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Publication - Advice and guidance

Razor clam surveys - Firth of Clyde 2023 and Solway 2024-2025: report

Published
25 April 2025
From
Acting Cabinet Secretary for Net Zero and Energy, +1 more … Director-General Net Zero
Directorate
Agriculture and Rural Economy Directorate, +1 more … Marine Directorate
Topic
Marine and fisheries
ISBN
9781836914624

This report describes a surveys carried out in the Firth of Clyde (2023) and Solway (2024 and 2025) to estimate the densities and sizes of razor clam, Ensis siliqua. The surveys were conducted as part of the Scottish Government’s electrofishing scientific trial.

View supporting documents Supporting documents

Appendix II: Report tables

Table 1: Tow details for 2023 Firth of Clyde survey – these are provided as a separate table in the Supplementary information accompanying this report.

Table 2: Summary statistics for shell lengths (mm) based on video measurements from all Category 1 (fully emerged E. siliqua within video frame) objects in the 2023 Firth of Clyde survey. “In trial” includes tows conducted within the present scientific trial area, “Out trial” includes tows conducted outside of the present scientific trial area.
Sites n mean SD median min max skew kurtosis
Irvine Bay 863 166.5 39.5 179 17 240 -0.86 -0.10
Ayr Bay 593 137.8 43.0 135 51 252 0.02 -1.14
Culzean Bay 274 142.9 42.4 139 33 232 0.02 -0.60
Turnberry Bay 851 145.7 45.2 154 20 236 -0.34 -0.90
In trial 2,581 150.5 44.1 158 17 252 -0.38 -0.89
Machrie Bay 688 145.7 36.4 145 38 246 0.00 -0.24
Carradale Bay 225 172.6 47.8 193 46 243 -1.03 -0.31
Saddell Bay 140 185.8 41.1 199 58 243 -1.75 2.24
Outside trial 1,053 156.8 42.6 155 38 246 -0.30 -0.78
Both areas 3,634 152.4 43.8 157 15 252 -0.36 -0.84
Table 3: Summary statistics for E. siliqua density estimates (number m-2) from the 2023 Firth of Clyde survey by shell length category (small < 100 mm; medium <= 100 mm to <150 mm; large >= 150 mm). “In trial” includes tows conducted within the present scientific trial area, “Out trial” includes tows conducted outside of the present scientific trial area.
Size Area N (tows) min max median mean SE of mean kurtosis
Large In trial 98 0.00 0.89 0.23 0.26 0.02 0.95
Large Out trial 31 0.11 0.77 0.41 0.39 0.03 -0.67
Large Both 129 0.00 0.89 0.26 0.29 0.02 0.07
Medium In trial 98 0.00 0.53 0.10 0.14 0.01 0.76
Medium Out trial 31 0.00 1.75 0.12 0.25 0.07 6.37
Medium Both 129 0.00 1.75 0.10 0.16 0.02 24.76
Small In trial 98 0.00 0.51 0.04 0.08 0.01 4.35
Small Out trial 31 0.00 0.40 0.05 0.08 0.02 3.83
Small Both 129 0.00 0.51 0.04 0.08 0.01 4.40
All In trial 98 0.00 1.41 0.37 0.47 0.03 -0.22
All Out trial 31 0.23 2.60 0.61 0.72 0.09 3.73
All Both 129 0.00 2.6 0.43 0.53 0.03 6.72
Table 4: Summary statistics for Ensis siliqua density estimates (number m-2) for the 2023 Firth of Clyde survey by site. Shell length categories are: Large >= 150 mm; Medium <= 100 mm to <150 mm; and Small < 100 mm). “In trial” includes tows conducted within the present scientific trial area, “Out trial” includes tows conducted outside of the present scientific trial area.
Size Site N (tows) min max median mean SE of mean kurtsosis
Large Irvine Bay 51 0.00 0.57 0.19 0.21 0.02 -0.18
Large Ayr Bay 18 0.06 0.56 0.24 0.26 0.04 -0.97
Large Culzean Bay 10 0.05 0.39 0.24 0.22 0.04 -1.66
Large Turnberry Bay 19 0.18 0.89 0.35 0.40 0.04 0.81
Large In trial 98 0.00 0.89 0.23 0.26 0.02 0.95
Large Machrie Bay 19 0.11 0.63 0.31 0.34 0.04 -1.39
Large Carradale Bay 7 0.30 0.64 0.52 0.49 0.05 -1.83
Large Saddell Bay 5 0.34 0.77 0.42 0.47 0.08 -1.04
