Manyeleti Crocodile Survey

Apr 2, 2012

MISSION  06 of  2012

Name of Mission: Manyeleti Crocodile Survey
Date of Mission: 3 April 2012
Pilot: Martin den Dunnen     
Aircraft used: Cessna 206        
Beneficiary: Dr Hannes Botha of the Scientific Services Division of the Mpumalanga Tourism and Parks Agency   

The objective of the flight:

The first objective of the flight was to establish the extent of damage to Main Camp Dam at Manyeleti after the flood event during January 2012; the second objective was to determine the population size and structure of the current Nile crocodile population present in Main Camp Dam.

Beneficiary’s report by             Dr Hannes Botha of the Scientific Services Division of the Mpumalanga Tourism and Parks Agency

The Nile crocodile population of Main Camp Dam in Manyeleti was last surveyed during October 2011 Results from that survey showed that 37 crocodiles were counted and that the adjusted total to include the possible undercount could be about 57 individual animals Based on this information, a detailed research programme was developed to investigate the biology and eco-toxicology of this population of crocodiles Main Camp Dam consists of two parts, a northern section situated on the Mthlowa stream and a southern section situated on the Nwaswitsonto StreamThe two sections share an L-shaped wall where they meet

Manyeleti Nile Crocodile IMG 6704
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The Mpumalanga Lowveld received heavy rains during January 2012 due to Cyclone Funso moving over central Mozambique from the Indian Ocean Over the four days from 16th January to 20th January a total of 311 mm of rain was measured at Manyeleti’s Main Camp However, a total of 345 mm of rain was measured near the source of the Nwaswitsonto Stream in the catchment of Main Camp Dam Consequently, on the 19th January 2012, the wall of the southern section of Main Camp Dam broke for the first time since its construction in 1976 The breech of the dam wall left the southern section of Main Camp Dam completely dry and field staff could not locate any crocodiles in this part of the dam Therefore it became critically important to survey the dam again from the air to inspect the extent of the damage to the southern section of the dam and to determine a baseline in terms of the size and structure of the Nile crocodile population currently present in the dam, and, based on that information, to gauge the effect of the flood damage on the Main Camp Dam Nile crocodile population and whether the proposed research programme can still be considered viable    

Manyeleti Nile Crocodile IMG 6725
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The first attempt to survey the area was made on 16th March 2012 but due to low cloud formations the pilot Martin den Dunnen could not reach the Manyeleti airstrip from Hoedspruit and had to abandon the flight A decision was taken to make a second attempt at surveying the dam on the 20th March 2012 – but this time my vehicle broke down and again the survey had to be postponed Finally, on the 3rd April 2012 we managed to get everything together and with fine open skies we flew over Main Camp Dam for about 15 to 20 minutes in Martin’s Cessna 206.

During the flight, we counted a total of 15 individual Nile crocodiles, four of these were between 1.5 and 2.0 metres long, 10 were between 2.0 and 4.0 metres long and 1 animal was over 4.0 metres in length Adjusting the total number of crocodiles seen, to account for the undercount, we estimate that about 23 Nile crocodiles currently still occur in the northern section of Main Camp Dam and none in the southern section of the dam

Was the objective met?          

Manyeleti Nile Crocodile IMG 6980
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The survey is considered successful because we managed to confirm that the southern section of Main Camp Dam was destroyed by floodwaters, leaving it with no water at all. But the northern section of the dam remain intact and does have a fair number of crocodiles. Therefore, clearly the flood events that occurred in January 2012 changed the distribution of the Nile crocodile population in Main Camp Dam dramatically. Further, the crocodile population is now somewhat smaller than during the 2011 survey – 32% of the crocodiles counted in 2011 are now unaccounted for. The difference in numbers spotted during the two surveys is due to 13 crocodiles in the under 1.5 m total length size class that were not seen during the 2012 survey. In fact not a single crocodile in this size class were spotted during the 2012 survey. This explains the change in the population structure from what seemed to be a stable population to one possibly indicating a declining population. Further follow-up surveys should be done to confirm the change in distribution, population structure and population size.

This up to date information will be used to make informed decisions regarding the proposed research on crocodiles as sentinel species for a range of adverse environmental impacts including major threats to public health.

The Scientific Services Division of the Mpumalanga Tourism and Parks Agency wishes to thank The Bateleurs for their extensive support and for making possible the survey of Nile crocodiles in Main Camp Dam at Manyeleti Game Reserve. We also wish to thank Martin den Dunnen for his time and flying skills which made the survey hugely successful.

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