1. Abstract
We examined the effectiveness of using photographic mark-recapture techniques as the
method of marking the Nile crocodile (Crocodylis niloticus) to estimate their population at
Sunset Dam, Kruger National Park. C. niloticus is an important keystone species found
throughout Africa whose populations are in flux. Due to their tenuous status it is necessary to
properly monitor their populations. The technique of photographing and monitoring animals
based on unique markings has been used successfully for other animal populations. We show
that crocodiles have unique tail patterns that can be used to identify individuals, reducing the
need for invasive techniques which have shortcomings that may reduce their effectiveness at
estimating population. We analyzed mark-recapture data over two temporal scales: daily
(morning to afternoon), and day to day (one day to the next). Our results suggested there is an
equal likelihood of encountering right or left sides of the tail during the course of the day and the
ideal time of day to count and photograph crocodile tails is in the morning, from 9:00am to
11:30pm. The majority of crocodiles return to the water between 10:30am and 11:30am resulting
in fewer individuals basking on land in the afternoon as compared to the morning. Additionally,
warm sunny days would result in the greatest number of crocodile sightings. Our study strongly
suggests that the photographic mark-recapture method can be used in the future as an accurate
method of monitoring individuals and estimating populations of crocodiles in closed systems.
Introduction
The Nile crocodile (Crocodylis niloticus) is a keystone species in aquatic ecosystems
throughout Africa. They maintain ecosystem structure and function through selective predation
on fish specis, recycling nutrients, and maintenance of wet refugia in droughts (Bourquin 2007).
C. niloticus are threatened by hunting, degradation of suitable habitat, and prey loss (Wallace
and Leslie 2008, Fergusson 2010). Nile crocodiles require appropriate habitats and tend to
flourish in environments that are isolated from developed areas (Fergusson 2010). Due to
increased land development, it is necessary to have protected areas that maintain apposite
crocodile habitats. Due to their position at the top trophic level they also act as an indicator
species (Ashton 2010). One of the ways that C. niloticus is threatened is through poor water
quality. When pollutants enter the water, the poisons get magnified through higher trophic levels,
leading to considerable deaths of fish, which in turn leads to lethality in the crocodiles (Ashton
2010). Monitoring populations becomes even more imperative owing to the fact that there has
been increased interest in the sustainable harvesting of crocodiles (Hutton and Woolhouse 1989).
This, in addition to the constant fluctuations of crocodile populations and the increasing runoff of
pollutants into aquatic ecosystems, creates the necessity to closely monitor and manage
populations (Letnic and Connors 2006). Currently, crocodile populations are most frequently
observed using methods that only give relative abundance (Gese 2001). In order to more
Picture Perfect: a methodological study investigating photographic mark-recapture
technique for estimating the Nile crocodile (Crocodylis niloticus) population at Sunset
Dam in Kruger National Park
Category: Independent Project
Participants: Tavis Dalton, Sam Kubica, Olivia Vennaro, Claire Weston, Kristi Maciejewski (Advisor)
Site: Sunset Dam, Skukuza, Kruger National Park, Mpumalanga Province, South Africa
Key words: crocodile, mark-recapture, photography, population count

