Marine Environment & Ecology Residency and Movements of Whaler Sharks

Huveneers, C. et al. Movements of whaler sharks

Marine Environment & Ecology

Residency and movements of whaler sharks (Carcharhinus spp.) in Gulf St Vincent

C. Huveneers1,2, P.J. Rogers1, M. Drew2

SARDI Publication No. F2012/000246-1 SARDI Research Report Series No. 664

SARDI Aquatic Sciences PO Box 120 Henley Beach SA 5022

October 2012

Final Report to the Nature Foundation of South Australia

Huveneers, C. et al. Movements of whaler sharks

Residency and movements of whaler sharks (Carcharhinus spp.) in Gulf St Vincent

Final Report to the Nature Foundation of South Australia

C. Huveneers1,2, P.J. Rogers1, M. Drew2

SARDI Publication No. F2012/000246-1 SARDI Research Report Series No. 664

October 2012

Huveneers, C. et al. Movements of whaler sharks

This Publication may be cited as: Huveneers, C.1, 2, Rogers, P.J.1, Drew, M2 (2012). Residency and movements of whaler sharks

(Carcharhinus spp.) in Gulf St Vincent. Final Report to the Nature Foundation of South Australia. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2012/000246-1. SARDI Research Report Series No. 664. 35pp.

Front cover photo © Andrew Fox/Rodney Fox Shark Expeditions

1South Australian Research & Development Institute 2Flinders University

South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024

Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.sardi.gov.au

DISCLAIMER The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI Aquatic Sciences internal review process, and has been formally approved for release by the Research Chief, Aquatic Sciences. Although all reasonable efforts have been made to ensure quality, SARDI Aquatic Sciences does not warrant that the information in this report is free from errors or omissions. SARDI Aquatic Sciences does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it.

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Printed in Adelaide: October 2012

SARDI Publication No. F2012/000246-1 SARDI Research Report Series No. 664

Author(s): C. Huveneers1, 2, P.J. Rogers1, M. Drew2

Reviewer(s): E. Brock and M. Loo

Approved by: Dr. J. Tanner Science Leader – Marine Environment & Ecology

Signed:

Date: 25 October 2012

Distribution: Nature Foundation of South Australia, Flinders University, SAASC Library, University of Adelaide Library, Parliamentary Library, State Library and National Library

Circulation: Public Domain 3

Huveneers, C. et al. Movements of whaler sharks

TABLE OF CONTENTS

1 INTRODUCTION ...... 10 2 METHODS ...... 12 2.1 Data analysis ...... 15 3 RESULTS ...... 17 3.1 Tagging events ...... 17 3.2 Capture and tagging ...... 17 3.3 Residency ...... 21 3.4 Movements ...... 21 3.5 Spatio-temporal variations ...... 23 3.6 Additional detections ...... 25 4 DISCUSSION ...... 26 5 MEDIA COVERAGE AND COMMUNITY OUTREACH ...... 30 6 ADDITIONAL SUPPORT ...... 31 7 REFERENCES ...... 32

Huveneers, C. et al. Movements of whaler sharks

LIST OF TABLES

Table 1. Details of fishing trips carried out in GSV to internally tag Carcharhinus brachyurus and C. obscurus with acoustic transmitters ...... 17

Table 2. Summary of detections obtained from acoustically tagged sharks in South Australian waters. GSV = Gulf St Vincent. Metro = Adelaide metropolitan region...... 20

Huveneers, C. et al. Movements of whaler sharks

LIST OF FIGURES

Figure 1. Locations of receivers deployed in GSV between 2008 and 2012. Black circles represent receivers deployed in April 2008, dark grey circles represent receivers deployed in March 2010; red circles represent receivers deployed in December 2010, blue circles represent receivers deployed in May 2011...... 13

Figure 2. Locations of acoustic receivers deployed in South Australia illustrating the acoustic coverage off the South Australian coastline...... 14

Figure 3. Internal tagging procedure of a Carcharhinus brachyurus showing (a) captured shark, (b) incision and tag insertion, (c) suturing, and (d) finished sutures...... 15

Figure 4. Histogram of the number of Carcharhinus brachyurus and C. obscurus caught per fishing trip using longlines in GSV (17 trips total)...... 18

Figure 5. Size-frequency of sharks captured and tagged in GSV. White bars represent male Carcharhinus brachyurus, black bars represent female C. brachyurus, and gray bars represent C. obscurus. Male and female C. obscurus were combined due to small sample size...... 19

Figure 6. Histogram of the minimum distance travelled for the 24 tagged sharks detected by receiver more than 1 km away from each other in the GSV. White bars represent Carcharhinus brachyurus and black bars represent C. obscurus...... 22

Figure 7. Map showing the movements of a 1,250 mm TL female Carcharhinus obscurus (red dot), and a 1,900 mm TL female C. brachyurus (blue dot) detected outside of GSV. ... 23

Figure 8. Number of sharks detected per month by the GSV receivers. White bars represent sharks detected by the Long Spit receivers; black bars represent sharks detected by the metropolitan receivers; and grey bars represent sharks detected by the remaining receivers in GSV (Zanoni, Barge, offshore Long Spit and western side of GSV). (a) Carcharhinus brachyurus, (b) C. obscurus...... 24

Figure 9. Number of detections of whaler sharks in Gulf St Vincent between: A) March 2010–December 2010, B) December 2010–May 2011, C) May 2011–December 2011, and D) December 2011–May 2012...... 25

Figure 10. Number of detections of a single white shark (Carcharodon carcharias) off Glenelg Beach between the 13th of August 2008 and the 10th of September 2008. Size of circles represents the number of detections by the receivers, smallest circle is nine detections, largest circle is 47 detections...... 26

Huveneers, C. et al. Movements of whaler sharks

ACKNOWLEDGMENTS

This project was carried out under PIRSA Exemption number 9902364 and 9902458. Tagging was carried out under Flinders University ethics approval number E360.

