Saturday, 17 July 2021

Trouble in Myanmar: The worrying case of Burmese Amber.

Cretaceous ‘Burmese Amber’ has been extensively worked at several sites across northern Myanmar (though mostly in Kachin State) in the last 20 years. The amber is fairly clear, and often found in large chunks, providing an exceptional window into the Middle Cretaceous Insect fauna, as well as preserved examples of small Vertebrates, feathers from Birds and other Dinosaurs, and even the only known Ammonite preserved in amber. However, the trade in amber from Myanmar has raised deep concerns, as has the wider nature trade in gemstones from the country, due to the deteriorating Human rights situation in the country, and the highly exploitative working conditions at many mines there. Most noatably, in 2017 the Myanmar military seized direct control of the region, forcing many local residents (who were accused of being supporters of the Kachin Independence Army) to flee, and bringing in new workers from other parts of the country.

In April 2020 Emily Rayfield, Jessica Theodor, and David Polly of the Society of Vertebrate Paleontology sent a letter to the editors of over 250 scientific journals, raising concern about the trade in amber from Myanmar, Human rights abuses within the country, the ongoing conflict situation in the region, and the blurring of the distinction between public and private collections that had occurred in some journals with regard to material from the region (in order for a study to be published in a journal, the material involved should be held in a collection that has a predetermined policy on the making of material available to other researchers, such as a museum or university collection, rather than in private ownership).

Flowers preserved in amber from Kachin State, Myanmar. Myanmar Amber Museum.

This was followed in May 2020 by an editorial published in the Journal of Systematic Palaeontology in which editors Paul Barrett and Zerina Johanson, stated that that journal would no longer be publishing articles based wholly or in part upon amber from Myanmar, whether newly collected or from historic collections, citing concerns about working conditions at mines in Myanmar, the use of money obtained from the sale of amber and other gemstones to by arms and fund conflicts in the region, and the widespread illegal removal of amber from the country.

The issue has been addressed again in the June 2021 issue of the journal Nature Ecology and Evolution, with an editorial and a series of articles by scientists with views on the topic.

In the first of these papers, a group of scientists led by Chao Shi of the College of Marine Science and Biological Engineering at Qingdao University of Science and Technology and the Key Laboratory for Plant Diversity and Biogeography of East Asia at the Kunming Institute of Botany, argue that while the Human rights situation in Myanmar is now severe enough to justify a ban on the use of new specimens from the country in published scientific studies, a great deal of this material is already present in musuem and university collections around the world, and that it would be unreasonable to exclude this material from future studies.

A mining camp in a forest in Kachin State in 2010. Blood Amber/Kachin Development Networking Group.

In the second paper, Zin-Maung-Maung-Thein of the Department of Geology at the University of Mandalay, and Khin Zaw of the Centre of Ore Deposits and Earth Sciences at the University of Tasmania, raise concerns about Burmese Amber as a focus for 'parachute science', a term which refers to the practice of scientists from wealthy countries 'parachuting' into less well-off nations, collecting data or materials, then returning to their home nations to work on this material, without any benefit to the host nation, and often with scientists from that nation henceforth hampered from accessing the data or materials, due to their new location, and the high cost of accessing published information in many journals and other publications (ironically, this article is itself paywalled, and cannot be accessed without a subscription to Nature Ecology and Evolution, unless a fee is paid (US8.99 for the one-page article). In the case of Myanmar, amber is typically extracted then sold overseas, where it may be worked on by local scientists who are acting in good faith, but who in so doing are excluding scientists in Myanmar from accessing the same material. A study by Emma Dunne of the University of Birmingham and Nussaïbah Raja-Schoob of Friedrich-Alexander-Universität Erlangen-Nürnberg, and presented by Emma Dunne at a meeting of the Palaeontological Association in 2020, found that not a single publication on Burmese Amber in the English language published in the last 30 years included a local collaborator, whereas articles on Cainozoic Primates from Myanmar often did (suggesting that there is a local interest in palaeontology, and scientists in Myanmar who would be willing to work with with outside scientists). Dunne and Raja suggest that this difference may be because of the difference in status between amber and other fossils in Myanmar; in theory fossils are treated as antiquities in Myanmar, and a special permit is needed to export them, but amber is a 'gemstone' and may be exported without a permit (the export of gemstones, such as jade, rubies, and amber is a major earner of hard currencies for Myanmar). Zin-Maung-Maung-Thein and Khin Zaw suggest that scientists outside Myanmar wishing to work on this material should contact the government of Myanmar for permission, as well as museums and universities in the country to seek local collaborators.

