The spring 2018 mainland sea otter count began on April 26, and was completed by May 24, 2018. Overall viewing conditions this year were good and rounded off to the same conditions experienced during the 2017 spring census (View Score 2.4, 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 above normal for this time of year in most areas of the mainland range, and considerably above what was encountered during the 2017 spring census. Sea otters along the mainland coast were surveyed 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 in the spring (April 13–15) under fair to good survey viewing conditions (View Score = 1.5). Surface kelp canopies at San Nicolas Island were estimated to be near the seasonal normal. These data support the following U.S. Geological Survey Data Series:

The spring 2019 mainland sea otter count began on May 1 and was completed by July 9. Overall viewing conditions this year were very good, better than those encountered during the 2018 spring census (View Score = 3.0 this year compared to 2.4 last year, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). The surface canopies of kelp (predominantly Macrocystis pyrifera) were qualitatively noted by observers to be much less than the seasonal normal in the central portions of the range (from Monterey to Cayucos) and about normal near both ends of the range. Sea otters along the mainland coast were surveyed from Pigeon Point in San Mateo County in the north, to Santa Barbara Harbor in Santa Barbara County in the south. A separate, ground-based survey of the sea otter population at San Nicolas Island was completed earlier in the spring (April 19 - 23) under good-very good survey viewing conditions (View Score = 2.5). Macrocystis canopies at San Nicolas Island were estimated to be below normal for the time of year. These data support the following U.S. Geological Survey Data Series:

The spring 2019 mainland sea otter count began on May 1 and was completed by July 9. Overall viewing conditions this year were very good, better than those encountered during the 2018 spring census (View Score = 3.0 this year compared to 2.4 last year, where 0=poor, 1=fair, 2=good, 3=very good, and 4=excellent). The surface canopies of kelp (predominantly Macrocystis pyrifera) were qualitatively noted by observers to be much less than the seasonal normal in the central portions of the range (from Monterey to Cayucos) and about normal near both ends of the range. Sea otters along the mainland coast were surveyed from Pigeon Point in San Mateo County in the north, to Santa Barbara Harbor in Santa Barbara County in the south. A separate, ground-based survey of the sea otter population at San Nicolas Island was completed earlier in the spring (April 19 - 23) under good-very good survey viewing conditions (View Score = 2.5). Macrocystis canopies at San Nicolas Island were estimated to be below normal for the time of year. These data support the following U.S. Geological Survey Data Series:

The spring 2017 mainland sea otter count began on April 30, and although the shore-based counts were completed by May 12, 2017, the aerial counts were not completed until July 12, 2017. Overall viewing conditions this year were good, although not as good as conditions experienced during the 2016 spring census (View Score 2.4 versus 3.1, 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 considerably below normal for this time of year in most areas of the mainland range. Sea otters along the mainland coast were surveyed 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 in the spring (April 21–25) under good survey viewing conditions (View Score = 2.0). Surface kelp canopies at San Nicolas were also estimated to be considerably below the seasonal norm at the time of the survey. These data support the following U.S. Geological Survey Data Series: Tinker, M.T., and Hatfield, B.B., 2017, California sea otter (Enhydra lutris nereis) census results, spring 2017: U.S. Geological Survey Data Series 1067, 9 p., https://doi.org/10.3133/ds1067.

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)

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)

The GIS shapefile Extra limit counts of southern sea otters 2019 is a point layer representing the locations of sea otter sightings that fall outside the officially recognized range of the southern sea otter (Enhydra lutris nereis) in mainland California. These data were collected during the spring 2019 range-wide census. The USGS range-wide sea otter census has been undertaken each year since 1982, using consistent methodology involving both ground-based and aerial-based counts. The spring census provides the primary basis for gauging population trends by State and Federal management agencies. 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 defined by combining independent otters within a moving window of 10-kilometer stretches of coastline (as measured along the 10-meter bathymetric contour; 20 contiguous ATOS intervals each) and taking the northern and southern ATOS values, respectively, of the northernmost and southernmost stretches in which at least five otters were counted for at least 2 consecutive spring surveys during the last 3 years. 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 Extra limit counts of southern sea otters 2019 is a point layer representing the locations of sea otter sightings that fall outside the officially recognized range of the southern sea otter (Enhydra lutris nereis) in mainland California. These data were collected during the spring 2019 range-wide census. The USGS range-wide sea otter census has been undertaken each year since 1982, using consistent methodology involving both ground-based and aerial-based counts. The spring census provides the primary basis for gauging population trends by State and Federal management agencies. 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 defined by combining independent otters within a moving window of 10-kilometer stretches of coastline (as measured along the 10-meter bathymetric contour; 20 contiguous ATOS intervals each) and taking the northern and southern ATOS values, respectively, of the northernmost and southernmost stretches in which at least five otters were counted for at least 2 consecutive spring surveys during the last 3 years. 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 "Census summary of southern sea otter 2018" 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 2018 range-wide census. The USGS spring range-wide sea otter census has been undertaken each year since 1982, using consistent methodology involving both ground-based and aerial-based counts. The spring census 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 2018). 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. 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 behavior 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

The GIS shapefile "Census summary of southern sea otter 2018" 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 2018 range-wide census. The USGS spring range-wide sea otter census has been undertaken each year since 1982, using consistent methodology involving both ground-based and aerial-based counts. The spring census 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 2018). 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. 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 behavior 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