Sources/Usage: Public Domain. View Media Details

Sources/Usage: Public Domain. View Media Details

This new model will adjust for variations in survey areas and detection efforts, allowing for a more precise understanding of the true population numbers of southern sea otters. This approach departs from previous population index values, which often presented only minimum estimates due to uncorrected detection probabilities. 

The annual southern sea otter surveys extends across the range of the southern sea otter from Half Moon Bay south to Santa Barbara and San Nicolas Island. The sea otter census is a combination of survey efforts conducted by shore-based observers and aerial-based observers from a small airplane. The data collection informs sea otter-related management decisions by federal and state wildlife agencies.  

Since 1982, annual surveys have been conducted, resulting three-year running averages of total counts referred to as population indices. The population indices produced over this period have been used to represent trends in the southern sea otter population across time. However, these population indices likely only represented a minimum estimate of sea otters in California because total counts were previously uncorrected for detection probability. In addition, efforts since 2020 were modified from previous years due to issues related to weather, the COVID-19 pandemic, plane availability, and road access, resulting in a subset of the range being surveyed that was not directly comparable to previous full censuses. Currently, USGS is developing a model that will more accurately estimate the total number of southern sea otters in California. This model will use all years of survey data and account for potential sampling biases and variable survey coverage and detection conditions that previous estimates did not account for.  Results are expected to be released in 2025.  

The annual southern sea otter surveys are conducted cooperatively by scientists of the U.S. Geological Survey, California Department of Fish and Wildlife, Monterey Bay Aquarium, U.S. Fish and Wildlife Service, and the U.S. Navy, and with the help of experienced volunteers.