Population surveys of Nile crocodiles (Crocodylus niloticus) in the Murchison Falls National Park, Victoria Nile, Uganda

1. A 12-month-long survey (April 2013 to March 2014) for Nile crocodiles (Crocodylus niloticus) was conducted along a section of the Victoria Nile/Ramsar site of Murchison Falls National Park, in order to update the historic information on crocodile populations in the area, locating nesting areas, determining seasonality patterns and habitat use, and assess the current abundance and the population size trends since the 1960s. The methods employed included visual encounter surveys, transect counts and opportunistic methods, by using boats.2. In general, there were diurnal and seasonal fluctuations in the number of crocodile sightings. The crocodile sightings peaked between the months of June and August, with the highest mean number of sightings encountered on any single day being 67 (in July 2013), and the second peak was between January and March with  the highest mean of 118 recorded in January 2014. The second peak also coincided with the crocodile breeding  season. This clearly shows that the distribution of the sub-population sampled followed a climatic regime.3. Crocodiles were observed most frequently in water (37%). Grassy banks, islands, river mouths and sandy banks constituted about 47% of the habitats utilised by the crocodile population. Although basking was the most frequent type of activity performed by crocodiles (50%) over the entire survey period, their key activities varied significantly from month to month. Nesting was very visible during the last quarter of the year and the first quarter of the New Year.4. There was a clear decline of the abundance of crocodiles in this population between 1960s and nowadays. This declining trend was obvious also taking into account the various survey methodologies employed over the decades

A Key to the Genera of Snakes in Uganda

No Abstract

Population surveys of Nile crocodiles (Crocodylus niloticus) in the Murchison Falls National Park, Victoria Nile, Uganda

1. A 12-month-long survey (April 2013 to March 2014) for Nile crocodiles (Crocodylus niloticus) was conducted along a section of the Victoria Nile/Ramsar site of Murchison Falls National Park, in order to update the historic information on crocodile populations in the area, locating nesting areas, determining seasonality patterns and habitat use, and assess the current abundance and the population size trends since the 1960s. The methods employed included visual encounter surveys, transect counts and opportunistic methods, by using boats. 2. In general, there were diurnal and seasonal fluctuations in the number of crocodile sightings. The crocodile sightings peaked between the months of June and August, with the highest mean number of sightings encountered on any single day being 67 (in July 2013), and the second peak was between January and March with the highest mean of 118 recorded in January 2014. The second peak also coincided with the crocodile breeding season. This clearly shows that the distribution of the sub-population sampled followed a climatic regime. 3. Crocodiles were observed most frequently in water (37%). Grassy banks, islands, river mouths and sandy banks constituted about 47% of the habitats utilised by the crocodile population. Although basking was the most frequent type of activity performed by crocodiles (50%) over the entire survey period, their key activities varied significantly from month to month. Nesting was very visible during the last quarter of the year and the first quarter of the New Year. 4. There was a clear decline of the abundance of crocodiles in this population between 1960s and nowadays. This declining trend was obvious also taking into account the various survey methodologies employed over the decades

Herpetofaunal diversity and community structure in the Murchison Falls - Albert Delta Ramsar site, Uganda : Herpetofaunal diversity

1. The area of the Murchison Falls-Albert Delta is among the most important for conservation in East Africa dueto the high species richness, and the presence of several endemic species of conservation concern.2. Here, we report a study on the diversity patterns and community structure of the herpetofauna of this area.3. Field studies were conducted in the Albert Nile Delta Ramsar site between 1st October 2017 and 9th September2018. The data collection relied on Visual Encounter Surveys (VES), pitfall trapping, and dip netting. Descriptive statistics, i.e. species numbers in each transect were used as a measure of the present biodiversity, whereasChao1 and Chao species estimator algorithms were used to predict the potential number of species found ineach site/habitat.4. A total of 898 individuals representing 25 reptile species belonging to four orders, 15 families, and 20 generawere recorded during the 12 months of surveys.5. The data shows some non-random spatial and temporal patterns whereby there is a cyclic reptilian diversitypeaking during the December-March and again towards June-August-September which are peaks of the dryseason.6. The most frequently encountered species were Varanus niloticus, Crocodylus niloticus, Agama agama, Trachylepis maculilabris, and Lygodactylus guttularis, which accounted for almost 90% of all recorded individuals.7. A total of 27 amphibian species, belonging to nine families and 10 genera were recorded during the periodof the survey. The diversity and abundance graphs would indicate amphibians having bimodal peaks (September-December, and March-May). The diversity seemed to dip during the dry season months – which is theopposite case for reptiles

