Investigating Poor Growth of Hard Clams in New Jersey

Progress report for ONE22-415

Project Type: Partnership
Funds awarded in 2022: $28,713.00
Projected End Date: 07/31/2024
Grant Recipient: University of Connecticut
Region: Northeast
State: Connecticut
Project Leader:
Dr. Sylvain Deguise, DMV, PhD
Connecticut Sea Grant, University of Connecticut
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Project Information

Project Objectives:

Objective 1: To identify periods of slow growth during the annual production season using condition index as an indicator of metabolic energy balance. Data will be compared between sites and against historical data to describe timing and severity of changes in growth.


Objective 2: To use shell aging analysis of older clams to describe long-term patterns in hard clam growth within and between growing sites. 

Objective 3: Informed by observations from Objectives 1&2, identify changes in seasonal and long-term trends in environmental variables. Assess the sensitivity of hard clam growth and survival to conditions to provide insight on the regionally observed poor clam production. 

Outcomes/Deliverables: Quantification of the slow growth effects being observed by New Jersey clam farmers. Quantitative understanding of the extent and severity of this issue will aid farmers in attracting support to explore options to counteract the problem. Identifying the temporal sequence associated with poor performance will better inform future research so that studies are relevant to the problems facing the commercial sector. We intend for the results of the correlative study between environmental variables and clam performance to be applied to farm management and siting practices to help farmers make informed choices about their production plans.


Hard Clams (Mercenaria mercenaria) are one of the top three molluscan aquaculture products in the United States and are grown exclusively on the east coast from Massachusetts to Florida (Yang, 2016). Hard clams are one of the two shellfish species cultivated in New Jersey (the other being the Eastern oyster). A 2015 outlook report estimated that approximately 7.78 Million clams were sold for a farm gate value of $1.5 Million, acknowledging that this is most likely an underestimate based on the number of farmers that replied to the survey (Calvo, 2017). Farmers have recently reported to state biologists at NJDEP that hard clam growth on established leases in some estuaries has declined noticeably over the past 7 years. Investigations into the cause of the observations began with some growers individually obtaining pathology screenings of their product, but a definitive disease process explaining the slow growth and mortality was not evident.  After an especially poor season this past summer (estimate of ~350,000 market clams died), a grower, Dale Parsons of Parsons’ Seafood, contacted researchers at the NOAA Fisheries Milford Lab in Connecticut for possible explanations. There has been a great deal of interest from other growers in New Jersey, and especially the New Jersey Shellfisheries Council, to further understand these observations on these leases and the spatial extent throughout the state.   


One hypothesis discussed to explain the poor growth of hard clams, while oyster and scallop growth has not changed, is a metabolic energy imbalance caused by a combination of increasing metabolic demands and declining nutrient availability. Preliminary data from NJDEP’s continuous sampling of chlorophyll, an indicator of phytoplankton abundance, has shown declines in chlorophyll concentrations in the same areas the decrease in growth has been reported.  Research at the Milford Lab has shown a feeding conversion efficiency of 2% for hard clams, 25% for oysters, and 20% for scallops (Wikfors et. al.). It is possible that the clams are also facing environmental conditions that increase metabolic demand, such as increasing bottom water temperature. Those conditions, in addition to low food availability could explain why clam growth has slowed while other bivalve growth in the same growing areas has not.  


We propose to research the timing and cause of poor growth of cultured hard clams using condition index measurement, water quality data, and shell growth ring measurements. This information will provide empirical evidence on the rate and severity of the negative growth trends observed in cultured hard clams in the study areas. Results of the study will give farmers the tools to make important decisions on future farm use and provide important context to the future of hard clam aquaculture in the state and what, if anything, can be done to reverse the trend.  


We will conduct a comparative study between two historically productive aquaculture sites in New Jersey to evaluate seasonal and long-term hard clam growth trends as well as water quality.  One site is near Little Egg Harbor (LEH) Inlet in Barnegat Bay, New Jersey where Dale Parsons grows clams, oysters, and scallops in aquaculture gear. Since 2015 farmers in this region, including Dale Parsons, have observed significant declines in hard clam growth and survivorship. Similar observations have been made by ReClam the Bay, a non-governmental organization operating hard clam upwellers in Barnegat Bay. We will also collect samples from Paul Felder’s operation in Great Sound, a separate estuary in southern New Jersey which has maintained consistent productivity and growth in the same time period that LEH has witnessed declines.  By assessing growth patterns and water quality between sites, we hope to gain a better understanding of how aquacultured hard clams are responding to environmental changes and what conditions are most influential to their growth and survival.


