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Alaska Ecosystems Program

2007 Steller Sea Lion Survey Results

Figure 1, see caption
Figure 1.  Percentage of Steller sea lion sites surveyed and regional trends (percentage change between 2004 and 2007) determined from the 2007 nonpup Steller sea lion counts.

In conjunction with the ship-based Steller sea lion pup survey (see article in the July-September 2007 AFSC Quarterly Report), an aerial survey to assess trends in numbers of western stock adult and juvenile (nonpup) Steller sea lions in Alaska was conducted from 9 June to 6 July 2007. The objective was to photograph all terrestrial rookery and haul-out sites from Cape St. Elias (145W) to Attu Island (172E) (Fig. 1), using both medium format (5-inch film) and simultaneous digital, vertically-oriented photography with forward motion compensation. However, due to poor weather conditions and required aircraft maintenance, the survey was incomplete-covering 65 of the 87 trend sites from the 1970s and 124 of the 161 trend sites from the 1990s. As a result of this incomplete survey and the limited 2006 survey (see article in the July-September 2006 AFSC Quarterly Report), abundance trends are not available for the entire stock of western Steller sea lion nonpups. However, some western stock regions were completely surveyed, allowing for evaluation of regional trends (Fig. 1).

Trends of nonpup sea lion counts from 2004 and 2007 varied regionally. Summarizing from east to west, the 2007 count in the eastern Gulf of Alaska was 264 lower (-8%); counts in the central Gulf of Alaska, western Gulf of Alaska, and eastern Aleutians increased by 540 (13%), 431 (8%), and 163 (3%), respectively; and counts in the eastern portion of the central Aleutian Islands region declined by 858 or -20% (Fig. 1). Because most of the sites in the western part of the central Aleutians and in the western Aleutians were not photographed, trends in those regions are not reported. However, counts in 2004 and 2006 suggest that the western Steller sea lion population between Amchitka Pass and Attu Island continued to decline.

Despite the missing counts at some trend sites, available data indicate that the size of the adult and juvenile portion of the western Steller sea lion population throughout the majority of its range (Cape St. Elias to Tanaga Island: 145-178W) has remained largely unchanged between 2004 (n = 23,107) and 2007 (n = 23,118). More detailed results of the 2007 survey can be found in the NOAA Memorandum online at

By Jeremy Sterling and Lowell Fritz

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