Study Finds Growing Numbers of Octopuses, Squids in World's Oceans

The giant Australian cuttlefish (Sepia apama) was once in decline, but now its numbers have increased, as have populations of cephalopods in general over the past 60 years. SCOTT PORTELLI, WILDLIFE PHOTOGRAPHER

The global population of cephalopods—a group of animals that includes octopus, squid and cuttlefish—has been slowly but steadily growing for more than 50 years, new research shows.

The growth of these populations may be due in part to increasing temperatures, says Bronwyn Gillanders, a researcher at the University of Adelaide in Australia. Warmer waters allow some cephalopods to grow more quickly, get bigger and live longer, she says.

For example, Humboldt squid, (Dosidicus gigas), also known as jumbo squid, have increased in size and may live twice as long now than they did decades ago, a trend which scientists think is due to warmer water temperatures caused by the El Niño climate oscillation. Prior to the late 1990s, fisherman in South America sought jumbo squid that generally reached weights of four pounds. But since that time, there are many more large Humboldt squid, which can weigh more than 80 pounds, Gillanders says, and those can live two years as opposed to one year, as they used to.

The increase in world cephalopod populations may also be due to the decline in some fish species that prey upon the creatures, says Gillanders, lead author of a study describing the finding, published May 23 in the journal Current Biology.

It's unclear exactly what effects this may be having in different areas of the ocean, and whether or not these effects are positive or negative. On the one hand, the animals are "are voracious predators and could impact many prey species," Gillanders says. But "increases in cephalopod abundance may benefit marine predators which are reliant on them for food, as well as humans" who fish and eat them, she adds.

Most cephalopods are also cannibals, so it's possible the cannibalism may help check further increases in growth, Gillanders adds.

Ocean acidification, which is caused by the increase of carbon dioxide in the atmosphere, may hurt cephalopods, but research is just beginning to address this topic, she says.