2. accurately determine population size, these crocodiles must also be tagged, which in itself proves
to be a difficult and dangerous task.
Population counts are necessary because data acquired can be implemented to determine
abundance, survival rates, immigration and emigration, and other information used for the
development and maintenance of management plans (Gese 2001). Mark-recapture techniques
have been used in the past to ascertain population size, fecundity, and survival rate. However, the
most frequently used procedures have been found to provide an inaccurate, often
underrepresented, population assessment (Nichols 1992). Scientists have continued to use these
methods because few more accurate measures exist. Methods that are often used for crocodiles
are aerial surveys or nighttime spotlight searches, which are limiting. These require researchers
to see the eye shine of an individual, then approach it in order to determine size class and
species. Spotlight and aerial searches are only able to collect a rough estimate of abundance
while providing no data on the precision of measurements. Other common techniques involve
invasive methods, such as attaching radio collars or tagging scutes (Gese 2001). The trapping
may also lead to behavioral changes, such as trap-shyness, in which animals will actively avoid
recapture, or even trap-happiness, in which animals realize they will be released and often get
food rewards (Nichols 1992). Crocodiles, specifically, will become more wary and will actively
avoid recapture after having been captured and tagged once. This changes the recapture
probability (Nichols 1992).
New methodologies should be tested in order to find a method that provides a more
accurate population count and reduces the invasiveness and potential innacuracies of tagging.
One such developing methodology is the photographic mark-recapture technique. Using
completely non-invasive means, individuals of the population can be identified through
distinguishing features, such as coloration and patterns that are unique to an individual. Wild
dog, hyena, and lion populations have been successfully monitored using photographic mark-
recapture techniques (Hutton and Woolhouse 1989). This technique allow the researcher to act as
an observer, and leave the population undisturbed. This method can be applied to crocodiles
using the unique markings on the tail. Individual tails can be identified and logged, producing a
clear catalogue of all individuals in a closed population. Previous studies have used Nile
crocodile populations in the Olifants River in Kruger National Park as a study species for
photographic mark and recapture techniques (Swanepoel 1996). The benefit of using this method
over any other mark-recapture technique is its non-invasive nature. Estimates of abundance
obtained through photographic mark-recapture techniques have been proven to surpass those
determined from spotlight or aerial searches (Hutton and Woolhouse 1989).
Through the study of the population of crocodiles this study aims to achieve the
following objectives:
1. Test the efficacy of photographic mark-recapture techniques
2. Ascertain the sampling effort needed to determine an accurate population size
3. Provide the probability of recording both or either sides of the tail
4. Define the optimal crocodile basking conditions
Methods
Study Site
This study took place at Sunset Dam which is located in the Lower Sabie region of the
Kruger National park, Mpumalanga, South Africa (S 25.01622, E 31.25874). It is located

3. alongside a busy tourist tar road and is home to a resident crocodile and hippopotamus
population. Its substrate is granite based and it receives an annual summer rainfall of ±625mm
(Climate data org 2015). The dam is a popular watering hole for many species, with the most
frequent being impala, warthog, elephant, buffalo, kudu, giraffe and zebra. There are also a
number of wading birds that utilise the waterhole for feeding including: yellow billed storks,
wood sandpipers, three banded plovers, and little stints. Most of the dam is surrounded by 10m
of bare ground providing a large basking zone for crocodiles. However, a small section on the
eastern bank had some overhanging vegetation which was visually assessed. The dam also lies
close to the Sabie River, which flows about 200m to the east of Sunset Dam.
Figure 1. A map showing the location of Sunset Dam (indicated with a yellow star),
within Kruger National Park, Mpumalanga, South Africa, which was used as our study
site to test this method (Fight for Rhinos 2014, The Safari Company 2014).
Study species:
The Nile crocodile, is a large, aquatic, reptilian apex predator that grows to an average
length of 2.8 - 3.5m (Bourquin 2007). They are listed as lower risk on the IUCN 2009 Red List
which was last assessed in 1996 (Fergusson 2010).They are ectothermic and regulate their body
temperature by moving between the water and sun exposed banks in order to increase or
decrease their body temperature. C. niloticus are the most widely distributed of the African
crocodilian species and occur in 42 African countries (Bourquin 2007). They are found in a wide
variety of habitats including lakes, dams, rivers, freshwater swamps, and, on occasion, in
brackish waters (Fergusson 2010). Their diet changes depending on age. When they are young,
it mainly consists of insects and small aquatic invertebrates. As adults they predominantly feed
on vertebrates such as fish and small mammals (Fergusson 2010).
Experimental design:
This study took place over a four day period from the 14th-17th of April 2015. Seven
hours (9:00am- 4:00pm) were spent at the dam (on the fourth day only three hours (9:00am -
12:00pm) were spent at the dam) observing and photographically marking crocodiles. This time

