Research Article |
Corresponding author: Bruno Schmidt ( bruno.schmidt@hhdhyla.hr ) Academic editor: Johannes Foufopoulos
© 2020 Bruno Schmidt, Daria Kranželić, Đurđica Majetić, Boris Lauš, Ana Štih, Toni Koren.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Schmidt B, Kranželić D, Majetić Đ, Lauš B, Štih A, Koren T (2020) Distribution and conservation status of the herpetofauna of Dugi Otok Island, Croatia. Herpetozoa 33: 191-205. https://doi.org/10.3897/herpetozoa.33.e53525
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The first overview of the amphibians and reptiles of Dugi Otok Island, Northern Dalmatia, is presented, based on the published data and new records collected during the last twenty years. A total of 15 species are present on the island, of which only one was not recorded on our surveys. In comparison to other islands of Northern Dalmatia, Dugi Otok is the second most diverse island in terms of herpetofauna, just after Pag Island. The main threats to the amphibians and reptiles on the island are the disappearance and degradation of aquatic habitats, the abandonment and succession of traditional agricultural fields and olive groves and the increasing presence of several invasive species.
Adriatic Islands, Amphibia, conservation, field survey, protection, Reptilia
Amongst the numerous islands on the Croatian coast, Dugi Otok has always been interesting for its reptiles and amphibians. The herpetofaunal literature of the island includes questionable and invasive species records and has never been reviewed holistically. Our goal is to provide the first comprehensive report of the state of the island’s reptiles and amphibians. Given the growing anthropogenic pressures, it is important to provide a baseline of the current knowledge for the sake of future management and conservation.
Dugi Otok is an island located in the eastern part of the Adriatic Sea, in Croatia. It is located in northern Dalmatia and it belongs to the Zadar archipelago, along with Pag, Pašman, Ugljan, Vir and various other smaller islands and islets. With an area of 113.31 km2, Dugi Otok is the seventh largest island in the Adriatic Sea (
Most of the islands in the Adriatic Sea, including Dugi Otok, are quite young in origin and were isolated by rising sea levels due to the melting of the polar ice caps. Dugi Otok was separated approximately 10,000 years ago from the Dalmatian mainland (
A significant part of the landscape on Dugi Otok Island are karst fields or “polja”, flat areas traditionally used for crop cultivation or pastures. Due to their agricultural use, many of them encompass natural or artificial aquatic habitats, such as ponds or wells. On Dugi Otok Island, according to topographic maps and satellite imagery, about 50 such ponds and wells are known (Fig.
According to the Köppen climate classification, Dugi Otok has a Mediterranean climate with hot summers (Csa) (
A. A pond situated near Lojišće Bay on Dugi Otok, a typical aquatic habitat on the Adriatic Islands. (Photo by Ana Štih); B. Grassland habitats in the south of Dugi Otok (Photo by Ana Štih); C. Olive groves in the northern part of the Island, a suitable habitat for many reptile species. (Photo by Daria Kranželić).
Dugi Otok harbours several protected areas, the largest being Telašćica Nature Park, located in the southern part of the island. It was established in 1988 because of its rich flora and fauna, geomorphological features, important seabed communities and archaeological remains (
The first records of amphibians and reptiles on Dugi Otok were provided by
The aim of this research is to review the distribution and status of the herpetofauna of Dugi Otok Island, based on published literature data and new observations. Threats to the long-term conservation of threatened species are also discussed.
To obtain a more complete overview of the herpetofauna of the island, all available literature was consulted. Additionally, extensive field data about reptiles and amphibians of Dugi Otok were collected over the last 20 years by the authors. A total of 30 sites were explored, some of them only once, while the most promising were visited several times. Details about the surveyed localities are included in Suppl. material
List of visited localities:
In order to put our data into perspective, a comparison with the amphibians and reptiles of other north Dalmatian Islands was carried out (Table
According to the literature overview, 19 species, four amphibians and 15 reptiles, have been reported at one point or another for Dugi Otok Island (Table
Distribution of amphibians and reptiles on Dugi Otok. The numbering of the localities where a species was detected in this survey follows the list given in the Methods section (see also Fig.
