Annual California Sea Otter Census - 2015 Spring Census Summary
shapefiles and report included (see child items)
Dates
Publication Date
2015-09-17
Citation
Tinker, M.T., and Hatfield, B.B., 2015, Southwest U.S. Southern sea otter annual range-wide census results: U.S. Geological Survey data release, http://dx.doi.org/10.5066/F7F47M5C.
Summary
The spring 2015 mainland sea otter count began on 2 May and wasn’t completed until 2 July. The delay in finishing the census was due primarily to limited availability of the survey plane (because of the need for the plane during the oil spill in the Refugio State Beach area). Overall viewing conditions this year were more favorable than those during the 2014 spring census (View Score = 2.6 vs. 2.3, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). The surface canopies of kelp (Macrocystis sp.) were considered by most participants to be about normal for this time of year. Sea otters along the mainland were surveyed (using a combination of ground-based and aerial-based surveys) from Pillar Point in San Mateo County [...]
Summary
The spring 2015 mainland sea otter count began on 2 May and wasn’t completed until 2 July.
The delay in finishing the census was due primarily to limited availability of the survey plane
(because of the need for the plane during the oil spill in the Refugio State Beach area). Overall
viewing conditions this year were more favorable than those during the 2014 spring census (View
Score = 2.6 vs. 2.3, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). The surface
canopies of kelp (Macrocystis sp.) were considered by most participants to be about normal for this
time of year. Sea otters along the mainland were surveyed (using a combination of ground-based and
aerial-based surveys) from Pillar Point in San Mateo County in the north, to Rincon Point in the
south at the Santa Barbara/Ventura County line.
A separate ground-based survey of the sea otter population at San Nicolas Island was completed
earlier (April 17-April 20). Surface kelp canopies at the time of survey were estimated to be below
normal and survey viewing conditions were fair to good (View Score = 1.5). The population of sea
otters at San Nicolas Island, the most remote of the Channel Islands in southern California, is the
result of a translocation effort in 1987–1990 and remains geographically
distinct from the mainland range; however, this population is no longer classified as an
experimental population, and beginning in 2013 the San Nicolas counts have been added to the
counts for the mainland range to arrive at a California-wide index of abundance.
Detailed results from the annual survey are provided in the attached summary report.
The range-wide census is conducted to monitor trends in abundance of the southern sea otter, and thus provide State and Federal resource agencies with the information they need for effective management. Because the censuses represent uncorrected total counts (rather than sample-based surveys), they cannot be considered as accurate estimates of true population abundance. Instead, these data represent a valuable time-series of index counts, and provide the means of assessing spatial and temporal trends in relative abundance. The 3-year running average of the spring counts have been identified as the best index of trends and status of the population, because these averages decrease the influence of year-to-year sampling variance. The 3-year average counts are used by the U.S. Fish and Wildlife Service as a primary basis for management decisions (including de-listing or up-listing decisions) for this sub-species, which is listed as "Threatened" under the U.S. Endangered Species Act
