Nile Crocodile populations were depleted throughout much of their range due to hunting between the 1940s and the 1960s (in some countries as late as the 1970s). However, protection afforded by national legislation and international trade conventions (CITES) has resulted in recovery in many parts of the species’ range (Fergusson 2010). In general though, crocodile densities exhibit a significant negative correlation with human densities and it is likely that the status of crocodiles throughout Africa is closely linked with human densities and development patterns (Aust 2009). In addition, crocodile densities were found to be positively correlated with IUCN protected areas and it is likely that the future status of national populations will be linked to the extent and management of nationally protected habitat (Aust 2009).
Overall, Nile Crocodiles are not threatened with extinction, although there are increasing threats to populations existing outside protected areas, and in some instances within formally protected areas (Combrink 2011, Ferreira and Pienaar 2011, Calverley and Downs 2014, Behangana 2017). In some areas, human-crocodile conflict (HCC) has become a major problem and retaliation killings are a threat. Consequently, the management of HCC has now become the major focus of programs in several countries, replacing the previous emphasis on sustainable use through ranching and trophy hunting. Several countries have significant export quotas for wild harvested skins and these are mostly derived from programs nominally aimed at alleviating HCC (Fergusson 2010). A search of CrocBITE (the crocodilian attack database) for Crocodylus niloticus attacks only reveals a subset of actual HCC occurrence, remembering that not all attacks are reported (CrocBITE 2013, IUCN-SSC CSG 2017). However, fatal attacks from C. niloticus are the most numerous of all crocodilian species, even saltwater crocodiles (C. porosus), and pose a real threat to some conservation and management strategies and programs. Pooley (2015, 2016) has begun to piece together innovative ways to understand HCC by exploring the historical, cultural, social and ecological dynamics between crocodiles and humans at a sub-regional level.
The Nile Crocodile is one of the most commercially utilized crocodilians, the skin being acknowledged as one of the “classics” (Fergusson 2010). The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) does not yet recognise C. suchus, and reports annual trade exports of over 250,000 skins from the C. niloticus range states (CITES Trade Database 2017, Caldwell 2017). The majority of these are from Zimbabwe (50%), South Africa (30%) and Zambia (14%). The formal crocodile skin industry is now well established and market forces together with ongoing trade controls have largely negated illegal international trade in crocodile skins, which is thought to be insignificant. In the 1980s, the CITES Nile Crocodile Project played an important role in developing sustainable yield programs, emphasizing ranching as the preferred means of obtaining conservation benefits from crocodile utilization (MacGregor 2002).
Population status in each of the range states is presented separately where available.
Angola: Almost nothing about the distribution and densities of C. niloticus in Angola has been documented. Shacks and Bourquin (2013) conducted spotlight counts on a section of the Cuito and Cuando rivers in April 2013. From this limited work, it appears that healthy populations exist. Human-crocodile conflict is reported to be intense with crocodiles killed whenever possible. One community member reported that crocodile eggs, when found, were eaten by people. Large tracts of riverside vegetation are cleared for the plantation of casava, maize and sorghum and is very intensive along the southern Cuito system. This is likely to increase dramatically once the new tar road is complete and people start moving to the more developed riverside villages (Shacks and Bourquin 2013).
Botswana: Records estimate that up to 48,000 wild individuals were hunted 1957-1968, but the standing population at any one time is unknown (Pooley 1982). A 2004/05 survey of the Okavango Panhandle by Bishop et al. (2009) estimated 663 adults whilst Bourquin and Leslie (2011) estimated 649 adults of which 364 were females. The most recent survey reported an adjusted estimate of 549 adults, showing a relatively stable adult population of 25-30% of the total population (Bourquin and Shacks 2016a,b). However, Bourquin and Shacks (2016a, b) reported a drastic decline in the sub-adult population from 18% in 2008 to only 4% in 2016. This is possibly due to an observed decline in fish numbers, potentially from unsustainable fishing activities, given the heavy reliance of sub-adult C. niloticus on fish in their diet (Bourquin and Shacks 2016a). As there are no observed mortalities, it is presumed that these sub-adults may have moved out of the Panhandle. The total Botswana adult C. niloticus numbers are estimated to be greater than 4,000 (Isberg et al. 2016).
