Assessment of Thresher Shark vulnerability to the Australian … · 2016-07-19 · Assessment of...

Assessment of Thresher Shark vulnerability to the Australian commercial and recreational fisheries

M. Heard and C. Huveneers

SARDI Publication No. F2015/000619-1 SARDI Research Report Series No. 878

SARDI Aquatics Sciences

PO Box 120 Henley Beach SA 5022

November 2015

Final Report to Nature Foundation South Australia Inc.

Heard, M. and Huveneers, C. (2015) Thresher Shark Vulnerability

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Assessment of Thresher Shark vulnerability to the Australian commercial and recreational

fisheries

Final Report to Nature Foundation South Australia Inc.

M. Heard and C. Huveneers

SARDI Publication No. F2015/000619-1 SARDI Research Report Series No. 878

November 2015


II

This publication may be cited as: Heard. M. and Huveneers, C. (2015). Assessment of Thresher Shark vulnerability to the Australian commercial and recreational fisheries. Final Report to Nature Foundation South Australia Inc. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2015/000619-1. SARDI Research Report Series No. 878. 26pp. South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.pir.sa.gov.au/research

DISCLAIMER The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI internal review process, and has been formally approved for release by the Research Chief, Aquatic Sciences. Although all reasonable efforts have been made to ensure quality, SARDI does not warrant that the information in this report is free from errors or omissions. SARDI does not accept any liability for the contents of this report or for any consequences arising from its use or any reliance placed upon it. The SARDI Report Series is an Administrative Report Series which has not been reviewed outside the department and is not considered peer-reviewed literature. Material presented in these Administrative Reports may later be published in formal peer-reviewed scientific literature. © 2015 SARDI This work is copyright. Apart from any use as permitted under the Copyright Act 1968 (Cth), no part may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owner. Neither may information be stored electronically in any form whatsoever without such permission.

Printed in Adelaide: November 2015 SARDI Publication No. F2015/000619-1 SARDI Research Report Series No. 878

Author(s): M. Heard and C. Huveneers Reviewer(s): A. Mackay Approved by: J. Tanner Science Leader – Marine Ecosystems Signed: Date: 23 November 2015 Distribution: Nature Foundation SA, SAASC Library, University of Adelaide Library,

Parliamentary Library, State Library and National Library Circulation: Public Domain

http://www.pir.sa.gov.au/research


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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ......................................................................................................... IV

EXECUTIVE SUMMARY ........................................................................................................... 1

1. INTRODUCTION ................................................................................................................ 2

1.1. Background.................................................................................................................. 2

1.2. Objectives .................................................................................................................... 3

2. REPORT ............................................................................................................................. 4

Methods .............................................................................................................................. 4

Results and Discussion ....................................................................................................... 6

3. CONCLUSION ...................................................................................................................22

REFERENCES .........................................................................................................................23


IV

LIST OF FIGURES

Figure 1. Unstandardised catch and catch per unit effort (CPUE) of thresher sharks (Alopias sp.)

by the Gillnet Hook and Trap Sector of the Southern and Eastern Scalefish and Shark

Fishery…………………………………………………………………………………………… 12

Figure 2. Spatial representation of catch and catch per unit effort (CPUE) of thresher sharks

(Alopias spp.) by southern gillnet fishers from 1998 to 2011……………………………….. 13

Figure 3. Alopias vulpinus with Mini-PSAT prior to release (Photo – Paul Rogers) ……… 19

Figure 4. Deployment and pop-up locations of the Mini-PSAT deployed on a 1750 mm FL female

Alopias Vulpinus near Portland, Victoria in December 2012……………………….. 20

Figure 5. Depth and temperature profile of A. vulpinus throughout Mini-PSAT deployment. DAL

