Cetaceans in the Mediterranean Sea. Encounter rate, dominant species, and diversity hotspots

We investigated the presence and diversity of cetaceans in the Mediterranean Sea, analysing the data collected by 32 different research units, over a period of 15 years (2004–2018), and shared on the common web-GIS platform named Intercet. We used the encounter rate, the species prevalence, and the Shannon diversity index as parameters for data analysis. The results show that cetacean diversity, in the context of the Mediterranean basin, is generally quite low when compared with the eastern Atlantic, as few species, namely the striped dolphin, the bottlenose dolphin, the fin whale, and the sperm whale, dominate over all the others. However, some areas, such as the Alboran Sea or the north-western Mediterranean Sea, which includes the Pelagos Sanctuary (the Specially Protected Area of Mediterranean Interest located in the northern portion of the western basin), show higher levels of diversity and should be considered hotspots to be preserved. Primary production and seabed profile seem to be the two main drivers influencing the presence and distribution of cetaceans, with the highest levels of diversity observed in areas characterized by high levels of primary production and high bathymetric variability and gradient. This collective work underlines the importance of data sharing to deepen our knowledge on marine fauna at the scale of the whole Mediterranean Sea and encourages greater efforts in the networking process, also to accomplish the requirements of the Marine Strategy Framework Directive, with particular reference to Descriptor 1: biological diversity is maintained

Biogeography in the deep : hierarchical population genomic structure of two beaked whale species

Funding for this research was provided by the Office of Naval Research, Award numbers N000141613017 and N000142112712. ABO was supported by a partial studentship from the University of St Andrews, School of Biology; OEG by the Marine Alliance for Science and Technology for Scotland (Scottish Funding Council grant HR09011); ELC by a Rutherford Discovery Fellowship from the Royal Society of New Zealand Te Aparangi; NAS by a Ramon y Cajal Fellowship from the Spanish Ministry of Innovation; MLM by the European Union’s Horizon 2020 Research and Innovation Programme (Marie Skłodowska-Curie grant 801199); CR by the Marine Institute (Cetaceans on the Frontier) and the Irish Research Council; and MTO by the Hartmann Foundation.The deep sea is the largest ecosystem on Earth, yet little is known about the processes driving patterns of genetic diversity in its inhabitants. Here, we investigated the macro- and microevolutionary processes shaping genomic population structure and diversity in two poorly understood, globally distributed, deep-sea predators: Cuvier’s beaked whale (Ziphius cavirostris) and Blainville’s beaked whale (Mesoplodon densirostris). We used double-digest restriction associated DNA (ddRAD) and whole mitochondrial genome (mitogenome) sequencing to characterise genetic patterns using phylogenetic trees, cluster analysis, isolation-by-distance, genetic diversity and differentiation statistics. Single nucleotide polymorphisms (SNPs; Blainville’s n = 43 samples, SNPs=13988; Cuvier’s n = 123, SNPs= 30479) and mitogenomes (Blainville’s n = 27; Cuvier’s n = 35) revealed substantial hierarchical structure at a global scale. Both species display significant genetic structure between the Atlantic, Indo-Pacific and in Cuvier’s, the Mediterranean Sea. Within major ocean basins, clear differentiation is found between genetic clusters on the east and west sides of the North Atlantic, and some distinct patterns of structure in the Indo-Pacific and Southern Hemisphere. We infer that macroevolutionary processes shaping patterns of genetic diversity include biogeographical barriers, highlighting the importance of such barriers even to highly mobile, deep-diving taxa. The barriers likely differ between the species due to their thermal tolerances and evolutionary histories. On a microevolutionary scale, it seems likely that the balance between resident populations displaying site fidelity, and transient individuals facilitating gene flow, shapes patterns of connectivity and genetic drift in beaked whales. Based on these results, we propose management units to facilitate improved conservation measures for these elusive species.Publisher PDFPeer reviewe

The challenge of habitat modelling for threatened low density species using heterogeneous data : the case of Cuvier’s beaked whales in the Mediterranean

