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Manta rays (Manta spp.) are plankton-feeding elasmobranchs classified as Vulnerable to Extinction on the IUCN Red List for Threatened Species. Despite increasing public and scientific interest in manta rays, major knowledge gaps concerning their movement ecology and dispersal capabilities remain. Here we used pop-off satellite-linked archival transmitting (PSAT) tags to examine the horizontal movements and habitat use patterns of reef manta rays (M. alfredi) departing Lady Elliot Island in the southern Great Barrier Reef, Australia. Tagged individuals moved across a latitudinal range of 1,035 km, travelling up to 2,441 km in 118 days, diving down to 294.5 m and venturing up to 155 km off the continental shelf. Using random walk simulations, we showed that manta rays spent significantly more time in an offshore region characterised by the mesoscale cyclonic Capricorn Eddy, than would be expected by chance. A behaviour-switching state-space model suggested this area to be an important foraging ground for the species off eastern Australia. We document movements of one individual using offshore waters between two known aggregation regions off eastern Australia. Reef manta rays thus not only occupy inshore continental shelf and shelf-edge waters, but also use offshore environments to exploit productive hotspots and travel long distances. Our findings highlight the need to better understand their movement ecology for effective management.
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MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 510: 73– 86, 2014
doi: 10.3354/meps10910 Published September 9
INTRODUCTION
Understanding patterns of habitat use in vulnera-
ble, large and highly mobile marine species is crucial
to implementing effective, spatially explicit manage-
ment strategies (Block et al. 2005, Graham et al.
2012). This is especially true for plankton-feeding
elasmobranchs that depend on their ability to locate
minute and diffuse prey in a vast, dynamic and
changing ocean (Richardson & Schoeman 2004, Sims
et al. 2006). Planktivorous elasmobranchs occur at
low sub-population levels and for limited periods at
© The authors 2014. Open Access under Creative Commons by
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restricted. Authors and original publication must be credited.
Publisher: Inter-Research · www.int-res.com
*Corresponding author: fabrice@marinemegafauna.org
Movements and habitat use of reef manta rays off
eastern Australia: offshore excursions, deep diving
and eddy affinity revealed by satellite telemetry
F. R. A. Jaine1,2, 3,*, C. A. Rohner1,2,3, S. J. Weeks1, L. I. E. Couturier2,4,
M. B. Bennett4, K. A. Townsend5,6, A. J. Richardson2, 7
1Biophysical Oceanography Group, School of Geography, Planning and Environmental Management,
The University of Queensland, St Lucia, Queensland 4072, Australia
2Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research, Ecosciences Precinct, Dutton Park,
Queensland 4102, Australia
3Manta Ray and Whale Shark Research Centre, Marine Megafauna Foundation, Praia do Tofo, Inhambane, Mozambique
4School of Biomedical Sciences, and 5School of Biological Sciences, The University of Queensland, St Lucia, Queensland
4072, Australia
6Moreton Bay Research Station, The University of Queensland, Dunwich, Queensland 4183, Australia
7Centre for Applications in Natural Resource Mathematics, School of Mathematics and Physics,
The University of Queensland, St Lucia, Queensland 4072, Australia
ABSTRACT: Manta rays (Manta spp.) are plankton-feeding elasmobranchs classified as vulnera-
ble to extinction on the IUCN Red List for Threatened Species. Despite increasing public and sci-
entific interest in manta rays, major knowledge gaps concerning their movement ecology and dis-
persal capabilities remain. Here, we used pop-off satellite-linked archival transmitting tags to
examine the horizontal movements and habitat use patterns of reef manta rays (M. alfredi) depart-
ing Lady Elliot Island in the southern Great Barrier Reef, Australia. Tagged individuals moved
across a latitudinal range of 1035 km, travelling up to 2441 km in 118 d, diving down to 294.5 m
and venturing up to 155 km off the continental shelf. Using random walk simulations, we showed
that manta rays spent significantly more time in an offshore region characterised by the mesoscale
cyclonic Capricorn Eddy than would be expected by chance. A behaviour-switching state-space
model suggested this area to be an important foraging ground for M. alfredi off eastern Australia.
We document the movements of 1 individual using offshore waters between 2 known aggregation
regions off eastern Australia. Reef manta rays thus not only occupy inshore continental shelf and
shelf-edge waters but also use offshore environments to exploit productive hotspots and travel
long distances. Our findings highlight the need to better understand their movement ecology for
effective management.
KEY WORDS: Eddy · East Australian Current · Manta alfredi · Movements · Oceanography ·
Random walk · Satellite tracking · State-space analysis
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PEN
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Mar Ecol Prog Ser 510: 73–86, 2014
inshore aggregation sites, where they can be readily
observed. Therefore, obtaining daily data on their
behaviour and identifying the driving forces behind
their distributions are major challenges. Advances in
the fields of bio-logging science, geographic infor-
mation systems and ecological modelling have led to
the increasing use of animal-attached sensors to
remotely examine the movements, behaviour, physi-
ology and/or biophysical habitat of a wide range of
marine species (Cooke et al. 2004, Ropert-Coudert et
al. 2009, Costa et al. 2012). Such studies have shed
new light on the ecology of marine predators, unrav-
elling a variety of behaviours ranging from localised
movements made in relation to foraging opportuni-
ties (Sims et al. 2006, Papastamatiou et al. 2012) to
larger-scale migrations (Bonfil et al. 2005, Block et al.
2011). In most cases, movements are driven by the
availability of food resources (Zerbini et al. 2006,
Anderson et al. 2011), species-specific physiologies
(Pillans 2006) or the need to reproduce (Bonfil et al.
2005, Skomal et al. 2009).
Previous tracking studies have highlighted the im -
portance of productive regions or features, such as
oceanographic fronts and mesoscale eddies, in pro-
viding foraging opportunities (Polovina et al. 2000,
Bailleul et al. 2010) for marine species, including
plankton-feeding sharks (Sims & Quayle 1998, Sims
et al. 2003). Planktivorous elasmobranchs must
acquire sufficient energy from minute and diffuse
prey. As a result, bottom-up processes, whereby phy -
sical oceanographic features act to concentrate prey
items in specific water bodies, are likely to influence
predator distributions and their behavioural deci-
sions. For instance, basking sharks Ceto rhinus maxi -
mus congregate and feed on zooplankton blooms in
frontal areas of the northeastern Atlantic (Sims &
Quayle 1998, Sims et al. 2003). However, the disper-
sal capabilities, behavioural ecology and ha bitat use
patterns of other planktivorous elasmobranchs, such
as manta rays (Manta spp.), are currently not well
understood.
Manta rays are the largest of the batoid fishes and
have a circumglobal distribution in tropical and sub-
tropical waters (Marshall et al. 2009, Couturier et al.
2012). They are classified as vulnerable to extinction
on the IUCN Red List of Threatened Species (Mar-
shall et al. 2011a,b). Despite increasing public and
scientific interest in manta rays, major knowledge
gaps remain in their dispersal abilities, migratory
ecology and drivers for their observed distributions.
Until recently, most of the movement data available
for manta rays had been derived from re-sightings
of photographically identified individuals over rela-
tively long time periods (e.g. Kashiwagi et al. 2010,
Couturier et al. 2011) or from acoustic telemetry data
(e.g. Dewar et al. 2008, Deakos et al. 2011). Such
technologies provided the first insights into the
movement ecology of manta rays, highlighting diur-
nal visitations of reef manta rays Manta alfredi to
particular inshore sites (Dewar et al. 2008, Marshall
2008), movements between aggregation sites up to
500 km apart (Kashiwagi et al. 2010, Couturier et al.
2011) and seasonal migratory patterns in some
regions (Anderson et al. 2011, Couturier et al. 2011).
More recent telemetry studies have, for the first time,
documented the movement patterns of both giant
manta rays M. birostris and reef manta rays M.
alfredi foraging in shallow habitats off the Yucatan
Peninsula, Mexico, and in the Line Islands of the cen-
tral Pacific, respectively (Graham et al. 2012, Papas-
tamatiou et al. 2012). Such results have highlighted
the importance of productivity blooms in inshore,
coastal and coral reef ecosystems as key drivers for
the spatial distributions and foraging habitats of
manta rays (Graham et al. 2012, Papastamatiou et al.
2012).
In eastern Australia, M. alfredi occur at various
localities along the coast, with some individuals sea-
sonally migrating between sites up to 500 km apart
(Couturier et al. 2011). One major aggregation site
for M. alfredi is Lady Elliot Island (LEI) (Couturier et
al. 2011, Jaine et al. 2012), a small coral cay in the
southern Great Barrier Reef (GBR), located only a
few kilometres from the continental shelf edge (see
Fig. 1A). Here, M. alfredi occur year-round; they peak
in austral autumn and winter, coincident with en -
hanced local productivity and foraging activity (Jaine
et al. 2012). The presence of the mesoscale cyclonic
Capricorn Eddy, which forms in the lee of the bathy -
metry off LEI because of the variability in strength of
the southward-flowing East Australian Current (EAC)
(Weeks et al. 2010), is known to trigger upwelling of
cool, nutrient-rich sub-surface waters onto the shelf
and around the Capricorn-Bunker reefs (Kleypas &
Burrage 1994, Weeks et al. 2010). Previously, the
eddy has been suggested as an important driver of
reef manta ray occurrence in the area and, more
specifically, at LEI (Jaine et al. 2012). There, passive
acoustic telemetry showed that individual manta rays
can typically be observed daily over short time scales
(i.e. up to 23 d) and may then leave the surveyed area
for extended periods of time (i.e. weeks to months)
before returning to the site (Couturier 2013). To date,
it is unknown where they go and what they do
when not around LEI. In addition, it is unclear how
M. alfredi disperse along the eastern Australian
74
Jaine et al.: Movements of reef manta rays
seaboard when undertaking long-distance move-
ments (>300 km) and whether they commonly utilise
specific migratory corridors, as observed in other
species off eastern Australia (Bansemer & Bennett
2011, Smith et al. 2012) and in other regions (Zerbini
et al. 2006, Campana et al. 2011).
