Thorny skate Raja radiata Donovan 1807

STARRY SKATE^[75]

Description—

The thorny skate can be identified at a glance among skates of the Gulf of Maine by the fact that the row of thorns with which the midline of back and tail is armed are not only large and conspicuous, but do not number more than 19 at most from the nape back along the tail. There are also 2 or 3 large thorns on each shoulder; and one in front of each eye and one behind it; one close to the inner end of each spiracle; and other smaller thorns scattered on snout, pectoral fins, and tail. The bases of the thorns on the pectorals are star-shaped, a very distinctive character; those of the still larger thorns along the midline of the back are oval. Adult males have 2 rows of hooked, erectile thorns near the outer corners of the pectorals.

The anterior angle of the disc is considerably more obtuse than a right angle (110-140°), and the tip of the snout is blunt with the margins bulging somewhat a little in front of the level of the eyes; the outer corners of the pectorals are less broadly rounded than in either the little skate or the big skate; and the two dorsal fins may either be joined at the base or be separated by a short space. There are 36 to 46 series of teeth in each jaw, those of females and of young males with low cusps that are worn nearly smooth along the older rows; those of mature males a little sharper and spaced a little more widely.

Color—

Brown above, either uniform or slightly clouded, or spotted with darker, small specimens more conspicuously so than larger. Sometimes there is a white spot beside each eye, one on either side abreast of the nape, and another on each side on the rear part of the disc. The lower side is white, sometimes with irregular sooty or brownish blotches. Garman mentions a partial albino, white above with a few reddish brown and brown spots.

Size—

The thorny skate is about 4 inches (100 mm.) long from snout to first dorsal fin at hatching. The largest specimens so far recorded from American waters have been about 40 inches for the Nova Scotia Banks, 35¼ inches for Georges Bank, and about 31 inches for Massachusetts Bay. But some males may mature when only 21 to 22 inches long. One 32 inches long is about 23 inches wide.

Habits—

The thorny skate is a cool water fish, at home in temperatures from about 50° or so down nearly to the freezing point of salt water. It is also restricted in general to depths greater than about 10 fathoms, even in the northernmost part of its range. In the Gulf of St. Lawrence it lives indifferently on the ice cold banks and in the warmer water on the bottom of the deep Laurentian Channel. Average catches of 1 per haul at 26 to 35 fathoms, 22 per haul at 36 to 49 fathoms, and 5 per haul at 50 to 75 fathoms, in 42 trawl hauls, by the Eugene H fishing from Nantucket Lightship, the central part of Georges Bank, June 1951, suggest a rather definite preference for the intermediate depth zone, perhaps because of the food supply. But thorny skates have been taken at many stations, also, down to 336 fathoms off the American coast, and as deep as 459 fathoms near Spitzbergen.

The stomachs of thorny skates caught on Georges Bank contained shrimps, spider crabs, anemones, hydroids, and fish digested past identification.

The egg cases vary considerably in size, probably depending on the size of the parent fish. One from a fish 32 inches long, taken on Georges Bank, measured 3 by 2¼ inches exclusive of the horns. Others that have been measured from the Nova Scotia Banks ranged from 3 to 3½ inches in length. They are flat on one side, strongly convex [page 73] on the other, and are rough with narrow cross-ridges. A mass of delicate fibrils, matted together, extends along each of the longer sides and partly over the surfaces also. And each horn ends in a slender fibril.

General range—

The thorny skate is known on both sides of the northern Atlantic. In the east its range extends from the White Sea and Barents Sea to the North Sea, Dutch coast, and western part of the Baltic;^[77] in the west from West Greenland, Hudson Bay, Atlantic coast of Labrador, east and south coasts of Newfoundland, Grand Banks, Gulf of St. Lawrence and outer coast of Nova Scotia with the off-lying fishing grounds, to the Gulf of Maine, and thence westward and southward along the edge of the continental shelf to the offing of New York; and as a stray to the offing of Charleston, S. C.^[78]

Occurrence in the Gulf of Maine—

The thorny skate is not often seen close inshore along our coast, being restricted in general to moderately deep water (p. 72). But it is now known to be generally distributed in the deeper waters of the Gulf. Thus it is frequently taken on the New Brunswick side of the Bay of Fundy in depths of 10 fathoms or deeper, in 20 to 30 fathoms in St. Mary Bay on the Nova Scotia side. It has been recorded from Casco Bay; from Ipswich Bay, off Gloucester, Salem and Nahant, and off Provincetown; and we have taken it ourselves in numerous places in the Gulf at 14 fathoms and deeper, including the [page 74] vicinity of Mount Desert; Platts Bank; and in the bottoms of the deep troughs. It has also been trawled at many stations on Georges Bank, likewise along the upper part of the continental slope off southern New England, down to 336 fathoms.

There is nothing in the available record to suggest that it carries out any regular migrations, whether in or off shore, or along the coast. And it is more catholic in respect to its choice of bottom than some other skates, for while it is most plentiful on the good fishing grounds of sand, gravel, and broken shells, we have taken it at many stations in the Gulf on soft mud. And it is one of the most plentiful of Gulf of Maine skates at appropriate depths. Thus 325 were caught in 37 trawl hauls on the northeastern part of Georges Bank on one trip in 1929; again, in June 1951, we counted 432, from 42 trawl hauls (7 percent of the total catch of skates), on the Eugene H fishing from Nantucket Lightship to the south central part of Georges. We once caught 12 in the western side of the Gulf in a beam trawl only 8 feet across the mouth in 30 minutes; and we have taken 1 to 100 of them in 26 hauls with larger trawls, between Mount Desert Island and Massachusetts Bay.

Females containing eggs about ready to be laid, and deposited eggs in various stages of incubation, have been taken in Nova Scotian waters or in the Gulf of Maine, in April, June, July, and September, and they are to be expected there in winter as well, having been reported in January and February off Norway, and from February to June in Scottish waters.