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Figure 1. Schematic map of the Netherlands with locations of sea turtle strandings and sightings (1707-2013).

In 1972 Brongersma compiled all marine turtle records for the European North Atlantic Ocean. Although most cases were well documented, Brongersma reconstructed some. Historically, most marine turtle sightings and strandings have occurred along the coasts of France, Great Britain and Ireland (Gasc et al. 1997). Occasionally, however, sea turtles are observed in Dutch waters or found stranded on Dutch beaches. The Netherlands is located on the North Sea between Belgium and Germany, and borders the United Kingdom at sea. Twenty-one records of four species were reported for the Netherlands between 1707 and 1971. Due to their infrequent appearance, sea turtles did not receive much attention from Dutch herpetologists. However, the latest published atlas on the distribution of amphibians and reptiles in the Netherlands included a chapter on sea turtles (Hoogmoed 2009). In this publication 25 new records from 1972 to 2008 were described and discussed. Subsequently, an additional four records were added to the national database on sea turtles. This article presents an overview of all known sea turtle records in the Netherlands, which are also listed in Table 1 and shown in Fig. 1.

Table 1. All sightings and strandings of marine turtles in the Netherlands. Cond=Condition of turtle at time of observation. Ref=References: 1=Brongersma 1972; 2=Hoogmoed 2009; 3=Goverse et al. 2009a; 4=Goverse et al. 2009b; 5=Goverse et al. 2010; 6=Goverse et al. 2012.

Chelonia mydas. In 1889, three green turtles were found stranded in the province of Zeeland. Even though one was found alive, it later succumbed to its injuries. These turtles originated from an American ship transporting animals to the Antwerp Zoo in Belgium, and dead or weak turtles were thrown overboard into the river Scheldt (Brongersma 1972). Four more green turtles were found in 1934 and one in 1937. Four of these had inscriptions in the carapace, which suggested they were caught for the commercial turtle meat, leather, and soup industry in Europe (Brongersma 1972). Two plastron parts were found; one in a fishing net at Brown Ridge, North Sea (1968); the other on a beach on the island of Ameland, Friesland (1998; Brongersma 1972). Hoogmoed (2009) suggested that these were the remains of adult green sea turtles thrown overboard in the 1930s during transport to Hamburg. In 1952 a small living green turtle with a curved carapace length (CCL) of 36 cm washed ashore near Petten, Noord-Holland (Brongersma 1972). At that time the European commercial turtle industry was already closed.

Caretta caretta. The oldest record of a sea turtle in the Netherlands dates from 02 October 1707. Based on a drawing of this specimen, Brongersma (1961) concluded that it was a loggerhead turtle. The turtle was displayed in a pub in Amsterdam until it died a few days later. Other stranded loggerheads were recorded in 1894, 1927, 1954 and 1959 (Brongersma 1972). Three loggerhead turtle strandings have been recorded more recently. On 05 August 1998, a loggerhead was found at Vlissingen, Zeeland. This turtle was in a late stage of decomposition, and the head was missing (Hoogmoed 2009). On 02 March 2007, a small, dead loggerhead turtle (CCL 25 cm) washed ashore on a beach on the island of Vlieland, Friesland (Hoogmoed 2009). On 23 October 23 2008, a loggerhead turtle was found stranded at Groote Keeten, Noord-Holland (Goverse et al. 2009a). It was brought to the Seal Rescue Point at Callantsoog. This turtle was immediately sent to the seal and bird rescue center Ecomare, Texel. The turtle was in poor condition, with a relatively fresh wound at the base of the missing right front flipper. In addition, large amounts of gooseneck barnacles were also removed from the hind flippers. Because the rescue center did not have any experience with sea turtles, the turtle was transported on the following day to Burgers' Zoo at Arnhem. The turtle had a CCL of 52 cm with a weight of 15 kg. At the zoo, it was found that both eyes were infected and the turtle floated on the surface at an angle that suggested pneumonia. The turtle was kept in a 3 meters diameter, 50 cm deep basin. Over the next two weeks the water temperature was slowly increased to 25°C. Antibiotics were administered, and after 20 days the turtle could stay at the bottom of the tank. The turtle began to eat after eight days and fed on herring (Clupea harengus), squid, anchovy (Engraulis encrasicolus), whiting (Merlangius merlangus) and moon jellyfish (Aurelia aurita), along with supplemental multivitamins. The turtle weighed 19 kg after 4 weeks. Releasing it back into the North Sea was not an option due to the temperature of the water. Rehabilitated turtles from the United Kingdom are sent to Gran Canaria, Canary Islands, Spain (Penrose & Gander 2010). In the case of this turtle, it was decided to release the loggerhead from the coast of Portugal (Goverse et al. 2009a). On 22 July 2009, the turtle was sent to Zoomarine Albufeira, Algarve, Portugal, where it was tagged and released successfully 15 miles from the coast on 07 August 2009.

