Biological and Economic Optimization of Shell Size and Timing for Sea Scallop (Placopecten magellanicus) Ear-hanging in the Northeast U.S.

Progress report for ONE21-384

Project Type: Partnership
Funds awarded in 2021: $21,190.00
Projected End Date: 03/01/2023
Grant Recipient: University of Maine
Region: Northeast
State: Maine
Project Leader:
Dr. Damian Brady
University of Maine
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Project Information

Project Objectives:

This project seeks to explore two primary objectives: 1) what is the optimal scallop size range and the timing of drilling that maximizes scallop growth and minimizes mortality on ear-hanging lines, and 2) how do the scallop grader and the parameters deduced from objective 1 impact cost of ear-hanging production? Under objective 1, we will determine the effects of initial size and the timing of deployment on scallop growth and mortality. Under objective 2, we will quantify the impact of size grading, timing, and the subsequent scallop growth and mortality on cost of production. We plan to collect labor, operating, and capital costs over the course of the ear-hanging period (April - June) in addition to scallop growth and mortality information. These data will help growers and researchers identify production bottlenecks, better manage inventory, plan seasonal ear-hanging tasks, weigh the benefits of the practice against next best alternatives (net culture), and identify future research needs. There is a general consensus that ear-hanging improves growth. However, we contextualize the growth benefits with respect to cost of production.


The Atlantic Sea Scallop, Placopecten magellanicus, supports the 4th most valuable fishery in the U.S. (National Marine Fisheries Service, 2020a). Despite this success, the U.S. imports an almost equal amount of various scallop products, generating a substantial trade imbalance (Hale Group, Ltd, 2016; National Marine Fisheries Service, 2020b). In Maine, scallop landings consistently fetch high market prices (ME DMR, 2020; National Marine Fisheries Service, 2020b). Consumer preferences for Maine seafood, coupled with the freshness of the "day boat" scallop (landed daily and never frozen), have driven these price premiums (Coastal Enterprises, Inc., 2019). Therefore, given the strong demand, as evidenced by a significant trade imbalance and premium for Maine scallops, the U.S. market is primed for a domestically aquacultured product that is landed daily and available to consumers year round. 


Despite these suitable conditions, development of Maine's scallop aquaculture industry has been limited. As of 2021, the Maine Department of Marine Resources (DMR) is unable to collect adequate scallop aquaculture harvest data to report on annual landings. This is not due to lack of interest; there are currently 193 aquaculture leases in Maine that list scallops as an approved species (ME DMR, 2021), representing substantial potential. Rather, high capital and labor costs have stifled the sector (Coleman et al., unpublished). The majority of growers use cylindrical, tiered lantern nets to culture scallops. This method requires a prolonged culture period (3+ years) with frequent net cleanings and stocking density reductions, as scallops are severely sensitive to space limitations (Coleman et al., 2021; Côté et al., 1993; Parsons & Dadswell, 1992). Our proposed plan of work explores a solution to mitigate the space, growth, and labor issues associated with net culture. Ear-hanging, suspending individual scallops vertically in the water column from plastic "tags'', eliminates the need to handle nets over the grow-out process. Rather, scallops are pinned to vertical lines after ~12 months of growth and left to mature for another 1 - 2 years. The proposed project is directly focused on optimizing the ear-hanging method within a new environment (Maine) and for a new species (P. magellanicus). This work has the potential to directly reduce costs and increase net farm income, improve water quality (as scallops are an extractive filter feeding bivalve), enhance employment in coastal farming communities by providing well paying jobs, and improve quality of life for farmers and their employees.


We plan to assess the effects of timing and scallop size on ear-hanging success. We will use the specialized scallop grader to quantify size variation within nets on three separate dates (April, May, June), grade scallops into "small", "medium", and "large" size categories, and ear-hang experimental replicates of each size on each date. We will also record labor inputs (the time required for grading, drilling, and pinning), a critical parameter to determine cost of production for ear-hung scallops. These data will allow growers to make informed decisions regarding best husbandry practices. We will use this opportunity to weigh the benefits of ear-hanging against the associated costs.


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  • Andrew Peters - Producer


Materials and methods:

The proposed plan of work can be divided into two discrete sections, a biological and an economic component. We plan to combine the results from both sections to parameterize a bioeconomic model of scallop ear-hanging. 


