field guide to sharks, skates, and ratfish of alaskanmfs alaska fisheries science center’s race...

$25

Published by Alaska Sea Grant College ProgramUniversity of Alaska Fairbanks

Alaska

F i e l d G u i d e t o

Sharks, Skates, and Ratfish of AlaskaDuane E. StevensonJames W. OrrGerald R. Hoff John D. McEachran

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. Chondrichthyes—Alaska—Handbooks, manuals, etc. 2. Sharks—Alaska—Handbooks, manuals, etc. 3. Skates (Fishes)—Alaska—Handbooks, manuals, etc. 4. Chimaeridae—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

CreditsThis 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 FairbanksP.O. Box 755040 Fairbanks, Alaska 99775-5040Toll free (888) 789-0090(907) 474-6707 • fax (907) 474-6285www.alaskaseagrant.org Alaska

iii

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 Egg Cases 9 Key to the Sharks, Skates, and Ratfish of Alaska 14 Key to Egg Cases of Alaska Chondrichthyans 18 Ratfish Description 20 Shark Descriptions 38 Skate 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

Contents

The primary purpose of this guide is to encourage and simplify the identification of chondrichthyans—sharks, skates, and ratfish—found in Alaska waters. It is intended for professional fishery biologists as well as nonprofessional audiences. The guide has an identification key, designed primarily for the identification of specimens in hand. In addition, color photographs, maps, and diagrams, as well as text features such as diagnoses and similar species synopses, are included to aid users interested in rapid identification of specimens that cannot be examined closely.

This guide also includes a key to the egg cases of chondrichthyans found in Alaska. Because this life stage is poorly known for some species, it may not always be possible to identify an egg case to the species level. We hope that including this preliminary key will stimulate further investigation into the interspecific differences in this important and interesting life-history stage.

Species are arranged in the guide in the order that they appear in the key to adult fishes, with the ratfish first, followed by sharks and finally skates. In most cases, this means that the most similar species are grouped together.

Most of the specimens, photos, and distribution data used in the production of this guide were obtained during bottom trawl surveys conducted by the Resource Assessment and Conservation Engineering (RACE) Division of the National Marine Fisheries Service, Alaska Fisheries Science Center (NMFS AFSC). These surveys provide a wealth of data for scientists and fisheries managers throughout the region, and represent an invaluable aid to the effective stewardship of Alaska’s marine resources.

We hope this guide will be useful to a broad audience, including professional fishery biologists and fishery observers, commercial and recreational fishers, divers, and all others interested in learning more about Alaska’s chondrichthyan fish resources. We also hope that this guide will encourage conservation by providing the basis for better management and future research, as well as a tool to promote public awareness and understanding of these vulnerable and poorly known fishes.

Duane E. StevensonJames W. OrrGerald R. HoffJohn D. McEachran

Prefaceiv

v

Duane Stevenson and James Orr are research fisheries biologists at the National Marine Fisheries Service (NMFS), Alaska Fisheries Science Center’s Resource Assessment and Conservation Engineering (RACE) Division in Seattle, Washington. Their research interests include the taxonomy and systematics of many groups of fishes. In addition to published research, they have worked extensively within both the AFSC groundfish program and the North Pacific Groundfish Observer Program to provide training and produce field guides to several groups of Alaska fishes and invertebrates.

Gerald Hoff is also a research fisheries biologist at the NMFS Alaska Fisheries Science Center’s RACE Division in

Seattle. His research focuses on the biology and ecology of noncommercial deepwater fish species in the North Pacific. He has done extensive work on the ecology and reproduction of skates in Alaska with an emphasis on conservation of their marine habitats.

John McEachran is a professor in the Department of Wildlife and Fisheries Sciences at Texas A&M University in College Station, Texas. His research concerns the systematics 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 Identification Guide for Fishery Purposes.

About the Authors

Ray Troll is an artist and naturalist based in Ketchikan, Alaska. Troll is widely known for his accurate and often “offbeat” renderings of sea life. His fish-centric art can be seen on T-shirts, in numerous books, and in nationwide museum displays. He is a lifelong “sharkophile” and promoter of

underappreciated fish. Troll even has a New Zealand species of ratfish named after him: Hydrolagus trolli. Troll’s accolades include the Alaska Governor’s Award for Individual Artist, and an award from the Academy of Natural Sciences for achievement in natural history arts. See www.trollart.com.

About the Cover

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

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vi

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The work on which this guide is based is derived primarily from the unpublished research of J.D. McEachran, and was enhanced by the field observations of D.W. Kessler and R. Baxter. It also draws on the published works of Hart (1973), Eschmeyer et al. (1983), and Mecklenburg et al. (2002). The authors have received assistance from numerous scientists in the NMFS AFSC Resource Assessment and Conservation Engineering (RACE) Division, Resource Ecology and Fisheries Management (REFM) Division, and North Pacific Groundfish Observer Program (NPGOP); as well as the captains and crew of a number of chartered fishing vessels, particularly the F/V Aldebaran, F/V Arcturus, F/V Dominator, F/V Gladiator, F/V Morning Star, F/V Northwest Explorer, F/V Sea Storm, and F/V Vesteraalen; and several North Pacific groundfish observers. The majority of photographs were taken by NMFS personnel

on groundfish trawl surveys conducted by the Alaska Fisheries Science Center. Others were provided by Nancy Kohler (NMFS Northeast Fisheries Science Center), the North Pacific Groundfish Observer Program, Alexei Orlov (Russian Federal Research Institute of Fisheries and Oceanography [VNIRO]), and others. The photo sources are listed on page 76. Anatomical diagrams and tooth illustrations were prepared by Duane Stevenson, with many of the tooth illustrations relying on the observations of Bigelow and Schroeder (1948). Stippled line drawings of the sharks were prepared by Tim Gunther (www.gunthergraphics.biz). Theodore Pietsch (University of Washington), David Ebert (Pacific Shark Research Center), Ken Goldman (Alaska Department of Fish and Game), and Bob Lauth (NMFS, Alaska Fisheries Science Center) reviewed earlier versions of this manuscript.

Acknowledgments

1

Sharks, skates, and ratfish constitute important components of Alaska’s marine ecosystems. Most of these fishes are relatively large compared with other marine fauna. They are thought to be long-lived and have low reproductive rates, and therefore may be some of the most vulnerable components of the ecosystem. Unfortunately, many aspects of the life history of these species, including longevity, fecundity, 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 researchers. However, they are a large component of fisheries bycatch, and as the important biological characteristics of cartilaginous fishes are recognized, interest in their diversity and conservation is increasing.

The sharks, skates, and ratfish are members of the class Chondrichthyes, also known as the chondrichthyans, which includes two main evolutionary lineages: the holocephalans and the elasmobranchs. The holocephalan lineage is represented by several extinct forms, as well as the recent forms known as chimaeras, represented in Alaska by the spotted ratfish. Holocephalans are distinguished from other

chondrichthyans by the presence of a gill cover overlying the gill openings. Approximately 34 species of chimaeras are currently known from the world’s oceans. The elasmobranch lineage is much more diverse, with over 930 extant species worldwide. This lineage, distinguished from holocephalans by the presence of 5-7 gill openings on each side of the head, includes the sharks and rays (including skates, sawfishes, and guitarfishes).

DiversityThe marine waters of Alaska feature a broad diversity of chondrichthyans, including the relatively small and enigmatic spotted ratfish, representatives of at least four orders of sharks, and many species of skates. Alaska’s shark fauna includes open water predators, a large planktivore, and several bottom-dwelling species found from the intertidal zone to depths of over 2,000 meters. Some species are transient or seasonal visitors to Alaska, while others are constant residents that can be quite abundant in some areas. Distribution and abundance patterns are poorly known for pelagic shark species.

Introduction

The skates of this region have frustrated scientists and naturalists for decades. Due to their diversity and apparent external similarity, as well as gaps in the taxonomic knowledge of the group, skates have historically been considered very difficult to identify. Moreover, the terms “skate” and “ray” are often used interchangeably and are not clearly and universally defined. In general, “ray” is a more inclusive term that may be used to indicate any flattened elasmobranch, while “skate” denotes a specific order of flattened elasmobranchs (Rajiformes). We use the more precise term “skate” for all the flattened elasmobranchs included in this guide because they are all in the order Rajiformes.

Sexual DimorphismMany chondrichthyan species are sexually dimorphic. This can create identification difficulties as the morphological differences between males and females of a single species may appear more dramatic than the differences between two similar species. This phenomenon is most obvious in skates, in which males have paired claspers, one extending from the base of each pelvic fin, and in many species adult males have alar and malar hooks on the dorsal surface. Male skates

also tend to have a much more scalloped body shape, with a broad shallow indentation on the leading edge of each pectoral fin, while the females are much more rounded or diamond-shaped. Male chimaeras have an accessory clasping organ on the head in addition to the pair of claspers at the base of the pelvic fins, while females have neither. Shark species tend to show relatively little sexual dimorphism, with the exception of the presence of claspers in males (some species exhibit minor differences in tooth shape and relative fin placement). In most chondrichthyans, females reach a larger maximum size than males.

ReproductionThe chondrichthyans of Alaska exhibit a broad diversity of reproductive strategies. Most of Alaska’s chondrichthyans, including the spotted ratfish, the brown cat shark, and all skates, are oviparous, depositing thick leathery egg cases containing one to several embryos directly onto the seafloor. The embryo develops for an extended period (months to years) inside the egg case and the juvenile emerges fully developed. The remaining sharks of Alaska exhibit some form of viviparity. After an extended period of development inside the female, the young of these species are born looking much

2Introduction

3

like miniature adults. The spiny dogfish, Pacific sleeper shark, and bluntnose sixgill shark exhibit aplacental viviparity, in which the developing embryos are completely dependent on the nutrition provided by a yolk sac. Basking, thresher, salmon, and great white shark embryos receive their nutrition from the consumption of additional nonviable ova that are produced by the female—a reproductive strategy known as oophagous viviparity. The blue shark exhibits placental viviparity, in which the embryo is nourished directly from the female through placental tissue.

