Using opportunistic sightings to infer differential spatio-temporal use of western Mediterranean waters by the fin whale

The fin whale (Balaenoptera physalus) is a cosmopolitan species with a resident population in the Mediterranean Sea. Due to its habitat, open seas often far from ports and airfields, and its long-distance migratory behaviour, studying and monitoring its distribution is costly. Currently, many opportunistic sightings (OS) reports are available, which provide a source of potentially useful, low-cost information about the spatio-temporal distribution of this species. Since 1993, the Spanish Institute of Oceanography has compiled a dataset comprising 874 records of OS of nine species of cetaceans in the western Mediterranean Sea and adjacent waters. The aim of this study was to use this dataset to investigate the differential use of these waters by the fin whale when compared with other cetaceans. We compared the presence of fin whales with the presence of any other cetacean species in the dataset. Binary logistic regression was then used to model these occurrences according to several spatio-temporal variables expected to reflect their habitat use. Several significant models reveal that fin whales are more prone than other cetaceans to use the waters over the slope of the Gulf of Lion in summer. This finding confirms that the Gulf of Lion is an area of importance for this species and suggests that the slope of the continental shelf could be particularly important. Our study shows how OS can be a source of useful information when appropriately analyzed

Coexistencia y uso diferencial del mar Mediterráneo occidental por las especies residentes de pequeños delfínidos.

En el mar Mediterráneo occidental coexisten tres especies residentes de delfines: el delfín común (Delphinus delphis), el delfín listado (Stenella coeruleoalba) y el delfín mular (Tursiops truncatus). La situación de los delfines en este área puede representar un caso especial de simpatría, ya que estas especies son relativamente similares y están amenazadas, por lo que la competencia entre ellas podría conllevar problemas adicionales. Se hace, por tanto, necesario investigar el complejo patrón de coexistencia parcial y uso diferencial parcial de las aguas entre estas especies. Desde el punto de vista de la biogeografía de la conservación, es un desafío determinar cómo estas tres especies de delfines conviven y evitan la exclusión competitiva en el contexto de dichas amenazas. El Instituto Español de Oceanografía dispone de un conjunto de datos de avistamientos oportunistas de especies de delfines. Utilizando estos datos, construimos tres variables binarias, que consisten en el avistamiento de una especie frente al avistamiento de cualquiera de las otras dos especies. Obtuvimos tres modelos de probabilidad significativos en función de un conjunto de variables explicativas espacio-temporales. Para analizar estos modelos desde la perspectiva de la teoría de conjuntos borrosos, se aplicó la función de favorabilidad a los modelos de probabilidad, así como las operaciones borrosas de superposición y entropía. Los resultados muestran que los delfines comunes están favorecidos de manera diferencial en la parte oriental del área de estudio y en áreas alejadas de las principales rutas de navegación. Los delfines listados están favorecidos de manera diferencial en la parte occidental del área de estudio, sobre aguas profundas, cerca de las principales rutas de navegación y en verano y primavera. Por último, los delfines mulares están favorecidos de manera diferencial en la parte medio-occidental del área de estudio, en invierno y sobre aguas poco profundas.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Spatial and temporal partitioning of the Western Mediterranean Sea by resident dolphin species

A classic issue in ecology is to understand how similar species coexist in a given area (i.e., sympatry). The situation of dolphins in the Western Mediterranean Sea may represent a special case of sympatry in that three similar species (the short-beaked common dolphin [Delphinus delphis], the striped dolphin [Stenella coeruleoalba], and the bottlenose dolphin [Tursiops truncatus) are under strong human impacts in the same area. From the viewpoint of ecology and conservation biology, it is challenging to determine how these three dolphin species live together and avoid competitive exclusion in the setting of such impacts. The Spanish Institute of Oceanography has a dataset of dolphin species opportunistic sightings. Using these data, we constructed three binary variables, comprising the sighting of one species versus the sighting of either of the other two species. We obtained three significant probability models after performing logistic regression of these binary variables on a set of spatio-temporal explanatory variables. We analysed these models from the perspective of fuzzy set theory by applying the favourability function to the probability models, fuzzy operations overlap, and entropy. The results show that common dolphins are differentially favoured in the eastern part of the study area and far away from main shipping routes. The striped dolphin was differentially favoured in the western part of the study area, above deep waters, near main shipping routes, and in summer and spring. Finally, bottlenose dolphins were differentially favoured in the mid-western part of the study area, in winter, and over shallow waters.Peer reviewe

Chapter 21

Marine megafauna typically include large pelagic sharks, sea turtles, seabirds, and marine mammals. These megafauna are mainly associated with pelagic ecosystems through which they undertake long-distance migration. The Alboran Sea connects the Atlantic Ocean and Mediterranean Sea and is thus a relevant hotspot for marine megafauna. In this area, the overlap between various human activities—such as marine traffic or fisheries on the north and south coasts—and pollution entails the capture or mortality of marine megafauna. We review the main research and findings on marine megafauna in the Alboran Sea and discuss research approaches that could provide suggestions for the effective management of large marine ecosystems

Chapter 21

Marine megafauna typically include large pelagic sharks, sea turtles, seabirds, and marine mammals. These megafauna are mainly associated with pelagic ecosystems through which they undertake long-distance migration. The Alboran Sea connects the Atlantic Ocean and Mediterranean Sea and is thus a relevant hotspot for marine megafauna. In this area, the overlap between various human activities—such as marine traffic or fisheries on the north and south coasts—and pollution entails the capture or mortality of marine megafauna. We review the main research and findings on marine megafauna in the Alboran Sea and discuss research approaches that could provide suggestions for the effective management of large marine ecosystems.En prens