Starting from June, CERT advised the authorities and citizens to comply with a Code of Conduct (Table 1) in the presence of the bottlenose dolphin – a species protected by national and international regulations (Table 2). This code of conduct became especially important when the dolphin began to occur regularly in the city area of Venice – particularly in the San Marco Basin and in the waters in front of San Marco Square (Figure 2) – soon becoming a phenomenon of great interest to citizens, tourists and the media.

Within the San Marco Basin, there were several records of blatant violations of current regulations, including guided tours to approach the animal, attempts to take close-up pictures, attempts to touch or offer food to the animal, and the throwing of various objects into the water. Such inappropriate behaviours could encourage the dolphin to interact more closely with humans, creating possible hazards for both the animal and the people. Disturbing and feeding a wild dolphin in Italy is punishable by law, and may represent a criminal offence (Table 2).

Following observations of the dolphin’s exposure to the risk of collision with boats in the San Marco Basin – an area of intense vessel traffic – as well as photographic documentation of lesions on its dorsal fin and dorsum consistent with propeller impact (first observed on November 12^th, 2025; Figure 3), a coordinated large-scale intervention was carried out on November 15^th, 2025, to test strategies for guiding the animal away from the highest-risk area (Capitaneria di Porto, 2025). Throughout the intervention, backed by the experts from CERT, dolphin behaviour was monitored in relation to boat traffic and acoustic disturbance.

Under the coordination of the Harbour Master’s Office and CERT, a total of 14 motorboats and patrol boats (approximately 7–14 m in length) operated by the main municipal authorities were deployed, arranged in two rows. The first row consisted of 6 boats equipped with acoustic deterrent devices (Acoustic Deterrent Device Model DiD01 by STM Products, Verona, Italy; SPL 168 dB re 1 μPa at 1 m), spaced approximately 30 metres apart; the second row, positioned about 10 m further back, consisted of 8 boats, 7 of which were equipped with metal bars to produce percussive underwater noises. The driving attempt began at 9:30 a.m. and ended at 11:00 a.m. – after losing sight of the dolphin at 10:30 a.m.

The attempt to drive the dolphin away from the San Marco Basin was successful in terms of short-term dolphin displacement. During the intervention, the dolphin moved away from the San Marco Basin, towards Sant’Elena and then further south, towards the island of La Grazia – approximately 3 km away from its original location. Its response to combined anthropogenic disturbance (spatial deterrence by boats and acoustic deterrence by loud sounds) was assessed visually by the CERT experts onboard. The dolphin appeared calm and exhibited regular surfacings at a normal speed of travel (less than 4 km/h) while moving away from the sources of disturbance. However, at the end of the intervention the dolphin returned to the San Marco Basin – the area it seems to prefer – where its presence was recorded again at 11:30 a.m.

The literature describing the occurrence of two cetacean species that used to be abundant in the northern Adriatic in historical times – common dolphin and bottlenose dolphin – is sometimes inconsistent, due in part to imprecise taxonomy and some confusion originating from the use of scientific and common names (possibly including the potentially misleading word ‘common’ in ‘common dolphin’). Specifically, Nardo (1854) listed the common dolphin as the only regular cetacean species in the Adriatic. De Marchesetti (1882) claimed that the most common species was Delphinus delphis, and that ‘Delphinus tursio’ (= T. truncatus) was less frequent. Faber (1883) considered D. delphis as the most common cetacean in the Adriatic, while according to Brusina (1889)D. delphis and T. truncatus were both common. Trois (1894) reported that common dolphins caught in the inner channels of the Venetian Lagoon were often put for sale at the Venice fish market, and reported that D. delphis was more abundant than T. truncatus in the northern Adriatic. Common dolphins were even reported to follow ships into ports (Kolombatović, 1882; Trois, 1894). Ninni (1901, 1904) considered D. delphis very common in the Adriatic Sea compared with ‘D. tursio’, which he considered rare. Inconsistencies including the report of a ‘D. tursio’ that was 6 m long (Ninni, 1901) suggest that cetological accounts by this author must be taken with caution. Vatova (1928) listed D. delphis as common throughout the Adriatic, while ‘T. tursio’ was considered ‘very rare’. However, the same author subsequently listed both species among the commonest marine animals to be found near Rovinj, Croatia (Vatova, 1932). D. delphis was the only cetacean listed as frequent in the catalogue of mammals of former Yugoslavia (Đulić and Tortić, 1960).

In the 1940s, large groups of common dolphins could still be seen near the coast in the Gulf of Trieste, but by the late 1970s there had been a noticeable decrease in this species in the northern Adriatic (Pilleri and Gihr, 1977). In the Venetian Lagoon, the occurrence of any dolphins has become a rare event since the 1970s (Rallo, 1976, 1979; Bearzi and Ferretti, 2000).