This project was funded by the Nature Foundation South Australia Inc, and the Neiser Foundation. Acoustic receivers were provided by the Australian Animal Tagging and

Monitoring System (AATAMS) as part of the Integrated Marine Observing System (IMOS)/National Collaborative Research Infrastructure Strategy (NCRIS), the Institute of Marine and Antarctic Studies, the University of Adelaide, and the Department of the Environment, Water and Natural Resources. PIRSA provided financial support for the deployment and recovery of acoustic receivers.

The authors would like to thank Matt Heard, Christopher Lamont, Andrew Lowther, Matt Lloyd, Crystal Beckmann, and Surf Life Saving South Australia for their assistance in the field. Matt Lloyd, Bruce Jackson, Tony Fowler, Shea Cameron, and Mike Steer helped with diving to deploy, recover, and download receivers. Rachel Robbins, Barry Bruce, and Russ Bradford provided information about the detections outside of Gulf St Vincent.

Huveneers, C. et al. Movements of whaler sharks

EXECUTIVE SUMMARY

Two species of whaler sharks are found in South Australia, the dusky shark (Carcharhinus obscurus) and the bronze whaler (C. brachyurus). These species are commercially targeted, primarily during summer by longline fishers within the Marine Scalefish Fishery. Although whaler sharks have been identified as having particularly slow reproductive outputs, the effect of the fishery on these species is unknown.

This study used acoustic telemetry to investigate the movement and residency of Carcharhinus brachyurus and C. obscurus in Gulf St Vincent (GSV) and provides preliminary information that could be used to assess the suitability of spatially explicit management.

Twenty-nine Carcharhinus brachyurus and seven C. obscurus were acoustically tagged off Long Spit during 28 fishing trips. The residency and movements of these sharks were monitored by 50 acoustic receivers deployed along the Adelaide metropolitan coast, Long Spit and on the western side of GSV.

Carcharhinus brachyurus and C. obscurus showed some affinity to the location where they were tagged, with a similar detection period between GSV and Long Spit receivers (about 170 and 270 days for C. brachyurus and C. obscurus, respectively). Fifty-seven percent and 75% of C. brachyurus and C. obscurus tagged for over a year were detected within GSV for a period longer than 365 days.

The residency index for the area covered by the receivers within GSV and around Long Spit was low for both species suggesting that while the detection period of whaler sharks within GSV and at Long Spit was relatively long, they were not detected on many of the days during this period.

Both species were mostly detected by the northern Gulf St Vincent (NGSV) and Long Spit receivers, with only six C. brachyurus (26%) also detected by the metropolitan receivers. There was a temporal fluctuation in the number of C. brachyurus detected in the NGSV/Long Spit regions with more sharks detected in the summer months (October–March) than in winter (June–August). While C. obscurus were not detected along the metropolitan region, similar temporal patterns were observed between C. brachyurus and C. obscurus within the NGSV and Long Spit regions.

One C. brachyurus and one C. obscurus were also detected by receivers deployed as part of other projects providing evidence of travels up to 1,050 km in 102 days.

The results from the present study showed that Long Spit is likely to be an important area for C. brachyurus and C. obscurus as they were detected regularly and for up to nearly two

Huveneers, C. et al. Movements of whaler sharks

years by receivers deployed in that area. The small residency index, however, suggests that the tagged sharks only spent a short amount of total time within the area and that a marine reserve within this location would only protect C. brachyurus and C. obscurus an average of 3% and 2% of the time, respectively.

Sharks tagged around the Long Spit region did not actively use the metropolitan region, with only a few detections from C. brachyurus obtained on the metropolitan receivers.

Temporal variation in the number of whaler shark present (specifically C. brachyurus) has previously been documented in New South Wales, Argentina, and South Africa. These migratory patterns are likely to be directly related to temperature, prey fields, or reproductive schedules and should be further investigated.

Huveneers, C. et al. Movements of whaler sharks

1 INTRODUCTION

Whaler sharks are coastal and pelagic sharks that inhabit temperate and tropical waters. Two species of whaler sharks are found in South Australia, the dusky shark (Carcharhinus obscurus) and the bronze whaler (C. brachyurus) (Last and Stevens, 2009). Sharks are often described as a group of conservation concern due to their life history characteristics (slow reproductive cycles, smaller litter sizes, slow growth rates, late ages-at-maturity) and slow rebound potential resulting in a high susceptibility to overfishing (Holden, 1973; Musick, 1999; Stevens et al., 2000). Specifically, whaler sharks have been identified as having particularly slow reproductive outputs, with the life history traits of C. obscurus making it among the most vulnerable vertebrates to depletion by fisheries (Romine et al., 2009). As a result, C. obscurus was recently listed under the International Union for the Conservation of Nature (IUCN) Red List as ‘Vulnerable’ (Musick et al., 2009) and was nominated in 2010 for listing under the Australian Commonwealth Government’s Environmental Protection Biodiversity and Conservation Act.

Whaler sharks (including C. obscurus) are commercially targeted in various fisheries around Australia (Simpfendorfer et al., 1999; Macbeth et al., 2009; Fowler et al., 2010). In South Australia, C. brachyurus and C. obscurus are targeted during the warmer months between September and May. The fishing effort directed at whaler sharks increases during the snapper closure when commercial fishers focus on alternative species (Jones, 2008). The annual commercial catches of whaler sharks have averaged about 90 tonnes since 1990 with most of the catches taken within Gulf St Vincent (GSV) and Spencer Gulf (Rogers et al. in press-a). Whaler sharks are also targeted off metropolitan Adelaide from jetties and boats by recreational and game fishers (Jones, 2008; Rogers et al., in press-a). The effects of the fishing pressure from both sectors and the resilience of whaler sharks to the current fishing levels are unknown. Demographic studies have shown that populations of C. obscurus would decline even at low levels of fishing mortality, especially if mature animals are caught, and suggest that regulatory measures may be required to ensure sustainable fishing pressure and recovery of depleted populations (McCauley et al., 2007; Romine et al., 2009).

