Sardine fishing nets will remain empty for a fourth straight year along the West Coast, where biologists are comparing the dramatic decline of the schooling fish to the infamous collapse that led to the downfall of Monterey’s once-thriving Cannery Row.

The northern Pacific sardine population, stretching from Mexico to British Columbia, has plummeted 97 percent since 2006, according to an assessment released this week by the National Marine Fisheries Service and the Pacific Fishery Management Council.

The perilously low numbers give regulators no choice but to close fishing, which had been scheduled to start July 1, from Mexico to the Canadian border.

The 14 voting members of the fishery council, which makes policy along the coasts of California, Oregon and Washington, will meet April 8 in Portland, Ore., to discuss the results, but everyone agrees a fishing ban is inevitable. The council is required by federal law to close ocean fishing when the numbers fall this far below conservation objectives.

“This sardine population has completely crashed,” said Ben Enticknap, a scientist for Oceana, an ocean conservation advocacy group. “It is alarming.”

The sardine population is at just under 3 percent of its peak population in 2006, when the tiny fish— which are measured using their collective weight as if inside a fishing net — reached 1,774,784 metric tons, according to the National Oceanic and Atmospheric Administration.

The latest assessment projects that 52,065 metric tons of sardines will be swimming along the West Coast on July 1. That’s well below the 150,000 metric-ton threshold required for commercial fishing. Last year’s estimate was 86,586.

Biologists blame the collapse on natural fluctuations — which have been common throughout history, according to recent sediment studies — as well as changing ocean conditions. Conservationists, however, believe overfishing made a bad situation worse.

Enticknap said regulators allowed sardine fishing to continue until 2015 despite warnings by scientists that the population was ready to collapse. He said the same mistake was made in the mid-1950s when the Monterey Bay canneries made famous by John Steinbeck’s novel “Cannery Row” began failing.

Stiff quotas and catch limits required under federal law by the 1976 Magnuson-Stevens Fishery Conservation and Management Act helped save the tiny epipelagic fish, and their population increased throughout the 1990s.

In the 2000s, Monterey Bay once again became the Bay Area hub of sardine fishing, with a large population also thriving off the coast of San Francisco.

Fishing fleets hauled in huge quantities of the nutrient-rich fish around the Channel Islands in Southern California and along the Oregon coast. It wasn’t unusual for a boat to bring in up to 65 tons a day of sardines, which are generally frozen in big blocks for use as bait in commercial long-line fishing and for feed at Australian and Japanese bluefin tuna farms.

The catch was bringing in $10 million to $20 million in annual revenue until the latest collapse.

At the April meeting, Oceana will ask fishery managers to declare the population overfished and develop a recovery plan.