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Publication - Research and analysis

Crab and lobster fisheries - stock assessments: results 2016 to 2019

Published
20 March 2023
Directorate
Marine Directorate, +1 more … Agriculture and Rural Economy Directorate
Topic
Marine and fisheries
ISBN
9781805255871

Results of Scottish regional brown crab (Cancer pagurus), velvet crab (Necora puber) and lobster (Homarus gammarus) stock assessments carried out by Marine Scotland Science (MSS) for the period 2016 to 2019.

View supporting documents Supporting documents

6. Tables

Table 1

Crab and lobster species landed into Scotland by UK vessels between 2009 and 2020.

Landings (tonnes)
2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Brown crab 9465 10546 11832 10892 10891 12306 11089 12158 11882 10352 9996 6670
Velvet crab 2728 2474 2147 2032 1576 1641 1494 1607 1611 1190 1608 1566
Deep-water crab 11 6 8 0 2 16 2 1 1 0 0 0
Northern stone crab 6 3 1 2 0 0 1 0 0 0 0 0
Green crab 226 214 237 301 272 225 194 164 124 101 112 108
European lobster 1092 1100 1219 1132 1026 1208 1042 1143 1222 1219 1225 1089
Spiny lobster 4 6 5 13 9 5 4 1 2 2 2 1
Squat lobsters 2 1 1 1 1 1 1 1 1 1 1 1

Table 2

Minimum landing size (MLS) regulations in Scotland for commercially important crab and lobster species (CW – carapace width mm; CL carapace length mm).

Species MLS (mm) Area Year measure introduced
Brown Crab 150 (CW) All areas except Shetland 2018
Lobster 87 (CL) East Coast 1999
90 (CL) West Coast (except Solway Firth) 2018
Velvet Crab 70 (CW) All areas 2018

Table 3

MSS Market sampling statistics, number of animals measured, number of trips sampled and percentage of trips sampled for brown crab by assessment area, 2016-19.

Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Animals measured 2016 205 4314 7589 0 9417 79908 6187 1606 1782 413 13165 577
2017 738 3896 7776 26 741 23108 2307 2523 3468 878 2559 0
2018 1230 1974 4344 0 0 4579 2945 1381 1566 654 1420 251
2019 140 1862 1822 0 182 11164 4229 1094 1010 482 243 318
Trips sampled 2016 2 22 26 0 11 467 4 12 19 6 10 3
2017 11 22 32 1 3 203 3 17 31 12 6 0
2018 8 23 25 0 0 32 3 12 23 11 4 3
2019 3 15 21 0 1 114 4 6 26 11 1 1
Percentage of trips sampled (%) 2016 0.9 0.6 2.3 0 3.1 16.8 3.7 2.5 0.5 0.3 6.1 0.5
2017 3.2 0.5 1.7 1.1 0.8 6.6 2.9 2.5 0.8 0.6 3.5 0
2018 1.8 0.5 1.0 0 0 1.0 4.5 1.5 0.7 0.5 2.3 0.3
2019 0.5 0.3 0.9 0 0.3 3.7 5.1 0.6 0.7 0.4 0.7 0.1

Table 4

MSS Market sampling statistics, number of animals measured, number of trips sampled and percentage of trips sampled for velvet crab by assessment area, 2016-19.

Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Animals measured 2016 1633 1518 2708 0 0 25109 0 2552 2844 1448 0 0
2017 2665 1122 3358 0 0 14616 0 2809 1847 3708 0 0
2018 1765 1232 3570 0 0 4661 0 2246 1392 3700 0 0
2019 957 2150 3909 0 0 13134 0 1351 2034 3561 0 505
Trips sampled 2016 9 13 17 0 0 121 0 6 18 10 0 0
2017 15 10 22 0 0 80 0 7 13 21 0 0
2018 11 10 21 0 0 29 0 5 17 25 0 0
2019 10 16 25 0 0 81 0 2 18 27 0 4
Percentage of trips sampled (%) 2016 6.2 0.4 1.6 0 0 5.6 0 1.0 0.9 0.5 0 0
2017 8.6 0.3 1.3 0 0 3.5 0 1.1 0.6 1.0 0 0
2018 7.2 0.3 1.1 0 0 1.3 0 0.8 1.0 1.3 0 0
2019 7.5 0.4 1.2 0 0 3.8 0 0.3 0.7 1.4 0 1.1

Table 5

MSS Market sampling statistics, number of animals measured, number of trips sampled and percentage of trips sampled for lobster by assessment area, 2016-19.

Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Animals measured 2016 76 361 1881 0 49 5604 178 2163 1480 691 0 0
2017 859 864 1598 3 7 3377 184 1940 2024 839 0 0
2018 304 888 1705 0 0 2492 79 1885 1156 618 0 0
2019 317 1182 1117 0 0 2844 148 2264 2153 1201 0 58
Trips sampled 2016 3 14 27 0 1 206 3 32 31 13 0 0
2017 21 12 36 1 1 138 2 10 41 18 0 0
2018 11 21 30 0 0 96 3 11 23 24 0 0
2019 6 23 28 0 0 99 5 150 43 32 0 2
Percentage of trips sampled (%) 2016 0.6 0.3 2.3 0 0.4 7.8 3.1 5.3 0.6 0.7 0 0
2017 4.4 0.2 1.8 1.2 0.3 4.9 2.2 1.3 0.8 0.8 0 0
2018 2.3 0.3 1.2 0 0 3.3 6.1 1.5 0.5 1.0 0 0
2019 1.0 0.4 1.1 0 0 3.5 7.7 17.5 0.8 1.2 0 0.3

Table 6

Biological parameters used in stock assessment for brown crab, velvet crab and lobster.

Growth parameters Length-Weight relationship Terminal group Fishing Mortality Natural Mortality Source
K L∞ a b F M
Brown crab Males 0.197 220 0.000059 3.214 0.5 0.1 Chapman, 1994
Females 0.172 220 0.000302 2.8534 0.5 0.1 Chapman, 1994
Shetland Males 0.188 246 0.00008 3.166 0.406 0.242 Tallack, 2002
Shetland Females 0.224 227 0.00024 2.895 0.174 0.256 Tallack, 2002
Velvet crab Males 0.105 103 0.0003 3.0389 1.9 0.1 Chapman, 1994
Females 0.118 100 0.0009 2.7405 1.1 0.1 Chapman, 1994
Shetland Males 0.463 107 0.0011 2.75 0.31 0.576 Tallack, 2002
Shetland Females 0.463 100.1 0.0038 2.42 0.202 0.576 Tallack, 2002
Lobster Males 0.11 173.4 0.000126 3.36 0.5 0.1 Chapman, 1994
Females 0.13 150 0.000919 2.922 0.5 0.1 Chapman, 1994
Shetland Males 0.112 188 0.0017 2.797 0.316 0.1 Mouat et al., 2006
Shetland Females 0.136 184 0.0004 3.123 0.452 0.1 Mouat et al., 2006

Table 7

Size at 50% maturity, Lmat (mm) for brown crab, velvet crab and lobster.

Lmat Source
Brown crab
Shetland Males 104.3 Tallack, 2007 (data from Shetland)
Females 133.5
Orkney Males 92 Haig et al., 2016 (data from Orkney)
Females 97
East coast Males 100.6 Mesquita et al., 2020 (data from East coast)
Females 128.1
West coast Males 106.5
Females 127.2 Mesquita et al., 2020 (data from Hebrides)
Velvet crab Males 45 Tallack, 2002 (Shetland data)
Females 56
Lobster
East Coast & Males 80 Lizárraga-Cubedo et al., 2003 (data from Firth of Forth)
South East Females 79
Other areas Males 98 (data from Hebrides)*
Females 110

* Potentially higher variability between assessment areas along the west coast.

Table 8

Percentage of total landings into Scotland of brown crab 2016–2020, by assessment area.

