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Publication - Research and analysis

Razor clam surveys - Firth of Clyde and Solway: report

Published
6 December 2024
Directorate
Marine Directorate
Topic
Marine and fisheries
ISBN
9781836018858

This report describes a survey carried out in the Firth of Clyde (2023) and Solway (2024) 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 class 1 objects (fully emerged E. siliqua within video frame) 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 Number of 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
Out trial 31 0.11 0.77 0.41 0.39 0.03 -0.67
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
Out trial 31 0.00 1.75 0.12 0.25 0.07 6.37
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
Out trial 31 0.00 0.40 0.05 0.08 0.02 3.83
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
Out trial 31 0.23 2.60 0.61 0.72 0.09 3.73
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 Number of 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
Ayr Bay 18 0.06 0.56 0.24 0.26 0.04 -0.97
Culzean Bay 10 0.05 0.39 0.24 0.22 0.04 -1.66
Turnberry Bay 19 0.18 0.89 0.35 0.40 0.04 0.81
In trial 98 0.00 0.89 0.23 0.26 0.02 0.95
Machrie Bay 19 0.11 0.63 0.31 0.34 0.04 -1.39
Carradale Bay 7 0.30 0.64 0.52 0.49 0.05 -1.83
Saddell Bay 5 0.34 0.77 0.42 0.47 0.08 -1.04
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
Ayr Bay 18 0.05 0.41 0.16 0.18 0.03 -0.58
Culzean Bay 10 0.14 0.51 0.21 0.27 0.04 -1.36
Turnberry Bay 19 0.07 0.48 0.19 0.23 0.03 -1.12
In trial 98 0.00 0.51 0.10 0.14 0.01 0.76
Machrie Bay 19 0.02 1.75 0.16 0.38 0.11 2.37
Carradale Bay 7 0.02 0.14 0.04 0.07 0.02 -1.81
Saddell Bay 5 0.00 0.06 0.04 0.03 0.01 -1.92
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
Ayr Bay 18 0.00 0.53 0.10 0.14 0.03 1.30
Culzean Bay 10 0.02 0.20 0.08 0.10 0.02 -1.78
Turnberry Bay 19 0.03 0.37 0.11 0.15 0.03 -1.24
In trial 98 0.00 0.53 0.10 0.14 0.01 0.76
Machrie Bay 19 0.00 0.45 0.03 0.08 0.02 2.83
Carradale Bay 7 0.00 0.15 0.11 0.11 0.02 -0.15
Saddell Bay 5 0.02 0.09 0.05 0.05 0.01 -1.66
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
Ayr Bay 18 0.16 1.13 0.53 0.58 0.07 -1.33
Culzean Bay 10 0.30 0.85 0.62 0.59 0.07 -1.73
Turnberry Bay 19 0.36 1.41 0.81 0.78 0.07 -0.89
In trial 98 0.00 1.40 0.37 0.47 0.03 -0.22
Machrie Bay 19 0.23 2.60 0.61 0.79 0.15 1.04
Carradale Bay 7 0.38 0.92 0.68 0.66 0.08 -1.63
Saddell Bay 5 0.38 0.92 0.49 0.55 0.10 -1.07
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 Turn-berry Bay Machrie Bay Saddell Bay Carra-dale 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 recorded class 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
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
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
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
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
2023 2,581 152.5 44.1 160 17 254 -0.38 -0.89
Table 7: Counts and percentages of different size categories (Large >= 150 mm; Medium <= 100 mm to <150 mm; and Small < 100 mm) of whole E. siliqua within each site comparing shell lengths from the 2017 and 2023 Ayrshire coast surveys.
2017 2023
Count Percentage Count Percentage
Large size class 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 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 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 – these are provided as a separate table in the Supplementary information accompanying this report.

Table 10: Summary statistics for E. siliqua density estimates (number m‑2) from the 2024 Fleet Bay, Solway survey. Shell length categories are: Small < 100 mm; Medium <= 100 mm to <150 mm; Large >= 150 mm.
Size Number of tows Min Max Median Mean SE of Mean Kurtosis
Large 16 0.11 1.65 0.77 0.77 0.09 0.65
Medium 16 0.07 1.11 0.34 0.40 0.07 0.93
Small 16 0.02 0.40 0.14 0.16 0.03 -0.22
All 16 0.27 2.12 1.34 1.32 0.11 -0.13

Contact

Email: mss.fisheries.advice@gov.scot

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