The evolution of oceanographic conditions off Peru during 1996-1998, including the 1997-1998 El Niño, is studied with in-situ data from coastal tide gauges and with satellite data from the Advanced Very-High Resolution Radiometer (AVHRR), European Remote-sensing Satellite (ERS), National Aeronautics and Space Administration (NASA) Scatterometer (NSCAT), Ocean Color and Temperature Scanner (OCTS), and Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Maximum anomalies of in-situ sea level (>22 cm) and sea surface temperature (SST) (>4°C) occurred near Callao at 12°S in June-July 1997 and December 1997-January 1998. Scalar wind speed at the coast increased between May 1997 and June 1998, indicating the anomalous océanographie conditions do not result from cessation of coastal upwelling. Monthly unrestricted catch of small pelagic fish surpassed 1 million tons between December 1996 and June 1997, as catchability increased during the onset of warm conditions. Satellite data contributed to a recognition that the anomalous conditions in April-June 1997, which facilitated unseasonably high catches, were part of a large-scale perturbation. This spurred the implementation of regulatory mechanisms to protect the stock, despite strong opposition from the fishing industry. However, later in the event, misinterpretation of satellite data led to premature claims that El Nino was ending and subsequent poor decision-making and confusion by different actors in society. The prediction of return to normal conditions was premature, as the second peak of the El Niño arrived in December 1997-January 1998. Observations and numerical model simulations from a planktonic ecosystem model are compared with variations of the Peruvian catch of small pelagic fish to quantify the impact of El Nino on pelagic fish catch. The two highest correlation coefficients, r, computed between monthly fish catch and several biological and physical variables were associated with cross-shelf SST difference (r = -0.55) and modeled food available for fish (r = 0.50).
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