From small‐scale habitat loopholes to decadal cycles: a habitat‐based hypothesis explaining fluctuation in pelagic fish populations off Peru

Abstract

The Peru‐Humboldt Current system (HCS) supports the world's largest pelagic fisheries. Among the world's eastern boundary current systems, it is the most exposed to high climatic stress and is directly affected by El Niño and La Niña events. In this volatile ecosystem, fish have been led to develop adaptive strategies in space and time. In this paper, we attempt to understand the mechanisms underlying such strategies, focusing on the El Niño 1997–98 in Peru from which an extensive set of hydrographic, capture and acoustic survey data are available. An integrated analysis of the data is crucial, as each has substantial shortcomings individually; for example, both catch data and acoustic surveys may easily lead to wrong conclusions. Existing hypotheses on anchovy and sardine alternations lead us to a ‘habitat‐based’ synthetic hypothesis. Using our data, an integrated approach evaluated how fish responded to habitat variation, and determined the consequences in terms of fish‐population variability. Various factors occurring at a range of different spatio‐temporal scales were considered: interdecadal regime (warm ‘El Viejo’/cool ‘La Vieja’ decadal scale); strength and the duration of the El Niño Southern Oscillation event (interannual scale); population condition before the event (interannual scale); fishing pressure and other predation (annual scale); changes in reproductive behaviour (intra‐annual scale); presence of local upwelling (local scale). During El Niño 1997–98, anchovy was able to exploit a small‐scale temporal and spatial ‘loophole’ inside the general unfavourable conditions. Moreover, sardine did not do better than anchovy during this El Niño and was not able to take advantage of the ‘loophole’ opened by this short‐term event. Our results question the traditional view that El Niño is bad for anchovy and good for sardine.

The future of coastal upwelling in the Humboldt current from model projections

“…This marine ecosystem is highly susceptible to changes in upwelling patterns, such as alteration in frequency or magnitude (Aravena et al 2014). Significant potential impacts due to climate change have been projected on the spawning rate of small pelagic fish, such as the Peruvian anchovy Engraulis ringens and the sardine Sardinops sagax (Brochier et al 2013), despite the projected temperatures remaining within accepted ecological ranges (Bertrand et al 2004). Small pelagic species strongly depend on zooplankton availability and the exceptional phytoplankton productivity in coastal upwelling zones .…”

Long-term changes in zooplankton size distribution in the Peruvian Humboldt Current System: conditions favouring sardine or anchovy

“…Besides deductive and laboratory evidence, several larger scale empirical studies in the HCS showed an association of anchovy with cold coastal upwelling and mixed upwelling oceanic waters (Bertrand et al 2004, Swartzman et al 2008. Additionally, in the California Current system (CCS), Rykaczewski & Checkley (2008) suggested that high coastal upwelling regimes were associated with higher anchovy production while wind curl generated upwelling, which tends to be weaker, was more associated with sardine dominance.…”

Influence of temperature on the zoeal development and elemental composition of the cancrid crab, Cancer setosus Molina, 1782 from Pacific South America

“…The persistent stable temperate conditions in a broad range of the Humboldt Current allow larvae to develop all year round (for review see Fischer and Thatje, 2008). As one of the world's most productive ecosystems, the Humboldt Current supports one of the world's largest fisheries (Bertrand et al, 2004) which is of high economical importance for the adjacent countries (Ryther, 1969;Urban and Tarazona, 1996;Food and Agricultural Organization, 2006). The availability of resources is highly dependent on the global coupled ocean-atmosphere phenomenon El Niño Southern Oscillation (ENSO) (Lehodey et al, 2006).…”