By Miguel Morais, 24th March 2022
Angola’s coastline is home to intricate and dynamic ecosystems but there is still much we don’t know about the status of its biodiversity, including that of sea turtles that come to breed on its sandy beaches. Although conservation projects are working to promote sustainable development, sea turtle conservation in this area is hampered by fragile social systems, inadequate law enforcement, and pressures exerted on the natural environment by a growing human population.
To address these issues, the Kitabanga Project was founded by Agostinho Neto University in 2003. Kitabanga is a word in Kimbundu, one of the languages spoken in the country, meaning giant turtle and referring to the leatherback turtle, one of the three species of sea turtle nesting in Angola. Since its inception, the project has tirelessly gathered data, raised awareness and promoted the conservation of sea turtles along the Angolan coast through its research and community outreach activities. Of the species nesting on Angola’s beaches between October and March each year, the olive ridley turtle is the most abundant one. Yet for a long time, reliable data on just how abundant this species is in the country were lacking because there was no systematic monitoring.
Therefore, to quantify nesting activities of olive ridley turtles in the area, we conducted aerial surveys each February during 2011–2015, just after the peak of nesting activity. From a helicopter, trained observers recorded all nesting activities along the coast, looking for signs of nests and turtle tracks in the sand. We confirmed these aerial sightings with ground surveys at the beaches regularly monitored by the Kitabanga Project. During 2011–2020, the Project expanded its permanent beach monitoring sites from three (23 km) to seven (54 km), to monitor nesting across a wider range of latitudes. At the seven permanent monitoring sites, regular surveys recorded all nesting activity during 2011–2020.
Counting the number of nests gives some indication of the number of female turtles coming to the beaches to lay their eggs, but the number of clutches per female varies, not only between species and locations, but also between individual turtles. Data obtained from tracking olive ridley turtles in Angola showed that some turtles nest up to three times in a season, whereas others nest only once, and not all return to nest in subsequent years. We therefore estimated the number of breeding females in the population based on the assumption that each female laid one to three clutches per season, and an average interval of 1.5 years between subsequent nesting seasons.
Previously it had been documented that Gabon harboured the largest olive ridley population in the Atlantic, with c. 900–5,400 females nesting there annually. However, our data revealed that in fact many more breed in Angola, with 27,000–83,000 females nesting annually during our study period. This also makes Angola one of the most important non-arribada nesting populations globally for the olive ridley turtle. The term arribada—Spanish for arrival—is used to describe a synchronized mass-nesting event of sea turtles, which is in contrast to the solitary nesting behaviour observed in Angola. The olive ridley population we documented in Angola was even larger than some arribada populations reported from other countries such as Mexico, Nicaragua and Costa Rica. Given this context and the previous lack of long-term data for olive ridley turtles in the eastern Atlantic, our findings are of vital importance for population assessments of this species not only at a regional scale, but on a global level.
In recent years, Kitabanga Project has protected more than 400,000 nests that produced more than 4,500,000 hatchlings. The project not only collects data on sea turtles along extensive coastal areas, but also has a strong commitment to environmental education and social inclusion of local community members. Our findings will help to continue the development of evidence-based conservation strategies to protect sea turtles in Angola, in collaboration with the people that share their habitats.
The article Surveys of the Angolan coast uncover the largest olive ridley nesting population in the Atlantic and the largest non-arribada population globally is available in Oryx—The International Journal of Conservation.