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Map of the Mediterranean Sea showing the locations cited in the text. Numbers indicate the following localities: (1) Estepona; (2) Málaga; (3) Almería; (4) Gulf of Vera; (5) Principality of Monaco; (6) island of Ischia and Campanian Archipelago; (7) Naples; (8) island of Kalamos; (9) Gulf of Corinth.
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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...
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... (Heyning & Perrin, Fig. 1. Two short-beaked common dolphins photographed in the eastern Ionian Sea show the characteristic morphology of the species: short beak, narrow dark flipper stripe, occasional white patch in dorsal fin. Photo by G. Bearzi. 1994;Rosel, Dizon & Heyning, 1994). Only short-beaked common dolphins inhabit the Mediterranean Sea (Fig. 2) and adjacent water bodies, and therefore throughout this paper references to 'common dolphins' can be understood to mean this ...
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... The data of the presence, abundance, distribution, and conservation status of the majority of the non-fishable taxonomic groups (i.e., vertebrate species: sea birds, sea turtles, and cetaceans) throughout the historical series under study were incomplete, which prevented the complete modeling of the ecosystem. Additionally, although we found little information of the presence of cetaceans, birds, and sea turtles in marine areas [34,[45][46][47][48][49][50][51][52][53][54][55][56], we included them in the analysis when possible. It is important to note that all of the biomass data for exploited species utilized in this study solely represent the landings of commercially caught species and should not be considered an accurate reflection of the total biomass extracted from the ocean as it excludes discards, illegal, and recreational fishing due to the lack of official databases. ...
The goal of this project is to assess the state of marine biodiversity in the Natura 2000 marine network in Spain and analyze the impact of fishing policies on it. The study focuses on three marine demarcations in Spain: North Atlantic, South Atlantic, and the Strait of Gibraltar and Alborán Sea. The research uses the DPSIR (Drivers of Change-Pressure-State-Impact-Response) framework, a multi-criteria analysis approach to understand the relationships between biodiversity loss, fishing, marine ecosystem integrity, and the provision of ecosystem services. Our results revealed a significant decline in biodiversity since 1985 in the four marine areas studied; this loss was more pronounced in the Gulf of Cadiz (in Andalusia) and less intense in the northern regions of Spain (Galicia and Asturias). This trend aligns with the global degradation of marine ecosystems and loss of biodiversity caused by human activities. The main drivers behind this decline are economic factors promoting industrial fishing and overexploitation. However, there has been a reduction in the industrial fishing fleet since the 2000s, supported by the European Maritime and Fisheries Fund for transitioning toward sustainable fishing methods. Despite the increase in regulations and the establishment of marine protected areas, these measures have not been effective enough to stop the loss of marine biodiversity. The results highlight the importance of combining administrative measures such as creating marine protected areas and implementing fisheries management regulations with the preservation of cultural services provided by these ecosystems. Successful governance models that involve collaboration between fishermen and decision-makers have been observed in northern Galicia and the Gulf of Cádiz.
... The Mediterranean sub-population of common dolphin has undergone a drastic reduction in the past decades as a consequence of ever-increasing human pressures on the species range of distribution (Bearzi et al., 2021). Habitat loss and fragmentation, alongside the indirect effects of overfishing, unintentional captures during fishing operations, and take, have strongly contributed to the decline of dolphin numbers across the entire region (e.g., Bearzi et al., 2003;Bearzi et al., 2004;Bearzi et al., 2008;Cañadas and Vaźquez, 2017;Mussi et al., 2019). Overall, 32 primary sightings of common dolphins, mostly in the western portion of the basin and in the Strait of Sicily (see Nivière et al., 2024), were recorded during the ASI aerial surveys, with a total estimate of 66,359 individuals (95% CI=31,054 -141,801). ...
