Review Article |
Corresponding author: Mario F. Broggi ( mario.broggi@adon.li ) Academic editor: Yurii Kornilev
© 2023 Mario F. Broggi.
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:
Broggi MF (2023) Occurrence and tentative population status of the Balkan Terrapin (Mauremys rivulata, Valenciennes, 1833) on Greek islands. Herpetozoa 36: 233-247. https://doi.org/10.3897/herpetozoa.36.e100533
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The distribution of Mauremys rivulata on Aegean islands was summarized by Broggi in 2012. Here, the study area encompasses all Greek islands, including the Ionian Islands, and the two Turkish islands of Gökceada and Bozcaada. For the first time, I attempt to estimate the status and size of the populations on the islands. This is a subjective assessment based on my personal visits to most islands and not on IUCN criteria. Mauremys rivulata was found on 29 Greek islands, plus two Turkish islands in the Aegean Sea. Five previously mentioned sites are doubtful, and on the three islands of Sifnos, Syros and Ithaca the species appears to be extinct. On 12 islands I assess its status as “threatened with extinction”. On seven, mostly larger, islands its populations are probably less vulnerable. Efforts must be made for the long-term protection of M. rivulata on the Greek islands.
conservation, Reptilia, status, Testudines, threats
The first description of the Balkan Terrapin Mauremys rivulata was provided by Valenciennes, on Bory de Saint-Vincent’s scientific expedition (1833) to Morea (Peloponnese), under the name Emys rivulata (
The Balkan Terrapin is an impressive animal, reaching a carapace length of 25 cm, while the 4–10 hatchlings that leave the nest measure 3–4 cm. The species is distributed from the Croatian coast southwards in south-eastern Europe, including Greece, via Turkey to Israel and Syria in the Middle East. It is adapted to a warm Mediterranean climate. In the northern parts of its range it hibernates; while in southern climates it may aestivate over the summer. It occurs in running waters, seasonal ponds and pools, lakes, brackish lagoons, but also drainage systems, e.g. ditches, as well as reservoirs. Only fast-flowing streams are not colonised. The Balkan Terrapin is more tolerant of poor water quality than the European Pond Terrapin (Emys orbicularis) which co-occurs in part of the range of M. rivulata, and is thus also found in over-fertilised waters or, as mentioned, brackish water.
Due to its tolerance to salinity, the Balkan Terrapin may cross extensive distances at sea, as demonstrated by
Mauremys rivulata does not normally feed at water temperatures below 13 °C. It is a generalist and opportunist, feeding on plants as well as on small animals. It can occur in densities of 19–217 individuals, in eutrophic waters even up to 2000 individuals per hectare (
From the early 19th century on, the Greek herpetofauna has fascinated the international research community. The first herpetological “discoverer” was the Russian Jacques von Bedriaga, publishing his work “Die Amphibien und Reptilien Griechenlands” in German (Bedriaga 1883). After the turn of the century, with a peak in the 1930s, the Viennese Professor Franz Werner published 12 articles on the herpetofauna of the Greek islands. He was accompanied and followed by the Viennese Otto Wettstein with “Herpetologia aegaea” in 1953 and a supplement in 1957. This has been described as the “German wave” in herpetological research as far as the language of the written contributions was concerned. Since the early 1970s, the number of field herpetologists working on Greek islands has increased. They are referred to by
The Mediterranean region has been visited annually since 1972 by a group of nature lovers from the Botanical-Zoological Society Liechtenstein-Sargans-Werdenberg from the Alpine Rhine Valley (Table
. Dates of excursions to Greek and Turkish Islands. This list includes all the islands visited in the Aegean and Ionian Sea. No Balkan Terrapins were observed on the islands not mentioned in the article.
