Why We Sucked At Counting Fish (Until Now)
When Galileo trained his homemade telescope
on the night sky, it transformed from a black pool populated by a few thousand stars into
a sparkling sea filled with ten times the number. And today, with the help of bigger
and better telescopes, we know that our home galaxy – the Milky Way – is an ocean of as
many as 400 billion stars. However, telescopes can’t help us peer into
the watery oceans here on Earth, so to count their inhabitants, we’ve used fish trawls
to drag them up into the light – and then – more often than not – onto our plates.
But now we don’t have to fish fish in order to count fish. In 2010, Spanish researchers
sailed around the world with an ultra high-powered SONAR, shooting sound waves into the depths
and using the reflected signals to spot inhabitants. While previous net counts had given us a global
estimate of about 300 trillion fish, the fish-o-scope method revealed that our oceans are home to
roughly ten times that number. One reason previous counts were so much lower
seems to be that fish actively hide from approaching trawls. In one study, scientists took a SONAR
scan while dragging an open net through the water behind them, and check this out: so
many fish got out of the way that their relative absence highlights the whole path of the trawl.
We don’t know exactly how they manage to avoid the nets, but deep-ocean dwellers like
the fangtooth, lantern fish, and stoplight loosejaw, all of which were especially undercounted
by fish trawls, may take warning cues from their neighbors flashing bioluminescent spots.
Another deep water fish, the finger-sized bristlemouth, turns out to be the most populous
vertebrate on our planet. There are an estimated quadrillion bristlemouths swimming the world’s
oceans. That’s a few thousand fish for every star in the Milky Way.
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