Daily anchovy (Engraulis ringens) egg mortality rates in different spawning zones along the Chilean coast

The daily egg mortality (Z) of small pelagic fish can be modulated by environmental variables as well as by population derived factors such as egg production and/or dispersion and aggregation processes. The anchovy daily egg mortality rate was compared across spawning areas distributed in the North (18∘25’S-26º03’S), Central (34º30’S-37º10’S), and South (38∘S-41∘20’S) zones along the Chilean coast. Daily egg production (P0) and Z were estimated through a generalized linear model (binomial negative) from egg count data obtained in yearly Daily Egg Production Method applications (2002–2014). Co-variables included P0, the spawning area (SA), sea surface temperature (SST), phytoplankton biomass (Chl-a), alongshore wind (V) and an index of the El Niño-Southern Oscillation (ENSO) during the spawning period (August–September).Egg mortality was significantly higher in the North zone, influencing spatial differences rather than yearly effects. Egg mortality was not associated with ENSO, but correlated positively with P0, SA, SST, and V, and negatively with Chl-a. The best model explained 42.3% (P<0.01) of the egg mortality rates and included SST and Chl-a. In the South zone, the egg mortality was significantly correlated with P0 and V, which was interpreted as density-dependent effects and winds driving egg concentration processes rather than dispersion. The Lloyd’s patchiness index was computed as an index of egg aggregation by embryonic development stages (Group A: early development, Group B: middle development, and Group C: close to hatching). The spawning area was negatively correlated with the patchiness index of Groups A and B in the North zone. Overall results suggested that anchovy eggs survival would be dependent on dispersion in the North zone but concentration and retention in the South spawning area and thereafter coincident with reproductive tactics of adults in the North and South areas, respectively.