A revision of daily egg production estimation methods, with application to Atlanto-Iberian sardine. 1. Daily spawning synchronicity and estimates of egg mortality

Abstract

Assumptions of daily spawning synchronicity and estimation of egg mortality for Atlanto-Iberian sardine are revised in the context of daily estimators of egg production. An extensive database of ichthyoplankton surveys from 1985 to 2008, aggregated at different levels, is used, a set of mortality models is derived, and a comparison among them is carried out using standard statistical techniques. Analysis of the database shows Atlanto-Iberian sardine to be a late-evening spawner, in agreement with previous knowledge, but suggests a lengthier daily period of spawning. Comparison among the set of mortality models used suggests that estimates of mortality from single surveys for Atlanto-Iberian sardine are often unreliable, and that the mean estimates obtained after aggregating data from various years are statistically significant, more robust, and in line with existing information gathered from the literature.