Although few species of sharks represent a real danger to humans, this animal is one of the most feared in the world (perhaps Steven Spielberg’s film had something to do with it …). However, in the real world things are rather the other way around, and human activity has a huge impact on many of these inhabitants of our seas.
In a work published in the journal Fish and Fisheries , a team of scientists has presented a new method to calculate the vulnerability of each species of shark to fishing and other human activities, including climate change, in various scenarios. For this, three key factors were taken into account: the total area that each species occupies compared to the fishing area, the probability that a shark will be caught by the fishing methods used and, finally, the speed with which an individual can be replaced. In addition, the species were divided into ecological groups based on the habitats and depths at which they live. This is because risks vary between habitats, and depth determines both the risk of capture from different fishing modes and the likely impact of climate change.
As they explain in a note published by the University of Melbourne, the researchers applied this method to the 132 species of sharks in South Australia and their close relatives. The results revealed that, although sharks are a group that has suffered a multitude of extinction events involving high levels of carbon dioxide, current rates of temperature change are much faster, particularly in the waters of southeastern Australia.
“As our waters warm, we can expect species that live in sand and mud on the continental shelf to move south into deeper (and cooler) waters on the outer continental shelf, or to move towards where the deepest and coldest water gushes out of South Australia ”, explain the scientists. ” Species that live on and around reefs are likely to be more affected, as most reefs are in shallow waters and species that currently exist may end up being displaced by incoming subtropical species.”
The researchers assessed the risks to sharks in low, medium and high greenhouse gas emission scenarios in 2100, and in two fishing scenarios: before and after a major reform that began in 2006 that significantly reduced fishing pressure . It was at this time, for example, that Australia banned most fishing below 700 meters of depth.
Beware of climate change
In addition to overfishing, the carbon dioxide emitted by human activities causes the warming and acidification of the oceans. In Australia, trawling put many shark species at risk, but the aforementioned fisheries reform appears to have minimized the problem.
When the variable climate change is considered in isolation, the results of the model revealed that the highest emissions scenario for 2100 would seriously increase the vulnerability of many species. However, when the risks of current fishing stress and the high emissions scenario were combined, it was found that 25 species of sharks would be at high risk, 70 species at medium risk and 37 species at low risk. “The results tell us that if climate change is not controlled, we cannot be complacent and settle for these ‘good practices’ in fisheries management,” the authors say.
The researchers indicate that their method can be adapted to be used in other parts of the world and with other types of animals to identify the main threats to each species in specific regions.
