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New insights on the presence and distribution of the endangered short-beaked common dolphin Delphinus delphis in Italian waters.

Authors:
Daniela Silvia Pace at Sapienza University of Rome
Daniela Silvia Pace
Barbara Mussi
Barbara Mussi
Sabina Airoldi at Tethys Research Institute
Sabina Airoldi
  • Tethys Research Institute
Jessica Alessi at ALESSI Consulenze ambientali marine & MeRiS - Mediterraneo Ricerche e Sviluppo APS
Jessica Alessi
  • ALESSI Consulenze ambientali marine & MeRiS - Mediterraneo Ricerche e Sviluppo APS
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Abstract

Pooled data on the endangered short-beaked common dolphin Delphinus delphis collected in the central Mediterranean Sea over 2000-2014 period by different research groups in Italy were analysed. A total of 266 encounters with 4675 common dolphins was attained. The species was mainly recorded in the central and southern Tyrrhenian Sea (around Ischia island and Strait of Messina), in both pelagic and neritic habitats. Mixed groups of common dolphin with other cetacean species were observed in 78 occasions. Group size ranged from 1 to >100 individuals, with differences between study areas. The presence of calves was consistently documented around Ischia only.
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46_Congr SIBM form testi v. 03_apr_2014 v.1
46° Congresso della Società Italiana di Biologia Marina
Roma, 10-12 giugno 2015
D.S. PACE1-2, B. MUSSI1, S. AIROLDI3, J. ALESSI4-5, A. ARCANGELI6, F. ATZORI7,
M. AZZOLIN8, I. CAMPANA9, A. CELONA10, C. FIORI4-5, C. GIACOMA8, G. GNONE11,
C. LUPERINI12, R. MANGANO13, A. MIRAGLIUOLO1, A. MOULINS14, S. NUTI15,
G. PELLEGRINO16, M. ROSSO14, F. SALVIOLI15, P. TEPSICH14-17, M. TRINGALI16
1 OCEANOMARE DELPHIS Onlus, Via G. Marinuzzi 74 – 00124 Rome, Italy; 2Dep. of Environmental Biology,
‘Sapienza’ University of Rome – Italy; 3Tethys Research Institute, Viale G. B. Gadio 2 – Milan, Italy; 4MENKAB:
il respiro del mare, Via Quarda Sup. 20/6 – Savona, Italy; 5Dep. of Earth, Environmental and Life Sciences
(DISTAV), University of Genoa, Italy; 6ISPRA, Via Vitaliano Brancati 48 – Rome, Italy; 7AMP Capo Carbonara,
Via Roma 60 – Villasimius, Cagliari, Italy; 8Dep. of Life Sciences and Systems Biology, University of Turin –
Italy; 9Accademia del Leviatano, Viale dell’Astronomia 19 – Rome, Italy; 10Necton Marine Research Society, Via
G. Gozzano 47 – Catania, Italy; 11Acquario di Genova, Ponte Spinola – Genoa, Italy; 12Dep. of Earth Science,
University of Pisa – Italy; 13DELPHIS Aeolian Dolphin Center, Via Duca delle Grazie 22 – Santa Flavia, Palermo,
Italy; 14CIMA Research Foundation, Via A. Magliotto 2 – Savona, Italy; 15CE.TU.S., Lungo Canale Est –
Viareggio, Lucca, Italy; 16Ketos, Corso Italia 58 – Catania, Italy; 17Dep. Informatics Bioengineering Robotics and
System Engineering (DIBRIS), University of Genoa, Italy
danielasilvia@oceanomaredelphis.org
NUOVE CONOSCENZE SULLA PRESENZA E DISTRIBUZIONE DELLA
SPECIE MINACCIATA DELFINO COMUNE DELPHINUS DELPHIS
NEI MARI ITALIANI
NEW INSIGHTS ON THE PRESENCE AND DISTRIBUTION OF THE
ENDANGERED SHORT-BEAKED COMMON DOLPHIN
DELPHINUS DELPHIS IN ITALIAN WATERS
Abstract – Pooled data on the endangered short-beaked common dolphin Delphinus delphis collected in the
central Mediterranean Sea over 2000-2014 period by different research groups in Italy were analysed. A
total of 266 encounters with 4675 common dolphins was attained. The species was mainly recorded in the
central and southern Tyrrhenian Sea (around Ischia island and Strait of Messina), in both pelagic and
neritic habitats. Mixed groups of common dolphin with other cetacean species were observed in 78
occasions. Group size ranged from 1 to >100 individuals, with differences between study areas. The
presence of calves was consistently documented around Ischia only.
