Clam Populations Research Articles

Características de una población sobreexplotada de concha navaja, Ensis macha, en Bahía Independencia, Perú, durante el 2004

Quantitative monthly samplings, in 2004, were carried out to estimate the density and biomass of Ensis macha (Molina 1782), from Morro Quemado area, Bay Independence, Pisco. The present study analyzes biometric relationships, growth parameters and somatic production using the ELEFAN I routine and the Crisp’s method. During the year 2004 the rate of exploitation (E= 0.69 y-1) was significantly bigger than the values of 2003 and the monthly landings (maximum of 335 t) and fishing effort (maximum of 848 trips) were twice increased. These changes induced in the same year a significant decrease of population mean density (D= 54.13 ind. m-2) and the halfway reduction of somatic production (P= 81.99 gAFDW m-2 y-1) and P/B rate (0.38 y-1) values, regarding the values of the previous year. Also, a significant increment of total mortality rate (2.84 y-1) and the fishing mortality rate (1.97 y-1) were twice increased, regarding the previous year. It is assumed that the population of razor clams already was a overfishing commercial resource in the 2003 and that the increment of fishing pressure in the 2004, particularly during the second semester, intensified its overfishing resource condition.

The invasive Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) in Northern Adriatic Sea: Population genetics assessed by an integrated molecular approach

The coastal lagoons of the Northern Adriatic Sea are among the most worldwide productive locations of Manila clam Ruditapes philippinarum. Although introduced in Italy in 1983 from the Indo-Pacific, fishing and exploitation of Manila clam improved during the years as Italy became the leading country in Europe for production of this shellfish. Despite its commercial importance, genetic structure of R. philippinarum in Northern Adriatic Sea has not been previously investigated. Here we present the first genetic study on Manila clam populations inhabiting a Mediterranean area, assessed by both mitochondrial ( 16S rDNA) and nuclear DNA (microsatellite loci). Our study showed that this species has a limited genetic differentiation at the mitochondrial level, but a higher rate of genetic diversity can be identified by polymorphic markers as microsatellites. In particular, out of 28 alleles, 7 private ones were recorded for the Venice Lagoon populations, 2 for those of Scardovari and one for the Po River Delta populations. These molecular markers suggest the occurrence of at least two different introduction events from different recruitment stocks, representing a powerful tool not only to assess genetic diversity of an introduced species, but also helpful information to manage aquaculture and fishery stocks, and to warrant food quality, safety and for the authentication of shellfish products, and traceabilty path.

Growth and population dynamics of the giant clam Tridacna maxima (Röding) at its southern limit of distribution in coastal, subtropical eastern Australia

The Solitary Islands Marine Park in northern New South Wales hosts eastern Australia’s southernmost coastal population of the giant clam Tridacna maxima. This small population of clams was monitored and measured over a 12-yr period to determine patterns of distribution, dynamics and growth rates. Most (31) of the 40 specimens found were present at the most offshore location (North Solitary Island) and growth rates were similar to those recorded on the southern Great Barrier Reef. Recruitment rates were very low (<2 yr-1 across the whole Park) and loss of individuals was mostly associated with periods of large swell. The importance of North Solitary Island for Tridacna reflects the results of other studies demonstrating a strong tropical influence, mediated by the East Australian Current, at this, the most offshore island on the NSW coast.

Suspension feeding by the Atlantic slipper limpet ( Crepidula fornicata) and the northern quahog ( Mercenaria mercenaria) in the presence of cultured and wild populations of the harmful brown tide alga, Aureococcus anophagefferens

