Density and Abundance of Delphinus delphis in Waters South of Samos Island, Greece (Eastern Mediterranean Sea)

Abstract

The Mediterranean subpopulation of short-beaked common dolphin Delphinus delphis is ranked as endangered on the IUCN (International Union for Conservation of Nature) Red List because it has sharply declined during the last decades, resulting in sparse and decreasing populations. Monitoring the conservation status of this endangered dolphin species is particularly relevant to fulfil targets under the range of several international agreements. Moreover, estimating the abundance of D. delphis is essential to verify the effectiveness of conservation action to maintain safe population levels in the Mediterranean Sea and to suggest appropriate modifications to limit potential threats. In this regard, a monitoring program of the short-beaked common dolphin in Samos Island (Greece) was carried out from 2016 to 2019, adopting a random line transect sampling method. The overall density and abundance estimates of D. delphis, obtained by applying conventional distance sampling (CDS) on sighting data, were 0.15 individuals/km2 (CV = 13.27%; 95% CI = 0.11–0.19 individuals/km2) and 51 individuals (CV = 13.27%; 95% CI = 40-66 individuals), respectively. Although, a longer time series of sighting data should be collected and a larger area should be investigated to better understand the population trend of D. delphis and its residency pattern, the results contribute to setting up a baseline reference for future assessment of its population in the Eastern Aegean Sea.

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

“…The first estimates of common dolphin aerial densities in the Mediterranean Sea were of 0.16 km −2 in the Alboran Sea (Forcada & Hammond, 1998) and 0.14 km −2 in Maltese waters (Central Mediterranean;Vella, 2005). It has also been recently estimated off Samos island (Greece) to be 0.15 km −2 (Pietroluongo et al, 2020). Common dolphin encounter rate measures were reported for the Alboran Sea (1.74 km −1 ) (Cañadas & Hammond, 2008), the Gulf of Vera (0.36 km −1 ), the North Aegean (0.015 km −1 ) (Milani et al, 2021), the island of Ischia with declining encounter rates between 2000 and 2015, from 0.31 km −1 to 0 km −1 (Mussi, Vivaldi, Zucchini, Miragliuolo, & Pace, 2021).…”

“…Long-term research and monitoring on D. delphis in the Mediterranean have provided some local abundance estimates. These include the Alboran Sea (Cañadas & Hammond, 2008;Cañadas & Vázquez, 2017;Forcada & Hammond, 1998), the waters around the Maltese islands (Central Mediterranean;Aissi & Vella, 2015;Vella, 2005Vella, , 2016, the Inner Ionian Sea Archipelago (Bearzi et al, 2003(Bearzi et al, , 2005(Bearzi et al, , 2008, the Thracian Sea (Milani et al, 2021), and more recently the eastern Aegean Sea, south of Samos island (Inch, Pietroluongo, & Hepburn, 2018;Pietroluongo et al, 2020). The first estimates of common dolphin aerial densities in the Mediterranean Sea were of 0.16 km −2 in the Alboran Sea (Forcada & Hammond, 1998) and 0.14 km −2 in Maltese waters (Central Mediterranean;Vella, 2005).…”

First Assessment of Micro-Litter Ingested by Dolphins, Sea Turtles and Monk Seals Found Stranded along the Coasts of Samos Island, Greece

“…Samos is a Greek island located in the north-eastern Aegean Sea with approximately 140 km of coastline. The island is included in the Central Aegean Important Marine Mammal Area [ 43 ] and is confirmed as an important habitat for cetaceans [ 44 ] and seals [ 45 ]. The Aegean Sea is also listed among the areas of the Eastern Mediterranean considered as critical since it has the largest percentage of oceanic foraging grounds for loggerhead turtles [ 46 ].…”

Environmental variables influencing occurrence and distribution ofDelphinus delphisin the eastern Aegean Sea (eastern Mediterranean Sea)

“…More recently, its occurrence has been confirmed by sightings (Inch, Pietroluongo & Hepburn, 2018;Pietroluongo et al, 2020;Milani et al, 2021) and stranding events (Pietroluongo et al, 2022). In addition, preliminary abundance estimates have been provided (Pietroluongo et al, 2020) and its role as a keystone species in the marine food web of the northern Aegean Sea has been demonstrated (Tsagarakis et al, 2010). However, still little information is available about the distribution and critical habitat of the species throughout the entire area of the eastern Aegean Sea.…”