Assessing the Threat of Amphibian Chytrid Fungus in the Albertine Rift: Past, Present and Future

<div><p><i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>), the cause of chytridiomycosis, is a pathogenic fungus that is found worldwide and is a major contributor to amphibian declines and extinctions. We report results of a comprehensive effort to assess the distribution and threat of <i>Bd</i> in one of the Earth’s most important biodiversity hotspots, the Albertine Rift in central Africa. In herpetological surveys conducted between 2010 and 2014, 1018 skin swabs from 17 amphibian genera in 39 sites across the Albertine Rift were tested for <i>Bd</i> by PCR. Overall, 19.5% of amphibians tested positive from all sites combined. Skin tissue samples from 163 amphibians were examined histologically; of these two had superficial epidermal intracorneal fungal colonization and lesions consistent with the disease chytridiomycosis. One amphibian was found dead during the surveys, and all others encountered appeared healthy. We found no evidence for <i>Bd</i>-induced mortality events, a finding consistent with other studies. To gain a historical perspective about <i>Bd</i> in the Albertine Rift, skin swabs from 232 museum-archived amphibians collected as voucher specimens from 1925–1994 were tested for <i>Bd</i>. Of these, one sample was positive; an Itombwe River frog (<i>Phrynobatrachus asper</i>) collected in 1950 in the Itombwe highlands. This finding represents the earliest record of <i>Bd</i> in the Democratic Republic of Congo. We modeled the distribution of <i>Bd</i> in the Albertine Rift using MaxEnt software, and trained our model for improved predictability. Our model predicts that <i>Bd</i> is currently widespread across the Albertine Rift, with moderate habitat suitability extending into the lowlands. Under climatic modeling scenarios our model predicts that optimal habitat suitability of <i>Bd</i> will decrease causing a major range contraction of the fungus by 2080. Our baseline data and modeling predictions are important for comparative studies, especially if significant changes in amphibian health status or climactic conditions are encountered in the future.</p></div

Prevalence of <i>Bd</i> positive genera in tested samples (CI, Wilsons score).

<p>Prevalence of <i>Bd</i> positive genera in tested samples (CI, Wilsons score).</p

MaxEnt response curves illustrate how the likelihood for <i>Bd</i> occurrence is influenced by maximum temperature of warmest month (Bio5) and the mean annual precipitation (Bio12).

<p>A. Shows the probability of presence of <i>Bd</i> as it relates to Bio5 when all other environmental variables are kept at their average values. B. Shows the same as in A, except that Bio5 alone was used for model calibration. C. Shows the probability of presence of <i>Bd</i> as it relates to Bio12 when all other environmental variables are kept at their average values. D. Shows the same except that Bio12 alone was used for model calibration. The red line is the mean of 100 bootstrap runs with +/- one standard deviation (blue).</p

<i>Bd</i> prevalence in sampled amphibians in current or proposed protected areas throughout the Albertine Rift.

<p><i>Bd</i> prevalence in sampled amphibians in current or proposed protected areas throughout the Albertine Rift.</p

Predicted future habitat suitability and <i>Bd</i> distribution in 2080.

<p>A. Illustrates the predicted current distribution and risk of <i>Bd</i> to amphibians in 2015 using all locations in the modeling (<i>Bd</i> records obtained in this study and previous studies [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145841#pone.0145841.ref029" target="_blank">29</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145841#pone.0145841.ref032" target="_blank">32</a>]). B. An average of the model output from the three General Circulation Models that shows the future distribution of where amphibians are likely to be at risk for <i>Bd</i> infection in 2080 under the A2a scenario. Our results predict a large range contraction of suitable habitat for <i>Bd</i> with future climate change.</p

Genera assessed for the disease chytridiomycosis that were also <i>Bd</i> positive by PCR.

<p>Genera assessed for the disease chytridiomycosis that were also <i>Bd</i> positive by PCR.</p