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Annual California Sea Otter Census: 2015 Spring Census Summary

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Publication Date


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,


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 [...]

Child Items (3)


Principal Investigator :
M. Tim Tinker
Distributor :
U.S. Geological Survey - ScienceBase
Metadata Contact :
William M Perry
USGS Mission Area :
SDC Data Owner :
Western Ecological Research Center


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


Spatial Services

ScienceBase WMS


  • USGS Data Release Products
  • USGS Western Ecological Research Center



Data source
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Additional Information


Type Scheme Key
doi unknown doi:10.5066/F7F47M5C

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