Published Research
Beal, B.F., Bayer, R., Kraus, M.G., Chapman, S.R.
1999. A unique shell marker in juvenile, hatchery-reared individuals of the softshell clam, Mya arenaria L., Fishery Bulletin 97(2), 380-386.
Soft-shell clam juveniles reared under hatchery conditions at the Beals Island Regional Shellfish Hatchery and the Downeast Institute for Applied Marine Research & Education for a unique disturbance line on the shell at the size when placed into the field under any sedimentary conditions. This marker is called the "hatchery mark," and it enables investigators to place juvenile M. arenaria in the field without marking individuals uniquely. After some time in the field after which shell growth is apparent, one can easily measure the size of the clam at the time when it was transplanted and then measure the final shell length. The difference between final and initial shell length (SL) is the absolute growth of the clam during the period it was in the field. The photos below show that the "hatchery mark" forms on clams as small as 6 mm to as large as 12-15 mm SL.
Disturbance line (hatchery mark). Clam was planted on 4 May 1989 at Duck Brook Flat (Cutler, Maine) and grew to size shown by 6 August 1989.
Another example of the "hatchery mark." Most individuals were 12-15 mm when planted on 1 November 1988.
Beal, B.F.
1983. Predation of juveniles of the hard clam Mercenaria mercenaria (Linne) by the snapping shrimp Alpheus heterochaelis Say and Alpheus normanni Kingsley, Journal of Shellfish Research 3(1), 1-9.
Abstract
Two species of snapping shrimp, A. heterochaelis and A. normanni , collected near Beaufort, North Carolina, during June 1982, and then held in the laboratory, used their major chelae to crush and consume juveniles of the hard clam Mercenaria mercenaria. Snapping shrimp (19.1 to 39.4 mm in total body length [TL]) ate clams in the largest size-class (15.1 to 20.0 mm in shell length), but preferred smaller clams when offered equal numbers in this large size-class and in each of three smaller size-classes. Female snapping shrimp, regardless of species, exhibited a statistically higher predation rate than males when the results of five separate experiments were combined. The major chelae of the females of specimens of A. heterochaelis (>32.0 mm TL) were smaller than those of equal size males. Alpheus heterochaelis (19.1 to 27.2 mm TL) had a larger major chela for a given body length than did specimens of A. normanni; however, predation rates of the two species were not significantly different. The number of clams crushed was related to both the size of the major chelae and total body length for A. normanni, but not for A. heterochaelis. Alpheus spp. inflict two types of shell damage which are identical to those caused by blue crabs. These results imply that previous studies may have overestimated the importance of crab predation and underestimated or ignored the importance of predation by snapping shrimp.
Kraus, M.G.; Beal, B.F.; McMartin, L.
1992. A comparison of growth rates in Arctica islandica (Linnaeus, 1767) between field and laboratory populations. Journal of Shellfish Research 11(2), 289-294.
Abstract
Fifty juveniles of the ocean quahog, Arctica islandica, (estimated between 2 and 5 years old) were collected from a commercial bed in eastern Maine in Aug of 1987. These quahogs were kept in the laboratory at ambient seawater temperatures in sediment until Dec, 1987, when they were individually marked, measured and placed in a sand-filled tray at the Darling Marine Center in Walpole, Maine. During the next 3 years, they received only ambient seawater from the Damariscotta River at a constant flow of 6 l/min. Individuals were remeasured after one year (Dec, 1988) and again in Mar, Jun, Sep and Dec of 1989 and finally in Dec, 1990. After two years in the laboratory, individuals had grown from a mean shell length (SL) of 9.6 mm plus or minus 0.29 SE to a commercial size with a mean SL of 46.6 mm plus or minus 0.50 SE. In three years, the mean SL was 53.9 mm plus or minus 0.58 SE. The results indicate that this species has the potential of being cultured in shallow-water sites protected from predators.
Vadas, R.L., Beal, B.F.
1987. Green algal ropes, a novel estuarine phenomenon in the Gulf of Maine. Estuaries 10(2), 171-176.
Abstract
During late summer and early autumn of both 1984 and 1985 the authors observed and photographed the development of a green algal bloom on intertidal mudflats in eastern Maine, USA. The bloom culminated in the formation of thick (8-10 cm) mats and long (> 50 m) serpentine rope-like structures. The algal mat was polytypic but composed primarily of Enteromorpha intestinalis L. The authors describe the probable sequence of events which led to the formation of algal ropes. The processes involved appear to parallel the development of ball-like masses in other algae. Algal ropes developed after mat formation, as prevailing winds and tidal currents rolled individual and entwined strands across the mudflat. The great mass of algae eventually became embedded into the sediment surface producing anoxic conditions in the substrate up to several cm deep. The ecological significance and possible negative effects of this altered environment on a commercially important bivalve species are discussed.
A clam flat in upper Whiting Bay (eastern Maine) in May 1985. Wooden stakes mark 1/4-m2 plots.
