The ocean’s most fearsome and majestic predators face increasing risks from warming global ocean temperatures, scientists found in two international studies released this week.
Both studies revealed new information about sharks that surprised scientists and added to a growing body of research raising concerns about rising ocean temperatures and the impacts of human activities on ocean ecosystems.
Large sharks, tuna and other predators are diving far deeper into the ocean than previously expected, a study led by Camryn Brown, an associate scientist at Woods Hole Oceanographic Institution, has concluded. The study also found that disruptions to ocean ecosystems due to climate change and mining — without careful consideration of the risks and benefits — could threaten species at the top of the ocean food chain, harming conservation efforts and commercial fishing.
The second study, based in Ireland, looked at the family lineage and biology of small-toothed sand tiger sharks, one of several species appearing more often in that region as oceans warm.
Andrew Clayton, director of the International Fisheries Project at The Pew Charitable Trusts, said the two studies add weight to growing concerns about the impacts of climate change on the world’s fish and fisheries and the need for better global and regional governance.
“It will require new approaches to ecosystem-based management, with long-term plans that respond to signals from things like sea surface temperatures,” Clayton said.
Track deep dives for sharks, tuna and swordfish
Scientists were surprised to find Frequent deep dives among sharks and other large predators When they compared satellite tag data with audio data, in the Woods Hole study. This research, part of an ongoing deep-ocean project with an international team of collaborators, has been published in the journal Proceedings of the National Academy of Sciences.
What the researchers looked at:
- Information from 344 electronic tags on 12 large species, including white sharks, tiger sharks, whale sharks, yellowfin tuna and swordfish.
- More than 45,000 days in the life of a fish.
- A 3D model that compares diving information with acoustic data for the daily migration of fish, molluscs, crustaceans and other species from the ocean’s “twilight zone” during the day to surface waters at night to feed.
What they found:
- Sharks and other predators have made a surprising number of visits to the “twilight zone.” Also called the Mediterranean region, it is located approximately between 650 feet and 3,280 feet below the surface.
- Some of the fish had “really crazy eccentricities,” diving much deeper than expected, to depths of 3,000 or 6,000 feet, a depth known as the midnight zone for low-light conditions.
“No matter what apex predator you look at, or where you look in the global ocean, they all spend time in the deep ocean,” Brown said. “All of these animals that we think of as living on the surface of the ocean, use the deep-ocean method more than we previously thought.”
Although the research has found that prey makes it advantageous for predators to dive deep, even though they face little light, high pressure and near-freezing temperatures, Brown said fish can dive for other reasons that are not yet fully understood.
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Warm waters can threaten young sand tiger sharks
In April, a juvenile sand tiger shark washed up on a beach on the Irish coast, something that had never happened before.
“We knew we had to go and check its anatomy given its position in the shark family tree,” said Nicholas Payne, director of the biodiversity and conservation program at Trinity College Dublin. Smalltooth sand tiger sharks are thought to have diverged from megalodon sharks up to 20 million years ago.
Their findings feed into broader concerns about the plight of many shark species in the face of climate change and overfishing, Payne told USA TODAY.
What they found:
During the dissection, scientists found that the sand tiger shark may share a similar trait with the white shark and the largest fish to ever live on Earth – the extinct prehistoric megalodon. This is the ability to keep certain areas of their bodies warmer than the surrounding ocean, which helps sharks be more powerful and athletic. Another recent study found that basking sharks have the same ability, called regional heat absorption.
The findings mean that many other sharks are likely to have warm bodies, which could put them at greater risk from warming sea temperatures, according to the study published this week in the journal Biology Letters.
Scientists believe changing environments in the deep past were a major contributor to the extinction of the megalodon, because it was unable to meet its required energy requirements, said Haley Doulton, lead author of the study.
“We know that sea temperatures are warming at alarming rates again now, and the baby-toothed tiger that washed up in Ireland was the first tiger seen in these waters,” Dolton said. “This means its range has changed, perhaps due to warming waters, so some alarm bells are ringing.”
Climate change poses risks to ocean ecosystems and fishing
The deep-dive study follows the publication in August of a study, co-authored by Brown and others, which found that the effects of rising ocean temperatures can already be seen in the oceanic habitats of many shark species and other highly migratory predators in the Atlantic. Off the US coast and the Gulf of Mexico. Both regions are among the fastest warming regions.
“Climate change is expected to fundamentally change the status quo of where these species are found and how they live,” Brown said in August. The research concluded that 12 species will face widespread loss of suitable habitat in those areas by the end of the century, in some cases by 70%. Among the fish species included in the August study were the porbeagle, the shortfin mako, five species of tuna, and Sailfish, marlin, and swordfish.
The scientists concluded that along with projected climate changes, additional impacts from overlapping fishing efforts, predator distribution and deep-sea mining could put vital ecosystems at risk. Because such disturbances threaten species at the top of the food chain, harming conservation efforts and the economically important commercial fishing industry, the researchers said it is important to protect and continue learning more about the deep ocean.
Clayton said the studies also demonstrate the urgent need to finalize the development of a global framework for regional fisheries management organizations.
He said the WHO-led study underscores the need to take “precautionary” measures, not only about capturing top predators, but also about leaving enough fish for the predators. “It is not good enough to manage one species”
For example, there has been emerging research on commercial twilight zone fishing. “We are often looking for the next fish to exploit without thinking about the predators that depend on those fish at that moment.”
If exploitation begins before scientists understand how ecosystems work, “there is a really high risk of causing damage that cannot be easily reversed,” he said. Alice Della Pennaco-author and collaborator at the University of Auckland, New Zealand.
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