Species: Delphinus delphis (Linnaeus 1758)
The adult common dolphin reaches 2.5 meters and weighs 75 kg. Coloration is variable: black or blackish on the back and sides, creamy white belly and chest with a series of yellow, gray, and white hues along the sides and belly.
A typical dark inverted triangle is recognizable, more or less at the dorsal fin, and a black ring around the eye extends forward.
The common dolphin swims fast by making large jumps, being able to dive to fairly deep depths (280 meters) and for durations exceeding 8 minutes.
It uses both pelagic and coastal habitats, often in association with striped and bottlenose dolphins.
It feeds on epipelagic and mesopelagic fish. Stomach contents of stranded individuals in the Ligurian Sea and the Mediterranean confirm that their diet relies mainly on surface bluefish; cephalopods and crustaceans are also prey.
Mediterranean Conservation Status
In 2003 the Mediterranean subpopulation of common dolphin was listed as Endangered on the IUCN Red List. In 2021, the conservation status was confirmed, specifying that the Mediterranean subpopulation contains fewer than 2,500 mature individuals and undergoes an estimated continuing decline of at least 20% over two generations; finally, a 66% reduction in the subpopulation over the last three generations is suspected, the causes of which have not ceased and may not be reversible
Common dolphins in the Mediterranean have experienced a dramatic decline in abundance in recent decades and have almost completely disappeared from large portions of their range. Several interacting factors, from natural fluctuations to the impact of anthropogenic activities, may have caused this impressive decline.
Available data highlight that anthropogenic threats are most implicated in the extinction of the species; these include xenobiotic contamination, direct kills, bycatch in fishing gear, and habitat degradation.
CMS App. I (sottopopolazione Mediterranea), App. II (popolazioni del Mare del Nord e del Mar Baltico, del Mediterraneo, del Mar Nero e del Pacifico tropicale orientale).
CITES App. II
Bern Convention App. II
Convenzione di Barcellona, Protocollo SPA/BD, Allegato II
EU Habitats Directive: Allegato IV
The local population
The first evidence of common dolphin presence in the waters of the Gulf of Naples dates back to the XIX century when the Royal Museum of Zoology of the University of Naples acquired several specimens of the species, 12 of which are still preserved.
The local population of common dolphins in Ischia has been monitored by Oceanomare Delphis since 1997; encounters with the animals have occurred in all seasons of the year and have been concentrated in the coastal heads of the submarine canyon system of Cuma.
Photo-identification analyses have identified a total of 94 individuals. A core group of 12 identified females was seen together in nine different years during the study period.
Data collected over time show that the waters around the island of Ischia provide a feeding, breeding, and critical nursery area for this local population, offering favorable conditions for giving birth and raising young.
Thanks to studies undertaken by Oceanomare Delphis, the island of Ischia has been defined as a "critical habitat" for the species in the IUCN Cetacean Conservation Plan (Revees et al, 2003) and an "Area of Conservation Importance" in the ACCOBAMS Common Dolphin Conservation Plan.
In addition, habitat use maps delivered to the Italian Ministry of the Environment allowed the establishment of a pelagic area dedicated to the protection of the species critical habitat (the coastal heads of the Cumaean submarine canyon system) within the Marine Protected Area of the Islands of Ischia Procida and Vivara, "Kingdom of Neptune."
Finally, the waters of Ischia and Ventotene have been recognized as an Important Marine Mammals Area (IMMA) by the IUCN, with common dolphin, bottlenose dolphin, and minke whale as key species (Marine MammalsProtectedAreas Task Force, 2017).
Despite several attempts to protect the local common dolphin population "on paper," no concrete action has ever been taken to safeguard these animals, which have declined in recent years until they almost disappear.
In fact, the analysis of photo-identification data and the continuous decline in encounter rates monitored over 16 years (2002-2015) testify to how the area has been a hotspot for the local (mostly resident) population for years and that now this population is dying or moving to other locations.
Various human activities at sea can impact the common dolphin in the study area, among the most significant being disturbance and habitat degradation (including traffic and noise pollution) and overfishing of food resources.
The data presented by Oceanomare Delphis offer a strong argument for explicit and urgent population-specific conservation and management strategies to be developed and applied locally for common dolphins, considering that they depend on the area for vital biological processes.
Like other odontocetes, the common dolphin is a highly vocal species capable of producing:
Spectrogram of clicks and whistles of common dolphin
Most of the available knowledge about the acoustic signals of common dolphins in the Mediterranean Sea is related to the structural characteristics of whistles, their emission pattern associated with various behavioral states, and their geographic variation within the basin.