65 percent of the production was from New York, the remainder, in order of descending importance, was from Rhode Island, New Jersey, Virginia, North Carolina, Massachusetts, South Management for Carolina, Maryland, and Maine. In that same year, commercial pro­ Increasing Clam duction of the soft clam in the eastern Abundance United States totalled about 660,000 bushels, or 4,365 t of meat, with a landed value of about $12 million. Ap­ proximately 80 percent of the produc­ CLYDE L. MacKENZIE, Jr. tion was from Maine, the remainder was from Maryland, Massachusetts, New York, Rhode Island, and New Jer­ sey (U.S. Department of Commerce, Introduction and resource managers focus their at­ 1978a-i). In recent years, the demand tention on methods for increasing clam for clams has far exceeded production, Low abundance of the hard clam, production. bringing increasingly higher prices. In Mercenaria mercenaria, and soft clam, Low clam abundance does not stem 1977, clam prices reached an all-time Mya arenaria, in beds of the eastern from a limited biotic potential of the high: Hard clams of the littleneck United States has always had a strong clams. Indeed, only a minute fraction category (longest shell lengths, 5-5.7 limiting effect on local employment and of the potential is realized as a clam cm =2-2.25 inches) brought fishermen incomes as well as market supplies of yield to fishermen. The limitations on more than $30 a bushel; soft clams clams. Unlike agriculture, where pro­ abundance are to be found in environ­ brought fishermen from $15 to slightly gressive methods for increasing pro­ mental constraints, such as predation, more than $20 a bushel. Hard clams and duction have resulted in flourishing on the biotic potential. General aware­ soft clams within the length range 5-6.5 crops, the clam fishery is severely ness that clam abundance can be in­ cm (2-2.6 inches) bring by far the high­ handicapped by a complete lack of creased through environmental im­ est demand and prices in the market. practicable methods to increase clam provement has been absent. This paper Clams are within that length range only abundance in beds through environ­ presents background information on the about 2 years in most areas, then grow mental improvement. The beds are wild clam fishery, data on biological and en­ beyond it and have much less value. and yield variable and limited clam vironmental factors that govern clam Ritchie (1977) reported that in 1975 quantities, and thus fishermen often abundance, and suggestions for de­ nearly 17,000 part-time and full-time have uncertain employment and criti­ veloping a strategy and tactics for in­ fishermen gathered the hard clam, and cally low incomes. Because clam creasing clam abundance. 7,000 part-time and full-time fishermen supplies to the market are limited, gathered the soft clam. Background prices have constantly risen in recent The Need for More Clams years, with a tendency to price clams Clam Fishery Statistics out ofa broad-base market. The price of The condition of uncertain and low the hard clam has soared during the In 1977, the year of latest available clam abundance has consistently domi­ 1970's, producing a strong inflationary data, commercial production of the nated the working atmosphere of the effect in the market. The situation, de­ hard clam in the eastern United States leterious to the fishery and the market, totalled about 1.2 million bushels (1 could be rectified through increased bushel =35.21), or6,045 metric tons (t) Clyde L. MacKenzie, Jr. is with the Northeast Fisheries Center, Sandy Hook Laboratory, Na­ clam abundance in beds. Thus, it is of meat, with a landed value of slightly tional Marine Fisheries Service, NOAA, High­ imperative that shellfish researchers more than $25 million. Approximately lands, NJ 07732.

ABSTRACT-An urgent need exists to in­ on the vagaries of environmental factors to this paper, a strategy and tactics are crease clam abundance in beds ofthe east­ provide clams in beds, all ofwhich are wild. suggested for increasing clam abundance ern United States in order to improve the The hard clam and soft clam each have a by at least severalfold through improving economic status ofclam fishermen and local sufficiently large biotic potential to stock environments of setting clam larvae, clam communities as well as to increase clam beds with clam populations of maximum spat, and juveniles. The concept differs supplies at stable market prices. Hereto­ abundance, but environmental factors sup­ from conventional management based fore, clamfishermen have depended entirely press it, keeping clams in low abundance. In merely on gathering controls.

10 Marine Fisheries Review Figure I.-Hard clams and trash gathered during a 5-minute raking by a fisherman through a bed in Great South Bay, New York, 1975. Small clam shells (the remnants of clams killed by predators), most seed clams, and predators had passed through the rake as it was being pulled. The fisherman gathered only about 1.5 bushels of clams (about 1,000 clams) during the day, showing that clam abundance was low. A fisherman commonly took 5 bushels of clams (3,500 clams) a day a few years earlier.

clam fishery (Fig. I). The dependence Pollution has had detrimental effects contributes to optimum conditions for by fishermen on clams gathered makes on the clam fishery. The clam beds in clam survival begins to deteriorate un­ them hunger for stable supplies and in­ polluted zones have been legally closed controllably, it is necessary to find creased abundance of clams. Fisher­ to gathering for direct public consump­ means to remove other limiting factors men fear that clam supplies will be­ tion, leaving fewer available clam beds to maintain or increase clam abun­ come depleted and thus are haunted by (Ritchie, 1977). In some closed beds, dance. For example, deteriorating insecurity. Moreover, their earnings clams are more abundant than in clean water quality could lead to reduced are usually slightly below that in most beds, an invitation to potential numbers of ready-to-set clam larvae, other occupations. On the other hand, poachers. Increased clam supplies in resulting in smaller populations. But clam fishermen are autonomous, inde­ clean beds would obviate that situation. this could be offset by an improved pendent, and somewhat self-sufficient. Coastal towns, counties, and rural setting environment for larvae or an A scarcity of alternative work that fea­ areas where a clam fishery constitutes improved survival environment for spat tures this freedom, and a lack of skills an important factor in their economies, and juvenile clams. in other well-paying occupations, binds view the fishery as a major supplier of Clams support a sizable recreational full-time clam fishermen to the beds. jobs and income. They want the fishery fishery, especially in New England and As a result, when clams become scarce, to support as many people as possible in Long Island, N.Y., where the hard conditions of life become hard for a stable, prosperous condition. clam grows in shallow water and the fishermen. Clam fishermen desperately Whenever clam supplies become soft clam intertidally. The recreational want increased employment security, at scarce, total gainful employment and clam fishery is a tourist attraction in least modest prosperity, and the expec­ earned income drop, resulting in a some localities. Variable and low clam tation of a good life for their children, weakened economy. A management abundance makes the fishery uncertain. all of which can be realized through program that supports a stable, pros­ increased clam abundance. perous clam fishery should be the aim Causes of Low Clam Abundance The clam fishery has always featured of a community government. The an irregular supply situation: Long minor problems and cost involved in The causes of low clam abundance periods of dearth may be followed by establishing it would be far smaller than (Table 1) are not hard to identify; they gluts. Consistently ample supplies the problems and costs that stem from are: low setting densities of spat and would facilitate merchandising and scarce clam supplies. predation on spat and juvenile clams stabilize prices. When any environmental factor that (Fig. 2). Descriptions of the factors that

October J979 Jl A

HARD CLAM FISHERMEN

c

OYSTER DRILLS; 1.3 TO MUD CRAB; FAMILY XANTHIDAE - 2.0 em WIDE 2.0 em HIGH

SPAWN J NG SI lES o 24 E HARVESTABLE SiloS MOON SNAIL ;;; 30 18

u>­ :z w..J CRABS => 12 o w..J .. :::: 15 m>- 0 6 ':lovsr ,z DRILLS 0+--+---1f-.--+--+-+----+---+-+----+---+----i 5 15 25 35 45 55 65 PREDATORS LIVE DEAD CLAMS CLAMS LENGTH (MM)

Figure 2.-0bservations of the hard clam fishery in Great South Bay, Long Island, N.Y., in June 1975. Fisherman (A) takes the clams which, as larvae, were able to set in the bottom, avoided predators (B, C) and grew to and above the minimum legal gathering length, 5 cm (2 inches) or near equivalent, which is much longer than the smallest length at maturity, 3.2 cm, as shown in the length-frequency distribution of live clams in the Bay (0). Numbers ofclam predators and live and dead clams are compared (E); dead clams ranged from 4.5 to 45 mm long. Mortality in clams was not measured in the length group from setting, about 0.2 mm, to 4.5 mm; mortality from predation in the group was probably substantial (MacKenzie, 1977a).

