| Summary: | 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). δ15N, δ13C and δ18O 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. === Los cetáceos han estado y están actualmente sujetos a diferentes tipos de amenazas. Para su correcta gestión y conservación, la mayoría de las poblaciones de grandes cetáceos han sido categorizadas en “stocks”, considerados como unidades de gestión aisladas y demográficamente independientes. Muchas técnicas de investigación pueden contribuir en la definición de estas unidades, como los estudios morfométricos, los estudios de marcaje y recaptura, la genética y el seguimiento por satélite. El objetivo principal de esta tesis es evaluar las potencialidades de los marcadores químicos, tales como los isótopos estables y las concentraciones de algunos elementos, como herramientas para la investigación de los patrones de distribución y del nivel de estructuración de las poblaciones de cetáceos. Para ello, se han considerado tres casos modelo: el cachalote del Atlántico Nororiental, la ballena franca del Atlántico Suroccidental, y el rorcual común del Atlántico Norte. Se analizaron las proporciones isotópicas de δ15N, δ13C y δ18O en muestras de dientes de cachalote y de hueso de ballena franca y rorcual común; y las concentraciones de flúor y de metales pesados (Zn, Pb, Ti, Sr, Cu) en muestras de hueso de rorcual común. Cada marcador proporcionó, a diferentes niveles, información valiosa sobre las poblaciones estudiadas. Al interpretar los resultados, surgieron algunas dificultades relacionadas con la complejidad de los ciclos migratorios de los cetáceos, la posible intervención de mecanismos de regulación homeostática, y las características de los tejidos investigados. Sin embargo, los resultados destacaron cierto nivel de estructuración dentro de las poblaciones de cachalotes del Atlántico Norte y de ballenas francas del Atlántico Suroccidental, que actualmente están ambas consideradas como unidades de gestión únicas. Por otra parte, los resultados obtenidos en las poblaciones de rorcual común del Atlántico Norte contribuyeron a evidenciar la complejidad de los patrones migratorios y del nivel de conectividad entre sus poblaciones, desafiando la adecuada definición de sus límites y de su grado de aislamiento. En general, los resultados de la tesis destacan las potencialidades de los marcadores químicos como herramienta complementaria a las técnicas utilizadas tradicionalmente para la investigación de la estructura y demografía de las poblaciones de cetáceos.
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