Two fishery scientists have predicted a collapse in the West Coast sardine population based on several factors that parallel the fishery’s dramatic collapse in the mid-1900s.

If they’re right – and there is some scientific debate – the valuable sardine fishery in the Pacific Northwest would collapse along with the population, as it did in the 1950s.

In an article for the Proceedings of the National Academy of Sciences, scientists Juan Zwolinsky and David Demer describe the factors that led to the fishery’s collapse in the 1940s and 50s.

And they draw direct parallels to conditions they’re seeing today. Chief among the parallels is a cyclical shift toward colder ocean temperatures (a phenomenon called decadal oscillation), as well as a collapse of the international sardine fishery. The scientists found in their own survey work that the total volume of sardines in the Pacific is declining and competing mackerel are increasing.

“This situation occurred in the mid-1900s, but indices of current oceanographic conditions and the results of our acoustic-trawl surveys indicate it likely is recurring now, perhaps with similar socioeconomic and ecological consequences,” they wrote.

They also found that people are catching more of the oldest and largest fish as they were in the 1940s, a finding they called “alarming.” The larger fish produce more offspring and migrate farther north from spawning grounds in Mexico and California, making them more likely to be the ones caught off the coasts of Oregon, Washington and British Columbia. Based on their findings, Zwolinsky and Demer recommended that the Pacific sardine fishery – which caught $12.3 million worth of sardines in 2010 – be scaled back to prevent overfishing.

As Science News reported late last month, Boris Worm of Dalhousie University said the sardines are important not just for people but also for whales, seabirds and other predatory fish. And the early indicators of an impending collapse give managers a chance to adjust fisheries before its too late.

“The hopeful story here is that we have much better technology and understanding for monitoring the health of this stock today than we had in the 1950s,” says Worm. With more regulation now, fisheries managers can adjust quotas. “We have a conscious choice to keep sardines around or to collapse them.”

The Seattle Times reported today, the environmental groups Pew Environment and Oceana are worried about the worldwide overfishing of small forage fish – including sardines – because of the critical role they play in the ocean’s food chain. They’ve asked fishery managers to start taking the entire ecosystem into account before allowing fisheries to target forage fish. From The Seattle Times:

“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.’”

But fishery management hasn’t changed to reflect the concerns raised by Zwolinsky and Demer or environmental groups – at least not yet. In fact Oceana sued the National Marine Fisheries Service in December over sardine and other forage fish management for failing to take the ecosystem into account before setting fishing limits.

Kerry Griffin, with the Pacific Fishery Management Council, said the Council’s assessment of sardine stocks in 2011 actually showed an increase in the population. Thus, the Council voted to increase sardine fishing limits coastwide from 46,000 metric tons in 2011 to more than 97,000 metric tons in 2012.

To figure out how many sardines the fishing fleet will be allowed to catch, the Council looks at science on daily egg production, an aerial survey of sardine schools, and an on-the-water survey that uses nets and sounding technology. (Curiously, the two scientists who are predicting a sardine collapse are the ones who conduct one of the surveys for the stock assessment.)

“There are some mixed messages,” Griffin said. “Our most recent stock assessment shows an increase in the population. There are indications that there could be a downward trend, but this is a very difficult fish to predict population-wise.”

Griffin said sardines are naturally prone to boom-and-bust cycles, so it’s also hard to tell whether declines in the population are being caused or aggravated by overfishing.

Paul Shively, a regional campaign manager for the Pew Environment Group, said the possible collapse of sardines supports his group’s request for fishery managers put other forage fish off-limits to fishing.

“This is exactly why we need to take a precautionary approach with these species they currently are not targeting,” he said. “This is what can happen. There are some natural fluctuations that aren’t all fishery based, but when you fish the bottom out of something and when there’s that much pressure on such an important species, you need to make sure there’s something left for the large predator species.”

Sardines are generally considered a sustainable seafood option because they’re low on the ocean food chain, and scientists predict they’re all we’ll have left in 40 years if current global trends of overfishing larger fish continue.

Shively said if people were only catching forage fish for human food the world stocks would probably be fine.

“But that’s really not what it’s being used for,” he said. “Most of it is being reduced into fish food or used as long-line bait.”