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Quantifying the recreational catch of southern bluefin tuna off the Victorian coast

Southern bluefin tuna Fish_Licence_logo

Project number: R09/10/03
June 2012
Recreational Fishing Grants Program Research Report

Executive Summary

Fisheries Victoria initiated this study, following consultation with the Victorian recreational fishing community, to provide the first quantified estimate of the recreational daytime trailer-boat catch of Southern Bluefin Tuna (SBT) off the south west Victorian coast.

The on-site survey designs used by Fisheries Victoria scientists to estimate the total catch and effort of the recreational SBT fishery were based on methods developed by Robson (1960) and Robson and Jones (1989); and are consistent with the methodological recommendations presented by the Australian Government to the Commission for the Conservation of Southern Bluefin Tuna (Rowsell et al. 2008).

The survey designs used in this study and the study findings were independently peer reviewed by a world-leading authority on recreational fishing surveys.

Boat ramp interviews of fishing parties of recreational anglers targeting SBT were conducted over the period March to July 2011 at Apollo Bay, Warrnambool, Port Fairy and Portland. To quantify the catch of the Victorian recreational SBT fishery, and obtain statistics of when and where SBT were caught, a total of 1924 fishing parties were interviewed from recreational trailer-boats. The number of calendar days when interviews were conducted varied between ports; Portland (81 days), Port Fairy & Warrnambool (57 days) and Apollo Bay (24 days).

The estimated number of SBT caught and retained in Victoria for the March to July 2011 period was about 19,700, (± 2800 s.e.). It is estimated that a further 6900 (± 1500 s.e.) SBT were also caught and released in the same period.

The estimated total weight of tuna caught and retained by recreational anglers in Victoria was about 240 tonnes (± 31 s.e.). The estimated number of boat trips by recreational anglers in Victoria where SBT was targeted was about 6200 (± 800 s.e.).

The true recreational catch of SBT from Victoria will be higher than estimated because:

  • Data from moored vessels were not included
  • Data from fishers travelling by sea to Victoria from South Australia were not included
  • The use of maximum trailer count did not capture all completed fishing trips. 

The majority of SBT were taken in waters over the continental shelf off Portland between April and May 2011.

Fisheries Victoria acknowledges the financial support provided by the Victorian Recreational Fishing Licence Trust to fund this study.

General Methods

Project design, methods and statistical analyses for this project are described in detail in Appendix 1.

Estimates of SBT catch were made using information collected through on-site interviews of fishing parties returning to boat ramps. Additional information was collected from:

  • An on-board observer program on charter vessels
  • A research angler diary program.

Three different onsite survey designs were chosen to estimate catch and effort for the SBT fishery, in four Victorian ports over five months.

The survey commenced on 2 February 2011 and was completed on 31 July 2011. Boat ramps surveyed in south western Victoria included those at Apollo Bay, Warrnambool, Port Fairy and Portland (Figure 1).

Interview data from on-site surveys were used to determine when, where, and how SBT were caught during the survey period.

Telephone interviews with selected Fisheries Officers provided data to support a qualitative assessment of any SBT catch and effort outside the scope of the boat-ramp surveys.

Map showing location of Portland, Port Fairy, Warrnambool and Apollo Bay on the South West coast of Victoria

Figure 1 . Location of ports used by recreational anglers to target southern bluefin tuna in western Victoria.

Grids were used by creel-clerks to ascertain where anglers target southern bluefin tuna during their fishing trip. Bathymetry contours illustrate depths from 50–200 m.

General Results

Results are provided in detail in Appendix 2.

Survey data

Survey data from February showed:

  • Limited targeting of SBT by recreational anglers
  • No catch of SBT by recreational anglers.

Survey data collected from 1 March 2011 to 31 July 2011 were used in the analyses.

A total of 1924 fishing parties were interviewed. The number of calendar days when interviews were conducted varied between ports; Portland (81 days), Port Fairy & Warrnambool (57 days) and Apollo Bay (24 days).

Estimates of total catch and total effort

Total catch

The estimated total retained daytime catch of SBT from the Victorian recreational trailer-boat fishery between March and July was about:

  • 19,700 (± 2800 s.e.) fish
  • 240 (± 31 s.e.) tonnes.

It is estimated that about 6900 (± 1500 s.e.) SBT were also caught and released in the same period.

The majority of the retained catch was landed in:

  • Portland (90%)
  • The months of April and May (81%).

Total effort

Total effort was estimated at about 6200 trips (± 800 trips s.e.).

Fishing effort was greatest:

  • Out of Portland with 83% of the total effort
  • In April with 43% of the total effort.

Fishing effort was focussed on waters over the continental shelf mainly in areas off Portland and Port Fairy.

Uncertainty

While these results are the best available estimates of catch, effort and associated measures of precision for this recreational fishery, limitations to the sampling designs and their practical implementation mean that fishing effort, catch totals and their associated measures of precision have been underestimated.

