Habitat preferences among three top predators inhabiting a degraded ecosystem, the Black Sea

Abstract

Summary: This study investigated whether there is evidence of widespread niche partitioning based on environmental factors in the Black Sea and tested the hypothesis that physiographic factors may be employed as predictors. It addresses poorly researched areas with good habitat potential for the only three cetacean subspecies living in this area: the Black Sea short-beaked common dolphin (Delphinus delphis spp. ponticus), the Black Sea bottlenose dolphin (Tursiops truncatus spp. ponticus) and the Black Sea harbour porpoise (Phocoena phocoena spp. relicta). Generalized additive models (GAMs) were used to analyse data collected from multiple sources. In total, 745 sightings of the three species between 1998 and 2010 throughout the Black Sea were included. The analysis found depth and sea surface temperature to be the most important variables for separating the occurrence of the three species. Common dolphins occurred mainly in deep waters and in areas where the sea surface temperature was low, bottlenose dolphins were distributed primarily in shallower and warmer waters than common dolphins, and harbour porpoises were distributed in shallower waters with lower sea surface temperature than bottlenose dolphins. This study suggests strong niche segregation among the three cetacean species. The study is also the first contribution to the basic information of cetacean species distribution and habitat preferences in the Black Sea as a whole. Knowledge of the distribution of the three dolphin species in the study area is essential to establish conservation measures for these populations.Keywords: Black Sea; bottlenose dolphin; common dolphin; GAM; habitat preferences; harbour porpoise; niche segregation; spatial modelling. Preferencias de hábitat de tres superpredadores en el mar NegroResumen: El presente trabajo analiza si existen evidencias de partición de nicho en base a factores ecológicos básicos en el mar Negro, así como si dichos factores pueden ser empleados como predictores de distribución en zonas pobremente muestreadas con respecto a las tres especies de cetáceos que habitan el área: el delfín común del mar Negro (Delphinus delphis spp. ponticus), el delfín mular del mar Negro (Tursiops truncatus spp. ponticus) y la marsopa del mar Negro (Phocoena phocoena spp. relicta). Se usaron Modelos Aditivos Generalizados (GAMs) para analizar grupos de datos provenientes de múltiples fuentes. En total fueron incluidos 745 avistamientos de las tres especies entre los años 1998 y 2000. El análisis indica que las variables profundidad y temperatura superficial del mar fueron las más influyentes a la hora de segregar las especies espacialmente. La distribución del delfín común indicó una relación positiva con aguas más profundas y frías, mientras el delfín mular y la marsopa con aguas más superficiales y cálidas, tendiendo esta última a localizarse en aguas más frías con respecto al delfín mular. Este trabajo sugiere, por lo tanto, que existe una importante segregación de nicho entre las tres especies de cetáceos. Este análi...

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

“…The limitation of this method is that, due to the lack of a dedicated sampling, the interpretation of the results should be limited to the differential spatio-temporal use of the study area by the target species when compared with the other species in the same dataset. Specifically, we used a dataset with only presences in a similar way as other studies such as Esteban et al (2013) and Sánchez-Cabanes et al (2017), which provide useful information about the differential distribution of the analyzed cetacean species. This information is valuable when attempting to infer key areas for the life cycle of the species, as is the slope of the Gulf of Lion for fin whales in summer.…”

Seasonal dynamics of occurrence and group size of three species of cetaceans (Delphinidae and Phocoenidae) on the southwestern coast of the Black Sea

“…Previous studies by Gladilina and Gol'din (2016) showed that there is a clear difference in group size and distribution density of the bottlenose dolphin among the coastal areas of the Crimean peninsula. Sea depth, surface temperature and salinity can affect the pattern of occurrence and movements of cetaceans (Marini et al 2015, Sanchez-Cabanes et al 2017. The predictive models for the Black Sea cetaceans reveal that depth might be a significant factor that influences their distribution, pointing to a likely association of the common dolphin with greater depths of up to 2250 m, while the bottlenose dolphin and the harbour porpoise prefer the depths of 200-250 m (Sanchez-Cabanes et al 2017).…”

“…Sea depth, surface temperature and salinity can affect the pattern of occurrence and movements of cetaceans (Marini et al 2015, Sanchez-Cabanes et al 2017. The predictive models for the Black Sea cetaceans reveal that depth might be a significant factor that influences their distribution, pointing to a likely association of the common dolphin with greater depths of up to 2250 m, while the bottlenose dolphin and the harbour porpoise prefer the depths of 200-250 m (Sanchez-Cabanes et al 2017). Surface temperature is another important predictor of occurrence, with the common dolphin preferring colder waters and the other two species preferring warmer waters (Sanchez-Cabanes et al 2017).…”

“…The predictive models for the Black Sea cetaceans reveal that depth might be a significant factor that influences their distribution, pointing to a likely association of the common dolphin with greater depths of up to 2250 m, while the bottlenose dolphin and the harbour porpoise prefer the depths of 200-250 m (Sanchez-Cabanes et al 2017). Surface temperature is another important predictor of occurrence, with the common dolphin preferring colder waters and the other two species preferring warmer waters (Sanchez-Cabanes et al 2017). It has been reported that the common dolphin avoids the Azov Sea and is generally absent in the Kerch Strait, which has low water salinity (BSC 2008).…”

“…The short-beaked common dolphin occurs from the shore waters to many kilometres off the coast, but it is mostly observed in the open sea because it feeds on small schooling fishes (Hammond et al 2008). The harbour porpoise is a typical coastal species that often visits lagoons, inlets, and even rivers (Reeves and Notarbartolo di Sciara 2006, Birkun et al 2014, Sanchez-Cabanes et al 2017). There have been cases in which porpoises have gone upstream the Danube up to the city of Izmail and lake Yalpuh in the Odessa region of Ukraine (Birkun 2006).…”