4. was spent inside the vehicle in order to avoid disturbing or influencing the natural behavior of
the crocodiles. Throughout the day vehicle location would change in order to give us the best
possible view of various groups of crocodiles positioned around the dam. This allowed us to
take photographs of the crocodile tails at the optimal angle for producing a clear and detailed
image. Every 30 minutes, starting at 9:00am, crocodiles were counted and divided into various
positional classes (left, right, in water & neither) depending on what side, if any, of their tail was
visible. Any crocodile that had either side of its tail visible was photographed using a Panasonic
DMC-FZ200 camera. Using binoculars with a minimum magnification of 10x40, a Nikon field
scope (ED), and photographs, a nine scale section of the tail was drawn which showed the
varying black and grey patterns. This nine scale section is the last nine scales on the side of the
crocodile’s tail before the top tail scutes combine from two into one scute (Swanepoel 1996)
(Figure 2). Any tails that were not drawn immediately in the field were recorded in a catalogue
with numerical identification, picture identification number, and the distance in metres that the
crocodile was from the point of observation. This distance was calculated using a rangefinder
(Foresty 550 6x21 6o). These pictures were later catalogued by picture identification number for
further inspection later on. The nine scale section was used to identify individual crocodiles and
used for the mark-recapture method. Finally, a database was compiled of all the photographs and
graphics of tails. Every new crocodile photographed and drawn was cross referenced with the
catalogue in order to determine if it was a new individual tail or a recapture.
Figure 2. An example of a photograph of a crocodile tail along with its associated tail
drawing of nine selected scales, used for marking the individual crocodiles.
Additionally, every hour starting at 9:00am, temperature, wind direction, and wind speed
were recorded. Starting at 9:00am, five individual crocodiles were also observed and their
movements were tracked for the duration of the morning. At the beginning of the day the
weather conditions (e.g. sunny, partly cloudy, cloudy or drizzling) were also noted. Throughout
the day, animals using the water hole for drinking were identified and the time of utilisation was
noted. Any disturbance which affected the movement of the crocodiles’ basking was also noted
along with the time at which it occurred (Appendix 1). Comparisons were made on a day-to-day
basis for three mark-recapture periods (day 1 to day 2, day 2 to day 3, and day 3 to day 4) and on
three daily mark-recapture periods (morning to afternoon, day 1, 2, and 3).
Mark-Recapture Analysis
One method of obtaining the size of a closed population with single markings and
recaptures is through the Lincoln-Petersen model. Using photographic mark-recapture and the
Lincoln-Petersen method together works well because it satisfies all the assumptions necessary
to gain an accurate population count: the population is closed, the chances of getting recaptured
are the same as they were for being captured the first time, marking an individual has no effect

5. because the technique is non-invasive, the crocodiles can never lose their mark, since they are
being identified by markings that already exist on their body, and lastly all marks were reported
on the second day (Krebs 1999).
Every photograph was put into a word document with its corresponding drawing and a
general size description (Appendix 2). It was then compared to other photographs for each
recapture period. Using the Lincoln-Peterson model:
(N = (MC)/R)
where N = The population size estimate
M = The total number of usable photographs taken during the first sampling period
C = The total number of usable photographs taken during the second sampling
period
R = The number of tail images in the second sampling period that were recaptures
from the first sampling period
A population estimate was calculated for each recapture period (Krebs, 1999). The recapture
periods included day 1 morning to afternoon, day 2 morning to afternoon, day 3 morning and
afternoon, day 1 to day 2, day 2 to day 3, and day 3 to day 4.These findings were then compared
to our final observational count of individuals. Comparisons were also made between time of
day and position of the crocodiles’ tails and between temperature and percentage of crocodiles
basking.
Statistical analysis:
We estimated the sampling effort required to accurately assess population size using the
mark-recapture method. A graph was constructed to show the difference between unique right
tail accumulation and unique left tail accumulation. Using Statistica (Prism, version 6.0), we ran
a t-test to determine if there was any significant difference between the accumulation rates of the
two sides of the tail. Significance was determined when p < 0.05. We plotted percentage of
crocodiles basking outside of the water and change in temperature over time to ascertain how
change in temperature correlates with percent basking. In addition, we compared average
percent basking between the morning sampling period and the afternoon sampling period using a
t-test. This allowed us to determine if there was a significant change in out-of-water crocodile
abundance between morning and afternoon. We also plotted average basking percentage over
temperature to depict an optimal temperature range for crocodile basking and the associated
photographic capture likelihood.
Results
Field Observations
Over the four day study period the highest observational count that we were able to
obtain was 31 individuals. This included both crocodiles basking on the land and visibly
swimming in the water. Observational counts varied substantially, but given that we assumed
that Sunset Dam was a closed population, we inferred that our highest observational count was
the most accurate.

