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Namibia: Managing Game for Optimal Production and Sustainability
By Dr Ulf Tubbesing, 1 June 2012

opinion


Introduction

Over the past 30 years game ranching in southern Africa has shown extensive growth, with a major beneficial impact on conservation as well as the economy.

But fragmentation of habitat by game fences, over-exploitation of trophy animals and poor management techniques pose a serious threat to the genetic make-up and quality of our wildlife.

The growing international tendency of people to visit countries that still support vast and unspoilt natural landscape and wildlife holds much promise for Namibia (e.g. Namibia voted world's top travel destination by UK-based Wanderlust travel magazine in 2011). I predict that game ranching has an excellent future and will grow from strength to strength.

Fragmentation of habitat

With the transition to game ranching, the perimeter fences around many farms have been replaced by "game proof" fences with the following "benefits" to the land owner:

Legislation gives ownership over the game as well as a greater control and authority regarding the hunting, capturing and selling of game on his or her land.

They ensure that game purchased at great cost will stay on the farm.

For some species (wildebeest) a double fence is "prescribed" by Veterinary Services.

An often overlooked, yet serious negative effect of game fences is that they effectively fragment the habitat of wild animals. This hinders both the dispersal of groups or individuals (usually male and offspring from maternal herds), as well as migrations, thus limiting the breeding between individuals of neighbouring, non-related populations. Inbreeding is the obvious consequence.

Consequences of small population size

In small, isolated populations mating amongst relatives and inbreeding are unavoidable. These populations suffer from accelerated inbreeding and loss of genetic diversity leading to reduced reproductive fitness (inbreeding depression).

Example: Six years ago a farmer purchased and released 3 giraffes (1 bull and 2 cows) on his farm. This original founder group has now grown to a total of 13 animals (4 successive calves by each cow and then in the last two years the first born heifers were mated by their father and have now also calved). Inbreeding is obvious!

What makes this case even worse is that, in all probability the founder group would have originated from the same farm (since capture and transport costs are thus optimised). Their herd of origin most likely also grew from a small nucleus like the one under discussion. To manage his giraffe population, the farmer now sells 2 bulls and 2 cows (most likely to a single new buyer) etc.

When considering the risk of inbreeding one has to look at the effective population size (Ne) of the species in question. This consists only of the effectively breeding animals (sexually mature and active) within the population thus making a genetic contribution towards the next generation. It is heavily influenced by the sex ratio in the population and is much smaller than the actual population size obtained by a game count. A hartebeest herd of 29 animals which comprises 15 sexually mature cows, one breeding bull and 13 sub-adults would have an Ne = 4(15)/16 = 3,75. The loss of genetic diversity within a small, inbred population is not regained as the population grows in number.

Example: 10 years ago a farmer bought and released 60 red hartebeest on his farm. He allowed this population to grow to about 200 (over 6 years with a 30% annual population growth and some trophy take-off). In addition to an annual trophy harvest of 10 bulls, he now has 50 hartebeest captured and sold annually to "manage" the hartebeest population on his farm. Since he considers his hartebeest herd to be of adequate size and stable, no new animals were ever brought into the herd. What do you think of the overall genetic composition of his herd? If this were your farm, what would you do?)

Avoid cross-breeding between sub-species

The cross-breeding between closely related species and or sub-species is another serious conservation concern. Species at highest risk in southern Africa are:
Black and blue wildebeest;
Plains and mountain zebra;
Common and black-face impala;
Blesbok and bontebok;
Waterbuck and lechwe.

A typical example of such a problem is where, due to veterinary fence specifications, both blue and black wildebeest (or other species mentioned above) are commonly kept together in a relatively small "wildebeest/game camp".

Blue wildebeest bulls, with their larger size, easily dominate the black wildebeest bulls and may successfully mate with black wildebeest cows, resulting in hybrid offspring. This situation is aggravated through irresponsible trophy hunting, where dominant bulls/stallions are removed from breeding herds, leaving them "open for abuse" by males from another sub-species.

The common sense solution to this potential problem is to avoid keeping these closely related species on the same (small) property or, more importantly in close proximity.

Plan your trophy take-off carefully. The trophy of a hybrid animal is essentially worthless!

Dr Ulf Tubbesing, Veterinarian, Game Rancher & Game Dealer.