SourcesThis guide combines morphological information from the authors’ extensive field collections and examination of museum specimens, with detailed distribution data based on resource-assessment surveys, observer collections, and information from the scientific literature. The result is the most comprehensive overview of Alaska’s cartilaginous fish fauna ever produced for use in the field. This guide includes all species of chondrichthyans (including chimaeras, sharks,

and skates) that have been reliably recorded from Alaska waters. It does not include some of the species that have been traditionally included in the faunal works of the region (e.g., Wilimovsky 1954, Mecklenburg et al. 2002), such as the manta ray (Manta birostris), shortfin mako shark (Isurus oxyrinchus), and Pacific angel shark (Squatina californica), because these species have not yet been confirmed from Alaska waters.

The book was designed for use in the field. As such, priority is given to characteristics useful in the field, as well as distribution information gleaned from the authors’ extensive recent field experience. The book is not an exhaustive review of the current state of knowledge for these fishes. For an introduction to the literature on these fishes, and for additional information on their taxonomic history and geographic ranges, the reader is encouraged to consult the references on p. 74. Some excellent sources of information on shark and skate life history, behavior, reproduction, and fisheries management are Hamlett (1999, 2005), Carrier et al. (2004), and Musick and Bonfil (2004).

Introduction

4

This guide includes a dichotomous key to adult chondrichthyans of Alaska (pp. 9-13) as well as a key to the egg cases of the oviparous species. The portion of the key devoted to sharks primarily uses fin placement and morphology to distinguish the species, while the skate section relies on the presence or absence of various thorn series, as well as coloration pattern and, to a lesser extent, disc and fin shape. Although these suites of characters are generally quite reliable, and with practice easy to use, some of the included species exhibit a great deal of morphological variation. This is particularly true with respect to the relative size and strength of thorns in a few species of skates. Thus, users should remain open to the possibility that a particular specimen may have highly reduced thorns or, conversely, may even have a thorn in the “wrong place.” With experience, users will begin to recognize these variants as intraspecific anomalies and will not be discouraged by the occasional odd specimen.

Species KeyThe reader attempting to identify an adult is encouraged to start with the “Key to the Sharks, Skates, and Ratfish of Alaska” beginning on p. 9 and proceed to the individual species

descriptions to confirm the identification by comparison with similar species. The specialized terminology used in the key and species descriptions is defined on the anatomical diagrams (pp. 6-8) or in the glossary.

Diagnosis and PhotosAfter working through the key and proceeding to the species accounts, consult the diagnosis of the presumptive species. This diagnosis includes a suite of characteristics that will unambiguously identify that species to the exclusion of all others known from Alaska. In addition to the diagnosis, each species account includes photos as well as information on dentition, coloration, body shape, reproduction, maximum size, and geographic and bathymetric range. When possible, skate species descriptions include a photo of a male and a female to highlight shape differences. (Note that ventral views of the Okhotsk and deepsea skates show everted spiral valves.) A single-page composite of all Alaska sharks (p. 68), a composite of teeth for each shark species (p. 69), and a composite of dorsal views of all skates found in Alaska waters (p. 70) are included after the species descriptions for quick reference.

Using This Guide

IllustrationsEach skate species description also includes a thorn diagram, while each shark species description includes a tooth illustration. Thorn diagrams indicate which thorn series are typically present in that skate species. Series that may be present or absent are indicated in parentheses. The name of each thorn series and its respective abbreviation is on the skate diagram on p. 7. The total midline thorn count is the sum of the nuchal, mid-dorsal, tail, and interdorsal thorns. Tooth illustrations depict the lateral (external) view of one upper and one lower tooth, generally representing the fourth tooth from the center on the left side of the jaw. When possible, thorn or tooth characteristics, along with the range map and other characters, should be used to confirm the identification.

Similar SpeciesThe “similar species” section of the species account includes other chondrichthyans known from Alaska waters that may be confused with the species in question, as well as the characteristics useful in distinguishing them. This section should be consulted to provide final confirmation of the diagnosis.

Egg Case KeyThe reader attempting to identify an egg case is encouraged to start with the “Key to Egg Cases of Alaska Chondrichthyans” (pp. 14-16). The terminology used in this key is illustrated in the egg case diagrams on p. 8. The key is based on characters such as case length and width, surface texture, spine morphology, keel width, and byssal thread attachment. With the exception of the deepwater species Amblyraja badia, all egg-case characters were verified with specimens taken from inside adult females. Although egg-case size is dependent on maternal size, many species exhibit non-overlapping size ranges and therefore the length and width of an egg case can also be useful for identification. The egg cases of Bathyraja violacea and B. interrupta are presently indistinguishable, and these two species are grouped together in the egg-case key. An egg-case photo is provided with each species account.

MeasurementsAll adult lengths included in this book are total length. Egg case size refers to case length (i.e., without horns) or case width, including keels, and all egg case dimensions are given in millimeters (mm). All depths are given in meters (m).

5Using this Guide

6General Anatomy of Sharks

dorsal-fin spine first dorsal fin

second dorsal fin

caudal keel

caudal fin

anal finclasper (male)pelvic fin

pectoral fin

gill slitsmouth

nostrileye

spiracle

7

General Anatomy of Skates

scapular thorns (S)

mid-dorsal thorns (D)

tail thorns dorsal fins

caudal fin

interdorsal thornsclasper (male)

cloaca

pelvic fin

Ventral

Dorsal

pectoral fin

gill slits

alar hooks

spiracleorbital thorns (O)

rostral thornlets

malar hooksnuchal thorns (N)

pseudosiphon

dorsal lobe

ventral lobe

Skate Clasper

8

byssal threadsattached on anterior horns

byssal threadsattached at anterior margin

byssal threadsattached at mid-case

byssal threadsattached at posterior margin

byssal threadsattached on posterior horns

posterior horns

keelmid-casekeel width

mid-case width(includes keels)

case length

anterior horns posterior margin

anterior margin

Egg Case Dorsal View

anterior horns (with dorsal curl) dorsal surface

posterior hornsventral surface

Egg Case Lateral View

General Anatomy of Egg Cases

9

1 One gill slit on each side of head, covered by an opercle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 18 Spotted ratfish (Hydrolagus colliei)

Gill slits 5-7, on sides or underside of head 2

2 (1) Body not flattened, nearly round in cross section; pectoral fins not enlarged or fused with head; gill openings on side of head Sharks 3

Body distinctly flattened; pectoral fins large and fused with head, giving the body a disc shape; gill openings on underside of head Skates 11

3 (2) Anal fin absent 4

Anal fin present 5

4 (3) Single spine at front of each dorsal fin; pectoral fins large and pointed; caudal fin with two distinct lobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 20 Spiny dogfish (Squalus acanthias)

No spine at front of dorsal fins; pectoral fins small and rounded; caudal fin without distinct lobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 22 Pacific sleeper shark (Somniosus pacificus)

5 (3) Gill slits 6; single dorsal fin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 24 Bluntnose sixgill shark (Hexanchus griseus)

Gill slits 5; two dorsal fins 6

6 (5) Gill slits highly elongate, extending from dorsal surface of head nearly to ventral midline of body; teeth very small, with flattened, posteriorly directed cusp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 26 Basking shark (Cetorhinus maximus)

Gill slits restricted to side of head; teeth relatively large, sharp, with one or more cusps 7

K e y t o t h e S h a r k s , S k a t e s , and Ratfish of Alaska

7 (6) Front of first dorsal fin posterior to front of pelvic fins; caudal fin weakly developed; maximum length less than 70 cm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 28 Brown cat shark (Apristurus brunneus)

Front of first dorsal fin anterior to front of pelvic fins; caudal fin well developed; maximum length greater than 70 cm 8

8 (7) Caudal fin extremely heterocercal, with upper lobe many times length of lower lobe; teeth without serrations or cusps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 30 Thresher shark (Alopias vulpinus)

Caudal fin not extremely heterocercal; teeth with serrations or cusps 9

9 (8) Pectoral fin, head, and body long and narrow; two posterior-most gill slits above pectoral-fin base; caudal fin distinctly heterocercal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 32 Blue shark (Prionace glauca)

Pectoral fin, head, and body short and robust; all gill slits anterior to pectoral-fin base; caudal fin nearly homocercal 10

10 (9) First dorsal-fin base almost directly above pectoral-fin base; teeth with lateral cusps, not serrate; secondary lateral keel on caudal peduncle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 34 Salmon shark (Lamna ditropis)

First dorsal-fin base almost entirely posterior to pectoral-fin base; teeth without lateral cusps, serrate; no secondary lateral keel on caudal peduncle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 36 Great white shark (Carcharodon carcharias)

11 (2) Snout firm to tip; pectoral-fin rays fall distinctly short of tip of snout 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Amblyraja and Raja)

Snout flexible, especially near tip; pectoral-fin rays nearly reach tip of snout 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Bathyraja)

12 (11) Two or three pairs of scapular thorns; small rostral thorns (thornlets) present on dorsal surface near tip of snout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 38 Roughshoulder skate (Amblyraja badia)

Scapular thorns and rostral thorns absent 13

10Key to the Sharks, Skates, and Ratfish of Alaska

13 (12) Posterolateral margin of pelvic fin slightly concave; base of pectoral fin with large ocellus surrounded by ring of light spots; ventral surface nearly white; body diamond-shaped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 40 Big skate (Raja binoculata)

Posterolateral margin of pelvic fin deeply notched; base of pectoral fin with ring of dark pigment; ventral surface dark; body diamond-shaped, with elongate snout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 42 Longnose skate (Raja rhina)

