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Habitat use and movement patterns of tiger sharks (Galeocerdo
cuvier) in eastern Australian waters
Rebecca S. Lipscombe
1
, Julia L. Y. Spaet
2
, Anna Scott
1
, Chi Hin Lam
3
, Craig P. Brand
4
, and
Paul A. Butcher
1,4
*
1
National Marine Science Centre, Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, PO
Box 4321, Coffs Harbour, NSW 2450, Australia
2
Evolutionary Ecology Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK
3
Large Pelagics Research Center, School for the Environment, University of Massachusetts Boston, Gloucester, MA, USA
4
NSW Department of Primary Industries, National Marine Science Centre, Coffs Harbour, NSW 2450, Australia
*Corresponding author: tel: þ61 438 650 129; e-mail: paul.butcher@dpi.nsw.gov.au.
Lipscombe, R. S., Spaet, J. L. Y., Scott, A., Lam, C. H., Brand, C. P., and Butcher, P. A. Habitat use and movement patterns of tiger sharks
(Galeocerdo cuvier) in eastern Australian waters. – ICES Journal of Marine Science, doi:10.1093/icesjms/fsaa212.
Received 14 July 2020; revised 14 October 2020; accepted 15 October 2020.
Understanding the movement of marine predators is vital for effective conservation and management. Despite being targeted by shark con-
trol programs, the tiger shark, Galeocerdo cuvier, is poorly studied off eastern Australia. To investigate the horizontal movement and habitat
use in this region, 16 sharks (157–384 cm total length) were tagged with MiniPAT pop-up satellite archival tags in 2018 and 2019. Eleven of
these individuals were also fitted with satellite-linked radio transmitting tags. After release, most sharks moved off the continental shelf and
headed north, associating with seamounts as they moved towards Queensland. During their time at liberty they transited through temperate,
sub-tropical and tropical waters and spent the majority of time in the upper 50 m of the water column and at temperatures between 22 and
25˚C. Horizontal movement was focused in waters off the continental shelf. Increased movement over shelf waters occurred during the aus-
tral spring and summer when the East Australian Current is at its strongest and warm waters encroach the continental shelf. Broad latitudinal
movement along the east coast of Australia was evident and highlights the connectivity between tropical and warm-temperate regions.
Keywords: archival tag, bather protection, carcharhinid, geolocation, satellite tag, shark management
Introduction
Analysis of the spatial dynamics and patterns in shark movement
has become detailed and accurate, revealing complex horizontal
and vertical habitat use and behavioural patterns (Barnes et al.,
2016;Spaet et al., 2017). While previously limited to mark-
recapture studies, over the last two decades, satellite and acoustic
technology has increased our ability to document broad-scale
movement, migration, residency, and philopatric behaviour
(Holmes et al., 2014;Werry et al., 2014). In addition, evaluation
of depth and temperature preference and diving behaviour can be
performed through archived data and biologging (Andrzejaczek
et al., 2019a) and has revealed dynamic vertical movements and
plasticity of habitat use (Holmes et al., 2014;Afonso and Hazin,
2015).
The tiger shark, Galeocerdo cuvier (Carcharhinidae), is a large
predatory shark that is currently listed as ‘Near Threatened’ on
the International Union for Conservation of Nature Red List of
threatened species (Ferreira and Simpfendorfer, 2019). Galeocerdo
cuvier have a global distribution and utilize both nearshore and
offshore habitats (Fitzpatrick et al., 2012;Holmes et al., 2014) in
tropical and warm-temperate regions (Last and Stevens, 2009).
On the east coast of Australia, G. cuvier shows a high level of in-
teraction with commercial, recreational and illegal fisheries due
to its broad-scale movements (Field et al., 2009;Macbeth, 2009;
Butcher et al., 2015). Yet, movement along the east coast of
Australia is relatively undocumented, with only one previous
study encompassing New South Wales (NSW) and Queensland
(QLD) waters (Holmes et al., 2014).
V
CInternational Council for the Exploration of the Sea 2020. All rights reserved.
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ICES Journal of Marine Science (2020), doi:10.1093/icesjms/fsaa212
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Interactions with fisheries are not the only management issue
for G. cuvier on the east coast of Australia (Butcher et al., 2015),
as they are also one of the main species targeted in state shark
control programmes (Reid et al., 2011;Holmes et al., 2012).
To minimize the threat of some shark species to water users, gov-
ernment shark control programmes have been in place in both
NSW and QLD for over 50 years and use a combination of shark
nets and/or baited drumlines (Reid et al., 2011). Galeocerdo cuvier
was among three ‘target’ species of shark that were identified as a
threat to humans, being responsible for several deaths and severe
injuries on the east coast of Australia (McPhee, 2014). Although
shark bites are rare, they receive excessive media attention and
community concern (Fraser-Baxter and Medvecky, 2018).In
2015, the NSW Government implemented the ‘Shark
Management Strategy’ (Simmons and Mehmet, 2018). This strat-
egy uses a multidisciplinary approach and involves the trials of al-
ternative or new tools for bather protection including SMART
drumlines (Guyomard et al., 2019) and drones (Colefax et al.,
2019;Butcher et al., 2019).
