Photographic Data Collection
In the summers of 2019 and 2020, we captured 2267 photos across seven
haul-out sites around Casco Bay, Maine, U.S.A. (Seal Rock, Wilson Cove,
Brandt Ledges, Mitchell Fields, Branning Ledge, Whaleboat, and Bustin’s
Ledge; see Figure 1 ). During a single visit to each site, we
took photos for 30 minutes to one hour from a 22-foot Eastern motorboat
equipped with a 90-horsepower engine, an open deck, and a low-profile
console. All site visits occurred in the summer (moulting season) of
each year, with exact dates dependent on weather and tides, as some of
the sites are inaccessible at high tide. We used a Nikon COOLPIX P1000
digital camera with a 125x optical zoom, 16MP backside illuminated CMOS
sensor, built-in NIKKOR lens, 35mm equivalent focal length range of
24–3000mm, and a 250x Dynamic Fine digital zoom which gives the user an
equivalent focal length of 6000mm. The camera is also equipped with
Nikon’s Dual Detect Optical Vibration Reduction, which provides 5 stops
of optical image stabilization to ensure clear telephoto shots. We
photographed at a minimum distance of 54.9 m (60 yards) from haul-out
sites with the engine in low throttle or off to create minimal
disturbance to the seals. We took multiple photographs of each
individual seal as the boat drifted past the site. For this preliminary
study, we processed a total of 415 images in 2019 and 1114 images in
2020 across the seven locations in Casco Bay (Table 1 ).