Marine reserves are often listed as useful management options to protect marine organisms from extensive fishing pressure (Chapman et al., 2005; Heupel and Simpfendorfer, 2005; Lester et al., 2009; Bond et al., 2012; Knip et al., 2012). Marine reserves are generally suitable for species that spend a relatively large amount of time within the protected area (Chapman et al., 2005). A recent analysis of the Australian gamefish tag-recapture program suggests that whaler shark movement may be limited, with 50% of the sharks recaptured <10 km from the tagging location, and the mean distance moved being 195 km for the 40 10

Huveneers, C. et al. Movements of whaler sharks

recaptured sharks (Rogers et al., in press-a). A similar pattern of low rates of movement has been documented by a tagging program in South Africa, where 91% of the 648 recaptured C. obscurus moved <100 km (Hussey et al., 2009).

However, conventional tagging only provides information on the release and capture locations and does not provide data on the movement patterns of sharks in between these locations. Information on how often and how long sharks use specific areas, or how far and how frequently they disperse is central to evaluating the potential efficiency of using marine reserves to protect sharks from anthropogenic impacts. Acoustic telemetry enables continuous recording of the presence/absence of tagged organisms at specific locations and assessment of their residence time and site fidelity. This technology is increasingly being used to assess the efficiency of marine reserves for various organisms including lobster (MacArthur et al., 2008), teleosts (Bryars et al., 2012), and sharks (Chapman et al., 2005; Knip et al., 2012).

This study used acoustic telemetry to provide an understanding of the movements and residency of C. brachyurus and C. obscurus within GSV. The data obtained will be useful to assess the suitability of marine reserves for protection and management of these sharks, and will help to better understand the potential impact of the fishing effort shift, which takes place during the summer months in South Australia. Specifically, we aim to: • Assess the suitability of spatially explicit management measures to protect C. brachyurus and C. obscurus from anthropogenic impact; • Investigate the seasonality, residence time, and movement patterns of C. brachyurus and C. obscurus in the GSV; and • Initiate a network of acoustic receivers within South Australia.

Huveneers, C. et al. Movements of whaler sharks

2 METHODS

In April 2008, ten acoustic receivers were deployed as a curtain off Glenelg Beach from about 400 m from the ‘ Glenelg blocks’ to about 8 km offshore (Figure 1). Receivers were placed about 800 m from each other to allow overlapping acoustic coverage. In March 2010, four additional receivers were deployed. Two receivers were deployed in northern Gulf St Vincent (NGSV) at Long Spit, located about 40 km northwest of the Port River. Single receivers were deployed at Semaphore Reef and Black Pole at St Kilda near the northern entrance to the Port River. In December 2010, a further 13 receivers were deployed, including four receivers off the Semaphore Jetty, extending 4 km offshore. This curtain was designed to include the receiver previously deployed off Semaphore and to ensure acoustic coverage of Semaphore Reef. Four receivers were deployed off the Torrens River mouth extending 3.2 km offshore, and two were deployed off Grange Beach extending 1.6 km offshore. An additional three receivers were deployed around the Port River/St-Kilda area. In May 2011, 21 receivers were deployed through a joint project aimed at increasing the understanding of snapper (Pagrus auratus) movement in NGSV. Finally, in October 2011, another receiver was added off Long Spit. In summary, 50 acoustic receivers were deployed over the course of the study. As a result of these staged deployments, the acoustic coverage varied throughout the study (Figure 1). Receivers were coated in anti-fouling paint, and either affixed to a 1.65 m long steel post that was hammered into the substratum to at least 0.6–0.8 m depth, or affixed to a post embedded within a 70–90 cm diameter concrete-filled car tyre.

Huveneers, C. et al. Movements of whaler sharks

A B C D

10 km

Additionally, 24 acoustic receivers were deployed as part of three different projects to complement the South Australian acoustic network (Figure 2). Ten acoustic receivers were deployed by CSIRO around the Neptune Islands for a study of the distribution and behaviour of white sharks (Carcharodon carcharias) in response to berleying. Two receivers were deployed at each of Dangerous Reef and Liguanea Island by the Fox Shark Research Foundation to investigate C. carcharias movements between seal colonies, and ten receivers were deployed off Kangaroo Island to monitor western blue groper (Achoerodus 13

Huveneers, C. et al. Movements of whaler sharks

gouldii). The network of receivers forms part of the Australian Animal Tagging and Monitoring System (AATAMS), established to monitor the movements and migrations of tagged organisms around Australia.

Spencer Gulf

Gulf St Vincent

Neptune Islands

Kangaroo Island

N 25 km

Figure 2. Locations of acoustic receivers deployed in South Australia illustrating the acoustic coverage off the South Australian coastline.

Carcharhinus brachyurus and C. obscurus were caught using floating longlines, and rod and line. Longlines consisted of floating rope main-lines with 1.7 mm stainless steel leaders with up to 110 16/0 stainless steel circle hooks attached to the main-line by the way of a stainless steel clip. The main-line was up to 2.2 km long, anchored and marked at each terminal end with 20 to 70 cm diameter rubber floats. Hooks were spaced along the main-line at intervals of 7–12 m apart with small floats every two hooks. Sharks caught off St Kilda were caught in collaboration with recreational fishers who used suspended baits under balloons using heavy tackle (30–80 lb line) and leaders of 1.5–1.7 mm nylon-coated wire attached to 12/0 or 14/0 J-style hooks.

Once captured, sharks over two metres were restrained alongside the boat using a small rubber sling, sharks less than two metres were brought onboard onto a foam mattress. Seawater was circulated across the gills of each shark using a bilge pump to ensure continuous oxygenation throughout the surgery. A small incision (1.5–2 cm) was made 14

Huveneers, C. et al. Movements of whaler sharks

posterior to the pelvic fins to insert a Vemco V16-6H tag into the body cavity. The minimum and maximum time interval between each pulse transmission was set at 50 and 110 seconds, respectively. The incision was stitched using 2–3 non-continuous external sutures (3/0 Monosyn absorb violet 70 cm, needle tapercut) (Figure 3). Oxytetracycline at a dose of 20 ml/kg body weight was injected into the dorsal musculature to prevent infection, while a plastic head conventional identification tag (Hallprint™, Hindmarsh Valley) was inserted into the muscle below the first dorsal fin to aid identification in case of recapture, or capture by commercial or recreational fishers. Prior to being released, the total length (TL) of each shark was measured to the nearest 0.5 mm. The maturity stage of males was assessed based on the degree of clasper calcification (Walker, 2007). The state of maturity of females was determined based on the published size-at-first maturity of 2290 mm TL for C. brachyurus (Walter and Ebert, 1991) and 2200 mm fork length (FL) for C. obscurus (Simpfendorfer et al., 1999). Two sharks were externally tagged by recreational fishers under the first dorsal fin in the dorsal musculature using a pole and stainless steel applicator. For external tagging, V16-6H tags were affixed to a stainless steel dart tag (Hallprint™, Hindmarsh Valley) using fast setting epoxy (Knead it®).

