Barange begins this article by describing how the 1992 United Nations (UN) Conference on Environment and Development in Rio de Janeiro, Brazil, highlighted the need for ecosystem level management of marine resources. He then outlines the legal and institutional efforts since the 1992 Rio conference. These include the UN Convention on the Law of the Sea, the Food and Agriculture Organization (FAO) of the UN agreements, and the Kyoto Declaration on Fisheries and Food Security of 1995.
Barange states that these new legal efforts were developed because marine fisheries are at a crossroads: “In 1999, about 50% of all marine fisheries were fully exploited, 20% were overexploited, and a further 10% were depleted (FAO 2000). In the 1990’s, the annual rate of increases of marine catches decreased to almost zero, and may even be negative (Watson and Pauly 2001). This indicates that, on average, the world’s oceans have reached their maximum production, estimated to be about 80-100 million metric tons (FAO 2000).”
One response to this very serious situation is the development of ecosystem-based management systems (EBMS). This article addresses the question of whether we know enough about the structure, function, and components of marine ecosystems to predict the ecological impact of current and past fishing practices.
Barange highlights three areas of scientific development over the last decade which are especially relevant to this issue:
In this section Barange describes large changes in marine species on the 100 - 1000 year scale. Figure 1 shows very large variation in anchovy abundance off the coast of California from the years 280 – 2000 based on fish scale deposits in sediments. He states that gradual anthropogenically-driven change (due to global warming, for instance), will not likely result in greater changes than those that have occurred naturally. Instead, “the perception is that the real effects of global change on marine ecosystems will be the result of interactions [emphasis added] between anthropogenic pressures and natural cycles of variability.”
Here Barange describes how the worldwide abundance of pelagic fish cycles (e.g., sardines, Pollock, mackerel) in synchrony on decadal scales. Studies of atmospheric pressure and circulation suggest that fish production may be in part regulated by global environmental cycles (wind, in this case). This is contrary to many people’s assumption that local-scale processes mostly regulate fisheries.
Photographs of catches from bottom trawlers off Alaska (Fig. 4) dramatically illustrate what Barange calls a “regime shift.” Before 1977, the fishery was largely based on invertebrates; after 1977, finfish were the dominant catch. This shift appears to be related to a change in climate on a decadal scale. Warmer waters off the northeast coast lead to decreased zooplankton abundance and increases in most Alaskan salmon stocks.
Ecologists know that pressures on both the top and bottom of food webs can cascade through all trophic levels. However, Barange notes that we do not know how resilient marine systems are to such cascading changes, or how species diversity affects these cascades. Given the interdecadal abundance cycles described above, resilience may also vary with fish production.
Barange highlights three areas of scientific development over the last decade which are especially relevant to this issue. The figures listed below are in the “Figures” section of this Issue.