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Polar Ecosystems Program

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

The NMML Polar Ecosystems Program (PEP) conducted seasonal aerial surveys of harbor seals in southern Cook Inlet (south of Nikiski) and the Barren Islands during June, August, and October 2003 (see previous issues of the Quarterly Report). These surveys were conducted as part of a study of harbor seals in Cook Inlet under an Interagency Agreement between the Department of Interior’s Minerals Management Service (MMS) and NMFS. Photographs from the three surveys were digitized, and seals were counted in the digital images. Visual estimates of seals were recorded at sites where an accurate count could be acquired without a photograph, i.e., when small numbers of seals were present and easily distinguished from the haul-out substrate. A total of 1,124 images and 527 visual estimates were obtained during the June survey; 593 images and 651 visual estimates were obtained during the August survey; and 261 images and 921 visual estimates were obtained during the October survey.

Preliminary analysis indicates that as many as 7,021 seals were seen hauled out during one survey day in June. This maximal count occurred on the last day of the June survey (18 June 2003) and may have been influenced by an increase in the number of pups present as the pupping season progressed during the survey. In August, as many as 7,475 seals were seen hauled out during one survey day. The counts in October were much lower, with a maximal count of 1,995 seals on one day. This dramatic decline probably relates to a change in the seals’ behavior, with a decrease in haul-out time following pupping (May– June) and molting (August–September) seasons and a related increase in foraging and swimming time in winter. This preliminary summary includes only animals that were hauled out during the survey and does not correct for the proportion of seals that were at sea. Harbor seal haul-out behavior is affected by environmental conditions (e.g., weather and tidal state), time of day, and date (seals exhibit seasonal haul-out patterns related to breeding, pupping, molting, etc.). Future analyses will adjust for the effects of these environmental and temporal covariates on the number of seals hauled out.

In February, we inspected four time-lapse camera systems that had been deployed on a small islet near Aurora Lagoon in Kachemak Bay (26 km ENE of Homer, Alaska), a site commonly used by harbor seals. The four camera systems were deployed and began collecting imagery on 21 October 2003. The systems were programmed to capture one digital image every hour for 8 hours surrounding local solar noon each day (9 images per day) and were designed to function unattended for up to 6 months. Although all four cameras recorded images, each system exhibited brief interruptions in the scheduled image collection, and all stopped collecting images by 28 December 2003 (maximum operational duration of 69 days). Some images were obscured by snow or ice on the camera-housing window. A total of 1,147 useable images were captured by camera systems during this first test deployment. Currently, we are continuing to develop this new research technology by investigating ways to reduce snow cover on the housing windows and to eliminate or minimize the impact of brief interruptions to each system’s operation.

By Mike Simpkins, Peter Boveng, and Robert Montgomery

Continued Studies on Vessel Disturbance of Harbor Seals in Disenchantment Bay, Alaska

The Polar Ecosystems Program will continue studies examining the potential effects of cruiseship traffic on harbor seals hauled out on floating ice. Studies were first initiated in 2002 when shipboard observations and aerial surveys of harbor seals were undertaken in Disenchantment Bay, near Yakutat, Alaska. These studies were conducted under a cooperative agreement between the Yakutat Tlingit Tribe, the North West CruiseShip Association, and NMFS. Analyses of behavioral data have thus far shown that seals vacate ice floes with increasing frequency as cruise ships approach within 500 m. Aerial surveys suggested that the vast majority of harbor seals haul out in the western half of the bay in areas with ice cover greater than 50%. However, it is possible that ice conditions were anomalous during the latter surveys in 2002 due to the Hubbard Glacier advancing and blocking the normal tidal exchange with Russell Fjord. This unusual event combined with an unexpected decline in seal abundance during pupping (abundance peaks during pupping elsewhere) pointed to a need for a replicate of the aerial surveys. Surveys in 2004 will begin just prior to the seal pupping period (late April) and continue through mid-July. Cruiseships are scheduled to first enter Disenchantment Bay on 11 May.

Though the aerial transects will match those from the 2002 survey, new techniques will be employed to enhance the quality of imagery from which both seals and ice cover are quantified. Higher resolution imagery will allow for more detailed analyses, such as distinguishing size classes of animals (i.e., adults, juveniles, and pups). Such enhancements will be made possible by using a computer-controlled digital camera that will stream images to the hard drive at regular intervals. We also expect to eliminate technical problems (e.g., condensation and vibration) by using a DHC-2 Beaver plane equipped with a belly camera hatch as opposed to the wing-mounted video camera employed in 2002. By having the camera system housed entirely within the plane, both digital still and video imagery can be collected simultaneously as a fail-safe backup and to allow for comparisons. Data on the locations of cruiseships will be collected using remote-operated cameras currently being installed by the Yakutat Tlingit Tribe as a means to monitor vessel traffic in Disenchantment Bay. In addition to these changes, surveys of harbor seals will be expanded to Icy Bay, a nearby glacial fjord that cruiseships have–until now–only rarely visited. Icy Bay surveys will serve as a control and, thus, provide for valuable comparisons with Disenchantment Bay particularly relating to seasonal fluctuations in abundance.

By John Jansen and Shawn Dahle

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