There and back: the elusive and secretive lifestyle of the freshwater eels of South Africa

The African Longfin Eel, A. mossambica in a stream in the Western Cape

Photo: Dr Jeremy Shelton FRCSA

Under a big boulder in the Molweni river lives an elusive and mysterious creature: the African Longfin eel or Anguilla mossambica in scientific nomenclature. Many of its kind can be found in the Kloof area throughout the Molweni catchment – you may even have been lucky enough to have seen the famous ones which are well known to the visitors of Memorial Park. While these fish might be familiar to some of the readers, they are an ecologically important species that are unfortunately poorly understood, poorly protected and potentially highly threatened and/or exploited by humans across the globe.

While being spawned at sea, freshwater eels can spend most of their life in freshwater and that stage of their lives can last between 7 and 50 years depending on the species, sex and geographic location. Out of the 16 eel species that can be found in the world, four are present in east/southern Africa, these are: the African Longfin Eel (A. mossambica); the African Mottled Eel (A. bengalensis); the Shortfin Eel (A. bicolor), and the Giant Mottled Eel (A. marmorata). While the African Longfin eel (A. mossambica) is endemic to Africa, the other species are well distributed and can be found as far as the Pacific Ocean – The Giant Mottled Eel has even supposedly been recorded in the Galapagos Islands!

An impressive Giant Mottled Eel A. marmorata (158 cm!) caught during an eel survey in the Keiskamma River in Eastern Cape in 2018

Photo: Dr Sean Marr, SAIAB

A unique lifestyle

All freshwater eel species around the world have a rather unique lifestyle as they are long distance migratory fish. They are a catadromous species which means they are born at sea but spend most of their adult life in freshwater. So that seemingly quiet life that the local African Longfin Eel is living under a rock in the Molweni river is really just a phase between different long distance (and possibly dangerous) travels.

Successful Longfin eels have to undertake three enormously challenging journeys during during their lifetime: the first one will take them from the sea where they are born to the freshwater systems, the second one is possibly facultative and will take them on their migration up rivers, the last one will take them back to where they were born, to breed and die. The life-time round trip for a typical South African eel is of at least 1000km!

Suspected breeding area for African freshwater eels and the oceanic currents which transport the young eels to the coast in the South West Indian Ocean

Photo: © Kerry Brink WFMF

But where do they actually go? This is still a mystery! Well… not entirely. The exact location of their breeding grounds is still subject of much debate, but the general consensus is that they breed west of Madagascar in the Mascarene Plateau, an oceanic plateau that covers a distance of 2000km between the Seychelles and Reunion Islands. Why, When and How they do this is still a mystery that needs to be unravelled.

The photos below show the various life stages of eels.

Just after birth and on their trip to the coast they are called “Glass eels” because of their transparency

Source: Bournemouth Global Environmental Solutions

By the time they are ready to start migrating up rivers they are juveniles and are known as “elvers”. The photo shows an elver of A. mossambica.

During the period they live in freshwater rivers they are known as “Yellow eel” because of their coloration

Once they are ready to return to the sea to breed, they transform into a bright white/silver coloration with enlarged eyes and are known as “Silver eels”

Migration is a risky business

During their migrations from the sea to freshwater rivers and back, the eels face many dangers. At sea, they mainly face predation by other marine species and fishing by humans – though the fishing for eels is not a common risk in Southern African Oceans as there is not a huge demand locally for eels as food. They are also at risk as a result of global climate change and the resultant uncertainty on the impact this may have on the oceanic currents that bring the young eels toward our freshwater systems.

The dangers however, become more perilous once they finally reach the coast and the inland freshwater systems where human activities have greatly damaged their precious habitats. The main problems they face are barriers from small weirs to major dams. Unfortunately, most east/southern African countries that are home for the eels are water-scarce and as a result many dams have been built on the rivers resulting in significant threats to the their ability to migrate upstream. With growing demand for development and water, this threat is likely to continue to escalate.

Dams and weirs create two significant problems for the eels viz. they create a physical barrier to migration and they disrupt the natural hydrological regime of the rivers. With regard to the problem created by barriers let’s look at the Umgeni river where we know through our research that eels are not be doing very well at present. Elvers (young eels under 15 cm) have amazing super-hero-style abilities to overcome huge obstacles and we know that they are capable of “climbing-up” the natural barrier of Howick Falls which are approximately 95 m high. In addition, they have previously been found in the upper reaches of most of the catchments in KwaZulu Natal thus demonstrating their ability to navigate significant natural obstacles.

Humans have however created a massive new problem in the artificial barriers formed by large dams such as Inanda, Nagle and Midmar. This results in the eels taking much longer to migrate upstream and as they “grow” over time they become too big to overcome obstacles they once climbed easily as they lose their amazing climbing skills when they reach approximately 17cm in size. Fortunately for the eels of Kloof, the Molweni catchment does not have any significant man-made obstacles and we know that the Longfin eel is present upstream of the Kloof Falls in the Krantzkloof Nature Reserve!

The ideal solution (from the World Fish Migration Foundation)

There are possible technical solutions to these man-made barriers such as fish-ladders, but these are almost unheard of in South Africa.

