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Climate change to cut global shark populations by 44% in coming decades


Shark populations are expected to plunge by up to 44 percent by the year 2100. In addition, the sharks that do survive could possibly lose much of their capacity to perceive the scent of food.
 
A study appearing in the journal Proceedings of the Royal Society B investigates the impact of ocean acidification and climate change on sharks.
 
“With this study we show, for the first time, that cartilaginous fishes (sharks and rays) may face similar biological impairments with high carbon dioxide and warming as those observed previously for bony fishes,” Rui Rosa, lead author of the study, told Discovery News.

“Besides habitat degradation and overfishing, ocean acidification also directly affects shark fitness and survival.” 
 
Human activities such as cement production, deforestation, and the burning of fossil fuels including oil, coal, and natural gas account for the excess carbon dioxide released into the atmosphere. Carbon dioxide can dissolve into our oceans, causing a reduction in their pH levels and consequently acidifying waters.
 
A lethal plunge
 
In an experiment, Rosa and her colleagues collected shark embryos from Lungsod Ng Cebu, Philippines. 60 of these were then incubated at the U.K.’s Tropical Marine Center, with a number of them being subjected to the predicted higher temperatures and lower pH levels of 2100.
 
Thirty days after the hatching of the embryos, the survival of the creatures exposed to the acidified and warmer conditions nosedived by up to 44 percent. The survivors, on the other hand, “became more lethargic,” according to Rosa.
 
The changes in our waters by 2100 could have a greater impact on tropical sharks, “because they have evolved in a relatively more stable environment,” Rosa explained. Examples of such sharks include the bull shark, bamboo shark, great hammerhead shark, nurse shark, tiger shark, scalloped hammerhead shark, whale shark, whitetip reef shark, and zebra shark
 
When ‘swimming noses’ lose the ability to ‘smell’
 
A separate but similar study was published in the journal Global Change Biology. Like in the first experiment, the researchers exposed sharks to the expected decreased pH levels. This time, however, the focus was on the effect these changes had on the ability of sharks to sense their food’s odor.
 
Sharks use hearing and an ability that allows them to detect electrical impulses to hunt down prey. They have another sense, however, which is comparable to our own sense of smell. It is called chemical sensing, and it plays an integral factor in the success of their hunts.
 
Sadly, “the sharks’ tracking behavior and attacking behavior were significantly reduced,” stated lead author Danielle Dixson, a School of Biology at the Georgia Institute of Technology assistant professor.
 
“Sharks are like swimming noses,” she explained, “so chemical cues are really important for them in terms of finding food.”
 
While sharks have adapted to past changes in ocean acidification and temperature, the current changes are proceeding at an alarming rate.
 
“It’s the rate of change that’s happening that’s concerning,” Dixson said in conclusion. “Sharks have never had to deal with it this fast.” — TJD, GMA News
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