A troubling new study found that extreme fluctuations in ocean temperatures are causing more mass die-offs of migratory marine animals, such as bull sharks.
What happened?
According to the Guardian — which summarized the paper published in Nature Climate Change — warmer oceans near the tropics are forcing sharks, manta rays, and other marine species to change their migration patterns. They often get caught in intense currents of cold water rising from the ocean depths — called ocean upwellings — which can be fatal.
As the researchers explained, a current of intense cold water off South Africa's coast led to a mass die-off of more than 260 marine animals across 81 species in 2021. During this event, a surviving bull shark that had been satellite tagged got swept into an upwelling with water temperatures 10 degrees Celsius (50 degrees Fahrenheit) below the norm for tropical marine species.
While the shark quickly swam closer to the surface to flee the frigid waters, many other animals weren't so lucky.
"It was eerie to see so many species washed up dead. You'd think they would have swum away, but they got squeezed. They couldn't escape," Ryan Daly, one of the paper's authors, told the Guardian.
Why are more frequent ocean upwells concerning?
Sadly, mass die-off events caused by chilly ocean waters have occurred off South African and Australian coasts for at least 40 years, as reported by the Guardian.
Scientists found that between 1981 and 2022, cold upwelling events in these areas had become more frequent and intense, killing species such as whale sharks, convict surgeonfish, bigeye trevallies, and common blacktip sharks.
While tagged bull sharks seemed to adapt by fleeing to estuaries, swimming closer to the surface, and moving to colder areas exclusively in warm seasons, researchers told the Guardian they are "vulnerable to sudden and protracted temperature shifts."
"There are bull sharks that run the gauntlet of a cool area to get to thermal refuges. Upwellings could kill off this unique genetic diversity," Daly told the outlet.
Delayed upwellings driven partly by the changing climate are already affecting coastal ocean ecosystems, according to a study in the Proceedings of the National Academy of Sciences.
In turn, this may result in declining populations of species humans depend on for food.
What's being done about it?
Daly told the Guardian that the study highlights the need to reconsider our approach and knowledge of marine conservation.
"We need to think about expanding conservation areas and prioritizing different species," he said. "We need to think out of the box."
Thankfully, the importance of protecting our oceans is on more people's radar recently, as evidenced by Dominica establishing the world's first sperm whale reserve and volunteers conserving marine biodiversity surrounding the Philippines.
We can also help our ocean friends by reducing the pollution we produce that causes disruptions in ocean ecosystems. Cutting down on the plastic products you buy, switching to all-electric appliances, and installing solar panels can all effect meaningful change.
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