Historical Overfishing and the Recent Collapse of Coastal Ecosystems

E COLOGY T HROUGH T IME REVIEW Historical Overfishing and the Recent Collapse of Coastal Ecosystems Jeremy B. C. Jackson,1,2* Michael X. Kirby,3 Wolfgang H. Berger,1 Karen A. Bjorndal,4 Louis W. Botsford,5 Bruce J. Bourque,6 Roger H. Bradbury,7 Richard Cooke,2 Jon Erlandson,8 James A. Estes,9 Terence P. Hughes,10 Susan Kidwell,11 Carina B. Lange,1 Hunter S. Lenihan,12 John M. Pandolfi,13 Charles H. Peterson,12 Robert S. Steneck,14 Mia J. Tegner,1† Robert R. Warner15 Ecological extinction caused by overfishing precedes all other pervasive longer term cycles or shifts in oceanographic human disturbance to coastal ecosystems, including pollution, degrada- regimes and productivity (15–17). To help ad- tion of water quality, and anthropogenic climate change. Historical abun- dress this problem, we describe ecosystem dances of large consumer species were fantastically large in comparison structure predating modern ecological studies with recent observations. Paleoecological, archaeological, and historical using well-dated time series based on biological data show that time lags of decades to centuries occurred between the (18, 19), biogeochemical (20, 21), physical onset of overfishing and consequent changes in ecological communities, (22), and historical (23) proxies that are infor- because unfished species of similar trophic level assumed the ecological mative over a variety of spatial scales and bio- roles of overfished species until they too were overfished or died of geographic realms (24). Although proxies vary epidemic diseases related to overcrowding. Retrospective data not only in precision and clarity of the signals they mea- help to clarify underlying causes and rates of ecological change, but they sure, the use of multiple proxies that give the also demonstrate achievable goals for restoration and management of same ecological signal greatly increases confi- coastal ecosystems that could not even be contemplated based on the dence in results. Precision in age dating varies limited perspective of recent observations alone. from centuries to a single year, season, or event in the exceptional case of varved sediments, ice Few modern ecological studies take into ac- manatees, dugongs, sea cows, monk seals, croc- cores, and written historical records (25). Pre- count the former natural abundances of large odiles, codfish, jewfish, swordfish, sharks, and cision decreases with the amount of biological marine vertebrates. There are dozens of places rays are other large marine vertebrates that are or physical disturbance to the sediment ana- in the Caribbean named after large sea turtles now functionally or entirely extinct in most lyzed (26). whose adult populations now number in the coastal ecosystems (3–10). Place names for We exploited data from many disciplines tens of thousands rather than the tens of mil- oysters, pearls, and conches conjure up other that span the period over which anthropogen- lions of a few centuries ago (1, 2). Whales, ecological ghosts of marine invertebrates that ic changes may have occurred. Because our were once so abundant as to pose hazards to hypothesis is that humans have been disturb- 1Scripps Institution of Oceanography, University of navigation (11), but are witnessed now only by ing marine ecosystems since they first California, San Diego, La Jolla, CA 92093Ð0244, USA. massive garbage heaps of empty shells. learned how to fish, our time periods need to 2Center for Tropical Paleoecology and Archeology, Such ghosts represent a far more profound begin well before the human occupation or Smithsonian Tropical Research Institute, Box 2072, problem for ecological understanding and European colonization of a coastal region. 3 Balboa, Republic of Panama. National Center for management than currently realized. Evi- Broadly, our data fall into four categories and Ecological Analysis and Synthesis, 735 State Street, Suite 300, Santa Barbara, CA 93101, USA. 4Archie dence from retrospective records strongly time periods: Carr Center for Sea Turtle Research and Department suggests that major structural and functional 1) Paleoecological records from marine of Zoology, University of Florida, Gainesville, FL changes due to overfishing (12) occurred sediments from about 125,000 years ago to 5 32611, USA. Department of Wildlife, Fish, and Con- worldwide in coastal marine ecosystems over the present, coinciding with the rise of mod- servation Biology, University of California, Davis, CA 95616, USA. 6Department of Anthropology, 155 Pet- many centuries. Severe overfishing drives ern Homo sapiens. tengill Hall, Bates College, Lewiston, ME 04240, USA. species to ecological extinction because over- 2) Archaeological records from human 7Centre for Resource and Environmental Studies, Aus- fished populations no longer interact signifi- coastal settlements occupied after about tralian National University, Canberra, ACT 0200, Aus- cantly with other species in the community 10,000 years before the present (yr B.P.) tralia. 