The IUCN Red List of Threatened Species™ ISSN 2307-8235 (online) IUCN 2020: T156206333A170381113 Scope(s): Global Language: English Delphinus delphis Gulf of Corinth subpopulation, Common Dolphin Assessment by: Bearzi, G., Bonizzoni, S. & Santostasi, N. View on www.iucnredlist.org Citation: Bearzi, G., Bonizzoni, S. & Santostasi, N. 2020. Delphinus delphis(Gulf of Corinth subpopulation). The IUCN Red List of Threatened Species 2020: e.T156206333A170381113. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T156206333A170381113.en Copyright: © 2020 International Union for Conservation of Nature and Natural Resources Reproduction of this publication for educational or other non-commercial purposes is authorized without prior written permission from the copyright holder provided the source is fully acknowledged. Reproduction of this publication for resale, reposting or other commercial purposes is prohibited without prior written permission from the copyright holder. 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THE IUCN RED LIST OF THREATENED SPECIES™ Taxonomy Kingdom Phylum Class Order Family Animalia Chordata Mammalia Cetartiodactyla Delphinidae Scientific Name: Delphinus delphis Gulf of Corinth subpopulation Linnaeus, 1758 Parent Species: See Delphinus delphis Common Name(s): • English: Common Dolphin • French: Dauphin commun • Spanish; Castilian: Delfin Comun • Albanian: Delfin i zakonshem عئاشلا نيفلدلا ,Arabic: Al-dolpheen Al-sha'eh • • Greek, Modern Kino delfini, Κοινό δελφίνι (1453-): יוצמ ןיפלוד ,Hebrew: Dolphin matzuy • • Italian: Delfino comune • Slovenian: Navadni delfin • Turkish: Tırtak Taxonomic Notes: This is a subpopulation of the Common Dolphin, Delphinus delphis Linnaeus, 1758. See also the global assessment for this species (Hammond et al. 2008) and the assessment of the Mediterranean Sea subpopulation (Bearzi 2003). Assessment Information Red List Category & Criteria: Critically Endangered D ver 3.1 Year Published: 2020 Date Assessed: June 16, 2019 Justification: Fewer than 50 mature individuals exist within this subpopulation. The Common Dolphin Gulf of Corinth subpopulation was estimated to contain an average of 22 (95% CI 16–32) individuals (Santostasi et al. 2016). Even assuming an upper CI limit and 100% being mature individuals (i.e. complete absence of immatures), the abundance of mature individuals would be well below the threshold for classifying this subpopulation as Critically Endangered under criterion D (number mature < 50). As the Common Dolphin Gulf of Corinth subpopulation is isolated from conspecifics (Bearzi et al. 2016), the assessment must be based on unaltered IUCN Red List criteria (Gärdenfors et al. 2001). When assessing subpopulations, the occurrence and status of conspecific units that may affect the risk of extinction within the region should be considered (Taylor 2005). Common Dolphin are not known to occur in the adjacent Gulf of Patras. The closest area with quantitative information on abundance and trends is the Inner Ionian Sea archipelago, where Common Dolphins have declined dramatically (Bearzi et al. 2008, 2006; Piroddi et al. 2011). Therefore, based on the available information, it cannot be assumed that © The IUCN Red List of Threatened Species: Delphinus delphis Gulf of Corinth subpopulation – published in 2020. 1 https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T156206333A170381113.en Common Dolphins surviving in the eastern Ionian Sea may represent a ‘source’ population capable of having a ‘rescue effect’ on the Gulf of Corinth Common Dolphin subpopulation. Sharp declines also have been documented for the Adriatic Sea, with almost complete eradication of a species that was historically abundant (Bearzi et al. 2004). Geographic Range Range Description: The Gulf of Corinth Common Dolphin subpopulation is confined to the central portion of the Gulf of Corinth, Greece, with no evidence of individuals ever crossing the narrow Strait of Rion which connects the Gulf of Corinth to open Mediterranean Sea waters (Frantzis et al. 2003, Bearzi et al. 2016), including across seven years (2011–2017) of intensive survey effort and tracking of dolphin movements (Bonizzoni et al. 2019; also see Figure 1 in the Supplementary Information). Species distribution models based on seven years of intensive surveys (2011–2017; Bonizzoni et al. 2019) predicted a preferred habitat situated in the central/southern sector of the Gulf of Corinth, with hotspots of Common Dolphin distribution encompassing 512 km². The area of occupancy varied between 234 and 311 km² in years 2011–2015, while the total area of occupancy was 708 km2. The extent of occurrence varied between 448 and 651 km² in years 2011–2015. The total extent of occurrence was 1,014 km² (Santostasi et al. 2018). For further information about this species, see Supplementary Material. Country Occurrence: Native, Extant (resident): Greece FAO Marine Fishing Areas: Native: Mediterranean and Black Sea © The IUCN Red List of Threatened Species: Delphinus delphis Gulf of Corinth subpopulation – published in 2020. 