12 Marine Fisheries Review govern clam abundance are presented Table 1.-Some recorded den."'e. of the hard clam and soft clam, Atlantic coast of the Un"ed States. later in the paper. Density Clam lengths Fishermen remove most legal-length Location (number/m') (mm) Data source clams (at least 5 cm, or near equivalent) Hard clam from beds. Some clam populations can Connecticut Long Island Sound 0.9 5 to 10 MacKenzie, endure, however, under steady and 1977a heavy gathering by fishermen. A large New York number ofclam beds along the Atlantic Northport Bay 6.5 al least five MacKenzie, coast have yielded clams to fishermen year classes 1977a for many years, some since the 1800's. Hard clam beds in Great South Bay, Great South Bay 18.4 4.5 to 63 MacKenzie, 1977a N.Y. , and soft clam beds in Edgartown New Jersey Great Pond, Mass., have yielded clams Raritan Bay continuously to fishermen for at least (Horseshoe Cove) 14.0 4.5 to 105 MacKenzie. the past 25 years. Whenever clam 1977a supplies have been reduced by fisher­ Lower Little Egg Harbor 34 510 84 Carriker. 1961 men to low densities, they returned when gathering was temporarily post­ South Carolina Santee River '18 to 24 not available Rhodes et ai., poned and underlength clams grew to 1977 the minimum legal gathering length. Soft clam Some clam populations do not en­ Maine dure under gathering by fishermen. The Sagadahoc Bay 10.810 192.7 10 to 68 Spear. 1953 populations are characterized by: 1) Massachusetts Boston Harbor '320 10 3.200 a few year Turner. 1952 sparse and sporadic setting; 2) declin­ classes ing setting densities of spat; or 3) in­ 1 Approximate creasing predation on juvenile clams. 'Approximate. includes beds with most dense clam populations. Some clam populations grow gradually over an extended period and eventually sity cannot be impaired by steady ceptionally favorable, while in still are comprised mostly of relatively old gathering by fishermen. Recruitment of others, setting rarely occurs (footnote clams, to be discovered and gathered by legal length clams in a bed would be I; pers. obs). Probably, annual fre­ fishermen. nearly the same whether or not gather­ quencies of clam setting are about the Belding (1930, 1931) reported large ing occurs. same in beds in other localities. declines in hard clam and soft clam Clams set during the warm months. Annual Setting Frequency abundance in Massachusetts near the In Rhode Island, hard clam spat set beginning of this century. At that time, of Clam Spat from June through September (Land­ the market demand was increasing, the The annual setting frequency of clam ers, 1954a). In Maine, soft clam spat number of fishermen increased corre­ spat in beds has not received extensive set mostly from June through Sep­ spondingly, and thus fewer clams in the study. The few existing reports and ob­ tember with the major portion ofsetting regular beds were available to each servations show that nearly every year coming during I or 2 weeks out of the fisherman. The fishermen discovered clam setting takes place in some hard season (footnote 1); in Rhode Island, virgin hard clam populations in deeper clam beds in New York (MacKenzie, from May through October (Landers, water, which they gradually depleted. 1977a) and New Jersey (Carriker, 1954a); and in Chesapeake Bay, from It is likely that the virgin populations 1961; MacKenzie, 1977a), and in some March to November (footnote 2). had grown over a long period and were soft clam beds in Maine (Glude, 1955; Three factors promote or favor regu­ comprised mostly of old clams. Deple­ footnote 1), Massachusetts (pers. lar clam setting in beds. The first is that tion occurred because the magnitude of obs.), and Chesapeake Bay 2.3 • In other an ample number of mature female subsequent spat setting was insufficient beds, clam setting takes place only clams is nearly always present in every to overcome predation losses and sup­ when environmental conditions are ex- bed. The number remains ample be­ port continuous gathering by fisher­ cause each female releases millions of men. Belding (1930, 1931) attributed eggs a season (Table 2); thus, a few the reduced availability and depletion females can produce sufficient eggs to to "overfishing." The term "overfish­ 'Letter dated 3 October 1978 from W. R. Welch, seed beds with large quantities of clam ing," however, implies that popula­ State of Maine, Fisheries Research Station, West spat. Usually, large numbers of mature tions of spawning clams are reduced to Boothbay Harbor, Maine. 'Letter dated 3 October 1978 from H. T. Pfitzen­ females occur in beds because: 1) Pred­ such low density that reproduction is meyer, University of Maryland, Chesapeake ators do not consume all spat and impaired. If clams below the minimum Biological Laboratory, Solomons, Md. juvenile clams and cannot take clams 3Letter dated 2 October 1978 from D. S. Haven, legal gathering length and some above Virginia Institute of Marine Science, Gloucester above certain lengths; 2) fishermen re­ it are left in the beds, spat setting den- Point, Va. tain only the hard clams and soft clams

October 1979 13 that have at least the mInImum legal gathering length and leave in the beds below-length clams, many of which are mature (Fig. 3); and 3) after gathering clams, fishermen leave in the beds a quantity of legal length clams which are impractical to gather, yet capable of spawning. (The minimum legal length for clam retention has been in effect throughout nearly all the present cen­ tury.) The second factor is that the spawn­ ing season lasts a few months. During some part, if not all, of most seasons, environmental factors that stimulate mass spawning of clams and support some survival and setting of clam lar­ vae exist. The third factor is that fishermen do not degrade the clam environment while gathering clams; clams can set and grow in beds after, as well as be­ fore, gathering. Figure 3 .-Fishermen are required by regulation to return clams less than 5 em (2 inches) long or near equivalent, termed seed, to the beds. The regulations help to ensure future adequate spawning capacity and yields of the clams from the beds. Biological and Environmental Shown here is the gathering of soft clams by hydraulic jet and rake on Martha's Factors that Govern Clam Vineyard. Mass. Clams are jetted from the bottom by one man. and are then raked up Abundance by his partner. Note the 2-inch measure for clams on the handle of clam rake. Biotic potential, environmental re­ quirements, and environmental resis­ tance are the factors that govern the Table 2.-0ata on biotic potentlal'of the hard clam and soft clam, Atlantic coast of the abundance of clams reaching the legal United States. gathering length. The factors are dis­ Hard Soft cussed later in this section. Productivity clam Data source clam Data source Smallest length at Odum ( 1971 ) defines biotic potential sexual maturity (cm) 3.2 Belding. 1931 1.3 to 1.9 Hanks, 1963 as the maximum intrinsic capacity in a Eggs spawned per population to increase, and environ­ year (millions) 25 Davis and mental resistance as the sum total of Chanley. 1956 '1 to 5 Stickney, 1964 environmental limiting factors that pre­ Potential setting vent the biotic potential from being density of spat unknown unknown reached. Fluctuations in every aspect of Actual setting density of spat 2Up to more than clam productivity, i.e., number of eggs (number!m2) 125 Carriker, 1961 108,000 Turner. 1951 spawned, number of larvae that de­ Annual growth velop, spat density, and spat and increment (mm) 7 to 13 Belding. 1931 '8 to 35 Hanks. 1963 juvenile survival and growth, are gov­ Physiological erned by environmental resistance; the survival/year very high Haven and number of clam spawners has less im­ Andrews, 1956 unknown portance in governing the density of Physiological More than More than longevity 25 years Belding, 1931 10 years Belding. 1930 clam spat. Environmental resistance is the difference between the biotic poten­ , Eggs released during a single spawning. 20nly a few determinations were made. tial and the actual clam quantities which 'Chesapeake Bay only. grow in beds. The amount of environ­ mental resistance to which clams are subjected varies constantly. When en­ vironmental resistance in a bed in­ endures, clam abundance becomes cause the biotic potential of the clams is creases and endures, clam abundance higher. Clam populations increase in always much larger than reached in becomes lower; when it decreases and relation to environmental resistance be- beds.

