US Navy

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Marine Species Monitoring

Haul-Out Counts and Photo-Identification of Pinnipeds in Narragansett Bay, RI

Introduction & Objectives

Harbor seal (Phoca vitulina concolor) and gray seal (Halichoerus grypus) distribution along the U.S. Atlantic coast has changed 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). This study aims to document seal presence at a haul-out site near Naval Station Newport.  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 is occurring in collaboration with Naval Facilities Engineering Command Atlantic, where biologists are performing a similar study in Chesapeake Bay, Virginia.  Together, these studies will provide valuable baseline information for the future assessment of seal movement, site fidelity and indices of relative abundance in each 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 are conducted at a haul-out site near Naval Station Newport in Narragansett Bay. The number of seals hauled out and in the water is recorded during each count throughout the season. Photographs of seals are collected between counts for photo-identification to be used to determine site fidelity 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

The initial pilot study was completed in May 2015. The haul out site near Naval Station Newport was observed on 36 days during the 2014-2015 season.  Harbor seals were observed on 24 of those days.  The maximum number of seals hauled out was 44 seals on April 16, 2015 and the average for the season was 15 seals.  Additionally, a local non-profit, Save the Bay, provided seal sighting data from 1992-2013 that includes 112 locations throughout Rhode Island waters.  That data was analyzed for historical and spatial patterns.

During the 2015-2016 field season, seals were present from November 2015 until April 2016.  Over 25 survey days, a total of 553 harbor seals were observed.  Seals were observed on 23 of the 25 (92%) survey days. Similar to the 2014-2015 season, highest counts were recorded in the months of February and March.  The highest count on March 17, 2016 was 46 seals hauled out and 3 in the water. The average number of seals observed for the season was 22. 

Preliminary photo-identification was conducted with WILD-ID analysis software (Bolger 2012).  The results confirm the presence of matches within the photo database, indicating some degree of site fidelity.  This was confirmed with visual matching of photographs.  WILD-ID may not be the best software to make population level assessments, although it can answer some questions regarding site fidelity and preference.  Currently, we are using the Extract-Compare software (Hiby, 2015) package to analyze the same photo database and compare the results.  Counts, photo-identification, data collection and analysis will continue for the 2016-2017 field season. 

Bolger, D. T., T.A. Morrison, B. Vance, D. Lee, H. Farid. (2012). A computer-assisted system for photographic mark–recapture analysis. Methods in Ecology and Evolution, 3, 813-822.

Hiby, L. (2015). Downloadable software for automated photo-id of seals. Accessed on 9/10/2015.

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