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Horizontal movements and habitat use of satellite-tagged whale sharks (Rhincodon typus) off western Madagascar

Endang Species Res
Vol. 36: 49– 58, 2018 Published May 17
Whale sharks Rhincodon typus, the world’s largest
fish, aggregate seasonally in certain areas within
their circumtropical distribution (Rowat & Brooks
2012). The western Indian Ocean (WIO) hosts several
coastal whale shark feeding areas, with high densi-
ties of sightings documented around Praia do Tofo in
Mozambique (Cliff et al. 2007, Pierce et al. 2010,
Rohner et al. 2013, 2015a), Mahé in the Seychelles
(Rowat et al. 2009, 2011) and Mafia in Tanzania
(Rohner et al. 2015a). Whale sharks are also widely
distributed in the oceanic waters of the WIO, particu-
larly within the Mozambique Channel (Sequeira et
al. 2012). Their presence in the coastal areas is typi-
cally related to high prey abundance (Rohner et al.
2015b, 2018), while in offshore waters their move-
ments are likely correlated with productive frontal
zones (Ramírez-Macías et al. 2017, Ryan et al. 2017).
Limited data are available on whale shark move-
ments within the WIO, although genetic data support
a single subpopulation within the Indo-Pacific (Cas-
tro et al. 2007, Schmidt et al. 2009, Vignaud et al.
2014). However, international photo-identification
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Movements and habitat use of satellite-tagged
whale sharks off western Madagascar
Stella Diamant1,2,3, Christoph A. Rohner2, Jeremy J. Kiszka1,4,
Arthur Guillemain d’Echon1, 3, Tanguy Guillemain d’Echon1,3, Elina Sourisseau1,3,
Simon J. Pierce1, 2,*
1Madagascar Whale Shark Project, Nosy Be, Madagascar
2Marine Megafauna Foundation, Donner Pass Rd., Truckee, CA 96161, USA
3Mada Megafauna, Nosy Be, Madagascar
4Department of Biological Sciences, Florida International University, North Miami, FL 33181, USA
ABSTRACT: Whale sharks Rhincodon typus, the world’s largest fish, are routinely sighted off the
northwest coast of Madagascar, particularly off the island of Nosy Be. Dedicated whale shark
tourism has been developing in the area since 2011. During our first dedicated survey, from Sep-
tember to December 2016, we photo-identified 85 individual whale sharks ranging from 3.5 to 8 m
in total length (all juveniles). None had been previously identified from surrounding countries. We
tagged 8 sharks with tethered SPOT5 tags in October 2016, with tracking durations of 9 to 199 d.
Kernel density plots showed that the main activity hotspot for tagged sharks was around the Nosy
Be area. Three individuals were resighted back at Nosy Be in late 2017 after having lost their tags.
A secondary hotspot was identified off Pointe d’Analalava, 180 km southeast of Nosy Be. Five
sharks swam off the shelf into the northeastern Mozambique Channel, between Madagascar and
Mayotte, and one of these continued to near the Comoros islands. Two sharks swam to southern
Madagascar, with minimum track distances of 3414 and 4275 km. The species is presently unpro-
tected in Madagascar, although a small proportion of the high-use area we identified in this study
is encompassed within 2 marine protected areas adjacent to Nosy Be. Whale sharks are globally
endangered and valuable to the local economy, so there is a clear rationale to identify and mitigate
impacts on the sharks within the 2 hotspots identified here.
KEY WORDS: Satellite tagging · Population ecology · Conservation biology · Kernel density
analysis · Marine megafauna
Endang Species Res 36: 49– 58, 2018
comparisons have shown limited connectivity be -
tween the known feeding areas in the region, which
include Djibouti, the Maldives, Mozambique, the
Seychelles, South Africa and Tanzania (Brooks et al.
2010, Andrzejaczek et al. 2016, Norman et al. 2017)
along with the Arabian Gulf and Gulf of Oman
(Robinson et al. 2016). The few published satellite
tracks from the WIO have not shown significant
interchange between these feeding areas (Gifford et
al. 2007, Rowat et al. 2007, 2009, Brunnschweiler et
al. 2009, Rohner et al. 2018). However, interpretation
of these results is complicated by the biased popula-
tion structure at these sites, with all the aforemen-
tioned feeding areas dominated by male sharks, typ-
ically juveniles (Rohner et al. 2015a, Norman et al.
