Abstract
Relatively scant information is available on the Risso’s dolphin in comparison to the other species regularly present in the Mediterranean Sea. Recently, its conservation status has been updated to Endangered by the International Union for Conservation of Nature (IUCN) in this Sea. Therefore, the need to increase information on its biology and ecology is even more urgent. This study reports the first preliminary information on the behavioral traits of the species occurring in the Gulf of Taranto (Northern Ionian Sea). Data on predominant behavioral activity states and on a set of group composition variables (group formation, cruising speed, dive duration and interaction between individuals) were collected from April 2019 to September 2021, applying the focal-group protocol with instantaneous scan sampling. Group size, depth and group composition variables were compared between activity states. Results highlight that both the group size and the several variables considered varied significantly depending on activity state. The group size was significantly smaller during feeding than resting and traveling and a characterization in terms of group formation, cruise speed, dive duration and interaction between animals is provided for the different activity states. Moreover, a list of behavioral events which occurred, as well as their relative frequency of distribution among activity states, is reported. Finally, details on the sympatric occurrences between Risso’s and striped dolphins, as well as the repetitive interaction observed between adult individuals and plastic bags floating on the sea surface, are reported and discussed.
Highlights
The importance of incorporating behavioral ecology into conservation strategies has long been debated [1] and in the last two decades, several studies have highlighted that a better understanding of the behavioral ecology of highly social species is crucial to implementing effective conservation actions [2,3,4,5]
To date in the Mediterranean Sea, the largest and deepest semi-enclosed basin in the world [14], research studies on cetacean behavior have mainly been focused on the vocal behavior and on acoustic monitoring of behavioral responses, in the presence of an anthropogenic source of stress, of different species such as striped (Stenella coeruleoalba) and common bottlenose dolphin (Tursiops truncatus), sperm (Physeter macrocephalus) and fin whales (Balaenoptera physalus) i.e., [15,16,17,18,19,20]
This study aims to provide the first data on the diurnal behavioral pattern of a local population of Risso’s dolphin occurring in the Gulf of Taranto, Northern Ionian Sea (Centraleastern Mediterranean Sea) and monitored since 2013 [63,64,65,66,67,68,69,70,71,72]
Summary
The importance of incorporating behavioral ecology into conservation strategies has long been debated [1] and in the last two decades, several studies have highlighted that a better understanding of the behavioral ecology of highly social species is crucial to implementing effective conservation actions [2,3,4,5]. Baseline information about ecological aspects of behavior (i.e., behavioral patterns, daily activity budget and their spatiotemporal variations) of regular cetacean species occurring in the basin is scarce and fragmented. Several studies on this topic mainly refer to striped dolphin [21,22,23,24], common bottlenose dolphin [25,26,27,28,29] and fin whale e.g., [30,31,32], whereas no or negligible information is available for Risso’s dolphin (Grampus griseus). Mar.pScai.tEtneg.r2n02o2,f10t,h17e5 species, in view of the recent revision of its conservation status by 3thofe IUCN from Data Deficient [60] to Endangered [61,62]
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