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RESEARCH ARTICLE
Population Structure, Abundance and
Movement of Whale Sharks in the Arabian
Gulf and the Gulf of Oman
David P. Robinson
1,7
*, Mohammed Y. Jaidah
2
, Steffen Bach
3
, Katie Lee
4
, Rima
W. Jabado
5
, Christoph A. Rohner
6
, Abi March
4
, Simone Caprodossi
7
, Aaron
C. Henderson
8
, James M. Mair
1
, Rupert Ormond
1,9
, Simon J. Pierce
6
1Heriot-Watt University, Edinburgh, United Kingdom, 2Qatar Ministry of Environment, Doha, Qatar,
3Maersk Oil Research and Technology Centre, Doha, Qatar, 4Environment Department, University of
York, York, United Kingdom, 5Gulf Elasmo Project, Dubai, United Arab Emirates, 6Marine Megafauna
Foundation, Truckee, CA, United States of America, 7Sharkwatch Arabia, Dubai, UAE, 8School of Field
Studies, Turks & Caicos Islands, South Caicos, 9Marine Conservation International, Edinburgh, United
Kingdom
*sharkwatcharabia@gmail.com
Abstract
Data on the occurrence of whale sharks, Rhincodon typus, in the Arabian Gulf and Gulf of
Oman were collected by dedicated boat surveys and via a public-sightings scheme during
the period from 2011 to 2014. A total of 422 individual whale sharks were photo-identified
from the Arabian Gulf and the northern Gulf of Oman during that period. The majority of
sharks (81%, n = 341) were encountered at the Al Shaheen area of Qatar, 90 km off the
coast, with the Musandam region of Oman a secondary area of interest. At Al Shaheen,
there were significantly more male sharks (n = 171) than females (n = 78; X2 = 17.52, P <
0.05). Mean estimated total length (TL) for sharks was 6.90 m ±1.24 (median = 7 m; n =
296). Males (7.25 m ±1.34; median = 8 m, n = 171) were larger than females (6.44 m ±1.09;
median = 7 m, n = 78; Mann-Whitney U test, p <0.01). Of the male sharks assessed for
maturity 63% were mature (n = 81), with 50% attaining maturity by 7.29 m and 100% by
9.00 m. Two female sharks of >9 m individuals were visually assessed as pregnant. Con-
nectivity among sharks sighted in Qatari, Omani and UAE waters was confirmed by individ-
ual spot pattern matches. A total of 13 identified sharks were re-sighted at locations other
than that at which they were first sighted, including movements into and out of the Arabian
Gulf through the Strait of Hormuz. Maximum likelihood techniques were used to model an
estimated combined population for the Arabian Gulf and Gulf of Oman of 2837 sharks ±
1243.91 S.E. (95% C.I. 1720–6295). The Al Shaheen aggregation is thus the first site
described as being dominated by mature males while the free-swimming pregnant females
are the first reported from the Indian Ocean.
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 1/18
a11111
OPEN ACCESS
Citation: Robinson DP, Jaidah MY, Bach S, Lee K,
Jabado RW, Rohner CA, et al. (2016) Population
Structure, Abundance and Movement of Whale
Sharks in the Arabian Gulf and the Gulf of Oman.
PLoS ONE 11(6): e0158593. doi:10.1371/journal.
pone.0158593
Editor: Chaolun Allen Chen, Biodiversity Research
Center, Academia Sinica, TAIWAN
Received: January 22, 2016
Accepted: June 17, 2016
Published: June 30, 2016
Copyright: © 2016 Robinson et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: Logistics for this project were provided by
the Qatar Ministry of Environment (QMOE) and
Maersk Oil Research and Technology Centre
(MORTC). SB acted as an independent researcher
throughout this study with financial support in the
form of a salary from the MORTC. The MORTC did
not have any additional role in the study design, data
collection and analysis, decision to publish, or
preparation of the manuscript. DPR’s work on this
manuscript was supported by two small grants from
Introduction
The whale shark, Rhincodon typus (Smith, 1828), is the world’s largest fish. This species is dis-
tributed throughout tropical and warm temperate seas [1]. The whale shark is one of three fil-
ter-feeding shark species, and preys on a variety of nektonic and planktonic organisms [1,2].