The predictable aggregative behavior of whale
sharks leaves them particularly vulnerable to human
impacts. The species was uplisted to globally Endan-
gered on the IUCN Red List of Threatened Species in
2016 because of overfishing, bycatch and ship strikes
(Pierce & Norman 2016). The species remains unpro-
tected in several WIO nations, although the 2017 list-
ing of the whale shark in Appendix I of the Conven-
tion on Migratory Species (CMS) means signatory
nations are now required to prohibit take. Significant
declines in sightings have been noted in long-term
hotspots in Mozambique (Rohner et al. 2013) and the
Seychelles (D. Rowat pers. comm.) as well as broadly
within the northern Mozambique Channel (Sequeira
et al. 2012). Further data are required to determine
whether these local declines in whale shark sightings
represent a spatial shift in distribution or a genuine
population-level decrease in abundance.
The distribution, status and abundance of whale
sharks are poorly documented in Madagascar (Jon-
ahson & Harding 2007, Kiszka & van der Elst 2015).
Jonahson & Harding (2007) conducted an interview-
based survey of whale sharks in Madagascar
known locally in the Sakalava dialect as marokin-
tana, meaning many stars — and identified the island
of Nosy Be in the northwest as the area with the most
consistent sightings. Follow-up fieldwork by the
Wildlife Conservation Society in 2005 and 2006 iden-
tified 15 individual whale sharks off Nosy Be, with a
mean total length (TL) of 6.1 m (R. Graham pers.
comm.). Dedicated whale shark tourism started in
2011, although dive operators had been searching for
whale sharks opportunistically prior to 2007 (Jonah-
son & Harding 2007). There are presently no regula-
tions specifically pertaining to whale shark tourism,
but best-practice voluntary guidelines were imple-
mented by most operators over the 2016 and 2017
season. Operators perceive sightings off Nosy Be to
be increasing to the present, although it is unclear
whether these sightings may be correlated to a rising
search effort as tourism increases. Whale sharks are
wide ranging, and local existing marine protected
areas (MPAs) in northwestern Madagascar, includ-
ing the community-managed Ankivonjy (1394 km2,
located 50 km southeast of Nosy Be) and Ankarea
(1356 km2, 50 km northeast of Nosy Be), are unlikely
to offer adequate protection for this species. To gen-
erate management measures for whale sharks in
Madagascar and in the WIO, information on their
movements and population structure is needed.
Here we used tethered satellite tags to provide the
first data on the spatial habitat use of whale sharks in
the Nosy Be area and more broadly within the south-
western Indian Ocean. Our primary objective was to
identify contemporary high-use areas by the sharks
to determine whether enhanced management or pro-
tection of the sharks is likely to be required.
Study area and boat surveys
Eighty-one whale shark surveys, both in conjunc-
tion with tourism operators and on a private vessel,
were conducted between September and December
2016 off the island of Nosy Be (13.39° S, 48.20° E) in
Antsiranana Province in northwestern Madagascar
(Fig. 1). Search efforts were focused southwest of
Nosy Be to about 10 km offshore, based on the expe-
rience of tourism professionals. Whale sharks were
sighted when swimming close to the surface, often in
association with mackerel tuna Euthynnus affinis
and seabirds (particularly Laridae). Research was
conducted with the approval of and in partnership
with the Centre National de Recherches Océano -
graphiques (CNRO) in Madagascar.
Individual sharks were identified using standard-
ized underwater photographs of each flank immedi-
ately posterior to the gills (Arzoumanian et al. 2005,
Meekan et al. 2006). These images were uploaded to
the online Wildbook for Whale Sharks (www.whale- photo library, and a pattern-matching
algorithm was used to identify individuals (Arzou-
manian et al. 2005, Holmberg et al. 2008). Individual
whale shark encounters were defined as a sighting of
Diamant et al.: Whale shark movements off Madagascar 51
Fig. 1. Horizontal movements of whale sharks tagged with SPOT5 tags in Madagascar. (A) Eight individual shark tracks, all
originating from Nosy Be; (B) transmission sites from within the northwestern Madagascar area showing locations of marine
protected areas (MPAs)
Endang Species Res 36: 49– 58, 2018
an identified shark on a distinct day. TL was esti-
mated visually to the nearest metre, and sex was
assessed based on the presence (males) or absence of
claspers (Norman & Stevens 2007, Rohner et al.