Key-words: distribution, Delphinus delphis, common dolphin, Mediterranean Sea
Introduction – The short-beaked common dolphin (Delphinus delphis Linnaeus, 1758)
is a small odontocete found worldwide. Currently, its abundance is in steep decline
throughout the central and eastern Mediterranean (Bearzi et al., 2003) with the only
notable population remaining in the Alboran sea (Canadas and Hammond, 2008). This
drop during the last few decades raised conservation problems and in 2003 the
Mediterranean short-beaked common dolphin ‘subpopulation’ was listed as endangered
in the IUCN Red List of Threatened Animals. This species is present in very low
numbers in Italian waters. Currently, it is reported to be present around Ischia and
Lampedusa Islands and very rarely in Adriatic sea (Habitat Directive Reporting, 2014).
Here, pooled data on presence, distribution, group size and association with other
species is presented, thanks to a common effort by different research groups in Italy.
Methods – Data on D. delphis groups were collected over 2000-2014 period within
Pèlagos Sanctuary (PS), central (CT) and southern (ST) Tyrrhenian sea, Sicily Channel
(SC) and western Ionian Sea (WI). Dedicated visual surveys with structured sampling
46_Congr SIBM form testi v. 03_apr_2014 v.1
46° Congresso della Società Italiana di Biologia Marina
Roma, 10-12 giugno 2015
design were conducted by trained observers in good weather condition (Beaufort <3).
Different platforms of observation (ferries, sailing vessels, inflatables, fishing/motor
boats, oceanographic vessel) were employed. A group of common dolphin was defined
as an aggregation of all the dolphins within visual range. A visual count or estimate of
the number of animals in the focal group was recorded. Age class was assessed
whenever possible through size-based estimates. In some cases common dolphins were
individually photo-identified through long-term natural marks on dorsal fins.
Results – A total of 266 encounters with 4675 common dolphins was recorded (40
from ferries and 226 from other platforms). The species was mainly recorded in the
central (n=73 sightings, principally around Ischia) and southern (n=109 sightings,
mainly in the Strait of Messina) Tyrrhenian sea, in both pelagic and neritic habitats. A
number of 54 encounters were located in the Pelagos Sanctuary area, 24 in the Sicily
Channel (principally around Lampedusa island) and 5 in the Western Ionian. Group
size ranged from 1 to >100 individuals, with differences in average between study
areas (PS=5.9±6.3; CT=33.5±35.1; ST=13.9±10.6; SC=34.9±18.8; WI=29.8±18.9).
The presence of immature animals (juveniles, calves and newborns) was repeatedly
documented around Ischia island only. Mixed groups of common dolphin with other
cetacean species were encountered on 78 occasions in all study areas, with striped
dolphin (Stenella coeruleoalba Meyen, 1833) observed in 58 ‘mixed’ cases and
bottlenose dolphin (Tursiops truncatus Montagu, 1821) in 10 ones (all near Lampedusa
island). Other associated species included Risso’s dolphin (Grampus griseus Cuvier,
1812), sperm whale (Physeter macrocephalus Linnaeus, 1758) and fin whale
(Balaenoptera physalus Linnaeus, 1758). ‘Mixed’ encounters occurred mainly during
feeding and/or travelling activities, in few cases social interactions between common
dolphins and other species were documented (principally with striped dolphins around
Ischia island). A number of 20 photographically identified individuals were captured in
the Pelagos Sanctuary, with resightings between 2004 and 2010, and 97 around Ischia
Island, with 70 resightings over the years. No match between the PS and CT areas were
currently found. Photoidentification catalogues in ST and SC are still in progress.
