Abstract
Simple SummaryThe distribution and abundance of three Delphinidae species (striped dolphin, bottlenose dolphin, and common dolphin) were investigated in an extended area of the Mediterranean Sea. Data from nondesigned transect line surveys were modeled in order to investigate important marine areas for marine mammals. The results indicated that the environmental covariates significantly affecting marine mammals’ distribution/abundance were depth and distance from 200 m isobaths for striped dolphin, latitude/longitude and depth for bottlenose dolphin, and latitude/longitude and chlorophyll concentration for common dolphin. Maps of predictions were designed in order to communicate the results of important hot spot areas throughout the Mediterranean.Monitoring of Delphinidae species population patterns in the Mediterranean Sea was carried out in a sequence of surveys employing different approaches. Data from seven-year surveys with small catamaran sailing boats were analyzed under model-based approaches. Density Surface Models were used to produce spatial distribution prediction of three Delphinidae species (Stenella coeruleoalba, Tursiops truncatus, and Delphinus delphis) in an extended study area covering much of the Mediterranean Sea. A classical distance sampling protocol was applied in order to calculate the detection probability of clusters. Static (depth, slope, distance from the coast, and distance from isobaths of 200 m) and nonstatic (sea surface temperature and chlorophyll) variables were used to predict the species distribution/abundance in a generalized additive model context. Stenella coeruleoalba was found to be the dominant species, with an extended distribution in the study area; its abundance was significantly affected by both depth and distance. Tursiops truncatus and Delphinus delphis illustrated a significant abundance correlation with depth and chlorophyll, respectively, while both species showed a robust longitude correlation. Our model pinpoints the significance of nondesigned transect line surveys, suggesting the importance of specific habitat areas for future monitoring and conservation aspects of marine mammals.
Highlights
As distribution and abundance are influenced by by a series of variables that are mostly difficult to obtain at a vast scale, Density Surface Models (DSMs) can be characterized a series of variables that are mostly difficult to obtain at a suggesting vast scale, DSMs can be characterized as as comprehensively predictive rather than explanatory, the potential covariates that comprehensively predictive rather than explanatory, suggesting theand potential covariates that significantly affect spatial distribution
Spatial abundance and distribution predictions may propose affect the establishment of important areas for marine mammals (IMMAs) and environmental may propose the establishment important areas mammals (IMMAs) environmental variables that affect distribution, of helping in this wayfor themarine protection of habitats from aand series of activities variables that affect waysurveys
Among the dynamic variables sea surface temperature (SST) and CHL, the CHL variable seemed to affect only the distribution of the common dolphin, a fact that may be interpreted from the documented higher primary productivity in the Alboran Sea [62]
Summary
The importance of marine mammal monitoring in the Mediterranean basin has been highlighted by a series of studies for evolutionary, adaptation, and subpopulation patterns of these speciesAnimals 2020, 10, 260; doi:10.3390/ani10020260 www.mdpi.com/journal/animalsAnimals 2020, 10, 260 in time and space [1,2,3,4] and in a framework of monitoring abundance and distribution in different strata and the factors that may affect such patterns [2,5,6,7,8,9,10,11,12,13].Accommodating 7% of global biodiversity [14], the Mediterranean constitutes, at the same time, a stage of multiple human pressures to marine species habitats [11,15]. The importance of marine mammal monitoring in the Mediterranean basin has been highlighted by a series of studies for evolutionary, adaptation, and subpopulation patterns of these species. Animals 2020, 10, 260 in time and space [1,2,3,4] and in a framework of monitoring abundance and distribution in different strata and the factors that may affect such patterns [2,5,6,7,8,9,10,11,12,13]. The Mediterranean has complex patterns of water circulation [16] Environmental conditions such as sea surface temperature and chlorophyll concentration could affect directly or in more complex ways the distribution patterns and abundance of regular biota residents, such as 12 marine mammal species [17].
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