Mysterious African manatees inspire a growing chorus of champions

 

By Petro Kotzé, via Mongabay

 

As a young student, Aristide Kamla had “big plans” when he traveled to Lake Ossa in Cameroon to conduct his master’s degree fieldwork with the little-known African manatee. He was hoping for a manatee count and a management plan to come out of the expedition on the roughly 4,000-hectare (10,000-acre) lake.

But securing grants was difficult for this budding researcher, so his first funder was his mother. Kamla says she gave him $500, a “huge” amount for the family’s modest means.

It almost ran out before he saw a single manatee.

Months later, on the brink of abandoning ship, a local fisherman put him back on track. The fisherman taught him, Kamla says, to go early when the lake lay still like a mirror before the wind rose, to be quiet and patient, and to look for the small signs. They were bubbles, floating poop, or the serendipitous breath that breaks the water’s surface. “The fishermen know the species better than anybody.”

Kamla was galvanized. His eventual thesis focused on the distribution, habitat use and local perception of the African manatee (Trichechus senegalensis) in Lake Ossa and Douala-Edéa National Park. Subsequently, his work continues to contribute to our understanding of the species and its conservation, and has become more important than ever.

This year, Kamla won the prestigious Whitley Award, which grants him 50,000 British pounds ($66,000) for his ongoing project on the world’s least-known manatee.

The African mermaid

The world’s forgotten sirenian grazes in the remote rivers, mangroves and lagoons of the west coast of Africa. Using its whisker-like hairs, known as vibrissae, to detect objects, the elusive African manatee expertly navigates the famously dark and murky waters of Central Africa. Some call these large, aquatic mammals Mamowata, a magical spirit that was once human. Others liken the languorous, wrinkled giants to mermaids.

The stuff of lore, the inconspicuous African manatee is hard to see despite its size, and, consequently, difficult to study and conserve. Few people are experts on the species, but Kamla says he hopes the recognition of his work by the Whitley Fund for Nature will help propel the so-called sea cow onto the international stage.

Kamla says his own journey with the manatee has been nothing less than a calling from God. Growing up in Cameroon’s mountainous west, far from the coast, his mother forbade him from swimming in the streams out of fear of the water spirits. As a result, he never did.

But when he had to research Cameroon’s aquatic megafauna for his ecology degree studies at the University of Dschang, Kamla finally met the “weird animal” that would become his life’s passion.

The weird and wonderful manatee

Manatees were once thought to be an unusual tropical form of walrus, but sirenians (manatees and the dugong) are today considered the closest living relatives of elephants. Like elephants, manatees rip up plants and roots with their muscular upper lips and grind their food with “marching molars” that are replaced by back teeth that move forward as they wear. Their rudder-like flippers have toenails reminiscent of their terrestrial past, and a large, round, paddle-like tail propels their oblong bodies forward.

Their thin, fine hair is believed to help them feel water currents, like the lateral line in fish. Their small, sleepy eyes are considered poor, but they use visual cues like vegetation, water depth and coastline features to help guide them.

There are three species of manatee. The West Indian manatee (Trichechus manatus) is found in the coastal Caribbean, from the eastern United States to northern Brazil. The Amazonian (Trichechus inunguis) is the smallest manatee and occurs in the rivers of the Amazon Basin. But the African manatee has the largest range of its brethren, spanning 21 countries along the western side of Africa in an area larger than the U.S., from the Senegal River to the Longa River in central Angola.

West African manatees roam rivers more than 3,000 kilometers (1,900 miles) inland in Guinea, Mali and Chad, and around the tropical islands off Guinea-Bissau. They inhabit various aquatic ecosystems, from equatorial rainforests to rivers bordering the Sahara Desert to the marine waters off the coast of West Africa. The African manatee is also unusual because, unlike the West Indian and Amazonian manatees, its diet includes a healthy helping of mollusks and fish.

The IUCN Red List considers all manatee species vulnerable to extinction. While population trends for the West Indian and Amazonian manatees are declining, for the African manatee it’s recorded as “unknown,” though researchers believe it to also be in decline.

Some of what we suspect we know of the African manatee is based on knowledge of the better-studied, and more easily spotted, Florida manatee, a subspecies of the West Indian manatee.

African manatees face multiple threats, including poaching for their meat and medicinal purposes, or drowning as bycatch in fishing nets. Dams are an additional serious threat, says Lucy Keith-Diagne, another expert on the species and executive director of the African Aquatic Conservation Fund. She says she’s seen the carnage firsthand.

During the four years of her Pew Marine Fellowship project to report on threats to manatees in four countries, Keith-Diagne and her colleagues documented more than 1,000 dead manatees, primarily killed by poaching and bycatch, but also by dams. (They also documented 50 live manatees that escaped capture or were shipped, many illegally, to aquariums in Asia).

For example, when Keith-Diagne led a study that fitted the first (and so far only) African manatees with satellite trackers, she was only able to access the manatees because they’d become trapped in an agricultural dam on the Navel, a tributary of the Senegal River. The manatees swam through openings during high water levels in the rainy season and couldn’t leave when the water receded. The first year after dam construction, four died. The following year, Keith-Diagne’s team rescued five and fitted three with the trackers. Results showed they traveled more than 308 km (191 mi) after their release.

Beyond trapping manatees or crushing them in their gates, hydroelectric and agricultural dams have also isolated manatee populations in major waterways like the Niger and Senegal rivers and Lake Volta in Ghana. And more major hydroelectric dams are in the pipeline.

These threats can only be moderated if we know more about the manatees. Keith-Diagne says her initial attempts, around 2006, were “really hard.” She recalls tough, wet and moldy months boating up unsurveyed rivers, trying to find the “incredibly cryptic, elusive manatees” to understand their movement and distribution.

