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"Overfished" isn't just about fishing

Tanner CrabTanner Crab.

When you see the word “overfishing” in the NOAA Fisheries Status of Stocks report to Congress, released this week, it’s only natural to think that fishermen must be causing it, right?  Although fishing certainly adds significant pressure, stocks can also become “overfished” for many other reasons, including natural mortality, disease, and natural population cycles.

Environmental changes are another significant contributor. A fish’s environment (habitat) includes physical factors, such as temperature and bottom type, as well as chemical factors, such as oxygen levels and dissolved minerals. The habitat needs for each stage of a fish's life cycle—egg, larvae, juvenile, and adult—vary within the same water body. So changes in these environmental factors can greatly affect the population of a stock.

For example, in the Bering Sea off the coast of Alaska, scientists are seeing decreases in Tanner crab populations, which led to the recent determination that the species is overfished.  Scientists are finding that the primary driver of this decrease is not fishing pressure but rather changes in the crab’s habitat.

They saw that, since the first formal surveys of southern Tanner crab in the early 1970s, the eastern Bering Sea populations have fluctuated greatly, with peaks in abundance (or biomass) in 1975, 1990, and 2007. But since 2007, the number of mature male Tanner crabs declined substantially and fell below a threshold in 2009 that led to its overfished status. NOAA scientists are assessing whether this population drop may have been influenced by climate impacts such as increased seawater temperature and ocean acidification.

Managing fisheries using an ecosystem approach

Test Your Habitat IQ More than 3,000 species of fish inhabit America's coastal rivers, marshes, coral reefs, seagrass beds, deep ocean canyons, and other ocean habitats. So healthy coastal and marine habitat is critical to rebuilding and sustaining our nation's fisheries

One of the greatest long-term threats to commercial and recreational fisheries is the loss of marine, estuarine, and other aquatic habitats. Other fish habitats have been so greatly harmed that fish populations cannot recover without our help. Impacts from certain fishing practices, as well as coastal development, threaten to alter, damage, or destroy these habitats.

Fisheries management relies on intensive studies of the relationship between fish and their habitat. NOAA Fisheries works with regional fishery management councils and state and local partners to ensure that fisheries are managed using an ecosystem approach, looking at the entire system instead of just one small area. 

For the Tanner crab, NOAA is developing a stock rebuilding effort that will begin during the 2012-2013 fishing year.  NOAA will carefully monitor changes in the crab’s environment so the stock can be managed effectively.

As for other fish around the country, NOAA is working to identify essential fish habitat for every life stage of federally managed species, and continues to focus on restoring and protecting coastal habitat.

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