El Niño Southern Oscillation (ENSO) effects on fisheries and aquaculture

The survival of pre-industrial societies was tightly connected to climatic variation. The prominent global driver of year-to-year variation in the climate system is the El Niño Southern Oscillation (ENSO), a basin-scale phenomenon involving a coupling between the atmosphere and the ocean. The El Niño phenomenon was first recognized by South American fishers during the 1600s and was described as an unusual, warm ocean current off the coast of Peru. During strong El Niño events, tropical species arrive from the north while native fish species either migrate southwards or collapse, the most famous case being that of the Peruvian anchovy or anchoveta, populations of which typically collapse during these events. Seabirds and mammals along the Peruvian coast that largely depend on anchoveta for their food, as well as those occurring on the nearby Galapagos Islands, can also decline dramatically. The unusually warm water also causes heavy rain that can result in the coastal desert undergoing a floral bloom, while also being destructive to crops, property and infrastructure. In the course of the twentieth century, it was recognized that El Niño was not only a tropical coastal current but a large-scale phenomenon that affects weather patterns across the globe. The last five millennia have witnessed about 20 major El Niño events, which have radically affected the history of many societies in different parts of the world. ENSO impacts on climate, fisheries and aquaculture have recently been the focus of numerous scientific works but also stimulated considerable (and often overlysensational) media coverage. It should, however, be recognized that no two El Niño events are quite alike and that this diversity results in a variety of ecological as well as institutional and socio-economic responses. The recent discovery that ENSO is far more diverse than previously recognized highlights a pressing need to synthesize the impact of the different ENSO types on fisheries and aquaculture, two key components of the global food supply system. In addition, the possible effects of climate change on these sectors can be partly illustrated from the current effects of ENSO events, which are themselves affected by climate change. This document aims to synthesize current knowledge on the impact of the variety of ENSO events on fisheries and aquaculture in the context of a changing climate, and to identify existing and/or recommended adaptation/coping strategies to address ENSO-related events. After introducing the context of this document (Chapter 1), Chapter 2 describes the diversity of ENSO events. This document considers five types of ENSO events: Extreme El Niño, Moderate Eastern Pacific (EP) El Niño, Moderate Central Pacific (CP) El Niño, Coastal El Niño and Strong La Niña events. Chapter 3 discusses our current capability to predict ENSO events. It highlights that operational forecasts can provide accurate ENSO predictions up to nine months before the ENSO peak, but are currently unable to predict the type of El Niño that will occur, even at short lead-times. Chapter 4 discusses ENSO events in the context of climate change and shows that, although current climate model projections point towards a robust doubling of the frequency of extreme ENSO events, these models do not allow us to confidently assess if and how the overall ENSO activity (amplitude, frequency and pattern) will change in the future. Chapter 5 provides a global overview of ENSO impacts on ocean conditions, storms, climate and marine capture fisheries, indicating that ENSO alters climate, weather patterns and tropical cyclones (TCs) as well as oceanic conditions and productivity across the globe through atmospheric and oceanic teleconnections. These ENSO impacts are, however, sensitive to ENSO flavour. Global marine landings are reduced during extreme El Niño (−3.2 million tonnes) and EP El Niño (−0.7 million tonnes), increase during La Niña