Annual California Sea Otter Census - 1985-2014 Spring Census Summary

Dates

Publication Date: 2018-01-12
Start Date: 1985
End Date: 2014

Citation

Tinker, M.T., and Hatfield, B.B., 2018, Annual California sea otter census—1985-2014 spring census summary: U.S. Geological Survey data release, https://doi.org/10.5066/F7445JQ5.

Summary

This dataset represents an archived record of annual California sea otter surveys from 1985-2014. Survey procedures involve counting animals during the "spring survey" -- generally beginning in late April or early May and usually ending in late May early June but may extend into early July, depending on weather conditions. Annual surveys are organized by survey year and within each year, three shapefiles are included: census summary of southern sea otter, extra limit counts of southern sea otter, and range extent of southern sea otter. The surveys, conducted cooperatively by scientists of the U.S. Geological Survey, California Department of Fish and Wildlife, U.S. Fish and Wildlife Service and Monterey Bay Aquarium with the help of [...]

Summary

This dataset represents an archived record of annual California sea otter surveys from 1985-2014. Survey procedures involve counting animals during the "spring survey" -- generally beginning in late April or early May and usually ending in late May early June but may extend into early July, depending on weather conditions. Annual surveys are organized by survey year and within each year, three shapefiles are included: census summary of southern sea otter, extra limit counts of southern sea otter, and range extent of southern sea otter. The surveys, conducted cooperatively by scientists of the U.S. Geological Survey, California Department of Fish and Wildlife, U.S. Fish and Wildlife Service and Monterey Bay Aquarium with the help of experienced volunteers, cover about 375 miles of California coast, from Half Moon Bay south to Santa Barbara. The information gathered may be used by federal and state wildlife agencies in making decisions about the management of this threatened marine mammal. These data, in conjunction with findings from several more in-depth studies, may also provide the necessary information to assess female reproductive rates and changes in reproductive success of the California sea otter population through time.

For more information on annual California sea otter surveys, including most current surveys and associated data and corresponding USGS Data Series reports, go to: https://www.sciencebase.gov/catalog/item/5601b6dae4b03bc34f5445ec

The GIS shapefile "Census summary of southern sea otter" provides a standardized tool for examining spatial patterns in abundance and demographic trends of the southern sea otter (Enhydra lutris nereis), based on data collected during the spring range-wide census. This census has been undertaken each year using consistent methodology involving both ground-based and aerial-based counts. This range-wide census provides the primary basis for gauging population trends by State and Federal management agencies. This shapefile includes a series of summary statistics derived from the raw census data, including sea otter density (otters per square km of habitat), linear density (otters per km of coastline), relative pup abundance (ratio of pups to independent animals) and 5-year population trend (calculated as exponential rate of change). All statistics are calculated and plotted for small sections of habitat in order to illustrate local variation in these statistics across the entire mainland distribution of sea otters in California. Sea otter habitat is considered to extend offshore from the mean low tide line and out to the 60m isobath: this depth range includes over 99% of sea otter feeding dives, based on dive-depth data from radio tagged sea otters (Tinker et al. 2006, 2007). Sea otter distribution in California (the mainland range) is considered to comprise this band of potential habitat stretching along the coast of California, and bounded to the north and south by range limits defined as "the points farthest from the range center 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". The polygon corresponding to the range definition was then sub-divided into onshore/offshore strips roughly 500 meters in width. The boundaries between these strips correspond to ATOS (As-The-Otter-Swims) points, which are arbitrary locations established approximately every 500 meters along a smoothed 5 fathom bathymetric contour (line) offshore of the State of California.

The GIS shapefile "Extra limit counts of southern sea otters" is a point layer representing the locations of sea otter sightings that fall outside the officially recognized range of the southern sea otter in mainland California. These data were collected during the spring range-wide census. Sea otter distribution in California (the mainland range) is considered to comprise a band of potential habitat stretching along the coast of California, and bounded to the north and south by range limits as defined above. However, a few individual sea otters (almost always males) can frequently be found outside this officially recognized range, and these "extra-limital" animals are also counted during the census.

The GIS shapefile "Range extent of southern sea otters" is a simple polyline representing the geographic distribution of the southern sea otter in mainland California, based on data collected during the spring range-wide census.