The same intertidal flat in July 1985.
The same intertidal flat near the wooden stakes on 6 September 1985.
Wild juveniles of the soft-shell clam, Mya arenaria, entrapped in the green algae in Sept. 1985.
Green algal ropes form in late August and early September 1985.
Beal, B.F., Parker, M.R., Vencile, K.W.
2001. Seasonal effects of intraspecific density and predator exclusion along a shore-level gradient on survival and growth of juveniles of the soft-shell clam, Mya arenaria L., in Maine, USA. Journal of Experimental Marine Biology and Ecology 264, 133-169.
Abstract
The relative roles that predation and competition play in regulating populations of infaunal marine bivalves in soft-bottom systems are strikingly different. Exploitative competition for food typically occurs at elevated densities, but crowding rarely results in mortality and competitive exclusion. Predation by decapods, gastropods, and, sometimes asteroids, is more important in controlling patterns of distribution and abundance. Most field tests leading to this synthesis have been conducted between 35°N and 35°S and/or with bivalves in the families Veneridae and Tellinidae. To test the robustness of these ecological processes at another geographic setting (45°N) using a species from another family within the suspension-feeding guild (Myidae), we performed a short-term field manipulation at an intertidal mud flat in eastern Maine, USA. We followed survival and growth of 10,080 juveniles (12.4-mm shell length (SL)) of the soft-shell clam, Mya arenaria L., in field enclosures with and without predator-deterrent netting at three densities (330, 660 and 1320 m-2) along a tidal gradient over four sampling intervals from April to December 1996. We used a generalized completely randomized block design to assess variation in these dependent variables within a given tidal height (high, mid, and low) on a particular date. Mortality varied seasonally, peaking (13.6%) between August and September when seawater temperatures were warmest. No significant mortality occurred after September, when mean (±95% CI) percent survival pooled over all treatments was 72.9±8.5%. Netting (6.4-mm aperture) effectively excluded predators along the tidal gradient as overall mean clam survival, independent of tidal position, was 88.7±4.1% in protected units (plastic plant pots with AREA=181 cm2), but decreased from upper and mid tide levels (82.9±6.1%) to lower on the shore (66.3±9.7%) in unprotected units. Density-dependent mortality resulted in reduced survival (by 4.6%) in clams stocked at the two highest levels however, numbers of dead clams with undamaged valves provided little evidence that this effect was due to starvation. Incremental growth also varied seasonally with greatest amounts of shell added during June-August at all tidal levels. Shell growth stopped or slowed significantly after September at all tidal positions. Mean SL increased with decreasing tidal height (December sizes: HIGH=20.6±2.9 mm, MID=24.1±1.0 mm; LOW=28.2±1.2 mm); however, submergence time alone failed to explain completely these differences. Density-dependent growth was detected once (August-September). Animals at the two highest densities experienced a growth depression of ca. 7%. We conclude predation, rather than competition, is more important in regulating populations of soft-shell clams in this intertidal location.
Flake Point Bar (Jonesport, Maine) where the field experiment (April - December) 1996 was performed.
Beal, B.F., Lithgow, C.D., Shaw, D.P., Renshaw, S., Ouellette, D.
1995. Overwintering hatchery-reared individuals of the soft-shell clam, Mya arenaria L.: a field test of site, clam size, and intraspecific density. Aquaculture 130, 145-158.
Abstract
Soft-shell clams (Mya arenaria L.) are a commercially important intertidal bivalve in Maine, USA where they are managed as a common property resource. Ten million 8-12 mm clam juveniles are reared annually at the Beals Island Regional Shellfish Hatchery and are transplanted onto publicly-owned mudflats during the fall or early winter. The success of this strategy is unpredictable because of sporadic occurrence of winter ice formation and subsequent scouring of the intertidal zone. These events, in addition to other severe winter storms, can result in complete mortality of the transplanted seed. Transplanting hatchery-reared seed in the spring, therefore, is preferable, but until now there has been no economically effective technique to hold millions of soft-shell clam seed over the winter. A field experiment designed to test the interactive effect of clam size and density on survival was conducted during the winter of 1991-1992 at a sheltered and exposed site near Beals, Maine, USA. Three sizes of hatchery-reared clam seed (Small, shell length [SL]; Medium, 8.2 mm SL; Large, 11.5 mm SL) were used. Clam density was approximate and depended on clam size (Small, 18 750 ind, 37 500 ind, and 56 250 ind; Medium, 11 000 ind and 22 000 ind; Large, 4500 ind and 9000 ind). Clams of each size/density combination were added separately to nylon window screen, zippered bags (aperture = 1.8 mm). Bags containing clams were housed in wooden-framed subunits (0.45 m x 0.45 m x 0.08 m) covered with a 12 mm extruded mesh netting. Subunits were arranged vertically in groups of 4-6 and were submerged 1m above the bottom in shallow water (3-8 m) from November 1991 to April 1992. Mean survival of medium and large size clams at both sites was 97.7%. Significant density effects were detected for both size groups at the sheltered site, although the difference between treatment levels was less than 2%. Mean survival of small clams pooled across sites was 67.8%. At the sheltered site, clams in the uppermost level of the overwintering units had consistently lower survival rates than those nearer the bottom. Density effects for small clams were detected only at the sheltered site where animals held at the highest density had significantly higher survival rates than animals at either of the two lower densities (75.3% vs. 60.3%). Clam loss over the winter may be reduced by suspending seed in seawater instead of transplanting it to intertidal flats.
