Abundance of Saltwater Crocodile Hatchlings is Related to Rainfall in the Preceding Wet Season in Northern Australia

Fukuda, Yusuke; Saalfeld, Keith

doi:10.1655/herpetologica-d-13-00096r3

Cited by 13 publications

(13 citation statements)

References 8 publications

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“…At each response interval (short-body condition, intermediate-growth, and long-term-survival), salinity had negative effects on crocodile indicator parameters. An adequate supply of freshwater is necessary to maintain good health and increase survival of crocodiles in South Florida, and where freshwater is limited or where nursery habitat is further from nesting habitat, there is additional stress imposed on individuals [22,63,[96][97][98]. Our results show that crocodiles are effective ecological indicators of ecosystem responses to restoration of Everglades estuaries and underscores the need for continued long-term research to evaluate restoration progress.…”

Section: Discussionmentioning

confidence: 66%

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

et al. 2021

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The federally threatened American crocodile (Crocodylus acutus) is a flagship species and ecological indicator of hydrologic restoration in the Florida Everglades. We conducted a long-term capture-recapture study on the South Florida population of American crocodiles from 1978 to 2015 to evaluate the effects of restoration efforts to more historic hydrologic conditions. The study produced 10,040 crocodile capture events of 9,865 individuals and more than 90% of captures were of hatchlings. Body condition and growth rates of crocodiles were highly age-structured with younger crocodiles presenting with the poorest body condition and highest growth rates. Mean crocodile body condition in this study was 2.14±0.35 SD across the South Florida population. Crocodiles exposed to hypersaline conditions (> 40 psu) during the dry season maintained lower body condition scores and reduced growth rate by 13% after one year, by 24% after five years, and by 29% after ten years. Estimated hatchling survival for the South Florida population was 25% increasing with ontogeny and reaching near 90% survival at year six. Hatchling survival was 34% in NE Florida Bay relative to a 69% hatchling survival at Crocodile Lake National Wildlife Refuge and 53% in Flamingo area of Everglades National Park. Hypersaline conditions negatively affected survival, growth and body condition and was most pronounced in NE Florida Bay, where the hydrologic conditions have been most disturbed. The American crocodile, a long-lived animal, with relatively slow growth rate provides an excellent model system to measure the effects of altered hydropatterns in the Everglades landscape. These results illustrate the need for continued long-term monitoring to assess system-wide restoration outcomes and inform resource managers.

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Section: Discussionmentioning

confidence: 66%

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

et al. 2021

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“…Annual variability in climate affects the ability of C. porosus to exploit local environments in various ways, which ultimately influences their reproductive effort and success (Nichols 1987;WMI 2007). Breeding of C. porosus occurs in the wet season (November-April), nesting tends to be reduced after a prolonged dry season, and rainfall at the start of the wet season triggers courtship and breeding (Webb 1991;Fukuda and Saalfeld 2014). We incorporated this environmental stochasticity into our model by adjusting reproduction (F 4 ) according to the extent and timing of wet season rainfall between 1971 and 2019 (Fig.…”

Section: Environmental Stochasticitymentioning

confidence: 99%

“…We assumed that the transition (G i ) and persistence (P i ) of each class was as shown in Table 1 and estimated the retention rates of N 2 , N 3 and N 4 from their relative densities derived from the time-series data of spotlight surveys in 12 tidal rivers across the study area (Fig. 1; Fukuda et al 2011;Fukuda and Saalfeld 2014).…”

Section: Change In Fertilitymentioning

confidence: 99%

“…Generally, there are three types of nesting habitat in the study area , namely, Type 1 ¼ spring-fed freshwater swamps draining to tidal rivers, Type 2 ¼ upstream freshwater swamps, and Type 3 ¼ floodplains adjoining mangrove-lined tidal rivers. In Type 1 habitats, mortality due to flooding is low, but in Type 2 and 3 habitats flooding due to both rain and tidal effects results in the highest egg mortality (Webb 1977;Hill and Webb 1982;Fukuda and Saalfeld 2014). From the empirical data associated with the long-term harvest (WMI 2007;G.…”

Section: Current Harvest Effectsmentioning

confidence: 99%

“…The population has recovered steadily since 1971 and the objective of management has consequently shifted from one of conservation (Messel et al 1981) to sustained-yield harvesting with limited population control in some situations (Webb and Manolis 1993;Saalfeld et al 2015Saalfeld et al , 2016. Population control involves the removal of some crocodiles to reduce human-crocodile conflict around human settlements (Nichols and Letnic 2008;Fukuda et al 2014). The sustained yield harvest strategy adopted incentivises landowner conservation of crocodile populations and habitat on their land by allowing them to use crocodiles for commercial gain (Webb and Manolis 1993).…”

Section: Introductionmentioning

confidence: 99%

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

Fukuda¹,

Webb²,

Edwards³

et al. 2021

Wildl. Res.

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ContextThe 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. AimsWe conducted 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. MethodsOn 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 resultsThe 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 ~102000 non-hatchlings (>0.6m crocodiles), of which 42.2% are large (>2.1m 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 135500 eggs if the harvest of large crocodiles remains small (<500 per year). ConclusionsAlthough egg harvest has little impact on population size and structure, population size is sensitive to adult harvest. ImplicationsCrocodile populations are highly sensitive to adult survival, which needs to be taken into account when considering future harvest scenarios.

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The influence of crocodile density on the prevalence of human attacks

Baker,

Campbell,

Udyawer

et al. 2024

People and Nature

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Large predator attacks on humans often provoke calls for animal population reduction, assuming it will reduce such incidents. Whilst this seems logical, there is currently little evidence supporting a consistent link between large predator density and attacks on humans. Here, we assessed whether large predator density is linked to the frequency of attacks on humans using estuarine crocodile (Crocodylus porosus) data in the Northern Territory (NT), Australia. Over the past 50 years, the estuarine crocodile population in the NT has grown from a few thousand to over 100,000 non‐hatchling individuals. Crocodile and human population densities have been closely monitored throughout this period, allowing the frequency of attacks on humans to be assessed over a wide range of densities for both populations. Our analysis showed an increase in the frequency of attacks on humans as the crocodile population recovered from very low levels in the 1970s. However, the attack rates stabilised around 2009, despite crocodile density and the human population continuing to increase. Based on the relationship between crocodile density and human‐attack frequency, scenario modelling suggested that the crocodile population would need to be culled to a critically endangered level (e.g. 90% population reduction) to reduce attacks on humans from 2.16 to 1.16 attacks per year. We conclude that whilst crocodile density significantly influences crocodile attack rates at low crocodile population sizes, this relationship becomes weaker as the density increases. For estuarine crocodiles in the NT, a plateauing of attack risk occurred once crocodile density attained ~2 crocodiles per km of river, and we argue that this was because high crocodile densities instigated management (e.g. removal of bold animals, exclusion zones) and education initiates by the government (e.g. ‘Be crocwise’ campaign) that subsequently evoked a change in human behaviour around waterways and stabilised the attack rate. Read the free Plain Language Summary for this article on the Journal blog.

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Abundance of Saltwater Crocodile Hatchlings is Related to Rainfall in the Preceding Wet Season in Northern Australia

Cited by 13 publications

References 8 publications

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

American crocodiles (Crocodylus acutus) as restoration bioindicators in the Florida Everglades

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

The influence of crocodile density on the prevalence of human attacks

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