Moreau, K.

Nimmegeers, S.

Vanhee, W.

Open Marine Archive

1356  | ICES WGCSE REPORT 2011 
 
Stock Annex 6.8: Sole VIIa 
Stock-specific documentation of standard assessment procedures used by ICES. 
Stock   Irish Sea Sole (Division VIIa) 
Working Group  WGCSE 
Date   6 February 2011 
Revised by  WKFLAT 2011/Sofie Nimmegeers, Willy Vanhee, Kelle 
   Moreau 
A. General 
A.1. Stock definition 
Sole occur throughout the Irish Sea, but are found more abundant in depth less than 60 
m. Recent information on stock identity, distribution and migration issues is included in 
the report of WKFLAT 2011. Cuveliers et al. (2011) combined the results obtained from 
ten microsatellite markers (long-term estimate of population structure) with results from 
otolith microchemistry analyses (short-term estimate of connectivity) on adult sole popu-
lations in the Northeast Atlantic area. Major large-scale differentiation was detected be-
tween three distinct regions (Baltic transition area, North Sea, Irish/Celtic Seas) with both 
types of markers. The assignment success of individuals to their collection location was 
much higher based on otolith edge microchemistry compared to the genetic assignments 
at all sampling locations, except for the Irish Sea. Only 28.6% of individuals (n=30) caught 
in the Irish Sea could be assigned to their catch location based on otolith edge micro-
chemistry, whereas this region showed high genetic self-assignment scores (ca. 60% of 91 
individuals) suggesting a spawning population that is genetically distinct. 32% of the 
misclassifications based on otolith microchemistry were allocated to the neighbouring 
Celtic Sea. These results are consistent with tagging studies of sole in the Irish Sea and 
Bristol Channel, showing mainly local recruitment and limited movement of sole outside 
the management areas (Horwood et al., 1993). Therefore, the management unit is consid-
ered to correspond to the stock unit for Irish Sea sole. 
A.2. Fishery 
There are three main countries fishing for sole in the Irish Sea; Belgium, taking the bulk 
of the landings (60–80% in recent years). UK and Ireland taking about 20% and 10% re-
spectively of the sole landings. The Netherlands and France take the remainder. Ap-
proximately 25 Belgian beam trawlers are operating in the Irish Sea, targeting sole. The 
UK trawl fleet and the Belgian beam trawls operate predominantly in the eastern part of 
the Irish Sea (Liverpool Bay and Morecambe Bay). Sole catches from Ireland are mainly 
coming from bycatches in the Nephrops fishery (operation in the northwest of the Irish 
Sea). 
When fishing in VIIa it is prohibited to use any beam trawl of mesh size range 70–90 mm 
unless the entire upper half of the anterior part of such a net consists of a panel of netting 
material attached directly to the headline of the net, extending towards the posterior of 
the net for at least 30 meshes and constructed of diamond-meshed netting material of 
ICES WGCSE REPORT 2011  |  1357 
 
which no individual mesh is of mesh size less than 180 mm. The Irish otter trawl fleet 
employs either a 70 mm mesh with square mesh panels or more commonly an 80 mm 
mesh. Similarly the Belgian and UK(E&W) beam trawls use 80 mm mesh gear. Otter 
trawlers targeting roundfish have, since 2000, used 100 mm mesh gear. 
It was concluded at the 2000 working group and confirmed in 2001 that the cod recovery 
measures first enacted (EU Regulations 304/2000 and 2549/2000 + revisions in 2001–2003) 
in 2000 would have had little impact on the sole fishery. The closed area in 2001 covered 
a reduced area confined to the west of the Irish Sea and therefore is also expected to have 
had little effect on the level of fishing effort for sole The spawning closure for cod in 2002 
is also unlikely to have had an impact on the sole fishery. The effort regulations and 
maximum daily uptake, implemented in 2003 will delay the uptake of the quota but is 
also unlikely to be restrictive for the total uptake. It is unlikely that any measures con-
cerning the cod management plan in the Irish Sea had restrictions on the sole fishery after 
2003. 
Discard are estimated to be minor. Preliminary data indicate ranges from 0 to 2% by 
weight discarded. 
Although no data are available on the extent of misreporting of landings from this stock, 
it is not considered to be a problem for this stock. 
A.3. Ecosystem aspects 
No information. 
B. Data 
B.1. Commercial catch 
Quarterly age compositions are available from UK(E&W), Belgium and Ireland, as well 
as quarterly landings from France and Northern Ireland. The total international age com-
position is obtained using a combined ALK from UK(E&W), Belgium and Ireland raw 
data, responsible for 99% of the total international sole landings. The combined ALK is 
applied to the length distributions of the separate countries to obtain an aggregated age 
composition. 
Catch weights were obtained from the combined AWK (UK(E&W), Belgium and Ireland 
raw data). 
Stock weights were obtained using the Rivard weight calculator 
(http://nft.nefsc.noaa.gov./) that conducts a cohort interpolation of the catch weights. 
B.2. Biological 
Currently there are no direct (from tagging) or independent (from survey information) 
estimates of natural mortality. Therefore, annual natural mortality (M) is assumed to be 
constant over ages and years, at 0.1 yr-1. 
The maturity ogive used in this and previous assessments is based on survey information 
for this stock: 
1358  | ICES WGCSE REPORT 2011 
 