= Days at liberty following tag deployment…………………………………………………… 21

Figure 6. Depth distribution (% frequency) for A. vulpinus during night (21:00 – 05:00h; black

bars) and day (06:00 – 20:00h; shaded bars)…………………………………………….. 21

LIST OF TABLES

Table 1. Descriptive statistics and reliability analysis for the variables used to measure

tournament anglers beliefs about catching, releasing and the existence value of sharks. Item

wording is identical to the survey. Items were measured on a five-point scale with responses

ranging from (0) strongly disagree to (4) strongly agree…………………………………….. 16

Table 2. Binary logistic regression analysis testing the effect of tournament angler beliefs about

catching, releasing and the existence value of sharks on their behaviours when fishing for pelagic

sharks…………………………………………………………………………………… 17


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ACKNOWLEDGEMENTS

Funding was provided by Nature Foundation SA Inc Research Grants, Save Our Seas

Foundation, Neiser Foundation, Humane Society International, SARDI Aquatic Sciences and

Flinders University. Paul Rogers assisted with the pop-up satellite tag deployment. This project

was only possible through the assistance of recreational anglers and game fishing clubs. We

thank Shane and Deb Sanders, Brodie Carter, Dennis and Kerry Heineke, Paul Irvine, Roger

Chadderton, Dave Magilton, Marty Ellul, Michael Drew and Chris Heard for their assistance during

the capture and satellite tagging of sharks. Surveys were conducted at tournaments organised

by; Bass Strait Game Fishing Club, Portland Sport and Game Fishing Club, Port MacDonnell

Offshore Angling Club, Sydney Game Fishing Club, Newcastle and Port Stephens Game Fish

Club, Jervis Bay Game Fishing Club and Adelaide Game Fishing Club. We thank the organisers

at these clubs for their assistance and support. This study was conducted under the Flinders

University animal welfare ethics permit E349 and Social and behavioural research ethics was

approved by the Flinders University Social and Behavioural Ethics Committee (Approval no.

5398). Tagging was conducted under the Victorian Department of Primary Industries general

research permit RP 1048.


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EXECUTIVE SUMMARY

Common thresher sharks (Alopias vulpinus) are large pelagic sharks that have been identified

as being of conservation concern, because of reported population declines in the Atlantic

Ocean. Alopias vulpinus have been listed as Vulnerable globally on the IUCN Red List and

have recently been included in Appendix II of the Convention on Migratory Species. The

recognition of the vulnerability of thresher sharks to overfishing, and international concerns for

their conservation status, recently led the Indian Ocean Tuna Commission (IOTC) to adopt a

ban on targeting or retaining any species of thresher sharks. Despite the fact that the

conservation need for thresher sharks has been identified internationally, there is a lack of

robust scientific data required to assess the potential threats to populations in Australian

waters. This project uses catch data from fisheries managed by the Australian Fisheries

Management Authority to investigate the spatial and temporal trends in thresher shark

catches. Additionally, we conducted a survey of game and recreational fishing tournaments at

nine locations across South Australia, Victoria and New South Wales to assess the behaviour

and attitude of recreational fishers towards thresher sharks. We also deployed a Mini Pop-up

Satellite Archival Transmitter tag on one adult female common thresher shark, to provide some

insight into their vertical movement patterns and habitat utilisation. The findings of this study

will inform decision making processes specific to the management of thresher sharks in

Australian waters.


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1. INTRODUCTION

1.1. Background

Many species of sharks exhibit life history traits that result in a low intrinsic rate of population

increase (i.e., late maturity, long longevity and gestation period, small litter size, and expected

high juvenile survival rate) (Dulvy et al. 2014). The slow life-history characteristics and low

reproductive rates of some shark species make them more susceptible to overfishing than the

earlier-maturing, shorter-lived teleosts with which they are frequently captured (Stevens et al.

2000). Out of all the shark species, pelagic sharks have been identified as a group of particular

conservation concern due to their specifically low reproductive potential, high susceptibility to

overfishing, increase in direct targeting driven by the demand for shark fin and meat, and

inefficient or unsuitable fisheries management regulations on the high seas (Dulvy et al. 2008;

Camhi et al. 2009).

