Ecology and conservation of marine turtles in Kenya

Abstract

Conservation requires comprehensive data about the target species or ecosystem. For marine turtles, obtaining such data can be challenging due to their migratory and cryptic nature, as well as their long and complex life histories. This hampers our ability to assess fundamental parameters such as population size and reproductive output, and to design adequate spatial conservation measures. In this thesis, I aim to comprehensively synthesize the available information regarding marine turtles along the African continental east coast and address several of the identified knowledge gaps with multiple long- term data sets from Watamu, Kenya, that were collected by a grassroots community-based organisation. More specifically, in Chapter 1, I combine results from a systematic literature review with perspectives from Kenya, Tanzania, Mozambique, South Africa and the Western Indian Ocean (WIO) region, provided by marine turtle experts, to create a comprehensive assessment of the biology and conservation of marine turtles along the African continental east coast. I highlight the importance of this sub-region as foraging and nesting grounds, identify knowledge gaps and threats to turtles, and discuss strengths and impediments in turtle conservation. In Chapter 2, I analyse turtle nesting data collected at Watamu between 2000 and 2020 and show promising signs of recovery for green (Chelonia mydas) and olive ridley turtle (Lepidochelys olivacea) nesting. I also present information crucial to the conservation of turtle populations in the WIO. Following this, in Chapter 3, I present the first empirical data on estimated green turtle primary sex ratios in Kenya. The analysis I present demonstrates balanced sex ratios are achieved in clutches that incubate in-situ and that the conservation intervention of clutch relocation induces a female-biased sex ratio. Lastly, in Chapter 4, I examine the data from an incentive-based bycatch mortality mitigation program that has been in operation in Watamu since 1998. I provide insights into small-scale fisheries turtle bycatch and show the importance of coastal areas as foraging grounds for juvenile green and hawksbill turtles (Eretmochelys imbricata). In conclusion, this thesis has identified and addressed fundamental knowledge gaps about marine turtles along the African continental east coast and Kenya, whilst demonstrating the potential of community-based conservation in achieving conservation outcomes and bolstering ecological knowledge.