One component of the shark management strategy in NSW is
to further quantify the movements and behaviour of target sharks
like G. cuvier to help minimize human–shark interactions. Here,
we aim to characterize broad-scale movement of G. cuvier and ex-
amine habitat use between coastal and pelagic environments
along the east coast of Australia using satellite-linked radio trans-
mission and pop-up archival tagging technologies.
Material and methods
Tagging
Targeted fishing for G. cuvier occurred between 13 February 2018
and 23 July 2019 using SMART drumlines (Guyomard et al.,
2019) and vertical droplines (Williams et al., 2016). Sharks were
caught at Lennox Head (28"480S, 153"360E), Ballina (28"500S,
153"330E), Evans Head (29"060S, 153"250E), and Coffs Harbour
(30"170S, 153"060E), NSW, Australia. SMART drumlines were
baited with 0.75–1.0 kg sea mullet, Mugil cephalus and deployed
500 m offshore on sandy substrate in 6–10 m water depth. Vessels
monitoring the SMART drumlines were immediately alerted of
the capture via email, text message, and phone call and attended
to the shark within 30 min. Up to four droplines were deployed
off Coffs Harbour only, between 1400 m and 4000 m from shor-
ein depths between 25 and 35 m over rocky reef substrate.
Mainlines were vertically orientated, consisting of 80 m of 8-mm
diameter polypropylene/polyethylene blend rope and weighted to
the seabed by a 4-kg Danforth anchor and 5 m of 10-mm galva-
nized chain. A large A3 polyform buoy (43.2 cm diameter #
58.4 cm length) was attached to the top of the mainline with two
smaller buoys (27.9 cm diameter #38.1 cm length) connected to
the main buoy. Three gangions were attached from the top of the
mainline at 8-m intervals. Each gangion comprised 2.8 m of 2-
mm diameter stainless steel wire attached to a stainless steel clip
and a 16/0 non-offset circle hook. Each hook was baited with
$0.5 kg of M. cephalus or Australian salmon, Arripis trutta. All
sharks were kept in the water during tagging operations. Full
details of the tagging procedure and shark capture and handling
are provided in Spaet et al. (2020a). Each shark was classified as
juvenile (<259 cm total length [TL]), sub-adult (259–329 cm TL)
or adult (>330 cm TL) according to the life history descriptions
by Werry et al. (2014) and Whitney and Crow (2007).
Tag details and programming
Archival tagging
Sharks were tagged with MiniPAT pop-up satellite archival tags
(MiniPAT), Wildlife Computers (Redmond, WA, USA), to re-
cord ambient light-level, depth (accuracy 61% of reading), and
water temperature (accuracy 60.1"C). MiniPATs were pressure
rated to 2000 m and had a pre-programmed deployment of 120 d
(n¼3) or 180 d (n¼13), after which they released from the ani-
mal and commenced transmission of archived data to the
ARGOS network. During deployment, tags were programmed to
record and archive a time series of temperature ("C), water depth
(m), and ambient light, with a sample interval of 5 min for data
transmission upon release. Recording of summary data occurred
over 24 h and consisted of depth-temperature profiles, light-level
curves, and percentage of time spent in the mixed layer. If tag-
defined mortality occurred, the tags inbuilt premature release de-
vice activated and the tag released from the shark. Activation of
this release ensued if one of the following three parameters was
met for 4 consecutive days: (i) the tag was recording a constant
depth of 0 m, (ii) the tag was recording a constant depth 62.5 m,
or (iii) the tag remained at, or below 1 400 m. MiniPATs (12 cm
length, volume 60 cm
3
) were tethered using a 15-cm filament of
1.3-mm diameter stainless steel wire covered with black heat
shrink and crimped at either end. Tags were secured to each shark
using either a stainless steel anchor plate (Speed et al., 2013) or
bolt attachment. Anchor attachment required implantation of a
5 cm titanium plate $5 cm into the basolateral dorsal muscula-
ture using a handheld tagging pole. Tags were inserted at an angle
of 45"towards the shark’s head, which ensured that the tag as-
sumed a trailing position on the body. Bolt attachment involved
passing a stainless steel bolt through the tether loop on the
MiniPAT and a pre-drilled 4-mm hole at the base of the dorsal
fin in conjunction with a satellite-linked radio transmitting tag
(Wildlife Computers ‘SPOT6’ tags) .
