Killer whale presence leads to white shark desertion of Farallon Island feeding grounds Jim Tietz [email protected]

Along the California Coast, wildlife at Farallon Islands those coastal sites. Reduced white sharks and killer whales National Wildlife Refuge, we food availability for white are top marine predators. were able to show that white sharks may lead to poorer body These two species occasionally sharks escape the islands when condition making their annual come into contact with one killer whales show up. winter migration to the central another, but these interactions Pacific more perilous. On the mostly go unnoticed by We found that the number of other hand, the reduction of predation events by white humans. white sharks at the Farallon sharks correlated with the Islands resulted in fewer On 4 October 1997, Point Blue number of northern elephant pinnipeds being depredated. Farallon Island biologists seals counted, with an average documented a pair of killer of 40 pinnipeds killed by sharks whale females that attacked per year. However, when killer Main Points and consumed a white shark, whales were within 3 km of the the first time this had been island, which occurred in 2009, documented. Only two shark 2011, and 2013, the number of White sharks leave the Farallon Islands when killer predations on pinnipeds were pinnipeds killed by sharks whales come within 3 km noted for the remainder of the declined by 62% compared to during the fall. season, a decline of 95% previous years. The tagging The predation rate on compared to previous years. It data confirmed that the white pinnipeds drops to near zero was a mystery, though, where sharks deserted the Farallon after killer whales occur near the islands. the sharks went. Islands within a day of their close encounters with killer White sharks redistribute From 2006-2013, Point Blue whales and redistributed themselves to mainland sites along the California Coast. collaborators at Stanford themselves to other locations University and Monterey Bay along the California Coast, such Aquarium tagged 165 white as Año Nuevo and Tomales Jorgensen, S.J., S. Anderson, F. sharks with acoustic tags at Ferretti, J.R. Tietz, T. Chapple, P. Point. Kanive, R.W. Bradley, J. Moxley, and Tomales Point, Año Nuevo, and B.A. Block. 2019. Killer whales the Farallon Islands to monitor The redistribution of white redistribute white shark foraging pressure on seals. Scientific Reports. their movements along the sharks from the Farallon Islands California Coast. Combining the to other locations could Point Blue Contribution number 2051 shark tagging data with Point increase competition with other Blue’s long-term monitoring of white sharks already present at

March 2019, Point Blue Conservation Science visit www.pointblue.org/publication-briefs