Occurrence of common dolphins (Delphinus delphis) in the Gulf of Trieste and the northern Adriatic Sea

Abstract

1. The Mediterranean common dolphin (Delphinus delphis), considered to have been very common in the past, had undergone a dramatic decline across most of the basin by the end of 1970s. In the northern Adriatic Sea, one of the regions with most available historical information, the common dolphin is thought to have been the most common and abundant cetacean throughout most of the 20th century.However, by the end of 1970s, it had virtually disappeared from the region and is now considered generally absent from the entire Adriatic Sea. This contribution summarizes the occurrence of common dolphins in the Gulf ofTrieste and provides a brief review of published records in other parts of the Adriatic Sea. 3. Systematic boat surveys in the wider area of the Gulf of Trieste between 2002 and 2019 confirmed that the common bottlenose dolphin (Tursiops truncatus) is the only regularly occurring cetacean species in this area. Despite this, several records of common dolphins were documented in the Gulf of Trieste between 2009 and 2012, through sightings of live animals or recovery of dead stranded animals.4. Dorsal fin markings allowed the photo-identification of some of these, suggesting that at least four different live individuals (three adults and one calf) occurred here in recent times. Most cases involved single adult individuals, but one included a mother-calf pair that was temporarily resident in a port for several months, a behaviour atypical for this species. Photo-identification showed that the presumed mother had previously been sighted in the Ionian Sea in Greece, over 1,000 km from the Gulf of Trieste, making this the longest documented movement for this species worldwide. 5. At present, the common dolphin continues to be rare in the region.

The conservation of the endangered Mediterranean common dolphin (Delphinus delphis): Current knowledge and research priorities

“…This would increase the number of individuals identified in each location, at the same time facilitating matching between contiguous areas, improving population size estimates, social structure, and site fidelity studies. In fact, a reported observation by Genov et al (2012, 2021) of D. delphis long‐distance movement between the Ionian and Adriatic seas may support recent findings highlighting that common dolphin dispersal from a natal area may likely involve long‐distance movements of females (Ball et al, 2017).…”

“…Records of D. delphis have been documented in other Italian waters (Mussi et al, 2016; Pace et al, 2016, 2019), in the Pelagos Sanctuary (Pace et al, 2015), Ischia Island (Mussi et al, 2021; Mussi & Miragliuolo, 2003, 2005), near Lampedusa Island (Pace et al, 2015), off western Sardinia (IUCN, 2017), at Cap Bon, north‐east Tunisia (Aissi & Vella, 2015; Benmessaoud, Chérif, Bradai, & Bejaoui, 2012), in the eastern Ionian Sea (Frantzis & Herzing, 2002), in the Aegean Sea (Dede & Öztürk, 2007; Giannoulaki et al, 2017; Ryan et al, 2014), in the Levantine Sea (Boisseau et al, 2010; Brand et al, 2021; Kerem et al, 2012), in Libyan waters (Benamer, 2016), and along the Algerian west coast (Larbi Doukara, 2021; Larbi Doukara, Bouslah, Bouderbala, & Boutiba, 2016) and the Moroccan coast (Masski & De Stephanis, 2015). In the Adriatic Sea, common dolphins appear to be extremely rare in recent times (Genov, Kotnjek, & Centrih, 2021), despite historically well‐documented presence (Bearzi, Notarbartolo di Sciara, Reeves, Cañadas, & Frantzis, 2004). From this overview, to accurately understand the distribution of the common dolphin in the Mediterranean, it is clear that long‐term small‐scale studies that include a seasonal component and which are ideally supplemented by various platforms of observations (marine and aerial) should be considered throughout the full range of the species in the region (Pace et al, 2019; Stockin & Vella, 2005).…”

“…These difficulties may explain the limited number of studies dealing with photo‐identification that have been published on this species worldwide (Pawley, Hupman, Stockin, & Gilman, 2018; Stockin & Vella, 2005). In fact, only 16 peer‐reviewed works have been found including those by Neumann et al (2002); Bearzi et al (2005, 2008); Bearzi, Bonizzoni, Agazzi, Gonzalvo, and Currey (2011); Bearzi, Bonizzoni, Santostasi, Eddy, and Gimenez (2016); Genov, Bearzi, Bonizzoni, and Tempesta (2012); Bamford and Robinson (2015); Hupman (2016); Mason, Salgado Kent, Donnelly, Weir, and Bilgmann (2016); Santostasi, Bonizzoni, Bearzi, Eddy, and Gimenez (2016); Inch et al (2018); Pawley et al (2018); Santostasi, Bonizzoni, Gimenez, Eddy, and Bearzi (2021); Bouma, Pawley, Hupman, and Gilman (2018); Mussi et al (2021); and Genov et al (2021).…”

Bottlenose dolphins in the north‐western Adriatic Sea: Abundance and management implications

“…Intentional killings are thought to have triggered the eradication of common dolphins, the recovery of which was later compromised by prey depletion and habitat degradation (Bearzi et al, 2003; Bearzi, Holcer, & Notarbartolo di Sciara, 2004). Records of common dolphins have become rare (Bearzi & Notarbartolo di Sciara, 1995; Genov et al, 2012; Genov et al, 2020), whereas bottlenose dolphins have persisted and, in recent decades, have been the only cetaceans encountered regularly in northern Adriatic waters (Bearzi, Holcer, & Notarbartolo di Sciara, 2004; Bearzi et al, 2008; Bearzi et al, 2009; Fortuna et al, 2018).…”

Bottlenose dolphins (Tursiops truncatus) in the north‐western Adriatic Sea: Spatial distribution and effects of trawling

“…The Adriatic Sea has been intensively fished for decades and is one of the seas most subject to trawling, worldwide (Eigaard et al, 2017; Gissi et al, 2017; Amoroso et al, 2018; FAO, 2018; Ferrà et al, 2018; Russo et al, 2019). In the basin's northern sector, elasmobranchs and other fish have suffered sharp declines due to overfishing and other human impacts (Coll et al, 2009; 2010; Fortibuoni et al, 2010; Lotze, Coll & Dunne, 2011; Fouzai et al, 2012; Ferretti et al, 2013; Barausse et al, 2014; Fortibuoni et al, 2017), and one dolphin species that used to be abundant in this part of the Mediterranean—the common dolphin Delphinus delphis —has vanished (Bearzi, Holcer & Notarbartolo di Sciara, 2004; Genov, Kotnjek & Centrih, 2020). Over‐exploitation of fish stocks and loss of biodiversity have been exacerbated by the mechanical and biological damage to the seabed by destructive fishing methods.…”