Observation of the Week, 10/27/16

Our Observation of the Week is a pair dueling Great White Sharks seen by @serpophaga off of the Farallon Islands!

Located about thirty miles west of San Francisco, the Farallon Islands are small spurs of rock jutting up from the Pacific Ocean and famous for their bird, seal, whale, and shark denizens. Throughout the years, the islands’ wildlife was decimated by seal hunters, egg collectors (500,000 eggs per month were collected in the mid-nineteenth century), and others, but the site is now a protected wildlife refuge. Researchers from Point Blue Conservation Science and the U.S. Department of Fish and Wildlife have studied the plants and animals there for decades, and recently iNat user Adam Searcy (@serpophaga) spent some time on the islands to help with surveys.

“Much of the fall work on the Farallones involves censusing and banding migrant birds,” says Adam. “We attempt to find and identify every bird that arrives on the island every day (and every butterfly, dragonfly, etc.) In addition to this work, there are pinniped censuses and tag re-sighting, cetacean surveys, and shark monitoring. Weather permitting, a sentry is on 'shark watch' for most daylight hours every day for most of the fall season (= shark season).”

This shark attack was spotted by the biologist who was on shark watch and radioed to the others that a “close and large attack” was occurring off the East Landing. Adam says “many attacks we observe are too distant to allow for good photographic opportunities--that was not the case with this attack.” He and others rushed to the site and by the time they got there the shark was “well into feeding on the carcass.” The large amount of blood and the oil slick indicated that the prey was a Northern Elephant Seal, males of which can reach sizes of 14 ft (4 m) in length and 5,000 lbs (2,300 kg) in weight (the females are quite a bit smaller). Adam goes on to say, “as we watched, a second shark appeared and began powering into the carcass alongside the first animal. This quickly turned into what appeared to be a scuffle between the two sharks, with tails flailing above the water. After about ten minutes, the carcass was finished, the blood pool dissipated and the sharks went on their way.”

The Great White Shark population of the Farallones is considered to be genetically distinct from other members of their species, and sharks tagged there have been tracked to Hawaii and Guadalupe Island, which is off of Baja California. Males tend to return every year, females every other year, and many have been identified by researchers who use scars and other markings to distinguish them.

Adam has now returned to the mainland, but contributed nearly ninety observations to iNat during his stint on the Farallones. He says he uses it as “a digital companion to my regular field notes. The community of amateur enthusiasts and experts are also most useful when I branch out into groups that I'm unfamiliar with, e.g., lichens. I posted a bunch of lichen observations from the Farallones and I've been happy to receive assistance in identification from the iNat community.”

Adam is also encouraged by iNat’s large community: “One aspect of iNaturalist that has encouraged me to upload more and more observations (and I've only just begun in the last 8 months or so) is its ability to generate detailed biodiversity data on a scale that was previously unimaginable,” he says. “Having a global army of enthusiastic contributors will lead to more refined understandings of where organisms currently are, where they are expanding, and where they are contracting. Even uploading observations of common organisms across their range may lead to documentation of changes in status and distribution. Citizen science at work!”

- by Tony Iwane


- Adam’s kept a blog of some of his adventures, definitely worth a read!

- In 1997, whalewatchers witnessed an Orca and a Great White Shark battle off of the Farallones. National Geographic made a video about it.

- San Francisco PBS station KQED made two short videos about the Farallones, one more about the ecosystem, the other focusing on the life of researchers there. 

Posted by tiwane tiwane, October 28, 2016 00:47

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