Cultured soft-shell clams being added to an 18-inch x 18-inch bag constructed of window screening.
Filling overwintering bag with cultured soft-shell clams (Downeast Institute; Winter 2002)
Overwintering cage constructed of vinyl lobster trap wire with two bags of cultured clams. Each bag contains approximately 25,000 clams (ca. 10 mm SL).
Beal, B.F.
2002. Adding value to live, commercial size soft-shell clams (Mya arenaria L.) in Maine, USA: results from repeated, small-scale, field impoundment trials. Aquaculture 210, 119-135.
Abstract
The soft-shell clam (Mya arenaria L.) fishery in the state of Maine, USA, is worth $5-10 million annually and is primarily based on the sale of live individuals. More than 80% of the catch is sold for the "steamer clam" market that is highly seasonal due to supply and demand. Prices paid to harvesters for live clams throughout the year increases by as much as 70% during a 4-month period between early spring and late summer. If clams harvested in the spring could be held until late summer, a value-added product could be developed in this fishery. From April to August 1996, at an intertidal and subtidal location in eastern Maine, I tested whether it was biologically feasible to impound commercially harvested clams (shell LENGTH=44-75 mm) at densities between 720 and 850/m2 using cages and nets (1.12 m2) to protect animals from predators. Survival was 91.7% (n=12) and 91.6% (n=6) at the intertidal and subtidal site, respectively. There was no discernible shell growth during this period and there was no difference between initial and final clam weights. The methodology was transferred to commercial harvesters in two Maine communities: Wiscasset (1997 and 1998) and Perry (2000). Impounded clams (x=21.8 kg/cage; n=18) lost, on average, 5 kg/cage in 1997 and 1998, whereas no significant net loss in wet weight occurred in cages deployed in 2000 (x=23.2 kg/cage; n=3). Differing harvesting and handling methods of individual clammers, prior to impounding clams, likely explains the variation in weight lost during the impounding periods. The difference in price per live kilogram between the beginning of the impounding period and the August sale date resulted in an average gain of $13.60/cage for clammers in 1997 and 1998 and $57.73/cage in 2000. Simple culture techniques can be used to increase the value of the live harvest of soft-shell clams along the coast of Maine. Clam impoundments may be a way for communities that co-manage the public clam resource with the state's marine resource agency to generate funds to pay for traditional management schemes, as well as enhancement programs that employ hatchery-reared juveniles. In addition, an indirect benefit of clam impoundments might be to create spawner sanctuaries since animals are impounded during the time when gamete release occurs.
A "clam pound." Constructed of vinyl-coated lobster trap wire, this pound contains one-bushel of commercial size soft-shell clams (> 50 mm SL). Survival from April to August 1996 was ca. 95%.
Beal, B.F., Kraus, M.G.
2002. Interactive effects of initial size, stocking density, and type of predator deterrent netting on survival and growth of cultured juveniles of the soft-shell clam, Mya arenaria L., in eastern Maine. Aquaculture 208, 81-111.
