Resumen de Use of chemical markers in the study of distribution range and population structure of large cetaceans = Uso de marcadores químicos en el estudio del rango de distribución y de la estructura de poblaciones de grandes cetáceos
Cetaceans have historically been object of heavy exploitation, and are still currently subject to different threats. For conservation and management purposes, most of the large cetacean populations have been categorized in stocks, considered as isolated and demographically independent management units. Many research techniques may contribute in the definition of these stocks, such as morphometric studies, mark recapture studies, genetics, satellite tracking. This thesis focuses on the development and application to cetacean populations of chemical markers of geographical origin and spatial movements. The main objective of the thesis is to evaluate the potentialities of chemical markers, such as stable isotopes and element concentrations, to investigate the patterns of distribution, the level of structuring and, when possible, the migration routes, of cetaceans populations. All these variables are essential to ensure the implementation of proper management measures and to guarantee the conservation of these animals. Three case studies were considered: the Eastern North Atlantic sperm whale (Physeter macrocephalus); the South Western Atlantic right whale (Eubalaena australis), and the North Atlantic fin whale (Balaenoptera physalus). ?15N, ?13C and ?18O values were analyzed in the dentinal growth layers of sperm whales from Denmark and NW Spain, in bone of right whales from Southern Brazil and Northern Argentina, and in bone of fin whales from W Iceland and NW Spain; concentrations of fluoride and selected metals (Zn, Pb, Ti, Sr, Cu) were analyzed in bone of fin whales from W Iceland and NW Spain. To establish the validity of each marker, the degree of compliance of each of the following four properties has been investigated: i) the basal levels of the chemical marker in the environment present significant gradients; ii) the chemical marker can be detected and measured in the tissues of whales; iii) the variability of the chemical marker within each population is moderate or, alternatively, it is predictable through measurable parameters, so that its effect can be taken into account; and iv) the values of the chemical marker in the body tissues reflect basal levels in a predictable and consistent manner. Each marker provided, at different levels, valuable information regarding the studied populations. Some difficulties emerged, connected with the complexity of the migratory cycles of whales, the possible intervention of homeostatic regulation mechanisms, and the characteristics of the tissues investigated. Nevertheless, results highlighted the occurrence of structuring within the North Atlantic sperm whale population, as well as within the South Western Atlantic right whale population, which are both currently considered as a single management unit. Moreover, results regarding the North Atlantic fin whale populations contributed to highlight the complexity of migration patterns and of the level of connectivity among the currently accepted stocks, challenging the proper definition of their limits and their degree of isolation within the basin. Some further research is recommended to deepen the knowledge about the North Atlantic fin whale population structure, as well as to investigate the levels of chemical markers in other tissues with different turnover characteristics, such as skin or baleen plates. Overall, the results obtained from the analyses performed in this thesis underline the power of chemical markers as a complementary tool to the traditional techniques used for investigating the structure and demography of cetaceans’ populations.
