Trophic Cascades in a Formerly Cod-Dominated Ecosystem
by Kenneth Frank et al. in Science 10 June 2005 vol. 308 pg. 1621-1623
Journal abstract: Removal of top predators from ecosystems can result in cascading effects through the trophic levels below, completely restructuring the food web. Cascades have been observed in small-scale or simple food webs, but not in large, complex, open-ocean ecosystems. Using data spanning many decades from a once cod-dominated northwest Atlantic ecosystem, we demonstrate a trophic cascade in a large marine ecosystem. Several cod stocks in other geographic areas have also collapsed without recovery, suggesting the existence of trophic cascades in these systems.
My commentary: This title doesn't need to be translated, since you now know what trophic means (from the previous article). There isn't any data obtained by sophisticated satellite imaging here, and the basic story is simple. The continental shelf off of Nova Scotia used to be a rich fishing ground for large predator fish: cod, haddock, hake, pollock, cusk, redfish, plaice, flounder, and skate. By 1993 these species had all been fished close to extinction, and a moratorium on further fishing was enacted. Never the less, in the last decade these populations have not rebounded.
However, there have been dramatic increases in the populations and landings (harvests) of the species these large fish used to eat, primarily Northern Snow crab and shrimp. In addition, while populations of small zooplankton have remained fairly stable, the concentration of larger zooplankton, which the crabs and shrimp feed on, has decreased (this justifies the term "cascades" in the title).
The total monetary value of the increased crab and shrimp harvests are actually much larger than the value of the larger fish that just to come from the region. However, the authors warn of the risks of "fishing down the food web", with all its unknown consequences.