Seal Ecology and Assessment Research in the Northwest Atlantic
We study the ecology of seals in the Northwest Atlantic to support conservation management and promote public stewardship of a healthy and diverse marine environment.
There are two main species of seals that breed and forage in the U.S. Northwest Atlantic: harbor seals and gray seals. We research these seal populations to learn more about how many there are, where they live, and what they eat. This helps us understand their role in the ecosystem, and how they might be affected by factors like changing climate conditions.
As sentinels of the marine environment, seals can provide insight into the state of a changing ecosystem. One site where the Northeast Fisheries Science Center and their partners conduct research is Muskeget Island, where teams survey, capture, and sample animals to collect information on population abundance, individual animal health, diet, and behaviors.
Our seal research program focuses on harbor seal and gray seal ecology, principally in New England and Mid-Atlantic waters from Maine to Virginia. We monitor the abundance of both populations primarily using aerial photographic surveys along important haul-out sites such as beaches, sand bars, jetties, ledges, and rock piles that seals use to rest and give birth.
We conduct harbor seal abundance surveys along the coast of Maine in late May to early June to coincide with the peak pupping period. These surveys provide an index of the number of pups born and of the total population. We conduct gray seal abundance surveys during the pupping season in January at colonies in Massachusetts and Maine, with the main goal of monitoring the annual number of pups born. We also conduct seasonal surveys at other times of year along coastal waters to monitor both harbor seal and gray seal abundance and habitat use. We use both manned and uncrewed aircraft to monitor the seal populations.
Using multiple approaches to estimate diet composition improves our understanding of what seals eat and how this varies in space and time. We examine harbor seal and gray seal diets by the following methods:
- Analysis of seal fecal material collected at several haul-out sites on Cape Cod and in Nantucket Sound
- Examination of seal stomachs collected from animals accidentally killed in commercial fishing operations
- Studying fatty acids in the blubber of live or dead animals
Our staff have recently begun to experiment with using DNA in stomach contents to identify prey, and also work with research partners who study diet via stable isotopes in hair and blood. We will integrate this information into ecosystem models so we can better understand the nutritional relationships among marine species and how much seal predation contributes to natural mortality of commercially important fish stocks.
Movements and Distribution
We capture and tag harbor seals and gray seals to improve estimates of abundance and to better understand habitat use at sea and on land. Satellite tags provide information on seasonal movements throughout U.S. and Canadian waters as well as haul-out and diving behavior. In addition, longer-lasting acoustic tags provide information on the presence and survival of individual seals in particular areas. See satellite tracks of gray seal pups tagged in 2023.
We also live-capture and sample harbor and gray seals. We work closely with our academic, government, and non-government research partners to conduct captures and to collect and analyze tissue, serological, and genetic samples. From these samples we gain information on the health of the animals, presence of disease and contaminant loads in the wild population, diet, and stock structure.
Our staff analyzes annual mortality associated with incidental capture in commercial fishing gear and evaluates the potential impact of other human activities on seal populations. Serious injury and mortality estimates are incorporated into annual stock assessment reports.
Scientific staff collaborate with regional universities, non-profit research organizations,and multiple government agencies to conduct seal research in the western North Atlantic region. Our staff are also members of international scientific groups that focus on North Atlantic seals.
- The Northwest Atlantic Seal Research Consortium
- Viral Ecology of Marine Mammals
- Animal Telemetry Network
- The Marine Animal Identification Network
- International Fund for Animal Welfare Cape Cod Stranding Network
- National Marine Life Center
- Whalenet Satellite Tagging
- Provincetown Center for Coastal Studies seal programs
- Cape Cod National Seashore
- Monomoy National Wildlife Refuge
- Nantucket National Wildlife Refuge
- Massachusetts Audubon - Wellfleet Bay Wildlife Sanctuary
- The Atlantic Marine Conservation Society
- Seals and Sealing in Canada
- International Council for the Exploration of the Sea Harp and Hooded Seal Working Group
- Gray Seal Pupping Cam
- The Marine Lipids Lab, Dalhousie University
- The Ocean Tracking Network
- NOAA’s Marine Mammal Health and Stranding Response
- Marine Mammals of Maine
- Massachusetts Division of Marine Fisheries
News and Outreach
- Gray Seals: Sentinels of Our Shared Marine Habitat
- Aerial Surveys Monitor Growing Gray Seal Populations off the Northeastern United States
- Sharing Seal Space by the Seashore
- Researchers return to study gray seal pups
- White sharks and gray seals off Cape Cod
- The adventure continues on Seal Island, Maine
- Going "Sealing" from the Gloria Michelle
- NOAA's drones document gray seal pups
- Share the Shore with Seals
- 2018 U.S. Navy Marine Species Monitoring
- Marine Mammal Stock Assessment Reports
- Bycatch and Serious Injury and Mortality Reports
- Wood, S.A., E. Josephson, K. Precoda, and K.T. Murray. 2022. Gray seal (Halichoerus grypus) pupping trends and 2021 population estimates in U.S. waters. Northeast Fisheries Science Center reference document 22-14. DOI: 10.25923/9hjq-gb82
- Sigourney, D.B., K.T. Murray, J.R. Gilbert, J.M. Ver Hoef, E. Josephson, and R.A. DiGiovanni, Jr. 2021. Application of a Bayesian hierarchical model to estimate trends in Atlantic harbor seal (Phoca vitulina vitulina) abundance in Maine, U.S.A., 1993–2018. Marine Mammal Science. DOI: 10.1111/mms.12873
- Murray, K.T., J.M. Hatch, R.A. DiGiovanni Jr., and E. Josephson. 2021. Tracking young-of-the- year gray seals Halichoerus grypus to estimate fishery encounter risk. Mar. Ecol. Prog. Ser. 671:235–245.
