FEATURE ARTICLE
Ecologically Sustainable Yield
Marine conservation requires a new ecosystem-based concept for fisheries management that looks beyond sustainable yield for individual fish species
Stephen L. Katz, Richard Zabel, Chris Harvey, Thomas Good, Phillip Levin
Marine Resources
A spectacular diversity of habitats lies in the world's oceans, which cover 361 million square kilometers and constitute more than 99 percent of the biosphere's volume. Some habitats, such as coral reefs, seagrass meadows and kelp forests, are relatively well known. Others, such as deep-sea plains and vast open waters, are alien to most people.
We are only beginning to appreciate the depth and breadth of marine diversity, but it surely rivals that on land. Coral reefs, for instance, occupy only 0.1 percent of the earth's surface, yet they may support as many as 9 million species. There also could be millions of species in the deep sea, once thought to be a vast desert. At higher taxonomic levels, marine systems are much more diverse than those on land. Of the 34 recognized animal phyla, 33 can be found in the ocean, and 15—including comb jellies, echinoderms and lampshells—are exclusively marine. Because certain marine groups, especially bottom-dwelling invertebrates, are poorly known, enormous diversity remains to be discovered. For instance, 20 new families, 100 new genera and 200 new species were recently found in or near hydrothermal vents.
Humans have exploited marine ecosystems for at least 10,000 years, but overharvesting was not a significant issue when human populations were small and fishing gear was mostly lines and hooks. Nonetheless, the first known anthropogenically caused collapse of a marine stock occurred about 3,000 years ago, when peoples on the Peruvian coast continued to harvest shellfish that had been depleted by a natural disturbance. With the technological advances of the Industrial Revolution, such as the internal combustion engine and refrigeration, the ability of humans to extract fish from the sea, particularly in offshore regions, increased dramatically. The resulting increased frequency of stock collapses led to the realization that the sea is not infinitely bountiful. More recent developments include factory trawlers, which harvest a disproportionate share of the world's fish.
Commercial fishing now directly kills enormous numbers of fish: More than 90 million metric tons are captured annually for consumption, and about 30 million metric tons are discarded as bycatch. Worldwide, 25 to 30 percent of exploited stocks experience overfishing, despite numerous incidents of stock collapse. Moreover, fishing trawls dragged across the seafloor have devastating effects on benthic communities, with impacts similar to clear-cutting in forests. By killing benthic invertebrates as well as key predators, fishing affects food webs and fundamentally alters community composition.
Why are many marine fisheries overexploited? Fisheries provide 19 percent of the animal protein consumed by human beings worldwide and generate jobs for more than 200 million people, mostly in small-scale fisheries. Understandably, this creates enormous social, economic and political pressure to maintain current fishing levels. As fisheries managers juggle diverse and conflicting objectives, political agendas and scientific uncertainties, they often err on the side of overexploitation, despite calls for caution from organizations such as the Food and Agriculture Organization of the United Nations. Such conflicts in fisheries management are typically characterized simply as science versus politics, but we suggest that there may be a deeper problem: The fundamental goals of modern fisheries management may be incompatible with sustaining marine ecosystems. Currently, a primary goal of "sustainable" fishing is to preserve the long-term viability of target species. But sustaining those species may depend also on protecting the vast biodiversity of the world's oceans, which by definition will require a more holistic approach to resource management.
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