (2.5 ft). 12 13. Great White Shark, Carcharodon carcharias, to 6.4 m (21 ft). 11 14. Bluntnose Sixgill Shark, Hexanchus griseus, to 4.8 m (16 ft). 19 14 15. Spotted Ratfish, Hydrolagus colliei, to 100 cm (3 ft). 13 16. Brown Cat Shark, Apristurus brunneus, to 71 cm (2.5 ft). 17. Longnose Skate, Raja rhina, to 142 cm (4.5 ft). 18 17 15 18. , Bathyraja abyssicola, to 157 cm (5 ft). 16 19. Bering Skate, Bathyraja interrupta, to 86 cm (3 ft). 20. Blue Shark, Prionace glauca, to 3.8 m or more (12.5 ft).

Acknowledgments The work on which this guide is based is derived primarily on groundfish trawl surveys conducted by the Alaska from the unpublished research of J.D. McEachran, and was Fisheries Science Center. Others were provided by Nancy enhanced by the field observations of D.W. Kessler and R. Kohler (NMFS Northeast Fisheries Science Center), the North Baxter. It also draws on the published works of Hart (1973), Pacific Groundfish Observer Program, Alexei Orlov (Russian Eschmeyer et al. (1983), and Mecklenburg et al. (2002). The Federal Research Institute of Fisheries and Oceanography authors have received assistance from numerous scientists [VNIRO]), and others. The photo sources are listed on page 76. in the NMFS AFSC Resource Assessment and Conservation Anatomical diagrams and illustrations were prepared by Engineering (RACE) Division, Resource Ecology and Fisheries Duane Stevenson, with many of the tooth illustrations relying Management (REFM) Division, and North Pacific Groundfish on the observations of Bigelow and Schroeder (1948). Stippled Observer Program (NPGOP); as well as the captains and crew line drawings of the sharks were prepared by Tim Gunther of a number of chartered fishing vessels, particularly the F/V (www.gunthergraphics.biz). Theodore Pietsch (University of Aldebaran, F/V Arcturus, F/V Dominator, F/V Gladiator, F/V Washington), David Ebert (Pacific Shark Research Center), Ken Morning Star, F/V Northwest Explorer, F/V Sea Storm, and F/V Goldman (Alaska Department of Fish and Game), and Bob Vesteraalen; and several North Pacific groundfish observers. Lauth (NMFS, Alaska Fisheries Science Center) reviewed earlier The majority of photographs were taken by NMFS personnel versions of this manuscript.

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Introduction Sharks, skates, and ratfish constitute important components chondrichthyans by the presence of a gill cover overlying of Alaska’s marine ecosystems. Most of these fishes are the gill openings. Approximately 34 species of are relatively large compared with other marine fauna. They are currently known from the world’s oceans. The elasmobranch thought to be long-lived and have low reproductive rates, and lineage is much more diverse, with over 930 extant species therefore may be some of the most vulnerable components worldwide. This lineage, distinguished from holocephalans of the ecosystem. Unfortunately, many aspects of the life by the presence of 5-7 gill openings on each side of the head, history of these species, including longevity, fecundity, and includes the sharks and rays (including skates, , and food habits, are poorly known. Because cartilaginous fishes ). do not support large commercial fisheries, they have received comparatively little attention from fisheries managers and Diversity researchers. However, they are a large component of fisheries The marine waters of Alaska feature a broad diversity of , and as the important biological characteristics of chondrichthyans, including the relatively small and enigmatic cartilaginous fishes are recognized, interest in their diversity spotted ratfish, representatives of at least four orders of and conservation is increasing. sharks, and many species of skates. Alaska’s shark fauna includes open water predators, a large planktivore, and The sharks, skates, and ratfish are members of the class several bottom-dwelling species found from the intertidal Chondrichthyes, also known as the chondrichthyans, which zone to depths of over 2,000 meters. Some species are includes two main evolutionary lineages: the holocephalans transient or seasonal visitors to Alaska, while others are and the elasmobranchs. The holocephalan lineage is constant residents that can be quite abundant in some areas. represented by several extinct forms, as well as the recent Distribution and abundance patterns are poorly known for forms known as chimaeras, represented in Alaska by the pelagic shark species. spotted ratfish. Holocephalans are distinguished from other