In a recent review of the extinction risk of chondrichthyans, thresher sharks were ranked as

the most threatened family of sharks and the 7th most threatened family overall (Dulvy et al.

2014). Thresher sharks are commercially fished throughout their ranges, with the common

thresher (Alopias vulpinus) being the most commercially important species (Cartamil 2009).

Serious declines have already occurred where this species has been heavily fished. For

example, in the eastern central Pacific drift gillnet fishery, landings declined to 27% of peak

levels during the 1980’s, and in the Northwest Atlantic reported landings collapsed 80%

between 1986 and 2000 (Hanan 1993; Baum et al. 2003). Due to these declines, A. vulpinus

has been listed in Appendix II of the Convention of Migratory Species and assessed as

Vulnerable globally under the IUCN Red List (Goldman et al. 2009).

The common thresher shark is a relatively large, highly migratory pelagic shark with a

cosmopolitan distribution in subtropical and temperate seas (Last et al. 2009). Current

knowledge of the movements of this species in Australian waters is limited to one satellite tag

deployment off eastern Australia (Stevens et al. 2010). In an assessment of the diet of thresher

sharks off southern Australia, Australian anchovy (Engraulis australis) were found to be the

most important prey species (Rogers et al. 2012).

The recognition of the vulnerability of thresher sharks to overfishing, and rising international

concerns for the conservation status of this group of sharks, led the Indian Ocean Tuna

Commission (IOTC) to adopt a resolution banning targeted fishing for all species of thresher

sharks in 2010. As part of this resolution, each IOTC member, including Australia, is to ensure

that action is taken under their national legislation to implement conservation and

management measures to protect thresher sharks. Apart from tracking studies conducted on


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one bigeye thresher (A. superciliosus) and one A. vulpinus off the east Australian coast,

virtually nothing is known about the movement patterns of thresher sharks in Australian

waters. The extent of interactions with recreational and commercial fisheries and vulnerability

of these sharks to current fishing practices is largely unknown. These data are required to

assess the status of thresher sharks in Australian waters and inform the management of this

species.

1.2. Objectives

The objective of this study was to assess thresher shark vulnerability to Australian commercial

and recreational fisheries through a combination of literature review, database searches,

questionnaire surveys, and tracking. Specifically, we aimed to address the following

objectives:

1. Collate catch data from Commonwealth agencies to assess the extent and magnitude

of thresher shark catches in Australian waters;

2. Conduct a questionnaire survey of the game and recreational fishing industry to assess

the behaviour and attitude of recreational fishers towards thresher sharks and other

pelagic shark species; and

3. Tag common thresher sharks with Mini-PSATs to investigate their movements and

migratory patterns in southern Australia.


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2. METHODS

2.1. Catch Data Analysis

The Australian Fisheries Management Authority (AFMA) was contacted with a request for

catch records for thresher sharks (Alopias sp.) within their jurisdiction. The catch data obtained

included both fisheries-dependent logbook data and independent observer data. Data were

reviewed and compared to changes in management regulations and fishing practices (e.g.

exclusion of international vessels from the fishery), to understand the effect of these changes

on catch rates. The temporal variation in thresher shark catches was estimated for the Gillnet

Hook and Trap Sector (GHTS) by plotting the total number of thresher sharks caught per year

and the catch-per-unit-effort (CPUE) estimated by calculating the total catch of thresher sharks

per km of net set. As thresher sharks are predominantly caught as bycatch in these fisheries,

effort from vessels that had no recorded thresher shark catches for the whole time period was

excluded from the analysis. The CPUE was then calculated for 1° square areas across the

range of the fishery and mapped to identify areas where thresher shark catches are highest.

