Optimal oceanographic conditions in the distribution of the anchovy and changes after the 1997–1998 El Niño event

In order to determine the optimal conditions of the oceanographic variables in the habitat of the anchovy “Engraulis ringens” (hereafter referred to as anchoveta for short) were used data of the cruises realized for Instituto del Mar del Peru (IMARPE) between 1985 and 2015. We used generalized additive models (GAM) with the Tweedie distribution; the dependent variable was the Nautical Area Scattering Coefficient (NASC) value for anchoveta obtained from echo sounder. Tested covariates were temperature, salinity and dissolved oxygen at the surface of the sea, distance from the coast, year, latitude-longitude, and Oceanic index El Niño 1+2. Results showed that the anchoveta habitat is conditioned to lower temperatures in the winter (14.2–18.5°C) and higher in summer (from 16.9–23.6°C). In summer, the anchoveta was detected in waters with lower salinity due to the approach of warm currents from Ecuador in the northern sector and the discharge of the rivers in the coastal sector; the salinity range associated with anchoveta distribution is usually narrow (32.01–35.21 psi). Oxygen values observed in the anchoveta distribution fluctuated between 4.3 and 8.6 mL.L
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. After the 1997–1998 El Niño event, anchoveta was found in ranges of these three oceanographic variables that were slightly wider than values found before the 1997–1998 El Niño; likewise, other authors found wider ranges for other variables, such as upwelling efficiency, cold coastal waters, equatorial Kelvin waves, zooplankton biomass, and sea surface temperature. Seasonal adaptation of anchoveta environmental conditions over time is due to their resilience and adaptability to extreme values of their habitat; these characteristics must be taken into account in order to generate predictive models of distribution and biomass for this species.