spatial dynamics and habitat preferences of juvenile white ... · juvenile white sharks –...

Spatial dynamics & habitat preferences of juvenile white sharks – identifying critical habitat and options for monitoring recruitment Final report June 2008

B. D. Bruce • R.W. Bradford Final report to the Department of Environment,Water, Heritage and the Arts

Spatial dynamics and habitat preferences of juvenile white sharks – identifying critical habitat and options for monitoring recruitment

B. D. Bruce and R. W. Bradford

CSIRO Marine and Atmospheric Research

June 2008

FINAL REPORT TO THE DEPARTMENT OF THE ENVIRONMENT, WATER, HERITAGE AND THE ARTS

© Commonwealth of Australia 2008 This work is copyright. You may download, display, print and reproduce this material in unaltered form only (retaining this notice) for your personal, noncommercial use or use within your organisation. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. Requests and inquiries concerning reproduction and rights should be addressed to Commonwealth Copyright Administration, Attorney General’s Department, Robert Garran Offices, National Circuit, Barton ACT 2600 or posted at http://www.ag.gov.au/cca

The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment, Heritage and the Arts or the Minister for Climate Change and Water.

While reasonable efforts have been made to ensure that the contents of this publication are factually correct, the Commonwealth does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication.

National Library of Australia CataloguinginPublication entry

Author: Bruce, B. D. (Barry David)

Title: Spatial dynamics and habitat preferences of juvenile white sharks [electronic resource]: identifying critical habitat and options for monitoring recruitment / B. D. Bruce, R. W. Bradford.

ISBN: 9781921424380 (pdf)

Notes: Includes index. Bibliography.

Subjects: White sharkHabitatAustralia. White shark—TerritorialityAustralia. White shark—monitoringAustralia.

Other Authors/Contributors: Bradford, R. W. (Russell), 1963 CSIRO. Marine and Atmospheric Research.

Dewey Number: 597.330994

Cover design by Lea Crosswell (CMAR, Hobart)

http://www.ag.gov.au/cca

SUMMARY ....................................................................................................................1

INTRODUCTION ..........................................................................................................3 Life history stage definitions ....................................................................................4 Site selection .............................................................................................................5

SITE 1: TRIGLOW BEACH, WESTERN AUSTRALIA ............................................6 Methods .....................................................................................................................7 Results .......................................................................................................................8 Discussion .................................................................................................................9

SITE 2: STOCKTON BEACH, NEW SOUTH WALES...........................................10 Methods ...................................................................................................................10 Capture and tagging of sharks ...........................................................................11 Data handling and processing............................................................................14 Behavioural modes – data comparisons ...........................................................14

Results .....................................................................................................................15 Tagging ................................................................................................................16 PSAT tag – Shark S6 ...........................................................................................17 Tracking data overall movement patterns .......................................................18 Satellite tracking tags......................................................................................18 Swimming speed .............................................................................................21 Individual track narratives ..............................................................................22

Discussion – overall movement patterns ..............................................................38 Depth swimming behaviour ....................................................................................41 Discussion – depth swimming behaviour .............................................................54 Deep diving behaviour ........................................................................................54

Temperature ............................................................................................................55 Discussion ...............................................................................................................59

ACOUSTIC TAGS ......................................................................................................60 Results .....................................................................................................................60 Discussion ...............................................................................................................61

SURVEY AND MONITORING METHODS ..............................................................61 Vesselbased surveys .............................................................................................62 Methods................................................................................................................62 Results .................................................................................................................62 Discussion ...........................................................................................................63

Aerial surveys..........................................................................................................63 Methods................................................................................................................64 Results .................................................................................................................65 Discussion ...........................................................................................................67

ACKNOWLEDGEMENTS .........................................................................................68

REFERENCES ...........................................................................................................68

APPENDIX 1 ...............................................................................................................71

i

Spatial dynamics and habitat preferences of juvenile white sharks

SUMMARY

Juvenile white sharks (1.82.6 m total length) in eastern Australia show broadscale patterns of movement ranging from southern Queensland to north eastern Tasmania and across the Tasman Sea to New Zealand. These patterns are the most extensive documented for white sharks of this size anywhere in the world and extend our knowledge of the habitat niche for juvenile white sharks to include the open ocean. Juvenile white sharks showed two main behavioural modes, temporary residency and travelling, patterns similarly described for subadult and adult white sharks. Residency sites were clustered into three primary residency regions in eastern Australia (Fraser Island [Qld], Stockton BeachHawks Nest [NSW] and Corner InletLakes Entrance [Vic]) and a single primary residency region east of New Zealand on the northern boundary of the Chatham Rise. Residency regions were areas known for the abundance of suitable prey, however other seemingly similar areas exist along the eastern Australian coast that were not used as residency sites by sharks tagged as part of this study.

Resident juvenile white sharks largely restricted their movements to between the shore and the 100120 m depth contour. The depth preferences shown by juvenile white sharks while resident and travelling were highly bimodal with time spent primarily at the surface (05 m) and in the 60100 m zones. When seaward of the continental shelf, juvenile white sharks showed bimodal depth preferences of the surface and depth zones ranging between 300 and 1000 m, depending on the individual shark. The 984 m depth recorded by one juvenile shark is the deepest recorded dive for a white shark in Australian waters and one of the deepest dives recorded for this species anywhere in the world.

Juvenile white sharks experienced temperatures ranging from 68 oC to 2426 oC. The most common temperature range occupied (over 45% of their time) was 1820 oC. However, tracking during this study was conducted primarily over the spring – summer period, the timing being determined by the availability of sharks for tagging at Stockton Beach. Thus, these temperature data may be biased by the time of year the study was undertaken. Tracking during autumn and winter is required to fully elucidate the influence of temperature on the spatial dynamics and distribution of juvenile white sharks in Australian waters. This will require future tagging and tracking in southern Australian waters (eg Victoria or South Australia) commencing during the summerautumn period.

Juvenile white sharks occur in other Australian states, suggesting that important juvenile habitats may exist in regions other than east coast waters. Such reports include areas of Western Australia, South Australia and western Victoria. The linkages between these various regions and the eastern Australian sites are unclear. Similarly, it is unclear if the juvenile sharks present in these areas are sourced from a common or from different pupping grounds. Identification and investigation of these other juvenile residency regions and the linkages between them is a critical requirement for further research.

No youngoftheyear white sharks were located at tagging sites during the study. This combined with the obvious temporary residency and highly mobile nature of juveniles provides no further indication of the location of pupping by white sharks in Australian waters. The location of pupping grounds and habitat requirements for youngoftheyear white sharks requires further targeted research in Australian waters.

The identification of a limited number of primary residency regions in eastern Australia and the common usage of these regions by tagged sharks suggests that monitoring even one of these sites may offer insight into juvenile abundance and recruitment levels over time. Vesselbased and

1


aerial surveys offer promise for developing an abundance index for juvenile white sharks provided they are seasonally targeted at primary residency regions. Stockton Beach may be an ideal location for such monitoring. However, tagged sharks showed a high degree of site specificity to particular areas of beaches in the region and did not venture to other beaches in the region where juvenile white sharks were reported to occur. This site specificity and the linkages between beaches across the Port Stephens region requires further evaluation to ensure that monitoring of the Stockton Beach site will provide a representative sample of abundance in this overall region.

The range of sizes observed, and site specificity shown, suggests that individual sharks may return to Stockton Beach in subsequent years until they reach sizes that prompt a change in behaviour and occupancy of juvenile habitat. Further monitoring at this site in particular is required to determine the number of years over which individuals do so in order to evaluate the true significance of such residency regions. In addition the return of tagged sharks to Stockton Beach would offer an unparalleled opportunity to retrieve SPLASH tags and download their entire archived data set.

Although subadult and adult white sharks have been recorded undertaking openocean forays and crossocean basin excursions, juvenile white sharks have previously been considered to be a coastal life history stage. Our data now confirms that white sharks as small as 1.92.1 m can similarly make both offshore forays as well as crossocean basin excursions and, in doing so, dive to depths close to 1000 m. These behaviours may expose juvenile white sharks to incidental capture in pelagic fisheries targeting squid, tuna and swordfish where, due to their size, they may be mistaken for other species such as mako sharks (Isurus oxyrinchus).

2


INTRODUCTION Research on white sharks in Australian waters has previously focused on subadult and sharks > 3.0 m in length (Robbins 2007, Bruce et al. 2006, Bruce et al. 2005a + b, Malcolm et al. 2001, Bruce 1992) that are commonly observed in the vicinity of seal and sea lion colonies. Australian research and similar international studies using electronic tags (Weng et al. 2007b, Bruce et al. 2006, Bonfil et al. 2005, Boustany et al. 2002) have identified that white sharks >3.0 m in length can make extensive coastal migrations coupled with periods of temporary residency, may show a propensity for returning to specific sites – sometimes on a seasonal basis, and make excursions into the open ocean. These data have shed new light on the spatial dynamics, linkages between populations and habitat preferences of white sharks. In doing, so they have also illustrated the advantages in using satellite technology as a research tool for the species. However, despite these advances, comparatively little effort has been directed at determining the movements and habitat preferences of juvenile (≤ 3.0 m) or youngoftheyear (YOY ≤ 1.75 m) white sharks.

Juvenile white sharks have generally been reported from nearshore environments (Weng et al. 2007a, Bruce et al. 2006, Dewar et al. 2004, Reid and Krogh 1992, Cliff et al. 1989, Klimley 1985) where they may be most vulnerable to incidental capture in commercial and recreation fishing and, where in place, beach protection programs. Seasonal aggregations of juvenile white sharks are known to occur on certain parts of the Australian coast, usually along surf beaches and coastal reefs, and presumably in response to the presence of prey. Specific areas where such aggregations are known to occur on the east coast of Australia are the Stockton Beach region of central New South Wales (late winterspring) and the Corner Inlet region of eastern Victoria (summerautumn). Conventional tagging and preliminary satellite tracking suggest that sharks from these two regions may be part of the same highly mobile population and that they may follow similar routes to travel between them (Bruce et al. 2006). There are seemingly similar habitats elsewhere, but these do not have the same consistent reports of juvenile white sharks. Thus it is possible that the Stockton and Corner Inlet regions are important nursery grounds for white sharks. However, there are no reliable data on the spatial dynamics of juvenile white sharks at these sites nor do we know how important or unique these two areas are. Juvenile white sharks in both areas are currently subject to incidental capture in recreational and commercial fishing operations. In addition, Stockton Beach is one of the 51 metropolitan beaches currently meshed as part of the NSW Shark Control Program (SCP) (Reid and Krogh 1992).