(a) (b)

Figure 3. Internal tagging procedure of a Carcharhinus brachyurus showing (a) captured shark, (b) incision and tag insertion, (c) suturing, and (d) finished sutures.

2.1 Data analysis

A Chi-square (χ2) test was used to determine if the sex ratio of each C. brachyurus and C. obscurus differed from unity. A two-sample Kolmogorov-Smirnov (K-S) test (Massey, 1951) was used to test the difference in size distribution between sexes for C. brachyurus. This

Huveneers, C. et al. Movements of whaler sharks

was not undertaken for C. obscurus because of the small sample size (n=9). Combining sexes, a K-S test was also used to compare the size distributions of the two species.

For the analysis of presence and absence of acoustically tagged sharks, receivers were grouped into four clusters: GSV (all receivers), Long Spit (receivers deployed around the Long Spit area); metropolitan (receivers within 10 km of metropolitan Adelaide), and NGSV (remaining receivers). Residency was assessed for each acoustically tagged shark based on the detected period or the number of days between the date of tagging and the last detection. A residency index (RI) was calculated by dividing the number of days a shark was present within a monitored region by the monitored period (number of days between date of tagging and last download). An individual was considered ‘present’ within the array if it was detected at least twice within a 24-hour period. This eliminated the possibility of ‘false detections’, which may occasionally occur when there are multiple acoustic tags present within range of an array of receivers (Pincock, 2011). A value of 0 indicated no residency and a value of 1 indicated a high degree of residency.

The minimum distance travelled per shark was calculated by adding the distance between receivers between consecutive detections. Because the receiver range is about 600–800 m, distances less than 1,000 m were excluded as these were likely due to two receivers detecting the same transmission (e.g., from a shark moving between two receivers) rather than sharks moving from one receiver to the other. The temporal variation of detections was assessed by comparing the number of sharks detected within each region per month. The spatial variation of detections was compared between the various monitoring periods according to the timing of receiver deployments and downloads. Values provided in the results are mean ± standard error, unless stated otherwise.

Huveneers, C. et al. Movements of whaler sharks

3 RESULTS

3.1 Tagging events

Twenty-eight field trips were conducted with the aim to capture and tag C. brachyurus and C. obscurus between October 2009 and April 2012, with all trips occurring between October and April (Table 1).

Table 1. Details of fishing trips carried out in GSV to internally tag Carcharhinus brachyurus and C. obscurus with acoustic transmitters

No of line No of No of sharks Date Location Gear type set hooks caught 30/10/2009 St Kilda Longline 1 40 0 11/11/2009 St Kilda Longline 1 70 0 2/12/2009 Goanna Longline 1 80 0 31/01/2010 Long Spit Longline 2 180 10 17/03/2010 Long Spit Longline 2 240 0 25/10/2010 Long Spit Longline 2 103 0 10/11/2010 Long Spit Longline 2 200 0 24/11/2010 Long Spit Longline 2 96 2 13/01/2011 Long Spit Longline 1 150 7 31/01/2011 Long Spit Longline 2 100 6 19/10/2011 Long Spit Longline 2 208 3 26/10/2011 Black pole Rod and reel 1 1 0 1/11/2011 Black pole Rod and reel 1 1 0 3/11/2011 Long Spit Longline 2 190 17 8/11/2011 Glanville/Black pole Short long line 1 50 1 9/11/2011 Black pole Rod and reel 1 1 0 17/11/2011 Black pole Short long line 1 50 1 14/02/2012 Long Spit Longline 1 92 11 23/02/2012 Long Spit Longline 1 110 0 4/04/2012 Long Spit Longline 1 100 1 16/11/2009- St Kilda Rod and reel 3 3 5 30/11/2010* * Eight game fishing trips were undertaken off St Kilda with recreational fishers to deploy acoustic tags.

3.2 Capture and tagging

A total of 64 C. brachyurus and C. obscurus were captured during 28 field trips. The number of sharks caught per trip ranged from 0–17 (2.9 ± 1.0), with no sharks caught during seven longlining trips (41% of longlining trips) (Figure 4). By-catch species included snapper (P. auratus), smooth rays (Dasyatis brevicaudata), Port Jackson sharks (Heterodontus portusjacksoni), and smooth hammerheads (Sphyrna zygaena). Sharks that were

Huveneers, C. et al. Movements of whaler sharks

considered to be too small to be internally tagged with a V16 acoustic tag or that were not in healthy condition were tagged with a conventional identification tag and released.

Frequency 2

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Number of shark caught Figure 4. Histogram of the number of Carcharhinus brachyurus and C. obscurus caught per fishing trip using longlines in GSV (17 trips total).

Gender was assessed for 54 of the 64 (87%) tagged sharks with no significant deviation in the sex ratio from 1:1 for C. brachyurus (0.96:1, n=45, χ2=0.02, P=0.88) or C. obscurus (0.80:1, n=9, χ2=0.11, P=0.74). The size of the sharks caught ranged from 710–1900 mm TL for C. brachyurus and 960–1700 mm TL for C. obscurus. However, 97% of C. brachyurus and 70% of C. obscurus ranged between 710–1500 mm TL (Figure 5). There was no significant difference in the size distribution between sexes for C. brachyurus (Kolmogorov- Smirnov test, t=1.12, P=0.16). Combining sexes, C. obscurus were larger than C. brachyurus (K-S test, t=1.61, P=0.01). Based on clasper calcification, all males were sexually immature. Based on our comparisons with published sizes-at-maturity, all females were classified as immature.

