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Research Article
Management of Human-Crocodile Conflict in
the Northern Territory, Australia: Review of
Crocodile Attacks and Removal of Problem
Crocodiles
YUSUKE FUKUDA,
1
Northern Territory Department of Land Resource Management, P.O. Box 496, Palmerston, Northern Territory 0831, Australia
CHARLIE MANOLIS, Wildlife Management International Pty. Limited, P.O. Box 530, Karama, Northern Territory 0813, Australia
KRISTEN APPEL, Parks and Wildlife Commission of the Northern Territory, P.O. Box 496, Palmerston, Northern Territory 0831, Australia
ABSTRACT We reviewed the historical records of attacks by saltwater crocodiles (Crocodylus porosus) and the
removal of problem saltwater crocodiles in the Northern Territory of Australia. Between 1977 and 2013,
5,792 problem crocodiles were removed, of which 69.04% were males and 83.01% were caught within the
Darwin Crocodile Management Zone where suitable breeding habitats were hardly available. The most
common size class was 150–200 cm and their mean size did not change significantly over years. This reflected
the greater mobility of juvenile males as the majority of problem crocodiles, dispersing from core habitats that
were occupied by dominant individuals. Eighteen fatal attacks and 45 non-fatal attacks occurred between
1971 and 2013. The rate of crocodile attacks, particularly non-fatal cases, increased over time. This increase
was strongly related to the increasing populations of both humans and crocodiles, and the increasing
proportion of larger (>180 cm) crocodiles. The management of human-crocodile conflict (HCC) should
incorporate both human (e.g., public education and safety awareness) and crocodile (e.g., population
monitoring, removal of problem crocodiles) components. Crocodiles in the 300–350-cm class were most
responsible for attacks, and they should be strategically targeted as the most likely perpetrator. Approximately
60% of attacks occurred around population centers including remote communities. Problem crocodile capture
and attacks both peak in the beginning (Sep–Dec) and end (Mar–Apr) of the wet season. However, fatal
attacks occurred almost all year around. Attacks by crocodiles >400 cm often resulted in death of the victim
(73.33%). Local and male victims were much more common than visitors and females, respectively. The most
common activity of victims was swimming and wading. Despite the increasing rate of attacks over time, the
Northern Territory’s management program, and in particular the removal of problem crocodiles from urban
areas, is considered to have reduced potential HCC. Public education about crocodile awareness and risks
must be maintained. Ó2014 The Wildlife Society.
KEY WORDS carnivore, crocodile attack, Crocodylus porosus, human-wildlife conflict, population, predator, problem
crocodile, public safety, saltwater crocodile.
Depleted populations of large carnivores represent a
particularly difficult conservation challenge, because success
in increasing wild populations can come with the social,
political, and economic cost of increased conflict with people
(Treves and Karanth 2003, Treves et al. 2006, Dickman
2010). The rebuilding of wild crocodilian populations has
often resulted in increased human-crocodile conflict (HCC;
Steubing 1983, Conover and Dubow 1997, Aust et al. 2009,
Gopi and Pandav 2009, Wallace et al. 2011, Webb 2012),
and with larger and more aggressive crocodilians, conflict
involves people being severely injured or killed (Mekisic and
Wardill 1992, Scott and Scott 1994, Caldicott et al. 2005,
Gruen 2009, Wamisho et al. 2009). Saltwater crocodiles
(Crocodylus porosus) are of particular concern, because 1) they
are the largest of extant crocodilians and can exceed 6 m in
length and 1,000 kg in weight (Britton et al. 2012), 2) they
feed on large prey items including people and domestic stock
(e.g., cattle, horses, and water buffalo), 3) they are widely
distributed in the Indo-Pacific region (Webb and Manolis
1989, Webb et al. 2010), and 4) they occupy a variety of water
bodies, including marine and freshwater wetlands critical to
the livelihoods of many people.
The Northern Territory of Australia represents the
southern part of the range of saltwater crocodiles. Wild
populations in the Northern Territory were severely depleted
by unregulated commercial harvesting (1945–1970), were
eventually protected (1971), and have increased in abundance
and biomass since then (Messel et al. 1981, Webb et al.
1984). They are now considered almost fully recovered in the
core habitats of tidal rivers and associated floodplains (Webb
et al. 2000, Fukuda et al. 2011) but are still expanding into
Received: 25 July 2013; Accepted: 18 June 2014
Published: 16 September 2014
1
E-mail: yusuke.fukuda@nt.gov.au
The Journal of Wildlife Management 78(7):1239–1249; 2014; DOI: 10.1002/jwmg.767
Fukuda et al. Human Crocodile Conflict in Australia 1239
upstream sections of rivers (Letnic and Connors 2006) and
the sea (Nichols and Letnic 2008). In some of these areas,
residents have no institutional memory of crocodiles being
present and their re-appearance poses a risk to public safety
where the types of recreational water activities undertaken
assume the absence of crocodiles. Crocodiles that appear
in or near human settlement are considered a risk to people
and/or livestock and defined as problem crocodiles (Leach
et al. 2009).
Despite the risk to public safety, saltwater crocodiles are an
important and valuable natural resource in the Northern
Territory, exploited through commercial farming and
ranching (Leach et al. 2009), tourism (Ryan 1998), and
customary use (Lanhupuy 1987). Crocodiles and their eggs
are harvested in a sustainable manner for commercial use and
land owners receive royalties for these harvests (Leach et al.