Comparison of data sources

Comparing data from onsite boat ramp interviews of trailer-boat fishers with data collected by observers from charter boats and by research anglers showed:

  • Fishing grounds used by charter boat fishers were similar to the grounds used by trailer-boat fishers
  • The release rate from charter boats with onboard observers is the same as that of the trailer-boat fishers
  • Research anglers had higher release rates than charter boat fishers and trailer-boat fishers.

Regional and monthly SBT size differences

Regional differences in the SBT fishery were apparent.

The lengths of SBT landed at Portland, Port Fairy and Warrnambool for each month from March to July ranged from 67 to 163 cm (fork length, FL), with mean weights ranging from a little over 9 kg to over 18 kg.

While fewer fish were harvested out of Apollo Bay, anglers caught large SBT at Big Reef (the main fishing grounds off Apollo Bay). SBT landed in Apollo Bay ranged from 78 to 190 cm FL, with a mean weight of 54 kg.

General Discussion

Victorian recreational catch of SBT

This study provides the first estimate of the recreational catch of SBT from Victorian waters. The estimated recreational catch of SBT from south western Victoria during 2011 was about 240 tonnes (± 31 s.e.). The 2011 Victorian recreational SBT catch is equivalent to 6% of Australia’s current commercial catch allocation of SBT (4015 tonnes, AFMA 2009) .

Moored vessels were only found at Portland and were excluded from analyses. Data from moored vessels indicated a further 594 SBT were caught and retained. This represents about 15% of reported SBT retained by trailer-boat fishing parties interviewed at Portland.

The National Recreational and Indigenous Fishing Survey (NRIFS) in 2000/01 calculated that 1327 (± 541 s.e.) tonnes of all tuna species (including bonito) were caught by recreational anglers, nationally. The diarists included in the NRIFS sample did not report any SBT from Victorian waters in their catches during the survey period (Henry and Lyle 2003) .

Anglers released 25% of SBT caught in Victoria. This release rate is lower than the average release rate of all tuna species (including bonito) determined by the NRIFS in 2000/01 (34%).

In the Victorian fishery, release rates were driven principally by anglers reaching the Victorian bag limit of 2 tuna per day per angler. Few anglers discarded SBT in Victoria because they were unwanted. Anglers appear to make the most of this temporally limited fishery by catching and keeping their bag limit.

Expert opinion survey

Information provided by Fisheries Officers supported the assumptions of this study by:

  • Indicating anglers only targeted SBT in south western Victoria from those ports monitored in 2011
  • Indicating that any incidental catches elsewhere were likely to have been insignificant when compared with catches in south western Victoria during 2011.

Charter boat fishers and Research Anglers

Comparing charter boat (observer) and research angler data with trailer-boat angler survey data suggests that both fished in similar areas.

Comparing charter boat (observer) with trailer-boat angler survey data suggests that release rates were similar, while release rates from research anglers were higher than from other data sources.

Much of the data used in the calculation of catch and released catch was self-reported by fishing parties at interview. Although data derived from charter boat (observers) and research anglers can not directly validate the trailer-boat angler survey data (due to each method having their own biases), it was useful for comparative purposes.

The catch: what, when, who and where?

While most recreational anglers began targeting SBT in March 2011, it is likely that a small number of anglers began searching for SBT earlier in the year.

During March the majority of angers targeted SBT up to 100 km from the coast. In subsequent months, greatest effort was applied closer to shore where SBT were found in greater numbers. Larger SBT (>150 cm) were mainly caught in deeper waters off Portland and Big Reef (south west of Apollo Bay).

Catch rates (number of SBT caught per fishing party hour) of SBT varied both spatially and temporally. The highest catch rates were observed in May. Interestingly, the modal length of SBT caught during the year decreased. This suggests that larger SBT entered Victorian waters first, followed by smaller fish.

Between March and July, SBT was the target species of choice for the majority of anglers launching from Portland and Apollo Bay. Anglers launching from Port Fairy and Warrnambool were targeting snapper (40%) and SBT (30%).

A number of local anglers participate in this fishery. Additionally, it was found that 55% of anglers targeting SBT were from the Melbourne region.

A small proportion of anglers may have launched from ports in South Australia to catch SBT in Victorian waters. Port MacDonnell in South Australia is approximately 25 km from the border. The scale of this fishing activity was outside the scope of this study and has not been quantified.

Conclusion

The recreational catch of SBT from Victorian waters in 2011:

  • Is about 19,700 fish (± 2800 s.e.), equivalent to around 240 tonnes (± 31 s.e.)
  • Represents 6% of Australia ’s commercial catch allocation (in terms of weight)
  • Is centered off Portland in coastal waters over the continental shelf
  • Attracts anglers from across Victoria (99%), New South Wales (0.6%) and South Australia (0.4%).

Acknowledgements

This research was funded by the Victorian Government to improve recreational fishing in Victoria through revenue from Recreational Fishing Licences.