2.2. Recreational Fishery Survey

Surveys were undertaken at boat ramps and game fishing competitions throughout South

Australia, Victoria, and New South Wales. A short 5–10 min questionnaire (Appendix 1) was

administered to tournament anglers at boat ramps to collect data on angler’s catch of pelagic

sharks, release practices, gear preference, and general perceptions about pelagic sharks and

pelagic shark fishing. Respondents were asked questions about their fishing effort (days

fished) and catch of pelagic sharks (mako, thresher and porbeagle sharks) over the previous

12 months. Fishers who had fished for, or caught, a pelagic shark in the previous 12 months

were also asked about the release rate for each species and reasons for retaining or releasing

sharks, as well as the gear that they use when targeting pelagic sharks. Angler’s attitudes

towards sharks were evaluated through questions pertaining to three different topics: (1)

importance of releasing sharks in a good condition; (2) value of catching sharks; and (3)

conservation of sharks. Belief questions in each of the three domains were grouped and the

mean calculated to create an index for each domain. Scores with a value over two represent

a positive belief with higher mean scores (>3) indicating strong positive beliefs (Table 1).

We used binary logistic regression models to test the combined effects of fishers’ beliefs about

the importance of releasing a shark in good condition, value of catching a shark, and existence

values of sharks on the various behaviours of anglers when fishing for pelagic sharks. Gear

specific behaviours were aggregated into binary measures separating anglers who used best

practice measures (e.g. circle hooks, non-stainless steel hooks and monofilament leader) and


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those who did not. For each logistic regression model, the model was simplified by using a

backward-stepwise regression procedure that eliminated the non-significant variables. Odds

ratios were used as a measure of effect size for each dependent variable (a higher ratio

indicates a greater effect size) and concordance statistics (indicated the percentage of

observations correctly predicted by the model) were used to assess the predictive ability of

each model.

2.3. Satellite Tagging

Fishing was conducted in the Southern Ocean from Port MacDonnell (∼38°10 S 140°17 E) to

Lady Julia Percy Island (∼38°25 S 142°01 E). One common thresher shark was caught on rod

and reel using 37 kg tackle with a drag pressure of 9 kg. Terminal tackle consisted of 14/0

tuna circle hooks baited with blue mackerel attached to 2 m of 90 kg monofilament leader.

Once beside the boat, the shark was restrained in a 3 m long aluminium sling. Fork length

(FL) and sex was recorded and a Mini Pop-up Satellite Archival Transmitter (Mini-PSAT,

Microwave Telemetry Inc., Columbia, MD, USA) was inserted approximately 4 cm into the

shark’s dorsal musculature. The Mini-PSAT was tethered to an umbrella dart-tag head using

a 15 cm-long 136 kg monofilament line (1.3 mm diameter). Following tag attachment, the hook

was removed and the shark released. Location and time of capture were recorded using the

research vessel’s global positioning system (GPS).

The Mini-PSAT was programmed to archive data on pressure (depth), ambient temperature,

and light intensity (geolocation) every two minutes. At the end of the recording period the Mini-

PSAT released from the shark using electrolysis and data were transmitted via the ARGOS

satellite network. However, the full archived dataset only becomes available if the tag is

retrieved. Data from the first 24 hours were not included in the analysis to reduce any possible

effects of the capture and tagging procedure. Percentage histograms of time spent at depth

were plotted and aggregated for night and day using sunrise and sunset times calculated using

the Mini-PSAT light sensor. Data-interpolating variational analysis gridding tools

(http://modb.oce.ulg.ac.be/projects/1/diva) in OCEAN DATA VIEW (ver. 4: Alfred Wegener

Institute, Bremerhaven, Germany) was used to construct depth and time (DAL) integrated

thermal habitat profiles using paired temperature and depth data.


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3. RESULTS AND DISCUSSION

3.1. Catch Data

Due to lack of reporting requirements prior to 1998 on non-target species within Australian

Fisheries Management Authority (AFMA) fisheries, we only analysed records of thresher

sharks caught from 1998 onwards. Over this period, catches from the GHTS of the Southern

and Eastern Scalefish and Shark Fishery (SESSF) represent almost all (98%) of current

catches of thresher sharks retained by commercial fishers in Australian waters.

