Managing and Monitoring Bottom Cage Placement in Deep Water Oyster Culture

Progress report for FNE21-989

Project Type: Farmer
Funds awarded in 2021: $13,570.00
Projected End Date: 08/31/2022
Grant Recipient: Blue Stream Aquaculture LLC
Region: Northeast
State: Massachusetts
Project Leader:
Blue Stream Shellfish LLC
Expand All

Project Information

Project Objectives:

This project seeks to improve upon deploying deep water oyster cages by assisting in the placement and by developing a means to visualize the cage distribution on the bottom. To achieve this goal, we propose the following objectives:

  1. Develop a means to ensure that cages released from the surface will land on the bottom in an orientation to ensure optimal growth of the seed within. By testing two different means to maintain cage orientation as it falls, we will evaluate the efficacy of promoting an upright landing and will monitor the cost in terms of both time and expense to apply the deployment techniques. The success of the enhanced cage release, in terms of proper cage orientation, will be compared to a control of an unencumbered release of the cage from the surface.
  2. Develop a method to visualize the orientation and placement of cages on the bottom using commercially available “fish finder” technology. With the application of side-scan sonar, the farmer will observe a three-dimensional representation of the array of cages on the bottom with fine enough resolution to monitor both overall placement relative to other cages and the orientation of the cage as it lands.

This proposal addresses the USDA-SARE need for “improved productivity” leading to “an increase in net farm income”. Additionally, increasing the number of oysters in the water at any location underlines the role oysters play in mitigating nutrient additions and improving compromised marine habitat (Parker and Bricker 2020). Any advancement in oyster farming technology leading to more oyster farms addresses the USDA-SARE need of “improvement of water quality and protection of natural resources.”

Diversifying farm production is a critical strategy to enhance the success of a farm. Farm crop diversification leads to increased capacity to mitigate financial and production risks associated with market volatility/saturation and environmental changes (Lancaster and Torres, 2019). Blue Stream Aquaculture (BSA) has engaged in expanding farm production through the addition of the eastern oyster (Crassostrea virginica) to the suite of aquatic products produced by BSA.

Entering into oyster aquaculture in Massachusetts is a challenging undertaking with each town regulating its own shellfish resources. In many locales, the available space conventionally used to farm shellfish, i.e. intertidal and very shallow sub-tidal (<2 foot depth at low tide) waters is becoming fully occupied or is limited due to physical/natural resource/social constraints. Many of the opportunities to initiate an oyster farm have now moved to deeper off-shore locations, especially south of Cape Cod with limited availability of intertidal/shallow sub-tidal space (Ward 2012, CEI 2018).

Deeper locations reduce the risk of interference to crop production from an environmental problem, such as shore-side sewage or petroleum spills; from tampering by inadvertent or intentional human activities, including poaching of the crop; or from growing reticence from upland land-owners to allow farming in their viewscape or near-shore recreational areas (Cheney et al. 2010, Beckensteiner et al. 2020).

Shellfish farming in deeper waters requires a new set of technologies to farm effectively. The goal of this study is to develop new methods by adapting available technologies for deeper water farmers to manage their sites in an efficient and productive way. By providing a means for farmers to ensure that the growout cages are placed on the substrate in the proper orientation and that the cage placement efficiently uses the space available, farmers can significantly improve upon their operations in a difficult environment.

In oyster farming, seed oysters are placed in plastic mesh bags that are held in vertical stacks using metal racks or wire mesh cages, with multiple rows and columns of compartments to hold the bags. An intertidal farmer intentionally places the cages or racks in an efficient space use pattern, making sure that the bags are oriented in the correct configuration to ensure the seed are evenly dispersed in the bag and capable of adequate feeding. An off-shore farmer cannot see their gear to ensure proper placement.

One concern is the attitude of the cage on the bottom. If dropped from the surface, the cage may land in a number of different orientations other than the required upright landing on the cage runners. Upright orientation elevates the bags off the bottom reducing the risk of silt smothering the oysters. Having a properly oriented bag allows seed to spread across the internal surface of the bag, providing proper spacing for optimal feeding. Should the cage land on its side or upside down, the oyster bag is in direct contact with the bottom leading to smothering or the seed are clumped together along the edge crease in a dense assemblage rather than as a monolayer. Anything other than a cage landing upright is detrimental to oyster production. By allowing the cage to free fall from the surface, i.e. dropping cages into the water, there is no control as to how the cage lands at the bottom and no means to observe the final cage orientation.

