The Pacific herring—an oily, silvery, schooling fish—is rarely high on the list of marine animals people fret about.

But for the second straight year, the Canadian government has ignited a skirmish in British Columbia by moving to let fishing nets scoop up spawning herring, despite objections from scientists, Native people, and even commercial fishing groups.

"Last year it almost got to a war—locals were geared up to block fishing boats in port," said Tony Pitcher, a fisheries scientist with the University of British Columbia. "There were more police on the dock than there were local people."

This unusual battle is part of a global debate about the future of some of the oceans' most important fish: the abundant schools of sardines, squid, smelt, anchovies, and herring that serve as forage for larger animals in the sea.

Scientists like Pitcher argue that too few governments take into account the essential role these forage fish play in marine systems before deciding how many of them can be caught.

Herring, in particular, are energy-rich creatures that often swim close to shore and provide nutritious meals for everything from pelicans and sea ducks to humpback whales, sea lions, sharks, larger fish, and even bears.

"They are the Kobe beef of the forage-fish world," said Julia Parrish, a seabird ecologist with the University of Washington, in Seattle. "You have to eat four times as much of some other fish to get the same energy content."

View Images Herring travel in tight groups and sometimes perform "flash expansion" maneuvers, as each individual arcs away at once, shattering the school. It forms again seconds later. Photograph by Paul Nicklen, National Geographic Creative

A Global Problem

In many places around the world, herring populations are quite healthy. Norwegian herring still support the globe's second largest fishing fleet.

But herring populations in other spots may be a mere fraction of what they once were. Archaeologists counting herring bones at 171 sites along North America's west coast recently found evidence they said suggested that the fish had been abundant for thousands of years. Modern herring stocks, on the other hand, swing wildly, and after a decline many don't roar back as fast or as high as they once did.

Herring populations outside Juneau, Alaska, crashed in 1982 and have never come back. Prince William Sound herring collapsed in 1993. Washington State's largest herring population has declined 90 percent since 1973, and herring that used to live for ten years now rarely survive more than four.

These issues aren't limited to North American waters. Some Baltic Sea herring populations have fallen below their long-term average, and the fish are smaller and thinner than they used to be. North Sea herring are getting older as fewer young fish survive. One of Japan's largest herring populations has been too small to fish for several decades.

"Herring are a linchpin in the food chain," said Phil Levin, who oversees ecosystem sciences at the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center in Seattle. But throughout much of the Pacific, "what you see over and over is a pretty dramatic decline—there's less herring, they're smaller, and the older, bigger herring seem to be gone."

Scientists recently have started cataloging potential consequences.

In 2011, researchers found that everywhere they looked—the Atlantic Ocean, the Pacific, or the seas around Antarctica—seabirds declined whenever forage fish numbers plummeted.

Last fall, scientists determined that diving seabirds like Western grebes or common murres, which depend on herring and other forage fish, are 16 times more likely to be dwindling than are birds that also eat other fish.

"There's obviously something going on with herring, and it's not good," said Ignacio Vilchis, formerly with the University of California, Davis, who led the seabird research.

View Images The herring that return to Vancouver Island each spring attract birds, whales, sea lions, and even bears to feast on the energy-rich fish or their eggs. Photograph by Martin Smart, Alamy

Fishing for Roe

It's against this backdrop that conflict arose in Canada.

There, for decades, fishing boats had gathered tens of thousands of tons of herring to be used for fish oil. Then they instead began gathering them for their roe, which is popular in sushi. But along three major areas in British Columbia, the schooling creatures have been so slow to come back that there hasn't been a fishing season in a decade.

Yet when scientists with the Canadian Department of Fisheries and Oceans recommended last year that fishing remain curtailed, the head of the agency, the minister in Ottawa, overruled her own team and ordered fishing open. (The season eventually was halted by court injunction.)

This year the government again is pushing to open the herring roe fishery—and once again both sides are dug in.

"We can't risk them taking any more," said Guujaaw, ex-president of the Council of the Haida Nation on Haida Gwaii, also known as the Queen Charlotte Islands. "Herring are central to everything here."

To understand just how, consider the herring ballet that begins off the islands each spring.

That's when spawning fish swarm in by the millions, darting and turning in tight schools into bays and inlets, where they release so many eggs the emerald waters turn white and seem to come alive.

"It will look like the water is churning," said the NOAA's Levin. "Predators below are chasing the fish. Eagles and birds are suddenly everywhere, picking them off. Then come the seals and the killer whales. In a single cove you'll see the whole food chain at work."

The seals eat the fish, and the killer whales chase the seals. Humpback whales release bubbles that envelop balls of herring, confusing the fish long enough for the whales to slurp them up. Kelp is blanketed with herring roe, six or seven layers on a single strand. Gray whales vacuum the eggs off the bottom. When seaweed washes onto the beach, bears swipe eggs off the kelp.

It's noisy. It's electric. And it leaves a distinct smell in the air, a fresh, not-unpleasant odor similar to celery.

"The whole thing is pretty magical," Levin said.

View Images In Deep Bay, British Columbia, spawning herring turn the sea white as fishing boats line up to gather them for their roe. Photograph by Paul Nicklen, National Geographic Creative

Native People Depend on Them

The herring still come to Haida Gwaii, but in nowhere near the numbers they once did. No one can say for certain why.

Herring declines can have many causes: Overfishing, oil spills, toxic runoff, disease, coastal habitat destruction, and perhaps climate change can all contribute to the decline of a particular stock. Even the recovery of once-troubled populations of whales and marine mammals may depress herring numbers.

Levin, in Seattle, is part a team of scientists from California to Alaska investigating herring declines.

"Who knows?" asked Don Hall, a herring biologist with the Nuu-chah-nulth tribe along the west coast of Vancouver Island. "Fishing probably contributed, and then something else helped make it worse."

The Canadian government insists herring stocks have started improving, and that fishing nets would take only a small fraction. But outside scientists are skeptical—of the government's numbers, and also of the idea that herring numbers alone should be the primary basis for deciding whether to open the fishery.

"They didn't take into account the food herring eat or the organisms that rely on herring for food," Pitcher said. "It's just not precautionary enough."

Government officials declined to answer questions. They released a statement saying that they have "decided to allow harvest opportunities for Pacific herring," yet still plan to "take into full consideration all views."

The Native tribes on Vancouver Island and on Haida Gwaii don't believe that. They fear fishing will harm birds or jeopardize recovery of humpback whales and other marine mammals. They worry there won't always be enough herring for their own people, who smoke, fry, and pickle the fish, but also eat the eggs raw or on kelp, cook them with butter or salt, and freeze them.

"Even in this day and age, our people still gather a lot of their food," said Guujaaw.

With spawning season only weeks away, tribal leaders are preparing for more court battles—and the possibility of a blockade. They've found a surprising ally: The United Fishermen and Allied Workers' Union, which might have been expected to favor reopening the herring fishery, has criticized the Canadian government and urged its members to avoid fishing for herring near tribal waters.