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Geoduck Aquaculture:
An Examination of Predator Protection Methodology and Potential
Environmental Impacts
C.M. Pearce, Y.X. An, J.M. Blackburn,
L.J. Keddy, D.L. Paltzat, S.W. Williams
Fisheries and Oceans Canada
Pacific Biological Station
Project Objectives
Intertidal and subtidal projects with objectives:
(1) To assess the effect of different forms of predator protection on survivorship and growth of juvenile clams
(2) To assess the potential effects of geoduck culture on the benthic environment
(3) To assess the potential effects of harvesting the clams with a high-powered water jet on the benthic environment
Intertidal Study Site
Location: Head of Nanoose Bay, BC
Intertidal plot: ~0.5 m chart datum
Plot size: 20 m x 3 m
Experimental Treatments
Predator Protection
• PVC tube protection methodology as used in WA
• Examining 3 factors:(1) PVC tube diameter (10.2 vs. 15.2 cm)
(2) PVC tube length (25.4 vs. 30.5 cm)
(3) Size of mesh screen on the PVC tubes (6 vs. 12 mm)
• 8 treatments with 30 reps per treatment (240 tubes total)
Intertidal Research Plot
Intertidal Research Plot
Experimental Protocols
Growth and Survivorship
• Seed (SL: 20-60 mm) out-planted in July 2005 after having measured shell length and wet weights
• Density of two seed per tube (hand planted)
• Planted at 0.5-m tidal height
• Growth (SL and WW) and survivorship assessed after 12 months, upon removal of clams
Experimental Protocols
Assessing Impacts on Benthic Environment
• Benthic sediment samples taken before outplanting and immediately after for determination of:
(1) Sediment grain size (4) TOC and TN
(2) Percent organics (5) Infaunal diversity
(3) Sulphide/ORP
• Samples also collected at 4, 6, 10, and 12 months of experiment (post-seed)
• Clams then extracted with stinger and sediment samples taken immediately after and at 4 and 6 months (post-harvest)
Experimental Protocols
Assessing Impacts on Benthic Environment
• Benthic sediment samples collected at each sample period within culture plot (0 m) and at 5, 10, 25, and 50 m distance from plot along 3 transects
(3 replicates)
(1) Parallel to shore line at same tidal height as plot
(2) Perpendicular to shore line towards ocean
(3) Perpendicular to shore line towards beach
Collection of Sediment Samples
Results
Growth (length and wet weight)
(1) Significantly better in the larger diameter (15 cm) than in the smaller diameter (10 cm) pipes
(2) Significantly better in the shorter (25 cm) than in the longer (30 cm) pipes
(3) Significantly better in the larger mesh (12 mm) than in the smaller mesh (6 mm) pipes
Survivorship(1) Not significantly affected by pipe diameter, pipe length, or
mesh size (average survivorship: 47.7 ± 2.5 %)
Results
Pre-seed vs Post-seed Pre-harvest vs Post-harvest
Seeded Plot Research Plot Seeded Plot Research Plot
(0 m) (0-50 m) (0 m) (0-50 m)
Variable
Percent Organics NS NS S, reduction NS
[Sulphide] at 2 cm S, reduction S, reduction NS NS
[Sulphide] at 4 cm S, reduction S, reduction NS NS
ORP at 2 cm NS NS NS S, reduction
ORP at 4 cm NS NS NS S, reduction
Total Organic Carbon NS NS NS NS
Total Nitrogen NS NS NS NS
Results
Pre-seed vs Post-seed Pre-harvest vs Post-harvest
Seeded Plot Research Plot Seeded Plot Research Plot
Variable (0 m) (0-50 m) (0 m) (0-50 m)
Grain Size
>2 mm NS NS S, reduction NS
1-2 mm NS NS NS NS
500 μm-1 mm NS NS NS NS
250-500 μm NS NS NS NS
125-250 μm NS NS S, increase NS
63-125 μm NS NS S, increase NS
45-63 μm NS NS S, increase NS
<45 μm NS NS NS NS
Results
0
4
8
12
16
Jun 05
Aug 05
Jan 06
Jul 06
Jul 06
Jan 07
0
10
20
30
40
50
60
70
80
90
Jun 05
Aug 05
Jan 06
Jul 06
Jul 06Jan 07
Conclusions
(1) Growth better in the larger diameter pipes than in the smaller diameter pipes
(2) Growth better in the shorter pipes than in the longer pipes
(3) Growth better with the larger mesh than with smaller mesh
(4) Planting and harvest have some impacts on the benthic environment, but relatively minimal
Future Research
• Impacts on nearby “sensitive habitat” (e.g. eelgrass and kelp beds)
• Monitoring potential impact of commercial-scale aquaculture development– Benthic impacts– Water column impacts
Acknowledgements
Funding: DFO ACRDP, BC MAL, Manatee Holdings Ltd.
