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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002 


Impact of Climate Variability on
Small Pelagic Fish Stocks - a
Comparative View*

Jürgen Alheit

Baltic Sea Research Institute, Seestr. 15, 18119
Warnemünde, Germany,

Small pelagic fishes such as the sardine, anchovy, herring, and others, represent about 20 - 25 % of the total annual world fisheries catch. They are widespread and occur in all oceans. They support important fisheries all over the world and the economies of many countries depend on those fisheries. They respond dramatically and quickly to changes in ocean climate. Most are highly mobile, have short, plankton-based food chains, and some even feed directly on phytoplankton. They are short-lived (3-7 years), highly fecund, and some can spawn all year round. These biological characteristics make them highly sensitive to environmental forcing and extremely variable in their abundance. Thousandfold changes in abundance over a few decades are characteristic for small pelagics, and well-known examples include the Japanese sardine, sardines in the California Current, anchovies in the Humboldt Current, sardines in the Benguela Current, and herring in European waters. Their drastic stock fluctuations often caused dramatic consequences for fishing communities, entire regions and even whole countries. Their dynamics have important economic consequences as well as ecological ones. They are important food sources for larger fish, seabirds, and marine mammals. The collapse of small pelagic fish populations is often accompanied by sharp declines in marine bird and mammal populations that depend on them for food. Major changes in abundance of small pelagic fishes may also be accompanied by marked changes in ecosystem structure, for example, in abundance and species composition of zooplankton. The great potential plasticity in the growth, survival and other life-history characteristics of small pelagic fishes is the key to their dynamics and makes them ideal targets for testing the impact of climate variability on marine ecosystems and fish populations.

Huge populations of sardiny and anchovies live in the upwelling ecosystems of the eastern boundary currents (California, Humboldt, Canary, and Benguela Currents) and in the waters around Japan. They support important fisheries, mainly for fish meal, and the well-being of the economy of the riparian countries of upwelling systems depends heavily on these fisheries. The dynamics of these anchovy and sardine populations are characterised by their inverse relationships. When one species is doing well and supports a large biomass and high production, the other species usually sustains a rather low biomass. These shifts between sardine-dominated and anchovy-dominated states seem to restructure the entire ecosystem, as concomittant qualitative and quantitative changes in ecosystem components other than the sardine and anchovy populations have been observed. Because of their dramatic and long-lasting nature, these switches have been termed "regime shifts". The causes of regime shifts and teleconnection patterns between the dynamics of small pelagics are not clear.

* Keynote presentation

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