Satellite tagging
SPOT6 tags were used to support MiniPAT light-based position
estimates and were positioned so that the wet/dry sensor was ex-
posed to air when the dorsal fin broke the water’s surface, en-
abling ARGOS satellites to identify the shark’s location. These
positions are classified on a scale of decreasing accuracy using
seven location classes (LC) from 3, 2, 1, 0, A, B, and Z (CLS,
2011). LC3 is the most reliable and accurate with an error of
<250 m, LC2 has an error between 250 and 500 m, LC1 between
500 and 1500 m and LC0 to LCB >1500 m, and LCZ indicates no
position was recorded. SPOT6 tags (maximum battery life 280 d,
53 g, length 8.1 cm) were attached to the dorsal fin using 50-mm
stainless steel bolts.
In addition to MiniPAT and SPOT6 tags, all sharks were fitted
with acoustic transmitters (Supplementary Table S1); however,
acoustic data were disregarded from the analysis as only one fix
existed for each shark. The study was conducted under research
permits from NSW DPI Scientific Research (P01/0059[A]),
Marine Parks (P16/0145-1.1), and Animal Care and Ethics (07/
08) permits and Southern Cross University Animal Care and
Ethics Committee Animal Research Authority (19/036).
Track reconstruction and data analysis
Sharks were instrumented with satellite-linked radio transmission
and pop-up satellite tags that provide a myriad of positional
2R. S. Lipscombe et al.
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estimates and quality. Radio fixes were all opportunistic in na-
ture, as a shark’s fin needed to break the sea surface long enough
to communicate with an orbiting satellite. As a result, positional
information was often clustered in space and time, yet varied
over the course of a deployment. Positioned via light-based geo-
location estimation, MiniPATs offered the least accurate
positions (Galuardi and Lam, 2014), yet given a shark’s
occupancy in the epipelagic layer, good light-level readings were
usually available throughout the deployment period. After visual
inspection of all available positional data, the following geo-
positional strategy was adopted:
(1) Use only positions from ARGOS satellites (T11 and T16)—
these sharks provided regular fixes. Shark T11 had 19 of its
23 tracked days covered by ARGOS fixes, so the combined
approach produced an estimated track mostly driven by
ARGOS fixes. Light-based estimated positions, which have
lower accuracy than ARGOS fixes, were very much
“drowned” out by higher accuracy ARGOS fixes. In this case,
the combined approach achieved interpolation among
ARGOS fixes across days when there was no ARGOS fixes.
Rather than interpolation within the Hidden Markov Model
(HMM), we used a standardized method for interpolation of
all sharks with crawl (Johnson et al., 2008;Johnson and
London, 2018) after estimation of tracks for each shark.
Furthermore, shark T16 had 114 out of 180 or 63% tracked
days covered by ARGOS fixes. In order for the HMM to con-
verge and successfully produce an estimated track, multiple
ARGOS fixes had to be sacrificed. Since the model had to
reconcile the two data streams of different accuracies, a high
proportion of ARGOS fixes had made the HMM struggle.
Subsequently, we chose to rely only on ARGOS here because
it is unclear how the reconcilation was conducted within the
HMM—the detailed inner workings of the model remain
opaque with limited useful published studies documenting
them (https://wildlifecomputers.com/blog/using-gpe3-to-im
prove-geolocation-estimates). Most position fixes were
flagged with LC A and B, i.e. positions with unquantifiable
error. However, it is established that class A and B messages
can be as valuable as those of higher quality classes (1, 2, 3)
(e.g. Costa et al., 2010). We also evaluated the temporal evo-
lution of position fixes, which showed consistency over time
and presented few outliers that zig-zagged out of the overall
trajectory trend.
(2) Provide ARGOS positions to improve Wildlife Computers’
Hidden Markov Model (HMM) for light-based geolocation
(T10)—this shark had clustered but irregular ARGOS fixes.
A hybrid approach was adopted by running the MiniPAT’s
light-based information through the manufacturer’s proprie-
tary Hidden Markov Model (Wildlife Computers, 2020),
with ARGOS fixes, subsampled daily, provided as known
positions to help ground the model. We ran the HMM with
1, 2, 3, and 4 ms
&1
as the prior. Since solutions were similar
throughout, we set the speed filter at 4 ms
&1
. This was the
highest speed that did not over-limit the model performance.
As the HMM continued failing to converge, known positions
were thinned 1 d at a time, to reduce clustering, until model
convergence was achieved. HMM especially struggled near
the East Coast where there were abundant small-scale sea-
surface temperature (SST) gradients that could have
swamped the model with conflicting signals.
(3) Light-based only geolocation via a Kalman-filter model,
trackit (T1, T2, T6, T14)—these sharks had few or no
ARGOS fixes, and therefore light-based geolocation was re-
quired. Previous problems by HMM with SST-matching
prompted the use of a light-only method, Trackit (Nielsen
and Sibert, 2007) for sharks that followed the coast through-
out the deployment. An extension to the same model, light,
and sea-surface temperature matching (Lam et al., 2010) was
applied for sharks that spent most of their time away from
the shelf break.
