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Bulletin of the United States Fish Commission 1889 ------------------------------------------------------------------------------------------- Page 316 also adorned with a row of conspicuous round black eyes around its base: the lungs or gills are between the two folds of the mantle, composed of fibers pointing outward, of delicate form and free at their outer edges, so as to float loosely in the water. The mouth is placed between the two inmost gills, where they unite. It is a simple orifice, destitute of teeth, but with four membranous lips on each side of the aperture. The mechanism by which respiration and nutrition are secured is elaborate and exceedingly interesting. The filaments of the gill fringe, when examined under a powerful microscope, are seen to be covered with numberless minute, hair-like processes, endowed with the power of rapid motion. These are called cilia, and when the animal is alive and in situ, with the valves gaping, may be seen in constant vibration in the water, generating by their mutual action a system of currents by which the surface of the gills is laved, diverting toward the mouth animalcules and other small nutritious particles. (++) The shell of the scallop has been described as "orbicular, rather higher than long, thin and translucent when young, thick, strong, and opaque when mature, equilateral, inequivalve, the lower valve being nearly flat and not attaining the edge of the upper valve by an eighth of an inch or more; upper valve moderately convex, valves widely gaping near the hinge, surface everywhere sculptured with radiating punctured lines or grooves about half as wide as the spaces between them, somewhat zigzag in their course. These lines are crossed by closely arranged lines of growth, which on the convex valve are scalloped or vaulted over the radiating lines; flattened valve white, convex valve dingy, reddish-brown, or flesh-colored. Hinge margin narrow, straight, ears equal, the notch in the lower valve rounded and shallow. Interior white, smooth, glossy, with minute radiating lines not corresponding to the exterior grooves." (4) 5. SIZE, GROWTH AND DEATH, HABITS, ETC. The scallop shares with other deep-water mollusks the obscurity concerning their life history which is thrown around them by the great difficulties in the way of a comprehensive research. The commercial fisherman, as a rule, is not a close observer of inconspicuous vital phenomena, and he can not be expected to depart beyond a certain point from the realms of practical business to delve in the domain of natural science. In the case of the particular species under consideration, the writer found that what would in almost any other sphere have been an exhaustive inquiry was almost barren of results. Until the establishment of large marine aquaria, in which the lives of fish, crustaceans, mollusks, and other orders can be studied with but little or no departure from the natural conditions, it would appear that a complete knowledge of the habits and of the most practical methods of propagation, cultivation, and protection of many of our important water animals will always be lacking. Viewed from the standpoint of size alone, the giant scallop is probably the largest edible mollusk on the Atlantic coast of the United States: The average diameter of the specimens taken for market on the coast of Maine is about 5 1/2 inches, although much larger individuals are not uncommon, and those the size of a nickel coin are sometimes brought up. The largest examples recorded from Mount Desert, Castine, and Little Deer Isle have been 9 inches in diameter. The edible muscular portion of a scallop of this size is about 3 inches in diameter and weighs 9 or 10 ounces. The average size of the "meat," however, is a little more than 1 inch in diameter. The general impression among fishermen is that the scallop is a rapid grower, reaching maturity in a few years. In this respect the giant scallop agrees with the probable (note 3) Overland Monthly, April, 1873. (note 4) Gould, Invertebrates of Massachusetts, 1870, pp.196,197. ----------------------------------------------------------------------------------------- GIANT SCALLOP FISHERY OF MAINE. PAGE 317 rate of growth in P. irradians, which has been more thoroughly studied than any other species in this country. The basis for the belief that the scallop attains the proximate limit of size in a few seasons is that frequently, in the spring, when the fishermen visit a ground on which they have worked the previous fall, the scallops are found to be so small that it hardly pays to take them, while in the succeeding autumn and winter they are as large as in the previous year. Mr. Heath states that the fishermen of Mount Desert Island find the scallops that are 4 or 5 inches in diameter to be the cleanest, brightest, and liveliest. Those of 8 inches look old, their shells are dingy, rough, and brittle, and are apt to be more or less honeycombed by the chambers of the boring-sponge. The duration of the life of a scallop after reaching maturity is thought to be quite brief. Some fishermen think that it dies within one year, and it seems probable that the life term is normally not more than 5 or 6 years. Mr. Benedict, as the result of observations off the Massachusetts coast, thinks that exceptionally at least the scallop attains great age. Mr. Vogell, of Castine, has also seen specimens that were so large, thick, and tough that he estimated their age at not less than 15 years. Unlike many mollusks, the scallop has the interesting and useful accomplishment of free locomotion in the water. By means of the powerful adductor muscle the animal is able to rapidly close its valves and to forcibly throw out the water between them. The resistance thus arising tends to swiftly propel the mollusk in the opposite direction by a series of short jerks. Few fishermen are aware of this phenomenon and few persons have ever witnessed it, owing to the depth at which the swimming operations usually occur. The sight of a school of scallops moving in unison through the water is said to be a very striking one. The small shallow-water species (P. irradians) is frequently seen swimming, or "dancing," as the sliding motion is termed; but only here and there on the Maine coast are fishermen found who have actually observed the habit in the giant scallop. This faculty of the scallop is probably exercised when in search of new