White sharks were first protected in Tasmanian waters in 1996 with full protection across all Australian waters achieved by 1998 (Malcolm et al. 2001), yet there are no current metrics with which to assess population status, the efficacy of protective legislation, or the effectiveness of Recovery Plan actions towards achieving the recovery of the species’ numbers in Australian waters. Captures, sightings and other forms of interactions with medium to large white sharks show considerable interannual variability (Cliff et al. 1989, Reid and Krogh 1992) that are most likely in response to shifts in distribution rather than changes in population size (Bruce 2008). Thus monitoring activity or abundance indices of white sharks > 3.0 m has so far been unsuccessful in discerning population trends from signal noise (CSIRO – unpublished data), albeit such monitoring may offer some indications in the longer term. Due to the species’ life history traits of low natural mortality and very low annual fecundity (Mollet and Cailliet 2002, Francis 1996) the abundance of juvenile (≤ 3.0 m) white sharks may offer a more timely and robust index of population recovery by providing an index of recruitment. However, the prerequisites for achieving this include knowledge of the location and extent of juvenile habitat, the time period during which juveniles occupy these habitats, their behaviour and the ability to observe and count juveniles in an effective way that correlates with abundance. Such information is currently lacking for juvenile white sharks both in Australian waters and across the species’ international distribution.

3


The primary objectives of this project were to track juvenile, including youngoftheyear (YOY) white sharks using satellitebased and acoustic technologies in order to identify:

a) habitat preferences for these life history stages; b) the location of nursery areas; and c) strategies for ongoing monitoring of population status.

In doing so this project addresses the following Priority 1 Australian White Shark Recovery Plan actions:

F4: Research directed at determining characteristics of white sharks that will contribute to identifying habitat critical to their survival.G1: Identify habitat critical to the survival of white sharks,

and, will contribute vital prerequisite information towards the following Priority 2 and 3 actions respectively.

G2: Consider white shark habitat in identifying and managing MPAs throughout the whiteshark’s (Australian) range.I1: Develop a quantitative framework to assess the recovery of the species.

Life history stage definitions

We define herein the following life history stages for white sharks in Australian waters:

a) Youngoftheyear (YOY) sharks (≤ 1.75m TL): Based on the size of full term pups, the smallest free swimming white sharks and estimated growth rates from the literature (Malcolm et al. 2001, Francis 1996, Cailliet et al. 1985, Wintner and Cliff 1999) we define white sharks in their first year, youngoftheyear, to be ≤ 1.75 m total length (TL).

b) Juvenile (JWS) sharks (> 1.75 m – 3.0 m TL): Juvenile white sharks are those sizes greater than YOY sharks but prior to the smallest sizes commonly observed at pinniped colonies (3.0 m). At these sizes, sharks primarily feed on teleosts (finfish) and elasmobranchs (other sharks and rays). Juvenile and YOY white sharks have been observed in similar locations (eg surf beach areas and off coastal reefs) and thus may share similar habitat requirements.

c) Subadult sharks (3.0 – 3.6 m TL [males]; 3.0 – 5.0 m TL [females]). Male and female white sharks mature at different sizes. Subadult sharks are those between the size at first arrival at pinniped colonies and the size at reaching maturity. Arrival at pinniped colonies defines a new predatory regime and ensuing predatory strategies in white sharks via the addition of marine mammals to their fish diet. The smallest size commonly observed at Australian pinniped colonies is 3.0 m.

d) Adult sharks (> 3.6 m TL [male]; > 5.0 m TL [female]). Adult white sharks are those that have reached sexual maturity based on data from Malcolm et al. (2001), Francis (1996), Pratt (1996) and Cailliet et al. (1985).

Unless otherwise stated, all lengths refer to total length (TL) as defined by Mollet and Cailliet (1996). All lengths and depths are specified in metres (m), including depth units on all figures.

4


Northern Territory

Queensland

Western Australia

Brisbane South Australia

New South Wales Perth

Sydney Adelaide Stockton Beach

Triglow Beach Vic Melbourne

Lakes Entrance

0 500 1000 Corner Inlet

kilometres Tas

Figure 1: Locations of study sites in Australian waters – Stockton Beach, Corner Inlet – Lakes Entrance region and Triglow Beach. Vic = Victoria; Tas = Tasmania.

Site selection Previous observations suggested two regions were likely to present opportunities to tag juvenile or YOY white sharks – Stockton Beach in central New South Wales (N. Otway NSW DPI pers. comm.) where juvenile white sharks predate on schools of Australian salmon (Arripis trutta) close to shore and the Corner InletLakes Entrance region of south eastern Victoria (Malcolm et al. 2001), where sharks feed on snapper (Pagrus auratus), which spawn off coastal reefs in the area – Figure 1. Both events are seasonal with observations suggesting a primarily summerearly autumn presence of white sharks at Corner InletLakes Entrance and a late winterlate spring presence at Stockton Beach.

This project commenced in May 2007 between these two event windows. Based on reports of juvenile white sharks taken as bycatch in commercial shark fisheries in the western Great Australian Bight in MarchApril 2007 and the presence of Australian salmon schools in the AlbanyEsperance area of Western Australia during May, the initial focus of the study was in this area. Triglow Beach, approximately half way between Albany and Esperance was selected as Site 1 for the study, followed by Stockton Beach, NSW as Site 2.

5


SITE 1: TRIGLOW BEACH, WESTERN AUSTRALIA

Triglow Beach (Figure 2) is the western end of a lengthy beach and vegetated dune system approximately 10 km east of Bremer Bay, Western Australia. The area is close (3 km northeast) to Doubtful Island Beach where we had previously tagged subadult and adult white sharks close to shore near a whale stranding event in 2004 (Bruce and Stevens 2004). Triglow Beach had been the site of a sperm whale stranding in November 2006. Some whale remains were still located on the beach and these were still providing a source of attraction for sharks (Figure 3). The combination of whale remains and passing schools of Australian salmon identified this area as a highly suitable site for encountering white sharks of a variety of sizes. The overall rationale for selecting Triglow Beach as the first site for tagging was that the timing still provided opportunities to subsequently tag at Stockton Beach and the Corner Inlet region in the event that no sharks were located or not all tags were deployed at any one site.

Figure 2: Triglow Beach, Western Australia

6


Figure 3: Sperm whale vertebrae and skulls (background objects) at Triglow Beach (May 2007) from a stranding of six individuals in November 2006.

Methods

A field trip was mounted to the area from 814 May 2007. Western Australian Fisheries provided onground logistics (vehicles, baits, small vessel support, staff, and ancillary capture gear) and the commercial fishing vessel Arid was chartered to provide an onwater platform (Figure 4).

Figure 4: The vessel Arid used for white shark tagging in Western Australia – May 2007.

7


Weather and logistics allowed access to the beach site from 913 May. A combination of techniques was used to search for sharks in the area:

a) Searches were made along the beach by vehicle and offshore from the beach by vessel over several kilometres for signs of salmon schools and shark activity.

b) Two baited set lines were deployed each day, and checked every two hours by small vessel supplied by WA Fisheries.

c) The vessel Arid was stationed 300 m offshore from the beach in approximately 34 m depth just inshore of the sand/sea grass boundary. We anchored in the vicinity of the remaining whale carcasses (which had been reduced to scattered bones – mainly skulls, vertebrae as well as isolated pieces of decaying blubber). These remains still produced a visible oil slick in the area. A tuna oil and minced fish berley slick was set each day from the Arid to attract any sharks in the vicinity.

Results

Day 1 (9 May): Baited set lines were deployed off the beach from 0900 to 1630 in depths of 812 m and checked every two hours. No shark activity was detected around the set lines, although one bait was taken between 1430 and 1630 at the shallower station. Searches along the beach failed to locate any visible shark activity.

The Arid was anchored about 1100 and commenced berleying. Various small eagle rays weresighted during the day from the anchored vessel station and a small hammerhead shark (1.0 m TL) approached the vessel at approximately 1400. No white sharks were sighted. Vessel and vehicle searches along the beach similarly failed to locate salmon or sharks in the general area.

Day 2 (10 May): Set lines were deployed at 1000 and Arid was on station by 1100. Searches were made along the beach by vehicle. No activity was detected around set lines during the day, and no schools ofsalmon or sharks were detected during beach checks. Various rays were present around the vessel during the day, indicating the berley trail was successfully providing an attraction to the area.

Set lines were deployed in the water overnight with hook and trace removed but with a hessian bag partially filled with fresh fish to act as an overnight attractant.

Day 3 (11 May): A small school of salmon was located in the western end of Triglow Beach and several fish werecaptured for bait. Additional salmon, kingfish and striped tuna were located in reef areas to the west of Triglow Beach during a search of the area. One of the hessian bags left on one of the set lines overnight had lacerations consistent with a shark bite.

Baited set lines (08301630) and berleying from the vessel station (09001600), however wereagain unsuccessful in securing any shark activity during the day.

Day 4 (12 May): Set lines were deployed 09001600; Arid was on station at 0930. No shark activity was detected around the set lines during the day.

8


A 4.0 m subadult female white shark approached the Arid about 1115 (Figure 5). A coded acoustic (listening station) tag was deployed on the shark as part of a joint CSIROWA Fisheries program on subadult and adult sharks. The shark only remained around the vessel for a period of 15 minutes before departing and was not sighted again.

Figure 5: A 4.0 m subadult female white shark approaches the tagging vessel at Triglow Beach, Western Australia.

A second 3.7 m female white shark approached the Arid about 1515. We attempted to tag this shark with a second acoustic tag but, despite the shark making several passes near the vessel, no clear tagging opportunity presented. The shark departed about 1600 and was not resighted.

Day 5 (13 May): Set lines were established as previously, vehicle checks were made along the beach and the Aridwas stationed in position off the beach from 09301645. No shark activity was detected.

The weather deteriorated rapidly on the night of 13 May and no further work was possible at thesite.

Discussion

Although conditions were conducive for both sighting and tagging juvenile white sharks at Triglow Beach, none were sighted. One 4.0 m subadult female was opportunistically tagged with a codedacoustic tag as part of our program examining spatial dynamics of white sharks in general. A second shark sighted was similarly too large to be tagged as part of the juvenile shark project. Neither shark spent much time in the vicinity and quickly left the area after initial interactions with the tagging vessel.

Previous satellite tracking has identified two primary modes of behaviour in white sharks – ‘temporary residency’ and ‘travelling’ (Bruce et al. 2006). In general, temporary residency occurs in areas that sharks have selected as feeding regions and thus where a source of prey is located.

9


These areas may themselves be transient, such as fish spawning areas, or sites where fish such as Australian salmon commonly occur in large schools, or they may be permanent such as pinniped colonies. Despite the permanency of the latter, individual sharks are still temporary residents. The behaviour of the two sharks sighted at Triglow Beach was consistent with sharks in travelling mode. Neither shark showed interest in baits placed under floats set behind the tagging vessel and they were both quick to depart after the first sighting.