Abstract
Recent declines in commercial harvests of soft-shell clams, Mya arenaria L., in Maine, USA, have prompted state and local officials to consider enhancing wild stocks with hatchery-reared seed. We conducted two manipulative field experiments in the soft-bottom intertidal zone during 1990 and 1991 in eastern Maine to assess effects of predation, intraspecific competition, and initial planting size on the survival and growth of cultured individuals of Mya. Experiment I (23 June 1990 to 13 June 1991) tested interactive effects of two planting sizes (small=8.5 mm shell length (SL); LARGE=11.8 mm SL) and protective netting on fate and growth of clams. Animals of each size were added to separate experimental units within each of 60 1-m2 areas delimited by a wooden box. To deter predators, 50 boxes were covered with a specific type of plastic netting that differed in aperture size (4.2, 6.4 and 12.8 mm) and degree of rigidity (flexible vs. extruded) while 10 boxes served as controls (without netting). Small clams grew at a faster rate than large clams, but both added approximately 18 mm of new shell by the end of the study. Growth was unaffected by netting size and rigidity, but 13% more clams were recovered alive after a year in protected vs. unprotected treatments (84% vs. 71%). Survival was independent of netting type. The presence of netting resulted in nearly a 3x—enhancement of wild spat ( < 15 mm SL) compared to unprotected controls (568.8±24.4 vs. 199.6±22.8 m2). This result suggests that the decline of wild stocks in eastern Maine may not be related to recruitment failure, but to post-settlement events, such as predation, which remove clams from the intertidal. In Experiment II (15 April to 6 October 1991), clam (14.6±0.2 mm SL) density was manipulated across four levels from 333 to 2664 m2 in protected (extruded netting, 12.8 mm aperture) and unprotected 1-m2 boxes. Survival within unprotected boxes was independent of stocking density (79%), but was inversely density-dependent in protected boxes (77% in the lowest density treatment increasing to a mean of 88% in the other three treatments). A negative cubic relationship explained the effect of density on growth. We present the first mariculture strategy for public stock enhancement or private entrepreneurs interested in rearing M. arenaria in Maine and the northeast US. Hatchery-reared juveniles 8-10 mm SL should be planted in the spring near or below mid tide levels at densities between 333 and 666 m2 and protected with flexible netting (6.4 mm aperture) raised several centimeters above the sediment surface. Netting should be removed from mud flats in the late fall before the threat of ice and severe winter storms. Animals should attain sizes between 25 and 30 mm SL during this time and reach a size refuge from burrowing and other predators. Growth to legal, commercial size (50.8 mm SL) should take another 2-4 years depending on geographic location and mean seawater temperature.
A six-inch (15 cm) diameter plastic plant pot used to contain cultured juveniles of soft-shell clams.
Beal, B.F., Mercer, J.P., O'Conghaile, A.
2002. Survival and growth of hatchery-reared individuals of the European lobster, Homarus gammarus (L.), in field-based nursery cages on the Irish west coast. Aquaculture 210, 137-157.
Abstract
At present, one of two strategies is employed by fisheries managers for enhancing wild stocks of homarid lobsters using hatchery-reared individuals. The first is repeated releases of large numbers (>5000 at a time) of postlarvae (stage IV and V; carapace length [CL]=5-7 mm) to selected bottom locations. This option exists primarily because these programs lack space, time, and/or the finances to rear animals to larger sizes that would most likely have initially higher survival rates. The second is to rear animals in the laboratory for 5-8 months to stage XII+ (CL=12-16 mm) and then release small numbers (<1000) of these relatively large juveniles. To date there has been no attempt to release large numbers of relatively large juveniles because the costs are too prohibitive. We have developed a low-cost, low-maintenance, field-based nursery caging system for rearing cultured lobsters, Homarus gammarus (L). Individuals (780 and ranging in CL from 5.2 to 7.2 mm) were reared in pre-fouled and unfouled containers (360 cm3) fabricated from an extruded plastic netting (3.2 mm aperture) and in pre-fouled plastic petri dishes (200 cm3) that were deployed in five near-bottom cages for 10 months (September 2000 to June 2001) at two subtidal sites located in a shallow, relatively exposed embayment on the west coast of Ireland. Animals apparently were able to survive and grow by suspension feeding on the plankton and/or foraging on the fouling community that settled on and within individual containers. Mean recovery rate (±95% CI) was independent of a priori fouling treatments, but was site-specific (42.1±7.9% and 27.8±13.7%; n=5). These rates are minimal estimates of survival because we found that at least 20% of the animals were capable of escaping from the mesh containers. Mean recovery in petri dishes that prohibited emigration was 53.3±37.02% at one site and 75.0±23.1% (n=5) at the other. These recovery rates compare favorably with survival rates of fed conspecifics held in the laboratory over the same time (54/81=66.7%). At the end of the experiment, animals in field cages had mean CLs that were significantly smaller than the fed controls. Because of costs incurred with maintaining small lobsters under laboratory conditions, results of this short-term, manipulative field experiment indicate that field-based nurseries represent an economically viable, third option for managers of lobster stock enhancement programs.
A stage V cultured European lobster, Homarus gammarus, used in field-based nursery experiment.
Laboratory and field work was conducted in 2000-2001 at the Shellfish Research Laboratory, Carna, Ireland.
A flow-through container constructed of extruded 4.2 mm plastic netting. One juvenile lobster was placed in each container. (A 15 cm Vernier caliper is shown for scale.)
Large (15 cm x 2.5 cm) Petri dishes used to contain a single lobster used in nursery trials.
A converted lobster cage (lobster nursery) constructed of vinyl-coated wire used to house flow-through containers with a single lobster each.
Flow-through containers were placed on each shelf (72 lobsters per nursery cage), and ten cages placed in the embayment adjacent to the Shellfish Research Laboratory from August 2000 to June 2001.
One of ten lobster nursery cages and flow-through containers after 10-months in the field.
Approximately 30% of lobsters in extruded mesh containers survived over the 10-month field trial. Lobsters doubled in size during this time.
Approximately 65% of cultured lobsters survived in the Petrie dishes over the 10-month field experiment. Lobster survival was signficantly higher in the dishes because animals could not escape since the dish cover and base were well-secured. The same was not the case for lobsters in the extruded mesh containers that allowed approximately 10-15% to escape.
