Featured Elasmobranch

March 2006

WHITEBROW SKATE

BATHYRAJA MINISPINOSA (ISHIYAMA and ISHIHARA, 1977)

FAMILY ARYNCHOBATIDAE (SOFTNOSE SKATES)

Identification: A moderate-sized skate with a long, pointed, flexible rostrum. The dorsal surface is covered with minute prickles except for the midback and anterior pelvic fin lobes that are smooth. Tail thorns present, nuchal thorns usually absent, but if present number less than three. The ventral surface is smooth. Dorsal is a uniform dark brown except for whitish coloration usually present around the inner margins of the eyes; this whitish coloration is a distinctive feature on this skate. Ventral surface variably dark to light brown, but not uniformly colored as dorsal surface; whitish areas around mouth, abdomen, and pelvic fin region.

Size: Maximum size is at least 95cm in total length for females and 83 cm for males.

Distribution: The whitebrow skate has been recorded in the Bering Sea, Aleutian Islands, Commander Islands, and the Sea of Okhotsk, off Hokkaido, Japan.

Habitat: Most often observed between 200 and 800 m deep, it may be found as shallow as 150 m down to a depth of 800 m.

Biology: Oviparous, the egg cases of B. minispinosa are small (~72mm) with tiny prickles, giving them a rough appearance. It is unknown how many or how often eggs are laid. Females reach first maturity at about 68cm, and males at around 70cm. The young eat mostly amphipods, while adults eat snow crabs and fishes.

General interest: As with most of the Alaskan skate species, almost no research has been conducted on the age, growth, feeding, distribution and reproduction of this species. Nearly all species of skates in the Eastern North Pacific are lacking sufficient life history information for fisheries management. There is currently no directed fishery for B. minispinosa; however, skates make up a majority of the bycatch grouped in the ‘other species’ category in Alaskan commercial bottom trawl and long-line fisheries. Research is underway at Moss Landing Marine Laboratories to estimate the age and growth of this species. The whitebrow skate is also sometimes called the smallthorn skate for the small prickles on the dorsal side of the disk.

By Shaara Ainsley
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road, Moss Landing, CA 95039
sainsley@mlml.calstate.edu