SITE 2: STOCKTON BEACH, NEW SOUTH WALES

Stockton Beach is a 30 km beach stretching between two estuaries, Newcastle and Port Stephens, on the New South Wales (NSW) central coast (Figure 1). The area is popular for commercial and recreational fishing, as well as surfing and four wheel driving and, is backed by one of the largest continuous mobile sand dune systems in eastern Australia. Stockton Beach has a history of juvenile white shark sightings in recent years, often close to schools of Australian salmon (Arripis trutta). The southern end of the beach is meshed as part of the NSW shark control program (Reid and Krough 1992).

Methods

Sharks were located from a 6 m vessel steaming along the seaward side of the surf zone (Figures 6 + 7). Sharks were generally easily seen in water where the sand bottom was visible.

Figure 6: Searching for juvenile white sharks – Stockton Beach, NSW.

10


Figure 7: Surf zone habitat at Stockton Beach, NSW.

Capture and tagging of sharks

Sharks sighted were approached and presented with a baited hook rig which consisted of a galvanised 12 O hook (with barbs partially removed) baited with whole mullet (Mugil cephalus) and attached to 12 mm silver rope via a short (1.0 m) steel trace. Sharks were gradually tired after hooking (Figure 8) and held in a stretcher in the water next to the vessel for the purpose of tagging. Sharks were given an oxygen feed while in the stretcher to facilitate recovery (Figure 9).

11

Figure 8: Catching a juvenile white shark, Stockton Beach NSW – photo courtesy of Dennis Reid, NSW DPI.


Figure 9: Juvenile white shark being administered oxygen in the handling stretcher just prior to release – photo courtesy of Dennis Reid, NSW DPI.

Three types of tags were fitted to juvenile white sharks: Wildlife Computer SPLASH tags, Wildlife Computer Mk10 PSAT tags and Vemco R64k coded acoustic tags.

12


SPLASH tags are data archiving units with sensors that sample water temperature, swim depth and light level against a time stamp. Tags transmit a unique code via the ARGOS satellite network that registers a location (Latitude/Longitude) for that tag each time the shark raises its dorsal fin, with tag attached, clear of the water provided that an appropriate satellite is in view. Location data is transmitted as priority and followed by sensor data if the shark remains at the surface for a sufficiently long period. SPLASH tags were positioned on the first dorsal fin of each shark and attached by stainless steel pins using the methods described by Bruce et al. (2006). SPLASH tags were programmed to collect and archive data at 10 second intervals and these data were compressed into sixhourly bins for transmission. Data were compared between day and night based on the periods identified in Table 1.

Table 1: SPLASH tag time bins for data transmission Period Eastern Standard Time (GMT + 10 h) Dawn 0400 1000 Day 1000 1600 Dusk 1600 2200 Night 2200 0400

Coded acoustic tags transmit a unique series of pulses that are detected and decoded by moored listening stations. Listening stations (Vemco VR2) record detections as tag numbers (eg tag 426) against a datetime stamp. Data can be downloaded from listening stations on their retrieval. Listening station arrays have been deployed by various institutions in Australian coastal waters and are gradually being developed as a tool for monitoring movement patterns of a variety of species worldwide (Jackson et al. 2007, Heupel et al. 2006, Bruce et al. 2005). Two major programs provide listening station coverage in eastern Australia. A national system of acoustic listening stations is being deployed under a program known as the Australian Acoustic Tracking and Monitoring System (AATAMS), which has links to the international Ocean Tracking Network (OTN) – (Jackson et al. 2007). The NSW Department of Primary Industries (NSW DPI) maintains a series of listening stations along the NSW coast including units at either end of Stockton Beach under a program referred to as the South Eastern Australian Coastal Acoustic Monitoring System – SEACAMS (Otway and Storrie 2006).

Acoustic tags were embedded in a high density float and both these and PSAT tags were attached by 15 cm tethers (200 lb braided stainlesssteel) to a 32 mm x 8 mm stainless steel dart. The darts were inserted in the dorsal musculature below the trailing edge of the first dorsal fin such that the tags towed clear of the fin and body (Figure 10). PSAT tags were programmed to archive data at 10second intervals and detach from the two sharks after 120 days.

13


Figure 10: A SPLASH tag fitted to the dorsal fin and an acoustic tag on a 2.6 m juvenile white shark ready for release.

Data handling and processing

The accuracy of ARGOS position estimates is coded by location class (LC) 3, 2, 1, 0, A or B, with LC3 being the most reliable and estimated to be within 150 m of true. The other numeric LC codes decline in reliability and can be within several kilometres of true. The accuracy of codes LC0, A and B are not defined, but various studies report that these classes may still provide accuracies to within a few kilometres (Eckert and Stewart 2001). We accepted all LC 3, 2 and 1 positions and used these to plot tracks. Positions described by LC0, A or B were accepted only if their location relative to a previous reliable numeric LC position was within reasonable swimming distance in any direction given the time frame between the transmissions. Reasonable swimming distance was based on a nominal cruising speed of 3 km h 1, which is the average swim speed reported for white sharks from previous tracking studies (Strong et al. 1996, Klimley et al. 2002). Data from SPLASH and PSAT tags were decoded via Wildlife Computers propriety software.

Behavioural modes – data comparisons Two primary modes of behaviour, ‘temporary residency’ and ‘travelling’, were identified based on the spatial scale of movement between averaged daily positions. Average daily position (ADP) was calculated by averaging all accepted ARGOSderived positions for a shark received on a single calendar day (00002359 local). A shark was considered temporarily resident to an area if ≥3 consecutive average daily positions fell within a circle of 40 km diameter, the period of residency then being the total number of days over which ADPs satisfied this criteria and provided that no more than five days elapsed between two consecutive ADPs. The choice of 40 km was arbitrary, but a shark travelling at its average swim speed of approximately 3 km h 1

would cross this distance in approximately 1213 hours. Thus we considered a period ≥3 days spent within a 40 km diameter to conservatively identify a shark that was temporarily resident. A shark was considered to be in travelling mode where consecutive ADPs did not meet these

14


criteria. Transmitted data of temperature and swim depth were compared between identified residency and travelling periods. Swimming speed was calculated based on distances between ADPs where such data were available for consecutive days.

Previous tagging of juvenile white sharks Data from the ten sharks tagged as part of this project were combined with that from tagging of two juvenile white sharks in the Corner Inlet – Lakes Entrance region of Victoria with positiononly satellite tags in 2000 and 2001 (see Malcolm et al. 2001 for details). This provided analyses for 12 juvenile white sharks in total.

Results

Conditions permitted access to Stockton Beach on 8, 10, 11 and 12 October 2007. During this period, approximately 30 sightings of juvenile white sharks were recorded, comprising up to approximately 22 individuals. Sharks were located close to shore and within 10 km of the northern end of Stockton Beach (Figures 11 + 12).

Figure 11: A 2.0 m juvenile white shark close to shore at Stockton Beach, NSW (photo courtesy of George Trinkler)

15


StocktonBeach

Shark sightings 8 12 Oct 2007

0

kilometres

2 4

Birubi Pt

Port Stephens

Figure 12: Locations of juvenile white sharks sighted at Stockton Beach, NSW 8 – 12 October 2007.

Tagging

Ten juvenile white sharks ranging in size from 1.92.6 m TL were tagged off Stockton Beach in October 2007 (Appendix 1). All 10 sharks were fitted with Wildlife Computer SPLASH tags and Vemco R64k coded acoustic tags; the smallest two sharks (each 1.9 m) were also fitted with Wildlife Computer Mk10 PSAT tags. The two juvenile white sharks tagged in a previous study (Malcolm et al. 2001) were 1.8 m and 2.4 m respectively.

Data were received from all satellite tracking tags deployed at Stockton Beach and Corner Inlet – Lakes Entrance for periods ranging from 22 to 129 days. This provided a cumulative period of 866 tracking days during which transmissions were received on 405 separate days. One PSAT tag (shark S6) prematurely detached, floated ashore and was retrieved after 28 days. The PSAT tag deployed on shark S9 failed to transmit on, or after, the scheduled release date despite the shark continuing to transmit its location via the attached SPLASH tag.

One shark was observed the day after it was tagged in the same area of Stockton Beach where it was initially located and tagged sharks were observed on a number of occasions by fishers and local surf life saving club staff up to one month after tagging (Figure 13). In all cases, sharks were behaving in an identical fashion to that observed prior to capture indicating that they quickly returned to normal behaviour after the handling process.

16


Figure 13: A tagged juvenile white shark approx one month after tagging – located close to shore at Stockton Beach, NSW (Photo courtesy of George Trinkler).

PSAT tag – Shark S6 On 9 November 2007 the PSAT tag from shark S6 was located by a member of the public on Noosa Beach, southern Queensland (Lat: 25° 55.8’ Long: S 153° 7.1’ E). The tag was intact and all data retrieved. Interestingly both tag tethers and their arrow heads were in place, but the tag head of the loop tether was folded almost in half suggesting that the tag had been dislodged by pulling with some force (Figure 14).

Figure 14: Tag heads from the returned PSAT tag deployed on shark S6. The tag head on left is bent around the tether pivot point indicating that it had been removed with some force.

17


The shedding of the PSAT tag by shark S6 was fortuitous in that it was quickly located and the data retrieved, but also interesting as to how it may have occurred. The tag showed no evidence in the way of tooth marks and scrapes to suggest that it had been shed as a result of interactions with a predatory fish or squid, a fate previously reported for some other dislodged PSAT tags (eg Gunn et al. 2003). The damage to one tag head suggests, however, that the tag was pulled out with some force. The shark obviously survived the encounter and continued to transmit its position via the attached SPLASH tag. The SPLASHbased Argos positions around the time of tag shedding place the shark in the vicinity of Noosa Beach, but reasons for the shedding of this tag are not obvious.

Tracking data overall movement patterns

Satellite tracking tags

Movements of juvenile white sharks covered an extensive range from the site of tagging at Stockton Beach in New South Wales, north, 850 km, to Fraser Island in southern Queensland; south, 900 km, to off Flinders Island in Tasmania and east, 2500 km, to the Chatham Rise in New Zealand waters. Movements of the two sharks tagged in the Corner InletLakes Entrance region ranged from that region south, 400 km, to Bicheno on the east coast of Tasmania and north, 1200 km, to Coffs Harbour in northern NSW (Figure 15).

