CONSIDERATIONS ON SAMPLING STRATEGIES FOR AN HOLISTIC APPROACH TO STOCK IDENTIFICATION: THE EXAMPLE OF THE HOMSIR PROJECT

Abstract Stock identification research can be classified as an observational study, the main characteristic of sampling being that there is no opportunity to repeat the process under similar conditions. To obtain useful information with this limitation, several considerations can be outlined. Time and space sampling require intensive field work. It is necessary to repeat sampling over time (more than 1 year of sampling) to estimate temporal stability of the investigated patterns. The spawning season should also be considered in the sampling process to assure the homogeneity of spawning populations and identify the spawning grounds. The ideal situation would be to sample the whole species’ distribution area making an a priori compromise between the effort and the biological information to be obtained. Inherent genetic variability of biological material is an important source of ecological variability. Therefore, performing all the different stock identification techniques on the same specimen reduces uncertainty when interpreting the results. The sampling logistics, taking into consideration the requirements of the different techniques applied, is a key-point in any stock identification project. We also considered the experience within the EU-funded project on horse mackerel stock identification research (HOMSIR), which has provided the chance to apply several techniques that play a key role in stock identification.