Cameroon, Gabon and Central African Republic: Declining C. niloticus populations have been reduced to the extent that they do not contribute significantly to the global population (Isberg et al. 2016). Recent surveys in Gabon estimate there are less than 500 adult C. niloticus with a limited coastal distribution (M. Shirley pers. comm. 2018). Historically, Behra (1987) reported more than 20,000 skins per year exported collectively from these countries prior to them joining CITES (1980-89), with severe population depletion in the mid-1980s.
Egypt: Since the 1950s, C. niloticus were virtually eradicated from the Nile River in Egypt but the construction of the Aswan Dam and formation of Lake Nasser in the 1960s allowed population recovery, with a current estimate of 15,000 to 20,000 individuals of which 20% are adults (CITES 2010, Shirley et al. 2012, i.e. 3,000-4,000). The re-establishment of this population was reflected in the transfer of the Egyptian population of C. niloticus from Appendix I to Appendix II of CITES in 2010, although with a zero export quota pending a sustainable management program.
Ethiopia: Historically, C. niloticus was abundant in Ethiopia but heavy hunting for skins from the mid-1950s resulted in more than 47 000 C. niloticus skins legally exported from 1965 to 1972. Several thousand of these were taken from the Rift Valley lakes. Legal hunting plus illegal killings near the border with Sudan have severely reduced the populations in Ethiopia (Pooley 1982, Gebre 2000). In 1972, commercial hunting of C. niloticus was prohibited in Ethiopia and C. niloticus was listed as a game animal which could only be hunted under permit (Whitaker and Whitaker 2007).
Although crocodiles occur elsewhere in Ethiopia, Lake Chamo has the largest and most important population. Anecdotal accounts note that crocodile abundance and nesting site availability have decreased since 2008 due to increased fishing pressure and more riparian lifestyles of local people (Shirley et al. 2014). Prior to this, Whitaker (2007) estimated up to 2,000 individuals inhabited the Lake with an estimated 350-500 breeding females producing 15,000-20,000 eggs annually. Shirley et al. (2014) counted a total of 1,443 individuals of all sizes, but did not include a section (Crocodile Market) with a high concentration of large crocodiles (Crocodile Market). To account for this, Shirley et al. (2014) used a correction factor and estimated the adult population (2+ meters) in Lake Chamo was 300+ C. niloticus. Ethiopia has a wild egg harvest limit of 3,000 eggs per annum, but only exported six skins in 2015 (Caldwell 2017).
Recently, a small number (n=5) of crocodile tissue samples from the Awash basin (± 145 km northeast of Lake Chamo), including the entire length of the Awash River, revealed that the crocodiles were C. suchus (Siege and Koch 2017). The lines of demarcation for these two species (C. niloticus and C. suchus) in Ethiopia are still being determined.
Kenya: There are healthy adult crocodile populations in all rivers (including feeder rivers) and lakes that are in National Parks and Reserves and protected by Kenya Wildlife Services (D. Haller pers. comm. 2016). These include the Mara, Sabaki/Galana, Tsavo, Meru, Ewaso Ng’iro and Turkwel Rivers as well as the north of Lake Turkana including Lake Sibilio National Park, Central Island and the Omo Delta. However, open areas which are, or have been, populated by people have seen a dramatic decline in crocodile populations over the last 10 years. For example, the Tana River, which is the longest river in Kenya, had a very large crocodile population but over the last 10 years has seen a rapid decline due to human intolerance. Despite this, there is still a conservative estimate of 1,500 adult crocodiles in the Tana River, despite anthropogenic effects continuing to pose a threat to both crocodile habitats and populations (D. Haller pers. comm. 2016). Three farms collect eggs on the Tana River, with approximately 15,000 eggs in the 2015/16 season (average nest size 32 eggs; D. Haller pers. comm. 2016), indicating a healthy adult population. Daniel Haller (pers. comm. 2016) estimates that the adult wild C. niloticus population in Kenya is greater than 4,000.
