Site fidelity, residence times and home range patterns of white ...

B. D. Bruce ■ J. D. Stevens ■ R. W. Bradford – CSIRO Marine and Atmospheric

Research, Hobart. Client: Department of the Environment and Heritage

F I N A L R E P O R T J U N E 2 0 0 5

Site fi delity, residence times & home range patternsof white sharks around pinniped colonies

Site fidelity, residence times and home range patterns of white sharks around pinniped colonies

FINAL REPORT

B. D. Bruce, J. D. Stevens and R. W. Bradford

CSIRO Marine and Atmospheric Research, Hobart June 2005

Report to the Australian Government Department of the Environment and Heritage Cover design by Lea Crosswell (CSIRO Marine and Atmospheric Research)

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 and Heritage. 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. © Commonwealth of Australia 2005 This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth, available from the Department of the Environment and Heritage. Requests and inquiries concerning reproduction and rights should be addressed to: Assistant Secretary Marine Division Department of the Environment and Heritage GPO Box 787 Canberra ACT 2601

National Library of Australia Cataloguing-in-Publication entry

Bruce, B. D. (Barry David). Site fidelity, residence times and home range patterns of white sharks around pinniped colonies. Bibliography. ISBN 1 921061 00 6. 1. White shark - Habitat - Australia. 2. White shark - Home range - Australia. 3. White shark - Seasonal distribution - Australia. I. Stevens, J. D. (John Donald), 1947- . II. Bradford, R. W. (Russell), 1963- . III. CSIRO. Marine Research. IV. Australia. Dept. of the Environment and Heritage. V. Title. 597.33

Final Report to the Australian Government Department of the Environment and Heritage – June 2005

CONTENTS

1. INTRODUCTION......................................................................................................... 1 1.1 Background ............................................................................................................... 1

1.2 Need .......................................................................................................................... 1

1.3 Objectives ................................................................................................................. 2

2. METHODS .................................................................................................................... 3 2.1 Vemco V16 R-Code acoustic transmitters................................................................ 3

2.2 Vemco VR2 listening stations .................................................................................. 4

2.3 Study sites ................................................................................................................. 6

3. RESULTS ...................................................................................................................... 8 3.1 VR2 monitoring periods ........................................................................................... 8

3.2 R-Code tagging ....................................................................................................... 11

3.3 Detection patterns ................................................................................................... 11

3.4 Residency periods and site fidelity ......................................................................... 16

3.5 Diel patterns of detection ........................................................................................ 19

3.6 Effects of berleying................................................................................................. 23

3.7 Movement between sites......................................................................................... 34

3.8 Shark pinniped interactions..................................................................................... 35

4. DISCUSSION .............................................................................................................. 36

5. FURTHER DEVELOPMENT................................................................................... 39

6. CONCLUSIONS ......................................................................................................... 39

7. ACKNOWLEDGEMENTS ....................................................................................... 39

8. REFERENCES............................................................................................................ 40


1

1. INTRODUCTION

1.1 Background White sharks (Carcharodon carcharias) are large, active apex predators occurring mainly in temperate coastal ecosystems. They have a global distribution and at times occur in oceanic environments, in the tropics, and down to depths of at least 1200 m. They are most common over the continental shelf (often close inshore) of southern Australia, South Africa, northern California and the north-east United States (Compagno 2001). While there is still much to learn of their biology and behaviour (see reviews in Klimley and Ainley 1996) white sharks are considered to be particularly vulnerable to human exploitation and are protected in many parts of the world. In Australia, white sharks occur mainly around the south of the continent but extend northwards to northern Queensland and northern Western Australia (Last and Stevens 1994). While they have not been commercially targeted in Australia on a large scale, they were taken by recreational anglers in some areas and are still taken in beach meshing programs and as by-catch in some commercial fisheries. Because of concerns over their population status they are currently protected in all State and Commonwealth waters. This includes listing on the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) that requires a Recovery Plan for the species. Some research on white sharks, mainly short–term movement patterns and some biological and behavioural work, was carried out in the 1980s in Australia (Tricas 1985; Strong et al. 1992; Bruce 1992). However, the recent protective legislation and necessity for a Recovery Plan has been the impetus for increased research effort into the population status of this species. Malcolm et al. (2001) and Bruce et al. (in press) provided information on the biology and status of white sharks in Australian waters and investigated movement patterns using a combination of conventional and electronic tags. Data from these studies suggest that individual white sharks can travel over 100s, perhaps 1000s of km. These sharks are generally uncommon and the chances of interactions with fishing operations or other activities are relatively low for most areas. However, there are areas (sites) where white sharks aggregate or where individuals frequently revisit. These include pinniped colonies that are prime feeding areas for adult and sub-adult animals. These are most likely critical habitat areas for this species and it is in these areas where they are most vulnerable to impacts from fishing operations.

1.2 Need Despite enacting protective legislation in all Australian waters there is still little firm knowledge of how best to make such protection effective. Methods of reducing by-catch in commercial fisheries, identification of critical habitat, the potential effectiveness of protected areas and the effects of berleying by ecotourism operators for viewing white sharks around pinniped colonies are critical issues for the effective protection and management of white shark populations in Australian waters. There is a need to understand critical habitat areas in developing threat abatement plans, in terms of residency periods, site fidelity and seasonal variations in rates of occupancy and movement patterns between these sites. This is required so as to minimise the impacts of fishing on white sharks in these areas.