Dr Murray MacDonald, Dr Leanne Gunthorpe, Dr James Andrews, and Mr Jon Presser provided review and comments on this report.

We also appreciate the constructive advice and comments provided by the independent reviewer, Dr Aldo Steffe, on the survey design, catch and effort estimation process and on earlier drafts of this report.

Data for this report were collected by a number of DEPI staff, and research anglers that include (alphabetically) David Ball, Natalie Bridge, Therese Bruce, Peter Cavanagh, Allister Coots, Graeme Cottier, Shane Cromie, John Doduro, Troy Duthie, Chris Epskamp, Scott Gray, Daniel Grixti, Daniel Hoey, Pieta Linberg, Doug Levings, Doug MacFarlane, Mick Mahney, Camilla Martins, Cameron McCallum, Paul McCoy, Pam Oliviero, Cameron Ordner, Jeremy Porter, Wendy Skene, Tim Smith, Greg Tresize, Fabian Trinnie, Geoff Wilson.

Fisheries officers from across Victoria provided information on SBT as a part of the expert opinion telephone survey (Charlie Cooper, Ian Westhorpe, David Burgess, Mark Asplin, Rod Barber, Errol Parmigiani, Matt Bateson, David Bull, and Chris Agwin).

Skippers from the fishing vessels Reggie, May S, Game On, Orca 3, Reel Time, Think Big, kindly assisted DEPI observers.

Research anglers provided additional information that was used to compare with on-site survey data.

Greatest thanks to the many recreational anglers who willingly shared information to creel-clerks. Without their involvement this project would not have come to fruition.

We also thank:

  • All the shire council staff who assisted us with the traffic counters
  • WA Fisheries for advice on camera installation
  • The Portland IT company who installed the cameras.

Fisheries Victoria acknowledges the financial support provided by the Victorian Recreational Fishing Licence Trust to fund this study.

References

  • AFMA (2009) Southern Bluefin Tuna Fishery Management Plan 1995, 2009-2011 SBT Australian National Catch Allocation Determination, Fisheries Management Act 1991, Australian Fisheries Management Authority.
  • Butler A, Althaus F, Furlani D and Ridgway K (2002) Assessment of the conservation values of the Bonney upwelling area: a component of the Commonwealth Marine Conservation Assessment Program 2002-2004. Report to Environment Australia .
  • Caton AE (1991) Review of aspects of southern bluefin tuna biology, population and fisheries. (Eds RB Deriso, WH Bayliff) pp. 181–350. (Inter-American Tropical Tuna Commission).
  • Cochran WG (1977) Sampling Techniques. John Wiley & Sons: New York. pp. 74-76.
  • Griggs LH and Richardson K (2005 ) New Zealand tuna fisheries, 2001 and 2002 New Zealand Fishery Assessment Report 2005/4.
  • Henry GW and Lyle JM (2003) The national recreational and indigenous fishing survey. FRDC Project No. 99/158
  • Nieblas AE, Sloyan BM, Hobday AJ, Coleman R and Richardson AJ (2009) Variability of biological production in low wind-forced regional upwelling systems: A case study off southeastern Australia . Limnology and Oceanography 54, 1548–1558.
  • Pollock KH, Jones CM and Brown TL (1994) Angler survey methods and their applications in fisheries management. American Fisheries Society, Bethesda, Maryland, Special Publication 25.
  • R Development Core Team (2008) R: A language and environment for statistical computing. R Foundation for Statistical Computing Vienna, Austria .
  • Robson DS (1960) An unbiased sampling and estimation procedure for creel censuses of fishermen. Biometrics 16: 261–277.
  • Robson DS and Jones CM (1989) The theoretical basis of an access site survey design. Biometrics 45:83–98.
  • Rowsell M, Moore A, Sahlqvist P and Begg G (2008) Estimating Australia's recreational catch of southern bluefin tuna. Bureau of Rural Resources, Australian Government. CCSBT-ESC/0809/17.

Appendix 1.

The mathematical formulas in Appendix 1cannot be translated correctly into HTML - for a full copy of the report including Appendix 1, please email chris.padovani@depi.vic.gov.au  

Appendix 2. Detailed Results

Survey results

Across the survey, 2.1% of anglers approached refused to participate in the interview process. Refusals were classified as:

  • Partial refusal (1.0%)
  • Full refusal (0.6%)
  • Language barriers (0.5%).

Targeted-effort and catch data were obtained from the partial refusals and interviews with language difficulty categories. This information was included in the data set used to calculate total recreational effort and catch. With full-refusals, catch or effort could not be determined and this information was not included in estimates. Boats with people not fishing and classified as out of scope contributed 2.3% of interviews.

A total of 1924 fishing parties were interviewed from March to July 2011 (Table 1).

On scheduled interview days:

  • At Portland
    - 81 interview days were recorded
    - 2846 boat trailers were counted
    - 1405 interviews were completed.
  • At Port Fairy and Warrnambool (combined)
    - 57 interview days were recorded
    - 554 boat trailers were counted
    - 309 interviews were completed
  • At Apollo Bay
    - 24 interview days were recorded
    - 354 boat trailers were counted
    - 210 interviews were completed.

