The Historical Ecology of Queensland’s Australian Saltwater Crocodile (Crocodylus porosus)

Human wildlife conflict is a critical aspect of many societies, as it often plays a large role in government decisions. The iconic saltwater Australian crocodile (Crocodylus porosus) is one example of a species that has become the subject of human-wildlife conflict in Queensland, Australia. Decades of intensive hunting in Queensland, beginning at the time of the Second World War, drastically depleted crocodile populations, leading to a federal embargo on crocodile exports in 1972 and their protection in Queensland in 1974. Since protection, populations appear to be recovering with increasing densities in the north and increased sightings along the southernmost edge of their observed range. However, research has indicated that population recovery is slower than in the adjacent Northern Territory, although the drivers of this slow recovery and southern sightings remain unknown. Two potential drivers include range expansion due to climate change or re-colonization of areas from which they were previously extirpated. This study uses a variety of spatial and temporal density analyses in relation to human population size to examine the abundance and range status of crocodiles in Australia. It compares the distribution of sightings, nests and attacks over pre-exploitation (1871-1944), heavy exploitation (1945-1971) and post-exploitation (1972-2015) time periods to assess three related hypotheses: First, crocodile populations are expanding outside of known historical ranges. Second, crocodile populations have recovered to historical baseline abundances in areas that abut regions of high human population density. Third, crocodile attack rates have increased over time relative to human population size. While crocodile ranges do not appear to be expanding, they do heavily overlap with the highest anthropogenically altered areas. Furthermore, although crocodile abundance is difficult to characterize, attack rates have remained relatively low since the pre-exploitation period. These findings suggest that coastal development and crocodile removal plans may be driving crocodiles outside of natural habitat ranges and that the recent southern sightings likely represent the re-colonization of crocodiles in former southern ranges. This study aims to provide management with historical information of crocodiles in relation to current trends to aid in successful management that allows crocodile populations to recover, while maintaining low instances of human-crocodile conflict.