Forty-four C. brachyurus (21 male, 19 female and four unknown sex) and nine C. obscurus (five males and four females) were tagged with conventional identification tags. An acoustic tag was inserted in 36 of the 53 (69%) conventionally tagged sharks. Of those, 29 were C. brachyurus (15 male, 12 female and two unknown) and seven were C. obscurus (four male and three female).

Huveneers, C. et al. Movements of whaler sharks

n = 22 C. brachyurus female nC. brachyurus male = 23 nC. obscurus combined = 9

Acoustic detections of tagged sharks Thirty sharks (83% of tagged sharks) were detected over the monitoring period (October 2009 to May 2012). Of those, 25 were C. brachyurus (86% of tagged C. brachyurus) and five were C. obscurus (71% of tagged C. obscurus). One of the male C. brachyurus (780 mm TL) was constantly detected by only one receiver and potentially died within the array. Detections from another shark, (1,230 mm TL female C. brachyurus) were likely to be ‘false detections’ due to ping collisions between the tag from the dead shark and other tags present within the range of one receiver. These were identified following the acceptance criteria developed by the manufacturer (Pincock, 2008). Removing the detections from the dead shark and false detections, the number of detections per shark ranged from 4–1,272 (293 ± 55.3 detections) (Table 2).

Huveneers, C. et al. Movements of whaler sharks

Table 2. Summary of detections obtained from acoustically tagged sharks in South Australian waters. GSV = Gulf St Vincent. Metro = Adelaide metropolitan region.

Detection period Number of days detected Residency index Total length Date No of Species Sex (mm) tagged Detections GSV Long Spit GSV Long Spit Metro GSV Long Spit Metro C. brachyurus Male 1365 19/10/2011 16 93.63 1.93 2 1 0 0.010 0.005 0 C. brachyurus Male 1150 3/11/2011 380 68.29 68.29 16 16 0 0.082 0.082 0 C. brachyurus Male 950 19/10/2011 279 62.75 62.75 14 14 0 0.067 0.067 0 C. brachyurus Female 1060 3/11/2011 95 10.94 10.94 3 3 0 0.015 0.015 0 C. brachyurus Female 1030 3/11/2011 452 127.84 105.64 28 20 0 0.144 0.103 0 C. brachyurus Male 920 3/11/2011 197 79.72 79.72 12 12 0 0.062 0.062 0 C. brachyurus Male 890 3/11/2011 7 2.06 2.06 1 1 0 0.005 0.005 0 C. brachyurus Female 1900 3/11/2011 31 33.70 1.95 5 1 0 0.026 0.005 0 C. brachyurus Male 780 31/01/2010 0 0 0 0 0 0 0 0 0 C. brachyurus Female 1100 31/01/2010 767 675.97 675.97 39 15 20 0.047 0.018 0.024 C. brachyurus Female 1060 31/01/2010 188 698.41 698.41 15 10 5 0.018 0.012 0.006 C. brachyurus Male 1320 31/01/2010 0 0 0 0 0 0 0 0 0 C. brachyurus Female 1230 31/01/2010 119 638.06 525.47 5 3 1 0.006 0.004 0.001 C. brachyurus Female 1100 24/11/2010 0 0 0 0 0 0 0 0 0 C. brachyurus Male 740 13/01/2011 0 0 0 0 0 0 0 0 0 C. brachyurus Unknown Unknown Unknown 659 * * 20 7 * * * C. brachyurus Male 1540 24/11/2010 405 401.25 401.25 25 24 0.046 0.045 0.000 C. brachyurus Unknown Unknown Unknown 113 * * 7 1 * * * C. brachyurus Male 1140 13/01/2011 318 119.43 0 11 0 12 0.023 0 0.025 C. brachyurus Female 1230 14/01/2011 0 0 0 0 0 0 0 0 C. brachyurus Female 915 31/01/2011 134 276.35 276.35 4 3 1 0.009 0.006 0.002 C. brachyurus Male 850 31/01/2011 9 32.19 0.00 1 1 0.002 0 0.002 C. brachyurus Female 1360 14/02/2012 365 31.08 31.08 10 10 0.110 0.110 0 C. brachyurus Female 1150 14/02/2012 22 52.35 52.20 2 2 0.022 0.022 0 C. brachyurus Female 1030 14/02/2012 224 79.91 26.19 12 9 0.132 0.099 0 C. brachyurus Male 1040 14/02/2012 595 56.37 35.75 14 2 0.154 0.022 0 C. brachyurus Male 990 15/02/2012 0 0 0 0 0 0 0 0 C. brachyurus Male 1140 15/02/2012 576 65.18 23.72 10 3 0.111 0.033 0 C. brachyurus Male 950 15/02/2012 1272 63.46 0 32 0.356 0 0 C. obscurus Male 1700 31/01/2010 0 0 0 0 0 0 0 0 C. obscurus Male 1070 31/01/2010 99 99.43 99.43 5 5 0.006 0.006 0 C. obscurus Male 1850 13/01/2011 0 0 0 0 0 0 0 0 C. obscurus Male 1870 14/01/2011 82 407.91 407.67 11 2 0.023 0.004 0 C. obscurus Female 1190 14/01/2011 559 402.70 346.16 35 14 0.072 0.029 0 C. obscurus Female 1190 14/01/2011 4 457.55 457.55 0 0 0 0 C. obscurus Female 1250 15/02/2012 226 38.57 30.77 9 5 0.100 0.056 0 * Tagging was undertaken by recreational fishers who did not record the tagging date. Hence, values could not be calculated.

Huveneers, C. et al. Movements of whaler sharks

3.3 Residency

Within GSV, C. brachyurus and C. obscurus were detected for an average period of 174 ± 49 days (range 1–697 days) and 281 ± 88 days (range 1–457 days), respectively. The tagged sharks showed some affinity to the location where they were tagged, Long Spit, with a similar detection period (171 ± 56.1 days, range 1–697 days and 268 ± 86 days, range 1– 457 for C. brachyurus and C. obscurus, respectively). Fifty-seven percent and 75% of C. brachyurus and C. obscurus tagged for more than a year were detected within GSV for a period longer than 365 days.