Large Out trial 31 0.11 0.77 0.41 0.40 0.03 -0.67
Medium Irvine Bay 51 0.00 0.26 0.05 0.06 0.01 3.02
Medium Ayr Bay 18 0.05 0.41 0.16 0.18 0.03 -0.58
Medium Culzean Bay 10 0.14 0.51 0.21 0.27 0.04 -1.36
Medium Turnberry Bay 19 0.07 0.48 0.19 0.23 0.03 -1.12
Medium In trial 98 0.00 0.51 0.10 0.14 0.01 0.76
Medium Machrie Bay 19 0.02 1.75 0.16 0.38 0.11 2.37
Medium Carradale Bay 7 0.02 0.14 0.04 0.07 0.02 -1.81
Medium Saddell Bay 5 0.00 0.06 0.04 0.03 0.01 -1.92
Medium Out trial 31 0.00 1.75 0.10 0.25 0.07 6.37
Small Irvine Bay 51 0.00 0.13 0.01 0.02 0.00 1.74
Small Ayr Bay 18 0.00 0.53 0.10 0.14 0.03 1.30
Small Culzean Bay 10 0.02 0.20 0.08 0.10 0.02 -1.78
Small Turnberry Bay 19 0.03 0.37 0.11 0.15 0.03 -1.24
Small In trial 98 0.00 0.53 0.10 0.14 0.01 0.76
Small Machrie Bay 19 0.00 0.45 0.03 0.08 0.02 2.83
Small Carradale Bay 7 0.00 0.15 0.11 0.11 0.02 -0.15
Small Saddell Bay 5 0.02 0.09 0.05 0.05 0.01 -1.66
Small Out trial 31 0.00 0.45 0.10 0.25 0.07 6.37
All Irvine Bay 51 0.00 0.82 0.29 0.29 0.03 0.25
All Ayr Bay 18 0.16 1.13 0.53 0.58 0.07 -1.33
All Culzean Bay 10 0.30 0.85 0.62 0.59 0.07 -1.73
All Turnberry Bay 19 0.36 1.41 0.81 0.78 0.07 -0.89
All In trial 98 0.00 1.40 0.37 0.47 0.03 -0.22
All Machrie Bay 19 0.23 2.60 0.61 0.79 0.15 1.04
All Carradale Bay 7 0.38 0.92 0.68 0.66 0.08 -1.63
All Saddell Bay 5 0.38 0.92 0.49 0.55 0.10 -1.07
All Out trial 31 0.23 2.60 0.61 0.72 0.09 3.73
All All 129 0.00 2.60 0.43 0.53 0.03 6.72
Table 5: Total counts of incidental organisms observed in the 2023 Firth of Clyde survey by location in 2023.
Tows within the trial area Tows outside the trial area
Irvine Bay Ayr Bay Culzean Bay Turnberry Bay Machrie Bay Saddell Bay Carradale Bay
Crab 348 84 123 171 69 19 28
Sandeel 170 23 5 55 28 14 8
Hermit crab 149 10 8 56 11 4 9
Starfish 82 4 10 39 9 1 9
Flatfish 23 3 7 20 3 4 2
Fish (misc) 4 10 7 7 6 1 1
Surf clam 1 0 0 8 0 0 0
Brown shrimp 2 0 0 2 0 0 1
Cormorant 4 0 0 0 0 0 0
Brittlestar 3 0 0 0 0 0 0
Edible crab 1 1 0 1 0 0 0
Eider duck NA 0 0 2 0 0 0
Scallop NA 0 1 0 1 0 0
Fish (gurnard?) 1 0 0 0 0 0 0
Octopus NA 0 0 0 1 0 0
Pipefish 1 0 0 0 0 0 0
Table 6: Summary statistics for E. siliqua shell lengths (mm) based on Category 1 objects (fully emerged E. siliqua within video frame) comparing results from the 2017 and 2023 Ayrshire coast surveys.
Site Year n mean sd median min max skew kurtosis
Irvine 2017 249 167.4 27.4 170 108 235 0.007 -0.92
Irvine 2023 863 168.5 39.5 181 17 242 -0.86 -0.10
Ayr 2017 386 157.0 31.4 158 67 225 0.07 -0.99
Ayr 2023 593 139.8 43.0 137 51 254 0.02 -1.14
Culzean 2017 160 170.0 31.9 182 99 236 -0.47 -1.07
Culzean 2023 274 144.9 42.4 141 33 234 0.02 -0.60
Turnberry 2017 586 161.5 28.1 167 29 230 -0.48 0.20
Turnberry 2023 851 147.7 45.2 156 20 238 -0.34 -0.90
All 2017 1,381 162.2 30.0 166 30 236 -0.23 -0.56
All 2023 2,581 152.5 44.1 160 17 254 -0.38 -0.89
Table 7: Counts and percentages of different size classes (Large >= 150 mm; Medium <= 100 mm to <150 mm; and Small < 100 mm) of Category 1 objects (fully emerged E. siliqua within video frame) within each site comparing shell lengths from the 2017 and 2023 Ayrshire coast surveys.
Large size class 2017 2023
Count Percentage Count Percentage
Irvine Bay 171 68.7 610 70.7
Ayr Bay 217 56.2 258 43.5
Culzean Bay 112 70.0 105 38.3
Turnberry Bay 385 65.7 439 51.6
Medium size class Count Percentage Count Percentage
Irvine Bay 78 31.3 180 20.9
Ayr Bay 167 43.3 200 33.7
Culzean Bay 47 29.4 127 46.4
Turnberry Bay 194 33.1 250 29.4
Small size class Count Percentage Count Percentage
Irvine Bay 0 0.0 73 8.5
Ayr Bay 2 0.5 135 22.8
Culzean Bay 1 0.6 42 15.3
Turnberry Bay 7 1.2 162 19.0