We are grateful to the ACCOBAMS Secretariat for their support in this work, including a small grant for the analysis.The Mediterranean population of Cuvieŕs beaked whale (Ziphius cavirostris), a deep-diving cetacean, is genetically distinct from the Atlantic, and subject to a number of conservation threats, in particular underwater noise. It is also cryptic at the surface and relatively rare, so obtain robust knowledge on distribution and abundance presents unique challenges. Here we use multiplatform and multiyear survey data to analyse the distribution and abundance of this species across the Mediterranean Sea. We use a novel approach combining heterogeneous data gathered with different methods to obtain a single density index for the region. A total of 594,996 km of survey effort and 507 sightings of Cuvier’s beaked whales, from 1990 to 2016, were pooled together from 24 different sources. Data were divided into twelve major groups according to platform height, speed and sea state. Both availability bias and effective strip width were calculated from the sightings with available perpendicular distance data. This was extrapolated to the rest of the sightings for each of the twelve groups. Habitat preference models were fitted into a GAM framework using counts of groups as a response variable with the effective searched area as an offset. Depth, coefficient of variation of depth, longitude and marine regions (as defined by the International Hydrographic Organization) were identified as important predictors. Predicted abundance of groups per grid cell were multiplied by mean group size to obtain a prediction of the abundance of animals. A total abundance of 5799 (CV = 24.0%) animals was estimated for the whole Mediterranean basin. The Alborán Sea, Ligurian Sea, Hellenic Trench, southern Adriatic Sea and eastern Ionian Sea were identified as being the main hot spots in the region. It is important to urge that the relevant stakeholders incorporate this information in the planning and execution of high risk activities in these high-risk areas.PostprintPeer reviewe

Biogeography in the deep: hierarchical population genomic structure of two beaked whale species

The deep sea is the largest ecosystem on Earth, yet little is known about the processes driving patterns of genetic diversity in its inhabitants. Here, we investigated the macro- and microevolutionary processes shaping genomic population structure and diversity in two poorly understood, globally distributed, deep-sea predators: Cuvier’s beaked whale (Ziphius cavirostris) and Blainville’s beaked whale (Mesoplodon densirostris). We used double-digest restriction associated DNA (ddRAD) and whole mitochondrial genome (mitogenome) sequencing to characterise genetic patterns using phylogenetic trees, cluster analysis, isolation-by-distance, genetic diversity and differentiation statistics. Single nucleotide polymorphisms (SNPs; Blainville’s n=43 samples, SNPs=13988; Cuvier’s n=123, SNPs= 30479) and mitogenomes (Blainville’s n=27; Cuvier’s n=35) revealed substantial hierarchical structure at a global scale. Both species display significant genetic structure between the Atlantic, Indo-Pacific and in Cuvier’s, the Mediterranean Sea. Within major ocean basins, clear differentiation is found between genetic clusters on the east and west sides of the North Atlantic, and some distinct patterns of structure in the Indo-Pacific and Southern Hemisphere. We infer that macroevolutionary processes shaping patterns of genetic diversity include biogeographical barriers, highlighting the importance of such barriers even to highly mobile, deep-diving taxa. The barriers likely differ between the species due to their thermal tolerances and evolutionary histories. On a microevolutionary scale, it seems likely that the balance between resident populations displaying site fidelity, and transient individuals facilitating gene flow, shapes patterns of connectivity and genetic drift. Based on these results, we propose management units to facilitate improved conservation measures for these elusive species