Despite some inconsistencies, the historical information indicates that the Venetian Lagoon used to be part of the natural range of dolphins in the Adriatic Sea (Ceresole, 1894; Trois, 1894). Common dolphins – once the most common species – have been largely eradicated (Bearzi et al., 2004). However, bottlenose dolphins – the only cetacean species that occurs regularly in the northern Adriatic in present times (Bearzi et al., 2024a) – might progressively return to the Venetian Lagoon, possibly encouraged by the availability of suitable prey, and could reside in inland waters at least occasionally if allowed to do so.

The behaviour of the solitary bottlenose dolphin observed between June and December 2025 is consistent with the typical behaviour of the species. The dolphin likely entered the lagoon and subsequently settled in the waters south of Venice due to the high availability of prey in that stretch of the lagoon. Specifically, it was observed a number of times eating mullets (family Mugilidae) – a behaviour that is also well documented in photographic and video materials (Figure 4). Feeding on other species may also occur, but it was not convincingly documented. In one case, the bottlenose dolphin was observed ‘playing’ with a European seabass Dicentrarchus labrax weighing an estimated 5–7 kg – though it is unknown whether the dolphin could have subsequently ingested such a large fish.

While being regularly observed in the San Marco Basin, the dolphin did not spend all of its time there. On some days, it did not appear to be present at all in the Basin. There were sightings in the south-western part of Venice, up to the western mouth of the Grand Canal, just before the Ponte della Libertà, as well as throughout the Giudecca Canal and the Tronchetto Canal, including in relatively confined and shallow-water areas. On the eastern side of Venice, there were sightings in the channel of San Nicolò, almost as far as the Forte di Sant’Andrea.

In the Adriatic Sea, bottlenose dolphins are gregarious animals that tend to live in small to medium-sized groups, often ranging between 3 and 9 individuals (though groups composed of up to 70 individuals can occur); encounters with solitary individuals are not uncommon (see Table 4 in Bearzi et al., 2024a). Cases of solitary bottlenose dolphins that have settled in bays, lagoons, inland waters and even harbours have occurred in various parts of the world, including in the Adriatic Sea (Lockyer, 1990; Wilke et al., 2005; Nunny and Simmonds, 2019a, b; Simmonds and Nunny, 2022; Nunny et al., 2025). In some of these cases, the individuals returned to the open sea or joined their conspecifics after a period of solitary life; in other cases, they remained longer or even permanently within relatively confined areas. However, there have been several cases of solitary bottlenose dolphins coming to an untimely death due to irresponsible human behaviour (Nunny and Simmonds, 2019a; IJsseldijk et al., 2020).

Bottlenose dolphins occur in coastal areas and inland waters worldwide (Leatherwood and Reeves, 1990). In the Mediterranean, they inhabit a wide variety of habitats including continental shelf waters, lagoons and enclosed seas (Bearzi et al., 2009). These can include areas disturbed by noise and vessel traffic, where the dolphins may spend much time when prey is available in sufficient quantities (Marley et al., 2017; Bearzi et al., 2019; Piwetz, 2019). It is unquestionable that these animals are exposed to risks, perhaps especially when they are alone, but it must be noted that life in the open sea also involves various threats. Specifically, bottlenose dolphins off the coast of Veneto and in other Adriatic areas spend much of their time foraging in the wake of trawlers, often scavenging in their immediate proximity (Bearzi et al., 1999; Genov et al., 2008, 2019; Rako-Gospić et al., 2017; Miočić-Stošić et al., 2020; Bonizzoni et al., 2021, 2023b). They can also forage in the vicinity of purse seines (Zorica et al., 2018; Rudd et al., 2022) and are known to take fish and other organisms from gill and trammel nets – a behaviour that occasionally results in dolphin mortality (Đuras Gomerčić et al., 2009; Đuras et al., 2021; Li Veli et al., 2023; Pietroluongo et al., 2025). Furthermore, Adriatic bottlenose dolphins can forage in the immediate proximity of coastal fish farms (Pleslić et al., 2021). Such opportunistic behaviour is also common in coastal areas of Greece, where the species was recorded amid traffic from barges and other fish farm vessels (Bonizzoni et al., 2023a) as well as in highly polluted bays (Bonizzoni et al., 2014).

