A pilot study was launched in 1993 to determine the movements of crocodiles in the Olifants River in
Kruger National Park (KNP). This turned into a research project in 1994 and lasted for five years until
1998. The objectives of the study were to determine movement, study nesting preferences and to
investigate the possible effects of metal pollution in crocodiles.
The movements of the total population were studied by doing regular foot counts, four times per annum.
The basis for movement was found on the principle that a change in numbers signified movement. Foot
counts were supported by spot counts at three different locations in the study area at 14 day intervals.
The foot counts were done along a pre-determined route, followed with every count, and this resulted in
data indicating a definite change in numbers at certain times of the year. A comparison was made
between the movements of crocodiles in large bodies of open water (lakes & estuaries), a so called
"closed" system and the Olifants River or "open" system. There was a movement of the population
during August of every year, followed by another one in December/Jan and yet another in May. The
largest movement, in August, co-coincided with the prelude to mating and ultimately nesting.
The spot counts indicated that there was a smaller and probably localized movement during May and
December of each year. This corresponds to nesting behaviour and the flood status of the river. All
indications are that major movements took place during periods of high flow and thus during the rain
season (Sept - Feb). A major flood was experienced during February 1996 which changed the geomorphology of the river.
In addition to the foot and spot counts, eleven large adult crocodiles were fitted with radio transmitters to
monitor their movements for a period of one year (1997 -1998). The results indicated that movements
over large distances occurred. The longest distance covered was in access of 36 km. Some individuals
returned to the location of origin, thus completing a round trip from their point of departure. The majority
of crocodiles fitted with transmitters left the protection of KNP, spent time in neighbouring Mozambique and some returned to Kruger after an average period of three months. Indications are that there is a lack
of territorial dominance amongst large individuals at certain times of the year, allowing for less restricted
movement up and down the river. A difference was found between the movements of crocodiles in the
Olifants River as opposed to a large body of water eg. a lake or estuary.
The second objective was to collect data on nesting preference, nest content and egg dimensions. A
total of seven parameters were measured including slope, distance to water, height above water, soil
type, vegetation, exposure to direct sunlight and the size of the female. Besides these parameters, a
comparison was made between egg size, mass and length and the correlation with female size. The
results indicated that egg mass and length increased with an increase in female size. The average
clutch size was 34 eggs. A difference was found between two nesting years (1997 and 1998) with the
larger females nesting in 1998 (egg mass 122.7g). A higher rainfall was measured for 1998, leading to
the conclusion that smaller females nested during dryer years. The larger females, because of physical
abilities, dug deeper nests ,36 cm in 1998 as opposed to 25 cm in 1997. No difference was found
between nesting habits elsewhere in Africa and that in the Olifants River.
Twelve individuals of varying sizes ranging from 1.4 m to 4.1 m, were collected from three locations and
various tissue samples were analysed for metal content. Tissue from muscle, liver, kidney and fat were
analysed for Al, Cu, Cr, Fe, Mn, Ni, Pb, Section ranger and Zn. As this was the first data of its kind to be
collected, no meaningful conclusions could be reached, except to offer the data as base line data and for
future comparisons. There was however a correlation between Fe concentration in muscle tissue and
body size, total length (TL). An increase in TL resulted in an increase in Fe concentration. The opposite
were found with Fe in fat tissue. Smaller crocodiles (TL) had higher concentrations of Fe in their fat
tissues.
Besides the large amount of base line data that resulted from this study, it also highlighted the shortage of knowledge on this species, particularly in Kruger, to enable us to manage and protect them successfully. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10285 |
| Date | 20 December 2013 |
| Creators | Swanepoel, D. G. J. |
| Contributors | Ferguson, Neil S., Perrin, Michael R. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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