Humpback Whales Can’t See as Well as Scientists Thought, and It Might Explain Why They Keep Getting Tangled in Fishing Gear Despite having big eyes, the whales can’t make out details of objects more than a few body lengths away, according to a new study Humpback whales have poorer eyesight than previously thought, according to a new study. by wildestanimal via Getty Images With large, grapefruit-sized eyes, it would make sense if humpback whales had decently strong eyesight. So, why do these intelligent cetaceans continue to become entangled in fishing gear? Scientists have dissected the left eye of a juvenile humpback and revealed the species’ eyesight is weaker than biologists previously suspected. Their results, published Wednesday in the journal Proceedings of the Royal Society B, carry implications for how humans can help humpback whales steer clear of fishing nets. When lead author Jacob Bolin, at the time studying marine biology at the University of North Carolina Wilmington, cut open the specimen with his colleagues, they found that the white of the whale’s eye was particularly thick at the back. This made the humpback’s focal length—the distance between the eye’s lens and retina—shorter than expected, as Bolin tells bioGraphic’s Marina Wang. Longer focal length usually indicates sharper eyesight, so this was one sign that humpbacks may have poor vision. Another limitation they discovered involved the number of retinal ganglion cells, which are like “the pixels of the eye,” as Bolin says to the New York Times’ Elizabeth Anne Brown. These neurons are responsible for converting the image on the retina at the back of the eye into electrical signals for the brain. The dissection revealed that humpback whales have a surprisingly low density of these cells, especially compared to humans. The whale had, at most, 180 retinal ganglion cells per square millimeter; humans, meanwhile, have up to about 40,000 in the same area. The researchers also found that the humpback whale could see at 3.95 cycles per degree (CPD), a measure of vision determined by how many pairs of black and white lines an animal can make out in one degree of visual space. Humans have much higher visual acuity, between 60 to 100 CPD, per the paper. Researchers investigate a preserved humpback whale eyeball. Michael Spencer / UNCW The team processed these observations with computer models to simulate how humpback whales see their environment. Their visualizations demonstrated that while the animals can see large, faraway shapes, like schools of fish, they can only detect smaller details within about three to four body lengths of the whale, according to a University of North Carolina Wilmington statement. (That’s about 150 to 200 feet.) Overall, humpback whale eyesight is surprisingly less sharp than what scientists had suggested it might be, given the size of their eyeballs, per a Nature research highlight. That means humpback whales might not see fishing nets until it’s too late. Researchers measuring the dissected humpback whale eye.  Michael Spencer/UNCW “[A low CPD] is bad for a human, but not bad for a whale at all,” says Thomas Cronin, a visual ecologist at the University of Maryland, Baltimore County, who did not participate in the study, to bioGraphic. Whales don’t typically need sharp vision to catch their prey, he adds. In other words, if humans’ boats and nets didn’t get in their way, the whales could get along perfectly well. “This work helps fill a major gap in our understanding of the sensory ecology of large whales, how humpbacks experience their world,” Lori Schweikert, a co-author of the study and neurophysiologist at the University of North Carolina Wilmington, explains in the statement. Elena Vecino Cordero, a biologist at the University of the Basque Country in Spain who has previously analyzed whale eyes but didn’t participate in the study, tells the New York Times that the research might even be overestimating humpback whale eyesight because of how the dissected eye may have changed after spending more than a decade in a jar. Ultimately, the researchers suggest their work could help inspire fishing net designs that are more visible to humpback whales and potentially result in fewer entanglement incidents. Get the latest stories in your inbox every weekday.