Here, we used satellite telemetry to explore the
horizontal movements of individual M. alfredi de -
parting LEI and gain insight into their movement
patterns and habitat use in eastern Australia. We
used random walk model simulations and a 2-state
behaviour-switching state-space model (SSM) to
test the hypotheses that (1) manta ray distributions
within the southern GBR region are influenced by
the presence of the nearby Capricorn Eddy and (2)
movements of M. alfredi along the eastern Aus-
tralian seaboard are directed towards productive
regions. Our results suggest that reef manta rays
not only occupy inshore continental shelf and shelf-
edge waters but also are capable of using offshore
environments to exploit productive hotspots or
travel long distances.
MATERIALS AND METHODS
Manta ray tagging
Fieldwork was conducted at LEI (23° 06’ S,
152° 42’ E) in the southern GBR. Ten Manta alfredi
were fitted with pop-off satellite-linked archival
transmitting (PSAT) tags during austral winter 2010
(n = 2), summer 2010-2011 (n = 2) and winter 2011
(n = 6; Table 1). Prior to tag deployment, each indi-
vidual was identified, its size (disc width, WD) was
estimated and its sex was determined using con-
ventional manta ray photographic identification
and laser photogrammetry techniques (Deakos
2010, Couturier et al. 2011, Marshall & Pierce
2012). Tags were deployed on free-swimming indi-
viduals while free diving using a 320 kg Dyneema
braid leader and an umbrella-shaped plastic dart
inserted into the dorsal musculature, away from the
body cavity, with a customised tagging pole. Eight
manta rays (M1−M8) were equipped with Mk10
pop-up archival transmitting (Mk10-PAT) tags
(Wildlife Computers), and manta rays 9 and 10 (M9
and M10) were equipped with Standard Rate X-
Tags (Microwave Telemetry) (Table 1). Most tagged
individuals were re-sighted within a few minutes
post tag deployment, having resumed their previous
foraging or cleaning activity and appearing to be
unaffected by the devices.
Tag programming and geolocation
Mk10-PAT tags were programmed to record ambi-
ent light levels, sea temperature and pressure (to
allow for calculations of swimming depth) at 30 s
intervals and detach from the individual after 90 to
120 d. Depending on the tags, the binned data to
be transmitted to the Argos satellite system (www.
argos- system.org) upon release were summarised
over time intervals of 6 or 12 h. By default, X-Tags
recorded the same parameters every 2 min; however,
based on the total deployment period of 120 d, the
transmitted data were summarised into 15 min bins.
Upon release, 8 of the 10 deployed tags transmitted
the summarised data successfully. Tags 66701 and
18379, deployed on M3 and M9, respectively, failed
to transmit to the Argos system and were thus consid-
75
Manta Tag Sex Size Tag type Pop-off Date (dd/mm/yy) Duration (d) Tag
no. no. (WD, m) location Tagging Pop-off Planned Realised retrieved
M1 47726 M 3.50 Mk10-PAT 24°08' S, 153°16' E 27/06/10 30/08/10 120 65 Yes
M2 60518A F 3.50 Mk10-PAT 22°25' S, 151°39' E 28/06/10 5/10/10 120 99 Yes
M3 66701 F 3.75 Mk10-PAT 5/01/11 120
M4 66702 F 3.50 Mk10-PAT 23°28' S, 151°26' E 5/01/11 11/02/11 120 37 No
M5 66700 M 3.25 Mk10-PAT 23°40' S, 152°27' E 19/06/11 17/09/11 90 90 No
M6 66703 F 3.75 Mk10-PAT 23°30' S, 152°48' E 19/06/11 15/10/11 120 118 Yes
M7 66705 F 4.25 Mk10-PAT 22°45' S, 151°41' E 19/06/11 14/10/11 120 117 Yes
M8 60518B F 4.00 Mk10-PAT 22°22' S, 153°30' E 20/06/11 18/09/11 90 90 Yes
M9 18379 M 3.75 X-Tag 20/06/11 120
M10 18380 F 4.25 X-Tag 24°09' S, 152°37' E 20/06/11 18/10/11 120 120 Yes
Table 1. Information on the deployment of pop-off archival satellite-transmitting tags on photographically identified, sexed
and measured Manta alfredi. Tagging location was 23°06’ S, 152° 42’ E for all mantas. WD= disc width
Mar Ecol Prog Ser 510: 73–86, 2014
ered as ‘lost’. An additional 6 tags washed ashore
over a wide geographic range, from Maroochydore,
Sunshine Coast (Queensland, 26.6° S, 153.9° E), to
Shoalwater Bay (Queensland, 22.4° S, 150.7° E), and
were physically retrieved by members of the public,
allowing 100% of the higher-resolution archived raw
data to be examined (Table 1). Transmissions from
the remaining 2 tags (66 700 and 66 702) enabled
varying amounts of data to be obtained and analysed
(921 and 1565 messages, respectively).
Daily manta ray positions were estimated using the
‘Track&Loc’ geolocation filter developed at Collecte
Localisation Satellites (CLS, www.cls.fr), France. The
algorithm relies on an SSM to represent process
(movement) and observation uncertainty. Under -
water positioning is achieved using an Ensemble
Kalman filter applied to light-level measurements,
with sea surface temperature (SST) and bathymetry
data used to better constrain the tracks (Royer et al.
2005, Nielsen et al. 2006, Nielsen & Sibert 2007,
Royer & Lutcavage 2008, 2009). This process allowed
for the reconstruction of movement tracks based on
daily position estimates. Tracks were then plotted
and analysed for patterns of space utilisation, in
ArcGIS 10 (ESRI, www.esri.com).
Eddy affinity simulations
To test the hypothesis that manta ray distributions
within the southern GBR region are influenced by
the presence of the cyclonic Capricorn Eddy, we
used random walk model simulations to compare the
proportion of time spent in the eddy region by ‘real’
tracked manta rays and model manta rays. For each
tag, random movements of model manta rays were
simulated in R (Ihaka & Gentleman 1996) using the
SDMTools package, such that each model ray fea-
tured the same starting location and total track
length as the respective tracked manta ray. Distances
between successive daily positions, termed step-
lengths, were randomly chosen from the real manta
ray’s step-length frequency distribution, and a ran-
dom turn angle drawn from a uniform distribution
was selected at the end of each step. Each step of
the model manta rays was validated against a high-
resolution (i.e. 100 m) digital bathymetry map gene -
rated using the gbr100 dataset (Beaman 2010) to
preclude model rays from crossing land. The re-
orientation angle was replaced if the prior step was
rejected. For each tag, movement tracks for 1000
model manta rays were simulated, and the propor-
tion of time (in days) spent within the Capricorn Eddy
region was recorded and compared to that of the real
manta ray.
Behavioural analysis
A behaviour-switching SSM was fitted to move-
ment data collected for real manta rays to discrimi-
nate behavioural activity from movement patterns
and examine behavioural hotspots within the region
of interest. Behaviour-switching SSMs have previ-
ously been used to successfully infer the ‘hidden’
behavioural state of an animal based on movement
properties such as turn angles, step-lengths and
autocorrelation in speed and direction derived from
tracking data (Jonsen et al. 2005, Breed et al. 2009,
2012). Here, we fitted the 2-state switching corre-
lated random walk model originally described by
Jonsen et al. (2005) and refined in Breed et al. (2009)
to our Manta alfredi data. This model has been suc-
cessfully applied to various guilds of marine species
to discriminate ‘transiting’ from ‘foraging’ behav-
ioural states (e.g. pinnipeds: Breed et al. 2009, sea
turtles: Maxwell et al. 2011, cetaceans: Bailey et al.
2009 and giant manta rays M. birostris: Graham et al.
2012). We implemented the model in R and Win-
BUGS (www.winbugs-development.org.uk). To fit
the model, 2 Markov Chain Monte Carlo simulations
were computed for 10 000 iterations, with a ‘burn-in’
factor of 7000 and ‘thinning’ of 5, leaving 600 sam-
ples per chain as output to estimate each model
parameter (see Breed et al. 2009). Model output was
examined for differences between the autocorrela-
tion parameter γand the behavioural state transition
parameter αof the 2 states, indicative of true differ-
entiation of the associated movement patterns.