feeding grounds or of water of a more congenial temperature. It is a matter of personal experience with the fishermen of certain localities to find that the scallop beds shift from time to time, although these wholesale migrations are not nearly so extensive as might be supposed and in some localities are unknown, although not for that reason alone necessarily absent. Inquiry in the vicinity of Mount Desert Island failed to elicit the knowledge of any perceptible change in the position of the beds in that vicinity, which have been operated from the same positions since the establishment of the fishery. Mr. Vogell, speaking of the beds in the vicinity of Castine, says they do sometimes shift, and that there will at times be good fishing on a ground which a week before was destitute of scallops. He assigns the search for food as the cause of the movements. Mr. Gray, of Cape Rosier, has observed that in the summer, after the water becomes warm, the scallops are apt to leave the sites frequented during the cooler months and seek deeper water or retire to grounds with a different character of bottom. The general opinion among fishermen in that section is that upon the return of cold weather, about October 1, they "pod up" on hard, pebbly shoals, with a strong current, for the purpose, it is supposed, of undergoing the reproductive process. Information received in the fall of 1890 stated that no scallops were being found on some grounds that were profitably worked in the spring of the same year, while new End of page 317 ======================================================================== GIANT SCALLOP FISHERY OF MAINE. PAGE 318 beds were discovered in spots on which no scallops were previously known. In the same locality beds have apparently shifted in a single day; but such striking migrations are thought to be undertaken only by small bodies of scallops. 6. PARASITES OF THE SCALLOP (a) Crabs. Like the oyster, the scallop is the host of a species of crab (Pinnotheres maculatum) peculiar to it and to the common mussel (Mytilus edulis). This parasite is lodged in the gill cavity of the mollusks and appears to exert no injurious effect on their life or growth. Mr. Rathbun writes regarding it: "It attains a larger size than the oyster-crab, and, as in the case of the latter, the females alone are parasitic, the males having only been found swimming at the surface of the sea. We have never heard of this species being eaten, probably because neither the mussel nor the smooth scallop has ever been much used as a food in this country. In the summer of 1880, while dredging off Newport, Rhode Island, the United States Fish Commission steamer Fish Hawk came upon extensive beds of the smooth scallop, from a bushel of which nearly a pint of these crabs were obtained. Again, in 1881, the same species was encountered in great abundance by the same. party in Vineyard Sound, in Mlytilus edulis: As an experiment, they were cooked along with the mussels and found to be very palatable, although their shell is, perhaps, somewhat harder than that of Pinnotheres oatreum.*(4) Mr. F. W. Lunt, of West Tremont, Maine, informs the writer that four or five crabs are sometimes found lodged in a single scallop, and that even as many as ten have occasionally been observed. That the crab is not a constant inhabitant is well known, and some fishermen have never seen it. Mr. L. F. Gott, of Tremont, in preparing several hundred bushels of scallops for market, did not find a single crab. So far as can be learned, the crabs are never eaten on the Maine coast. (b) Boring-sponges. The shells of many scallops, but more especially those of larger size, are more or less eaten by a boring-sponge (Cliona sulphurea), which attacks the shell and honeycombs it in all directions. The upper valve appears to be more frequently affected. Ordinarily the sponge does not pierce the hard, glistening, inner lining of the shell, but confines its ravages to the softer outside layers. When the nacre is perforated, however, the irritation produced causes the scallop to throw over the opening a secretion of lime salts which quickly repairs the injury, and no harm results to the animal. The inner surfaces of some specimens are covered with small papillary elevations that are supposed to have been produced in this way. The fishermen, as a rule, do not think the sponge is responsible for the borings seen in the shells, but attribute them to a small worm that finds a shelter in the sponge. This worm is by some fishermen thought to be a real enemy of the scallop, and it is said that specimens of the mollusk are often found that have been bored through and killed by it. The truth of the matter seems to be that the chambers and channels seen in the scallop-shell are mads by the boring-sponge, which may sometimes cause the death of the animal by irritation or otherwise. After reaching a certain age the sponge generally dies, and the unoccupied recesses are then appropriated by a worm which is harmless so far as any power to bore through the shell is concerned. Mr: Richard Rathbun, to whom I am indebted for the foregoing suggestion, informs me that there is no worm affecting the shellfish in our waters that is capable of puncturing a shell, (Note 5) The Fisheries and Fishery Industries of the United States: Section 1, text, page 766. --------------------------------------------------------------------------------------------------------- BULLETIN OF THE UNITED STATES FISH COMMISSION.
PAGE 319 although there are numbers of species that frequent the recesses and holes made by boring-sponges, etc. (c) Fish. A small fish of the genus Liparis (the "sea snails," so called) is sometimes found in the scallop, where it goes for protection. It is supposed that in escaping from an enemy it darts between the open valves of a scallop, and these, closing, imprison the fish. It appears to exert no injurious effects on the mollusk, and, no doubt, is glad to escape as soon as the captor opens its valves. (d) Annelids. A number of species of worms are parasitic on the shell of the scallop. The worm tubes of some of them are large and strong, and, with the sponges, often bind the scallops together in a dense mass, as mentioned hereafter. A small annelid of the genus Spirorbis occurs abundantly on specimens of the scallop collected by the writer in Maine; the species is shown on the accompanying figure of the scallop shell. C. THE FISHERY. ================================== |