2009). This incentive-driven conservation system adds
economic value to the species and motivates the community
to tolerate and conserve wild populations of crocodiles
(Webb and Manolis 1993, Hutton et al. 2002). Conse-
quently, management goals are somewhat diametrically
opposed, improving public safety by removing problem
animals and educating the public about the risk, while
encouraging crocodile population growth to support ongoing
commercial uses by people.
We describe 1) HCC with a particular reference to the
dynamics of human and crocodile populations, 2) the
development of public safety programs including education
and the removal of problem crocodiles, and 3) patterns and
trends in problem crocodiles and attacks on humans in
the Northern Territory, Australia. After quantifying HCC
and its relationship with human and crocodile populations,
we provide a series of recommendations to guide the
management programs to reduce HCC.
STUDY AREA
The study area was the northern, coastal regions of the
Northern Territory, Australia (Fig. 1), encompassing the
natural historical distribution of C. porosus in the Northern
Territory, where it inhabited a range of freshwater and saline
water bodies, including beaches, billabongs, floodplains,
lagoons, lakes, mangroves, rivers, swamps, and waterholes
(Webb and Manolis 1989, Fukuda et al. 2007). The climate
was monsoonal with distinct wet (Nov–Apr) and dry (May–
Oct) seasons. The dry season was characterized by the coldest
(May–Aug) and the hottest (Aug–Nov) periods of the year
(Webb 1991). The mean minimum and maximum tempera-
ture typically ranged between 228C and 328C and the annual
rainfall was around 1,700 mm (Station Number 14015,
Darwin Airport; Bureau of Meteorology 2014). During
the wet season, heavy rainfalls flooded water bodies and
floodplains, enabling more extensive movement of saltwater
crocodiles (Webb 1991, Campbell et al. 2013). Courtship
and mating for saltwater crocodiles began in the late dry
season, and nesting occurred during the wet season (Webb
and Manolis 1989, Fukuda and Cuff 2013). During the
cooler times of the dry season, the activity of saltwater
crocodiles may be reduced, but they will continue to feed to
Figure 1. Study area in the Northern Territory, Australia, with approximate locations of saltwater crocodile attacks between 1979 and 2013 (n¼63).
1240 The Journal of Wildlife Management 78(7)
some degree throughout the year (Webb et al. 1978, Taylor
1979).
The study area covered several townships (Table 1),
including the state capital, Darwin, and many large and small
indigenous communities. The main land use was indigenous
use (any land uses by indigenous or Aboriginal groups in
their lands to which access is controlled by authorities or land
councils), pastoralism, conservation (national parks and
reserves), and tourism (Fig. 1). Local communities, including
indigenous and non-indigenous groups, hold diverse
perceptions towards crocodiles as a culturally or ecologically
significant species, natural resource, and predator of humans
and livestock (Lanhupuy 1987, Webb and Manolis 1989,
Fijn 2013).
Australian freshwater crocodiles (Crocodylus johnstoni)
also inhabited the study area, mainly in freshwater bodies
upstream of tidal influence (Webb et al. 1983, Webb and
Manolis 1989). We did not include C. johnstoni in this study
because this smaller species posed few HCC issues (Webb
and Manolis 1989, Delaney et al. 2010) and its attacks on
humans were rare and reported elsewhere (Hines and
Skroblin 2010, Somaweera 2011).
METHODS
Population Sizes
The Northern Territory has a relatively small human
population (approximately 234,800 in 2012), concentrated
within the Greater Darwin Region (approximately 131,900
people in 2012) that includes, Darwin, Darwin Harbour, and
its surrounding urban and rural residential areas (Australian
Bureau of Statistics [ABS] 2013). Towns and communities
in the study area have different human population sizes
(Table 1) and approximately 30% of the entire population in
the Northern Territory are indigenous (ABS 2006). The
human population in the Northern Territory has been
constantly increasing and the increase is expected to continue
(ABS 2013). We derived the human population in the
Greater Darwin Region from ABS (2013) and described the
trend by fitting a linear regression to the mean population in
5-year periods for 1979–2013 with 1971–1978 grouped as
1 period.
At the time of protection in 1971, saltwater crocodiles in
the Northern Territory were considered commercially
extinct because of uncontrolled hunting, and the population
was estimated to be between 3,000–5,000 non-hatchlings
(Webb et al. 1984, Richardson et al. 2002). Extensive
monitoring programs since protection showed consistent
increases in crocodile populations across the Northern
Territory (Messel et al. 1981, Webb et al. 2000, Fukuda
et al. 2011). Although the degree of recovery differs between
sub-populations because of intrinsic habitat quality (Fukuda
et al. 2007, 2011), the overall population, now estimated to
be 80,000–100,000 non-hatchlings (Y. Fukuda, Northern
Territory Department of Land Resource Management,
unpublished data), is considered to be approaching
carrying capacity and the abundance level that existed in
1945, before the period of uncontrolled hunting (Leach
et al. 2009, Fukuda et al. 2011). The monitoring surveys of
crocodile populations showed that as the number of
crocodiles recovered, the mean size of individuals in the
population also increased (Fukuda et al. 2011). Using data
derived from Fukuda et al. (2011) and the historical surveys
of crocodile populations in 12 tidal rivers monitored
between 1971 and 2013, we described the trends in the
relative density of saltwater crocodiles (sighting/km of river)
and the proportion of crocodiles >180 cm total length by
fitting linear regressions to the mean of these indices in
5-year periods, except for 1971–1978, which was grouped as
1period.
