The 2019 census of southern sea otters (Enhydra lutris nereis), also known as California sea otters, was conducted from early May to early July along the mainland coast of central California and in April at San Nicolas Island in southern California. The range-wide index, defined as the 3-year average of combined counts from the mainland range and San Nicolas Island, was 2,962, a decrease of 166 sea otters from the index for the previous year. The 5-year average trend in the range-wide index, including both the mainland range and San Nicolas Island populations, was flat at 0.12 percent growth per year. The northern range boundary was not calculated because of limitations in survey resources required to survey areas north of the range from the previous year (2018); however, the southern range boundary expanded slightly by 0.5 kilometer, where a negligible trend in sea otter counts (0.55 percent growth per year) corresponded to the lack of meaningful population range expansion at the southern periphery.
Hatfield, B. B., Yee, J. L., Kenner, M. C., & Tomoleoni, J. A. (2019). California sea otter (Enhydra lutris nereis) census results, spring 2019: U.S. Geological Survey Data Series 1118 (p. 12).