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Characteristics, distribution and ecology
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Author: Hubbs and Follett, 1947

Field Marks:
Heavy spindle-shaped body, short conical snout, moderately large bladelike teeth with lateral cusplets, long gill slits, large first dorsal fin with dark free rear tip, minute, pivoting second dorsal and anal fins, strong keels on caudal peduncle, short secondary keels on caudal base, crescentic caudal fin, dusky blotches on ventral surface of body.

Diagnostic Features:
Snout short, length of snout about 2.7 times in distance from eyes to first gill opening; first upper lateral teeth with strongly oblique cusps. Colour: first dorsal fin uniformly dark, no light rvar tiD: ventral surface of body white with dusky blotches.

Geographical Distribution:
Coastal and oceanic. North Pacific: Japan and the Koreas, Sea of Okhotsk to Bering Sea and w southward to southern California and possibly Baja California, Mexico.

Habitat and Biology:
A common coastal-littoral and epipelagic shark with a preference for boreal to cool temperate waters, found at depths from the surface to at least 152 m. Salmon sharks are common in continental offshore waters but range inshore to just off beaches; they also are abundant far from land in the North Pacific ocean basin, along with their salmon prey. Salmon sharks occur singly and in schools or feeding aggregates of several individuals. They are swift-swimming sharks, maintaining a body temperature well above ambient water temperature.

This shark is ovoviviparous, with uterine cannibalism; litter size is up to4 young.

The salmon shark is a proverbially voracious feeder on Pacific salmon (Oncorhynchus), though lancetfishes, daggerteeth (Anotopterus), lumpfishes, sculpins, Atka mackeral (Pleurogrammus), pollock, and tomcod are also eaten.

The salmon shark has been regarded as potentially dangerous because of its large size and relationship to known dangerous species, but has never or seldom been implicated in an attack on people. There are a few unsubstantiated attacks reported for the species, but possibly by confusion with the great white shark. Recently divers have seen and photographed schools of adult salmon sharks underwater, with no aggressive or threatening overtures on the part of the sharks (B. Lea, pers.comm.).

Size:
Maximum total length about 305 cm, males maturing between 180 and 240 cm.

Interest to Fisheries:
Fished in the North Pacific by Japanese coastal longliners and by sports anglers in Alaska and Canada using rod and reel. They are commonly caught by Japanese, US and Canadian offshore salmon gillnetters but are currently discarded. They are occasionally trammel-netted by halibut fishermen off California and recently have begun to show up in numbers in gillnets set by thresher fishermen in northern-central California, but are presently not considered as marketable. The bulk of the fish currently caught are considered a nuisance for the damage they do to salmon nets.

The flesh of the salmon shark is used fresh for human consumption in Japan, where it is processed into various fish products, and to a lesser extent in Alaska and California. Its oil, skin (for leather), and fins (for sharkfin soup) are utilized also.

Remarks:
See Nakaya (1971) for a detailed comparison of this species with Lamna nasus. Pillai and Honma (1978) reported L. ditropis from the southern Indian Ocean, without data confirming the identification. Presumably the species in question was Lamna nasus, which is known from the southern Indian Ocean (open sea from 800 to 965 km, northeastern of Kerguelen Island and from 640 to 800 km SSE of St. Paul Island, unpublished record by L.J.V. Compagno; also near Kerguelen Island, Duhamel and Ozouf Costaz, 1982).

Type material:
Holotype: Museum of Comparative Zoology, Harvard U., MCZ 36471, adult male. Type Locality: La Jolla, California, depth 92 to 107 m.

Salmon shark (Lamna ditropis)