Zalophus californianus have traditionally preferred nurseries in the Channel Islands, but the population of pups born off Northern California’s coast began skyrocketing in 2016. Births at both sites went from a few dozen pups to more than 500. The trend has only intensified since; more than a thousand pups born at the Farallones, and between 500 and 700 at Año Nuevo, in 2017 according to NOAA; similar numbers are expected this year, although final counts are not yet available. Such high census numbers are unprecedented since robust surveys began in 1975. The move appears to coincide with the onset of “the blob,” a marine heat wave that formed off the California coast starting in 2014. California sea lions prey on species that get scarce during warm water conditions. Burgeoning sea lion numbers and the need for more rookery sites could also help explain the expansion to northern nurseries. A coalition of scientists from UC Santa Cruz, the UC Natural Reserve System, and NOAA’s Marine Mammal Laboratory is studying the phenomenon. Great white sharks also have changed their habits during recent warm water conditions. Instead of migrating further south in late fall, young great whites took advantage of the balmy temperatures and lingered near the southern California coast year round.

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Photo: Patrick Robinson, UCSC
 

California sea lion nurseries are moving north as Año Nuevo Island and the southeast Farallon Islands experience a record-breaking boom in sea lion births. Zalophus californianus have traditionally preferred nurseries in the Channel Islands, but the population of pups born off Northern California’s coast began skyrocketing in 2016. Births at both sites went from a few dozen pups to more than 500. The trend has only intensified since; more than a thousand pups born at the Farallones, and between 500 and 700 at Año Nuevo, in 2017 according to NOAA; similar numbers are expected this year, although final counts are not yet available. Such high census numbers are unprecedented since robust surveys began in 1975. The move appears to coincide with the onset of “the blob,” a marine heat wave that formed off the California coast starting in 2014. California sea lions prey on species that get scarce during warm water conditions. Burgeoning sea lion numbers and the need for more rookery sites could also help explain the expansion to northern nurseries. A coalition of scientists from UC Santa Cruz, the UC Natural Reserve System, and NOAA’s Marine Mammal Laboratory is studying the phenomenon. Great white sharks also have changed their habits during recent warm water conditions. Instead of migrating further south in late fall, young great whites took advantage of the balmy temperatures and lingered near the southern California coast year round.

About the author

Bay Area native Kathleen M. Wong is a science writer specializing in the natural history and environment of California and the West. With Ariel Rubissow Okamoto, she coauthored Natural History of San Francisco Bay (UC Press, 2011), for which she shared the 2013 Harold Gilliam Award for Excellence in Environmental Reporting. She reports on native species, climate change, and environmental conditions for Estuary, and is the science writer of the University of California Natural Reserve System.