Adaptive methods for quota setting

An adaptive management system is likely to be far more robust than a system based on population estimates (Holling 1978, Bell 1986, Martin 1999). Firstly, because the confidence intervals on population estimates are very large. Secondly, the area of interest is not the total number of animals in the population but the number of adult males older than (say) 5 years – which is only about 3% of the population.

1. Age of Trophies

The key parameter to be monitored is the age of trophies taken from the population. If a criterion is set that there should always be a sufficient number of prime breeding males, then the requirement is that amongst the trophies (regardless of the selectivity of the hunting regime) there should be a representative number of males in the age classes above 5 years old. As soon as the cohort of hunted animals is missing all of the age classes older than 5 years of age, this is a robust indicator that the population is being overhunted and the quota should be reduced.

An initial quota might be set by applying 3% to the population estimate but thereafter that quota should be adjusted upwards or downwards by the empirical data derived from measuring trophies.

No methods of ageing animals from their dentition have been described for reedbuck, waterbuck, lechwe and puku. Horn measurements can be used initially while developing ageing criteria based on dentition.

2. Adult sex ratios

.It is assuemed, that as long as the ratio of adult females to adult males does not exceed 3:1 quotas are sustainable. To apply such a system entails no more than the collection of sufficient field observations towards the end of the hunting season to be able to calculate the adult sex ratio within reasonable confidence limits. However, the method assumes that the age-specific parameters used in the population model are somewhere near correct. The technique could be improved by collecting field observations throughout the hunting season and observing the change in adult sex ratios in the course of this. Taking this a step further, this data could be collected as part of the monitoring of population numbers through a road strip count method or a line transect patrolling system. Both of these methods could be applied by local community monitoring staff with some training. It is logical that conservancies should take on this monitoring rôle in all areas where the species are hunted in conservancies since it is effectively their resource.18 In State protected areas where there is hunting this would be the responsibility of the parks staff.