Conclusions – Preliminary, pooled data on short-beaked common dolphins in Italian
waters showed the great potential of this new research network and provided a novel
picture on the presence and distribution of the species between 2000 and 2014. CT
(Ischia island), ST (Strait of Messina) and SC (Lampedusa island) resulted marine
areas that are deemed significant ecosystems or habitats for the endangered D. delphis.
These regions seem to give strong arguments for specific management strategies to be
developed and applied for a species that rely on these areas for important biological
processes (i.e. feeding/breeding). The persistent presence of the species is of notable
importance given the apparent susceptibility of the Mediterranean subpopulation to
coastal anthropogenic effects.
References
BEARZI G., REEVES R.R., NOTARBARTOLO DI SCIARA G., POLITI E., CANADAS A.,
FRANTZIS A., MUSSI B. (2003). Ecology, status and conservation of common dolphins Delphinus
delphis in the Mediterranean Sea. Mamm. Rev., 33: 224–252.
CAÑADAS A., HAMMOND P.H. (2008) – Abundance and habitat preferences of the short-beaked
common dolphin Delphinus delphis in the southwestern Mediterranean: implications for conservation.
Endang. Species Res., 4: 309–331.
Habitat Directive Reporting (2014) –
http://ec.europa.eu/environment/nature/knowledge/rep_habitats/index_en.htm

Supplementary resource (1)

Pace CWC Rev def
Data
November 2015
Daniela Silvia Pace · Barbara Mussi · Sabina Airoldi · Jessica Alessi · M. Tringali
... In shallower waters, it can be observed in mixed groups with the common bottlenose dolphin Tursiops truncatus [5,6]. In offshore waters over the continental slope it can be observed in mixed groups with the striped dolphin Stenella coeruleoalba [3,[7][8][9][10][11][12][13][14]. A specific case exists in the Gulf of Corinth where D. delphis has usually been recorded in mixed groups with the striped dolphin and the Risso's dolphin Grampus griseus [15][16][17][18][19]. ...
... Currently, records of this species are documented in the Pelagos Sanctuary, near Lampedusa Island and in the Messina Strait [13], off western Sardinia [24], in the Cap Bon area (northern Tunisia) [25], in the eastern Ionian Sea [15], in the Aegean Sea [26][27][28], and in the Levantine Sea [29,30]. Local abundance estimates of this species have only been provided for long-term monitored areas such as the Alborán Sea [4,11], the waters off Malta [31], the Inner Ionian Sea Archipelago [6,32,33], the Gulf of Corinth [17,18,34], and the Thracian Sea [35]. ...
... The small-sized aggregation of common dolphin groups is probably due to a behavioral feeding strategy caused by the distribution of prey (small pelagic fish) over many small patches in the study area [5,28,54], which leads dolphins to split into smaller groups for more efficient predation [55]. On the other hand, the presence of highly productive marine areas and the high seasonal abundance of prey leads to the formation of larger groups of D. delphis as observed in the western Alborán and southern Almeria [4,11], in the Tyrrhenian Sea [8,13,14] and in waters off Malta Island [31]. Indeed, the presence of small pelagic fish such as sardine and anchovy resulted in an important explanatory variable in the modelling of the distribution of the common dolphin as reported by the authors of [28] in the Aegean Sea. ...
Density and Abundance of Delphinus delphis in Waters South of Samos Island, Greece (Eastern Mediterranean Sea)
Article
Full-text available
  • Mar 2020
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.
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... The shortbeaked common dolphin Delphinus delphis is an example of a marine mammal with potential isolation local populations in the Black Sea. Delphinus delphis is relatively abundant in the westernmost portion of the Mediterranean Sea (Alboran Sea), central and southern Tyrrhenian Sea, around the Maltese islands, eastern Ionian Seas, especially Inner Ionian Sea Archipelago and Gulf of Corinth, and in parts of the Aegean Sea, TSS, and the Black Sea ( € Ozt€ urk 1996;Cañadas and Hammond 2008;Piroddi et al. 2011;Pace et al. 2015;Vella and Vella 2016). Different population dynamics appear to function in the eastern and western Mediterranean, and two genetically discrete eastern and western Mediterranean populations have been reported based on nuclear microsatellite and mitochondrial DNA (mtDNA) data (Natoli et al. 2008). ...
