Taking Stock

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It’s just another piece in an endlessly complicated puzzle. Scientists looking at the collapse of the George’s Bank cod stock — it is currently at just eight per cent of healthy levels — and other fish stocks off the northeastern United States think they have made a discovery that could explain why the stock hasn’t rebounded.

And it’s not foreign overfishing or, in fact, illegal fishing of any kind. The concern is that the stocks involved have not been recovering, despite almost two decades of ever-increasing regulation.

At least part of the problem may be warming ocean waters, not only because fish have their own preferences about water temperature, and move northwards as waters warm, but because a key part of the food source for juvenile cod is disappearing.

Larval cod feast on two different types of copepods — a small, shrimp-like anthropod. Those two species, Pseudocalanus sap and Centropages typicus, are very small, in the ranges of 0.04 to 0.10 of an inch, a perfect snacking size for the larval fish.

But, in recent years, warmer waters have seen fewer and fewer of the tiny plankton being caught in scientific plankton surveys in the area. As well, there has been a pattern of changing and patchy temperatures, meaning that the plankton that were available were spread out in different, separate areas.

Scientists at the Northeast Fisheries Science Center in Woods Hole, Mass., aren’t certain of the full impact of the missing plankton.

What is clear, though, is that the basic mechanics that fisheries scientists have used in the past to calculate the relative health of fish stocks may be wildly inaccurate: if the baseline of how many larval cod turns out to be wrong, that error can obviously magnify itself all up the line and be reflected in the number of fish that actually manage to survive to adulthood.

There is plenty of research still to be done, but there are some facts that have become pretty clear: Steve Cadrin, a scientist with the University of Massachusetts, pointed out to Capecodonline.com that the idea the ocean is a homogenous ecosystem with predictable results has been turned on its ear: “In recent decades there have been so much profound (environmental) changes, that assumption is not even close to true.”

And that means that cod success models — and models for other species as well — could be wildly inaccurate, at least until scientists can find a new normal that gives them a clean, predictive baseline. With continuing environmental changes, that kind of certainty could be a long time coming.

It is, of course, research being done on a far-distant fish stock — and, for that matter, on a significantly different part of the Atlantic Ocean.

It’s not without lessons to be learned and points to ponder.

Organizations: Northeast Fisheries Science Center, University of Massachusetts

Geographic location: George, United States, Woods Hole

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