We use cookies to collect anonymous data to help us improve your site browsing experience.

Click 'Accept all cookies' to agree to all cookies that collect anonymous data. To only allow the cookies that make the site work, click 'Use essential cookies only.' Visit 'Set cookie preferences' to control specific cookies.

Set cookie preferences

Your cookie preferences have been saved. You can change your cookie settings at any time.

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

8. Annexes

8.1. Annex A: Sampling Data – Decisions on which Species/Areas Stock Assessments Were Run

Table A 1
Decision Table for Brown Crab
Brown crab Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Assessed in (2013-2015)? √ √ √ √ √ √ √ √ √ √
N individuals/landings sampled ok good good poor good good good good good good good ok
N years available for average LF good good good poor ok 3 good good good good good good ok 3
Sampling seasonality (quarters) good good good poor good good good good good good good good
LFD shape ok good good poor good good good good good ok good ok
Assessment 2016-2019 √ √ √ √ √ √ √ √ √ √ √
Table A 2
Decision Table for Velvet Crab
Velvet crab Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Assessed in (2013-2015)? √ √ √ √ √ √ √
N individuals/landings sampled good good good poor poor good poor good good good poor poor
N years available for average LF good good good poor poor good poor good good good poor poor
Sampling seasonality (quarters) good good good poor poor good poor good good good poor ok 3/4
LFD shape good ok good poor poor good poor good good good poor ok
Assessment 2016-2019 √ √ √ √ √ √ √
Table A 3
Decision Table for Lobster
Lobster Clyde East Coast Hebrides Mallaig North Coast Orkney Papa Bank Shetland South East South Minch Sule Ullapool
Assessed in (2013-2015)? √ √ √ √ √ √ √ √
N individuals/landings sampled ok good good poor poor good ok good good good poor poor
N years available for average LF good good good poor ok 2 good good good good good poor poor
Sampling seasonality (quarters) good good good poor ok 1/2 good good good good good poor ok 3/4
LFD shape good good good poor poor good ok good good good poor poor
Assessment 2016-2019 √ √ √ √ √ √ √ √

Table A 4

Legend for Decision Tables

N individuals/landings sampled

POOR: No sampling or very few animals sampled (average < 100 per year)

OK: Few animals sampled (average < 500 per year)

GOOD: Several animals sampled (average > 500 per year)

N years available for average LFD

POOR: < 2 years

OK: 2/3 years

GOOD: 4 years

Sampling seasonality

POOR: Less than two quarters sampled over the 4 year period

OK: Two or three quarters sampled over the 4 year period

GOOD: All quarters sampled over the 4 year period

LF shape

POOR: No data or very few animals sampled

OK: LF with some spikes

GOOD: Approximately normal with no spikes

8.2. Annex B: Length Frequency Distributions

Figure B 1 : Brown crab carapace width (mm) frequency histogram by assessment area averaged over the period 2016-19. The data presented are aggregated by 5 mm increments and shown as a proportion of the total landings.
displays the brown crab carapace width frequency histogram by assessment area, averaged over the period 2016-19 for both males and females. The length distributions in most areas for which sampling data is available appear to approximately follow a normal distribution.
Figure B 2 : Velvet crab carapace width (mm) frequency histogram by assessment area averaged over the period 2016-19 for males and females. The data presented are aggregated by 3 mm increments and shown as a proportion of the total landings.
displays the velvet crab carapace width frequency histogram by assessment area, averaged over the period 2016-19 for both males and females. The length distributions in most areas for which sampling data is available appear to approximately follow a normal distribution. Sampling data was not available in the Mallaig, North coast, Papa Bank and Sule areas.
Figure B 3 : Lobster carapace length (mm) frequency histogram by assessment area averaged over the period 2016-19 for males, females (berried also shown). The data presented are aggregated by 5 mm increments and shown as a proportion of the total landings.
displays the lobster carapace length frequency histogram by assessment area, averaged over the period 2016-19 for males, non-berried females and berried females. The length distributions in most areas appear to be right skewed with a relatively long right tail. Sampling data was not available in the Sule area.