Population genetic structure of the short-beaked common dolphin from the Black Sea and the Turkish Straits System
Article
  • Jul 2020
Our study aims to assess the population connectivity, evolutionary history, and conservation status of the short-beaked common dolphin in the Black Sea and Turkish Straits System (TSS). We also include DNA sequences from the Atlantic Ocean and the Mediterranean Sea to provide a regional perspective to our localized study. Analysis of 366 base pairs of mitochondrial DNA D-loop fragments from 37 samples collected from short-beaked common dolphins in the Black Sea, TSS, and Aegean Sea revealed 13 haplotypes, eight of which have not been previously reported. While analysis of samples archived on GenBank revealed 89 different haplotypes across the region. The haplotype network contains two main peripheral groups that include individuals from all locations. Haplotypes from the Atlantic Ocean are scattered across the network and no obvious population separation was detected. Some shared haplotypes potentially indicate multi-directional colonization events of the Mediterranean Sea from the eastern Atlantic Ocean. Moreover, some less widely distributed haplotypes suggest some level of more recent genetic connectivity through the Strait of Gibraltar and the TSS and point out the importance of these straits in the dispersal of short-beaked common dolphins. The haplotype and nucleotide diversity values were lower in the Black Sea, TSS, and western Mediterranean Sea when compared to the Atlantic Ocean, supporting the expansion of Atlantic populations into the Mediterranean and the Black Seas. Differentiation was observed between the Atlantic Ocean, and the Mediterranean Sea, TSS and the Black Sea based on Фst but not between Mediterranean and the Black Seas. For common dolphins, which have high dispersal potential, the protection of open seas and narrow seaways to enhance connectivity may be crucial.
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... These depths (<40 m) and distances from the coast (<1.5 km) were chosen to ensure common bottlenose dolphins were recorded in absence of visual identification. Despite the fact that the common dolphin (Delphinus delphis) is also present in the waters surrounding Lampedusa (Pace et al., 2015), in the present study area the species was never reported in literature or observed by the authors in over 400 h of observations between 2006 and2009 (La Manna, pers. commun.). ...
Assessing geographical variation on whistle acoustic structure of three Mediterranean populations of common bottlenose dolphin (Tursiops truncatus)
Article
  • Apr 2017
  • BEHAVIOUR
Whistles are acoustic signals produced by bottlenose dolphins particularly during social interactions. Here, we compare whistle from three Mediterranean areas (Croatia, Sicily and Sardinia) to investigate the presence of acoustic divergence and to discuss the possible causes of variability. Whistle parameters differ significantly between populations, but PCA highlight that the majority of variability is due to a limited number of frequency parameters. Cluster and DFA show that the Croatian population is acoustically divergent from the western populations of Sicily and Sardinia. This divergence could be consistent with geographical isolation, and a possible genetic differentiation between populations, and/or an adaptation to the acoustic environment. Moreover, in a comparison of whistle parameters of different Mediterranean populations with those of previously published Atlantic populations, it was revealed that the Sicilian population was acoustically closer to Atlantic populations. Our results represent a contribution to identifying acoustically differentiated populations of bottlenose dolphins in the Mediterranean.