14 (12) Scapular thorns present (may be reduced) 15

Scapular thorns absent 18

15 (14) Denticles absent from area surrounding tail thorns; orbital thorns present (but often obscure) 16

Denticles present in area around and between tail thorns; orbital thorns absent 17

16 (15) Dorsal surface generally brown, often with a few light spots or blotches; total midline thorn count typically 32 or less . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 44 Alaska skate (Bathyraja parmifera)

Dorsal surface olive green with many dark spots or blotches and brighter yellow patches; total midline thorn count typically 31 or more . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 46 “Leopard skate” (Bathyraja sp. cf. parmifera)

17 (16) Mid-dorsal row of thorns usually interrupted; tail thorns reduced along length of tail, 0-2 reduced thorns between dorsal fins; dorsal surface brown; clasper without pseudosiphon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 48 Bering skate (Bathyraja interrupta)

Mid-dorsal row of thorns continuous (may be worn down in older specimens); tail thorns not reduced along length of tail, 1-2 strong thorns between dorsal fins; dorsal surface gray; clasper with pseudosiphon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 50 Aleutian skate (Bathyraja aleutica)


18 (14) Ventral surface typically creamy white; dorsal surface uniform brown or brown with pale, yellow, or green and black blotches; disc with thorns absent; median tail thorns weakly developed and progressively smaller toward tip of tail 19

Ventral surface dusky, dark, or blotchy; dorsal surface uniformly dark or dark with light blotches; disc with or without thorns; median tail thorns generally well developed along entire length of tail 21

19 (18) Dorsal surface of disc dull brown with black spots and blotches (no pale, yellow, or green blotches); denticles unevenly distributed on disc, often leaving bare patches; tail length less than or equal to precaudal length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 52 Okhotsk skate (Bathyraja violacea)

Dorsal surface of disc usually with at least two pale or yellowish spots near pelvic fins, often with complex pattern of bright yellow or olive-green spots and blotches; denticles fine, dense, and evenly distributed on disc; tail length greater than or equal to precaudal length 20

20 (19) Disc small and rounded; dorsal coloration brown, usually with variable pale and black blotching, including a pale round ocellus near each pelvic-fin base; tail may have yellow blotches; clasper with pseudosiphon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 54 Mud skate (Bathyraja taranetzi)

Disc of moderate size and triangular; dorsal coloration brown to olive-green with extensive yellow blotching and smaller black spots, including a large irregularly shaped yellow blotch near each pelvic-fin base; tail with distinct yellow band near base; clasper without pseudosiphon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 56 Butterfly skate (Bathyraja mariposa)

21 (18) Ventral surface of disc and tail covered with fine denticles; snout somewhat elongate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 58 Deepsea skate (Bathyraja abyssicola)

Ventral surface of disc and tail smooth, without denticles; snout not elongate 22


22 (21) Mid-dorsal thorns present and strong . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 60 Commander skate (Bathyraja lindbergi)

Mid-dorsal thorns absent 23

23 (22) Nuchal thorns absent; dorsal and ventral surfaces uniformly dark brown to black, except for white patches often present around mouth and cloaca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 62 Roughtail skate (Bathyraja trachura)

Nuchal thorns present (rarely absent); dorsal surface usually with light blotches on disc or white patches between eyes; ventral surface dusky or blotchy to dark brown 24

24 (23) Nuchal thorns weak, 1-3 (rarely absent); dorsal surface uniformly gray-brown to dark brown, usually with white patches between eyes; ventral surface medium brown, usually with white patch around mouth and/or cloaca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 64 Whitebrow skate (Bathyraja minispinosa)

Nuchal thorns moderate, 1-7; dorsal surface gray with white blotches; ventral surface of disc dusky or blotchy, with dark tail typically separated from lighter disc by a distinct line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 66 Whiteblotched skate (Bathyraja maculata)


14

1 Case elongate, spindle or club shaped, without pair of horns at each end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 18 Spotted ratfish (Hydrolagus colliei)

Case ellipsoid to rectangular, with pair of horns at each end 2

2 (1) Case ellipsoid, small, length less than 60 mm; anterior horns with elongate tendrils; posterior horns short . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 28 Brown cat shark (Apristurus brunneus)

Case rectangular, length greater than 60 mm; anterior horns without elongate tendrils; posterior horns short to long 3

3 (2) Case length more than 200 mm; length of any horn less than 1/4 mid-case width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 40 Big skate (Raja binoculata)

Case length less than 165 mm; length of any horn more than 1/4 mid-case width 4

4 (3) Posterior horns short, less than half of mid-case width, never overlapping; case width more than 100 mm; case smooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 42 Longnose skate (Raja rhina)

Posterior horns long, more than half of mid-case width; case width less than 100 mm; case with low longitudinal ridges or bristly, fuzzy, or furry texture 5

5 (4) Case with rows of longitudinal spines creating heavily textured surface; keel narrow and indistinct 6

Case with rows of low longitudinal ridges creating smoothly ridged texture; keel wide and distinct 10

Key to Egg Cases of Alaska Chondrichthyans

6 (5) Case length less than 77 mm, width less than 60 mm; case with longitudinal spinous rows creating rough rasp-like texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 64 Whitebrow skate (Bathyraja minispinosa)

Case length more than 80 mm, width more than 50 mm; case with longitudinal spinous rows creating fuzzy or furry texture 7

7 (6) Case length less than 100 mm; case width less than 65 mm 8

Case length more than 110 mm; case width more than 70 mm 9

8 (7) Case with rows of short saw-like spines arranged in continuous bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 60 Commander skate (Bathyraja lindbergi)

Case with rows of elongate slender conical spines with bifid tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 66 Whiteblotched skate (Bathyraja maculata)

9 (7) Byssal threads attached on posterior horn; mid-case keel thick, dark, opaque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 50 Aleutian skate (Bathyraja aleutica)

Byssal threads attached even with posterior margin; mid-case keel thin, brown, translucent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 58 Deepsea skate (Bathyraja abyssicola)

10 (5) Case length more than 100 mm; case width more than 75 mm 11

Case length less than 100 mm; case width less than 75 mm 13

11 (10) Keel ending abruptly on mid-anterior horns; all horns slender and smooth with loose curl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 38 Roughshoulder skate (Amblyraja badia)

Keel extending entire length of anterior horns; all horns flat and wide; anterior horns with tight curl 12

12 (11) Byssal threads attached on anterior horn distal to anterior margin of case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 44 Alaska skate (Bathyraja parmifera)

Byssal threads attached at anterior margin of case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 46 “Leopard skate” (Bathyraja sp. cf. parmifera)

15Key to Egg Cases of Alaska Chondrichthyans

13 (10) Anterior horns curling ventrally; keel width approximately equal to horn width at mid-posterior horn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 62 Roughtail skate (Bathyraja trachura)

Anterior horns curling dorsally; keel width less than horn width at mid-posterior horn 14

14 (13) Anterior horns slender with loose curl; keel absent on anterior horns; case length less than 75 mm 15

Anterior horns wide with tight curl; keel prominent on anterior horns; case length more than 75 mm . . . . . . . . . . . . . . . page 48 Bering skate (Bathyraja interrupta) or page 52 Okhotsk skate (Bathyraja violacea)

15 (14) Case width less than 50 mm; keel width at mid-case 3 mm or less . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 54 Mud skate (Bathyraja taranetzi)

Case width more than 55 mm; keel width at mid-case 4 mm or more . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 56 Butterfly skate (Bathyraja mariposa)

16Key to Egg Cases of Alaska Chondrichthyans

18

Spotted Ratfish Hydrolagus colliei

egg case

Diagnosis The only chondrichthyan in Alaska with a single gill opening on each side of the head. Opercle without skeletal support; anterior dorsal fin with a long, sharp spine.

Dentition Teeth fused to form grinding plates.

Coloration Silver to golden brown or green dorsally with many prominent white spots; white ventrally; eyes reflect green.

Body shape Caudal region tapering to a point.

Reproduction Oviparous; accessory clasping organ on head in males. Egg case maximum size is 20 cm long.

Maximum length 100 cm.

Range Gulf of Alaska to Baja California and Gulf of California.

Depth Intertidal to 971 m.

Remarks The spotted ratfish is quite common throughout the Alexander Archipelago and is regularly encountered on NMFS bottom trawl surveys as far north as Lituya Bay. The three isolated records from the northern and western Gulf of Alaska are unverified RACE database records from the mid-1980s.

Similar species The spotted ratfish is the only species of chimaera known from Alaska. One or perhaps two additional undescribed species are known from deep water off California.

In Alaska waters, the spotted ratfish is found in the Gulf of Alaska.

spotted Ratfish Hydrolagus colliei 19

20

Upper tooth

Lower tooth

Spiny DogfishSqualus acanthias

Diagnosis The only Alaska species of shark with a spine on the leading edge of each dorsal fin; anal fin absent.

Dentition Upper and lower teeth with single low cusp.

Coloration Gray to medium brown dorsally, with small white spots; pale gray to white ventrally.

Body shape Elongate, slim, with distinctly heterocercal caudal fin.

Reproduction Viviparous (yolk-sac).

Maximum length 2 m.

Range Worldwide in temperate and subarctic waters.

Depth Generally benthic, intertidal to 1,244 m.

Remarks Although the spiny dogfish has been reported from throughout the Bering Sea and as far north as Kotzebue Sound (Mecklenburg et al. 2002), trawl survey records from the past 15 years indicate that they are very rare in this region.

Similar species The spiny dogfish is the only shark in Alaska with a spine on the leading edge of each dorsal fin. The only other shark in Alaska that lacks an anal fin is the Pacific sleeper shark (see p. 22).

