Sharp decreases in survival probabilities in the long-finned pilot whales in Strait of Gibraltar

Abstract

The Strait of Gibraltar has some of the highest maritime activity in the world. Its populations of cetaceans are threatened by noise, chemical pollution, and collisions by the many boats crossing the strait. One of the greatest threats identified in cetaceans in the Mediterranean are epizootics that severely affect the most sensitive vital rate in long-lived species: adult survival. By a multi-event analysis of a 16-year database of long-finned pilot whale photo identification capture–recapture data, we analysed adult survival in the Strait of Gibraltar’s resident population and evaluated the possible effects of epizootics on this vital rate. We identified the large effect of a morbillivirus epizootic that occurred in 2006–2007, but we also revealed a second collapse in survival in 2011, probably due to another morbillivirus epizootic. These episodes seem to affect sexes differently, with females being less affected than males. Interestingly, the morbillivirus epizootic not only sharply decreased survival after the episode, but the effect extended over time, probably showing post-epizootic sequelae. These disease outbreaks have increased during the last decades worldwide and could be linked to anthropogenic threats such as organochlorine contamination. This may explain the high frequency of epizootics in the Gibraltar area. We warn about the conservation status of this long-finned pilot whale population and recommend the application of measures to reduce contamination on this nutrient-rich area to improve conditions for many marine species inhabiting this area.