Thresher Shark Alopias vulpinus 30 Upper tooth Lower tooth
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. Reproduction Viviparous (oophagous). 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
Blue Shark Prionace glauca 32 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. Depth Pelagic, surface to 350 m. 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 heavybodied 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
Salmon Shark Lamna ditropis 34 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. Reproduction Viviparous (oophagous). Maximum Length 3.1 m. Range Bering Sea to Mexico in the eastern Pacific; to Korea in the western Pacific. Depth Pelagic, surface to 792 m. 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 pectoralfin 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
Great White Shark Carcharodon carcharias 36 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. Reproduction Viviparous (oophagous). 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
Roughshoulder Skate Amblyraja badia 38 dorsal ventral egg case Rostral Nuchal Orbital Scapular Mid-dorsal Dorsal diagram showing thorns on disc.
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 graybrown, 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 39
Big Skate Raja binoculata 40 dorsal ventral egg case Nuchal Orbital Dorsal diagram showing thorns on disc.
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 41