The loss of diversity means that where fishermen might have once caught 10 different species in an area on average, now they catch only five. "It's not yet extinction; it's local fishing out of species," says Myers. "Where you once had a range of a species in dense numbers, now you might catch one or two of a certain species."
While other studies have looked at local or regional populations of fish over time, it has been difficult to discern the underlying cause of decreases or increases of catch. This study is the first to step back to examine climate impacts and fishing in unison at a global scale. It shows that environmental changes affect fish populations year-to-year, but overfishing is the primary driver of long-term declines in the variety of big fish.
"This study brings to the surface something that was buried," says Daniel Pauly, a fisheries biologist from the University of British Columbia Fisheries Centre. "The long-term trend of decline is not discernable at first because there are lots of things happening like the short-term effects of El Nino."
"We know there are decadal patterns in climate and ocean ecosystems," adds Nathan Mantua of the University of Washington's Climate Impact Group. "If this were the only factor, we might expect declines to be quickly reversible. What they've shown here is that we're on a curvy one-way street, with clear trends towards a reduction in biodiversity. There is real cause for alarm here."
Scientists say losing the variety of fish does not bode well for the future health of open oceans. A robust portfolio of different species is a key to maintaining our supply of fish in the long term and the ability of these living resources to rebound from environmental changes.
Contact: Jessica Brown