Increasing Pressure to Harvest Small Fish Worries Scientists
March 20, 2012
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.
(From The Bellingham Herald / by Craig Welch) – Species like 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 fishmeal in tuna pens or as bait for recreational or commercial fishing.
And these creatures are often the fish 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 like 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 auklets and puffins. It happened in the Atlantic, the Arctic, in Europe and off the U.S. West Coast.
Then, late last month, another pair of scientists determined that sardine populations from California to Washington appeared likely to collapse in coming years, just as they had during the “Cannery Row” days of the middle 20th century.
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, then the loss of some well-known predators.
“In the big picture, there are growing concerns globally that some forage fish stocks are unhealthy and the way we harvest them is unsustainable,” said Bill Sydeman, a marine biologist with California’s Farallon Institute and member of the team that worked on the bird study.
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 some 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 changes and other factors. And the big battle shaping up is what to do next – whether to study and protect the important tiny schooling creatures we don’t really fish yet at all.
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 see the future stability of an ocean food chain already in flux.
“We know that predator species, marine mammals and seabirds are very dependent on forage species,” said Paul Shively, with the Pew Environment program that is working to prevent expansion of commercial forage-fish harvests. “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.”
In many cases, those impacts aren’t clear.
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 our 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.
“The majority of the biomass is really tied up in just a handful of species,” said Levin, with the fisheries service. “With some predators there are two or three that play the same role, so that if one goes down, something else can functionally do the same job. That’s not so much true with forage fish. There’s not as much redundancy.”
Populations of many of these creatures rise and fall in boom-and-bust patterns with cyclical ocean conditions. And some top predators, like Columbia River sturgeon, are opportunists and will feed on pretty much anything, from endangered smelt to healthier stocks of anchovies, clams and shrimp.
“You couldn’t draw a straight line that says the demise of smelt will result in the demise of sturgeon populations – it’s not that straightforward,” said Olaf Langness, a biologist with the Washington Department of Fish and Wildlife.
But other creatures, such as squid – the largest fishery by volume in California – are so ecologically essential it’s not clear what would happen if their populations went bust. In part that’s because they’re so notoriously hard to study. One researcher compares counting squid to “managing a fog bank.”
“Pretty much everything eats market squid,” Sydeman said. “But we know very little about its abundance, about what drives populations, about the actual needs of predators.”
There is no evidence that squid are in decline, which leaves some to think fishing poses little problem. But researchers increasingly acknowledge they can’t say for certain.
“I, and some others, have resisted the notion that there’s an eminent threat that’s right around the corner” with forage fish in general, said John Field, a forage-fish expert with the National Marine Fisheries Service’s Southwest Fisheries Science Center in California. “It’s more that there’s a need for a longer view about things that aren’t currently actively managed.”
The Pacific Fisheries Management Council, the federal body that manages ocean fishing on the West Coast, is this year debating the future of forage-fish harvesting.