The “ACCOBAMS Survey Initiative” (ASI) is a pilot programme aimed at establishing an integrated and coordinated monitoring system for cetaceans across the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and contiguous Atlantic (hereafter “ACCOBAMS”) area. Conducted in coordination with Mediterranean coastal countries, it supports the implementation of European and regional policies, in particular the EU Marine Strategy Framework Directive and the Ecosystem Approach process. In summer 2018, a synoptic survey was conducted across the Mediterranean Sea and contiguous Atlantic area, combining visual monitoring from aircrafts with visual and passive acoustic monitoring from vessels. Species density and abundance were estimated through design-based approach in a line-transect sampling framework. Based on data arising from the aerial survey only, uncorrected design-based abundance was obtained for striped (N=426,744, CV=0.13), common (N=65,359, CV=0.4), bottlenose (N=63,333, CV=0.17), and Risso´s dolphins (N=26,006, CV=0.3), Cuvier’s beaked whales (N=2,929, CV=0.4) and long-finned pilot whales (N=5,540 CV=0.4). A merged category of either striped or common dolphins resulted in 212,483 individuals (CV=0.26). Fin whales abundance of 1,749 animals (CV=0.3) was corrected for both availability and perception biases and resulted in 3,282 (CV=0.31). The ASI survey offers an overall picture of the distribution and abundance of cetaceans throughout the Mediterranean basin, providing robust estimates to be considered as a baseline for future regional systematic monitoring programmes. The ASI survey is the first step towards establishing a long-term monitoring program across the entire ACCOBAMS area, and, as such, it sets the basis for further future basin-wide monitoring efforts using systematic, shared, coordinated and comparable methods. The information gathered will further enhance knowledge on cetacean status, facilitating the development of informed conservation and mitigation measures, as well as supporting the implementation of international obligations. Furthermore, the outcomes of this survey will support both place- and threat-based conservation efforts in the ACCOBAMS area, through the identification of Important Marine Mammal Areas and Cetacean Critical Habitats. Here the results of the ASI survey are presented and discussed alongside proposed management and conservation actions aimed at ensuring the persistence of cetacean populations in the region.
... Historically, common dolphins (Fig. 5) used to be abundant in the Adriatic Sea, including in its northern portion, but extensive killings (see the Intentional killings section) are thought to have substantially contributed to their eradication. The species declined in the first half of the 20 th century, and its recovery was later compromised by prey depletion caused by overfishing, and by habitat degradation (Bearzi et al., 2003(Bearzi et al., , 2004Bearzi and Genov, 2022). Below, we report some information on common dolphin occurrence in the Adriatic Sea published in the reviews by Bearzi et al. (2004) and Genov et al. (2021), with amendments and updates. ...
The Adriatic Sea is one of the Mediterranean areas most exposed to cumulative human stressors. This semi-enclosed and largely shallow basin has been subjected to intensive exploitation and destructive fishing practices for decades, resulting in biodiversity decline and poor ecosystem health. Diversity of cetaceans is lower than in other parts of the Mediterranean, and the extant dolphins and whales have been facing threats that include the combined effects of habitat loss and degradation, prey depletion, incidental mortality and injury caused by fisheries, anthropogenic noise, chemical contamination and climate change. Here, we report information for the nine cetacean species known to occur in the basin (classified as either regular, visitor or vagrant), plus three species characterized by a single record. For these species, we review evidence from field research and other studies-with a bias towards the common bottlenose dolphin *Tursiops truncatus* (by far the most intensively-studied cetacean in this area). We also describe and characterize the main threats to cetaceans in the Adriatic, relying on recent literature as well as historical information that helps frame the present status of cetaceans in the context of past human impacts (particularly the extensive killing campaigns conducted until the 1960s). Finally, we provide management recommendations to inform and guide the action that must be taken in compliance with extant legislation, marine conservation directives and international commitments to protect marine biodiversity.
... In visual surveys, estimating the group size of a large school of active dolphins is a difficult task and the estimates can vary considerably between observers (Gerrodette et al., 2002). The average group size was estimated to be 10 individuals in this study, which was consistent with other studies averaging between 4 and 30 individuals (Notarbartolo di Sciara et al., 1993;Bearzi et al., 2003;Cañadas and Hammond, 2008;Boisseau et al., 2010;Notarbartolo di Sciara and Tonay, 2021) in the Mediterranean, although larger aggregations are known (Watkins et al., 1987;Boisseau et al., 2010;Notarbartolo di Sciara and Tonay, 2021). In acoustic surveys, group size cannot be estimated directly during surveys and most studies use visual events to determine group size of the acoustic events (Barlow & Taylor, 2005;Pirotta et al., 2015). ...
