Background

In spite of a recent increase in population (Márquez et al. 2005) the Kemp's ridley turtle Lepidochelys kempii (Garman 1880) is considered the most threatened sea turtle species in the world, being categorized as critically endangered by the International Union for Conservation of Nature (IUCN) (Marine Turtle Specialist Group 1996). The Kemp's ridley turtle has a small, restricted geographic range compared to other sea turtles species (Zug et al. 1997). The nesting areas of this species are mainly located in the Mexican coast of the Gulf of Mexico (Márquez, 1990; Bowen et al. 1994) with some secondary isolated rookeries in Texas, Florida, South Carolina and North Carolina (Meylan et al. 1990; Bowen et al. 1994; Johnson et al. 1999).

Adult and immature Kemp’s ridley occur year-round in the Gulf of México, and juveniles are found at sea in the northwestern Atlantic Ocean as far as Nova Scotia and Canada (National Marine Fisheries Services US, Service FaW and SEMARNAT 2011). Occasionally some small turtles are also known to drift into European waters during the winter months (Brongersma 1972; Márquez 1994; Witt et al. 2007). There are several documented records showing the presence of Kemp’s ridley turtle in the waters around Azores (Brongersma 1972; Bolton and Martins 1990), Madeira (Brongersma 1972), British Islands and France (Brongersma 1972; Witt et al. 2007; Penrose and Gander, 2015) and in the Mediterranean Sea (Brongersma and Carr 1983; Tomás et al. 2003; Oliver and Pigno 2005; Tomás and Raga 2008; Insacco and Spadola 2010; Carreras et al. 2014).

In the NW Iberian Peninsula, previous documented records included only two individuals in the coast of Galicia (Spain), the most recently in 1998 (Fernández 1988; Faraldo and Galán 1999), and one individual in Portugal in 2001 (Dellinger 2008).

The present study provides a new report on the presence of and an increase in the records of Kemp’s ridley turtles in the waters around the NW Iberian Peninsula within a short time of ten months. Our work also contributes to the knowledge of the distribution of this species in the north-eastern Atlantic and provide insights to the main threats in the area to contribute to conservation efforts of this species in international waters.

Methods

Study area

The NW Iberian Peninsula coast is about 1,500 km long ranging from Ría de Ribadeo (43°33.20’ N; 07°02.00’ W Spain) to Peniche (39°21.00’ N; 09°22.00’ W Portugal) (Fig. 1). The Galician coastline (about 1,200 km in length between Ría de Ribadeo and River Miño estuary) is characterized by a series of large, coastal inlets (rías). The NW Portuguese coast (about 300 km in length between River Minho and Peniche) presents a wider and flat continental shelf (40–70 Km) (Fiúza 1983). This whole area has the influence of winds from south and south-west in autumn and winter, and northerly winds in spring and summer.

Fig. 1
figure 1

Location of four new records of stranded Kemp's ridley turtle in the NW Iberian Peninsula between February and November, 2014. Turtles are numbered in chronological order (Table 1)

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Data collection and analysis

In the study area, two stranding networks are established: Coordinadora para o Estudo dos Mamíferos Mariños (CEMMA) in Galicia (NW of Spain) and Sociedade Portuguesa de Vida Selvagem (SPVS) in Portugal, since 1990 and 2000, respectively. These strandings networks record turtles and marine mammals stranded on the beaches, collect samples for Galician and Portuguese Marine Animal Tissue Banks and recover injured individuals for rehabilitation. They are coordinated via a 24 h telephone hotline.

Turtles were moved by the strandings networks mobile units to rehabilitation installations of CEMMA and SPVS to proceed with the veterinary examination and rehabilitation of the two individuals found alive and to carry out the necropsy of the dead ones following detailed protocols (Sociedad Española de Cetáceos 1999; Wyneken 2001). Turtles were measured (total length [TL]; straight carapace length [SCL]; curved carapace length [CCL]; straight carapace width [SCW] and curved carapace width [CCW] according to Bolten 1999), weighed, identified to species level, and the likely cause of death determined based on a complete external and internal examination. In cases when there was evidence of multiple lesions, the most severe and recent was assigned as the primary cause of stranding.

The approximated age of the turtles was estimated using the carapace length and applying reference growth models (Chaloupka and Zug, 1997; Zug et al. 1997).

