Although scientists are witnessing a decline in numerous populations of fish species in the world's oceans, cephalopods - including octopus, cuttlefish and squid - have increased over the past 60 years. The findings stem from a study from the University of Adelaide that examined the global database of cephalopod catch rates in order to reveal their long-term trends.
"Our analyses showed that cephalopod abundance has increased since the 1950s, a result that was remarkably consistent across three distinct groups," said Zoë Doubleday of the University of Adelaide and lead author of the study. "Cephalopods are often called 'weeds of the sea' as they have a unique set of biological traits, including rapid growth, short lifespans and flexible development.
"These allow them to adapt to changing environmental conditions (such as temperature) more quickly than many other marine species, which suggests that they may be benefiting from a changing ocean environment."
Declining ocean temperatures are raising concerns over the habitability of the world's oceans for the marine species within them. However, the new data suggests that all species are not on the decline. Furthermore, the current study stemmed from research on the decreasing population of the Giant Australian cuttlefish, which is now rebounding.
"There has been a lot of concern over declining numbers of the iconic Giant Australian cuttlefish at the world-renowned breeding ground in South Australia's Spencer Gulf," Doubleday said. "To determine if similar patterns were occurring elsewhere, we compiled this global-scale database. Surprisingly, analyses revealed that cephalopods, as a whole, are in fact increasing, and since this study, cuttlefish numbers from this iconic population near Whyalla are luckily bouncing back."
The team is considering the possibility that the rise in cephalopod numbers could be caused by the alterations in the marine environment caused by human activities such as global warming and climate change.
"Cephalopods are an ecologically and commercially important group of invertebrates that are highly sensitive to changes in the environment," said Bronwyn Gillanders of the University of Adelaide and co-author of the study. "We're currently investigating what may be causing them to proliferate - global warming and overfishing of fish species are two theories. It is a difficult, but important question to answer, as it may tell us an even bigger story about how human activities are changing the ocean."
The findings were published May 23 in Current Biology.