Madagascar: The Nile crocodile is widely distributed throughout the country, particularly in the river and lake systems bordering the northwestern and western sides of the high plateau, and the northeast of the country (CITES 1997). Survey data confirm that wild C. niloticus population densities are low throughout the rivers and lakes of Madagascar, even in the areas where C. niloticus were previously relatively abundant. This is the result of continued unregulated hunting of crocodiles of all sizes, in contravention of Madagascar’s obligations under CITES, given its transfer from Appendix I to II was primarily for ranching with a modest problem animal quota in 1997. An extensive artisanal hunting and manufacturing industry has always existed and is largely unregulated. Management capacity and resources were unable to control either harvests or trade, which were blatantly illegal. A ban on exports was imposed by CITES Standing Committee (2010-2014). Madagascar’s wild crocodile population is severely depleted, and the time and space it needs to recover are not being provided. National parks may play a key role as refuge areas, if sufficient crocodiles and nesting habitats remain, and hunting can be controlled (Ottley et al. 2008).
For 12 nesting areas, sufficient data are available from 1996 to 2003 to quantify trends in nesting effort. Each of the 12 nesting areas has shown reduced nesting, ranging from -33% in the Bemarivo and Marotondro Rivers, -52% in the Maningoza River and -55% in the Sambao River. The estimated mean decrease in nesting (-45%) is thought to reflect trends across Madagascar as a whole, and equates to a mean rate of decrease of around -10% per annum in nesting adults. Blatantly illegal hunting and trade is the main reason for these declines, which have increased since 2000. Since the trade ban was lifted, some evidence indicates excessive uncontrolled harvesting has continued, with management capacity severely constrained and unlikely to improve without serious assistance and intervention. The population seems destined to decline further, with or without international trade.
Malawi: Along a 38 km stretch of the southern boundary to the eastern shore of Lake Malombe in the Liwonde National Park, 676 crocodiles >1 m were counted equating to 17.8 crocodiles/km (Leroux and Reid 2016). Outside of protected areas, hunting of C. niloticus is allowed under trial tourist hunting concessions. The revenue generated for the Malawi Government from hunting license fees and trophy fees ($ 150 per crocodile: 2011-2013) for eight C. niloticus hunters hunting 16 crocodiles, exclusive of the cost of CITES permits, veterinary health certificates and trophy export fees totaling $ 9 796 in 2012 (Macpherson 2013).
Mozambique: The last survey conducted in the lower Zambezi was in 2009 with a total population estimate of 400-500 individuals. Of these 25% were estimated to be adults (112 adults; Fergusson 2009). Between 2006 and 2015, an average of 20,000 and 10,000 live hatchlings were exported to South Africa and Zimbabwe respectively, for ranching (CITES Trade Database 2017, Caldwell 2017). A helicopter survey of the Maputo Special Reserve counted 29 individuals in both 2015 and 2016 (Neubert pers. comm. 2017).
Namibia: Population survey data for Namibia are limited, with the most comprehensive survey carried out in the eastern river systems (Brown et al. 2004). They estimated 66 adults in a portion of the Okavango River (just northwest of the bridge on the Trans-Caprivi highway south to the Botswana), 1928 adults in the Kwandu-Linyanti-Lake Liambezi-Chobe system and 214 in the Namibian portion of the Zambezi River. A more recent survey by Du Preez et al. (2014) along the length of the Okavango River from Angola to Botswana estimated 204-486 adult crocodiles. This represents a 3.1-7.4-fold increase in adult numbers in less than one generation. Lyet et al. (2016) conducted a survey in the more remote Kunene River (352km; western Namibia) and estimated an adult C. niloticus population of 567 individuals. Versfeld (2016) surveyed the protected and uninhabited Lower Kunene River and estimated 806 individuals.
