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Alaska Ecosystems Program

Flying Beneath the Clouds at the Edge of the World: the Use of an Unmanned Aircraft System to Survey the Endangered Steller Sea Lion in Western Alaska

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Watch Stella, an unmanned aircraft system, during summer 2014 field investigations of the endangered Steller sea lion in western Alaska. Video credit NOAA Fisheries.

The National Marine Fisheries Service (NMFS) has used occupied aircraft since the 1970s to obtain aerial images of Steller sea lions hauled out throughout coastal Alaska. The subsequent counts of animals captured within those images form the basis for annual population estimates which are used by NMFS for management purposes.  The agency listed   the Steller sea lion as threatened range-wide under the Endangered Species Act in 1990. Seven years later NMFS identified two stocks in the United States and elevated the listing of the western population to endangered due to persistent drops in abundance. Continued assessment surveys indicate that the portion of this population in the western Aleutian Islands has continued to decline.

The Alaska Ecosystem Program (AEP) at the Alaska Fisheries Science Center coordinates Steller sea lion surveys to estimate abundance during the same summer time period when sea lions are hauled out at their greatest densities. Flying surveys in Alaska is not without its challenges, especially along the 1,200 miles of the Aleutian Island chain, which is serviced by only three airfields. Inclement weather such as low ceilings, fog, and high winds coupled with remote and scarce airfields have impeded the success of aerial surveys in the Aleutians both temporally and spatially. This is especially true for the westernmost part of the Aleutians, where timely surveys are critical for assessing changes in a relatively small, declining, subpopulation.  During the summer of 2012,  the AEP survey crew made it to the farthest west airfield on Shemya Island but was able to conduct survey flights only 1 of the 18 days stationed on the island due to fog and low ceilings.  Similar restrictions have prohibited surveys in the Rat Island group, just east of Shemya, since 2008-09 (see map for island locations).

refer to caption
Aerial image captured by the APH-22 hexacopter of Steller sea lion site Cape Wrangell on Attu Island from 200 feet above the animals. Inset: juvenile with a permanent brand, ~100, indicating that this male was branded in 2013 as a pup on the site, Cape Sabak on Agattu Island.

Such continual impediments to successful survey efforts prompted the AEP to look into the feasibility of unmanned aircraft systems (UAS) to survey hard-to-reach areas in the western Aleutians. The result is an APH-22 hexacopter (Aerial Imaging Solutions),  an insect-like UAS that measures 32 inches in width, 12 inches in height,  weighs only 4.5 pounds, with a high resolution digital camera mounted underneath the domed body. Biologists depend on the camera to capture high-resolution images for analysis after survey flights.

The aircraft may be tiny but it requires two skilled pilots certified by the Federal Aviation Administration to fly it: LT. Van Helker (NOAA Corps) and AEP biologist Kathryn Sweeney. While one pilot flies the aircraft using a remote radio controller, the other constantly monitors the skies for other aircraft or obstacles that could pose risks. The ground station mounted on a tripod includes a color screen streaming a live view of what the downward facing camera ‘sees,’ with the camera engaged to photograph when triggered by the pilot. Another screen provides data on battery level, altitude, distance from take-off location, and time in the air.  Nicknamed “Stella” by AEP staff, the craft can stay airborne for as long as 23 minutes and sustain flight in winds as high as 20 knots (typical for the region).  Unlike the occupied survey aircraft which flies at about 750 ft and requires access to airfields, Stella flies as low as 150 ft and is portable to survey areas by vessel.

During the 2014 Steller sea lion survey, NMFS biologists stationed on board the U.S. Fish and Wildlife Service research vessel Tiĝlâx focused efforts in the western Aleutian Islands. Simultaneously, a twin Otter aircraft (operated by NOAA Aircraft Operations Center) surveyed eastward along the Aleutian Islands. The overall objective was to obtain visual counts from land  and aerial images from both aircraft types to complete a survey throughout the entire Aleutian Island chain during late June to early July. Biologists on the Tiĝlâx  also conducted visual surveys of  permanently marked sea lions branded as pups or adults and serviced and download images from remote cameras stationed at various sea lion sites in the area.

map showing 2014 survey sites
Steller sea lion terrestrial haul-out sites successfully surveyed in the Aleutian Islands and western Gulf of Alaska during June and July 2014 by biologists from the ground, hexacopter, and occupied aircraft.

Of the 178 sites in the Aleutian Islands, 153 were successfully surveyed, making the 2014 survey the most successful survey of Steller sea lion pups and non-pups since the 1970s. The research vessel visited 23 sites in the remote western Aleutians from Attu Island to the Rat Islands where pilots flew Stella over 11 of the most populated sites, capturing more than 1,500 images. The twin Otter crew surveyed east of the Rat Islands along the Aleutians (130 sites) and well into the western Gulf of Alaska (42 sites).

Using the hexacopter to survey the 11 sites required a total of 17 flights adding up to approximately 4 hours of total flight time. This is a testament to the swift efficiency UAS technology brings to abundance surveys, especially in this area of concern which has proven so difficult to survey over the past 45 years. Stella flew over 1,589 sea lions with only one instance of disturbing just 5 animals into the water. This low (0.3%) disturbance rate is significantly less than the 5% disturbance caused by occupied aircraft, adding even greater value to the stealth that Stella provides. Biologists also examined the images captured by the UAS to identify branded animals that were missed by visual observers on the ground. This adds yet another tool to the increasing utility of UAS technology in future NMFS surveys.

Counts from the 2014 Steller sea lion survey have not yet been finalized; however, preliminary counts from the 23 remote sites surveyed by the research vessel or UAS confirm a continued decline of Steller sea lions in the western Aleutian Islands. The 2014 Steller sea lion survey report will report updated counts and abundance trends and should be available on the AFSC website in winter 2015 .

To learn more about our Steller sea lion research in Alaska, please watch the video on the NOAA Fisheries YouTube channel.

All images and fieldwork were conducted under NMFS ESA/MMPA Permit 18528.

By Kathryn Sweeney


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