RESULTS
Over the course of this study, tags remained
attached to Manta alfredi for a mean period of 92 d
(± 29 SD, range 37 to 120 d). Five of the 8 tags that
successfully transmitted to the Argos system re -
ported on or near the programmed pop-up date,
with 3 detaching prematurely for unknown reasons
(Table 1). Overall, 5874 transmissions were received
by the Argos system, with raw light-level data avail-
able for the 6 recovered tags. Geolocation estimates
ranged in accuracy between 7.3 and 75.5 km2(me -
dian = 18.4 km2± 23.1 SD), depending on tag deploy-
ment duration and spatial extent of the movements
recorded.
76
Jaine et al.: Movements of reef manta rays
Spatial dynamics
Tagged Manta alfredi were tracked over 736 d,
with movements recorded across a latitudinal range
of 1035 km and with a mean track length of 1169 km
± 640 SD (Fig. 1B). Track length varied among indi-
viduals, with M6 travelling the farthest (2441 km in
118 d), whereas M4 moved only 314 km in 37 d
(Table 2). Female M. alfredi (n = 6) dispersed farther
than males (n = 2) (Fig. 1C), despite no significant dif-
ference in their respective mean track lengths (t =
−0.99, p = 0.38) and mean speeds (t = −0.59, p = 0.58).
Median speed across all tags, derived from daily
move-steps, was 0.4 km h−1 ± 0.5 SD, and maximum
speed recorded was 3.5 km h−1 for M8 (Fig. 1D). Esti-
mated swimming speeds across all tags were typi-
cally slow (i.e. <0.75 km h−1) near LEI and directly off
the shelf but increased when individuals dispersed to
other regions. Daily maximum diving depths re cor -
ded by the PSAT tags revealed that the tracked rays
dived down to 294.5 m (maximum depth range 56 to
294.5 m), with greater maximum depths logged off
the shelf near LEI (Fig. 1E).
Seven of the 8 tracked M. alfredi remained within
the GBR region, while M10 moved off the shelf in
waters over 2000 m deep and travelled southward to
28° S and back in 120 d (Fig. 1B). The southward leg
of the journey was covered at ~24 km d−1 (Fig. 1D).
M10 then spent ~50 d near the shelf edge off More-
ton Island and North Stradbroke Island (NSI). Start-
ing on Day 82, M10 moved 155 km eastward off the
shelf before turning northward and broadly retracing
its earlier southward movement, until the tag de -
tached near LEI, coincident with the detection of the
Capricorn Eddy and shelf intrusions in the satellite
signal (Fig. 2). The other manta rays tagged at LEI
(M1, M2 and M4−M8) all moved directly off the shelf
near the tagging site, where they remained for a
period of 50.7 d ± 28.3 SD before moving back onto
the shelf and dispersing farther within the GBR. M1,
M2 and M4−M8 moved up to 520 km from LEI (mean
farthest linear distance from tagging site was 247 km
± 149 SD in 77 d ± 16 SD).
Activity hotspots and eddy affinity
Movement tracks recorded across all tags (n = 8)
highlighted a major activity hotspot off the shelf near
LEI (Fig. 1B), where the mantas spent 58.5% (range
2.5 to 87.5%) of their time. There was a second hot -
spot off the shelf ~100 km east of Moreton Island
based on movement data for M10 only, which spent a
considerable amount of time in this area (42% of total
track).
Results from the random walk simulations varied
among tags (Fig. 3). Only 2 of the 8 simulations were
significant, where real manta rays spent significantly
more time in the eddy region than the 1000 models
(Table 3). However, since each simulation can be
regarded as an independent test of whether manta
rays spent more time than random in the eddy,
results from the 8 tests, each with 1000 model itera-
tions, were combined using a proportion test. To -
gether, these simulations revealed that real manta
rays spent significantly more time in the eddy region
than model rays (p < 0.001).
Behaviour
The 2-state behaviour-switching SSM discrimi-
nated transiting and foraging activity from the track-
ing data (Fig. 1F). Of the total tracking positions (n =
77
Manta Min. horizon- Track Max. Step-length Speed (km d−1) Time (%) Mean speed (km h−1)
no. tal displace- length depth (km d−1) Median Max. Fora- Tran- Fora- Tran-
ment (km) (km) (m) Mean Max. ging siting ging siting
M1 63 523 283 8.2 31.9 0.3 1.3 100.0 0.0 0.3
M2 218 1023 167 10.3 34.7 0.3 1.4 76.8 23.2 0.3 0.7
M4 137 314 56 8.5 61.0 0.2 2.5 78.4 21.6 0.2 0.9
M5 53 1089 96 12.0 63.6 0.4 2.7 82.4 17.6 0.5 0.6
M6 69 2441 140 20.7 75.5 0.6 3.1 41.5 58.5 0.6 1.2
M7 183 1243 196 10.6 43.7 0.3 1.8 66.7 33.1 0.4 0.7
M8 210 1365 294.5 15.2 84.4 0.6 3.5 26.7 73.3 0.5 0.8
M10 7 1351 97.2 11.1 31.6 0.4 1.3 0.0 100.0 0.5
Table 2. Movement metrics for 8 Manta alfredi tracked by pop-off archival satellite-transmitting tags. Minimum horizontal dis-
placement = distance between tag deployment and detachment locations. Speed is estimated from daily move step-lengths.
Foraging and transiting behaviours are inferred from state-space analysis of movement data
78
Jaine et al.: Movements of reef manta rays
736), 53.5% were determined as the ‘foraging’ state,
while the ‘transiting’ state made up the remaining
46.5%. Results revealed important foraging activity
across all but one (M10) track in the eddy region, off-
shore of LEI. The foraging behavioural state made up
~95% of locations recorded in the eddy region. A
secondary foraging location off the Swain Reefs was
also highlighted based on tracking data for M8,
which made up 3.6% of total locations across all tags.
DISCUSSION
Using satellite telemetry and spatial analyses, we
showed that reef manta rays not only occupy inshore
continental shelf and shelf-edge waters but also use
offshore environments to exploit productive hotspots
or undertake long-distance movements. All but 1
manta ray tagged in the southern GBR spent a sub-
stantial amount of time in the Capricorn Eddy region,
off the continental shelf. A behavioural analysis of
the tracking data further suggested that they may
use this area as a foraging ground. Using offshore
waters, 1 manta ray travelled 520 km southward to
another known aggregation region before returning
to the tagging region.
Spatial dynamics
Reef manta rays tagged in the southern GBR
moved across a wide geographical area along the
eastern Australian coastline, covering a latitudinal
range of 1035 km (between 20° S and 28° S). Al -
though minimum horizontal displacements (i.e. dis-
tances between tagging and pop-off locations) were
relatively small and suggestive of localised move-
ments of individuals (Table 2), track reconstruction
revealed more extensive movements. Reef manta
rays travelled up to 2441 km in 118 d and dispersed
as far as 520 km from the tagging site, occupying
both regional shelf and offshore waters. This is, to
date, one of the largest directional movements
recorded and the first horizontal movement tracks
obtained for Manta alfredi using satellite telemetry.
Tracked reef manta rays displayed some degree of
affinity to the southern GBR. Despite recording some
of the longest movement tracks and moving the far-
thest away from LEI, M6 and M10 eventually
returned to the southern GBR towards the end of
their respective tagging periods. The 6 other tagged
individuals remained within the southern GBR
region during their tracking periods. These results
suggest some degree of fidelity to the region,
79
Fig. 1. Study region showing (A) typical regional oceanographic setting (Moderate Resolution Imaging Spectroradiometer
[MODIS] sea surface temperature, June 2010), marked by the southward flow of the core East Australian Current (EAC) and
the cyclonic Capricorn Eddy (CE) forming in the lee of the shelf topography; (B) movement tracks for Manta alfredi tagged at
Lady Elliot Island (n = 8), with daily position estimates (filled circles); (C) spatial dynamics of male (n = 2) and female (n = 6)
M. alfredi; (D) swimming speed estimated from daily position estimates; (E) daily maximum diving depth for tracked M. alfredi
(n = 8); and (F) behaviour inferred from state-space analysis of the tracking data. Blue shading in (B−F) indicates water depth,
where lightest colours are depths < 200 m, and darkest colours are depths > 2000 m
Manta Days in eddy Time in eddy Successful model Unsuccessful model p-value
ray region region (%) simulations simulations
M1 55 84.6 101 899 0.101
M2 65 65.6 154 846 0.154
M4 32 86.5 92 908 0.092
M5 79 87.8 16 984 0.016
M6 55 46.6 40 960 0.040
M7 71 60.7 125 875 0.125
M8 30 33.3 328 672 0.328
M10 3 2.5 647 353 0.647
Total 390 58.5 1503 6497 <0.001
Table 3. Time spent by each tracked Manta alfredi in the Capricorn Eddy region and output from the random walk simulations for
each track, including numbers of successes, failures and resulting p-value for the test comparing the proportion of time spent in
the eddy by tracked and model manta rays. Successful and unsuccessful simulations refer to the numbers of model rays that
successfully (or unsuccessfully) spent as much time in the eddy region as real manta rays
Mar Ecol Prog Ser 510: 73–86, 2014
which supports previous findings by Couturier et al.