6. The morning yielded a higher percentage of basking crocodiles with more tails being
identified and drawn than in the afternoon sessions. There were four main parts of the bank that
the majority of the crocodiles used for basking, two were located on the southern part of the dam,
one on the western side, and one on the northern side (Figure 3). Other areas around the dam
were also utilized less frequently. There was only one bathing crocodile seen on the eastern bank
of the dam where cars were a constant disturbance close to the waters edge. Crocodiles were
observed feeding on catfish on five different occasions during the study and there were also two
failed impala catching attempts observed.
Figure 3. Schematic of Sunset Dam illustrating common crocodile basking locations. The size of
the red stars indicate relative frequency of utilisation with larger stars demonstrating greater
frequency.
The waterhole was also utilised by various herbivores, such as Cape buffalo, elephant,
zebra, impala, kudu, baboons, warthog, wildebeest, giraffe, and zebra. There were also several
bird species present including various herons, storks, and kingfishers. The busiest time at the
waterhole was between 9:00am - 11:00am. Generally on hotter days there were more species and
more individuals utilising the waterhole than on cooler days. The fourth day was the coolest day,
no idividuals were seen at the dam the entire morning. The animals did sometimes cause a
disturbance. On day two, at 15:05pm, an elephant bull chased five basking crocodiles into the
water (Appendix 1).
Mark-Recapture
Applying the Lincoln-Peterson model to the mark-recapture data between the sampling
periods, morning and afternoon, we were able to estimate population size for days 1-3 (Table 1).
Day 4 was not included in the daily mark-recapture calculations given that we only identified
tails in the morning and not in the afternoon due to bad weather conditions. Population sizes are
defined by number of tail sides, not by number of individuals. Given the relatively equal

7. probability of seeing the left or right side, the population produced by the Lincoln-Peterson
model can be divided in half to produce an approximate population size for Sunset Dam.
Table 1. Mark-recapture data from days 1-3 and corresponding population size determined by
the Lincoln-Peterson equation: N = (MC)/R.
Day 1 Day 2 Day 3
Morning Captures (M) 5 19 10
Afternoon Captures (C) 6 16 7
Recaptures (R) 1 5 1
Population Size 30a 60a 70a
a it is important to note that each determined population is defined by number of tail sides not
number of individuals.
We also completed mark recapture analysis over three day-to-day sampling scales,
between days 1 and 2, days 2 and 3, and days 3 and 4, and found high variation in population
size between these three sampling periods (Table 2). For sampling periods days 1 to 2 and 3 to 4
the number of recaptures was five, but due to the small sample of day 3 and 4 calculated
population size was nearly half that of sampling period days 1 and 2.
Table 2. Mark-recapture data between days 1 and 2, days 2 and 3, and days 3 and 4, as well as
corresponding population size determined by the Lincoln-Peterson equation: N = (MC)/R.
Days
1&2
Days
2&3
Days
3&4
Day 1 Captures (M) 10 Day 2 Captures (M) 30 Day 3 Captures (M) 16
Day 2 Captures (C) 30 Day 3 Captures (C) 16 Day 4 Captures (C) 10
Recaptures (R) 5 Recaptures (R) 6 Recaptures (R) 5
Population Size 60a Population Size 80a Population Size 32a
a it is important to note that each determined population is defined by number of tail sides not
number of individuals.
Sampling Effort
We found that over the duration of the study period the number of unique tails identified
was very high in the first few days and far lower in the last two days. On day 1, 10 unique tails
were identified, on day 2, 23 unique tails were identified, on day 3, seven unique tails were
identified, and on day 4, two new tails were identified (Figure 4). This concluded our study with
a final tally of 44 unique tails. This included both left and right tails.
In addition we compared the cumulative number of unique left tail captures to the
cumulative number of unique right tail captures (Figure 4). There was no significant difference
between unique left tail accumulation and unique right tail accumulation (t = -0.86, P = 0.966, n
= 45).

