Magazine article Oceanus

Do Marine Protected Areas Really Work?

Magazine article Oceanus

Do Marine Protected Areas Really Work?

Article excerpt

Georges Bank experiment provides clues to longstanding questions about closing areas to fishing

Closing parts of the ocean to fishing to preserve fish stocks holds great intuitive appeal. Similar resource management tools have been used as far back as the Middle Ages, when European kings and princes controlled access to forests and streams, and the fish and wildlife in them. In Hawaii, chiefs established and maintained networks of no-fishing "kapu" zones, with violations punishable by death.

Today, Marine Protected Areas, or MPAs-areas of the ocean temporarily or permanently closed to harvesting-are being proposed to restrict not only fishing, but also mineral and hydrocarbon extraction, and other activities. Some advocates of MPAs suggest that at least 20 percent of the coastal and open ocean should be set aside and permanently zoned to protect ecosystems, sustain fish stocks, and reduce conflicts between users of the oceans.

But the key question remains: Do MPAs really work? It is the modern incarnation of a longstanding question: How can we best ensure sustainable fisheries?

A Victorian model

In the 19th century, scientists vigorously debated the effects of fishing on fish populations and ecosystems. A majority of scientists accepted the paradigm that the oceans were unlimited. Thomas Henry Huxley, a preeminent Victorian naturalist, famously stated in 1884 that: "... the cod fishery, the herring fishery, the pilchard fishery, the mackerel fishery, and probably all the great sea-fisheries, are inexhaustible; that is to say that nothing we do seriously affects the number offish ... given our present mode of fishing. And any attempt to regulate these fisheries consequently... seems to be useless."

The debate culminated in one of the first documented experiments to determine the effects of fishing. In 1886, one bay in Scotland remained open while another was closed to fishing for 10 years. The focus of the experiment was plaice, a valuable commercial fish. Over the decade, plaice in the closed bay increased significantly compared to plaice in the open bay. It was an early, instructive demonstration that fishing does have impacts on fish populations, and that regulation is effective for conservation.

Some ABCs of MPAs

Since then, seasonal and longer-term closures have been an important fishery management tool, and they have protected spawning fish and nursery areas, preserved vulnerable habitats, and reduced fishing pressure.

But by themselves, MPAs cannot attain all of today's fishery management objectives. And they can create unintended consequences. Preventing harvesting in some areas, for example, inevitably results in people fishing in other, perhaps more vulnerable, locations.

MPAs have now been established throughout the world ocean, from the tropics to the poles. Most are relatively small. Many are neither adequately enforced nor monitored to determine their effectiveness.

Of those that have been scientifically monitored, many are in tropical and subtropical areas. Fish in these regions live most of their lives in specific habitats, such as reef structures, and don't stray from them. Their fidelity to a small territory is an important part of the potential success of their marine reserve. Populations do increase in such reserves, and some studies suggest a spillover effect from the reserve that augments fisheries nearby.

By contrast, in temperate, boreal, and subarctic systems-where most of the major world fisheries reside-many fish populations are wide-ranging and often exhibit extensive seasonal migrations. Can a reserve by itself be a successful fishery management tool for these fish?

The Georges Bank 'experiment'

In 1994, federal regulations established a number of year-round fishery closures on Georges Bank and adjacent areas. This shallow bank has sustained fisheries of legendary abundance for hundreds of years until the mid-20th century, when the heavily fished stocks declined steeply. …

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