Beal, B.F., Vencile, K.W.
2001. Short-term effects of commercial clam (Mya arenaria L.) and worm (Glycera dibranchiata Ehlers) harvesting on survival and growth of juveniles of the soft-shell clam. Journal of Shellfish Research 20(1), 1145-1157.
Abstract
In Maine, USA, commercial fisheries for soft-shell clams, Mya arenaria L., and blood worms, Glycera dibranchiata Ehlers, occur simultaneously on muddy intertidal flats. Local and state clam managers frequently close flats to shellfishing for conservation purposes, but have no jurisdiction over wormers who are legally permitted to harvest G. dibranchiata on any intertidal flat. This sometimes causes conflicts, especially when wormers dig in clam conservation areas where clammers have enhanced stocks with wild or cultured "seed" clams (<1 cm shell length, SL). Clammers believe wormers kill or injure small clams directly or indirectly while commercially harvesting G. dibranchiata. To help resolve these long-standing conflicts, we worked collaboratively with clammers and wormers and used an experimental approach to test the short-term interactive effects of clam and worm harvesting, harvesting intensity, time of harvest after seeding, and predator exclusion on the fate of small wild and cultured M. arenaria at an intertidal mud flat in Brunswick, ME. We added 50 cultured juveniles of M. arenaria (SL = 12.5 mm) to 120 1-m2 plots, 40 of which were undisturbed controls (20 protected with plastic netting--6.4 mm aperture; 20 unprotected) from May to August 1996. The remaining 80 plots were assigned to one of 16 treatments. One half of the plots were protected from predators with the same plastic netting used in the undisturbed control plots. One half of the plots were harvested by a professional wormer or clammer who searched each plot for commercial size blood worms and soft-shell clams, respectively. Plots were harvested either once (after two weeks or four weeks) or twice (two weeks + two weeks, or four weeks + four weeks). Any effect due to clamming or worming on cultured clams or wild individuals of similar size was masked by clam losses exceeding 95% in the unprotected control plots. Intense predation by horseshoe crabs, Limulus polyphemus L. and the nemertean worm, Cerebratulus lacteus Leidy, are blamed for the high mortalities among clams. Only in protected plots was any effect detected and this depended on clam origin. Compared to the fate of cultured clams in protected controls, worming had no effect, but clamming contributed an additional 15% loss. Both types of commercial harvesting reduced wild clam numbers significantly compared to controls, but effects due to worming were more benign than effects due to clamming probably because wormers excavate less volume of sediments than clammers do as commercial size G. dibranchiata are shallow burrowers compared to commercial size M. arenaria. Unless clam managers actively take steps to deter predators by using netting or other means, blood wormers should continue to harvest commercially from areas closed to shellfishing without reprisal or fear that they are causing damage to populations of juvenile soft-shell clams.
The study showed that clamming can have a negative effect on the survival of clam spat.
Beal, B.F., Chapman, S.R.
2001. Methods for mass rearing stages I-IV larvae of the American lobster, Homarus americanus H. Milne Edwards, 1837, in static systems. Journal of Shellfish Research 20(3), 337-346.
Abstract
We conducted a series of five laboratory experiments (7-18 days in duration) to test the interactive effects of stocking density, aeration rates, and food types on survival of American lobster (Homarus americanus) larvae through their first three planktonic stages (I-III) to the postlarval stage (IV). Experimental units and culture protocols were designed to replicate a 1:100 scaled-down version of equipment used in association with a fishermen-sponsored, stock enhancement lobster hatchery located in Cutler, Maine. The first four trials revealed that extremely high rates of aeration (ca. 240 mL air sec super(-1)) were necessary to distribute larvae and food sufficiently to reduce cannibalistic encounters; however, the best survival from stage I-IV (at stocking densities of 7-26 L super(-1) fed ad libitum with enriched Artemia) was only 24%. The final experiment (stocking density = 20 L super(-1)) yielded a mean survival rate ( plus or minus 95% CI) of 75.8 plus or minus 10.2% (range = 62.7% to 90.7%; n = 6). One important difference between the last and first four experiments was how stage I larvae were managed prior to their culture. In the first four trials, unfed larvae were collected from a relatively small (46 cm x 30 cm x 20 cm), screened capture basket located near the discharge pipe of a broodstock holding tank at the hatchery where they may have resided for > 12 hr. Larvae used in the final laboratory experiment were collected directly from the broodstock tank within 30 min after being liberated from the mother's swimmerets. Larvae, at relatively high densities within the screened box, likely had many more cannibalistic encounters prior to their culture than those collected directly from the broodstock tank and, therefore, suffered high rates of mortality during the first four laboratory trials. Mass rearing methods for larval American lobsters developed in conjunction with these laboratory experiments were used successfully by staff at the Cutler Marine Hatchery from 1988 to 1992.
