Science

New Research Shows a Bad Forecast for Cod in a Rapidly Changing Climate

The effects of differing NAO trends across the North Atlantic. Image via www.climate.gov

This summer, two scientific articles examined the outlook for Atlantic cod populations in a rapidly changing climate, and unfortunately for an already struggling species in New England, the forecast is not so great.

And the science says…

The first article discusses the effects of a phenomenon called the North Atlantic Oscillation (NAO) on New England cod populations. The NAO is the naturally-occurring, dominant mode of climate variability in the North Atlantic. Since the mid- to late-70s, the NAO has trended in a more “positive phase,” raising winter sea surface temperatures and influencing local variables such as ocean mixing and salinity. Some scientists hypothesize a connection between a positive trend and increased greenhouse gas emissions.

Comparing NAO trends to stock assessment data, the researchers determined that, over the course of this time period, the NAO has negatively affected cod recruitment. Furthermore, the negative effects seen in larvae persisted in adult cod. Overall, the scientists estimated that “the NAO has contributed to 17 percent and 9 percent of the overall decline in adult biomass in the Gulf of Maine and Georges Bank stocks since 1980, respectively.”

The second article analyzes the impacts of end-of-century levels of ocean acidification on Atlantic cod larvae and recruitment, the results of which showed these levels doubled the daily mortality rates of larvae and decreased recruitment averages to as low as 8 percent of current recruitment.

Though this study focused on two cod populations in the eastern North Atlantic, ocean acidification is a global issue and the study’s results should not be dismissed for New England cod populations.

Why are these studies important in New England?

The Gulf of Maine is warming faster than almost any other ocean area on the planet and the impacts of ocean acidification are already being felt in our coastal fisheries and communities. While some fish can migrate to cooler waters to avoid the impacts of rising ocean temperatures, the impacts of a positively-trending NAO and ocean acidification cannot be avoided. And, as mentioned in the second article, fish that migrate north may in fact be more affected by ocean acidification because colder water absorbs more carbon dioxide.

Furthermore, overfishing in New England has been a major issue for years and now given the effects of a rapidly changing climate, fish populations will have a harder time recovering to sustainable levels. New England’s cod populations have plummeted so far that even given the strictest fishing limits it will be years before they numbers come back – if they ever do. That’s not to say, however, that we should throw our hands in the air and leave it up to fate.

The impacts of the NAO and ocean acidification are inevitable, but both papers look to bright side: we can use these studies and new knowledge of our ocean ecosystems to better manage our fisheries. Both the NAO and ocean acidification follow predictable or expected trends. Scientists and fishery managers should use the knowledge provided by these trends to manage fisheries from an ecosystem-based perspective. By accounting for expected changes in the ocean environment, we can help sustain fish populations in the future.

If there is any hope for the Atlantic cod in New England, managing for a changing environment is a must. And if anything, this management approach can help other stocks from falling into the same dire circumstances.


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