Improvement and demonstration of subtidal cage culture methods to cultivate oysters in Delaware Bay, New Jersey

Project Overview

Project Type: Farmer
Funds awarded in 2012: $14,910.00
Projected End Date: 12/31/2012
Region: Northeast
State: New Jersey
Project Leader:
Elder Point Oyster Company

Annual Reports


  • Animals: shellfish


  • Animal Production: general animal production
  • Production Systems: holistic management

    Proposal summary:

    The eastern oyster, Crassostrea virginica, is a commercially and ecologically important species in the Delaware Bay. However, the Bay’s oyster fishery has declined with current harvests representing less than 10% of peak harvest levels. This decline is largely attributed to the emergence of two oyster diseases that have caused significant losses of the resource. Oyster aquaculture has been emerging as a viable industry in estuaries and coastal waters along the eastern U.S.. In New Jersey, the development of intensive oyster culture has been slow and limited to the intertidal areas of the lower Delaware Bay, where rack and bag culture methods have been used to grow selectively bred disease resistant oysters. The increasing availability of disease resistant oyster seed creates an opportunity for sustainable and profitable aquaculture to occur in the face of disease. In 2010, a small group of oysterman began evaluating the production potential of subtidal cage culture of disease resistant oyster stocks as a means to revitalize production on the largely abandoned leased planting grounds of Delaware Bay. Our trial evaluation produced promising results. This project will improve handling and husbandry methods of oysters and further demonstrate the tremendous potential of cage-culture as a means to increase Delaware Bay oyster production to spur the economic growth of struggling Bayshore communities and promote the sustainability of the Delaware Bay oyster resource, and its many economic and ecological benefits.

    Project objectives from proposal:

    The purpose of this project is to improve cage-oyster culture technologies and methodologies to minimize handling costs and enhance profitability of subtidal oyster aquaculture on leased bottoms of the Delaware Bay. Specifically this project will:

    1. Evaluate the production of oysters grown in two types of cage systems (1) tiered rack and bag and (2) stacked flip top.
    2. Examine fouling and ease of handling of the two types of cage systems.
    3. Optimize husbandry practices to maximize production and minimize labor costs.
    4. Modify vessel gear to improve handling of cage culture systems.

    Task 1. Preparation of cage systems and vessel modifications. Two types of oyster cages will be evaluated in this project. The first type, which was used in prior trials, is a three tiered-rack that accommodates 3 bags. Each bag has the capacity to hold 750 seed oysters to 250 market-sized oysters during the course of oyster grow-out. This design has the benefit of accommodating bags with different mesh sizes allowing the farmer to adjust the mesh size as oysters grow. However, the racks can tip due to the narrowness of structure, additionally we believe that the increased surface area provided by both rack and bag may increase fouling and decrease water circulation thereby reducing oyster growth rates. The second cage type will be purchased as a kit from Ketchum Traps ( The kits will be used to construct 3’ x 4’ interlocking vinyl covered steel mesh trays. These cages have a top lid that opens allowing for easy access to oysters within the cage and negate the need for handling bags. These larger trays also have a larger mesh size, so they will not accommodate smaller seed oysters; however, we anticipate that they will make handling submarket oysters more efficient and allow for faster growth rates than the bag and 3-tier cage system. In order to deploy and retrieve the broader flip top tray, I will need to modify my vessel via the addition of a new boom. Cage construction will occur in April 2012 with the project leader and crew being responsible for these tasks. The boom will be manufactured and installed by a local company.

    Task 2. Deployment of oyster cages. One hundred thousand ½”and 1½” oyster seed will be obtained from Atlantic Capes Fisheries (ACF) in early May 2012. ACF will purchase the disease resistant seed from Rutgers University’s NJ Aquaculture Innovation Center. If available, triploid oysters will be used.

    Small seed oysters (up to ½”) will be placed in 3/8th” mesh bags at approximately 750 oysters per bag. The bags will be placed in the 3-tier cages. Larger seed will be placed in either 7/8th” bags in a 3-tiered cage or in the larger flip top cage at density of 500 oysters per bag, or 1000 oysters per larger cage. Fifty of each of the two types of cages will be deployed in early May 2012. The cages will be deployed in the Maurice River Cove area on NJ Shellfish Lease C190 and C-193.