8. Figure 4. Graph showing number of unique crocodile tails observed per day over four days of
mark-recapture data collection. Accumulated left, right, and combined sides are shown.
Probability of Identifying the Left or the Right Side of the Tail
The probability of viewing the right side of the tail was on average higher than that of
viewing the left. This is seen in both the percentage of left/right and the total number of
left/right, which is 17%(L)/21%(R) and 25(L)/32(R) respectively. Crocodiles lay at an angle or
had their tail partially in the water 21% of the time which made drawing their tail unfeasible. The
greatest percent of crocodiles basking throughout a morning was 92% (day 3), while the lowest
was 28% (day 4). The afternoon’s greatest percentage basking occurred on days 2 and 3 with
50% of crocs basking while the lowest occurred on day 1 where 25% of the crocs were basking.
The greatest percentage of left tails seen in a single sampling period was 31% on day 1 during
the morning and the greatest percentage of right tails seen in a single sampling period was 31%
on day 3 during the morning (Figure 5).
0
5
10
15
20
25
30
35
40
45
50
1 2 3 4
NumberofUniqueTails
Day
Both Tail Sides Left Side Right Side

9. Figure 5. Graph representing the percentage of crocodiles in the water, out of the water with
their right side visible, out of the water with their left side visible, and out of the water with
neither side visible (i.e. facing towards us, away from us, or are partially obstructed).
Effects of Temperature and Time of Day on Crocodile Out-of-Water Basking Percentage
We found that the percentage of crocodiles basking was highest in the morning sampling
period and was significantly lower in the afternoon sampling period (t = 7.15, df = 12, P < 0.05,
n = 14) (Figure 6). Over the four day study period we experienced a minimum and maximum
temperature of 19.6o C and 36.6o C respectively. Over the four days, temperature reached its
maximum between 12:00pm and 2:00pm. This coincided with the decrease in the percent of
crocodiles basking (Figure 6). Crocodile basking percentage was highest between 25oC and 30o
C respectively (R2 = 0.64) (Figure 7).

10. Figure 6. Graph displaying change in percent of crocodiles basking and change in temperature
over time. Basking crocodiles are defined as being at least partially out of the water. Percentages
were calculated using the observational count of 31 as the denominating value and then averaged
over the study duration of four days. Temperature was also averaged over the four days.
Figure 7. Graph displaying change in percent crocodiles basking with change in temperature.
Basking crocodiles are defined as being at least partially out of the water. Percentages were
calculated using the observational count of 31 as the denominating value and then averaged over
the study duration of four days. Temperature was also averaged over the four days.
0
5
10
15
20
25
30
35
40
0
10
20
30
40
50
60
70
80
9:00
9:30
10:00
10:30
11:00
11:30
12:00
12:30
13:00
13:30
14:00
14:30
15:00
15:30
16:00
16:30
Temperatue(oC)
%ofCrocodilesBasking
Time of Day
Percentage Basking Temperature
R² = 0.6464
0
10
20
30
40
50
60
70
80
90
100
15 20 25 30 35 40
%ofCrocodilesBasking
Temperature (oC)

