Lessons from Coral Reefs
The collapse of human societies has commonly involved unsustainable overexploitation of resources and rapid population growth, followed by an environmental catastrophe, such as a prolonged drought, that destroyed the remaining resources. Collapse was some
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Lessons from Coral Reefs Enri c Sala and Jeremy B. C. Jackson
The collapse of human societies has commonly involved unsustainable overexploitation of resources and rapid population growth, followed by an environmental catastrophe, such as a prolonged drought, that destroyed the remaining resources. Collapse was sometimes averted by expansion into new territories to tap unexploited resources, which served as spatial subsidies that fueled further population growth. Finally, when expansion was no longer possible, collapse was even more sudden and severe (figure 11.1). Collapse of marine ecosystems and fisheries has followed a strikingly similar pattern (figure 11.1). Fisheries managed to achieve “maximum sustainable yield” are especially vulnerable to environmental disturbance. Most are already at or below their lower limits of productivity. Increased fishing capacity supported by new technologies or economic subsidies may help to maintain or even increase catches in the short term, as in the case of cod. Then, when the fishery finally collapses, fishers move on to other species, which are generally smaller and grow faster. The economic collapse of one species ripples throughout the ecosystem as others become sequentially overexploited. No one accepts responsibility for these mistakes. Without historical memory, few even remember them. So the cycle of overfishing is repeated over and over until there are almost no fish left. J.B.C. Jackson (eds.), Shifting Baselines: The Past and the Future of Ocean Fisheries, DOI 10.5822/978-1-61091-029-3_11, © Island Press 2011
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Figure 11.1. Historical sequence of events in which overexploitation of local resources and environmental disturbance may lead to the collapse of societies and ecosystems. Access to distant resources may delay the collapse of the system at the risk of decreasing the future possibility of recovery.
Atlantic bluefin tuna provide a fascinating example of this shifting baselines problem in fisheries. Every year these giant fish migrate throughout the Mediterranean to reproduce. Numbers that are unimaginable today were caught in giant almadraba traps, an ancient technique of setting nets in a maze to capture the tuna in a central pool. Aristotle witnessed waters boiling with a moving tide of giant tuna. In the Middle Ages, the same technology was still being employed, and in the mid-1600s a single trap on the southern coast of the Iberian Peninsula caught up to 100,000 tuna every year. There were hundreds of such traps throughout the Mediterranean, and catches began to decrease several centuries ago (figure 11.2). The
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Figure 11.2. Catches of bluefin tuna (Thunnus thynnus) in two sites in southern Spain, from 1525 to 1740. Note that small periodic fluctuations that could be attributable to variation in environmental factors are negligible compared with the larger decline after 1550, presumably caused by fishing. (Unpublished data from the archives of
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