The extremely adaptable and opportunistic behaviour of the bottlenose dolphin (Shane et al., 1986; Bearzi et al., 2019) is ultimately one of the main factors that has allowed this species to survive in the northern Adriatic Sea, where less resilient and adaptable species such as the common dolphin have almost completely vanished (Bearzi et al., 2024a). In other words, taking risks is the price bottlenose dolphins pay to survive in a marine environment that has been exposed to extremely high levels of human impact in recent decades. The Adriatic is a highly degraded and overexploited sea (Colloca et al., 2017; Eigaard et al., 2017; Gissi et al., 2017; Ferrà et al., 2018; Ramírez et al., 2018; Russo et al., 2019) that has experienced regime shifts caused by fishing (Sguotti et al., 2022) and dramatic losses of biodiversity (e.g. Ferretti et al., 2013). The Adriatic Sea has been fished intensively since historical times, and is one of the most intensively trawled areas worldwide (Amoroso et al., 2018). A recent study used a quantitative indicator of biological state of seabed sedimentary habitats in 24 regions around the world exposed to bottom trawling, and found that the Adriatic Sea had by far the poorest seabed status (Pitcher et al., 2022).

In such a context, the ‘dolphin of Venice’ did not cause concern because of its presence in a lagoon environment where dolphins were historically present, but more specifically because of its occurrence near San Marco Square – one of the most popular and busiest tourist areas in the world. Due to the frequent occurrence of interactions with humans within this area, the dolphin appeared to be halfway between Stage 1 (“Dolphin establishes itself in a limited home range; not interested in people”) and Stage 2 (“Dolphin may start to follow boats; interested in people”) described for solitary dolphins by Nunny and Simmonds (2019a). The combination of an exceptional setting such as the San Marco Basin and the dolphin’s confident behaviour challenged the institutional duty to ensure the protection and welfare of a wild animal, calling for swift management measures as well as appropriately high levels of environmental awareness and education on the part of the community.

To prevent the dolphin from settling in a high-risk area in the long term, the use of fixed acoustic deterrents was suggested by CERT based on previous positive experience with a different species (specifically striped dolphins Stenella coeruleoalba) in the same area. Such deterrents could be deployed at strategic points within the San Marco Basin. However, the experts involved agreed that while it is possible that the animal would move to less-disturbed feeding areas due to the acoustic deterrents, it is also possible that it would become accustomed to the noise produced by the deterrents, and continue to use the same area despite their presence.

Decades of research indicate that it may be difficult to deter opportunistic odontocete species from approaching spots where food is promptly available (Bearzi et al., 2019). While acoustic deterrents may drive bottlenose dolphins away for varying periods of time, they rarely cause them to abandon their feeding areas (or sources, in the case of fishing gear). The duration of a study appears to be an important variable affecting results, with deterrence more likely to be observed in short-term studies, and habituation more likely in longer-term studies (e.g. Buscaino et al., 2009, vs Buscaino et al., 2021).

Still, the use of acoustic deterrent devices on trawl nets has not produced significant results with bottlenose dolphins (see Table 4 in the review by Bonizzoni et al., 2022). Ineffective deterrence on those nets could be due at least in part to the noise generated by the powerful engines of trawl vessels, as well as by the friction and contact of trawl nets, otter boards and other groundgear with the seabed (Bearzi et al., 2024b). In the case of the ‘dolphin of Venice’, such scientific evidence may be relevant, considering that any deterrents used in the San Marco Basin would also be placed in a noisy environment. Specifically, Sound Pressure Levels (SPL) recorded in the San Marco Basin were between 90 and 120 dB re 1 μPa (Bolgan et al., 2016), while commonly used ‘dolphin deterrent devices’ produce noises around 165 dB re 1 µPa at 1 m, with SPL at 50 m from the source being approximately 110 dB.

A comprehensive review by Tixier et al. (2021) concluded that acoustic deterrence is the most widely used approach worldwide, but also the least effective when it comes to reducing marine mammal feeding on nets and other fishing gear, considering habituation. Most commonly used dolphin deterrents are operated at source levels intended to prevent or minimise hearing damage, whether temporary or permanent (e.g. Southall et al., 2019). Still, existing empirical studies reported non-auditory impacts including behavioural avoidance, altered foraging patterns and physiological indicators of stress (Richardson et al., 1995; Hildebrand, 2005). Additionally, several authors have raised concerns that long-term or cumulative exposure may increase the risk of auditory injury, especially in small odontocetes like harbour porpoises Phocoena phocoena (Olesiuk et al., 2002; van Beest et al., 2017; Findlay et al., 2021, 2024; Todd et al., 2021; Elmegaard et al., 2023). Finally, acoustic deterrents can increase underwater noise levels, with potential effects on fish and other species (Goetz et al., 2015; Bolgan et al., 2016; Findlay et al., 2018).

The information above, as well as the evidence reported in Section 3.2, suggests that acoustic deterrents may not be an effective tool to drive the dolphin away from the San Marco Basin, and should only be used if the animal is considered to be in imminent danger. If acoustic deterrents were to be deployed based on important justification, it would be crucial to carefully assess their potential impact based on expert advice and published information specific to bottlenose dolphins (e.g. Finneran et al., 2005, 2023).