Although significant gaps in our knowledge of its biology still exist [3], the whale shark has
been classified as Vulnerable on the IUCN Red List of Threatened Species [4] due to anthropo-
genic pressures, particularly directed fisheries in south-east and south Asia [5–10]. A challenge
in conservation assessment to date has been a lack of knowledge on the population ecology of
mature whale sharks.
Whale sharks form feeding aggregations in a number of regions around the world, including
Western Australia [11], Belize [12], northern Mexico [13], the Philippines [14], Djibouti [15],
Mozambique [16], Tanzania [17], the Maldives [18,19], the Seychelles [20,21], Red Sea [22]
and Qatar [23]. All of these aggregation sites, excepting the Red Sea where the sex ratio is 1: 1
[22], are frequented primarily by juvenile males [15,19,24–27]. In most areas, the mean total
length (TL) of sharks is between 6 and 8 m [27], the exceptions being Djibouti and the Red Sea
where smaller mean sizes of 3.7 m and 4.0 m respectively have been documented [15,22]. In
male whale sharks, visual assessment of claspers can be used to determine maturity [17,28].
Size at maturity for males varies from approximately 7 m in the Caribbean [29] to 8 m in West-
ern Australia [28,29], with sizes estimated visually, to 9.16 m in Mozambique [27] estimated by
laser photogrammetry [30]. Maturity in free-swimming female whale sharks cannot be assessed
unless pregnancy is visibly indicated by a distended and swollen abdomen [31,32]. The few
places in the world where pregnant female whale sharks have been documented include sites
off the Pacific and northwestern Caribbean Sea coasts of Mexico [13,33], Taiwan [34], and
around the northern Galapagos Islands off Ecuador [32,35]. Based on those limited data, size
at maturity for females is approximately 9 m [36].
The use of photographic identification in elasmobranchs is a reliable and non-intrusive
method of identifying individual animals and obtaining information about populations [37].
Taylor [38] took images of whale sharks at Ningaloo Reef, Australia in an attempt to use scars
as a means of identification and found that the colour patterns on the sides of the sharks were
unique and stable over time. It was concluded that these patterns could be used to confirm the
identification of individuals. Norman [39] found that the area behind the fifth gill slit and
above the pectoral fin was well-suited to identify individual whale sharks; two sharks were
identified at Ningaloo over a 12-year period confirming stability for at least this period. Sight-
ings and re-sightings of individuals within a population can be used in maximum likelihood
models to estimate population size and residency [40–42]. The Lagged Identification Rate
(LIR) metric, defined by Whitehead [43] as the probability of re-identifying an individual that
was identified some lag time earlier, is a useful modelling approach for opportunistic sighting
data and best-fit LIR models have now been widely applied to estimate population parameters
[36,37,40,42,44].
Before 2010 there were few regional records of whale sharks in the literature from the Ara-
bian Gulf and Gulf of Oman [45–51], with the majority reported in the local press. Here we
show that the Al Shaheen area is in fact a globally-significant whale shark hotspot, and the first
to be dominated by mature male whale sharks. Connectivity within the Arabian Gulf and Gulf
of Oman is established, allowing us to provide the first regional population estimate for this
globally threatened species.
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 2/18
the Save Our Seas Foundation. SJP’s work on this
manuscript was supported by the Shark Foundation
and private donors. The journal publication fees for
this manuscript were provided by the MORTC. All
other funders, apart from collaborators from the
QMOE, had no role in the preparation or decision to
publish the manuscript.
Competing Interests: The commercial affiliation for
this project does not alter the authors' adherence to
PLOS ONE policies on sharing data and materials.
Materials and Methods
Study area
This study incorporates the Arabian Gulf, the Strait of Hormuz and North-West Gulf of Oman
(Fig 1). This area is one of the most economically-important waterways in the world, with
heavy ship traffic related to oil and gas transportation [52]. The Gulf of Oman is up to 2000 m
deep while the Arabian Gulf is shallow throughout, with a maximum depth of just over 90 m
[53]. Marine environmental conditions in the Arabian Gulf are among the most extreme on
the planet [54], exposed to sea surface temperatures regularly exceeding 35°C, and reaching
40°C in some areas in mid-summer, and dropping to below 10°C during winter. The lack of
precipitation and high evaporation rate results in salinity ranging from 28–60 ppt. The Gulf of
Oman has more stable and moderate conditions, as the southwest monsoon causes cool-water
upwellings. Surface temperature rarely exceeds 30°C and salinity is normal at around 35 ppt
with little variation over the year [54].
