Namibian crocodiles research

This video is called Underwater Encounter with the Nile Crocodile – Swimming with Crocodiles – Episode 1 – BBC Two.

From New Era (Windhoek):

Namibia: Study Quantifies River Crocs

By Irene !hoaës, 23 April 2013

A recent report on the Nile crocodile (Crocodylus niloticus), the only type of croc species in Namibia, revealed that the main crocodile sub-population occurs in the Caprivi Region with a population estimate of 1 314 crocodiles over 2 metres in size.

However, a significant percentage of this population occurs within international border waters and therefore is technically shared with neighbouring countries. An estimated 28 percent of Caprivi’s hippopotamus population theoretically belongs to neighbouring countries and it would be reasonable to assume a similar percentage for crocodiles, since the two species share a similar habitat.

Thus the estimated population size for northeastern Namibia, excluding the Okavango River population west of the Caprivi Region, is approximately 946 adult crocodiles. A study in 2011 estimated a male to female sex ratio of 1:1.3 in the Okavango Delta panhandle region of northern Botswana, and it would be reasonable to assume similar ratios for Namibia. If these assumptions are correct, there are approximately 529 adult female crocodiles and 417 males.

“It is important to note that this probably represents a conservative estimate,” a 2012 study by the ministry of environment and tourism states. In Namibia the Nile crocodile is protected and approximately 10 percent of the available crocodile habitat falls within or on the borders of protected areas. However in the Caprivi Region, 74.0 percent can be found in protected areas, while 12.0 percent can be found in conservancies and 14.0 percent in undesignated or communal land.

In Namibia, natural populations occur in the major river systems in the north of the country, including the Kunene, Kavango, Kwando, Chobe and Zambezi rivers. West of Caprivi, information on the status of crocodile populations is relatively lacking. Crocodiles occur throughout the course of the Namibian section of the Okavango River, but no systematic population surveys have taken place upstream of the Caprivi section.

The Okavango River supports the highest concentration of humans per kilometre of river frontage in northeastern Namibia, while crocodile densities show a strong negative correlation with human densities on this river, revealed 2004 and 2009 studies. “It is likely that direct and indirect human pressure is a significant conservation threat to the future of crocodiles living outside of protected areas on the Namibian section of the Okavango River,” according to the 2012 study report.

No crocodile surveys have been carried out on the Kunene River, however, data on human/crocodile conflict from conservancy event books and anecdotal accounts suggest the population is significant and stable along the entire Namibian section. The unique characteristics of this aquatic ecosystem and relative geographical isolation suggest there could be important biological and/or ecological differences in this sub-population.

Until such time as detailed population surveys can be carried out on the upper Okavango and Kunene rivers, it would be reasonable (and probably conservative) to assume that these river sections effectively double Namibia’s crocodile population. The Okavango crocodile population is linked to the East Caprivi population via the Selinda Spillway. Notable concentrations occur around the eastern Caprivi floodplains and Muhango National Park on the Okavango River.

In general, densities decline away from protected areas. River fertility and concentrations of fish and other natural prey species are probably the most important determinants of population density in most cases. “This would explain the persistent population along the Zambezi River section and the unexplained density variation between protected and non-protected areas,” states the report.

The Kwando River basin drains Kalahari quartzite soils and thus the river has a very low nutrient content. Crocodiles do not occur in the Orange River, most likely because the water and local climate are too cold. Nile crocodiles are capable of limited oceanic movements thus the prevailing currents and water temperatures make marine sightings in Namibia highly unlikely.

Even crocodiles need their five a day, it seems. At least half of all species of alligator and crocodile supplement their meaty diet with the flesh of fruit: here.

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