(4) No movement estimation for sharks at liberty for <2 weeks
(T4, T8, T12).
Results from the above cases were down-sampled to daily posi-
tions by using the first position of the day, for any day with mul-
tiple positions. Gap filling was then done on any missing days
(mostly for case 1) with the R package, crawl (Johnson et al.,
2008;Johnson and London, 2018). Priors for uncertainty for both
latitude and longitude were arbitrarily set at 0.5"for ARGOS
positions, since classes A and B were of unknown accuracy.
Similarly, priors were set at 0.25"for HMM estimates, which are
the search grid cell size. Lastly, error estimates supplied from the
Trackit model were directly input as uncertainty priors.
Due to errors associated with light-based geolocation data, all
distances calculated for sharks using light-based methods only are
estimates and may not be accurate. Track length was estimated in
Google Earth after plotting daily positions derived from track re-
construction analysis. An estimate of the average movement rate
per day was then calculated by dividing track length by days at
liberty. Patterns of habitat use and diel differences of G. cuvier
were examined after depth and temperature data archived by
MiniPATs were divided into periods of day and night. Due to
varying day lengths along the east coast of Australia, calculations
were based on sunrise and sunset times at Brisbane, QLD.
Utilization of depth and preference for environmental variables
were examined through histogram analysis and depth behaviour
of individual sharks plotted in a time series over the length of de-
ployment. Paired t-tests were performed to test for significant
diel differences in the average depth and temperatures occupied
by G. cuvier (Royer et al., 2020).
Results
Release condition and tag performance
Sixteen G. cuvier (13 females and 3 males) ranging from 157 to
384 cm TL (mean 6SD of 252.5 661.5 cm, Table 1) were tagged
with MiniPATs . At the time of tagging, 75% were juveniles (157–
251 cm TL; 10 females and 2 males), 6% were sub-adults (284 cm
TL; 1 male), and 19% were adults (330–384 cm TL; 3 females).
Eleven of these sharks (9 females and 2 males) were also tagged
with SPOT6 satellite tags (Table 1). Despite being released in a
healthy condition, T8 died 10 d after release, with the depth pro-
file recording a constant depth of 55 m for 4 consecutive days,
which initiated the premature release of the MiniPAT. At the
time of death, T8 was $34 km east from the southern tip of
Fraser Island, QLD (25˚470S, 153˚250E), and had travelled
$335 km (straight line distance).
Ten of the 16 MiniPATs deployed provided depth and temper-
ature data, while positional information was analysed for seven of
Habitat use and movement patterns of tiger sharks 3
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those sharks (Supplementary Table S1). Track estimation was not
conducted for four sharks: one shark did not report (T3) and
three sharks had short deployments of under 11 d (T4, T8, and
T12).MiniPATs deployed on T10, T14, and T16 were the only
MiniPATs that remained attached to the shark for their entire
pre-programmed deployment of 180 d, with the remaining
MiniPAT deployments shorter than programmed (120–180 d),
ranging from 7 to 140 d. Archived depth and temperature data
for T10 and T16 was less than the actual deployment of 180 d,
with only 166 and 144 d available for analysis. After 9 d at liberty,
the MiniPAT from T4 detached and was recovered, providing the
entire archived data for analysis. The MiniPAT on T3 released
from the shark after 8 d, and although the tag was retrieved, no
data were recorded due to unknown reasons. MiniPATs from T5,
T7, T9, and T15 either failed to release from the shark on the pro-
grammed dates or failed to reach the surface or connect to the
ARGOS system after reaching the surface. The MiniPAT from
T13 released after 180 d and washed ashore at Kirra Beach in
southern QLD (28˚090S, 153˚310E), $277 km (straight line dis-
tance) from the release site, where it was found by a member of
the public who discarded it, preventing data recovery.
Horizontal movements
Geolocation maps were constructed for seven sharks (Figure 1
and Supplementary Figure S2), with tracking periods between 20
and 180 d. In the first 24 h post-release, six of the seven sharks
moved offshore, across the continental shelf edge (>30 km) in a
general easterly direction. The only shark to remain inshore over
the continental shelf (<30 km) for >48 h post-tagging was T6.
Regardless of the season they were tagged, most sharks moved in
a northerly direction from NSW to QLD waters within 15 d of re-
lease. Two sharks, T10 and T16, both with deployments ¼180 d,
returned to NSW waters during the austral spring (March, April,
and May) and summer (December, January, and February) after
160 and 179 d post-release, respectively.
