Octopus, squid and cuttlefish booming

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Giant Australian cuttlefish (Sepia apama) males fighting. A collapse in its population led to the surprising discovery that, overall, numbers of cephalopods are growing.
Credit: Science Photo Library

Climate change holds no fears for the octopus, squid and cuttlefish, numbers of which have been booming for 60 years, new research shows.

A report in Current Biology documents a steady increase in global numbers of cephalopods since the 1950s, which has laughed off over-fishing, warmer oceans and increasing pollution.

The research, led by Zoe Doubleday of the University of Adelaide, in Australia, overturns previous theories that cephlapod numbers rose and fell in cycles.

Paradoxically it was a fall in numbers of one species – the giant Australian cuttlefish – that led to the findings. To work out why, Doubleday and her colleagues collated fishery data and previous scientific surveys on 35 species of cephalopods across all major ocean regions from 1953 to 2013.

That showed that while numbers did fluctuate year to year, overall numbers kept rising.

“The consistency was the biggest surprise,” Doubleday told reporters. “Cephalopods are notoriously variable, and population abundance can fluctuate wildly, both within and among species.”

Scientists are not entirely sure why, but their adaptability is believed to be a large part of the explanation.

“Cephalopods have a unique set of biological traits, including rapid growth, short lifespans and flexible development. These allow them to adapt to changing conditions more quickly than many other marine species,” Doublesday said.

However, the jury is out as to whether the trend can continue. Ocean acidification is expected to impair the development of some cephalopods and, with dwindling fish stocks, humans can be expected to fish for squid and other cephlapods in greater numbers.

Doubleday also points to one of their less appealing traits – a tendency to cannibalism.

“They’re highly cannibalistic—they might start eating each other if they overgrow,” Doubleday told Gizmodo.

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