A second concern is determining the actual placement and distribution of the cages within the site. As is true with all farming, spatial distribution of the crop is a critical factor to ensure optimal growth. Plants/cages placed too close together may reduce production of individuals. Also, random placement of plants/cages does not lead to optimal utilization of the space to maximize area production.

These two problems require two solutions and we propose to solve both. The first is to devise a means to lower cages to the bottom rapidly but with assurance that the cage will land upright. The second is to visualize the distribution of cages to ensure that the space is used optimally and that cages are not bunched where they interfere with each other.


Click linked name(s) to expand/collapse or show everyone's info
  • Joshua Reitsma - Technical Advisor
  • Dr. Arthur Trembanis


Materials and methods:

Research Plan

To address the objectives, we propose to complete the following:

Objective 1) Develop a means to ensure that cages released from the surface will land on the bottom in an upright orientation.

As a compartmented cage is dropped from the boat into deep water, it is critical that the cage lands upright on its runners when it settles on the bottom. However, given the uneven weight distribution within the cage due to initial loading of seed in the bags, coupled with the hydrodynamic forces of wind, waves and currents, a cage can easily be flipped on its side or upside down as it free falls. Once that happens, the seed in the individual bags would be jammed into the creased edge of the bag and/or buried in the silt/mud at the sediment surface. Survival and growth will be compromised, as a dense assemblage of oyster seed can rapidly become food-limited and/or smothered. Therefore, it is essential that the cage land upright where the seed can distribute as a monolayer across the flat expanse of the horizontal bag.

Once released from the surface, the farmer has no control as to the orientation of the cage as it free falls. Alternatively, they could lower each cage using a line from a winch on deck but that would take an excessive amount of extra time, significantly reducing the number of cages handled in a day. Building a mechanism into the cage to maintain the proper orientation as the cage free falls would be a great advantage. Think of it as a parachute for oyster cages. BSA proposes to evaluate a simple tool to maintain cage orientation as it falls. By attaching a buoy on a short tether to the top of the cage, it would generate buoyancy at the top, allowing the cage to hang in an upright position as it falls. The question to be answered is - what is the proper buoy size and attachment point to ensure the correct orientation?

Buoys come in a variety of sizes. We will test an array of buoys with increasing buoyancy to determine the minimum size that is effective in maintaining cage orientation during free fall. (Note, the stocked cage weighs a minimum of 80 lbs in the water.) A suite of buoys will be tested with varying degrees of buoyancy  and will include two different attachment points, either in the center of the cage top or at the four corners at the top. We will complete a minimum of 10 drops of each test condition in approximately 24 feet of water. The final orientation of the cage on the bottom will be determined with each drop and tabulated to calculate the probability that the cage will land in the proper orientation under the test conditions, based on size and buoy placement. For comparison, the control test condition is an unaltered cage dropped unencumbered.

We will monitor cage orientation on the bottom using the sonar visualization method developed in Objective 2 as well as with GoPro cameras mounted inside the cage. Two GoPros will be mounted with one pointing down towards the bottom of the cage while the second is oriented laterally towards the open side of the cage. The sonar image and the video recorded during each drop will be analyzed to determine the cage orientation upon landing.

Objective 2) Develop a method to visualize the orientation and placement of cages on the bottom using commercially available “fish finder” technology.

Being able to “see” oyster cages on the bottom is critical for farmers to expand into deeper waters. One means to observe 3-D structures on the bottom has traditionally been side-scan sonar (Savini 2011). Until recently, this technology was prohibitively expensive but, as electronic technology has advanced, side scan is becoming less costly. It now is routinely employed in electronic fish finders that are available for recreational fishermen. The resolution of the technology has also advanced such that one can identify relatively small structures, not only by their overall shape but also by the composition of the materials making up the structure, based on the sound reflecting density of the material.

BSA has worked with Art Trembanis to identify a commonly available side-scan fish finder with interpretive software and linked to an on-board GPS to visualize cages as they are deployed on the bottom. Once installed and set up, BSA will complete observations to assess the effectiveness of the electronics to visualize bottom cages. By manipulating the extent of bottom scanned, we will observe the relative positioning of multiple cages in a 10-cage grouping, as is currently planned for BSA farm operations (Leavitt 2019). As a result, we will be able to optimize space use while maintaining a high level of production. Cages can be repositioned as necessary. Following fine tuning of the instrument, BSA will provide a minimum of 20 transects to characterize the placement and orientation of 10-cage trawl lines at the farm site.

