The very bad vision of the hosted whales, on the edge of myopia, at the origin of their collisions with boats, according to a study – Liberation

A study that could finally lift the veil on the multiple collisions of cetaceans with frigates, sailboats and other boats. Or on the many tangles of bumpy whales in the fishing nets. A study by the British scientific journal Proceedings of the Royal Society B. published Wednesday May 21 and relayed by the New York Timesreveals that the eyes of these cetaceans – larger animals on the planet – offer a very mediocre vision.

A visual acuity so bad – especially since the whale sees in black and white – that it only allows the animal to perceive its environment and the largest forms present in the form of very blurred black silhouettes. And even if his eyes reach the size of a soccer ball, they also do not allow them to distinguish the smallest elements present in their space. The only condition for detecting something clear: being extremely close to the targeted object. Poor vision from a distance and clear vision: all leads to say that the humpback whales are myopic.

Jacob Bolin, biology researcher at the University of North Carolina and co -author of the study, reports that because of this very bad vision, the lines of fishing nets can be practically invisible to them. They cannot see them until the last moment. Result : They fail to avoid them, tangle there and can remain blocked for hours, or even days.

These new elements could inspire new « Strategies in order to make fishing devices more visible » And helping whales to avoid fatal meetings with men, urges the American daily Lorian Schweikert, a biologist who participated in the study.

To carry out this research, Jacob Bolin and his team of biologists dissected a young humpback whale eye. The animal had been found failed on a beach in North Carolina in 2011, but its organs had nevertheless been able to be kept intact for future studies.

Biologists have notably discovered that the low density of lymph node cells of the hosted whales – a type of neurons located in the retina and allowing vision – constituted the main obstacle to their good visual acuity. The highest density noted by Jacob Bolin in the eye of the whale was indeed about 180 retinal nodes per square millimeter. Conversely, men have between 35,000 and 40,000 per square millimeter, while some birds can have up to 70,000 per square millimeter. The bumpy whale is far behind.

Scientists were also able to establish that a third of the depth of the hunter whale eye consisted of sclerotic, this white of the eye surrounding the eye globe, and which therefore does not intervene in vision. The gigantic size of their eyes therefore does not rhyme with a good view.

These different elements thus make it possible to establish first tracks and to explain why these cetaceans are so vulnerable to collisions with the boats, as during the Vendée Globe. A tragedy widely passed over in silence.

« This work makes it possible to fill an important gap in our understanding of the sensory ecology of the big whales, of the way in which the humpback whales perceive their world », underlined Lori Schweikert, assistant professor of biology and marine biology.