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The social behaviour of the common bottlenose dolphin Tursiops truncatus (Montagu, 1821) in the coastal waters of Lampedusa Island (Strait of Sicily, Italy)
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Research on social structure and residency provides important information on the dynamics of a population, improving knowledge of the species' behaviour and ecology. This study investigated the social network, site fidelity, and residency patterns of common bottlenose dolphins ( Tursiops truncatus ) off Lampedusa Island. Direct visual detection and photo‐identification methods were used to collect data during 124 boat‐based surveys conducted from 2013 to 2020. A total of 117 groups (mean size 4.5 ± 3.3) were sighted; 73 well‐marked animals were identified, of which 59% were resighted over the years. The estimate of social differentiation was 0.72 ( SE = 0.07), suggesting differentiated social groups within the community. Data were somewhat representative of the true social system, as the correlation coefficient was close to 0.4. However, the half‐weight index averaged 0.07 (±0.03), indicating individuals' low tendency to associate. Five social clusters were identified with strong relationships between individuals within each cluster, in which 94% of maximum association indices were ≥0.4. The data also highlighted preferred and avoided associations and stable relationships. The removal of individuals with the highest values of strength and eigenvector centrality from the network did not affect its connectivity, suggesting inherent robustness. Despite the different levels of site fidelity among individuals, the results indicated rather high levels of yearly sighting rate. Temporary migration into and out of the area shown by this study indicates that Lampedusa coastal waters are an important, regularly used bottlenose dolphin habitat. These results suggest extensive ranging behaviour, which implies the need for networking between institutions and organizations from the various states bordering the Strait of Sicily to address conservation efforts and inform regional management of the Mediterranean bottlenose dolphin population.
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Two Decades of Coastal Dolphin Population Surveys in Israel, Eastern Mediterranean
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Full-text available
  • Feb 2023
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.
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Dynamics of Cetacean Mixed-Species Groups: A Review and Conceptual Framework for Assessing Their Functional Significance
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Numerous species of cetaceans have been recorded in mixed-species groups (MSGs). By forming groups with individuals of different species, cetaceans may reduce predation risk, improve foraging, and gain social benefits. Most accounts of cetacean MSGs, however, are descriptive and little is known about their functions. Furthermore, research has been hindered by inconsistent use of terminology and the lack of a conceptual framework to guide investigations. We reviewed the cetacean literature to compare how MSGs have been termed and defined, to assess their characteristics, to evaluate what is known about their potential functions, and to provide directions for future study. In total, we reviewed 203 studies reporting observations of cetacean MSGs. These MSGs involved 54 different species, predominantly delphinids, that formed 216 different species pairs with varied morphologies and levels of relatedness. Cetacean MSGs occurred across the globe, from tropical to cold temperate seas, from shallow coastal waters to the open ocean, and varied in characteristics such as group size and frequency of occurrence. Only 27 of the reviewed studies proposed and discussed the potential functions of cetacean MSGs, suggesting reduced predation risk (5 species pairs), improved foraging (17 species pairs), and social benefits (12 species pairs) as the main drivers. In most cases, however, the factors that drive the formation of cetacean MSGs remain unknown. Amongst the reviewed studies, MSGs were referred to by various terms, often with no explicit definitions. To reduce this inconsistency, we recommend that future studies use only the term mixed-species group which we define as individuals of two or more species found in close spatial proximity due to mutual or unreciprocated attraction derived from evolutionary grouping benefits. There were also few structured investigations to confirm MSG occurrence and to analyse their potential causes and consequences. To facilitate the study of cetacean MSGs, we developed a conceptual framework that establishes diverse approaches to, firstly, distinguish MSGs from chance encounters and aggregations and to, secondly, investigate their potential functions. This is necessary if we are to advance this field of study and improve our understanding of the role that MSGs play in species and community ecology.
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Imperiled Common Dolphins of the Mediterranean Sea
Chapter
  • Apr 2021
The Mediterranean Sea is one of the world's seas most affected by human activities. In this region, concern for the conservation status of the common dolphin *Delphinus delphis* has been expressed since the 1990s. Systematic culling campaigns and intentional takes represented a major cause of mortality between the 1870s and the 1970s. These killings slowed down or largely ceased in the 1970s, but other negative human impacts have increased dramatically since then. Ongoing depletion of key prey caused by overfishing, as well as food-web competition with fisheries, have been identified as important threats in recent decades. Factors that likely contributed to making common dolphins increasingly less common also include incidental mortality in fishing gear, habitat degradation, and the effects of chemical pollutants, underwater noise, and climate change. These impacts may have increased demographic fragmentation, resulting in low density or scattered occurrence across most of the basin, small group sizes, and occasional admixture with striped dolphins *Stenella coeruleoalba*. Formal commitments to protect Mediterranean common dolphins have been made repeatedly in national and international fora, but conservation action has remained largely on paper.