In the final paper, Paul Barrett, Zerina Johanson and Sarah Long of the Natural History Museum again visit the dual legal nature of fossils in Burmese Amber, pointing out that the current situation is a 'legal quagmire' which researchers should contemplate very carefully before entering.

Finally, the editorial piece, having considered these issues, lays out the current policy for the publication of studies based upon material from Myanmar (or other troubled or contentious areas), across all Nature journals; to whit that the export of material must be in line with both local and international law, and that any material used in such studies should be deposited in a recognised museum, collection or accessible repository. 

The tip of the wing of a fledgeling Cretaceous Bird, trapped in Burmese Amber. Ming Bai/Chinese Academy of Sciences.

Whilst this editorial policy would seem to go some way towards addressing the problems of Burmese Amber, it by no means resolves all the issues raised within the articles. Notably, the number of publications featuring material from Burmese Amber has been rising sharply since 2010, and in particular since 2017, when the Myanmar military is reported to have taken over the amber-producing mines, and news of Human rights abuses associated with the mines began to emerge. Thus, one of the major concerns about Burmese Amber is behaviour of the ruling military junta, which is accused of both abusing the rights of miners, and of using money from the sale of amber to buy arms and fund conflicts against minority groups within Myanmar. This cannot be addressed by complying with Myanmar's export laws, since those laws are drawn up by, and serve the interests of, those accused of committing Human rights abuses. 

Neither can the problem of parachute science be resolved simply by making sure that specimens are in collections where they are (in theory) available to scientists from their home country. No matter how good the intentions of such countries, the cost of travelling to them in order to study material is often prohibitively expensive, particularly if more than one country needs to be visited to see scattered specimens. This is compounded by an increasing tendency by governments in Europe and North America to refuse to allow researchers from other parts of the world to enter their countries at all, something which plays well with sections of the western media that have taken to scapegoating immigrants at every opportunity, but which compounds the injustice of having material removed from countries to be studied in other parts of the world.

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Monday, 12 July 2021

Hunting preferences in Chimpanzees, and their implications for early Human hunters.

Chimpanzees, Pan troglodytes, are one of our closest non-Human relatives (along with Bonobos, Pan paniscus), sharing 96% of our genome, and many behavioural traits. Due to this, Chimpanzee behaviour is often used as a proxy for early Hominid behaviour (Hominids being Humans, and anything more closely related to Humans than it is to Chimpanzees and Bonobos). Chimpanzees were for a long time thought to be herbivorous, but the numerous studies of these Apes carried out since the 1960s have shown them to be omnivores, which actively hunt a wide range of prey, including smaller Primates, Chimpanzees are now known to engage in cooperative group hunting using a range of stone tools, which makes understanding this aspect of their behaviour particularly intriguing to scientists trying to understand the origins of such behaviours in Hominids.

The optimal foraging theory predicts that an Animal will chose prey that provides the maximum energetic return from capturing and consuming it without getting injured in the process. Chimpanzees are particularly interesting in this regard, as different groups of Chimpanzees favour different types of prey, and use different tools and hunting techniques, traits which are identified as evidence for the development of distinct cultures among different groups. Notably, many Chimpanzees live in areas where there is a marked seasonal variation in prey availability, requiring them to switch hunting techniques while still accessing the best available prey. This is predicted to be the largest size of prey that can be captured safely by Chimpanzees in any area at any given time, with Chimpanzee cultural traits evolving to maximise this return. Meat derived from hunts is divided among the group, with the first choice of meat usually going to the most mature members of the group, thereby promoting collaboration within the group over solitary hunting.

A Chimpanzee consuming an Ashy Red Colobus Monkey, Piliocolobus tephrosceles, in the Kibale National Park, Uganda. BBC Earth.

In a paper published in the journal Ecology and Evolution on 4 May 2021, Cassandra Bugir of the Conservation Biology Research Group at the University of Newcastle, Thomas Butynski of the Eastern Africa Primate Diversity and Conservation Program, and Matt Hayward, also of the Conservation Biology Research Group at the University of Newcastle, and of the Mammal Research Institute at the University of Pretoria, and the Centre for African Conservation Ecology at Nelson Mandela University, present the results of a study in which they searched the existing literature on Chimpanzee diet and behaviour in order to determine prey preferences amongst different Chimpanzee groups, and the factors which drove their prey selection choices.

