Northeast Multispecies Bottom Trawl Survey

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What We Survey

The Multispecies Bottom Trawl Survey covers a range of bottom habitats from the Scotian Shelf off the coast of Nova Scotia, Canada, to Cape Lookout, North Carolina. It is a shelf-wide, multi-season, annual survey conducted in the spring and fall to monitor the Northwest Atlantic continental shelf ecosystem. The survey samples bottom-dwelling or demersal fish and invertebrate species abundance and distribution, as well as collecting oceanographic and acoustic data.

We collect data to monitor trends in:

• Relative abundance
• Spatial distribution
• Recruitment
• Maturity
• Growth
• Species diversity
• Disease
• Life history

Why We Survey

The survey collects fish, acoustic, and oceanographic data that provide critical inputs to regional stock assessments for more than 40 species. These species are managed by the New England and Mid-Atlantic Fishery Management Councils and the Atlantic States Marine Fisheries Commission. Our survey provides basic ecological data on fish, including age, maturity, growth rates and food habits.

This information is critical to understanding the relationship between fish and their environment. Data from this survey helps us:

• Conduct stock assessments to sustainably manage living marine resources
• Inform fishery management decisions
• Better understand the life history and population dynamics of commercially important species
• Monitor and predict how ocean conditions may impact and shift species distributions
• Increase long-term economic and social benefits derived from fishing
• Ensure a safe and sustainable supply of seafood
• Protect essential fish habitat
• Conduct ecosystem assessments that help us understand oceanographic and environmental change
• Provide biological samples and taxonomic reference specimens for museums and academic partners

The Bottom Trawl Survey supports the requirements outlined in the Magnuson–Stevens Act, Marine Mammal Protection Act, Endangered Species Act, and other related laws and policies.

How We Survey

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The Autumn Multispecies Bottom Trawl Survey time series began in 1963. A spring survey season was added in 1968. The spring and the fall seasons have remained consistent throughout the timeseries—with an additional winter flatfish survey conducted for a subset of years.

Survey seasons consist of 60 days at sea, across three roughly 20-day legs. Originally, the survey was conducted on the NOAA Ship Albatross IV. In 2009, the survey transitioned to the NOAA Ship Henry B. Bigelow and its sister ship NOAA Ship Pisces. To ensure the timeseries would be maintained with this transition, in 2008, researchers conducted an extensive calibration study to evaluate catchabilities and estimate calibration coefficients between the Albatross and Bigelow survey protocols.

Sampling Methods

The Multispecies Bottom Trawl Survey uses a stratified random sampling design. Scientists divide the survey area into strata by depth contours, ranging from 30 to 1,200 feet. Survey stations are then randomly selected within each strata. A standard tow is 20 minutes long at 3 knots speed over ground—equating to approximately 1 nautical mile in distance. Tows begin when the trawl first touches the bottom—as indicated by trawl net sensors—and end when the winches are reengaged at haul back.

At each trawl station, we collect:

• Oceanographic data via vertical CTD casts
• Weights of all species encountered
• Lengths of finfish and most invertebrate species

At a subset of stations, we collect:

• Ichthyoplankton samples via oblique bongo tow
• eDNA samples that are filtered with a Smith-Root eDNA sampler

Survey Protocols for the NOAA Ship Henry B. Bigelow 

Survey Gear and Technology:

Survey tows are conducted using a standardized 3-bridle, 4-seam bottom trawl rigged with a rockhopper sweep. Net mensuration sensors are mounted on the doors, net wings, and headrope to measure the trawl net geometry and bottom contact. The sensors provide a live feed of the trawl and door position, orientation, bottom contact, speed over ground, water speed through the net, and the temperature and depth. This real-time data allows scientists to constantly monitor the net performance as it fishes to ensure its standardized operation as a scientific instrument.

The Multispecies Bottom Trawl Survey uses an autotrawl system during all trawling operations to automatically equilibrate tension in the towing warps. This improves and further standardizes gear performance.

We deploy CTDs at all trawl stations and complete an oblique bongo tow at a subset of those predetermined stations. Throughout the survey, several sounders continuously record multi-frequency acoustic data for active acoustic surveying of fish stocks, and to provide detailed bathymetric mapping.

Deployment and Retrieval:

Scientific bottom trawling relies on precise vessel control and gear management to collect marine life from the ocean floor. The process begins at the stern of the ship, where the trawl net is streamed into the water. Crew members transfer the trawl wires from the net reel to heavy trawl doors, which act as wings to keep the mouth of the net spread wide and on the bottom. Using winches, the wires are unspooled to lower the doors and the attached net down to the seafloor. Throughout this descent, the vessel maintains a steady speed to ensure the doors remain upright and the net stays fully open as it makes contact with the seafloor.

Once deployed, the vessel spends 20 minutes trawling along the ocean floor to gather a representative sample of local marine species. At the end of the sampling period, the winches haul the doors back to the ship, lifting the net off the seafloor and up through the water column. After securing the doors on board, the crew transfers the main wires back to the net reel, pulling the net up the stern ramp and onto the deck.

The catch is released directly into a holding deck area—called a checker pen—from the rear section of the net. Conveyors then transport the organisms from the checker pen into the vessel's onboard laboratory, where research scientists immediately sort, identify, and process the sample by species.

