2011 commonwealth bass strait central zone scallop fishery survey:
DESCRIPTION
2011 Commonwealth Bass Strait Central Zone Scallop Fishery Survey:. 160 sample tows conducted during January 2011 survey. . Western Protected Zone. 5 main regions of scallops identified. These groupings will be used to describe results. . 2010 Open Zone. Viable Area 10. - PowerPoint PPT PresentationTRANSCRIPT
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TAFI is a joint venture between the State Government and the University of Tasmania
2011 Commonwealth Bass StraitCentral Zone Scallop Fishery Survey:
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• 160 sample tows conducted during January 2011 survey.
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Est kg scallop per1000m sample tow
Ñ 0#S 0.01 - 30#S 30 - 60#S 60 - 120#S 120 - 240
#S 240 - 500
#S 500 - 620
40°00' 40°00'
39°30' 39°30'
148°00'
148°00'
148°30'
148°30'
8 0 8 16 KilometersN
• 5 main regions of scallops identified.
• These groupings will be used to describe results.
Western Protected Zone
2010 Open Zone
Viable Area 10
South Viable Area 10
2009 Open Zone
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Western Closed Zone
0
200
400
600
800
1000
1200
1400
60 64 68 72 76 80 84 88 92 96 100
104
108
112
116
120
124
128
132
136
140
Num
ber
Caug
ht
Maximum Diameter
Discard Rate = 25%
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2010 Open Zone
60 63 66 69 72 75 78 81 84 87 90 93 96 99 102
105
108
111
114
117
120
123
126
129
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
2,000
Maximum diameter
Num
ber C
augh
t
Disard Rate = 10.8%
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Viable Area 10
60 63 66 69 72 75 78 81 84 87 90 93 96 99 102
105
108
111
114
117
120
123
126
129
0
50
100
150
200
250
300
350
400
450
Maximum diameter
Num
ber c
augh
t
Discard Rate = 16.4%
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South Viable Area 10
60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100
102
104
106
108
110
112
114
116
118
120
122
124
126
128
130
0
50
100
150
200
250
300
350
400
450
Maximum diameter
Num
ber c
augh
t
Discard Rate = 78.9%
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2009 Open Zone
60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100
102
104
106
108
110
112
114
116
118
120
122
124
126
128
130
0
200
400
600
800
1000
1200
1400
1600
Maximum diameter
Num
ber m
easu
red
Discard Rate = 37.8%
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Region
Western Closed Zone
2010 Open Zone
Viable Area 10
Sth Viable Area 10
2009 Open Zone
No. Tows 45 35 19 25 23% tows < 30kg 69 3 58 80 17% tows > 30kg < 60kg 18 46 26 4 13% tows > 60kg 13 51 16 16 74Discard 25% 11% 16.40% 79% 38%
Survey Results: Summary
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Oct / Nov 2010 vs January 2011
Black tows = January 2011Grey tows = Oct / Nov 2010
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Oct / Nov 2010 vs January 2011Red = January 2011
Grey = Oct / Nov 2010
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Oct / Nov 2010 vs January 2011Red = January 2011
Grey = Oct / Nov 2010
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Oct / Nov 2010 vs January 2011Red = January 2011
Grey = Oct / Nov 2010
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TAFI is a joint venture between the State Government and the University of Tasmania
2010 Commonwealth Bass StraitCentral Zone Scallop Fishery Surveys:
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• 184 sample tows conducted outside 2009 and 2010 legislative open areas.
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• 4 main regions of scallops identified: • NW of western protected zone• western protected zone• southern protected zone• W & SW of 2009 legislative
open region
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40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100
104
108
112
116
120
124
128
0
2
4
6
8
10
12
14
16
NW Survey Region
Maximum Diameter
Perc
enta
ge C
ontr
ibut
ion Discard Rate
= 30% Discard Rate = 30%
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40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100
104
108
112
116
120
124
128
0
2
4
6
8
10
12
14Western Protected Zone
Maximum Diameter
Perc
enta
ge C
ontri
butio
n Discard Rate = 15.5%
4 tows2 tows
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68 71 74 77 80 83 86 89 92 95 98 101
104
107
110
113
116
119
122
125
128
131
134
0
100
200
300
400
500
600
Maximum Diameter
Num
ber C
augh
t
Discard Rate = 19%
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0
2
4
6
8
10
12
14 Southern Protected Zone
Maximum Diameter
Perc
enta
ge C
ontr
ibut
ion
Discard Rate June = 72.5%
0
2
4
6
8
10
12
14
16 Southern Protected Zone
Maximum Diameter
Perc
enta
ge C
ontr
ibut
ion
Discard Rate Nov = 48.6%
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Biomass Estimates2 Key Questions:1) Is the population of scallops in a survey region able to be
harvested under the BSCZSF harvest strategy and fishery rules? In particular:
a) Are scallop abundances suitable for harvesting?b) Does the population structure meet discard rate
rules?2) Can the data collected from discrete regions of the fishery
be used to calculate biomass? In particular, is the spatial coverage of sample tows sufficient for meaningful biomass estimates?
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Abundances too low for commercial harvest?
Small number of tows covering small area
Discard rate too high (48.6% in November 2010)
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Abundances generally too low for commercial harvest? Higher abundance tows cover small areaDiscard rate too high (30%)
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Western Protected ZoneAbundances may be suitable for commercial harvest? Population structure meets discard rate rules (=15%)Acceptable spatial coverage of sample tows
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Western Protected Zone biomass estimatePost Stratification
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Western Protected Zone biomass estimatePost Stratification
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1) 100m bufferArea = 8.9km2
2) 250m bufferArea = 19.4km2
5) 2000m bufferArea = 119.0km2
6) 5000m bufferArea = 291.3km2
4) 1000m bufferArea = 66.8km2
Western Protected Zone biomass estimatePost Stratification
3) 500m bufferArea = 37.7km2
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Western Protected Zone biomass estimate
100m (black)
250m (grey
)
500m (yello
w)
1,000m
(blue)
2,000m
(pink)
5,000m (green)
Area (km2) 8.9 19.4 37.7 66.8 119.0 291.3Upper 95% CI
816 1,777 3,449 6,120 10,896
26,677
Mean 593 1,291 2,506 4,446 7,919 19,381Lower 95% CI
369 850 1,563 2,773 4,936 12,085
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Western Protected Zone biomass estimate
100m (black)
250m (grey
)
500m (yello
w)
1,000m
(blue)
2,000m
(pink)
5,000m (green)
Area (km2) 8.9 19.4 37.7 66.8 119.0 291.3Upper 95% CI
816 1,777 3,449 6,120 10,896
26,677
Mean 593 1,291 2,506 4,446 7,919 19,381Lower 95% CI
369 850 1,563 2,773 4,936 12,085
2008Area (km2) 68Upper 95% CI 4,567Mean 2,956Lower 95% CI 1,344
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Summary1. In general, more data is needed across the fishery
2. Western Protected Zone (WPZ) currently meets opening criteria
3. However, biomass figures are indicative only
4. There may be a smaller cohort coming through in the WPZ that is currently under-represented in dredge samples