Circular 162. the Soft-Shell Clam
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HE OFT iHELL 'LAM UNITED STATES DEPARTMENT 8F THE INTERIOR FISH AND WILDLIFE SERVICE BUREAU OF COMMERCIAL FISHERIES Circular 162 CONTENTS Page 1 Intr oduc tion. • • • . 2 Natural history • . ~ . 2 Distribution. 3 Taxonomy. · . Anatomy. • • • •• . · . 3 4 Life cycle. • • • • • . • •• Predators, diseases, and parasites . 7 Fishery - methods and management .•••.••• • 9 New England area. • • • • • . • • • • • . .. 9 Chesapeake area . ........... 1 1 Special problem s of paralytic shellfish poisoning and pollution . .............. 13 Summary . .... 14 Acknowledgment s •••• · . 14 Selected bibliography •••••• 15 ABSTRACT Describes the soft- shell cla.1n industry of the Atlantic coast; reviewing past and present economic importance, fishery methods, fishery management programs, and special problems associated with shellfish culture and marketing. Provides a summary of soft- shell clam natural history in- eluding distribution, taxonomy, anatomy, and life cycle. l THE SOFT -SHELL CLAM by Robert W. Hanks Bureau of Commercial Fisheries Biological Labor ator y U.S. Fish and Wildlife Serv i c e Boothbay Harbor, Maine INTRODUCTION for s a lted c l a m s used as bait by cod fishermen on t he G r and Bank. For the next The soft-shell clam, Myaarenaria L., has 2 5 years this was the most important outlet played an important role in the history and for cla ms a nd was a sour ce of wealth to economy of the eastern coast of our country . some coastal communities . Many of the Long before the first explorers reached digg ers e a rne d up t o $10 per day in this our shores, clams were important in the busin ess during October to March, when diet of some American Indian tribes. Early other o c cupat ions wer e difficult to find . colonists relied on the abundant cla m A b out 18 75 a new demand for soft- shell stocks during periods of privation, although c lam s a r o s e as clam bakes and shore they rarely used clams as a regular food dinner s b ecame inc r ea singly popular durmg item. In the mid-1800's an important bai t the summer. Clams became important a s a clam fishery, supplying trawl bait for c od cons umer i t em for t he fir st time, and this fishermen, was established by some N e w demand f o r clams is still important to the England coastal communities. Later, w ith nort h e r n f isher y . Around 1900, canned the decline in demand for bait clams, c l a ms became incr easingly important, and consumer interest developed in canned for the next 40 year s most clam s went clams- -maintaining the fishery at a high to the canner ies . During thlS period clam level up to the early 1940's. The modern m ing was p r ohibit ed in some areas dUrIng trend is toward the marketing of fresh o r the summer by State law, thereby concen frozen clam meats that are generally tra t i n g p r oduction in the winter when there served as fried clams in most areas, but wa s little competition from other industries fresh clams, steamed in the shell, a re f o r lab o r , and clam prices were low. still popular in coastal regions. Since the l ate 1930's most clams have In recent year s, clam supplies from the been used i'1 the fresh shucked trade and New England area have declined, primaril y recently cooked and uncooked frozen due to the activity of a voracious predator. p roducts have become popular . Clams are With the introduction of mechanical digging p rima r ily used in the fried clam retail methods, a new source of clam produc tion m a r k e t and, with the lncrease in population, has been developed in the Chesapeake B ay better p reserving and marketing methods, region, and the soft- shell clam continues a nd extensive pubbcity by large restaurant to occupy a prominent position in our chains, t he demand for clams is gradually coastal shellfisheries. inc reasing . New England has traditionally been the Ear ly p r oduction records are not easlly center of soft- shell clam production, though obtaine d, b ut the first figutes given In the no commercial interest in c lam s w as Federal statistics indicate a fairly hI h evidenced before the middle 1 8 00' s. C l a ms, leve l of production had been estabhshed by of course, had been dug extensively before 1880 (fig . 1) . The! Tew England fi shery has this period, but since they were ever y b e e n mar ked by a consistently high, b t where available and demand for t h em as var iable, level of productIon untll recent food and bait was probably on an i n dividual year s . The actual dollar val e of he basis, they were not a market i tem. In fishe r y r eached the 2 million mark d rm the period around 1850 the fir st real the 10 years from 1945 to 1 55 even tho h commercial fishery began w ith the demand this per iod marked a drastic decl n m 13 12 j\ r-\ 2000 II . ~ \ 10 /. \ III 1500 9 . ! .,; ... III o .. III ... 