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.
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.
Additionally, say some scientists, there are so many natural reef and rocky-bottom habitats that artificial reefs are just a drop in the bucket.
Jon Dodrill, an environmental administrator with the Florida Fish and Wildlife Conservation Commission, notes that although man-made reefs selectively attract more fish than natural reefs and rocky or hard-bottom seabeds, "it's such an insignificant part of the hard-bottom complex, I don't believe it's doing any harm. But I also don't think it's conserving stocks."
Others feel that they are more detrimental than that. Felicia Coleman, a fisheries ecologist at Florida State University, says that it is arrogant to assume that we know enough to artificially recreate a complicated ecosystem.
She notes that in places like Alabama - a state with a 38-mile coastline - so many artificial structures have been sunk that the marine community has completely changed. While some claim to be trading an unproductive community for a more productive one, Dr. Coleman asks, "Productive to whom?"
Coleman then points to another quandary: Gag groupers are one of the species that uses reefs to reproduce. However, she points out, "the migratory pathways of groupers have evolved over geologic time." Thus, sinking artificial reefs might have a deleterious effect.
Until recently, the "science" of artificial reefs in the United States was anything but science. People bound together old tires or sank a car in an attempt to create their own, personal fish havens.
Science is, however, beginning to catch up with practice. William Lindberg, a professor of fisheries and aquatic sciences at the University of Florida, is attempting to understand how reefs work so that future artificial structures can be designed to be beneficial to gag grouper populations. William Hernkind, a biology professor at Florida State University, is doing similar research with spiny lobsters.
William Seaman, the associate director of Florida's Seagrant Program, believes this new research is encouraging. Instead of throwing reefs into the open ocean and hoping something will happen, he says, the next step is to create artificial reefs that are beneficial to different species. "What we're trying to do worldwide," Seaman says, "is to get away from the 'if you build it, they will come' mentality."
The research of these scientists and their peers is grabbing the attention of fisheries managers. Mr. Dodrill, who is in charge of reef monitoring and permits in Florida, says that now the focus needs to be on restoring natural ecosystems. "I think that artificial reefs, under certain circumstances, can and do provide superior habitat." But at the moment, he says, "that advantage is neutralized by heavy fishing."
But a new mentality will not come easily. Many fishermen still believe artificial reefs are producing fish. "If you give them a place to hang out, you give them a place to reproduce," says David Dexter, executive director of the Alabama Coastal Conservation Association.
Dr. Hernkind, however, disagrees. As a fisherman, he says, "I enjoy them, but I don't kid myself about them being a natural enhancement to the environment. I view [artificial reefs] as fish-attracting devices. As a scientist, however, I'd like to be sure that they're not doing any harm, and in some places I'm not at all sure."
(c) Copyright 2000. The Christian Science Publishing Society