Namibia’s crocodile population was transferred from Appendix I to Appendix II in 2004 (CITES 2004) and reported exporting 274 wild skins of the 1,458 total skins in 2014 (Caldwell 2017).
Rwanda - Akagera National Park (ANP) consist of a large number of lake systems including the Akagera River which flows along its eastern boundary. Biennial C. niloticus helicopter surveys commenced in August 2015 with 198 individuals counted (Gruner pers. comm. to Xander Combrink 2018). In August 2017, 500 crocodiles were counted, but more waterbodies may have been included. Gillnet mortalities and snaring are the main threats to the population. The population for the Park is likely to exceed 1,000 non-hatchings, but more surveys are required before nesting activities and the population size structure throughout ANP numerous lakes and river systems can be quantified.
South Africa: Populations of wild C. niloticus are now confined to the north-eastern corner of South Africa following extirpation from the Eastern Cape since 1903 (Jacobsen 1988). Currently the four largest and possibly secure populations remaining in South Africa today are Kruger National Park (KNP), the Limpopo River outside KNP, the Lake St Lucia estuarine system and the Phongolo Nature Reserve (inlet section where the Phongolo River flows into the Pongolapoort Dam, enclaved and protected by the nature reserve). Numerous other small populations also exist. Overall in South Africa, there is a conservative estimate of greater than 8,000 C. niloticus >1m in total length, of which more than 4,000 are considered to be adults (Isberg et al. 2016).
Within KNP, a large number of crocodile mortalities, thought to be caused by pansteatitis after consuming rancid fish, has reduced the C. niloticus population in the Olifants River from 760 to 480 individuals (D. Govender pers. comm. 2016). The most recent survey of the Olifants River (October, 2017; Department of Economic Development, Environment & Tourism, LEDET) counted 3,326 individuals and reported that the crocodile population was relatively stable, with minor fluctuations in the upper reaches possibly due to the changes in water level in the Flag Boshielo Dam (Lippai 2018). The Letaba River crocodile population has recovered slightly since a decline noted in 2015 but remains low (Lippai 2018) and may be ‘threatened’ locally.
Outside of KNP in the Limpopo Province, a crocodile census in November 2016 on the Limpopo River and its tributaries conducted by the Limpopo Provincial Government (LEDET) noted 85.1% increase in crocodile numbers compared to 2003. 1,233 adults were counted constituting 80.1% of the population (Egan et al. 2016). The survey report concludes that crocodile numbers are increasing in the Limpopo system, with crocodile migration into seasonal waters during the rainy season (Lippai 2018). Again within the Limpopo Province, the Olifants River has seen a recent stabilisation in overall numbers (2012 = 445, 2015 = 450 and 2017 = 440). This represents a 53.3% increase since the surveys by Jacobsen (1984) between 1979 and 1981 (= 287 crocodiles) with the largest breeding aggregation associated with the Flag Boshielo Dam. Despite the increases in these rivers, the Letaba River population has decreased by >75% since 2012 (2012 = 200; 2017 < 50; V. Egan, pers. comm. 2018). A further 436 individuals were counted in five smaller populations within Limpopo Province in 2017 and showed a 20–50% decline since the survey in the preceding year most likely because water levels within the dam were low and the animals were suspected to have burrowed.
The Lake St Lucia estuarine system, situated within the iSimangaliso Wetland Park World Heritage Site, contains the largest C. niloticus population within a single waterbody in South Africa and hosts the largest estuarine C. niloticus population in Africa. Furthermore, it is the most southern viable breeding population throughout its range (Leslie and Spotila 2001). In 1972, Tony Pooley counted 356 individuals after releasing 486 individuals between 1967 and 1976. In 1993, 975 crocodiles were counted and until 2008, the population appeared stable (941 individuals), but in a 2017 survey only 564 individuals were counted.
