Effect Of Enso On The Distribution And Concentration Of Catches And Reproductive Activity Of Anchovy Engraulis Ringens In Northern Chile

Abstract Anchovy makes up 90% of pelagic fishery catches in northern Chile. For the present work, anchovy ( Engraulis ringens , Jenyns 1842) catches between 1997 and 2016 were analyzed to determine changes in distribution, concentration, and reproductive behavior before, during, and after ENSO events, using spatial indexes: gravity center ( GC ), inertia, coverage ( CI ), Gini index, and gonadosomatic index ( GI ). At the start of ENSO , anchovy catches increased and concentrated along the coast (rising Gini index), while CI decreased. During ENSO , Gini decreased, registering a southward displacement of the GC and smaller catches. In the long run, anchovy occupied lesser area (< CI ) starting from 2008, concentrating in coastal areas. It developed a size structure composed mainly of specimens smaller than 17.0 cm. In addition, specimens < 12.0 cm were positively correlated with thermal anomalies, CI and MEI , reaching more than 60% of the catches during the 1997–1998 and 2015–2016 ENSO cycles. Results suggest that the warm phase of ENSO alters the anchovies’ reproductive activity, delaying its onset up to 4 weeks, and reducing GI intensity to 50%, due to increased participation in the reproductive process of individuals 12.0–13.5 cm. Therefore, large‐scale environmental processes, such as ENSO , significantly affect size structure and contribute to reduction of occupied area and higher reproductive activity of small‐size anchovies.