Systematic species list | Localities detected in this survey | Literature records | Red Book status *** | Conservation status | |
---|---|---|---|---|---|
Amphibians | |||||
* | Bufo bufo (Linnaeus, 1758) | – |
|
LC | |
1. | Bufotes viridis (Laurenti, 1768) | 2, 8b, 9, 11, 13, 14, 20, 21, 22, 25, 26, 27, 28, 30 |
|
LC | Strictly protected |
2. | Hyla arborea (Linnaeus, 1758) | 2, 6, 8b, 18, 21, 22, 25, 28, 30 |
|
LC | Strictly protected |
* | Pelophylax ridibundus (Pallas, 1771) | – |
|
LC | |
Reptiles | |||||
3. | Testudo hermanni Gmelin, 1789 | 9, 27 |
|
NT | Strictly protected |
4. | Trachemys scripta Thunberg in Schoepff, 1792 ** | 21, 27 |
|
/ | |
5. | Caretta caretta (Linnaeus, 1758) | 1 |
|
VU | Strictly protected |
6. | Hemidactylus turcicus (Linnaeus, 1758) | 2, 11, 16, 22, 26 |
|
LC | |
7. | Podarcis melisellensis (Braun, 1877) | 2, 3, 4, 5, 6, 7, 8a, 10, 11, 13, 14, 15, 18, 20, 22, 27, 28, 29 |
|
LC | Strictly protected |
8. | Podarcis siculus (Rafinesque-Schmaltz, 1810) | 18, 25, 26, 27, 28 |
|
LC | |
9. | Pseudopus apodus (Pallas, 1775) | 2, 4, 5, 6, 7, 8a, 11, 13, 14, 16, 18, 19, 20, 21, 27, 28, 29 |
|
LC | Strictly protected |
* | Xerotyphlops vermicularis (Merrem, 1820) | – |
|
NA | |
10. | Elaphe quatuorlineata (Lacepede, 1789) | 6, 8a, 12, 13, 14, 18, 19 |
|
NT | Strictly protected |
11. | Hierophis gemonensis (Laurenti, 1768) | 2, 3, 4, 5, 6, 7, 8a, 16, 21, 27, 28 |
|
LC | Strictly protected |
12. | Malpolon insignitus (Geoffroy de St-Hilaire, 1809) | 6, 8a, 14, 16, 17, 19, 22, 23, 24, 27, 28, 29 |
|
LC | |
13. | Natrix natrix (Linnaeus, 1758) | 20 |
|
LC | |
14. | Telescopus fallax (Fleischmann, 1831) | – |
|
NT | Strictly protected |
15. | Zamenis situla (Linnaeus, 1758) | 3, 18, 27 |
|
NT | Strictly protected |
* | Vipera ammodytes (Linnaeus, 1758) | – |
|
LC | Strictly protected |
Records (sources below) of reptiles and amphibians found on other north Dalmatian Islands. Asterisks (*) indicate questionable records not included in the official island species list.
Dugi Otok | Kornati | Žut | Murter | Pag | Pašman | Prvić | Ugljan | Vir | Žirje | Iž | Olib | |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Surface area (km2): | 113 | 32 | 15 | 18 | 284 | 60 | 2.4 | 51 | 22 | 15 | 17 | 26 |
Amphibians | ||||||||||||
Bufo bufo (Linnaeus, 1758) | * | |||||||||||
Bufotes viridis (Laurenti, 1768) | x | x | x | x | ||||||||
Hyla arborea (Linnaeus, 1758) | x | x | ||||||||||
Pelophylax ridibundus (Pallas, 1771) | * | x | ||||||||||
Reptiles | ||||||||||||
Testudo hermanni Gmelin, 1789 | x | x | x | x | x | |||||||
Emys orbicularis (Linnaeus, 1758) | x | x | ||||||||||
Trachemys scripta Thunberg in Schoepff, 1792 | x | x | ||||||||||
Caretta caretta (Linnaeus, 1758) | x | x | x | |||||||||
Hemidactylus turcicus (Linnaeus, 1758) | x | x | x | x | x | x | x | |||||
Tarentola mauritanica (Linnaeus, 1758) | x | |||||||||||
Lacerta trilineata Bedriaga, 1886 | x | |||||||||||
Podarcis melisellensis (Braun, 1877) | x | x | x | x | x | x | x | x | x | |||
Podarcis siculus (Rafinesque-Schmaltz, 1810) | x | x | x | x | x | x | x | x | ||||
Pseudopus apodus (Pallas, 1775) | x | x | x | x | ||||||||
Xerotyphlops vermicularis (Merrem, 1820) | * | |||||||||||
Dolichophis caspius (Gmelin, 1789) | x | |||||||||||
Elaphe quatuorlineata (Lacepede, 1789) | x | x | x | |||||||||
Hierophis gemonensis (Laurenti, 1768) | x | x | x | x | x | x | ||||||
Malpolon insignitus (Geoffroy de St-Hilaire, 1809) | x | x | x | x | x | x | ||||||
Natrix natrix (Linnaeus, 1758) | x | x | ||||||||||
Platyceps najadum (Eichwald, 1831) | x | |||||||||||
Telescopus fallax (Fleischmann, 1831) | x | x | x | x | x | |||||||
Zamenis longissimus (Laurenti, 1768) | x | |||||||||||
Zamenis situla (Linnaeus, 1758) | x | x | x | x | x | |||||||
Vipera ammodytes (Linnaeus, 1758) | * | x | x | |||||||||