(2011). Using photographic identification techniques,
Couturier et al. (2011) documented dispersal by
M. alfredi to other known aggregation sites along
the eastern Australian seaboard, likely associated
with seasonal migratory movements. Similarly, van
Duinkerken (2010) identified the dispersal of individ-
ual M. alfredi along the southern Mozambican coast.
There, acoustically tagged M. alfredi typically showed
high fidelity to particular sites along the coast and
occasionally dispersed throughout the entire 95 km
long acoustic array. Long-distance movements and
80
Fig. 2 (this page and next page). Spatial and temporal dynamics of Manta alfredi M10 in relation to the oceanographic condi-
tions. Moderate Resolution Imaging Spectro radio me ter (MODIS) sea surface temperatures (left column panels) and chl acon-
centrations (right column panels) are presented for movements of M10 (white track) tracked between (A) June 19 and July 18,
2011, (B) July 19 and August 18, 2011, (C) September 19 and October 18, 2011, and (D) November 19 and December 18, 2011.
Data are presented at monthly intervals for clarity only, although dy namics at finer temporal resolutions have been in -
vestigated and did not differ. ‘CE’ marks the presence of the Capricorn Eddy feature in the satellite signal, and white arrows
denote intrusions of upwelled oceanic wa ters onto the shelf. EAC = East Australian Current
Jaine et al.: Movements of reef manta rays
migrations are typically attributed to the need to
reproduce and exchange genetic material between
members of separate populations (Bonfil et al. 2005,
Skomal et al. 2009) or the search for abundant food
resources (Zerbini et al. 2006, Anderson et al. 2011).
The question of sex-biased dispersal in M. alfredi
could not be assessed here because of our limited
data, despite tagged females noticeably dispersing
farther than the 2 males.
The mean and maximum speeds observed here,
derived from daily distances travelled, were similar
to those observed in other M. alfredi sub-popula-
tions (e.g. van Duinkerken 2010). Despite the low
spatial and temporal resolution of the collected
data, results suggested that reef manta rays can
travel distances of up to ~85 km d−1, averaging
speeds of ~3.5 km h−1. In the future, the use of
additional sensors (e.g. accelerometers) will help
collect more accurate, higher-resolution swimming
speed data, which may provide additional insights
into the movement ecology of these planktivorous
elasmobranchs.
81
Fig. 2 (continued)
Mar Ecol Prog Ser 510: 73–86, 2014
Eddy affinity and offshore foraging
The offshore Capricorn Eddy region was the pri-
mary site of occupancy for most satellite-tagged rays.
Mesoscale eddies, such as the Capricorn Eddy, stim-
ulate and redistribute biological production in the
ocean, thus creating attractive pelagic habitats for
free-ranging, higher trophic level marine organisms
(Chelton et al. 2011, Godø et al. 2012). Our results
suggest that manta rays may exploit offshore meso -
scale eddies for foraging purposes and corroborate
several other studies that showed the importance of
mesoscale eddies as offshore foraging grounds for a
variety of marine species (e.g. seabirds: Weimers -
kirch et al. 2004, Cotté et al. 2007; pinnipeds: Bailleul
et al. 2010, Dragon et al. 2010; cetaceans: Woodworth
et al. 2012).
Cyclonic eddies are known to enhance nutrient
enrichment and subsequent primary production in
subtropical western boundary systems (Falkowski et
al. 1991, McGillicuddy et al. 1998, 2007, Weeks et al.
2010). In the case of the Capricorn Eddy, turbulent
momentum exchanges with the strong southward-
flowing EAC that flows along the edge of the GBR
shelf produce a lateral stress on the mass of water in
the lee of the Swain Reefs. This drives cyclonic
(clockwise) and radially outward eddy circulation,
leading to the upwelling of cooler, nutrient-enriched
water in the centre of the eddy (Bakun 1996, Weeks
et al. 2010). The resulting upwelled waters flow
82
Fig. 3. Representative unsuccessful (M5) and successful (M10) random walk simulations. Panels in the first column, ’observed
track’, present the movement track (red line) and daily position estimates (filled circles) for each individual manta ray. The second
column, ‘simulation’, shows the geographically unconstrained 1000 random walks (blue) generated for each respective Manta
alfredi (red) from the step-length frequency distribution and the typical Capricorn Eddy region (black circle) (x- and y-axes are
degrees of longitude and latitude, respectievly). The third column, ‘time in eddy region’, indicates the proportion of time spent in
the eddy region by 1000 unconstrained random walks (white bars) compared to that of each respective M. alfredi (red line)
Jaine et al.: Movements of reef manta rays
coastward in the near-surface upper layer, eventu-
ally accumulating near LEI and the Capricorn-
Bunker reefs. Interestingly, the primary activity area
of tagged and presumed foraging Manta alfredi in
this study was the southeastern portion of the eddy
region, most likely because of the consistently en -
hanced productivity in this area triggered by eddy
dynamics.
Reef manta rays tagged in the southern GBR spent
extended periods off the shelf, undertaking deep
dives, presumably foraging, and occasionally moving
back onto the shelf. This result supports findings
from Braun et al. (2014), who documented offshore
deep-diving behaviour of satellite-tracked M. alfredi
directly adjacent to shallow coral reefs. Together,
these results challenge previous assumptions that
reef manta rays primarily rely on inshore productiv-
ity blooms as foraging habitats and highlight that
regional and mesoscale oceanographic investiga-
tions are needed to better understand habitat use
patterns of these large, free-ranging planktivores.
Moreover, a recent study by Couturier et al. (2013)
suggested that M. alfredi in eastern Australia do
not predominantly rely on near-surface zooplankton
prey during coastal feeding events and suggested
that deep and/or demersal zooplankton may be an
important part of the diet. The movement patterns
and depths recorded by tagged M. alfredi in this
study, suggestive of extensive off-shelf foraging and
greater diving activity in a region of well-
documented upwelling (Kleypas & Burrage 1994,
Weeks et al. 2010), may thus provide additional
insights into the foraging ecology of the species in
eastern Australia. More detailed analyses of the
recovered high-resolution depth data will help fur-
ther explore the diving behaviour and vertical habi-
tat use of M. alfredi.
Movements between aggregation regions
A census for manta ray sightings in eastern Aus-
tralia provided the first insight into the geographical
distribution and movement patterns of Manta alfredi
in the region (Couturier et al. 2011). Results from the
photographic survey revealed that M. alfredi is pres-
ent along ~3000 km of coastline, from Torres Strait in
northern Queensland to Sydney in central New
South Wales, and highlighted several inshore loca-
tions as key aggregation sites for the species (Cou-
turier et al. 2011). More importantly, some M. alfredi
appear to migrate between waters off NSI, Byron Bay
or the Solitary Islands in spring-summer (mid-
October to mid-April) and the southern GBR in
autumn-winter (Couturier et al. 2011, Jaine et al.
2012). Here, we found that 1 reef manta ray moved
southward from LEI to near NSI and returned to the
southern GBR in 120 d, providing the first movement
track for M. alfredi travelling between known aggre-
gation regions along the eastern Australian sea -
board.
The movement patterns of this 1 individual indi-
cated that reef manta rays can use offshore waters,
including the EAC flow, to travel up and down the
eastern coast of Australia (Fig. 2). Despite the single
observation here, 35 individual M. alfredi have been
repeatedly re-sighted previously between LEI and
the southern sites of NSI, Byron Bay and the Solitary
Islands (Couturier et al. 2011), and it is thus likely
that more individuals undertake similar movements
because of the variability and seasonality in the EAC
flow. For example, during summer reef manta rays
are common in the southern portion of the coast
(Couturier et al. 2011), coincident with increased
EAC intensity and subsequent enhanced biological
productivity (Oke & Middleton 2000, Roughan &
Middleton 2004, Nieblas et al. 2009). In winter, when
the EAC flow is weaker and the core EAC waters do
not extend as far south, reef manta ray numbers peak
in the southern GBR (Jaine et al. 2012), coincident
with a clear satellite signal of the Capricorn Eddy
and associated enhanced productivity (Kleypas &
Burrage 1994, Weeks et al. 2010).
Although limited to 1 individual, the observed
movements of M10, which travelled between the
southern GBR and NSI, could suggest that enhanced
productivity off these sites may act as a driver for
M. alfredi migrations. The individual, tracked over
winter-spring 2011, moved to spend a considerable
amount of time off the shelf-edge near NSI. Although
the behavioural SSM analysis revealed transiting-
only behaviour for this individual, most likely
because of the very directional nature of its move-
ment patterns, the extended period spent off the
shelf edge off NSI suggests otherwise. Despite anec-
dotal records of M. alfredi foraging in NSI coastal
waters, the NSI study site is primarily known as a
popular manta ray cleaning station. However, while
no published study has yet documented upwelling
frequency and productivity in the area, in situ
oceanographic data clearly show that upwelling
events occur and are most pronounced with in -
creased EAC intensity in spring-summer (S. J. Weeks
pers. obs.). The individual slowed down when
approaching the shelf-edge region off NSI and spent
the following ~50 d in the area before moving farther
83
Mar Ecol Prog Ser 510: 73–86, 2014
offshore and eventually returning to the southern
GBR. While remotely sensed SSTs and chl aconcen-
trations for the corresponding period do not show
strong inshore EAC flow or sharp fronts off NSI, typ-
ically indicative of inshore upwelling processes, the
departure from and subsequent return to LEI appear
to coincide with increased intensity of the Capricorn
Eddy and shelf intrusions, as seen in the satellite sig-
nal (Fig. 2). It is thus possible that this individual may
have been searching for other productive hotspots
along the eastern Australian seaboard.
