When Sardines Thrive, Anchovies Don't
Published 7:00 pm, Wednesday, January 8, 2003
It's a fishy tale some California researchers relate: Pacific sardines and anchovies seem to take turns in abundance.
For 25 years the ocean waters are a bit warmer than average and it's "hold the anchovies" _ time for sardines to thrive.
Then things cool somewhat and the scale tilts toward the little anchovy for another quarter century or so, report Francisco P. Chavez and a team of researchers at Monterey Bay Aquarium Research Center in Moss Point, Calif.
Writing in Friday's issue of the journal Science, the group suggests a change may be under way even now.
Their studies indicate that cool anchovy-rich periods extended from about 1900 to 1925 and from 1950 to 1975. Warmth-seeking sardines ruled from 1925 to 1950 and from 1975 to the mid-1990s.
"We know that these cycles are related to changes in ocean circulation and atmospheric" effects on the ocean, primarily by winds, Chavez said.
One result is a change in the depth of the thermocline, the subsurface border between warmer surface water and colder deep water, he said.
But the researchers haven't figured out how the physical changes cause the two species of fish to alternate, Chavez said.
"The $64 million question is what causes the changes in the physical ocean and the atmosphere."
Identifying change, the team of researchers said, "is much easier than understanding the process determining it."
But it has an impact, promoting great fishing industries and then causing them to crash with the loss of one species or the other.
John Steinbeck chronicled one such event in his book "Cannery Row," set amid closing canneries when the sardines disappeared.
These cycles also show that the abundance of organisms can swing wildly because of natural variations, not just human impact, Chavez said.
"Further, these natural variations are not limited to one geographical area but occur over fairly large scales, from Alaska to the tip of Chile," he said. "What surprised me the most was that these same cycles seemed to be occurring everywhere in the Pacific and that few realized that they were related."
Knowing about such cycles helps people studying global warming and other subjects, Chavez said. Scientists can more accurately gauge whether warming is occurring if they are aware of natural cycles and can allow for them in studying climate data.
Arthur J. Miller of the Scripps Institution of Oceanography in La Jolla, Calif., said scientists have long discussed reasons why sardines will predominate at some times and anchovies at others.
Chavez is offering an explanation that could account for this happening at about the same time in places as far apart as Japan, Chile and the United States, said Miller, who was not part of the research team. The time scales for these changes have not been well known, Miller said.
To many people, Pacific Ocean cycles are identified with the warming and cooling known as El Nino and La Nina _ Spanish for little boy and little girl _ that can affect weather worldwide.
But El Ninos, for example, occur every three years to seven years, while the sardine-anchovy cycle takes 25 years to 50 years to complete.
So the Chavez team is proposing the names El Viejo _ Spanish for "old man" _ for the sardine regime and La Vieja _ "old woman" _ for its counterpart.
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