Life-cycle of the American lobster, Homarus americanus.
A 400-liter container used to rear lobster larvae (stage I-IV) used at the Cutler Hatchery from 1986-1992. The three most important aspects of rearing mass quantities of lobster larvae are: 1) obtaining stage I larvae immediately after they have been released from the female (any residence time in a small container, especially without food, is deadly for the recently hatched stage I larvae); 2) bubbling the seawater in the rearing container so vigorously that the water appears to be boiling (this is necessary to keep animals away from each other during the culture period of up to 16 days); and 3) overfeeding with live, enriched Artemia (brine shrimp).
Cultured microalgae are used to enrich brine shrimp to feed to lobster larvae.
Stage IV lobster on crushed soft-shell clam shells (June 2007; Beals, Maine).
Beal, B.F., Chapman, S.R., Irvine, C., Bayer, R.C.
1998. Lobster (Homarus americanus) culture in Maine: A community-based, fishermen-sponsored, public stock enhancement program. Gendron, L (ed.). Proceedings of a Workshop on Lobster Stock Enhancement held in the Magdalen Islands (Quebec) from October 29 to 31, 1997. pp. 47-54. [Can. Ind. Rep. Fish. Aquat. Sci./Rapp. Can. Ind. Sci. Halieut. Aquat.]. no. 244.
Abstract
In 1985, Maine's lobster fishermen spoke with a unified voice as their Lobstermen's Association (MLA) voted to ask the Maine State Legislature to allow a portion of their annual license fees to be placed into a fund created specifically for stock enhancement through hatchery production of juvenile American lobster (Homarus americanus). The Legislature approved MLA's request and, because the Maine Department of Marine Resources (DMR) administers the license fees, gave the DMR the responsibility of creating a fair mechanism to disburse those funds. The eastern Maine fishing village of Cutler was awarded the grant money, and 400 citizens organized themselves into a Hatchery Committee. The funds allowed the Cutler Marine Hatchery to become an entity specifically for the productcion of juvenile lobsters for stock enhancement. Funding of this fishermen-sponsored community-based public stock enhancement program ended in 1992 and there have been no funds for lobster hatcheries in Maine since that time. The Cutler Marine Hatchery produced an average of 175,000 stage 4 and 5 animals each year from 1986 to 1991 for release to the wild for stock enhancement purposes. This hatchery did not have the capability of holding thousands of lobsters in separate containers to reach a size where they could be tagged effectively and without injury. Consequently the hatchery became interested in developing a strain of genetically blue lobsters to use them as markers for this and other hatch-and-release programs. Results suggest that cultured blue lobsters have no significant behavioral differences in attempting to escape predation compared with normal colored individual, and that behavior across a variety of different substrates was also similar.
Vadas Sr., R. L., Beal,B., Dowling,T., Fegley, J.C.
1999. Experimental field tests of natural algal diets on gonad index and quality in the green sea urchin, Strongylocentrotus droebachiensis: a case for rapid summer production in post-spawned animals. Aquaculture 182, 115-135.
Abstract
We tested whether the roe (gonads) of "post-spawned", green sea urchins, Strongylocentrotus droebachiensis, from barren grounds could be enhanced in the field during summer. Experiments were initiated using a low roe-yielding (barren ground) population, which also served as a field control. Specifically, we determined the ability of naturally occurring macroalgae to increase roe yield and enhance roe color relative to field controls. Sixty experimental cages with algae and five test animals per cage (mean test diameter=50.0 mm) were suspended along the seaward end of a commercial lobster impoundment on Beals Island, Maine, on 18 June 1996. Urchins were fed ad libitum all (mixed diet) or one of four species of macroalgae (Palmaria palmata, Alaria esculenta, Laminaria saccharina and Ulva lactuca). Four replicate cages of each algal treatment and 20 individuals from the control population were sampled (without replacement) every 3 weeks until 20 August. This design permitted the use of orthogonal contrasts in both one- and two-factor ANOVAs. These analyses revealed significant enhancement, relative to controls, of both color and roe yield (gonad index doubled or tripled within 2 months). Algal-fed animals attained a mean gonad index greater than 10%, the minimum commercial standard in Maine, while field populations ranged from 4% to 6%. These analyses revealed differential roe enhancement among palatable seaweeds. The red alga, P. palmata, induced the quickest and highest response, singly, among the four algae tested. Roe production on P. palmata was generally higher, but similar to that of the mixed diet. The two kelp species, A. esculenta and L. saccharina, consistently produced the lowest yields. Roe yields were correlated with protein levels in the algae. Our study also provides some insight into seasonal allocation of energy and nutrients into gonadal tissue. These data show that off-season allocation to gonadal tissue is biologically feasible in the absence of photoperiodic manipulation and that summer enhancement could be used to meet the off-season (August) market demand for roe in Asia.