One individual (T2) remained in NSW waters for the entire
145 d at liberty from February to July 2018 and spent 85% of its
deployment in warmer (19–23˚C) offshore waters. T2 reached its
most southern location $356 km east of Pambula, NSW
(36"190S, 153"540E), in April (austral autumn), but by July (aus-
tral winter) returned to inshore waters off NSW, $90 km north
of its tagging location. Shark T1, tagged on the same day at the
same location, remained on the continental shelf for 86% of its
deployment, with 4 d spent off the continental shelf edge within
the first week after tagging (Figure 1). Of the six sharks that trans-
ited north into QLD waters, all swam either along the shelf edge
or in offshore waters.
The greatest distance travelled was by T10, covering $6937 km
(straight line distance) in 180 d ($39 km d
&1
), between Newcastle,
NSW (32"55’S, 151"47’E) (Figure 1), and the Whitsunday Islands
off the coast of Mackay, QLD. Shark T6 made the most substantial
move north eastward ($1030km straight line distance) from Coffs
Harbour, NSW, into the waters of New Caledonia $650 km west of
the mainland (Figure 1). Post-tagging, T16 moved north and off-
shore to the Great Barrier Reef in <1 month and then spent
3 months and 43% of its deployment on and surrounding Lihou
Reef (17"240S, 151"400E) adjacent to Cairns, QLD. During its 20 d
at liberty, T11 displayed the highest movement rate at 61.5km d
&1
,
travelling $1 235 km north from Coffs Harbour, NSW, maintaining
a path throughout the Tasman Basin, over the Queensland,
Brisbane, and Recorder Seamounts until it reached the southern
Coral Sea (23"440S, 154"40E). A similar northerly offshore route was
also undertaken by T14 and T16 after tagging in the austral winter
(June, July and August), with both sharks traversing near the
Brisbane, Moreton, and Recorder Seamounts. T16 continued on
this north east path over the Fraser Seamount before entering the
Cato Trough in the Coral Sea (154"540S, 23"200E). Overall, broad-
scale horizontal movement differed greatly among conspecifics.
Depth, temperature, and vertical habitat use
Tagged G. cuvier spent considerable time at, or within 1 m of the
surface (depths recorded above 0 m were omitted from analysis).
Overall, 71% of time was spent within 50 m of the surface and
96% of time in the upper 100 m of the water column (Figure 2a).
Table 1. Summary of biological details, tag deployment, and tracking data for 16 Galeocerdo cuvier tagged off the mid-north coast of eastern
Australia.
ID Sex
Total
length
(cm) Tagging date
Tagging location,
Lat. (˚S), Long. (˚E) Tag type
Date
detached
Days
tracked
Track
length
(km)
Average
movement
(km d
&1
)
T1 F 188 13 February 2018 30.279, 153.203 SPOT, MiniPAT, acoustic 19 March 2018 34 926 26.5
T2 F 242 13 February 2018 30.290, 153.169 SPOT, MiniPAT, acoustic 07 August 2018 145 3726 25.7
T3 F 229 23 January 2019 28.855, 153.612 MiniPAT, acoustic 30 January 2019 – – –
T4 F 234 23 January 2019 29.589, 153.264 MiniPAT, acoustic 02 February 2019 9 – –
T5 M 248 25 January 2019 30.323,153.179 MiniPAT, acoustic – – – –
T6 F 251 29 March 2019 30.323, 153.180 SPOT, MiniPAT, acoustic 19 May 2019 51 2563 50.3
T7 F 216 29 March 2019 30.323, 153.180 SPOT, MiniPAT, acoustic – – – –
T8 F 223 24 April 2019 28.813, 153.613 SPOT, MiniPAT, acoustic 09 May 2019 10 – –
T9 M 157 08 May 2019 30.228, 153.179 SPOT, MiniPAT, acoustic 20 October 2019 – – –
T10 F 236 08 May 2019 30.237, 153.184 SPOT, MiniPAT, acoustic 04 November 2019 180 6937 38.5
T11 M 284 09 May 2019 30.328, 153.151 SPOT, MiniPAT, acoustic 01 June 2019 21 1235 61.5
T12 F 228 14 May 2019 30.317, 153.147 SPOT, MiniPAT, acoustic 26 May 2019 8 – –
T13
a
F 212 14 May 2019 30.322, 153.180 MiniPAT, acoustic – – – –
T14 F 354 11 June 2019 28.827, 153.595 MiniPAT, acoustic 13 December 2019 180 3342 18.5
T15 F 384 09 July 2019 28.837, 153.615 SPOT, MiniPAT, acoustic – – – –
T16 F 330 23 July 2019 28.872, 153.604 SPOT, MiniPAT, acoustic 23 January 2020 180 6257 33.9
a
T13 detached after 180 d but the tag was found by a member of the public who subsequently discarded the tag, preventing data recovery.
4R. S. Lipscombe et al.