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The conservation of the endangered Mediterranean common dolphin (Delphinus delphis): Current knowledge and research priorities
Article
Full-text available
  • Feb 2021
  • AQUAT CONSERV
Preservation of endangered species is now recognized as a relevant component of regional and global conservation actions achieved through the maintenance of the remaining populations in a favourable conservation status. The Mediterranean common dolphin (Delphinus delphis) is listed as an Endangered subpopulation in the International Union for Conservation of Nature Red List, with declining numbers in some of the areas where it has been studied for numerous years. Prey depletion, fisheries bycatch, pollution, health risks, and climate change are among the recognized threats that the species is facing in the region. The existing national, regional, and international legislation pertinent to Mediterranean countries should aid greater science–policy management integration and support innovative research and monitoring towards effective conservation. The challenges inherent in studying the pelagic D. delphis should not preclude the use of long-term, year-round, multiplatform surveys, side by side with the latest molecular tools, which aid our understanding of its populations' genetic diversity, resistance to diseases, and resilience in a semi-enclosed fast-changing sea. Addressing the multiplicity of problems confronting the species requires collaborative effort at all levels to share and merge resources, data, and expertise more efficiently. In this review, we provide an overview of the current knowledge on the Mediterranean common dolphin, the main threats, and knowledge gaps that are priorities for addressing its conservation, while providing clear recommendations for effectively safeguarding the species and its habitat at both local and regional levels. https://onlinelibrary.wiley.com/doi/10.1002/aqc.3538
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The decline of short‐beaked common dolphin (Delphinus delphis) in the waters off the island of Ischia (Gulf of Naples, Italy)
Article
  • Oct 2019
This study presents data on a local population of short‐beaked common dolphin monitored in the waters off Ischia Island (Gulf of Naples, Italy) over a 16‐year period (2000‐2015). We examine dolphin occurrence and distribution and perform photoidentification analysis. The data presented support the hypothesis that the waters around Ischia Island represent a feeding area, as well as a calving and an important nursery area for this local population, providing favourable conditions in which to give birth and raise calves. The levelling‐off of the photoidentification curves together with the continuous decline of the encounter rate lead us to believe that the area has been a hotspot for a local population (mainly resident) for years and that now this population is dying (has died) or is moving (has moved) to other locations. Several expanding human activities at sea have the potential to impact on the common dolphin in the study area, the most significant possibly being habitat disturbance and degradation (including traffic and noise pollution) and overexploitation of food resources by the fishery. The data presented in this study 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 rely on the region for important biological processes.
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An integrated approach for cetacean knowledge and conservation in the central Mediterranean Sea using research and social media data sources
Article
  • Jun 2019
  • AQUAT CONSERV
1. Sources of data other than those derived from conventional research protocols may contribute valuable information to fill gaps in knowledge about cetacean occurrences and diversity in a given area and help address conservation issues. 2. The performance of a method to examine cetacean communities based on presence records systematically derived from shared photographs and videos posted by boaters and maritime operators on social media (e.g. YouTube and Facebook) combined with patchy distributed visual/acoustic data collected by researchers has been evaluated. 3. Records (N = 1,274) gathered over a 10-year period (2008-2017) have been used to obtain insights into species' presence and habitat selection in a scattered study area of the central Mediterranean Sea (Italy). The effectiveness of the method, practical and theoretical advantages, limitations, and challenges of using data originated from social media for research and conservation purposes are discussed. 4. Seven out of the eight cetacean species regularly residing in the Mediterranean have been reported in the area, with different relative densities. Maximum entropy modelling techniques have been applied to the datasets derived from (a) social media, (b) research surveys, and (c) the combination of the two, using six fixed variables as proxies for cetacean presence. Distance from the coast and depth emerged as the main variables predicting encounters, with specificities related to the ecology of the species. 5. The approach was reliable enough to obtain broad-scale, baseline information on cetacean communities in the region, on the basis of which initial conservation recommendations and future research programmes can be proposed. 6. With the increasing need for studying whale and dolphin population ecology coming from national/international directives, support from citizens to aid research may act as a practical, inexpensive solution to gathering extensive spatial-temporal data for regional‐scale monitoring and for the development of management priorities. Daniela Silvia Pace and Antonella Arcangeli are contributed equally to this article