Across all four ports during the survey period, anglers reported catching 4,172 SBT.

Total recreational SBT catch and effort

Length

The mean length and mean estimated weight of SBT landed in the survey is shown in Table 2.

Effort

The estimated total number of fishing trips targeting SBT between March and July 2011 was 6184 (± 794 s.e.). This effort was distributed by port and month as shown in Table 3.

Fishing effort (fishing trips) was greatest:

  • Out of Portland with 83% of the total effort
  • In April with 43% of the total effort.

Retained catch

The estimated total retained catch of SBT from the Victorian fishery between March and July (179 days) was 19,737 (± 2796 s.e.) fish.

SBT catch was greatest:

  • Off Portland (90%)
  • In May (8504 SBT) and then in April (7408 SBT).

By weight, anglers harvested an estimated 243 tonnes (± 30.7 s.e.) of SBT from the Victorian fishery. The majority of the retained catch was landed in:

  • Portland (88%)
  • The months of April and May (83%).

Released catch

Recreational anglers caught and released a further 6942 (± 1483 s.e.) SBT.

Rates of release of SBT varied with port of origin. Anglers from:

  • Portland, released 25% of their total catch
  • Port Fairy and Warrnambool, released 31%
  • Apollo Bay, did not release any fish.

Anglers indicated SBT were released because:

  • Keeping the fish would exceed the bag-limit (79% of anglers)
  • The fish were unwanted (11%)
  • The fish were considered to be undersized (5%), even though there is no recreational size limit for SBT.

Sensitivity of Catch Estimates

The estimates of landed catch from the Victorian recreational catch, derived from using alternative length-weight relationships were potentially:

  • 41 tonnes less (i.e. -17%) using parameters from the SBT fisheries management plan (AFMA 2009)
  • 41 tonnes more (i.e. +17%) using parameters published by Griggs and Richardson (2005) (Figure 2).

Table 1 . Survey designs showing stratification of primary (dates) and secondary (times) sampling units and numbers of trips, numbers of fishing party interviews and SBT-fishing party interviews obtained.

* denotes shift types where maximum trailer count was used as a proxy for the total number of completed boat trips

Port

Month

Day-type

Days (N)

Shift-type

Number of shifts(n)

Number of trips (all activities)

Interviews (all activities)

Interviews (SBT trips)

Portland

March

Week day

22

Early

4

10

10

1

 

March

Week day

22

Late

3

23*

19

0

 

March

Weekend

9

Early

4

22

22

2

 

March

Weekend

9

Late

4

256*

90

45

 

April

Week day

18

Early

2

7

6

2

 

April

Week day

18

Late

6

222*

95

80

 

April

Weekend

12

Early

3

53

52

39

 

April

Weekend

12

Late

9

989*

445

400

 

May

Week day

22

Early

4

26

26

20

 

May

Week day

22

Late

5

267*

87

80

 

May

Weekend

9

Early

3

59

56

54

 

May

Weekend

9

Late

6

417*

128

123

 

June

Week day

21

Early

4

59

56

53

 

June

Week day

21

Late

5

40*

34

31

 

June

Weekend

9

Early

3

62

56

51

 

June

Weekend

9

Late

6

157*

85

74

 

July

Week day

21

Early

3

1

1

1

 

July

Week day

21

Late

5

10*

8

2

 

July

Weekend

10

Early

1

4

4

0

 

July

Weekend

10

Late

9

162*

125

98

Port Fairy & Warrnambool

March

Week day

22

Early

2

8

3

0

 

March

Week day

22

Late

5

40*

28

10

 

March

Weekend

9

Early

2

13

13

0

 

March

Weekend

9

Late

7

28*

24

3

 

April

Week day

18

Early

3

0

0

0

 

April

Week day

18

Late

6

36*

24

7

 

April

Weekend

12

Early

3

9

9

3

 

April

Weekend

12

Late

6

225*

93

61

 

May

Week day

22

Early

1

0

0

0

 

May

Week day

22

Late

7

19*

15

12

 

May

Weekend

9

Early

4

5

5

0

 

May

Weekend

9

Late

5

58*

35

34

 

June

Week day

21

Early

2

2

2

1

 

June

Week day

21

Late

7

11*

5

3

 

June

Weekend

9

Early

3

3

3

3

 

June

Weekend

9

Late

6

31*

20

16

 

July

Week day

21

Early

3

0

0

0

 

July

Week day

21

Late

5

11*

3

1

 

July

Weekend

10

Early

4

2

2

2

 

July

Weekend

10

Late

6

53*

25

18

Apollo Bay

April

Week day

18

All day

3

8*

8

8

 

April

Weekend

12

All day

5

37*

27

27

 

May

Week day

22

All day

12

29*

0

0

 

May

Weekend

9

All day

8

132*

60

43

 