Nominal catches of thresher sharks in the GHTS were below 320 individuals per year between

1998 and 2011. The number of sharks caught slightly decreased in 2007, when catches went

as low as 130 sharks. CPUE of Alopias sp. was about 0.01 kg.km-1 from 1998 to 2011, apart

for 1999–2000 when catches were higher than 0.06 kg.km-1 and 2010 when CPUE was 0.055

kg.km-1 (Fig. 1). Catches from the GHTS were spread throughout South Australian, Victorian,

and Tasmanian waters, with the highest catches occurring along the Victorian coast and

eastern coast of Tasmania (Fig. 2).

Figure 1. Unstandardised catch and catch per unit effort (CPUE) of thresher sharks (Alopias

sp.) caught by gillnet in the Gillnet Hook and Trap Sector of the Southern and Eastern

Scalefish and Shark Fishery.

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CPUE


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Figure 2. Spatial representation of catch per unit effort (CPUE) of thresher sharks (Alopias

spp.) by southern gillnet fishers from 1998 to 2011.

3.2. Recreational Fishery Survey

We surveyed 201 tournament anglers, of which the vast majority (95%) were male.

Respondents ranged in age from 18 to 74 years, with most in their 30s (39%) or 40s (26%)

and the remainder aged under 30 (20%), or 50 and over (19%). Forty-five percent of

respondents had completed a trade or apprenticeship, 31% had completed high school or

less, and 24% had attained a university degree. There was a fairly even split of respondents

from each state, with 37% from South Australia, 32% from New South Wales, and 31% from

Victoria. Comparison of these results with the 2003 national recreational fisheries survey

(Jarzynski 2003) indicates that our sample was biased towards males, but it is likely that this

is a reflection of the higher participation rates of males in fishing tournaments (Oh et al. 2013).

Most surveyed tournament anglers (58%) had fished pelagic sharks in the year prior to being

surveyed. These anglers caught 4.45 ± 5.35 (mean ± SD) pelagic sharks over this time.

Tournament anglers caught a total of 459 sharks, of which 445 (97%) were Isurus oxyrinchus

CPUE(kg/km net per hour )


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and 14 (3%) were Alopias vulpinus. No anglers reported catching porbeagles (Lamna nasus).

Respondents reported releasing 282 (61%) of the captured sharks and tagging 106 (24%)

prior to release. In total, 70 respondents gave reasons for why they released some or all of

the pelagic sharks that they caught. Approximately 30% of respondents cited size (either ‘too

big’ or ‘too small’) as a reason for releasing pelagic sharks. Tagging, either for research or

competition points, was also cited by approximately 30% of the respondents. The most

common reason for retaining sharks (69%) was for consumption, while retaining sharks for

tournaments accounted for 33% of the reasons cited.

Of the anglers that responded to gear specific questions (n=91), the majority (76%) used only

wire rather than monofilament trace when targeting sharks. Almost half (48%) reported using

only J-hooks, while slightly less (36%) used only circle hooks, with the remainder (16%) using

a combination of both styles when targeting sharks. Half of the respondents reported using

non-stainless steel (i.e. degradable) hooks, with 40% using stainless steel hooks and the

remaining 10% using both stainless and non-stainless hooks.

Anglers’ beliefs about the importance of releasing a shark in a good condition, value of

catching a shark, existence value of sharks, threats to sharks, and protection of sharks are

presented in Table 1. Tournament anglers generally had positive beliefs surrounding the value

of catching a shark, the importance of releasing a shark in a good condition, and the existence

value of sharks. The highest score was recorded for questions about the importance of

releasing sharks in good condition (mean scale score = 3.69 out of 4), so that they survive

and the willingness of anglers to use tackle and handling practices to ensure this.