Samos 12–20.4.1975 | Tilos 8–11.10.2004, 15–23.4.2005 |
Lesbos 9–23.4.1978 | Nisyros 24–27.4.2005 |
Naxos 28.4–4.5.1984 | Amorgos 19–28.4.2006 |
Lefkas 19.5–24.5.1985 | Lipsi 10–20.4. 2007 |
Ikaria 17–30.4.1986 | Patmos 17.4.2007 |
Samothrace 25.4–6.5.1987 | Kos 9.4.2007 |
Rhodes 23.4.1988 | Ithaca 15.4–24.4.2008 |
Karpathos 24.4–6.5.1988 | Alonissos 13–25.4.2009 |
Kythira 30.4–4.5.1989 | Serifos 11–19.4.2010 |
Chios 23.4–3.5.1991 | Paros 20.4.2010 |
Kefalonia 15–23.4.1993 | Kea 9–19.4.2011 |
Andros 8.4–19.4.1995 | Crete 10–12.4.2012 |
Thassos 25–29.5.1996 | Gavdos 12–19.4.2012 |
Kalymnos 19–24.4.1997 | Kimolos 5–17.4.2013 |
Leros 25–28.4.1997 | Polyegos 15.4.2013 |
Kos 19–20.4.1997 | Elafonissos 6–14.4.2014 |
Gökçeada 27.4–7.5.1998 | Kythira 6–18.4.2015 |
Milos 18–24.4.1999, 18.4.2013 | Limnos 17–28.2016 |
Sifnos 25–30.4.1999 | Kefalonia 13–26.4.2017 |
Ikaria 24–4.5.2000 | Skopelos 9–15.6.2019 |
Astypalea 23–29.4.2001 | Skiathos 16.6.2019 |
Symi 23.4–1.5.2002 | Kythnos 28.5–8.6. 2021 |
Sesklia 28.4.2022 | Ios 8–17.4.2022 |
Skyros 19–30.4.2003 | Santorini 18–19.4. 2022 |
Fourni 14–24.4.2023 |
My tasks as excursion leader were island selection, finding literature and, for some time, logistical organisation, which I have since handed over to a colleague. Strikes, strong winds, and Covid-19 have presented logistical challenges. Procuring literature used to be much more difficult before the internet, as the writers came from many states and often used their respective native languages. There was an exchange of writings and experiences, and the number of field herpetologists working on Greek islands was manageable. During the past 20 years, the number of researchers has increased dramatically. Mostly young Greek university graduates have joined, and the language of publication is now predominantly English.
Maps of the islands to be visited were not commercially available in the early days. They were partly hand-drawn and very rudimentary. Today we have suitable GIS-based maps of most (e.g., Anavasi, Skai, Orana, Terrain Map). On them, it is easier to locate hydrological objects with appropriate signatures, such as the indication of springs, permanently flowing watercourses, swamps, lagoons, old water mills, cisterns and wells. Google Maps also provides an overview of hydrological catchment areas with its aerial photographs. The WWF-Greece’s Wetland Inventory of the Greek Archipelago is an important reference source (www.oikoskopio.gr/ygrotopio). In addition, the location data from the literature for the water-loving species of the herpetofauna were used. These are all transferred to the maps.
Once we arrived on an island, we first took a tour to familiarise ourselves with the topographical features. Then the objects marked on the map were systematically visited. The hydrologically productive units were verified in the field and searched if the terrain allowed. In the process, there were always opportunities to talk to local people, who usually wanted to know where we came from and what we were looking for. This was explained in basic terms. In addition, word typically got around on smaller islands about what aspect of the island’s natural history these “strangers” were particularly interested in. An island diary was kept, and the geographical information system was used to record the locations and the observations. Towards the end of the island stay, work was already being done on the manuscript for possible publication, so as to record impressions while they were still fresh.
Mauremys rivulata is still found on 29 Greek islands plus on two Turkish islands. Five sites are doubtful and on three islands the species appears to be extinct (Fig.
Distribution map of the Balkan Terrapin (Mauremys rivulata, Valenciennes, 1833) on Greek islands. Red dot – occurrence, cross – extinct. 1. Corfu; 2. Lefkada; 3. Kefalonia; 4. Ithaca †; 5. Zakynthos; 6. Thassos; 7. Samothrace; 8. Gökçeada (Imbros); 9. Limnos; 10. Bozcaada (Tenedos); 11. Skiathos; 12. Skopelos; 13. Lesbos; 14. Skyros; 15. Psara; 16. Chios; 17. Euböa (Evia); 18. Andros; 19. Tinos; 20. Kea; 21. Kythnos; 22. Mykonos; 23. Ikaria; 24. Samos; 25. Syros †; 26. Serifos; 27. Sifnos †; 28. Paros; 29. Naxos; 30. Kos; 31. Rhodes; 32. Crete; 33. Gavdos.
Andros (380 km2)
The first record is by Werner (1937).