Male green urchin, Strongylocentrotus droebachiensis, spawning in a tank at the Downeast Institute on May 16, 2011.
Beal, B.F.
2006. Relative importance of predation and intraspecific competition in regulating growth and survival of juveniles of the soft-shell clam, Mya arenaria L., at several spatial scales. Journal of Experimental Marine Biology and Ecology 336, 1-17.
doi:10.1016/j.jembe.2006.04.006
Abstract
Predation appears to be the single most important biotic factor regulating populations of bivalves in estuarine and coastal soft sediments. However, the relative roles of predation and intraspecific competition are rarely investigated simultaneously over different spatial scales, making generalities about these mechanisms difficult. Using juveniles of the soft-shell clam, Mya arenaria (initial mean shell length [SL] ± 95% CI = 12.4 ± 0.13 mm), I tested the interactive effects of predator deterrence and intraspecific density (660 vs. 1320 individuals m− 2) on growth and survival responses over a 185-day period from May to November 2003 at spatial scales that spanned four orders of magnitude: embayments, sites within embayments, tidal gradients, and blocks that were 10,000's, 1000's, 100's, and 5 m apart, respectively. Replicate field experiments were conducted from May to November 2003 at the upper and lower tidal heights at each of two intertidal mud flats (sites) within each of two embayments (Passamaquoddy Bay [PB] and Cobscook Bay [CB]) in eastern Maine.
Mean survival, relative growth, and the abundance of wild recruits each varied significantly over all spatial scales. Predation was the most important factor affecting clam survival, explaining 45% of the total variability, whereas embayment, sites within embayments, tidal gradient, and intraspecific density collectively accounted for less than 10% of the variation. At all four intertidal sites, clam survival in experimental units designed to deter predators averaged 72%, but the degree of enhancement varied between embayments (PB = 61%; CB = 267%). Average survival rate was higher (by 12–16%), but growth was slower (by ca. 50%) in upper vs. lower intertidal blocks; however, the patterns differed for both variables between sites within each embayment. The effect of increasing intraspecific clam density was to lower survival by ca. 17% (56% [660 m− 2] vs. 48% [1320 m− 2]) in both embayments, but growth was unaffected. Overall, clams doubled in SL, although mean relative growth was 15% greater in CB than PB. Tidal gradient, sites within embayments, and blocks were the three most important factors explaining 35%, 19%, and 22% of total variation in relative clam growth, respectively. In Maine and the northeast US, juveniles of Mya reach their highest abundance above mean low tide levels. Experimental evidence presented here suggests that differential predation along the tidal gradient is the dominant factor controlling clam abundance and distribution patterns in the intertidal zone.
Collecting samples from Half Moon Cove - West (Cobscook Bay) on November 21, 2003.
Pulling the six-inch plant pots from the intertidal flats on November 21, 2003.
An open enclosure with a tag indicating that the sample was taken from the low-water mark at Half Moon Cove - West (Cobscook Bay), and that it initially was seeded with 24 cultured soft-shell clam juveniles, and that the experimental unit was in the first block.
Processing the samples (washing the samples through sieves) at the University of Maine at Machias
Hatchery-reared soft-shell clams with a "hatchery mark" that allows one to measure the initial size and the final size to obtain a growth rate on an individual that one did not have to mark uniquely. The tag for this sample indicates that in May 2003, the clam juveniles were planted in the lower intertidal at Gleason Cove (Passamaquoddy Bay) at a density of 12/6-inch plant pot (experimental unit) that was protected with plastic mesh netting. The unit was in position 2-2 in the first of five blocks at that tidal height.
Beal, B.F.
2006. Biotic and abiotic factors influencing growth and survival of wild and cultured individuals of the soft-shell clam (Mya arenaria L.) in eastern Maine. Journal of Shellfish Research 25, 461-474.