Logistic regression models revealed that anglers that placed a higher value on catching sharks

were more likely to fish for pelagic sharks (Table 2). Tournament anglers’ decisions to practice

catch and release of pelagic sharks was influenced by positive beliefs around the existence

value of sharks, while the question of whether more regulations were required for fishing of

sharks was also included in the model (Table 2).

Anglers were more likely to use circle hooks if they placed greater value on catching sharks

and had more positive beliefs around the protection of sharks (Table 2). The importance of

releasing a shark in good condition was also included in the hook shape model (Table 3).

Beliefs around existence value of sharks, as well as the belief that sharks need to be protected

led to an increased use of monofilament leader (Table 2). Model concordance statistics show

that the predictive accuracy of the models was quite high for catch and release, hook shape,

and leader material, while the model related to the targeting of pelagic sharks was weaker

(Table 2).


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Positive attitudes towards sharks recorded in this study showed that tournament anglers will

most likely be open to measures that ensure better management of these species.

Tournament anglers are not as supportive of protection of sharks, and need to be better

informed about the potential threats that recreational and commercial fishing may pose to

shark populations. Increased advocacy for the existence value of sharks, as well as the value

of catching a shark should lead to higher rates of catch and release fishing and increased use

of best practice. The impact of social norms and the lack of a relationship between the desire

to release sharks in good condition and the use of best practice methods (e.g. circle hooks)

requires further investigation. Because fishing is more central to the lives of tournament

anglers, as indicated by their greater frequency of fishing when compared to non-tournament

anglers, it is reasonable to expect them to be better informed, more politically organised and

active, and generally more supportive of management rules (Ditton et al. 1992). Gaining the

support of recreational anglers, and particularly tournament anglers, is crucial for the

successful management of pelagic sharks in Australian waters. Increased emphasis on

tagging competitions at tournaments and promotion of best practice developed for the capture

and release of pelagic sharks should lead to lower impacts of tournament anglers on pelagic

shark populations. Subsequent changes in behaviours of tournament anglers may also have

a broader influence on the behaviours of recreational anglers when targeting pelagic sharks.


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Table 1. Descriptive statistics and reliability analysis for the variables used to measure tournament angler’s beliefs about catching, releasing and the existence value of sharks. Item wording is identical to the survey. Items were measured on a five-point scale with responses ranging from (0) strongly disagree to (4) strongly agree.

Behaviour dimensions and items Mean Score

SD

Importance of releasing a shark in a good condition 3.69

I would be willing to use tackle and special handling practices that minimise damage to released sharks 3.55 0.703

I like to ensure that a shark is released in a good condition 3.73 0.517

It is important to me that all the fish that I release survive 3.78 0.486

Value of catching a shark 2.78

Catching a shark adds to the enjoyment of my fishing trip 3.46 0.798

I prefer to catch fish than sharks** 1.61 1.087

I enjoy the challenge of catching a shark 3.49 0.701

I target sharks when I go fishing 2.55 1.125

Existence value of sharks 3.36

It is important to have viable populations of sharks 3.23 0.786

It would be better if there were fewer sharks in the sea** 3.43 0.809

Sharks are a good sign of a healthy marine ecosystem 3.44 0.706

Individual items

Sharks are good to eat 2.81 1.048

Commercial fishing is a threat to shark populations 3.31 0.846

Recreational fishing is a threat to shark populations 1.10 0.954

Sharks need to be protected 1.61 1.185

Sharks should be conserved as they have a right to exist 2.99 0.932

** Item reverse coded for calculation of overall dimension score


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Table 2. Binary logistic regression analysis testing the effect of tournament angler beliefs about catching, releasing and the existence value of sharks on their behaviours when fishing for pelagic sharks.