CONCLUSIONS
This study presents the first satellite-derived move-
ment dataset for the reef manta ray Manta alfredi in
Australia. In addition to showing that M. alfredi move
across relatively large scales (i.e. > 500 km), this
study highlights that reef manta rays spend consider-
able time in offshore pelagic waters. Our results
show that eastern Australian manta rays have an
affinity for a relatively stable mesoscale cyclonic
eddy, which may comprise an important foraging
ground for the species. Further, we document the
movements of 1 individual between 2 popular aggre-
gation regions off the eastern Australian seaboard
using offshore waters. Together, our findings suggest
that M. alfredi may commonly use offshore waters to
undertake movements between aggregation sites
and exploit ephemeral productivity hotspots. Al -
though threats to M. alfredi are comparatively low in
eastern Australia, these findings highlight the need
for enhanced knowledge about the movements of
manta rays to be considered when implementing re -
gional management strategies.
Acknowledgements. We thank Dr. J. Brunnschweiler and
Dr. C. Huveneers for providing feedback on earlier versions
of the manuscript. We also thank Dr. G. Breed for help with
interpretation of the output from the behaviour-switching
SSM, as well as the ‘Track&Loc’ team at CLS, Argos, France,
for assistance with geolocation analysis and PSAT tag data
monitoring. We gratefully acknowledge the NASA Ocean
Biology Processing Group for provision of Moderate Resolu-
tion Imaging Spectroradiometer satellite data. We are grate-
ful to the various helpers who contributed to the fieldwork,
including C. Garraway, A. Rakovski, R. Jeffery, K. Fiora, C.
Ansell, R. Cheseldene-Culley, A. Donnelly and M. Roma -
novski. This study was supported by Australian Research
Council Linkage Projects grant LP110100712, a research
grant from the PADI Foundation, Sibelco, an anonymous
donor, Earthwatch Institute Australia and Lady Elliot Island
Eco Resort. Fieldwork was conducted under Great Barrier
Reef Marine Park permit G09/29853.1 and ethics approval
SBMS/071/08/SEAWORLD.
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86
Editorial responsibility: Nicholas Tolimieri,
Seattle, Washington, USA
Submitted: June 11, 2013; Accepted: June 10, 2014
Proofs received from author(s): August 29, 2014
... Unlike their benthic relatives, mantas swim primarily by dorsoventral oscillation (flapping) of the pectoral fins reminiscent of some aerial flyers, which generates lift with high propulsive efficiency [25]. These efficient swimmers are capable of long-distance migrations [26][27][28][29][30], but more frequently demonstrate high site fidelity and residency [31][32][33][34][35][36][37][38][39][40][41][42][43]. The two known manta species (Mobula birostris and Mobula alfredi) have been listed as endangered and vulnerable, respectively, on the IUCN Red List, predominantly due to targeted fishing and bycatch [44,45]. ...
... Determining how kinematics vary among behaviors is crucial to understanding how manta rays utilize their habitat. Behavior-correlated swimming speeds have been extrapolated from manta ray satellite telemetry data [26,54], which provide insightful information on large-scale movement patterns, but lack fine-scale data necessary for kinematic analyses, as behaviors were inferred and not directly observed. Previously, researchers have relied on estimations of swimming speeds in the field to calculate prey density threshold of mantas, but empirical measurements of swimming speed would improve inference for future studies on feeding ecology, migration, and energetics [55,56]. ...
... As such, animals may optimize their hydrodynamic efficiency, as seen in mantas rolling up cephalic fins to reduce drag while swimming and conserve energy while traveling [63]. Since no significant differences were found between fine-scale (0.718 m·s −1 ) and large-scale swimming speeds (0.687 m·s −1 ), we propose that fine-scale swimming speeds can be reasonably extrapolated to larger-scale movements, but are slower than previously reported swimming speeds of traveling mantas (0.97 m·s −1 ) calculated from satellite telemetry data [26]. Wingbeat frequencies of trav- ...
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Drones have become increasingly popular tools to study marine megafauna but are under- utilized in batoid research. We used drones to collect video data of manta ray (Mobula cf. birostris) swimming and assessed behavior-specific kinematics in Kinovea, a semi-automated point-tracking software. We describe a ‘resting’ behavior of mantas making use of strong currents in man-made inlets in addition to known ‘traveling’ and ‘feeding’ behaviors. No significant differences were found between the swimming speed of traveling and feeding behaviors, although feeding mantas had a significantly higher wingbeat frequency than traveling mantas. Resting mantas swam at a signifi- cantly slower speed and wingbeat frequency, suggesting that they were continuously swimming with the minimum effort required to maintain position and buoyancy. Swimming speed and wingbeat frequency of traveling and feeding behaviors overlapped, which could point to other factors such as prey availability and a transitional behavior, influencing how manta rays swim. These base- line swimming kinematic data have valuable applications to other emerging technologies in manta ray research.
... This study revealed that for the group as a whole, there was little difference between the varying anchor materials and designs. However, as a large proportion of studies have been to-date performed on the Mobulidae with their very tough skin equipped with a denticular surface (Graham et al., 2012;Jaine et al., 2014;Peel et al., 2019), soft-skinned species are not well represented so this should be taken with caution. ...
Thesis
Full-text available
Information about the movement, seasonality, and use of habitats by marine animals is vital for the mitigation of potential anthropogenic impacts. Ray species may be particularly at risk as they regularly inhabit coastal and estuarine waters. In New Zealand to-date, there has been scant research on the ecology of native ray species in estuarine habitats. In particular, there is a dearth of knowledge pertaining to the spatio-temporal use of the range of habitats within estuaries. The research detailed in this thesis was aimed at addressing the shortfall of information. First, a review of the methodology utilised in ascertaining movement behaviour in non-shark-like batoid elasmobranch species was carried out, as optimisation of tagging research technique underpins the ability to track behaviour of these organisms for long periods. Most studies reviewed adopted tag anchor techniques used on teleost fishes or sharks. As a consequence, the quality of information pertaining to ray habitat use and movements was, in many circumstances, poor. Synthesis of tag longevity using differing anchor methods and field and aquarium longevity experiments led to a recommendation of nylon umbrella darts for soft-skinned non-shark-like rays such as Bathytoshia brevicaudata. Second, seasonality in habitat use within the Tauranga Harbour system was examined using monthly counts of the feeding excavations of Myliobatis tenuicaudatus. This study expanded previous estimations of seasonality and feeding habitat choice in estuaries. It determined that temperature-mediated sinusoidal seasonal patterns in feeding behaviour over a period of 24 months, differed in magnitude and peak month across a range of spatial scales. This could suggest some form of sequential habitat use. Unlike previous studies, evidence of ray feeding was found year-round. This behavioural pattern has implications for calculations of sediment turnover and transport. Peak turnover estimates of ray origin from this study doubled previous estimated calculations. In addition, infaunal prey density, and locational aspects of estuary ‘sub-habitats’ characterised as various ‘zones’ as compared to ‘harbour basin’ habitats, were all found to be influential in the prediction of M. tenuicaudatus feeding activity. There were inverse seasonal differences in the relationship between densities of large infaunal bivalves (putative prey items) and ray feeding activity, suggesting that during some periods, other prey types (soft bodied organisms) may also be important. Suggestions are made that perceived predator risk and human disturbance may have a role in driving habitat preferences in addition to prey density. This study also found that natural mangrove fringe is preferred by M. tenuicaudatus for feeding habitat over areas of ‘fringe’ that had been trimmed to prevent mangrove spread. The implications of this are significant as there is a reduction in ideal feeding habitat with ongoing mangrove trimming regimes. Finally, quantification of metal body burden of M. tenuicaudatus identified low levels of some heavy metals in rays from Tauranga Harbour when compared to Porirua Harbour, and that metals in rays from the outer coast of the Bay of Plenty region were likely to be of volcanic origin. Significantly different metal assemblages of estuarine and offshore animals combined with feeding evidence found year-round in Tauranga Harbour, suggests a separation in populations between these areas. Overall however, it is clear that metal content in Tauranga Harbour rays lies below FZANZ levels of concern and the harbour may be classified as relatively unpolluted. However, the behavioural patterns of rays clearly lead them away from shallower sub estuary areas, that are known to be more contaminated by anthropogenic activity. In conclusion, this thesis provides previously unknown information about the habits and ecology of the important estuarine mesopredator M. tenuicaudatus in the context of anthropogenic risk associated with an urbanised harbour ecosystem. The information will allow informed management of harbour activities and developmental options with regard to conservation of an ecologically important species.