AGE 1 2 3 4 5 
6 AND 
OLDER 
Mat. 0.00 0.38 0.71 0.97 0.98 1.00 
Proportions of M and F before spawning were set to zero, as in previous years. 
Males and females of this stock are strongly dimorphic, with males showing much re-
duced rates of growth after reaching maturity, whereas females continue to grow. Given 
the minimum landing size of 24 cm the majority of landings represent mature females. 
B.3. Surveys 
One survey is used in the assessment of VIIa sole: the UK beam trawl survey (UK (BTS-
3Q)). 
Area covered 
Irish Sea; 52°N to 55°N; 3°W to 6°30’W. 
Target species 
Flatfish species, particularly juvenile plaice and sole. Length data recorded for all finfish 
species caught; samples for age analysis taken from selected species. 
Time period 
1988–2009: September (continuing) 
Gear used 
Commercially rigged 4 m steel beam trawl; chain matrix; 40 mm codend liner. 
Mean towing speed: 4 knots over the ground. Tow duration: 30 minutes. Tow duration 
for trips in 1988–1991 was 15 minutes; in 1992 comparative tows of 15 and 30 minutes 
length were carried out, and subsequent cruises used a standard 30 minute tow. The data 
from earlier years were converted to 30 minutes tow equivalent using relationships for 
each species derived from the comparative work in 1992. 
Vessel used: R.V. Endeavour (Cefas) 
Survey design 
Survey design is stratified by depth band and sector (Depth bands are 0–20, 20–40, 40+). 
Station positions are fixed. Number of stations = 35 in the eastern Irish Sea, 15 in the 
western Irish Sea, and 16 in St George’s Channel (primary stations). Sampling intensity 
highest in the eastern Irish Sea, in the main flatfish nursery and fishery areas. 
Method of analysis 
Raised, standardized length frequencies for each station combined to give total length 
distribution for a stratum (depth band/sector). Sector age–length keys applied to stratum 
length distributions 1988–1994; stratum age–length keys applied 1995 onwards. Mean 
stratum cpue (kg per 100 km and numbers-at-age per 100 km) are calculated. Overall 
ICES WGCSE REPORT 2011  |  1359 
 
mean cpue values are simple totals divided by distance in metres (or hours fished). Popu-
lation number estimates derived using stratum areas as weighting factors. 
The September beam trawl survey has proven to estimate year-class strength well, and 
providing 50% to over 90% of the weighting to the total estimates of the incoming years 
classes. 
B.4. Commercial cpue 
Cpue and effort series were available from the Belgium beam trawlers, UK(E&W) beam 
and otter trawlers, the Irish otter trawlers and from two UK beam trawl surveys (Sep-
tember and March). 
Cpue for both UK and Belgian beam trawlers has declined since the beginning of the 
time-series, but has remained relatively constant over the last decade, with a renewed 
increase over the last few years (2008–2009 for Belgium and 2007–2009 for UK). 
Effort from both commercial beam trawl fleets increased from the early seventies until 
the late eighties. Since then Belgian beam trawl effort has declined over the nineties, in-
creased again in the period 2000–2005 and subsequently dropped to much lower values 
in 2008–2009 (the lowest values since 1984). In the nineties, the UK beam trawl effort fluc-
tuated around a lower level than the late eighties, and dropped during the 21st century to 
the lowest value of the time-series in 2009. 
Indices of abundance derived from the UK September survey (UK (BTS-3Q)) (data from 
1988 onwards) are shown in WGNSDS 2002 (Table 12.2.2). High abundance indices for 
the UK September survey (UK (BTS-3Q)) can be seen for year classes 1989, 1995 and 1996. 
The dataseries from the UK March beam trawl survey (UK (BTS-1Q)) is rather short 
(from 1993 to 1999), and therefore difficult to interpret. 
B.5. Other relevant data 
No information. 
C. Assessment: data and method 
Model used: XSA 
Software used: IFAP/Lowestoft VPA suite 
Model Options chosen since 2004: 
ASSESSMENT 
YEAR 2004 2005 2006 2007-2010 
WKFLAT 
2011 
Assessment 
Model 
XSA SURBA XSA XSA XSA 
Fleets      
BEL-CBT 1975–2003 
4–9 
 omitted omitted omitted 
UK-CBT 1991–2003 
2–9 
 omitted omitted omitted 
UK (BTS-3Q) 1988–2003 
2–9 
1988–2004 
1–9 
1988–rec yr 
2–7 
1988–rec yr 
2–7 
1988–rec yr 
2–7 
1360  | ICES WGCSE REPORT 2011 
 