... The bottlenose dolphin mostly lives on the continental shelf (Bearzi et al., 2009;Cañadas et al., in review), while the striped dolphin is an oceanic species that is usually found in open waters (Cañadas et al., in review;Notarbartolo di Sciara and Tonay, 2021). The common dolphin can be observed in both inshore and offshore waters (Bearzi et al., 2003). By grouping species together, the variation in species occurrence and distribution within a study area would not be significant if the detectability across species were equal. ...
Estimating the detection probability of small cetaceans using either visual or acoustic surveys is difficult because they do not surface or vocalise continuously and can be imperceptible to an observer or hydrophone. Animals seen at the surface may have lower vocalisation rates, while submerged individuals may be more vocally active. This study aims to estimate visual, acoustic and combined detection probability by using Mark-Recapture Distance Sampling (MRDS) methodology. We used vessel-based visual sightings and acoustic data (based on click identification) collected simultaneously during the ACCOBAMS Survey Initiative in summer 2018 onboard the R/V Song of the Whale. This study focused on small cetaceans in the Mediterranean Sea, including the most commonly-encountered species, the striped dolphin (Stenella coeruleoalba). We identified duplicate events between visual and acoustic platforms using a decision tree based on time and distance thresholds to estimate g(0) (the detection probability on the trackline) for small cetaceans. A total of 30 duplicate events were identified from 107 and 109 events identified by the visual and acoustic platforms respectively. We tested the models with two key functions. With a hazard-rate key function, the g(0) was estimated at 0.52 (CV=21.0%) for both platforms combined, 0.29 (CV=25.6%) for the visual platform and 0.32 (CV=25.1%) for the acoustic platform. With a half-normal key function, g(0) was estimated at 0.51 (CV = 21.7%) for both platforms combined, 0.29 (CV = 25.6%) for the visual platform and 0.33 (CV = 23.2%) for the acoustic platform. Our results illustrate that passive acoustic monitoring can be used as an independent platform in MRDS to estimate the detection probability. Our estimate of g(0) was well below 1, far from the perfect detection commonly assumed for abundance estimation. Without correction for detection biases, total abundance would be underestimated by a factor of two when using both acoustic and visual data. This highlights the importance of using dual-platform surveys to estimate detection probability in order to improve abundance estimates and conservation efforts.
... However, management units are currently based on Australia and New Zealand having separate populations (Barceló et al. 2021). Given recent declines of common dolphins observed internationally (e.g., in the Mediterranean Sea; Bearzi et al. 2003;Piroddi et al. 2011;Vella et al. 2021), careful management based on a fuller understanding of the reproductive biology of male common dolphins on both sides of the Tasman Sea is required to ensure the longterm viability of the species in this region. As male life history is comparatively less described (Chivers 2009), this study will complement recently published data on female common dolphin reproductive parameters (Palmer et al. 2022), offering population-level insights to common dolphins in New Zealand waters. ...
Reproductive parameters were assessed in 64 male common dolphins (Delphinus delphis) examined post-mortem from strandings and bycatch in New Zealand between 1999 and 2020. The stages of male sexual maturation were assessed using morphological measurements and histological examination of testicular tissue. Age was determined via growth layer groups (GLGs) in teeth. The average age (ASM) and length (LSM) at attainment of sexual maturity were estimated to be 8.8 years and 198.3 cm, respectively. Individual variation in ASM (7.5–10 years) and LSM (190–220 cm) was observed in New Zealand common dolphins. However, on average, sexual maturity was attained at a similar length but at a marginally younger age (< 1 year) in New Zealand compared to populations in the Northern Hemisphere. All testicular variables proved better predictors of sexual maturity compared to demographic variables (age and total body length), with combined testes weight the best outright predictor of sexual maturity. Reproductive seasonality was observed in male common dolphins, with a significant increase in combined testes weight in austral summer. This aligns with most other studied populations, where seasonality in reproduction is typically observed. Given the known anthropogenic impacts on New Zealand common dolphins, we recommend that these findings be used as a baseline from which to monitor population-level changes as part of conservation management efforts.
Supplementary Information
The online version contains supplementary material available at 10.1007/s00227-023-04266-5.