Lepidochelys kempii. Brongersma (1972) described the two records of Kemp’s ridleys, occurring in 1954 and 1970. A third stranding was recorded on 13 January 2007 near IJmuiden, Noord- Holland. This small turtle (CCL 23.6 cm) was found alive but died soon afterwards. On 21 November 2008, another small, living Kemp’s ridley (CCL 25.0 cm) was found near Westenschouwen, Zeeland (Epperly et al. 2013; Goverse et al. 2009b). It was partly buried in the sand, and the carapace was covered with oil. The turtle was in poor condition and was immediately brought to the Rotterdam Zoo for rehabilitation. At intake, the turtle weighed 2.24 kg, looked very weak, and swam out of balance, suggesting pneumonia. The water temperature was slowly increased from 14°C on the date of arrival to 22°C on 30 November. On 12 December, the turtle started to eat European sprat (Sprattus sprattus), and its weight increased to 2.49 kg. This Kemp’s ridley joined the loggerhead transport of 22 July 2009, to Zoomarine Albufeira, Algarve, Portugal, for rehabilitation. Up until that point the staff of the Rotterdam Zoo had assumed it was a young loggerhead turtle. In Portugal, however, the turtle was identified as a Kemp’s ridley, which caused the release plan to be modified. Kemp’s ridley turtle nesting sites are restricted to a number of beaches along the Gulf of Mexico, and most post-hatchlings and immature turtles remain within the Gulf of Mexico. However, some hatchlings and immature turtles journey across the Atlantic Ocean (Plotkin 2007). To date, it is unknown if Kemp’s ridley turtles can return successfully from Europe back to the Gulf of Mexico on their own. In three cases stranded Kemp’s ridleys from Europe were transported overseas to the U.S.A. to be released; one from France (Pritchard 1996), and two from the United Kingdom (pers. com. R. Penrose 2009; Penrose & Gander 2010). Zoomarine Albufeira also decided to transport the Kemp’s ridley to the U.S.A. However, the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 delayed the release by a year. Finally, on 29 November 2011, the Kemp's turtle arrived at Mote Marine Lab in Florida, U.S.A. After a short quarantine period it was released on 27 December 2011 at Lido Beach, Florida. Prior to its release, the turtle’s CCL measured 54.5 cm with a mass of 31 kg (Epperly et al. 2013).

On 10 December 2011 another Kemp’s ridley was found (Goverse et al. 2012). This turtle was found stranded alive near the village of Monster, Zuid-Holland. With the help of the animal rescue team, the turtle was immediately brought to SEA LIFE Scheveningen in Zuid-Holland. This turtle had a CCL of 30 cm and weighed 1.85 kg. The turtle was placed in a 24°C tank, and medical care, such as iodine for small carapacial wounds, and antibiotics were given. After a month the turtle began eating. Again, the decision was made to return this Kemp’s ridley to the U.S.A. for release in the Gulf of Mexico. On 01 November 2012, the turtle was transported to Houston, Texas, and further transported to the Animal Rehabilitation Keep (ARK) in Port Aransas, Texas. After acclimatisation the turtle was successfully released in the Gulf of Mexico on 09 November 2012. Both rehabilitated Kemps’ ridleys were equipped with satellite transmitters; their tracks could be viewed via <https://seaturtle.org>.