11. Discussion
This study was investigating a new methodology of marking and recapturing crocodiles.
We found photographic mark-recapture to be a beneficial technique due to the non-invasive
nature coupled with the easily identifiable unique scale pattern found on crocodile tails, which
creates the perfect form of identification. When using the Lincoln-Petersen equation to estimate
population size, all the criteria were met: there could be no change in behavior of photographed
individuals and the markings can never be lost, a key concern when tagging. Peak basking time
offers a perfect opportunity to capture the tail markings, and in ideal conditions, the population
estimate can be found in one day. Each crocodile tail has a unique pattern of scales, and can be
easily identified with proper equipment. This method could be used to measure individual
movements and patterns, such as survival rate and spatial movements. Over the duration of this
study we created a catalogue of all the unique tails in the dam, which can be used for future
studies in order to measure survival rates or track individuals (Appendix 2).
Although this technique has the potential to be an extremely accurate measure of
population, there are some drawbacks to using this method. Obtaining the proper equipment is
essential. For this technique to be applied properly, crocodiles must be able to be photographed
even if they are lying 200m away. Some of the tails that we were able to see were unidentifiable
from the pictures because our equipment was not sufficient to meet our needs. Crocodiles are
often coated with mud, or algae from the dam, which restricts the visibility of the tail. Other
obstructions included logs, vegetation, or other animals, which could block our view of the tail.
During our observations we found the best time to capture the tail pattern is when the crocodile
first emerges from the water, because the pattern is easily seen and is less likely to be obstructed
our view, which requires constant routine vigilance. There was also the problem of encountering
the left or right side of the tail. Since tail patterns are not symmetrical, it is impossible to know if
a picture of the right side of the tail is from the same crocodile as a photograph taken of the left
side unless you definitively witnessed the crocodile turning. Another concern is the high
dependency on the weather. The fourth day was rainy and cold, resulting in very few crocodiles
basking. The high dependence on temperatures and cloud cover coupled with the difficulties of
capturing tails in the proper position can result in a limited sample size.
When using this method in future studies, we would suggest capturing images in the
mornings, from 9:30am to 11:30am; the times at which most of the population of Sunset Dam
was basking, offering the largest sample size to capture. It would also be beneficial to have the
full access around the area being sampled. Our study was restricted to one side of the dam,
limiting our ability to capture the most tails. Future studies would benefit from having the ability
to access the area of study from all sides to increase the number of both right and left captures.
During this study, we were not consistent with the scales depicted in the graphic. For this reason,
it was often more useful to identify crocodiles from the photograph rather than the graphic.
During our study, we determined through observational counts that there were 31
individuals in the crocodile population at Sunset Dam. We also found that there was no
significant difference in the probability of seeing left or right sides of the tail. When comparing
tail markings to match individuals we can see that it would be equally beneficial to choose to
catalogue either the right or left sides of tails. Over the duration of the study period we saw a
decrease in the number of unique tails found each day, however we can infer that an effective
sampling effort would be extended longer than a four-day sampling period. The total number of
unique tails found was 44 in a population containing 62. When using the Lincoln-Petersen

12. equation to acquire a population estimate we found that when comparing within day two,
capturing in the morning and recapturing in the afternoon, the population was estimated to
contain 60 individuals, a number that was closest to our observational count. From these results
we can assume that using one day at optimal temperature and weather conditions could result in
an accurate sampling effort. However, we have found that days with bad conditions do not
produce a large enough sampling size to create an accurate population estimate. Additionally, a
smaller sampling effort will not provide a complete identification for all individuals in a
population. Therefore, we believe that applying a larger sampling effort across multiple days
with the photographic mark-recapture technique would provide an effective method of
determining population size and individual identification.
When determining the probability of photographing the left or right sides of the tail, we
found that there was a greater probability of seeing the right side. Around 21% of the time, the
angle of the tails prevented good pictures from being taken, however, future studies at different
sites might be able to have a wider range of movement, and therefore better angles of sight,
increasing the number of photographable tails. On average, the total precentage of seeing the
right side was 21%, versus the left side at 17%. The difference between right and left sides were
not significant, and we theorize that it would not make a difference which side of the tail is used
to identify crocodiles.
We could see from the graph comparing temperature and percentage of crocodiles
basking that the optimal capture time is in the mornings from 9:00am-11:30pm on sunny days.
This is potentially due to the fact that crocodiles are ectothermic, and prefer to keep their bodies
at a temperature of 28-30° C (Grigg and Ganns 1993). Crocodiles will often enter and exit the
water according to weather fluctuations. Previous research has shown that crocodilians will exit
the water once air temperature exceeds water temperature (Smith 1979). If the air temperature
shifts below or above their optimal range, the individual will reenter the water. Our results
support those found by Smith (1979). We determined that the highest percentage of crocodiles
(70%) were basking at temperatures of 25-30° C, which is within in the range of their optimal
body temperature. We observed that most crocodiles exited the water between 10:30am and
11:30am every day. This correlates with the point at which their optimal temperature range was
exceeded. On day four, none of the crocodiles reentered the water, we inferred that this was due
to the low ambient temperature. It was also noted that the larger crocodiles would move more
infrequently than the smaller crocodiles, which we believe to be a thermoregulatory
physiological mechanism. Due to the smaller surface area to volume ratio of larger adult
crocodiles, they would need to thermoregulate less strictly because their internal body
temperature changes more slowly in response to the environment (Smith 1979).
Our research provides a good baseline study that can be used to monitor crocodile
populations in other rivers or dams across Africa. The photographic mark-recapture technique is
a beneficial method of monitoring population sizes. It is also a useful tool for identifying
individuals within many species. The catalogue compiled and provided in Appendix 2 can be
used for future research on survival rates and individual monitoring of the crocodile population
in Sunset Dam.
Acknowledgements
We would like to thank Kristi Maciejewski for her assistance on our project. We would
also like to thank SANparks for allowing us to work at Sunset Dam.