Click linked name(s) to expand/collapse or show everyone's info
  • Kira Dacanay (Researcher)
  • Dale Parsons - Producer (Researcher)
  • Eric Robillard (Researcher)
  • Gary Wikfors (Researcher)
  • Paul Felder - Producer (Researcher)


Materials and methods:

Farmers Dale Parsons and Paul Felder are participating in the research portion by leading data collection effort. 

The following is our plan for upcoming sampling season (3/23-12/23):

Sampling Locations: Clams will be collected from Dale Parsons’ lease site in Little Egg Harbor, Barnegat Bay, NJ and from Paul Felder’s site in Great Sound, NJ. Water quality monitoring data will be collected from the closest operating stations to each site.

Objective 1:   To assess growth throughout the production season, we will sample 30 clams from each site on a monthly basis between March and October . Selected clams will be 1-2” in size, as farmer observations note this size-class appears to have slower growth than others. Clams will be shipped overnight on ice to the Milford lab for condition indexing. Condition index is a useful and widely used indicator of bivalve nutritive status (Crosby and Gale 1990). Clams will be scrubbed and dried before collecting whole wet weight (g), in addition to shell length, width, and depth measurements (mm). Tissue condition and gonad status will be assessed visually, and a small tissue sample may be collected to evaluate the presence of eggs or sperm microscopically. The soft tissue and valves will be separated and dehydrated independently in an oven at 60°C for 48 hours before collecting dry soft tissue and shell weights. Condition index will be calculated using the formula (Walne and Mann, 1975; Rainer and Mann, 1992): 

               Soft tissue dry weight (g)                
                 ----------------------------------     x 1000  

Dry shell weight (g) 

Shell growth and condition index will be plotted over time and generalized mixed-effect modeling methods will be used to compare shell growth and condition index within and between sites. 

Objective 2: Following condition index measurements, the clean, dry valves will be shipped to the Woods Hole Lab for age and growth estimates. To assess long term growth trends, we will also collect up to 50 large clams (> 4 inches) estimated to be >10 years old from near each aquaculture site. Collection of large clams will occur once during the study. Once at the Woods Hold Lab, we will excise from the valve the chondrophores using a pair of diamond-impregnated blades. We will then glue the chondrophore onto a slide, and produce a thin-section (0.25 mm thick) using a low-speed saw. For age determinations we will place the thin section onto a microscope and view it under transmitted light at 50-100x. We will follow published protocols to estimate the annual periodicity of increment formation of M. mercenaria (Peterson et al. 1983, Peterson et al. 1985, Jones et al. 1990, Ridgway et al. 2011).

Objective 3:  We will describe continuous water quality monitoring data routinely collected by NJDEP at LEH and Great Sound during the clam sampling period. Water quality variables include: specific conductivity, salinity, temperature, dissolved oxygen concentration, dissolved oxygen percentage, turbidity, and chlorophyll concentration. To supplement NJDEP observations and obtain site specific data, we will deploy temperature data loggers and tiltmeters at both aquaculture sites where clam samples are being collected. The loggers will be placed at the water bottom to capture temperatures surrounding the clam as well as being drawn into the mantle cavity. Mean values will be aggregated by month, and environmental data will be incorporated into the mixed-effect models of shell growth and condition index to assess the sensitivity of hard clam growth to each variable.  

Research results and discussion:

Two Project planning meetings have been held to discuss and plan for sampling in the 2023 summer season.  Collaborators Gordon and Parikh presented preliminary work at the Milford Aquaculture Seminar 1/14/23.  Preliminary data collection was conducted at Dale Parsons' lease sites in Little Egg Harbor, NJ and discussion with scientific collaborators has led to small changes in sampling plan for the 2023 season.  More rigorous growth data will be collected by following a subset of clams at each site and measuring size at the beginning and end of the season.  We placed temperature loggers at the water surface, bottom water, and embedded in the sediment to determine if there are significant differences in temperature at different location.  We decided that only the temperature logger at the bottom water location is needed for future sampling. Also, the need for current data has been discussed and tiltmeters will be used to measure currents at both sites for the entire season.  Materials for Shell aging process have been purchased and preliminary aging has been done on clams from Dale Parsons farm to refine methods.  The methods for aging have not changed from the original plan. 

Collaborator Gordon will attended February NJ Shellfish Council meeting to discuss the project progress and confirm participation with Great Sound Farmer.  Collaborators Gordon and Parikh will return to NJ in March to set up sampling at each site and confirm the logistics with partner farmers.  