During the monitored period, the RI within the area covered by the GSV receivers was very low averaging 0.069 ± 0.018 (range 0–0.36) and 0.040 ± 0.020 (range 0–0.36) for C. brachyurus and C. obscurus, respectively. Residency around Long Spit receivers was even lower (0.034 ± 0.008, maximum: 0.110 and 0.019 ± 0.010, maximum: 0.056 for C. brachyurus and C. obscurus, respectively). Carcharhinus brachyurus was the only species detected by the receivers within the metropolitan region, and had a lower RI of 0.003 ± 0.0016 (maximum: 0.025), although there were more receivers deployed in that region than around Long Spit. These values suggest that while the detection period of whaler sharks within GSV and at Long Spit was relatively long, they were not detected on many of the days during this period.

3.4 Movements

Individual Carcharhinus brachyurus were detected by 1–20 receivers (mean 7 receivers). While 21 of the 23 detected C. brachyurus (91%) were detected by NGSV and Long Spit receivers, six sharks (26%) were detected by the metropolitan receivers and four sharks (17%) were detected by receivers from NGSV, Long Spit, and metropolitan regions. Carcharhinus obscurus were detected by fewer receivers (range 1–9, mean 5 receivers) with all detections obtained by receivers deployed in the NGSV and Long Spit regions. No C. obscurus were detected within the metropolitan region.

Based on the acoustic receivers deployed in the GSV, the minimum travelled distance of sharks ranged from 1.7–413.5 km (68.2 ± 19.6 km) and 35.3–87.2 km (68.2 ± 15.10 km) with 62% and 100% of C. brachyurus and C. obscurus travelling less than 100 km, respectively (Figure 6). 21

Huveneers, C. et al. Movements of whaler sharks

2 Frequency (number) Frequency 1

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 Distance (km)

The shark that travelled the longest distance was a 1,100 mm TL female C. brachyurus, which moved between Long Spit, the Barge and the Zanoni, and the metropolitan region on six occasions, moved between Long Spit and the NGSV region once and between the NGSV and the metropolitan region once. This shark also moved between the Barge and the Zanoni, and Long Spit on five occasions. The fastest swimming speed recorded between receivers more than 3 km apart was 2.6 m/s (or 9.4 km/h).

Two of the tagged sharks were detected by receivers deployed as part of other projects (Figure 7). A 1,250 mm TL female C. obscurus was detected by a receiver deployed offshore from Long Spit on the 16th of March 2012 and was next detected on the 23rd of March 2012 off Dangerous Reef, Spencer Gulf. This represented a minimum travelled distance of 245 km in 6 days or 40 km day-1. A 1,900 mm TL female C. brachyurus was detected on the 5th of November 2011 and was next detected on the 15th of March 2012 off Corner Inlet, Victoria. This represented a minimum travelled distance of 1,050 km in 102 days or an average of 10.3 km day-1 over 3 months.

Huveneers, C. et al. Movements of whaler sharks

Figure 7. Map showing the movements of a 1,250 mm TL female Carcharhinus obscurus (red dot), and a 1,900 mm TL female C. brachyurus (blue dot) detected outside of GSV.

3.5 Spatio-temporal variations

The spatio-temporal variation in the detections of the tagged sharks is difficult to interpret due to the expanding acoustic coverage throughout the monitoring period, a couple of essential receivers being faulty and stopping recording prematurely, and the non- simultaneous download of all receivers.

Detections from receivers deployed along the metropolitan region were obtained from December 2010 to December 2011. Receivers from the NGSV region were deployed in May 2011 and subsequently downloaded in May 2012. During these periods, the number of sharks detected by the receivers varied between 0 and 11. The receivers deployed in the NGSV and Long Spit regions detected more C. brachyurus per month (mean 6 and 4.9 C. brachyurus, respectively) than receivers deployed along the metropolitan region (mean 0.7 C. brachyurus). There was a temporal fluctuation in the number of C. brachyurus detected in the NGSV/Long Spit regions with more sharks detected in the summer months (October– March) than in winter (June–August). Although the small number of C. brachyurus detected off the metropolitan region might have biased the ability to observe a similar trend, no temporal variation could be distinguished from the detections along the metropolitan region (Figure 8). While C. obscurus were not detected along the metropolitan region, similar temporal patterns were observed between C. brachyurus and C. obscurus within the NGSV and Long Spit regions.

Huveneers, C. et al. Movements of whaler sharks

12.00 (a) 10.00

8.00

6.00

4.00

2.00 detected of sharks Number 0.00 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

4 (b)

1 detected of sharks Number 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Throughout each of the monitoring periods, the number of detections varied across receivers, with more detections generally obtained from receivers deployed at Long Spit and in the NGSV region (Figure 9). The period from December 2010 to May 2011 was the only period during which most of the detections were obtained from the receivers deployed off the metropolitan region. This is likely due to the only receivers deployed at Long Spit being faulty and not recording any data. During the two following monitoring periods, Long Spit was the region from which most detections were obtained.

Huveneers, C. et al. Movements of whaler sharks

Figure 9. Number of detections of whaler sharks in Gulf St Vincent between: A) March 2010– December 2010, B) December 2010–May 2011, C) May 2011–December 2011, and D) December 2011–May 2012.

3.6 Additional detections

The receivers deployed as part of this study also detected other species tagged through different projects.

A total of 29 snapper were tagged as part of a study investigating their movement and residence times. Over 180,000 detections from 19 snapper were obtained between May 2011 and May 2012 on 17 of the receivers, including receivers from the NGSV and Long Spit regions. No snapper were detected by receivers off the metropolitan region. Further information about the results obtained from the tagged snapper can be obtained from Fowler et al. (2012).

