Earlier this year, reports of the results of study which estimated the number of white sharks off central California made headlines. Researchers formulated the estimate after surveying known and unknown white shark specimens, which were observed at the surface. Individual sharks were identified based on each shark’s unique markings.
Dr. Michael Domeier of Marine CSI has recently posted commentary on the methodology used in the above mentioned study. Domeier cites that the study assumed that the sampled white shark population was a closed population. Domeier goes on to say that the long term monitoring of white sharks at Isla de Guadalupe has shown that adult white sharks leave and join the population, which violates the assumption of a closed population.
Additionally, Domeier states that the assumption that individual sharks have an equally probability of being observed has been invalidated by previous research.
Domeier concludes that since estimate was based on “faulty assumptions” the estimate is invalid. He also states that the actual number of white sharks in the respective region is “likely dramatically higher” than the estimate reported in the published study.
Dr. Domeier’s full discussion of this study can be found at the Marine CSI website.
National Geographic’s Expedition Great White premieres tonight at 9pm on the National Geographic Channel. However, you don’t have to wait tonight to get a sneak peek. National Geographic has made the episode “First Bites” available on Expedition Great White YouTube page (the episode is embedded below).
Expedition Great White focuses on a research team, headed by researcher Dr. Michael Domeier, whose goal is to gather tracking data on great white sharks at Isla de Guadalupe (filmed in the fall of 2008). Domeier’s team uses a catch-and-release technique to SPOT (Smart Position or Temperature Transmitting) tag great white sharks in order to provide researchers with real-time tracking information. After hooking and bringing in a white shark using a rod and reel, the shark is then brought onto a platform and raised out of the water in order to have a satellite tag attached to the shark’s dorsal fin. In addition to attaching the SPOT tag to the white shark, samples were also taken from the shark for research efforts.
Unlike traditional pop-up tags that report data after detaching from the shark and surfacing, the tags that Domeier’s team uses in Expedition Great White reports real-time data whenever a tagged white shark surfaces. The tags are expected to be able to transmit for six years.
Domeier’s catch and release method drew some criticism last year after an incident at the Farallon Islands, in which a hook was stuck in the mouth of a captured great white shark, requiring that the hook be cut with part of the left stuck in the shark’s mouth. However, Domeier’s team has since reported that the shark’s tag is still reporting data, and the shark is in good health.
While elements of Domeier’s methods may seem questionable to some, the results of his efforts in terms of producing real-time data could prove invaluable in terms of gaining knowledge about white shark behavior. Personally, I can find merit with both sides of the argument. I expect that the airing of the Great White Expedition series will drum up the debate once, again, and it will likely bring up interesting arguments both for and against Domeier’s techniques.
Updated tracking data from Domeier’s tagging efforts can be viewed at MarineCSI.org (click on the small map image for a larger view).
A recent article that appeared online at the LA Times website suggests that great white sharks (Carcharodon carcharias) and giant squid (species from the Architeuthis genus) might “battle” it out in the depths of the Pacific. The theory, which other media outlets are running with as if it were scientifically proven, seems entirely based on research of migratory patterns of white sharks being conducted by Michael Domeier.
Dr. Michael Domeier’s “catch and release” technique for tagging sharks, which was employed last year at Guadalupe Island and featured on a new National Geographic series, has come under some criticism from other shark researchers, as of late, after the technique was used on two sharks off the Farallones Marine Sanctuary. San Francisco’s ABC-7 ran the following report yesterday on the topic.
The incident involved with the shark at the Farallones, in which a portion of the hook was left in the white shark’s throat, is sure to draw criticism from those who believe this technique is too invasive and harmful to the sharks involved. The incident also lends support Peter Klimley’s remarks that the costs might outweigh the benefits of this technique.
What jumped out at me the most, while watching this feature, was the fact that when the technique was first covered by Outdoor Magazine in the article Great White!, the article stated, “While it’s fishing in every sense of the word, it’s imperative that the sharks are released into the sea unharmed and unstressed.” Domeier’s comments in the ABC-7 report indicate that stressing the shark is an important aspect of the technique. However, the statement in the Outdoor Magazine article is not directly attributed to anybody involved in the research, so it might have been an error on the part of the author, John Burgman.
I have little doubt that Domeier has good intentions with this tagging program, and that the goal of the program is to gain more knowledge of the species, by doing multi-year tracking (which Domeier says is not possible with the harpooning method), in order to help protect white sharks. Domeier has a long-standing track record of white shark research, which can’t be ignored. However, I have a feeling that those who are critical of the technique will be put off by Domeier’s demeanor and perceived attitude displayed in the interview clips featured in the ABC-7 report (which may have been a result of clever editing, for all I know). In addition, the photo of the team apparently in a gung ho cheer after landing one of the white sharks at Guadalupe island probably won’t sit well with critics, either.
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