14 Marine Fisheries Review The ecological principle of limiting vive from the spat stage to the minimum 7 m. In summer, temperatures must rise factors, which is commonly used in ag­ legal gathering length. above 15°C for spawning, but remain riculture, applies to clam populations. The available information on: 1) Bi­ below 33°C for effective larval de­ It can be explained as follows: if all otic potential, 2) environmental re­ velopment (Loosanoff et aI., 1951). environmental factors in beds remain quirements, and 3) environmental resis­ Larvae seem to prefer bottoms of sand optimum for clams, clam populations tance of the hard clam and soft clam is and a mixture of sand and mud which have maximum and sometimes in the summarized below. contain sufficient loose material to soft clam, excess abundance; if any permit them to burrow as spat (Car­ factor is less than optimum, popula­ riker, 1961). For some clam seed to tions will be reduced proportionately; Hard Clam survive, a bed must have few predators, and if any factor has a value of zero, or some protective cover, such as Biotic Potential even if all others remain optimum, the stones and eelgrass, Zostera marina; resulting populations will be small or Table 2 lists information on the biotic clams are most numerous in beds in nonexistent. potential of the hard clam. The clam which predators are scarce or cover Early shellfish biologists did not can spawn at least 2 years before reach­ from predators is available (MacKen­ study the causes and magnitudes of ing the minimum legal gathering length zie, 1977a). mortality in larvae and juvenile (Fig. 2). Each adult female spawns Environmental Resistance shellfish. They confined their investiga­ millions of eggs a year, physiological tions to adults. Nevertheless, mortality survival is high, and spat grow to the The temperature and salinity ex­ in clam larvae spat, and juveniles is minimum legal gathering length in 5-6 tremes that suppress growth of hard large, many times larger than in adults. years. Clam larvae are dispersed in the clam larvae have been determined. Recently, it has been shown that the water and while developing are carried Larvae grew slowly at and below magnitudes of setting density and pre­ about by currents; when fully de­ 17 .5OC and at 32.5°C, and at and below dation on hard clams that are less than veloped, larvae set randomly in beds. 17.5%0; growth was fastest at 20.0° to 1.5 to 2 cm long determine relative The biotic potential is sufficiently large 30.0°C and 20.0 to 27.0%0, in labora­ clam abundance, while predation on to stock beds with at least hundreds of tory cultures (Davis and Cala­ hard clams longer than 5 cm is neglible clams over a wide length range per brese, 1964). (MacKenzie, 1977a). Probably, the square meter within several years. Some sediment types suppress set­ same is about true in the soft clam. Spat The hard clam sets in lower densities ting and growth of the hard clam. Bot­ and juvenile clams suffer large mortal­ and grows more slowly than the soft toms of mud (Carriker, 1961; Keck et ity because a new generation of preda­ clam, but the hard clam can live longer. aI., 1974), coarse gravel, or shell (Car­ tors appears each summer simultane­ Quantities of full-length empty hard riker, 1961) are less desirable for clam ously with each new generation of clam shells, the remnants of dead setting and consequently contain fewer clams, both then being at peak abun­ clams, and live clams are about equal in clams than sand. Growth is relatively dance (Turner, 1953). The juvenile beds, but more full-length soft clam slow in sediments that contain quan­ predators begin feeding immediately on shells than live soft clams occur in beds; tities of silt-clay (Pratt and Campbell, spat and juvenile clams; moreover, the smaller shell quantity shows greater 1956). adult predators select juvenile clams longevity in the hard clam. The contrast The predators of hard clam larvae when mixed sizes are available. As they between shell quantities in beds of the have not been identified. Nevertheless, grow, the hard clams that survive be­ hard clam and the eastern oyster, Cras­ it has been suggested that one or more come increasingly invulnerable to pre­ sostrea virginica, is striking. Usually, bottom-dwelling invertebrate species dation because the predators are not oyster beds contain oyster shell de­ may consume the larvae (Carriker, then sufficiently large to bore, crack, or posits which are several meters deep; 1961). The known predators of bur­ swallow them (MacKenzie, 1977a). the beds contain a great many more rowed hard clams over the entire range The largest soft clams may escape most shells than live oysters. The difference of the clam include: Moon snail, predators by burrowing deeply. in shell quantities shows that the hard Polinices duplicatus (Mead and Much remains to be learned about the clam lives much longer than the oyster, Barnes, 1904; Belding, 1931; Carriker, factors that limit or constrain setting of which commonly lives a few years. 1951, 1961; MacKenzie, 1977a); oys­ clams and survival of spat and juvenile ter drills, Urosalpinx cinerea, Eu­ Environmental Requirements clams. Currently, little is known about: pleura caudata (Carriker, 1951, 1955, 1) The predators of clam larvae; and 2) The hard clam is adapted to salinities 1957, 1961; MacKenzie, 1977a); the effect of associated biota growing from about 15 %0 (Chanley, 1957; An­ whelks, Busycon canaliculatum, Busy­ on and anlOng bottom sediments on set­ drews, 1970; Castagna and Chanley, con carica (Belding, 1931; Carriker, ting density of the clam spat. Only 1973) to 35%0 (Belding, 1931; Davis, 1951; MacKenzie, 1977a); blue crab, speculative estimates have been made 1958), and normally grows in sand, Callinectes sapidus (Carriker, 1951, of typical setting densities of clam spat sand-gravel-stone, and mud, at depths 1956,1959,1961; Castagna and Kraeu­ and the percentages of clams that sur- from about the low tide mark to at least ter, 1977; MacKenzie, 1977a); green

