How many deaths are caused by crocodiles each year?
We were asked by the Gates Foundation to estimate of the number of deaths caused by crocodiles each year (Gates 2014). Even considering that we run a unique database on crocodile attack statistics, this is not a straightforward question to answer. That's because a certain percentage of attacks that happen each year are never reported, recorded, acknowledged or even witnessed. Even worse, we don't know what this percentage is. We're fairly sure it's a minority of incidents, but it also varies between species and countries. The species that's likely responsible for the most attacks, the Nile crocodile, also happens to be one of the worst-reported in terms of crocodile attack incidents from certain countries in Africa. See the next question for more on this. But to answer the question, we averaged the number of annual incidents in recent years, added an estimate for incidents we suspect are missing (based on information from local officials and specialists in the regions concerned), and considered what proportion were likely to be fatal (based on each species average), resulting in an estimated 1,000 fatalities per year. Although this is a reasonable ballpark figure, it shouldn't be taken too literally. Hopefully as we collect more information from areas previously lacking in it, we'll get a better understanding of these statistics.
Which species is responsible for the most attacks?
The Nile crocodile, Crocodylus niloticus, is usually implicated in the most attacks each year. It is often said that it kills more people in Africa than any other animal, a statistic which appears to be true (Lamarque et al. 2009). Yet according to the CrocBITE database, they rank second to the number attacks by the saltwater / estuarine crocodile, Crocodylus porosus. This raises two important points. The first is that there are a lot more attacks annually by saltwater crocodiles throughout their range than previously suspected. Many attack reports are published in obscure places, typically in a variety of languages, and often these reports disappear from public record quickly. CrocBITE contributors are able to archive most of these reports before they disappear, although historical records are a different story (see below). However, the second point is that Nile crocodile attacks are undoubtedly under-represented in the database; in many countries data are difficult to obtain, and many attacks go unreported. In some countries the number of attacks annually seems extreme; in Mozambique it has been estimated that over 300 attacks occur annually (Anderson and Pariela 2005), and perhaps 150 occurring in Namibia on a mixture of humans and cattle (Murphy 2007 cit. Lamarque et al. 2009). With reporting in such poor condition it is difficult to know how accurate these figures really are, but it seems very likely given the potential danger posted by Nile crocodiles and the common water use by local people around crocodile populations that Nile crocodiles remain the species responsible for the most attacks worldwide.
Are the number of attacks increasing over time?
Generally, the answer would seem to be yes because crocodilian populations are increasing, human populations are increasing, and the potential for conflict between them is increasing. However, in reality it is difficult to judge the rate at which this is happening given our current knowledge. The answer also varies between countries because management plans vary, not to mention the trends in variables such as human population growth, crocodilian population growth, habitat loss, water use, and more. Remarkably few countries keep any kind of official records of attacks by crocodilians on humans, never mind any kind of formal database. Reconstructing these historical records for CrocBITE has taken nearly three years so far, and we are beginning to understand the strengths and weaknesses of the data. The majority of attack data come from media reports for those countries where no official records are kept, and these are highly transient. Even some reports that we archived less than 12 months ago have already disappeared from the internet; many of these were reports from local news agencies whose websites have since disappeared, or have been removed from their limited set of archives. The further back in time we go, the less detailed information is available on attacks as short summaries that miss important details replace the original reports. Therefore, while the trend over time has been for a greatly increasing number of crocodilian attack reports overall, the reality is less clearly defined. This is where CrocBITE is essential as an archival tool, so that we can build up a more complete picture of trends over time, and hence have a better understanding of conflict issues and areas of concern.
What about new species like Crocodylus suchus?
Although there are 23 recognised species, there is a lot of interest in crocodilian taxonomy and several species will likely be subdivided into new species in the near future. The one most relevant to CrocBITE is the Nile crocodile. There is very strong genetic and phylogenetic evidence that the "Nile crocodile" is actually two distinct species, one in eastern and southern African countries (Crocodylus niloticus) and the other in central and western African countries (Crocodylus suchus) (Hekkela et al. 2011). At present all attacks by either of these species are classified under Nile crocodile (C. niloticus) but we plan to separate them into distinct species at the right time. The reason for not separating them yet is partly because attack data from African countries are extremely patchy and under-representative, and partly because C. suchus is not yet formerly recognised as a distinct species by the IUCN or CITES. There are legal, conservation and management implications of separating the Nile crocodile into two species, not a task to be taken lightly.
What attacks if any have been excluded from CrocBITE?
We have decided to exclude certain categories of crocodilian attacks because they fall outside the scope of this project. The first group of attacks excluded are incidents occurring in captivity, typically involving zoo staff, crocodile farm staff, or private keepers. The purpose of CrocBITE is to provide a better understanding of the conflict between wild populations of crocodilians and humans, and incidents occurring in captivity do not provide any useful information about human-crocodile conflict, although they do tell us a lot about incorrect handling procedures, inadequate safety protocols, and human error.
The next group of attacks we have excluded are incidents involving work-related contact with crocodilians; people whose job it is to catch or interact with crocodilians for any purpose. This does create some grey areas. For example, rangers who capture problem crocodilians are sometimes bitten because they are putting themselves in direct contact with the animals; there are a large number of such incidents, usually minor. However, workers who collect eggs from wild crocodilian nests are trying to avoid direct contact with the animals. We have still chosen to exclude these at this point.
The third group of attacks are any incidents where no injuries were caused, as these are typically not reported even though they clearly indicate the potential for conflict, and/or a failure to address potential conflict. We have also excluded attacks on domestic animals.
All other wild attacks where it has been confirmed that a crocodilian was responsible are included in the database.
Anderson, J. and F. Pariela, 2005. Strategies to mitigate human-wildlife conflict in Mozambique. Report for the National Directorate of Forests and Wildlife, Mozambique. Food and Agriculture Organization of the United Nations, Rome.
Gates, B., 2014. The Deadliest Animal in the World. https://www.gatesnotes.com/Health/Most-Lethal-Animal-Mosquito-Week
Hekkala, E., M.H. Shirley, G. Amato, J.D. Austin, S. Charter, J. Thorbjarnarson, K.A. Vliet, M.L. Houck, R. Desalle and M.J. Blum, 2011. An ancient icon reveals new mysteries: mummy DNA resurrects a cryptic species within the Nile crocodile. Molecular Ecology 20(20):4195-8
Lamarque, F., J. Anderson, R. Ferguson, M. Lagrange, Y. Osei-Owusu and L. Bakker, 2009. Human-wildlife conflict in Africa. Causes, consequences and management strategies. FAO Forestry Paper 157. Food and Agriculture Organization of the United Nations, Rome. 102 pp.
Murphy, C., 2007. Community-based crocodile management. Travel News Namibia. <no longer online>