1Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, UK
2Local Ocean Conservation, Watamu, Kenya
Although considered rare, leatherback turtles (Dermochelys coriacea) are found throughout the Southern West Indian Ocean (SWIO) and have been recorded in Kenyan waters (Frazier, 1975; Zanre, 2005; Hamann et al., 2006). The only known significant nesting of leatherbacks in the region occurs at the Maputaland rookery in South Africa and Mozambique (Nel et al., 2013; Pereira et al., 2014). In Kenya, nesting has been recorded for green turtles (Chelonia mydas), hawksbill turtles (Eretmochelys imbricata) and olive ridley turtles (Lepidochelys olivacea) at various places along the coast (Okemwa et al., 2004; Olendo et al., 2017). One of these locations is the beach of the Watamu Marine National Park (WMNP), which is considered a key nesting site in Kenya (Okemwa et al., 2004). The majority of the nests laid on this beach are from green turtles, although olive ridley and hawksbill turtle nests have been recorded too (Okemwa et al., 2004).
Since 1997, Local Ocean Conservation (LOC) has been monitoring the beach of the WMNP (3.385472°S, 39.980611°E) and surrounding areas, under the auspices of the Kenya Wildlife Service (KWS). A team of trained beach and nest monitors (hereafter “monitors”) patrol the beach of the WMNP every night for two hours either side of high tide, resulting in a minimum patrol effort of four hours per night. The nesting turtle reported here was encountered during one of these patrols.
The monitors spotted the turtle at the end of a night patrol, in the early morning of the 23 January 2014. The nesting event took approximately 150 minutes and finished after sunrise. This is longer than the total nesting time reported in other sources: of 93 minutes (Carr & Ogren, 1958) and 113 minutes (Eckert & Eckert, 1985) and 118 minutes (Reina et al., 2002).
The nesting female measured 156.1cm long (curved carapace length; CCL) and 106.0cm wide (curved carapace width; CCW), which is within the size range of a mature female leatherback in the Indian Ocean (Eckert et al., 2012). The turtle looked to be in good condition, but she did have a deep cut on the left shoulder. It was noted that the cut was not bleeding and looked like an old wound. It was a clean cut which suggests that it was caused by a knife. It is possible that the turtle became entangled in fishing gear and was injured as she was cut free. However, the injury did not unduly affect the nesting process.
Due to the presence of tourism activities and the high volume of foot traffic in the vicinity of the nesting site, there was a significant risk of the nest being trampled. If the nest was fenced off and signposted, this would have attracted more attention and created a risk of it being disturbed. It was, therefore, decided to move the clutch approximately 200m along the beach to a more secluded area. This was done immediately after the clutch was laid using methods similar to those outlined by Mortimer (1999). The clutch was made up of 91 eggs and 6 shelled albumen gobs. Average clutch size in the Maputaland rookery is 104 eggs (range: 60-160).
As per standard LOC protocol, the nest was monitored daily for signs of disturbance or hatching. After 77 days the nest had not shown signs of hatching and since the average incubation of leatherback nests is approximately 60 days (Eckert et al., 2012), it was decided to excavate the nest. The entire clutch had failed to produce hatchlings and inspection of the unhatched eggs showed no visible signs of embryonic development. It is more likely the eggs died during early stages of embryonic development than being infertile (Bell et al., 2004). Why the nest failed is unknown, as the LOC monitors need to relocate cluctches regularly and the success rates are similar to those left in-situ (70-80% hatching success, van de Greer, unpubl. data).
Although leatherback turtles have been encountered in the seas around Watamu before, nesting has never been reported anywhere along the Kenyan coast. This nesting event is unique in being the first documented leatherback nesting events in Kenya. The Maputaland rookery is approximately 3,000km south of Watamu and is the closest known consistent nesting site. Tracking of post-nesting females from this rookery has shown that a significant portion of the population migrates north along the Mozambican coast and settles in the Sofala Banks area (Robinson et al., 2016; Harris et al., 2018). None of the tagged turtles, however, continued their migration along the coast into Tanzanian waters or Kenya beyond. One individual did appear to be heading further north in the open waters of the Mozambique Channel but even this track stops circa 650km short of the Tanzanian border (Harris et al., 2018) and 1,500km short of WMNP. An alternative origin of the Watamu female is the rookery on Little Andaman Island (India), which is approximately 6,000km from Watamu. Post-nesting females from Little Andaman Island were tracked migrating into the SWIO, one of which appeared to be heading for Tanzania or Kenya (Swaminathan et al., 2019).
Video of the nesting event can be viewed at https://youtu.be/pr2JoaLlr4w or by searching on YouTube for “Leatherback sea turtle laying eggs and swimming in Kenya”.
The authors would like to thank the Kenya Wildlife Service for their continued support of the LOC sea turtle conservation efforts. The authors would also like to thank ALan Rees for feedback on the draft manuscript. Local Ocean Conservation would like to acknowledge support for the Beach & Nest Monitoring program from AFEW, SWOT, Pulse Africa, TUSK Trust and the Anderson family. Local Ocean Conservation would like to thank Joseph Kiptum for his many years of hard work and dedication protecting Watamu’s nesting turtles.
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