Results

In 2014 four new individuals of Kemp’s ridley turtle were recorded stranded on the NW Iberian Peninsula coast (two in Spain and two in Portugal) (Fig. 1). The four turtles were identified as Lepidochelys kempii based on their diagnostic features: the presence of a small pore near the rear margin of each of the inframarginal scutes, the coloration of the skin (white bright green), the circular shape of the carapace, the presence of five pairs of coastal scutes, and triangular head with two pairs of frontal scales (Márquez, 1990). The four specimens had SCL of between 19.5 and 26.8 cm (Table 1), and therefore they were considered juveniles in their oceanic life stage (Collard and Ogren, 1990; Witherington et al. 2012). The first three individuals stranded between 11th February and 5th March, within 22 days, and the fourth one stranded on 11th November. Two of the turtles reported in the present study were found alive and were transferred to rehabilitation centres in less than two hours, but died after one and two days (Table 1).

Table 1 Biometry and geographic data of the four new records of stranded Kemp's ridley turtle in the Iberian Peninsula
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The first individual, found alive in Cangas do Morrazo, Spain, presented small carapace and plastron abrasions, no food in digestive tract and emaciation was noticeable in the neck (Fig. 2), indicating malnourishment. The second individual, found dead on Carnota, Spain, had head, carapace and plastron abrasions, consistent with stranding, and goose barnacles (Lepas anatifera) on the plastron. The third individual, found alive in Cantanhede, Portugal, had head and carapace abrasions, probably due to stranding, an ulcerative lesion in the carapace and epibiont crustaceans (goose barnacles, Lepas anatifera). Internal observations of its organs indicated sepsis. The fourth individual, found dead in Figueira da Foz, Portugal, had lacerations on its anterior flippers, consistent with incidental capture in nets, hematomas in posterior flippers and evidence of feeding (crustaceans, unidentified crabs) in upper digestive tract.

Fig. 2
figure 2

Kemp’s ridley turtle stranded in Cangas do Morrazo, Spain, 11/02/2014. Emaciation was noticeable in the neck

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Discussion

The four turtles were juveniles with a SCL of between 19.5 and 26.8 cm, so according to published growth models derived from skeletonchronological studies in relation with the carapace length (Chaloupka and Zug, 1997; Zug et al. 1997), they had an estimated age of 2 years for the first three individuals and nearly 3 years for the fourth turtle. The time of year in which they stranded is consistent with previous records of the species found stranded on the European continental coasts, that are more usually found during the autumn and winter (Brongersma 1972; Witt et al. 2007). Goose barnacles found on the first and third turtles are commonly attached to floating objects and when they are found on dead or weak turtles that indicates that they spent a long period floating at the water’s surface (De Loreto and Bondioli, 2008), and that is likely associated with a chronic condition such as poor nutrition, chronic infections, parasitic diseases, immune deficiency or a combination of some or all of these causes (Deem et al. 2009).

In the NW Iberian Peninsula, and especially during winter, the seawater temperature is low, sometimes below 10 °C. The average sea surface temperature during the first three stranding events (February and first week in March) was around 12 °C (Feldman and McClain 2014). This low temperature could have been sufficient to affect the sea turtles physiology leading to cold-stunning events, in which turtles become lethargic and float at the water’s surface and, as a result, they may be unable to swim or feed (Schwartz 1978). Therefore, lack of feeding due to the low seawater temperature could explain the large weight differences up to 38 % (0.99 kg and 1.37 kg) between the two individuals that had similar lengths to those found alive in February and March (Table 1). In the case of the turtle stranded in November in Portugal, sea temperature was around 18 °C and therefore cold stunning event is unlikely to explain this turtle stranding. Considering the necropsy findings, this individual was probably a victim of incidental capture by fisheries. Interactions with coastal fisheries, especially interactions with gill or trammel net fisheries, represents an important anthropogenic threat to other sea turtle species (loggerhead Caretta caretta and leatherback Dermochelys coriacea) in the Portuguese continental coast (Nicolau et al. 2014).

Conclusions

Four new records in one year are a significant increase compared to previous data for the species in this area. In UK and Republic of Ireland an increase in the stranded Kemp's ridley turtle has also been reported in 2014 with 7 stranded turtles, while in the previous ten year period 2004–2013 the average rate was just 1 stranded individual (Penrose and Gander, 2015). It will be important to pay attention to the occurrence of the species in the next years in the European coasts to find out whether the 2014 numbers are isolated findings or whether they indicate a trend.