June

Week day

21

All day

20

74*

46

33

 

June

Weekend

9

All day

8

20*

20

9

 

July

Week day

21

All day

21

14*

9

4

 

July

Weekend

10

All day

10

40*

40

17

Total

 

 

 

 

263

3754

1924

1471


Table 2. Summarising the sample, stratified by port and month, of 2659 SBT lengths (L) measured at the boat ramp (FL, cm) and the mean weight (W) estimated from length weight regression (Caton 1991) . 0 = nil catch

Port

Month

n

Mean length (FL, cm)

Standard Error (FL, cm)

Mean estimated Weight (kg)

Standard Error Weight  (kg)

Portland

March

55

95

5

17.36

0.077

 

April

880

88

5

14.08

0.083

 

May

728

83

6

12.16

0.076

 

June

530

77

4

9.66

0.049

 

July

252

77

4

9.68

0.045

 

 

 

 

 

 

 

Port Fairy & Warrnambool

March

6

97

4

18.37

0.074

 

April

95

90

9

15.19

0.235

 

May

69

86

4

13.18

0.058

 

June

16

80

3

10.58

0.036

 

July

11

76

4

9.19

0.051

 

 

 

 

 

 

 

Apollo Bay

March

0

 

 

 

 

 

April

3

97

16

19.75

0.316

 

May

5

176

8

105.34

0.428

 

June

9

112

44

39.90

1.530

 

July

0

 

 

 

 

Table 3 . Estimated retained SBT catch (± s.e.), released catch (± s.e.), catch weight (tonnes, ± s.e.) and effort (number of trips, ± s.e.) of recreational anglers targeting SBT from four Victorian ports during March-July 2011.

Port

Month

Catch retained (number)

SE catch ret.

Catch released (number)

SE catch rel.

Catch retained (tonnes)

SE catch retained (tonnes)

Effort (trips)

SE Effort (trips)

Portland

March

272

146

49

46

4.7

2.5

238

130

April

6390

1534

1827

510

89.9

20.6

2139

447

May

7862

2119

3527

1292

88.2

19.7

1801

515

June

2552

812

447

188

25.2

8.2

772

323

July

668

161

190

98

6.5

1.5

201

59

TOTAL

17744

2747

6040

1406

214.5

29.7

5151

768

Port Fairy and Warrnambool

March

85

85

0

0

1.6

1.6

18

18

April

1011

393

332

250

14.6

5.8

392

148

May

635

321

437

396

8.5

4.7

209

117

June

115

51

45

40

1.2

0.5

49

22

July

121

55

88

59

1.2

0.6

86

46

TOTAL

1967

520

902

474

27.1

7.6

754

197

Apollo Bay

March

0

0

0

0

0.0

0.0

0

0

April

7

4

0

0

0.1

0.1

113

36

May

7

2

0

0

0.7

0.2

93

16

June

12

2

0

0

0.5

0.1

52

5

July

0

0

0

0

0.0

0.0

21

0

TOTAL

26

4

0

0

1.4

0.2

279

39

Total Fishery

 

19737

2796

6942

1483

243

30.7

6184

794

Note: Zero effort targeting SBT or catch was recorded for February.

This graph shows the different length/weight relationships for this species found by different studies. The variation may be the result of the condition of the fish measured, how much they have recently eaten or measurement errors. Future studies need to undertake more work in this area as the relationship used can influence the results considerably.

Figure 2 . Average weight (W) for length (FL) where W=aFLb, with a and b from Caton (1991: Solid line) used in the present study.

Average weight for length from the SBT Fishery Management Plan (AFMA 2009; dotted line), and from Griggs and Richardson 2005 (dashed lines) are also presented. Data points (squares) are measured weights of a sample (n=22) of SBT landed in the Victorian recreational fishery in 2011.

Expert opinion survey

Results of the expert opinion survey of Fisheries Officers indicated that in 2011:

  • SBT were only targeted and landed by recreational anglers in south western Victoria
  • Access points were restricted to the boat ramps at Portland, Warrnambool, Port Fairy and Apollo Bay, as other ramps in south western Victoria do not have the infrastructure to launch large vessels
  • The vast majority of recreational anglers target SBT during daylight hours. Some vessels are moored overnight on the water near Portland due to the lack of accommodation.

Regional and temporal relative distribution of catch, effort and catch rates

Catch

The relative spatial and temporal distribution of the SBT catch of fishing parties interviewed across the survey period (March to July 2011) is shown in Figure 3. During:

  • March
    - SBT catches were low
    - Fishing occurred mainly offshore of Portland
  • April and May
    - SBT were caught mainly on the continental shelf between Portland and to the west of Warrnambool
    - The greatest number of SBT were caught within approximately 50 km of the Portland coastline
  • June and July
    - The largest catches of SBT occurred within 25 km of the Portland coastline
    - Very few fish were caught further offshore.

