The warm equatorial areas are where marine life is most diverse. However, fishing vessels are more likely to catch sharks and tuna in cold oceanic regions.
More species live near the equator than in temperate or polar regions, and for a century, scientists suspected that predation helped to explain this phenomenon.
The researchers argued that competition for predation drove evolution among prey species, which in turn encouraged the evolution of predators. Now, if there was more predation in the tropical seas, there should be more diversity there than in the colder seas, near the poles.
However, according to a recent investigation led by Marius Roesti, from the University of Bern, Switzerland, predators are not more active near the equator and it is not in this region that fishing vessels capture more animals. On the contrary.
The team collected data from different fishing commissions around the world, between 1960 and 2014. Based on this information, the scientists analyzed the number of hooks placed in a given location in the ocean and the number of predatory fish caught. In total, 900 million fish were caught, according to the scientific article published on Nature.
Roesti and his team found that the largest amount of predatory fish caught occurred in the middle latitudes of the ocean, approximately between 30 and 60 degrees north and south of the equator. The discovery suggests that it is here that predators are most active and interact most with prey species.
“We have no idea why,” said Roesti, according to the New Scientist.
The researchers also found that the number of predatory fish caught by fishing vessels has decreased over the years, and Roesti believes that this is mainly due to overfishing.