Two Decades of Coastal Dolphin Population Surveys in Israel, Eastern Mediterranean

SIMPLE SUMMARY: In the Mediterranean Sea, near the coast of Israel, two dolphin species reside; the common bottlenose dolphin and the common dolphin. These two have been observed by researchers over the last 20 years and have been sighted along different parts of the coast. The two species therefore have different preferences of habitat and in order to evaluate environmental characteristics that are important for each species, statistical models were used to evaluate patterns in their occurrence. Common bottlenose dolphins were found to inhabit the entire length of coast and often chose to swim near fishing trawler vessels. Common dolphins were found to inhabit only the southern section of the Israeli coast and typically chose to swim in shallower waters than the common bottlenose dolphins. It is evident that the two species choose different habitats and the common bottlenose dolphins adapt according to human presence and disturbances, while the common dolphins have more specific preferences that are still not fully understood. ABSTRACT: Along the Mediterranean coast of Israel, two near-shore dolphin species are prevalent; Tursiops truncatus (least concern, IUCN) and Delphinus delphis (endangered, IUCN). Ship-board surveys and sporadic sightings over the last two decades have shown that the two differ in distribution—T. truncatus is found along the entire coast and D. delphis only in the south. The environmental and anthropological factors affecting these species’ spatial distribution and determining their habitat preferences in this area are largely unknown. This work is a first attempt at summarizing 20 years of observations and studying habitat preferences for both species, by use of Generalized Additive Models. T. truncatus was found to be present in all areas of the continental shelf where survey effort coverage was sufficient, with a high affinity towards bottom trawlers. Model results showed D. delphis distribution to be associated to (shallow) water depths, though the factors driving their limited latitudinal distribution currently remain unknown. It is evident that T. truncatus and D. delphis are present in segregated areas of the Israeli continental shelf and T. truncatus currently sustains a delicate balance with continuously shifting human activities, while the drivers of D. delphis distribution are more specified, yet still not fully understood.