Model Parameter df Estimate SE X² p Odds ratio

Target pelagic sharks

Value of catching a shark

1 -.521 0.198 6.895 0.009 0.594

Constant 1 1.447 0.467 9.599 0.002 4.249 Model X² = 7.255, df = 2 p = 0.007 Concordance 57%, n = 201 (target pelagic sharks = 84, do not target pelagic sharks = 112)

Catch and release

Existence value of sharks

1 -1.319 0.448 7.291 0.007 0.268

More regulations are required for the fishing of sharks**

1 -0.505 0.271 3.491 0.062 0.603

Constant 1 5.132 1.459 12.362 0.00 169.281 Model X² = 13.784, df = 3, p = 0.003 Concordance 77%, n = 84 (retain all = 22, release all or some = 62)

Hook Shape Sharks need to be protected**

1 0.478 0.201 5.675 0.017 1.614

Value of catching a shark

1 1.243 0.407 9.313 0.002 3.467

Importance of releasing a shark in good condition

1 -0.841 0.494 2.897 0.089 0.431

Model X² = 12.961, df = 3, p = 0.005 Concordance 65%, n = 95 (Circle = 40, J-hook = 55)

Leader Material

Existence value of sharks

1 -1.055 0.477 4.885 0.027 0.348

Sharks need to be protected**

1 -0.403 0.183 4.861 0.027 0.668

Constant 1 1.773 1.040 2.908 0.088 5.887 Model X² = 9.061, df = 2, p = 0.011 Concordance 76%, n = 106 (Wire = 86, Monofilament = 26)

** Item reverse coded for calculation of overall dimension score


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3.3. Satellite Tagging

Fishing was carried out during January to March 2012 and December 2012 to April 2013. Fishing

was conducted on 30 days, and totaled over 200 hours. Despite this extensive effort, only a single

1.75 m FL female A. vulpinus was caught and subsequently tagged, off Portland, Victoria, in

December 2012. Although the Mini-PSAT was programmed to release after 180 days, it released

prematurely after 79 days at liberty. The tag popped-up 12 km away from the tagging location

(Fig. 4). Following pop-up, only 31% of the data recorded by the tag was transmitted over a seven

day period before the battery expired. The tag was, however, recovered near Portland 18 months

later in August 2014, making the full archived record available. This provided depth and

temperature readings at two minute increments for the entire 79-day deployment.

Depth records suggest that the shark went to the continental shelf and returned inshore at least

twice during the tagging period. Dive profiles showed oscillatory dive behavior between the

surface and to a maximum depth of 146 meters. This shark inhabited a temperature range

between 14 °C and 20 °C, with the coldest temperatures coinciding with time spent at depth during

the first two weeks following tag deployment (Fig. 5). Diving behavior was clearly influenced by

time of day. This shark showed a preference for surface waters (<20 m) during the night and

utilized a greater proportion of the water column during the day (Fig. 6). Diel movement has

previously been reported for thresher sharks tagged off the west coast of the USA, where it was

attributed to higher levels of foraging behavior during the day (Cartamil et al. 2011).


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Figure 3. Alopias vulpinus with Mini-PSAT prior to release (Photo – Paul Rogers)


20

Figure 4. Deployment and pop-up locations of the Mini-PSAT deployed on a 1750 mm FL female

Alopias Vulpinus near Portland, Victoria in December 2012.


21

Figure 5. Depth and temperature profile of A. vulpinus throughout Mini-PSAT

deployment. DAL = Days at liberty following tag deployment.

Figure 6. Depth distribution (% frequency) for A. vulpinus during night (21:00 – 05:00h;

black bars) and day (06:00 – 20:00h; shaded bars).


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4. CONCLUSION

The paucity of data around the movements of thresher sharks in Australian waters highlights the

need for further investigation of this species in this region. Positive attitudes of tournament fishers

towards pelagic sharks provide a promising avenue to engage with recreational fishers on the

issue of conservation and management of thresher sharks. Tournament anglers showed a strong

desire to release sharks in good condition, and promotion of best practice catch and release

through game fishing clubs should decrease the impacts of recreational fishing on pelagic sharks.

