On the size of the Peru upwelling ecosystem

Previously published estimates of the area of the Peru upwelling ecosystem vary by more than an order of magnitude. In an effort to improve this situation, we used a 24-month sequence of SeaWiFS satellite images of chlorophyll in the surface water off Peru from 51S to 18.51S during September 1997–August 1999 to estimate the size of the nutrient enhanced productive habitat associated with the upwelling. The first 12month period was marked by El Ni * no conditions, the second by strong upwelling. Using a chlorophyll threshold of >1.0mgm to define the limit of the productive habitat resulted in maximum area estimates of 120 10 km during September 1997–August 1998, and 220 10 km during September 1998–August 1999. The latter result is consistent with an area estimate we calculated using total fishery landings and a regression relating fishery yields per unit area to annual primary production per unit area. Although yearto-year variation in the annual mean size of the upwelling ecosystem must be significant, even discounting El Ni * no events, our analysis has shown that at least five of the extreme earlier values are not good estimates of the size of the productive habitat. We may now be close to knowing the average size of the ecosystem to within a factor of about two. r 2001 Elsevier Science Ltd. All rights reserved.