Public Safety Program
Public safety is one of the priorities in the management of
saltwater crocodiles in the Northern Territory (Leach et al.
2009, Fukuda et al. 2012). The Northern Territory
Government’s public safety program consists of 2 major
components, education for safety awareness and the removal
of problem crocodiles. The public education program for
crocodiles started in the late 1970s with the goal of raising
the awareness of the risk of crocodile attack (Butler 1987),
and was sustained at different levels of intensity depending
on the public concern triggered by occasional crocodile
attacks (G. Webb, Wildlife Management International,
unpublished data). It also involved the installation and
maintenance of warning signs in crocodile habitats with
frequent human access, providing information exhibits and
talks at local events and schools, and advertizing public
notices in a variety of media (e.g., television, radio,
newspaper, and website). During the 1990s, less effort was
expended on media and school outreach, but in the last
decade, government revitalized the public education pro-
gram, “Be CROCWISE,” with dedicated staff and funding
to deliver the message about crocodiles and efforts to
maintain public safety in the Northern Territory (Leach et al.
2009, Parks and Wildlife Commission of the Northern
Territory [PWCNT] 2014).
Table 1. Population centers in the study area of the Northern Territory,
Australia, and their human population size, the number of saltwater
crocodile attacks between 1979 and 2013, and estimated saltwater crocodile
breeding habitat within a 50-km buffer around each of the population
centers. Note that the 3 attacks in Oenpelli were also contained within the
50-km proximity of Jabiru.
Population center
Human
population
(2011)
Crocodile
attacks
(1979–2013)
Breeding
habitat
(km
2
)
Borroloola 926 2 481
Daly River (Nauiyu) 625 6 1,123
Darwin 120,586 7 460
Jabiru 1,129 7 1,685
Katherine 5,798 0 0
Maningrida 2,292 3 980
Ngukurr 1,056 1 513
Nhulunbuy 4,072 8 145
Oenpelli (Gunbalanya) 1,171 3 1,358
Wadeye 2,111 0 1,224
Ramingining 833 3 1,857
Timber Creek 231 1 239
Fukuda et al. Human Crocodile Conflict in Australia 1241
The removal of problem crocodiles began in the late 1970s
as government started receiving reports from the public
about crocodiles considered a risk to people, livestock, or
domestic animals. As the crocodile population continued to
recover, the concern spread across the Northern Territory,
and the removal of problem crocodiles, especially around
human settlements, became a permanent feature of the
crocodile management program. Since the inception of the
problem crocodile program in the early 1980s, the removal of
problem crocodiles has concentrated on Darwin and its
environs. This area was defined as the Darwin Crocodile
Management Zone (DCMZ; Fig. 2) in 2009 as a
management response to increasing crocodile populations
and HCC around the urban areas (Leach et al. 2009, Fukuda
et al. 2012). The DCMZ encompasses the Greater Darwin
Region that contains approximately 56% of the human
population in the Northern Territory (ABS 2013), and
around 70% of the population in the study area (TNRM
2013). Captured problem crocodiles are not returned to the
wild, because C. porosus, particularly males, have a strong
homing instinct (Walsh and Whitehead 1993, Read et al.
2007, Campbell et al. 2010). Instead, they are transported to
crocodile farms in most cases to be used as stock (Leach et al.
2009). All the crocodiles in this study were treated in
accordance to the Animal Welfare Act (Northern Territory
of Australia 2013) and the Code of Practice on the Humane
Treatment of Wild and Farmed Australian Crocodiles
(Natural Resource Management Ministerial Council 2009).
Outcomes of the problem crocodile management such as the
location and number of problem crocodiles removed are
reported regularly to the public through the media and
government reports (Leach et al. 2009, Fukuda et al. 2012,
PWCNT 2014).
We compiled the historical data for saltwater crocodiles
caught as problem crocodiles between 1977 and 2013 from
internal government databases. We did not include the data
for crocodiles captured 1) primarily for commercial or
traditional use, 2) in Kakadu National Park, because they
were relocated within the park rather than removed (Lindner
2004; G. Linder, Parks Australia, unpublished data), and 3)
by non-government staff, because these crocodiles were also
used for commercial purposes and the distinction between
problem crocodile and commercial use was not clear. We
excluded data for 1998 from the analysis because they were
incomplete. We also excluded hatchlings (<0.6 m) that were
rarely captured as problem crocodiles. The detail of each
problem crocodile record included the date and location of
the capture, and the species, sex, and total length of the
crocodile.
We analyzed the historical data on problem saltwater
crocodiles with respect to 1) numbers caught annually and
mean total length in each year over time using analysis of
variance (ANOVA), 2) total length distribution in 50-cm
categories using a Chi-square test, 3) sex difference in the
size distribution using a Chi-square test, 4) seasonal
(monthly) distribution of captures using a Chi-square test,
Figure 2. Saltwater crocodile attacks (fatal and non-fatal) between 1979 and 2013 (n¼63), problem saltwater crocodiles captured between 1977 and 2013
(n¼5,792), and saltwater crocodile breeding habitats in and around the Darwin Crocodile Management Zone (DCMZ) in the Northern Territory, Australia.