... There have been reports of recreational vessels catching tuna for the market. 5 Local cetacean populations therefore face a variety of anthropogenic threats and have been classified as 'vulnerable' and 'critically endangered' (Azzolin et al., 2020;Bearzi et al., 2003;2008;Carpinelli et al., 2014;Castellote et al., 2012;Esteban et al., 2014;Verborgh et al., 2016). Photography is a valuable tool to monitor external traumata. ...
The Strait of Gibraltar is an important habitat for seven regularly occurring cetacean species. These waters are heavily used for fishing and therefore experience extraordinary levels of shipping traffic. Photography provides a valuable and non-invasive tool to monitor the health of cetacean populations, where external injuries may indicate specific anthropogenic impacts, such as vessel strikes or fishery interactions. We manually screened 27,866 photos taken during whale-watching operations between 2016-20 for human-induced injuries. Injuries of potential anthropogenic origin were detected in 228 cases. The severity of these injuries ranged from superficial linear marks to severe traumas that may affect survival and fitness. Severe injuries included a gunshot wound, vessel-related traumata and abrasions, signs of previous severe entanglements and deep lacerations which could stem from recreational fishery activities or propellor cuts and occasionally served as an entry point for dermal infections. In 2007, Spanish legislation introduced regulations on how to approach cetaceans by boat, but recreational fishery vessels have been commonly observed to disregard this law. We therefore urge stricter control and enforcement of existing laws and collaboration between the Spanish and Moroccan authorities to mitigate the human impact on cetaceans in this region.
... The rest of the species were sporadically recorded in the area, as seen in other regions of the Mediterranean (Azzellino et al., 2008;Gnone et al., 2011). Due to the low number of sightings of common dolphins, sperm, pilot and Cuvier's beaked whales the results should be considered carefully but the information of their presence is extremely important, especially in cases such as common dolphins and the sperm whales, species whose Mediterranean subpopulations are considered endangered (Bearzi et al., 2003;Lanfredi et al., 2021;Pirotta et al., 2021;Vella et al., 2021). ...
This study provides information on cetacean occurrence in the central Catalan coast (NE Iberian Peninsula), an area characterised by an underwater canyon system. Encounter rates (ER), relative abundances (RA) and sea- sonality were assessed for eight species. This information was combined with physiographic features of the seafloor to understand their influence on cetacean distribution. Data were collected along 189 surveys from January 2017 to December 2022. In total, 479 sightings of eight species of cetaceans were recorded. Striped, bottlenose and Risso’s dolphins and fin whales were the most frequently sighted. ER and RA were similar or higher than in other areas of the Mediterranean Sea. Species were distributed differently according to physio- graphic features: bottlenose dolphins in coastal waters and Risso’s dolphins and fin whales above the Garraf underwater canyon system. These results highlight the importance of the central Catalan coast, particularly the underwater canyon system, for at least four species of cetaceans.
... 24, 2023 | 77 the Mediterranean subpopulation has experienced an alarming decline, now showing only a patchy distribution throughout the basin Cañadas and Hammond, 2008). This basin-wide decline is due to a variety of factors, including bycatch, prey depletion due to overfishing and habitat degradation, marine traffic, chemical and noise pollution, marine debris and outbreaks of disease (Aguilar et al., 1999;Bearzi et al., 2003;Costello et al., 2010;Harwood, 2001;Sutherland et al., 2010). ...
... Group sizes reported in the Aegean Sea are typically lower, rarely exceeding 35 individuals (Alan et al., 2018;Milani et al., 2019;Pietroluongo et al., 2020). Variation in dolphin group sizes can be related to the animal's activities, prey availability, predator presence and habitat preference (Acevedo-Gutiérrez, 2002;Bearzi et al., 2003Bearzi et al., , 2005Bearzi et al., , 2008Mann et al., 2000;Santos and Rosso, 2007). Previous studies report a tendency to encounter smaller groups within coastal protected waters, while dolphins may form larger aggregations in open waters to facilitate detection of patchy food sources within a vast area and increase protection from predators (Santos and Rosso, 2007;Würsig, 1986). ...