Fig 1. The locations of all study sites and other points of interest for whale sharks in the region, with the Arabian Peninsula (inset).
doi:10.1371/journal.pone.0158593.g001
Population Ecology of Whale Sharks in Arabia
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Data collection
Data were collected through public submissions of photographs and dedicated field studies.
Seafaring individuals, such as fishers, oil platform workers, leisure divers and tour boat opera-
tors, were encouraged to submit any information on sightings of whale sharks in this region to
the online forum Sharkwatch Arabia (www.sharkwatcharabia.com). Participants were
requested to provide as much information as available about each encounter, including date
and time, location, size, sex and the presence of associated fauna. All encounters were subse-
quently submitted to the Wildbook for Whale Shark database (www.whaleshark.org) to investi-
gate broader-scale connectivity.
Platform-based observations in Al Shaheen
Platform stationed staff working for Maersk Oil provided opportunistic observations of whale
sharks in Al Shaheen. These sightings, often supported by video and photographs, were logged
on a daily basis for four years from 2011 to 2014. The platforms are elevated, with 360° views of
the surrounding waters. All workers were briefed to report sightings and to record the time of
the sighting, along with the estimated number of sharks, to their designated sightings collator.
One person stationed on each of the eight platforms was asked to collate the sightings on a
daily basis from their platform workers and log every time a shark or group of sharks was
observed. Only the maximum number of sharks observed per day in one group from one plat-
form was used in the analysis to eliminate repeat observations and only sharks reported during
daylight hours were used in the final analyses.
Dedicated surveys in Al Shaheen
Permissions for fieldwork and data collection on whale sharks in the Al Shaheen region of
Qatar were given by the Qatar Ministry of Environment. The whale shark has been classified as
Vulnerable on the IUCN Red List of Threatened Species [4] but is not protected in Qatari
waters where the fieldwork was carried out. Data collection was non-invasive using only
photography.
Forty-one at-sea surveys took place during May to September: 7 in 2011, 16 in 2012 and 9 in
each of 2013 and 2014. For safety reasons, no surveys could be conducted when wind speed
exceeded 12 knots. Surveys were carried out from a 10 m vessel, powered by twin 250hp
engines, which took approximately 2 hours to reach the study area, with the start time ranging
from 5 to 9 am. Time in the field ranged from four to six hours. During each survey, a set route
was followed among the eight fixed gas platforms. Whale sharks were detected from sightings
of the first dorsal and or caudal fin breaking the surface of the water.
Upon sighting either an individual or aggregation of sharks, a GPS location and time was
recorded and shark numbers were visually estimated from the boat. A team of 2–4 researchers
then entered the water, using snorkelling gear and equipped with digital cameras. Researchers
took photographs of the flank area on each shark behind the fifth gill slit and above the pectoral
fin on the left side of the shark for the purposes of individual identification (IDs) [55]. The sex
of each shark was determined by the presence (males) or absence (females) of claspers. Matu-
rity status of male whale sharks was assigned based on the visual inspection of the length and
thickness of claspers using the criteria described in Rohner et al. [27]. Pregnancy in female
sharks was assessed using both estimated TL and the presence of a distinctive swollen abdomen
as described in Acuña-Marrero et al. [32].
Images collected during fieldwork in Al Shaheen were processed for visual matching using
I
3
S software [56] and also submitted directly to the online database Wildbook for Whale Sharks
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 4/18
to look for matches from other observers. The length at which 50% of males reach maturity
(TL50) was calculated using a generalised linear model (GLM) with a binary logit function.
Estimation of total length
Where possible, the size of each animal was estimated, usually by comparison with the boat or
another snorkeler. A subset of sharks was measured using laser photogrammetry. Green lasers
(Sea Turtle Scuba Inc.) were placed 50 cm apart in a custom made steel frame and aligned in
parallel. A camera in an underwater housing was placed between the two lasers in the middle
of the frame. Lasers were calibrated each day before use by measuring the distance between the
projection of the lasers against a marker at varying distances up to 10 m. Images were taken
perpendicular to the sharks and only clear images which displayed the animal in a stretched
position were used. Methods developed by Rohner et al. [27,30] were used to estimate total
length from a measured body proportion. To test the accuracy of researcher length estimates,
laser photogrammetry estimates were compared to the researchers’visual estimates. Laser pho-
togrammetry was performed throughout the 2012 season and 13 sharks had a suitable image
for analysis as well as an independent visual size estimate.