Species Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Brown crab (%) 2016 0.6 13.3 19.8 0.2 8.6 20.3 7.3 2.3 5.1 9.0 10.7 2.8
2017 1.5 15.3 15.7 0.1 7.5 21.2 6.8 4.1 5.5 10.3 8.2 3.8
2018 1.9 17.2 13.9 0.2 5.8 20.3 6.0 5.4 5.8 12.6 6.7 4.2
2019 2.7 17.8 11.5 0.5 4.5 19.5 5.4 6.1 5.9 17.2 5.3 3.6
2020 1.1 20.0 12.2 0.5 4.3 22.2 6.2 7.1 5.5 14.5 3.8 2.6

Table 9

Percentage of total landings into Scotland of velvet crab 2016–2020, by assessment area.

Species Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Velvet crab (%) 2016 3.5 12.9 17.2 1.5 0.5 26 0 7.3 5.2 23.9 0 2.0
2017 2.6 19.2 15.3 1.3 0.4 22.5 0 7.0 6.1 24.2 0 1.4
2018 2.0 18.1 16.6 1.4 0.9 23 0 8.1 5.4 22.5 0 2.0
2019 1.1 18.7 16.5 1.2 0.6 21.5 0 9.8 9.1 19.7 0 1.8
2020 0.9 20.0 15.8 2.5 0.4 25.1 0 11.8 7.6 14.7 0 1.1

Table 10

Percentage of total landings into Scotland of lobster 2016–2020, by assessment area.

Species Year Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Lobster (%) 2016 3.2 23.4 11.7 0.1 1.3 10.8 0.3 4.8 33.7 9.4 0 1.3
2017 3.2 29.8 11.4 0.1 1.4 9.8 0.3 4.8 28 9.6 0.1 1.5
2018 2.5 30.4 14.7 0.2 1.0 8.4 0.1 3.3 28 9.6 0.1 1.7
2019 2.3 25.1 14.2 0.2 1.0 9.7 0.2 3.8 30.1 11.0 0.1 2.3
2020 2.0 24.0 17.0 0.4 1.0 11.0 0.2 3.7 26.8 12.2 0 1.7

Table 11

Brown crab. Size-based indicators as a ratio between mean length, L̅, and mean length of the largest 5%, Lmax5% and the respective reference points (average for 2016-19). Values larger than 1 (green) and equal to 1 (yellow) indicate exploitation consistent with FMSY.

Assessment area L̅ / LF=M Lmax5%/0.9L∞
Males Females Males Females
Clyde** - 0.99 - 0.99
East Coast 0.98 0.99 0.96 0.99
Hebrides 1.03 1.03 1.01 1.00
Mallaig - - - -
North Coast * - - - -
Orkney 1.00 1.01 1.00 1.00
Papa Bank 1.04 1.02 1.07 1.02
Shetland 0.98 1.00 0.88 0.97
South East 1.00 0.99 0.97 0.97
South Minch 1.00 1.00 0.99 0.99
Sule** - 1.01 - 1.00
Ullapool - - - -

* Average 2016-19 not calculated as 2018 data were missing.

** Average 2016-19 for males not calculated as 2019 data were missing.

Table 12

Velvet crab. Size-based indicators as a ratio between mean length, L̅, and mean length of the largest 5%, Lmax5% and the respective reference points (average for 2016-19).

Assessment area L̅/LF=M Lmax5%/0.9L∞
Males Females Males Females
Clyde 0.96 0.95 0.89 0.89
East Coast 0.96 0.95 0.91 0.88
Hebrides 0.99 0.97 0.95 0.93
Mallaig - - - -
North Coast - - - -
Orkney 0.97 0.96 0.93 0.92
Papa Bank - - - -
Shetland 0.97 0.97 0.90 0.91
South East 0.98 0.97 0.93 0.92
South Minch 0.96 0.94 0.90 0.89
Sule - - - -
Ullapool* - - - -

*Average 2016-19 not calculated as 2016-2018 data were missing.

Table 13

Lobster. Size-based indicators as a ratio between mean length, L̅, and mean length of the largest 5%, Lmax5% and the respective reference points (average for 2016-19). Values larger than 1 (green) and equal to 1 (yellow) indicate exploitation consistent with FMSY.

