Ecological segregation inferred using chemical tracers and contamination assessment of five toothed whales in the Northwest Iberian Peninsula

The first objective of this PhD was to determine the degree of ecological segregation between five sympatric species of toothed whales (i.e. common dolphin Delphinus delphis, harbour porpoise Phocoena phocoena, bottlenose dolphin Tursiops truncatus, striped dolphin Stenella coeruleoalba and long finned pilot whale Globicephala melas) inhabiting a restricted and highly productive area, the North West Iberian Peninsula (NWIP). To this end, chemical parameters analyses were used as an “alternative method” of assessing diet and habitat of these animals over different periods of integration, complementing the information given by traditional methods of investigation such as stomach contents, faeces analyses and field observations. The second objective was to evaluate the contamination status of these species in order to estimate the toxicological risk these populations face and to complete the existing database. In this context, trace elements, carbon and nitrogen stable isotopes, as well as persistent organic pollutants (POPs) were selected as chemical parameters for our investigations.Firstly, the chemical parameters were used as ecological tracers of populations (or parts of populations) by drawing an image of the diet and habitat of the species at different time scales. We estimated that the food web has five trophic levels, with toothed whales occupying the top positions, with no significant difference in trophic positions among them, ranging from 4.3 to 5.3. While the analysis of a single chemical parameter did not completely segregate between the five species, the information gained by combining the analyses of several long-term ecological tracers (i.e. nitrogen and carbon stable isotopes in teeth and renal cadmium concentrations) revealed ecological niche segregation in two dimensions of this niche (the trophic and the spatial dimensions). However, year-to-year or seasonal variations could not be investigated, except for in common dolphin, and thus temporary overlap cannot be excluded. Additionally, we showed that polychlorinated biphenyls (PCBs) profiles could be a relevant tracer of the foraging ecology of taxonomically close species, allowing a fine separation of the species as result of their different patterns. This was particularly clear for the harbour porpoise and striped dolphin.Secondly, the contamination status of the species in this area was evaluated, with concentrations interpreted in the light of biological and ecological factors. But the bioaccumulation of trace elements appeared to be less predictable than that of POPs. Bottlenose dolphins and harbour porpoises were found to have higher PCBs concentrations than the rest of the analysed NWIP toothed whales, as well as those of adjacent NE Atlantic waters.The main results of this PhD highlight the relevance of exploiting these chemical parameters as ecological tracers, as well as their usefulness in the comprehensive study of structure and function of ecosystems through the role of top predators. Combined with the information on anthropogenic activities, this work can also contribute to the development and implementation of management plans and mitigation measures for these five species of toothed whales in the NWIP.