In Alaska waters, the spiny dogfish is found in the Gulf of Alaska and Bering Sea, with one record from Kotzebue Sound.

spiny Dogfish Squalus acanthias 21

22

Pacific Sleeper Shark Somniosus pacificus

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with the combination of no anal fin and no dorsal spines.

Dentition Upper teeth long, narrow, and sharp; lower teeth with short low cusps.

Coloration Gray to black dorsally; only slightly lighter ventrally.

Body shape Large, stout, and flabby, with small flaplike, flexible fins.


Maximum length Documented to 4.4 m, possibly to 7 m or more.

Range North Pacific from Chukchi Sea to Baja California in the eastern Pacific; to Taiwan in the western Pacific.

Depth Benthic, intertidal to 2,000 m.

Remarks The Pacific sleeper shark (sometimes called the mud shark) is encountered throughout the Gulf of Alaska and Aleutian Islands, as well as on the outer shelf and upper slope of the Bering Sea. The Chukchi Sea specimen, reported by Benz et al. (2004), washed up onshore near Point Hope.

Similar species The Pacific sleeper shark is one of only two sharks in Alaska that have no anal fin. The other is the spiny dogfish, which has a strong spine at the leading edge of each dorsal fin. The small, flexible, flaplike fins and posterior position of the first dorsal fin are also characteristic of this species.

In Alaska waters, the Pacific sleeper shark is found in the Bering Sea, Aleutian Islands, and Gulf of Alaska.

Pacific sleeper shark Somniosus pacificus 23

24

Bluntnose Sixgill Shark Hexanchus griseus

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with six gill slits on each side of the head; also the only species with a single dorsal fin.

Dentition Lower jaw with 6 comb-shaped teeth.

Coloration Dark gray to brown dorsally; light gray to white ventrally.

Body shape Stout, with broad, rounded head.


Maximum length 4.8 m.

Range Tropical and temperate North and South Pacific, North and South Atlantic, and Indian Ocean; eastern Aleutian Islands.

Depth Benthic or pelagic, surface to 2,500 m.

Remarks The bluntnose sixgill shark has only been recorded twice in Alaska waters, once south of Unimak Pass (Larkins 1964) and more recently from Southeast Alaska on a 1999 NMFS bottom trawl survey.

Similar species The bluntnose sixgill shark is the only shark in Alaska with six gill slits on each side of the head. The only other sharks in the world with six gill slits are the bigeye sixgill shark (Hexanchus nakamurai), frill shark (Chlamydoselachus anguineus), and sixgill sawshark (Pliotrema warreni), all of which are only found in California waters and farther south.

The bluntnose sixgill shark has been recorded twice in Alaska.

Bluntnose sixgill shark Hexanchus griseus 25

26

Basking Shark Cetorhinus maximus

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with gill slits that nearly encircle the head. Also the largest species found in Alaska waters.

Dentition Teeth minute, hooked.

Coloration Brown to gray or black dorsally, often with irregular light patches; lighter ventrally, often with white blotches and spots.

Body shape Large and robust, with elongate snout.

Reproduction Viviparous (oophagous).

Maximum length 10 m or more.

Range Worldwide in temperate seas; northern Gulf of Alaska.

Depth Pelagic, near surface.

Remarks According to Compagno (1984), the range of the basking shark extends to the Kenai Peninsula. The indicated record in the western Gulf of Alaska is from a 1981 NMFS bottom trawl survey.

Similar species The basking shark is the second largest fish in the world (the whale shark is the largest). Its extremely large gill slits and minute hooked teeth distinguish it from all other sharks.

In Alaska waters, the basking shark is found in the Gulf of Alaska.

Basking shark Cetorhinus maximus 27

28

Brown Cat Shark Apristurus brunneus

Upper tooth

Lower toothegg case

Diagnosis The only Alaska species of shark with two dorsal fins and the leading edge of the first dorsal fin posterior to the leading edge of the pelvic fin.

Dentition Teeth with 3-5 cusps, the central cusp largest.

Coloration Uniform dark brown; fin margins darker brown to black.

Body shape Elongate, small; caudal fin long, almost entirely below body midline.

Reproduction Oviparous. Egg case 50 mm.

Maximum size 71 cm.

Range Southeast Alaska to Central or South America.

Depth Benthic, 33-1,306 m.

Remarks The brown cat shark is known from only two Alaska records, both from Southeast Alaska. The northern record was reported by Wilson and Hughes (1978), and the southern record was collected on a 2005 NMFS bottom trawl survey.

Similar Species The brown cat shark is the smallest shark in Alaska. The longnose cat shark (Apristurus kampae) does not occur north of southern Oregon, and can be distinguished from the brown cat shark by its larger gill slits, and white fin edges.

In Alaska waters, the brown cat shark is known from only two records in the Gulf of Alaska.

Brown cat shark Apristurus brunneus 29

30

Upper tooth

Lower tooth

Thresher SharkAlopias vulpinus

Diagnosis The only Alaska species of shark with a distinctly elongate upper caudal-fin lobe.

Dentition Teeth small, somewhat triangular, without lateral cusps or serrations.

Coloration Slate blue, brown, or black dorsally; white ventrally.

Body shape Moderately elongate, fusiform; pectoral fin long, upper caudal lobe extremely long.


Maximum length 6.4 m.

Range Circumglobal in warm to temperate seas; southeast Gulf of Alaska.

Depth Pelagic, surface to 366 m.

Remarks The thresher shark is known from only one questionable Alaska record. Although the specimen was landed in a commercial catch offloaded in Sitka, its collection locality is unknown (Mecklenburg et al. 2002).

Similar species The thresher shark is the only shark in Alaska with an extremely elongate upper caudal lobe. Three species of thresher sharks are known worldwide. The other two are known only from tropical and subtropical waters in the Pacific.

In Alaska waters, the thresher shark is known from only one location in the Gulf of Alaska.

Thresher shark Alopias vulpinus 31

32

Blue Shark Prionace glauca

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with triangular, serrate teeth and a distinctly heterocercal caudal fin.

Dentition Upper teeth elongate, triangular, serrate; lower teeth recurved, serrate.

Coloration Dark blue dorsally; bright blue on sides; white ventrally.

Body Shape Elongate, slender, with long pectoral fins.

Reproduction Viviparous (placental).

Maximum Size 3.8 m or more.

Range Worldwide in temperate and tropical seas; northern Gulf of Alaska.


Remarks The blue shark has been recorded near shore as far west as Kodiak in the Gulf of Alaska, but it is apparently only present in Alaska waters during periods of uncommonly warm surface temperatures.

Similar Species The blue shark is a very slender, open-water species unlikely to be confused with any other shark in Alaska. The region’s other open-water sharks (e.g., great white and salmon sharks) are more heavy-bodied species with shorter pectoral fins and a more homocercal caudal fin.

In Alaska waters, the blue shark is found in the Gulf of Alaska.

Blue shark Prionace glauca 33

34

Salmon Shark Lamna ditropis

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with a strong double lateral keel on the caudal peduncle, first dorsal-fin base almost directly above pectoral-fin base, and teeth not serrate.

Dentition Teeth large and bladelike, with one pair of lateral cusps and no serrations.

Coloration Bluish gray to brown dorsally; white ventrally.

Body Shape Stout, powerful, with conical snout; caudal fin nearly homocercal, with prominent double lateral keel; second dorsal and anal fins very small.


Maximum Length 3.1 m.

Range Bering Sea to Mexico in the eastern Pacific; to Korea in the western Pacific.


Remarks The salmon shark is a large, highly migratory species. It may be locally abundant in Alaska waters, particularly near high concentrations of prey items such as herring or salmon. A large majority (up to 90% in Prince William Sound) of the salmon sharks encountered in Alaska waters are females.

Similar Species The salmon shark is a robust species most commonly confused with the great white shark. It can be distinguished from the great white shark by its more acutely pointed conical snout, the first dorsal-fin base almost directly above the pectoral-fin base, and by the tooth shape. The secondary lateral keel on the caudal fin of the salmon shark is unique among Alaska sharks.

In Alaska waters, the salmon shark is found in the Gulf of Alaska and Bering Sea.

salmon shark Lamna ditropis 35

36

Great White Shark Carcharodon carcharias

Upper tooth

Lower tooth

Diagnosis The only Alaska species of shark with large, triangular, serrate teeth and a nearly homocercal caudal fin.

Dentition Teeth large, triangular, serrate.

Coloration Pale brown to gray or even nearly black dorsally; white ventrally.

Body Shape Large, robust, powerful; caudal fin nearly homocercal, with prominent single lateral keel; second dorsal and anal fins very small.


Maximum Length 6.4 m or more.

Range Worldwide in temperate seas; northern Gulf of Alaska.

Depth Pelagic, surface to 1,280 m.

Remarks According to Compagno (1984), the distribution of the great white shark extends to the western end of the Kenai Peninsula. Several sightings have been reported in Southeast Alaska over the past 50 years, but this species apparently only ventures into Alaska waters during years of abnormally high sea surface temperatures.

Similar Species The great white shark is most commonly confused with the salmon shark in Alaska, as both are robust, strong swimmers with a similar body shape. The great white shark can be distinguished from the salmon shark by its more blunt, rounded snout, the pectoral-fin base entirely in front of the first dorsal-fin base, and by tooth shape.

In Alaska waters, the great white shark is found in the Gulf of Alaska.

great White shark Carcharodon carcharias 37

38

Roughshoulder Skate Amblyraja badia

Dorsal diagram showing thorns on disc.

DoRsal venTRal

egg case

Rostral

Orbital

Scapular Nuchal

Mid-dorsal

39

Diagnosis The only Alaska species of skate with rostral thornlets. Also the only species that has scapular thorns in combination with a dark ventral surface.

Denticles Dorsal surface evenly covered with denticles; ventral surface smooth.

Coloration Dorsal surface gray-brown, with darker spots and blotches; ventral surface gray-brown, with white blotches on snout and abdomen, and near mouth.