TOC/TN Analyses: Maureen Soon, UBC
Technical Assistance: Chanelle Mathieu, Laura Skinner, Damien Barnes (Katimavik volunteers)
March Klaver, Ryan Sherman, Caroline Fox (DFO)
Results (Shell Length)
Source of Variation Significance
Pipe Diameter (D) P < 0.05
Pipe Length (L) P < 0.05
Mesh Size (M) P < 0.0001
D x L NS
D x M P < 0.05
L x M NS
D x L x M NS
Results (Shell Length)
P<0.05P<0.0001
10 15Pipe Diameter (cm)
0
50
100
150
Cha
nge
inS
hell
Leng
th(%
)
12 mm6 mm
Mesh Size
P<0.005NS
6 12Mesh Size (mm)
0
50
100
150
Cha
nge
inS
hell
Leng
th(%
)
15 cm10 cm
Pipe Diameter
Results (Shell Length)
25 30Pipe Length (cm)
0
50
100
150
Cha
nge
inS
hell
Leng
th(%
)
P<0.05
Results (Wet Weight)
Source of Variation Significance
Pipe Diameter (D) P < 0.05
Pipe Length (L) P = 0.06
Mesh Size (M) P < 0.0001
D x L NS
D x M NS
L x M NS
D x L x M NS
Results (Wet Weight)
10 15Pipe Diameter (cm)
0
200
400
600
800
1000
1200
Cha
nge
inW
etW
eigh
t (%
)
P<0.05 P=0.06
25 30Pipe Length (cm)
0
200
400
600
800
1000
1200
Cha
nge
inW
etW
eigh
t (%
)
Results (Wet Weight)
Mesh Size (mm)
0
200
400
600
800
1000
1200
Cha
nge
inW
etW
eigh
t (%
)
126
P<0.0001
Results (Survivorship)
Source of Variation Significance
Pipe Diameter (D) NS
Pipe Length (L) NS
Mesh Size (M) NS
D x L NS
D x M NS
L x M NS
D x L x M NS
Pipe Diameter(cm)
Pipe Length(cm)
Mesh Size(mm)
Survivorship %(mean ± SE)
10 25 6 45.0 ± 6.5
10 25 12 38.3 ± 7.1 (min)
10 30 6 45.0 ± 7.7
10 30 12 51.7 ± 7.8
15 25 6 55.0 ± 6.5 (max)
15 25 12 50.0 ± 6.3
15 30 6 48.3 ± 7.4
15 30 12 48.3 ± 7.8
Overall 47.7 ± 2.5
Results (Survivorship)
Environmental Data Caveats
• Infaunal species data not yet ready
• Results somewhat complicated due to 3-way analysis (date, transect, distance)
• Talk will focus on the effect of date – post-seeding versus pre-seeding comparison– post-harvesting versus pre-harvesting comparison
• Talk will focus on specific results within the seeded plot (0 m data) and on general results within the experimental area (0-50 m)
Results (Percent Organics)
ABC ABBCD
BCDBC
A
DCD
Range of means: 1.16 - 1.86%
Date
0
1
2
30 m
ABC ABCBC
ABABC
AABC
C
Date
0
1
2
3
4
5
6Range of means: 1.46 - 1.83%
0-50 m
Results (Sulphide, 2 cm)
Date
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9Range of means: 0.019 - 0.162 ppm
0-50 m0 m
Date
0.0
0.1
0.2
0.3
0.4
0.5Range of means: 0.005 - 0.327 ppm
Results (Sulphide, 4 cm)
Range of means: 0.018 - 0.540 ppm
0 m
Date
0.0
0.2
0.4
0.6
0.8
1.0
1.2Range of means: 0.031 - 0.332 ppm
0-50 m
Date
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Results (ORP, 2 cm)
Date
0
100
200
300
400
5000-50 m
Range of means: 249.4 - 318.0 mV
0 mRange of means: 230.3 - 342.3 mV
Date
0
100
200
300
400
500
Results (ORP, 4 cm)
Date
0
100
200
300
400
5000-50 m
Range of means: 250.1 - 315.3 mV
0 mRange of means: 240.0 - 324.0 mV
Date
0
100
200
300
400
Results (TOC %)
Date
0.0
0.2
0.4
0.6
0.8
1.0
1.20 m
Range of means: 0.164 - 0.500 %
0-50 mRange of means: 0.246 - 0.384 %
Date
0.0
0.5
1.0
1.5
Results (TN %)
Date
0.00
0.02
0.04
0.06
0.08
0.10
0.120-50 m
Range of means: 0.033 - 0.051 %
0 mRange of means: 0.027 - 0.046 %
Date
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Results (Grain Size, 0 m)
Date
0
1
2
3
4
5
6
7
8
9
1-2
mm
Gra
inS
ize
(%)
Date
0
10
20
30
500
um-1
mm
Gra
inS
ize
(%)
Date
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
<45
umG
rain
Siz
e(%
)
Date
0
10
20
30
>2
mm
Gra
inS
ize
(%)
Date
0
10
20
30
40
50
60
250-
500
umG
rain
Siz
e(%
)
Date
0
10
20
30
125-
250
umG
rain
Siz
e(%
)
Date
0
5
10
15
20
63-1
25um
Gra
inS
ize
(%)
Date
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
45-6
3um
Gra
inS
ize
(%)
Results (Grain Size, 0-50 m)
Date
0
10
20
30
40
50
>2
mm
Gra
inS
ize
(%)
Date
0
10
20
30
40
500
um-1
mm
Gra
inS
ize
(%)
Date
0
10
20
30
40
50
60
70
250-
500
umG
rain
Siz
e(%
)
Date
0
10
20
30
40
125-
250
umG
rain
Siz
e(%
)
Date
0
5
10
15
1-2
mm
Gra
inS
ize
(%)
Date
0
10
20
30
63-1
25um
Gra
inS
ize
(%)
Date
0.0
0.5
1.0
1.5
2.0
2.5
45-6
3um
Gra
inS
ize
(%)
Date
0.0
0.5
1.0
1.5
<45
umG
rain
Siz
e(%
)