Spatial analyses
All whale shark encounter locations reported through the project were input to ArcGIS 10.2.1.
The “kernel density tool”was used to calculate occurrence magnitude per km
2
. To determine
areas of overall and core habitat usage, 50% and 95% Volume Contours (PVC) were produced.
Both kernel density and PVC were produced following the methodology outlined in MacLeod
[57].
Regional population estimates
The residence time for individuals within the study area was investigated by using the “move-
ment”module of SOCPROG 2.4 [58] to calculate the Lagged Identification Rate (LIR), the
probability that an animal identified from an area will be re-sighted again after a variable lag
time [40]. All whale sharks that had been individually identified from within or outside the
Gulf from both dedicated fieldwork and submitted encounters were used for this analysis. All
individuals were linked to a location from January 2010 to December 2014. The lowest value
from quasi-Akaike information criterion (QAIC) values were used to select the best fitting resi-
dence model, accounting for over-dispersion of data [43].
The LIR analysis was extended to split the study area into two sub-areas: inside and outside
the Arabian Gulf. The LIR then represented the probability that an individual identified within
one area will be re-sighted in the other area after a specified time lag [40]. A fully-mixed model
was fitted to the data as photo-ID results showed that some movement between areas did occur
(see Results). The model also accounted for movements to a third, hypothetical area (i.e. out-
side the Gulf region). Data were bootstrapped for 100 repetitions to calculate confidence inter-
vals (C.I.) and standard errors (S.E.)
Results
Sightings, photo-identification and seasonality
Three hundred and forty-one individual whale sharks were identified from 980 useable identi-
fication photographs taken during fieldwork in Al Shaheen from 2011 to 2014. Both sex and
size were recorded for 249 individuals. A total of 4350 whale shark sightings were reported
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 5/18
from Al Shaheen between 2011 and 2014 while only one other whale shark was reported out-
side of this area, from a man-made waterway in Doha in 2012.
Excluding Al Shaheen, 81 individual whale sharks were identified from the Arabian Gulf
and Gulf of Oman from records starting in 2004, including the Musandam (n = 46) and Day-
maniyat Islands (n = 27) in Oman, and Fujairah (n = 8) in UAE (Fig 2).
Ninety-five whale shark encounters were reported from the Musandam (Oman). Sightings
were most frequent at Lima Rock (Fig 3) with 64 encounters, followed by Octopus Rock with
19 encounters. Fifty whale shark encounters were reported from the Daymaniyat Islands, with
19 encounters made at the dive sites ‘Junn’and ‘Aquarium’and nine sharks from ‘Sira’.
Forty-three whale shark encounters were reported from UAE waters. The majority of sharks
were seen off Fujairah on the East coast, with 10 sharks encountered at the dive site Martini
Rock followed by six sharks encountered at Dibba Rock. A feeding aggregation of approxi-
mately 10 sharks was reported by fishermen from 35 km off Fujairah in 2012. Twelve sharks
were reported from inside the Arabian Gulf coast of the UAE; all but three of these sharks were
reported from marinas and ports. Two sharks were encountered by members of the public in
2013 off Jumeirah Beach and one shark was reported from the Salman Oil Field about 100 km
offshore of mainland UAE. Body size of sharks ranged between an estimated 4 and 6 m TL.
Most sharks, at all sites, were encountered in the summer months from April to October,
although sharks were encountered year-round outside of Al Shaheen. Sharks seen from
November to March were usually single individuals, while aggregations were common from
Fig 2. Kernel density analysis showing the overall regional occurrence of whale sharks based on submitted sightings.
doi:10.1371/journal.pone.0158593.g002
Population Ecology of Whale Sharks in Arabia
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April to October. This pattern was consistent with observations from oil platform workers in
Al Shaheen (Fig 4).
Population ecology in Al Shaheen
Sixty individual sharks were identified during 2011, 178 during 2012, 119 during 2013 and 128
during the 2014 season (Table 1). The percentage of re-sighted sharks varied between 13% and
59% with the mean inter-annual re-sight rate being 41%. Re-sights of sharks identified in previ-
ous years were seen in all subsequent field seasons from 2012 to 2014.