Bugir et al. sought out data on both the prey type selected by Chimpanzees, and abundance data on the prey being taken, excluding from their study previous research where this was not provided and could not otherwise be determined. They were particularly interested in the prey species taken, the availability of those prey species, the number of each type of prey taken, the type of tools used to capture the prey, and the size and sex ration of hunting groups, and size of the prey in kilograms.

In some cases data on prey bodyweights were not available, but it was possible to estimate this from other studies of the prey species. The mean adult bodyweight of a male Chimpanzee was estimated at 41.2 kg, based upon data from previous studies, which was used as the standard against which prey bodyweight could be compared, as adult male Chimpanzees are the members of the group which do the most hunting.

Bugir et al. found a total of thirteen usable studies from four different localities, two in Uganda and two in Tanzania, and covering the period from 1984 to 1997. This yielded data on 20 prey species, hunted at 76 differnt times and places. Eleven of the 20 prey species were targeted on three or more occasions, which was deemed sufficient data for further analysis.

The four sites where data on Chimpanzee predation were obtained. Bugir et al. (2021).

The most favoured prey of the Chimpanzees at three of the four study sites was the Ashy Red Colobus Monkey, Piliocolobus tephrosceles. Infant and juvenile Bushbuck, Tragelaphus scriptus, and Western Guereza Colobus Monkey, Colobus guereza occidentalis, were all taken preferentially when available. However, Bugir et al. do note that their study was based upon a series of snapshots, and could have missed important changes in prey preference. 

The Chimpanzees also appeared to avoid certain potential prey species, notably Olive Baboon, Papio anubis, Blue Duiker, Philantomba monticola, Gentle Monkey, Cercopithecus mitis, and Red-tailed Monkey, Cercopithecus ascanius. This appears to indicate that Chimpanzees have an upper size preference for prey at about 7.6 kg, with species larger than this being avoided, and those slightly below it being preferred. This indicates that an adult male Chimpanzee will take prey up to 18% of its own size.

Chimpanzee prey preferences determined by mean Jacobs’ index values ±1 SE calculated from 13 studies at four sites. Significantly preferred prey, taken in excess of their abundance, are delineated by black bars. Gray bars denote significantly avoided prey which are less likely to be pursued irrespective of their abundance. Blue bars are prey that are taken or avoided according to their availability. Bugir et al. (2021).

There is also an apparent relationship between the sex ratio within a group, and the likelihood that the Chimpanzees will develop a preference for certain types of prey. This appears to be a far greater contributing factor than group size, prey body weight, or hunting method.

Having preferred prey species and avoiding potential prey which is to large to be taken safely is a trait that Chimpanzees share with other predators; in the case of Chimpanzees the upper size limit for prey appears to be about 7.6 kg. Larger prey, such as Baboons or Ungulates, are generally avoided, although immature members of these species may be hunted. This is a much lower threshold than that of Humans living in hunter-gatherer societies, who will typically take prey up to a limit of 276% of the size of an adult female. Meat plays an important role in the diet of both species, but is clearly much more important to Humans, with up to 60% of the diet of Humans living in hunter-gatherer societies coming from Animals, including about 35% from Mammals, while the Chimpanzee diet is typically about 4% meat. This suggests that the preference for meat may have been a major driver in the brain-size increase seen in Humans compared to Chimpanzees, and that Chimpanzees cannot be seen as apex predators in the way that Humans, Lions, and Tigers are.

The largest driver of variation in prey choice appears to be the sex ration within groups of Chimpanzees, with groups with a high proportion of males taking a much wider range of prey. In all Chimpanzee groups males are the primary hunters, but females sometimes join hunting expeditions, and make use of tools when they do so.

The main purpose in hunting among Chimpanzees appears to be social, whereas in Human hunter-gatherers meat is a substantial part of the diet, and thus Humans appear to fit the optimal foraging model better than Chimpanzees, with Humans efficiently hunting a wide range of prey, with masses ranging from 2.5 kg to 535 kg, using techniques that are safe to themselves and which yield high energy returns. However, Humans may be being driven to target a wider range of prey by their own success, with many Human hunters living in 'empty forests' in which the majority of potential prey species have either been wiped out, or are present at only very low densities. 