Dermochelys coriacea. Prior to 1971, only three records of leatherback turtles in the Netherlands are known in the scientific literature (Brongersma 1972). The oldest record dates from 1777. The other two records are from 1961 and 1968 (one sighting and one stranding, respectively). The substantial increase of observations after Brongersma (1972) is striking. For the period between 1972 and 2005, Hoogmoed (2009) documented nineteen new records. This includes seven dead turtles, seven sightings and five live turtles. Of the latter group, four were caught but died soon after and ended up in the collection of zoological museums.

In 2009, another three leatherbacks were recorded (Goverse et al. 2010). The first one was found stranded on 20 September 2009, on a beach near Huisduinen, Noord-Holland. The carcass exhibited injuries consistent with a boat propeller but whether this caused the turtle’s death is unknown. A week later a sighting was reported near the shore of the island of Texel. This turtle was observed several times in the same area between 27 September and 18 October 2009. On 07 October 2009, a dead leatherback was taken out of the sea 23 nautical miles northwest of Goeree-Overflakkee, Zuid- Holland. The carcass was handed over to Naturalis Biodiversity Center.

Cheloniidae. One unidentified hard-shelled sea turtle was documented by Brongersma (1972). This sea turtle was found alive in 1971 near Valkenisse, Zeeland. The turtle was put in fresh water but died a few days later and was buried to get rid of the smell.

Fig. 2 shows all natural strandings and sightings in the Netherlands by decadal increments (n=40). Although there is a recorded increase in observations, the numbers are too small to draw any conclusions. Witt et al. (2007) reported an increasing trend for the number of leatherback turtle sightings and strandings at the European continental shelf. They stated that this trend is likely reflective of increasing awareness and promotion of public reporting schemes for marine vertebrates, but it may, in part, also reflect an increasing number of leatherbacks in the Northern Atlantic (Turtle Expert Working Group 2007). Increased boat traffic may also contribute to the increase in observations.

Figure 2. The number of natural strandings and sightings (n=40) (excluding the 10 green turtles that were shipped to Europe and thrown overboard).

Additionally, factors that could have contributed to increased observations include the number of visitors on beaches, which has increased enormously since the time period covered by Brongersma (1972). Also, the information infrastructure has improved concurrently during this time, so sightings and strandings are more likely to be reported to the relevant institutions and (local) media. This may explain, at least for the Netherlands, the increased number of leatherback records compared to the period reported by Brongersma (1972); three records before 1972 versus 22 records after 1972.

Most strandings and sightings (84%) with a documented month occurred between August and December (Fig. 3). Records of leatherback turtles in the North-eastern Atlantic show a seasonal pattern, increasing during summer and declining during late autumn and winter (Witt et al. 2007). In the Netherlands, 88% (n=24) of the leatherback observations were between August and December. These turtles may have entered the North Sea after leaving their foraging grounds. However, patterns of seasonal occupation inferred from public sightings records must be interpreted with caution as they lack correction for spatial and temporal (seasonal) bias in survey effort (Witt et al. 2007). The numbers of observed hard-shelled turtles are to small to detect a trend.

Figure 3. All natural strandings and sightings presented per month. Two of the 40 documented strandings did not have an associated month recorded (Un=unknown species, Cm=Chelonia mydas, Lk=Lepidochelys kempii, Cc=Caretta caretta, Dc=Dermochelys coriacea).

