Nine years of leatherback turtle Dermochelys coriacea hatching and emergence success on Bioko Island, Equatorial Guinea

Analyzing trends in leatherback turtle Dermochelys coriacea reproductive success provides insights into species fitness and responses to environmental pressures, including changes in temperature and beach characteristics. Despite the Gulf of Guinea hosting the world’s largest leatherback nesting aggregation, reproductive success data in the region remain limited, with most studies focusing on the northwestern Atlantic and Pacific populations. Bioko Island, Equatorial Guinea, in the southeastern Atlantic, ranks second in the Gulf of Guinea for leatherback nesting encounters after Gabon. Over 9 nesting seasons, we assessed hatching and emergence success of in situ leatherback nests on 2 key nesting beaches along Bioko’s southern coastline (Beach E: 2008-2014; Beach D: 2016-2019) and explored the relationship between nest temperature and success rates. Overall, good hatching success was (mean ± SE) 0.27 ± 0.03, and emergence success was 0.21 ± 0.02, both lower than global averages (0.55 ± 0.17 and 0.48 ± 0.19, respectively). Success rates varied significantly between beaches: Beach D had higher hatching (0.64 ± 0.07) and emergence success (0.56 ± 0.08; n = 21) compared to Beach E (0.21 ± 0.03 and 0.16 ± 0.02, respectively; n = 125), and interannual variation occurred on Beach E. Temperature data suggest that beach slope and precipitation are likely to have contributed to these differences. Our findings contribute valuable insights into leatherback reproductive success in the southeastern Atlantic, highlighting Bioko’s importance for regional populations. Addressing geographic biases and identifying reproductive trends inform global conservation efforts and underscore spatiotemporal variation in a key nesting area.