Table 8: Tow details for Ayr coast survey (Firth of Clyde) in 2017 – these are provided as a separate table in the Supplementary information accompanying this report.

Table 9: Tow details for Fleet Bay, Solway survey in 2024 – 2025 – these are provided as a separate table in the Supplementary information accompanying this report.

Table 10: Summary statistics for shell lengths (mm) based on video measurements from all Category 1 (fully emerged E. siliqua within video frame) objects in the 2024 – 2025 Solway survey.
Sites n mean sd median min max skew kurtosis
Wigtown Bay 683 131.6 33.9 130.7 25.7 235.7 -0.1 -0.45
Fleet Bay 1506 147.1 36.0 154.9 22.2 249.5 -0.59 -0.26
Kirkudbright Bay 639 136.3 40.8 146.8 24.5 243.8 -0.34 -0.96
All 2823 140.9 37.3 146.8 22.2 249.5 -0.41 -0.58
Table 11: Summary statistics for E. siliqua density estimates (number m-2) from the 2024 – 2025 Solway survey by shell size class (Small: < 100 mm; Medium: <= 100 mm to <150 mm; Large: >= 150 mm shell length).
Size Site N (tows) min max median mean SE of mean kurtsosis
Large Wigtown Bay 15 0.02 0.49 0.23 0.23 0.03 -0.49
Large Fleet Bay 20 0.11 1.65 0.74 0.77 0.08 0.35
Large Kirkudbright Bay 14 0.16 0.51 0.33 0.34 0.03 -1.06
Medium Wigtown Bay 15 0.08 1.00 0.19 0.38 0.08 -1.06
Medium Fleet Bay 20 0.07 1.11 0.35 0.45 0.07 -0.35
Medium Kirkudbright Bay 14 0.12 0.35 0.19 0.21 0.02 -0.56
Small Wigtown Bay 15 0.01 0.49 0.08 0.11 0.03 3.17
Small Fleet Bay 20 0.00 0.40 0.15 0.17 0.02 -0.82
Small Kirkudbright Bay 14 0.06 0.29 0.17 0.16 0.02 -1.47
All Wigtown Bay 15 0.21 1.55 0.50 0.71 0.12 -1.35
All Fleet Bay 20 0.27 2.42 1.37 1.38 0.12 -0.38
All Kirkudbright Bay 14 0.43 0.96 0.68 0.71 0.05 -1.50
Large All 49 0.2 1.65 0.36 0.48 0.05 1.32
Medium All 49 0.07 1.11 0.28 0.36 0.04 0.62
Small All 49 0.00 0.49 0.13 0.15 0.02 0.57
All All 49 0.21 2.42 0.88 0.99 0.08 -0.35

Contact

Email: mss.fisheries.advice@gov.scot

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