All About Animals

Traditional harvesting – In Kenya, the indigenous Pokomo people have eaten crocodile meat and eggs, but the increasing Pokomo population is placing additional pressure on numbers. Uncontrolled use of crocodiles for traditional medicine such as blood, fat, brains and other organs is posing  pressures on some populations.

Human-crocodile conflict – They are a large predator and the recovery of numbers in close proximity to an increasing human population often results in fatal conflicts. 2015 statistics compiled within CrocBITE report 58 fatal and 29 non-fatal attacks. However, reporting of attacks, both fatal and non-fatal, is poor across the range states of C. niloticus, so these numbers are conservative. It has been estimated that over 250 human fatalities occur each year in Kenya alone. Retaliation killings of crocodiles are common across range states.

Land use – They attack cattle as they drink at the water’s edge. In retaliation, Kenyan pastoralists have started to kill crocodiles using pesticide-laced meat in order to preserve their cattle herd. Furthermore, fishermen trap crocodiles with hooks, nets and laced bait and use the crocodile meat as baits for their fish traps, although considerable effort has been made by the Kenya Wildlife Service and the private sector (Nile Crocodiles Ltd) since 2014 to stop this practice. Similar land use pressures are occurring in Botswana, Madagascar (CITES 2016), Namibia, South Africa and Zimbabwe. Larger anthropogenic interference also alters population processes. For example, the Pongolapoort Dam in Ndumo Game Reserve, completed in 1972, allows artificial control of water flow rates and subsequent flooding. One consequence is that during flood events, the natural watercourse is diverted away from historical nesting grounds.

Food – unregulated or illegal overfishing in many range states is depleting fish stocks, which could have detrimental effects on populations.

 

Pollution – Increased nutrient and sediment profiles of the water column of the Olifants River, South Africa due to upstream mining, industrial and agricultural activities, and urbanisation. These have caused isolated large-scale fish mortality incidents. Histopathological investigation of dead crocodiles were found to have fed on these dead fish and succumbed to pansteatitis. Additional mining leases have been granted in the upper Olifants River and unless environmental protection mechanisms are implemented, the aquatic health may continue to decline. Similar pollution concerns are being raised in the South East Lowveld region in Zimbabwe, where rivers flow through large sugar plantations and fish health is starting to decline due to contamination with agricultural chemicals and fertilisers. Lead uptake by the ingestion of fishing sinkers has also been reported.

Invasive weeds – In 2001 it was reported that the invasive Triffid/Siam Weed, Chromolaena odorata, is found in Lake St. Lucia within the iSimangaliso (previously Greater St. Lucia) Wetland Park in South Africa. The weed could be detrimental in a number of ways. First, it was noted that many females were trying to dig holes to lay their eggs but could not dig through the fibrous root mats. Second, if the roots could be avoided, Chromolaena odorata shaded the nests reducing their average temperature by 5-6oC cooler relative to sun-exposed nests. Like all crocodilians, sex ratios  are determined by incubation temperature and nests shaded. Furthermore, as in other crocodilian species, hatchlings resulting from less than ideal incubation conditions can have a higher frequency of abnormalities, in addition to influences on post-hatching body size, residual yolk mass, growth and thermoregulatory behaviour. The worst case scenario is complete embryonic developmental failure (death) due to sub-optimal temperatures. Ezemvelo KZN Wildlife, the provincial conservation agency, have a programme to annually eradicate C. odorata from known nesting areas along the Mphathe Stream a few months prior to crocodile nesting. It was found that females do return to cleared sites for oviposition.

Habitat destruction – The habitat of Nile Crocodiles is being modified in numerous ways. For example, the Lake Flag Boshielo dam wall (South Africa) was raised by five meters in 2005 and the resultant rise in water level flooded the existing basking sites of the resident population; within four years the population had decreased from 135 individuals to 98, which was also reflected in the adult population. A similar situation was reported in the Ndumo Game Reserve (South Africa) after the construction of Pongolapoort Dam, which artificially controls water flow rates and subsequent flooding that has diverted the natural watercourse away from historical nesting grounds. In contrast, the construction of the Aswan Dam, Egypt have led to population expansions of Nile crocodiles there. Another example of habitat destruction is in Kenya and Madagascar where people are moving towards the river to cut out small plots to live and grow crops, leading not only reduced crocodile (nesting) habitat but exacerbating human-crocodile conflicts. Other habitat loss includes siltation of rivers due to anthropogenic factors such as clearing, burning and subsequent erosion.