ASSESSMENT 
YEAR 2004 2005 2006 2007-2010 
WKFLAT 
2011 
UK (BTS-1Q) 1993–1999 
2–9 
 1993–1999 
2–7 
1993–1999 
2–7 
omitted 
Time-ser. Wts tricubic 20yrs  linear 20 yrs linear 20 yrs uniform 
Power Model none  none none none 
Q plateau 5  5 7 4 
Shk se 0.8  1.5 1.5 1.5 
Shk Age-yr 5 yrs 
5 ages 
 5 yrs 
3 ages 
5 yrs 
3 ages 
5 yrs 
3 ages 
Pop Shk se 0.3  0.3 0.3 0.3 
Prior Wting none  none none None 
Plusgroup 10  8 8 8 
Fbar 4–7  4–7 4–7 4–7 
Input data types and characteristics: 
TYPE NAME  YEAR RANGE AGE RANGE 
VARIABLE FROM YEAR TO YEAR 
YES/NO 
Caton Catch in 
tonnes 
1970–last data 
year 
2–8+ Yes 
Canum Catch-at-age in 
numbers  
1970–last data 
year 
2–8+ Yes 
Weca Weight-at-age 
in the 
commercial 
catch 
1970–last data 
year 
2–8+ Yes 
West Weight-at-age 
of the 
spawning–
stock at 
spawning time 
1970–last data 
year 
2–8+ Yes-but based on back calculated 
catch weights 
Mprop Proportion of 
natural 
mortality 
before 
spawning 
1970–last data 
year 
2–8+ No-set to 0 for all ages in all 
years 
Fprop Proportion of 
fishing 
mortality 
before 
spawning 
1970–last data 
year 
2–8+ No-set to 0 for all ages in all 
years 
Matprop Proportion 
mature-at-age 
1970–last data 
year 
2–8+ No-the same ogive for all years  
Natmor Natural 
mortality 
1970–last data 
year 
2–8+ No-set to 0.1 for all ages in all 
years 
ICES WGCSE REPORT 2011  |  1361 
 
Tuning data: 
Type Name  Year range Age range 
Tuning fleet 1 UK (BTS-3Q) 1988–last data year 2–7 
Note : several other commercial tuning fleets – BEL-CBT (Belgian beam trawl fleet), UK-CBT (UK beam 
trawl fleet), UK-COT (UK otter trawl fleet), IRL-COT (Irish otter trawl fleet) – and two other surveys (UK 
(BTS-1Q) and Irish Juvenile Plaice Survey) have been used or made available in the past. A thorough inves-
tigation of the utility of these tuning indices was conducted at the 2002 working group. The results are 
summarized in the Stock Annexes of the reports of WGNSDS 2002–2008 and WGCSE 2009. 
D. Short-term projection 
Model used: Age structured deterministic projection 
Software used: MFDP 
Initial stock size: Taken from the XSA for ages 3 and older. The recruitment-at-age 2 in 
the last data year is estimated using RCT3. The long-term geometric mean recruitment 
(1970–penultimate estimate) is used for age 2 in all projection years. 
Maturity: the same ogive as in the assessment is used for all years (see table above) 
F and M before spawning: set to 0 for all ages in all years 
Weight-at-age in the stock: average weight of the last three years 
Weight-at-age in the catch: average weight of the three last years 
Exploitation pattern: average of the three last years, scaled to the last year’s Fbar (4–7) if a 
trend in F was detected (not scaled to the last year’s Fbar (4–7) if no trend in F was de-
tected) 
Intermediate year assumptions: status quo F 
Stock–recruitment model used: none 
Procedures used for splitting projected catches: not relevant 
E. Medium-term projections 
Medium-term projections were not conducted at WKFLAT 2011. The last medium-term 
projections were carried out in 2008. The settings used are described below. 
Model used: Age structured 
Software used: IFAP single option prediction 
Initial stock size: Same as in the short-term projections. 
Natural mortality: Set to 0.2 for all ages in all years 
Maturity: The same ogive as in the assessment is used for all years 
F and M before spawning: Set to 0 for all ages in all years 
Weight-at-age in the stock: Assumed to be the same as weight-at-age in the catch 
Weight-at-age in the catch: Average weight of the three last years 
1362  | ICES WGCSE REPORT 2011 
 