Aug 2006 / pg(s) 461-474
Abstract
A series of intertidal field experiments was conducted from 1986–2003 in eastern Maine to examine biotic and abiotic factors influencing the growth and survival of wild and cultured individuals of the softshell clam, Mya arenaria L. Separate experiments examined: (1) the efficacy of transferring sublegal wild clams (<50.8 mm SL) from areas near the high intertidal zone where shell growth was slow to areas where growth was predicted to be faster; (2) effects of tidal height on wild and cultured clam growth; (3) effects of spatial variation on cultured clam growth; (4) dispersion and growth of cultured juveniles in small experimental units; (5) effects of the naticid gastropod, Euspira heros Say, predation on survival of wild and cultured clams and (6) the species composition of large, crustacean predators that forage intertidally during periods of tidal inundation. Protective netting (4.2 mm aperture) increased recovery rate of transferred clams by 120% and resulted in a 3-fold enhancement of wild recruits. Effects of tidal height on wild clam growth revealed complex behaviors in >0 y-class individuals. Clams growing near the upper intertidal take >8 y to attain a legal size of 50.8 mm SL, whereas animals near the mid intertidal generally take 4.5–6.5 y. Unexpectedly, clams initially 38–54 mm SL and growing near the extreme low tide mark at a mud flat in Eastport, Maine, added, on average, <2 mm of new shell in a year, which was 8–10 mm SL less than animals at higher shore levels. It is hypothesized that biological disturbance by moon snails, that consumed >90% of clams at the low shore levels, contributed to this slow growth. In another field trial from 1986–1987, moon snails and other consumers were allowed access to clams ranging in size from 15–51 mm. E. heros preyed on clams over the entire size range and attacked clams between 31–40 mm at a rate that was nearly double what had been expected. Mean snail size was estimated to range from 10–52 mm shell height (SH), based on a laboratory study that yielded information about the linear relationship between snail size and its borehole diameter. In an experiment from June to September 1993, moon snails consumed >70% of juvenile clams (ca. 10 mm SL) within a month after planting at each of three tidal heights. Snail sizes ranged from 15–20 mm SD with larger individuals occurring near the upper intertidal zone. Green crabs, Carcinus maenas (L.) also prey heavily on softshell clam populations, but most studies that use shell damage to assign a predator have assumed that all crushing and chipping predation is because of this invasive species. An intertidal trapping study demonstrated that both green crabs and rock crabs, Cancer irroratus Say, are present during periods of tidal inundation, with the latter species accounting for ca. 40% of large crustacean numbers.
The northern moonsnail, Euspira heros, from an intertidal flat in Edmunds, Maine (1998)
Predation by moonsnails on juvenile, cultured soft-shell clams. Experiment was performed in Lubec (Haul-Up) in 2009.
Beal, B.F., Protopopescu, G., Yeatts, K., Porada, J.
2009. Experimental trials on the nursery culture, overwintering, and field grow-out of hatchery-reared northern quahogs (hard clams), Mercenaria mercenaria (L.) in eastern Maine. Journal of Shellfish Research 28, 763-776.
Dec 2009 / pg(s) 763-776
Abstract
The easternmost commercial population of hard clams, Mercenaria mercenaria, in Maine was discovered recently near the low intertidal in Goose Cove, in the town of Trenton (Hancock County). A fast- and slow-growing morph was identified that reaches commercial size (50.8 mm shell length) in 4 y and 5 y, respectively. Fast-growing individuals were selected as broodstock, and conditioned to spawn at the Downeast Institute. The fate and growth of cultured juveniles was followed for 5 mo beginning in July 2006 at 4 stocking densities (2,500–10,000 animals/1.1 m2 floating, nylon window screen-lined tray; n = 20) at a coldwater field nursery approximately 60 km east of Trenton, in the town of Beals, ME (Washington County). Survival was nearly 100%, and growth was density dependent, with animals attaining a final mean shell length ±95% confidence interval of 8.4 = 0.13 mm and 7.6 ± 0.218 mm in the lowest and highest density treatments, respectively. In November 2006, cultured seed was separated into 2 sizes (large, 8.7 ± 0.2 mm; small, 5.1 = 0.2 mm) and overwintered in window-screen bags (0.2 m2) at densities ranging from 0.6–1.6 kg (large) and 0.5–1 kg (small), representing approximate densities ranging from 3,360–15,510 individuals per bag. Bags were placed on horizontal shelves within modified lobster traps (overwintering containers) that were added to a 35,000-L tank receiving ambient seawater for 177 days until May 2007. Seawater temperatures during this interval ranged from -1-10°C. Survival rates exceeded 99%, and no negative effects resulting from stocking density were observed. Hatchery seed was transplanted in May 2007 to the lower intertidal at Goose Cove and a second intertidal location approximately 30 km east of Beals at Duck Brook Flat, in the town of Cutler, and the fate and growth of these juveniles was followed for 6–7 mo. Survival was independent of planting densities (330–1320 individuals/m2), and predator netting did not enhance survival compared with controls without netting. Growth was seasonal, with the greatest incremental shell increases occurring between early July and late September. Growth rates varied between planting locations, with clams adding approximately 10 mm shell length at Goose Cove between May and December (initial shell length, 8.2 mm; final shell length, 17.9 mm) and approximately 5 mm shell length at Duck Brook Flat between June and November (initial shell length, 9.3 mm; final shell length, 14.3 mm). Hard clam farming in eastern Maine may help to diversify a wild shellfish industry that is currently in decline for most species except lobsters; however, additional efforts are needed to explore alternative grow-out sites and methods to enhance growth rates.
Nursery trays for rearing hard clam, Mercenaria mercenaria, juveniles. Trays are lined with fiberglass window screening material (aperture ca. 2.4 mm). Black plastic is stapled to the wooden tray to deter seagulls from breaking through the screening and eating the small clams. Photo taken in October 2008 at Mud Hole Cove, Great Wass Island, Beals, Maine.
Juvenile hard clams cultured at the Downeast Institute during the summer and fall of 2008.