The distribution, conservation status and blood biochemistry of Nile crocodiles in the Olifants river system, Mpumalanga, South Africa

Abstract

The outlook for Nile crocodiles in the Olifants River does not look optimistic. Since the increase in capacity of the Loskop and Flag Boshielo Dams, the crocodile population was left with no basking or nesting sites and has declined over the past 30 years. Shortly after the Massingire Dam in Moçambique filled to full capacity an estimated 160 crocodiles died in the Olifants River Gorge, a couple of kilometres upstream from the dam. The Olifants River is acknowledged by many experts as one of the most polluted rivers in South Africa and acid mine drainage, industrial pollution and untreated sewage in the river are all contributing to the poor water quality of the river. Further, the Department of Water Affairs and Forestry acknowledge that water demand already exceeds their capacity to supply and that the situation will worsen considerably in the near future. Aerial surveys of Nile crocodiles in the Olifants River was carried out during December 2005 and November 2009. An average total population of 714 Nile crocodiles were counted and corrected to an estimated 1140 individual crocodiles to eliminate the effects of undercounting. The Kruger National Park and specifically the area of the Olifants River Gorge was found to be one of the preferred habitat areas for crocodiles in the Olifants River as was the Flag Boshielo Dam, the area between the Blyde River and the western boundary of the Kruger National Park and the Olifants River between the Loskop Dam and the Flag Boshielo Dam. Repeated nesting in areas such as the Kruger National Park, the Flag Boshielo Dam and the Olifants River between the Loskop Dam and the Flag Boshielo Dam confirmed that these areas are critically important to the nesting success of Nile crocodiles in the Olifants River. The Elands River was confirmed as an important refuge area for Nile crocodiles in the Groblersdal-Flag Boshielo Dam area of the Olifants River. Surveys revealed an estimated total of only 15 crocodiles in the Loskop Dam and confirmed that no crocodiles in the large (2.1 - 4.0m TL) and very large size class (>4.0m TL) are currently present in the population. Blood biochemistry results indicate that the Olifants River Nile crocodile population probably suffers from chronic inflammation (especially in the Loskop Dam and Olifants River Gorge populations), infectious disease (particularly in the Loskop Dam population but all other sites also showed elevated values), possible inadequate diet and malnutrition (especially during the pansteatitis outbreak of August/September 2008) and are suffering serious immune problems in the Olifants River Gorge. A conservation and management plan is suggested which identifies threats to the continued existence of a viable Nile crocodile population in the Olifants River. Finally, it is suggested that the conservation status and risk of extinction of Nile crocodiles in the Olifants River be upgraded to the Endangered category since it currently complies to the following criteria; EN A2abce; C2a(i) published in the IUCN Red List Categories and Criteria Version 3.1 (IUCN, 2001).