Introduction & Objectives

The occurrence of marine mammals in southern New England and the Mid-Atlantic has increased considerably since the early 2000s. This increase in observations of pinnipeds was first observed in stranding records. The harbor seal is widely distributed in the shallow coastal waters of the Northern Hemisphere and is commonly found along the U.S. East Coast (Maine to Virginia). Gray seals are found in coastal waters throughout the North Atlantic Ocean, often sharing habitat with harbor seals. A preliminary evaluation of movement data from tagged harbor seals collected between 2018 and 2022 (Ampela et al. 2021; DeAngelis 2023) indicate that harbor seals along the U.S. East Coast seasonally inhabit and transit through OPAREAS and could be impacted by military activities, specifically in the northwest Atlantic, as pinnipeds may be vulnerable to a variety of noise sources both nearshore and offshore. Currently, windfarms are developing rapidly along the U.S. Northwest Atlantic continental shelf. Thus, there is a pressing need to understand potential impacts to species like the harbor seal or gray seal, particularly if windfarms modify behavior or shift distribution into non-traditional areas that may overlap with Navy or other anthropogenic activities.

Most pinniped populations are monitored over wide areas of distribution which offers a broad picture of population numbers and fluctuations in distribution of a species. Site specific monitoring allows for more detailed monitoring of parameters of seal biology including abundance, social structure, activity budgets, timing of pupping, location and habitat of pupping areas, pup development and dispersal, site disturbance, etc. This type of monitoring is ideally carried out as a continuous series, leading to a better understanding of “stable” or “normal” seal behavioral parameters. For example, monitoring efforts have documented harbor seals modifying their daily and seasonal haul out patterns in response to human activity. They tend to prefer quiet, unpopulated areas and often exhibit a strong fight or flight response when disturbed (Nicholson 2000).

Technical Approach

Since 2018, the National Marine Fisheries’ (NMFS) Northeast Fisheries Science Center, the Naval Undersea Warfare Center (NUWC) Division Newport, the Atlantic Marine Conservation Society (AMSEAS), and Marine Mammals of Maine (MMoME), have partnered to capture and satellite tag harbor seals to study their movements and health status. To date, telemetry data has been collected on 23 harbor seals (2018-2022) (Table 4-1). Based on this telemetry work the movements of harbor seals overlaps with Navy Operation Areas or OPAREAS (VACAPES to the Boston OPAREAs)1, two of the Navy’s Living Marine Resources priority geographic regions in the Atlantic, and established and proposed windfarm areas. The information gained from studying harbor seal site fidelity and movement would not only provide information specific to harbor seals, but could also substitute for a lack of information for other marine species that are more difficult to research, but may also occupy similar ranges. A summary of the data collected in previous field seasons can be found in DeAngelis (2023).

The objectives of this project are to obtain data to measure baseline behavior to understand the physical or biotic factors that influence the movement and foraging tactics of harbor and gray seals; the amount of time seals spend in specific areas, particularly in Navy OPAREAS. Methods include: 1) aerial surveys to document harbor and gray seal haul outs in the Narragansett Bay OPAREA (from New York to Rhode Island); 2) ground and remote camera surveys; 3) deployment of satellite tags on harbor seals during the late fall through early spring; and, 4) analysis of satellite tag data collected from tags deployed on pinnipeds.

All work for this project is authorized under NMFS research permit # 21719.

Progress & Results

NUWCDIVNPT traveled to support a 12-day capture and tagging effort in Virginia organized the by Naval Facilities Engineering Systems Command Atlantic in February 2023, but no animals were successfully tagged. In addition, weather postponements during the remaining opportunities resulted in no harbor seals tagged in the northeast during the 2022/2023 season for this project.

Aerial surveys were conducted in January, March, and August 2023. Since harbor and gray seals appear to be leaving their natal sites in Maine earlier, an aerial survey was conducted in August to determine how soon they arrive in locations south of Maine. No harbor seals were observed at known haul out sites in any areas south of Maine during August. Gray seals were observed at certain locations, where they are known to haul out year-round; however, the total number of animals observed was considerably lower than counts conducted during peak season. On each of the aerial survey days observers were also deployed to land-based haul out sites in Narragansett Bay to conduct ground counts to then compare with counts taken from the aerial survey photographs. This offered insight into the total number of animals actually hauled out on a site versus what is visible from a land-based vantage point and the number of animals potentially missed using one survey technique versus another. Similar to previous field seasons, there were also three remote cameras set up at Naval Station Newport to monitor the harbor seal haul out located just offshore. One camera took pictures at 10-minute intervals and the two cellular-enabled cameras took motion-activated pictures.

Photos are manually reviewed to estimate the number of seals hauled out, duration of haul out, presence/absence, and note any other factors that could influence seal behavior. In-person observations were conducted primarily on the predicted low tide as that is when the maximum amount of habitat is available for haul out. We combined the in-person observations with the remote camera counts to determine peak number of animals across the field seasons. In general, harbor seal peak numbers occur in March and then begin to rapidly dwindle in April. As we have seen from the tag data, April is when harbor seals depart their southerly haul out sites to return northward to Maine for pupping, breeding, and molting. Recently windfarm construction activity has begun with an increase in boat activity transporting equipment through Narragansett Bay. Harbor seals are exhibiting an increase in vigilant behavior and frequency of flushing events. The duration of haul out appears to also have changed, but not enough data has been collected at this time to determine whether this is significant.