There were significantly more male sharks (n = 171) than females (n = 78; X
2
= 17.52,
P<0.05). Whale sharks at Al Shaheen ranged from 4 to 10 m TL (Fig 5), with an overall mean
of 6.9 m ± 1.24 TL (median = 7 m, n = 296). Mean TL for males (7.25 m ± 1.34; median = 8 m,
n = 171) was significantly larger than TL for female sharks (6.44 m ± 1.09; median = 7 m,
n = 78; Mann-Whitney Utest, p <0.01). Mean shark TL from laser photogrammetry was
Fig 3. The frequency of whale shark encounters at different sites around the Musandam Peninsula, together with the 50% and 95%
Percentage Volume Contours (PVC).
doi:10.1371/journal.pone.0158593.g003
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6.80 ± 1.10 m (median 6.74 m, n = 13; range 5.2–8.2 m). The corresponding mean TL for visual
estimates of the same sharks was 7.00 ± 1.15 m (median = 7 m, n = 13; range 5–9 m). There
was no significant difference in TL estimates derived from the two different techniques, with
only one individual differing by >1.00 m.
In sharks where both sex and size were recorded, there was a notable male bias (69%,
n = 249). Of the males assessed for maturity, 63% (n = 81) were mature. Males reached matu-
rity between 7 and 9 m TL, with TL
50
at 7.29 m (Chi
2
test: d.f. = 79, Res. Dev = 41.996,
p<0.0001). All sharks were mature at or above 9 m TL. Two 9 m TL females had conspicu-
ously distended and swollen abdomens, suggesting they were pregnant.
Fig 4. Regional whale shark encounters reported to the Sharkwatch Arabia project (Al Shaheen is shown on the right hand Y axis).
doi:10.1371/journal.pone.0158593.g004
Table 1. Inter-annual re-sight rates (%) for individual sharks first identified in Al Shaheen.
Year Identified sharks 2011 re-sights (%) 2012 re-sights (%) 2013 re-sights (%) Total re-sight (%)
2011 60
2012 178 13 13
2013 119 21 38 59
2014 128 15 27 8 50
Mean re-site rate (%) 41
doi:10.1371/journal.pone.0158593.t001
Population Ecology of Whale Sharks in Arabia
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Regional connectivity and population size
Thirteen sharks were re-sighted at different locations from those at which they were first
recorded (Fig 6). The majority of movements were between Musandam and Al Shaheen. The
longest duration between a re-sighting was four years, for a shark seen in Fujairah in 2010 and
re-sighted at Al Shaheen in 2014. The longest distance travelled was for a shark first identified
in the Daymaniyat Islands (in 2012) and re-sighted in Al Shaheen (2014), an estimated
straight-line journey of 828 km through the Strait of Hormuz.
Modelled LIR gradually declined from 1 to 100 days (Fig 7), suggesting that most sharks left
the area after a short period of residency, but there was a slight increase after approximately
one year, indicating periodic return to the study area by some sharks. Model G was the best fit
to the empirical data based on QAIC (Table 2). In this model scenario, there were an estimated
123.72 sharks ± S.E. 15.3062 (95% C.I. 95.3501–152.3211) within Al Shaheen on any given day.
The mean residency time within Al Shaheen was 28.78 days ± S.E. 9.3522 (95% C.I. 8.7195–
46.5447), and 62.74 days ± S.E. 16.7609 (95% C.I. 22.6607–86.947) outside of Al Shaheen.
Lagged Identification Rate was then redefined to model movement between two distinct
sub-areas: (1) Al Shaheen, and (2) the Gulf of Oman including the Strait of Hormuz. The fully
mixed model J (a1 = N) was the best fit (Table 2), although both fully-mixed models had a high
degree of support. These results indicate that sharks regularly move between the Arabian Gulf
Fig 5. Visual size estimates of whale sharks from Al Shaheen.
doi:10.1371/journal.pone.0158593.g005
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 9/18
and northern Gulf of Oman over inter-annual timescales. The estimated population size for
this entire area was 2837 sharks ± 1243.9 S.E. (95% C. I. 1720–6295.0).
Sharks were most likely to be re-sighted again within the same area, but there was also a
chance of sighting an individual across all areas (including outside the study region; Table 3).