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We need to understand the influence of repeated berleying at shark viewing sites on shark behaviour, and possible impacts of these activities on interactions between white sharks and pinnipeds (particularly the nationally threatened Australian sea-lion Neophoca cinerea) to provide a scientific basis for the management of white shark activities around pinniped colonies. Understanding white shark movement patterns is important for assessing the likely effectiveness of regional protective areas for their conservation. White shark populations are difficult to monitor and their status in Australia is still difficult to infer from available data. A logbook system is in place at ecotourist sites, one purpose of which is to provide an index of white shark activity that, combined with other developed indices around southern Australia, may be useful in the ongoing monitoring of their population status. To interpret sightings frequency at these sites, information is required on residence times, site fidelity and movements independent to the logbook data and over a continuous time period (rather than dependent on the infrequent presence of ecotourist operators). This is critical for developing a useful index to monitor the future status of white sharks and thus the impact of any threat abatement plan. It is generally believed that white shark predation on juvenile pinnipeds is a significant component of pinniped mortality (Le Boeuf and Crocker 1996). However, very little is known about how (and if) white sharks cue their movement patterns to the seasonal reproductive cycle of pinnipeds. If threat abatement measures for white sharks are effective, it is reasonable to assume that white shark numbers may increase and it will be important to have a greater understanding of these predator-prey relationships. This project aimed to provide information on site fidelity, residency times, activity patterns and the effects of berleying on white sharks through the use of acoustic listening stations at three locations. The original project collected data from April 2001 to October 2002. A subsequent project extended this period of data collection from October 2002 to March/May 2003 at the North Neptune Islands.

1.3 Objectives

(1) Provide information on site fidelity, residence times and home range patterns of white sharks.

(2) Determine movement patterns of white sharks between different sites (pinniped colonies) used to monitor white shark population status in South Australia.

(3) Determine the effects of repeated berleying at particular sites on the frequency at which white sharks visit those sites, their periods of residency and their behaviour.

(4) Examine seasonal movement patterns of white sharks in relation to pupping events at fur seal and sea-lion colonies in order to assess interactions between white sharks and pinnipeds and how these interactions may be influenced by changes in white shark numbers or behaviour.


3

Additional objective (5) To integrate data collected during an extension DEH project (Bruce et al. 2005) into this study to extend the data series to March/May 2003.

2. METHODS Vemco VR2 listening stations were deployed on the seabed at three locations (pinniped colonies) in South Australia and used to monitor the presence/absence of individual white sharks tagged with Vemco V16 R-Code acoustic transmitters.

2.1 Vemco V16 R-Code acoustic transmitters The V16 R-Code tags are 72 mm long and 17 mm in diameter, powered by a lithium battery giving a transmitter life of about 18–24 months. The tags transmit a unique six pulse string every 20–69 seconds on a frequency of 69 kHz. The pulse string contains the transmitter’s identification code. We attached the tags to a stainless steel dart-head via a 170 mm long stainless wire tether (Fig.1). Tags were implanted in the dorsal musculature of free-swimming sharks that were attracted to the boat with berley. Tagging techniques followed procedures already established with the Shark Cage-Dive Operators Association (SCDOA) and the Department of the Environment and Heritage (DEH) and are described in Bruce (1992). Tagging was carried out by researchers, or the SCDOA, under the supervision of the project team and under permit from Primary Industries and Resources South Australia (PIRSA) and with Animal Ethics clearance. The original plan was to tag 10 sharks at each of three locations.

Figure 1. R-Code acoustic tag with attachment head and tether.


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2.2 Vemco VR2 listening stations The listening stations are 360 mm long and 40 mm in diameter and powered by a single lithium C cell that can detect R-Code tags within a range of about 500 m underwater (Fig. 2). The VR2s record when R-Code tagged sharks enter the site, how long they stay there and when they leave, and can recognize the individual tags by their unique code. The VR2s have to be down-loaded and re-batteried at about six-month intervals. Each VR2 was bolted to a central, upright steel post projecting from a bottom mooring consisting of a concrete-filled, light truck tyre of approximately 80 kg weight (Fig. 3).

Figure 2. Vemco VR2 acoustic listening station.


5

Light truck tyre (concrete filled)

central post assembly

tie-down loops

subsurface bouy

Figure 3. Mooring design for listening stations. The moorings were deployed from the South Australian Research and Development Institute’s (SARDI) research vessel MRV Ngerin (Fig. 4) in April 2001.

Figure 4. Deploying moorings at Dangerous Reef from MRV Ngerin. Following initial deployments, which resulted in fairly heavy weed growth, subsequent units were wrapped in PVC tape and anti-fouled (Fig. 5). Retrieval of the VR2s was accomplished by divers working from a shark-proof cage deployed by a SCDOA vessel.


6

Listening stations were located from GPS positions. The divers unbolted the VR2 and replaced it with another unit. Data were down-loaded from the units via a PC interface.

Figure 5. Listening station and mooring showing initial signs of fouling.

2.3 Study sites Three study locations were chosen, the North Neptune Islands (35o 14’S, 136 o 04’E), South Neptune Islands (35o 20’S, 136 o 07’E), and Dangerous Reef (34o 49’S, 136 o 13’E) (Fig. 6a). The North and South Neptune Islands each have colonies of New Zealand fur seals (Arctocephalus forsteri) and Australian fur seals (Arctocephalus pusillus doriferus) and Dangerous Reef has a colony of Australian sea-lions (Neophoca cinerea). Three listening stations were deployed at each location in April 2001 (Fig. 6b–c).


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Figure 6a. Location of study sites at North and South Neptune Islands and Dangerous Reef.


8

0 0.5

Kilometres

North Neptune Is.

NN3

1

NN1

NN2

Figure 6b. Location of listening stations at the North and South Neptune Islands. Note the original NN2 station was lost due to rough weather. A replacement station was deployed inside the bay (arrow).

DR1

0 0.5

Kilometres

DR2

Dangerous Reef

1

DR3

Figure 6c. Location of listening stations at Dangerous Reef.

3. RESULTS

3.1 VR2 monitoring periods Listening stations were retrieved, re-batteried and redeployed in September/October 2001, March 2002, September 2002 and April 2003. Data analysed in this report covers the period from April 2001 to April 2003. Some minor repositioning of listening stations was carried out to allow better diving access during the project. The initial NN2 station

South Neptune Is.

