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Skates, with their disc-like outlines, thin as a shingle toward their outer edges, and with their rather long tails, are familiar objects along our shores. The outer edges of their pelvic fins are concave (convex in the sting rays), they have two very small dorsal fins on the rear part of the tail, but no distinct tail fin, and they lack the large tail spine that is so characteristic of the sting rays. The Gulf of Maine supports four species in abundance, while two others have been recorded on rare occasions.
The common skates look so much alike that fishermen seldom distinguish between them. For this reason we know very little about the individual differences in habits among the several species. All live chiefly on the bottom or close to it, spending much of the time partially buried in the mud or sand. They move through the water by undulations of the flexible pectoral fins, steering themselves with the tail. All are decidedly omnivorous, feeding largely on the larger Crustacea, such as shrimps, crabs, lobsters; on mollusks, worms, and to a greater or less extent on fish.
All the true skates lay large eggs with blackish or sea-green leathery shells, roughly oblong in outline, with a hollow tendril at each corner by which they become fastened to seaweeds or other objects. The empty eggshells, "mermaids purses," are familiar objects on our beaches among the flotsam along high water mark. While still in the egg the embryo skate develops temporary external gill filaments from the walls of the gill clefts, but these disappear completely before it hatches. Probably all our local skates spawn over a considerable part of the year, with incubation periods of several months up to a year or more.
To give some idea of their abundance on the offshore banks we may note that the average number of skates (all species together) taken on Georges Bank, per trip of 4 to 7 days, on 25 trips by several trawlers, January to December 1913, was about 800, the largest catch 4,520, the [page 61] poorest 82. Again, on a trip to the northeastern part of the bank, September 1929, on the otter trawler Kingfisher, 37 hauls yielded from 0 to 105 skates per haul (total 495) and 42 trawl hauls by the Eugene H, fishing from Nantucket Lightship, to the south-central part of Georges Bank in late June 1951 caught an average of 146 skates per haul (total, 6,130 skates), which works out at about 9 to 10 skates per acre. Probably they are equally abundant on Browns Bank; certainly they are familiar enough there, but statistics are not available of the actual numbers caught. Skates are also plentiful inshore as appears from catches of about 1 skate to 33 fishes of all kinds on long lines, at various localities in the Gulf of Maine.
In the Gulf of Maine, skates are only a nuisance for they bite the hook readily and often are caught in great numbers in otter trawls, most of them to be thrown back into the sea, the market demand for them being so small that the total landings reported for New England (Massachusetts and Maine) in 1947 was only 28,200 pounds; and 59,100 pounds for 1948. But some are now being landed in Maine for fish meal. They are much more highly valued in northwestern Europe for food with landings for the years just preceding World War II, running around 90 to 100 million pounds.
 Under aquarium conditions the incubation period for the little skate (R. erinacea) was 5 to 6 months (p. 69); and it ranged from 4½ to about 14¾ months for 6 common European skates; see Clarke, Jour. Marine Biol. Assoc. United Kingdom, vol. 12, No. 4, 1927, p. 587.
 Three mile hauls with the trawl sweeping a strip about 35 feet wide.
 Examples are: 15 miles off Monhegan I., Maine, June 24-25, 1913, total fish caught, 6,463; skates 170. Twenty miles east of Cape Cod, Nov. 11, 1913; total fish caught 6,532, skates 202. Jeffreys Ledge, Dec. 11-12, 1913; total fish caught 3,996, skates 62.
 Scattergood, Copeia, 1950, p. 169.