... Though M. alfredi are capable of travelling up to several hundred kilometres to visit seasonally-productive sites (Anderson et al., 2011;Couturier et al., 2014;Jaine et al., 2014), the 14 satellite or acoustically-tagged individuals in this study showed high residency to the Wayag lagoon, with a maximum movement of 47 km to the east of the lagoon. None of the acoustically-tagged individuals were detected within the an array of 23 acoustic receivers placed at all known M. alfredi aggregation sites in the Raja Ampat archipelago (Figure 1), including at the heavily-visited cleaning and feeding aggregation site Eagle Rock, just 36 km to the south of the Wayag lagoon (Setyawan et al., 2018). ...
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The behaviour and spatial use patterns of juvenile manta rays within their critical nursery habitats remain largely undocumented. Here, we report on the horizontal movements and residency of juvenile reef manta rays (Mobula alfredi) at a recently discovered nursery site in the Wayag lagoon, Raja Ampat, Indonesia. Using a multi-disciplinary approach, we provide further corroborative evidence that the lagoon serves as an important M. alfredi nursery. A total of 34 juvenile rays were photo-identified from 47 sightings in the sheltered nursery between 2013–2021. Five (14.7%) of these individuals were resighted for at least 486 days (~1.3 years), including two juveniles resighted after 641 and 649 days (~1.7 years), still using the nursery. Visually estimated (n=34) disc widths (DW) of juveniles using the nursery site ranged from 150–240 cm (mean ± SD: 199 ± 19), and the DW of two juveniles measured using drones were 218 and 219 cm. Five juveniles were tracked using GPS-enabled satellite transmitters for 12–69 days (mean ± SD: 37 ± 22) in 2015 and 2017, and nine juveniles were tracked using passive acoustic transmitters for 69–439 days (mean ± SD: 182 ± 109) from May 2019–September 2021. Satellite-tracked individuals exhibited restricted movements within Wayag lagoon. The minimum core activity space (50% Utilisation Distribution-UD) estimated for these five individuals ranged from 1.1–181.8 km2 and the extent of activity space (95% UD) between 5.3–1,195.4 km2 in area. All acoustically tagged individuals displayed high residency within the nursery area, with no acoustic detections recorded outside the lagoon in the broader Raja Ampat region. These juveniles were detected by receivers in the lagoon throughout the 24 h diel cycle, with more detections recorded at night and different patterns of spatial use of the lagoon between day and night. The observed long-term residency of juvenile M. alfredi provides further compelling evidence that the Wayag lagoon is an important nursery area for this globally vulnerable species. These important findings have been used to underpin the formulation of management strategies to specifically protect the Wayag lagoon, which will be instrumental for the survival and recovery of M. alfredi populations in Raja Ampat region.
... Individual detections were then eliminated if two subsequent detections between receivers resulted in unrealistic rates of movement. A swim speed of > 2 m/s was selected to filter these data, based on previous estimates for mobula rays [46][47][48]. To avoid analyzing unnatural movements associated with the capture-tagging process, detections recorded within 48 h post release were excluded. ...
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Background: Reef manta ray (Mobula alfredi) populations along the Northeastern African coastline are poorly studied. Identifying critical habitats for this species is essential for future research and conservation efforts. Dungonab Bay and Mukkawar Island National Park (DMNP), a component of a UNESCO World Heritage Site in Sudan, hosts the largest known M. alfredi aggregation in the Red Sea. Methods: A total of 19 individuals were tagged using surgically implanted acoustic tags and tracked within DMNP on an array of 15 strategically placed acoustic receivers in addition to two offshore receivers. Two of these acoustically monitored M. alfredi were also equipped with satellite linked archival tags and one individual was fitted with a satellite transmitting tag. Together, these data are used to describe approximately two years of residency and seasonal shifts in habitat use. Results: Tagged individuals were detected within the array on 96% of monitored days and recorded an average residence index of 0.39 across all receivers. Detections were recorded throughout the year, though some individuals were absent from the receiver array for weeks or months at a time, and generalized additive mixed models showed a clear seasonal pattern in presence with the highest probabilities of detection occurring in boreal fall. The models indicated that M. alfredi presence was highly correlated with increasing chlorophyll-a levels and weakly correlated with the full moon. Modeled biological factors, including sex and wingspan, had no influence on animal presence. Despite the high residency suggested by acoustic telemetry, satellite tag data and offshore acoustic detections in Sanganeb Atoll and Suedi Pass recorded individuals moving up to 125 km from the Bay. However, all these individuals were subsequently detected in the Bay, suggesting a strong degree of site fidelity at this location. Conclusions: The current study adds to growing evidence that M. alfredi are highly resident and site-attached to coastal bays and lagoons but display seasonal shifts in habitat use that are likely driven by resource availability. This information can be used to assist in managing and supporting sustainable ecotourism within the DMNP, part of a recently designated UNESCO World Heritage Site.
... The zooplanktivorous reef and oceanic manta rays (Mobula alfredi and M. birostris, respectively) are two of the ocean's largest species (Marshall et al., 2009;White et al., 2018). Fragmented populations of M. alfredi are widely distributed throughout the tropical and sub-tropical waters of the Indo-West Pacific Oceans, where they frequent coastal reef habitats, but also use offshore environments and the mesopelagic zone (Kashiwagi et al., 2011;Couturier et al., 2012;Braun et al., 2014;Jaine et al., 2014;Stevens et al., 2018a;Hosegood, 2020). Mobula birostris are distributed throughout all tropical oceans and also range into temperate waters. ...
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Manta ray populations worldwide are vulnerable to sublethal injuries resulting from human activities, e.g., entanglement in fishing line and boat strikes, which have the potential to impact an individual’s health, fitness, and behaviour. Sublethal injuries and physical abnormalities also occur naturally from predation events, deformity, parasites, and disease. To determine the type and frequency of anthropogenic and natural originated injury events affecting Mobula alfredi and M. birostris in the Maldives, we examined data from the Manta Trust’s Maldivian Manta Ray Project (MMRP) database, which contains 73,638 photo-identification (photo-ID) sightings of the two manta ray species from 1987 to 2019. The likely origin of each injury or physical abnormality was determined based on visual assessment of the photo-ID images. Multiple injuries to an individual originating from the same event were grouped for analysis. Generalised linear mixed models (GLMM) were used to investigate the relationship between the occurrence of injury events and the explanatory variables sex and maturity status for both species, with the additional variable site function (cleaning, feeding, cruising) investigated for M. alfredi. Spatial and temporal variations in M. alfredi injury events, and their origin and type, were investigated by calculating the percentage of injury events per sighted individual at each Maldivian atoll, and per re-sighted individual in each year from 2005 to 2019. For both species, injury events were predominantly of natural origin, with predatory bites being the most frequent type. The most common anthropogenic injury type was entanglement in fishing line. Injuries to M. alfredi were significantly more likely to be observed on juveniles than adults, males than females, and at cleaning stations as opposed to feeding or cruising sites. Neither sex nor maturity status were significant explanatory variables for the occurrence of injuries to M. birostris. Highest percentages of anthropogenic injuries per sighted M. alfredi were recorded in North Malé, South Malé, Baa, Addu, and Laamu Atolls, where boat traffic, fishing, and tourism activities are concentrated. Overall, this work greatly improves understanding of the sublethal threats faced by manta rays in the Maldives; identifying focus areas where conservation management actions are required to ensure more effective protection of this threatened species group.
... Monitoring in the open ocean may rely more heavily on proxies or surrogates than in inshore areas, since data collection can be logistically challenging and expensive. Monitoring populations of some of the more wide-ranging species of interest in offshore MPAs will require a combination of methods, such as satellite technology, drifting baited stereo-videography, spotter planes, drones, horizontal acoustics, and vessel-based sampling (Jaine et al., 2014;Bouchet and Meeuwig, 2015;Letessier et al., 2017). Physical and chemical data can be easier to obtain, and, when available, can be a good predictor for the distribution of some open ocean species (Trebilco et al., 2011;Reygondeau et al., 2012;Hewitt et al., 2015;Stephenson et al., 2020). ...
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Networks of no-take marine protected areas (MPAs), where all extractive activities are prohibited, are the most effective tool to directly protect marine ecosystems from destructive and unsustainable human activities. No-take MPAs and MPA networks have been globally implemented in coastal seas, and their success has been significantly enhanced where science-based biophysical guidelines have informed their design. Increasingly, as human pressure on marine ecosystems is expanding further offshore, governments are establishing offshore MPAs—some very large—or MPA networks. Globally, there are growing calls from scientists, non-government organisations, and national governments to set global conservation targets upwards of 30%. Given that most of the ocean is found either in the high seas or offshore within national Exclusive Economic Zones, large offshore MPAs or networks of MPAs must be a major component of these global targets for ocean protection. However, without adequate design, these offshore MPAs risk being placed to minimise conflict with economic interests, rather than to maximise biodiversity protection. This paper describes detailed biophysical guidelines that managers can use to design effective networks of no-take MPAs in offshore environments. We conducted a systematic review of existing biophysical design guidelines for networks of MPAs in coastal seas, and found consistent elements relating to size, shape, connectivity, timeframes, and representation of biophysical features. However, few of the guidelines are tailored to offshore environments, and few of the large offshore MPAs currently in place were designed systematically. We discuss how the common inshore design guidelines should be revised to be responsive to the characteristics of offshore ecosystems, including giving consideration of issues of scale, data availability, and uncertainty. We propose 10 biophysical guidelines that can be used to systematically design offshore networks of MPAs which will also contribute to the global goal of at least 30% protection globally. Finally, we offer three priority guidelines that reflect the unique conservation needs of offshore ecosystems: emphasising the need for larger MPAs; maximising the inclusion of special features that are known and mapped; and representing minimum percentages of habitats, or, where mapped, bioregions. Ultimately, MPA guidelines need to be embedded within an adaptive management framework, and have the flexibility to respond to emerging knowledge and new challenges.