Within estuaries of New York, USA, recurrent harmful brown tides ( Aureococcus anophagefferens) have contributed toward the collapse of two major bivalve fisheries (bay scallop, Argopecten irradians and northern quahog or hard clam, Mercenaria mercenaria), while populations of the Atlantic slipper limpet Crepidula fornicata have persisted in the presence of these blooms. Rates of suspension feeding by C. fornicata and M. mercenaria in the presence of different strains of A. anophagefferens and wild brown tide blooms were quantified to assess the potential impact of brown tides on slipper limpet and hard clam populations. Slipper limpets were capable of clearing all strains of A. anophagefferens at biomass-specific rates similar to an ideal food source ( Isochrysis galbana), whereas clearance rates of M. mercenaria fed toxic clones of A. anophagefferens were significantly lower than when fed I. galbana or non-toxic clones of A. anophagefferens ( p < 0.01). During brown tide blooms (10 4–10 6 cells mL −1) on the south shore of Long Island during 2008 and 2009, clearance rates of C. fornicata when fed bloom water were an order of magnitude greater than those of M. mercenaria ( p < 0.001). Finally, during mesocosm experiments, C. fornicata reduced bloom densities of A. anophagefferens (10 6 cells mL −1) by an order of magnitude in 3–4 days, whereas densities of A. anophagefferens in mesocosms stocked with equal or greater biomasses of M. mercenaria were unchanged. These results demonstrate that C. fornicata can actively feed in the presence of A. anophagefferens and suggest that this species could serve as a top-down control of blooms in shallow, poorly flushed estuaries.

Long-term effects of fishing on physiological performance of the Manila clam (&lt;i&gt;Ruditapes philippinarum&lt;/i&gt;) in the Lagoon of Venice

The Manila clam ( Ruditapes philippinarum ) is an important economic resource for fisheries in the Lagoon of Venice, where this species is fished and farmed. With the aim of evaluating possible fishing-induced long-term effects undergone by clam populations subjected to fishing efforts, physiological biomarkers were measured at organism level (clearance and respiration rates, scope for growth and survival-in-air test). Clams were collected on a seasonal basis from sites characterized by various fishing management practices: a free fishing area at S. Angelo and an area licensed for clam farming at Chioggia, where a non-fishing sub-area was established. R. philippinarum collected at S. Angelo generally showed reduced filtering activity and higher oxygen consumption, revealing general worsening in clam well-being in comparison with individuals from both Chioggia areas. This condition, resulting in lower standardized scope for growth values, may be explained by both environmental and fishing effort differences. Comparing Chioggia samples, better physiological performances were exhibited by clams from the non-fishing area, though no significant differences were observed. In winter, the survival-in-air test revealed the detrimental effects of fishing on clams, whereas in the other seasons this response generally seemed to be mostly related to other exogenous and endogenous factors. Although differences among sites and seasons were always statistically significant, all physiological parameters indicate the great tolerance of R. philippinarum to changing environmental conditions.

Grazing impact of the invasive clam Corbula amurensis on the microplankton assemblage of the northern San Francisco Estuary

Grazing by the overbite clam Corbula amurensis (formerly known as Potamocorbula) may be the cause of substantial declines in phytoplankton biomass and zooplankton in the San Fran- cisco Estuary (SFE) following its introduction in 1986. While grazing rates have been examined on bacteria, phytoplankton, and copepod nauplii, the consumption of protistan microzooplankton by C. amurensis has not previously been measured. In this study, laboratory feeding experiments revealed that C. amurensis cleared 0.5 l ind -1 h -1 of microzooplankton (ciliates) and 0.2 l ind -1 h -1 of chlorophyll (chl) a. Despite the higher clearance rate on microzooplankton, clams obtained more of their carbon from phytoplankton, which dominated the prey assemblage on most dates. When the measured clearance rates are extrapolated to field populations of clams, fractional loss rates (50 to 90% d -1 ) exceed the population growth capacity of microzooplankton. Although microzooplankton may not be a major component of the diet of these clams, C. amurensis may further alter food web dynamics through consumption of this important trophic intermediary, thus disrupting this link from bacteria and phytoplankton to higher trophic levels.