All 12 sharks showed periods of both temporary residency and travelling. Eastern Australian residency sites were not randomly distributed but clustered into three regions, Corner Inlet – Lakes Entrance (eastern Victoria); Stockton BeachHawks Nest (Port Stephenscentral NSW) and the Fraser IslandNoosa region of southern Queensland (figure 16). These were areas where either different sharks had overlapping and/or adjacent residency sites, or a single shark had multiple overlapping or adjacent residency sites. We termed these as ‘primary residency regions’. Two residency sites did not fall into these primary regions and were occupied by only a single shark for one residency period each. We termed these ‘secondary’ residency regions (Figure 16). One such region was occupied by shark S1 in the vicinity of Tuross Inlet, southern NSW after travelling from the Corner InletLakes Entrance primary residency region.

18


0 404000 800 17 Dec 2007

kilometres 44.3 S 160.1 E

Figure 15: Tracks of 12 juvenile white sharks (average daily positions) tagged at Stockton Beach (10) in October 2007 and Corner Inlet (2) in 2000 + 2001. Note that depth contours are only figured to 172o E.

Some sharks, while travelling, registered ADPs within the boundary of another shark’s residency site – these sharks were classified as ‘visitors’ to those sites and were generally observed passing through enroute to another residency region (Table 2).

Not surprisingly, the most significant residency regions for individual sharks were the sites where they were tagged. However, two sharks tagged at Stockton Beach (S6 + S8) also had residency periods at Corner InletLakes Entrance and a third Stockton shark (S12) visited this site but failed to register sufficient positions to determine residency. Shark S6 either visited or spent periods resident at all primary and secondary residency regions in eastern Australia. Shark S2, tagged at Corner Inlet, visited two of the three other eastern Australian residency regions while travelling north along the NSW coast.

Residency regions were not restricted to the eastern Australian seaboard. Shark S5 travelled across the Tasman Sea and occupied a secondary residency site in Cook Strait and then a primary region on the northern Chatham Rise, both in New Zealand waters (Figure 16).

19

New

ealand

Z

Fraser Is Noosa

Australia

Stockton Beach Hawks Nest

Tuross Inlet

Corner Inlet Lakes Entrance

Cook Str

Nth Chatham Rise 0 404 000 800

kilometres

Figure 16: Primary (circled – bold text) and secondary residency regions (plain text) for juvenile white sharks in eastern Australia and New Zealand. Filled circles denote residency sites and are colourcoded for individual sharks.


Periods of residency and travel suggest a seasonal pattern in eastern Australia. Southern areas were occupied during summerearly autumn followed by travel north during late autumnearly winter; northern residency sites were occupied primarily during spring followed by travel south during early summer (Table 2). These data are still preliminary and further tagging is required to elucidate full movement patterns.

20


Table 2: Residency sites and visiting periods. Note: Sites marked in bold are those where either multiple sharks were resident or a single shark had more than one period of residency (primary regions). Sharks marked in bold were tagged at the residency site, and arrows indicate direction of travel along the coast during visiting periods ↓ = south; ↑ = north. Residency site (region)

Residency sharks

Residency periods

Visiting (travelling) sharks

Visiting (travelling) periods

A. Corner Inlet – Lakes Entrance

S1, S2, S6, S8 Jan, Mar, Apr S12 Jan↓

B. Tuross Inlet S1 Apr S6, S8, S12 Jun↑, Dec↓ C. Stockton Bch – Hawks Nest

S5, S7, S8, S9, S10, S11, S12 S13, S14

Oct, Nov, Dec S2, S6, (S4) May↑, Jun↑, Dec↓

D. Fraser Island Noosa

S6 Nov (S4) Jun↑

E. Cook Str (NZ) S5 Jan F. Chatham Rise (NZ)

S5 Jan

The combined periods that individual sharks spent in travelling and residency modes were not significantly different (paired ttest, p = 0.893). The 12 sharks combined spent 285 days resident and 273 days travelling.

Swimming speed

Mean swim speed (all sharks combined) during residency (0.6 km h 1) was significantly lower than during travelling (2.7 km h 1) (ttest, p <<< 0.05). Swim speed histograms had different signatures between modes (Figure 17). Swim speed ranged from 0.22.2 km h 1 during residency mode and 0.45.8 km h 1 during travelling mode. Mean swim speed for shark S5 for the period spent travelling across the Tasman Sea was 3.7 km h 1 .

21


0

5

10

15

20

25

30

0.2 0.6 1 1.4 1.8 2.2 2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8

Swim speed (km per hour)

Frequency

Resident Travelling

Figure 17: Swim speed signature histogram – resident vs travelling (all sharks).

Individual track narratives

Sharks showed various individual patterns to their movements and these are detailed below.

Shark S5 Shark S5 remained in the Stockton Beach area after tagging until 14 November, recording positions primarily between the shore and the 100 m depth contour (Figure 18). On 1516 November S5 made a temporary move southwest along the coast by approximately 45 km before returning to the Stockton Beach area where it was again resident for 1719 November. S5 departed Stockton on 19 November, again heading southwest, 110 km, before returning briefly to Stockton Beach and then heading offshore, departing the continental shelf on 1 December. S5 initially headed south away from the continental shelf then slowly arced towards the southeast until reaching approx 44.3 oS 160.1 oE where its trajectory changed abruptly to the east (Figure 19). From this point S5 then tracked to the Hokitika region of the South Island of New Zealand. On reaching the New Zealand coast on 28 December, S5 turned northwards and travelled into Cook Strait on 2 January where it remained until 13 January. During this period, S5 was resident in an area north of Picton (24 January) before moving to the Kapiti Coast area west of Wellington (613 January). S5 departed Cook Strait, heading east onto the northern boundary of the Chatham Rise where it remained resident until the last transmission on 20 January 2008 (Figure 20).

22


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster

Figure 18: ARGOSderived positions (filled circles) for Shark S5 in the Port Stephens region of central NSW.

23

17 Dec 2007 44.3 S 160.1 E

Figure 19: Average daily positions for Shark S5 during travel across the Tasman Sea to New Zealand. A satellite image of sea surface temperature (SST) is included off eastern Australia for 6 December 2007. The circled ADP (17 December) denotes the abrupt change in the shark’s trajectory after that date.


24


Hokitika

Wellington

Chatham Rise

Kapiti Coast

0

kilometres

150 300

Figure 20: ARGOS – derived positions (filled circles) for Shark S5 in the New Zealand region.

Shark S6 Shark S6 remained in the Stockton Beach area for approximately one week after tagging, recording positions primarily between the shore and the 100 m depth contour (Figure 21). S6 departed the Stockton area on 16 October, initially heading northeast over continental slope waters and then up to 180 km offshore between 17 October and 1 November. S6 returned to slope waters off Ballina in northern NSW by 2 November, tracking steadily north and inshore, passing North Stradbroke Island (Qld) on 4 November, Noosa on 6 November and arriving at Fraser Island on 9 November where it remained resident until 15 November. During the period at Fraser Island, S6 recorded positions primarily between the shore and the 50 m depth contour. S6 departed the Fraser Island area on 16 November, heading south to the Noosa region where it remained resident from 1720 November. It then travelled steadily south along the coast returning briefly to Stockton Beach on 2 December, continuing south along the NSW coast until reaching the Corner InletLakes Entrance region of eastern Victoria, where it remained resident from 11 January 2008 until the last transmission on 17 January 2008 (Figure 22).

25


Sydney

0

New South Wales

50 25

kilometres

Stockton Beach

Newcastle

Port Stephens

Broughton Is

Seal Rocks

Forster


26

Fraser Is

Noosa

Queensland Brisbane

0 200

kilometres

400 Ballina

New South Wales

Stockton Beach

Sydney

Victoria

Lakes Entrance

Corner Inlet

Figure 22: ARGOSderived positions (filled circles) for Shark S6 along the east coast of Australia.


Shark S7 Shark S7 remained resident in the Stockton Beach region for the entire period of data transmission (10 October22 November 2007), recording positions primarily between the shore and the 100 m depth contour. However, the focal site from 13 October22 November was 20 km north of the site of tagging at Hawks Nest on the northern side of Port Stephens (Figure 23). The area occupied, based on transmitted positions) was quite specific, being a sevenkilometre section of beach heading north from Hawks Nest. There were no positions of S7 recorded from Stockton Beach after its move to Hawks Nest on 13 October.

27


Sydney

0

New South Wales

50 25

kilometres

Stockton Beach

Newcastle

Port Stephens

Broughton Is

Seal Rocks

Forster


Shark S8 Shark S8 remained resident in the Stockton Beach area from at least 11 October21 October and then again from 24 November15 December, recording positions primarily between the shore and the 150 m depth contour (Figure 24). Only two positions were received between 21 October and 24 November. Both of these were in the Stockton Beach area thus it is possible that S8 remained resident at Stockton for this entire period. S8 departed Stockton on 16 December, heading south along the NSW coast, reaching the Corner InletLakes Entrance region of eastern Victoria where it remained resident from 712 January 2008. S8 departed this region on 13 January heading to the east of Flinders Island (NE Tasmania) up to 20 January 2008, after which no further transmissions were received (Figure 25).

28


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


29

Fraser Is

Noosa

Queensland Brisbane

0 200 400

kilometres Ballina

New South Wales

Stockton Beach

Sydney

Victoria

Lakes Entrance

Corner Inlet

Flinders Is



Shark S9 Shark S9 remained resident in the Stockton Beach region from 1116 October 2007. No positions were received from 17 October 2007 to 7 January 2008, after which S9 was again resident at Stockton from 810 January (Figure 26). During periods of residency at Stockton Beach, S9 recorded positions between the shore and approximately the 120 m contour. No further positions were received from S9 until 17 March 08 when several positions were registered approximately 20 km west of Flinders Island in Bass Strait.

30


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


Shark S10 Shark S10 departed the Stockton Beach area on the day after tagging and headed 280 km north along the NSW coast reaching the vicinity of South West Rocks on 18 October (Figure 27). It then immediately turned south and returned to Stockton Beach on 24 October. S10 remained resident at Stockton from 24 October to 12 November 2007. S10 departed Stockton on 13 November, heading 80 km south before returning to Stockton on 15 November where it again remained resident until 21 November. S10 again departed Stockton on 22 November, heading 30 km south then 35 km offshore before returning on 28 November where it remained resident until 11 December. S10 then departed Stockton on 12 December, heading 245 km south to the vicinity of Jervis Bay on 24 December then returned north to Stockton Beach on 30 December, the date of the last position (Figure 28). During residency periods at Stockton Beach, S10 recorded positions from close to shore to approximately the 120 m contour.

31


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


32

Fraser Is

Noosa

Queensland Brisbane

0 200 400

kilometres Ballina

South West Rks New South Wales

Stockton Beach

Sydney

Jervis Bay

Victoria

Lakes Entrance

Corner Inlet

Flinders Is



Shark S11 Shark S11 was present in the Stockton Beach region after tagging on 12 and 16 October 2007, but did not record any positions from 1727 October. S11 was resident at Stockton from 28 October to 2 November recoding positions from the shore to the 100 m contour (Figure 29). No further positions were received after 2 November 2007.