Discussion
The Al Shaheen field off Qatar, where large aggregations of whale sharks occur in the boreal
summer months, is the main hotspot for whale shark occurrence within the Arabian Gulf and
region. Sharks aggregate here to feed on tuna spawn produced by mackerel tuna, Euthynnus
affinis (Cantor, 1849) [23]. Over 340 whale sharks have been identified from this site since
2011, indicating that the area is a globally-significant feeding area. The majority of whale
sharks encountered in Al Shaheen were mature males, and this is the first global site where a
significant proportion of mature male individuals have been reported. The second identified
regional hotspot was in the Musandam region of Oman. There were high levels of observed
Fig 6. Movements of 13 whale sharks identified from their spot pattern and re-sighted at different locations from those at which they were first
recorded.
doi:10.1371/journal.pone.0158593.g006
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 10 / 18
and modelled connectivity between the Arabian Gulf and Gulf of Oman, but no connectivity
with other Indian Ocean sites was noted. This high connectivity allowed the application of
maximum likelihood population models, providing the first regional population estimate for
the species: 2837 sharks ± 1243.9 S.E., albeit with broad 95% confidence intervals of 1720 to
6295 sharks.
Fig 7. The probability of re-identifying an individual whale shark over time (LIR; mean ±S.D.) within Al Shaheen compared to the best-
fitting movement model.
doi:10.1371/journal.pone.0158593.g007
Table 2. Model parameters and comparison for the Lagged Identification Rate of whale sharks.
Model Model descriptions for Al Shaheen ΔQAIC
A Closed 17050
Ba1=N 6334
C Emigration/mortality 6325
D Closed: emigration+reimmigration 6323
E a1 = N; a2 = Mean residence 6325
F Emigration+reimmigration+mortality 6317
G a1 = N; a2 = res time in; a3 = res time out 6270
H a1 = N; a2 = res time in; a3 = res time out; a4 = mortality 6298
Model descriptions for LIR between sub-areas
I Fully Mixed (a1) 0.0054
J Fully Mixed (a1 = N) 0
K Migration—Full Interchange (a1 = diffusion rate from area 1 to area 2; a2 = 1/N) 2.0054
L a1 = N; a2 = mean residence time in area 1 2
N = Population
doi:10.1371/journal.pone.0158593.t002
Population Ecology of Whale Sharks in Arabia
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Regional occurrence and abundance
Overall, the majority of sharks were encountered in the warm boreal summer months between
April and October. No whale shark feeding activity, from anywhere in the study region, has
been documented from outside these summer months. The seasonal nature of the aggregation
off Qatar matches the seasonal occurrence of whale shark sightings elsewhere around the
region. The Strait of Hormuz, situated north of the Musandam region of Oman, is the sole con-
nection between the Arabian Gulf and the Gulf of Oman. These are productive areas with high
coral coverage, fish numbers, and diversity. Within the Musandam region, most encounters
were recorded from around Lima Rock, particularly from the south side (Fig 3). Lima Rock is
accessible by speedboat for ‘day-tripper’divers from the town of Dibba, increasing diver num-
bers compared to less accessible sites further north that are only reachable by two or three-day
dive trips. Lima Rock is surrounded by an area of comparatively deeper water, and has strong
upwelling currents that may make this area more attractive to whale sharks. The Daymaniyat
Islands are a popular weekend diving destination for UAE and Oman residents. Whale sharks
were most frequently observed on the dive sites on the outside of the island chain, where feed-
ing has also been observed. Although there have been few records of surface feeding within the
Gulf of Oman, studies from elsewhere have shown that sub-surface zooplankton can constitute
a significant proportion of whale shark diet [2]. It is possible that feeding activities are underre-
ported. One shark was encountered at Octopus Rock in the Musandam and then re-sighted
exactly a year later in the same local area. Sharks encountered in Omani waters were re-sighted
one, two, three and four years apart and between different local hotspots showing a level of
affinity to the area. The majority of recreational diving off Oman occurs during the local week-
end, Fridays and Saturdays. Most encounters reported from the Musandam and Daymaniyats
occurred on weekends, suggesting that more sharks would be encountered if diving activity
increased over weekdays.
Within UAE waters, the majority of encounters with whale sharks took place at popular
coastal dive sites on the East coast. Similar to the Musandam, whale sharks have not been
reported to feed here or be resident to the area. However, one feeding aggregation was reported
from 35 km offshore. With a single exception, encounters from the west coast of the UAE were
from marinas or ports along the coast. Several dive companies frequently dive the waters of the
west coast of the UAE, but no whale sharks have been reported to date. One shark was reported
from a UAE platform worker from the Salman Oil Field. Similarly, whale sharks were rarely
reported from Qatari waters outside of Al Shaheen, with only one observation from mainland
Qatar. These sighting data, viewed as a whole, indicate that whale sharks rarely use the shal-
lower coastal waters around the Gulf. As regional whale shark encounters were mainly
recorded from popular recreational areas, data reported may be skewed towards these areas
and underestimate occurrence along this coastline.