Huveneers, C. et al. Movements of whaler sharks

Between 2007 and 2011, 134 C. carcharias were tagged around Australia with 83 C. carcharias tagged in South Australia, 37 of them during 2011–12. Of these, four were detected by a total of 14 receivers. The number of days C. carcharias were detected ranged from 1–10 and the number of receivers which detected C. carcharias ranged from 1–10. One shark was detected on 16 days between the 13th of August 2008 and 10th of September 2008 by the ten receivers deployed off Glenelg Beach (Figure 10). The other three C. carcharias were detected by receivers deployed off the Zanoni wreck, Long Spit and offshore from Long Spit (NGSV region). Carcharodon carcharias were only detected from July–October.

10 km

4 DISCUSSION

This study represents the first investigation of the small-scale movements and residency patterns of C. brachyurus and C. obscurus in southern Australian gulf waters. The results

Huveneers, C. et al. Movements of whaler sharks

showed that while sporadic detections from individual sharks within GSV were obtained for periods up to two years, they also indicated that both species were mobile and did not constantly remain within the tagging location or monitored areas. This study enabled assessment of spatio-temporal variation in the detection patterns of C. brachyurus and C. obscurus and showed a limited use of the metropolitan region with an increased use of GSV during warmer months.

Marine reserves are increasingly being identified as conservation and management tools for protecting vulnerable species from anthropogenic impacts (Agardy, 1997; Sobel and

Dahlgren, 2004). Although the full potential and costs of marine reserves are not completely understood, there is growing evidence of the benefits they provide to the marine environment (Lester et al., 2009). With an increasing need for effective marine conservation there has been a wealth of research focusing on the design (e.g. Botsford et al., 2003; Hastings and Botsford, 2003; Baskett et al., 2007), implementation (e.g. Kelleher, 1999; Roberts and Hawkins, 2000; Wielgus et al., 2008) and efficacy of marine reserves for commercially exploited and threatened species (e.g. Lowe et al., 2003; Parsons et al., 2003; Egli and Babcock, 2004). The design of a marine reserve for a target species should depend on the level of movement of that species (Gell and Roberts, 2003) and the intended goal of the reserve (fisheries vs. biodiversity conservation; Botsford et al., 2003). If a marine reserve is to provide effective protection for a target species, knowledge of the species home range, site fidelity, and movement is essential to marine reserve design and management (Kramer and Chapman, 1999; Chapman and Kramer, 2000). The results from the present study showed that Long Spit is likely to be an important area for C. brachyurus and C. obscurus as they were detected regularly and for up to nearly two years by receivers deployed in that area. The very small residency index, however, suggests that whaler sharks only spent a short amount of total time within the approximately 6 km2 acoustically covered area and that a marine reserve within this location would only protect C. brachyurus and C. obscurus an average of 3% and 2% of the time, respectively.

When marine reserves do not encompass a species entire home range or when organisms spend a large amount of time outside of a marine reserve, spatial closure can still remain effective if it includes critical habitats, such as breeding, nursery, or feeding areas (Game et al., 2009). Sharks caught off Long Spit were all immature suggesting that Long Spit is not a breeding ground for C. brachyurus and C. obscurus. Nursery areas for juvenile sharks can be defined as areas where (1) sharks are more commonly encountered in the area than other areas; (2) sharks have a tendency to remain or return for extended periods; and (3) the 27

Huveneers, C. et al. Movements of whaler sharks area or habitat is repeatedly used across years (Heupel et al., 2007). Some sharks used the

Long Spit area repeatedly across years and were more common at Long Spit than around the metropolitan region. Sharks did not, however, remain or return for extended periods with all sharks having a residency index below 0.11. The location and functioning of shark nurseries has been a focus of recent research (Heupel et al., 2007; Kinney, 2011) and regions that do not strictly fit Heupel’s (2007) definition can still be crucial to the maintenance of adult stocks (Yates et al., 2012). Although 50 receivers were deployed within GSV, the total acoustic coverage was limited relative to the total size of GSV. While sharks did not spend an extended amount of time within Long Spit specifically, they might spend most of their juvenile stage within the South Australian Gulfs. Long Spit might not be a discrete nursery area, but the large proportion of juvenile C. brachyurus and C. obscurus commercially caught within the Spencer Gulf and GSV suggests that the southern Australian gulfs represent ecologically significant habitats for the juvenile stages of these species (Rogers et al., in press-a).

The bathymetry of the Long Spit area is characterised by a long shallow sandbank extending in a west-southwest direction. The sandbank has a depth of about 6–8 m while the surrounding area is slightly deeper at around 10–12 m. This bathymetric feature might attract prey species in an otherwise relatively featureless seabed. A study investigating the stomach contents of pelagic sharks in gulf and shelf ecosystems off southern Australia found that the diet of C. brachyurus and C. obscurus overlapped, with sardine (Sardinops sagax), southern calamari (Sepioteuthis australis), and cuttlefish (Sepia sp.) being important prey of both species (Rogers et al., 2012). The abundance and diversity of these prey within the Long Spit region has not been established and it is unknown whether Long Spit is used as a foraging area because of higher prey abundance compared to surrounding areas.

Sharks tagged around the Long Spit region did not actively use the metropolitan region, with only a few detections from C. brachyurus obtained on the metropolitan receivers. Some of the receivers deployed off the metropolitan region were deployed close to natural or artificial reef system (e.g., Semaphore Reef, Glenelg Tyre Reef), where reef fish species are likely to be more abundant than in the surrounding area (Shepherd and Baker, 2008). Considering that the number of detections was not higher from receivers in proximity to these reef systems compared to other receivers in the metropolitan region, it is more likely that C. brachyurus were transiting between areas, rather than residing within the metropolitan region. This was also confirmed by the overall low number of detections by the receivers off the metropolitan region. 28

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The temporal variation of detections in the GSV receivers (excluding metropolitan receivers) or the Long Spit receivers coincides with the peak in commercial catches (Jones, 2008), suggesting a higher abundance of whaler sharks during the warm summer months. Whaler sharks were previously believed to be leaving the South Australian Gulfs during the winter months. Carcharhinus brachyurus, however, were still detected throughout winter, albeit to a lesser extent, indicating that at least some individuals remain within GSV. The reduced catches during winter in the commercial fishery might be related to a decreased frequency of feeding events or reduced fishing efforts. Metropolitan receivers detected sharks in May and August but not in June–July. This could, however, have been a bias related to the limited use of the metropolitan region.