Despite the differences in hunting emphasis, the 'empty forests' phenomenon may not be exclusive to Humans, with the Chimpanzees of the Kibale National Park in having apparently become so efficient at hunting Red Colobus Monkeys that that species is in danger of being wiped out in the area, which presumably would in turn result in the Chimpanzees being forced to switch to alternative prey.

Understanding the hunting preferences of Chimpanzees has the potential to improve our ability to conserve both the Chimpanzees themselves and their prey species. Knowing what is being hunted by Chimpanzees, and which groups of Chimpanzees are doing the hunting, gives us the ability to bolster prey-species populations, thereby improving the survival chances of the Chimpanzees themselves. This understanding also has the potential to give some insight into the behaviour of early Hominids, and thereby improve our understanding of our own ancestors. 

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Monday, 5 July 2021

Ruptured gas pipeline leads to fountain of fire in the Gulf of Mexico.

A fire broke out on the sea surface in the Gulf of Mexico, after a natural gas pipeline ruptured on Friday 2 July 2021. The pipeline, which connected the KU-C satellite platform on the Ku Maloob Zaap Oil Field, ruptured some time before 5.15 am local time, when the leaking gas ignited, with the fire being brought completely under control by 10.30 am. Although dramatic, nobody was hurt during the incident. It is unclear at this time how the pipeline was damaged, or how the leaking gas was subsequently ignited.

A fire on the surface of the Gulf of Mexico on 2 July 2021, caused by a ruptured natural gas pipeline. Manuel López San Martín/Twitter.

The Ku Maloob Zaap oil field is worked by the Mexican state-owned Petróleos Mexicanos (Pemex), in the Bay of Campeche, off the coast of Tabasco State, on the Yucatan Peninsula. The oil field is actually made up of three separate reserves, the Ku reserve, located in Kimmeridgian (Late Jurassic) deposits, the Maloob, which is in Late Cretaceous-Palaeocene strata, and the Eocene Zaap reserve. The field is worked by seventeen drilling platforms connected by 166 km of pipeline. The field has been worked since the early 1980s, with peak production reached in 2009, when the field was producing more than 130 million litres of oil and over three billion litres of natural gas per day, with production having declined steadily since that time.

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Sunday, 4 July 2021

Thousands of people evacuated after eruption on Mount Taal, the Philippines.

Thousands of people have been evacuated following an eruption on Mount Taal, on Luzon Island, the Philippines, on Thursday 11 July 2021. Activity on the 311 m high volcano began earlier in the week, when it began emitting large amounts of toxic sulphur dioxide gas, with the Philippine Institute of Volcanology and Seismology raising the alert level of the volcano following the eruption, which produced an ash column a kilometre high, and beginning evacuations of communities around Lake Taal, which is overlooked by the volcano. The vulcanologists are concerned by the sharp increase in seismic activity beneath the volcano, as such Earthquakes are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode.  

Eruption on Mount Taal, the Philippines, on 1 July 2021. AFP.

While the volcano is in itself dangerous, much of the concern is that Earthquakes or eruptions around it could trigger a landslide into the lake, triggering a tsunami wave. Tsunamis occur when large volumes of water are displaced by geological events, such as landslips or Earthquakes, forming waves which spread out through the surrounding water. Like other waves, tsunamis are not necessarily obvious in deep, open waters, but when they reach shallow or enclosed waterways can be extremely dangerous. This is because a tsunami isn't just a wave above the normal water-level, it is pressure wave beneath the surface, which is amplified in the enclosed space. A tsunami reaching the shore is typically preceded and followed by rapidly shallowing water. Thus people in areas prone to tsunamis know to evacuate the coast rapidly if the tide apparently goes out rapidly, since this is likely to be followed by the tide coming in rapidly. This gives us the English term 'tidal wave' which is no longer used, since it is inaccurate; the tides are caused by the gravity of the sun and moon, tsunamis are nothing to do with the tide. The term 'tsunami' comes from Japan, where earthquakes, and therefore tsunamis, are common.

How a landslip can trigger a tsunami. University of California, Santa Cruz/BBC.

