Humpback Whales May Not See Their Most Dangerous Threats

Run-ins with humans are the leading cause of death for humpback whales — and new research may explain why these gentle giants are so vulnerable to collisions with boats and entanglement in fishing nets.

The softball-size eyes of humpbacks offer shockingly poor vision, according to a study published Wednesday in the journal Proceedings of the Royal Society B. Unfortunately, this isn’t the kind of vision issue that can be corrected with a prescription (as much as we’d all like to see a whale in glasses).

Simulations indicate whales see most of their surroundings in shadowy silhouettes and struggle to resolve fine-scale details until they’re extremely close, said Jacob Bolin, who conducted the study while completing his marine biology degree at the University of North Carolina Wilmington. That means the spidery lines of fishing nets may be virtually invisible to humpbacks until it’s too late to avoid them.

Better understanding how humpbacks and other whales see could inspire “strategies for making fishing gear more visible” and help the whales avoid deadly encounters with humans, said Lorian Schweikert, a sensory biologist also at the University of North Carolina-Wilmington and an author of the paper.

To understand humpback vision, Mr. Bolin and his team dissected the eye of a juvenile humpback whale that died on a North Carolina beach in 2011. While most whales that wash ashore have been dead for weeks and are badly decomposed, this individual was euthanized on land. That afforded scientists an opportunity to study humpback anatomy.

Having such large eyes should, based on optical principles, be an asset: the longer the focal distance, or the length between the lens and the retina, the sharper the image, Mr. Bolin explained. But the researchers found that more than a third of the eye’s depth was taken up by meaty sclera, the white of the eye that’s not involved in vision.