Center for American Progress
By George Lapointe et al.
September 27, 2012

Science is integral to fishing operations. Without the ability to estimate how many fish exist in the ocean there’s no way to determine how many of them we can catch while allowing the remaining fish populations to stay viable. But fish live in a mostly invisible world beneath the ocean surface, they move around constantly, and they eat each other. This creates a dynamic population structure that’s incredibly difficult to track, making fish virtually impossible to count.

Thus, fisheries scientists—like political pollsters or other statisticians—must rely on imperfect data to make their predictions about the status and health of fish populations. They take these data—some of which they collect, some of which come from fishermen—and plug them into scientific models which, in turn, create estimates of population health. Because the entire population of a given species is frequently divided into subpopulations known as “stocks,” these estimates are called “stock assessments,” and they form the backbone of modern fishery management in the United States.

These assessments provide an estimate of the current state of a fish population and, in some cases, forecast future trends. This tells us whether fishery management goals are being met and indicates the type of conditions to which the fishery will have to adapt in the near future. In an ideal world, scientists would have the resources to provide managers with updated stock assessments for each species every year, but their expense and complexity mean they can only be updated periodically.

Regardless of how frequently they can be updated, strong, science-based stock assessments are the key to future sustainability, not just of the fish but also of the fishing industry. Fishing is an inherently unstable business, yet strong, accurate science can give fishermen a better understanding of whether their resource will remain healthy, and if it does, how many fish they will be allowed to catch. This in turn allows fishermen to make informed business decisions and stabilizes coastal economies.

But to commercial and recreational fishermen, who are on the water day in and day out, and whose livelihoods in some cases depend on their ability to catch fish or take people fishing, the stock assessment process can seem like a nebulous, convoluted exercise, the results of which often seem to them anything but scientific. Somewhat counter-intuitively, this perception can be reinforced by changes that sometimes occur in the stock assessments themselves.

In 2011, for example, a new stock assessment of one of New England’s key stocks, Gulf of Maine cod, showed it was in far worse shape than the previous assessment predicted. This kind of sudden fluctuation, while understandable from a scientist’s perspective as improvements are made in data collection and analysis, is infuriating to fishermen and can, as in the case with Gulf of Maine cod, endanger the entire industry.

In 2006 Congress amended the Magnuson-Stevens Fishery Conservation and Management Act, which governs our nation’s fisheries. One component of this amendment was a requirement for managers to set annual catch limits in all fisheries beginning in 2011 (2010 for overfished fisheries or those experiencing overfishing at that time). These limits cap the amount of fish that can be caught each year, and must be set to ensure overfishing does not occur, or in the cases of overfished fisheries, to ensure that they are rebuilt to sustainable levels within 10 years. Stock assessments provide the foundations upon which fishery regulators, including the regional fishery management councils and ultimately the National Oceanic and Atmospheric Administration, or NOAA, construct these catch limits.

This issue brief is intended to be a primer on stock assessments, asking and answering fundamental questions about the process. Until we develop technology that can take a snapshot of the entire ocean and count every fish, there will always be room for improvement in fisheries science. But the work being carried out today at NOAA’s fisheries science centers meets the threshold established in law—it is the “best available”—and as such, it must provide the foundation upon which our fishery management policy is constructed.

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