The side-scan instrument will also be used to locate, characterize and remove a debris field of abandoned shellfish aquaculture gear left on the BSA farm site by the previous owner/licensee. Following guidelines by Dr. Trembanis, we will use protocols similar to those he has developed for removing abandoned gear.

Overall evaluation of the effectiveness of this technology will be assessed in terms of ability to locate and observe individual cages as well as 10-cage arrays in 20-25 feet of water. Should the system not be able to locate individual cages (not anticipated given reported resolution), BSA will investigate placing additional materials on the cage to facilitate detection by the sonar system. Sound dense materials such as soft (pine) or hard (oak) wood bars; PVC, acrylic or UHMW plastics; or aluminum markers will be attached to the cage sides and/or top should it be necessary to augment the sonar detection capabilities.

Adapting a Humminbir

Research results and discussion:

Research Activities in 2021

The work completed to date has focused on Objective 2, where we proposed to adapt an existing technology (sidescan sonar) to the visualization of oyster cages and other materials deployed on the ocean bottom at our farm site, in 20+ feet of water depth.

This project has been awarded a no-cost extension to June 2022 due to delays in acquiring equipment and farm access issues. Because of the on-going microchip shortage, delivery of our Humminbird Solix 15 side scan fish finder was delayed until late summer. Delays in completing our proposed research were further confounded with work vessel problems encountered when we acquired a second oyster farm in August 2021. The outboard on our primary work skiff irreparably self destructed at about the time when we had completed the adaptations to the side scan to allow it to be transportable between vessels. We were able to undertake a single trial run of the side scan prior to losing the skiff and can confirm that the technology is working fine and that the end result of visualizing oysters cages on the bottom was successful. However, prior to cold weather setting in, we were not able to complete a series of transects to map the bottom of our farm site with cages in place using the SAR Hawk software designed specifically for that purpose. Therefore, we have had to delay the completion of the project until more favorable weather can be predicted at our farm sites.

A presentation on our progress to date was completed in anticipation of presenting this information at the Northeast Aquaculture Conference and Exposition, in Portland, ME, originally scheduled for early January but postponed (due to COVID) to April. While not the final version, we have attached a series of slides (as a pdf file) outlining our progress in adapting the Humminbird Solix 15 to allow it to be easily and quickly transported and set up on various work vessels. This flexibility in operation will allow the equipment to be easily tested and demonstrated to other farmers, if requested. To that end, we have already received two requests to demonstrate the equipment at farms in Maine and Rhode Island and we will follow up with these requests during the spring of 2022, as we continue to learn the intricacies of operating the system and software on the farm.

In summary and to date, the sidescan sonar apparatus has been modified to allow it to be transported between the various work platforms on the farm and has been initially tested on the farm to identify bottom cages as well as debris on the sea floor. Through the winter and spring, we will continue to test the apparatus to determine its level of resolution of bottom cage orientation as we have had issues with winter storms overturning cages on the farm. When a cage is flipped on its side, there is a high risk of losing product due to burial and crowded conditions with the aberrant orientation.

Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

1 Consultations

Participation Summary:

Education/outreach description:

NACE 2022 abstract_How do you find those oyster cages on your deep water farm

Abstract submitted for presentation at the Northeast Aquaculture Conference and Exposition to be held in Portland, ME. Originally scheduled for 12-14 January 2022, the conference has been postponed to 27-29 April 2022 due to COVID precautions.

Project Outcomes

2 Farmers changed or adopted a practice
1 Grant applied for that built upon this project
1 New working collaboration
Project outcomes:

Outcomes from activities in 2021

Meeting the first objective, to develop a buoy strategy that would allow individual cages to be dropped at the surface and land on the bottom in the correct orientation, has been postponed until the upcoming spring season due to unforeseen delays in acquiring equipment and access to the farm site.

Although still a work in progress because of a delay in receiving the sidescan instrument (due to the global microchip shortage), the application of sidescan sonar technology to our farm management (Objectve 2) has resulted in a more accurate representation of the distribution of oyster cages and other materials at our deep water farm site. We have successfully converted the sidescan into a mobile unit that allows us to temporarily and easily install the instrument on any of the four work platforms that we use on the farm. The technology has been employed to locate bottom cages that had lost their surface buoy connection as well as to adjust the cage placement on the farm to reduce the risk of gear entanglement and to optimize space use. We have also used the sidescan apparatus to monitor the amount of debris on the sea bottom that resulted from previous mismanagement of the farm site. We will use this information to facilitate clean-up of the site over the next year.

Information Products

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.