Population Dynamics of the Peruvian scallop Argopecten purpuratus during the El Niño Phenomenon of 1983

Abstract

Population size, growth, and mortality rates of the Peruvian scallop (Argopecten purpuratus were studied during the El Niño event of 1983 in the fishing area off Pisco, Peru. Gonadal index and larval abundance of this scallop as well as measurements of in situ temperature, dissolved oxygen, and plankton volumes were taken to record spawning activity and environmental conditions. The scallop population size exceeded 60 times that of "normal" years. It is thought to be due to a significant increase in survival rate of larval and juvenile scallops and/or intensified spawning activity with subsequent recruitment in the warm El Niño waters. Only small scallops (15–45 mm shell height) showed accelerated growth due to elevated temperatures. Total mortality (Z) was estimated as 2.5 and natural mortality (M) as 1.0. the hypothesis is proposed that A. purpuratus is a relict of a tropical/subtropical fauna inhabiting the Peruvian and Chilean waters in the Miocene, which has maintained its warmwater characteristics during evolution in the cold upwelling water because of periodic post-Miocene El Niño events.