SN3

SN1

SN2

Kilometres

0 0.5 1


9

was lost in heavy weather during the first deployment period and was replaced further into North Neptune bay to avoid heavy wave action and surge. Station SN2 proved difficult to service due to poor conditions at that site during retrieval trips. Battery failures limited detection coverage, particularly during the summer months. Table 1 and Fig. 7 show the monitoring periods for the different stations. Table 1. Monitoring periods for VR2s at the Neptune Islands and Dangerous Reef. North Neptune Is.

Total monitoring period (d)

Successful monitoring periods

No. days successfully monitored

NN1 735 18/4/01 – 13/12/01 20/3/02 – 8/4/03

642

NN2 735 8/10/01 – 11/2/02 20/3/02 – 31/8/02

534

NN3 735 18/4/01 – 28/4/01 8/9/01 –9/9/01 20/3/02 – 24/9/02

414

Overall 735 18/4/01 – 11/2/02 20/3/02 – 8/4/03

702

South Neptune Is.




SN1 735 18/4/01 – 8/2/02 21/3/02 – 7/4/03 698

SN2 735 18/4/01 21/3/02 – 10/2/03

403

SN3 735 18/4/01 – 10/12/01 21/3/02 – 7/4/03

639

Overall 735 18/4/01 – 8/2/02 21/3/02 – 7/4/03

699

Dangerous Reef




DR1 735 18/4/01 – 27/10/01 22/3/02 – 6/4/03

595

DR2 735 18/4/01 – 11/11/01 22/3/02 – 17/10/02 6/4/03

610

DR3 735 22/3/02 – 6/4/03 402 Overall 735 18/4/01 – 11/11/01

22/3/02 – 6/4/03

610


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18

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Figure 7. Listening station coverage (in black) at the Neptune Islands and Dangerous Reef.


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3.2 R-Code tagging A total of 28 sharks were tagged with R-Code transmitters; with deployments carried out throughout the project period (Table 2). We experienced difficulty in tagging sharks at both the South Neptune Islands and Dangerous Reef due to both the limited number of trips to these sites by operators and a lack of sharks attracted when on site. The decision was taken to deploy the remaining tags on sharks at the North Neptune Islands due to the more reliable access to sharks there, and because preliminary data showed movement between the North Neptune and South Neptune Islands, and the North Neptune Islands and Dangerous Reef. Table 2. R-Code tags deployed on white sharks at the Neptune Islands and Dangerous Reef. Site Number tagged Date first shark

tagged Date last shark tagged

Dangerous Reef 2 12/5/01 12/5/01 North Neptune Is. 22 16/6/01 28/9/02 South Neptune Is. 4 10/9/01 21/3/02

3.3 Detection patterns The total numbers of detections of tagged sharks over the study period at each of the sites are shown in Fig. 8. Due to a combination of battery failures and lost stations, there were periods of no coverage from any of the stations at the North Neptune Islands from 12 February 2002 to 19 March 2002 (36 days), at the South Neptune’s from 9 February 2002 to 20 March 2002 (37 days) and at Dangerous Reef from 12 November 2001 to 21 March 2002 (126 days) (Table 1, Fig. 7).


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3/0

20

9/0

2/0

2-

20

/03

/02

12

/11

/01

-2

1/0

3/0

2

Figure 8. Total number of shark detections at the North and South Neptune Islands, and Dangerous Reef (all sharks and stations combined; shaded bars are periods of no coverage).


13

Num

ber

ofta

gged

shar

ks

Figure 9. The pattern of detection (days after tagging) for sharks tagged at the North and South Neptune Islands and Dangerous Reef (all tags and all stations combined). At the North Neptune Islands, most detections of tagged sharks (n = 24) occurred in the period up to about 75 days after tagging, although detections continued for the duration of the experiment. A distinct group of detections occurred from about 360 to 425 days


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after tagging (Fig. 9). Six sharks were tagged at the South Neptune Islands, with all detections recorded within 13 days of tagging (Fig. 9). Only two sharks were tagged at Dangerous Reef, with all detections recorded within 25 days of tagging (Fig. 9). The duration of visits of tagged sharks to the three sites are shown in Fig. 10. A visit is defined as a period of consecutive days in which a particular shark was detected by any of the stations at the site. About 60 visits at the North Neptune Islands were of one day’s duration and while visits of up to 19 consecutive days were recorded, individual visits of between one and 12 days comprised most of the records (Fig. 10). All visits at the South Neptune Islands and Dangerous Reef were of between one and five days duration (Fig. 10). However, a shark had only to be missed for one day by the stations for it to break the continuous period for that particular visit. Although lack of detection for a period of one day does not necessarily mean that the shark had left the site, there were records of sharks moving back and forth between the North and South Neptune Islands over consecutive days, indicating that this indeed may occur.


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Num

ber

ofvi

sits

Figure 10. Duration of visits by tagged sharks to the North and South Neptune Islands, and Dangerous Reef (visit defined as period of consecutive daily detections).


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3.4 Residency periods and site fidelity The residency of sharks was assessed based on the percentage number of days that they were detected between the dates of tagging and the last retrieval of the listening stations. The average time between tagging and last retrieval of the listening stations at the North Neptune Islands (less any days when the listening stations were inoperative) was 488.5 days (range 169–643 days). Only five sharks were tagged less than a year before the end of the experiment. Tags 58, 173, 180, 183 and 185 were tagged 284, 174, 177, 174 and 176 days respectively, before the listening stations were removed. The proportion of time that tagged sharks spent at the North Neptune Islands varied from 0.5–20.8% (Fig. 11). Of the two sharks present for the greatest proportion of time at the North Neptune Islands, tag 36 (16.7%) was tagged 564 days before, and tag 58 (20.8%) was tagged 284 days before, final retrieval of the listening stations. Most tagged sharks spent 10% or less of their time at this site. The proportion of time that tagged sharks spent at the South Neptune Islands varied from 0.4–0.9% and the two sharks tagged at Dangerous Reef spent 1.4% of their time there (Fig. 11). Some sharks disappeared soon after tagging and were not recorded again, others reappeared sporadically and some were present for an extended period, disappeared and then returned about one year later suggesting seasonal visitation (Fig. 12).


