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Polar Ecosystems Program

Harbor Seal Surveys and Time-lapse Camera Deployments in Cook Inlet

The Polar Ecosystems Program (PEP) conducted seasonal aerial surveys of harbor seals in southern Cook Inlet (south of Nikiski) and the Barren Islands during April and June 2004. The surveys were conducted as part of a study of harbor seals in Cook Inlet, Alaska, under an Interagency Agreement between the Department of the Interior’s Minerals Management Service (MMS) and NOAA Fisheries. Counts of seals recorded in digital photographs from the two surveys are under way. In May, PEP deployed 10 time-lapse camera systems in southern Cook Inlet, expanding the coverage of a study described in previous AFSC Quarterly Reports (April-June 2003, October-December 2003, and January-March 2004). The cameras will provide hourly photographs for monitoring the numbers of harbor seals hauled out on shore throughout the year. Counts of the seals in the photographs will support a detailed investigation of factors influencing the haul-out behavior of harbor seals and will help to reduce uncertainty in estimates of population size obtained by aerial surveys.

Two of the new cameras were deployed at a seal haul-out site near Anchor Point, and eight cameras were deployed at two sites at Augustine Island. Cameras were mounted on fiberglass or wooden posts anchored by steel cable attached to earth anchors, which were driven into the dirt at each site by hand. To prevent power-related problems that occurred at the previous deployment at Aurora Rock, no more than three cameras were powered by one set of batteries. Further, the power source for each set of cameras was increased from 9V to 12V, and no two cameras were scheduled to take pictures at the same time (cameras were offset from each other by 2 minutes). All cameras were scheduled to take 19 pictures/day, providing more complete coverage of the longer summer day-length. Cameras will be returned to the “winter” schedule of 9 pictures/day when they are visited for maintenance and recovery of images in August.

By Mike Simpkins, Peter Boveng, and Robert Montgomery

Using Georeferenced Images to Study Harbor Seals on Floating Ice in a Tidewater Glacial Fjord

The Polar Ecosystems Program (PEP) completed 3 months of aerial harbor seal surveys during pupping (from May to July) in Disenchantment Bay, Alaska. These studies expand on those begun in 2002 to understand the relationships between harbor seals and the natural and anthropogenic factors of their environment including season, ice cover, and cruise ship visitation. This year, new techniques were employed that improve on previous data collection and allow for more detailed analyses.

A GPS-linked digital still camera that pointed downward from the belly of a DHC-Beaver aircraft was used as the primary means of sampling the distribution and abundance of harbor seals on floating ice. During each survey the camera recorded about 1,500 nonoverlapping images organized in 15 standard transects over ice-covered areas of Disenchantment Bay. Over the 12 weeks of the study, 21 surveys were flown on days that provided the highest contrast in ship visitation – which ranged from zero to five ships daily. Seven comparable surveys were flown in nearby Icy Bay, which reportedly is not visited by cruise ships. By using customized programs in conjunction with GIS software, images were batch processed and georeferenced to create a noncontiguous mosaic which will enable observers to “walk through” the transects, search for, and map seal groups – even individuals within groups. By analyzing high quality, still images within a GIS framework, seal detection is improved and the mapping of seal distributions is more precise and less prone to recording error than conventional video analysis (i.e., the technique used in 2002). Apart from this greater accuracy, the improved imagery will enable observers to discern size classes of seals from aerial photography and, in turn, allow testing of hypotheses relating to possible shifts in the structure of glacial fjord populations.

By John Jansen and Shawn Dahle


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