Ecological determinants and stochastic fluctuations of Tridacna maxima survival rate in Lakshadweep Archipelago

Compounding effects of slow life-history traits and adult-specific overharvesting have caused a range-wide decline of several giant clam populations. Erratic changes in these populations reported at isolated reefs, are attributable to stochastic fluctuations in recruitment and survival rates. These population rate parameters may be adversely influenced by the considerable and increasing human–reef economic interactions in tropical waters. The unsubstantiated knowledge on such influences hinders conservation management of species-habitat linkages particularly for species like the small giant clam (Tridacna maxima). Our study reports small giant clam survival rate, its ecological determinants and stochastic fluctuations from shallow lagoon waters of Lakshadweep Archipelago; a natural habitat not subjected to commercial giant clam harvesting. Survival rate was estimated by monitoring the status of identified individuals in belt-transects through successive years 2005–2009. The role of different factors in explaining the variation in survival rates was investigated at relevant scales: anthropogenic pressure at the population level in the reef, clam density at sub-population level in the belt-transects, and variables related to clams at the individual level. Effects were quantified through univariate regression techniques and Kaplan–Meier estimator coupled with generalized linear (logit link) models. Small giant clam survival rate in the reef decreased and its spatio-temporal fluctuations increased along the increasing gradient of human populations. Survival was density-independent. Size/age specific survival followed Siler distribution characterized by very low early-age survival, increased adult-age survival, and low older-age survival. Anchorage in coral substrate exerted a curvilinear effect, where survival of moderately anchored clams > loosely anchored clams >> deeply embedded clams. Our study recommends regular population monitoring in densely inhabited islands to detect incipient changes, which can subsequently be confronted by scientific lagoon bed management.

Regional Differences in Initial Settlement and Juvenile Recruitment ofMya arenariaL. (Soft-Shell Clam) in Maine

Clam landings have dramatically decreased in eastern Maine since 1982. Earlier studies demonstrated that densities of 0-y-old individuals of Mya arenaria L. were lower in Washington County on the eastern Maine coast than in Cumberland County on the southern Maine coast. Reduced juvenile recruitment could result from reduced larval abundances, high postsettlement mortality, or a combination of these factors. Attempts to assist recovery of populations experiencing reduced recruitment would vary depending on which combination of factors inhibited recruitment. In this study we measured initial settlement, short-term (<4 wk) postsettlement densities, and longer term (several months) postsettlement densities of 0-y-old juvenile M. arenaria in both eastern and southern Maine. Although there were seasonal and spatial differences, densities of juvenile clams were significantly greater in southern Maine over eastern Maine at each of these life history stages (initial settlement, and early and later postsettlement), generally by one or more orders of magnitude. These results suggest the low number of M. arenaria recruits in eastern Maine is a consequence primarily of reduced densities of larvae in near-shore waters rather than processes affecting postsettlement survival differentially between southern and eastern Maine. Because of the very low abundance of competent clam larvae in eastern Maine, restoration of clam populations there will require intensive efforts, such as seeding mudflats with hatchery-reared juvenile clams and managing subsequent clam survival.

Genetic variation and differentiation in wide ranging populations of razor clam (Sinonovacula constricta) inferred from AFLP markers

The genetic variation and differentiation of the razor clam Sinonovacula constricta distributed along the coast of China were studied through amplified fragment length polymorphism (AFLP) analysis. Six primer combinations generated 193 fragments. The H e values varied from 0.322 to 0.463 and the percentage of polymorphic loci ranged from 74.1% to 98.4%, which indicates a high level of genetic diversity. Cluster analysis by Nei’s pairwise distance grouped all specimens by geographical origins. AMOVA consistently showed that genetic variation among populations was 8.71%, and most of the variation came from the genetic variation within populations (91.29%). Genetic differentiation among the six populations was moderate; pairwise F ST ranged from 0.0282 to 0.1480, which indicated that S. constricta populations along the coast of China are genetically connected. Among all the six populations, the Beihai population is the mostly differentiated from the others, suggesting that Hainan Island and Leizhou Peninsula act as barriers to gene flow. All populations abide isolation by distance model as indicated by Mantel test, except for ZS (Zhoushan) and YQ (Yueqing) populations. Information obtained in this study will provide guidelines for conservation and fishery management of this species in the future.

