Modelling distributions of rare marine species : the deep-diving cetaceans

• Main Author: Virgili, Auriane
• Other Authors: La Rochelle, Monestiez, Pascal, Ridoux, Vincent
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Espèces rares; Modélisation d’habitat; Cétacés grands plongeurs; Baleines à bec; Cachalots; Kogiidés; Océan Atlantique Nord; Mer Méditerranée; Rare species; Habitat modelling; Deep-diving cetaceans; Beaked whales; Sperm whales; Kogiids; North Atlantic Ocean; Mediterranean Sea; envir; geo; North Atlantic
• Online Access: http://www.theses.fr/2018LAROS003/document

Deep-diving cetaceans, sperm- and beaked whales Physeteridae, Kogiidae and Ziphiidae, are rare marine species. Due to their low densities, wide distribution ranges and limited presence at the water surface, visual surveys usually result in low sighting rates. This paucity of data challenges the modelling of their habitat, prerequisite for their conservation. Models have to cope with a great number of zeros that weakens the ability to make sound ecological inferences. Consequently, this thesis aimed at finding a methodology suitable for datasets with a large number of zeros, determining how environmental variables influence deep-diver distributions and predicting areas preferentially used by these species. By testing the predictive performance of various habitat models fitted to decreasing numbers of sightings, I selected the most suitable model and determined that at least 50 sightings were needed to provide reliable predictions. However, individual surveys can rarely provide sufficient deep-diver sightings thus I merged many visual survey datasets to produce the first basin-wide deep-diver density maps in the North Atlantic Ocean and the Mediterranean Sea. Highest densities were predicted in waters from 1500-4000 m deep and close to thermal fronts hotspots were predicted along the continental slopes, particularly in the western North Atlantic Ocean. In addition, a model transferability analysis highlighted that habitat drivers selected by the models varied between contrasted large ecosystems. Finally, I discussed challenges related to statistical modelling applied to rare species and the management applications of this thesis. Les cétacés grands plongeurs, cachalots Physeteridae et Kogiidae, et baleines à bec Zipiidae, sont des espèces marines rares. Leur faible densité, aire de distribution étendue et faible disponibilité en surface génèrent de faibles taux d’observations. Cette particularité constitue un défi pour la modélisation d’habitat de ces espèces, préalable à leur conservation. Les modèles doivent ...