Reproduction Oviparous. Egg case large, with slender horns; keel ends abruptly on anterior horns. Egg case maximum size is 109 mm long by 86 mm wide.

Maximum Size 99 cm (immature female).

Range Bering Sea to Central America; Japan.

Depth 1,061-2,322 m.

Remarks The roughshoulder skate was only recently reported from Alaska for the first time (Stevenson and Orr 2005). It is found around the Pacific Rim in deep water, and is probably more widespread in Alaska waters than records indicate.

Similar Species The roughshoulder skate is most likely to be confused with the darker members of the genus Bathyraja, such as the Commander and roughtail skates, due to its dark dorsal and ventral coloration. However, the roughshoulder skate differs from all these species in having scapular thorns. All other species in Alaska with scapular thorns also have a light ventral surface.

In Alaska waters, the roughshoulder skate is known from three locations in the Bering Sea.

Roughshoulder skate Amblyraja badia

40

Big Skate Raja binoculata

Orbital Nuchal


DoRsal venTRal

egg case

41

Diagnosis The only Alaska species of Raja with the following combination of characters: anterior margin of disk concave; posterolateral margin of pelvic fin slightly concave; base of pectoral fin with large ocellus surrounded by light spots.

Denticles Fine denticles on dorsal surface, ventral surface smooth.

Coloration Dorsal surface brown to gray-brown, usually with large ocellus surrounded by smaller spots on pectoral fin; ventral surface white to light gray.

Reproduction Oviparous, with up to seven embryos per egg case. Egg case large, dome-shaped, with very short horns, greenish-yellow in color. Egg case maximum size is 300 mm long.

Maximum Size Documented to 204 cm, possibly to 244 cm.

Range Eastern Bering Sea, eastern Aleutian Islands, Gulf of Alaska to Baja California.

Depth 16-402 m.

Remarks The big skate is one of the most abundant skates in the Gulf of Alaska, and the largest skate species in Alaska waters. It has recently attained at least small-scale commercial importance.

Similar Species The big skate is most likely to be confused with the longnose skate, which is the only other member of the genus Raja in Alaska. It can easily be distinguished from the longnose skate by the shape of the snout and the shallow notch in the pelvic fins. The big skate also lacks a small dark ocellus on the dorsal surface of each pectoral fin and the ventral surface is nearly white.

In Alaska waters, the big skate is found in the Gulf of Alaska and Bering Sea.

Big skate Raja binoculata

42

Longnose SkateRaja rhina

Orbital Nuchal


DoRsal venTRal

egg case

43

Diagnosis The only Alaska species of Raja with an elongate snout and deeply notched pelvic fins.

Denticles Fine denticles on dorsal surface; ventral surface smooth.

Coloration Dorsal surface brown with dark blotches; may have ocelli on disk; ventral surface gray to black.

Reproduction Oviparous. Egg case large and smooth; large webbed keels on posterior and anterior margins; horns short, with a loose ventral curl. Egg case maximum size is 154 mm long by 121 mm wide.

Maximum Size At least 142 cm. NMFS records up to 180 cm are not verifiable.

Range Eastern Bering Sea to Baja California and Gulf of California.

Depth 9-1,069 m.

Remarks The longnose skate is another large species common in the Gulf of Alaska. It is generally found in deeper waters than the big skate, and is only very rarely encountered in the southeastern Bering Sea.

Similar Species The longnose skate is most likely to be confused with the big skate, but can be distinguished by its prolonged snout and deeply notched pelvic fins. Unlike the big skate, it also has a small dark ocellus on the dorsal surface of each pectoral fin and a relatively dark ventral surface.

In Alaska waters, the longnose skate is found in the Gulf of Alaska and southeastern Bering Sea.

longnose skate Raja rhina

44

Alaska Skate Bathyraja parmifera

Orbital

Scapular

Nuchal Mid-dorsal


DoRsal venTRal

egg case

45

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: naked area surrounding the tail thorns; orbital thorns and scapular thorns present (orbital thorns may be reduced); dorsal surface dark brown or golden brown, often with lighter spots or blotches; total midline thorns typically 32 or less. Row of mid-dorsal thorns may be complete or interrupted.

Denticles Evenly distributed on dorsal surface of juveniles, patchy on adults; ventral surface smooth.

Coloration Dorsal surface dark brown or golden brown, often with lighter spots or blotches; ventral surface brown to white.

Reproduction Oviparous. Egg case large, with rows of smooth low ridges and wide keel; byssal threads attached on anterior horns. Egg case maximum size is 140 mm long by 107 mm wide.

Maximum Size 135 cm.

Range Bering Sea, Aleutian Islands, Gulf of Alaska; western Bering Sea to Japan.

Depth 17-392 m.

Remarks The Alaska skate is perhaps the most common skate in Alaska waters. It is virtually the only species of skate found on the Bering Sea shelf, where it can be locally abundant. It appears to be uncommon in the Gulf of Alaska, particularly east of Kodiak, and is replaced in the western Aleutian Islands by the “leopard skate” (see p. 46).

Similar Species The Alaska skate is most similar to the leopard skate from which it differs in coloration. In the western Aleutians, the dorsal surface of the leopard skate exhibits a vivid olive-yellow leopard spotting pattern and the total midline thorn count is usually higher (31 or more).

In Alaska waters, the Alaska skate is found in the Gulf of Alaska, Bering Sea, and eastern Aleutian Islands.

alaska skate Bathyraja parmifera

46

“Leopard Skate” Bathyraja sp. cf. parmifera

Orbital

Scapular

Nuchal Mid-dorsal


DoRsal venTRal

egg case

47

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: naked area surrounding the tail thorns; orbital thorns and scapular thorns present (orbital thorns may be reduced); dorsal surface olive green with many dark spots or blotches and brighter yellow patches; total midline thorns typically 31 or more.

Denticles Evenly distributed on dorsal surface of juveniles, patchy on adults; ventral surface smooth.

Coloration Dorsal surface olive green with many dark spots or blotches and brighter yellow patches; ventral surface gray to white.

Reproduction Oviparous. Egg case large, with rows of smooth low ridges and wide keels; byssal thread attachment at anterior margin. Egg case maximum size is 128 mm long by 98 mm wide.


Range Western Aleutian Islands.

Depth 48-396 m.

Remarks The leopard skate is currently an undescribed species, soon to be formally named by the authors, which appears to be restricted in Alaska waters to the Aleutian Islands in Amchitka Pass and farther west. In addition to body shape and color differences, recent genetic studies provide additional evidence that it is a distinct species closely related to the Alaska skate.

Similar Species The leopard skate is most similar to the Alaska skate, from which it differs primarily in coloration. The dorsal surface of the Alaska skate is dark or golden brown, often with lighter spots or blotches, and the total midline thorn count is usually lower (32 or less).

The leopard skate is known only from the west-ern Aleutian Islands.

“leopard skate” Bathyraja sp. cf. parmifera

48

Bering Skate Bathyraja interrupta

Scapular

Nuchal (Mid-dorsal)


DoRsal

venTRal

egg case

49

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: orbital thorns absent; scapular thorns present; row of mid-dorsal thorns usually interrupted; tail thorns reduced, with 0-2 reduced thorns between dorsal fins.

Denticles Evenly distributed on dorsal surface; ventral surface smooth.

Coloration Dorsal surface light to dark brown; ventral surface white.

Reproduction Oviparous. Egg case of moderate size, with smooth low ridges; keel wide at mid-case, tapering on horns; byssal threads attached at mid-case and/or base of posterior horns; currently indistinguishable from egg cases of Bathyraja violacea; egg cases show considerable variation across the species range. Egg case maximum size is 95 mm long by 75 mm wide.

Maximum Size 86 cm.

Range Bering Sea, eastern Aleutian Islands, Gulf of Alaska, to California.

Depth 26-1,050 m.

Remarks This form is probably not a single species, but a species complex that extends from the western Bering Sea to southern California. In the southern part of its range, it is generally known as the sandpaper skate. Future taxonomic work hopefully will resolve this issue.

Similar Species The Bering skate exhibits a great deal of variation in the prominence of the thorns on the disc. Some specimens have greatly reduced thorns, and can therefore be misidentified as mud or Okhotsk skates. Specimens with well-developed thorns may be misidentified as Alaska or Aleutian skates, but differ from the

former in having denticles surrounding the tail thorns and from the latter in having a reduced or interrupted mid-dorsal thorn row as well as reduced interdorsal thorns.

In Alaska waters, the Bering skate is found in the Gulf of Alaska, Bering Sea, and eastern Aleutian Islands.

Bering skate Bathyraja interrupta

50

Aleutian Skate Bathyraja aleutica

Scapular

Nuchal Mid-dorsal


DoRsal venTRal

egg case

51

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: orbital thorns absent; scapular thorns present; row of mid-dorsal thorns usually continuous; tail thorns large, with 1 or 2 strong thorns between dorsal fins.

Denticles Evenly distributed on dorsal surface; ventral surface smooth.

Coloration Dorsal surface gray, with or without vague black ocellus on pectoral fin; ventral surface white with gray margin.

Reproduction Oviparous. Egg case large, covered in brownish bristles that form a fur-like mat; keel narrow, thick, opaque at mid-case; byssal threads attached distally on posterior horn. Egg case maximum size is 146 mm long by 100 mm wide.


Range Bering Sea, Aleutian Islands, and Gulf of Alaska to northern California; western Bering Sea to Japan.

Depth 15-1,602 m.

Remarks The Aleutian skate is one of the most widespread skates in Alaska, both geographically and bathymetrically. It is particularly common in the Aleutian Islands.