2015a). Maturity status in whale sharks was estab-
lished by visual observation of size for females, with
the assumption that <9 m sharks were immature
(Ramírez-Macías et al. 2012, Acuña-Marrero et al.
2014), and calcification of claspers for males (Norman
& Stevens 2007, Rohner et al. 2015a).
Satellite tagging
Tagging activities were carried out on snorkel from
a dedicated 4 m private vessel. Smart position or tem-
perature transmitting tags (SPOT5, Wildlife Comput-
ers) were used to collect positional data on shark
movements. SPOT5 tags are designed to transmit
near real-time animal positions. When at the surface,
they send short transmissions to the Argos satellite
system. Consecutive transmissions, when received
within a single satellite pass, are used to calculate the
tag’s location. We used SPOT5 tags over archival tag
models because they provide a detailed location with
a much smaller error than light level-derived loca-
tions, and the main aim of the study was to investi-
gate the horizontal movements of whale sharks in
detail. The SPOT5 tags were also set to collect and
transmit temperature data, which can be useful both
as a rough proxy for vertical movements and, as such,
to confirm that the tag remains attached to the shark
(Hearn et al. 2013) (see details of analyses in the next
subsection). Tags were connected to a small titanium
dart (Wildlife Computers) via a ~150 cm tether of
240 kg Dyneema braided line. The dart was inserted
into the skin using a pole spear so that the tag floated
approximately above the first dorsal fin. Most sharks
showed no obvious reaction to tagging, with the
minority of sharks that increased their swimming
speed immediately post tagging resuming their pre-
vious behavior in 1 to 2 min.
Track analysis
Once detached, floating tags were identified by
near-continuous transmissions to Argos in the first
few hours of the day over several consecutive days,
coupled with no significant vertical movement in -
ferred from time-at-temperature (TAT) histograms
(Hearn et al. 2013). We then applied the Douglas fil-
ter (Douglas et al. 2012) to remove unrealistic loca-
tions based on the error associated with the Argos
location class (lc: 3, 2, 1, 0, A, B, Z in decreasing order
of accuracy). We set the filter to include all locations
with lc 1 and used the maximum redundant dis-
tance method set to 10 km. The filter removed 127
locations, or 6.3% of the total 2029 locations, but kept
some B and A locations that had a relatively large
error radius but were deemed accurate by the filter.
We also corrected the time stamp from tag-recorded
UTC to local time during this step, meaning that the
limit of 300 transmissions a day UTC was split be -
tween 2 days in local time. This meant that the num-
ber of transmissions received per day could be larger
than expected, with transmissions in the late evening
and early morning local time. We used the Douglas
filter output for all subsequent analyses.
Tags did not transmit every day, and hence we
report the overall tracking duration as well as trans-
mitting days (Table 1). Horizontal track distance was
calculated by summing the straight-line distance
between consecutive locations and therefore repre-
sents the minimum possible distance the shark swam
horizontally. Analyses were conducted in R version
Tag Shark Sex TL Deployment Last Tracking Transmitting Track Speed Positions
ID (m) location duration (d) days distance (km) (km d–1) per day
142221 MD-151 M 4 27-Oct-16 22-Mar-17 147 68 2295 15.6 5.7 + 2.85 (1–12)
142222 MD-201 M 4 31-Oct-16 05-Dec-16 36 35 765 21.3 5.4 + 2.28 (1–9)
142223 MD-154 M 5.5 26-Oct-16 22-Jan-17 89 85 2160 24.3 4.7 + 2.15 (1–12)
142224 MD-196 F 7 29-Oct-16 14-May-17 198 50 4275 21.6 4.2 + 2.23 (1–11)
142226 MD-177 F 5 26-Oct-16 27-Nov-16 33 33 1126 34.1 4.5 + 2.32 (1–10)
142227 MD-153 M 6.5 28-Oct-16 05-Nov-16 9 7 191 21.2 4.7 + 1.70 (2– 7)
142230 MD-164 M 7 27-Oct-16 13-May-17 199 46 1439 7.2 4.3 + 2.38 (1 9)
142234 MD-169 M 5 28-Oct-16 17-Apr-17 172 69 3414 19.8 4.9 + 2.29 (1–13)
Table 1. Satellite track details of whale sharks tagged in Madagascar, with the tag number, shark ID on,
sex, estimated total length (TL), deployment and last transmission dates, tracking duration, number of transmitting days, overall
track distance, mean speed, and the number of positions per (transmitting) day (where values in parentheses indicate the range)
Diamant et al.: Whale shark movements off Madagascar
1.0.136 (R Core Team 2017). We created a density
raster using the kernel density estimation tool
heatmap in QGIS version 2.18.14 (QGIS Develop-
ment Team 2017) to visualize hotspots of whale shark
activity. Data input included all locations retained
following application of the Douglas filter, and we
used a kernel bandwidth of 10 km, a quartic kernel
shape, a cell size of 0.5 km and a decay ratio of 0. Val-
ues of 0 to 24.9% were removed from the output.