Exploitation pattern: Average of the three last years, scaled by the Fbar (3–6) to the level 
of the last year 
Intermediate year assumptions: F-factor from the management option table correspond-
ing to the TAC 
Stock recruitment model used: None, the long-term geometric mean recruitment-at-age 2 
is used 
Uncertainty models used: @RISK for excel, Latin Hypercubed, 500 iterations, fixed ran-
dom number generator 
• Initial stock size: Lognormal distribution, LOGNORM(mean, standard devia-
tion), with mean as in the short-term projections and standard deviation calcu-
lated by multiplying the mean by the external standard error from the XSA 
diagnostics (except for age 2, see recruitment below) 
• Natural mortality: Set to 0.2 for all ages in all years 
• Maturity: The same ogive as in the assessment is used for all years 
• F and M before spawning: Set to 0.2 for all ages in all years 
• Weight-at-age in the stock: Assumed to be the same as weight-at-age in the 
catch 
• Weight-at-age in the catch: Average weight of the three last years 
• Exploitation pattern: Average of the three last years, scaled by the Fbar (3–6) to 
the level of the last year 
• Intermediate year assumptions: F-factor from the management option table 
corresponding to the TAC 
• Stock–recruitment model used: Truncated lognormal distribution, TLOG-
NORM(mean, standard deviation, minimum, maximum), is used for recruit-
ment age 2, also in the initial year. The long-term geometric mean, standard 
deviation, minimum, maximum are taken from the XSA for the period 1960; 
4th last year. 
F. Long-term projections 
Model used: age structured deterministic projection 
Software used: MFYPR 
Inputs as for short-term projection. 
ICES WGCSE REPORT 2011  |  1363 
 
G. Biological reference points 
 Type Value Technical basis 
MSY  MSY Btrigger 3100 t Default to value of Bpa. 
Approach FMSY 0.16 Provisional proxy based on stochastic simulations 
assuming a Ricker S/R relationship (range 0.1–0.25). 
 Blim 2200 t Blim = Bloss. The lowest observed spawning stock (ACFM 
1999), followed by an increase in SSB. 
Precautionary Bpa 3100 t Bpa ̴ Blim * 1.4. The minimum SSB required ensuring a high 
probability of maintaining SSB above its lowest observed 
value, taking into account the uncertainty of assessments. 
Approach Flim 0.4 Flim = Floss. Although poorly defined, there is evidence that 
fishing mortality in excess of 0.4 has led to a general stock 
decline and is only sustainable during periods of above-
average recruitment. 
 Fpa 0.3 This F is considered to have a high probability of avoiding 
Flim. 
Precautionary approach reference points have not been changed during 1999–2006. In 
this period, Fpa was set at 0.45 on the technical basis of high probabilities of avoiding Flim 
and of SSB remaining above Bpa. In 2007, Fpa was changed to 0.3 due to the rescaling of 
SSB estimates. In 2010, MSY reference points were added by WGCSE. 
H. Other issues 
A management plan for Irish Sea sole could be developed, also taking into account the 
dynamics of the plaice stock in that area. 
I. References 
ICES. 2002. Report of the Working Group on the Assessment of Northern Shelf Demersal Stocks 
(WGNSDS). ICES CM 2002/ACFM:02. 448 pp. 
ICES. 2010. Report of the Working Group on the Celtic Seas Ecoregion (WGCSE), 13–19 May 2009, 
Copenhagen, Denmark. ICES CM 2009/ACOM:09. 1430 pp. 
ICES. 2010. Report of the Working Group on Celtic Seas Ecosystems, 12–20 May 2010, Copenhagen, 
Denmark. ICES CM 2010/ACOM:12. 1435pp. 


Stock Annex 6.8: Sole VIIa

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