Humans are changing the planet’s oceans through global warming and overfishing, and this may have caused a boom in the world’s octopus, squid and cuttlefish populations over the past 60 years, say scientists.
An international team of researchers led by the University of Adelaide’s Environment Institute compiled a global database of cephalopod catch rates from 1953 to 2013 to investigate long-term trends in abundance and found cephalopod numbers had greatly increased. The study was published today in Cell Biology.
“Cephalopods are a diverse group of animals that [live in] all marine habitats,” lead author Dr Zöe Doubleday tells SBS Science. “They are important sources of food for many animals, such as marine mammals, seabirds and fish, and they’re also predators themselves, so this increase has implications for the marine food web.”
Cephalopods are an integral component of many marine food chains and Doubleday describes them as the “weeds of the sea” because they’re quick to adapt.
“They’re short-lived, they’re very fast growing, and they can exploit new opportunities and adapt to change very quickly,” says Doubleday.
Most cephalopods have short lifespans of one to two years, reproduce at a young age and have a fast metabolism that allows for rapid and continuous growth.
The research began when the Doubleday and others started investigating declining numbers of the Giant Australian cuttlefish in South Australian water in 2013 – they have since bounced back – and they wanted to see if similar patterns could be identified in other species.
The authors speculate that global warming or overfishing, or even a combination of both, might help to explain why cephalopod numbers have increased in the past six decades.
“There’s a hypothesis that overfishing has reduced the competitors and predators of cephalopods, so that might be one reason why they’re expanding in their populations,” says Doubleday.
“Global warming might increase cephalopod [numbers] because cephalopods are very responsive to temperature, so temperature might accelerate their life cycles, it might increase their metabolic rate, and it can increase the amount they can reproduce.”
Professor David Booth, a marine ecology expert from the University of Technology Sydney, says the next step in the research should be to pinpoint whatever is responsible for the rise in cephalopod populations.
“What is the mechanism?” Booth tells SBS Science. “Is it a climate change signal and these things do better in warmer water, is it overfishing has backed off or fishers have switched to other species and let these flourish?”
“I think [the research] is a great start and now we need to look at specific species to find out if there are certain groups within these general groups that are doing better than others.”