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36 38 41 42 43 48 51 52 53 55 56 57 58 59 60 62 64 173

180

183

18539

Perc

enta

ge

Tag num ber

Figure 11. The number of days that sharks tagged at the North and South Neptune Islands, and Dangerous Reef were recorded there (days detected/effective monitoring days between tagging and last retrieval of the listening stations X 100).


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Days af te r tagging

Pre

sen

ce/A

bse

nce

De tec t ions No cove rage

0 50 100 150 200 250 300 350 4000

1

0

1

0

1

0

1

Shark 41

Sha rk 62

Sha rk 36

Sha rk 48

Figure 12. Different patterns of detection for individual tagged sharks at the North Neptune Islands over the study period.


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3.5 Diel patterns of detection North Neptune Islands (NN) The pattern of detections for all three stations combined (NN1, NN2 and NN3) showed a clear daily signal, being relatively low at night and increasing to a peak around midday. This was mainly a reflection of station NN2 located inside the bay, which had the greatest number of detections (Fig. 13). Station NN3, also located inside the bay, had a similar pattern peaking at 1300 h, but the increase in detections during the morning and the decrease in the afternoon were not quite as regular (Fig. 13). Station NN1 was outside the bay and it showed a more even spread of detections throughout the 24-h period, with no clear pattern and with the greatest number of detections recorded between 0700–0900 h (Fig. 13).


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100

0

NN1

NN2

NN3

1 3 5 7 9 11 13 15 17 19 21 23

Time (h)

Tota

lde

tect

ion

s

Figure 13. Hourly pattern of detections (all sharks) at the three North Neptune stations.


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South Neptune Islands (SN) The pattern of detections for all South Neptune stations combined showed peaks at night and during the day. Detections were low between 1800 and 1900 h, and then increased into the night remaining high until 0400 h before declining between 0500–0800 h. Detections then increased during the day, although there was a low period between 1300–1400 h (Fig. 14). When the stations were examined individually, SN1 reflected the pattern in the combined data with higher levels at night (2400–0300 h) and reaching a smaller peak in the middle of the day. The lowest period of detections was from 1900–2000 h (Fig. 15). Station SN2 was based on relatively little data and generally showed a higher level of detections from 0900–2100 h. Station SN3 showed a rather irregular pattern, but with generally higher detections from 1100–2000 h (Fig. 15).

1 3 5 7 9 11 13 15 17 19 21 23

Time (h)

Tota

lD

ete

ctio

ns

0

100

150

200

50

Figure. 14. All detections for combined South Neptune stations.


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200

150

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0

25

20

15

0

100

75

50

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0

SN1

SN2

SN3

1 3 5 7 9 11 13 15 17 19 21 23

Time (h)

Tota

ld

ete

ctio

ns

5 0

10

5

Figure 15. Hourly pattern of detections (all sharks) at the three South Neptune stations.


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Dangerous Reef (DR) Few detections were recorded at Dangerous Reef as only two sharks were tagged there (Fig. 16). However, the primary pattern suggested a higher level of detections during the day than at night. Station DR3 was not included in figure 16 as only two detections were recorded there (at 1900 h).

1 3 5 7 9 11 13 15 17 19 21 23

Time (h)

Tota

lD

ete

ctio

ns

0

5

10

15

Figure 16. Hourly pattern of detections (all sharks) at Dangerous Reef (hollow bars DR2, solid bars DR1).

3.6 Effects of berleying Most berleying by SCDOA operators is carried out inside the bay at the North Neptune Islands. Berleying is often maintained throughout the 24-h period, but is most intensive during daylight hours from about 0700–1900 h. Only occasional berleying is carried out either at the South Neptune Islands or Dangerous Reef. The latter site has been closed to berleying since November 2002. A comparison of detection patterns at the North Neptune Islands shows a clear difference between inside and outside the bay, with a clear daily signal in detections inside the bay (stations NN2 and NN3) peaking at midday (Figs. 13 & 17). In contrast, the pattern at NN1 outside the bay shows a more even spread of detections through the 24-h period (Fig. 13). While this is the pattern that might be expected if berleying was influencing the sharks inside the bay, the main seal colony is also inside the bay. Since white sharks are predominantly visual hunters, they might be expected to increase their visits inside the bay during the day. Further evidence supporting a ‘normal’ daily signal near pinniped colonies is provided by the pattern at Dangerous Reef (Fig. 16), although the data are more limited, and to a certain extent at South Neptune (where the stations span the area of the seal colony). However, the pattern of detections at South Neptune also shows high detection levels at night (Figs. 14 & 15).


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1 3 5 7 9 11 13 15 17 19 21 23

Time (h)

Tota

lD

ete

ctio

ns

0

500

1000

1500

Figure. 17. All detections for stations NN2 and NN3 combined. If berleying is influencing the shark’s behaviour, a difference in detection patterns between when the operators were on site and when they were not might be expected, particularly inside the bay where berleying activity is most concentrated. The pattern at NN1, outside the bay and about 800 m away from the main berleying station, showed little difference between days when operators were on site and when they were not. The exceptions were the periods from 0700–1000 when there were generally more detections when the operators were present, and from 1100–1600 h when more detections were recorded during times that the operators were absent (Fig. 18).


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0

4

8

12

0

4

8

12

1 3 5 7 9 11 13 15 17 19 21 23

0

4

8

12

Time (h)

De

tect

ion

s(%

)

NN1

NN2

NN3

Ber ley No ber ley

14

10

6

2

Figure 18. Detection patterns of tagged sharks at the North Neptune stations during berleying and no berley periods (% detections = (detections @x–h/sum(detections for site & treatment)*100.