October 1979 15 crab, Carcinus maenas (Dow and Wal­ Environmental Requirements 1948b; Turner, 1950, 1951; Smith and lace, 1952; Carriker, 1956, 1961); rock The soft clam is adapted to salinities Chin, 1953; Glude, 1955; Smith et al., crab, Cancer irroratus (MacKenzie, from about 2.5 %0 (Chanley, 1957; Pfit­ 1955; MacPhail et a1., 1955; Ropes, 1977a); mud crabs (Xanthidae) (Land­ zenmeyer and Drobeck, 1963; Cas­ 1968); spider crab, Libinia sp. (Turner, ers, 1954b; Carriker, 1956, 1959, tagna and Chanley, 1973) to 35 %o(Cas­ 1950, 1951); horseshoe "crab," 1961; MacKenzie, 1977a); starfish ,As­ tagna and Chanley, 1973); its larvae Limulus polyphemus (Belding, 1930; terias forbesi (Belding, 1931; Pratt and Turner, 1948, 1949, 1950, 1951; grow in salinities as high as 32 %0 (the Campbell, 1956); various rays (Das­ highest point tested) (Stickney, 1964). Turner et al., 1948a; Shuster, 1950; yatidae, Myliobatidae, and Rhino­ Smith and Chin, 1953; Smith et aI., The clam grows in intertidal flats and to pteridae) (Castagna and Kraeuter, depths of at least a few meters. Fine 1955; Carriker, 1961); starfish (Beld­ 1977); summer flounder, Paralichthys ing, 1930; Turner, 1948); eel,Anguilla sand, mud, and pebbly sand are suitable dentatus; tautog , Tautoga onitis; and rostrata (Wenner and Musick, 1975); sediments (Turner, 1950). In summer, puffer, Sphaeroides maculatus (Mac­ temperatures must rise to nearly lOoC winter flounder, Pseudopleuronectes Kenzie, 1977a). The total assemblage americanus (Medcof and MacPhail, for spawning, but not greatly exceed of predators never inhabits anyone bay 1952); and ducks (Belding, 1930). The 24°C or else the larvae will not develop or bed. total assemblage of predators never in­ (Stickney, 1964). A bed must have few Various field studies have shown that habits anyone bay, river, or bed. predators for some clam seed to sur­ predation substantially reduces hard vive. Field studies have shown that preda­ clam abundance (Landers, 1954b; Car­ tion substantially reduces soft clam riker, 1956, 1959, 1961; Castagna and abundance (Turner, 1948, 1950; Kraeuter, 1977; MacKenzie, 1977a). Environmental Resistance Turner et al., 1948a, 1948b; Dow and Wherever they are numerous, predators The temperature and low salinity ex­ Wallace, 1952; Smith and Chin, 1953; eliminate quantities of, and sometimes tremes that suppress the biotic potential Glude, 1955; MacPhail et a1., 1955; most, spat and juvenile clams-far of the soft clam have been determined. Smith et a1., 1955; Medcof and more clams than fishermen gather­ Clam larvae grew little at 8.6°C, but Thurber, 1959; Hanks, 1963; Edwards before the clams reach 5 cm in virtually grew at 14.6°C, the next higher tem­ and Huebner, 1977), comparable with all beds. The magnitude of predation perature tested; larvae were killed at its effect on hard clam abundance. was partially illustrated in two test areas 28.4°C within 14 days, but grew at Probably, the green crab is the most in New York where clams became 22.9°C, the next lower temperature destructive soft clam predator north of seven and eight times as dense (43.6 Cape Cod, taking most clams in com­ 2 tested, in laboratory cultures (Stickney, clams as compared with 6.5 clams/m , 1964). Burrowed clams were killed mercial beds when it is abundant and to 75 clams as compared with 9.5 (Glude, 1955; Hanks, 1963). During 2 when temperatures persisted in the high clams/m ) after predator numbers were 20"C range and salinities were 2%0 or the 1940's, soft clam production de­ greatly reduced by a single application lower in Maryland (Shaw and Hamons, clined sharply and became low, and of poison as in unpoisoned areas nearby 1974). through the mid-1950's, it remained (MacKenzie, 1977a). The bay anemone, Diadumene low, in Maine and Massachusetts. The leucolena, has been tentatively iden­ decline was caused by a sharp increase Soft Clam tified as a predator ofsoft clam larvae in in numbers of the green crab, which destroyed virtually all seed clams Biotic Potential Chesapeake Bay (MacKenzie, 1977b). The bay anemone is abundant in pol­ (Glude, 1955). During the late 1950's, Table 2 lists information on the biotic luted estuaries of northern New Jersey, clam production rose again and re­ potential of the soft clam. The clam can which contains soft clam beds, and Del­ mained sizable, at least through the late spawn at least a year before attaining aware Bay; its distribution along the 1960's, because the green crab became the minimum legal gathering length. remainder of the western Atlantic coast scarce (Welch, 1968). The magnitude Each adult female spawns millions of is incompletely known. of predation on the soft clam in Maine eggs per year, physiological survival is The known predators of burrowed and Massachusetts was further illus­ probably high, and spat grow to the soft clams over the entire range of the trated when the green crab and other minimum legal gathering length in 2-6 clam, include: Moon snail (Belding, predators were excluded with fences in years, depending on latitude. Clam lar­ 1930; Turner, 1948,1949,1950,1951; clam beds. Clam densities became vae are dispersed in the water and while Turner et aI., 1948a; Sawyer, 1950; many times higher inside than outside developing are carried about by cur­ Hanks, 1952; Smith and Chin, 1953; the fenced areas during a summer rents; when fully developed, larvae set Medcof and Thurber, 1959; Edwards (Turner, 1950; Smith and Chin, 1953; randomly in beds. The biotic potential and Huebner, 1977); lady crab Glude, 1955; Smith et a1., 1955; is sufficiently large to stock beds with at Ovalipes ocellatus (Belding, 1930; Hanks, 1963). least a few thousand clams over a wide Turner, 1948); blue crab (Belding, Some additional types of environ­ length range per square meter within a 1930; Turner, 1948, 1950; Turner et al. mental resistance are present in hard few years. 1948b); green crab (Turner et al., clam and soft clam beds. The circula-