The geology of the Philippines is complex, with the majority of the islands located on the east of the Sunda Plate. To the east of this lies the Philippine Sea plate, which is being subducted beneath the Sunda Plate (a breakaway part of the Eurasian Plate); further east, in the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Sea Plate. This is not a smooth process, and the rocks of the tectonic plates frequently stick together before eventually being broken apart by the rising pressure, leading to Earthquakes in the process. Material from the subducting Philippine Plate is heated by the temperature of the Earth's interior, causing lighter minerals to melt and the resultant magma to rise through the overlying Sunda Plate, fuelling the volcanoes of the Philippines.

Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.

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Understanding negative Human-Crocodile interactions in the La Encrucijada Biosphere Reserve, Mexico.

There are 24 extant species of Crocodilians, of which three can be found in Mexico; the Spectacled Caiman, Caiman crocodilus, and Morelet’s Crocodile, Crocodylus moreletii, both of which are considered to be of Least Concern under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, and the American Crocodile, Crocodylus acutus, which is considered to be Vulnerable. All of these are subject to Special Protection under Mexican law. Both the Spectacled Caiman and American Crocodile were previously heavily hunted for their skins, but this practice was banned in the 1970s, since when their populations have recovered somewhat, although they are still targeted illegally in some parts of the country.

A Morelet’s Crocodile, Crocodylus moreletii. Gautier Poupeau/Wikimedia Commons.

As Crocodilian populations have recovered, negative interactions with Humans have increased, something fuelled apparently by both the rise in Crocodilian numbers, and that of Humans, combined with changes in land use, and some widespread flooding incidents. Crocodiles are prone to pre-emptively defending both themselves and their territories, and females are particularly agressive during the nesting season, which can increase negative encounters with Humans, and American and Morelet's Crocodiles are calculated to be responsible for 2.9 and 0.5 fatalities per year respectively, across the Americas as a whole, but this is probably an underestimate, as not all incidents are recorded. 

Detailed recording and analysis of negative Crocodile-Human interactions can help scientists to understand the causes of such incidents, and come up with ways to minimise the number of such events. The Mexican State of Chiapas would be predicted to be a high risk one for such attacks, but the Worldwide Crocodilian Attack Database lists only four incidents for the state, making it likely to be an underestimate.

In a paper published in the journal Orynx on 21 May 2021, Giovany Arturo González-Desales of the Centro de Investigación en Ciencias Biológicas Aplicadas at the Universidad Autónoma del Estado de México, Luis Sigler of the Dallas World Aquarium, Jesus García-Grajales of the Universidad del Mar, Pierre Charruau of the Centro del Cambio Global y la Sustentabilidad A.C. Calle, and Martha Mariela Zarco-González, Ángel Balbuena-Serrano, and Octavio Monroy-Vilchis, also of the Centro de Investigación en Ciencias Biológicas Aplicadas at the Universidad Autónoma del Estado de México, investigate Crocodile attacks in the El Hueyate estuary in Chiapas State, as well as the wider situation in Mexico, focussing on whether such attacks are more common in the nesting season, and whether they increase with rising Human or Crocodile populations.

González-Desales et al. compiled monthly records of negative interactions between Humans and Crocodiles in Mexico from the Worldwide Crocodilian Attack Database, for the period 15 August 1993 to 8 June 2018. Using this data they calculated the distance from each attack to the nearest Crocodile nesting site for which data was available, as well as calculating the relationships between attack frequency and the density of the Crocodile and Human populations. They also look at a number of socio-economic factors in areas of Mexico where adverse Human-Crocodile interactions have been recorded, including economic activities, male education levels, Human population density, proportion of males in the Human population, and the proportion of those males who are economically active. González-Desales et al. concentrated on the male part of the Human population, as these are significantly more likely to be involved in negative interactions with Crocodiles.

The El Hueyate Estuary forms part of the La Encrucijada Biosphere Reserve on the Pacific coast of Chiapas State, Mexico. It comprises a 1086.5 km² buffer zone surrounding two core areas, El Palmarcito and La Encrucijada, which have a combined area of 316.2 km². Two Crocodilians can be found within this area, the Chiapas Caiman, Caiman crocodilus chiapasius, a subspecies of Spectacled Caiman, and the American Crocodile, Crocodylus acutus. These are found both in natural waterways, and Human-created environments such as dams, cattle ponds, fishery ponds and pampas, but are more common in the core zones than elsewhere. Both species nest and breed within the reserve. The reserve also contains 64 Human settlements, with a total population of 26 992 people; 28.5% of this population having no formal education of any type. The main sources of income for this Human population are fishing, agriculture and livestock breeding.

