The New Scientist reports that sardine stocks are depleted..not because of global warming, but because the oceans have cooled.
Western Canada’s sardine fleet returned with no fish this month. The loss of the fishery, normally worth CAN$32 million (US$30.7 million), took many by surprise. Yet researchers warned last year that it could happen.
There are still sardines off the US Pacific coast. But the vanishing of the Canadian fish is part of a process that could mean they all disappear for decades, says Juan Zwolinski of the University of California at Santa Cruz.
Pacific sardine populations fluctuate with water temperature. Colder water means fewer fish. Temperatures last fell in the 1940s, but heavy fishing continued, devastating the stock and ending fishing until sardines returned when waters warmed in the 1980s.
“We think this is set to happen again,” says Zwolinski, who tracked the population over the past century. He found that sardines have reproduced less since waters cooled in the 1990s. Almost all eggs now come from fish born a decade ago, which are nearly gone.
What’s more, acoustic results show that the fish have become smaller over the past decade, partly because of chillier water. This is a problem: the fattest sardines migrate farthest north, so the shrinking fish could help explain Canada’s shortage. Smaller fish also reproduce less. Read more »