San Francisco’s KGO-TV (ABC 7) reports that a recently published study on great white shark counts off of California’s central coast indicates that the number of white sharks is “surprisingly low.”
The study was published in The Royal Society’s Biology Letters. Researchers used photographs of dorsal fins to identify 130 unique white sharks at the Farallon Islands off Central California. An algorithm was then used to determine an estimate of 219 mature and sub-adult white sharks in Central California. The study notes that this number is “substantially smaller than populations of other large marine predators.”
Other researchers have pointed out that since this is the first study of its kind in the region that there is no baseline figure to compare the estimated count to.
Chris Lowe of CSULB’s SharkLab , quoted in a Discovery News, suggests that “using traditional marine mammal survey methods on a non-air breathing species” could result in lower numbers, since there could be a lower chance of seeing white sharks on the surface, as opposed to counting marine mammals who must surface to breathe.
Sean R. van Sommeran, of the Pelagic Shark Research Foundation, also chimed in on the topic in the comments section of the Discovery News article and stated that “the figure of 200-300 hundred adults has been conventional wisdom among California Field Researchers since the late 1990s.” He also went on to note that his research team has not seen “more or fewer” sharks since 1990 at the Farallones.
On a related note, the Shark Diver blog weighs in on the estimated numbers at the Farallon Islands, as well as count estimates at Isla de Guadalupe.
Dr. Domeier was issued a 1-year permit in September of 2009. During the 2009 white shark season, he and his team used the catch and release method to tag 2 male white sharks at the Farallones. However, a bit of controversy stirred up when one the tagged sharks was hooked in the esophagus, and the circle hook had to be cut and left in the shark. According to the draft environmental assessment, “the public and members of the other research teams studying white sharks in the region were concerned that the shark had died and that the tagging was being conducted primarily for a National Geographic television program.”
It should be noted that the hooked shark made its normal migration pattern after the incident, according to data supplied from the tag, and that the tag was still reporting normal data 8 months after it was hooked. (see Southern Fried Science’s interview with Dr. Domeier)
Supporters of Dr. Domeier’s SPOT tagging methods argue that this research provides invaluable data, which cannot be gathered using other methods, and that the data could be beneficial to the species. Those who oppose these tagging methods argue that the potential gains simply do not outweigh the risks.
The video above from NatGeoTV.com presents a theory that a killer whale from the L.A. Pod of orcas might have used tonic immobility during a 1997 attack on a great white shark at the Farallones. The theory suggests that the orca (identified as “CA2″) potentially rammed the unsuspecting white shark, stunning it. While the shark was still disoriented the orca could have either grabbed the great white while it was on its back or flipped it over. The orca could have then held the shark upside down in its jaws, keeping it in a state of tonic immobility until the shark drowned.
While there is no hard evidence or clear-cut video footage of orcas inducing tonic on sharks in the NatGeo feature, the video does include video evidence of killer whales attacking stingrays in New Zealand using a similar technique. As seen in the footage, the killer whales approach the rays upside and grab them with their mouths, then right themselves, so that the rays are upside-down and effectively immobilized. Researchers hypothesize that if orcas have learned to use this technique on rays, then it’s not far-fetched to assume they could use a similar technique on sharks.
On a side note, some of the underwater footage of the “great white shark” in this clip features a shark that is clearly not a white shark. While I admittedly am not great at identifying certain species of sharks, I’m guessing the footage features either a lemon shark or a bull shark. Anybody care to enlighten me on the species seen at around 3 minutes in?
Warning: Video contains somewhat graphic footage of shark finning and brief shots of white shark predation on a seal.
KQED aired the educational/information themed video “Great White Shark: The Man in the Gray Suit” back in April of this year. For a downloadable HD version of the video and more information, please visit the Quest website.
The video includes footage of white sharks at both the Farallon Islands and Isla de Guadalupe (although Guadalupe is never mentioned by name). The feature touches on topics including shark attacks and the “mistaken identity” theory, shark finning, migration patterns, shark behavior, and tagging programs.
According to the SF Weekly, Dr. John McCosker of the California Academy of Sciences included a tongue-in-cheek list of suggestions on how to be eaten by a white shark during his April 29th presentation, “Sharks: Why We Love, Fear, and Need Them.”
The overall theme of the presentation was one of shark conservation. However, McCosker apparently attempted to add some comedic elements to the talk with his tips on how to increase one’s odds for being involved in a white shark attack. His tips included…
making yourself look like a natural food source of the white shark by wearing a wetsuit and floundering a top a short surfboard
going swimming in areas in known white shark aggregation and feeding areas
diving for abalone around the Farallon Islands (also a known aggregation spot for large white sharks)
While McCosker’s tips were likely an attempt to keep the audience’s interest piqued. None of them are really a surefire bet to cause a white shark attack, much less result in being “eaten” by a white shark. Even the abalone diver scenario at the Farallones isn’t a guarantee for a shark attack, as can be seen in the video below featuring Ron Elliott’s famous sea urchin diving among the white sharks there.