Marine life on ‘junk food’ diet - and we’re to blame
Overfishing and changes in the climate could be putting marine birds and mammals on a "junk food" diet. But unlike humans, marine animals eating junk food diet are losing weight.
As predatory fish such as cod have been removed from the sea in large numbers, fish lower down in the food chain, such as sprat, have increased in numbers. But individually the sprats weigh less, and these leaner fish, biologists say, are effectively junk food.
They are poor sources of energy for predatory birds and mammals, and as a result these animals are also losing weight, says Henrik Osterblom of the University of Stockholm in Sweden.
For Michael Fogerty of the NOAA National Marine Fisheries Service the story is all too familiar. "There have been concerns on the East Coast of the US about the quality of prey for the bluefin tuna," he says.
Herring play a large part in the diet of tuna, but Fogerty and his colleagues have noticed that the herring too have increased in number but decreased in weight. This has resulted in a corresponding decrease in the weight of the tuna, they say.