La Encrucijada Biosphere Reserve, with the locations of the six negative interactions (cases) between people and crocodilians recorded during 2015-2018, five with American Crocodiles, Crocodylus acutus, and one (case 5) with a Spectacled Caiman, Caiman crocodilus chiapasius, and nests recorded in 2014. González-Desales et al. (2021).

González-Desales et al. carried out unstructured interviews with residents of settlements on the El Hueyate estuary between October 2013 and September 2014. They interviewed seventeen men and five women, all between 22 and 51 years old, out of a population of 543 people. All of those interviewed had either been involved in a Crocodile-related incident, or were related to someone who had. González-Desales et al. concentrated on gaining information about attacks, notably the date and location of any interactions, what people were doing at the time of the incidents, and any actions subsequently taken against the Crocodiles.

During March–October 2014 (the nesting season of both the Chiapas Caiman and the American Crocodile), González-Desales et al. carried out a series of surveys in the El Hueyate estuary, using a 6 m boat with a 15 horsepower outboard motor. They used a white LED light to search for Crocodiles at night, using the reflectiveness of the Animals' eyes to detect them, then carefully moving closer to identify their species. 

The Worldwide Crocodilian Attack Database contains 121 records of attacks on people by American Crocodiles in Mexico between 15 August 1993 and 8 June 2018; there are no records of any attacks by Caiman. These attacks were significantly more likely to occur close to nesting sites. Attacks were most common in municipalities where the Human population was below average, the economy dominated by service industries, and the male Human population had an average of 7.4 years of education.

Negative interactions by month involving Crocodylus acutus in Mexico, showing that the incidents are more frequent in nesting season. González-Desales et al. (2021).

Surveys of American Crocodiles in the El Hueyate estuary carried out in the years 1997, 1998, 2002, 2008, 2009, and 2010 found their population density varied between 1.14 and 7.11 individuals per km, with the 2014 survey carried out by González-Desales et al. finding an average of 1.5 Crocodiles per km. The previous surveys also found between 0 and 2.42 Caiman per km, with González-Desales et al. finding an average of 2.71 Caiman per km.

The interviews carried out by González-Desales et al. revealed six Crocodilian-related incidents in the El Hueyate estuary between 2005 and 2014, two of which resulted in loss of Human life, two in major injury (defined by González-Desales et al. as limb loss or permanent motor impairment), and two in minor injuries. Five of these incidents involved American Crocodiles, and one involved a Caiman.

(a) Relative abundance index (Crocodilians observed per km, during 1997-20014) of Crocodylus acutus and Caiman crocodilus chiapasius, and (b) the number of negative Human–Crocodilian interactions per year (during 2005-2018), in El Hueyate estuary, La Encrucijada Biosphere Reserve, Mexico. González-Desales et al. (2021).

The interviews carried out by González-Desales et al. also found that Crocodile attacks on domestic Animals (mainly Dogs) and livestock (Cattle and Pigs) were common in the El Hueyate estuary. As well as Crocodile attacks on Humans, incidents of Humans killing Crocodiles were common, with 30 reported Crocodile killings in 2011-2012, most of which which were in response to Crocodile attacks on Humans, domestic Animals, or livestock. Attacks on Humans were also more common near nesting sites, with five of the recorded incidents happening at such locations.

Previous studied have shown that most attacks on Humans by Saltwater Crocodiles, Crocodylus porosus, in Australia and Sri Lanka were associated with females defending nests, and González-Desales et al.'s work, the first detailed study of Crocodile attacks in Mexico, suggests that this also might be the case here. However, the Sri Lankan and Australian studies found that the number of attacks went up with increasing Crocodile population density, but that does not appear to be the case in Mexico.

The limited scale of the study makes it impossible to make to many inferences about the Crocodile population from it, but the report of Crocodiles being killed in response to attacks is of concern, as this appears to be on a large enough scale to have an impact on the Crocodile population, particularly if this involves females of reproductive age being killed in the breeding season. Previous studies have noted that Crocodiles are frequently killed in response to attacks on Humans in other parts of Mexico; this was also found to be a factor in Sri Lanka.

The records of Crocodile populations available for La Encrucijada suggest that the population underwent a dip following each recorded attack on a Human, supporting the idea that Human retaliatory action is having an impact on the Crocodile population. The population in the area is currently as low as it was before protection of these species was introduced in the 1990s, and it may be necessary to repeat some of the actions taken in the 1990s to protect the species, notably the removal of egg clutches and rearing of Crocodiles in captivity before releasing them back into the reserve. Actions such as this have been employed more recently in other parts of Mexico, with some success.

