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Dissertation
The ecology and physiology of the Nile crocodile, Crocodylus niloticus, in Lake St. Lucia, Kwazulu/Natal, South Africa
Doctor of Philosophy (Ph.D.), Drexel University
1997
DOI:
https://doi.org/10.17918/00007821
Abstract
Lake St. Lucia, located in Kwazulu/Natal, South Africa, supports what appears to be a relatively stable population of the Nile crocodile, Crocodylus niloticus. Distribution of crocodiles [greater than or equal to]2.0 m in total length varied seasonally and from year to year and distribution patterns were influenced primarily by the availability of fresh water and the presence of humans. Fish made up the majority of the diet or the subadult/adult crocodiles in the lake system, followed by crustaceans. Six primary nesting areas were identified in the lake system. Although the population of adult crocodiles appeared to be stable only a small percentage of the mature females nested every year. The low reproductive effort may be directly related to food quality. Laboratory incubation of eggs and histology of gonads indicated that the lower and upper pivotal temperature for St. Lucia's Nile crocodiles was 31.7 and 34.5[degrees]C, respectively. Crocodylus niloticus therefore had a female:male:female pattern of temperature-dependent sex determination. Incubation period and relative developmental rate were strongly temperature dependent. The majority of nesting crocodiles selected open, sunny, sandy areas in which to deposit their eggs. Nests were only found in shaded sites in the Mpate river nesting area and these sites were shaded by an alien plant known as Chromolaena odorata. Shaded site temperatures were below the pivotal temperature for St. Lucia's crocodiles and nests therefore probably produced a female-biased sex ratio. This plant is posing a serious threat to the continued survival of the Nile crocodile in St. Lucia. Our osmoregulatory study demonstrated that the Nile crocodile has the physiological ability to survive and thrive in periodically hyperosmotic environments, and that this species is considerably more euryhaline than has been acknowledged previously. However, its euryhalinity is of a somewhat restricted nature in that acute exposure to sea water leads to dehydration, mass loss and possibly death, but with a short acclimation period at lower salinities it survives and thrives in sea water. We concluded this study with management recommendations for the St. Lucia Nile crocodile population.
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Details
- Title
- The ecology and physiology of the Nile crocodile, Crocodylus niloticus, in Lake St. Lucia, Kwazulu/Natal, South Africa
- Creators
- Alison Jane Leslie
- Contributors
- James Robert Spotila (Advisor) - Drexel University, Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xxix, 401 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Drexel University
- Other Identifier
- 991021889008904721