Update 1.15.24

Gordon and Parikh visited NJ on March 20-21st 2023 to deploy sensors, collect the first series of samples, and set up growth measurement boxes.  The sensors included both a temperature logger, and a current meter at each site.  The samples collected were the first in the series of monthly samples for condition index. The growth measurement boxes were a new addition to the project that was a suggestion from other experts in hard clam aquaculture and was cheap to implement without additional funding.  The methods for the boxes were as follows:

Three clam boxes were planted at each farm and stocked with 35 clams.  The 35 clams in each box were labelled with unique markings with three colors of nail polish.  The patterns of nail polish were used to confirm identity of individual clams over the growing season.  After planting the clams in march, they were retrieved for measurement in July and replanted, and harvested in December for final measurements.  This gave us the ability to determine growth of each clam on the individual level at each site over a single growing season. 

Farmer partners (Parsons and Felder) shipped a sample of 30 clams monthly (April - December 2023) to the Milford Lab in CT for condition index and shell length measurements.  The samples were frozen on arrival to the lab and collaborators Gordon and Parikh have processed 3/4 of the samples.     

In July, collaborator Gordon visited the farm sites to check in with the farmers in person, and check on the sensors, collect condition index samples and record growth measurements on the clam boxes. 

In December, collaborator Gordon returned to the farms to collect the samples, and remove the growth boxes and sensors.  The growth and mortality within the boxes was recorded and the sensors were collected and data has been downloaded for analysis. 

Objective 2 Progress:

Over 200 dry clam shells were shipped to our collaborator at in Woods Hole and processed for age data.  50 older wild clams were sent from each growing site, 50 wild clams from a different area within Barnegat Bay, and the shells from each monthly sample of 3o clams after condition index processing. The monthly sampled clams are included as a baseline to look at age rings on clams with a known age.   This data includes the age of each clam and the distance between age rings for each clam. 

The growth of the clams during the first 3-4 years of life are the most important for farmers because that is generally the amount of time it takes to reach market size.  The next steps are to take the measurements recorded for each of the older clams during this 3-4 year period and create a time series showing how this early growth has changed from year to year and if there are any discernable patterns.  

Going forward:

The data processing for the project is nearly complete, and once complete we will begin to analyze the data over the next couple of months.  This will include running statistical analyses on growth, condition index, and environmental parameters at each site.  After data analysis is complete, the research portion of the project will be complete and we hope to publish is relevant scientific journals as well as create outreach material that can be distributed to the farming community in NJ and beyond.  Hard clam populations have dramatically changed in other Northeast states as well.  Concerns have received government funding in RI and NY, and similar discussions have been brought up in CT as well.  We hope that the lessons learned from this project can be applied to studying hard clams throughout the Northeast.  

Dale Parsons, one of the grower partners on this project, has applied for further funding through a SARE farmer grant, to study the microalgae in these growing areas to add further data to the discussion.  

Research conclusions:

Not available yet. 

Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Zach Gordon, Regional Aquaculture Liaison, is jointly appointed at Milford Lab and Connecticut Sea Grant providing a unique advantage in resources and the network to disseminate study results effectively.  As an aquaculture extension agent, Zach’s mission is to provide information to stakeholders to support economically, environmentally, and socially sustainable aquaculture.  The findings from this study will help the roughly 30 hard clam farming operations in New Jersey make decisions about the future of their farms. Zach will coordinate with Sea Grant extension colleagues in New Jersey, as well as Kira Dacanay of NJDEP Bureau of Shellfisheries, to present relevant information at the monthly meetings of the New Jersey Shellfisheries Council either virtually or in person.  Data and results will be shared openly to any industry members that express interest.  We are aware that hard clam producers across the Northeast are experiencing similar declines in production, and so presentations will also be given to the extended regional northeast community. We aim to host a workshop for producers and scientists at the Milford Aquaculture Seminar and Northeast Aquaculture Conference and Exposition. Offered material will include study findings and will emphasize the importance of stakeholder engagement to applied research, including the collaborative and iterative process that led to this project and outcomes. To disseminate results to a more national audience we plan to publish our findings in peer-reviewed journals and aim to provide OpenAccess to improve accessibility to industry. Lastly, we will work with the Milford Lab’s communications specialist, Kristen Jabanoski to develop a public facing project webpage and to regularly disseminate research highlights through NOAA’s and NJDEP’s web and social media platforms, the National Shellfisheries Association newsletter, and the East Coast Shellfish Growers Association newsletter

Project Outcomes

1 Grant applied for that built upon this project
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.