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Time spent in the mixed layer varied among individuals and
ranged from 46.1% to 93.1% (Table 2). Maximum depths varied
among individual sharks and ranged from 92 to 904 m (Table 2).
Only three sharks (T1, T4, and T8) did not dive below 200 m
(Figure 3), yet depths used by T1 were unlikely constrained by ba-
thymetry as time was spent in waters beyond the continental shelf
edge. Shark T4, at liberty for 9 d, recorded the lowest mean
(6SE) depth (10.2 60.03 m) and used the upper 30 m of the wa-
ter column more than any other of the tagged sharks (Table 2).
Mean (6SE) depth (37.19 60.38 m) and temperature (23.42
60.02 ˚C) varied among sharks (Table 2). No significant differ-
ence was evident in use of depth and temperatures, irrespective of
day or night (paired t-test, depth: t¼0.44, n¼10, p>0.05, tem-
perature: t¼0.35, n¼10, p>0.05). Cumulative time-at-
temperature data indicated tagged G. cuvier spent most of the
daylight hours in water temperatures between 24 and 25˚C, with
little variation between day and night (Figure 2b). Water temper-
atures occupied by tagged G. cuvier ranged from 6.7 to 28.9"C,
with 70.2% of the time between 22 and 25"C. Temperatures
<16"C were infrequently occupied, with the minimum tempera-
ture of 6.7"C during the deepest dive by T2 at 784.5 m.
Diving behaviour differed among conspecifics. For example,
depth profiles revealed oscillatory diving behaviour in T2
(Figure 4a), which was characterized by $1 brief dive per hour to
100–300 m, with consistent returns to the surface. This pattern
was also evident in T6, yet occurred more frequently at $3 dives
per hour (Figure 4b). Sharks T2, T6, T11, and T14 made
infrequent dives into the mesopelagic zone to depths of 400–
800 m (Figure 3). Each of these deep dives lasted between 40 and
60 min, concluding with the shark returning to the top 20 m of
the water column. Shark T11 completed the deepest dive to
904 m, with the descent from, and ascent to the surface taking
$40 min (Figure 4c). Other deep dives performed by T2, T6, T11,
and T14 occurred throughout the day and night, with no diel pat-
tern evident.
Discussion
This study describes the habitat use of G. cuvier throughout tem-
perate, sub-tropical, and tropical waters of eastern Australia. It
confirms previous work demonstrating that, although typically
found in warm tropical waters, this species also inhabits warmer
temperate regions (Holmes et al., 2014;Ferreira et al., 2015).
Individual movements varied regardless of season, with all but
one shark moving north into warmer QLD waters after tagging.
Similarities among sharks in broad-scale movement patterns were
evident, with a preference for offshore oceanic habitats. The use
of offshore waters beyond the continental shelf edge was often
characterized by long-distance directional movement >100 km,
with frequent travel over seamounts within the Tasman Basin in
the western Pacific Ocean. These broad-scale movements using
predominantly offshore waters are consistent with earlier studies
(Holmes et al., 2014;Werry et al., 2014) and highlight the con-
nectivity between tropical and warm-temperate regions in eastern
Australia.
Figure 1. Most probable tracks of seven tagged Galeocerdo cuvier reconstructed using positions from ARGOS and light-based geolocation to
provide daily positions. All maps were generated using the marmap package in R (Pante and Simon-Bouhe, 2013).
Habitat use and movement patterns of tiger sharks 5
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Increased movement over the continental shelf by sharks was
observed during the austral spring and summer. Ocean currents,
water temperature and prey distribution are known drivers of
shark movement (Heupel et al., 2015;Andrzejaczek et al., 2018)
and likely influenced this move from offshore waters. On the east
coast of Australia, the East Australian Current brings warmer wa-
ter nearer the coastline during summer months and encroaches
onto the continental shelf (Ridgway and Godfrey, 1997). Areas
where the continental shelf narrows generally see upwelling of
nutrient-rich water (south of 28.5"S and 31"S), thus increasing
primary productivity (Everett et al., 2014). This change in move-
ment is observed by Papastamatiou et al. (2013), who found
higher chlorophyll aconcentrations and warm ocean
temperatures (23–26˚C) were also attributed to change in the
movement of G. cuvier around the Hawaiian Islands. Together,
warmer water during summer, in combination with higher pro-
ductivity, could serve as an indicator for increased presence of G.
cuvier in inshore and coastal waters.
Tagged sharks displayed a preference for water between 22 and
25"C, similar to previous studies (Holmes et al., 2014;Ferreira
et al., 2015). Decreased temperatures were occupied infrequently
during deep dive excursions, confirming that G. cuvier are capable
of withstanding a much broader temperature range (4–31.2˚C).
