In Sub-Saharan Africa, tropical freshwater eels (Anguilla spp.) are ecologically important species that are poorly understood, poorly protected and potentially highly threatened and/or exploited. I’m dedicating my PhD to these secretive and mysterious creatures.
I’m often asked: why on earth are you studying eels in South Africa?! True. Coming from Europe where eels are highly valuable and considered a delicacy and where the research is plentiful, it doesn’t seem to make much sense. Well, I have to tell you, I have a strong (probably ill-advised) taste for adventure. But that’s not it.
There are 19 species of eel (and subs species) in the world: 4 of them are found in South Africa and along the East Coast of Africa, roughly from the Cape Region to Kenya and in the associated islands (Comoros, Mayotte, Madagascar, Reunion and Mauritius). This means that Sub-Saharan Africa holds 25% of the world biodiversity and yet, they are much understudied. If you look at the entire continent, it’s even a larger geographic area than the temperate European eel, Anguilla anguilla, which is also found in Northern Africa.
All eel species in the world have a rather unique lifestyle as they are long distance migratory
fish. That is where my fascination comes from as I am very much interested in spatial ecology and how the environment shapes one’s behavior and movements.
A unique life style, you say?
Freshwater eels (Anguilla spp.) are catadromous migratory fish species which means they are born at sea but spend most of their adult life in freshwater. A few long and epic journeys await them during their lifetime: The first one will take them from the sea where they were born to freshwater systems, the second one is possibly facultative and takes them up rivers, the last one will take them back where they were born, to breed and die. There and back, it’s a journey of up to and over 10000 km they face!
These fussy fish do not just breed anywhere in the sea. The exact location of their breeding grounds is still a bit of a debate. However, the consensus is that they supposedly breed east of Madagascar in the Mascarene Plateau, an oceanic plateau that covers an area of 2000 km long between the Seychelles and Reunion Island. Why that particular area? We’re not too sure but eels have specific preferences regarding salinity, temperature, geostrophic currents and depth. How they find that area? It is a mystery still to be uncovered.
Migration is a risky business
From sea to source and back, migrating eels face many dangers. At sea, they mainly face predation and fishing – though it’s not a big thing in this part of the world. They are also at risk of facing global change and the uncertainty of the effects on the oceanic currents. The danger seems to grow even bigger when they finally reach the coast and the inland freshwater: human activities have greatly damaged their precious habitats. The main problems they face are barriers to their migrations from small weirs to major dams. Unfortunately, most African countries they live in are water-scarce and development of water schemes is more and more threatening. Moreover most of these new obstacles are NOT equipped with relevant and effective fish ladders.
For instance, in KwaZulu-Natal in South Africa, we believe that their distribution has greatly decreased. Elvers (young eels <15 cm) have amazing super-hero-style abilities to overcome huge obstacles. They are known to be able to “climb up” Howick Falls which is about 95 m high, and be present far up in all the catchments of the province. Now, the problem is that there is more and more obstacles on their way up the rivers, meaning that they take more time to migrate. They grow then too big to overcome obstacles they once climbed up easily (they lose that crazy ability when they reach about 17 cm). Hence, their distribution is most likely being reduced significantly.
Cultural and spiritual values?
Speaking of Howick Falls, there is a legend that I really like. The stories of the mythical Inkanyamba! The Inkanyamba is a river monster in Xhosa and Zulu and has brought fear and awe for many generations. These monsters – believed to be inspired by local eels, live at the bottom of huge waterfalls. They are believed to be migratory and travel overland. They are also believed to be able to control the weather and have been associated with seasonal storms and drought. People fear them as they think that if they disturb the Inkanyamba, this will bring great disaster.
A similar story exists in the Zambezi River. The legend of the River God, Nyami Nyami, who is an important God for the Tonga people, who usually assume he is an aquatic snake, but to me, he is most definitely an eel! He is described as a snake-like creature with the head of the fish and is a benevolent god to the Tonga controlling the life in and around the river. He became quite famous with the construction of the Kariba Dam in the 50’s. During the dam wall construction, he and his wife got separated and many of the locals were relocated mostly against their will. The following year, tremendous flooding happened and the construction had to be halted. People said that the floods were Nyami Nyami’s work either because of his anger due to being separated from his wife, and because he was invoked by the Tonga’s. Elders claimed that the dam is still standing through their intervention but that to this day Nyami Nyami still wants to be reunited with his wife!
Across the 4 species range in Sub-Saharan Africa, many of these legends exist. They either tell the story of benevolent or fearful gods. I became interested in these stories recently as I think cultural aspects – that are pretty much unknown in the area – can be really interesting when it comes to conservation. For example, in New Zealand, eels are respected and considered sacred due to locals legends. While here, the legends seem to fade slowly away to leave in place indifference to these amazing creatures.
Nevertheless, there is still allot to learn about eels in Sub-Saharan Africa!
And, truth be told, it’s also a lot of fun.
I am amazed at how high elvers can climb! Really?