16 Marine Fisheries Review tion between bays and the ocean, Information Needed From ments inhibit setting of larvae, and if weather and climatic factors, currents, Each Clam Bed so, by about how much? 3) Do biota in surface sediments in­ and pollution also affect clam abun­ In developing methods to increase hibit setting of larvae, and if so, by dance. clam abundance in beds, the setting about how much? regularity of the clam would need to be The questions concerning the bottom determined and the factors that limit or Management Objective condition for survival are as follows: constrain clam setting and survival, The management objective of clam 1) What predator species ofclam spat identified. Only the limiting factors that and juveniles are present, during and beds should be to increase the abun­ can be practicably removed need to be immediately following the setting dance of clams that reach the minimum identified; thus, studies on effects such legal gathering length (5 cm, or near period of the spat? as temperature and salinity extremes equivalent). 2) What is the density of each pred­ need not be made. ator species, by juvenile and adult? As An estimate of setting regularity can an estimate, will the assemblage of Developing a Strategy be made from examination ofthe length predators in the numbers present kill a and Tactics for distribution of clams. Clams can be substantial percentage of clams, and if Increasing Clam Abundance sampled from the beds for measuring so, about what percentages in defined by using a hydrauiic suction sampler periods of time? The Basis for Increasing with a fine-mesh bag and operated by a Clam Abundance The following questions concerning scuba diver (Brett, 1964). All existing management of the beds should be Management for increasing clam clam lengths in proportion to their answered: abundance is based on the fact that numbers that exist in the beds need to be 1) Is it feasible to remove the clams become more abundant after included. For the hard clam, length abundance-limiting environmental their environments improve. The av­ groupings of about 10 mm intervals, factors? enue to increased abundance is through approximating annual growth incre­ 2) What are the costs and benefits of providing an improved environment for ments, are marked off and the number an action such as a reduction in predator each clam so its setting and survival ofclams in each is listed. Ifsome clams numbers? efficiency can be increased. appear in all groupings, it shows that Resources are then concentrated Usually, only one or two major setting has occurred every year; if gaps wherever the chances of increasing abundance-limiting factors exist in exist, setting has occurred irregularly. clam abundance seem best. Ideally, commercial clam beds, besides tem­ (Figure 2D shows a gap between 15 and when a major limiting factor is re­ perature and, in some areas, salinity 25 mm; thus, clams did not set in the moved, with little expense or effort, at extremes. If a major limiting factor of year represented by the gap, but they least a severalfold increase in clam clam setting were removed, and a major did set in the remaining years that were abundance will follow. The methods limiting factor of clam survival in the represented.) For the soft clam, appro­ for removing the limiting factors should spat or juvenile stage were also re­ priately wider length groupings would be conceived, constructed, and applied moved through predator reduction, be used. with surgical precision. clam populations would irrupt. Fur­ The factors that limit setting and sur­ thermore, if the factors were removed vival can be identified and assessed by: every year, thereby improving the clam 1) Making scuba examinations of the Possibilities of Increasing environment permanently, the beds beds; and 2) taking bottom samples for Setting Densities would then consistently carry clam later examination with a hydraulic suc­ 4 Undoubtedly, predation of soft clam populations of maximum abundance. tion sampler with a fine-mesh bag to larvae by the bay anemone, which has Predator reduction, by itself, might collect predators. Soft clam beds an unprotected, delicate body, could be produce almost the same result. Ad­ should be examined and sampled at greatly reduced by controlling the justments in temperature and probably high tide. Answers to the following anemone with a light application of salinity to accommodate the environ­ questions will provide the information granulated quicklime (CaO). The cor­ mental requirements of clams are im­ needed to evaluate bottom conditions rect grain size of quicklime has to be practicable in all beds. for setting of clam larvae and survival used: A screen of 10 meshes/25 mm 2 of clam spat and juveniles. The ques­ should retain only a trace of quicklime; tions concerning the bottom condition and one of 100 meshes/25 mm 2 should for setting are as follows: retain 98 percent of quicklime. The 4The carrying capacity of clam beds is probably somewhere between 100 and 250 clams, that have 1) Are predators of larvae present, anemones should be controlled im­ a full range of sizes, per square meter; an excess and if so, in what densities, and will mediately before the setting of clam number would need to be transplanted to other they kill a substantial percentage of lar­ spat. beds to allow adequate clam growth. Probably, hard clam beds can carry fewer clams than soft vae? Future studies can be made to diag­ clam beds. 2) Do grain sizes of surface sedi- nose and prescribe remedial action to

October J979 17 remove other constraints on setting 1958). Crab invasions could be con­ and 5 cm (2 inches) thick. A fine-mesh densities of the hard clam and soft trolled with methods suggested here. net towed behind the board might then clam. It may be possible to increase During the late 1940's and 1950's, catch the suspended predators (Fig. 4). setting densities by: 1) Removing a experiments using low wire fences to Most small clams which were lifted shell cover from the bottom; 2) hydrau­ exclude predators were conducted in from the sediments by the board would lically jetting the bottom to improve soft clam beds in Maine (Olude, 1955; likely pass through the net. The net grain sizes; and 3) spreading quicklime Hanks, 1963) and Massachusetts would have to be retrieved periodically to reduce the quantities of biota in sed­ (Turner, 1950; Smith and Chin, 1953; for emptying. The board-net might also iments. Smith et aI., 1955). As stated above, remove some predators that have high A major opportunity to increase clam the fences excluded most predators and specific density such as the oyster drills abundance is through controlling pred­ clam densities became many times and moon snail; trials would have to be ators of clam spat and juveniles. higher inside than outside the fenced conducted when the moon snail was on areas; the fences were impracticable to the surface. Before the board-net could Predator Reduction Possibilities maintain, however, and were not a be used, the bottom would have to be The prospects of predator reduction commercial success. During the early cleaned of loose algae, such as sea let­ are excellent because most predators, 1960's, a chemical method was tested tuce, Viva lactuca, and any shells juveniles and adults, remain on the bot­ to control the green crab: Pieces of fish which would plug the net. A wide tom surface, at least during the warmer soaked in poison were supported on dredge could be used for such prior months, often by day and nearly always lines strung across the mouths of cleaning. by night. On the other hand, the clams creeks, coves, and bays. Crabs entering A more elaborate possibility is a col­ are embedded: The hard clam is shal­ the areas fed on the fish and died before lector having two tandem components. lowly burrowed, but has a relatively reaching the clams (Hanks, 1961, The first would lift the predators by high specific density; the soft clam is 1963). However, the poisoned fish directing a water current at the bottom deeply burrowed. It should be possible lines also were not a commercial suc­ and the second would catch them above to remove predators from the bottom cess. the bottom on a screen. The predators without disturbing the clams. Most Mechanical methods need to be de­ could be brought to the surface by suc­ clam beds have surfaces of sand with veloped for removing predators from tion hose for disposal. only small quantities of shells and clam beds. The moon snail which surfaces in stones, which means that shells and larger numbers by night than by day Developing Mechanical Methods stones will not interfere with predator (Medcof and Thurber, 1959) could be for Predator Removal removal. removed by night with a wide surface The frequency of predator removal The methods should remove juvenile dredge or skimmer having a sufficiently would depend on whether or not the and adult predators, and should do so fine screen bag to hold the snails. beds were subjected to recurrent pred­ without damaging or removing clams, In some clam beds, oyster drill abun­ ator invasions. In beds that are not or otherwise disturbing the bottom. The dance appears to be limited by the especially subjected to predator inva­ methods should be simple, inexpen­ availability of surface shells to which sions, removal of most juvenile and sive, and capable of removing pred­ the drills attach their egg cases when adult predators once or twice during or ators from extensive areas within a spawning. The beds, e.g., those in immediately following the setting short time; anything which adds to the Oreat South Bay, N. Y., have scattered, period of the clam spat should lead to a complexity and expense of the methods mostly small, shells on their surfaces. severalfold increase in dam abun­ should be avoided. Probably, shell removal would lead to a dance. Clams are then at peak abun­ Some predators, such as crabs and reduction of oyster drill abundance. dance, and mortalities of clam spat the starfish, have relatively low specific The predator board-net could be used from predation are substantial. Some density and can be easily lifted from the for removing the shells. predators, such as the oyster drills and bottom by a slight water current which Any biological researchers and re­ mud crab, migrate little, and therefore will not disturb clams. A board-net source managers who decide to spe­ reinvasions by the two predators would array which consists ofa pressure board cialize in clam production should be be negligible. In some areas, the blue towed over the bottom followed by a able to develop effective tactics for re­ crab, rock crab, green crab, or horse­ net could remove predators that have moving predators from clam beds shoe "crab" may randomly enter beds low specific density. Using scuba, we within a few months. The clam produc­ and destroy many clams. The green have observed that the turbulence tion specialists should have imagina­ crab migrates onto intertidal soft clam created behind a wooden board, held in tion, mechanical ability, a feel for beds at high tide and off at low tide, a bridle and towed at a 45° angle over working with nature, and probably always remaining on the bottom surface the bottom, lifts crabs and starfish off have the capability to use scuba. They (Dexter, 1947; Edwards, 1958), and the bottom. The board was 4.25 m (14 would need a vessel, testing equip­ feeding mostly by night (Naylor, feet) long, 30.5 cm (12 inches) wide, ment, and testing beds, besides the