Within the Phongolo Nature Reserve, Summers (2015) recorded 432 crocodiles in Pongolapoort Dam of which 41% were adults. Champion and Downs (2017) recorded 30 nest in 2009, but all nests flooded in January 2010. Summers (2015) recorded 38 nests in 2014 with a density of 4.9 nests/km.
Calverley and Downs (2017) reported that the number of nests located in Ndumo Game Reserve has remained comparable (~11 nests/year) between 1964-1993 despite significant increases in population number from approximately 300 to 850 crocodiles. A 2017 aerial survey recorded 516 individuals (C. Hanekom, pers. comm., 2018). The Lake Sibaya population was estimated to be between 164 and 374 adult crocodiles in 1970, but declined to 64 adults in 1985 and 7 in 2009 (95-98% reduction; Combrink et al. 2011) despite being a provincial protected area. For these reasons, C. niloticus has recently been regionally defined as vulnerable with an estimated >30% decline (Harvey and Marais 2014). Although C. niloticus in South Africa is on Appendix II of CITES pursuant to Resolution Conf. 11.16 (Rev. CoP15) for “Ranching”, no wild harvest of eggs occurs (Leslie and Spotila 2001) but a proportion of the skins exported from South Africa are from ranched hatchlings derived from Mozambique (Caldwell 2017).
Tanzania: No recent population estimates are available for Tanzania. A 2012 survey reported that the Selous Game Reserve still has “one of the most impressive Nile crocodile populations in Africa” (Mwita and Games 2012). Although the crocodile density in the Selous Game Reserve fluctuates considerably, it was noted that some rivers (Rufiji, Ulanga and Ruaha) showed an increase in crocodile densities, whilst the Kilombero River showed a decline. An overall significant increase in crocodile numbers within the Rufiji Lakes was also noted, although this was not consistent with a decrease noted in the Mzizima River. Outside of the Selous Game Reserve, there are also inconsistencies. Densities within the Ruaha National Park , Rubondo Island, Malagarassi River and Ruvuma River have increased from the previous survey in 2008 (Mafole et al. 2008). However, no crocodiles were seen in the previously concentrated Rungwa River and Lake Rukwa, potentially due to disturbance from fishing activities (Tanzanian Crocodile Survey 2012). Tanzania wildlife authorities are planning to carry out land and aerial surveys in the southern National Parks and Game Reserves in July/August 2018.
Uganda: The first aerial survey of the Murchison Falls National Park in 1967 counted 700 crocodiles (Cott 1969) whilst two years later, only 505 crocodiles were counted (Parker and Watson 1970). There was a steep decline through the 1970s with an average of 171 individuals counted in aerial surveys. The most recent survey (2013/14) reported 218 individual crocodiles (Behangana et al. 2017) suggesting the population has stabilised over the last 40 years. 41% of these 2013/14 survey were medium to large crocodiles, which is equivalent to approximately 89 adults (Behangana et al. 2017). Since 1991, there has been wild egg collection in the area (Thorbjarnarson and Shirley 2009) and Behangana et al. (2017) suggested the number of nests harvested should be re-evaluated to allow the C. niloticus population to recover.
Zambia: Nile Crocodiles are still found, often in large numbers, in most of the major rivers (Zambezi, Kafue, Luangwa, Kabompo, Lunsemfwa, Chambeshi, Lunga, Lufupa and Lufubu Rivers), lakes (Tanganyika, Bangweulu, Mweru, Mweru-wa-Ntipa, Kariba and Lusiwasi) as well as Itezhi-Tezhi Dam (W. Thomas pers. comm. 2017; P. Reilly pers. comm. 2018). Spotlight surveys from the 270 km stretch of the lower/middle Zambezi River, between Kariba and Cahora Bassa dam, occurred in 2006 and 2009 and reported adjusted crocodile numbers of 1,984 and 2,257 crocodiles, respectively (approximately 397 and 451 adults, respectively). This was a statistically significant increase estimated at 5% population growth per annum (Wallace et al. 2013).