The second problem dams and weirs create are their impact on water flow. It is believed that the recruitment of young eels into freshwater systems is significantly linked to the hydrological regime of the river. Basically, they get geared to swim up the rivers when the rivers start to flow strongly after rains! This means that their dispersal into a particular catchment could be impacted on negatively when flow is regulated by humans. A flow-regulating dam such as Inanda in the lower part of the Umgeni catchment, would therefore not only represent a formidable physical obstacle to migration, but would also block the natural signals that stimulate the eels to migrate up the rivers.

If the eels are fortunate enough to overcome all these dangers, threats and barriers, they still have to ultimately go back to the sea to breed! Unfortunately, we have very little data and information on this part of their ecology as it relates to east/southern Africa.

The threat of trade

Across the globe with the fortunate exception of southern Africa, freshwater eels are considered a delicacy and have a high economic value. The eel fishing industry in southern Africa is generally opportunistic and we only have anecdotal information on its activities. The previous lack of local research into the species could also be possibly linked to the absence of any significant commercial interest compared to Asia or Europe.

Have you ever heard of Angulas or Unagi? These are highly sought-after traditional dishes in Europe and Japan respectively. To give you an example, a small portion of Angulas in the Basque country in France/Spain can cost up to 35 euro (approximately R550). With European eels being overfished their stocks have been depleting dramatically such that the European Eel (A. Anguilla) is now critically endangered and a few years ago the European Union banned their export to international markets.

This, together with a constantly increasing demand from the Asian market, has resulted in a growing interest from international investors to farm the African Longfin eels, (A. mossambica). Some countries from the region (including Madagascar) have recently entered the global trade and could potentially play a significant role in the fate of Longfin eels in the coming years.

Longfin Eel in hiding!

Photo: Dr Jeremy Shelton FRCSA

The value of legends and myths

Dealing with eels is not just about facts and figures! There is a legend that I really like, and it has to do with the famous Howick Falls and the story of the mythical Inkanyamba! The Inkanyamba is a legendary river “monster” in both Xhosa and Zulu folklore and has brought fear and awe for many generations. These legendary monsters are inspired by local eels which are believed to live at the bottom of huge waterfalls. Legend has it that they are migratory and travel overland – Yes, eels can move overland! They are also believed to be able to control the weather and have been associated with seasonal storms and drought. The Inkanyamba are feared as it is believed that disturbing them would lead to great disaster.

Another very famous legend is that of Nyami Nyami the river god who stalled the construction of Kariba Dam. The following extract is from Zambezi.com – Tourist information about the Nyami Nyami, The Zambezi Travel & Safari Co.

“Nyami Nyami otherwise known as the Zambezi River God or Zambezi Snake spirit is one of the most important gods of the Tonga people. Nyami Nyami is believed to protect the Tonga people and give them sustenance in difficult times. The River God is usually portrayed as male.

Variously described as having the body of a snake and the head of a fish, a whirlpool or a river dragon, the Nyami Nyami is seen as the god of Zambezi Valley and the river before the creation of the Kariba Dam. The Nyami Nyami is regularly depicted as a snake-like being or dragon-like creature with a snake’s torso and the head of a fish. It can be found as pendants on jewelry, usually carved out of wood, stone or bone, occasionally ivory, silver or gold both as a fashion accessory and as a good luck charm similar to the wearing of a St Christopher medallion. Elaborate traditionally carved walking sticks depicting the Nyami Nyami and its relationship with the valley’s inhabitants are popular with tourists visiting Zambia and have historically been given as gifts to prestigious visitors.

It is the traditional role of tribal elders and spirit mediums to intercede on behalf the inhabitants of the river valley when Nyami Nyami is angered.

The Nyami Nyami is said to reside in the Zambezi River and control the life in and on the river. The spirits of Nyami Nyami and his wife residing in the Kariba Gorge are God and Goddess of the underworld. The Tonga people believe the building of the Kariba Dam deeply offended Nyami Nyami, separating him from his wife. The regular flooding and many deaths during the dam’s construction were attributed to his wrath. After the Dam was completed the Tonga believe that Nyami Nyami withdrew from the world of men.”

Similar legends can be found in many other parts of the world including New Zealand and most of the Pacific Islands where they are also considered to be sacred and are important tourist attractions. These stories should not be allowed to fade away and leave place to indifference as they can be relevant and important when it comes to conservation.

A way forward

I hope that this article and the enormous challenges I have described that our beautiful eels have to face have not depressed you with regard to their future! There are a number of research projects currently underway and we hope to close the gap in our knowledge to ensure better conservation and management of our river health and all the fish that live in them. A very positive aspect of eels is that, aside from their charisma, they are also considered to be an “umbrella” species which means that if conditions are good for eels then it is likely that a whole range of other species will also be in a healthy state.

So just imagine an eel carrying an umbrella giving shelter to all the other species in our rivers. Any conservation effort we undertake for eels will have a direct spin-off for other species and that includes us humans as well!

Let’s connect people, rivers and fish (well, eels!).

A great photo of a healthy A. mossambica in a very clear stream in the Western Cape

Dr Jeremy Shelton FRCSA

About the author

Céline Hanzen is a PhD candidate at UKZN Pietermaritzburg. She studied at the University of Liege (Belgium) where she obtained her BSc Biological Sciences and MSc Biology.

She is currently researching the “Distribution, genetic diversity and behavioural ecology of freshwater eels and implications for river management in KwaZulu-Natal” under the supervision of Dr G O’Brien and Prof CT Downs.