Yahoo News 10 million fish devoured in 'largest slaughter ever recorded'
A staggering 10 million fish were devoured by larger prey in what researchers have called ' the largest slaughter ever recorded'.
Oceanographers observed the bloody phenomenon recently when they explored a wide swathe of ocean off the coast of Norway during the height of the spawning season for capelin — a small Arctic fish about the size of an anchovy. Billions of capelin migrate each February from the edge of the Arctic ice sheet southward to the Norwegian coast, to lay their eggs.
Norway’s coastline is also a stopover for capelin’s primary predator, the Atlantic cod. As cod migrate south, they feed on spawning capelin, though scientists have not measured this process until now.
Using a sonic imaging technique, the team from MIT and Norway watched as random capelin began grouping together to form a massive shoal spanning tens of kilometres. As the capelin shoal formed a sort of ecological “hotspot,” the team observed individual cod begin to group together in response.. The swarming cod overtook the capelin, quickly consuming over 10 million fish, estimated to be more than half of the gathered prey.
The dramatic encounter, which took place over just a few hours, is the largest such predation event ever recorded, both in terms of the number of individuals involved and the area over which the event occurred.
As climate change causes the Arctic ice sheet to retreat, capelin will have to swim farther to spawn, making the species more stressed and vulnerable to natural predation events, such as the one the team observed.
“We are seeing that natural catastrophic predation events can change the local predator-prey balance in a matter of hours,” says Nicholas Makris, professor of mechanical and ocean engineering at MIT. “That’s not an issue for a healthy population with many spatially distributed population centres or ecological hotspots.
"But as the number of these hotspots decreases due to climate and anthropogenic stresses, the kind of natural ‘catastrophic’ predation event we witnessed of a keystone species could lead to dramatic consequences for that species, as well as the many species dependent on them.”