... Re ports from fishermen support the hypo thesis that the occurrence of manta rays inside the estuary is seasonal (Medeiros et al. 2015). Migra- Author copy tory be havior is common for manta rays that demonstrate seasonal aggregation and habitat fidelity, undertaking short-and long-distance migrations, visiting specific sites at specific times of the year to reproduce, to feed, or to be cleaned (Marshall et al. 2009, Kashi wagi et al. 2011, Jaine et al. 2014, Stewart et al. 2016a. Manta rays are ectothermic and do not have the capability to accumulate fat; therefore, they need to constantly feed to maintain their large body mass (Alexander 1996). ...
Article
ABSTRACT: Improving our knowledge on the behavior of threatened species is essential for developing effective conservation actions. The Paranaguá Estuarine Complex (PEC), southern Brazil, is the only estuary in the world where manta rays have been observed performing breaches seasonally. The exact role of this breaching behavior and the environmental factors connected to it are unknown. Our goals were to determine the spatial distribution, and the temporal and environmental factors that influence the breaching behavior of this endangered group in a dynamic estuarine habitat for the first time. Manta rays were observed breaching in the PEC during austral summer and early autumn, when the sea surface temperature (SST) and precipitation were high. Generalized additive models revealed that the presence and frequency of the breaches were both influenced by the SST and hours of daily effort, while the breaching frequency was also influenced by the wind direction and speed, percentage of moon illumination, and year. The breaches were mainly concentrated near the mouth of a river. Likely these factors influenced not only the occurrence and behavior of manta rays, but also the distribution of their food source, potentially providing optimal conditions for foraging and reproduction. Based on the coloration pattern, it is possible that the observations were of Mobula cf. birostris. These results provide valuable insights into the breaching behavior of manta rays in estuarine waters that will assist future conservation initiatives and research on their behavioral ecology, to optimize fishery management and contribute to developing sustainable ecotourism in the PEC.
Article
Traditional eddy detection methods can well identify eddies with long lifespans (usually >4 weeks) and strong hydrographic features. Eddies with shorter lifespans or intermittent features are arduous to detect and might be eliminated or misclassified during the detection. However, these eddies have been reported as a majority of the mesoscale eddies in global oceans. This study developed a novel eddy identification method for those eddies. Different from the traditional eddy detection performed based on a snapshot of observations in the horizontal plane, this novel identification method was developed on the evolution of eddies in the temporal dimension. It efficiently avoids the failure in detecting eddies with inconspicuous features during some stages of their evolutions and also eliminates excessive detection. The developed method was implemented to detect Capricorn Eddies based on 26 years of sea-level anomaly from satellite altimetry. Capricorn Eddies are transient and intermittent phenomena induced as a result of the East Australian Current colliding with the continental shelf edge near the Fraser Island, Australia. Using the new identification method, the characteristics of Capricorn Eddies, including their temporal and spatial scales, intensity preferences and evolution details, were resolved. Remarkable seasonal variations of the Capricorn Eddies were also revealed. Based on these findings, a comprehensive overview of Capricorn Eddies, which is crucial for further understanding the variabilities of regional biogeochemical processes and ocean ecosystems, was provided. The developed method will also provide potential insight into the unrevealed eddies in the global oceans.
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Ecological niche modeling (ENM) provides information on the potential environmental barriers to a species that can be tested in phylogeographic studies. A previous ENM analysis of the benthic coastal stingray Hypanus marianae revealed a low suitability area for its occurrence at the São Francisco River (SFR) mouth, the fourth largest river flowing into Southwestern Atlantic. Hence, phylogeographic analyses were used to test the hypothesis of two populations: one north and another south of SFR outflow. We sampled 109 specimens in six localities throughout the species’ geographic distribution and sequenced mitochondrial (cytb) and nuclear (rag1) markers. Our analyses corroborated the existence of two groups (ΦST = 0.68, P < 0.0001) within H. marianae, partially agreeing with the ENM results. The commonest mitochondrial haplotype (H2) was shared among almost all localities, except Salvador, where all individuals shared the same and unique haplotype. This group is restricted to a shallow bay area close to SFR, as predicted by the ENM. However, its plume was not effective in isolating a continental island 55 km off the Brazilian coast. While the broad north group is protected in a few Marine Protected Areas, our results suggest that the restricted southern one deserves to be managed specifically.
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Our understanding of the genetic connectivity of manta ray populations and the drivers that shape genetic structure is still limited. This information is crucial to identify the spatial boundaries of discrete populations and guide decisions on units to conserve. In this study, we use genome-wide single nucleotide polymorphisms (SNPs) to assess the genetic structure and diversity of reef manta rays Mobula alfredi at a local scale within New Caledonia and regionally in the western Pacific Ocean. We provide the first evidence of fine scale genetic differentiation in M. alfredi, found between the 3 cleaning station aggregation sites in New Caledonia (n = 65) (N = 2676 SNPs, FST = 0.01, p < 0.0001). Furthermore, population structure was evident at the regional scale between individuals from New Caledonia (NC, n = 73) and East Australia (EA, n = 19) on the basis of genetic differentiation statistics (3619 SNPs, FST = 0.096, p < 0.0001) and clustering algorithms, with unidirectional gene flow detected from east (NC) to west (EA). These results reveal that reef manta rays can form genetically distinct groups within a relatively small geographic range and highlights the need to consider genetic structure when designating management units for conservation action and planning.
Thesis
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Mobulid rays (family Mobulidae) are epipelagic zooplanktivores separated into two genera, Manta (2 species) and Mobula (9 species). Despite their economic importance in the tourism industry, mobulid rays currently face severe fisheries pressures worldwide which threatens the survival of many populations. These rays are considered long-lived and have low fecundity, which make them particularly vulnerable to fisheries exploitation. The paucity of data on the ecology and biology of these species has hindered the ability to effectively assess their conservation status and needs. Available information on mobulid species in peer-reviewed and grey literature was reviewed in this study to identify the critical knowledge gaps on their biology, ecology and conservation. The current lack of baseline data on mobulid species relates to the inherent challenges associated with studying large, wide-ranging pelagic animals. Manta rays (Manta spp.) predictably aggregate at particular sites where they can be easily approached by divers. These aggregation sites provide unique opportunities for scientists to investigate population dynamics of these otherwise elusive species. This thesis examined the population of the reef manta ray Manta alfredi off eastern Australia at several aggregation sites. The reef manta ray is the most common mobulid species encountered in east Australian waters and, although the species is a popular tourist attraction, information on its population biology and ecology was non-existent in this part of the world prior to this study. Photographic identification techniques were used to identify individual reef manta rays at eight sites along the coast between Osprey Reef, northern Great Barrier Reef, Queensland and the Solitary Island Marine Park, New South Wales. A total of 716 individuals were identified between 2007 and 2012, including 636 at Lady Elliot Island (LEI), southern Great Barrier Reef. Over 60% of individuals identified along this coastline were resighted at least once between 2007 and 2012 and the mean number of sightings per individual was 3. The sex ratio of this population was significantly biased toward females with an overall 1.3:1 female-to-male ratio observed. Reef manta rays are present all year around at LEI, although they are seen in higher numbers in winter, whereas they are mainly seen off North Stradbroke Island and Byron Bay from mid-spring to mid-autumn. Seasonal movements were observed between these locations with 56 individuals identified at both LEI and North Stradbroke Island (c. 380 km to the south), 12 at LEI and Byron bay (c. 500 km to the south) and one at LEI and North Solitary Island (c. 650 km to the south). Robust design population models were used to estimate the population size of the winter aggregation at LEI over a four-year period using the program MARK. The model estimated up to 532 individuals in the population within one winter season and that survivorship of reef manta rays between consecutive iii years was exceptionally high (φ=1). This abundance estimate is the largest assessed for a seasonal aggregation of reef manta rays at a single site. The superpopulation size estimate of this winter aggregation at LEI was 601 individuals over the 4-year study period. This study demonstrated that the habitat around LEI forms a key aggregation site for a large portion of the reef manta ray population in east Australian waters. Passive acoustic telemetry techniques were used to examine the residency and site fidelity patterns of the reef manta ray at LEI. Five acoustic receivers were moored around the island between June 2009 and September 2012 and a total of 33 acoustic transmitters were deployed on reef manta rays. All tagged animals returned to this site within their recorded period with some individuals visiting the area for up to 23 consecutive days. Using a general linear mixed effects modelling approach, we analysed the hourly visitation patterns of manta rays with respect to environmental and temporal parameters. Diel phase, wind direction, month, wind speed and moon phase all had significant effects on the presence of manta rays at LEI. Individuals were significantly more likely to be present during daytime and in calmer weather conditions, which may be linked with behavioural thermoregulation and cleaning activities. A strong seasonal pattern was detected with more individuals present in winter around LEI. Sea temperature was not directly linked with this pattern. It is hypothesised that food availability may be a key parameter for this seasonal aggregation. The high degree of site fidelity of some individuals at LEI underpins the importance of this site as a key habitat for reef manta rays. Stable isotope and fatty acid signature analyses were conducted on reef manta ray muscle tissue biopsy samples to examine the species’ assimilated diet. Muscle tissue δ15N and δ13C values, and the fatty acid signature were compared to those derived from different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). A trophic position estimate of three was derived from stable isotope δ15N values, and the relatively high levels of the fatty acid trophic marker 18:1ω9 (>13% of total fatty acids) confirmed that the reef manta ray is a secondary consumer. Near-surface and epipelagic zooplankton fatty acid composition indicated a dominant flagellate-based food source with high levels of docosahexaenoic acid (>20% of total fatty acids). The reef manta ray had relatively high levels of docosahexaenoic acid (>10% of total fatty acids) also indicating a flagellate-based food source in the diet. High ω6 fatty acid levels (>17% of total fatty acids) and slightly enriched δ13C values (-17.3‰) in reef manta ray tissue suggest that the species does not feed predominantly on near surface pelagic zooplankton, but obtains a major part of its diet from another source. The closest match is with demersal zooplankton, suggesting it is an important part of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to iv the horizontal and vertical movement patterns of the reef manta ray. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs. The current study has expanded our knowledge of a regionally important population of the reef manta ray, and has provided new insights into key aspects of the species’ ecology. This thesis used a combination of methods based on practical and rigorous approaches and brings new perspectives to the study of wide ranging marine species. ‘Citizen science’ provided important empirical data on the longevity, site affinity, seasonal movement and distribution of the reef manta ray population along the eastern seaboard of Australia. Robust sampling design and appropriate population models were used to estimate the population size of a large annual aggregation of manta ray across several consecutive years. Acoustic telemetry data were analysed through an original statistical approach able to integrate individual behaviour of the tagged individuals. Non-lethal approaches were used to study the diet of reef manta rays and provided results that challenge key aspects of the current paradigm about the diet and feeding ecology of the species. These methods are replicable and will contribute to the standardisation of methodologies and modelling in mobulid species research.