Targeting effort

The relative spatial and temporal distribution of the targeted effort of interviewed fishing parties for SBT across the survey period (March to July 2011) is shown in Figure 4. During:

  • March
    - Effort was light, though the fishing grounds were quite extensive
  • April and May
    - The greatest effort was applied to waters off Portland
    - Lower levels of fishing effort occurred in the waters to the east of Warrnambool and at Big Reef (south east of Apollo Bay)
  • June and July
    - Effort focused on waters immediately adjacent to Portland, Port Fairy, and Big Reef.

Catch Rates

The relative spatial and temporal distribution of SBT catch rates (number of SBT caught per fishing party hour ) of interviewed fishing parties across the survey period (March to July 2011) are shown in Figure 5. During:

  • March
    - Catch rates were between 0 and 1.5 SBT per fishing party hour across all of the fishing grounds
  • April
    - Catch rate increased to between 0.5 and 2.0 SBT per fishing party hour in the near-shore fishing grounds off Portland and Port Fairy
  • May
    - The highest catch rates were recorded from both inshore and offshore waters between Portland and Warrnambool
    - More than 2 SBT per fishing party hour were caught
  • June and July
    - The catch rate was greatest on continental shelf waters off Portland and to a lesser extent off Port Fairy and Warrnambool.

Catch rates (across the survey period March to July) were greatest when anglers targeted SBT in waters <100 m depth (Figure 6).

Size of SBT

The length frequency distribution of SBT caught and retained in south western Victoria, and measured by creel clerks is shown in Figure 7.

Over the survey period (March to July 2011) the size of SBT caught and retained by anglers declined. The dominant size class was:

  • 95 cm FL (range 75 to 100 cm FL) in March
  • 85 cm FL (range 70 to 115 cm FL) in April
  • 85 cm FL (range 85 to 100 cm FL) in May
  • 75 cm FL (range 65 to 95 cm FL) in June
  • 75 cm FL (range 65 to 95 cm FL) in July.

While SBT larger than 155 cm FL were caught, these represented only 0.3% of the total number of SBT recorded.

Angler Targeting Preference

The targeting preferences of anglers are shown in Figure 8. The majority of anglers fishing from the ports of:

  • Portland (>70%) and Apollo Bay (>50%) targeted SBT
  • Port Fairy and Warrnambool (>40%) mainly targeted snapper. Only 30% of anglers fishing from Port Fairy and Warrnambool targeted SBT.

Of the anglers that target SBT:

  • 92% troll using hard bodied and skirted lures
  • 6% use artificial lures and bait
  • 1% use baiting methods.

Angler Profile

Anglers targeting SBT were from:

  • Victoria (98.9%)
  • NSW (0.6%)
  • SA (0.4%).

Most Victorian anglers reside in or close to Portland, Port Fairy, Warrnambool, Apollo Bay, Geelong and Melbourne (Figure 9). Approximately 55% of all anglers targeting SBT came from the Melbourne region.

Comparison of sources for catch and effort data

On-board observer

DEPI observers accompanied five fishing charters vessels on 15 different occasions during May and early June 2011.

During these trips anglers:

  • Caught 177 SBT
  • Released 41 (23%)
    - This release rate is similar to that obtained by the on-site boat ramp survey (25% over all)
    - Most SBT were released because fishing charters had already caught their combined bag limit
  • Fished in areas codes F3, F4, G3, K14 (see Figure 1)
    - These are similar to the fishing grounds reported from the on-site boat ramp surveys.
    - Anglers made repeat trips to the same fishing area to target SBT (64% of the time)
    - At other times (36% of the time) anglers fished grounds adjacent to areas fished when observers were on-board.

Research Angler Diary

From April to July, seven research anglers:

  • Caught 257 SBT
  • Released 177 (69%)
    - The release rates of research anglers were mainly influenced by two non-typical anglers who released 75% and 90% of their catch.

Comparison of size data

The size of SBT measured by on-board observers and research anglers (combined) shows a trend of decreasing length over time. This is similar to the data collected by the on-site creel clerks.

During June and July, the modal length recorded by observer and research anglers was 5 cm larger than that collected by the on-site surveys. Such differences are likely due to fish shrinkage or inconsistencies with the method used to measure the fish (using tape versus a flat measuring board).

Numbers of Southern Bluefin Tuna Caught: March

Map showing numbers of SBT caught during March. Numbers were less than 50 in 10 areas around Portland and heading towards Port Fairy.

Numbers of Southern Bluefin Tuna Caught: April

Map showing numbers of SBT caught during April. Most numbers were between 1-300 and off the coast of Portland, Port Fairy and Warrnambool areas with one area near Portland with over 300. There is also one area just west of Apollo Bay that had between 1 and 50.

Numbers of Southern Bluefin Tuna Caught: May

Map showing numbers of SBT caught during May. Most catches were around the Portland and Port Fairy areas and numbered from 1 to over 300. The higher numbers were closer to Portland.