1242 The Journal of Wildlife Management 78(7)
and 5) correlation between number of problem crocodiles
and mean rainfall in each month (Bureau of Meteorology
2014). We chose a weather station (14015, Darwin Airport)
nearest to the DCMZ where most problem crocodiles were
captured. We did not test the correlation between the
number of problem crocodiles and the rainfall in each year
because the capture effort was not standardized but rather
had been increasing over time. For example, the number of
traps used to catch problem crocodiles in the DCMZ
increased from 33 in 2009 to 65 in 2012 (T. Nichols,
Northern Territory Department of Land Resource Manage-
ment, unpublished data).
Crocodile Attacks
We compiled historical records of crocodile attacks in the
Northern Territory since 1971 by 1) collating the internal
reports and databases kept by the Northern Territory
government agencies and police, 2) interviewing victims,
witnesses, police officers, or rangers involved in the incidents,
3) searching the media such as archived newspapers and
websites, and 4) consulting with an independent database
(C. Manolis, Wildlife Management International, unpub-
lished data). We excluded attacks 1) involving escapees from
crocodile farms, 2) that occurred on people working with
crocodiles (e.g., handling crocodiles or collecting eggs),
3) that did not result in any injury or death of humans, and
4) which were not confirmed as crocodile attacks (e.g.,
victims went missing without witnesses or evidence). Details
collected for each incident included 1) the date, time,
location, and severity of attack, 2) total length of the
crocodile, and 3) age, sex, origin (local or visitor), race
(indigenous or non-indigenous), and activity of the victim
at the time of the incident.
We grouped crocodile attacks into 5-year periods between
1971 and 2013 but grouped 1971–1978 as 1 period because
no crocodile attacks occurred during that period. We then
calculated the mean number of attacks (fatal, non-fatal, and
combined) in each period and compared the means between
periods using ANOVA. If we found a significant effect, we
fitted a linear regression to further examine the trend.
We examined the seasonal distribution of crocodile attacks
by dividing the crocodile attack data into months (Jan–Dec)
and performing a Chi-square test. We also tested the
similarity of the monthly distribution between crocodile
attacks and problem crocodiles using a Chi-square test.
To examine trends with regard to the size of crocodile
involved in attacks, we grouped the total length data into 50-
cm increments and examined their distribution using a Chi-
square test. We summarized the detail of the victims (age,
sex, local or visitor, indigenous or non-indigenous, day or
night, activity, and position) to identify patterns and trends.
To explore potentially important areas for future HCC
management in the study area, we performed a spatial
analysis, in which we identified the human population
centers in the Northern Territory and drew a 50-km buffer
around each center to calculate the number of the historical
crocodile attacks and the total area of the habitat predicted
suitable for C. porosus within each buffer. We obtained the
human population size from ABS (2013) and the spatial data
for the breeding habitat from Fukuda et al. (2007).
To examine the relationships between the frequency of
crocodile attacks and the human and crocodile populations,
and the proportion of large individuals in the crocodile
population, we fitted generalized linear models (GLMs). We
used the number of crocodile attacks (fatal and non-fatal
combined) as the response variable, and the densities of
human and crocodile populations and the proportion of
crocodiles >180 cm in total length as a single explanatory
variable in each model. We grouped all the variables at every
5 years between 1971 and 2013, except for 1971–1978, which
we grouped as 1 period, as in the other analyses. We used the
log link function in the Poisson family for GLMs because the
response variable was count data and the data showed non-
linear relationships (Fig. 3). We compared the model fit by
calculating the deviance explained by each model (1-residual
deviance/null deviance) and Akaike’s Information Criterion
corrected for small sample size (AIC
c
). We used ArcGIS
(version 10.0; Environmental Systems Research Institute,
Inc., Redlands, CA) for the spatial analysis and producing
maps, and R (version 2.12.0; http://cran.r-project.org/,
accessed 25 Jun 2014) and Microsoft Excel 2010 (Microsoft
Corporation, Redmond, WA) for all the statistical analyses.
RESULTS
The density of the human population in the Greater
Darwin Region increased constantly between 1971 and 2013
(r
2
¼0.99, P<0.01; Fig. 3A). A logistic regression was the
best fit for the crocodile population density (residual standard
error ¼0.05, df ¼5; Fig. 3B) and the proportion of >180-cm
long crocodiles (residual standard error ¼0.05, df ¼5;
Fig. 3C).
Between 1977 and 2013, 5,792 non-hatchling C. porosus
were recorded as being caught as problem crocodiles in the
Northern Territory, mostly (4,910 crocodiles, 83.01%) in the
DCMZ. The actual number of crocodiles caught in 1998
remains unknown (thus, excluded from the analysis), but an
estimated additional 32 crocodiles may have been caught.
For capturing method, trapping accounted for 71.22% of
all captures, harpoon for 24.04%, hand catch for 2.21%,
and other methods for 2.52%. Of total problem crocodiles,
69.04% (3,999 crocodiles) were male, 27.92% (1,617
crocodiles) were female, and 3.04% (176 crocodiles) were
unknown sex. The total number of problem crocodiles
increased from 2 in 1977 to 317 in 2013. The mean total
length for each year ranged from 149.0 cm to 240.19 cm, but
it did not change significantly over years (F
1, 5,790
¼2.664,
P¼0.10; Fig. 4).