Similar Species The Aleutian skate’s thorn pattern most closely resembles those of the Bering, Alaska, and “leopard” skates. However, the Aleutian skate can be distinguished from the Bering skate by the strength of the mid-dorsal and interdorsal thorns, and from the Alaska and leopard skates by the presence of denticles around the tail thorns. The coloration of the Aleutian skate may be vaguely similar to that of the whiteblotched skate, but the thorn pattern is markedly different.

In Alaska waters, the Aleutian skate is found in the Gulf of Alaska, Aleutian Islands, and Bering Sea.

aleutian skate Bathyraja aleutica

52

Okhotsk Skate Bathyraja violacea

Dorsal diagram showing absence of disc thorns.

DoRsal venTRal

egg case

53

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: disc free of thorns; large diamond-shaped disc, with tail length less than or equal to precaudal length; dorsal surface without pale or yellow blotches; ventral surface white or cream-colored.

Denticles Dorsal surface with patches of small fine denticles; ventral surface smooth.

Coloration Dorsal surface gray to brown, often with dark reticulations; ventral surface white or cream-colored.

Reproduction Oviparous. Egg case of moderate size, with smooth low ridges; keel wide at mid-case, tapering on horns; byssal threads attached at mid-case and/or base of posterior horns; presently indistinguishable from egg cases of the Bering skate.

Maximum Size 73 cm.

Range Western Aleutian Islands; western Bering Sea to Japan.

Depth 124-510 m.

Remarks The distribution of this species is poorly known, but it appears to be much more common in the western Bering Sea and Sea of Okhotsk. It can be difficult to distinguish from the Bering skate.

Similar Species The Okhotsk skate generally has no thorns on the disc, and therefore can be confused with the mud skate or butterfly skate. However, the mud skate is smaller and rounded, and males have a pseudosiphon on the clasper. In the Aleutians, both the mud skate and the butterfly skate can easily be distinguished from the Okhotsk skate by the presence of vivid greenish or yellow blotching on the disc. The Bering skate occasionally has greatly reduced thorns, and also can be confused with the Okhotsk skate.

In Alaska waters, the Okhotsk skate is known from only one location.

okhotsk skate Bathyraja violacea

54

Mud Skate Bathyraja taranetzi


DoRsal venTRal

egg case

55

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: disc free of thorns; disc small and rounded, with tail length greater than precaudal length; ventral surface white or cream-colored; pseudosiphon present in males.

Denticles Small and fine, evenly distributed on dorsal surface; ventral surface smooth.

Coloration Dorsal surface brown with small darker blotches, and usually a large lighter spot on posterior part of pectoral fin; ventral surface white or cream-colored. In Aleutians, dorsal surface with distinctive yellow spots and blotches.

Reproduction Oviparous. Egg case small and elongate, with rows of smooth low ridges; keel narrow, absent from horns; byssal threads attached

at mid-case; anterior horns with loose curl. Egg case maximum size is 73 mm long by 48 mm wide.

Maximum Size 77 cm.

Range Bering Sea and Aleutian Islands; western Bering Sea to northern Kuril Islands.

Depth 58-1,054 m.

Remarks The mud skate is relatively common in the Aleutian Islands and on the upper continental slope in the Bering Sea. Specimens from the Aleutians are often brightly colored, with prominent yellow blotching.

Similar Species The mud skate, like the butterfly and Okhotsk skates, has no thorns on the disc. However, it is smaller and the disc is more rounded than on either of the other species, and the pseudosiphon is absent in males. In the Aleutian Islands, the coloration

of the mud skate is very similar to the butterfly skate, but the mud skate tends to have a well-defined large yellowish ocellus at the base of each pectoral fin and lacks the broad yellow band at the base of the tail. In the Bering Sea, specimens generally lack the bright yellow blotching, although a pale yellow ocellus is often present at the base of each pectoral fin. The Okhotsk skate has no distinct light coloration on the dorsal surface.

In Alaska waters, the mud skate is found in the Aleutian Islands and Bering Sea.

Mud skate Bathyraja taranetzi

56

Butterfly SkateBathyraja mariposa


DoRsal venTRal

egg case

57

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: disc free of thorns; disc of moderate size and diamond-shaped, with tail length greater than precaudal length; ventral surface white or cream-colored; pseudosiphon absent in males.


Coloration Dorsal surface distinctively mottled with bright yellow blotches and smaller black spots on a greenish brown background, with distinct yellow band near base of tail; ventral surface white.

Reproduction Oviparous. Egg case of moderate size, with smooth low ridges; keel moderately wide at mid-case, absent on horns; byssal threads attached at mid-case and/or base of posterior horns. Egg case maximum size is 74 mm long by 58 mm wide.

Maximum Size 76 cm.

Range Central Aleutian Islands.

Depth 90-448 m.

Remarks This recently discovered species (Stevenson et al. 2004) is currently only known from the central Aleutian Islands. Its striking color pattern is similar to that often exhibited by mud skates in this region.

Similar Species The butterfly skate, like the mud skate and the Okhotsk skate, lacks thorns on the disc. The butterfly skate differs from the mud skate in the general shape of the disc, the absence of a pseudosiphon on the clasper in adult males, and in specific aspects of the dorsal coloration (see mud skate). Unlike the butterfly skate, the Okhotsk skate has no distinct light coloration on the dorsal surface.

The butterfly skate is known only from the central Aleutian Islands.

Butterfly skate Bathyraja mariposa

58

Deepsea Skate Bathyraja abyssicola

Nuchal


DoRsal venTRal

egg case

59

Diagnosis The only Alaska species of Bathyraja with fine denticles on the ventral surface.

Denticles Fine, evenly distributed on dorsal and ventral surface.

Coloration Dorsal surface gray to brown; ventral surface gray to black, mouth and cloaca whitish.

Reproduction Oviparous. Egg case large, covered in fur-like mat of brownish bristles; keel narrow, thin, brown, translucent at mid-case; byssal threads attached at base of posterior horn. Egg case maximum size is 126 mm long by 84 mm wide.


Range Bering Sea, Aleutian Islands, Gulf of Alaska to southern California; western Bering Sea to Japan.

Depth 362-2,904 m.

Remarks The deepsea skate is currently known from only five collections in Alaska waters. Specimens from the Bering Sea were collected in deep water (951-1,400 m), but the specimens from the Aleutians and southeast Alaska were taken in much shallower waters (500 and 440 m, respectively).

Similar Species The deepsea skate is the only species of skate in Alaska with denticles covering the ventral surface. Its generally dark ventral coloration and thorn pattern resemble that of the whitebrow skate. However, in addition to the ventral denticles, the deepsea skate has a somewhat prolonged, triangular snout and lacks white patches in the interorbital space.

In Alaska waters, the deepsea skate is known from five collections.

Deepsea skate Bathyraja abyssicola

60

Commander SkateBathyraja lindbergi

Mid-dorsalNuchal


DoRsal venTRal

egg case

61

Diagnosis The only Alaska species of Bathyraja with the following combination of characters: scapular and orbital thorns absent; nuchal and mid-dorsal thorns present.

Denticles Few, unevenly distributed on dorsal surface; ventral surface smooth.

Coloration Dorsal surface pale gray to gray-brown or black; ventral surface gray to black, darker around pectoral and pelvic fin margins, white around mouth and nostrils.

Reproduction Oviparous. Egg case small, with covering of stringy fibers and cusp-like ridges; keel thin, narrow; byssal threads attached at mid-case. Egg case maximum size is 96 mm long by 62 mm wide.


Range Bering Sea, Aleutian Islands, and Gulf of Alaska; western Bering Sea to Japan.

Depth 126-1,193 m.

Remarks The Commander skate is primarily an upper continental slope species, commonly encountered during bottom-trawl surveys of the Aleutian Islands and Bering Sea. It appears to be much less common in the Gulf of Alaska, although recently captured specimens (July 2005) extend the known range of the species eastward to the Alexander Archipelago.

Similar Species The Commander skate is most similar to the roughtail and whitebrow skates, with which it shares a generally dark dorsal and ventral surface. However, it can be distinguished from these other dark species by the thorn pattern. The whitebrow skate lacks mid-dorsal thorns and the roughtail skate usually has no thorns at all on the disc.

In Alaska waters, the Commander skate is found in the Gulf of Alaska and Bering Sea.

commander skate Bathyraja lindbergi

62

Roughtail SkateBathyraja trachura


DoRsal venTRal

egg case

63

Diagnosis The only Alaska species of Bathyraja with the disc free of thorns and a dark ventral surface.


Coloration Dorsal and ventral surfaces dark brown to black; mouth and cloaca whitish.

Reproduction Oviparous. Egg case moderate in size; keel wide at mid-case and on horns; anterior horns curl ventrally; byssal threads attached at base of posterior horns. Egg case maximum size is 85 mm long by 80 mm wide.

Maximum Size 92 cm.

Range Bering Sea to Baja California; western Bering Sea to Japan.

Depth 213-2,550 m.

Remarks The roughtail skate (also known as the black skate) is a continental slope species, and is generally only encountered in Alaska waters at depths greater than 400 m. Although records from the central and western Aleutians are lacking, this is most likely due to a lack of sampling effort at the appropriate depths. Aleutian records shown are from Ishihara and Ishiyama (1985).

Similar Species The roughtail skate is similar in overall coloration to the Commander and whitebrow skates, although it lacks the white interorbital patches commonly seen on the whitebrow skate. However, both the Commander and whitebrow skates have at least nuchal thorns, while the roughtail skate generally lacks all disc thorns.

In Alaska waters, the roughtail skate is found in the Gulf of Alaska and Bering Sea.

Roughtail skate Bathyraja trachura

64

Whitebrow Skate Bathyraja minispinosa

Nuchal


DoRsal venTRal

egg case

65

Diagnosis The only Alaska species of Bathyraja with white patches around the eyes. Also distinguished by the following combination of characters: scapular, orbital, and mid-dorsal thorns absent; nuchal thorns present, but weak (occasionally absent); ventral surface dark, without denticles.