Total number | 19 | 7 | 7 | 2 | 19 | 2 | 3 | 9 | 2 | 10 | 3 | 2 |
Out of all species reported for Dugi Otok, five have been assessed and are listed in the Red Book of Amphibians and Reptiles of Croatia: C. caretta as Vulnerable (VU) and T. hermanii, E. quatorlineata, T. fallax and Z. situla as Near Threatened (NT) (
Species records are based on following references: Kornat:
Bufo bufo (Linnaeus, 1758) – Common Toad
Only one literature record is available for B. bufo from Dugi Otok (
Bufotes viridis (Laurenti, 1768) – European Green Toad
The first record of B. viridis on Dugi Otok was given by
Hyla arborea (Linnaeus, 1758) – European Tree Frog
The occurrence of the H. arborea on the island has been reported by many researchers (
Pelophylax ridibundus (Pallas, 1771) – Marsh Frog
Pelophylax ridibundus was mentioned only once for Dugi Otok (as Rana ridibunda) by
Testudo hermanni Gmelin, 1789 – Hermann’s Tortoise
The only literature record of this species on Dugi Otok was given by
A. Hermann’s Tortoise (Testudo hermanni Gmelin, 1789) found on Dugi Otok in Božava. The individuals were kept as pets in a garden (Photo by: Daria Kranželić); B. A Four-lined snake, Elaphe quatuorlineata (Lacepede, 1789), found on Dugi Otok near the Sakarun cove (Photo by Toni Koren); C. A Leopard Snake, Zamenis situla (Linnaeus, 1758), found on Dugi Otok near Komorine (Photo by: Bruno Schmidt).
Trachemys scripta (Thunberg in Schoepff, 1792) – Pond Slider
The Pond Slider is a non-native invasive species in Croatia.
This terrapin species is native to North America and is considered to be one of the 100 most invasive species in the world (
Caretta caretta (Linnaeus, 1758) – Loggerhead Sea Turtle
The first observation of this species was made in 1990 in the waters surrounding Dugi Otok (
Hemidactylus turcicus (Linnaeus, 1758) – Turkish Gecko
This is a common and widespread species on the island (
Podarcis melisellensis (Braun, 1877) – Dalmatian Wall Lizard
The species was first recorded by
Podarcis siculus (Rafinesque-Schmaltz, 1810) – Italian Wall Lizard
This species was reported on Dugi Otok only recently in the southern part of the island (
Pseudopus apodus (Pallas, 1775) – European Glass Lizard
Pseudopus apodus was reported early on to be common in karst fields and maquis on Dugi Otok (
Xerotyphlops vermicularis (Merrem, 1820) – European Worm Snake
Elaphe quatuorlineata (Lacepede, 1789) – Four-Lined Snake
The first record of the E. quatuorlineata on Dugi Otok was made by
Hierophis gemonensis (Laurenti, 1768) – Balkan Whip Snake
The first record of H. gemonensis on Dugi Otok was made by
Malpolon insignitus (Geoffroy de St-Hilaire, 1809) – Eastern Montpellier Snake
Natrix natrix (Linnaeus, 1758) – Grass Snake
Several records of this species exist for the island (
Telescopus fallax (Fleischmann, 1831) – European Cat Snake
This is one of the rarest snake species on the island and has been mentioned only twice in literature. The first record was made by
Zamenis situla (Linnaeus, 1758) – Leopard Snake
This is another elusive species, mostly active at sunset and sunrise (
Vipera ammodytes (Linnaeus, 1758) – Nose-Horned Viper
The Nose-Horned Viper has been mentioned only once for Dugi Otok by
The Adriatic islands, in general, do not represent optimal habitats for amphibians, due to their karstic origins and limited number of freshwater habitats. Accordingly, the low number of amphibian species on Dugi Otok is not surprising and reflects patterns that have been observed on other islands in Croatia (
Compared to amphibians, reptile diversity is much greater on the Adriatic Islands, because reptiles prefer higher temperatures and are less limited to humid environments (
The main threat to amphibians and reptiles in the Mediterranean area, as well as on Dugi Otok, is the loss, fragmentation and degradation of habitats as a direct or indirect result of human activities (