Unusual increase in the surf clam (Maxtra sulcataria REEVE) population off Kamimiyata in Tokyo Bay

Unusual increase in the surf clam (Maxtra sulcataria REEVE) population off Kamimiyata in Tokyo Bay

GENETIC VARIABILITY OF POLYMESODA EROSA POPULATION IN THE SEGARA ANAKAN CILACAP

Abstract Mud clams Polymesoda erosa in the Segara Anakan Cilacap are highly exploited by the local communities for daily consumption. This is presumed causing population decline and potentially causing loss of genetic diversity. Genetic diversity level within population can be obtained by population genetic study using molecular marker such as randomly amplified polymorphic DNA (RAPD). Here we amplified RAPD marker using ten arbitrary primers to assess genetic diversity of P. erosa population in the Segara Anakan Cilacap to provide genetic data for its sustainable use. The result proved that the used RAPD marker has high polymorphisms. The mud clam population was also showed a high level of heterozigosity and genetic diversity. This has important implication for the management plan towards ustainable use of P. erosa in the Segara Anakan Cilacap.  Key words: mud clam, RAPD, polymorphism, genetic diversity

Isolation and characterization of 9 polymorphic microsatellite markers for the endangered boring giant clam (Tridacna crocea) and cross-priming testing in three other Tridacnid species

We report the development and characterization of nine microsatellite markers from the Tridacna crocea genome. In a wild population of 20 individuals from Ulugan Bay in the Republic of the Philippines, we observed an average of 9 alleles per locus and expected heterozygosity ranging from 0.41 to 0.92. Cross-species priming was tested in three additional Tridacna species with moderate success. These markers will be used in studies of fine-scale population genetic structure and gene flow in T. crocea. The markers may also be useful in a forensic context by identifying source populations of giant clams collected illegally for the live aquarium trade, while protecting legal exports from aquaculture facilities.

A companion modeling approach applied to fishery management

Don Hoi Lord, a coastal wetland in the upper gulf of Thailand, is famous for the razor clam ( Solen regularis), which is a source of food and income for local fishermen. However, the razor clam population is significantly decreasing so the aim of this study was to analyze the razor clam fishery and develop a management plan engaging the different stakeholders in collective discussions. A participatory modelling approach was used, including (a) agent-based modelling (ABM) and (b) role-playing games (RPG). First, an individual-state distribution model of the razor clam population was designed and calibrated to synthesise knowledge. Two RPG sessions supported by this biological model were organised to initiate collective learning and promote discussion among stakeholders. After playing with the baseline scenario showing the actual harvesting situation, discussions led to the definition of alternative scenarios for clam management such as establishment and rotation of zones closed for harvesting, and quota systems. These scenarios developed during the RPG sessions were more deeply investigated with an agent-based model that included fishermen agents and the individual-state distribution model of the razor clam population. Simulations of different scenarios (reserve, quota and combination of reserve and quota) were produced to enable better informed discussion between different stakeholders. Stakeholders have acknowledged that management through rotating reserves is not efficient if the duration of reserves is too short. They have realised that the efficiency of reserves is hard to assess without better data on clam recruitment. They have also explored another management option which is the quota system. In the final stage, the local participatory process was endorsed by the incumbent regional policy-making actor. Unfortunately, because of rapid administrative rotation the project abruptly lost support. This unexpected event emphasises the need for continuous monitoring of all actors entering and/or leaving the system, which can radically change the interactions among them and, therefore, the whole management context.