Tags recorded temperatures in 12 predefined bins:
<5°C, 5 to 10°C, then every 2.5°C to 32.5°C, and
>32.5°C. Temperatures were measured every 10 s
and integrated over 3 separate time periods for each
24 h day (morning = 06:00 −12:00 h; afternoon =
12:00− 18:00 h; night = 18:00−06:00 h) to calculate
TAT histograms. There were large gaps in the TAT
time series because tags only transmitted data on 45%
of tracking days overall. We did not plot these gaps,
meaning that the x-axes of TAT plots are chronologi-
cal but not continuous. We extracted bathymetric
data using the xtractomatic package in R (Men dels -
sohn 2015) for those records in the TAT time series
that also had a simultaneous location transmitted. We
divided depth data into (1) on the continental shelf
(<200 m deep) and (2) off the shelf (>200 m) for
graphical output.
Eighty-five individual whale sharks were recorded
from 166 separate encounters between September
and December 2016: 18 females (size range 5−7.5 m
TL), 66 males (size range 3.5−8 m TL), and 1 shark of
unknown sex. All were immature, based on a lack of
clasper calcification in males and the estimated TL of
females. None of these sharks had been previously
identified in surrounding countries.
Tag performance and horizontal movements
Eight juvenile whale sharks, 6 males and 2 females
ranging from 4 to 7 m TL, were tracked between
October 2016 and May 2017 (Table 1). The SPOT5
tags stayed attached for 9 to 199 d (mean ± SD = 110
± 78.3 d). Data were transmitted on 7 to 87 d (mean ±
SD = 49 ± 24.7 d). The 4 tags that stayed on for >100 d
transmitted on <50% of the days (range = 23−46%),
while the 4 tags with shorter retention times trans-
mitted on most days (mean ± SD = 93 ± 10.1%, range
= 78−100%). Tags transmitted a mean of 4.8 locations
per transmitting day. Straight-line horizontal track
distances ranged from 191 to 4275 km, with 6 of the 8
tracks longer than 1000 km. Sharks travelled at a
mean horizontal speed of 21 km d−1.
Tagged whale sharks spent substantial time near
the tagging area around Nosy Be, but some broader
movements to the west into the Mozambique Chan-
nel and to the south along the west coast of Madagas-
car were also recorded (Fig. 1A). Two whale sharks
swam to the southern end of Madagascar, with MD-
196 moving offshore in the southern Mozambique
Channel before returning to the Nosy Be area and
MD-169 following the continental shelf break south
before losing its tag southeast of Madagascar. One of
these (MD-196) and 4 other sharks swam off the shelf
into the northeastern Mozambique Channel, be -
tween Madagascar and Mayotte, and one (MD-154)
continued to near the Comoros islands (Fig. 1B). Two
sharks (MD-153 and MD-201) stayed on the shelf,
albeit over relatively short tracking durations (9 and
36 d, respectively). Kernel density estimates dis-
played 2 whale shark activity hotspots (Fig. 2) on the
continental shelf, one close to the tagging locations
near Nosy Be and a secondary hotspot ~180 km to the
southeast near Pointe d’Analalava.