1.Biological analysis of size grading and ear-hanging timing on scallop growth and mortality

We will take a nested effects approach to determine whether timing and/or size improve ear-hanging production through effects on growth and mortality. This experiment will involve two treatments. The first treatment will be the date on which the scallops are graded, drilled, and pinned to dropper lines. We plan to perform this task on three separate occasions: once each in April, May, and June. These three dates simulate when growers ear-hang early (April), a typical example (May), and a late example (June). Every month that growers must hold scallops in lantern nets prior to ear-hanging is a use of valuable time and net space. Ear-hanging "early" (April) can expedite the process and maximize grow-out time spent on ear-hanging lines. However, the process of grading, drilling, and pinning can be stressful to juvenile scallops, and allowing more time for shell growth and ear-hanging "later" (June) may lead to better survival in the long term. On each date, we will use the various screen diameters compatible with the grader to sort scallops into three distinct size classes: 38 - 48 mm (small), 49 - 59 mm (medium), and >60 mm (large). These size grades comprise the second treatment, and will allow us to test the hypothesis that larger scallops are more capable of surviving the physiologically stressful ear-hanging process. We will ear-hang 2 replicate dropper lines of each size class on each date for a total of 18 dropper lines (900 scallops total) from April - June. We will use calipers to measure the shell height of all scallops on each line (n = 50) on each date that they were ear-hung (April, May, or June) to establish initial conditions. Over the course of the following 5 months, we will measure the shell height of all experimental scallops (ear-hung on all dates) once each in August and October. We will also count the number of scallops remaining on each line, as well as dead scallops still attached to the line, to track mortality. On the final measurement date in October, we will dissect a representative sample (n=30) from each experimental treatment (date x size class) to assess final adductor muscle, gonad, and viscera (all remaining tissue) mass. 

The grader will also allow us to efficiently capture the size distribution of scallops within nets prior to ear hanging. While this is a sub-objective of the current plan of work, it will provide valuable insight that complements the main objectives. The mean shell height (the distance from the "hinge" to the furthest edge of the shell) of scallops within a net is a useful metric for growers to track growth over the course of a season. However, if we are able to observe an effect of size grade and timing on growth or mortality in our experiment, understanding the breakdown of sizes within nets will be a useful tool that can allow growers to track inventory and the availability of different size scallops at different points in the year. On each date (April, May, June), we will grade out all scallops within a representative sample of lantern nets based on the same 38 - 48 mm (small), 49 - 59 mm (medium), and >60 mm (large) size classes. The quantity of scallops within each size class will be assessed volumetrically.

We plan on utilizing a variety of statistical analyses to determine whether size grade or date will have an effect on scallop performance. We will calculate shell height specific growth rate, the percent change in shell height per day, for each replicate line based on the average shell height on each measurement date. This metric will allow us to standardize growth between scallops of different starting sizes. We will also calculate a mortality rate (% mortality per day). Finally, we will standardize the final wet weight of the various soft tissue components we measure by shell height to compare between scallops in different treatments that may vary by size. We will then use a two-way (date x size class) analysis of variance (ANOVA), to determine differences in specific growth rate, mortality, and tissue mass between experimental treatment groups. 


2. Economic analysis of ear-hanging

Based on the values obtained from the biological component of the study, the growth and mortality rates, as well as the labor and capital cost requirements over the course of the ear-hanging sessions, we plan to parameterize a bioeconomic model of scallop ear-hanging. Given that detailed information on the procedural and cost requirements of juvenile scallop culture (the first year of growth in nets) already exists (see Previous Work, Coleman et al., unpublished), the proposed work would fill in the ear-hanging specific data that is currently unavailable in the Gulf of Maine. The most important variable in the bioeconomic model will be the labor component. Specifically, we will track the quantity of scallops ear-hung over the course of the project (April - June) as a function of labor (time and personnel) under normal operations of the partner farmer's business. Normal operations in this sense exclude any time dedicated to measuring scallops or recording data. At the end of the project, we will work with Mr. Peters to sum materials costs, labor, and capital expenditures amortized over the lifespan of the equipment. We will also project growth and mortality, based on the biological component of the project, to inform final yield. Based on these inputs, our goal is to arrive at a cost of production figure (USD scallop-1) using a simple spreadsheet based financial model. This information (cost of production) is already available for net cultured scallops, and will provide a useful comparison of the two methods directly relevant to industry members. 