The total length of males ranged from 70 cm to 541 cm, and
for females from 95 cm to 370 cm. The proportion in each
total length class was not equally distributed between males
and females (x2
9¼443:98, P<0.01), although the most
common total length class was 150–200 cm for both males
and females (Fig. 5). When males and females were
combined, the total length classes were not equally
distributed (x2
9¼6;164:53, P<0.01).
Fukuda et al. Human Crocodile Conflict in Australia 1243
The number of problem crocodiles also differed between
months (x2
11 ¼215:60, P<0.01), with the highest number
in April and the lowest number in January (Fig. 6). We did
not find a significant correlation between the number of
problem crocodiles caught in each month and the mean
monthly rainfall (r¼0.25, P¼0.36). However, the
monthly distribution of problem crocodiles showed signifi-
cant correlation with the monthly rainfall 2 months earlier
(r¼0.82, P<0.01; e.g., problem crocodile numbers in Apr
were related to the mean rainfall in Feb).
15 20 25 30 35 40
Human density (person/km
2
)
A
1971-1978
1979-1983
1984-1988
1989-1993
1994-1998
1999-2003
2004-2008
2009-2013
1971-1978
Year
Adju sted r
2
= 0.99
P <0.01
0123456
Crocodile density (sighting/km)
B
1971-1978
1979-1983
1984-1988
1989-1993
1994-1998
1999-2003
2004-2008
2009-2013
1971-1978
Year
Residual standard error = 0.05
df = 5
020406080
Proportion of >180 cm crocodile (%)
C
1971-1978
1979-1983
1984-1988
1989-1993
1994-1998
1999-2003
2004-2008
2009-2013
1971-1978
Year
Residual standard error = 5.68
df = 5
15 20 25 30 35 40
0 5 10 15 20
Human density (person/km
2
)
Crocodile attacks
D
Devian ce explai ned = 0 .71
AICc = 42.24
2345
0 5 10 15 20
Crocodile density (sighting/km)
Crocodile attacks
E
Devian ce explain ed = 0.70
AICc = 42.33
20 30 40 50 60 70
0 5 10 15 20
Proporti on of >180 cm c rocodil e
Crocodile attacks
F
Deviance explained = 0.63
AICc = 44.42
Figure 3. Changes since protection (1971) in (A) human population density in the Greater Darwin Region of the Northern Territory, Australia, (B) saltwater
crocodile density in the 12 monitored rivers, (C) proportion of saltwater crocodiles larger than 180 cm in the 12 monitored rivers, and changes in the number of
crocodile attacks against (D) human population density, (E) saltwater crocodile density, and (F) proportion of saltwater crocodiles larger than 180 cm. We fit a
linear regression in (A), a logistic regression in (B) and (C), and a generalized linear model (Poisson family with log link) in (D), (E), and (F).
0
50
100
150
200
250
300
350
0
50
100
150
200
250
300
350
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
Mean total length (cm)
Problem crocodiles
Year
Problem crocodiles
Mean total length
Figure 4. The number of problem saltwater crocodiles caught between 1977
and 2013 (n¼5,792), and the mean total length for each year in the
Northern Territory, Australia. Bars on mean total length show standard
errors.
0
200
400
600
800
1000
1200
Problem crocodiles
Total length (cm)
Female Male
Figure 5. The number of male and female problem saltwater crocodiles in
different total length classes caught between 1977 and 2013 in the Northern
Territory, Australia (n¼3,999 for male and n¼1,617 for female).
1244 The Journal of Wildlife Management 78(7)
The first crocodile attack in the Northern Territory after
protection of the species occurred in 1979. Between 1971 and
2013, 63 attacks on humans by wild C. porosus were recorded,
of which 28.57% (18 attacks) were fatal and 71.43%
(45 attacks) were non-fatal. The mean number of crocodile
attacks (fatal and non-fatal combined) was significantly
different between the 5-year groups (F
1, 41
¼32.35,
P<0.01; Fig. 7) and showed a linear increase over year-
groups at a rate of 0.36 (r
2
¼0.76, P<0.01) every 5 years.
We found a more profound difference between year-groups
for the mean number of non-fatal attacks (F
1, 41
¼20.53,
P<0.01) than fatal attacks (F
1, 41
¼6.46, P¼0.01). The
mean of non-fatal attacks showed a linear increase at a rate of
0.27 (r
2
¼0.67, P<0.01) every 5 years whereas the linear
increase of the mean of non-fatal attacks was 0.09 (r
2
¼0.48,
P¼0.03).
Although apparent variation existed between months in the
number of crocodile attacks (fatal and non-fatal combined;
Fig. 8), the difference between months was not statistically
significant (x2
11 ¼17:19, P¼0.11). The difference in
monthly distribution between crocodile attacks and problem
crocodiles captured was not significant (x2
11 ¼17:22,
P¼0.10).
The total length of 54 crocodiles, representing 85.71%
of all attacks, was known (Fig. 9). The proportion of
attacks differed significantly between total length classes
(x2
9¼26:96, P<0.01) with the most common total length
in the 300–350 cm class (Fig. 9). The most common total
length for non-fatal attacks was also 300–350 cm, whereas
for fatal attacks it was 400–450 cm. Attacks by very large
(>400 cm) crocodiles were mostly fatal (73.33%). The total
length of crocodiles responsible for non-fatal attacks ranged
from 80 cm to 450 cm but ranged from 320 cm to 510 cm
for fatal attacks. In the case of 2 non-fatal attacks involving
4.0-m long crocodiles, the victims were able to escape with
assistance from other people, and the result of the attack
would have been different otherwise.