33


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


Shark S12 Shark S12 was resident in the Stockton Beach area after tagging until at least 19 October, from 28 October to 9 November and from 19 November to 25 November. No positions were received between these periods, thus it is possible that S12 was resident at Stockton for the entire period after tagging until at least 25 November, recording positions from the shore to the 100 m contour (Figure 30). No positions were received from 26 November to 18 December. S12 was present off the coast in the vicinity of Jervis Bay, 250 km south of Stockton, on 19 December and then it tracked steadily south reaching the Lakes Entrance area of eastern Victoria on 29 December (Figure 31).

34


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


35

Fraser Is

Noosa

Queensland Brisbane

0 200 400

kilometres Ballina

South West Rks New South Wales

Stockton Beach

Sydney

Jervis Bay

Victoria

Lakes Entrance

Corner Inlet

Flinders Is



Shark S13 Shark S13 departed Stockton the day after tagging on 12 October, heading north (60 km) to the vicinity of Seal Rocks where it remained resident from 1719 October. S13 then returned south to the vicinity of Hawks Nest, just north of Port Stephens where it remained resident from 20 October to 1 November 2007, recording positions primarily between the 100 and 120 m contours (Figure 32).

36


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


Shark S14 No positions were received from shark S14 until 28 October when it registered several positions off Stockton Beach. S14 was subsequently resident at Stockton Beach until at least 22 November 2007, the date of the last transmission, recording positions from the shore to the 120 m contour (Figure 33).

37


Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster


Discussion – overall movement patterns

Juvenile white sharks in eastern Australia show broadscale patterns of movement ranging from southern Queensland to north eastern Tasmania and across the Tasman Sea to New Zealand. These patterns are the most extensive documented for white sharks of this size anywhere in the world. In similarity to that reported for subadult and adults (Weng et al. 2007b, Bruce et al. 2006, Bonfil et al. 2005), juvenile white sharks in this study combined periods of residency at a limited number of specific sites with directed movement patterns between these sites. Three primary residency regions were identified in eastern Australia, Corner InletLakes Entrance (Victoria), Stockton BeachHawks Nest (New South Wales) and Fraser Is (Queensland). The Corner InletLakes Entrance region was previously identified as a seasonal aggregation site for juvenile white sharks by Malcolm et al. (2001). Bruce et al. (2006) hypothesized that white sharks in eastern Australia formed part of a single, highly mobile population. Data from this study support this hypothesis. It seems logical to conclude, based on the movement patterns

38


documented in this study, that many if not all of the juvenile white sharks at Stockton Beach are the same individuals that occur seasonally in Victoria and Queensland.

The highly mobile nature of juvenile white sharks provides little further evidence of pupping grounds in Australian waters. No sharks either sighted or tagged at Stockton Beach during this study, or the Corner Inlet area, were small enough to be considered neonates or youngoftheyear (YOY). Sightings of YOYsize white sharks have been reported at Stockton Beach and sharks of this size are reported in data from the NSW shark control program (D. Reid, NSW DPI, pers. comm, Malcolm et. al. 2001), but these are rarely encountered in these residency regions compared to juveniles in the two to fiveyear classes. It is thus clear that these primary residency regions represent juvenile habitat rather than pupping grounds.

The location of pupping grounds and the habitat requirements of youngoftheyear white sharks requires further targeted research in Australian waters. Malcom et al. (2001) suggested that areas of the Great Australian Bight may include pupping grounds based on the capture of both adult sharks and neonates. During the course of this study, a neonate white shark was caught in coastal waters near Port Phillip Bay (Vic) and photographically documented suggesting that pupping may also occur in some Bass Strait waters or adjacent areas.

The identification of a limited number of primary residency regions in eastern Australia suggests that these sites may be ideal locations for monitoring juvenile white shark abundance and thus offer opportunities to monitor population status by way of a recruitment index. This is discussed further under ‘Survey and monitoring methods’ below. Why these specific regions, as opposed to other similar beach areas along the east Australian coast, are attractive to white sharks is unclear. The presence of abundant prey such as schools of Australian salmon, mullet and various other elasmobranchs (eg rays), no doubt plays a role. However, the presence of such prey is not unique to these specific regions.

Sharks tagged at Stockton Beach showed a remarkable level of site fidelity. Nearly all activity was restricted to the northern half of the beach. Sharks that departed and subsequently returned did so to this same area, even when such journeys took individuals hundreds of kilometres distant. One exception was Shark S7, which moved from Stockton Beach and took up residence at Hawks Nest on the northern side of Port Stephens. This shark then remained at Hawks Nest until its tag’s last transmission. These patterns suggest that individual juvenile white sharks can take up residence in very specific areas of beach front and remain in or return to very specific sites. Interestingly, observations by local members of the public in the Port Stephens area suggest that the sites where our tagged sharks remained resident are not the only areas in the region where juvenile white sharks occur (G. Trinkler, Port Stephens pers. comm.). Beach areas between Port Stephens and Forster are known for juvenile white shark sightings and it is possible that individuallyspecific areas of residency may extend along a broader area of this coast than the tagging in this study suggests. The site specificity of sharks and the linkages between beaches in the region needs further evaluation to ensure that monitoring of, for example, the Stockton Beach site will provide a representative sample of abundance in this overall region.

Other data also suggest that a limited number of specific beaches along the NSW coast represent juvenile habitat for white sharks. Captures of white sharks in the NSW shark control program are not evenly distributed among meshed beaches. Of the 51 beaches meshed from 19902007, 29 beaches recorded captures of white sharks, but two beaches (Stockton and Wattamolla) accounted for approx 30% of all captures (Figure 34). Stockton Beach accounted for nearly 20% of all captures supporting the importance of this area for juvenile white sharks.

39


0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0

ava bo ch

b dy ki mo

no re sw

war

Beach

Percentage of total cap

tures

Stockton Beach

Wattamolla Beach

Figure 34: Captures of white sharks in the NSW Shark Control Program (19902007) by individual beach (Data courtesy of D. Reid, NSW Department of Primary Industries); beach identification (other than Stockton and Wattamolla) has not been included, but is available on request.

Interestingly, it is the southern area of Stockton Beach where meshing occurs, not the northern end where tagged sharks in this study were resident. This further suggests that individual sharks, when resident, may be specifically so to particular areas of a beach. Overall, it is clear that white sharks are neither randomly nor evenly distributed in coastal environments, and some areas are more attractive and regularly used as residency sites than others. This provides further support for the ‘hotspot (café)highway’ hypothesis of Bruce et al. (2006) for eastern Australia.

Juvenile white sharks also occur in other Australian states, suggesting that important juvenile habitat may exist in other regions. Such reports include areas of Western Australia, South Australia and western Victoria (R. McAuley, WA Fisheries pers. comm., K. Stannard, Whitetag Victoria pers. comm., Malcolm et al. 2001). The linkages between these various regions and the eastern Australian sites is unclear. Similarly, it is unclear if the juvenile sharks present in such areas are sourced from a common or from different pupping grounds. Identification and investigation of these other juvenile residency regions and the linkages between them is a critical requirement for further research.

Three juvenile white sharks spent periods seaward of the continental shelf in open ocean waters. One of these individuals (Shark S5) took 28 days to cross the Tasman Sea at a mean swim speed of 3.7 km h 1. The movements of S5 were highly directed with no evidence that this shark spent any periods of temporary residency during the Tasman Sea crossing. The shark’s trajectory on departure from shelf waters suggests that its path was initially influenced by the southward flow of the East Australian Current. The shark then arced steadily in a southeasterly direction to approx 44 oS 160 oE, where it abruptly changed trajectory and headed in an easterly direction to New Zealand. This is an area of the Tasman Sea where the northern boundary of a broad frontal zone, Subtropical convergence zone (or subtropical frontal zone – STF), is commonly located (Stanton and Ridgway 1988). It is possible that meeting the northern boundary of the STF prompted the shark to change trajectory and suggests the possibility that such oceanographic

40


features may play a role, for white sharks, in navigation in the open sea. A similar change in trajectory occurred for a white shark travelling south of South Africa after it encountered a similar broad frontal zone – equivalent to the STF. This shark then also turned abruptly east and tracked a highly directed path to the Western Australian coast (Bonfil et al. 2005).

The timing of Shark S5’s movements was remarkable. This shark did not show any evidence of slowing its pace of movement until it reached Cook Strait and the Kapiti Coast in New Zealand waters some 33 days after departing the NSW coast. Within days of its arrival, reports of white shark sightings of various sizes made by fishers and recreational divers were independently conveyed to the authors by New Zealand colleagues. This area of Cook Strait offers a summer jack mackerel (Trachurus sp) and gummy shark (Mustelus sp) fishery and has previous records of interactions with white sharks (C. Duffy, Department of Conservation, New Zealand, pers. comm.). It thus seems that this particular juvenile white shark, timed its departure from NSW to reach Cook Strait and coincide its arrival with a seasonal hotspot of prey abundance.

Movements of juvenile white sharks into open ocean waters raise the possibility of them interacting with pelagic fishing operations targeting tuna and billfish. Such fisheries previously were not considered as possible threats to juvenile white sharks.

Depth swimming behaviour In general, sharks showed a bimodal pattern of depth preferences, favouring the surface and 60100 m depth zones (Figure 35). This pattern differed little between day and night although there was a general tendency for shallower depths to be occupied during night periods (Figure 36a). This pattern varied between individuals and habitats with some sharks showing marked diel differences in depth preferences – shark S6 for example swam exclusively at depths of 1001000 m during daytime periods when undertaking its offshore excursion (Figure 36b). Details of time spent at depth for each individual shark are contained in Figures 3758.

41


0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (%)

Figure 35: Time spent at depth – all sharks combined

0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (%)

Resident Travelling

(a) (b)

Figure 36: Time spent at depth, all sharks combined (a) Day vs Night; (b) Residency vs Travelling

42


Time at depth details for individual sharks

Shark S5

0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Figure 37: Shark S5 – Time at depth (all)

0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Resident Travelling

(a) (b)

Figure 38: Shark S5 – Time at depth (a) Day vs Night; (b) Resident vs Travelling

Shark S5 made a Tasman Sea crossing between central NSW and New Zealand from 128 December (Figure 39).