A Chiapas Caiman, Caiman crocodilus chiapasius, reproductive female in Isla La Concepcion, La Encrucijada Biosphere Reserve. Giovany Arturo González-Desales/Orynx.

González-Desales et al. report that, since 2011, people living in the El Hueyate estuary have abandoned spear fishing, for fear of being attacked by Crocodiles, and that they have begun to destroy Crocodile eggs as a way of controlling the Crocodile population. This appears to indicate that both Humans and Crocodiles are currently suffering as a result of negative interactions between the species. González-Desales et al. also note that while Crocodile attacks have obvious impacts on the Human population, both as a result of death and injury to Humans, and the loss of valuable livestock, the loss of Crocodiles can cause problems, as it is linked to a rise in the populations of other Animals (mostly small Mammals, Birds, and Arthropods) which cause problems for agriculture.

González-Desales et al. believe this makes it important to properly monitor Human-Crocodile interactions in areas such as the El Hueyate estuary, and develop strategies facilitate coexistence, such as ecotourism or even sustainable harvesting. To properly conserve Crocodile populations it is not enough to simply pass laws protecting them; conservation efforts should involve local stakeholders such as governmental and non-governmental agencies, local businesses, particularly those involved in tourism, the media, and the general public.

The majority (78.5%) of Crocodile attacks in the El Hueyate estuary happen between February and September, the breeding season of the American Crocodile. This is similar to the situation seen with the Mugger Crocodile, Crocodylus palustris, in India, where 71.8% of attacks occur during the breeding season. The main economic activity in the El Hueyate estuary is fishing, with most attacks by Crocodiles happening when people are fishing close to nests in the breeding season. The population of the estuary believe that attacks are more common when Crocodile numbers are high, but González-Desales et al. could find no evidence to support this; if anything, attacks were more common when Crocodile numbers were low, possibly suggesting that people were lass wary at these times, and therefore more at risk.


American Crocodile, Crocodylus acutus, hatchlings in Isla La Concepción. Humberto Yee/Orynx.

The size of the Crocodiles appears to be another important factor, with the average size of Crocodiles attacking Humans in Mexico being 2.8 m, and 36 of the recorded Crocodile attacks on the Worldwide Crocodilian Attack Database for which size was available being by Animals in excess of 2 m. All of the attacks in the El Hueyate estuary involved Crocodiles between 1.5 and 3.7 m in length, and all of the incidents during the breeding season, when Crocodiles were either breeding, nesting, or looking after neonates. 

For a variety of other Crocodile species, it has been demonstrated that attacks on Humans occur when Human activities take them into the Crocodile's territories, and this appears to be the case for the Mexican Crocodiles. González-Desales et al. found a strong correlation between Crocodile attacks, the Crocodile breeding season, and Human economic activities, something which has previously been demonstrated on the Mexican Pacific coast. There does not appear to be any direct corelation between Crocodile population sizes and frequency of attacks. However, this probably needs to be monitored more closely, in order to find the best ways to protect both local populations and tourists. Local economic activities and the locations of Crocodile nesting sites should also be taken into account when planning Crocodile management strategies.

Negative interactions between Humans and Crocodiles appear to be increasing in Mexico, and the reasons for this need to be studied in order to develop good strategies to manage Human-Crocodile activities. Conservation policies need to take into account both Crocodile behaviour and Human economic activities in order to prevent the unwanted killing of Crocodiles; simple prohibitions on such activities are not enough. Public education campaigns are also very important, giving people the tools to beter avoid Crocodile attacks, and protecting Crocodiles by emphasising the ecological, and therefore economic, importance. A diverse range of stakeholders need to be involved in conservation efforts.

Finally, González-Desales et al. make a number of recommendations for Crocodile management in Mexico, including the monitoring of tourism activities close to Crocodile nesting sites during the breeding season, the provision of better public information on Crocodile behaviour, the protection of eggs by artificial rearing, and the development of strategies for Crocodile management that also take into account the economic needs of local Human populations. Some of these strategies have already been implemented in the El Hueyate estuary, and do appear to have prevented further Crocodile attacks; these include the provision of signs warning people of the presence of Crocodile nests, and the active involvement of local people in protecting those nests. 

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