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At NN2, the pattern of detections during berleying and non-berleying periods was much the same. However, there was a tendency for proportionately more detections between 1000–1900 h during berleying periods (Fig. 18). At station NN3, the pattern between berleying and non-berleying periods was similar with detections peaking at 1100 and1300 h, respectively. On a proportional basis, more detections were recorded between 0900–1200 h during berleying periods than during non-berleying periods (Fig. 18). If berleying is influencing shark behaviour it might be reasonable to expect that the number of detections per day for an individual shark would be higher on berley days compared to no berley days. We examined the mean numbers of detections per day for individual sharks, comparing between berley and no berley days for both the inside–bay and the outside–bay stations. Only sharks that were detected on a minimum of four berley and four no berley days were considered for analyses. Data were log transformed and the ratio of detections on berley:no berley days were compared based on a Normal approximation. On an individual basis, sharks spent significantly more time in the bay during berleying periods as opposed to non-berleying periods (Table 3). The 95% confidence limits indicate that on average sharks spent 1.35 to 5.45 more time in the bay during berleying periods. However, outside the bay there was no difference in the amount of time a shark spent within range of the listening station (Table 3). This indicates that the effects of berleying did not extend to areas outside of the bay. Table 3: Mean number of detections for individual sharks on berley and no berley days inside the bay and outside the bay at North Neptune Island.

Inside Bay Outside Bay Shark ID Berley No berley ln (B/NB) Shark ID Berley No berley ln(B/NB) 36 89.4 44.4 0.70 36 21.9 15.5 0.34 43 99.7 20.8 1.57 39 3.7 2.4 0.44 54 1.9 1.8 0.047 41 7.3 6.2 0.16 58 20.0 10.1 0.68 52 12.7 7.9 0.48 62 45.8 6.2 2.00 53 7.2 3.2 0.80 173 3.1 5.6 –0.58 183 2.0 3.5 –0.57 185 4.0 13.9 –1.24 If berleying is influencing shark behaviour it might also be reasonable to expect that the number of sharks visiting a site would be higher on berley days compared to no berley days. Overall this does not appear to be the case (Fig. 19). Statistically we examined the mean number of sharks present (by month) on berley and no berley days for both the inside–bay and the outside–bay stations. Only months with greater than one shark for each berley/no berley category were considered for analysis. Data were similarly log transformed and the ratio of detections on berley:no berley days were compared based on a Normal approximation.


27

Freq

uenc

y(%

)

No . sha rks pe r day Figure 19. Frequency distribution of the number of sharks recorded per day at station NN1 (outside the bay) and stations NN2 and NN3 (inside the bay) on berley and no berley days (frequency = number of days with x sharks/number of berley or no berley days x 100). In total there were 133 berley and 390 no berleying days within the bay. Outside the bay there were 172 berley and 407 no berley days. There were no significant differences in the mean number of sharks visiting either the inside–bay or the outside–bay sites (Table 4). This indicated that berleying was not actively attracting more sharks to the study site.


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Table 4: Mean number of sharks detected by month on berley and no berley days inside the bay and outside the bay at North Neptune Island (the number of different sharks per month per category are shown in parenthesis). Inside Bay Outside Bay Month Berley No berley Berley No berley Jan. 0.29(1) 0.37 (2) 0.00 (0) 0.00 (0) Feb. 0.00 (0) 0.20 (2) 0.00 (0) 0.00 (0) Mar. 0.00 (0) 0.09 (1) 0.00 (0) 0.00 (0) Apr. 0.00 (0) 0.13 (2) 0.00 (0) 0.10 (1) May 0.00 (0) 0.08 (1) 0.00 (0) 0.09 (1) Jun. 0.64 (3) 0.69 (2) 0.08 (2) 0.43 (3) Jul. 1.00 (1) 0.37 (1) 1.35 (6) 0.33 (5) Aug. 0.33 (1) 0.59 (2) 0.25 (1) 0.66 (4) Sep. No coverage No coverage 1.93 (9) 1.91 (8) Oct. 1.06 (6) 1.36 (6) 1.93 (6) 1.49 (12) Nov. 2.00 (4) 1.18 (8) 1.00 (2) 0.70 (9) Dec. 1.57 (4) 0.86 (6) 0.80 (3) 0.54 (5) We also looked for possible influences of berleying at the individual shark level by examining the pattern of detections for eight sharks inside the bay at North Neptune. However, at this level the amount of data were often limiting. The majority of sharks (36, 43, 51, 56, 62) followed the pattern of having most detections during the day and while there were often slight differences in the pattern between berleying and non-berleying periods, there was nothing obvious to suggest that these differences were due to the effects of berleying (Figs. 20–23, shark 62 not shown).

2 4 6 8 10 12 14 16 18 20 22

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Figure 20. Detections by hour for shark–tag 36 at stations NN2 and NN3 (black bars = berley days; hollow bars = no berley days).


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Figure 23. Detections by hour for shark–tag 56 at stations NN2 and NN3 (black bars = berley days; hollow bars = no berley days). Shark 58 (Fig. 24) showed a more expanded period of diel activity but the highest levels were still detected from 0700–1600 h for berleying and non-berleying periods combined. A minor peak in activity was recorded at 0400 h during non-berleying periods. During berleying periods, the shark was consistently recorded from 0900–1800 h over several non–consecutive berley days. Shark 52 (Fig. 25) showed an atypical pattern of detections within North Neptune bay. Apart from an activity peak at 1200–1300 h, most activity was detected during the night time period with a peak at 2100 h. Few detections were recorded during berleying periods and these were all during the 1800–2100 h period. Shark 53 (Fig. 26) showed a mostly daytime detection pattern during berleying periods, although there was a minor peak between 0200–0600 h. Activity during non-berleying periods was less clear and more evenly spread over the 24-h period, with the exception of a peak between 0100 and 0300 h. This peak comprised visits on several non–consecutive days, so appears to be a consistent pattern in this shark.


31

2 4 6 8 10 12 14 16 18 20 22

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Figure. 24. Detections by hour for shark–tag 58 at stations NN2 and NN3 (black bars = berley days; hollow bars = no berley days).