43

Time spent (%) 0 10 20 30

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000



0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (%)

0 10 20 30 40 50 60 70

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

(a) (b)

Figure 39: Shark S5 Time at depth during crossing of Tasman Sea, 128 December 2007 (a) All ; (b) Day vs Night

Shark S6

44

(a) 0 10 20

Time spent (%)

30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

Depth

60 100

100 200

200 300

300 500

500 1000

>1000

Day Night

0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (% )

Resident Travelling

(b)

Figure 41: Shark S6 – Time at depth (a) Day vs Night); (b) Resident vs Travelling


Shark S6 also spent a limited period of its track in waters up to 160 km seaward of the continental shelf (17 October1 November 2007). Depth profiles during this period varied from the overall pattern above (Figure 42).

0 10 20 30

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (% )

0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

(a) (b)

Figure 42: Shark S6 – Time at depth during offshore excursion, 17 October1 November 2007: (a) all; (b) day vs night.

45

Time spent (%)

0 10 20 30 40 50 60

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Figure 43: Shark S7 – Time spent at depth (all)

0 20 40 60 80

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (%)

Resident

(a) (b)

Figure 44: Shark S7 – Time at depth (a) Day vs Night; (b) Resident. Note: no data available for travelling phase


Shark S7

46

Time spent (%)

0.00 10.00 20.00 30.00 40.00

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000


0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Resident Travelling

(a) (b)



Shark S8

47

0 10 20 30 40 50 60

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

(a) 0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Resident

(b)

Figure 48: Shark S9 – Time at depth (a) Day vs Night; (b) Resident. Note: no data available for travelling periods


Shark S9

0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)


48

0 20 40 60 80

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Dep

th

Time spent (%)

Day Night

Dep

th

(a) Time spent (% ) (b) 0 20 40 60 80

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Resident Travelling

Figure 50: Shark S10 – Time at Depth (a) Day vs Night; (b) Resident vs Travelling


Shark S10

0 20 40 60 80

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)


49

Time spent (%)

0 20 40 60 80

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000


0 20 40 60 80 100

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (% )

Day Night

0 20 40 60 80 100

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (% )

Resident

(a) (b)

Figure 52: Shark S11 – Time at depth (a) Day vs Night; (b) Resident. Note: no data available for travelling periods


Shark S11

50


Shark S12

0 10 20 30 40 50 60 70

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)


0 20 40 60 80

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

0 10 20 30 40 50 60 70

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Resident Travelling

(a) (b)

Figure 54: Shark S12 – Time at depth (a) Day vs Night; (b) resident vs travelling

51

Time spent (%) 0 10 20 30

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000



Shark S13

0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (% )

Day Night

0 10 20 30 40 50

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (% )

Resident Travelling

(a) (b)


52

Time spent (%)

0 10 20 30 40 50

Depth

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000


0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Day Night

(a) 0 10 20 30 40

Surface

5 10

10 20

20 30

30 40

40 50

50 60

60 100

100 200

200 300

300 500

500 1000

>1000

Depth

Time spent (%)

Resident

(b)

Figure 58: Shark S14 – Time at depth (a) Day vs Night; (b) Resident. Note: no data available for travelling phase


Shark S14

53


Discussion – depth swimming behaviour Juvenile white sharks, when in coastal waters, showed a propensity for depths between the surface and 100 m. All sharks showed a bimodal pattern of depth utilisation with strong preferences for the 05 m and 60100 m depth zones. Depth utilisation had two forms – either time spent at the surface and bottom over 60120 m depths or between the shore in shallow water (< 5 m) and the 100120 m depth contours. These behaviours have direct consequence for fisheries interactions. Fishing inside the 100120 m depth contour in primary residency regions has a higher chance of interactions with juvenile white sharks than such activities directed further offshore. This effect was noted by Pepperell (1992) in his historical analysis of sharks caught by gamefishing off the NSW coast where a decrease in numbers of juvenile white sharks taken relative to other shark species occurred when such fishing effort shifted from inshore grounds to the shelf edge and beyond.

The banning of commercial gillnetting within three nautical miles (5.6 km) of the Victorian coast in 1988 is believed to have had a benefit for juvenile white sharks (CunninghamDay 2001, Stevens 2002) by reducing fisheries interactions, albeit its introduction was targeted at minimising the take of school sharks (Galeorhinus galeus) from inshore waters. Whilst there has no doubt been a positive effect from this restriction, even this area falls well short of the 100120 m depth contours in most regions. Tagged juvenile white sharks commonly transmitted positions between 6 and 14 km, and up to 40 km, from shore when in the primary residency region off Corner InletLakes Entrance.

The 60100 m depth zone has been noted as significant during travelling periods for white sharks in other areas of Australian waters. This was the depth zone followed by a subadult female shark moving between Spencer Gulf and the Head of the Great Australian Bight, South Australia, and is a region over which several tracks of other subadult and adult white sharks overlap through the same region (authors’ unpublished data, Bruce et al. 2006).

Overall, there was no significant difference between depths occupied by sharks during the day and night although this varied somewhat between individuals and was dependent on habitat (shelf vs offshore waters). In general, sharks spent a higher proportion of time in shallower depths during periods of residency, although data are somewhat skewed by the deep diving behaviour of three sharks during offshore travelling periods.

Deep diving behaviour The depths recorded by the three sharks that undertook offshore excursions (up to 984 m) are the deepest depths to which juvenile white sharks have been reported diving. Weng et al. 2007a reported juvenile white sharks diving to nearly 400 m and Dewer et al. (2004) reported dives to 240 m for a single YOY shark. Depths reached by juveniles in this study are equivalent to those reported for subadult and adult white sharks (Weng et al. 2007b, Bonfil et al. 2005, Boustany et al. 2002). Depth per se is probably not a constraint to juvenile white sharks in either Australian or other waters but rather it is likely that temperature is a deciding factor – see temperature section below.

Bimodal depth behaviour was also a feature during these offshore excursions with sharks most commonly occupying the surface and one of the three depth zones between 3001000 m. These depths are also similar to those reported for subadult and adult sharks during offshore excursions (Weng et al. 2007b, Bonfil et al. 2005). Other reports of deep diving by juvenile white sharks in

54


Australian waters have come from underwater video footage. A juvenile white shark was filmed using a baited underwater video camera system set on the bottom at a depth of 343 m in the GAB in March 2008 (R. Daley/A. Williams CSIRO, pers. comm.) and a juvenile white shark was filmed by an ROV at approximately 350 m depth off Exmouth, WA in early 2007 (D. Riggs, pers. comm.).

Although subadult and adult white sharks have been recorded undertaking open ocean forays and cross ocean basin excursions (Weng et al. 2007b, Bonfil et al. 2005, Boustany et al. 2002), juvenile white sharks have previously been considered to be coastal life history stages. Our data now confirms that white sharks 1.92.1 m can similarly make both offshore forays as well as cross ocean basin excursions and, in doing so, dive to depths close to 1000 m. These behaviours off eastern Australia expose juvenile white sharks to incidental capture in pelagic longline fisheries targeting tuna and swordfish where due to their size, they may be mistaken for makos (Isurus oxyrinchus).

Temperature

Sharks experienced temperatures ranging from 68 oC to 2426 oC with the majority of their time in temperatures ranging from 1422 oC. The most common temperature range occupied (over 45% of their time) was 1820 oC (Figure 59). This varied slightly between individuals (Figure 60). The exceptions were sharks S5, S6 and S8 which recorded slightly cooler peak ranges of 1418 oC. These three sharks recorded offshore and deep diving behaviour. The highest temperature ranges were recorded by sharks S6 and S12 at 2426 oC. Shark S6 recorded these temperatures in southern Queensland; S12 recorded these temperatures on a single day (14 December) during an extended period when no positions were recorded. Shark S9 recorded more extreme temperatures of <4 oC to 6 – 8 oC and > 30 oC on 27 February and 15 March 2008 respectively but neither depth data nor positions were reported for these dates thus it is possible that these data were corrupted on transmission.

55

4< 46 68 8 01 2101

4121

6141

8161

0281

2202

4222

6242

8262

03>

0

5

10

15

20

25

30

35

40

45

50

Time spent (%)

Temperature (C)

Figure 59: Time spent at temperature – all sharks combined. Note : The extremely low (<4 oC) and high (>30 oC) temperatures recorded by Shark S9 have not been included in this summary as they are unlikely to be accurate – see text.


56


0

10

20

30

40

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperatue (C)

Time spen

t (%)

0

10

20

30

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

0

10

20

30

40

50

60

70

<4 46 68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time sp

ent (%)

0

10

20

30

40

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

0

10

20

30

40

50

60

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

0

10

20

30

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

Shark S7 Shark S8

Shark S5 Shark S6

Shark S9 Shark S10

Figure 60: Time at temperature for sharks tagged at Stockton Beach (cont).

57

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

1 2 0

Shark S11

0

1 0

2 0

3 0

4 0

5 0

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

6 0

Shark S12

0

2 0

4 0

6 0

8 0

1 0 0

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

0

1 0

2 0

3 0

4 0

5 0

<4 46

68

810

1012

1214

1416

1618

1820

2022

2224

2426

2628

>30

Temperature (C)

Time spen

t (%)

Shark S13 Shark S14

Figure 60 (cont.): Time at temperature for sharks tagged at Stockton Beach.


Data from the returned PSAT tag recorded temperatures ranging from 6.75 oC to 23.3 oC, the lowest temperature being recorded at a depth of 984 m off central NSW (Figure 61).

58


Figure 61: Temperature – depth profiles for six subadult sharks (dark blue; CSIRO unpublished data) and Shark S6 (light blue).

Discussion

The minimum temperature encountered by juvenile white sharks in this study, at 6.75 oC, was lower than those reported in other studies on juveniles (8.49.0 oC) but within ranges reported for white sharks in general (Weng et al. 2007a, Bonfil et al. 2005, Dewar et al. 2004, Boustany et al. 2002, Klimley et al. 2002) and specifically white sharks in Australian waters (Figure 61).

Not surprisingly, due to their offshore and deep diving behaviour, Sharks S5, S6 and S8 experienced the lowest temperatures ranging from 810 oC to 1012 oC. These are within the ranges reported by other authors for juvenile white sharks (Weng et al. 2007a, Dewar et al. 2004, Klimley et al. 2002). The PSAT tag returned from shark S6 recorded its lowest temperature of 6.75 C during a dive to 984 m. This temperature was not reflected in the SPLASH tag data because no data were transmitted for the particular day that the shark made that depth.

Tracking during this study was conducted over the springsummer period, the timing being determined by the availability of sharks for tagging at Stockton Beach. Thus, these data may be biased by the time of year the study was undertaken. Tracking during autumn and winter is required to fully elucidate the influence of temperature on the spatial dynamics and distribution of juvenile white sharks in Australian waters. This will require future tagging and tracking in southern State waters (eg Victoria or South Australia) commencing during the summerautumn period.