In case acoustic deterrents are deployed, one should consider the possibility that the dolphin will become accustomed and gradually learn to tolerate their sounds. If deterrents have no lasting effect, they should be promptly removed. Deterrence should be limited to the time the dolphin remains in the high-risk area of the San Marco Basin, after ascertaining that the animal does not show abnormal behaviour – while recognising that evidence of physiological stress can be difficult or impossible to assess visually. Even if considered scientifically and ethically acceptable, as well as logistically and technically feasible, it should be noted that acoustic deterrence requires a specific exemption from existing directives. Finally, one should consider that forcing a dolphin to move away from a favourite feeding area may not represent good practice in terms of environmental education and public awareness (see Section 4.5). It is therefore necessary to carefully consider the quality of communication, as well as the contents and implications of the message being conveyed to the public (Nunny et al., 2025).

Some Venetian citizens and organisations suggested that in order to ‘save’ the dolphin it would be necessary to capture and transfer it elsewhere. As reported above, the animal appeared to be in good health, and actively fed in the Venetian Lagoon. Based on observations conducted in the context of this study, the dolphin would not need to be saved, and it would be important to avoid interventions that could endanger it, or lead to serious accidents that would inevitably be amplified by the media.

Capturing the dolphin must be strongly discouraged for the following reasons:

Capturing and handling the animal would present logistical difficulties in the face of considerable costs, with modest chances of success and high risks for the animal and the operators. It would therefore be a disproportionate measure in relation to current management needs, as well as an unacceptable measure from an ethical and animal welfare point of view.

Even if the bottlenose dolphin could be captured without incidents and transferred to the open waters of the northern Adriatic Sea, it is likely that an animal that has learned to feed in inland waters, and became accustomed to high levels of disturbance, could eventually choose to visit other inland waters – or even return to the same area as before, where it knows it can find an abundant prey supply. Finally, the hypothesis of capturing the animal and transferring it to a facility under human care would be inappropriate for a number of ethical, scientific and legal reasons (Lott and Williamson, 2017; Marino, 2018, 2025). Specifically, keeping dolphins in a controlled environment is considered inappropriate in many parts of the world, and particularly in Europe, where dolphinaria are closing in several locations and attempts are being made to release dolphins.

In past centuries, seeing dolphins in the inland waters and lagoons of the northern Adriatic Sea was not uncommon. In present times, however, the ‘dolphin of Venice’ has become a phenomenon and a matter of concern. A primary challenge is managing the behaviour of people who – not being equipped with sufficient understanding of cetacean biology, animal welfare, and existing rules on proper conduct – attempt to exploit the animal’s presence for their own amusement or profit. As we have seen, extreme cases of inappropriate interaction have ranged from deliberate attempts to touch and feed the animal – with potentially serious consequences in terms of dolphin habituation – to the close approach of boats performing manoeuvres that increase the risk of injuries (such as those that were actually inflicted to the dolphin). These practices have occurred in other areas around the world (Lockyer, 1990; Orams, 2002; Durden, 2005; Cunningham-Smith et al., 2006; Smith et al., 2008; Carzon et al., 2023) and have occasionally resulted in the mortality of solitary dolphins (Nunny and Simmonds, 2019a; IJsseldijk et al., 2020). They must be strongly discouraged.

Studies on interactions with wildlife in habitats shared with our species suggest that – given good management practices – coexistence is not only possible but even desirable (Bearzi et al., 2019). Exploring ways of instilling tolerance and promoting the type of social change that leads to widespread appreciation of wildlife is crucial. Specifically, dolphins play an important role as both flagship species (Smith and Sutton, 2008) and charismatic animals (Albert et al., 2018) that can capture public attention and mobilize support for broader marine conservation initiatives (Thomas-Walters and Raihani, 2017) – with the caveat that the perceived charisma of some animals may not lead to the protection of their own species (Courchamp et al., 2018). Ultimately, the goal is coming to view wild creatures with the wonder and respect they deserve, while identifying the most appropriate ways to coexist (Wilke et al., 2005; Bearzi et al., 2019; Nunny and Simmonds, 2019a).

Ensuring full compliance with current regulations (Table 2) and strict adherence to the Code of Conduct drawn up by experts from CERT (Table 1) represents the first step in this direction. Further progress could be made through a specific Action Plan, ideally prepared by specialists with extensive expertise in 1) the study and protection of bottlenose dolphins (especially in Adriatic waters), and 2) the mitigation of negative interactions between cetaceans and humans through best management practices, education, and awareness raising.