Climate and Cod

by |July 27, 2016
Atlantic cod, Gadus morhua. Photo: Hans-Petter Fjeld via Wikimedia Commons.

Atlantic cod, Gadus morhua. Photo: Hans-Petter Fjeld via Wikimedia Commons.

The dramatic decline in a once-abundant cod fish population off the New England coast has largely been attributed to overfishing. But a new study co-authored by researchers at the University of California-Santa Barbara and Columbia University and published today in the journal PLOS ONE finds that the climatological phenomenon known as the North Atlantic Oscillation also contributes―and in a predictable way that may enable fishery managers to protect this cod fishery from future collapse.

Since the 1980s in particular, the once-seemingly inexhaustible stocks of Gadus morhua have declined dramatically. In 2008, a formal stock assessment forecasted that stocks would rebound, but by 2012, they were once again on the verge of collapse, and in 2014 the National Oceanic and Atmospheric Administration instituted an unprecedented six-month closure of the entire Gulf of Maine cod fishery to allow stocks to recover.

The North Atlantic Oscillation is a periodic climatic phenomenon that, like El Niño, causes changes in water temperatures, though the mechanism is different, and it affects the North Atlantic rather than the Pacific. And like El Niño, the North Atlantic Oscillation may also be affected in terms of both strength and frequency by climate change.

The researchers―Kyle Meng of UC Santa Barbara’s Bren School of Environmental Science & Management, Kimberly Lai Oremus of Columbia University’s School of International and Public Affairs and Steve Gaines of the Bren School―found that since 1980, North Atlantic Oscillation conditions have accounted for up to 17 percent of the decline in New England cod stocks.

Lai Oremus is a student in the SIPA/Earth Institute PhD Program in Sustainable Development and a 2011 graduate of the MPA program in Environmental Science and Policy. Meng is a 2013 graduate of the PhD program in Sustainable Development.

The study arose out of an opportunity presented by a climatological anomaly: “In the 1980s, the North Atlantic was stuck in a positive phase of NAO,” the North Atlantic Oscillation, said Meng, an economist. “We show not only that positive NAO conditions diminish a few consecutive cohorts of cod larvae, but also that this effect follows a cohort as it matures.”

“This study does something new in that we followed the effect of climate variability on cod throughout their life cycle,” Lai Oremus said. “We also find evidence suggesting how, through fishing, human actions might be exacerbating the effect.”

The connection to this climate cycle means that the North Atlantic Oscillation can be used to predict the future size of the stock, which would allow for improved management.

“We’re not just saying that the climate is part of the problem; we’re showing how it can be used to forecast and respond in an appropriate and cheap way,” said Gaines. “Many papers show that cod are in bad shape and identify climate as part of the problem. But what they don’t do is give us a management solution.”

This post is adapted from a news release produced by James Badham of the Bren School of Environmental Science & Management. Read the full story here.

For more information on the study, contact Kyle Meng, 805-893-5049 or kmeng@bren.ucsb.edu.

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