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New Research Reveals That Humpback Whales’ Vision Is Weaker Than Previously Thought, Which May Explain Accidents With Nets.
Humpback whales have enormous eyes. Because of this, many scientists believed that they had quite efficient vision.
But a new study revealed the opposite. The vision of these whales is weaker than previously imagined. And this may explain why these animals often get caught in fishing gear.
Discovery Begins With A Dissection
The research was led by Jacob Bolin from the University of North Carolina in Wilmington.
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He and his team were dissecting the left eye of a juvenile humpback whale when they noticed something unexpected: the sclera was particularly thick at the back. This affects the focal length, which is the measurement between the lens and the retina.
The greater this distance, the better the vision tends to be. But in this case, the focal length was shorter than expected. This indicates that the whale may have difficulty seeing details, especially from afar.
Few “Pixels” In The Eyes
Another important point was the density of ganglion cells in the retina.
These cells are like the “pixels” of vision. They convert the image entering the eye into electrical signals that go to the brain.
The whale studied had only 180 cells per square millimeter. Humans, in comparison, have up to 40,000 in the same area.
In other words, the image captured by the whale’s eye has far fewer details than human vision. This reinforces the idea that humpbacks do not see clearly.
Measurement Of Visual Acuity
The scientists also measured the visual acuity of humpback whales. To do this, they used a unit called cycles per degree (CPD).
This calculates how many pairs of black and white lines an animal can distinguish in one degree of vision.
The humpbacks reached 3.95 CPD. In contrast, humans can reach 60 or even 100 CPD. This shows that these animals’ vision is quite limited compared to that of humans.
Computer Simulation Supports The Findings
Based on the data collected, the team created computational models. The goal was to simulate how a humpback whale perceives its environment.
The simulation indicated that the whale can see large shapes, such as schools of fish, but only perceives small details at a distance of 45 to 60 meters — the equivalent of three or four times its body length.
Poor eyesight may not be a problem in nature, but it is different when fishing nets come into play.
Humpbacks may only notice these obstacles when they are very close. At that point, it may be too late to divert.
According to Thomas Cronin, a visual ecology expert at the University of Maryland, this low visual acuity is not detrimental to a whale.
They do not need perfect vision to hunt. Their feeding depends more on locating large masses of prey, which they detect through other senses.
Weak Vision, But Sufficient For What They Need
However, when boats and nets appear in their path, weak vision becomes a problem. Whales have not evolved to deal with this.
The co-author of the study, Lori Schweikert, said that this work helps to better understand how humpbacks experience the world around them.
This new understanding could lead to practical solutions. One example would be fishing nets designed to be more visible to these animals.
However, not all scientists are entirely convinced. Elena Vecino Cordero, a biologist at the University of the Basque Country, pointed out that the eye used in the research had been stored in a jar for over ten years.
This may have affected its characteristics and could have led the researchers to overestimate the limitations of the vision.
Still, the study offers a plausible explanation for the entanglement of humpbacks. And it may pave the way for measures that reduce such accidents. If the nets become more visible, perhaps whales will have a better chance of avoiding them in time.
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