Bivalve population health: Multistress to identify hot spots

This study investigated some stress (metals, parasites) and response (immunity, metallothionein) factors in two cockle and two Manila clam populations. Data from eight seasons were averaged to obtain global baseline values. Stress/response characteristics of each population were compared to population health status that was determined through population dynamics parameters. Four different scenarios were discussed: (1) a lightly stressed cockle population with correct population health but with a risk of deterioration (hot spot); (2) a lightly stressed introduced cockle population threatened of extinction. In this case ecological factors were suspected; (3) a moderately stressed clam population with moderate adaptative response. The population was sustainable but the level of stress should not increase (hotspot); and (4) a stressed clam population and unfavourable ecological conditions preventing clam settlement. This monitoring highlighted that the discrepancy between population health and stress levels could be due to insufficient response by bivalves and/or by unfavourable ecological factors.

Reproduction of the Cortes GeoduckPanopea globosa(Bivalvia: Hiatellidae) and Its Relationship with Temperature and Ocean Productivity

ABSTRACT This article describes the timing of gametogenic development and spawning in a population of geoduck clams, Panopea globosa (Dall 1898), from the Upper Gulf of California and its relationship to temperature changes and primary productivity. Clams were collected monthly over 1 year (March 2008 to March 2009), and salinity, dissolved oxygen, and substrate type were recorded during each survey. Standard histological analyses and measurements of oocyte diameters were used to describe the timing of gametogenic development and spawning. Satellite data for temperature and chlorophyll were gathered to test a general conceptual planktonic larval development model. The results demonstrated that reproductive activity was triggered by a steep decrease in temperature 4 months prior to the peak of productivity. Thus, larval development matches favorable conditions, as predicted by Cushing's Match—Mismatch Hypothesis.

Oocyte Cohort Analysis: Criteria for an Evaluation of the Reproductive Cycle inSolen marginatus(Pennánt, 1777), (Bivalvia: Solenacea) in Southern Tunisia

The purpose of this study was to develop an oocyte maturation scale and to retrace the development of the oocyte cohorts in razor clam populations of Solen marginatus (Bivalvia: Solenacca Mollusca) sampled in the tidal area of Maltine Wadi (El Mares, Gulf of Gabes, Southern Tunisia). The development of an oocyte maturation scale could help reproductive cycle monitoring and the assessment plan in the search for populations. The results included 7,535 oocyte measurements during a 1-y sampling period from May 2007 to May 2008. Based on the qualitative and quantitative analyses of the oocyte measuring activities, we assume a 4-stage maturation process: I, gametogenesis commencement from November through to March, the oocyte diameters are smaller than 15 µm; II, oocyte growth from April through to May, the oocyte diameters range between 15 µm; and 25 µm; III, oocyte maturation from May through to October, oocyte diameters range between 25 µm and 40 µm; and IV, resorption of the gonads from May through to October, the oocyte aspects are irregular, disrupted, or burst. The development of the indices of the dry condition and the oocyte cohorts shows major reproductive activity of the species from April through to October. Initial maturation commences in May followed by a major gamete emission in June. Maturation recovery occurs in July followed by oocyte growth, which continues, and appears to be more rapid during summer and early autumn. The first gamete emission occurs in May during the first oocyte cohort maturity accession and continues until late October, with an irregular time interval between the emissions.

Determining the Ecological Role ofEuspira lewisii: Part I: Feeding Ecology

The predatory naticid snail Euspira lewisii, Lewis moon snail, native to the west coast of North America, is stated to be an economic threat to the shellfish aquaculture industry in British Columbia (BC). This species is being manually removed from the intertidal ecosystem, yet little is known about the ecology of this species. Enclosures and beach shell assemblages were used to determine the prey preference, feeding rates, and community impacts of E. lewisii. In the enclosures, Protothaca staminea, the native little neck clam, was found to be the preferred prey, whereas the commercially valuable Manila clam, Venerupis philippinarum, was avoided when E. lewisii was offered other clam prey choices. Drilled shells collected from the intertidal revealed similar feeding preferences. The feeding rate averaged for a variety of clam species was found to be 0.09 clams/day or 1 clam every 14 days. The feeding rate was dependent on prey species, and was highest for the preferred species and significantly lower on avoided species. The overall impact of E. lewisii to the bivalve community was found to be low. Based on these results, E. lewisii consumed only approximately 3% of the clam population over 1 y, assuming maximal feeding rates and typical population densities found on the west coast of BC. E. lewisii has minimal impacts to the Manila clam industry in BC and control measures are not necessary for this species. Baseline ecological field studies are important for gaining an understanding of poorly understood species, especially those considered threats to industry.

