Fish egg mortality is relevant for ecological studies and also required to estimate egg production by the Daily Egg Production Method (DEPM), with a consequent effect on the Spawning Stock Biomass (SSB) estimation. An external mortality model for anchovy (Engraulis encrasicolus) eggs in the Gulf of Cadiz is estimated in order to overcome the high variability introduced by yearly estimates for mortality and therefore improve the egg production estimation. To establish the model, extra data on abundances by development stage were obtained by revising all the data from several research surveys that included plankton sampling, carried out in waters of the Gulf of Cadiz during 2005-2014. A total of 31119 anchovy eggs were classified into the 11 stages described by Moser and Ahlstrom, 1985. For each sample the information on water temperature, sampling depth and location was also recovered. The process to estimate mortality and egg production include 3 steps: 1) estimation of daily cohort abundance by age; 2) mortality estimation considering variables such as temperature and geographical strata; 3) P0 calculation using the mortality values obtained in step 2. The results show a clear effect of temperature in the egg mortality rate and also a spatial pattern in its distribution which are then reflected in the egg production estimate