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During the winter months, from June to September, humpback whales Megaptera novaeangliae breed and calve in the waters of the Great Barrier Reef (GBR) after migrating north from Antarctic waters. Clearly defined wintering areas for breeding and calving comparable to those identified in other parts of the world have not yet been identified for humpback whales in the GBR Marine Park (GBRMP), mainly because of its large size, which prohibits broad-scale surveys. To identify important wintering areas in the GBRMP, we developed a predictive spatial habitat model using the Maxent modelling method and presence-only sighting data from non-dedicated aerial surveys. The model was further validated using a small independent satellite tag data set of 12 whales migrating north into the GBR. The model identified restricted ranges in water depth (30 to 58 m, highest probability 49 m) and sea surface temperature (21 to 23 degrees C, highest probability 21.8 degrees C) and identified 2 core areas of higher probability of whale occurrence in the GBRMP, which correspond well with the movements of satellite tagged whales. We propose that one of the identified core areas is a potentially important wintering area for humpback whales and the other a migration route. With an estimated increase in port and coastal development and shipping activity in the GBRMP and a rapidly increasing population of whales recovering from whaling off the east Australian coast, the rate of human interactions with whales is likely to increase. Identifying important areas for breeding and calving is essential for the future management of human interactions with breeding humpback whales.
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Recent successful efforts to increase protection for manta rays has highlighted the lack of basic ecological information, including vertical and horizontal movement patterns, available for these species. We deployed pop-up satellite archival transmitting tags on nine reef manta rays, Manta alfredi, to determine diving behaviors and vertical habitat use. Transmitted and archived data were obtained from seven tagged mantas over deployment periods of 102-188 days, including three recovered tags containing 2.6 million depth, temperature, and light level data points collected every 10 or 15 seconds. Mantas frequented the upper 10 m during daylight hours and tended to occupy deeper water throughout the night. Six of the seven individuals performed a cumulative 76 deep dives (>150 m) with one individual reaching 432 m, extending the known depth range of this coastal, reef-oriented species and confirming its role as an ecological link between epipelagic and mesopelagic habitats. Mean vertical velocities calculated from high-resolution dive data (62 dives >150 m) from three individuals suggested that mantas may use gliding behavior during travel and that this behavior may prove more efficient than continuous horizontal swimming. The behaviors in this study indicate manta rays provide a previously unknown link between the epi- and mesopelagic layers of an extremely oligotrophic marine environment and provide evidence of a third marine species that utilizes gliding to maximize movement efficiency.
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Assessing the trophic role and interaction of an animal is key to understanding its general ecology and dynamics. Conventional techniques used to elucidate diet, such as stomach content analysis, are not suitable for large threatened marine species. Non-lethal sampling combined with biochemical methods provides a practical alternative for investigating the feeding ecology of these species. Stable isotope and signature fatty acid analyses of muscle tissue were used for the first time to examine assimilated diet of the reef manta ray Manta alfredi, and were compared with different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). Stable isotope δ(15)N values confirmed that the reef manta ray is a secondary consumer. This species had relatively high levels of docosahexaenoic acid (DHA) indicating a flagellate-based food source in the diet, which likely reflects feeding on DHA-rich near-surface and epipelagic zooplankton. However, high levels of ω6 polyunsaturated fatty acids and slightly enriched δ(13)C values in reef manta ray tissue suggest that they do not feed solely on pelagic zooplankton, but rather obtain part of their diet from another origin. The closest match was with demersal zooplankton, suggesting it is an important component of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to the horizontal and vertical movement patterns of this giant planktivore. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs.
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Southern Hemisphere humpback whales Megaptera novaeangliae migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. It has been hypo- thesized that the population wintering off eastern South America migrates to feeding grounds near the Antarctic Peninsula (ca. 65° S, 60° W) and/or South Georgia (54° 20' S, 36° 40' W), but direct evi- dence to support this has never been presented. Between 19 and 28 October 2003, 11 humpback whales (7 females and 4 males) were instrumented with satellite transmitters off Brazil (ca. 18° 30' S, 39° 30' W) to investigate their movements and migratory destinations. Mean tracking time for the whales was 39.6 d (range = 5 to 205 d) and mean distance travelled was 1673 km per whale (range = 60 to 7258 km). Movements on the wintering ground showed marked individual variation. Departure dates from the Brazilian coast ranged from late October to late December. Whales migrated south through oceanic waters at an average heading of 170° and travelled a relatively direct, linear path from wintering to feeding grounds. Two whales were tracked to feeding grounds in offshore areas near South Georgia and in the South Sandwich Islands (58° S, 26° W) after a 40 to 60 d long migration. Historical catches and current sighting information support these migratory routes and destinations. This study is the first to describe the movements of humpback whales in the western South Atlantic Ocean.
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Observations from an intensive oceanographic field program which took place in 1998-1999 about the separation point of the East Australian Current (EAC) show significant spatial and temporal variability of the EAC. Upstream of the separation point, southward flowing currents are strong, with subinertial velocities of up to 130 cm s-1 in the near-surface waters, whereas downstream currents are highly variable in both strength (1-70 cm s-1) and direction. Upwelling is observed to occur through both wind-driven and current-driven processes, with wind effects playing a lesser role. By contrast, the encroachment of the EAC upon the coast has a profound effect on the coastal waters, accelerating the southward (alongshore) currents and decreasing the temperature in the bottom boundary layer (BBL) by up to 5°C. As the axis of the jet moves onshore, negative vorticity increases in association with an increase in nonlinear acceleration. During this time, bottom friction is increased, the Burger number is reduced, and the BBL shut-down time lengthens. The observed upwelling is attributed to enhanced onshore Ekman pumping through the BBL resulting from increased bottom stress as the southerly flow accelerates when the EAC encroaches across the continental shelf.
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Photo-identification techniques were used to investigate temporal and spatial distributions of Carcharias taurus (Rafinesque, 1810) in relation to maturity, sex and pregnancy status at 19 sites along Australia's eastern coastline. Of 931 individual sharks identified between 2004 and 2008, 479 were female (271 mature, 208 immature) and 452 male (288 mature, 164 immature). Mature, non-gravid females and mature males were mostly observed in the southern to central parts of this species range, along the eastern coast of Australia, in early summer to early winter. These sharks subsequently moved northward, and mating occurred in late spring to early summer in waters off the coast of northern New South Wales and southern Queensland. Pregnant C. taurus aggregated at Wolf Rock in southern Queensland, at the most northerly part of their known range, from late summer to early winter. These sharks subsequently migrated south to pup in central and southern waters of their range in late winter to late spring. Immature sharks of both sexes moved less than mature sharks, showed no synchronised migration patterns, and were mostly restricted to central and southern waters. The improved understanding of sex-and maturity-based migration of C. taurus provided here should facilitate a conservation strategy appropriate for this species in Australian waters.
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