However, it is unlikely that these temperatures could be sustained
for long periods. Cold tolerance has been documented by the oc-
casional catch of conspecifics in Icelandic waters (Matsumoto
Figure 2. Time spent (6SE) during day (white bars) and night (black bars) at (a) depth (50 m bins) and (b) temperature (2"C bins) for
10 MiniPAT-tagged Galeocerdo cuvier.
6R. S. Lipscombe et al.
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et al., 2005) and in the Tasman Sea (Holmes et al., 2014) and sup-
ports the movement south into higher latitudes observed in this
study.
Sharks in this study often moved near seamounts in the
Tasman Basin on their transit north during the austral autumn
and winter, indicating that the oceanographic conditions and
prey availability at these locations might play a role in driving
seasonal offshore movement (Holmes et al., 2014;Werry et al.,
2014). Indeed, the seasonal variability in physical conditions at
seamounts influences their use by many other species of shark
(Oliver et al., 2011;Barnett et al., 2012), pelagic fish (Morato
et al., 2010), and turtles (Santos et al., 2007). These unique areas
of high biodiversity, and therefore food resource availability, may
influence the movement of G. cuvier to off-shelf habitats as ob-
served in this study. The findings of Ajemian et al. (2020) support
this use of deeper offshore waters, although their observations
were for sub-adult and adult G. cuvier, a higher use of off-shelf
waters during autumn and winter months was documented.
The distances travelled between northern QLD to southern
NSW demonstrate the broad latitudinal range that G. cuvier cov-
ered along the east coast of Australia. Large-scale movements are
not uncommon for G. cuvier and distances travelled by T10
($6937) and T16 ($6257 km) are consistent with previous stud-
ies (Heithaus et al., 2007;Holmes et al., 2014). Other shark spe-
cies, e.g. bull sharks, Carcharhinus leucas ($1770 km), and white
sharks, Carcharodon carcharias ($40 000 km)have also exhibited
similar dispersal behaviour along the east coast and into interna-
tional waters (Heupel et al., 2015;Spaet et al., 2020ab). The ex-
tensive movements performed by G. cuvier highlight the need for
multi-jurisdictional management among Australian states in re-
gard to shark mitigation measures, conservation strategies, and
fisheries management.
Highly directional swimming was observed in most sharks and
was often interspersed with localized movements over a smaller
spatial scale (<35 km). This behaviour was particularly evident in
individuals with longer deployments when they reached the Great
Barrier Reef, QLD, throughout the austral winter and spring.
Specifically, localized movements occurred for 71d (over $30 km)
for T16 as it moved around Lihou Reef (17˚240S, 151˚400E)
(Figure 1). This behaviour could be attributed to resource avail-
ability and foraging and could potentially be linked to the nesting
of green turtles, Chelonia mydas during October to April
(Department of Environment and Energy, 2011). Seasonal
availability of a particular resource, e.g. sea turtles, has been
exploited by tiger sharks (Fitzpatrick et al., 2012;Acu~
na-Marrero
et al., 2017). Extended tag deployments and a larger sample size of
tagged animals could illuminate on potential residency patterns.
The infrequent utilization of deeper oceanic waters, >600 m,
by three G. cuvier was associated with their horizontal movement
off the Australian continental shelf and consisted of a brief but
fast, near-vertical descent with an immediate, but slower return
to the surface. Previous studies suggest that deep-diving behav-
iour in G. cuvier is a means for navigation, with the use of topog-
raphy and bathymetric features providing orientation between
locations during broad-scale movement (Holland et al., 1999;
Holmes et al., 2014). Although difficult to quantify, the use of
brief, deep dives for orientation has been recorded in both C.
carcharias and shortfin mako sharks, Isurus oxyrinchus, during
migrations (Francis et al., 2019;Rogers et al., 2015). A similar
dive profile describing powered descents was described by
Nakamura et al. (2011) in G. cuvier tagged in Hawaii and has also
been observed in I. oxyrinchus (Sepulveda et al., 2004). Originally,
Weihs (1973) predicted that negatively buoyant fish would per-
form a gliding motion with a shallow angle upon descent, to con-
serve energy. This theory proved correct for some predatory
fishes (Andrzejaczek et al., 2019b),yet, was inconsistent with the
characteristic rapid vertical descent observed in previous studies
of G. cuvier, with navigation and foraging more likely explana-
tions for the deep-diving behaviour (Nakamura et al., 2011;
Holmes et al., 2014).