Commercial gillnet data from the GHTS of the SESSF indicates that there are hotspots for

thresher shark catches which may provide avenues for management of fisheries to reduce the

encounterability of thresher sharks to fishing gear. Tagging data displayed diel movement

patterns and broad depth utilization; such data can be used to assess the level of temporal and

spatial overlap with different fishing gears and contribute to the hierarchical assessment of the

vulnerability of thresher sharks within Australian waters. Future research should use a hierarchical

semi-quantitative risk assessment in which habitat characterisation obtained from satellite

transmitters will be overlayed with information collected from the literature review, databases

interrogation, and recreational fishery surveys to assess the threats to thresher sharks in

Australian waters.


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REFERENCES

Baum, J.K., Myers, R.A., Kehler, D.G., Worm, B., Harley, S.J., and Doherty, P.A. (2003) Collapse and conservation of shark populations in the North Atlantic. Science 299, 389-392.

Camhi, M., Valenti, S., Fordham, S., Fowler, S.L., and Gibson, C. (2009) 'The Conservation Status of Pelagic Sharks and Rays: Report of the IUCN Shark Specialist Group Pelagic Shark Red List Workshop.' (IUCN Species Survival Commission Shark Specialist Group.: Newbury, UK)

Cartamil, D. (2009) Movement patterns, habitat preferences and fisheries biology of the common thresher shark (Alopias vulpinus) in the Southern Californian Bight. University of California, San Diego

Cartamil, D.P., Sepulveda, C.A., Wegner, N.C., Aalbers, S.A., Baquero, A., and Graham, J.B. (2011) Archival tagging of subadult and adult common thresher sharks (Alopias vulpinus) off the coast of southern California. Marine Biology 158(4), 935-944.

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Appendix 1

Pelagic shark survey

SECTION 1 – These questions focus on fishing for Pelagic Sharks (Mako, Thresher and Porbeagle)

In the past 12 months, how many days have you fished for pelagic sharks (Mako, Thresher and Porbeagle)?

……………………….

Approximately how much have you spent on your boat and tackle specifically to fish for pelagic sharks?

$....................

In the past 12 months, how many sharks have you caught?

Mako:………………… Thresher:………………. Porbeagle:……………………

How many (if any) of these sharks were released?


How many (if any) of these sharks were tagged prior to being released?


If sharks were released, what were your reasons for releasing them?

If sharks were retained, what were your reasons for retaining them?

What types of hooks do you use when fishing for pelagic sharks?

Hook Shape: Circle J Hook Other

Material: Stainless steel Non stainless steel

Leader type: Monofilament Wire Other

Do the fishing restrictions on sharks limit your fishing experience?

Yes No

What do you think is happening to the numbers of pelagic sharks?

Increasing Decreasing Stable


26

SECTION 2- General attitudes towards sharks Please tick the box corresponding to your response to the statements provided.

Statement Response

Strongly

agree Agree Neutral Disagree

Strongly disagree

I like to ensure that a shark is released in a good condition

I would be willing to use tackle and special handling practices that minimise damage to released sharks

It is important to me that all the fish I release survive

Catching a shark adds to the enjoyment of my fishing trip

I prefer to catch fish rather than sharks

Sharks are good to eat

I enjoy the challenge of catching a shark

I target sharks when I go fishing

More regulations are required for recreational fishing of sharks

Commercial fishing is a threat to shark populations

Recreational fishing is a threat to shark populations

Sharks need to be protected

It is important to have viable sharks populations

It would be better if there were fewer sharks in the sea

Sharks are a sign of a healthy marine ecosystem

Sharks should be conserved as they have a right to exist

SECTION 3- General Demographic

Age: ............................ Sex: M F Postcode: ...........................

Education:

High school or less University degree or higher Trade or apprentice

How many years have you been fishing for?

…………………………..

How many days a have you spent fishing in the last 12months?

……………………..

On your last fishing trip how much did you spend on;

Fuel $................. Bait $................. Tackle $................. Ramp Fees $.................

Other $.................

Any further comments?

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