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California sea otter (Enhydra lutris nereis) census results, spring 2018
| Content Provider | Semantic Scholar |
|---|---|
| Author | Hatfield, Brian B. Yee, Julie L. Kenner, Michael C. Tomoleoni, Joseph A. Tinker, M. Tim |
| Copyright Year | 2018 |
| Abstract | The 2018 census of southern sea otters (Enhydra lutris nereis) was conducted from late April to mid-May along the mainland coast of central California and in April at San Nicolas Island in southern California. The 3-year average of combined counts from the mainland range and San Nicolas Island was 3,128, a decrease of 58 sea otters from the previous year. The 5-year average trend in abundance, including both the mainland range and San Nicolas Island populations, remains positive at 1.3 percent per year. Continuing lack of growth in the range peripheries likely explains the cessation of range expansion. Introduction and Methods A range-wide census is conducted collaboratively each spring by the U.S. Geological Survey, the California Department of Fish and Wildlife, the Monterey Bay Aquarium, and others, to monitor trends in abundance and distribution of the southern sea otter (Enhydra lutris nereis), and thus provide State and Federal resource agencies with the information requested for effective management. The standardized census has been conducted and completed annually since 1982, except for 2011, when weather conditions prevented survey completion. The survey entails a combination of aerial and shore-based counts, providing an uncorrected and exhaustive count of the entire range of the sea otter in coastal California. Shore-based counts are used in all areas accessible by groundbased observers, except in regions where otters are often located far offshore (such as shallow, sandy embayments) and, therefore, are more difficult to count reliably from the shore. In these areas, aerial surveys are flown along contiguous transects oriented parallel to the shore and covering all areas between the coastline and the 60-m depth contour. Details of survey methods, as well as data and metadata from this survey and surveys from previous years, are available in Hatfield and others (2018). The spring 2018 mainland sea otter count began on April 26 and was completed by May 24. Overall viewing conditions this year were good, like those observed 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 (predominantly Macrocystis pyrifera) were (qualitatively) noted by observers to be greater than seasonal normal in most areas of the range, and much greater than those noted 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 (fig. 1). 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-good survey viewing conditions (View Score = 1.5). Macrosystis canopies at San Nicolas Island were estimated to be seasonally normal. 2 California Sea Otter (Enhydra lutris nereis) Census Results, Spring 2018 sac18-4103_fig01 Pigeon Point Rincon Point Pillar Point |
| File Format | PDF HTM / HTML |
| DOI | 10.3133/ds1097 |
| Alternate Webpage(s) | https://pubs.usgs.gov/ds/1097/ds1097.pdf |
| Alternate Webpage(s) | https://doi.org/10.3133/ds1097 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
