Animal Conservation

Large white feeding area | EurekAlert! Scientific news


PICTURE: Aaron Carlisle tags salmon shark in previous study of shark travel patterns After

Credit: Photos courtesy of Jack Musick and Scot Anderson

Perhaps no other ocean creature lives in the human imagination like the great white shark. But while great white sharks may be plentiful in the minds of beachgoers across the country, there are only a handful of places in the world where white sharks can be consistently found. In these regions – such as Central California, Guadalupe Island in Mexico, South Australia, and South Africa – they are usually found clustered in small hot spots, often located around seal colonies.

Researchers have estimated that white shark populations are incredibly small, with only hundreds of large adults and a few thousand total white sharks in one of their global populations. This has made protecting white sharks a priority for conservation with many countries, including the United States and Mexico, having laws in place to prevent the species from being captured and killed.

After discovering a previously unknown white shark hotspot in the central Gulf of California, a new study involving University of Delaware assistant professor Aaron Carlisle suggests that these low numbers of North Pacific white sharks is, especially those listed in the Gulf of California, might be underestimated. In addition, the researchers found that the mortality rates of these white sharks could also be underestimated, as illegal fishing for the species was discovered in the Gulf of California, suggesting that fishermen were killing many more. white sharks than previously thought.

The research results were published in Letters of conservation. Daniel J. Michigan, from the Department of Integrative Biology at the University of Windsor in Ontario, Canada, was the lead author of the article and Carlisle, assistant professor in the School of Marine Science and Policy at UD at College of Earth, Ocean and Environment, was co-author of the article.

Underestimated mortality

For this study, Madigan interacted with a small group of local fishermen and for several months this group killed around 14 great white sharks. Of that number, almost half could have been mature females. This was a conservative estimate as other groups would have killed additional sharks during this time.

To show just how important this new source of mortality could be, Carlisle referred to a review of the status of the National Oceanic and Atmospheric Administration (NOAA) Endangered Species Act on white shark populations as of 2012. In Using the best information available at the time, the NOAA report estimated that the adult female death rate for the entire eastern Pacific was probably around two per year.

“He found, in just two weeks, more mortality in this one location than we expected for the entire ocean,” Carlisle said. “It was pretty clear then that, well, something big is going on here.”

Carlisle explained that the estimate of mortality from the previous NOAA study could have been wrong because calculating the mortality of animals in the ocean – determining how many of them die naturally or not – is one of the most difficult to quantify population measures.

What makes this finding particularly interesting is that this population of white sharks – the eastern Pacific population of white sharks – is perhaps the most studied group of sharks on the planet. Here, in the midst of all this scientific research, was a seemingly robust population of white sharks that had eluded scientific study.

“It’s been about 20 years since a new ‘population’ of white sharks was discovered,” Carlisle said. “The fact that the eastern Pacific has so much infrastructure focused on white sharks and we didn’t know there were those sites in the Gulf of California was quite mind-blowing.”

Next steps

Now that the aggregation has been identified, Carlisle said there were many more scientific questions that needed to be answered.

There is an urgent need to study and quantify the shark population at the new aggregation site. In particular, it is not known whether these sharks are among other known populations of white sharks in the eastern Pacific, which include populations found in central California and on Guadalupe Island in Mexico, or if they belong to a third unknown population.

They also want to know how long the aggregation sites have been there and how long people have been fishing at these sites.

“One of the big points of this article was to raise the red flag and let managers and scientists know that this is happening and that this population is out there and needs to be studied,” Carlisle said. “Hopefully it will be studied by some local researchers who are invested and working with local fishing communities as these fishing communities are all heavily dependent on marine resources and fishing.”

Carlisle stressed that the researchers are not looking to cause problems for the local fishing communities they worked with for the study.

Instead, these communities may have the opportunity to learn about other opportunities with these animals through pathways like ecotourism, educating them that these sharks are worth more and could. provide a more regular flow of living rather than dead income.

“It seems like a perfect situation for ecotourism, just like it is on Guadalupe Island,” Carlisle said. “There could be huge opportunities to build businesses around these shark populations, and that’s just from a management point of view. From a scientific point of view, there are all kinds of fun things. that you could do. “

Still, Carlisle said that more than anything, this article highlights how little we know about what happens with sharks in the ocean.

“Even though we’ve studied these animals so much, we still know so little,” Carlisle said. “How many fish are there in the ocean is a very old question, but a very difficult one to answer.”


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