Sharks have been around for about 450 million years, outliving dinosaurs and experiencing several mass extinctions. However, their numbers in the open oceans have plummeted by an alarming 70% in the past 50 years, and many species are endangered.
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More than a third of all sharks and rays today are threatened with extinction, due to overfishing, habitat loss, pollution and climate change. This means that with increasing environmental pressure, Time is running out to save the sharks of the world. As apex predators, sharks are vital to maintaining the stability and health of marine ecosystems.
Not surprisingly, however, for species that roam much below the surface in the world’s oceans, much remains unknown about the effects that environmental changes are having.
Hard data on shark populations is needed to inform conservation and limit-management strategies of high seas, especially when these oceanic areas are often outside national jurisdictions. family.
As a result, researchers are adopting new methods to advance knowledge of sharks, including using genetic techniques that could help uncover their genetic history. Professor Einar Eg Nielsen, a population geneticist at Technical University of Denmark (DTU), further explains how shark populations have changed over time that could provide information on pressure environment, how closely individuals are related, and how much genetic diversity is being maintained. Lynby.
‘You can see that generally a species is doing well. But it can mask that it is doing well in some areas and not well in others,’ he said.
‘You need information about populations to manage them appropriately. But if you don’t have genomic markers with full resolution, then you can’t disrupt population structure. ‘
Function template
That’s why DiMaS The project he co-led carried out genetic research on sharks. This initiative aims to expand information on the recent history of sharks to help assess how they might respond to climate change and fishing-related stress in the future.
The team focused on the shortfin mako shark (Isurus oxyrinchus), which is caught commercially but also caught by chance in seas around the globe. Species is classified as endangered on the IUCN Red Listis often considered the ultimate inventory of the conservation status of the world’s species.
The researchers collected nearly 1,000 jaw and vertebrae samples spanning three centuries from museums, national fisheries and private collections, including modern specimens from fisheries institutes. . After separating the lower quality ones, they selected half for genome analysis.
“The problem with these monsters is that they’re all over the place, so it’s very difficult to get really good samples,” said Professor Nielsen. ‘But by joining forces with other organizations, we can get more samples to be able to look at patterns over time.’
Despite the dramatic decline in their numbers, the analysis revealed several potential causes for cautious optimism about the long-term prospects of the makos as the team found that the Their genetic diversity has not decreased significantly in recent years.
Dr Romina Henriques, formerly at DTU, co-leader of DiMaS, and now a population geneticist at the University of Pretoria in South Africa, says the high degree of connectivity between different populations of shortfin mako can be can help with this.
“The fact that there is this strong connection suggests a greater resilience,” she said.
Connection wobbly
However, things are not quite so easy. It appears that the degree of connectivity has changed over time, and that some populations may have historically been more isolated and therefore potentially more vulnerable, Dr Henriques said.
“What I find very interesting is that this connection changes over time, so you have some populations of shortfin mako that appear to be more distinct than others,” she said. ‘What we think is you can have some isolated populations, but there’s quite a bit of movement.’
Another caveat is that with their potential lifespan of 30 years or more, shortfin makos have a relatively long lifespan. Since pressure from fishing has only increased in the second half of the last century, it may simply not have been enough time for any recent population declines to filter through a decrease in genetic diversity. .
But regardless of what further research uncovers, the widespread movement of shortfin mako sharks and the connections between populations highlight the need for fishing and conservation that must be managed in the changing area. because only in individual areas, Dr. Henriques said.
“That means conservation is not just country-based, it’s regional,” she said. ‘It doesn’t matter if two or three countries decide ‘no more mako fishing’, because they will naturally leave the protected areas. “
Oxygen depletion
Another important area of research is how climate change might affect sharks’ ocean habitats through its effect on oxygen levels, making the animals vulnerable to overfishing. .
Because warmer waters dissolve less oxygen, studies suggest that climate change is depleting levels in the oceans and leading to an expansion of the so-called oxygen minimum zone (OMZ). It is thought this could squeeze oceanic areas where many sharks, fish and other marine animals can exist into a smaller space.
Professor David Sims, marine ecologist at the Society of Marine Biology in Plymouth, explains: ‘One theory is that the shark is compressed vertically into the top layer, into a smaller and smaller volume of water. , and this benefits the higher catches of the fishermen. and the University of Southampton, UK.
On the basis that at present not much is known about these effects, Ocean Deoxyfish The project that Professor Sims leads is to explore the phenomenon in sharks, as well as in tuna. “Ultimately, what we want to do is be able to predict the distribution of sharks in an oceanic deoxygenated world,” he said.
Such exploration has been aided by developments being made in tagging devices that can be attached to the fins of sharks. ‘Over the last 20 years, there have been real advances in marine telemetry – marine biology, as it’s called – using miniature electronics to track sharks to inform movement, their behavior and ecology, as well as their interactions with the environment”. Professor Sims.
In the early stages of Ocean Deoxyfish, the results prompted the researchers’ hypothesis. In a study at the OMZ in the tropical eastern Atlantic Ocean off the coast of Africa, the team found that vertically compressed blue shark habitat. Their maximum diving depth appears to be about 40% less than in other areas, potentially increasing their fishing vulnerability.
Cycle of Doom
However, the picture is complicated as sharks may also benefit from increased feeding opportunities in these compressed regions as prey seek to avoid hypoxic waters with low oxygen levels on their own.
“There’s a self-perpetuating cycle of doom going on,” Professor Sims said. ‘The sharks are seeing an opportunity to feed, but fishermen are also taking advantage of the opportunity to be able to catch more sharks per unit of time.’
Ocean Deoxyfish researchers are developing increasingly sophisticated tracking tags that will record oxygen levels in addition to shark movements and typical measurements such as temperature, pressure and depth. The data will be uploaded directly to the satellite, avoiding the need to retrieve the tags.
The new tags will also capture video footage of what Professor Sims describes as a ‘shark’s-eye view’ of the animals’ behaviour, allowing researchers to see what they are doing while diving. He added that blue sharks appear to be capable of at least making some dives into low-oxygen waters, which he thinks may have something to do with their eating of squid that can tolerate being in the water. this water area.
“It would be great if you caught that and found out what they were doing there,” he said. ‘What we hope is that we’ll have these tags capture the pursuit of these deep-water cephalopods [such as squid] in the low oxygen region. ‘
Ultimately, he hopes that projects like his will contribute to the long-term management of sharks and other species that live in the oceans.
“Overfishing is reducing these populations to unprecedented levels,” he said. ‘There is a need for a greater degree of interaction between climate change research and fisheries management than before.’
Written by Gareth Willmer
The source: Horizon
