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Mputa and Mercury in East Africa (Episode 10: Fishy Ugandan Tales)

Over the past few months I have been conducting field work in the Lake Victoria basin, in Uganda, for my Masters research, which explores the topic of mercury contamination in Africa. In this series of blog posts I’ve shared pictures and discoveries about some of the most interesting wildlife and encounters I came across while here. For the final post of this series I thought I would share some stories about the specie that I’ve spent the most time with during these past months: the Nile perch, locally known as “Mputa”.

The Nile perch was introduced to Lake Victoria in the 50’s and 60’s for commercial fisheries and sport fishing.  Since this time, it has been fished by the tons annually, fuelling East Africa’s economy. The most incredible thing about these fish are their fast growth rates and the massive size they can reach. In Lake Victoria, fish over 100kg in mass are regularly caught. Even in the smaller satellite lakes surrounding Lake Victoria, like Lake Nabugabo, where I spent most of my summer, large perch are often pulled out of the water.  This summer, the biggest one caught by the local fishers of Nabugabo was 31kg.  I was with them when they pulled it out of the small wood canoe it was brought back to shore in.  Three men stood together to lift this massive creature. It was so big, they dropped it! When it was finally out of the canoe, I was really excited to get the chance to stand beside it and compare it’s size to mine. This is by far the biggest freshwater fish I have ever seen.

31kg Nile perch, caught in Lake Nabugabo, Uganda (Photo by Logan Smith)
31kg Nile perch, caught in Lake Nabugabo, Uganda (Photo by Logan Smith)

Although big fish like this are caught from time to time at Nabugabo, most Nile perch that I came across over the course of the summer were much smaller.

Juvenile Nile perch, caught in Lake Nabugabo, Uganda (Photo by Logan Smith)
Juvenile Nile perch, caught in Lake Nabugabo, Uganda (Photo by Logan Smith)

I was glad to get the chance to see such a broad range of fish sizes, as it will be really interesting to see how the size of the fish affects the mercury that’s found in their systems. I also spent a great deal of time looking for perch from different habitat types, as I’m particularly interested in seeing how habitat-use influences mercury contamination. I found perch swimming out in the open-water, by the forest-edge and at the edge of wetlands.

Open-Water Fishing on Lake Nabugabo, Uganda
Open-Water Fishing on Lake Nabugabo, Uganda
Forest-Edge Fishing on Lake Nabugabo, Uganda
Forest-Edge Fishing on Lake Nabugabo, Uganda
Working in the Wetlands Surrounding Lake Nabugabo, Uganda
Working in the Wetlands Surrounding Lake Nabugabo, Uganda

Now, back in Canada at McGill University, I will be bringing the Nile perch samples I’ve collected to the lab to determine their mercury concentrations. I am interested in this contaminant because it’s a potent neurotoxin that can have devastating effects on both wildlife and human health. Mercury’s availability in the environment has significantly increased over the past century as a results of human activities. It finds its way into aquatic ecosystems through the burning of forests and coal, the creation of reservoirs and mining activities. When there is too much mercury in our waterways, fish can end up confused, incapable of escaping predators and making young.  These negative effects can scale up to population and community level responses that can be devastating for entire ecosystems, as well as the fisheries industry.

In Africa, over two and half million people are engaged in activities related to fisheries and rely on them to ensure their livelihoods. Fish are also an accessible an essential food supply in many regions of the continent. In spite of this, little information is available on mercury contamination in Africa. Through the research I have been conducting in the Lake Victoria Basin, which is the largest tropical lake in the world and Africa’s largest inland fishery, I hope to help ensure the sustainability of the fisheries of Africa and improve our monitoring strategies of this potentially deadly contaminant.  In you are interested in following my research in the future you can visit my website at:

http://biology.mcgill.ca/grad/dalal/Site/Welcome_Bienvenue.html

Comments

  1. Anthony Ricigliano
    New York
    September 6, 2013, 3:21 pm

    Interesting. Love fishing.