18 Marine Fisheries Review PREDATOR BOARD-NET

Figure 4.-Conceptual model of a board-net which could be tried for removing predators from clam beds. Adjustments in board distance from the bottom, distance between board and net, size of floats and weights on net, mesh size, and towing speed, and possible addition of small doors on net, could be made while testing the board-net to remove predators, but not remove the clams. Inset shows side view of board-net being towed and how predators might be lifted by board and enter net. A board-net of this width has the potential to remove predators from a few hectares (several acres) of bottom in an 8-hour day. In 1979, the cost of its construction would be about $600; $300 for the board and supporting structures, and $300 for the net. necessary time. Development of pred­ The ingredients of quicklime are brate numbers would not be affected in ator-removal methods will involve trial natural components of bay and es­ areas other than the clam beds. and error testing, by night as well as by tuarine water and shells, and also flow Incorporating Methods Into Practice day, followed by sampling of predator into the water from farmland treated and clam densities. After the predators with lime. A light bottom application of It will do little good to develop effec­ have been removed from the beds, clam spread quicklime dissolves in 2-3 days. tive methods for removing predators densities would be compared periodi­ The mechanical methods for removing from clam beds unless they are put into cally with those in control beds. A hy­ predators would be used for only brief practice. The development process will draulic suction sampler with a fine­ periods, and thus would not interfere not be complete until the new methods mesh bag and operated by a scuba diver with navigation. Predator numbers result in increased abundances, yields, can be used to measure the densities. would become greatly reduced, thereby employment, incomes, and supplies. Eventually, documentation of costs and shifting typical numerical ratios of Any effective method to be success­ benefits of using the methods would be predator to prey in wild beds; the new fully put into practice must qualify as needed. As a precaution against dam­ ratio would be similar to one that occa­ follows: 1) Meet an urgent need; 2) be age to commercial beds, methods sionally occurs in beds when predators technically and operationally feasible; should be tested, perfected, and proven become scarce from natural causes and 3) offer no damaging risks to the beds; effective on small areas. where afterwards clam populations ir­ 4) will not impinge on other interests; rupt. Predator reduction in clam beds and 5) will yield a return that exceeds Side Effects of would be followed by large increases in the investment which, primarily, Predator Reduction numbers of polychaetes, other mol­ should be low. Probably, with clams, a Predator reduction on clam beds lusks, and other invertebrates, along method would have to produce at least a would not impinge on other interests. with the clams. Predator and inverte- twofold increase in clam abundance at

October 1979 19 an annual cost within the range of about tunity to examine all features and per­ Increasing Abundance of $75-$125 per hectare ($30-$50 per formances of the method; all angles Ocean Clams acre) to be attractive enough to imple­ should be freely discussed, criticisms Ocean clams inhabit an environment ment. An effective method, which has aired, or alternative methods sug­ which is probably far from optimum for been conceived, constructed, and gested. Then, after such deliberations, maximum clam setting and survival applied with precision, would undoubt­ the specialists should sample public efficiency. Thus, it may be possible to edly yield much larger increases for opinion about whether or not to imple­ increase abundance of clams by im­ roughly the same cost. ment. Probably, fishermen and local proving their environments. The com­ It should be recognized that imple­ people will respond favorably to a new mercial ocean clams off the Atlantic mentation of a method on commercial method which clearly promises in­ coast of the United States are the surf clam beds will be one of the most creased production and monetary clam, Spisula solidissima, and ocean difficult hurdles in the translation of an gains, and will urge the specialists to go quahog, Arctica islandica. The clam idea into more clams. Implementation ahead. If not, the specialists should predators include gastropods, crabs, is difficult because it means impinge­ consider whatever revisions were and starfish. Application of methods to ment directly upon the livelihoods of suggested. remove any major factors that limit clam fishermen and other people in During the implementation phase, clam setting and reduce predator num­ local communities. Accordingly, when personnel who will use the method will bers to improve clam environments the time gets close to implementation, have to be trained. may not be practicable in the ocean. an uncertainty will likely develop Political Support for Program Nevertheless, the idea should be tested. within fishermen and local people con­ cerning whether the use of a method A management program, of what­ Conclusion will be beneficial; they will not want to ever size, for maintaining high clam risk the little security and the employ­ abundance in beds would be under the The objective of clam management, ment and incomes that the fishermen sponsorship of the governing body of a to increase clam abundance in beds and already have. The fact that no such community. Such a program would consequent yields and supplies, can be method has ever been used on any clam have to be established by the respective achieved when practicable, low-cost bed will amplify the uncertainty. civic authority which is fiscally em­ methods are developed and used for Naturally, clam production special­ powered to undertake such a project. It removing predators from clam beds. ists would be at first eager to implement would entail the will, determination, The examples from test areas in wild their method, especially if they have and commitment of those involved, clam beds of substantial increases in been deeply committed to its develop­ who are entrusted to make such deci­ abundance of the hard clam and soft ment. However, they may come to fear sions. The production specialist would clam following poisoning and fenc­ that negative reaction will arise among have to meet with the civic body to ing-out, respectively, of predators the fishermen and local people, which explain the designed process for in­ show that clam abundance will also in­ could lead to criticism of their work, creasing clam yields, and submit evi­ crease substantially after predators are damage to their reputations, and per­ dence of its potential effectiveness. removed from other wild clam beds. manent loss of their credibilities. If it Computed evidence of tangible in­ Studies should be undertaken to deter­ happens, specialists should not leave creases in yields, concomitantly in­ mine whether or not setting densities of the development process at this point. creased employment and incomes, will clam spat can be increased with practi­ Specialists make a mistake by leaving a be highly influential in winning support cable methods. A permanent increase designed and developed system before for, and later maintaining, the program. in clam abundance and yields will vi­ it has been properly implemented, be­ talize the clam fishery and thus meet Clam Production Specialists cause subsequent implementation by basic human needs by: 1) Increasing the Guide Program others than the developers is rarely suc­ economic security, stability, and pros­ cessful. After the establishment of a man­ perity ofclam fishermen; 2) stimulating The decision about whether to im­ agement program to increase clam the economy oflocal communities; and plement a method lies with the fisher­ abundance in a locality, it is advisable 3) increasing clam supplies at more sta­ men and local people because they have for production specialists to consult, at ble prices in the market, without sub­ community responsibility over the least 1 or 2 days a year, with operating stantial cost in money or time. beds. Accordingly, the specialists must personnel on the beds. Such consulta­ Heretofore, clam management has thoroughly demonstrate the method on tions would include an examination of been designed to conserve clam popula­ the testing beds and supply convincing the beds and pertinent discussions to tions and ensure continuous clam evidence of its effectiveness by show­ keep the program on track and improve yields. As stated above, various state ing them samples of higher abundance efficiency. A program may gradually and local regulations restrict the clam of juvenile clams. The fishermen and fail to function if not stimulated by such sizes and quantities to be gathered and local people should have ample oppor- consulting. the types of gathering gear. The con-

