Humpback whales' very poor vision, bordering on myopia, is the cause of their collisions with boats, according to a study.

A study that could finally lift the veil on the multiple collisions of cetaceans with frigates, sailboats and other boats. Or on the numerous entanglements of humpback whales in fishing nets. A study in the British scientific journal Proceedings of the Royal Society B, published Wednesday, May 21 and relayed by the New York Times , reveals that the eyes of these cetaceans - the largest animals on the planet - offer very poor vision.

Such poor visual acuity—especially since the whale only sees in black and white—that it only allows the animal to perceive its surroundings and the largest shapes as very blurred black silhouettes. And even though its eyes are the size of a football, they also do not allow it to distinguish the smallest elements present in its space. The only condition for detecting something clearly: being extremely close to the object targeted. Poor distance vision and clear near vision: everything thus leads to the conclusion that humpback whales are myopic.

Jacob Bolin, a biology researcher at the University of North Carolina and co-author of the study, reports that due to this very poor vision, fishing net lines can be practically invisible to them. They may only see them at the last moment. As a result, they are unable to avoid them, become entangled in them, and can remain stuck for hours or even days.

These new findings could inspire new "strategies to make fishing gear more visible" and help whales avoid fatal encounters with humans, Lorian Schweikert, a biologist who participated in the study, urged in the American daily.

To carry out this research, Jacob Bolin and his team of biologists dissected the eye of a young humpback whale. The animal had been found washed up on a North Carolina beach in 2011, but its organs were still preserved intact for future studies.

In particular, biologists have discovered that the humpback whale's low density of ganglion cells—a type of neuron located in the retina that enables vision—is the main obstacle to their good visual acuity. The highest density Jacob Bolin found in the whale's eye was about 180 retinal ganglia per square millimeter. In contrast, humans have between 35,000 and 40,000 ganglia per square millimeter, while some birds can have up to 70,000 ganglia per square millimeter. The humpback whale is thus far behind.

Scientists were also able to determine that a third of the depth of the humpback whale's eye is made up of sclera, the white of the eye that surrounds the eyeball and is therefore not involved in vision. The gigantic size of their eyes therefore does not equate to good vision.

These various elements thus make it possible to establish initial leads and explain why these cetaceans are so vulnerable to collisions with boats, as during the Vendée Globe. A tragedy that has largely gone unreported.

"This work fills an important gap in our understanding of the sensory ecology of large whales, how humpback whales perceive their world," said Lori Schweikert, assistant professor of biology and marine biology.