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Ecology, status and conservation of short‐beaked common dolphins Delphinus delphis in the Mediterranean Sea
Article
Full-text available
  • Sep 2003
  • MAMMAL REV
1. The recent decline in the Mediterranean population of short‐beaked common dolphins Delphinus delphis has been the subject of scientific controversy and political indifference. Research on these animals has been very limited and there has been no large‐scale, systematic effort to assess and monitor their abundance and distribution. The consequent lack of data has prevented a good understanding of historical and ongoing trends. 2. Nonetheless, literature and osteological collections confirm that common dolphins were widespread and abundant in much of the Mediterranean Sea until the late 1960s and that their decline occurred relatively quickly. Today, common dolphins remain relatively abundant only in the westernmost portion of the basin (Alboràn Sea), with sparse records off Algeria and Tunisia, concentrations around the Maltese islands and in parts of the Aegean Sea, and relict groups in the south‐eastern Tyrrhenian and eastern Ionian Seas. Otherwise, these dolphins are rare in, or completely absent from, Mediterranean areas where information is available. 3. Circumstantial evidence and qualitative judgements by the authors suggest that the following factors may have contributed to the decline of common dolphins: reduced availability of prey caused by overfishing and habitat degradation; contamination by xenobiotic chemicals resulting in immunosuppression and reproductive impairment; environmental changes such as increased water temperatures affecting ecosystem dynamics; and incidental mortality in fishing gear, especially gillnets. The cumulative importance of these factors is poorly understood, and as a result, few conservation measures have been implemented. 4. This paper reviews current knowledge and suggests priorities for action aimed at identifying and mitigating the main threats to common dolphins in the Mediterranean, with the ultimate goal of restoring the species’ favourable conservation status in the region.
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Abundance and habitat preferences of the short-beaked common dolphin Delphinus delphis in the southwestern Mediterranean: Implications for conservation
Article
  • May 2008
The Mediterranean sub-population of short-beaked common dolphin is believed to have suffered a steep decline in the Mediterranean in recent years, and in 2003 it was listed as endangered in the IUCN Red List of Threatened Species. Effective conservation will depend critically on our understanding of the relationship between the species and its habitats. The Alboran Sea is believed to be the most important remaining Mediterranean habitat for this species, and thus constitutes a vital source of information for the development of conservation measures. We used spatial modelling to estimate the abundance and explore the habitat use of common dolphins in this area, examining regional, seasonal and interannual variations, as well as the influence of biological factors such as presence of calves, interspecific relationships and behaviour. From 1992 to 2004, 37 385 km of non-systematic line transects generated 738 sightings in a 19 189 km2 study area. The point estimate of abundance was 19 428 (95 % CI = 15 277 to 22 804) dolphins. Seasonal and geographical variations in abundance were detected, with higher average density in summer than in winter, and in the Western Alborán Sea than in the east Gulf of Vera, which has different physical/environmental characteristics. No overall trend in abundance was observed in the Alborán area. However, a decline was observed in the Gulf of Vera, with a summer density 3-fold lower in the period from 1996 to 2004 than in 1992 to 1995. A potential link of this decline with prey depletion due to the exponential growth of aquaculture in the area is discussed. Clear differences inhabitat use were also found when examining the influence of biological factors. In particular, groups with calves and groups that were feeding preferred more coastal waters. This result could have important implications for the development of conservation measures for this species in the Mediterranean.
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Ecology, status and conservation of common dolphins Delphinus delphis in the Mediterranean Sea
  • Jan 2003
  • MAMMAL REV
  • 224-252
  • Bearzi G R Reeves R
  • D I Notarbartolo
  • G Sciara
  • Politi E Canadas
  • A Frantzis
  • A Mussi B
BEARZI G., REEVES R.R., NOTARBARTOLO DI SCIARA G., POLITI E., CANADAS A., FRANTZIS A., MUSSI B. (2003). Ecology, status and conservation of common dolphins Delphinus delphis in the Mediterranean Sea. Mamm. Rev., 33: 224-252.