The Marine Mammal Laboratories' California Current Ecosystem Program (AFSC/NOAA) in collaboration with Point Blue Conservation Science initiated long-term studies to determine pup abundance of the California Stock of northern fur seals. The California Stock is comprised of northern fur seals inhabiting San Miguel Island (and Castle Rock, and islet ~1 km northwest) and the Farallon Islands (specifically, Southeast Island) off California. Pup production is the sum of the numbers of live pups and dead pups for a given pupping season. This in turn is used as index to estimate total population abundance. Population abundance is vital to knowing the status of a particular stock or the entire species, as well as knowing what factors are driving population trends. Metadata and datasets corresponding to these studies are reported in Stock Assessment Reports (SAR) for the U.S. Congress and other stakeholders.

The NEFSC has been conducting aerial surveys of gray seal pupping colonies since 2005 to monitor the number of pups born in U.S. waters. Surveys are flown from either a Cessna 252, Cessna Skymaster, or NOAA Twin Otter at altitudes ranging from 180-230 meters, using hand-held or belly-mounted Canon camera systems. Surveys may also be conducted with Uncrewed Aircraft Systems (UAS) at select colonies. Ideally, surveys are flown after all pups are born and before they start leaving the colony, but in some years surveys may have been flown before or after this optimal window. Furthermore, not all colonies may have been surveyed each year due to logistics or if the site was not yet an established pupping colony. The Northeast Fisheries Science Center has been conducting aerial surveys of harbor seals since 1983 to monitor the abundance of the population in U.S. waters. Surveys are flown during the pupping season when animals are concentrated on the coast of Maine and timed to coincide with peak pupping estimated to be around the end of May. Surveys are flown from a NOAA Twin Otter at 230 meters within 2 hours of low tide using a hand-held Canon camera and fixed 300mm lens. Close to 1,000 ledges are surveyed and grouped into bay units for analysis.

Population monitoring studies of harbor seals in Glacier Bay National Park, Alaska, have spanned five decades from the 1970’s to the present (Streveler 1979; Calambokidis et al. 1987; Mathews & Pendleton 2006; Womble al. 2010; Womble et al. 2020; Womble et al. 2021), representing one of just a few sites in in Alaska where such long-term monitoring effort exists. Monitoring methods for harbor seals at terrestrial sites have remained consistent since 1992 allowing for quantifying distribution, abundance, and trend of harbor seals in Glacier Bay National Park. This file includes data includes count data of harbor seals from digital photographs collected during aerial photographic surveys conducted in Glacier Bay National Park & Preserve in southeastern Alaska to assess the distribution, abundance, and trend of harbor seals at terrestrial and glacier ice sites (McBride Inlet and Tarr Inlet) from 2004 to 2023. Aerial photographic surveys were conducted from May-September, with most surveys occurring during May-June (pupping period) and July-September (molting period). Replicate aerial surveys (2-4 surveys during pupping and molting period) were conducted to increase precision in the trend estimates of harbor seals. If it was not possible to complete at least 4 replicate surveys on different days during one tidal cycle, then surveys were attempted during the second low tidal cycle of the month, weather permitting. From 2004-2025 this project was led by Jamie N. Womble (National Park Service), please contact Jamie if you have questions regarding these data, at jamienwombleak@gmail.com. Please see associated publications for more details. Womble, J.N., Williams, P.J., McNabb, R., Prakash, A., Gens, R., Sedinger, B. and Acevedo, C. (2021). Harbor Seals as Sentinels of Ice Dynamics in Tidewater Glacier Fjords. Frontiers in Marine Science, 8, pp.1-16. https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.634541/full Blanchet, M.A., Vincent, C., Womble, J., Steingass, S. and Desportes, G., (2021). Harbour Seals: Population Structure, Status, and Threats in a Rapidly Changing Environment. In Oceans (Vol. 2, No. 1, pp. 41-63).https://www.mdpi.com/2673-1924/2/1/3 Womble, J.N., Ver Hoef, J.M, Mathews, E.A., Gende, S.M. (2020). Calibrating and adjusting counts of harbor seals in a tidewater glacier fjord to estimate abundance and trends 1992-2017. Ecosphere 11(4), p.e03111. https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.3111 Womble, J.N. 2012. Foraging ecology, diving behavior, and migration patterns of harbor seals (Phoca vitulina richardii) from a glacial fjord in Alaska in relation to prey availability and oceanographic features. Ph.D. Dissertation. Oregon State University, Corvallis, Oregon. Blundell, G.M., Womble, J.N., Pendleton, G.W., Karpovich, S.A., Gende, S.M., Herreman, J.K. (2011) Use of glacial ice and terrestrial habitats by harbor seals in Glacier Bay, Alaska: costs and benefits. Marine Ecology Progress Series 429:277- 290. https://www.int-res.com/articles/meps_oa/m429p277.pdf Allen, S.G., Brown, E., Faulkner, K., Gende, S.M., Womble, J. N. (2011) Conserving pinnipeds in Pacific Ocean parks in response to climate change. Park Science 28:48-52. https://www.researchgate.net/profile/Jamie-Womble/publication/258407609_Conserving_pinnipeds_in_Pacific_Ocean_parks_in_response_to_climate_chnage/links/0f3175372b3ec3667c000000/Conserving-pinnipeds-in-Pacific-Ocean-parks-in-response-to-climate-chnage.pdf Womble, J.N., Pendleton, G.W., Mathews, E.A., Blundell, G.M., Bool, N.M., Gende, S.M. (2010) Harbor seal decline continues in the rapidly changing landscape of Glacier Bay National Park, Alaska, 1992-2008. Marine Mammal Science 26:686-697https://onlinelibrary.wiley.com/doi/10.1111/j.1748-7692.2009.00360.x?msockid=14da1e5b94b961b802740be595036098 Womble, J.N., Pendleton, G.W., Mathews, E.A., Gende S.M. (2015). Status and trend of harbor seals at terrestrial sites in Glacier Bay National Park from