Assessment area L̅/LF=M Lmax5%/0.9L∞
Males Females Males Females
Clyde* - - - -
East Coast 0.91 0.93 0.85 0.90
Hebrides 0.95 0.99 0.88 0.98
Mallaig - - - -
North Coast - - - -
Orkney 0.94 0.99 0.90 1.01
Papa Bank** - - - -
Shetland 0.94 0.92 0.85 0.82
South East 0.88 0.91 0.78 0.82
South Minch 0.92 0.95 0.84 0.92
Sule - - - -
Ullapool - - - -

* Average 2016-19 not calculated as 2016 data were missing.

** Average 2016-19 not calculated as 2018 data were missing.

Table 14

Brown crab fishing mortality (Fbar) from Length Cohort Analysis (2016-19) in relation to FMSY. Fishing mortality calculated across a fixed range of 145-190 mm CW interval (150-200 mm for Shetland).

Assessment area Fbar FMSY FMSY basis
Males Females Males Females
Clyde 0.43 0.39 0.29 0.38 LCA 2016-19
East Coast 0.66 0.47 0.28 0.33 LCA 2016-19
Hebrides 0.41 0.40 0.35 0.33 LCA 2016-19
Mallaig - - - - -
North Coast 0.43 0.44 0.24 0.29 LCA 2016-19
Orkney 0.51 0.36 0.36 0.34 LCA 2016-19
Papa Bank 0.25 0.29 0.32 0.34 LCA 2016-19
Shetland 0.56 0.44 0.36 0.36 LCA 2016-19
Shetland par* 0.83 0.59 0.80 1.68 LCA 2016-19
South East 0.64 0.48 0.40 0.36 LCA 2016-19
South Minch 0.54 0.44 0.35 0.33 LCA 2016-19
Sule 0.41 0.39 0.34 0.35 LCA 2016-19
Ullapool 0.48 0.30 0.43 0.30 LCA 2016-19

*Fs calculated using Shetland biological parameters

Table 15

Velvet crab fishing mortality (Fbar) from Length Cohort Analysis (2016-19) in relation to FMSY. Fishing mortality calculated across a fixed range of 60-80 mm CW interval (75-85 mm for Shetland).

Assessment area Fbar FMSY FMSY basis
Males Females Males Females
Clyde 0.36 0.51 0.16 0.28 LCA 2016-19
East Coast 0.32 0.49 0.23 0.16 LCA 2016-19
Hebrides 0.15 0.32 0.16 0.20 LCA 2016-19
Mallaig - - - - -
North Coast - - - - -
Orkney 0.21 0.34 0.19 0.22 LCA 2016-19
Papa Bank - - - - -
Shetland 0.47 0.82 0.41 0.57 LCA 2016-19
Shetland par* 2.31 2.62 3.83 6.42 LCA 2016-19
South East 0.22 0.33 0.20 0.23 LCA 2016-19
South Minch 0.27 0.52 0.21 0.38 LCA 2016-19
Sule - - - - -
Ullapool - - - - -

*Fs calculated using Shetland biological parameters

Table 16

Lobster fishing mortality (Fbar) from Length Cohort Analysis (2016-19) in relation to FMSY. Fishing mortality calculated across a fixed range of 95-130 mm CL interval (110-155 mm for Shetland).

Assessment area Fbar FMSY FMSY basis
Males Females Males Females
Clyde 0.58 0.37 0.25 0.30 LCA 2016-19
East Coast 0.44 0.38 0.13 0.35 LCA 2016-19
Hebrides 0.41 0.26 0.18 0.32 LCA 2016-19
Mallaig - - - - -
North Coast - - 0.11 0.34 LCA 2002-05
Orkney 0.36 0.23 0.17 0.31 LCA 2016-19
Papa Bank 0.27 0.16 0.19 0.31 LCA 2016-19
Shetland 0.42 0.56 0.23 0.21 LCA 2016-19
South East 0.70 0.58 0.27 0.38 LCA 2016-19
South Minch 0.52 0.36 0.26 0.32 LCA 2016-19
Sule - - - - -
Ullapool - - 0.17 0.33 LCA 2006-08

Contact

Email: carlos.mesquita@gov.scot

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