Basic knowledge about populations of short‐beaked common dolphins (Delphinus delphis) in the eastern part of the Mediterranean Sea is still lacking. Classified as ‘Endangered’ in an IUCN assessment released in 2022, it is necessary to gain baseline knowledge to understand the species’ population status and develop impactful conservation measures. The current study conducted boat surveys, employing visual and acoustic techniques between January 2019 and July 2022 in the Dilek Peninsula National Park, central Aegean Sea. Results revealed the continuous coastal presence of common dolphins, with subadults recorded during every sighting in low group sizes. Travelling‐related activities made up 58% of observed behaviour while resting comprised just 1%. Whistles were produced in the range of 1.83–48kHz with a peak frequency of 10.4kHz and median duration of 0.54s. Concave whistles were the most frequently recorded whistle type. Whistles were found to be generated when dolphins were interacting with boats and diving/travelling fast, forming 53% and 31% of whistle production respectively. The continuous presence of common dolphins, particularly subadults, emphasises the importance of the Dilek Peninsula. Whistle parameters show similarities with other common dolphin populations of the Mediterranean and Black Sea, albeit with shorter durations. The high whistle presence during boat interactions requires investigation to assess whether whistles carry avoidance or predatory messages, or whether there are potential consequences for the species’ energy budget. The current study presents preliminary information on the behavioural context of acoustic patterns. Further research is essential to understand the click and whistle characteristics within the biological, environmental and anthropogenic variables of their surroundings.
... The IUCN has classified these populations on a range from vulnerable to critically endangered (Azzolin et al., 2020;Bearzi et al., 2003;Carpinelli et al., 2014;Castellote et al., 2012;Esteban et al., 2014;Verborgh et al., 2016). The Strait is intensively fished (Burgos et al., 2013;García-Tiscar, 2009) and the use of illegal driftnets has been reported (Tudela et al., 2005;Tydeman and Lutchman, 2012). ...
Cetacean populations in the Strait of Gibraltar are heavily impacted by human activities. Photographs are a valuable tool to monitor the external health of cetaceans. We visually screened 27,866 pictures taken during whale watching operations in the years 2016–2020 for abnormal conditions, such as emaciation, dermal diseases and epizoic infestations. Prevalence levels could not be calculated as data were obtained opportunistically. Dermal diseases were detected in 566 sightings and occurred in all species. Bottlenose dolphins were most strongly affected (n = 192). Hypopigmented skin lesions were most common in all species (n = 291). Tattoo skin disease‐like lesions affected 16 animals (T. truncatus: n = 12; G. melas: n = 3; D. delphis: n = 1). Other observed conditions include expansive annular lesions in three juvenile pilot whales. Furthermore, we report the presence of open wounds in 28 animals (G. melas: n = 23; T. truncatus: n = 2; P. macrocephalus: n = 3). In three pilot whales, these wounds did not heal over a period of several years. Epizoic and ectoparasitic infestations include the observation of Xenobalanus spp. and Pennella balaenopterae. Multiple fin whales were sighted with very high numbers of Pennella balaenopterae, ranging up to 84 parasites per host. Emaciation was mainly detected in bottlenose dolphins (n = 36) and seemed to affect these animals more severely during specific years, potentially indicating fluctuations in prey availability. KEYWORDS: CETACEANS; DERMAL DISEASES; EMACIATION; ECTOPARASITES; STRAIT OF GIBRALTAR
... Common dolphins occur as a series of geographically separate subpopulations, several of which can be distinguished in European waters (e.g., Bearzi et al. 2003), as well as two subspecies, that is, D. d. delphis and D. d. ponticus. ...
... Common dolphins remain relatively abundant in the Alborán Sea, in the northern half of which abundance has been estimated at 19,428 (95% CI ¼ 15,277-22,804) from nonsystematic line transects carried out between 1992 and 2004 (Cañadas and Hammond 2008). Several one-off estimates in other regions of the Mediterranean basin were summarized by Bearzi et al. (2003). Negative trends in abundance were recorded in several Mediterranean areas, including (1) the Gulf of Vera, Balearic Sea, where common dolphin numbers decreased threefold from 1992-1995(Cañadas and Hammond 2008; (2) the southeastern Tyrrhenian Sea waters off the island of Ischia, Italy, where the species appears to have vanished in recent years (Mussi et al. 2019); (3) the northern Adriatic Sea, where common dolphins were historically abundant but have virtually disappeared since the 1980s (Bearzi et al. 2004a;Genov et al. 2020); and (4) the Inner Ionian Sea Archipelago, Greece, where the species has declined since the mid-1990s (Bearzi et al. 2006. ...