Eleven of the 15 stranded hard-shelled sea turtles were alive when found, but most died soon after finding. Most stranded turtles were very weak, cold-stunned, ill, and/or treated incorrectly. The three latest stranded sea turtles in the Netherlands were fortunate. They were the first successfully rehabilitated sea turtles for the country.

As long as sea turtle species are listed on the IUCN Red List of Threatened Species we believe we should make all efforts to save each turtle we can. In absence of a stranding protocol, we took the initiative to develop one (<http://www.ravon.nl>). Hopefully this will help increase the chances of survival for any future stranded sea turtles.

Acknowledgements. Thanks to all the team members and organisations that were involved in the rehabilitation of the three rehabilitated sea turtles.

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BRONGERSMA, L.D. 1972. European Atlantic turtles. Zoologische Verhandelingen. Rijksmuseum van Natuurlijke Historie te Leiden. 318pp.

DOYLE, T.K., J.D.R. HOUGHTON, P.F. O'SUILLEABHAIN, V.J. HOBSON, F. MARNELL, J. DAVENPORT & G.C. HAYS. 2008. Leatherback turtles satellite-tagged in European waters. Endangered Species Research 4: 23-31.

EPPERLY, S.P., A. NUNES, H. ZWARTEPOORTE, L. BYRD, M. KOPERSKI, L. STOKES, M. BRAGANÇA, A.D. TUCKER & C.R. SASSO. 2013. Repatriation of a Kemp's Ridley from the Eastern North Atlantic to the Gulf of Mexico. Marine Turtle Newsletter 136:1-2.

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GODLEY, B.J., M.J. GAYWOOD, R.J. LAW, C.J. MCCARTHY, C. MCKENZIE, I.A.P. PATTERSON, R.S. PENROSE, R.J. REID & H.M. ROSS. 1998. Patterns of marine turtle mortality in British waters (1992-1996) with reference to tissue contaminant levels. Journal of the Marine Biological Association of the United Kingdom 78: 973-984.

GOVERSE, E., J. DRUBBEL & F. GRÜNEWALD. 2012. Nederlandse Kemps zeeschildpadden in het nieuws. RAVON 43 14: 17-19.

GOVERSE, E., M.L. HILTERMAN, P. BONNET & R. DE RUITER. 2010. De lederschildpad: spectaculaire nieuwe waarnemingen in Nederland en een statusoverzicht. RAVON 35 12: 5-10.

GOVERSE, E., M. HILTERMAN, M. JANSE, A. OOSTERBAAN & H. ZWARTEPOORTE. 2009a. Dikkopschildpad: Een bijzondere dwaalgast in Nederland. RAVON 32 11: 8-12.

GOVERSE, E., M.L. HILTERMAN, M. JANSE & H. ZWARTEPOORTE. 2009b. Kemps zeeschildpad: een nòg bijzonderder dwaalgast in Nederland. RAVON 33 11: 38-43.

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PENROSE, R.S. & L.R. GANDER. 2010. British Isles & Republic of Ireland Marine Turtle Strandings & Sightings Annual Report 2009. Marine Environmental Monitoring, Penwalk, Llechryd, Cardigan, Ceredigion, West Wales. 25pp.

PLOTKIN, P.T (Ed.). 2007. Biology and conservation of ridley turtles. John Hopkins University Press, Baltimore. 356pp.

PRITCHARD, P.C.H. 1996. Kemp's ridley, lost in France, returns to Florida. Florida Naturalist 69: 13, 22.

TURTLE EXPERT WORKING GROUP. 2007. An assessment of the leatherback turtle population in the Atlantic Ocean. NOAA Technical Memorandum NMFS-SEFSC-555. 116pp.

WITT M.J., A.C. BRODERICK, D.J. JOHNS, C. MARTIN, R. PENROSE, M.S. HOOGMOED & B.J. GODLEY. 2007. Prey landscapes help identify potential foraging habitats for leatherback turtles in the northeast Atlantic. Marine Ecology Progress Series 337: 231-243.