According to our own experience (
Bozcaada (Tenedos) (37 km2)
The first record on this Turkish Aegean island comes from Tosunoglu et al. (2009) in a description of the island’s herpetofauna. However, only one location is given. Similarly,
Chios (843 km2)
Werner (1935) was the first to describe M. rivulata on Chios, followed by
Corfu (585 km2)
First recorded by
Crete (8 450 km2)
The first record after Bedriaga (1882) was by
Euboea (Evia) (3 684 km2)
First mentioned by
Gavdos (33 km2)
Gökçeada (Imbros) (279 km2)
First record by
Ikaria (255 km2)
First recorded by
Our second visit to the island in 2000 confirmed the wide distribution in the north-west at all altitudes. However, the large populations seem to have halved (
Kea (132 km2)
First record by
When we visited the island in 2011, the estuary at Pisses was completely occupied by tourist infrastructure and there was no longer any space for M. rivulata. However, the manager of our accommodation, the “Red Tractor” in Korissia, told us that there are still Balkan Terrapins in the Mylopotamos valley, which is difficult to access, and that they are periodically washed out to sea during heavy rainfall. During our stay on the island, we were able to find three more occurrences in water-rich valleys away from the estuary (
Kefalonia (787 km2)
First recorded by
Kos (287 km2)
First recorded by
Kythnos (99 km2)
First recorded by Bedriaga (1882). Werner (1935) saw M. rivulata at the lagoon near Lutra, as did
Lefkada (325 km2)
First record by De Betta according to Bedriaga (1882), and cited in
Lemnos (476 km2)
First found by
Lesbos (1 633 km2)
First recorded by Werner (1935).
On 5.7.2005, a peculiar behaviour of the Balkan Terrapin was observed on the beach of Skala Eressos in the southwest of the island (
Milos (151 km2)
First recorded by Bedriaga (1882). Schweizer (1935), the self-taught “Snake Hansi” from Allschwil (Canton Baselland) and acquaintance of my father, states: “[M. rivulata] is found in large numbers in the pond area of freshwater accumulations on Milos, furthermore I also saw them on the beach in rush-covered, salty marsh ponds”.
Mykonos (105 km2)
First recorded by Bedriaga (1882). The species is later mentioned several times as occurring on Mykonos, but seems to be cited only from older sources. Not so by
Naxos (389 km2)
First record by
Paros (193 km2)
Psara (44 km2)
Rhodes (1 401 km2)
First recorded by
Samos (477 km2)
First recorded by Werner (1935). The first natural history excursion to a Greek island took us to Samos in April 1975. I likely saw in the distance both species of terrapin at the archaeological site of the Temple of Hera, but I could not confirm this, as, at a time of political tension between Turkey and Greece, we were expelled by the local military and had some problems with our cameras and binoculars and we were forced to hand in slide films.
The island of Samos has been herpetologically studied several times, by Ioannidis et al. (1994),
The island has been visited by several nature photographers, such as
Samothrace (178 km2)
First found by Werner (1935).
Serifos (75 km2)
First recorded by Bedriaga (1882).
Skiathos (49 km2)
Skopelos (96 km2)
First recorded by
Skyros (209 km2)
First recorded by
Thassos (380 km2)
First reported by
Tinos (194 km2)
First recorded by Bedriaga (1882).
Zakynthos (406 km2)
First recorded by
Ithaca † (118 km2)
Sifnos † (74 km2)
Syros † (102 km2)
First recorded by Bedriaga in 1882.
Amorgos? (126 km2)
Chalki? (27 km2)
Kythera? (278 km2)
So far, M. rivulata has not been recorded here, although Pieper (1970) does not rule out its occurrence. I have been on the island twice, in 1989 and 2015, and think Kythera offers potential habitats for the species, especially in the north of the island and in the beach lagoon of Kakia Lagada. Stavros Emmanuel, a local biologist, said a friend of his had seen terrapins in the Karavas area in the north of the island. My search was in vain, but this is something to keep in mind.
