Census summary of southern sea otter 2016

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.

本GIS形状文件（GIS shapefile）"Census summary of southern sea otter 2016"是一款标准化工具，用于基于2016年春季全分布范围普查采集的数据，分析南部海獭（Enhydra lutris nereis）的种群丰度空间格局与种群动态趋势。自1982年起，美国地质调查局（USGS）每年开展两次全分布范围海獭普查，分别于5月和10月进行，采用统一的地面计数与航空计数相结合的调查方法。春季普查的结果被认为比秋季普查更为精准，是州级与联邦管理机构评估种群动态趋势的核心依据。本形状文件包含一系列从原始普查数据衍生而来的汇总统计指标，具体包括海獭种群密度（每平方公里栖息地内的海獭数量）、线性密度（每公里海岸线范围内的海獭数量）、幼崽相对丰度（幼崽与独立个体的数量比）以及5年种群趋势（以指数变化率计算得出）。所有统计指标均针对小块栖息地单元进行计算与可视化呈现，用以展示2016年时加州海獭整个大陆分布范围内各指标的局域变异情况。海獭栖息地被划定为从平均低潮线向海延伸至60米等深线的海域：基于无线电标记海獭的潜水深度数据（Tinker et al 2006, 2007），该深度范围覆盖了99%以上的海獭觅食潜水活动。加州海獭的大陆分布范围被认为是沿加州海岸延伸的潜在栖息地带，其南北边界由如下分布极限定义：在最近两次春季普查中，或在前一年满足相同标准的前提下，距离分布中心最远的、在10公里连续海岸线范围内（沿10米等深线测量）统计到5只及以上海獭的点位。对应上述分布范围定义的多边形要素随后被划分为宽度约500米的近岸条带与远岸条带。这些条带之间的边界对应ATOS（As-The-Otter-Swims，海獭游动路径）点位，即沿加州近海经过平滑处理的5英寻等深线（线要素）每隔约500米设置的任意点位。