Guest Contributor | Mar 20, 2018 | 0
Managing Game for Optimal Production and Sustainability – Part 2
The impact of (selective) game harvesting on population genetics
Our ancestors have transformed wild animals into highly productive domesticated cattle, sheep etc. as we know them today by selection of and breeding with individuals with desirable characteristics for breeding stock. The way we exploit our wild animals today will exert similar selection pressures on the future game populations.
Several studies concentrating on the production of trophy quality animals have proven the following basic principles:
Horn traits are heritable and passed from parents to offspring.
Trophy development is genetically based yet strongly environmentally influenced. Genes that lead to large horns in a good habitat will not automatically result in large horns in a habitat unsuitable for the species in question.
The largest-horned, males tend to be older, mature and dominant. They are better able to defend their harems and are thus the better breeding stock.
The males with the best genetic make-up for trophy production are likely to also be the fastest growers thus demonstrating good “trophy potential” at an earlier age.
Traits associated with large horns in bulls/rams are likely also linked to traits that increase reproductive fitness in females. Artificial selection for small horns may thus lead to poor reproductive performance at population level.
Paradoxically, injudicious trophy/biltong hunting (excessive shooting of pre-prime or prime breeding males), as it is commonly practised, culls those animals with the most desirable traits (big body and horns at an early stage). This selection pressure is in conflict with natural selection. It leads to those males with small bodies and horns remaining in the herd as future breeding bulls. This is likely to reduce the overall fitness of that population.
Probably the best researched and documented case of the evolutionary effects of trophy hunting on a species was done on an isolated bighorn sheep population at Ram Mountain, Alberta. Good statistics kept over 35 years, combined with pedigree and genetic data clearly demonstrate that bighorn rams now have body weight and horn lengths reduced by 20% and 26% respectively.
Management practices, e.g. trophy hunting and prescribe sex-specific “culling” which, if not done carefully, will have significant impacts on population sex ratio and dynamics. In the absence of mature breeding bulls/rams, the young males are usually still able to fertilize females.
However, studies documented the following harmful effects of such a herd composition:
Breeding herds, in the absence of mature males, tend to be excessively harassed by young males. This results in reduced food intake, poor condition and lowered conception rates as well as reduced survival of offspring.
Calving/lambing is delayed and less synchronous which may lower summer survival and autumn body condition of offspring, resulting in higher winter mortality.
In many species calving synchrony is an important strategy to lower predation rates. Protracted calving / lambing periods predispose the offspring to higher predation losses.
Genetic management of game
Minimise habitat fragmentation through the creation of larger open, unfenced game areas (conservancies) to enable free migration of animals.
To minimise inbreeding we must, when stocking up a game ranch, establish and maintain adequately sized populations, ideally originating from different founder groups, rather than stocking up with small groups of different species. We should, from time to time, introduce new stock into existing populations to maintain some genetic diversity.
In stock farming new genetic material is usually introduced by buying in a new breeding bull or ram. Except in very small (and expensive) groups of wild animals e.g. Rhino, Roan and Sable antelope, introducing new males into a breeding herd makes little sense for a number of reasons:
The stock farmer can buy high quality breeding bulls or rams from stud breeders. This is rarely the case with wild animals. Most game ranchers hold on to their prime males since their trophy value usually exceeds the price he would get in selling these animals alive.
To avoid fighting and losses between the old and new stud, the stock farmer will remove the old bull/ram from the herd before introducing the new breeding male. On a game ranch this is seldom possible. New bulls or rams purchased must thus first displace the resident studs from their herds. This will result in losses (mostly amongst the newly acquired stock) due to fighting. Breeding bulls or rams on stock farms also do not have the added handicap of doubling up as trophies.
Cows/ewes are usually cheaper than mature bulls and it is likely that these will, within the first season, all be covered by the dominant males on the property. Surely this is the better approach! Remember, females carry essentially the same genes as far as heritability of trophy quality etc is concerned.
New stock introduced to a game ranch should ideally originate from:
A herd genetically unrelated to the existing population. It is advisable to keep records of the origin of game bought in.
If at all possible the animals should originate from game of equal (at least) or superior genetic stock.
A similar habitat, to make the adaptation easier and less stressful.
Stock free of disease and parasites. This reduces the risk of introducing disease onto the farm (e.g. bringing in Kudu from an area with a current rabies outbreak is likely to infect your herd).
The potentially deleterious impact of selective (trophy) harvesting may be avoided by a practical and ethical approach to trophy hunting. Limit the trophy hunt to that part of the male population that is either showing undesirable characteristics (poor body and trophy size and conformation or disease) and/or old males that are beyond their prime breeding age.
Remember, good quality trophy males, just as a good red wine take time to mature and are thus a scarce and valuable commodity. We must treat them as such, look after them and charge the hunters accordingly. If we do this, the quality of Namibian trophies will improve and the revenues earned from the trophy hunt will increase. Selling trophies at a discounted rate (special offer) on a specific game ranch will, in time, have serious deleterious effect both on the quality and quantity of future trophies produced as well as the financial bottom line. If this malpractice takes on national proportions, it will soon wipe Namibia off the list of hunting destinations to visit.