2 https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T156206333A170381113.en Population The Gulf of Corinth subpopulation was estimated as 22 Common Dolphins (95% CI 16–32) based on photographic capture-recapture covering the entire known range, conducted between 2011 and 2015 (Santostasi et al. 2016). The Gulf also hosts animals of intermediate Striped x Common Dolphin pigmentation (55 individuals, 95% CI 36–84; Santostasi et al. 2016), recently confirmed to be individuals with mixed ancestry (hereafter 'admixed'; Antoniou et al. 2018). Common Dolphins occur in this gulf only in mixed-species groups with Striped Dolphins (Bonizzoni et al. 2019). Living exclusively within mixed-species groups with the 60-fold more abundant Striped Dolphins likely developed as an adaptation to low Common Dolphin numbers (Frantzis and Herzing 2002). While mixed-species groups may bring advantages to either species, Striped and Common Dolphins are closely related and inter-mating is known to occur in the Gulf of Corinth (Antoniou et al. 2018). The resulting hybridisation and introgression are significant threats for rare species coexisting with more abundant species (Allendorf et al. 2001, Levin 2002). Hybridisation may lead to the local eradication of a population due to genetic swamping (where ‘pure’ species are progressively replaced by hybrids), or demographic swamping (where population growth rates are reduced due to the expression of deleterious alleles and the production of maladaptive hybrids). In the Gulf of Corinth, the production of hybrid offspring (Antoniou et al. 2018) can negatively affect the status of Common Dolphins (Santostasi et al. 2018). There is a clear population boundary between Common Dolphins occurring in the western and the eastern Mediterranean Sea, with additional differentiation in the Ionian Sea (Moura et al. 2013, Natoli et al. 2008). Geographic isolation of Common Dolphins in the Gulf of Corinth has been proposed based on absence of records in the western quarter of the Gulf and in the adjacent Gulf of Patras (Bearzi et al. 2011, Frantzis 2009, Frantzis et al. 2003), as well as consistent absence west of 22°08'30''E across seven years of intensive monitoring (Bearzi et al. 2016, Bonizzoni et al. 2019). Geographic isolation may have led to genetic differentiation, but information is scant. Genetic evidence from three Common Dolphins and 25 Striped Dolphins sampled in the Gulf of Corinth suggested significant differentiation for both species from individuals in the adjacent Ionian Sea and other Mediterranean areas (Gkafas 2011, Gkafas et al. 2007, Moura 2010, Moura et al. 2013). Extinction probabilities were estimated by Santostasi et al. (2018). Based on a quasi-extinction threshold of two mature individuals and a constant growth rate, the subpopulation qualifies as Endangered based on criterion E. The introduction of environmental variability greatly increased the quasi-extinction probability, which becomes ≥0.5 and qualifies the Common Dolphin subpopulation as Critically Endangered based on criterion E. Regarding the expected abundance of mature individuals after three generations, for all the scenarios more than 90% of the projected abundance would fall in the interval 0–50 mature individuals, indicating that, even if the subpopulation does not go extinct, it will remain below the abundance threshold that qualifies it as Critically Endangered. The inclusion of temporal stochasticity led to a ≥ 50% probability of quasi-extinction in all scenarios. The effect of demographic stochasticity is likely present in the study subpopulation, given its small size. Therefore, the subpopulation may be also listed as Critically Endangered under criterion E. Current Population Trend: Unknown © The IUCN Red List of Threatened Species: Delphinus delphis Gulf of Corinth subpopulation – published in 2020. 3 https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T156206333A170381113.en