Most attacks (56 attacks; 88.89%) occurred while victims
were in the water or on land at the water’s edge; 2 attacks
(3.17%) involved crocodiles leaving the water and walking on
land to attack people, in 1 case even entering a tent in which
occupants were sleeping, and 5 attacks (7.94%) were directed
at people sitting in boats. Fatal attacks mainly occurred in
deep water (>0.5-m depth; 83.33%), but non-fatal attacks
were more common in shallow water (<0.5 m; 42.22%;
0
100
200
300
400
500
600
0
100
200
300
400
500
600
700
800
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Mean rain (mm)
Problem crocodiles
Month
Problem crocodiles
Rain
Rain 2 months earlier
Figure 6. The number of problem saltwater crocodiles caught in each
month (n¼5,763), and mean monthly rainfall at Darwin (closed symbols
with solid line) between 1977 and 2013 in the Northern Territory, Australia.
The open symbols with dashed line are the mean monthly rainfall shifted
later by 2 months. Bars show standard errors.
2312235
0
335
7
11
5
11
0
5
10
15
20
Crocodile aacks
Year
Non-fatal
Fatal
(1.0 ±0.32)
(0.0)
(1.20 ±0.37)
(1.20 ±0.58)
(1.80 ±0.37)
(2.60 ±0.68)
(1.60 ±0.40)
(0.32 ±0.66)
Figure 7. The number of fatal and non-fatal saltwater crocodile attacks in
the Northern Territory, Australia divided into 5-year periods between 1979
and 2013 (n¼63); we grouped 1971–1978 as 1 period because no attacks
occurred during this time period. In brackets is the mean annual number of
total crocodile attacks (SE).
0
100
200
300
400
500
600
700
800
0
2
4
6
8
10
12
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Problem crocodile
Crocodile aacks
Month
Non-fatal
Fatal
Problem crocodiles
Figure 8. The number of saltwater crocodile attacks between 1979 and
2013 (n¼63) and the number of problem saltwater crocodiles captured
between 1977 and 2013 (n¼5,763) by month in the Northern Territory,
Australia.
0
2
4
6
8
10
12
14
16
50-100 100-150 150-200 200-250 250-300 300-350 350-400 400-450 450-500 500-550
Crocodile aacks
Total length (cm)
Non-fatal
Fatal
Figure 9. The number of fatal and non-fatal saltwater crocodile attacks in
the Northern Territory, Australia between 1979 and 2013 in different total
length classes (n¼54).
Fukuda et al. Human Crocodile Conflict in Australia 1245
Table 2). Both fatal and non-fatal attacks occurred more
commonly in daytime (61.11% for fatal and 66.67% for non-
fatal). The most common activities at the time of fatal attacks
were swimming and wading (77.78%), diving (16.67%), and
fishing (5.56%). The most common activities at the time of
non-fatal attacks were swimming and wading (37.78%),
fishing (20.0%), and hunting (20.0%; Table 2).
For both fatal and non-fatal attacks, male victims were
more common than female, and local people were much
more common than visitors (Table 3). The number of
indigenous victims was slightly lower than non-indigenous
victims in non-fatal attacks, but the proportions were equal
in fatal attacks. The age of victims ranged widely (7–55 years
for fatal attacks and 5–75 years for non-fatal attacks) with a
mean of 26.28 years for fatal attacks and 32.98 years for non-
fatal attacks.
Within the study area, we identified 12 major population
centers (Table 1). Within the 50-km buffer of these centers,
38 crocodile attacks (60.32% of total attacks) occurred
between 1971 and 2013. Darwin, Katherine, and Nhulunbuy
had the largest human populations, whereas Nhulunbuy,
Jabiru, and Darwin had the highest number of attacks. The
largest amounts of breeding habitat were predicted in
Ramingining, Jabiru, and Oenpelli.
The number of crocodile attacks showed an exponential
increase as a function of the density of human population, the
density of crocodile population, and the proportion of >180-
cm crocodiles (Fig. 3D–F). The models showed similar
support for these variables (difference in deviance explained
<0.08 and DAIC
c
<2.18), but the fit did not improve greatly
when these variable were combined in 1 model (deviance
explained ¼0.79, AIC
c
¼55.01).
DISCUSSION
Despite the current population size of saltwater crocodiles
being similar to that estimated before intensive hunting
started in 1945 (Webb et al. 2000, Fukuda et al. 2011), our
results showed a higher frequency of attacks in recent years
(3.20 attacks/year for 2009–2013; Fig. 7) than was estimated
by Manolis and Webb (2013) for northern Australia between
1855 and 1945 (2.38 attacks/year). The greatly increased
human population relative to pre-1945 is considered to be a
key factor contributing to this difference. Improved
communication, especially in remote areas, may also
contribute to a higher number of crocodile attacks reported
in recent years.
The increasing frequency of crocodile attacks in the
Northern Territory since 1971, as the C. porosus population
has increased, is also evident in other countries such as
East Timor, Malaysia, and Solomon Islands where protec-
tion and conservation actions have led to depleted C. porosus
populations recovering (Sideleau and Britton 2012; Lading
2013; C. Manolis, Wildlife Management International,
unpublished data). In these cases, as with other successful
crocodilian programs, the focus of management changes
from conservation to mitigation of HCC (Crocodile
Specialist Group [CSG] 2014).
