Changes in the distribution and abundance of saltwater crocodiles (Crocodylus porosus) in the upstream, freshwater reaches of rivers in the Northern Territory, Australia

2006 ◽  
Vol 33 (7) ◽  
pp. 529 ◽  
Author(s):  
Mike Letnic ◽  
Greg Connors
Keyword(s):  
Sea Level ◽  
Potential Distribution ◽  
Size Structure ◽  
Northern Territory ◽  
Warning Signs ◽  
Potential Range ◽  
Lates Calcarifer ◽  
Marine Habitats ◽  
Crocodylus Porosus ◽  
Helicopter Survey

Since they were declared a protected species in 1971, populations of saltwater crocodiles (Crocodylus porosus) have increased in the tidal rivers, freshwater swamps and marine waters of the Northern Territory. The recovery of the C. porosus population has been accompanied by an increase in the incidence of ‘problem crocodiles’ that represent a threat to people in freshwater and marine habitats. Despite the implications for human safety, little is known about C. porosus populations in the freshwater reaches of rivers, well upstream of tidal influence. In this study, we examined the density and body-size structure of C. porosus populations in three freshwater rivers using a combination of data from spotlight and helicopter surveys conducted between the 1980s and 2005, and the inland extent of C. porosus using distribution records in the Northern Territory. Since the 1980s, the density of C. porosus in upstream, freshwater reaches of the Daly and Roper rivers has increased, as has the inland extent of C. porosus on the Daly River. Although C. porosus was not detected in spotlight surveys of the Victoria River, helicopter survey and anecdotal records indicate that C. porosus was present after 1989. In all, 52.1% of the crocodiles sighted in spotlight surveys were 2.1–3.4 m long. Distribution records show that C. porosus occurs up to 235 km inland and at elevations of up to 126 m above sea level. The potential distribution of C. porosus is likely to be similar to that of barramundi (Lates calcarifer), a readily identifiable diadromous fish that must spawn in estuarine waters and occurs at elevations of up to 178 m above sea level. Because the density and inland extent of C. porosus in freshwater rivers is likely to increase, it is recommended that: (1) programs communicating crocodile awareness use the linkage between the presence of barramundi and the potential presence of C. porosus; (2) that crocodile warning signs be erected in upstream areas within the potential range of C. porosus; (3) that research be conducted on developing techniques to detect and exclude C. porosus from swimming areas; and (4) that widespread systematic surveys be undertaken to document the inland extent of C. porosus.

Osmoregulatory ability predicts geographical range size in marine amniotes

2021 ◽  
Vol 288 (1948) ◽  
Author(s):  
François Brischoux ◽  
Harvey B. Lillywhite ◽  
Richard Shine ◽  
David Pinaud
Keyword(s):  
Dietary Habits ◽  
Range Size ◽  
Geographical Range ◽  
Physiological Data ◽  
Potential Range ◽  
Marine Habitats ◽  
Species Vulnerability ◽  
Ideal System ◽  
Physiological Tolerances ◽  
Osmoregulatory Ability

Species that are distributed over wide geographical ranges are likely to encounter a greater diversity of environmental conditions than do narrowly distributed taxa, and thus we expect a correlation between size of geographical range and breadth of physiological tolerances to abiotic challenges. That correlation could arise either because higher physiological capacity enables range expansion, or because widely distributed taxa experience more intense (but spatially variable) selection on physiological tolerances. The invasion of oceanic habitats by amniotic vertebrates provides an ideal system with which to test the predicted correlation between range size and physiological tolerances, because all three lineages that have secondarily moved into marine habitats (mammals, birds, reptiles) exhibit morphological and physiological adaptations to excrete excess salt. Our analyses of data on 62 species (19 mammals, 18 birds, 24 reptiles) confirm that more-widely distributed taxa encounter habitats with a wider range of salinities, and that they have higher osmoregulatory ability as determined by sodium concentrations in fluids expelled from salt-excreting organs. This result remains highly significant even in models that incorporate additional explanatory variables such as metabolic mode, body size and dietary habits. Physiological data thus may help to predict potential range size and perhaps a species' vulnerability to anthropogenic disturbance.

Problem crocodiles, Crocodylus porosus, at Nhulunbuy, Northern Territory: an assessment of relocation as a mangaement strategy

1993 ◽  
Vol 20 (1) ◽  
pp. 127 ◽  
Author(s):  
B Walsh ◽  
PJ Whitehead
Keyword(s):  
Carrying Capacity ◽  
Northern Territory ◽  
Effective Strategy ◽  
Wet Season ◽  
Rates Of Return ◽  
Saltwater Crocodile ◽  
Crocodylus Porosus ◽  
Remote Sites ◽  
Total Capture ◽  
Capture Rates

