The annual population index is calculated from visual surveys conducted via telescope observations from shore and via low-flying aircraft along the California coastline by researchers, students, and volunteers from USGS, CDFW's Office of Spill Prevention and Response, Monterey Bay Aquarium, UCSC, USFWS and U.S. Bureau of Ocean Energy Management.
This year, the surveyed coastline spanned from Pillar Point in San Mateo County, south to Rincon Point near the Santa Barbara/Ventura County line, and also included San Nicolas Island.