Crocodile attacks occurred across the study area, but attacks
were concentrated around or near remote communities such
as Daly River, Jabiru, and Nhulunbuy (Table 1). Given that
these rural communities contain a high proportion of
indigenous residents (ABS 2006) and their traditional
livelihood requires access to water bodies (e.g., fishing and
hunting), public education may need to focus more attention
on this segment of the population. However, the proportions
of indigenous and non-indigenous victims did not differ
significantly (Table 3), suggesting that both groups conduct
the risk-associated activities (Table 2) at similar rates and
public education should be applied to both sectors. A
strikingly high proportion of attacks involved local residents
(Table 3), and in view of the highly transient nature of the
human population in the study area (Morgan 2011), public
education should be maintained as a continuous process.
Despite the extremely large size of human population in the
DCMZ (>56% of the Northern Territory), that only 6
attacks (1 fatal and 5 non-fatal) have occurred since 1971 is
considered to reflect to a large degree the effectiveness of the
public safety programs including education and the removal
of problem crocodiles. Given that the frequency of crocodile
attacks is strongly related to the increasing human
population (Fig. 3), more crocodile attacks could have taken
place without the intensive removal of crocodiles within the
DCMZ.
Table 2. Activity and position of fatal and non-fatal crocodile attacks in the Northern Territory, Australia between 1979 and 2013.
Attack
Activity Position
Swimming
and wading Fishing Hunting Diving Other
Deep
water
Shallow
water
Water’s
edge
On
boat Other
Fatal (n¼18) 14 (77.78%) 1 (5.56%) 0 3 (16.67%) 0 15 (83.33%) 2 (11.11%) 1 (5.56%) 0 0
Non-fatal (n¼45) 17 (37.78%) 9 (20.0%) 9 (20.0%) 3 (6.67%) 7 (15.56%) 14 (31.33%) 19 (42.22%) 5 (11.11%) 5 (11.11%) 2 (4.44%)
Table 3. Detail of the victims of fatal and non-fatal crocodile attacks in the Northern Territory, Australia between 1979 and 2013.
Attack
Age (years) Sex Origin Race
Range Mean Male Female Local Visitor Indigenous Non-indigenous
Fatal (n¼18) 7–55 26.28 3.08 13 (72.22%) 5 (27.78%) 15 (83.33%) 3 (16.67%) 9 (50.0%) 9 (50.0%)
Non-fatal (n¼45) 5–75 32.98 2.59 36 (80.0%) 9 (20.0%) 42 (93.33%) 3 (6.67%) 19 (42.22%) 26 (57.78%)
1246 The Journal of Wildlife Management 78(7)
Most problem crocodiles (83.01%) were caught within the
DCMZ and these problem crocodiles were migrants from
adjacent rivers, because C. porosus are highly mobile (Read
et al. 2007, Campbell et al. 2010) and no major breeding
habitat occurs within the zone (Table 1 and Fig. 2) to
account for their origin. Male problem crocodiles (69.04%)
were more common than females, reflecting the greater
mobility of males as reported by tracking studies (Brien et al.
2008, Campbell et al. 2013). The most common class of
problem crocodiles were 150–250-cm (Fig. 5), and the mean
total length of captured crocodiles did not significantly
change over years (Fig. 4), indicating that these immature
juvenile males have always been the major contributor to the
problem crocodile issue in the DCMZ. This is consistent
with observations that smaller male C. porosus show greater
range of movement than larger, more dominant males in core
habitats (Campbell et al. 2013). Likewise, in areas outside
the DCMZ (e.g., Flora and Katherine Rivers), problem
C. porosus have migrated from downstream habitats into
upstream freshwater areas with no breeding habitat.
However, the average total length of problem saltwater
crocodiles in the Katherine River is remarkably large (e.g.,
>3.1 m; Letnic et al. 2011).
The peaks in problem crocodile capture and crocodile
attacks in March–April and September–December (Fig. 8)
mark the beginning and end of the wet season (Fig. 6) and
coincide with the species’ nesting season (Nov–Apr). Early
rains in November–December fill up rivers and associated
freshwater floodplains, triggering increased dispersal of
crocodiles (Webb 1991, Campbell et al. 2013). Crocodiles
move back to permanent water bodies as the floodplains dry
out in March–April. A number of other factors may also
contribute to higher encounter rates with crocodiles in these
periods, such as seasonal human activities (e.g., swimming in
hotter months of Oct and Nov, and recreational fishing when
fish flush into the floodplains in Nov and Dec). The effort
put into catching problem crocodiles also increases in these
months (D. Best, Northern Territory Department of Land
Resource Management, unpublished data). Lower numbers
of problem crocodile captures and crocodile attacks in May–
August may relate to decreased activity of crocodiles during
the coolest time of the year (e.g., reduced appetite and
feeding), although this period also coincides with the peak of
tourist visitation and associated human activities around
water (Tourism NT 2012).
We are unclear why we did not find significant change in
the number of fatal attacks over years, whereas we found a
steady increase in the number of non-fatal attacks (Fig. 7).
The increase in the latter is strongly related to key factors
for which our models show similar support (Fig. 3), namely
the increasing human and crocodile populations and the
increasing size of individuals in the crocodile population.
