Distribution, abundance and habitat use of deep diving cetaceans in the North-East Atlantic

Abstract

In spite of their oceanic habitat, deep diving cetacean species have been found to be affected by anthropogenic activities, with potential population impacts of high intensity sounds generated by naval research and oil prospecting receiving the most attention. Improving the knowledge of the distribution and abundance of this poorly known group is an essential prerequisite to inform mitigation strategies seeking to minimize their spatial and temporal overlap with human activities. We provide for the first time abundance estimates for five deep diving cetacean species (sperm whale, long-finned pilot whale, northern bottlenose whale, Cuvier's beaked whale and Sowerby's beaked whale) using data from three dedicated cetacean sighting surveys that covered the oceanic and shelf waters of the North-East Atlantic. Density surface modelling was used to obtain model-based estimates of abundance and to explore the physical and biological characteristics of the habitat used by these species. Distribution of all species was found to be significantly related to depth, distance from the 2000m depth contour, the contour index (a measure of variability in the seabed) and sea surface temperature. Predicted distribution maps also suggest that there is little spatial overlap between these species. Our results represent the best abundance estimates for deep-diving whales in the North-East Atlantic, predict areas of high density during summer and constitute important baseline information to guide future risk assessments of human activities on these species, evaluate potential spatial and temporal trends and inform EU Directives and future conservation efforts

Combining multiple visual surveys to model the habitat of deep‐diving cetaceans at the basin scale

“…In the Mediterranean Sea, our predictions were consistent with the documented presence of beaked whales and sperm whales in the Alborán, Tyrrhenian and Ligurian Seas (Arcangeli, Campana, Marini, & MacLeod, ; Cañadas et al, ; Lanfredi et al, ; Praca & Gannier, ) and along the eastern coasts of the Mediterranean Sea (Podestà et al, ). In the North Atlantic Ocean, the highest relative densities of beaked whales and sperm whales were predicted along the slope, a result consistent with those of Rogan et al () and Roberts et al (). In the north‐west Atlantic Ocean, higher relative densities of kogiids were predicted in warmer and deeper waters, which is consistent with their known ecology (McAlpine, ) and the predictions of Mannocci, Roberts, Miller, and Halpin () except for predictions off the coast of Florida.…”

“…Due to the very low sighting rates of deep‐diving cetaceans, each survey taken separately cannot provide enough data to investigate the habitats of these rare species. In contrast to Rogan et al (), we did not assemble data collected with similar protocols but data collected with different variants of the line‐transect distance sampling protocol, which meant standardizing the data according to their core communalities before developing a single spatial model. Ideally, at a time when shared databases are becoming increasingly important (e.g., OBIS SEAMAP – https://seamap.env.duke.edu/, EMODnet – https://www.emodnet.eu/), implementing standardized survey methods would greatly improve data compatibility, by enhancing the level of communalities in shared datasets, and helping to describe large‐scale habitats and distributions of marine species.…”

“…Due to the very low sighting rates of deep-diving cetaceans, each survey taken separately cannot provide enough data to investigate the habitats of these rare species. In contrast to Rogan et al (2017), we did not assemble data collected with similar protocols but data collected with different variants of the line-transect distance sampling protocol, which meant standardizing the data according to their core communalities before developing a single spatial model. Ideally, at a time when shared databases are becoming increasingl y important (e.g., obIs seaMap -https://seamap.env.…”

New information on the diet of True's beaked whale (Mesoplodon mirus, Gray 1850), with insights into foraging ecology on mesopelagic prey

“…, Oudejans , Rogan et al . ). Despite the information compiled in these studies, knowledge on the ecology of True's beaked whales is poorly known and usually gleaned from the small number of strandings.…”

“…However, during the last two decades, our knowledge on the ecology of several species in this family has dramatically increased. Different studies in Ireland have suggested that the deep areas of the Rockall Trough, Porcupine Bight, and slope systems off the northwest of Ireland, where bathymetry might be >1,000 m depth, may provide important habitats for beaked whales (Boisseau et al 2011, Wall et al 2013, Oudejans 2014, Rogan et al 2017. Despite the information compiled in these studies, knowledge on the ecology of True's beaked whales is poorly known and usually gleaned from the small number of strandings.…”