8.3. Annex C: Brown crab and Velvet Crab per Recruit Analysis using Different Biological Parameters

Figure C 1 : Male brown crab biomass and yield-per-recruit ( YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis was run using two different sets of biological parameters (Shetland and rest of Scotland).
shows male brown crab biomass and yield-per-recruit (YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis presented in this figure used two different sets of biological parameters, using (1) the parameters estimated for the majority of areas in Scotland and (2) parameters estimated for the Shetland Islands. Biomass shows a decreasing trend with effort. The maximum yield is generally found in the 50% to +50% effort interval using the Scotland parameters while for the Shetland parameters, maximum yield corresponds to an effort increase above 100% (flat-topped yield curve).
Figure C 2 : Female brown crab biomass and yield-per-recruit ( YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis was run using two different sets of biological parameters (Shetland and rest of Scotland).
shows female brown crab biomass and yield-per-recruit (YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis presented in this figure used two different sets of biological parameters, using (1) the parameters estimated for the majority of areas in Scotland and (2) parameters estimated for the Shetland Islands. Biomass shows a decreasing trend with effort. The maximum yield is generally found in the 50% to +50% effort interval using the Scotland parameters while for the Shetland parameters, maximum yield corresponds to an effort increase above 100% (flat-topped yield curve).
Figure C 3 : Male velvet crab biomass and yield-per-recruit ( YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis was run using two different sets of biological parameters (Shetland and rest of Scotland).
shows male velvet crab biomass and yield-per-recruit (YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis presented in this figure used two different sets of biological parameters, using (1) the parameters estimated for the majority of areas in Scotland and (2) parameters estimated for the Shetland Islands. Biomass shows a decreasing trend with effort. The maximum yield is generally found in the 50% to +50% effort interval using the Scotland parameters while for the Shetland parameters, maximum yield corresponds to an effort increase above 100% (flat-topped yield curve).
Figure C 4 : Female velvet crab biomass and yield-per-recruit ( YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis was run using two different sets of biological parameters (Shetland and rest of Scotland).
shows female velvet crab biomass and yield-per-recruit (YPR) predictions given changes from current effort by assessment area, data from 2016-19. The YPR analysis presented in this figure used two different sets of biological parameters, using (1) the parameters estimated for the majority of areas in Scotland and (2) parameters estimated for the Shetland Islands. Biomass shows a decreasing trend with effort. The maximum yield is generally found in the 50% to +50% effort interval using the Scotland parameters while for the Shetland parameters, maximum yield corresponds to an effort increase above 100% (flat-topped yield curve).

8.4. Annex D: List of Abbreviations

BGS British Geological Survey

BPR Biomass-per-recruit

Cefas Centre for Environment, Fisheries and Aquaculture Science

CL Carapace length

CPUE Catch per unit effort

CW Carapace width

ELEFAN Electronic length frequency analysis

EU European Union

F Fishing mortality

Fbar Average fishing mortality

FFM Future fisheries management strategy

FMAX Fishing mortality rate that maximizes YPR

FMD Fisheries Management Database

FMSY Fishing mortality consistent with achieving MSY

GAM Generalized additive model

HCR Harvest Control Rule

ICES International Council for the Exploration of the Sea

K Grow rate parameter

KW Kilowatt

L̅ Mean length

L∞ Asymptotic size parameter

LBI Length-based indicator

Lc Size at first capture

LCA Length Cohort Analysis

LF=M Expected length in the landings when fishing mortality is equal to natural mortality

LFD Length frequency distribution

Lmat Maturation size

Lmax5% Mean size of the largest 5% of individuals in the landings

LPUE Landings per unit effort

m Metre

M Natural mortality

MLS Minimum Landing Size

mm Millimetre

MoU Memorandum of Understanding

MSE Management Strategy Evaluation

MSS Marine Scotland Science

MSY Maximum Sustainable Yield

NAFC North Atlantic Fisheries College

OHIFP Outer Hebrides Inshore Fisheries Pilot

OSF Orkney Sustainable Fisheries

REM Remote electronic monitoring

RIFG Scottish Regional Inshore Fisheries Group

SPiCT Surplus production model in continuous time

TAC Total Allowable Catch

UHI University of the Highlands and Islands

VMS Vessel Monitoring System

WGCRAB Working Group on the Biology and Life History of Crabs

YPR Yield-per-recruit

Table D 1

Crab and lobster fishery assessment areas and abbreviations

Clyde - CL

East Coast - EC

Hebrides - HE

Mallaig - MA

North Coast - NC

Orkney - OR

Papa Bank - PA

South East - SE

Shetland - SH

South Minch - SM

Sule - SU

Ullapool - UL

Contact

Email: carlos.mesquita@gov.scot

Back to top