The rate of crocodile attacks may continue to increase
because both human and crocodile populations are expected
to keep increasing; although, the rate of increase in both may
slow over time (Fukuda et al. 2011, ABS 2013). This is
consistent with the number of non-fatal attacks by American
alligators (Alligator mississippiensis) being higher in Florida,
USA, where the populations of humans and alligators are
much larger than those of humans and C. porosus in Australia
(Langley 2005, 2010), and where there is greater encroach-
ment of urban expansion into alligator habitats. However,
fatal attack by A. mississippiensis is much less common than
that by C. porosus, because of the less aggressive behavior and
smaller size of the former (Harding and Wolf 2006, Langley
2010, Brien et al. 2013).
In C. porosus, 73.33% of attacks by very large (>400 cm)
individuals resulted in death (Fig. 9). Combining fatal
and non-fatal, the 300–350-cm total length class was
responsible for more crocodile attacks than any other size
classes. Given their relatively young age estimated using the
size-age relationships derived by Webb and Messel (1978),
300–350-cm crocodiles were most likely born after protec-
tion in 1971. These post-protection crocodiles may be less
wary of humans than the survivors of intensive hunting that
hatched before protection (Webb and Messel 1979). For
crocodiles less than 300 cm total length, an adult human may
represent a prey size that is simply too large to handle.
Fatal attacks commonly occurred in deeper water (Table 2),
possibly reflecting the habitat preference of very large
crocodiles (>400 cm total length) but also the greater
difficulty of escape for victims. In contrast, non-fatal attacks
associated with smaller crocodiles occurred more commonly
in shallow water or at the water’s edge, where crocodilians
catch most of their prey (Webb and Manolis 1989). In only a
few cases were victims not in direct contact with the water
(e.g., fishing on a boat, sleeping on beach, or camping near
the water’s edge). Crocodiles also attack people for self-
defense or to exclude intruders from their territory (Caldicott
et al. 2005).
Swimming and wading in crocodile habitats clearly poses a
high risk of attack (Table 2), and were also the most
common activity of victims of attacks by A. mississippiensis in
the United States (Langley 2005, 2010) and Nile crocodiles
(C. niloticus) in Africa (Fergusson 2004, CSG 2014).
Consumption of alcohol by victims is noted as a factor
contributing to crocodile attacks (Caldicott et al. 2005) as it
may cause people to undertake activities that they would not
otherwise have done. In this study, of 44 adult victims
outside of Aboriginal lands, where alcohol is largely
prohibited, 10 (22.73%) were known to have been drinking
alcohol prior to the attack. These numbers are likely to be
underestimated as intoxication status was not often
reported. Non-fatal attacks happened more commonly in
daytime (Table 2), presumably because some activities such
as fishing and hunting were more commonly conducted
during daylight hours. Also, a higher rate of fatal attacks
than non-fatal attacks at night may indicate that crocodiles
generally feed more actively at night (Webb and Manolis
1989).
MANAGEMENT IMPLICATIONS
We provide the following recommendations to reduce HCC.
Given that most problem crocodiles are relatively young
males migrating from other river systems, the management
of problem crocodiles can be more strategic and efficient by
Fukuda et al. Human Crocodile Conflict in Australia 1247
examining their movement patterns and concentrating
capture effort in areas where crocodiles enter and exit the
management zones. The removal of problem crocodiles and
safety awareness education should be maintained year round.
Increasing management effort in areas with a high number of
crocodile attacks such as Jabiru, Nhulunbuy, and Daly River
may be beneficial. Attacks occur throughout the year and
caution should be exercised at all times whilst in crocodile
habitats. Increasing number of crocodile attacks is strongly
related to the increasing human and crocodile populations,
and the increasing proportion of >1.8-m crocodiles. This
indicates that the management of problem crocodiles 1)
should continue to incorporate components on both human
(e.g., public education and safety awareness) and crocodile
(e.g., population monitoring, removal of problem crocodiles)
and 2) may be most effective if 300–350-cm total length
crocodiles are strategically targeted as the most likely
perpetrator. Public education through a range of the media
is the most effective means of informing the public about the
potential danger of water-related activities in crocodile
habitats, particularly swimming and wading that should be
avoided unless a sign says that it is safe. Public education
programs need to apply to both indigenous and non-
indigenous sectors. However, cultural values of crocodiles as
a totem to some indigenous people should be taken into
consideration. In the long-term, the ability of authorities to
conserve and maintain large populations of a predator such as
the saltwater crocodile will rely on the ability to create
positive incentives (e.g., through sustainable use and
tourism) for conservation.
ACKNOWLEDGMENTS
This study was conducted as part of crocodile management
programs by the Northern Territory Government of
Australia. We thank T. Nichols and D. Best at the Parks
and Wildlife Commission of the Northern Territory, G.
Lindner at Parks Australia, K. Boddington, S. Bradley,
and M. Casey at the Northern Territory Police, Fire and
Emergency Services (NTPFES), and many others from
various organizations for providing the data and associated
information on historical crocodile attacks. We also
appreciate the contribution of numerous rangers across the
Northern Territory for capturing problem crocodiles and
providing the data. A. Fisher, G. Edwards, K. Saalfeld, A.
Walters, G. Webb, H. Campbell, and B. Crase provided
helpful comments on this study.
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