Seasonal migration of whaler sharks (specifically C. brachyurus) has previously been documented in another Australian state and other countries. Off New South Wales, Australia, C. brachyurus are present during Spring–Autumn between September and May, the numbers peaking between February and April (Krogh, 1994). In Argentina and New Zealand, C. brachyurus are only found in coastal waters during summer (Cox and Francis, 1997; Lucifora et al., 2002). Off South Africa, C. brachyurus are abundant in the warm waters off KwaZulu-Natal during winter. Their numbers decline dramatically in spring and summer (Cliff and Dudley, 1992), when they move to cooler Cape waters (Smale, 1991). Similarly in the Southwest Atlantic, C. brachyurus are most common in warm-temperate waters during cool months. These migratory patterns are likely to be related to temperature (Cliff and Dudley, 1992), prey fields, or reproductive schedules and should be further investigated to improve our understanding of the drivers underpinning the movements of these species.

Two sharks, a C. brachyurus and a C. obscurus, travelled long distances with one shark travelling more than 1,000 km to Victoria, Australia. Large-scale movement of C. brachyurus and C. obscurus is not uncommon. A previous study assessing the movements of whaler sharks in southern Australia based on data from a tag-recapture program showed that four out of the 40 recaptured sharks (10%) were recaptured more than 1,000 km from the tagging location (Rogers et al., in press-a). Carcharhinus obscurus have been found to travel up to 2,736 km between Spencer Gulf, South Australia and northwest Western Australia (Rogers et al., in press-b). Similar large-scale movements have been observed in other countries with distances of up to 1,374 km recorded in South Africa (Dudley et al., 2005; Hussey et al., 2009), and 3,800 km in the Northwest Atlantic (Kohler et al., 1998). Carcharhinus brachyurus 29

Huveneers, C. et al. Movements of whaler sharks

were shown to move long distances along the South African continental coastlines (Cliff and

Dudley, 1992). The lack of C. brachyurus population genetic structure between Australia and New Zealand across the Tasman Sea (Benavides et al., 2011a) and between the C. obscurus populations from the east and west Australian coasts (Benavides et al., 2011b) also supports that these whaler shark species are capable of large-scale movements.

This study initiated the South Australian acoustic monitoring network, which has already shown to benefit several other studies and has been incorporated within the Australian Animal Tagging and Monitoring System (AATAMS), part of the Integrated Marine Observing System (IMOS). The detections of other organisms (i.e., P. auratus, C. carcharias) obtained by the receivers deployed for this study have been provided to the relevant research groups. Additional detections of the whaler sharks tagged as part of this study were also obtained from other receivers highlighting the benefits of sharing the detections between studies and of the AATAMS network.

5 MEDIA COVERAGE AND COMMUNITY OUTREACH Since the receivers were allocated by AATAMS and funding was obtained from the Nature Foundation of South Australia, the whaler shark project was exposed in ‘The Advertiser’ and within the Nature Foundation of South Australia newsletter. We also presented some of our group’s research to various community events such as the University of the Third Age, fundraising events towards shark conservation, and to various tourist groups undertaking white shark cage-diving expeditions. Details of the media coverage and community presentation are presented below: • Nature Foundation of South Australia Nature Matters Newsletter (May 2010). Article about whaler shark and white shark projects. • ‘The Advertiser’ (27th April 2010) Fish and implant tracking chips. Article about the whaler shark tagging project. • Huveneers, C. November 2009/December 2010/January 2010/May 2010/June 2010. Shark research in South Australia. Rodney Fox Shark Expeditions, North Neptune Island, South Australia • Huveneers, C. December 2010. Shark research in South Australia. University of the Third Age (U3A) Club – Aldinga Library, South Australia • Huveneers, C. January 2010. Shark ecology in South Australia. Presentation towards a shark fundraising event in collaboration with CCSA, Adelaide, South Australia • Huveneers, C. October 2010. Shark research in South Australia. CCSA Fish Forum

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• Huveneers, C. November 2010. Shark research in South Australia. Department of

Ophthalmology, Flinders Private Hospital • Huveneers, C. November 2010. Friendly sharks? What we know about sharks in South Australia. Friends of the Sea and Sand of Whyalla Conservation Park • Huveneers, C. February 2011. Shark ecology and ethical considerations. Invited speaker at Flinders University Animal Welfare Day • Huveneers, C. March 2011. Shark and friends: intro and research in South Australia. University of the Third Age (U3A) Club – Port Adelaide Library • Scope, Channel 10. Apex Predators. (6th of August 2011). Story about whaler shark acoustic tracking project.

6 ADDITIONAL SUPPORT The GSV monitoring project has been successful at attracting funds and in-kind support from various additional agencies. This includes: • Twenty tags from the Nature Foundation of South Australia ($10,000); • Twenty tags/year for three years, acoustic receivers, and logistic support from a philanthropic private investor ($66,000); • Acoustic receivers and logistic support including salaries from the Adelaide and Mount Lofty Ranges NRM Board ($25,000); • Loan of six acoustic receivers from the University of Adelaide (valued $9,000); • Loan of ten receivers and ten acoustic releases for 24 months from TAFI/IMAS (value $30,000); • Loan of nine receivers from DEWNR (valued $13,500); • An FRDC project to tag snapper within the GSV (~$100,000); • Forty-seven tags for snappers from PIRSA Fisheries ($19,000); • Logistic support from PIRSA Fisheries and Aquaculture to tag snappers, deploy, and download 20 receivers during two years; • Logistic support from the Surf Life Saving Club through the use of their jet boat to download receivers; • A successful ARC Linkage grant aimed to assess the sustainability of whaler sharks which attracted $20,000/year for 3 years ($60,000) from the fishing industry; and • Thanks to the support obtained from the combination of these organisations, a PhD project (~$24,000/year scholarship) based at Flinders University has now been initiated to assess the vulnerability of whaler sharks to southern Australian fisheries.

Huveneers, C. et al. Movements of whaler sharks

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