20 Marine Fisheries Review servation management concept some­ John B. Pearce, and John Ziskowski. temperature and salinity on the feeding habits of the boring snails, Polinices heros and what parallels management of many of Michele Cox drew the figures. Polinices duplicata. In Fifth report on investi­ the wildlife resources, such as freshwa­ Literature Cited gations of the shellfisheries of Massachusetts, ter fish, waterfowl, and upland game of p. 33-37. Dep. Conserv., Div. Mar. Fish., Andrews, J. D. 1970. The mollusc fisheries of Commonw. Mass., Boston. our nation. It differs in that attempts Chesapeake Bay (USA). Proc. Symp. Mol­ ____ . 1961. Chemical control of the green have been made to increase wildlife lusca, Mar. BioI. Assoc., India, Part Ill, p. crab, Carcinus maenas (L.). Proc. Natl. 847-856. Shellfish. Assoc. 52:75-86. abundance within the three categories Belding, D. L. 1930. The soft-shelled clam . 1963. The soft-shell clam. U.S. through environmental improvement. fishery of Massachusetts. Dep. Conserv., Div. Fish Wildl. Serv., Circ. 162, 16 p. The management goals have been suc­ Fish. Game, Commonw. Mass., Mar. Fish. Haven, D. S., and J. D. Andrews. 1956. Survival Ser. I, 65 p. and growth of Venus mercenaria, Venus cam­ cessfully reached through the legal re­ ____ . 1931. The quahaug fishery of Mas­ pechiensis, and their hybrids in suspended strictions on clam gathering, but under sachusetts. Dep. Conserv., Div. Fish. Game, trays and on natural bottoms. Proc. Natl. the conservation concept, clams can Commonw. Mass., Mar. Fish. Ser. 2,41 p. Shellfish. Assoc. 47:43-49. Brett, C. E. 1964. A portable hydraulic diver­ Keck, R., D. Maurer, and R. Malouf. 1974. and do become scarce for years. No operated dredge-sieve for sampling subtidal Factors influencing the setting behavior of lar­ attitudes and solutions within the con­ macrofauna. J. Mar. Res. 22:205-209. val hard clams, Mercenaria mercenaria. Proc. Carriker, M. R. 1951. Observations on the pene­ Natl. Shellfish. Assoc. 64:59-67. cept exist to increase clam abundance. tration of tightly closing bivalves by Busycon Landers, W. S. 1954a. Seasonal abundance of Imposing increased restrictions on and other predators. Ecology 32:73-83. clam larvae in Rhode Island waters, 1950-52. gathering clams will never create in­ ____ . 1955. Critical review of biology and U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. control of oyster drills Urosalpinx and Eu­ 117,29 p. creased clam abundance. This has been pleura. U.S. Fish Wild!. Serv., Spec. Sci. ____ . 1954b. Notes on the predation ofthe evidenced when freshwater fish, water­ Rep. Fish. 148, 150 p. hard clam, Venus mercenaria, by the mud fowl, and upland game did not increase ____ . 1956. Biology and propagation of crab, Neopanope texana. Ecology 35:422. young hard clams, Mercenaria mercenaria. J. Loosanoff, V. L., W. S. Miller, and P. B. Smith. with the imposition of increased restric­ Elisha Mitchell Sci. Soc. 72:57-60. 1951. Growth and setting of larvae of Venus tions on fishing and hunting. ____ .1957. Preliminary study ofbehavior mercenaria in relation to temperature. J. Mar. Conventional management for the of newly hatched oyster drills, Urosalpinx cin­ Res. 10:59-81. era (Say). 1. Elisha Mitchell Sci. Soc. MacKenzie, C. L., Jr. 1977a. Predation on hard conservation of clam populations 73:328-351 . clam (Mercenaria mercenaria) populations. should be replaced with a management . 1959. The role of physical and Trans. Am. Fish. Soc. 106:530-537. biological factors in the culture ofCrassostrea -. 1977b. Sea anemone predation on concept which embraces conservation and Mercenaria in a salt-water pond. Ecol. larval oysters in Chesapeake Bay (Maryland). and increased clam abundance through Monogr. 29:219-266. Proc. Natl. Shellfish. Assoc. 67:113-117. environmental improvement. Perma­ . 1961. Interrelation of functional MacPhail, J. S., E. 1. Lord, and L. M. Dickie. morphology, behavior, and autecology in early 1955. The green crab-a new clam enemy. nent increases in clam abundance can stages of the bivalve Mercenaria mercenaria. Fish. Res. Board Can., Prog. Rep. Atl. Coast be brought about through a combina­ J. Elisha Mitchell Sci. Soc. 77:168-241. Stn. 63:3-12. tion of: 1) a continuation of the regula­ Castagna, M., and P. Chanley. 1973. Salinity Mead, A. D., and E. W. Barnes. 1904. Observa­ tolerance of some marine bivalves from es­ tions on the soft-shell clam (5th paper). 34th tions prohibiting the gathering of small tuarine environments in Virginia waters on the Annu. Rep., Comm. Inland Fish., Rhode Is­ clams; 2) problem-oriented research western Mid-atlantic coast. Malacologia land, p. 29-48. 12:47-96. Medcof, J. C., and J. S. MacPhail. 1952. The and development, and implementation , and J. N. Kraeuter. 1977. Mer­ winter flounder-a clam enemy. Fish. Res. ofmethods and programs for improving cenaria culture using stone aggregate for pred­ Board Can., Prog. Rep. Atl. COdSt Stn. 52:3-7. clam environments by clam production ator protection. Proc. Natl. Shellfish. Assoc. , and L. W. Thurber. 1959. Trial 67: 1-6. control ofthe greater clam drill (Lunaria heros) specialists; 3) establishment of the Chanley, P. E. 1957. Survival of some juvenile by manual collection. J. Fish. Res. Board Can. programs by decision-making civic bivalves in water of low salinity. Proc. Natl. 15:1355-1369. bodies, authorized and willing to do it; Shellfish. Assoc. 48:52-65. Odum, E. P. 1971. Fundamentals of ecology. 3d Davis, H. C. 1958. Survival and growth of clam ed. W. B. Saunders Co., Phila., 574 p. and 4) guidance by the production and oyster larvae at different salinities. BioI. Pfitzenmeyer, H. T., and K. G. Drobeck. 1963. specialists in the years after programs Bull. (Woods Hole) 114:296-307. Benthic survey for populations of soft-shelled ____ , and A. Calabrese. 1964. Combined clams, Mya arenaria, in the lower Potomac have been established. effects of temperature and salinity on de­ River, Maryland. Chesapeake Sci. 4:67-74. Removing the constraints on clam velopment of eggs and growth of larvae of M. Pratt, D. M., and D. A. Campbell. 1956. En­ abundance in beds, which have hereto­ mercenaria and C. virginica. U.S. Fish Wildl. vironmental factors affecting growth in Venus Serv., Fish. Bull. 63:643-655. mercenaria. Limnol. Oceanogr. 1:2-17. fore consistently deprived clam fisher­ ____ , and P. E. Chanley. 1956. Spawning Rhodes, R. J., W. J. Keith, P. J. Eldridge, and V. men, local communities, and the mar­ and egg production of oysters and clams. Bioi. G. Burrell, Jr. 1977. An empirical evaluation ket, will benefit everyone. Bull. (Woods Hole) 110: 117-128. of the Leslie-DeLury method applied to es­ Dow, R. L., and D. E. Wallace. 1952. Observa­ timating hard clam, Mercenaria mercenaria, tions on green crabs (c. maenas) in Maine. abundance in the Santee River estuary, South Acknowledgments Maine Dep. Sea Shore Fish., Fish. Circ. Carolina. Proc. Natl. Shellfish. Assoc. 67:44­ 8: 11-15. 52. I am grateful to a number of fisher­ Edwards, D. C., andJ. D. Huebner. 1977. Feed­ Ritchie, T. P. 1977. A comprehensive review of men, especially Butler Flower, Luther ing and growth rates of Polinices duplicatus the commercial clam industries in the United Jeffries, Cyrus Norton, and Emil preying on Mya arenaria at Barnstable Harbor, States. U.S. Dep. Commer., NOAA, Natl. Massachusetts. Ecology 58: 1218-1236. Mar. Fish. Serv., Wash., D.C., 106 p. Usinger, for providing essential infor­ Glude, J. B. 1955. The effects oftemperature and Ropes, J. W. 1968. The feeding habits of the mation. The manuscript was critically predators on the abundance of the soft-shell green crab, Carcinus maenas (L.). U.S. Fish reviewed by John Mahoney, J. Knee­ clam, Mya arenaria, in New England. Trans. Wild!. Serv., Fish. Bull. 67:183-203. Am. Fish. Soc. 84: 13-26. Sawyer, D. B. 1950. II. Feeding activities of the land McNulty, Anthony L. Pacheco, Hanks, J. E. 1952. The effect ofchanges in water boring snail, Polynices duplicara. In Third re-

