Seal Abundance Aerial Survey
Monitoring the Distribution and Abundance of Harbor Seals and Gray Seals in northeastern US waters.
What We Survey
The Northeast Fisheries Science Center monitors populations of harbor seals and gray seals, primarily throughout the waters of Maine, New Hampshire, Massachusetts, Rhode Island, and New York. We conduct surveys when seals gather in large numbers on shore, either to give birth or to molt. During surveys, we photograph seals so we can count pups, juveniles, and adults.
Why We Survey
We conduct aerial surveys of gray and harbor seal populations every 5–8 years to collect data on their numbers and distributions. We use the data to estimate the total abundance of each population, monitor mortality or serious injury events, and document how seals use coastal habitats.
These data are critical for meeting the statutory requirements of the Marine Mammal Protection Act. They also help inform Unusual Mortality Event investigations and environmental impact reports.
How We Survey
We conduct surveys from a NOAA Twin Otter or similar chartered aircraft at altitudes ranging from 590–754 feet. We use hand-held or belly-mounted camera systems to photograph seals.
To estimate gray seal abundance, we survey all known pupping colonies, ideally after all pups are born in January and before they start leaving the colony. It typically takes about 3 days to survey the colonies. We have conducted aerial surveys of gray seal pupping colonies, primarily in Maine and Massachusetts, since 1994.
We also conduct some surveys using uncrewed aircraft flown within the pilot’s line of sight at a maximum altitude of 400 feet.
Since 2016, we have conducted uncrewed aerial surveys of Muskeget, the largest grey seal pupping colony, with other collaborators. At some locations we also use uncrewed surveys to monitor for animals entangled in fishing gear or marine debris.
For harbor seals, we survey nearly 1,000 ledges along the Maine coastline during peak pupping season, which typically occurs around the end of May. Flights take place within 2 hours of low tide, and the entire survey takes approximately 2 weeks to cover all sites. We have conducted aerial surveys of harbor seals since 1981.
All research is conducted under a Marine Mammal Protection Act research permit.
Sampling Methods
The goal of each survey is to photograph all animals hauled out on land within the study area. At least two people then manually count the number of animals in each image.
For both harbor and gray seal surveys, counters tally the number of pups and non-pups in the images. We use these data to estimate the total number of seals in the population.
For some surveys, we have been evaluating software such as VIAME or other machine learning tools to automate seal counting.
Survey Gear and Technology
In 2025 and 2026, we used a new belly-mounted camera system mounted in a NOAA Twin Otter for gray seal surveys. This camera configuration, called Knowledge-based Image Acquisition ManagER and Archiver, was developed by the Polar Ecosystems Program at NOAA’s Alaska Fisheries Science Center in partnership with Kitware.
The system uses three 120-megapixel cameras and three infrared cameras to collect photographs during flight.
Researchers have also used fixed-wing, vertical takeoff and landing, and multi-rotor unmanned aircrafts to fly the gray seal surveys.
Data Collection
Data Use
Data from seal surveys support scientific products used in annual Marine Mammal Protection Act Stock Assessment Reports, Unusual Mortality Event investigations, Environmental Impact Reports, and public-facing data portals for other research investigations, which are used primarily by scientists and resource managers.
Access Our Data
Interactive maps of survey sites can be found on our Pinniped Distribution Query Tool.
Who’s Involved
NOAA Scientists
Partners
- Alaska Fisheries Science Center Marine Mammal Laboratory
- National Ocean Service Remote Sensing Division
- Oceans Unmanned
- Duke University