The Squid’s Blurred Vision: Judging Distance Underwater

Written by on January 27, 2014 in Invertebrates, Marine Life

Squid are able to capture prey quickly and precisely, which is impressive considering how difficult it is to judge an object’s distance and size underwater. Now, researchers at the University of Queensland (UQ) have discovered how the bigfin reef squid, Sepioteuthis lessoniana, can perceive distance.

The “little fella” that Dory thinks she’s talking to in this clip from Finding Nemo turns out to be a huge whale. How is it possible that she thought a whale was a little fish? Well, distance is a tricky thing in the water, especially in the featureless open ocean.

Bigfin reef squid.

Bigfin reef squid. Photo credit: via photopin cc.

UQ PhD student Wen-Sung Chung explains in a news release that “The tools for distance judgment that animals use on land are of no use at any distance underwater, even in the clearest waters.”

But being able to judge distance and size is crucial for an animal picking out its next meal. The animal needs to know whether the prey is big enough to go after, or so big that it poses a threat.

In the case of the bigfin reef squid, its brain actually presses against its eye, resulting in a retinal bump that causes blurred vision. Mr. Chung and other scientists from UQ’s Queensland Brain Institute found that the squid uses a characteristic bobbing motion to balance-out the blurred vision, allowing it to accurately target prey.

The squid’s distorted eyes have been overlooked in the past because the soft body is easily deformed when it’s caught. To compensate for this, Mr. Chung developed a device that allowed the eye shape to be observed in free-swimming squid.

The researchers studied other species and found that one other squid species and five types of cuttlefish also show retinal bumps. The bumps haven’t been seen in any species of deep sea squid, which shows that light availability in different depths causes squid to develop different eye designs.

You can read the full study here: Range-finding in squid using retinal deformation and image blur.

Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .


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