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Swanepoel, D. 1996. Identification of the Nile crocodile Crocodylus niloticus by the use of
natural tail markings. Koedoe 39(1): 113-115.

14. Wallace, K. and A. Leslie. 2008. Diet of the Nile crocodile (Crocodylus niloticus) in the
Okavango Delta, Botswana. Journal of Herpetology 42(2): 361-368.

15. Appendix 1. Table of daily weather conditions and the diversity of species sighted at the dam
Date Temperature
Range
Wind Speed and
Direction
Weather
Conditions
Animal species seen throughout
the day (in order of appearance)
Notes
14/4/2015
Day 1
27.2 oC -
36.1 oC
north west wind, high
wind speed of 3.8m/s at
09:00 and then calmer
with wind speeds
around1.0m/s for the
remained of the day.
Sunny with
very sparse
clouds
Hippopotamus, crocodile, impala,
warthogs, zebra baboons
15/4/2015
Day 2
23.6 oC -
32.6 oC
south west wind, high
wind speed in the
morning (3.9m/s) falling
to approximately 1m/s
until the afternoon, and
then picking up again to
approximately 2m/s.
Mostly
cloudy
Hippopotamus, crocodile, Cape
buffalo, impala warthogs,
elephant, giraffe, kudu, baboons,
various wading birds including:
storks, herons, and spoonbills
throughout the day.
Buffalo herd present from
09:00 – 09:35
Hippopotamus fight
between 10:00 and 11:00
Elephant herd present
from, 11:09 – 11:58.
Bull elephant chased five
crocodiles into the water at
15:07
16/4/2015
Day 3
25.8 oC -
36.6 oC
south west wind, wind
speed over 1m/s
between 09:00 and
10:00 and less than 1m/s
for the remainder of the
day.
Partly sunny Hippopotamus, crocodile, Cape
buffalo, impala warthogs,
elephant, giraffe, kudu, baboons,
various wading birds including:
storks, herons, and spoonbills
throughout the day.
17/4/2015
Day 4
19.1 oC -
19.8 oC
south west wind, wind
speed approximately
1.5m/s from 09:00 –
11:00 and picked up to
3.6 respectively at
12:00.
Cloudy and
drizzling
Various birds including: storks,
herons, spoonbills, and
kingfishers.
No other animals were
seen the morning of the
fourth day.
*Left site at 12:00

16. Appendix 2. Crocodile tails photographs and graphics catalogue. Red ID code boxes indicate recaptures from day to day. This does not include recaptures from
morning to afternoon. Single ID number (exp. 7) denotes a morning marking, ID number plus (a) (exp. 7a) denotes afternoon marking.
Date/Morning
Afternoon
ID/Side ofTail/
Distance away
Picture/ Photograph ID Graphic
14/4/2015 M 6L 155m Claire 212 & 213 Kristi 100-2523
14/4/2015 M 13R No
distance
Sam 101-0908
14/4/2015 M 7R 170m Olivia #482 103-0509
14/4/2015 M 9R 139m Sam 101-0887