59


ACOUSTIC TAGS Results

At the time of writing this report, data downloads during the period after sharks were tagged were available for few existing listening stations on the east coast of Australia. In addition, many stations planned under AATAMS and OTN arrays were yet to be deployed. Downloads of existing stations and deployments of new stations are expected to occur during the latter part of 2008 and presumably with them, further indications of juvenile white shark movement patterns.

Data downloads were available for stations forming part of the SEACAMS network at Seal Rocks, 60 km north of Stockton Beach (data supplied by NSW DPI). Two stations recorded 10 detections of shark S6 on 1 December 2007 from 1353 to 1357 (local time). SPLASH tag data placed shark S6 approximately 17 km southeast of Seal Rocks at 1900 on 1 December and subsequently some 78 km south of Seal Rocks on 2 December (Figure 62). This corresponded to the return journey of S6 after it had travelled as far north as Fraser Island in Queensland (Figure 22).

Sydney

0 25

kilometres

New South Wales

50

Stockton Beach

Newcastle

Broughton Is

Port Stephens

Seal Rocks

Forster

%%%%%%%%% Seal Rocks (SEACAMs) listening stations

%%%%%%%%%

A

B

Figure 62: Positions for Shark S6 (filled pink circles) relative to Seal Rocks listening station array. A – SPLASH tag location on 1 December 2007; B – SPLASH tag location on 2 December 2007.

60


Discussion

The detection of shark S6 at listening station arrays deployed by NSW DPI primarily to examine movements of grey nurse sharks confirms the utility of widespread deployments of such technology in programs such as SEACAMS, AATAMS and OTN, all of which contribute to the Integrated Marine Observing System (IMOS) framework in Australian waters. Previous adhoc detections of subadult and adult white sharks tagged with acoustic tags at the Neptune Islands in South Australia have been recorded at listening stations targeting grey nurse sharks at South West Rocks and in crossshelf arrays set off Albany and Esperance (Western Australia) targeting juvenile southern bluefin tuna (authors’ unpublished data; A. Hobday, CSIRO pers. comm.). The extensive coastal movements of white sharks of all sizes in Australian waters makes them ideal candidates for monitoring movements via listening stations. The identification of primary residency regions based on satellite tracking suggests that targeting these regions with listening station deployments will maximise the efficacy of listening station programs for examining white shark movement patterns.

At present, all tags on white sharks (juvenile, subadult and adult) in Australian waters are located externally and attached as per this project via a stainless steel arrowhead and short tether. It is unknown for juvenile white sharks what the rate of tag shedding is, however subadult and adult white sharks have been observed to shed such tags at various periods after tagging. The longest period where acoustic tags can be confirmed in place and operating after tagging is two years (Bruce et al. 2005a). Considering current tags have up to 10 years of life, a twoyear attachment period does not realise the full potential for this technology and other methods of deploying acoustic tags on white sharks should be investigated. The primary means of securing acoustic tags to fish species (including sharks) is by way of internal placement via surgery (eg Heupel and Simpfendorfer 2002). Such tags are permanently in place and evidence to date is that such tags do not cause adverse reactions in species tagged. Internal placement of acoustic tags in juvenile white sharks would be a practical solution to tag shedding and would eliminate the possible undesirable effects of tag fouling that have been observed in grey nurse sharks tagged with external tags (Anon 2003). Surgical procedures are simple and effective, requiring a small incision into the gut cavity, where the acoustic tag is inserted. In the case of sharks, stitches are rarely required as the musculature of the body cavity effectively closes and secures the wound.

Placing longlife (10year) acoustic tags inside juvenile white sharks combined with the deployment of longterm acoustic listening station arrays in Australian waters offers an incredible opportunity to follow the movement patterns of individual sharks as they progress through various life history stages in Australian waters. Such research, when supported by listening station deployments targeted at primary residency regions (identified for juveniles, subadults and adults), will provide details of the timing of behavioural shifts leading to occupancy of lifehistory stage specific critical habitat. It is recommended that such studies be a focus of white shark research in Australian waters in future years.

SURVEY AND MONITORING METHODS

The identification of a limited number of common primary residency regions suggests that targeted surveys of those regions at the appropriate time of year may provide data on juvenile abundance. Preliminary trials of aerial surveys and vesselbased spotting methods were undertaken at two residency regions – Stockton Beach (vessel survey) and the Corner InletLakes Entrance region (aerial survey).

61


Vesselbased surveys

The success in locating juvenile white sharks at Stockton Beach suggested that regular vesselbased surveys may be useful for monitoring juvenile abundance and patterns of site usage. Initial trials were undertaken over fixed distances during the last day of field operations in October 2007. This trial was then used to design a survey log sheet (Figure 63). NSW DPI subsequently conducted six surveys along the northern end of Stockton Beach, three each on 16 November and 4 December 2007.

Figure 63: Log book used for vesselbased juvenile white shark survey trials at Stockton Beach, NSW.

Methods

Visual surveys of juvenile white sharks were undertaken in an identical fashion to that used for locating white sharks for capture. A 6 m vessel approached the surf zone, recording the depth when the bottom was first visible – this was used as a measure of water clarity. The vessel then steamed parallel to the shore behind the surf zone, where possible keeping the bottom in view so that sharks were easily sighted. Distance surveyed was marked by start and stop positions (GPSbased latitude and longitude), the objective being to cover a 10 km stretch of beach on each transect. The number of sharks sighted, their GPS location and their size was recorded during each transect survey.

Results Vesselbased surveys recorded 25 sightings of juvenile white sharks equating to an average of 0.83 sharks per kilometre of beachfront searched. Sharks were recorded only on surveys

62


undertaken on 16 November 2007. No sharks were sighted in the three survey transects on 4 December. Sharks were most commonly located in the northern area of the survey zone (Figure 64) and this matched the transmitted satellitebased positions of the tagged sharks over their periods of residency. Sharks sighted ranged from 1.82.5 m TL and thus were similar in size range to those sighted during tagging exercises in October 2007. One shark sighted on these surveys was tagged with both SPLASH and acoustic tags, but the identity of this shark could not be confirmed.

Figure 64: Locations of individual white sharks sighted on three vesselbased surveys of Stockton Beach (16 November 2007) by NSW DPI.

Discussion Vesselbased surveys were highly successful in locating juvenile white sharks at Stockton Beach. However, the nature of the activity (close to the surf zone) meant that surveys could only be conducted in low swell conditions and ideally with clear water, cloud free skies and light winds. Although these conditions do not always prevail at Stockton Beach, there is considerable merit in standardising on such conditions to ensure comparability in results between surveys.

Such surveys would appear to be a highly effective measure of shark activity at Stockton Beach.

Aerial surveys

The aerial survey was trialled as part of a larger (snapshot) survey of Victorian waters that served several purposes. First, we were interested in examining surf zone areas throughout Victoria for

63


evidence of other sites where tagging might be undertaken on juvenile white sharks (a similar site to Stockton Beach); second, we wanted to test the hypothesis that sharks could be located from the air in the Lakes EntranceCorner Inlet area identified from satellite tracking data as a primary residency region; third, we wanted to provide firsthand information on the challenges of identifying sharks from the air.

Methods Victorian coastal waters were surveyed from the air from a Westpac Life Saver Rescue plane made available to the project by Surf Life Saving Victoria (SLSVic), (Figure 65).

Figure 65: Westpac Life Saver Rescue plane used for aerial surveys of the Victorian coastline.

Three flight paths were designated and flown over a series of dates in April 2008 (Figure 66). The first of these targeted the Corner InletLakes Entrance area where satellite tag data indicated the location of a primary residency site.

64

Flight path

Survey areas

EssendonAirport

Flight path approx 420 nm Flight path approx 350 nm

Flight path approx 260 nm

Figure 66: Flight paths taken during aerial surveys of Victorian coastal waters by Westpac Life Saver Rescue aircraft in April 2008. Coloured circles indicate positions transmitted from four juvenile white sharks in the area that were tagged at Stockton Beach, NSW.


Results Two sharks estimated at approximately 2.02.5 m were sighted on the survey of the Corner Inlet Lakes Entrance region in the vicinity of a predicted primary residency region (Figure 67).

Both sharks were sighted at the same locality and were within 200 m from shore close to schools of baitfish that were nominally identified as anchovy based on school morphology and behaviour (F. J. Neira TAFI pers. comm.). Sharks were tentatively identified as juvenile white sharks based on morphology, however identification could not be unequivocally confirmed from the air (Figure 68).

65

Melbourne Lakes Entrance

#

Sharks sighted #

Corner Inlet

0 50 100

kilometres

Figure 67: The location of sharks sighted during aerial surveys of the Corner InletLake Entrance primary residency region. Large filled circles are the locations of residency sites identified from satellite tracking of juvenile white sharks. Yellow line indicates the primary residency region for juvenile white sharks in the area.


66


Figure 68: A 2.02.5 m shark, tentatively identified as a juvenile white shark, approaching a school of baitfish in the Lakes Entrance region.

Discussion

Only two sharks were sighted despite searching 100 km of beach front in the Corner InletLakes Entrance region. Despite the low number sighted, sharks were readily spotted over the sand bottom and this would appear to be a highly successful method for counting sharks in shallow surf zone areas. However, in similarity to vesselbased surveys, aerial surveys are only successful where a clear sand bottom is visible, in conditions of light winds, clear skies and clear water, and specifically for juvenile white sharks, only if species identification can be verified by groundtruthing. Groundtruthing is best achieved by vessel as juvenile white sharks are easily approached and identified under good weather conditions.

Overall, both vesselbased and aerial surveys offer promise for developing an abundance index for juvenile white sharks provided they are seasonally targeted at specific localities – the primary residency regions. The movement of individual juvenile white sharks between the limited number of primary residency regions in eastern Australia suggests that monitoring even one of these sites may offer insight into juvenile abundance and recruitment levels over time. The accessibility and logistics available in the vicinity of Stockton Beach suggests that it is an ideal region to establish a longterm juvenile monitoring program by way of targeted vessel and or aerial surveys. Options may exist for local authorities to undertake such surveys and, particularly in the case of aerial based work, local tourist flight operators who regularly fly the Stockton Beach dune and surf zone areas. The latter would require a logbook system similar to vesselbased survey forms above.

67


ACKNOWLEDGEMENTS

This project could not have been completed without the assistance of NSW DPI (Bill Talbot, Peter Gallagher, James Sakker, Dennis Reid, Chris Gallen, Megan Storrie, Nick Otway); Western Australian Fisheries (Rory McAuley, Justin Childlow); Monterey Bay Aquarium (John O’Sullivan), University of Hawaii (Kevin Weng), Mark Payne, David Riggs, George Trinkler, Julian Pepperell, Kent Stannard, Surf Life Saving – Victoria (Brett Ellis) and the Westpac Life Saver Aerial Patrol (Victoria).