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Figure 26. Detections by hour for shark–tag 53 at stations NN2 and NN3 (black bars = berley days; hollow bars = no berley days). Little berleying is carried out at South Neptune Island, so examining the detection patterns of sharks at this site would make a useful comparison. However, only three of the 14 sharks recorded at South Neptune Island were recorded sufficiently frequently to plot the diel frequency of their detections. Shark 47 (Fig. 27) was detected between the hours of 0600 and 2100 h, with a peak in activity at 1700 h. Insufficient detections were recorded to comment further on the diel pattern. Shark 52 (Fig. 28) recorded the highest number of detections of any shark recorded at South Neptune. Data were only available during berleying periods and showed a pattern of detections that was higher at night and that peaked at 0100 h. Few detections were recorded during the day. Interestingly, shark 52 also had a primarily night-time activity pattern when within the bay at North Neptune (Fig. 25), in contrast to the daytime activity pattern of other sharks at this site. However, the data at the North Neptune Islands were limited.


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2 4 6 8 10 12 14 16 18 20 22

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Figure 27. Detections by hour for shark–tag 47 at South Neptune Island (black bars = berley days; hollow bars = no berley days).

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Figure 28. Detections by hour for shark–tag 52 at South Neptune Island (black bars = berley days; hollow bars = no berley days). Shark 185 (Fig. 29) showed a different activity pattern that extended throughout the 24-h period, with most detections between 1700–0100 h.


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0

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Time (h) Fig. 29. Detections by hour for shark–tag 185 at South Neptune Island (black bars = berley days; hollow bars = no berley days).

3.7 Movement between sites Individual sharks tagged at each of the three sites are shown in Table 5, as are sharks recorded at these sites. Sharks were recorded moving between North and South Neptune Islands, from North Neptune to Dangerous Reef and from Dangerous Reef to North Neptune.

Twelve sharks of the 22 tagged at North Neptune were recorded at South Neptune (54.5%). Only four sharks were tagged at South Neptune and none of these were recorded at North Neptune. Of the two sharks tagged at Dangerous Reef, one was recorded at North Neptune (50%), and one shark tagged at North Neptune was recorded at Dangerous Reef (5.3%). One shark, tagged at North Neptune, was recorded at all three sites.


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Table 5. Sites at which sharks were tagged and recorded. Sites recorded Site tagged Shark NN SN DR North Neptune (NN) 36 X X 38 X 39 X 41 X 42 X 43 X X 48 X X 51 X 52 X X 53 X X 55 X 56 X X 57 X X X 58 X 59 X X 60 X X 62 X X 64 X 173 X 180 X 183 X X 185 X X South Neptune (SN) 40 X 47 X 63 X 65 X Dangerous Reef (DR) 54 X X 61 X

3.8 Shark pinniped interactions The pinniped colonies at the Neptune Islands consist mainly of New Zealand fur seals (Arctocephalus forsteri), together with a few Australian sea-lions. In contrast, the colony at Dangerous Reef is mainly Australian sea-lions. New Zealand fur seals pup in early to mid December and the pups take 8–9 months before they are weaned. The pups first venture into the water in about mid January and from then until about April both the pups and adults (which have to return regularly to feed their pups) are probably at their most vulnerable (Nick Gales, Australian Antarctic Division, Hobart, personal communication). During this time, when they are close to the island they are mainly out of the water at night. In contrast, New Zealand fur seals at the Neptune Islands are probably least vulnerable from September to November when they are not tied to their pups and are away from the islands feeding for longer periods. Australian sea-lions pup on a 17.5–month cycle and at Dangerous Reef the pupping periods over the course of this study would have been as follows:


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Start of pupping season End of pupping season February 1999 August 1999 August 2000 February 2001 February 2002 August 2002

4. DISCUSSION It was intended to tag approximately equal numbers of sharks at the three sites. Due to logistical difficulties this was not possible and only two sharks were tagged at Dangerous Reef, and four at the South Neptune Islands. The remaining tags were deployed at the North Neptune Islands, making a total of 22 for that site. As planned, three listening stations (VR2s) were deployed at each site. Unfortunately, battery failures in some VR2s and the loss of one station due to bad weather resulted in breaks in monitoring coverage over the study period, although between 402 and 698 days were successfully monitored at each site. Based on the North Neptune Islands, the site for which most data were available, sharks were generally recorded in the days immediately following tagging with the overall number of detections (all tags combined) dropping to a low level after about 80 days. This suggests that some of the tagged sharks remained in the general area of the North Neptune Islands for up to about two and half months following tagging. There was considerable variation for individual sharks, with some showing no seasonal pattern, while others left the site and then reappeared about a year later suggesting a seasonal occurrence. At pinniped colonies elsewhere, individual white sharks have been reported at the Farallon Islands off northern California during autumn in different years, suggesting seasonal visits (Anderson and Goldman 1996). One shark at the Farallons was sighted 15 times over seven seasons, in the same area off the islands. This shark was sighted only twice at different locations at the islands (Goldman and Anderson 1999). Two sharks identified at the Farallons were also recorded considerable distances away (one of them in southern California) also in autumn, but in different years, suggesting alternate feeding locations (Anderson and Goldman 1996). At the North Neptune Islands, there was evidence that some sharks were more transient while others spent longer periods at this site (up to 21%), although the average amount of time individuals were recorded there over the study period was less than 10%. Of 43 white sharks identified from tags or distinctive marks by Strong et al. (1992) from Dangerous Reef, the Neptune Islands and a number of other islands in the lower Spencer Gulf region between April 1989 and February 1991, 49% were subsequently re-sighted, always at their original locations. One female was seen on 24 occasions over a 580-day period, and two other females were seen 15 times over periods of 179 and 207 days. These three sharks were only seen at Dangerous Reef suggesting a relatively high degree of site attachment for these individuals. Acoustic tracking studies carried out previously in the area showed three patterns of movement described by Strong et al. (1992) as ‘downstream circling’, ‘island patrolling’ and ‘inter-island cruising’. Downstream circling was thought to be in response to remnants of the berley trail used to attract them,


