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BOTTLENOSE DOLPHIN

Tursiops truncatus

Red List Category & Criteria: Vulnerable A2cde

Geographic Range:

Bottlenose Dolphins are widely distributed throughout the Mediterranean Sea. Although historically their distribution may have been continuous, at least in coastal waters, it is now marked by gaps with low densities that may be either natural or the result of anthropogenic effects (e.g., intensive exploitation, whether deliberate or indirect; habitat degradation or loss). Range includes inshore, coastal and offshore waters to near the continental slope.

Bottlenose Dolphins occur in most coastal waters of the basin and have been reliably reported in the waters of Albania, Algeria, Croatia, Cyprus, France, Gibraltar (U.K.), Greece, Israel, Italy, Montenegro, Morocco, Slovenia, Spain, Tunisia and Turkey.  They occur regularly around many of the region’s offshore islands and archipelagos (Bearzi et al. 2008). Many of the Mediterranean areas inhabited by these dolphins are subject to intensive human use, e.g. the straits of Gibraltar, Bonifacio, and Messina, and the gulfs of Lion, Genoa, and Trieste. he effects of past extermination campaigns (Bearzi et al. 2004) and a variety of ongoing threats probably have contributed to the patchiness of the current distribution of Bottlenose Dolphins across the region.

Population:

Total population size is unknown but may be in the low 10,000s based on observed densities in areas that have been surveyed (Bearzi et al. 2008). Further subpopulation structure exists and may require future assessments at a finer geographical scale. 
A declining trend is inferred, refering specifically to the time since the early 1940s (i.e., over the last three generations). It is uncertain whether the subpopulation is still declining and if so, at what rate.
Mediterranean Bottlenose Dolphins are genetically differentiated from those inhabiting the contiguous eastern North Atlantic Ocean and Scottish waters.  Based on nuclear and mitochondrial DNA analyses, distinct populations have been identified across the Black Sea and the Mediterranean Sea (Natoli et al. 2005). Five populations were identified: Black Sea, eastern Mediterranean, western Mediterranean, eastern North Atlantic and Scottish. The Black Sea population showed the highest differentiation from other populations. Significant genetic differentiation was observed between populations from the eastern and the western Mediterranean. The boundary between the western Mediterranean and the eastern North Atlantic was the weakest observed, although the two populations still showed significant genetic differentiation. There is no basin-wide estimate of numbers and the most reliable information comes from a few local studies  (Bearzi et al. 2008). Relatively recent, broad-scale shipboard surveys (4,000–80,000 km²) showed that in some Mediterranean areas Bottlenose Dolphins are present both near shore and offshore, and densities can range between four and 20 animals per 100 km²(Ben Naceur et al. 2004, Forcada et al. 2004, Cañadas and Hammond 2006, Gómez de Segura et al. 2006, Bearzi et al. 2008c). Although the total population size in the Mediterranean remains uncertain, it unquestionably exceeds the threshold level for red listing as Vulnerable under the D criterion.

Indirect but convincing evidence of dolphin abundance in historical times can be found in early accounts describing interactions with fisheries and systematic attempts to exterminate dolphins (including Bottlenose Dolphins) in Mediterranean coastal waters (Bearzi et al. 2008).

The only Mediterranean area with quantitative historical information that can be used to infer population trends over time scales of more than a couple of decades is the northern Adriatic Sea. There, Bottlenose Dolphin numbers likely declined by at least 50% in the second half of the 20th century, largely as a consequence of deliberate killing initially, followed by habitat degradation and overfishing of prey species (Bearzi et al. 2004). For some other parts of the northern Mediterranean, e.g. Italy and southern France, the available information is less precise but suggests similar trends (Blanco and González 1992, Borrell et al. 2000). In an area off southern Spain where the species has been studied intensively, abundance estimates have shown variability but no trend since the early 1990s (Cañadas et al. 2006).

Habitat and Ecology:

Bottlenose Dolphins in the Mediterranean are often regarded as predominantly ‘coastal’ or ‘inshore’ animals but this designation may be misleading as they can be encountered in continental shelf and shallow plateaux waters at any distance from the coast (Bearzi et al. 2008). They inhabit a wide variety of habitats including continental shelf waters, lagoons and enclosed seas, and the waters surrounding islands and archipelagos (Bearzi et al. 2008). In the Alborán and Balearic Seas they occur across the entire shelf, along the shelf edge and in deep waters of the continental slope, and in productive waters 200–500 m deep (Cañadas et al. 2002, 2005, Forcada et al. 2004). In the Strait of Gibraltar, at or near the western limits of what is defined here as the Mediterranean region, Bottlenose Dolphins occur mainly in water 200–600 m deep, over steep slopes (de Stephanis et al.2008). In Greek waters they are found in coastal areas, straits, gulfs, semi-closed eutrophic waters, and steep coasts with no continental shelf (Frantzis et al. 2003, Bearzi et al. 2005, 2008).

