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When the predators become the prey: Which shark species are the most threatened by human impacts

22 Jul 2014

Sharks are an evolutionary work of art. They have persisted from a time before dinosaurs and have done so remarkably unchanged, until now. With human threats and overexploitation of them as resources, sharks move closer to extinction every day.  Some of the driving forces are targeted fisheries, bycatch, habitat loss, and pollution. Because most of these are human caused threats the shark species that are most at risk are the ones that live at depths less than 200 meters. This is mostly due to shallow fishing lines and biotoxins that live on the surface. Larger species of shark are also declining at a larger rate. Species such as angel sharks, Squalus squatina and thresher sharks, Alopias macrourus are among the most threatened species of shark because they are large bodied shallow dwellers.


Some of the least threatened shark species are the opposite, small bodied deep dwellers such as lanternsharks (Etmopterus pusillus), catsharks (Scyliorhinus canicula) , and kitefin sharks(Dalatias licha).


Not only do size and depth play a role, location does as well. Some of the highest targeted areas for shark population decline include the Caribbean Sea and Western Central Atlantic Ocean, Eastern Central Atlantic Ocean, Southwest Indian Ocean, and the China Seas. In these areas shallow waters, high species diversity and a large number of threatened species rapidly accelerate the decline.  Understanding which species are the most threatened can help target conservation efforts. Knowing the factors to look for can help show which species may be at risk in the future as well.


Time has shown how adaptable sharks are to the state of their environment, and this is no different. Deepwater populations of shark species that have never been seen before are popping up suggesting that they are finding a way to persist in these new conditions to avoid human impact. Though this effort is promising, it might be too little too late. Sharks such as the hammerhead sharks (Sphyrnidae), porbeagle shark (Lamna nasus) and shortfin mako shark (Isurus oxyrinchus) are at >99% population loss, yet no global mechanism of conservation has been put in place for shark conservation. This should be a call to action. With these risk factors as starting points hopefully shark conservation will have a starting point and move to the foreground of conservation efforts.



By Maryssa Beckman


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