Ocean Science

Sounds Fishy To Me

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Science  14 May 2010:
Vol. 328, Issue 5980, pp. 793
DOI: 10.1126/science.328.5980.793-a

Habitat volume (red) of the Peruvian anchovy

CREDIT: ARNAUD BERTRAND

A worrying increase in the number of reports of oxygen minimum zones (OMZs) in the world's oceans has important implications for fisheries and for climate change. OMZs are intense sites of denitrification, which contributes significantly to levels of atmospheric N2O, an important greenhouse gas that also depletes ozone. The ecological sequelae of OMZ formation can be profound because few species are able to avoid or tolerate extreme oxygen depletion. Consequently, where the upper depth limit of the OMZ approaches the surface, there is less vertical habitat available for pelagic organisms. Acoustic echoes reflect off small fish and zooplankton; where the echoes stop, life stops, and here lies the oxycline. Bertrand et al. have used this method off the coast of Peru, where the world's largest anchovy fishery is fed by a huge upwelling of nutrients associated with an OMZ. They estimated from survey data that the volume of oxygenated water available to the fishery was about 9000 km3 and ranged from a depth of 15 to 140 m with a marked latitudinal gradient. This method not only can be used to monitor changes in the oxycline but also offers a picture of the structure of an otherwise apparently featureless environment.

PLoS ONE 5, e10330 (2010).

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