US Navy


Marine Species Monitoring

Haul-Out Counts and Photo-Identification of Pinnipeds in Chesapeake Bay, Virginia

Introduction & Objectives

Harbor seal (Phoca vitulina concolor) and gray seal (Halichoerus grypus) distribution along the U.S. Atlantic coast has shifted in recent years, with an increased number of seals reported in southern New England and the mid-Atlantic region (Kenney 2014; Waring et al. 2016). Data from NOAA surveys previously recognized New Jersey as the southern extent for harbor and gray seals (NOAA 2015), though occasional sightings and strandings were reported as far south as Florida and North Carolina for harbor and gray seals, respectively (Waring et al. 2016). More recently, a small group of harbor seals (<50) has been found to haul out seasonally in the Chesapeake Bay, Virginia (Waring et al. 2016), yet there are no published survey data for seals in Virginia. The presence of gray seals and harp seals (Phoca groenlandica) has also been reported in Virginia, but there has been no systematic documentation of non-stranded animals. 

This study aims to document seal presence at select haul-out locations in the lower Chesapeake Bay, an important area to Navy training and testing activities.  In order to acquire a better understanding of the seals’ seasonal occurrence, habitat use, and haul-out patterns in this area, seasonal counts and photo identification methods are being utilized.  This study will provide valuable baseline information for the future assessment of seal movement, site fidelity and indices of relative abundance in the region.

Kenney, R. D. (2014). Marine mammals of Rhode Island, part 5, harbor seal. Accessed on 11 May 2015.

NOAA. (2015). Ecology of the Northeast U.S. Continental Shelf – Seals. Accessed on May 11, 2015.

Waring, G. T., Josephson, E., Maze-Foley, K., & Rosel, P. E. (2016). U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments - 2015. (NOAA Technical Memorandum NMFS-NE-238). Woods Hole, MA: U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service (NMFS), Northeast Fisheries Science Center. p. 501.

Technical Approach

A series of systematic, land-based counts of all seal species will be conducted at 4 haul-out locations in the lower Chesapeake Bay. The number of seals hauled out and in the water will be recorded during each count throughout the season. Photographs of seals will be collected between counts for photo-ID and a capture-recapture study (if data permits). Photographs will be used to develop a local catalog and will also be compared to regional catalogs.

Progress & Results

For the first field season of the study, 13 survey days were completed from November 2014 to May 2015. A total of 1 gray seal and 112 harbor seals were sighted among the CBBT haul-out sites. Seals were observed on all survey days except one. Highest counts were recorded in February and March (though seal counts were not conducted in January, so this result may be biased). During the 2015–2016 field season, surveys were conducted from October 2015 to May 2016. A total of 184 harbor seals and 1 gray seal were sighted from December 2015 to April 2016. Seals were observed on 15 of the 21 (71.4 percent) survey days. Similar to the first field season, highest counts were recorded in the months of February and March.

Photo-ID conducted via visual matching has shown that individuals have been resighted both within a season and across multiple seasons, indicating at least some degree of seasonal site fidelity. Of the 52 uniquely identified harbor seals, six (11.5%) were determined, to be present in the study area on more than one occasion. Identifiable re-sightings (or recaptures) for these six harbor seals spanned from five days to 1,820 days (median = 37 days). One individual was sighted on five separate surveys between December 2015 and March 2016.

Counts and photo-ID data collection have continued for the 2016–2017 field season. As of March 2017, 23 surveys have been conducted for the 2016-2017 field season. A total of 304 harbor seals have been sighted and no gray seals. Seals have been observed on 18 of the 23 (78.3 percent) survey days. So far, highest counts have been recorded in the months of January and February.