Terrestrial Diet Dependence in an Unprotected Nile Crocodile (Crocodylus niloticus) Population

Nile Crocodile (Crocodylus niloticus) populations that exist outside of protected areas are under threat in South Africa. They are believed to predominantly feed on fish, but they also take prey from the terrestrial system, which brings them into conflict with humans and hampers their management. Here, we use stable light isotope analysis to explore the diet of an unprotected Nile Crocodile population in the Olifants River, Mpumalanga and Limpopo Provinces. Nitrogen stable isotope ratios were obtained from fish and crocodile populations along the length (+/- 430 km) of the river. The catchment is severely polluted with elevated delta N-15 values at nutrient hotspots, which provides a basis for tracking the trophic response of crocodiles to the longitudinal profile of fish delta N-15 values. Crocodiles did not respond to changes in the delta N-15 values of fish populations and dietary predictions based on size-specific diet to tissue discrimination factors suggests a nonaquatic food base. These results suggest terrestrial diet dependence in one of the few viable Nile Crocodile populations from outside protected areas, posing unique challenges to their conservation.

Automated summary

Unprotected Nile Crocodile populations outside of protected areas in South Africa face threats due to their terrestrial diet, which leads to conflict with humans. Research shows that these crocodiles do not respond to changes in fish populations.