8 o 0 Z / \l c( III III 7 ~ Z -' o ~ \.'" ./ % .. / ~ 6 1000 I= ... "'",;Jib, S / \ ~ z 5 I / .. c( ~ ~ > U 4 Now E".,.... / ~ ~ I / 0 0 ./ III "'-. ~:\/ 500 A. 3 Chesapeake Bay ,\-. : 2 ·~bs ~ . i _ ~Ibs ) Middle Atlantic ~/ )/i.__ --. i ·· / .-.... 1880 IBM 1890 legs 1900 19O5 1910 191' 1920 1925 19~O 19M 19 40 19 45 195-0 19" 1960 (J 1884 1889 1894 1899 1904 1909 1914 1919 1924 1929 1934 1939 1944 1949 19!54 1~9 YEAR INTERVAL Figure 1.--Pounds of meat production and value of soft-shell clams from three major areas of the Atlantic coast. production of almost 6 million pounds. New NA TURAL HISTORY England clams have a decidedly favored price differential and are valued at almost Distribution twice the price of their southern counter part. New England production figures for The soft- shell clam is found from the recent years are the lowest (between 2 and coast of Laborador to the region of Cape 3 million pounds) on record for nearly a century. Hatteras, N.C. On the European coast it has been recorded from northern Norway Following World War II, particularly to the Bay of Biscay, France. Aroun4 1879, after 1950 when the "Maryland" escalator young clams were a ccidentally introduced dredge was invented and introduced, the into San Francisco Bay, Calif., with ship soft- shell clam fishery in Chesapeake Bay ments of seed oysters from the Atlantic rose to dominate production. Production coast. Since then they have spread from was almost double the New England output Monterey, Calif., to Alaska. The soft- shell in 1960 although the total value of clam s clam is also found along the western Pacific from the two areas was nearly identical. coast from the Kamchatka Peninsula to the The southern fishery is now limited only southern regions of the Japanese islands. by market demand as great quantities of This species, therefore, lives on every virtually virgin stocks are available. Almost coastline in the northern hemisphere, but all southern clams are shipped to the New it is only in the United States, particularly England area, for the market demand is on our eastern coast, that these clams still centered in the north. have become commercially important. 2 Taxonomy shell, which lives in deeper northern water s, and is of no commercial interest. The soft-shell clam belongs to that group Anatomy in the animal kingdom known as the phylum Mollusca. They are further arranged, to A discus sion of clam anatomy requires gether with other bivalves, into the class the establishment of certain directional PeZecypoda and because of certain character landmarks. The siphon (neck) is considered istics of gill structure are placed in the to be posterior while the opposite (head or order EuZamellibranchia. All of the structurally mouth) end is anterior. The hinge area is similar clams are then grouped in the family the back or dorsal region while the front, Myacidae. On the western Atlantic coast there with the exposed mantle edge (rim) is are only two recorded species of clams in ventral. These terms are in underlined the genus Mya; they are Mya arenaria, our com bold type in figure 2. It follows that having mercially important clam, and Mya truncata, a front, back, and head, the clam will also characterized by a short, square-ended have a right and left side. Posterior excurrent siphon incurrent siphon onal pallial cavity posterior adductor muscle epibranchial cavity kidney mass Dorsa I cut mantle edge heart (intestine passes through) crystalline style sheath (style within) brown or Keber's gland intestine digestive gland stomach Ventral mout anterior visceral outline foot Cllt mantle edge opening Anterior Figure 2.--Soft-shell clam internal anatomy 3 The external appearance of the soft- shell The interior of the visceral mass can be clam is an irregular ellipsoid with the two exposed by tearIng away the outer wall, valves, or shells, about equal in size. The uncovering the large brown liver and t he right shell is usually slightly larger than gonad (a tissue spread throughout the body). the left. When closed the two valves may Embedded in this gonad and surrounding touch along the ventral edge but gape widely connective material lie the long, coiled in front, allowing passage of the foot, and intestine, the crystalline style within its in back, allowing extrusion of the siphons.