We will use the financial model to explore sensitivities across a range of parameters tested in the biological portion of the study. For example, if we observe a relationship between ear-hanging date and mortality, we will be able to simulate the effects of the full range of mortality rates on cost of production using the financial model. Additionally, if we deduce that the grader improves efficiencies during the ear-hanging process, we can use the financial model to quantify the magnitude of these efficiencies. We will track changes in cost of production under a variety of growth, mortality, timing (ear-hanging date), and final yield (adductor muscle wet weight) scenarios.

Research results and discussion:


The field portion of the project is slated to begin in April, 2022, as scheduled. To date, we have begun the process of sourcing the specialized scallop grader from Japan that is essential to the completion of the project. We have also started to trial the same model scallop grader (see photo and video), courtesy of Coastal Enterprises Inc., on Andrew Peter's vessel (the partner farmer). Preliminary grading sessions indicate that the equipment is compatible with all electrical sources on Andrew's vessel and is (albeit anecdotally) effective at sorting farmed scallops into various size classes. We are continuing to monitor the growth of the scallops that will be used in the upcoming ear-hanging season and await the arrival of Andrew's grader. 

Click here to watch video clip of the scallop grader.



Participation Summary
1 Farmers participating in research

Education & Outreach Activities and Participation Summary

2 Consultations
1 On-farm demonstrations
1 Workshop field days

Participation Summary:

1 Farmers participated
2 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

The ability to effectively communicate the results of this work to industry, public, and research audiences is one of the strong suits of the project team. Coleman is adapting a bioeconomic model of scallop lantern net aquaculture to be used as a budgeting tool with aquaculture business specialists at the Maine Aquaculture Association (MAA). MAA is a non-profit trade association that represents Maine Aquaculturists and provides business planning tools for both new and experienced growers. Despite the fact that interest in scallop aquaculture is rapidly growing in the Northeast U.S., little information exists to help growers project future profits and losses based on current production practices. The financial models generated from this project would not only be used as an analytical tool by the UMaine research team, but also incorporated into MAA's suite of business planning tools for new and experienced growers. 


Brady is a contributor to the Aquaculture in Shared Waters (ASW) class, a hands-on technical workshop run annually by University of Maine Sea Grant. ASW annually prepares ~ 75 fishermen and farmers to operate aquaculture businesses, exposing them to a diversity of species (seaweed, oysters, mussels, and scallops), and culture methods. The technical and financial information from this project would be readily incorporated into the ASW scallop unit, as little information currently exists regarding the efficacy of ear-hanging from a business standpoint. 


Mr. Peters is a member of the Maine Aquaculture Co-op (MAC). Coleman also attends MAC meetings and contributes scientific and research updates. The MAC hosts the majority of scallop growers in Maine. Mr. Peters and Coleman will relay the results of this information back to MAC growers. MAC members, other than Mr. Peters, have also made substantial investments in ear-hanging equipment, and the results of this study would be directly applicable to their businesses. 


Lastly, Brady and Coleman plan to publish the results of the ear-hanging bioeconomic analysis in a relevant academic journal. As mentioned above, the UMaine research team has experience formally analyzing scallop growth and mortality data and building aquaculture financial models. This work will fill a data gap that would be readily useful to managers, industry, and the academic community.


To date, we have conducted a field day and farm equipment demonstration with another scallop grower. Using the same model scallop grader that we have ordered for the project, on a short term loan from Coastal Enterprises Inc., we have conducted a "dry-run" of scallop grading with juvenile "seed". As a result of this connection, we have also coordinated with Coastal Enterprises Inc. (CEI) on the purchase of the grader.

Learning Outcomes

1 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

As a result of the field day and grader demonstration (see photos attached), we shared knowledge related to the specialized equipment with one other scallop farmer. The project has not yet started, but we intend to conduct similar outreach activities upon collection of data.

Project Outcomes

Project outcomes:

The project is slated to begin in April of 2022. We are on track for a timely start and intend to leverage our collected data for future projects, decision making, and funding. 

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.