Impacts of stage-specific acute pesticide exposure on predicted population structure of the soft-shell clam, Mya arenaria

A combined laboratory and modeling approach was used to assess the impact of selected pesticides on early life stages of the soft-shell clam, Mya arenaria. Clams were exposed for 24h as veligers or pediveligers to the broad-spectrum herbicide hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1h,3h)-dione; Velpar®], the phenoxyacetic acid herbicide, 2,4-D (2,4-dichlorophenoxyacetic acid; Agway® Super BK 32), or phosmet (Imidan®). In addition, juvenile clams were exposed for 24h to 2,4-D and their growth monitored for 21 months. Laboratory experiments indicated veligers were more sensitive to acute pesticide exposure than pediveligers, with 2,4-D exposed veligers exhibiting the lowest survival among all treatments. Relative to controls, juvenile clams exposed to 0.5ppm 2,4-D had enhanced survival following the initial 3 months of grow out. Juveniles exposed to 0.5, 5 and 10ppm 2,4-D showed an initial growth delay relative to control clams, but at 21 months post-exposure these clams were significantly larger than control clams. Data from the larval and juvenile exposures were used to generate a stage-specific matrix model to predict the effect of pesticide exposure on clam populations. Impacts on simulated clam populations varied with the pesticide and stage exposed. For example, 2,4-D exposure of veligers and pediveligers significantly reduced predicted recruitment as well as population growth rate compared to controls, but juvenile exposure to 2,4-D did not significantly reduce population growth rate. With the exception of veligers exposed to 10ppm, hexazinone exposure at the both veliger and pediveliger stages significantly reduced predicted recruitment success compared to 0ppm controls. Hexazinone exposure also reduced modeled population growth rates, but these reductions were only slight in the pediveliger exposure simulations. Veliger and pediveliger exposure to phosmet reduced modeled population growth rate in a dose-dependent fashion. Changes in modeled population stable stage distributions were also observed when veligers were exposed to any pesticide. These results suggest that both the stage of exposure and the specific toxicant are important in predicting effects of pesticide exposure on soft-shell clam populations, with earlier life stages showing greater sensitivity to the pesticides tested.

Influence of Perkinsus Infection on the Physiology and Behavior of Adult Manila Clam Ruditapes philippinarumi

Annual catch landings of the Manila clam Ruditapes philippinarum have decreased in Japan since the early 1980s because of the decreased size of many Manila clam populations. It is hypothesized that Perkinsus olseni infection contributed to these decreases. However, the effect of Perkinsus infection on the survival and physiology of Manila clam is poorly understood. We examined the influence of Perkinsus infection on clearance rate, tolerance against high water temperature, and burrowing activity in a captive adult clam population. Infection intensity did not affect clearance rates, burrowing activity, or tolerance against high water temperature. In addition, we monitored infection intensity in wild, adult clams from a tidal flat lacated in western Seto Inland Sea over a one-year period. Infection levels were relatively stable in the wild population between June 2004 and May 2005, but we noted a significant decrease in the infection intensity at the end of the spawning period in November 2004. However, in the present study, clear evidence showing the negative impact of Perkinsus on clam physiology and survival was not obtained.

Experimental Trials on the Nursery Culture, Overwintering, and Field Grow-Out of Hatchery-Reared Northern Quahogs (Hard Clams),Mercenaria mercenaria(L.), in Eastern Maine

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 m 2 floating, nylon window screen-lined tray; n ¼ 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 m 2 ) 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 -1-10C. 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/m 2 ), 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.