The size of Bottlenose Dolphin groups varies according to biogeographic region, prey availability, activity and other factors. Most encounters have been with groups of fewer than ten individuals (Bearzi et al. 2008). Associations with other cetacean species are uncommon, although in some areas mixed aggregations with Short-beaked Common Dolphins (Delphinus delphis) and Long-finned Pilot Whales (Globicephala melas) have been observed (Bearzi et al. 2008).

In Mediterranean coastal waters Bottlenose Dolphins target primarily demersal prey during feeding sessions characterized by dives lasting 3–5 min and occasionally up to 8 min, depending on water depth (Bearzi et al. 2008). Reported prey items include demersal species such as European Hake (Merluccius merluccius), European Conger (Conger conger), Red Mullet (Mullus barbatus), Striped Red Mullet (Mullus surmuletus), Common Cuttlefish (Sepia officinalis), Common Octopus (Octopus vulgaris) and a variety of other bony fishes and molluscs (Bearzi et al. 2008). As most studies have relied on stomach contents from stranded animals, inferences may be subject to bias (Barros and Clarke 2002). In some Mediterranean areas Bottlenose Dolphins also feed on Clupeidae or other epipelagic prey (Bearzi et al. 2008).

In the Mediterranean Sea, predation is regarded as a minor cause of mortality. Bottlenose Dolphins, as well as other small Mediterranean delphinids, are preyed upon occasionally by sharks, principally Great White Sharks (Carcharodon carcharias) but also several other species (Fergusson 1994, Morey et al. 2003). The numbers of large sharks have declined drastically in Mediterranean waters over the past century (Ferretti et al. 2008) and this may have reduced predation pressure considerably.  Other potential dolphin predators, such as the Killer Whale (Orcinus orca) and the False Killer Whale (Pseudorca crassidens), are rare in the Mediterranean (Notarbartolo di Sciara 1987, Reeves and Notarbartolo di Sciara 2006).

Major Threat(s):

  • Fishery-related mortality

  • Prey depletion

  • Contamination by xenobiotics

  • Epizootic outbreaks

  • Climate change

Conservation Actions:

Several of the existing laws and treaties in force today (reviewed in Bearzi et al. 2008) could provide a potentially solid framework for the conservation of Bottlenose Dolphins and for the protection of their habitat in the Mediterranean region. Unfortunately, implementation and enforcement of those instruments have not been consistently effective. Actions taken to date have not been adequate to maintain a ‘favourable’ status of Bottlenose Dolphin populations (as advocated by the EU Habitats Directive) or to prevent further population decline. Tangible actions to protect Bottlenose Dolphins and other Mediterranean cetaceans have been surprisingly few, especially if one considers the large number of existing laws, regulations and agreements that have been in place for years and even decades (Bearzi et al. 2008).

About a hundred national Marine Protected Areas (MPAs) of different types, sizes and purposes have been established in Algeria, Croatia, Cyprus, France, Greece, Israel, Italy, Lebanon, Malta, Monaco, Morocco, Slovenia, Spain, Syria, Tunisia and Turkey, but specific measures for cetacean conservation are rarely included in their management plans. A notable exception is the 87,000 km² cetacean sanctuary created in 1999 by France, Italy, and the Monaco Principality in the Corso-Ligurian-Provençal Basin (the ‘Pelagos Sanctuary’; Notarbartolo di Sciara et al. 2008). In addition, three years of provisional protection (from July 26th, 2006) were granted to the waters east of the islands of Losinj and Cres (Croatia) following a proposal for the creation of a special zoological reserve for dolphins. However, that period has expired and so far no protection measures have been enforced. If appropriately managed, MPAs could contribute to Bottlenose Dolphin conservation by preserving their prey and habitat, reducing the risks of mortality in fishing gear, providing refuge from noise and other types of disturbance, raising awareness, stimulating research and facilitating exchange of information (Hoyt 2005). However, levels of enforcement are often low and many of the existing Mediterranean MPAs merely represent ‘paper parks’ (Bearzi 2007, Guidetti et al. 2008). Other types of action that can provide direct or indirect benefits to Bottlenose Dolphins include area-, season-, or fishery-specific reductions in fishing effort, changes to fishing gear or fishing practices to reduce incidental mortality, curtailment of inputs of toxic pollutants, and boating regulations.