California marine heat wave linked to fewer whale sightings and sharks closer to shore

Surface waters along the California coast are three to four degrees Celsius above normal during a marine heat wave that scientists say is changing wildlife patterns.

Andrew Leising, a research oceanographer with the US National Oceanic and Atmospheric Administration, said the heat wave has lasted about six months.

Sara Lesser, a naturalist at the Aquarium of the Pacific in Long Beach, said tourist boats are seeing fewer whales and dolphins than in a normal year. She said warmer surface waters are pushing anchovies and sardines, which the animals feed on, into deeper or more northern waters.

Leising said sea lions could also be affected if females have to leave their pups for longer periods while searching for food. He also warned that toxic algae blooms could contaminate anchovy and sardine populations.

Dozens of pelicans and cormorants have been found dead near San Diego in recent months.

Harmful algae have been widespread in Monterey Bay, south of San Francisco. Two humpback whales were found dead on shore in early June.

Elliott Hazen of the University of California, Santa Cruz, said the deaths highlighted the amount of domoic acid in the ecosystem.

Lesser said younger great white sharks prefer warmer water and are being seen closer to shore. A recent video from Malibu showed a white shark near children, while three swimming bans were imposed at Huntington Beach in spring because sharks were considered aggressive.

The marine heat wave is coinciding with the return of El Niño, which warms parts of the Pacific and can disrupt global climate patterns.

Leising said the current El Niño could be stronger than the 2015–2016 event, when a marine heat wave contributed to widespread harm to birds, sea lions and whales in California.