Numbers of Southern Bluefin Tuna Caught: June

Map showing SBT numbers caught during June. There were two areas right near Portland that had over 300 catches and then a low number of areas around Portland, Port Fairy and west of Apollo Bay that had between 1-50 catches.

Numbers of Southern Bluefin Tuna Caught: JulyMap showing the numbers of SBT caught in July. One area at Portland had over 300 catches. There were a small number of areas near Portland and Port Fairy that had 1-100 catches.

Figure 3. Number of SBT caught off different regions of western Victoria in each month of the survey.

Data from non-interview days is not represented. Darker cells indicate greater number of fish caught.

Fishing Hours: March

Map showing fishing hours in different areas for March. Fishing hours were between 1-100 hours in areas around Portland and Port Fairy.

Fishing Hours: April

Map showing fishing hours for April by location. Highest is in some areas just west of Portland with over 300 hours. Other areas around Portland, Port Fairy, Warrnambool and west of Apollo Bay had 1-100 hours. 

Fishing Hours: May

Map showing fishing hours for May by location. Highest is in some areas just west of Portland with 200-300 hours. Other areas around Portland, Port Fairy, Warrnambool and west of Apollo Bay had 1-100 hours.

Fishing Hours: June

Map showing fishing hours by location for June. There one area near Portland with 200-300 hours and one with over 300 hours. A small number of other areas near Portland, Port Fairy had 0-50 hours. One area west of Apollo Bay had 100-200 hours.

Fishing Hours: July

Map showing fishing hours by location for July. There were two areas near Portland with 100-300 hours and a small number of areas to the west of Portland, around Port Fairy and to the west of Apollo Bay with 0-50 hours

Figure 4. Number of fishing party hours fishing for SBT off different regions of western Victoria in each month of the survey.

Data from non-interview days is not represented. Darker cells indicate greater number of hours fished.

Catch Rate: March

Map showing catch rate per hour for March which was between 0 and 1 in most areas off the coast of Portland.

Catch Rate: April

Map showing catch rate per fishing hour for April. It is highest in some areas close to the coast near Portland and Port Fairy - up to 2. Other areas around Portland, Port Fairy, Warrnambool and Apollo Bay had lower numbers of 0-0.5.

Catch Rate: May

Map showing the catch rate per hour for May. There was a catch rate of over 2 recorded in several areas between Portland and Port Fairy and other locations around these towns recorded a catch rate of 0 to 2

Catch Rate: June

Map showing catch rate per hour for June. There were catch rates of 2 and under recorded in areas near Portland, Port Fairy and west of Apollo Bay

Catch Rate: July

Map showing catch rate for July per hour. There was a catch rate of 0 to 2 recorded in 7 areas near to the coast of Portland and Port Fairy.

Figure 5. Number of SBT caught per fishing party hour (catch rate) off different regions of western Victoria in in each month of the survey.

Data from non-interview days is not represented. Darker cells indicate greater catch rate.

Graph showing catch rate of fish per hour compared to depth. A higher catch rate was recorded for 0 to 100 meters of just over 0.9 fish per hour. None of the other depths recorded anything over 0.2 fish per hour.

Figure 6. SBT caught per fishing party hour of fishing (catch rate) at various depth ranges for combined fishing ports throughout the sampling period.

Creel clerk data

Length frequency of SBT measured by creel clerks for March. Highest is nearly 50% for a 95cm fork length.

Length frequency of SBT measured by creel clerks for April. The range is from 70 to 115 fork length (cm). Highest is 85 cm at just over 40%

Length frequency of SBT measured by creel clerks for May. Range is from 65 to 100 Fork Length (cm). The highest is 85 cm at nearly 35% relative frequency.

 

Length frequency of SBT measured by creel clerks for June. Range is from 65 to 100 Fork Length (cm). The highest is 75 cm at nearly 60% relative frequency.

Length frequency of SBT measured by creel clerks for June. Range is from 65 to 95 Fork Length (cm). The highest is 75 cm at over 50% relative frequency. 

Observer and research angler data

Length frequency of SBT by Observer and research angler data for April. Range is from 80 to 95 Fork Length (cm). The highest is 85 cm at over 35% relative frequency.

Length frequency of SBT by Observer and research angler data for May. Range is from 50 to 95 Fork Length (cm). The highest is 80 cm at nearly 35% relative frequency.

Length frequency of SBT by Observer and research angler data for June. Range is from 70 to 90 Fork Length (cm). The highest is 80 cm at nearly 50% relative frequency.

Length frequency of SBT by Observer and research angler data for July. Range is from 70 to 80 Fork Length (cm). The highest is 80 cm at around 60% relative frequency.

Figure 7. Length frequency of SBT measured by creel clerks (left) and observer / research anglers (right) by month. Areas are combined.

Map showing angler residence throughout Victoria, the highest areas are from around the Melbourne bay area and along the west of the southern coast of Victoria with other lower areas throughout regional Victoria.

Figure 8. Percentage frequency distribution of species targeted at each port during the SBT survey period.