Dva zanimljiva terminološka rječnika

Authors thank United States Fleet Forces Command and Naval Facilities Engineering Command Atlantic for funding and support for the development of this gap analysis.Heterogeneous data collection in the marine environment has led to large gaps in our knowledge of marine species distributions. To fill these gaps, models calibrated on existing data may be used to predict species distributions in unsampled areas, given that available data are sufficiently representative. Our objective was to evaluate the feasibility of mapping cetacean densities across the entire Mediterranean Sea using models calibrated on available survey data and various environmental covariates. We aggregated 302,481 km of line transect survey effort conducted in the Mediterranean Sea within the past 20 years by many organisations. Survey coverage was highly heterogeneous geographically and seasonally: large data gaps were present in the eastern and southern Mediterranean and in non-summer months. We mapped the extent of interpolation versus extrapolation and the proportion of data nearby in environmental space when models calibrated on existing survey data were used for prediction across the entire Mediterranean Sea. Using model predictions to map cetacean densities in the eastern and southern Mediterranean, characterised by warmer, less productive waters, and more intense eddy activity, would lead to potentially unreliable extrapolations. We stress the need for systematic surveys of cetaceans in these environmentally unique Mediterranean waters, particularly in non-summer months.Publisher PDFPeer reviewe

ANALYSE DU COMPORTEMENT DES TURSIOPS TRUNCATUS EN PRESENCE DE CHALUT - Influence of trawling on behaviour and Surfacing rates of bottlenose dolphin in northern thyrrenian sea

Le grand dauphin (Tursiops truncatus) est une esp\ue8ce opportuniste, principalement ichtyophage, pouvant se nourrir de poissons, c\ue9phalopodes et crustac\ue9s appartenant au domaine nectonique et benthonique. Les interactions entre p\ueache et grand dauphin sont fr\ue9quemment observ\ue9es et document\ue9es, cela, quelques soient les techniques de p\ueache (Northridge et Hofmann, 1999). Ces interactions peuvent avoir d'importantes cons\ue9quences sur le rendement de la p\ueache et sur la conservation des c\ue9tac\ue9s (Perrin et al., 1994; Hall et Donovan, 2002). Cette \ue9tude analyse le comportement sp\ue9cifique de l'esp\ue8ce en pr\ue9sence de chalut. Les donn\ue9es relatives aux immersions/\ue9mersions enregistr\ue9es durant le suivi r\ue9alis\ue9 pour cette \ue9tude sont analys\ue9es de mani\ue8re \ue0 \ue9valuer l'influence de la technique de p\ueache sur le comportement respiratoire de l'esp\ue8ce. Cette \ue9tude, r\ue9alis\ue9e dans l'Archipel toscan de 2005 \ue0 2007, reporte 70 observations. Dans 33 % des cas, une interaction directe entre les dauphins et la chalutage a eut lieu. Dans l'Achipel toscan, le chalutage cible surtout les fonds de moins de 200m, et plus particuli\ue8rement les fonds inf\ue9rieurs \ue0 100m. Cette \ue9tude prend pour exemple, cinq cas d'interactions et montre que g\ue9n\ue9ralement les animaux suivent la route lin\ue9aire du chalut seulement lors de la phase de chalutage. L'analyse statistique sur le comportement en surface des animaux indique une variation significative li\ue9e \ue0 la pr\ue9sence du chalutage. Bottlenose dolphin (Tursiops truncatus) is an opportunistic species that feeds both on nectonic and benthic preys such as cephalopods, crustaceans and fishes. Interactions between fisheries and bottlenose dolphins have been observed and well studied all around the world and for different fishing techniques (Northridge et Hofmann, 1999). The interactions lead to negative impacts both on fishing catch and on cetacean conservation ). This study deals with specific bottlenose dolphin behaviour in the presence of trawlers. We analysed surfacing behaviour during the monitoring dedicated to determine how trawling influence bottlenose dolphin behaviour. Monitoring surveys took place in Tuscan archipelago from 2005 to 2007 during which 70 sightings have been collected. For 33% of sightings, we recorded direct interactions between dolphins and fisheries. In this area, trawling always occurred on sea bottom not deeper than 200m and preferably on 100m isobath. We paid attention to five cases of interactions. Results indicate that in all cases individuals follow the trawler's head only during haul. Surfacing pattern analysis indicates a significant difference between behaviour with and without trawlers

Cetacean and maritime traffic in deep sea waters, a relation to avoid?

This study tries to quantify and to compare the relation between cetacean and maritime traffic in pelagic waters (off continental shelf). Results showed that during cetacean sightings (n=753) nautical traffic (through seascape scan sampling) is reduced by 45,3% (P=0,0000) compared to control (n=985