October 1979 21 port on investigations of methods of improving of methods of improving the shellfish resources cember 1977. U.S. Oep. Commer., NOAA, the shellfish resources of Massachusetts, p. of Massachusetts. I. Investigations on the Natl. Mar. Fish. Serv., Curr. Fish. Stat. 7460, 16-17. Oep. Conserv., Oiv. Mar. Fish., soft-shell clam, Mya arenaria. Oep. Conserv., 6 p. Commonw. Mass., Boston. Oiv. Mar. Fish., Commonw. Mass., Boston, 1978c. North Carolina landings, Shaw, W. N., and F. Hamons. 1974. The present p. 5-15. annual summary 1977. U.S. Oep. Commer., status of the soft-shell clam in Maryland. Proc. ____ . 1951. Fourth report on investiga­ NOAA, Natl. Mar. Fish. Serv., Curr. Fish. Natl. Shellfish. Assoc. 64:38-44. tions of the shellfisheries of Massachusetts. Stat. 7514, 8 p. Shuster, C. N. ,Jr. 1950. III. Observations on the Oep. Conserv., Oiv. Mar. Fish., Commonw. . 1978d. South Carolina landings, natural history of the American horseshoe Mass., Boston, 21 p. annual summary 1977. U.S. Oep. Commer.. crab, Limulus polyphemus. In Third report on ____ . 1952. Fifth report on investigations NOAA, Natl. Mar. Fish. Serv., Curr. Fish. investigations of methods of improving the of the shellfisheries of Massachusetts. Oep. Stat. 7515, 6 p. shellfish resources ofMassachusetts, p. 18-23. Conserv., Oiv. Mar. Fish., Commonw. 1978e. Maryland landings, De­ Oep. Conserv., Oiv. Mar. Fish., Commonw. Mass., Boston, p. 3-32. cember 1977. U.S. Oep. Commer., NOAA, Natl. Mar. Fish. Serv., Curro Fish. Stat. 7459, Mass., Boston. 1953. A review of the biology of 4 p. Smith, O. R., J. P. Baptist, and E. Chin. 1955. some commercial molluscs of the east coast of I978f. Massachusetts landings, an­ Experimental farming of the soft-shell clam, North America. In Sixth report on investiga­ Mya arenaria, in Massachusetts, 1949-1953. tions of the shellfisheries of Massachusetts, p. nual summary 1977. U.S. Oep. Commer., NOAA, Natl. Mar. Fish. Serv., Curro Fish. Commer. Fish. Rev. 17(6):1-16. 39-74. Oep. Nat. Resour., Oiv. Mar. Fish., Stat. 7508, 8 p. ____ , and E. Chin. 1953. The effects of Commonw. Mass., Boston. predation on soft clams, Mya arenaria. Conv. 1978g. New York landings, annual , J. C. Ayers, and C. L. Wheeler. Add. Natl. Shellfish. Assoc. 1951:37-44. summary 1977. U.S. Oep. Commer. , NOAA, 1948a. Appendix [I. The horseshoe crab and Spear, H. S. 1953. A soft clam population census Natl. Mar. Fish. Serv., Curro Fish Stat. 7510, 6 boring snail as factors limiting the abundance p. in Sagadahoc Bay, Maine 1949-'50-'51. of the soft-shell clam. In Report on investiga­ Conv. Add. Natl. Shellfish. Assoc. 1951:89­ 1978h. Rhode Island landings, an­ tions of the propagation of the soft-shell clam, nual summary 1977. U.S. Oep. Commer., 103. Mya arenaria, p. 43-45. Oep. Conserv., Oiv. NOAA, Natl. Mar. Fish. Serv., Curro Fish. Stickney, A. P. 1964. Salinity, temperature, and Mar. Fish., Commonw. Mass., Boston. Stat. 7509, 6 p. food requirements of soft-shell clam larvae in , , and _ ____ . 1978i. New Jersey landings, annual laboratory culture. Ecology 45:283-291. 1948b. Appendix III. Further observations on summary 1977. U.S. Oep. Commer., NOAA, predators of the soft-shell clam. In Report on Natl. Mar. Fish. Serv., Curro Fish. Stat. 7511, Turner, H. J., Jr. 1948. Report on investigations investigations of the propagation of the soft­ of the propagation of the soft-shell clam, Mya 7 p. shell clam Mya arenaria, p. 47-49. Oep. Con­ Welch, W. R. 1968. Changes in abundance of the arenaria. Oep. Conserv., Oiv. Mar. Fish., serv., Diy. Mar. Fish., Commonw. Mass., Commonw. Mass., Boston, p. 3-9. green crab, Carcinus maenas (L.), in relation Boston. to recent temperature changes. U. S. Fish 1949. Report on investigations of U.S. Department of Commerce. 1978a. Maine Wildl. Serv., Fish. Bull. 67:337-345. methods of improving the shellfish resources of landings, annual summary 1977. U.S. Oep. Wenner, C. A., and J. A. Musick. 1975. Food Massachusetts. Oep. Conserv., Oiv. Mar. Commer. , NOAA, Natl. Mar. Fish. Serv., habits and seasonal abundance ofthe American Fish., Commonw. Mass., Boston, 22 p. Curr. Fish. Stat. 7507, 6 p. eel, Anguilla roslrata, from the lower ____ . 1950. Third report on investigations 1978b. Virginia landings, Oe- Chesapeake Bay. Chesapeake Sci. 16:62-66.

22 Marine Fisheries Review