Since 1986 the Conservation Commission of the Northern Territory has operated a programme to remove 'problem' saltwater crocodiles from waters in and adjoining the township of Nhulunbuy. Over a period of five years, 52 different saltwater crocodiles (44 male) were captured. Most (48) were released at remote sites designated by the traditional Aboriginal owners of the surrounding lands. Release distances from the township varied from 17 to 282 km (by coastline). Many crocodiles (47.9%), including those released at the most distant sites, returned to, and were subsequently recaptured at, the township. Total capture rates (initial captures and recaptures pooled) varied seasonally, with fewer crocodiles being caught in the cooler dry season. During the wet season capture rates remained high, but relatively fewer 'new' crocodiles were caught. Probability of recapture could not be related to distance and direction of release from the township, nor size and sex of the released crocodile. Frequency of capture of individual crocodiles (1-8 times) was also unrelated to these variables. The high rates of return indicate that relocation is unlikely to be an effective strategy for managing humancrocodile interactions, at least in areas where potential release sites already support saltwater crocodile populations near carrying capacity.

scholarly journals Melting ice: "Warning Signs"

2007 ◽  
Vol 8 ◽  
pp. 66-73
Author(s):  
Ghana S. Malla
Keyword(s):  
Global Warming ◽  
Sea Level Rise ◽  
Sea Level ◽  
Atmospheric Temperature ◽  
Warning Signs ◽  
Warning Sign ◽  
Gradual Change ◽  
Liquid Form ◽  
Greenhouse Gasses ◽  
The Times

Melting ice is one of the concerns of world climate scientists and planners. It is the gradual change of ice in the liquid form caused by increase in atmospheric temperature. Global Warming is the increase in atmospheric temperature caused by greenhouse effects (C02, CH4, N20 and CFCs). Increase in temperature of atmosphere by 1oC that has been occurred since 1860 AD (IPCC, 1996). Scientists predicted that the Earth would warm by 1.4 to 5.8oC by 2100. In case of Nepal, increase of temperature was recorded 0.06oC per year (DHM). Sea level rise causes by melting ice is recent warning sign. The Times Center, 2007 estimated sea level rise would be 51 -140 cm by 2100 AD. It affects wide variety of ecosystem, water resources, agriculture, life and livelihoods of people in the world. However, its impact is largely unpredictable and uncertainty. There were series of glacial outburst in Nepal since 1964, destroying ecosystem of surrounding region caused by global warming. Therefore, IPCC member's countries with United State of America (USA) must act quickly to reduce greenhouse gasses to overcome threat of melting ice. The Journal of AGRICULTURE AND ENVIRONMENT Vol. 8, 2007, pp. 66-73

Monitoring Crocodylus porosus populations in the Northern Territory of Australia: a retrospective power analysis

2001 ◽  
Vol 28 (6) ◽  
pp. 547 ◽  
Author(s):  
S. C. Stirrat ◽  
D. Lawson ◽  
W. J. Freeland ◽  
R. Morton
Keyword(s):  
Power Analysis ◽  
Northern Territory ◽  
Management Program ◽  
Survey Method ◽  
Management Information ◽  
River Systems ◽  
Pooled Data ◽  
Management Actions ◽  
Sampling Program ◽  
Crocodylus Porosus

In the Northern Territory of Australia, populations of the estuarine crocodile (Crocodylus porosus) have been subject to an annual egg harvest since the early 1980s. Since 1997, adult and juvenile crocodiles have also been harvested in some catchments. Annual surveys of crocodile populations are conducted in order to ensure that the harvest is sustainable. Boat surveys commenced in 1975 and helicopter surveys commenced in 1989. Retrospective power analysis was used to determine whether the sampling program meets the objectives of the Crocodile Management Program for the Northern Territory. Data collected during boat surveys vary in quality between river systems. The analysis of pooled data from 7 river systems with a residual standard deviation of 0.11 indicates that the power of the current spotlight survey method to detect a decline of 10% per annum in around 4 years is about 0.9. In this time the population would decline by around 33% and would fully recover in 8 years following the removal of the factor causing the decline. This allows detection of a decline within one-third, and recovery within two-thirds, of the estimated generation time of the saltwater crocodile and will allow management actions to be implemented before the impacts on populations are serious. The data from helicopter and boat surveys from a 10-year period were compared. Helicopter surveys did not provide useful management information.

scholarly journals The potential geographical distribution and phenology of Bemisia tabaci Middle East/Asia Minor 1, considering irrigation and glasshouse production

2020 ◽  
Vol 110 (5) ◽  
pp. 567-576 ◽  
Author(s):  
D. J. Kriticos ◽  
P. J. De Barro ◽  
T. Yonow ◽  
N. Ota ◽  
R. W. Sutherst
Keyword(s):  
Middle East ◽  
East Asia ◽  
Open Field ◽  
Bemisia Tabaci ◽  
Species Complex ◽  
Potential Distribution ◽  
Invasive Pest ◽  
Asia Minor ◽  
Potential Range ◽  
Pest Species

AbstractThe Bemisia tabaci species complex is one of the most important pests of open field and protected cropping globally. Within this complex, one species (Middle East Asia Minor 1, B. tabaci MEAM1, formerly biotype B) has been especially problematic, invading widely and spreading a large variety of plant pathogens, and developing broad spectrum pesticide resistance. Here, we fit a CLIMEX model to the distribution records of B. tabaci MEAM1, using experimental observations to calibrate its temperature responses. In fitting the model, we consider the effects of irrigation and glasshouses in extending its potential range. The validated niche model estimates its potential distribution as being considerably broader than its present known distribution, especially in the Americas, Africa and Asia. The potential distribution of the fitted model encompasses the known distribution of B. tabaci sensu lato, highlighting the magnitude of the threat posed globally by this invasive pest species complex and the viruses it vectors to open field and protected agriculture.

