Washington: Giant and colossal squids have super-sized eyes - with diameters measuring two or three times that of any other animal - which allows them to spot predatory whales from a distance in the pitch darkness of their deep-sea home, a new study has revealed.
Researchers have used complex computations to explain the massive 10-inch eyes of giant squids.
According to the researchers` calculations, animals living underwater would have no use for such large eyes if the goal were to see an average object, such as prey smaller than themselves.
That`s why even the eyes of large whales aren`t much more than 3.5 inches across.
"For seeing in dim light, a large eye is better than a small eye, simply because it picks up more light," said Dan-Eric Nilsson of Lund University.
"But for animals that live in the sea or in lakes, the optical properties of water will severely restrict how far away things can be seen.
"Through complex computations we have found that for animals living in water, it does not pay to make eyes much bigger than an orange. Making eyes larger than that will only marginally improve vision, but eyes are expensive to build and maintain."
For Nilsson`s team, that begged the question of why giant squid bother with their giant eyes.
Using a mathematical model of underwater vision, they tested the benefits of very large eyes for a broad range of tasks under various light conditions.
Those efforts showed that very large eyes aren`t much better than smaller ones unless one wants to see something that is itself very big, like a whale.
Giant squid may also be unique in that they are powerful enough to escape a sperm whale once they`ve spotted one, Nilsson said.
Giant squid sees a sperm whale at depths beyond daylight`s reach because of `bioluminescence`
"The answer is bioluminescence-light produced by small gelatinous animals when they are disturbed by the whale moving through the water," Nilsson said.
"It is well known that bioluminescence can reveal submarines at night, and diving sperm whales will become visible for the same reason," Nilsson added.
The study has been published online in Current Biology, a Cell Press publication.