Featured Elasmobranch

November 2006

ALASKAN MUD SKATE

RHINORAJA TARANETZI (DOLGANOV, 1983)

FAMILY ARHYNCHOBATIDAE (SKATES)

Identification: A smallish skate species with rhombic disc, a soft, flexible, short snout and a tail that is longer than its disc length in adults. Thorns are absent on disc, although nuchal thorns occasionally present, although weakly developed and numbering less than three, on some individuals. Tail thorns are indistinct and unevenly distributed. The dorsal surface is textured with minute fine prickles, and colored cinnamon or grayish with scattered small white and dark spots. Small oval white spot aside each orbit. Ventral surface smooth and light colored.

Size: Maximum reported total length is 77cm TL for females and 67 cm for males.

Distribution: The mud skate ranges from Pacific coast of Kuril Islands and Kamchatka to the Bering Sea and Aleutian Islands. There are unconfirmed reports from the western Gulf of Alaska.

Habitat: Commonly found in bottom trawls at 58 to 1,054 meters.

Biology: Oviparous, females mature at about 63 cm and males at about 55 cm. The egg cases are small, about 72 mm in length excluding its horns, the surface is smooth, finely striated, and thinly covered with silky fibers, and moderately wide lateral keels. The diet consists primarily of shrimps, cephalopods, tanner crabs, and small bony fishes.

General interest: A poorly known skate, it is sometimes placed in the genus Bathyraja. Two other related species, Bathyraja hubbsi and Rhinoraja longi have been synonymized with this species, although further taxonomic research is required to determine the status of these other species. This skate is taken as by-catch, but given its small size is likely not taken in as large a numbers as other larger species. A life history study on this species is currently under investigation as part of a Masters Thesis project at Moss Landing Marine Laboratories.

By Jasmine Fry
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road, Moss Landing, CA 95039
jfry@mlml.calstate.edu