Longnose Skate Raja rhina

Transcription

1 Longnose Skate Raja rhina 42 dorsal ventral egg case Nuchal Orbital Dorsal diagram showing thorns on disc.

2 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 43

3 Alaska Skate Bathyraja parmifera 44 dorsal ventral egg case Nuchal Orbital Scapular Mid-dorsal Dorsal diagram showing thorns on disc.

4 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 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 oliveyellow 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 45

5 Leopard Skate Bathyraja sp. cf. parmifera 46 dorsal ventral egg case Nuchal Orbital Scapular Mid-dorsal Dorsal diagram showing thorns on disc.

6 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. Maximum Size 139 cm. Range Western Aleutian Islands. Depth 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 western Aleutian Islands. Leopard Skate Bathyraja sp. cf. parmifera 47

7 Bering Skate Bathyraja interrupta 48 ventral dorsal egg case Nuchal Scapular (Mid-dorsal) Dorsal diagram showing thorns on disc.

8 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 midcase 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 In Alaska waters, the Bering skate is found in the Gulf of Alaska, Bering Sea, and eastern Aleutian Islands. former in having denticles surrounding the tail thorns and from the latter in having a reduced or interrupted middorsal thorn row as well as reduced interdorsal thorns. Bering Skate Bathyraja interrupta 49

9 Aleutian Skate Bathyraja aleutica 50 dorsal ventral egg case Nuchal Scapular Mid-dorsal Dorsal diagram showing thorns on disc.

10 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. Maximum Size 161 cm. 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 51

11 Okhotsk Skate Bathyraja violacea 52 dorsal ventral egg case Dorsal diagram showing absence of disc thorns.

12 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 midcase 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 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 53