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with the sharks criss-crossing the area downstream of the boat for periods up to 12 h after the cessation of berleying. Island patrolling was where the shark swam more freely around the particular island but didn’t travel more than 9 km from the shore during the tracking period. This behaviour was presumably related to hunting pinniped prey on the island. During inter-island cruising sharks took a more linear path with occasional visits to other islands en route. In South Australia, it would seem that white sharks have a relatively large home range that encompasses a number of island groups, and other habitats, that the sharks visit on a semi-regular basis checking them out for potential prey. This may be the pattern for the whole year, or at certain seasons they may make longer migrations to target prey sources in other locations. White sharks tagged in South Australia have been recaptured in northwest Australia, the head of the Great Australian Bight, and in New Zealand (Bruce et al. in press). Juvenile white sharks tracked in Victoria have been shown to seasonally migrate up the New South Wales coast, and probably into Queensland (Malcolm et al. 2001). Recent satellite tracking results have shown movement of a 3.6 m male from the Neptune Islands to the Rockhampton area in Queensland (23 o S) where it remained from June–October, before returning to Bass Strait in November and the Neptune Islands in January (our unpublished data). Another white shark tagged in October off Bremer Bay, Western Australia, with a pop-off archival tag (PSAT) moved to the North West Cape region (22 o S) of Western Australia in November (our unpublished data). Results from this study, where about half of the sharks tagged at North Neptune visited South Neptune (with some individuals making the journey several times), and where there was movement between the Neptune Islands and Dangerous Reef, support these observations. Acoustic tracking work at the Farallons in California documented movements equivalent to the island patrolling pattern in South Australia. Goldman and Anderson (1999) found that larger sharks (>4 m) tended to be more site-specific at the islands than smaller individuals and they suggested these older more experienced sharks tended to revisit sites where they had been successful in the past. Smaller individuals were still relatively inexperienced at hunting pinnipeds and tended to have a larger activity space round the islands. Goldman and Anderson (1999) thought that white sharks at the Farallons might stay longer than they did at any particular island in South Australia. Their explanation was that the Farallons had a higher density of pinnipeds (during autumn) than any of the islands in South Australia, where there were many more islands with pinniped colonies but with lower densities. However, Boustany et al. (2002) found that PSAT tagged white sharks at the Farrallons spent about 80% of their time in an open-ocean region of the north-eastern Pacific. Acoustic tracking of tiger sharks (Galeocerdo cuvier) in Hawaii showed movement patterns containing elements of both island patrolling and inter-island cruising that suggested relatively large home ranges encompassing more than one island and involved traversing of offshore waters (Holland et al. 1999). The overall diel pattern of detections at the North Neptune Islands showed a strong daily signal peaking between 1200–1300 h within the bay at stations NN2 and NN3. However, NN1 (outside the bay) showed a more even spread of detections through the 24-h period with no clear pattern and with the greatest number of detections recorded between 0700–0900 h. The pattern of detections for all South Neptune stations combined showed peaks


38

at night and during the day. This was mainly a reflection of station SN1. Stations SN2 and SN3 were based on less data, but generally showed increased detections during the day. Dangerous Reef also showed generally higher detection levels during the day. An increase in detections during the day may reflect sharks swimming closer to shore perhaps related to visual hunting of pinnipeds. A previous 17.5-h active track of a white shark at the Neptune Islands (our unpublished data) showed an offshore movement during the night and then a return close to the island the following morning. At Ano Nuevo, northern California, Klimley et al. (2001) monitored movements of tagged white sharks with a radio-acoustic positioning system over a two month period. Five tagged sharks visited the island repeatedly during periods ranging from 11 to 18 days with the sharks staying near the island both during the day and night. Observations on predation bouts on pinnipeds at the Farallon Islands (Klimley et al. 1992) suggested daytime feeding and these authors noted this was consistent with a high density of cone receptors at the center of the white shark’s retina. Although rods (which function in low light) are present in this species retina, their structure and the arrangement of the tapetal guanine plates are not orientated for maximum reflection of light. The latter are found in nocturnally active shark species (Gruber and Cohen, 1985). The majority of berleying by SCDOA operators is inside the bay at the North Neptune Islands in the vicinity of stations NN2 and NN3. While berleying may be maintained at a low level through the night, the intensity of berleying increases from about 0700 h to 1800 h. The diel patterns of detection at North Neptune are different inside and outside the bay. There is a strong daily signal in detections inside the bay compared to a more even detection pattern outside the bay at station NN1. However, the main seal colonies are inside the bay and as white sharks are primarily daytime hunters (based on the structure of their retina) this would seem to be a reflection of normal behaviour. A similar increase in daytime detections was evident at Dangerous Reef, but to a much lesser degree at South Neptune, where there are also seal colonies. The highest detection levels at station SN1 were actually at night. There was a generally consistent pattern between sharks with the main activity inside the bay at the North Neptune Islands during the daytime period of approximately 0600–1800 h, for both berleying and non–berleying periods. There was a possible bimodal peak in daytime activity that was sometimes detected during both berleying and non-berleying periods. This suggests that this bimodal pattern may not be in response to berleying, but a normal pattern of behaviour. There was no pattern among sharks to suggest a significantly different behavioural response during berleying periods. There did appear to be a proportional increase in the number of detections at station NN3 and NN2 during the day during periods of berleying. This was not evident at station NN1 outside the bay. This suggests berleying may have a localised effect resulting in sharks already present in the bay remaining there for a longer period of time compared with non-berleying periods. This localised effect, however, does not extend beyond the immediate area of berleying within the bay. There was some evidence of a difference in behaviour between sites for one shark (shark 52) that had a primarily night-time detection pattern at South Neptune but peaks in detections at 1300 h and 2100 h in North Neptune Bay.


