Croc Boffs Plan to Stick with Scaly Things

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UKZN has several research projects examining various aspects of the Nile crocodile emanating from the laboratory of terrestrial vertebrate biologist, Professor Colleen Downs of the School of Life Sciences in Pietermaritzburg.   

Postgraduate student research has been of key importance in the implementation and success of Downs’ Zululand Nile Crocodile work, with the emergence of many important and novel contributions to the understanding of these top predators and their role in ecosystems. 

Two such projects reached a successful conclusion when their authors, Mr Mark Summers and Dr Jonathan Warner, were capped with an MSc in Ecological Sciences and a PhD in Zoology respectively.  

Although Nile crocodiles are apex predators which occur throughout Africa in many aquatic ecosystems, their feeding ecology is poorly understood, along with the species’ risk of exposure to environmental contaminants such as heavy metals. Recent population declines of Nile crocodiles in South Africa have underscored the ecological value of this important predator to aquatic ecosystem health and function. This topic formed the basis of Warner`s PhD research. 

Working at Lake St Lucia, Kosi Bay and Ndumo Game Reserve, which are home to the largest crocodile populations in KwaZulu-Natal, Warner and his team captured 322 Nile crocodiles to help gain the knowledge of individual body size, sex and a range of other data for analyses of animal population demographics and size structure. 

Warner collected and analysed blood samples from 34 sub-adult and adult free-ranging Nile crocodiles for levels of lead concentrations. It was found that on average, crocodiles had higher levels of lead at Lake St Lucia than at Ndumo Game Reserve or Kosi Bay. This was attributed to lead sinker ingestion during gastrolith acquisition and to a lesser extent, fishing-bait theft. 

No clinical effects of lead toxicities were observed in these crocodiles, even though the highest levels of lead represented the most elevated levels of lead in blood recorded to date for any tissue in any free-ranging vertebrate. The data and field observations suggested adult Nile crocodiles were likely tolerant of elevated lead body burdens, but experimental studies on other crocodilian species suggested the lead levels in blood may have harmful or fatal effects to egg development and hatchling health. 

Master’s research by Summers’ was based at Pongolapoort Dam in Zululand and investigated the numbers, nesting ecology and behavioural aspects of gaping in Nile crocodiles. 

The study showed that the population of Nile crocodiles in the dam is increasing and remains in a healthy state compared with other populations in South Africa. Insights into their behaviour may be applicable to other crocodilian taxa. 

Both men were full of praise for ‘the tremendous supervisor support’ they received from Downs, the availability of resources and the level of research expertise at UKZN as well as its proximity to their study sites in Zululand and the School’s encouragement of full-time field work.  

In closing, Warner said:  ‘Crocodile research is physically demanding, time-consuming, and often dangerous. But I’ve been privileged to work with some very competent and fun people in the field.’ 

 Steve Camp

Pic: Shannon Wild