Photo by Paul Mannis via Flickr Creative Commons
Researchers have completed the first-of-its-kind census of white sharks that live off the California Coast and the numbers they found are making them nervous. There are three major populations of white sharks -- those that live off New Zealand and Australia, those that live off South Africa, and those that live along the west coast of the US. It is this last population researchers focused on to determine just how many are really around. By luring sharks in and photographing their unique dorsal fins, the scientists from UC Davis and Stanford University could count individuals. But they came up with just 131 individuals out of 321 photographs, which led them to a scientific estimate of a total of 219 individuals, and that is a lot less than they thought they'd find. Is this low number indicative of a serious problem for the great white shark species?Science Daily reports, "The study, published in the journal Biology Letters, is the first rigorous scientific estimate of white shark numbers in the northeast Pacific Ocean. It is also the best estimate among the world's three known white-shark populations."
California great whites are actually a very unique population. Previously, scientists thought that white sharks migrated all over the Pacific, but actually this population hasn't met outsiders in over 10,000 years. They're a distinct population from the other two, and have specific migration routes, including heading out to White Shark Cafe off Hawaii for part of every year.
From the photographs collected of individual sharks' dorsal fins, which have unique marks and jagged edges, the researchers estimate that there are 219 adult and sub-adult white sharks in the region. However, they want to conduct the census again in the area, as sharks come back to the same areas year after year. That way they can get the most accurate count as possible of the usually elusive animal.
Here is a video of the census project from UC Davis:
The troubling part is that the low number was surprising to the researchers, who note that not only is it less than they thought they'd find, but it's far less than other large marine predators -- even polar bears. Of course, trying to count animals that live all over the big wide sea is a tough job. UC Davis doctoral student Taylor Chapple notes, "[T]his estimate only represents a single point in time; further research will tell us if this number represents a healthy, viable population, or one critically in danger of collapse, or something in-between."
Before researchers can guess at what the low number indicates, they have to be sure that it is accurate, which means more tracking and photographing dorsal fins. Even if the species has historically had this small of a population, it is curious that there are fewer counted than other large predators like killer whales or polar bears.
By returning year after year to the same area to count the sharks, the researchers can get a better estimate of population trends. They note in their paper A first estimate of white shark, Carcharodon carcharias, abundance off Central California , "Our methods can be readily expanded to estimate shark population abundance at other locations, and over time, to monitor the status, population trends and protection needs of these globally distributed predators."
Shark populations all over the world are dipping significantly as the devastating practice of shark finning continues. White sharks are often caught for their teeth, jaws and fins which can fetch a big price in the marketplace. As a predator that takes years to come to sexual maturity and which reproduces slowly, any hit to their populations would require a long recovery time. The relatively low populations worldwide are part of the reason they're listed as vulnerable. Whether that is because of a reduction in food sources, overfishing, a change in overall ocean health or nothing to worry about at all is yet to be determined.
In the meantime, here's a fun video reminding us to give the animals their space:
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