Improving the NEFSC Bottom Trawl Survey
NEFSC and the Northeast Trawl Advisory Panel
Updated February 20, 2019
Our fisheries research surveys are crucial to understanding the overall status of commercially and recreationally important fishery stocks and predicting how the status of these stocks changes over time. At the Northeast Fisheries Science Center we value the expertise of industry and other stakeholders. We look for ways to collaborate with others to make our science better.
This is why we are active members of the Northeast Trawl Advisory Panel (NTAP), an industry advisory panel set up by the New England and Mid-Atlantic Fishery Management Councils. The panel includes commercial trawl fishermen, academic and industry gear experts, leaders of other regional surveys, state scientists, and NEFSC staff.
On this site, we are highlighting what the NEFSC is contributing to NTAP and how we are connecting NTAP's advice with our science planning, projects, and products. For more on NTAP, group meetings, and a full list of members, visit the NTAP site hosted by the Mid-Atlanic Fishery Management Council.
Northeast Trawl Advisory Panel Goals
- Understand NOAA/NEFSC trawl survey gear performance and methodology
- Evaluate ways to complement or supplement regional research surveys
- Improve understanding of NOAA/NEFSC trawl survey data quality and results
Northeast Trawl Advisory Panel Bottom Trawl Survey Working Group
A current focus area for the Northeast Trawl Advisory Panel is the NEFSC multispecies bottom trawl survey. A technical working group was formed in March 2018 to look at how the our survey trawl wingspread varies and hotw that variability affects catch rates, survey indices, and stock assessments in general. This working group was also asked to look at options for joint field research to better understand the potential effects of wingspread on catch rates. We continue to work through this group and within the larger advisory panel to evaluate and improve the survey and the use of the survey data in fisheries stock assessments.
Meet the Team
Updated February 20, 2019
To work effectively with the Northeast Trawl Advisory Panel, our science center has formed an internal team. This team works directly with the larger panel, provides a vital communication link with others in our science center, ensures we are getting the right information to the advisory panel, and takes the lead on any center activities required to put advisory panel ideas to work.
Short-Term Research Questions
Updated February 20, 2019
What is Acceptable Tolerance for Wingspread?
What Gear Configuration will Keep Wingspread within that Tolerance?
Upcoming Experiments and Field Work
2019 industry-based research platform selected:The NEFSC has contracted with Salt Pond Fisheries to charter the F/V Karen Elizabeth for 14 days to evaluate the catch efficiency differences of the standard NEFSC survey trawl at various net spreads. The F/V Karen Elizabeth has the capability to fish a twin-trawl rig, providing a great platform for gear comparison studies. The work is expected to occur in 2019.
Door Trials Henry Bigelow: In close consultation with the Northeast Trawl Advisory Panel, we set aside time during the 2018 Fall Bottom Trawl Survey to focus on achieving consistent net spread with the survey's trawl gear in shallow water, and planned to test several different trawl door types. Approximately 24 hours of testing were completed for the 66" Thyboron Type IV doors during calibration work leading up to the survey. We planned to test other door types using any sea days remaining after the survey was completed. These experiments did not occur owing to lost sea days, but will be rescheduled during a future field season.
2019 Flume tank demonstration: While the bottom trawl survey net currently in use was under development, a model of it was deployed in a flume tank at the Fisheries and Marine Institute at the Memorial University of Newfoundland. We are coordinating with the university to do that again so panel members can see how the model trawl net performs at various net spreads. We plan to observe the model at optimal spread, as well as at narrower- and wider-than-optimal spreads. We will be able directly measure the model trawl’s wingspread and headrope height. Also, observers will see what happens to the net as spread changes. Other observations may also be a focus as we discuss this project more with the NTAP. The results can inform the group’s understanding of how spread affects gear performance. In combination with the catch efficiency experiments planned on F/V Karen Elizabeth, this work can also help to better define an acceptable tolerance range for wingspread in our trawl survey tows.
Updated February 20, 2019
From 2014 to 2016 NEFSC focused on using NTAP-developed work to understand how flatfish behave around the scientific trawl gear used for the NEFSC bottom trawl survey. This experimental work translated into data and information that could then be used to determine how many groundfish in the path of the net are not captured and how that should be accounted for in stock aassessments.
Measuring Efficiency: The Twin Trawl Experiments
Three twin trawl studies have been conducted aboard the F/V Karen Elizabeth since 2015 to test how well the NEFSC research survey trawl captures flatfish. Two trawl nets were fished as closely together as possible through the same body of fish at the same time. Both trawls used NEFSC bottom trawl survey nets, one with the 16-inch rockhopper sweep as used in the survey and the other modified by replacing the rockhopper sweep with a chain sweep. The chain-sweep net was designed to ensure it captured as many fish as possible, and was considered 100% efficient at catching everything in the net's path. The catch in the rockhopper net was compared to the catch in the chain sweep net, and the rockhopper net was assigned a relative efficiency.
The first twin trawl experiment was in 2015 targeting yellowtail flounder, the next in 2016 targeting winter flounder and American plaice, and the third in 2017 targeted summer flounder, with red hake and winter flounder as secondary targets. A considerable amount of data was also gathered for other groundfish species, and used to inform assessments for winter flounder, windowpane flounder, and skates.
Applying Experimental Results
Understanding stock assessment model accuracy
In 2017, assessments for 19 Northeast groundish stocks were updated. Results of the 2015 and 2016 catchability experiments were used as a tool to check the accuracy of the bottom trawl survey biomass estimates for flatfish species in general, while specific approaches were developed for Georges Bank yellowtail flounder and witch flounder.
Setting catch advice when models are not enough
Sometimes modeling does not provide a clear enough picture of stock status to develop catch advice so alternative methods must be agreed. The results of the efficiency experiments have been used in several of these situations when the only measure available is an index of NEFSC bottom trawl survey catch per trawl haul over time. The estimates of trawl catchability for Gulf of Maine winter flounder, witch flounder, and Georges Bank yellowtail flounder were used to develop catch advice provided to managers.
Direct input to an assessment model
During the 2018 summer flounder assessment, results from the experimental work aboard the Karen Elizabeth were used within the assessment to convert data from the survey into a population estimate.
Papers and Reports
Quantifying NEFCS Trawl Survey Gear Efficiency
- Working Paper: Effect of trawl wingspread on Bigelow survey index
- Working Paper: Relative efficiency of chain and rockhopper sweeps used on NEFSC survey, and chain-sweep based, swept-area biomass estimates for 11 flatfish stocks
- Working Paper: Effect of variable wing spread on NEFSC bottom trawl survey index estimates for summer flounder