Ecología y conservación del rorcual común en el mediterráneo español

Abstract

Population structure of Northeast Atlantic and Mediterranean fin whales has been the subject of scientific and management debates for half a century. The aim of this thesis was to improve the knowledge about this population structure, with a particular focus on the Strait of Gibraltar, and to use it to inform the Spanish Mediterranean conservation plan. Therefore, direct observations and skin samples collected in the Strait of Gibraltar and combined with samples from the Northeast Atlantic and the Mediterranean regions, to investigate the level of connectivity for fin whales currently observed in the Strait of Gibraltar with these two contiguous regions through stable isotopes and population genetic analyses. Fin whales are currently using the Strait of Gibraltar as a seasonal migration corridor with remarkable directionality. Between May and October, all whales travelled to the Atlantic Ocean and between November and April most individuals were moving to the Mediterranean Sea. Photographic recaptures of naturally marked individuals suggest that these migratory movements are recurrent at least for some whales. Fin whales sampled in the Strait of Gibraltar presented seasonal differences in stable isotopes ratios consistent with the direction of migration, suggesting that they feed in the Northeast Atlantic Ocean during the summer months but also exploit Mediterranean prey during the winter months. These whales may share a common Northeast Atlantic feeding ground with other fin whales sampled in NW Spain, the Azores archipelago and west Iceland, but each at different times during the year. However, Strait of Gibraltar fin whales exhibited more genetic connectivity to individuals sampled in the NW Mediterranean Sea than with their Northeast Atlantic counterparts. Diversity indices and effective population size estimates were similar in Gibraltar and Mediterranean Sea whales and significantly lower than in Northeast Atlantic Ocean samples. Nevertheless, the evidence was stronger with mitochondrial DNA sequences than with nuclear microsatellites, which could be due to female philopatry in each basin and occasional male-mediated gene flow between basins. Together, these results suggest that fin whale inhabiting the Mediterranean Sea should be considered one Management Unit (MU). These whales are at risk from ship strikes, especially when they cross areas of intense maritime traffic such as the Strait of Gibraltar where the insufficient implementation of the 13-knot vessel speed recommendation leave them, in practice, unprotected. Underwater noise and limited food availability due to climate change were also major threats identified for this MU. An Action plan was proposed to ensure the conservation of fin whales in the Spanish Mediterranean.