Gulf of Maine Bottom Longline Survey
Our Gulf of Maine Bottom Longline Survey collects data on species that prefer rocky habitats—a habitat not efficiently sampled with trawl gear used in bottom trawl surveys
What We Survey
The Cooperative Gulf of Maine Bottom Longline Survey is conducted in the western and central Gulf of Maine. We work with our region’s commercial fishing community to collect fisheries data in rocky bottom habitats that complements data collected on our annual bottom trawl surveys. Rocky habitats are a challenge to sample with trawl survey gear. Our Bottom Longline Survey addresses that concern by using gear more likely to capture species that prefer rough-bottom habitat in the Gulf of Maine.
The survey provides data on commercially and recreationally important fish species as well as critical information about data-poor species.
Data-poor species include:
- Cusk (Brosme brosme)
- Atlantic wolffish (Anarhichas lupus)
- Thorny skate (Amblyraja radiata)
- Atlantic halibut (Hippoglossus hippoglossus)
Why We Survey
Our survey provides a more complete picture of the abundance, distribution, and biology of commercially and recreationally important fish that live in rocky habitats. Longlines are good at sampling for fish in rocky areas, increasing the data available to study these populations. As a result, stock assessments are more robust and fishery managers have better information to go on when crafting fishing regulations.
By working with fishermen to develop and execute this survey, we hope to build trust in the data produced.
How We Survey
We started the bottom longline survey in 2014. It runs annually in the spring (April to May) and again in the late fall (October to November). On average, each survey takes between 18 and 24 days to complete. The nature of this survey, and its offshore location, mean that bad weather can affect survey duration.
Our survey targets rocky habitat in the western and central Gulf of Maine. To ensure that our survey data complements data collected during our bottom trawl surveys, we sample in the same areas in that part of the Gulf and use the same methods for selecting sampling stations within each area. We sample at 38 rough-bottom stations and seven smooth-bottom stations each season. This results in station density comparable to that of our bottom trawl surveys, but weighted to sample more stations in structured habitat.
We work with captains and crew of the F/V Tenacious II and the F/V Mary Elizabeth to collect survey data, relying on their expertise to fish longline gear efficiently and consistently. During a survey, both vessels operate at the same time, with each vessel responsible for half of the survey stations. To complete the survey, we typically take three to six trips, each lasting 1 to 4 days.
For this survey, we use tub-trawl bottom longline gear. This consists of four 1,500-foot-long sections, called “bundles,” that are tied together to create a single longline string, or “set,” that is about 6,000 feet long. That length is consistent with the length of a standard bottom trawl survey tow distance of 1 nautical mile (6,076 feet).
Each bundle has 250 hooks. Prior to sailing, we bait each hook with frozen squid. Then we flake each pre-baited bundle into individual plastic tubs. “Flaking” means we coil the bundle into the tub so it can be pulled out rapidly with little risk of kinking, twisting, or knotting. Right before deployment, we tie the four bundles together and attach a buoy system at both ends. Our captains and crew manage this whole process.
Deployment and Retrieval
Longline sets are weighted at both ends with anchors to keep them in contact with the bottom of the ocean. They’re deployed 1 hour prior to the start of slack tide from the stern of the vessel. The captains deploy the gear along a targeted bottom type, making sure to stay within the required depth and station boundaries. They fish, or “soak,” the gear for 2 hours. When the soak time is complete, we retrieve the gear using the vessel’s hydraulic hauler. As the hauler reels in the longline, the captain removes fish from the longline’s hooks and the crew sorts them by species into baskets for further data collection and processing by the scientists.
Water and Current Data
The anchors at each end of the longline have depth and temperature sensors attached to them. We also collect water current data using a tilt sensor developed specifically for our longline gear. These current meters document the speed and motion of water to give us a measure of water current “strength” and orientation relative to the gear.
Video Habitat Assessment
To assess and classify rocky habitat, we’ve created a camera system consisting of a weighted cage outfitted with two dive lights and a GoPro camera that takes high-definition video. We deploy our camera system within 0.125 to 0.25 nautical miles of our longline sets, at the full range of depths sampled by the survey, up to 295 meters. On average we record video for 10 minutes at each station.
Catch Lengths and Weights
Using digital fish boards and scales, we measure and record lengths for each fish and aggregate species weights for all the catch. Once length and weight data are collected, we process some fish further to extract detailed biological samples.
Biological samples including otoliths (fish ear bones), individual weights, maturity status, gonad samples, and even whole fish are collected for use in research studies and stock assessments. We have also tagged fish or sampled them for genetic studies conducted by collaborating scientists. This survey presents a unique opportunity to collect more detailed samples for data-poor species that are not encountered as frequently by other surveys.
We continually make improvements to our data collection systems and catch processing at sea. We developed a tablet-based application to record station data, catch data, and biological samples. Our system has digital scales, electronic fish measuring boards, and barcode scanners wirelessly communicating with the tablets. This keeps the system compact and agile for use on small commercial fishing vessels.
Electronic Monitoring Technologies
Onboard the survey vessels, we use electronic monitoring equipment to collect data on the proportion of hooks that are still baited when the gear is retrieved. These data are critical in the development of new models that use hook availability to estimate species abundance, and that will support stock and ecosystem assessments into the future.
Cameras placed onboard the partner vessels capture footage of the survey's longlines while they are being retrieved from the water and pulled over the hauler. A video reviewer then watches every haul and records what came up on each hook. The proportions of baited, empty, or fish-occupied hooks are used to examine hook availability and catch rates. Non-fish catch, such as invertebrates or shells, may provide clues to the habitat and community structures that the species composition in the area into context.
We use data to develop indices of abundance for stock assessments. Data from this survey also inform stock assessments through contributions to age, maturity, and condition records, and inform science recommendations to fishery managers.
Access Our Data
- F/V Tenacious II and F/V Mary Elizabeth)
- Anderson Cabot Center for Ocean Life
- Greater Atlantic Regional Fisheries Office
- University of Massachusetts Boston
- University of Maine Orono
- University of Florida (Naylor Lab)
- Teem Fish
- University of Massachusetts Dartmouth