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Mounting Evidence Suggests Sharks Are In Serious Trouble

The views expressed are those of the author and are not necessarily those of Scientific American.


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Can you imagine oceans without sharks? We may soon have to, as new research suggests may already be 90% of the way there.

Studying shark populations can be tricky. As David Shiffman explains well, while there are a number of methods that can be used to study shark populations, quantifying just how far their numbers have fallen can be difficult. However, recent research out of the University of Hawaii suggests that the presence of humans has a severe and strong negative impact on sharks, driving down numbers by over 90%.

Sharks play a vital role in coral reef ecosystems. Yet every year, millions are killed for asian delicacies and disproven cancer cures. There is no question our shark fishing habits have devastated their populations; the only questions that remain are how much of an effect are we having, and can the sharks recover.

In an effort to answer the first, the research team crunched data from 1607 surveys from the NOAA Coastal Reef Ecosystem Division (CRED) to calculate the effect of human habitation on shark populations. The CRED team counted sharks throughout the Pacific using towed diver surveys, the most efficient and effective way to study open ocean creatures on a large spatial scale, and compared their counts with local human population numbers. Their results were clear – and sobering.

“Around each of the heavily populated areas we surveyed — in the main Hawaiian Islands, the Mariana Archipelago and American Samoa — reef shark numbers were greatly depressed,” said Marc Nadon, lead author of the study. “We estimate that less than 10% of the baseline numbers remain in these areas.”

The team also looked at other factors that might be affecting shark populations, including temperature and reef productivity. However, while sharks preferred warmer waters full of potential prey, the negative impact of humans dwarfed these effects. “Our results suggest humans now exert a stronger influence on the abundance of reef sharks than either habitat quality or oceanographic factors,” the authors wrote.

The team estimated that less than 100 people is enough to cut shark populations by 20%. Even 1,000 people – which is much less than the population of many small islands in the Pacific – was enough to decrease shark populations by 60%. As Nadon put it, “In short, people and sharks don’t mix.”

The findings are consistent with other research in the field. A 2003 paper, for example, found that shark populations in the Northwestern Atlantic dropped over 65% between 1986 and 2000. Similarly, a 2010 paper estimated that shark populations in the Chagos Archipelago had declined 90% since the 1970s. The more we study sharks, the worse the picture becomes, and the stronger the case becomes for conservation efforts. We simply cannot continue to treat these animals the way we do now, for all scientific evidence suggests the day is fast approaching when there will be no sharks left to exploit.

Reference: Nolan et al. Re-Creating Missing Population Baselines for Pacific Reef Sharks. Conservation Biology; DOI: 10.1111/j.1523-1739.2012.01835.x

Christie Wilcox About the Author: Christie Wilcox is a science writer and blogger who moonlights as a PhD student in Cell and Molecular Biology at the University of Hawaii. Follow on Google+. Follow on Twitter @NerdyChristie.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Foren 10:15 pm 04/27/2012

    Asian delicacies. I’d make fun of the rampant stupidity there, but there’s more than enough stupidity in the United States to counterbalance it. And I’m not sure that it’s any less harmful to the environment.

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  2. 2. mike112769 10:43 pm 04/27/2012

    Sharks play such a vital role in our ecosystem that they should be placed on the Endangered Species List immediately. They should be right next to whales on the List. How can people be so irresponsibly dumb? I sometimes stand in despair over the stupidity of mankind.

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  3. 3. payitfwd 12:08 am 04/28/2012

    We have exploited virtually every other species on the planet and treated the Earth like a garbage dump. However, whether it’s an Ice Age or a “superbug”, I have a feeling that this planet will have the last laugh.

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  4. 4. Behappy 2:43 pm 04/28/2012

    I vote to let the Sharks go as other species have become extinct. They hurt people and cause fear. Plus I am not so sure about the study being valid. It only means there are fewer sharks were people abode. Nature has ways to make adjustments just as it has over the millions of years history. Regards

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  5. 5. sijodk 5:10 pm 04/29/2012

    Mike: What may be stupid for humanity as a whole is not necessarily stupid for the individual. If fishing sharks feeds your hungry kids it’s quite understandable that you do it without worrying about the future of the planet.

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  6. 6. RCWhitmyer 6:40 pm 04/29/2012

    Sure let the tigers, bears, and lions go also, for oh my they hurt and scare people also. There are very few areas where people do not abode, and more people are struck by lighting than sharks. We are eliminating predators faster than nature can adjust, or the adjustment causes more harm to humans than the predator. Since most areas in N America now lack top predators whitetail deer have to be culled to minimize damage to forest, crops, landscaping, spread of lyme disease, and deadly motor vehical accidents. Any such culling in the ocean would very be diffcult if not impractical.

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  7. 7. RCWhitmyer 6:44 pm 04/29/2012

    Should be “than are biten by sharks” not “than sharks”.

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  8. 8. bucketofsquid 5:45 pm 05/3/2012

    The quickest way to save the ecosystem is to destroy major food sources. All we need is a dramatic shift in climate or a bad volcanic eruption or over hunting and the global ability to feed sufficient numbers plunges. It doesn’t take much hunger to lead to epidemic and migration which then further disrupt food production and distribution.

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  9. 9. jgrosay 6:01 pm 05/3/2012

    Just as a matter of curiosity, an ecological blasphemy: How many of other fish’ species numbers would be increased and will reach us and other top-of-pyramid predators as a side-effect of the reduction in the number of predator sharks? Will the reduction in the number of sharks affect the number of persons attacked by sharks in some places, and as a result the money income from tourists there will rise?. How much more CO2 will be emitted as a result of increases in activities negatively affected by sharks?. There was an old song in spanish entitled “Los que viven del cordero” -Those who live on lambs-. Poor sharks, they’re very beautiful animals, and they must be in the sea for some reason…

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  10. 10. Christie Wilcox in reply to Christie Wilcox 6:39 pm 05/3/2012

    Behappy, jgrosay and others who say ‘let them die’ – While sharks might seem scary, they are vital to our ocean ecosystems, and thus vital to us. All of the species we commercially fish need healthy ecosystems to thrive, so it is in our best interest to ensure our oceans stay healthy and productive. Studies have shown that loss of sharks actually harms other fish species, not increases them. That’s because sharks play an important role in the ecosystem, keeping certain species at bay and thus keeping the ecosystem balanced. They tend to eat mid level predators, whose increase can harm commercial fishes as well as herbivores, which keep coral ecosystems safe from algae overgrowth. When sharks are removed, the system gets out of whack. And as far as shark bites are concerned, they are extremely rare, and the loss of shark tourist activities from the absence of sharks would far outweigh any gain by less attacks. One study estimated that each and every reef shark in Palau is worth $1.9 million dollars in its lifetime if kept alive – and only $108 dead. Bottom line: the economics of the situation supports protecting sharks, too.

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