REFERENCES

Anon (2003). Review of grey nurse shark tagging research, Brisbane, 8 – 9 September 2003. http://www.environment.gov.au/coasts/species/sharks/greynurse/pubs/greynursetagging.pdf

Bonfil, R., Meyer, M., Scholl, M. C., Johnson, R., O’Brien, S., Oosthuizen, H., Swanson, S., Kotze, D. and Paterson, M. (2005). Transoceanic migration, spatial dynamics and population linkages of white sharks. Science 310: 100103.

Boustany, A. M., Davis, S. F., Pyle, P., Anderson, S. D., Le Boeuf, B. J. and Block, B. A. (2002). Expanded niche for white sharks. Nature 415. 3536.

Bruce, B. D. (2008). White sharks (Carcharodon carcharias). In Sharks of the Open Ocean. E. Pikitch and M. Camhi (eds). Blackwell Scientific.

Bruce, B.D., Stevens, J.D. and Malcolm, H. (2006). Movements and swimming behaviour of white sharks (Carcharodon carcharias) in Australian waters. Marine Biology 150: 161172

Bruce, B. D., Stevens, J. D. and Bradford, R. W. (2005a). Site fidelity, residence times and home range patterns of white sharks around pinniped colonies. Final report to Department of Environment and Heritage. CSIRO Hobart, 41 pp.

Bruce, B. D., Stevens, J. D. and Bradford, R. W. (2005b). Identifying movements and habitats of white sharks and grey nurse sharks. Final report to Department of Environment and Heritage. CSIRO Hobart, 10 pp.

Bruce, B. D., Stevens, J. D. and Bradford, R. W. (2005c). Designing protected areas for grey nurse sharks off eastern Australia. Final report to Department of Environment and Heritage. CSIRO Hobart. 55 pp.

Bruce, B. D. and Stevens, J. D. (2004). Tracking the movement patterns of large white sharks in Australian waters. Final report to the Aquarium of Western Australia and the AQWA Foundation. CSIRO Marine Research Hobart. 25 pp.Bruce, B. D. (1999). Shark behaviour and interactions with atsea aquaculture cages. Proceedings of the Marine Animal Interaction Working Group. Port Lincoln, SA, May 1998. PIRSA.

Bruce, B. D. (1992). Preliminary observations on the biology of the white shark, Carcharodon carcharias, in South Australian waters. In "Sharks: Biology and Fisheries" (Ed. J. G. Pepperell). Australian Journal of Marine and Freshwater Research 43: 111.

68

http://www.environment.gov.au/coasts/species/sharks/greynurse/pubs/greynursetagging.pdf


Cailliet, G. M., Natanson, L. Welden, B. and Ebert, D. (1985). Preliminary studies on the age and growth of the white shark, Carcharodon carcharias, using vertebral bands. Southern Californian Academy of Sciences, Memoirs 9: 49–60.

Cliff, G., Dudley, S. F. J. and Davis, B. (1989). Sharks caught in protective gill nets off Natal, South Africa. 2. The great white shark Carcharodon carcharias (Linnaeus). South African Journal of Marine Science 8: 131 144

CunninghamDay, R. (2001). Sharks in danger: Global shark conservation and status with reference to management plans and legislation. Universal Publishers. 228 pp.

Eckert, S. A. and Stewart, B. S. (2001). Telemetry and satellite tracking of whale sharks, Rhincodon typus, in the Sea of Cortez, Mexico, and the North Pacific ocean. Environmental Biology of Fishes 60: 299 – 308.

Francis, M. P. (1996). Observations on a pregnant white shark with a review of reproductive biology. pp 157–172. In: Great white sharks. The biology of Carcharodon carcharias. Eds. A. P. Klimley and D. G. Ainley. Academic Press, San Diego. 517 pp.

Gunn, J. S., Patterson, T. A., and Pepperell, J. G. (2003). Shortterm movement and behaviour of black marlin Makaira indica in the Coral Sea as determined through a popup satellite archival tagging experiment. Marine and Freshwater Research 54: 515525.

Heupel, M. R., Semmens, J. M. and Hobday, A. J. (2006). Automated acoustic tracking of aquatic animals: scales, design and deployment of listening station arrays. Marine and Freshwater Research 57: 1 – 13.

Heupel, M. R. and Simpfendorfer (2002). Estimation of mortality of juvenile blacktip sharks, Carcharhinus limbatus, within a nursery area using telemetry data. Canadian Journal of Fisheries and Aquatic Sciences 59: 624 – 632.

Jackson, G., O’Dor, R. and Harcourt, R. (2007). Ocean management goes global. ECOS (April – May) 136: 34 – 35.

Klimley, A. P. (1985). The areal distribution and autoecology of the white shark, Carcharodon carcharias, off the west coast of North America. Southern Californian Academy of Science, Memoirs. 9: 1540.

Klimley, A. P., Beavers, S. C., Curtis, T. H. and Jorgensen, S. J. (2002). Movements and swimming behaviour of three species of sharks in La Jolla Canyon, California. Environmental Biology of Fishes 63: 117135.

Malcolm, H., Bruce, B. D., and Stevens, J. D. (2001) A review of the biology and status of white sharks in Australian waters. Report to Environment Australia, Marine Species Protection Program, CSIRO Marine Research, Hobart. 81 pp.

Mollet, H. F. and Cailliet, G. M. (1996). Using allometry to predict body mass from linear measurements of the white shark. pp 8189. In: Great white sharks. The biology of Carcharodon carcharias. Eds. A. P. Klimley and D. G. Ainley. Academic Press, San Diego. 517 pp.

69


Otway, N. and Storrie, M., (2006). SEACAMS: Development, deployment and operation. Oral presentation given at the 2006 Australian Society for Fish Biology Conference, 28 August 1 September 2006, Hobart, Australia. http://www.dpi.nsw.gov.au/research/areas/systems research/aquaticecosystems/outputs/2006/732

Pepperell, J. G. (1992). Trends in the distribution, species composition and size of sharks caught by gamefish anglers off southeastern Australia. Australian Journal of Marine and Freshwater Research 43: 213 – 225.

Pratt, H. L., Jr. (1996). Reproduction in the male white shark. pp 131–138. In: Great white sharks. The biology of Carcharodon carcharias. Eds. A. P. Klimley and D. G. Ainley. Academic Press, San Diego. 517 pp.

Reid, D. D. and Krogh, M. (1992). Assessment of catches from protective shark meshing off New South Wales beaches between 1950 and 1990. Australian Journal of Marine and Freshwater Research. 43: 283296.

Robbins, R. L. (2007). Environmental variables affecting the sexual segregation of great white sharks Carcharodon carcharias at the Neptune Islands, South Australia. Journal of Fish Biology 70: 1350 – 1364.

Stanton, B. R. and Ridgway, N. M. (1988). An oceanographic survey of the subtropical convergence zone in the Tasman Sea. New Zealand Journal of Marine & Freshwater Research 22: 583–593.

Stevens, J.D. (2002). The role of protected areas in elasmobranch fisheries management and conservation. In: S.L. Fowler, T.M. Reed and F.A. Dipper (eds). Elasmobranch Biodiversity, Conservation and Management: Proceedings of the International Seminar and Workshop, Sabah, Malaysia, July 1997. IUCN SSC Shark Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK.

Strong, W.R. Jr., Bruce, B.D., Nelson, D.R. and Murphy, R.C. (1996). Population dynamics of white sharks in Spencer Gulf, South Australia. pp: 401414. in Great White Sharks: The biology of Carcharodon carcharias. A.P. Klimley & D.G. Ainley (eds) Academic Press.

Weng, K. C, O’Sullivan, J. B., Lowe, C. G., Winkler, C. E., Dewar, H. and Block, B. A. (2007a). Movements, behaviour and habitat preferences of juvenile white sharks Carcharodon carcharias in the eastern Pacific. Marine Ecology Progress Series 338: 211 – 224

Weng, K. C., Boustany, A. M., Pyle, P., Anderson, S. D., Brown, B. and Block, B. A. (2007b). Migration and habitat of white sharks (Carcharodon carcharias) in the eastern Pacific. Marine Biology 152: 857894.

Wintner, S. P., and Cliff, G. (1999). Age and growth determinations of the white shark Carcharodon carcharias, from the east coast of South Africa. Fishery Bulletin. 153169.

70

http://www.dpi.nsw.gov.au/research/areas/systems-research/aquatic-ecosystems/outputs/2006/732

APPENDIX 1

Details of juvenile white sharks tagged as part of this project and in 2000 – 2001 Shark 1 Sex Length Age estimates (yr) 2 Date

tagged Tag types3 Location of

tagging Date of last transmission

Days tracked

No. of transmission days

(m) (a) (b) (c)

S1 F 1.8 1.1 2.2 1.8 1/3/00 CS Corner Inlet 18/4/2000 49 42 S2 M 2.4 3.0 4.0 4.6 2/3/01 CS Corner Inlet 23/6/2001 129 71 S5 (3754)

M 2.1 2.0 3.1 3.1 8/10/07 SPL; RC Stockton Beach

20/1/2008 104 78

S6 (3753)

F 1.9 1.4 2.5 2.2 8/10/07 SPL; RC; PSAT

Stockton Beach

17/1/2008 98 40

S7 (3748)

F 2.4 3.0 4 4.6 10/10/07 SPL; RC Stockton Beach

22/11/2007 44 19

S8 (3750)

M 2.6 3.6 4.7 5.6 10/10/07 SPL; RC Stockton Beach

20/1/2008 102 46

S9 (3752)

M 1.9 1.4 2.5 2.2 11/10/07 SPL; RC; PSAT

Stockton Beach

10/1/2008 92 7

S10 (3749)

F 2.5 3.3 4.4 5.1 11/10/07 SPL; RC Stockton Beach

30/12/2007 81 60

S11 (3751)


2/11/2007 22 5

S12 (3755)


29/12/2007 80 17

S13 (3756)

M 2.1 2 3.1 3.1 11/10/07 SPL; RC Stockton Beach

1/11/2007 22 11

S14 (3757)


22/11/2007 43 9

1: Shark numbers are consecutive based on sharks tagged as part of a larger program than solely reported here – sharks S3 + S4 are larger animals reported on elsewhere (see Bruce et al. 2006 for details). Numbers in parentheses provide identification numbers for coded acoustic tags deployed on each shark 2: (a) after Calliet et al. 1985; (b) after Malcolm et al. 2001; (c) after Wintner and Cliff 1999 3: SPL – Wildlife Computers SPLASH tag; RC – Vemco/Amirix coded acoustic tag; PSAT – Wildlife Computers Mk 10 popoff archival tag; CS – CSIRO designed position only tag (see Bruce et al. 2006 for details)

71

spatial dynamics and habitat preferences of juvenile white ... · juvenile white sharks –...

Documents