For years fishermen, fisheries managers, and the academic/scientific community have been trying to understand the near collapse of Gulf of Maine cod stocks and explain the apparent failure of decades of rebuilding effort.
We all know the conversation.
Overfishing depleted the stocks and only a near-total suspension of effort would allow the species time to reset and replenish. Fishermen have been living under that stigma, and the resulting management strategy, for a long time.
But the cod have not come back.
Newer theory.
As lobster landings have soared, the notion that lobsters have been feeding ravenously on juvenile cod has gained popular acceptance. Not only do lobsters enjoy a diet of young cod, maybe there is also some sort of cosmic balance in keeping your largest natural predator in check by eating its young.
So maybe there is some truth to this idea.
But in any case, the cod have still not come back.
Now, a study by the Gulf of Maine Research Institute (GMRI) suggests a completely different – and far more worriesome – explanation for this ongoing crisis with cod.
Results of that study, recently published in Science magazine, show that the warming of Gulf of Maine waters — 99% faster than anywhere else on the planet — has reduced the capacity of cod to rebound.
This rapid warming is linked to changes in the position of the Gulf Stream and to climate oscillations in the Atlantic and the Pacific. These factors add to the steady pace of warming caused by global climate change.
“Managers kept reducing quotas, but the cod population kept declining,” said Andrew Pershing, GMRI’s chief scientific officer and lead author of the study. “It turns out that warming waters were making the Gulf of Maine less hospitable for cod, and the management response was too slow to keep up with the changes.”
Pershing and colleagues from GMRI, the University of Maine, Stony Brook University, the Bigelow Laboratory for Ocean Sciences, and NOAA’s Earth System Research Laboratory found that increasing water temperatures reduce the number of new cod produced by spawning females. Their study also suggests that warming waters led to fewer young fish surviving to adulthood.
According to the report, recovery of Gulf of Maine cod depends on sound fishery management and on future temperatures.
Cod are obviously a coldwater species, and the Gulf of Maine is at the edge of their geographic range. As the ocean warms, the capacity of the Gulf of Maine to support cod will decline, leading to a smaller population and a smaller fishery.
The study also shows the risk of not including temperature in fisheries models, especially for stocks like Gulf of Maine cod that are at the edge of their ranges. The warmer the climate gets, the less fisheries managers can rely on historical data.
Anyone who is not wondering what impact warming waters in the Gulf of Maine will ultimately have on lobster stocks is simply not paying attention.
And anyone who accepts the conclusions of this GMRI study has to recognize that – if correct – cod stocks are probably not coming back. Not now. Not ever. Unless somehow water temperatures go back down.
To us, this all raises many more questions than answers and points to an immediate and urgent need to know more about the impacts of rising seawater temperatures on fisheries of all kinds throughout the region. /cfn/
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