1 Introduction 2

The skates of this region have frustrated scientists and also tend to have a much more scalloped body shape, with naturalists for decades. Due to their diversity and apparent a broad shallow indentation on the leading edge of each external similarity, as well as gaps in the taxonomic pectoral fin, while the females are much more rounded or knowledge of the group, skates have historically been diamond-shaped. Male chimaeras have an accessory clasping considered very difficult to identify. Moreover, the terms organ on the head in addition to the pair of claspers at the “skate” and “ray” are often used interchangeably and are not base of the pelvic fins, while females have neither. Shark clearly and universally defined. In general, “ray” is a more species tend to show relatively little sexual dimorphism, with inclusive term that may be used to indicate any flattened the exception of the presence of claspers in males (some elasmobranch, while “skate” denotes a specific order of species exhibit minor differences in tooth shape and relative flattened elasmobranchs (). We use the more fin placement). In most chondrichthyans, females reach a precise term “skate” for all the flattened elasmobranchs larger maximum size than males. included in this guide because they are all in the order Rajiformes. Reproduction The chondrichthyans of Alaska exhibit a broad diversity of Sexual Dimorphism reproductive strategies. Most of Alaska’s chondrichthyans, Many chondrichthyan species are sexually dimorphic. This including the spotted ratfish, the brown cat shark, and all can create identification difficulties as the morphological skates, are oviparous, depositing thick leathery egg cases differences between males and females of a single species containing one to several embryos directly onto the seafloor. may appear more dramatic than the differences between two The embryo develops for an extended period (months to similar species. This phenomenon is most obvious in skates, years) inside the egg case and the juvenile emerges fully in which males have paired claspers, one extending from developed. The remaining sharks of Alaska exhibit some form the base of each , and in many species adult males of viviparity. After an extended period of development inside have alar and malar hooks on the dorsal surface. Male skates the female, the young of these species are born looking much like miniature adults. The spiny dogfish, Pacific sleeper shark, and skates) that have been reliably recorded from Alaska and bluntnose sixgill shark exhibit aplacental viviparity, in waters. It does not include some of the species that have been which the developing embryos are completely dependent traditionally included in the faunal works of the region (e.g., on the nutrition provided by a yolk sac. Basking, thresher, Wilimovsky 1954, Mecklenburg et al. 2002), such as the manta salmon, and great white shark embryos receive their nutrition ray (Manta birostris), shortfin mako shark Isurus( oxyrinchus), from the consumption of additional nonviable ova that are and Pacific angel shark Squatina( californica), because these produced by the female—a reproductive strategy known species have not yet been confirmed from Alaska waters. as oophagous viviparity. The blue shark exhibits placental viviparity, in which the embryo is nourished directly from the The book was designed for use in the field. As such, priority female through placental tissue. is given to characteristics useful in the field, as well as distribution information gleaned from the authors’ extensive Sources recent field experience. The book is not an exhaustive This guide combines morphological information from the review of the current state of knowledge for these fishes. authors’ extensive field collections and examination of For an introduction to the literature on these fishes, and museum specimens, with detailed distribution data based for additional information on their taxonomic history and on resource-assessment surveys, observer collections, and geographic ranges, the reader is encouraged to consult the information from the scientific literature. The result is the references on p. 74. Some excellent sources of information most comprehensive overview of Alaska’s cartilaginous fish on shark and skate life history, behavior, reproduction, and fauna ever produced for use in the field. This guide includes fisheries management are Hamlett (1999, 2005), Carrier et al. all species of chondrichthyans (including chimaeras, sharks, (2004), and Musick and Bonfil (2004).

Introduction 3 4 Using This Guide This guide includes a dichotomous key to adult descriptions to confirm the identification by comparison chondrichthyans of Alaska (pp. 9-13) as well as a key to the egg with similar species. The specialized terminology used in the cases of the oviparous species. The portion of the key devoted key and species descriptions is defined on the anatomical to sharks primarily uses fin placement and morphology to diagrams (pp. 6-8) or in the glossary. distinguish the species, while the skate section relies on the presence or absence of various thorn series, as well as Diagnosis and Photos coloration pattern and, to a lesser extent, disc and fin shape. After working through the key and proceeding to the species Although these suites of characters are generally quite accounts, consult the diagnosis of the presumptive species. reliable, and with practice easy to use, some of the included This diagnosis includes a suite of characteristics that will species exhibit a great deal of morphological variation. This is unambiguously identify that species to the exclusion of all particularly true with respect to the relative size and strength others known from Alaska. In addition to the diagnosis, each of thorns in a few species of skates. Thus, users should remain species account includes photos as well as information on open to the possibility that a particular specimen may have dentition, coloration, body shape, reproduction, maximum highly reduced thorns or, conversely, may even have a thorn size, and geographic and bathymetric range. When possible, in the “wrong place.” With experience, users will begin to skate species descriptions include a photo of a male and recognize these variants as intraspecific anomalies and will a female to highlight shape differences. (Note that ventral not be discouraged by the occasional odd specimen. views of the Okhotsk and deepsea skates show everted spiral valves.) A single-page composite of all Alaska sharks (p. 68), Species Key a composite of teeth for each shark species (p. 69), and a The reader attempting to identify an adult is encouraged to composite of dorsal views of all skates found in Alaska waters start with the “Key to the Sharks, Skates, and Ratfish of Alaska” (p. 70) are included after the species descriptions for quick beginning on p. 9 and proceed to the individual species reference. Illustrations Egg Case Key Each skate species description also includes a thorn diagram, The reader attempting to identify an egg case is encouraged while each shark species description includes a tooth to start with the “Key to Egg Cases of Alaska Chondrichthyans” illustration. Thorn diagrams indicate which thorn series are (pp. 14-16). The terminology used in this key is illustrated in typically present in that skate species. Series that may be the egg case diagrams on p. 8. The key is based on characters present or absent are indicated in parentheses. The name of such as case length and width, surface texture, spine each thorn series and its respective abbreviation is on the morphology, keel width, and byssal thread attachment. With skate diagram on p. 7. The total midline thorn count is the sum the exception of the deepwater species badia, all of the nuchal, mid-dorsal, tail, and interdorsal thorns. Tooth egg-case characters were verified with specimens taken from illustrations depict the lateral (external) view of one upper and inside adult females. Although egg-case size is dependent one lower tooth, generally representing the fourth tooth from on maternal size, many species exhibit non-overlapping size the center on the left side of the jaw. When possible, thorn ranges and therefore the length and width of an egg case can or tooth characteristics, along with the range map and other also be useful for identification. The egg cases of Bathyraja characters, should be used to confirm the identification. violacea and B. interrupta are presently indistinguishable, and these two species are grouped together in the egg-case key. Similar Species An egg-case photo is provided with each species account. The “similar species” section of the species account includes other chondrichthyans known from Alaska waters that may Measurements be confused with the species in question, as well as the All adult lengths included in this book are total length. Egg characteristics useful in distinguishing them. This section case size refers to case length (i.e., without horns) or case should be consulted to provide final confirmation of the width, including keels, and all egg case dimensions are given diagnosis. in millimeters (mm). All depths are given in meters (m).

Using this Guide 5