The spring 2009 sea otter count began on 4 May. There were unusually strong and persistent northwest winds – even for spring time along the central California coast – during the first 2 weeks of the survey. This was followed by a 3-week period of light winds and mild seas (also unusual). The ground counted sections of the survey were completed by 21 May, but the aerial portions - which could not be completed during the initial 2 weeks of the survey when the plane was reserved - were not finished until 11 June. Overall viewing conditions for this survey, 2.0, were less favorable than those during the spring 2008 survey (2.4, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). Macrocystis surface canopies were noted by many of the sea otter counters to be uncharacteristically dense and abundant for this time of year. The survey boundaries remained the same as in recent years: Point San Pedro, San Mateo County in the north to Rincon Point at the Santa Barbara/Ventura County line in the south.

The total sea otter count, 2654, was 3.8% lower than the spring 2008 count (Table 1). It is important to note that these counts are uncorrected and subject to year-to-year variance due to counting conditions, sea otter distribution and other factors. Because of this variability, the U.S. Fish and Wildlife Service’s Southern Sea Otter Recovery Plan recommends using the 3-year running average as the official index for monitoring population trends, as this metric reduces the influence of anomalously high or low counts from any particular year. The current 3-year running average (2813) is slightly lower than the previous year (Table 1), indicating that the cessation of recovery reported last year has continued. Encouragingly, the 3-year average in the number of pups counted is up slightly from last year. Overall, trends are suggestive of a population that is stable or slightly declining (Figure 1).

While the cessation of growth in the overall population is somewhat worrisome, it is important to recognize that there is a great deal of variation in trends and abundance within the mainland range. Local population trends (measured as the 5-year exponential rate of growth) are generally positive at the northern and southern portions of the range, but close to zero or slightly negative throughout the center portion the range (between Santa Cruz and Pismo Beach; Figure 2). The range center also supports higher sea otter densities, with the highest densities occurring around Monterey peninsula, the Big Sur coast down to Cambria, and Morro Bay south to Pismo Beach (Figure 3). Most of these high density areas correspond to female-dominated reproductive areas, as indicated by high ratios of pups to adults (Figure 4); in contrast, areas with a pup ratio close to zero (north of Pigeon Pt., Monterey Bay, south of Pt. Sur, Estero Bay, Pt. Sal to Pt. Arguello, and southeast of Pt. Conception) correspond to male-dominated regions.

Data on sea otter abundance, population dynamics and pup production are summarized in tabular form for 14 segments of the California coastline (Table 2). This year’s survey showed declines in the number of independent sea otters counted in 10 of these 14 coastal segments, including all 6 segments comprising the central portion of the range (Figure 5a). In contrast, increases in the number of pups were seen in 11 of the 14 coastal segments compared to spring 2008. Although no pups were seen in the two segments that encompass the extreme ends of the range, there were record numbers of pups seen in both segments adjacent to these (Figure 5b). Fewer independent sea otters were counted at the extreme ends of the range, southeast of Point Conception (-40) and north of Pigeon Point (-28), while the area with the largest increase compared to the previous year’s count (+64) was Estero Bay (Cayucos to Hazard Canyon). Complementary data from studies of radio-tagged sea otters (USGS, unpublished data) indicate that many males move regularly between male-dominated regions such as Pt. Conception and Estero Bay; thus, the decrease in numbers at the former area and the increase in numbers at the latter area may simply reflect redistribution of males between the two areas.

While fewer animals were counted at the extreme ends of the sea otter’s range along the mainland coast, the recognized range boundaries (Figure 6) remain the same as last year given the official definition of the range limits as “the points farthest from the range center (to the north and south) at which 5 or more otters are counted within a 10km contiguous stretch of coastline (as measured along the 10m bathymetric contour) during the two most recent spring censuses, or at which these same criteria were met in the previous year”. However, if the number and distribution of sea otters counted next spring are similar to those counted this year, the range limits will contract.

Further data summaries, in both tabular and GIS format, are available at the USGS-WERC web site: California Sea Otter Surveys. This survey is a cooperative effort between USGS-BRD-Western Ecological Research Center, CDFG–Marine Wildlife Veterinary Care and Research Center, Monterey Bay Aquarium and many experienced and dedicated volunteers, including those with the Point Lobos Natural History Association. Assistance was also received from staff of the U.S. Fish and Wildlife Service and the U.S. Minerals Management Service.