Problem crocodiles(Crocodylus porosus)in the freshwater, Katherine River, Northern Territory, Australia

2011 ◽  
Vol 35 (3) ◽  
pp. 858-863 ◽  
Author(s):  
Mike Letnic ◽  
Patrick Carmody ◽  
John Burke
Keyword(s):  
Northern Territory ◽  
Crocodylus Porosus

scholarly journals The current and future potential geographical distribution of the oriental fruit fly,Bactrocera dorsalis(Diptera: Tephritidae)

2007 ◽  
Vol 97 (4) ◽  
pp. 369-378 ◽  
Author(s):  
A.E.A. Stephens ◽  
D.J. Kriticos ◽  
A. Leriche
Keyword(s):  
Climate Change ◽  
Cold Stress ◽  
Potential Distribution ◽  
Fruit Fly ◽  
Climatic Conditions ◽  
Bactrocera Dorsalis ◽  
Potential Range ◽  
Climate Change Scenarios ◽  
Oriental Fruit Fly ◽  
The Impact

AbstractThe oriental fruit fly,Bactrocera dorsalis(Hendel), is a major pest throughout South East Asia and in a number of Pacific Islands. As a result of their widespread distribution, pest status, invasive ability and potential impact on market access,B. dorsalisand many other fruit fly species are considered major threats to many countries. CLIMEX™ was used to model the potential global distribution ofB. dorsalisunder current and future climate scenarios. Under current climatic conditions, its projected potential distribution includes much of the tropics and subtropics and extends into warm temperate areas such as southern Mediterranean Europe. The model projects optimal climatic conditions forB. dorsalisin the south-eastern USA, where the principle range-limiting factor is likely to be cold stress. As a result of climate change, the potential global range forB. dorsalisis projected to extend further polewards as cold stress boundaries recede. However, the potential range contracts in areas where precipitation is projected to decrease substantially. The significant increases in the potential distribution ofB. dorsalisprojected under the climate change scenarios suggest that the World Trade Organization should allow biosecurity authorities to consider the effects of climate change when undertaking pest risk assessments. One of the most significant areas of uncertainty in climate change concerns the greenhouse gas emissions scenarios. Results are provided that span the range of standard Intergovernmental Panel on Climate Change scenarios. The impact on the projected distribution ofB. dorsalisis striking, but affects the relative abundance of the fly within the total suitable range more than the total area of climatically suitable habitat.

Corrigendum to: Broad-scale environmental influences on the abundance of saltwater crocodiles (Crocodylus porosus) in Australia

2008 ◽  
Vol 35 (2) ◽  
pp. 170 ◽  
Author(s):  
Yusuke Fukuda ◽  
Peter Whitehead ◽  
Guy Boggs
Keyword(s):  
Environmental Influences ◽  
Strong Support ◽  
Northern Territory ◽  
The Other ◽  
Total Precipitation ◽  
Northern Australia ◽  
Landscape Modification ◽  
Geographical Variations ◽  
Crocodylus Porosus ◽  
Broad Scale

Saltwater crocodile (Crocodylus porosus) populations have recovered strongly across northern Australia over the 30 years since the species was protected from hunting. However, monitoring studies show large geographical variations in abundance across the Northern Territory, Queensland and Western Australia. The Northern Territory has considerably higher densities, raising questions about constraints on recovery in the other states. We examined broad-scale environmental influences on population abundance by modelling the species.environment relationships across northern Australia. The hypothesis-based models showed strong support for the linkage to (1) the ratio of total area of favourable wetland vegetation types (Melaleuca, grass and sedge to total catchment area, (2) a measure of rainfall seasonality, namely the ratio of total precipitation in the coldest quarter to total precipitation in the warmest quarter of a year, and (3) the mean temperature in the coldest quarter of a year. On the other hand, we were unable to show any clear negative association with landscape modification, as indicated by the extent of high-impact land uses or human population density in catchments. We conclude that geographical variations in crocodile density are mostly attributable to differences in habitat quality rather than the management regimes adopted in the respective jurisdictions.

Ecological niche modeling of coastal dune plants and future potential distribution in response to climate change and sea level rise

2013 ◽  
Vol 19 (8) ◽  
pp. 2524-2535 ◽  
Author(s):  
Gabriela Mendoza-González ◽  
M. Luisa Martínez ◽  
Octavio R. Rojas-Soto ◽  
Gabriela Vázquez ◽  
Juan B. Gallego-Fernández
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ecological Niche ◽  
Potential Distribution ◽  
Ecological Niche Modeling ◽  
Niche Modeling ◽  
Coastal Dune Plants ◽  
Future Potential ◽  
Dune Plants
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