Leatherbacks sea turtles in the southeast Atlantic Ocean: multiple threats analysis

PROSDOCIMI, L.; MORAIS, M; TIWARI, M.; FORMIA, A.; FERREIRA-AIRAUD, B.; GONDER, M.K.; HONARVAR, S.; MIANSEKO, N.; ELWEN, S.; BRABY, R.; BOLTEN A.B.

Simposio; 41th Annual Symposium on Sea Turtle Biology and Conservation; 2023

ISTS

The southeast Atlantic (SEA) is a major breeding and development area for the leatherback sea turtle. The major nesting beaches are located in Gabon and the Republic of Congo, with nesting taking place from November to April (peak in December and January). Mark-recapture data and satellite tracking studies have shown that leatherbacks nesting on Central African beaches migrate to multiple foraging areas off the coast of Africa and South America and are exposed to multiple threats. To better understand and quantify the major threats and potential impacts to leatherback populations in the SEA, we conducted a threats analysis. Threats were identified and classified for the different life stages and ecosystems inhabited by sea turtles into a matrix. We considered 8 life stages: nesting females, eggs, hatchlings, neritic juveniles, oceanic juvenile, neritic adult, and oceanic adult. We grouped all identified threats into six main threat categories: fisheries bycatch, resource use (direct and indirect use), habitat alteration, pollution, species interaction, and climate change. Additionally, as threats vary depending on the ecosystem inhabited by the turtles, we incorporated three environments: 1) terrestrial (beach), 2) neritic and 3) oceanic. Annual mortality was estimated for each life stage/ecosystem for each threat. As the information is very heterogeneous and it was difficult to assign actual mortality rates and we used a range of mortality values based on the best available information (e.g. published data, projects database information and expert opinion): 0 (no evidence of mortality); >0 (mortality has been documented or is likely to occur; however data are insufficient to estimate mortality); 1-100 (low mortality); 100-1000 (medium mortality); >1000 (high mortality). Sublethal effects for certain threats and life stages were also highlighted. Results indicated that fisheries bycatch (i.e. longline, trawl and gillnets) represent a major threat for leatherbacks in the SEA, with the gillnet fishery as the main source of mortality for adult turtles. In addition, nesting females, eggs and hatchling stages are subject to mortality by illegal harvest and habitat alteration. Gaps remain in our knowledge and understanding of the status and ecology of leatherback turtles in the eastern Atlantic and the regional population is categorized as Data Deficient on the IUCN Red List, but this study has highlighted significant threats and conservation priorities that effective management strategies need to urgently address.