Denticles Fine, evenly distributed on dorsal surface; ventral surface smooth.

Coloration Dorsal surface gray-brown to dark brown, interorbital region and margins of orbits white; ventral surface light to medium brown, mouth white.

Reproduction Oviparous. Egg case moderate in size, with distinct rows of raspy spines; byssal threads attached at mid-case and on posterior horns. Egg case maximum size is 76 mm long by 56 mm wide.

Maximum Size 92 cm.

Range Bering Sea, Aleutian Islands; western Bering Sea to Japan.

Depth 150-1,420 m.

Remarks The whitebrow skate is commonly encountered on the Bering Sea slope, usually at depths of 400 m or more. It has also been recorded from the western Bering Sea and far western Aleutians, but its presence in the central Aleutian Islands and the Gulf of Alaska has not yet been documented.

Similar Species The whitebrow skate is similar in overall coloration to the Commander and roughtail skates. Although this species was named for the white interorbital patches on the dorsal surface, these patches may be inconspicuous or even absent, particularly in smaller specimens. However, the whitebrow skate generally has strong nuchal thorns and no mid-dorsal thorns, while the Commander skate has strong mid-dorsal thorns and the roughtail skate usually has no thorns on the disc.

In Alaska waters, the whitebrow skate is found in the Bering Sea.

Whitebrow skate Bathyraja minispinosa

66

Whiteblotched Skate Bathyraja maculata

DoRsal

Nuchal


venTRal

egg case

Diagnosis The only Alaska species of Bathyraja with a distinct line on the ventral surface separating the uniformly dark tail from the light body. Also distinguished by the following combination of characters: scapular, orbital, and mid-dorsal thorns absent; nuchal thorns present and strong; ventral surface of disc light to dusky, without denticles.

Denticles Strong, evenly covering dorsal surface; ventral surface smooth.

Coloration Dorsal surface gray with white blotches; ventral surface blotchy gray, with dark border; underside of tail dark, separated from lighter ventral surface of body by distinct line.

Reproduction Oviparous. Egg case small, covered with stringy fibers and rows of slender conical spines ending in one or more tips; keel thin, narrow; byssal threads attached at mid-case and on posterior horns. Egg case

maximum size is 91 mm long by 57 mm wide.


Range Bering Sea, Aleutian Islands; western Bering Sea to Japan.

Depth 73-1,193 m.

Remarks The whiteblotched skate is common in the Aleutian Islands and on the Bering Sea continental slope. Although it appears to be rare in the Gulf of Alaska, it has recently been recorded as far east as Clarence Strait (J. Bizzarro, Pacific Shark Research Center, Moss Landing Marine Laboratories, pers. comm., 25 July 2006).

Similar Species The whiteblotched skate may be vaguely similar in dorsal coloration to the Aleutian skate, with light blotches on a generally gray background. However, the

whiteblotched skate has only nuchal thorns on the disc, while the Aleutian skate has nuchal, mid-dorsal, and scapular thorns.

In Alaska waters, the whiteblotched skate is found in the Gulf of Alaska, Aleutian Islands, and Bering Sea.

Whiteblotched skate Bathyraja maculata 67

68

Basking Shark

Photos of Alaska Sharks

Spiny Dogfish

Blue SharkThresher Shark

Bluntnose Sixgill Shark

Salmon Shark

Pacific Sleeper Shark

Great White Shark= 1 m

Brown Cat Shark

= 25 cm

69

Brown Cat Shark Thresher Shark Blue Shark Salmon Shark Great White Shark

Illustrations of Teeth of Alaska Sharks

Spiny Dogfish Pacific Sleeper Shark Bluntnose Sixgill Shark Basking Shark

70Photos of Alaska Skates (Dorsal View)

Big Skate

Longnose Skate

Alaska Skate

Aleutian Skate

Whitebrow Skate

Whiteblotched Skate

Roughtail Skate

Roughshoulder Skate

Okhotsk Skate

Mud Skate

“Leopard Skate”

Deepsea Skate

Butterfly Skate

Bering Skate

Commander Skate

= 0.5 m

71

Alar hooks Series of hook-shaped thorns on the dorsal surface near the lateral margins of the disc in male skates.

Benthic At the bottom of a body of water.

Bifid Divided into two equal lobes or parts by a median cleft.

Byssal threads Stringy fibers attached to the lateral edges and horns of egg cases of skates, sharks, and chimaeras.

Case length Smallest distance from the anterior margin of the egg case to the posterior margin, not including the horns.

Case width Greatest distance between the two sides of the egg case, including the keels.

Chondrichthyan A member of the class Chondrichthyes, which includes holocephalans and elasmobranchs.

Clasper A reproductive structure located along the posterior margin of the pelvic fins in male sharks and skates; also on the head in chimaeras.

Cloaca The combined opening of the digestive and urogenital system.

Denticle The hooked, toothlike scales found on sharks and skates.

Dichotomous key A key for the identification of organisms based on a series of choices between alternative characters.

Dimorphic Occurring in two distinct forms.

Disc The body of a skate anterior to the cloaca, composed primarily of the head, visceral cavity, and expanded pectoral fins.

Egg case The leathery protective covering that envelops the developing embryo of chimaeras, skates, and some species of sharks; also known as an egg capsule or mermaid’s purse.

Elasmobranch One of the two major lineages of chondrichthyans, including all living sharks and rays.

Heterocercal A caudal fin in which the upper lobe is larger and more elongate than the lower lobe.

Holocephalan One of the two major lineages of chondrichthyans, represented in the recent fauna only by chimaeras.

Homocercal A caudal fin in which the upper and lower lobe are similar in size and shape.

Horns Elongated extensions of egg cases, usually on all four corners, that taper or curl near the ends.

Glossary

Interdorsal thorns The one or two thorns on the dorsal surface of the tail between the two dorsal fins in skates.

Keel Flattened extensions on the lateral edges of skate egg cases that may extend onto the horns.

Malar hooks Series of hook-shaped thorns on the dorsal surface near the snout in males of some species of skates.

Mid-dorsal thorns A series of thorns on the dorsal surface of a skate along the midline posterior to the scapular thorns and anterior to the pelvis.

Morphological Having to do with general body form and structure.

Nuchal thorns A series of thorns on the dorsal surface of a skate along the midline posterior to the orbits and anterior to the scapular thorns.

Ocellus A round blotch or spot surrounded by a ring of pigment.

Oophagous A form of viviparity in which embryos receive their nutrition from the consumption of additional nonviable ova produced by the female.

Opercle A cartilaginous flap covering the gills and associated structures in chimaeras.

Orbital thorns Thorns along the medial rim of the orbit on the dorsal surface of a skate, highly variable in size.

Ova Eggs.

Oviparous A mode of reproduction in which the female deposits thick leathery egg cases, containing one to several embryos, directly onto the seafloor.

Pelagic Open waters of the sea.

Placental A form of viviparity in which the embryo is nourished directly from the female through a placental tissue.

Precaudal length In skates, the distance from the tip of the snout to the posterior margin of the cloaca.

Pseudosiphon A short groove found near the distal tip of the clasper in some skates.

RACE database (also RACEbase) A resource survey database maintained by the NMFS Alaska Fisheries Science Center’s Resource Assessment and Conservation Engineering (RACE) Division in Seattle, Washington.

Reticulations Lines forming a network.

Serrate Notched or toothed on the edge.

Spine A stiff, sharp fin ray found on the leading edge of the dorsal fins in the spiny dogfish; also see thorn.

Scapular thorns Thorns on the dorsal surface of a skate on either side of the midline posterior to the head.

72Glossary

Tail length In skates, the distance from the posterior margin of the cloaca to the tip of the tail (also known as caudal length).

Tail thorns In skates, a series of thorns on the dorsal midline of the tail posterior to the pelvis and anterior to the dorsal fins.

Thorn An enlarged, conspicuous denticle on the dorsal surface of a skate; also commonly referred to as a spine.

Total length The distance from the anterior-most tip of the snout to the posterior-most tip of the tail.

Total midline thorns The sum of all thorns in the midline series, including nuchal, mid-dorsal, tail, and interdorsal thorns.

Viviparous A mode of reproduction in which the young are born as free-swimming miniature adults after an extended period of development inside the female.

Yolk-sac viviparity A form of viviparity in which the developing embryos are completely dependent on the nutrition provided by a yolk sac inside the female.

73Glossary

74

Bigelow, H.B., and W.C. Schroeder. 1948. Sharks. In: Fishes of the western North Atlantic. Memoirs of the Sears Foundation for Marine Research 1(1):59-546.

Carrier, J.C., J.A. Musick, and M.R. Heithaus (eds.). 2004. Biology of sharks and their relatives. CRC Press, Boca Raton. 596 pp.

Castro, J.I. 1983. The sharks of North American waters. Texas A&M University Press, College Station. 180 pp.

Compagno, L.J.V. 1984. FAO species catalogue. Vol. 4. Sharks of the world: An annotated and illustrated catalogue of shark species known to date. Parts 1 and 2. FAO, Rome. 655 pp.

Compagno, L.J.V. 1999. Checklist of living elasmobranchs. In:W.C. Hamlett (ed.), Sharks, skates, and rays: The biology of elasmobranch fishes. Johns Hopkins University Press, Baltimore, pp. 471-498.

Ebert, D.A. 2003. Sharks, rays, and chimaeras of California. University of California Press, Berkeley. 284 pp.

Eschmeyer, W.N., E.S. Herald, and H. Hammann. 1983. A field guide to Pacific coast fishes of North America from the Gulf of Alaska to Baja California. Houghton Mifflin Co., Boston. 336 pp.

Hamlett, W.C. (ed.). 1999. Sharks, skates, and rays: The biology of elasmobranch fishes. Johns Hopkins University Press, Baltimore, 515 pp.