Map showing the location of angler residence in Victoria. The highest areas around Melbourne and particularly the bay areas as well as the west southern coast of Victoria. There is also a spread of lower numbers throughout regional Victoria.

Figure 9. Distribution of angler residence throughout Victoria by postcode district.

Darker cells indicate a greater number of anglers targeting SBT. Postcodes were provided by 890 anglers ( Victoria=881, South Australia = 4, NSW = 5).

Appendix 3. Technical Discussion

Effort estimates

Difficulties were experienced with the technologies (traffic counters and CCTV/web cameras) employed to obtain supplementary effort data. Because of these difficulties effort was estimated using the maximum trailer count (MTC) in the afternoon shift. Using MTC as a proxy for completed trips caused an underestimation of effort (and consequently catch) because not all completed trips are captured by this technique.

Maximum trailer count usually occurred near the beginning of the late shift. Most boats launched in the morning and returned to the boats ramps throughout the afternoon.

The use of MTC as a proxy for the count of completed trips assumes that no boats were launched after the MTC was observed and no boats were retrieved at the beginning of the late shift. This assumption might not hold all the time.

To improve estimates of catch and effort future surveys:

  • Should design the sampling strategy to manually count all completed trips each survey-day
  • Deploy more effective boat ramp telemetry solutions.

Out of Scope Vessels

The true recreational catch of SBT from Victoria will be higher than estimated because data from moored vessels and vessels travelling by sea from South Australia were not quantified.

Fishing parties from moored vessels were opportunistically interviewed at boat ramps as they came ashore. However it was not possible to collect the complete information from all moored vessels and the proxy measure of using maximum trailer count (MTC) did not apply to them. Thus, these vessels were excluded in calculating estimates.

Moored vessels were only found at Portland. Data from these vessels indicated a further 594 SBT were caught and retained. This represents about 15% of reported SBT retained by trailer-boat fishing parties interviewed at Portland.

A small proportion of anglers may have launched from ports in South Australia to catch SBT in Victorian waters. Port MacDonnell in South Australia is approximately 25 km from the border. The scale of this fishing activity was outside the scope of this study and has not been quantified.

Sensitivity of estimates to weight-length regression parameters

Estimated weight of SBT caught by recreational anglers is dependent on estimates of a and b used in the length-weight relationship W=aFLb. Although Caton’s (1991) length-weight relationship was used to estimate weight in this study, it may not be representative of the true relationship between length and weight of SBT caught in western Victoria in 2011. For example, the parameters specified in the SBT management plan (AFMA 2009) gave a lower estimate of the weight of the recreational catch, while parameters derived from New Zealand data gave a higher estimate. It is imperative that future studies measure and weigh a representative sample of the recreational catch so that the appropriate length-weight parameters for this fishery can be derived.

In this study, length of individual tuna was used to estimate the mean weight (from the length-weight relationship) and as a consequence variability around that mean weight was ignored and is a source of underestimation bias in the calculation of precision on the estimate of catch-weight. A more appropriate method of estimating weight based on length would be to develop a length–weight model which incorporated the variability around the mean individual weights.

Interestingly, the length frequency distribution of SBT determined from on-site surveys and compared with those obtained from the on-board observer and research angler programs shows that the modal length differed by ± 5 cm. Such differences are likely attributed to variables such as shrinkage and the method of measuring the fish (tape or flat board) at boat ramps compared to measuring recently caught fish on board vessel.

Sensitivity of effort and catch estimates to calculation method for Warrnambool and Port Fairy

Traditionally, the bus route survey method is suitable for a survey which involves a broad geographical area and has numerous access points (Pollock et al. 1994). The total effort for this type of survey method can be estimated either by interval count of anglers’ cars present at the car park, or from the direct expansion of completed trip interviews. Typically, in bus route survey designs, the starting location for each work shift is randomly selected and the work shift includes the driving time between multiple sites.

The scheduling of survey time at each ramp on a given day allowed the Warrnambool site to only be sampled at the start of a shift (0 to 40% coverage) or at the end of a shift (60 to 100% coverage). The middle part of the shift was never sampled at Warrnambool. In contrast, Port Fairy was scheduled to be sampled either at the start of the shift (0 to 60% coverage) or at the end of the shift (40 to 100% coverage). The issue of unequal coverage between the two ports was unintentional and introduced some bias into the data. This bias should be viewed in the context that it relates to a small portion of the catch and effort in two ports that contribute ~10% of the overall total fishery.

Learnings

Port based sampling provides an effective way to measure recreational effort and catch of SBT in Victorian waters. Increased accuracy and precision of estimates could be achieved by:

  • Changing the structured Early/Late shifts to provide full coverage of the entire day
  • Refining the use of automated traffic counters that accurately determine the boats launched and retrieved at ramps, and accurately counting them manually on sampled days
  • Develop a length–weight model from SBT data caught within the area of survey, each year a survey is completed
  • Develop an effective sampling strategy for moored vessels.