Symi? (58 km2)
Dimaki (2002) mentions M. rivulata for Symi, without giving any further location. I could not confirm this on my visit to the island (
Tilos? (61 km2)
There are no historical records for Tilos. When I visited the island, an adult M. rivulata was seen in a water reservoir covered with rubber sheeting south of Megali Chori on 18.4.2005 and subsequent days. There used to be two wetlands on the island, which no longer exist. As a result, the green frog has become extinct. Is this observation a release or a relict? The present situation is not suitable for the species to persist (
My favourite observations on the Greek islands for the last three decades have been of terrapins in their habitats. These possible habitats are consistently searched on every island visited. With experience, it is possible to spot the shy animals in their sunny positions from afar. The distribution of the Balkan Terrapin (Mauremys rivulata) in the Aegean Sea was described in the journal Herpetozoa (
In the Aegean and Ionian Islands, M. rivulata has been recorded on 29 Greek and two Turkish islands. Five further occurrences are described as questionable, with two of them probably due to misinformation; one of them has potential but remains without confirmed evidence; one refers to a dead deposit; and one is probably due to a release. On Syros, Sifnos and probably Ithaca it can now be assumed that the Balkan Terrapin is extinct. Population sizes appear to be small on most Greek islands but can only be based on estimates. Only from Samos counts are available (Speybroeck et al. 2019). Of all the islands mentioned as having M. rivulata present, I have no personal experience of Bozcaada, Corfu, Mykonos, Psara, Syros and Zakynthos.
The Mid-Aegean Trench (MAT) from Crete to Thassos created a sea barrier in the Aegean Sea. Except for sea turtles, Mauremys rivulata is the only local reptile species for which the MAT is practically non-existent. Just being a Terrapin is not sufficient to overlook the sea as a barrier. The pattern of occurrence of Emys orbicularis is contrary and more similar to the other reptiles and amphibians (
Substantial threats to M. rivulata also exist in other regions of Greece, see
In sections where there is still a long period of water retention in the watercourse, and the water in scours is retained for longer, refugial populations of M. rivulata can settle best. I have noticed such stream colonisations away from the estuary in Thassos, Samothrace, Andros, Lemnos, Kythnos, Kea and Serifos. But even in these more favourable conditions, water is being extracted for agriculture, accelerating their drying out. In addition, most of the natural springs are exploited. The Balkan Terrapin can also resort to using anthropogenic water accumulations such as open cisterns and sites for livestock watering (Fig.
For M. rivulata, there are no sufficient temporal data of its distribution on Greek islands with population estimates. My assessment of the endangerment status therefore does not follow the IUCN criteria for Red Lists of threatened and rare species. These are my personal subjective assessments based on visits to the islands. However, I have been systematically searching Greek islands for Mauremys occurrences for the last 30 years. Some of my observations are older, however, and a lot may have happened at the individual sites in the meantime. The threat to the species on Greek islands is generally considered to be high. The current occurrences are highly isolated and exchange with other populations is becoming increasingly difficult. Habitat destruction, but also climate fluctuations, can accelerate extinction. On 12 islands, namely Skyros, Skopelos, Skiathos, Psara, Paros, Mykonos, Milos, Kythnos, Kefalonia, Zakynthos, Gavdos and Bozcaada, the status “threatened with extinction” is appropriate. The status of some other islands is not yet known well-enough to make an assessment. On the other hand, larger confirmed occurrences are found on Gökçeada, Crete, Ikaria, Lemnos, Lesvos, Samos and Tinos. On some of these islands, populations are also found in streams, where they are more protected from threats.
The EU lists M. rivulata in Annexes II and IV of the Habitats Directive. It is a species in need of strict protection. Under Greek law (Presidential Decree 67/1981) the Balkan Terrapin is a protected species. It is also listed in the Red List of Threatened Animals of Greece (
The causes of threats have been presented. It is no longer possible to determine how many wetlands were destroyed in the last century, but a large number of small biotopes were likely affected. Catsadorakis and Paragamian (2007) started in 2004 by compiling an inventory of wetlands for the Aegean islands, excluding Crete. They recorded 352 wetlands, including lagoons, on 51 islands, that covered about 40 km2. The inventory was subsequently extended to the entire Greek archipelago (
I thank my long-time companions Dr. Peter Goop, Vaduz, and Mag. Günter Stadler, Frastanz (Vorarlberg) for their assistance in herpetological research. Wilfried Kaufmann, Balzers Liechtenstein (1935–2016) and Dr. Christian Burri, Untervaz Graubünden/Switzerland (1948–2022) have, sadly, passed away. A big thank you also goes to the reviewers of this contribution.