Following the conclusion of the study, 3 sharks
were resighted in the Nosy Be area after tag detach-
ment: MD-201 was sighted on 3 November 2017,
MD-151 was identified on multiple days in Septem-
ber and October 2017, and MD-177 was sighted on
23 July 2017.
There were 218 TAT records available for all tags
combined. Sharks moved through the entire tempera-
ture range of temperature bins, < 5 to > 32.5°C. Based
on the transmitted data, whale sharks spent most of
their time in the 27.5−30°C (59.4%) and 25−27.5°C
(29.5%) bins (Fig. 3a). Tag-derived sea surface tem-
perature values ranged from 27.3°C in October 2016
to a maximum of 29.8°C in February 2017, declining
to a minimum of 25.3°C in April 2017. Only 3.1% of
time was spent in <20°C. There were some apparent
diel differences observed among TAT data from the
morning (06:00−12:00 h), afternoon (12:00−18:00 h)
and night (18:00−06:00 h). Sharks spent 0.9% of the
afternoon in cool water <20°C, increasing to 3.3% in
the morning and 5.1% at night (Fig. 3).
Vertical movements, as inferred from the available
TAT time series, varied among individuals. Broadly,
Endang Species Res 36: 49– 58, 2018
sharks spent more time at cooler temperatures when
they were off the shelf and during the night and
morning. As an example, shark MD-177 (Fig. 4)
spent the first 12 d of its track on the continental
shelf, where it recorded no vertical excursions into
deep (cool) water. This shark then moved off the shelf
to the open ocean, over deep water. The recorded
temperature range then increased, with the shark
spending more time in cooler waters, especially at
night and during the morning (Fig. 4).
The Nosy Be area appears to be a globally signifi-
cant whale shark hotspot, with 85 individual sharks
identified during the 3 mo whale shark season (as
identified by local tourist operators) in 2016. By way
of comparison, 33 individual whale sharks were iden-
tified in Mozambique and 70 in Tanzania during
2016 (C.A.R. & S.J.P. unpubl. data). Two distinct
hotspots of whale shark activity were identified in
northwestern Madagascar, the first around the tag-
ging site off Nosy Be and a second 180 km south,
close to Pointe d’Analalava, identified by kernel den-
sity analysis of transmitted locations. Although the
Nosy Be hotspot is near (relative to observed shark
movement capability) previously identified whale
shark feeding areas around Praia do Tofo in Mozam-
bique (1760 km, Cliff et al. 2007, Pierce et al. 2010),
Mahé in the Seychelles (1250 km, Rowat et al. 2009,
2011) and Mafia Island in Tanzania (1120 km, Rohner
et al. 2015b), we found no evidence of movements to
or from these known sites through our tracking or
photo-identification datasets. However, the sharks
were tracked moving close to the islands of Comoros
and Mayotte (France) in the Mozambique Channel,
showing that international movement does occur.
Northwestern Madagascar, a significant whale
shark hotspot
Quantitative hotspot analysis determined that most
satellite tag transmissions occurred off the island of
Nosy Be, with a secondary hotspot used by 4 sharks
Fig. 2. Kernel density estimation of whale shark distribution based on transmissions of the satellite-tagged sharks (n = 8). MPA:
marine protected area
Diamant et al.: Whale shark movements off Madagascar
at Pointe d’Analalava, slightly to the south. These 2
areas were both identified as whale shark hotspots
by Jonahson & Harding (2007) through interview sur-
veys of fishers and dive operators, suggesting that
these areas are consistently used by whale sharks
across years. There was temporal overlap in use of
these 2 areas by the tagged sharks. Rowat & Brooks
(2012, p 1032) defined whale shark aggregations as
‘sites with >10 individuals in an area <1 km2.’ While
we did not observe tight groupings of multiple sharks
in this study, the relatively high number of whale
sharks documented in the Nosy Be area, and the
inter-annual site fidelity demonstrated by some
tagged sharks, indicates that this is an important sea-
sonal habitat for juvenile sharks.