The abandonment of former agricultural fields, vineyards and olive groves represents perhaps the main threat to the reptiles on the islands, as it can result in the fragmentation of suitable habitats, through the loss of basking spots and hiding places. Therefore, agricultural abandonment can impact reptile populations by limiting the amount of habitat available for reproduction and survival (
As is the case with other Adriatic Islands, feral domestic cats (Felis catus, Linnaeus, 1758) also represent an important threat to the herpetofauna of the island. A large number of domestic cats, often abandoned, can be seen in and around settlements, roaming free. Feral and abandoned cats were already recorded on Dugi Otok in
The impacts of an invasive mammalian predator are best seen in the case of the Small Indian Mongoose, Herpestes auropunctatus (Hodgson, 1836), which is present on several Adriatic Islands, like Korčula, Hvar, Čiovo and Škarda (
Although the amphibians and reptiles of Dugi Otok Island were first surveyed over 90 years ago, no critical review of their diversity has been completed to date. In total, 15 species are known to occur on the island. Four species, B. bufo, P. ridibundus, X. vermicularis and V. ammodytes, erroneously reported in the past, are currently considered to not be present. In comparison with other north Dalmatian Islands, Dugi Otok has a diverse herpetofauna, being second only to the twice larger Pag Island. Given the limited availability of freshwater habitats on Dugi Otok, the most threatened species are those connected to such habitats, like H. arborea and B. viridis. Reptile species can also be affected by this, for example, N. natrix, for which only a single recent observation exists on the island. In some parts of the island, vegetation succession constitutes a serious threat, as the number of open rocky or grassland habitats is very limited and heliothermic species like Z. situla or E. quatuorlineata are rare on the island.
Another threat to the herpetofauna of the island is the increasing presence of invasive species (e.g. domestic cats F. catus, Mosquito fish G. holbrooki and Pond Sliders T. scripta). In order to preserve the island’s fauna, a plan to regulate the number of alien invasive species should be established and implemented. On the island, four species from Annex II of the Habitats Directive have been recorded (Z. situla, C. caretta, T. hermanni and E. quatuorlineata); for these, monitoring protocols should be developed and implemented in order to track their population trends on the island. Our survey can be used as a baseline study on the diversity and distribution of amphibians and reptiles of Dugi Otok Island and as a starting point for future ecological studies and conservation actions.
We are grateful to the Public Institution of Nature Park Telašćica for partially financing a part of this research. Part of the data was also gathered through the EU Natura 2000 Integration Project – NIP (permit no. UP/I-612-07/14-48//64). We would also like to thank the Biology Students Association – BIUS and the Insula Tilagus project for financing a part of this research. Lastly, we would also like to thank the contributors for the records: Dean Karaica, Duje Lisičić, Helena Justić, Ivona Burić, Iva Čupić, Ivan Knezović, Ines Maksimović, Ivana Sučić, Jerko Bubica, Lucija Abramović, Miroslav Kaleb, Marija Kuljerić, Mateja Ilinić, Nino Mihoković, Paula Prpić, Petar Rabi, Renato Katić, Stefan Majnarić and Željka Koričan Igrc.
List of visited localities
Data type: localities data
Explanation note: The list of sites includes the toponym, a brief description of the habitat, altitude (in m above sea level), geographic coordinates, field visit dates, and observers’ initials. The localities are arranged geographically from northwest to southeast of the island.