Ocean Updates - May 2008
May 20, 2008
White Sharks at Point Reyes National Seashore
Have you ever seen a white shark at Point Reyes? How about one feeding on seal carcasses near the headlands? Would you like to know where and how often white sharks are seen, and what they are usually seen doing? This may be useful information if you dive or surf in open water at Point Reyes National Seashore (PRNS)!
Scot Anderson, Ben Becker and Sarah Allen published an article in the January 2008 edition of California Fish and Game on observational sightings of white sharks at Point Reyes National Seashore over 23 years and decoy surveys over 11 years.
Where are they seen? Most observations were clustered in three areas: Point Reyes Headlands, McClures Rock, and Tomales Point. White sharks are mostly seen close to shore, in water depths from 5 meters to 30 meter. This is likely because they need to keep sight of the surface where they capture their prey.
When are they seen? White sharks are observed at PRNS most frequently in the late summer and fall (August, September, October), which coincides with the seasonal peaks of pinnipeds: California sea lions congregate in the area when males migrate north in the fall, and northern elephant seals juveniles haul out in the fall. When Scot Anderson used decoys to track the frequency of white shark appearances, he found that they were seen approximately once every 6 hours at PRNS! However, this frequency is still less than the frequency in which they are sighted at the Southern Farallon Island: once every 1.9 hours.
What do they eat? At Point Reyes National Seashore, white sharks prey on pinnipeds that congregate onshore and they also scavenge on marine mammal carcasses (especially whales). At the Farallones and Año Nuevo, the pinniped population that white sharks primarily feed on are the northern elephant seals. However, this is not what Scot Anderson found at Point Reyes—the white sharks here seem to be feeding mostly on harbor seals and California sea lions. White sharks also scavenge off of marine mammal carcasses. Large dead marine mammals such as sperm whales, baleen whales, and northern elephant seas can leave an odor trail that can be carried for many kilometers. White sharks can track these “odor corridors” and follow them to the source. In 2004, when a dead sperm whale drifted to PRNS, as many as four white sharks came to feed on the carcass at one time. A large white shark (~943 kg) can survive up to 45 days after feeding on 30 kg of blubber from a dead cetacean!
Should I be concerned about attacks on humans? There were five human attacks by white sharks at PRNS over 23 years, all of which occurred in the fall season close to shore in water <10 m deep. All the victims survived. Those highest at risk appear to be people who dive for abalone, spearfish, or surf in open water in or near areas where sharks have been sighted, or near seal colonies. Please be careful, and report any white shark attacks to Park Law Enforcement at 415-464-5170.
Last updated: February 28, 2015