17. 14/4/2015 M 11R 112m Sam 101-0893 Left of three
14/4/2015 M 14R 143m Sam 101-0912
14/4/2015 A 2aL 55m Sam 101-0965
14/4/2015 A 3aR 152m Sam 102- 0002
14/4/2015 A 5aL 107m Sam 101-0997

18. 14/4/2015 A 6aR 107m Sam 101-0998
14/4/2015 A 7aL Sam 102-0016
14/4/2015 A 8aR Sam 102-0018
15/4/2015 M 1L 102m
1R

19. 15/4/2015 M 2R 102m
15/4/2015 M 3L 107m
15/4/2015 M 5bL 170m
15/4/2015 M 7L 170m

20. 15/4/2015 M 8L 170m
15/4/2015 M 10L 170m
15/4/2015 M 11R 106m
15/4/2015 M 12L 102m
15/4/2015 M 13L 200m Sam 102-0038

21. 15/4/2015 M 14R 150m Sam 102-0034
15/4/2015 M 19R 106m Sam 102-0045
15/4/2015 M 21R 170m Sam 102-0063
15/4/2015 M 22L 64m Sam 102-0064

22. 15/4/2015 M 23L 64m Sam 102-0066
15/4/2015 M 24R 136m Sam 102-0070
15/4/2015 M 25L 91m Sam 102-0071
15/4/2015 A 5aR 137m Sam 102-0121
15/4/2015 A 7aR 110m Sam 102-0126

23. 15/4/2015 A 8aR 110m Sam 102-013
15/4/2015 A 10aL 97m Sam 102-0143
10aR Sam 102-0155
15/4/2015 A 11aL 97m Sam 102-0144
15/4/2015 A 12aL 97m Sam 102-0146

24. 12aR Sam 102-0147
15/4/2015 A 13aR 121m Sam 102-0149
15/4/2015 A 15aL 137m Sam 102-0168
15/4/2015 A 16aL 112m Sam 102-0166
15/4/2015 A 17aR 112m Sam 102-0167

25. 15/4/2015 A 20aL 70m Sam 102-0171
20aR Sam 102-0172
15/4/2015 A 21aR 173m Sam 102-0173
16/4/2015 M 1R 102m Sam 102-0204, Kristi 100-2647
16/4/2015 M 7R 107m Sam 102-0208

26. 16/4/2015 M 8L 145m Sam 102-0209
16/4/2015 M 9L 146m Sam 102-0210
16/4/2015 M 10L Sam 102-0212
16/4/2015 M 11L Sam 102-0213
11R Sam 102-0225

27. 16/4/2015 M 13R 102m Sam 102-0235
16/4/2015 M 14R 248m Sam 102-0223, Kristi 100-2654
16/4/2015 M 15L 152m Sam 102-0231
16/4/2015 A 3aR 149m Sam 102-0250
16/4/2015 A 4aR 87m Sam 102-0256

28. 16/4/2015 A 6aL 122m Sam 102-0258
16/4/2015 A 7aL 106m Sam 102-0259
16/4/2015 A 9aL 42m Sam 102-0261
16/4/2015 A 10aL 106m Sam 102-0264
16/4/2015 A 11aR 69m Sam 102-0266

29. 17/4/2015 M 1R 106m Sam 102-0268
17/4/2015 M 2L 106m Sam 102-0274
17/4/2015 M 2R Sam 102-0269
3L 134m Sam 102-0271
17/4/2015 M 4L 127m Sam 102-0272

30. 4R Sam 102-0283
17/4/2015 M 5R 96m Sam 102-0275
17/4/2015 M 6L 99m Sam 102-0276
17/4/2015 M 7L 118m Sam 102-0278
17/4/2015 M 8R 122m Sam 102-0284