The spring 2011 survey was incomplete due to weather conditions and there were no “extra-limital” sightings of otters during the spring 1992 survey, hence no data or shapefile for “Extra limit counts 1992.”

For ease of access, an additional CSV file of the census summary from 1985-2014 is provided: "AnnualCaliforniaSeaOtter_Census_summary_1985_2014.csv"

References:
Tinker, M. T., Doak, D. F., Estes, J. A., Hatfield, B. B., Staedler, M. M. and Bodkin, J. L. (2006), INCORPORATING DIVERSE DATA AND REALISTIC COMPLEXITY INTO DEMOGRAPHIC ESTIMATION PROCEDURES FOR SEA OTTERS. Ecological Applications, 16: 2293–2312, https://doi.org/10.1890/1051-0761(2006)016[2293:IDDARC]2.0.CO;2
Tinker, M. T. , D. P. Costa , J. A. Estes , and N. Wieringa . 2007. Individual dietary specialization and dive behaviour in the California sea otter: using archival time–depth data to detect alternative foraging strategies. Deep Sea Research II 54: 330–342, https://doi.org/10.1016/j.dsr2.2006.11.012

Contacts

Point of Contact :: U.S. Geological Survey, Western Ecological Research Center
Originator :: M. Tim Tinker, Brian B. Hatfield
Metadata Contact :: U.S. Geological Survey, Western Ecological Research Center
Distributor :: U.S. Geological Survey - ScienceBase
USGS Mission Area :: Ecosystems
SDC Data Owner :: Western Ecological Research Center

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SeaOtterCensus_1985_2014_Summary.xml Original FGDC Metadata	View	33.86 KB	application/fgdc+xml
Spring1985_SeaOtterCensus.zip		560.49 KB	application/zip
Spring1986_SeaOtterCensus.zip		552.6 KB	application/zip
Spring1987_SeaOtterCensus.zip		542.04 KB	application/zip
Spring1988_SeaOtterCensus.zip		573.35 KB	application/zip
Spring1989_SeaOtterCensus.zip		590.99 KB	application/zip
Spring1990_SeaOtterCensus.zip		604.17 KB	application/zip
Spring1991_SeaOtterCensus.zip		649.82 KB	application/zip
Spring1992_SeaOtterCensus.zip		648.83 KB	application/zip
Spring1993_SeaOtterCensus.zip		653.14 KB	application/zip
Spring1994_SeaOtterCensus.zip		652.84 KB	application/zip
Spring1995_SeaOtterCensus.zip		653.57 KB	application/zip
Spring1996_SeaOtterCensus.zip		654.38 KB	application/zip
Spring1997_SeaOtterCensus.zip		654.77 KB	application/zip
Spring1998_SeaOtterCensus.zip		654.61 KB	application/zip
Spring1999_SeaOtterCensus.zip		763.44 KB	application/zip
Spring2000_SeaOtterCensus.zip		765.53 KB	application/zip
Spring2001_SeaOtterCensus.zip		764.89 KB	application/zip
Spring2002_SeaOtterCensus.zip		724.24 KB	application/zip
Spring2003_SeaOtterCensus.zip		709.68 KB	application/zip
Spring2004_SeaOtterCensus.zip		718.07 KB	application/zip
Spring2005_SeaOtterCensus.zip		725.47 KB	application/zip
Spring2006_SeaOtterCensus.zip		725.13 KB	application/zip
Spring2007_SeaOtterCensus.zip		740.57 KB	application/zip
Spring2008_SeaOtterCensus.zip		817.15 KB	application/zip
Spring2009_SeaOtterCensus.zip		824.31 KB	application/zip
Spring2010_SeaOtterCensus.zip		746.46 KB	application/zip
Spring2012_SeaOtterCensus.zip		742.86 KB	application/zip
Spring2013_SeaOtterCensus.zip		736.22 KB	application/zip
Spring2014_SeaOtterCensus.zip		740.08 KB	application/zip
AnnualCaliforniaSeaOtter_Census_summary_1985_2014.csv		11.44 MB	text/csv

Purpose

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 US Fish and Wildlife Service in its listing determinations (de-listing or up-listing) for this legally threatened population.

Annual California Sea Otter Census - 1985-2014 Spring Census Summary

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