- den Heyer, C.E., W.D. Bowen, J. Dale, J-F. Gosselin, M.O. Hammill, D.W. Johnston, S.L.C. Lang, K.T. Murray, G.B. Stenson and S.A. Wood. 2020. Contrasting trends in gray seal (Halichoerus grypus) pup production throughout the increasing northwest Atlantic metapopulation. Marine Mammal Science. DOI: 10.1111/mms.12773
- Wood, S.A., K.T. Murray, E. Josephson and J. Gilbert. 2019. Rates of increase in gray seal (Halichoerus grypus atlantica) pupping at recolonized sites in the United States, 1988-2019. Journal of Mammalogy.
- Hernandez, K.M., A.L. Bogomolni, J.H. Moxley, G.T. Waring, R.A. DiGiovanni Jr., M.O. Hammill, D.W. Johnston, L. Sette and M.J. Polito. 2019. Seasonal variability and individual consistency in gray seal (Halichoerus grypus) isotopic niches. Canadian Journal of Zoology 97(11): 1071–1077. DOI: 10.1139/cjz-2019-0032.
- Pace, R.M.III, E. Josephson, S.A. Wood, K. Murray and G. Waring (retired). 2019. Trends and patterns of seal abundance at haul-out sites in a gray seal recolonization zone. NOAA Tech Memo NMFS-NE 251; 17 p. DOI: 10.25923/qd3s-we77.
- Martins, M.C.I., L. Sette, E. Josephson, A. Bogomolni, K. Rose, S.M. Sharp, M. Neimeyer and M. Moore. 2019 Unoccupied aerial system assessment of entanglement in Northwest Atlantic gray seals (Halichoerus grypus). Marine Mammal Science 35:1613–1624. DOI: 10.1111/mms.12590
- Cammen, K.M., T.F. Schultz, W.D. Bowen, M.O. Hammill, W.B. Puryear, J. Runstadler, F.W. Wenzel, S.A. Wood and M. Kinnison. 2018. Genomic signatures of population bottleneck and recovery in Northwest Atlantic pinnipeds. Ecology and Evolution. DOI: 10.1002/ece3.4143
- Johnston, D.W., J. Dale, K.T. Murray, E. Josephson, E. Newton and S. Wood. Comparing occupied and unoccupied aircraft surveys of wildlife populations: assessing the gray seal (Halichoerus grypus) breeding colony on Muskeget Island, USA. 2017. Journal of Unmanned Vehicle Systems 5:178–191. DOI: 10.1139/juvs-2017-0012.
- Puryear, W.B., M. Keogh, N. Hill, N, J. Moxley, E. Josephson, K.R. Davis, C. Bandoro, D., Lidgard, A. Bogomolni, M. Levin, S. Lang, M. Hammill, D. Bowen, D.W. Johnston, T. Romano, G. Waring and J. Runstadler. 2016. Prevalence of influenza A virus in live-captured North Atlantic gray seals: a possible wild reservoir. Emerging Microbes and Infections 5(8):e81. DOI: 10.1038/emi.2016.77.
- Wood, S.A., T.R. Frasier, B.A. McLeod, J.R. Gilbert, B.N. White, W.D. Bowen, M.O. Hammill, G.T. Waring and S. Brault. 2011. The genetics of recolonization: an analysis of the stock structure of grey seals (Halichoerus grypus) in the northwest Atlantic. Canadian Journal of Zoology 89(6): 490–497. DOI: 10.1139/z11-012.