Giant squid have the largest eyes on Earth, about the size
of a basketball—but why do they need such big peepers? So they can see a sperm
whale in time to escape its gaping jaws, researchers report online today in Current
Biology. Seeing under water is tricky because light fades out at deeper
depths and water makes distant objects disappear even before they are too small
to see. But eyes are expensive to build and maintain, so such huge ones must
serve a purpose. In the new study, researchers developed a computer model to
look at what different-sized eyes could see at different water depths. In the
dark deep, sperm whales and other animals become "visible" because
their movements disturb small organisms that give off light, similar to a
flashing firefly. The modeling showed that basketball-sized eyes could detect
whales amid flashes of light from more than 120 meters away—giving the squid
enough of an edge to make a quick exit. Most organisms are not faced with such
big predators, so they don't need to see far away and thus get by with smaller
eyes.
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