Data Collection

Measuring and Weighing the Catch

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Once researchers sort the catch by species. Digital fish boards and scales are used to collect total species weights for each species caught. Non-commercially viable invertebrates (e.g., sea stars, sea urchins, sea mice), plant matter, and animal remains are weighed in aggregate. We record the length of each fish and commercially important invertebrate species, and obtain individual weights on a subset of species.

Each year, on average, scientists on the Multispecies Bottom Trawl Survey collect 275,000 individual lengths and 26,000 individual weights. We take further samples from some species to collect detailed biological data and specimens for NOAA Fisheries scientists and external partners.

Biological Samples

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We collect biological samples for use in research studies and stock assessments. Biological samples can include:

• Otoliths (fish ear bones)
• Individual weights
• Sex
• Maturity status
• Gonad samples
• Stomach contents
• Stomach volume
• Organ weights (e.g. livers, gonads, ovaries
• G+Fin clips
• Whole fish

We also apply tags and collect data from tagged fish. Occasionally, we transfer and maintain fish in a live well for researchers and aquarium exhibits.

Due to the large footprint of the survey and its purpose-built platform, the Survey presents a unique opportunity to collect large quantities of data and sample species that would otherwise be underrepresented in research.

Oceanographic Data

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Oceanographic sampling includes a CTD cast at all trawl stations. We collect instrument profiles of temperature, salinity, dissolved oxygen, chlorophyll fluorescence, and photosynthetically active radiation. At a subset of predetermined stations, oblique plankton tows allow for the estimation of zooplankton and ichthyoplankton abundance by taxon.

Plankton tow data is a vital source of information for assessments utilizing an egg index, such as Atlantic mackerel.

Environmental and Bathymetry Data

We continuously collect environmental data during survey operations, including surface dissolved pCO₂ (how much carbon dioxide is present in seawater), temperature, conductivity, pH, air temperature, wind speed and direction, and barometric pressure. We also conduct active acoustic sampling, which includes continuously recorded multi-frequency data collected across several sounders.

Additional Sampling Projects

We conduct eDNA sampling at a subset of survey stations. Water samples are collected via a Niskin bottle on the CTD rosette. These water samples are filtered and preserved for laboratory analysis of DNA markers via a Smith-Root eDNA sampler. Pairing eDNA with trawl catch records presents a unique opportunity to validate some species detected in the eDNA samples.

We have also piloted ocean acidification sample collections on the survey by collecting water from the surface, mid-depth, and 5 meters from the seafloor, using the rosette on the CTD. The samples are then fixed to preserve the pH and then analyzed onshore.

Processing Subsamples for Age and Growth

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We collect subsamples for age and growth research including fish ear stones, called otoliths. Each year, on average, scientists on the Bottom Trawl Survey collect 18,500 otoliths to be aged from more than 20 species—including haddock, summer flounder, black sea bass, and many more. Knowing the age distribution of a fish population helps to better monitor, assess, and manage stocks for long-term benefits.

More information about age and growth research in the Northeast 

View a list of the species collected for age and growth studies in the Northeast 

Habitat Data Collection

Habitat data typically includes materials like shells, substrate, plant matter, animal remains, and non-commercially viable invertebrates. We collect the total weight of these materials encountered during the trawl and record notes on the composition.

Sample Requests

Sometimes collaborators, partners, or other research scientists have special sample requests. When we receive a request, we collect the samples and store or preserve them following the requestor’s protocols. Once ashore, we arrange for sample pick-up or delivery.

Use this form to submit sample requests

Samples are accepted through January 1 for the spring survey and July 1 for fall surveys.

Other Subsampling Efforts and Partnerships

• NOAA Fisheries National Systematics Laboratory
• Population Dynamics in the Northeast

Data Use

Following completion of each survey season, we audit all data to confirm data conforms to survey data standards. The data we collect during this survey provide scientifically rigorous information and are used in a variety of ways, including:

• Research track working groups
• Stock assessments
• Commercial fishing catch limits
• NOAA Institutional Repository resources
• Scientific research and publications
• Resource Survey Reports

Access Our Data

Our trawl survey data are available through NOAA Fisheries InPort Library and by request. To request data, please contact Catherine Foley. We request that any use of this data is cited as:

"Bottom Trawl Surveys." InPort, NOAA Fisheries / Northeast Fisheries Science Center, www.fisheries.noaa.gov/inport/item/22557.

Survey Summaries

2026

• 2026 Spring Bottom Trawl Survey Completed in Northeast

2025

• 2025 Fall Bottom Trawl Survey Completed in Northeast
• 2025 Spring Bottom Trawl Survey Completed in Northeast

2024

• 2024 Fall Bottom Trawl Survey Completed in Northeast
• 2024 Northeast Spring Bottom Trawl Survey Summary

2023

• 2023 Fall Bottom Trawl Survey Completed in Northeast
• 2023 Northeast Spring Bottom Trawl Survey Summary

Who’s Involved

Chief Scientists

• Catherine Foley
• John Galbraith
• Dominique St. Amand
• Peter Chase

Partners

• Northeast Trawl Advisory Panel (NTAP)
• National Systematics Laboratory

Contacts

• Catherine Foley

Which Ships

• NOAA Ship Henry B. Bigelow
• NOAA Ship Pisces