The biased population structure of whale sharks
present, with the majority being juvenile male sharks,
is common within their coastal feeding areas (Rohner
et al. 2015a). While we inferred no specific behaviors
from tracking data, Nosy Be is also likely to be a feed-
ing area for these whale sharks. Most whale sharks
sighted, including all tagged sharks, were associated
with surface schools of mackerel tuna feeding on small
pelagic fishes (Clupeidae), which were presumably
also being targeted by the whale sharks. Omura’s
whales Balaenoptera omurai also feed in the same
area on zooplankton, occasionally in association with
whale sharks (Cerchio et al. 2015a). Giant manta rays
Mobula birostris and devil rays M. mobular and M.
thurstoni, which feed on zooplankton and small fishes
(Rohner et al. 2017), also co-occur in this area (M. Jon-
ahson & S. Harding pers. obs.), indicating a high level
of prey availability. No adult sharks were recorded
during field surveys, so it is unlikely to be a reproduc-
tive site. The temperature range (27.5−30°C) recorded
for locations on the shelf was similar to surface water
temperatures, indicating that little diving behavior
took place, which is further supported by the high
number of daily surface transmissions in this area.
Broad-scale movements through the southwestern
Indian Ocean
The 5 sharks tracked into January 2017 all moved
away from the Nosy Be area. January is typically the
Percentage of time
70 Morning
70 Night
Percentage of time
Temperature (°C)
Temperature (°C)
Fig. 3. Time-at-temperature for all tags combined, showing (A) the overall distribution and (B) the morning (06:00−12:00 h), (C)
afternoon (12:00−18:00 h), and (D) night (18:00−06:00 h) separately
Endang Species Res 36: 49– 58, 2018
start of cyclone season in northwestern Madagascar
(Brenier & Vogel 2017) and, related to this, dedicated
whale shark tourism ceases. Fewer transmissions
from tags were received after this time, suggestive of
diminished surface activity and more time spent on
directed travel. Four of the 8 tagged sharks moved
west of Nosy Be, towards the islands of Mayotte and
the Comoros, a region with seasonally high densities
of whale sharks (Sequeira et al. 2012). Two sharks,
MD-169 and MD-196, travelled to the south of Mada-
gascar, although MD-196 subsequently returned to
Nosy Be (a 4275 km horizontal distance in total). Both
sharks dived to cold temperatures of between 5.1 and
10°C while in oceanic waters. We have no contempo-
raneous data on vertical temperature profiles in this
region, but an array of oceanographic sensors across
the Mozambique Channel from 2003 to 2009 found
that on average, the temperature was close to 10°C at
500 m, 6°C at 1000 m and 4°C at 1500 m (Ullgren et
al. 2012). However, the passage of eddies southwards
through the array resulted in up to 8°C changes in
temperature at 110 m depth, so the relationship be -
tween depth and temperature is not strictly linear
within this dynamic system (Ullgren et al. 2012). A
whale shark tagged with a pop-up archival tag by
Brunnschweiler et al. (2009) in the southern Mozam-
bique Channel recorded temperatures of 9.2°C at
1092 m, 5.5°C at 1087 m and 4.2°C at 1264 m.
MD-169 moved to the southeast of Madagascar,
where an important upwelling system that can be
highly productive in the late austral summer had
been previously identified (Uz 2007, Huhn et al.
2012). A tagged whale shark from southern Mozam-
bique also moved to this area in autumn 2006
(Brunnschweiler et al. 2009). It appears that the
Indian Ocean tuna fishing fleet does not routinely
use the waters off southern Madagascar, so no ob -
server data on whale shark presence or absence have
been documented (Sequeira et al. 2012). Therefore,
while it is possible that this is an additional whale
shark foraging area, we are not aware of additional
data to support this hypothesis.
% of time
Whale Shark MD-177: Overall
25 - 27.5°C
> 32.5°C
17.5 - 20°C
10 - 12.5°C
25 - 27.5°C
> 32.5°C
17.5 - 20°C
10 - 12.5°C
% of time
||||| |||||| || |||| || | ||| || | | | | | | | | | | | | |
Fig. 4. Time-at-temperature data for whale shark MD-177, showing the percentage of time spent in each temperature bin
overall and during the 3 temporal bins: morning (06:00−12:00 h), afternoon (12:00−18:00 h) and night (18:00−06:00 h). In the
top left panel ‘On’ indicates that the shark was on the continental shelf in water <200 m; ‘Off’ indicates that it was off the shelf
in deeper water. Note that the x-axis is chronological but not continuous due to gaps in data transmission
Diamant et al.: Whale shark movements off Madagascar
Management and conservation implications
Northwestern Madagascar is a significant long-
term hotspot for a number of threatened marine me -
gafauna species, including whale sharks (Jonahson &
Harding 2007, this study), cetaceans (Cerchio et al.
