SOME
OBSERVATIONS ON MATUSADONA SHORELINE ISSUES
I understand that concerns have been expressed with regard to perceived declines of some plains game species within the Matusadona National Park; and the possible need for a hippo cull has been mooted by African Parks. This raises some complex issues, which I will try to deal with as briefly as possible; but before doing so it is worth noting the population estimates shown in 2014 Sebungwe surveys. These reported 59 zebra across the entire Park, all concentrated in the Matusadona hills (i.e. the escarpment southwards). None were recorded on the lowland/lakeshore components). As for eland: none at all were recorded within the Park.
However, the survey report also notes major declines in a range of species between 2001 (the previous comparable survey) and 2014. These include elephant (±70% decline); zebra (80% decline); waterbuck (58% decline); sable (80% decline); kudu (93% decline); and impala (62% decline). The report also notes that in most cases the declines started before 2001.
The following notes are primarily based on personal observation, but as a ”start point” it’s worth noting the following chart of lake levels during the history of the Kariba dam:
This shows that, with relatively minor variations, the lake remained at fairly high levels from 1964 until 1982. My own experiences began in ca. 1979, when – subjectively – there were few, if any, major concentrations of, or foci for, any lakeshore species. One had to look hard for wildlife on “game drives”, whether by boat or vehicle.
The dramatic decline of lake levels in 1982 brought about the equally dramatic changes in foreshore sightings and species populations experienced between then and the 1990’s. As I have written elsewhere (see https://matusamana.blogspot.com/) these low lake levels saw an explosion of grazers in particular. Dr Russell Taylor is the key authority on this but, as I recall, he cited a buffalo growth rate of 10% per annum for several years. Predators followed suit, and by the early 1990’s Matusadona held Africa’s second highest density of lions on its lowland portion.
This was followed by an equally dramatic population crash when the sequence of drought years ended in the ‘90’s; and – again subjectively – lakeshore sightings reverted to the scenario I had noted when I first visited the Park in the late 1970’s.
The salient point that has to be understood is that the Matusadona lakeshore – the Park’s prime tourism area – is a human artefact created by the lake and hence by the dam itself. The dam and its management are crucial factors in the well-being or otherwise of valuable once-natural ecosystem components both upstream and downstream - e.g. the Mana Pools alluvial terraces and the Matusadona foreshore & lowlands.
As a first point, then, it is equally important to note that, as things stand, the Kariba dam is currently managed solely for power generation, without consideration for any environmental issues that may arise. It’s worth noting that, broadly speaking, large releases through the dam can, if well-timed, be beneficial both upstream (by exposing Matusadona lakeshore areas) and downstream (by rejuvenating the Mana alluvial terraces).
It may therefore be useful for the Zambezi Society to consider approaching the Zambezi River Authority (ZRA) with a view to incorporating an environmental component into dam management . However, that is not the whole story. In the case of the Matusadona, confounding factors arise in the form of natural progression. The lakeshore populations depend primarily on the development of palatable grasses as lake levels fall. This area was initially colonised primarily by Panicum repens (torpedo grass), which most grazers consider extremely palatable. More recently, though, Panicum has – by observation – increasingly been replaced by considerable areas of various other forbs and grasses, many apparently unpalatable; thus – by inference – accompanied by growing grazing pressure on such Panicum as still develops.
As regards hippo: the 2014 survey quotes a Matusadona population of 404 animals, which – by definition – occur almost entirely on the Park shoreline (although they can range a surprising distance inland as well, if pressed for fodder). A hippo can eat up to 70kg of grass per day, which comes to a ballpark total of 28 tonnes per day. This – on the face of it – makes them a prime candidate for a “population reduction exercise” – i.e. a cull.
However, a fair number of elephant – around 500, according to the 2014 survey, also focused largely on the lakeshore - can also eat around 100kg a day. That includes browse, of course, and I don’t know how many have been lost to poaching since the survey, but in May this year we were regularly seeing groups of up to ten animals on the foreshore in the Palm Bay and Elephant Point areas. They can’t be ignored, either. All in all, the situation calls for some careful management planning.
Dick Pitman
THE ZAMBEZI SOCIETY
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