Annual California Sea Otter Census: 2016 Census Summary Shapefile

Dates

Publication Date: 2016-09-19
Start Date: 2016-04-17
End Date: 2016-05-11

Citation

Tinker, M.T., and Hatfield, B.B., 2016, Annual California Sea Otter Census - 2016 Spring Census Summary: U.S. Geological Survey data release, http://dx.doi.org/10.5066/F7FJ2DWJ.

Summary

The GIS shapefile "Census summary of southern sea otter 2016" 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 2016 range-wide census. The USGS range-wide sea otter census has been undertaken twice a year since 1982, once in May and once in October, using consistent methodology involving both ground-based and aerial-based counts. The spring census is considered more accurate than the fall count, and provides the primary basis for gauging population trends by State and Federal management agencies. This Shape file includes a series of summary statistics derived from the raw census data, including [...]

Summary

The GIS shapefile "Census summary of southern sea otter 2016" 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 2016 range-wide census. The USGS range-wide sea otter census has been undertaken twice a year since 1982, once in May and once in October, using consistent methodology involving both ground-based and aerial-based counts. The spring census is considered more accurate than the fall count, and provides the primary basis for gauging population trends by State and Federal management agencies. This Shape file 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 (as of 2016). 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.

Literature cited:

Tinker, M. T., D. P. Costa, A. Estes James, 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.

Tinker, M. T., J. A. Estes, K. Ralls, T. M. Williams, D. Jessup, and D. P. Costa. 2006. Population Dynamics and Biology of the California Sea Otter (Enhydra lutris nereis) at the Southern End of its Range. MMS OCS Study 2006-007. Page 253. Coastal Research Center, Marine Science Institute, University of California, Santa Barbara, California. MMS Cooperative Agreement Number 14-35-0001-31063.

These data support the following data series release: Tinker, M.T., and Hatfield, B.B., 2016, California sea otter (Enhydra lutris nereis) census results, spring 2016: U.S. Geological Survey Data Series 1018, 10 p., http://dx.doi.org/10.3133/ds1018.

Contacts

Point of Contact :: M. Tim Tinker
Originator :: M. Tim Tinker, Brian B Hatfield
metadata contact :: William M Perry
Distributor :: U.S. Geological Survey - ScienceBase

Attached Files

Attach Files

sorting

Metadata First

Recent First

Alphabetical

Click on title to download individual files attached to this item.

Shapefile: Census summary of southern sea otter 2016.zip
Census summary of southern sea otter 2016_FGDC.xml Original FGDC Metadata	View	29.77 KB
Census summary of southern sea otter 2016.CPG		5 Bytes
Census summary of southern sea otter 2016.dbf		945.52 KB
Census summary of southern sea otter 2016.prj		468 Bytes
Census summary of southern sea otter 2016.sbn		17.8 KB
Census summary of southern sea otter 2016.sbx		540 Bytes
Census summary of southern sea otter 2016.shp		646.4 KB
Census summary of southern sea otter 2016.shx		15.62 KB

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: 2016 Census Summary Shapefile

Dates

Citation

Summary

Summary

Contacts

Attached Files

Attach Files

sorting

Metadata First

Recent First

Alphabetical

Purpose

Rights

Map

Spatial Services

Communities

Tags

Provenance

Additional Information

Shapefile Extension

Item Actions

Use Item

View Item as ...

Save Item as ...

View Item...

Dates

Citation

Summary

Summary

Contacts

Attached Files Attach Files sorting Metadata First Recent First Alphabetical

Purpose

Rights

Map

Spatial Services

Communities

Tags

Provenance

Additional Information

Shapefile Extension

Item Actions

Use Item

View Item as ...

Save Item as ...

View Item...

Attached Files

Attach Files

sorting

Metadata First

Recent First

Alphabetical