Hamlett, W.C. (ed.). 2005. Reproductive biology and phylogeny of Chondrichthyes: Sharks, batoids and chimaeras. Science Publishers, Inc., Enfield, New Hampshire. 562 pp.

Hart, J.L. 1973. Pacific fishes of Canada. Fish. Res. Board Can. Bull. 180. 740 pp.

Ishihara, H., and R. Ishiyama. 1985. Two new North Pacific skates (Rajidae) and a revised key to Bathyraja in the area. Jpn. J. Ichthyol. 32:143-179.

Larkins, H.A. 1964. Some epipelagic fishes of the North Pacific Ocean, Bering Sea, and Gulf of Alaska. Trans. Am. Fish. Soc. 93:286-290.

Love, M.S., C.W. Mecklenburg, T.A. Mecklenburg, and L.K. Thorsteinson. 2005. Resource inventory of marine and estuarine fishes of the West Coast and Alaska: A checklist of North Pacific and Arctic Ocean species from Baja California to the Alaska-Yukon border. U.S. Geological Survey, Seattle. 276 pp.

Mecklenburg, C.W., T.A. Mecklenburg, and L.K. Thorsteinson. 2002. Fishes of Alaska. American Fisheries Society, Bethesda. 1037 pp.

Musick, J.A., and R. Bonfil (eds.). 2004. Elasmobranch fisheries management techniques. APEC Fisheries Working Group, Singapore. 370 pp.

Selected References

Sheiko, B.A., and V.V. Fedorov. 2000. Class Cephalaspidomorphi: Lampreys. Class Chondrichthyes: Cartilaginous fishes. Class Holocephali: Chimaeras. Class Osteichthyes: Bony fishes. Chapter 1. In: Catalog of vertebrates of Kamchatka and adjacent waters. Kamchatsky Pechatny Dvor, Petropavlovsk-Kamchatsky, Russia, pp. 7-69.

Stevenson, D.E., and J.W. Orr. 2005. New records of two deepwater skate species from the eastern Bering Sea. Northwestern Naturalist 86(2):71-81.

Stevenson, D.E., J.W. Orr, G.R. Hoff, and J.D. McEachran. 2004. Bathyraja mariposa: A new species of skate (Rajidae: Arhynchobatinae) from the Aleutian Islands. Copeia 2004(2):305-314.

Wilimovsky, N.J. 1954. List of the fishes of Alaska. Stanford Ichthyol. Bull. 4:279-294.

Wilson, D.E., and G.W. Hughes. 1978. The first record of the brown cat shark, Apristurus brunneus (Gilbert, 1891) from Alaskan waters. Syesis 11:283.

Zorzi, G.D., and M.E. Anderson. 1988. Records of the deep-water skates Raja (Amblyraja) badia Garman, 1899, and Bathyraja abyssicola (Gilbert, 1896) in the eastern North Pacific, with a new key to California skates. California Department of Fish and Game 74:87-105.

75Selected References

76

Alopias vulpinus . . . . . . . . . . . . . . . . . .H. Wes Pratt (NMFS Northeast Fisheries Science Center)Amblyraja badia . . . . . . . . . . . . . . . . .G. Hoff (NMFS Alaska Fisheries Science Center)Apristurus brunneus . . . . . . . . . . . . .D. Stevenson (AFSC), UW 29664 (adult)Alopias vulpinus . . . . . . . . . . . . . . . . . .H. Wes Pratt (NMFS Northeast Fisheries Science Center)Amblyraja badia . . . . . . . . . . . . . . . . .G. Hoff (NMFS Alaska Fisheries Science Center)Apristurus brunneus . . . . . . . . . . . . . .D. Stevenson (AFSC), UW 29664 (adult); D. Stevenson (egg case)Bathyraja abyssicola . . . . . . . . . . . .D. Stevenson (adults); G. Hoff (egg case)Bathyraja aleutica . . . . . . . . . . . . . . .G. Hoff Bathyraja interrupta . . . . . . . . . . . .D. Stevenson (dorsal); G. Hoff (ventral, egg case) Bathyraja lindbergi . . . . . . . . . . . . . .G. Hoff Bathyraja maculata . . . . . . . . . . . . .D. Stevenson (dorsal); G. Hoff (ventral, egg case) Bathyraja mariposa . . . . . . . . . . . . .G. Hoff (UW 47197)Bathyraja minispinosa . . . . . . . . . .G. Hoff (dorsal, egg case); D. Stevenson (ventral)Bathyraja parmifera . . . . . . . . . . . . .G. HoffBathyraja sp. cf. parmifera . . . . . . .J. Orr (AFSC)Bathyraja taranetzi . . . . . . . . . . . . .D. Stevenson (dorsal), UW 113189; J. Orr (ventral), UW 113189; G. Hoff (egg case)Bathyraja trachura . . . . . . . . . . . . . .G. HoffBathyraja violacea . . . . . . . . . . . . . .J. Orr (UW 113488, adults); A. Orlov (VNIRO; egg case)Carcharodon carcharias . . . . . . . . . .Greg Skomal (Massachusetts Marine Fisheries)Cetorhinus maximus . . . . . . . . . . . . .marinethemes.com/Saul GonorHexanchus griseus . . . . . . . . . . . . . . .Dan Kamikawa (NOAA Fisheries)Hydrolagus colliei . . . . . . . . . . . . . . .North Pacific Groundfish Observer Program archives (adults); D. Stevenson (egg case)Lamna ditropis . . . . . . . . . . . . . . . . . .Ken Goldman (ADFG)Prionace glauca . . . . . . . . . . . . . . . . .H. Wes Pratt (NEFSC)Raja binoculata . . . . . . . . . . . . . . . . .D. Stevenson (dorsal); K. Maslenikov (ventral; NMFS AFSC); G. Hoff (egg case)Raja rhina . . . . . . . . . . . . . . . . . . . . . . . .K. Maslenikov (adults); G. Hoff (egg case)Somniosus pacificus . . . . . . . . . . . . .S. Kotwicki (AFSC)Squalus acanthias . . . . . . . . . . . . . . .R. Lauth (AFSC)

Photo Sources

77

Alaska skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Aleutian skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Alopias vulpinus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Amblyraja badia . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Apristurus brunneus . . . . . . . . . . . . . . . . . . . . . . . . . 28Basking shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Bathyraja abyssicola . . . . . . . . . . . . . . . . . . . . . . . . . 58Bathyraja aleutica . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Bathyraja interrupta . . . . . . . . . . . . . . . . . . . . . . . . .48Bathyraja lindbergi . . . . . . . . . . . . . . . . . . . . . . . . . .60Bathyraja maculata . . . . . . . . . . . . . . . . . . . . . . . . .66Bathyraja mariposa . . . . . . . . . . . . . . . . . . . . . . . . . 56Bathyraja minispinosa . . . . . . . . . . . . . . . . . . . . . . .64Bathyraja parmifera . . . . . . . . . . . . . . . . . . . . . . . . .44Bathyraja sp. cf. parmifera . . . . . . . . . . . . . . . . . . .46Bathyraja taranetzi . . . . . . . . . . . . . . . . . . . . . . . . . . 54Bathyraja trachura . . . . . . . . . . . . . . . . . . . . . . . . . . 62Bathyraja violacea . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Bering skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Big skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Black skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Blue shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Bluntnose sixgill shark . . . . . . . . . . . . . . . . . . . . . . 24Brown cat shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Butterfly skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Carcharodon carcharias . . . . . . . . . . . . . . . . . . . . . 36Cetorhinus maximus . . . . . . . . . . . . . . . . . . . . . . . . . 26Chimaera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Commander skate . . . . . . . . . . . . . . . . . . . . . . . . . .60Deepsea skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Great white shark . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Hexanchus griseus . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Hydrolagus colliei . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Lamna ditropis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34“Leopard skate” . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46Longnose skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Mud shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Mud skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Okhotsk skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Pacific sleeper shark . . . . . . . . . . . . . . . . . . . . . . . . 22Prionace glauca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Raja binoculata . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Raja rhina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Roughshoulder skate . . . . . . . . . . . . . . . . . . . . . . . 38Roughtail skate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Salmon shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Sandpaper skate . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Somniosus pacificus . . . . . . . . . . . . . . . . . . . . . . . . . 22Spiny dogfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Spotted ratfish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Squalus acanthias . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Thresher shark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Whiteblotched skate . . . . . . . . . . . . . . . . . . . . . . . .66Whitebrow skate. . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Index to Common and Scientifi c Names

• Biological Field Techniques for Chionoecetes Crabs

• Biological Field Techniques for Lithodid Crabs

• Common Edible Seaweeds in the Gulf of Alaska

• Field Guide to Bird Nests and Eggs of Alaska’s Coastal Tundra

• Guide to Marine Mammals and Turtles of the U.S. Atlantic and Gulf of Mexico

• Guide to Marine Mammals of Alaska

• Guide to Northeast Pacific Flatfishes

• Guide to Northeast Pacific Rockfishes

• Marine Mammals of the Eastern North Pacific (waterproof fold-out brochure)

• North Pacific Albatrosses (laminated identification card)

• Ocean Treasure: Commercial Fishing in Alaska

• The Bering Sea and Aleutian Islands: Region of Wonders

• Many science conference proceedings on marine fisheries biology and management

Field guides and other fine books on Alaska marine resources are available from Alaska Sea Grant:

For full descriptions, prices, and ordering information for alaska sea grant publications and videos, visit our bookstore at

www.alaskaseagrant.org or call toll-free for a free catalog, (888) 789-0090.

Biological Field Techniques for

Lithodid Crabs William E. Donaldson ◆ Susan C. Byersdorfer

Published by Alaska Sea Grant College Program

field guide to sharks, skates, and ratfish of alaskanmfs alaska fisheries science center’s race...

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