8Department of Anthropology, University of Oregon, Eugene, OR 97403, USA. 9U.S. Geological (5). Overfishing and ecological extinction when worldwide sea level approached Survey, A-316 Earth and Marine Sciences Building, predate and precondition modern ecological present levels. These document human ex- University of California, Santa Cruz, CA 95064, USA. investigations and the collapse of marine eco- ploitation of coastal resources for food and 10Center for Coral Reef Biodiversity, Department of systems in recent times, raising the possibil- materials by past populations that range from Marine Biology, James Cook University, Townsville, QLD 4811, Australia. 11Department of Geophysical ity that many more marine ecosystems may small-scale aboriginal societies to towns, cit- Sciences, University of Chicago, 5734 South Ellis Av- be vulnerable to collapse in the near future. ies, and empires. enue, Chicago, IL 60637, USA. 12Institute of Marine 3) Historical records from documents, Sciences, University of North Carolina at Chapel Hill, Importance of Historical Data journals, and charts from the 15th century to 3431 Arendell Street, Morehead City, NC 28557, USA. Most ecological research is based on local field the present that document the period from the 13Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, studies lasting only a few years and conducted first European trade-based colonial expansion DC 20560Ð0121, USA. 14School of Marine Sciences, sometime after the 1950s without longer term and exploitation in the Americas and the University of Maine, Darling Marine Center, Orono, historical perspective (1, 8, 13). Such observa- South Pacific (23). 15 ME 04573, USA. Department of Ecology, Evolution, tions fail to encompass the life-spans of many 4) Ecological records from the scientific and Marine Biology, University of California, Santa Barbara, CA 93106, USA. ecologically important species (13, 14) and crit- literature over the past century to the present ically important environmental disturbances covering the period of globalized exploitation *To whom correspondence should be addressed. E- mail: [email protected] such as extreme cyclones or ENSO (El Ninõ– of marine resources. These also help to cali- †Deceased. Southern Oscillation) events (8), as well as brate the older records. www.sciencemag.org SCIENCE VOL 293 27 JULY 2001 629 E COLOGY T HROUGH T IME Time Periods, Geography, and Analysis mercantile powers incorporating distant re- the Americas, New Zealand, and Australia We recognize three different but overlapping sources into a developing market economy. the different stages are well separated in time, periods of human impact on marine ecosys- Global use involves more intense and geo- and the aboriginal and colonial periods began tems: aboriginal, colonial, and global. Ab- graphically pervasive exploitation of coastal, at different times in the different regions. original use refers to subsistence exploitation shelf, and oceanic fisheries integrated into Thus, we can distinguish between cultural of near-shore, coastal ecosystems by human global patterns of resource consumption, with stages, as well as between human impacts and cultures with relatively simple watercraft and more frequent exhaustion and substitution of natural changes due to changing climate. extractive technologies that varied widely in fisheries. In Africa, Europe, and Asia, these The addition of a deep historical dimen- magnitude and geographic extent. Colonial cultural stages are strongly confounded in sion to analyze and interpret ecological prob- use comprises systematic exploitation and de- time and space, so that their differential sig- lems requires that we sacrifice some of the pletion of coastal and shelf seas by foreign nificance is difficult to establish. However, in apparent precision and analytical elegance prized by ecologists (1, 13, 14). Paleoeco- logical, archaeological, and historical data were collected for many purposes, vary widely in methods of collection and quality, and are less amenable to many types of statistical analysis than well-controlled experiments. But none of these problems outweighs the benefits of a historical approach. Clearly, we cannot generate realistic null hypotheses about the composition and dynamics of ecosystems from our understanding of the present alone, since all ecosystems have al- most certainly changed due to both human and natural environmental factors (8, 16, 27, 28). Here, we briefly review long-term human impacts in several

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