Then, in 2009, she was introduced to genetic testing. This technique, using tissue samples, allowed her to identify the first four major populations through the species’ range. She and other African colleagues have more recently begun using environmental DNA (eDNA). This noninvasive technique allows for studying cryptic, low-density, or logistically difficult-to-study species.

For example, manatees shed genetic material into their environment through feces, mucus, saliva, gametes, skin cells and decomposing carcasses. Researchers can then detect this environmental DNA in water samples. The technology has been life-changing for researchers, Keith-Diagne says. An ongoing range-wide genetics study will tell us where distinct populations exist, estimate population numbers, and determine the diversity and relatedness of different African manatee populations. This will help us learn which populations are in trouble and which are doing well.

Another technique, stable isotope analysis of manatee ear bones and food, helped uncover the manatee’s surprising taste for fish and mollusks, though it also consumes a lot of plants. Awareness of its diet can inform management about which habitats to protect. Another technique to detect African manatees is passive acoustic monitoring, where researchers can detect their vocalizations.

With the application of ever-improving technologies for studying waterways — and more people trained to study the species — our knowledge of African manatees has expanded substantially. Keith-Diagne says that due to the increasing number of research papers, the species probably no longer carries the distinction of being “the least studied large mammal in Africa.”

Back in Cameroon, meanwhile, Kamla realized he could use technology to tap into the fishermen’s knowledge. As part of the work of the African Marine Mammal Conservation Organization (AMMCO), a nonprofit he started in 2012, he developed the Siren app. Fishermen use it to log marine mammal sightings and record reams of data, which are uploaded to a central database. Since its development in 2015, the app has expanded rapidly from the coast of Cameroon to seven other countries, including the Republic of Congo, Ghana, Senegal, and even the United Arab Emirates — well outside manatee habitat. Initially developed for African manatee sightings, fishermen now use the app to log multiple aquatic species.

Sightings have included the rare Atlantic pygmy devil ray (Mobula rochebrunei), which hasn’t been seen by scientists on the west coast of Africa for 40 years, and the critically endangered Atlantic humpback dolphin (Sousa teuszii), which has also evaded science for a decade.

By the early 2020s, AMMCO was also making excellent progress with manatee conservation at Lake Ossa and its surroundings, running educational campaigns and working to create alternative livelihoods to reduce poaching. The results were encouraging.

For more than four years, Kamla says, he hasn’t seen manatee meat being served in local restaurants, once a common sight. And it’s been even longer since he’s heard of any killings. This year, they celebrated their first manatee festival.

At the Nkam River, where AMMCO is also working, Kamla says numerous poachers have handed their weapons in, and a village chief personally destroyed poaching equipment.

Yet even as poaching waned, a new crisis emerged at Ossa. Likely caused by nutrient pollution from the Sanaga River, an invasive aquatic fern, the giant salvinia (Salvinia molesta) proliferated on the lake. First noticed in 2017, it had exploded by 2021, covering half of the lake. Kamla says the plants were like a thick carpet, preventing the manatees from surfacing to breathe. Unable to fish, fishermen turned to crop farming, which entailed deforestation. Manual removal of the plants proved futile.

Kamla won a battle to introduce the salvinia weevil, a beetle feeds on the ferns and is widely used as a biocontrol agent to tackle its spread. Since its introduction to Ossa, the weevil has helped reduced the giant salvinia coverage by 90%. It was this mammoth undertaking that led to Kamla receiving the Whitley Award this May.

The award money will help further reduce the invasive fern and identify the sources of pollution that cause it. Kamla says he also wants to deploy an acoustic sensor system to detect and deter logging of the riverside forest and further help fishers develop alternative livelihood options like aquaculture and ecotourism.

Keith-Diagne, who was Kamla’s Ph.D. supervisor, describes his accomplishments as “amazing.” She says he might even outpace her. “That’s the best you can hope for somebody you mentored and trained.”

After almost two decades of dedication to the African manatee, she says prospects for the species are looking up — but the current trend needs to be sustainable. Keith-Diagne says she wants to formalize an African Manatee Network to unify the expanding group of researchers and other experts dedicated to this gentle giant. Then, she says, we can find solutions together.

And so the story of the African manatee, that elusive mermaid, can be preserved for many more generations.

Citations:

Reep, R., Marshall, C., & Stoll, M. (2002). Tactile hairs on the postcranial body in Florida manatees: A mammalian lateral line? Brain, Behavior and Evolution, 59(3), 141-154. doi:10.1159/000064161.

Keith-Diagne, L. W. (2014). Phylogenetics and feeding ecology of the African manatee, Trichechus senegalensis (Doctoral dissertation). Retrieved from https://www.proquest.com/openview/332507deacdf17cdb367094f85f76a18/1?pq-origsite=gscholar&cbl=18750.

Keith-Diagne, L. W., De Larrinoa, P. F., Diagne, T., & Gonzalez, L. M. (2021). First satellite tracking of the African manatee (Trichechus senegalensis) and movement patterns in the Senegal River. Aquatic Mammals, 47(1), 21-29. doi:10.1578/am.47.1.2021.21.

Berta, A., Sumich, J. L., & Kovacs, K. M. (2015). Sirenians and other marine mammals: Evolution and systematics. Marine Mammals, 103-129. doi:10.1016/b978-0-12-397002-2.00005-3.

Deutsch, C. J., Reid, J. P., Bonde, R. K., Easton, D. E., Kochman, H. I., & O’Shea, T. J. (2003). Seasonal movements, migratory behavior, and site fidelity of West Indian manatees along the Atlantic coast of the United States. Wildlife monographs, 1-77.