The rapid increase in reports and successful identification of sharks by seafaring individuals
from 2004 to 2013 can be attributed to increased diving activity, an increase in the number of
underwater cameras in use, and improving awareness of how to report and submit an
Table 3. The probability of a shark originally identified from an area being re-sighted within a different area.
To Area
Al Shaheen Gulf of Oman Outside
Al Shaheen 0.9093 0.0338 0.0569
From Area: Gulf of Oman 0.1118 0.8856 0.0025
Outside 0.1364 0.2625 0.6011
doi:10.1371/journal.pone.0158593.t003
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encounter. The Sharkwatch Arabia project focused on engaging divers and dive centers
through social media such as Facebook and Twitter. These sites allow for easy sharing of
images and information. As social media presence and online networking tools grow, so will
the reach and success of citizen science initiatives such as Sharkwatch Arabia.
Population ecology in Al Shaheen, Qatar
The majority of regional encounters took place in the Al Shaheen area of Qatar, a major aggre-
gation site for whale sharks [23]. Three hundred and forty-one sharks were identified here
between 2011 and 2014, with a modelled estimate of 124 sharks present each day over the
aggregation season. Sharks varied in size from 4 to 10 m TL, with laser photogrammetric mea-
surements comparable to visual length estimates. The aggregation is male dominated, with a
median length of 8 m. Sharks below 5 m or in excess of 9 m length were rarely encountered. A
high proportion of adult sharks, particularly males, was documented. This is unique amongst
the predictable feeding aggregations examined to date, which are typically biased towards juve-
nile males [17,19,24–26,59]. The 7.29 m TL
50
for male maturity was similar to the 7 m estimate
from Quintana Roo in Mexico [36], lower than that reported from Western Australia (8 m,
[28]) and Mozambique (9. 16 m, [27]). Although Indian Ocean-level genetic population struc-
ture has not been shown in whale shark [60], these differences in maturity suggest that limited
broad-scale mixing may occur.
Two 9 m TL female sharks were visually assessed to be pregnant. To date suspected preg-
nant females have only been reported from Galapagos, the Gulf of California and the Gulf of
Mexico [31–33], while one confirmed pregnant female was examined in Taiwan [6]. To our
knowledge, Al Shaheen is the only site in the Indian Ocean basin where pregnant female sharks
have been observed. Size of maturity has also been estimated to be around 9 m in the Eastern
Pacific [32,36]. There have been several reports of neonatal sharks off the Balochistan coast in
Pakistan and the discovery of a 58.6cm free swimming neonate suggests that whale sharks do
give birth in the Northern Indian Ocean [61].
Modelled re-sighting data estimated a mean residency time of 29 days within Al Shaheen.
This was similar to the results of mark-recapture modelling of whale sharks from Ningaloo
Reef, where mean residency was estimated to be 33 days [62], and the estimated 24–33 days of
sharks off Quintana Roo in Mexico [33]. These latter two sites, which are noted feeding areas
for whale sharks [63,64], contrast with the relatively short estimated 12 day residency at Utila,
where sharks are feeding opportunistically on baitfish [42]. A high degree of inter-annual site
fidelity was also evident amongst Al Shaheen sharks, with 41% of sharks seen in more than one
year, even with the limited number of sampling trips that were possible. This re-sighting rate
was higher than most other whale shark aggregation sites, e.g. 22% in Utila, Honduras [42],
13% in Holbox, Mexico [29], 23% in Djibouti and 28% in Seychelles [26], and 35% in Western
Australia [62].
Surface water temperatures within the Arabian Gulf frequently exceed 35°C [53]. Water
temperatures from zero to 10 m depth at Al Shaheen, where the sharks are feeding for extended
periods of time, can exceed 33°C during the hottest months [23]. Berumen et al. [22] recorded
temperatures ranging from 8°C to 34°C from satellite-tagged sharks in the Red Sea. Whale
shark distribution appears to be limited by <21°C surface temperatures [65,66], but their
upper tolerance is not yet known. The presence of large numbers of whale sharks surface feed-
ing within the Arabian Gulf during the warm summer months for extended periods of time
shows that whale sharks are able to tolerate temperatures in excess of 30°C for hours at a time.
