In search of the optimal management strategy for Arabian oryx

Extirpated from the wild in 1972 by overhunting, Arabian oryx (Oryx leucory x) were re-introduced in Saudi Arabia in March 1990; 17 oryx were released into Mahazat as-Sayd, a 2244 km(2) fenced reserve in west-central Arabia, w hich lies at the periphery of their historical home range. The population h as increased to 346 animals. The National Commission for Wildlife Conservat ion and Development. and those that manage the herd, have recently asked, ' What is the optimal management strategy to assure long-term persistence of the species, given the absence of immigration and predation?' Food resource s, determinants of rates of mortality and birth, covary with unpredictable rainfall in Mahazat as-Sayd. Using data-driven assumptions, we developed a computer model that evaluated the probability of extinction (P-ex) under va rious management strategies: no intervention, removing a fixed number of an imals each year, removing a fixed percentage of animals each year, and remo ving all individuals above a threshold. In addition, we explored the probab ility that oryx populations would decline below two thresholds, called the probability of quasi-extinction (Pq-ex) under various management schemes. O ur analyses suggested that, without intervention, the oryx population had a high P-ex, Removing 15% of the current population provided a low P-ex, but this method also produced high values for Pq-ex and, as a by-product, wide fluctuations in population size (N). Although it required an assessment of both N and carrying capacity (K), the most successful management plan cons isted of removing all oryx above 70% of K. Adoption of this plan resulted i n low P-ex, low Pq-ex, and smaller fluctuations in N. Our study may provide a useful model for evaluating management plans for a variety of threatened animal populations in desert ecosystems.