2015a,b) and sea turtles (Bourjea et al. 2006). The
area is also a global hotspot of coral biodiversity (Bre-
nier & Vogel 2017). The presence of whale sharks, a
diversity of cetacean species and sea turtles in this
region is already a major tourism attraction for Nosy
Be, presenting both a biological and economic ration-
ale to manage the area for long-term sustainability.
Local interest in the species is high, and most tourism
operators have already implemented best-practice
voluntary guidelines for whale shark interactions off
Nosy Be.
It appears that whale sharks are at a low risk of
fishing-related injury or mortality within the Anki -
vonjy and Ankarea MPAs, located to the southwest
and northeast of Nosy Be, respectively, based on the
gear restrictions in place (Brenier & Vogel 2017). They
are currently afforded no official protection outside
these areas, and there is no legislation in place
specifically pertaining to elasmobranchs in the coun-
try (Humber et al. 2015). The recent listing of the
whale shark in CMS Appendix I (October 2017) does
compel Madagascar to prohibit take of the species,
with limited exceptions possible for traditional sub-
sistence use ( Dolphin
bycatch in gillnets has been documented in the Nosy
Be area, particularly from Nosy Faly to the east of
Nosy Be (Cerchio et al. 2015b). Whale sharks have
occasionally been caught or entangled in gillnets in
Madagascar (Jonahson & Harding 2007, Everett et al.
2015). Therefore, a restriction of gillnet use through-
out the identified whale shark activity centres to min-
imize the risk of accidental bycatch or directed fish-
ing is recommended. Management of tuna fisheries
in the area may also require attention, given the
strong association between whale sharks and mack-
erel tuna schools we observed.
Acknowledgements. Thanks to the staff of Les Baleines
Rand’eau and other tourism operators for their cooperation
and assistance with this study and to the Mada Megafauna
team for practical and logistical support. We thank field
assistants Fadia Al Abbar and Jens Paulsen for their work
over the 2016 season as well as Boris Andrianantenaina,
Mamy Rajaonarivelo and Gisèle Bakary from CNRO for
their help with research permits. Salvatore Cerchio, Dení
Ramírez-Macías, Clare Prebble and Alexandra Watts pro-
vided technical support, and Gonzalo Araujo and the
LAMAVE team in the Philippines as well as Ralph Pannell
from Aqua-Firma helped with logistical arrangements. This
study was financially supported by donations to S.J.P. and
C.A.R. from 2 private trusts, Aqua-Firma, the Shark Founda-
tion and Waterlust. Field costs for S.D. were covered by
the PADI Foundation, and camera equipment was donated
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Editorial responsibility: Rory Wilson,
Swansea, UK
Submitted: January 8, 2018; Accepted: March 15, 2018
Proofs received from author(s): May 8, 2018
ResearchGate has not been able to resolve any citations for this publication.
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Genetic and modelling studies suggest that seasonal aggregations of whale sharks (Rhincodon typus) at coastal sites in the tropics may be linked by migration. Here, we used photo-identification data collected by both citizen scientists and researchers to assess the connectedness of five whale shark aggregation sites across the entire Indian Ocean at timescales of up to a decade. We used the semi-automated programme I³S (Individual Interactive Identification System) to compare photographs of the unique natural marking patterns of individual whale sharks collected from aggregations at Mozambique, the Seychelles, the Maldives, Christmas Island (Australia) and Ningaloo Reef (Australia). From a total of 6519 photos, we found no evidence of connectivity of whale shark aggregations at ocean-basin scales within the time frame of the study and evidence for only limited connectivity at regional (100-1000km) scales. A male whale shark photographed in January 2010 at Mozambique was resighted eight months later in the Seychelles and was the only one of 1724 individuals in the database to be photographed at more than one site. On average, 35% of individuals were re-sighted at the same site in more than one year. A Monte Carlo simulation study showed that the power of this photo-ID approach to document patterns of emigration and immigration was strongly dependent on both the number of individuals identified in aggregations and the size of resident populations.