39

5. FURTHER DEVELOPMENT This study has demonstrated the potential for automated monitoring of tagged white sharks at pinniped colonies in South Australia to examine residency periods and site fidelity. Since these sites are probably important habitat for larger white sharks, it would be desirable to continue this listening station work at these sites for a longer period. This is particularly so in the light of logistic problems such as battery failure in the VR2s, loss of VR2s due to weather and the difficulty experienced in tagging sufficient sharks at the South Neptune Islands and Dangerous Reef. It is necessary to combine this work with active tracking of white sharks in the area, using acoustic telemetry and pop-off archival (PSAT) and satellite tagging to provide more information on activity space, home range and seasonal migrations.

6. CONCLUSIONS While we intended to monitor white shark movement at three pinniped colonies in the lower Spencer Gulf area, logistic problems resulted in most data being collected for one site, North Neptune Island. Detection patterns of tagged sharks suggested that most individuals remained in the area of the Neptune Islands for up to two and a half months, with individual visits usually lasting one to six days, although some sharks were continually detected for two weeks or more. Sites may be revisited on a seasonal or more sporadic basis as some sharks appear more resident to the area while others are more transient. Movements between different sites in this study, together with previous tracking and sighting data, suggest that white sharks in this region have a relatively large home range encompassing several island groups that they utilize for feeding. At certain times of the year they may migrate out of the area. The diurnal detection patterns for most sites suggest that white sharks are more active in the area during the day where they hunt pinnipeds using their visual sense; this observation is supported by the structure of their eye that is better adapted for daytime vision. Berleying appears to have a localized effect increasing the detection rate of tagged sharks for a relatively short period at sites close to the berleying operation.

7. ACKNOWLEDGEMENTS We are grateful to the White Shark Cage Dive Operators Association in South Australia, in particular to Rolf Czabayski of the ‘Calypso Star’, Ian Gordon, Rodney and Andrew Fox for help in deploying and retrieving listening stations and tagging sharks. Thanks also to Kate Rodda (SARDI), the skipper and crew of the MRV Ngerin, John Beaumont


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(SA Police) and Grant West (CSIRO Marine and Atmospheric Research) for logistic support, and to Mark Bravington (CSIRO Marine and Atmospheric Research) and Simon Wotherspoon (University of Tasmania) for advice and help with the statistics. This work was funded by The Natural Heritage Trust through the Australian Government Department of the Environment and Heritage.

8. REFERENCES Anderson, S. D., and Goldman, K. J. (1996). Photographic evidence of white shark movements in California waters. California Fish and Game 82 (4): 182–186. 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: 35–36. Bruce, B. D. (1992). Preliminary observations on the biology of the white shark, Carcharodon carcharias, in South Australian waters. In: Sharks: Biology and Fisheries Proceedings of an international conference on shark biology and conservation, Taronga Zoo, Sydney, Australia, 25 February–1 March 1991. (Ed. J. G. Pepperell). Australian Journal of Marine and Freshwater Research 43: 1–11

Bruce, B. D., Stevens, J. D., and Bradford, R. W. (2005). Identifying movements and habitats of white sharks and grey nurse sharks. Final Report to the Department of Environment and Heritage. CSIRO Marine Research, Hobart, Tasmania. 10 pp. Bruce, B. D., Stevens, J. D., and Malcolm, H. Movements and swimming behaviour of white sharks (Carcharodon carcharias) in Australian waters. Marine Biology. In press. Compagno, L. J. V. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, lamniformes and orectolobiformes). FAO species catalogue for Fishery Purposes No.1, Vol.2. 269 pp. Goldman, K. J., and Anderson, S. D. (1999). Space utilization and swimming depth of white sharks, Carcharodon carcharias, at the South Farallon Islands, central California. Environmental Biology of Fishes 56: 351–364. Gruber, S. H., and Cohen, J. L. (1985). Visual system of the white shark, Carcharodon carcharias, with emphasis on retinal structure. Memoirs of the Southern California Academy of Science 9: 61–72.

Holland, K. N., Wetherbee, B. M., Lowe, C. G., and Meyer, C. G. (1999). Movements of tiger sharks (Galeocerdo cuvier) in coastal Hawaiian waters. Marine Biology 134: 665–673.


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Klimley, A. P., Anderson, S. D., Pyle, P., and Henderson, R. P. (1992). Spatiotemporal patterns of white shark (Carcharodon carcharias) predation at the South Farallon Islands, California. Copeia 1992: 680–690. Klimley, A. P., and Ainley, D. G. (Eds.). (1996). Great white sharks. The biology of Carcharodon carcharias. Academic Press, San Diego, 517 pp. Klimley, A. P., Le Boeuf, B. J., Cantara, K. M., Richert, J. E., Davis, S. F., and Van Sommeran, S. (2001). Radio-acoustic positioning as a tool for studying site-specific behavior of the white shark and other large marine species. Marine Biology 138: 429–446. Last, P. R., and Stevens, J. D. (1994). Sharks and rays of Australia. CSIRO. Australia, 513 pp + 84 colour plates. Le Boeuf, B. J., and Crocker, D. E. (1996). Diving behaviour of elephant seals: implications for predator avoidance. In: Great white sharks. The biology of Carcharodon carcharias. (Eds. A. P. Klimley and D. G. Ainley). Academic Press, San Diego, 517 pp. 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. Strong, W. R., Murphy, R. C., Bruce, B. D., and Nelson, D. R. (1992). Movements and associated observations of bait-attracted white sharks, Carcharodon carcharias: a preliminary report. pp 13–20. In: Sharks: Biology and Fisheries. Proceedings of an international conference on shark biology and conservation, Taronga Zoo, Sydney, Australia, 25 February–1 March 1991. (Ed.). J. G. Pepperell. Australian Journal of Marine and Freshwater Research 43: 349 pp. Tricas, T. C. (1985). Feeding ethology of the white shark Carchardon carcharias. Memoirs of the Southern California Academy of Sciences 9: 81–91.

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