News

By Tiare “TJ” Fridrich, Manatee Biologist

African manatees are one of three manatee species in the world. Found along the western coast of Africa from Senegal to Angola, they inhabit a wide range of habitats, from offshore islands to inland lakes. Despite their wide range, very little is known about them. African manatees are notoriously difficult to observe in the wild, as much of their habitat is remote and hard to access. In fact, the African manatee is among the least understood marine mammals in the world. In Cameroon, one of the only places these manatees can be observed in the wild is in Lake Ossa. Lake Ossa is the largest natural lake in Cameroon, located in the lower basin of the Sanaga River. In recognition of the region’s high biodiversity, Lake Ossa and nearby portions of the river were designated a faunal reserve in the 1960s under the administrative authority in place at the time. More than 400 families live in the reserve and depend upon artisanal fishing and tourism for their livelihoods.

Researchers from the African Marine Conservation Organization (AMCO), a Cameroon-based non-governmental organization, have been researching manatees in Lake Ossa for over two decades. In 2017, the invasive aquatic plant giant salvinia, or Salvinia molesta, began to spread throughout the lake, choking out native plant species that the manatees feed on, and blocking water access for local fishermen. Salvinia spreads incredibly quickly, doubling in size every 7 to 10 days, and is not edible by manatees due to the plant’s high tannin content. As the salvinia spread, researchers saw a decline in the abundance of manatees in Lake Ossa and impacts to local fisheries.

In other African countries, researchers have successfully used biological controls—like introducing plant-predating insects—to manage invasive salvinia. Specifically, the salvinia weevil, or Cyrtobagous salviniae, has been effective in clearing areas of salvinia. To eliminate the salvinia from Lake Ossa and restore the African manatee population and habitat, AMCO designed a pilot project to introduce these weevils into Lake Ossa and, in 2019, partnered with Louisiana State University to acquire the insects and raise them in Cameroon. In 2021, AMCO released 3,000 weevils at a pilot site in the lake, and in one year, there was a 20% decrease in salvinia coverage. Within three years of the original weevil release, salvinia coverage in Lake Ossa declined by 80%. By late 2023, manatees had returned to Lake Ossa.

Alongside this project, AMCO is working with the local community to raise awareness of the importance of manatees to the Lake Ossa ecosystem and to reduce illegal poaching and accidental captures of manatees from fishing practices. To encourage a shift away from poaching and overfishing in the lake, AMCO partnered with the community members to encourage sustainable manatee-ecotourism practices and has also trained local fishermen to participate in citizen science, with over 80 local fishermen reporting opportunistic manatee sightings in Lake Ossa.

Save the Manatee Club is proud to have supported this project and many others spearheaded by AMCO and partners worldwide. To learn more about Save the Manatee Club’s support of our international research and conservation partners, visit our website at savethemanatee.org/worldwide.