Oscillatory diving behaviour was observed in two sharks within
this study, a pattern of diving also documented in other shark
species (Sepulveda et al., 2004:Spaet et al., 2017). Patterns dif-
fered slightly between the two sharks, yet were characterized by
distinct repetitive near-vertical descents and a short time spent at
depth, followed by a near-vertical ascent to the upper water col-
umn. These dive patterns are consistent with movement often at-
tributed to foraging and prey detection in G. cuvier of benthic
and surface prey (Nakamura et al., 2011;Heithaus et al., 2002). A
similar observation was made by Carey et al. (1990) and
Campana et al. (2011) in P. glauca, with oscillatory dives repeated
every few hours. Campana et al. (2011) speculated that these di-
ves are likely a strategy employed to increase foraging potential
and efficiency and reduce metabolic losses that occur when
remaining in warm surface waters during the day. Furthermore,
the most recent study by Andrzejaczek et al. (2020) surmises that
G. cuvier oscillatory diving patterns reduce energy output when
compared to horizontal swimming and can provide a cost-
efficient foraging strategy. Although thermoregulation has been
previously reported as the purpose for oscillatory diving in several
shark species (Carey et al., 1990;Thums et al., 2013), conspecifics
in this study did not display the same oscillatory diving behav-
iour. Therefore, it is likely that the vertical patterns observed in
this study indicate energy conservation and prey searching by
individuals.
This study examines the highly dynamic and complex habitat
use by G. cuvier off eastern Australia through the combined use
of satellite and archival technology. Variation among conspecifics
existed in both broad-scale horizontal movement and vertical
habitat use and was likely associated with navigation, resource
availability, foraging, energy conservation, and fluctuations in
water temperature. Movement to lower latitudes coincided with
decreasing water temperature at mid-latitudes and, while thermal
conditions may influence horizontal movement, a tolerance for
Table 2. Galeocerdo cuvier depth, water temperature, and time
spent in mixed layer (0–193 m) archived by MiniPAT pop-up
satellite tags (n¼10).
Shark
ID
Depth (m) Temperature (˚C)
Mixed
layer (%)Min–max Mean 6SE Min–max Mean 6SE
T1 1.0–173.0 36.9 60.36 15.6–27.5 23.4 60.05 46.1
T2 0.0–784.5 29.3 60.22 6.7–28.0 22.7 60.01 78.5
T4 0.0–92.0 10.2 60.03 17.8–27.2 23.2 60.01 93.1
T6 0.5–755.0 46.8 60.56 7.0–27.2 23.9 60.02 78.6
T8 0.5–150.0 44.9 60.41 15.6–25.8 24.1 60.03 75.6
T10 1.0–255.0 20.7 60.22 15.3–24.8 22.0 60.01 85.4
T11 1.0–904.0 36.6 60.71 6.8–25.6 24.3 60.01 92.7
T12 0.5–276.0 27.9 60.40 15.4–24.5 22.6 60.02 74.0
T14 0.5–560.0 39.9 60.31 9.9–28.9 23.4 60.01 90.1
T16 0.5–576.0 48.8 610.2 8.9–28.1 24.6 60.03 74.3
Habitat use and movement patterns of tiger sharks 7
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Figure 3. Depth profiles for ten MiniPAT-tagged Galeocerdo cuvier produced using summary data sampled at 5-min intervals (summary data
were used for all sharks except T4 where data were sampled at 3-s intervals providing the entire archive).
8R. S. Lipscombe et al.
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cooler water was evident through intermittent use of water below
the thermal preference of 22–25˚C. Increased cross-shelf activity was
observed during the austral spring and summer, which coincided
with a strengthening EAC, warmer water temperature, and changes
in prey distribution. Yet, it was evident that, despite being associated
with coastal waters and captured and released relatively close to
shore, G. cuvier spent majority of time in waters off the continental
shelf. To better understand the varied and extensive movements
documented in this study, long-term movement patterns and the in-
fluence of environmental drivers should be investigated.
Supplementary data
Supplementary material is available at the ICESJMS online ver-
sion of the manuscript.
Figure 4. Examples of diving behaviour from three MiniPAT-tagged Galeocerdo cuvier depicting (a) oscillatory diving of T2 on day 67, (b)
oscillatory diving of T6 on day 7, and (c) a deep dive of T11 on day 1. Profiles were produced using summary data sampled at 5-min intervals.
Habitat use and movement patterns of tiger sharks 9
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Funding
Funding was provided by the NSW Department of Primary
Industries, (NSW DPI Grant Number: SMS2015-20). Southern
Cross University provided funding towards an honours project to
R Lipscombe.
Acknowledgements
Primary support was provided by the New South Wales
Department of Primary Industries, Australia, through the Shark
Management Strategy. We would like to thank contracted
SMART drumline fishers from Ballina and Evans Head for their
assistance with this project.
Author contributions
RSL conducted fieldwork and wrote the manuscript, JLYS and
CHL analysed horizontal data, reconstructed tracks, and edited
the manuscript, AS edited the manuscript, CPB conducted field-
work, and PAB designed the study, conducted fieldwork, and
edited the manuscript.
Data availability statement
The data underlying this article will be shared on reasonable re-
quest to the corresponding author.
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Handling editor: Howard Browman
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