Annual California Sea Otter Census-1985-2014 Spring Census Summary
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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 percent 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
本数据集收录了1985年至2014年加州海獭年度调查的存档记录。调查工作于「春季调查」期间开展，通常始于4月下旬或5月初，多在5月下旬至6月上旬结束，但受天气条件影响可能延长至7月初。年度调查以调查年份为单位组织，每一年均包含三类地理信息系统（Geographic Information System, GIS）形状文件（shapefile）：南部海獭普查汇总数据、南部海獭超范围计数数据以及南部海獭分布范围数据。 本项调查由美国地质调查局（U.S. Geological Survey）、加州鱼类与野生动物局（California Department of Fish and Wildlife）、美国鱼类与野生动物局（U.S. Fish and Wildlife Service）以及蒙特雷湾水族馆（Monterey Bay Aquarium）的科研人员联合开展，并得到经验丰富的志愿者协助，调查范围覆盖加州海岸约375英里，从半月湾（Half Moon Bay）向南延伸至圣巴巴拉（Santa Barbara）。 所收集的信息可供联邦与州级野生动物管理机构用于制定该受威胁海洋哺乳动物的管理决策。结合多项更深入的研究结果，这些数据还可用于评估加州海獭种群的雌性繁殖率以及繁殖成功率随时间的变化情况。如需了解更多加州海獭年度调查的相关信息，包括最新调查项目、配套数据及对应的美国地质调查局数据系列报告，请访问：https://www.sciencebase.gov/catalog/item/5601b6dae4b03bc34f5445ec 「南部海獭普查汇总数据」（Census summary of southern sea otter）地理信息系统形状文件（shapefile）基于春季全范围普查采集的数据，为分析南部海獭（*Enhydra lutris nereis*）的种群丰度空间格局与人口统计趋势提供了标准化工具。该普查每年均采用统一方法开展，结合了地面计数与航空计数两种方式。这项全范围普查是州与联邦管理机构评估种群趋势的核心依据。该形状文件包含一系列从原始普查数据衍生的汇总统计量，包括海獭栖息地密度（每平方公里栖息地内的海獭数量）、线性密度（每公里海岸线内的海獭数量）、幼崽相对丰度（幼崽与独立个体的比例）以及5年种群趋势（以指数变化率计算）。所有统计量均针对小块栖息地分区计算并可视化，以展示加州海獭整个本土分布范围内各项统计量的局部差异。 加州海獭的栖息地被认定为从平均低潮线向海延伸至60米等深线的区域：根据无线电标记海獭的潜水深度数据（Tinker等，2006、2007），该深度范围覆盖了99%以上的海獭觅食潜水活动。加州本土范围内的海獭分布被认为是沿加州海岸延伸的潜在栖息地带，其南北边界由以下范围限值定义：「在最近两次春季普查中，于10公里连续海岸线段（沿10米等深线测量）内记录到5只及以上海獭的、距离种群中心最远的点位；或在前一年度满足该标准的点位」。根据该范围定义生成的多边形被进一步划分为宽度约500米的近岸/远岸条带，条带边界对应ATOS（As-The-Otter-Swims，随海獭游动路径）点位——这些点位为沿加州近海经平滑处理的5英寻等深线（线要素）每隔约500米设置的任意参考位置。 「南部海獭超范围计数数据」（Extra limit counts of southern sea otters）地理信息系统形状文件（shapefile）为点要素图层，代表在加州本土官方认定的海獭分布范围之外记录到的海獭目击点位。这些数据采集于春季全范围普查期间。如前所述，加州本土海獭分布范围为沿加州海岸延伸的潜在栖息地带，其南北边界按上述标准定义。不过，偶尔会有个别海獭（几乎均为雄性）出现在官方认定的分布范围之外，普查过程中也会对这些「超范围个体」进行计数。 「南部海獭分布范围数据」（Range extent of southern sea otters）地理信息系统形状文件（shapefile）为简单线要素，基于春季全范围普查采集的数据，代表加州本土范围内南部海獭的地理分布范围。2011年春季调查因天气条件影响未能完成全部工作；1992年春季调查未记录到任何超范围海獭目击事件，因此该年度无「超范围计数数据」及对应形状文件。 为便于获取，本数据集还提供了1985年至2014年普查汇总数据的额外逗号分隔值（Comma-Separated Values, CSV）文件：「AnnualCaliforniaSeaOtter_Census_summary_1985_2014.csv」 参考文献： 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
