MODELLING DISTRIBUTIONS OF RARE MARINE SPECIES: THE DEEP-DIVING CETACEANS

• Main Author: Virgili, Auriane
• Other Authors: AGROCAMPUS OUEST, Université de La Rochelle, Vincent Ridoux, Pascal Monestiez
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2018
• Subjects: Rare species; habitat modelling; deep-diving cetaceans; beaked whales; sperm whales; kogiids; North Atlantic Ocean; Mediterranean Sea; Espèces rares; modélisation d’habitat; cétacés grands plongeurs; baleines à bec; cachalots; kogiidés; océan Atlantique Nord; mer Méditerranée; [SDE]Environmental Sciences; North Atlantic
• Online Access: https://hal.science/tel-02265299; https://hal.science/tel-02265299/document; https://hal.science/tel-02265299/file/Virgili_Auriane.pdf

Deep-diving cetaceans, sperm- and beaked whales Physeteridae, Kogiidae and Ziphiidae, arerare marine species. Due to their low densities, wide distribution ranges and limited presence at the watersurface, visual surveys usually result in low sighting rates. This paucity of data challenges the modelling oftheir habitat, prerequisite for their conservation. Models have to cope with a great number of zeros thatweakens the ability to make sound ecological inferences. Consequently, this thesis aimed at finding amethodology suitable for datasets with a large number of zeros, determining how environmental variablesinfluence deep-diver distributions and predicting areas preferentially used by these species. By testing thepredictive performance of various habitat models fitted to decreasing numbers of sightings, I selected themost 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 visualsurvey datasets to produce the first basin-wide deep-diver density maps in the North Atlantic Ocean andthe Mediterranean Sea. Highest densities were predicted in waters from 1500-4000 m deep and close tothermal fronts; hotspots were predicted along the continental slopes, particularly in the western NorthAtlantic Ocean. In addition, a model transferability analysis highlighted that habitat drivers selected by themodels varied between contrasted large ecosystems. Finally, I discussed challenges related to statisticalmodelling applied to rare species and the management applications of this thesis. Les cétacés grands plongeurs, cachalots Physeteridae et Kogiidae et baleines à bec Zipiidae, sontdes espèces marines rares. Leur faible densité, aire de distribution étendue et faible disponibilité ensurface génèrent de faibles taux d’observations. Cette particularité constitue un défi pour la modélisationd’habitat de ces espèces, préalable à leur conservation. Les modèles doivent gérer l’abondance ...