The double-edged lure of man-made reefs
A few miles south of the Florida panhandle, 57 feet beneath the ocean's surface, lies a tugboat named Miss Louise. Flitting around her edges are schools of belted sandfish and gray snapper, with the occasional puffer or bright blue angelfish. Hundreds of sea urchins cling to the side of the boat, and arrow crabs scurry across the bottom.Skip to next paragraph
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Unlike most of the Atlantic's derelict ships, however, the Miss Louise was sunk on purpose.
The tugboat constitutes one of Florida's more than 1,500 artificial reefs - structures on which the state spends about $600,000 a year. From old army tanks to school buses to concrete culverts and abandoned oil rigs, artificial reefs come in all shapes and sizes and are popular with coastal residents. Fishermen like them for their ability to attract large numbers of fish in over-fished waters. Conservationists like them for their habitat restoration potential. Scuba divers flock to them for the diverse ecosystems the structures attract.
Artificial reefs, however, may not be such an ideal solution for either the fisherman's or ecologist's woes.
Artificial reefs draw large numbers of fish for the same reasons natural reefs do: They provide shelter, food, and a place for some species to spawn. They have holes and crevices in which both predator and prey can hide. But as with natural reefs, many of the commercially desirable fish do not actually use the reefs to reproduce. So instead of helping to increase fish populations, artificial reefs - like natural ones - only concentrate fish at a given site.
Fish often occur in even greater densities at artificial reefs than at natural ones, because the man-made reefs tend to be larger and provide more shelter. Most fishermen know this and, looking to increase their daily catch, carefully note the latitudes and longitudes of the reefs and set their lines directly above them.
Some experts, engaged in what they call the production-vs.-aggregation debate, say that artificial reefs are less a solution to the problem of overfished waters and more a contributing factor. According to James Bohnsack, a research fisheries biologist with the National Oceanic and Atmospheric Administration, artificial reefs are "a solution that's obvious, simple, and wrong."
Many people think that because they are catching more fish, the artificial reefs replenish depleted fishing stocks, says Dr. Bohnsack. Instead, they may be making the problem worse than it already is. An artificial reef concentrates fish that had previously been spread out over a large area, he explains. The fishermen catch them, the reef attracts new fish, then the fishermen catch those, too.
"It's like a sponge," he notes. "Squeeze out the water, and it'll soak up more."
Other scientists disagree. David Parker, a senior biologist in the marine section of California's Department of Fish and Game, says that artificial reefs may actually help distribute the fishing effort over a larger area. In California, he points out, "a lot of natural reef populations are widely known and are being fished day after day, so the artificial reefs reduce that pressure on a daily basis."
Even with the reduced pressure, many researchers say that the fish most likely to benefit from these new reefs are those species that need reefs to reproduce and whose populations are limited by the number of reefs in an area. But most of these species are not what sport or commercial fishermen are interested in. Most commercially viable fish - snappers, jacks, and some groupers - are simply migrating from natural to artificial reefs. Thus, their populations are being redistributed, not replenished.