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Pressure to harvest small fish worries ocean scientists

SEATTLE — As ocean scientists probe what ails some of the largest creatures in the sea, a wave of new research is urging them to look at the little things — specifically, the tiny schooling fish that make up the cornerstone of ocean food webs.

Species such as herring, smelt, sardines and squid are the food of choice for many of the ocean's top predators. But there is increasing pressure globally to harvest marine "forage fish" for everything from hog feed and fertilizer to fish meal in tuna pens or as bait for recreational or commercial fishing.

And these creatures are often the fish that scientists understand the least.

"The idea that forage fish are important isn't new," said Phil Levin, a biologist with the National Marine Fisheries Service in Seattle. "But if you take the fish out of the system, … what are the costs if those fish are no longer there to be eaten by birds or mammals or other fish? That's what we're talking about now."

Take, for example, the discovery late last year by an international team of scientists who tracked what happens to birds when the small fish they eat vanish.

Those researchers stumbled upon a remarkable pattern: Every time populations of ocean forage fish — small schooling creatures such as squid or anchovies — dipped below a third of their peak, seabird births also plummeted, according to the study published in late December in the journal Science. It happened with terns and gulls and with auklets and puffins. It happened in the Atlantic, the Arctic, in Europe and off the United States' West Coast.

Then, late last month, another pair of scientists determined that sardine populations from California to Washington appear likely to collapse in coming years. Other experts disputed the finding, but the debate highlighted an emerging conflict in marine science.

These tiny fish, while resilient, may be especially vulnerable to overfishing, climate change, habit loss and shifting ocean chemistry. And their loss could have profound impacts throughout marine ecosystems — far more so, even, than the loss of some well-known predators.

There's no clear pattern off the coast of Washington and Oregon. Fisheries for anchovies and herring are relatively small, and researchers say that while sardine populations have been in decline, there has also been a recent rebound and fishing pressure remains a fraction of what it was a half-century ago.

But other species — such as the tiny endangered oceangoing smelt called eulachon found in the Columbia River and its tributaries — are facing dramatic reductions from habitat loss, climate change and other factors. And the big battle shaping up is what to do next — whether to study and protect the important tiny creatures we don't really fish yet.

Some see potential future protein in the voluminous, glowing lanternfish that occupy deep waters in the Pacific or the slender eel-like sand lances that feed larger fish. But others worry about the future stability of an ocean food chain already in flux.

"We know that the demand for forage species is growing. But most of our laws exist to promote fishing — not to make sure we're considering impacts on the entire ecosystem," said Paul Shively, with the Pew Environment program that is working to prevent expansion of commercial forage-fish harvests.

The odd mechanics of the Pacific Coast help make California and the Pacific Northwest one of the world's most productive ocean environments.

The entire system is driven by the bottom of the food chain. When the wind blows, it causes water to rise from the deep, bringing with it fresh nutrients that fuel microscopic plant and animal life. Between those tiny phytoplankton and zooplankton communities and the salmon and whales for which the region is famous are a relatively small group of fatty schooling creatures, often dubbed forage fish because so many other creatures eat them.

Researchers call this food chain "wasp-waisted" because this middle section is relatively narrow. Far fewer species, perhaps a few dozen in all, make up the bulk of marine forage fish, and that makes them extraordinarily important.

Pressure to harvest small fish worries ocean scientists 03/24/12 [Last modified: Saturday, March 24, 2012 4:31am]
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