(ORDO NEWS) — Ocean warming is prompting tiger sharks to swim farther north and leave protected areas. Now these predators have become more vulnerable to fishing, and changes in their migrations can not only disrupt local ecosystems, but also increase the number of shark encounters with humans.
Scientists from the University of Miami (USA) assessed how the warming of water in the World Ocean, caused by global climate change, affected the movement of tiger sharks. The results of the research are presented in the journal Global Change Biology .
Over the past 40 years, the range of these heat-loving predators has expanded significantly throughout the North Atlantic.
Now, their annual migration paths are getting closer to the pole and extend beyond protected areas, making sharks the victims of fishing. In addition, changes in their migration disrupt natural ecosystems and increase the risk of human encounters.
Tiger sharks ( Galeocerdo cuvier ) are large predators reaching 5.5 meters in length, inhabitants of tropical and subtropical seas. During the cold months, they stay close to the equator, and the rest of the time they migrate along warm currents.
Historically, the waters off the northeast coast of the United States have been too cold for them, but in recent years, tiger sharks have frequented them. The reason was a serious change in the temperature of the oceans.
For 40 years, the US National Oceanic and Atmospheric Administration has tracked the migration of tiger sharks. Specialists caught and tagged the animals, and the re-capture provided information about their movements.
The authors of the article combined these data with newer ones collected as a result of ten years of satellite observations. Sensors attached to the sharks’ dorsal fins have made it possible to track the movements of predators without the need for recapture.
Comparing the information received with satellite data on the temperature of the ocean surface, the scientists saw how much the warming of the water has expanded the range of tiger sharks to the North Pole.
An increase in ocean water temperature of just one degree Celsius above average causes tiger sharks to swim 400 kilometers closer to the pole than usual. Warming has also affected the timing of migrations: sharks now arrive on the northeast coast of the United States on average 14 days earlier than 10 years ago.
The results of the study are critical to the conservation of tiger sharks, as new routes take them outside protected areas, making them vulnerable to commercial fishing.
In addition, changes in migration can have huge consequences for the ecosystem: after all, tiger sharks are apex predators, occupying the top of the food chains. Their movements can disrupt the established interactions of marine animals. In addition, now tiger sharks will increasingly meet people.
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