Harvesting predators: simulation of population recovery and controlled harvest of saltwater crocodiles Crocodylus porosus

Context. The population of saltwater crocodiles, Crocodylus porosus, in the Northern Territory, Australia, has been recovering from a period of intensive, unregulated harvest (1945-1971) since protection in 1971. Consequently, the management goal is shifting from restoring a seriously depleted population to managing an abundant population through controlled harvests for both commercial purposes and public safety. Aims. Weconducted this study to (1) examine whether the controlled harvest of eggs and adults since protection has had an adverse effect on population size and structure, and (2) explore the effect of future harvest scenarios on population size and structure by adjusting harvest levels of both eggs and adults. Methods. On the basis of 40 years of population monitoring data and knowledge of population attributes from previous research, we developed density-dependent, structured matrix population models to explore our aims. Key results. The models supported that the depleted population recovered rapidly under protection and that the harvest rates since protection were benign. The model estimated the 2017 harvested population, 46 years after protection, to be,102 000 non-hatchlings (.0.6 m crocodiles), of which 42.2% are large (.2.1 m total length) individuals. This is similar to the estimated population before the period of intensive, unregulated harvest. Like other crocodilians, the harvest simulations showed that the viability of the population is highly sensitive to adult survival rates. The estimated population should be able to sustain an annual harvest of up to 135 500 eggs if the harvest of large crocodiles remains small (,500 per year). Conclusions. Although egg harvest has little impact on population size and structure, population size is sensitive to adult harvest. Implications. Crocodile populations are highly sensitive to adult survival, which needs to be taken into account when considering future harvest scenarios.

Automated summary

The study found that controlled harvesting of saltwater crocodiles since protection has not had a negative impact on population size and structure. By simulating different harvesting scenarios, it was discovered that adult survival rates have a significant influence on the population's sustainability.