    Task 3. Cage maintenance. The oyster cages will be assigned to one of two husbandry routines—either biweekly, or monthly cleaning. On each assigned cleaning date the cages will be hoisted on board the vessel, fouling will be scored on a subsample of trays as indicated below, and the cages and oysters will be cleaned using high-pressure hoses. Bag densities will be split as oysters grow to maintain a standardized bag density of approximately 8-10 liters. Bags will be changed as needed and oysters will be culled into three groups including: (1) boxes (dead oysters), (2) smalls/submarkets, and (3) markets (>2 3/4th”). Bushel volumes of each will be recorded and subsamples will be collected for later evaluation of number per bushel and size. These measures will be used to estimate large overall production yields. Market oysters will be harvested and removed from the cage stock; submarket oysters will be redeployed.

    Labor times associated with handling each cage and husbandry method will be recorded. Maintenance tasks will be conducted by Project Leader, Barney Hollinger; project partner, Bill Riggin II, and two hourly crew members. Maintenance will occur throughout the grow out season May through November 2012. Following the grow out season the remaining submarket oysters will be moved to intertidal grow out areas in the lower Bay where overwintering success has been demonstrated in previous years.

    Task 4. Scientific assessments. A separate set of 16 cages (representing four replicates for each of two cage types and two husbandry regimes) will be specifically marked for a more rigorous scientific assessment of oyster mortality, growth, disease, and yield as described below in “How you will measure your results”. These cages will be established with 11/2” seed in early May. Maintenance will occur following the assigned husbandry regime (biweekly or monthly) and scientific assessments will be made in July and September 2012. The project team specified above will accomplish this task with guidance and assistance from the project technical advisor, Lisa Calvo, Rutgers University. Assessments will be conducted on separate days from normal production handling. Ms. Calvo will be responsible for the analysis of the scientific data.

    Task 5. A report and outreach materials will be prepared during the period of December 2012-February 2013. Outreach activities will occur during this same period and into March 2013 at regional and National meetings.

    The project design allows the evaluation of four production regimes (treatments) including: 2 cage types and 2 husbandry routines (Cage 1-biweekly, Cage 1-monthly, Cage 2-biweekly, Cage 2-monthly). Fouling will be qualitatively scored according to a simple scale developed in collaboration with Rutgers University scientists. On each tending date an assessment of fouling will be made on 5 cages of each type/routine. Treatment regimes will be designated at the initiation of the deployment by buoy type. Time needed to clean and work over the cage systems will be recorded in terms of vessel days, and man-hours.

    Oyster production in the four treatments will be evaluated in July 2012 and September 2012. Four replicate trays for each treatment (Cage 1-biweekly, Cage 1-monthly, Cage 2-biweekly, Cage 2-monthly) will be established for evaluation purposes. The evaluation trays will be handled similarly as the production trays; however, live market and dead oysters will only be culled out on assessment dates. Measurements will include: Dermo disease prevalence and intensity (on sample of 20 oysters), volumes of live and dead oysters, counts of dead oysters, and counts of an 8 L subsample of live oysters. Growth, as indicated by shell height will be measured on 25 individuals per treatment replicate. Rutgers University scientists will assist in evaluating the data using appropriate statistical analyses.

    The farmer will document yield tracked as number of oysters to market through time for all production trays.

    Project Outcomes
    1. The project will allow us to enhance husbandry routines by determining what frequency is needed to offer the best benefit in terms of production and labor costs.
    2. The project will enable us to assess production yield.
    3. The project will enable us to better understand oyster mortality losses and the causes of the mortality.
    4. The project will enable us to determine which cage type offers more efficient handling and conditions for better oyster growth.
    5. The project will enable us to modify existing vessel gear to facilitate handling of aquaculture cages.
    6. The project will allow us to demonstrate subtidal cage culture as a viable means to produce oysters on the leased grounds of the Delaware Bay.

    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.