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April 2004

Feature

 

African freshwater eels - new tools in environmental education

Dr Jim Cambray

Eels - few other animals have life cycles which depend on maintaining extensive pathways through oceans, estuaries and freshwater habitats. Life cycles which take so long to complete. Break one link in that cycle and an entire generation of eels might disappear. Dr Jim Cambray discusses the life cycles of these amazing creatures and how their story can be used towards effective environmental education.

A species of freshwater eels in a netThe health of our freshwater systems is an index of the health of our environment as a whole.

Three thousand of the 10 000 known freshwater fish species in the world are in danger of extinction in 30 years time. South Africa has a high number of threatened freshwater fish species. As far as we know none of the species of freshwater eels which occur in southern Africa are at the present threatened. However, the precautionary principle needs to be applied as we do not know enough about these fish.

There are 16 species of freshwater eels, family Anguillidae, in the world. We have four of these species in southern Africa. In terms of commercial fisheries they are divided into a potential of 7 eel fisheries around the world of which the African one is the last 'virgin' eel fisheries to be fished. It is worrying that two of the six eel fisheries being fished are in trouble due to a variety of factors. Detailed and long-term research is required on the African eels before they are exploited. Their numbers might already be severely reduced due to impoundments along our rivers, water abstraction, pollution, alien invasive predaceous fish species such as black bass and catfish and a host of other changes which we have done to our river systems which are the 'life-blood' of the freshwater eels. If they go below a certain critical number they might just disappear and their journey will be no more!

Slippa and Slippery

Freshwater eels have a very interesting life cycle which takes them on a long journey from their spawning grounds in the ocean north of Madagascar to high up in some of our river systems and then back again to the ocean off Madagascar to spawn. In Cambray's freshwater fish surveys he met many farmers who have seen the little elvers and the large eels in their rivers and thought that the eels bred in the rivers. Their lack of knowledge about the life history of these fish prompted Cambray to write an educational booklet on African freshwater eels.

The booklet is entitled "Slippa and Slippery - The adventures of two freshwater eels on the long swim for survival." In this booklet the story of the fascinating life history of our freshwater eels is told. The booklet is written in a story format with a father telling his two children about how two eels, Slippa and Slippery, make their way from the spawning grounds off the coast of Madagascar to a river system in South Africa and then back again to spawn. Many problems and dangers are encountered along the way including anglers, alien fish, crabs, weirs, poachers and even an Albany Museum ichthyologist! Many of these encounters are based on actual experiences I have had or observed along the river over the past 20 years. This booklet is well illustrated by the talented wildlife artist, the late Ray Black. At the end of the booklet are a number of fun activities which will help to reinforce the understanding of the eels life history. There is a quiz, a board game, an eel life history and teamwork exercise, eel life history puzzle and the freshwater eel geography lesson. In addition to this booklet on freshwater eels there is a pack of informative overhead notes which can be used by teachers. There is also a useful glossary and a section on interesting eel facts. Did you know that some Europeans used to think that skin rubbed with eel oil caused one to see fairies!

The life history cycle of freshwater eels

Enter here for the full imageOur four African freshwater eels breed in the ocean off Madagascar. The eggs develop into larval eels called leptocepalli (singular leptocephallus) and are leaf like and float with the currents along the African coast. They change into glass eels which are see through and one can see the internal organs of the fish. They sense the freshwater and move into our river systems and become a brownish grey. They move at night up the river systems with females travelling the furthest upstream. Males may stay as long as 8-10 years in freshwater and females up to 20 years. This is why they are called freshwater eels as they spend the majority of their life in freshwater BUT have to migrate out to sea to breed.

The four African eels provide a great challenge to us all for they provide a true test of functioning ecosystems and public responsibility.

Few other animals have life cycles which depend on maintaining "extensive pathways" through oceans, estuaries and freshwater habitats. Life cycles which take so long to complete. Break one link in that cycle and an entire generation of eels might disappear.

Responsibility for this life cycle rests with all who share any part of the "extensive pathway". While a pollution event on the high seas would require national input - the effect of "uninformed persons" should not be discounted. For example - injudicious (sp) chemical spraying for mosquitoes outside a holiday home on an estuary; a flooded cattle dip or a diesel spill from a hospital boiler. There is also the likelihood of over fishing by commercial concerns. All feasible human errors with possible long term effects.

This book is intended to make South Africans aware of the wondrous, but easily disturbed, life-cycle of our African freshwater eels.


More information:

Booklet available from the Albany Museum @ R10 plus postage. Contact: J.Cambray@ru.ac.za; phone Pat Black @ 046 6222312; Fax: 046 6222398.

Freshwater environmental education resources from WWF, Sharenet and the Makana Biodiversity Centre of the Albany Museum

 

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