There is evidence for behavioural thermoregulation influencing whale shark dive patterns in
cooler temperatures [67], and they may seek to cool their internal temperature in warmer
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 13 / 18
waters [68]. Al Shaheen is likely to be the aggregation site where whale shark experience the
warmest water temperature, so a more detailed evaluation of their coping strategies may pro-
vide insight into their long-term response to a warming ocean climate.
Regional connectivity and population size
Within the Indian Ocean, limited international connectivity has previously been observed
[17,59,62], which has precluded the estimation of population size at a regional scale. In the
present study, whale sharks were recorded and re-sighted in all significant regional hot spots,
suggesting that individual sharks are moving freely between the Arabian Gulf and Gulf of
Oman. The largest number of shared individuals was noted between Musandam and Al Shah-
een, the two areas with the greatest number of recorded encounters (Fig 2). Model selection
identified a fully-mixed model as the most likely scenario. Regional population size was esti-
mated at 2837 ± 1243.9 S.E. The broad 95% confidence intervals bounding this estimate, 1720
to 6295 sharks, indicate that this should be treated as a rough approximation. However, as the
first broad-scale population estimate that has been obtained for whale shark, it is an important
step towards understanding relative abundance of this species and developing management
strategies for the conservation of this globally threatened species.
Conclusions
Research in Al Shaheen began comparatively recently, in 2011, and has already documented
high abundance, long residency time and philopatric behaviour to the site. The reason for the
unique adult male bias observed in the Al Shaheen feeding aggregation has not been identified,
but the sex and size-based segregation inherent in whale shark aggregations globally makes this
an interesting topic to investigate. The high connectivity, and relatively small regional popula-
tion size makes the quantification and mitigation of human threats, and potential management
measures, a priority within the region.
Supporting Information
S1 Fig. An image of a large female whale shark and researcher taken in Al Shaheen.
(TIF)
S2 Fig. An image of the remote and mountainous Musandam Governorate of Oman.
(TIF)
S3 Fig. An aerial image of a whale shark aggregation in the Al Shaheen area showing typical
density of feeding sharks and variation in size.
(TIF)
S1 Data. Whale shark encounter reports in the Arabian Gulf and Gulf of Oman up to and
including 2014.
(XLS)
Acknowledgments
We thank everyone involved in the Qatar Whale Shark Research Project, as well as the staff at
the Qatar Ministry of Environment, Maersk Oil Research and Technology Centre (MORTC),
Qatar and the Qatar Coast Guard for providing the platform to carry out field research in
Qatar. We thank Ali Abdulrahmen from the MORTC for his support and help throughout the
fieldwork; the Maersk Oil platform workers for their continued and dedicated support with
Population Ecology of Whale Sharks in Arabia
PLOS ONE | DOI:10.1371/journal.pone.0158593 June 30, 2016 14 / 18
data collection, especially Soren Stig for his continued enthusiasm. We thank Jonathan Ali
Khan and Warren Baverstock for their support and help with the Sharkwatch Arabia initiative
and thanks also go to every contributing individual and dive center for submitting images or
reporting their whale shark encounters, in particular the Emirates Diving Association. We also
thank Jennifer Schmidt for helpful comments on the manuscript and the Save Our Seas Foun-
dation for their support. Chistoph Rohner and Simon Pierce’s contribution to this project were
supported by two private trusts, the Shark Foundation, Aqua-Firma, and Waterlust.
Figures throughout this manuscript were created using ArcGIS1software by Esri, please
visit www.esri.com. We acknowledge the use of free vector and raster map data sourced from
www.naturalearthdata.com.
This research has made use of data and software tools provided by Wildbook for Whale
Sharks, an online mark-recapture database operated by the non-profit scientific organization
Wild Me.
Author Contributions
Conceived and designed the experiments: DR MJ SB KL RJ CAR AM SC AH JM RO SP. Per-
formed the experiments: DR MJ SB KL RJ CAR AM SC AH JM RO SP. Analyzed the data: DR
MJ SB KL RJ CAR AM SC AH JM RO SP. Contributed reagents/materials/analysis tools: DR
MJ SB KL RJ CAR AM SC AH JM RO SP. Wrote the paper: DR MJ SB KL RJ CAR AM SC AH
JM RO SP.
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