Rivers located near or within National Parks (Wallace et al. 2013, W. Thomas pers. comm. 2017) and communal lands (P. Reilly pers. comm. 2018) host the largest numbers of crocodiles. Nyirenda’s (2015) survey in 2007 along the lower Zambezi River noted crocodile densities of 20.62 crocodiles/km river in National Parks compared to 7.45 crocodiles/km river in non-protected river areas. This trend reflects anthropogenic disturbances and retaliation killings of C. niloticus for attacks on humans (injuries and deaths) and damage caused to fish nets. Innovative conservation measures benefiting local communities sharing crocodile habitats, and bearing the costs of living with crocodiles, is one approach to linking crocodile conservation with consummate benefits (Nyirenda 2015). Locating crocodile producers in communal lands is an approach which could be implemented. Overall, the Zambian C. niloticus population is thought to be increasing, with an estimated 2,000-4,000 adults (Isberg et al. 2016).
Zimbabwe: Listed in Appendix II of CITES (Res. Conf. 11.16), the most recent report by the Crocodile Farmers’ Association of Zimbabwe (CFAZ) stated that 1,594 nests (60,328 eggs) were collected in 2015 from 4 areas throughout Zimbabwe (CFAZ 2015). Compared to the previous year, egg collection was noted to have increased in Park Estates but had decreased from Communal and Forestry Lands. Egg destruction and crocodile persecution are considered the reasons behind the decreased collection on Communal Land, despite reducing the revenue from egg royalties. In 2014, 80.4% of eggs were collected from Lake Kariba. Since 1997, the level of collections from the other areas (Kazungula, Upper and Lower Zambezi) has declined and, supported by anecdotal evidence, was cause for conservation concern (Crocodile Farmers Association of Zimbabwe 2015). Aerial surveys were carried out on three river systems within the Gonarezhou National Park, in the south-east of Zimbabwe, and concluded that the number of C. niloticus had increased, but that this was due to significant increases in the Runde River alone (Zisadze-Gandiwa et al. 2012). The lack of population increase (or stability) in the Mwenezi and Save Rivers was mainly attributed to habitat loss through siltation and retaliation killings (Zisadze-Gandiwa et al. 2012). The authors recommended that egg harvests from these two River systems should be halted and the CFAZ report (2015) confirms that no eggs have been collected from this area since 2010. Surveys conducted in 2016 estimated the combined Zambezi River and Lake Kariba adult population to be 8,205-15,333 (Games et al. 2016) and from the greater Gonarezhou National Park (including upstream zones of the Save, Runde, Tokwe, Chiredzi, Mutirikwe and Mwenezi Rivers) to be 1307 adults (Childes et al. 2016). The authors found a direct correlation between human activities (e.g. fishing, herding livestock, washing, etc.) and the complete absence of crocodiles (zero), which highlights the conservation consequences of human crocodile conflict.
No recent population data exists for the range States of Burundi, Congo, Democratic Republic of Congo, Equatorial Guinea, Eritrea, Somalia, South Sudan, Sudan and Swaziland.
Nile Crocodile populations have been depleted throughout much of their range. Remnant populations of Nile crocodiles exist in eastern Mauritania and northern Chad (Smet 1999, Shine et al. 2001). Taken as a whole, the global population of C. niloticus remains abundant and widespread, and is considered stable. The numerous depleted populations still in steep decline are a major concern, despite the security of the global population as a whole.
Outside its’ natural range, C. niloticus have been wild-caught and genetically confirmed in southern Florida, USA most likely as either released pets or zoological escapees (Rochford et al. 2016). Rochford et al. (2016) raise concerns about the potential risk of human-crocodile conflicts as well as the potential for hybridization with the indigenous C. acutus population. Neither risk has so far been realised.
