Moreau, K.

Nimmegeers, S.

Vanhee, W.

Open Marine Archive

232  | ICES WKFLAT REPORT 2011 
 
Stock Annex: Ir ish Sea sole VIIa 
Stock   Irish Sea Sole (Division VIIa) 
Working Group  WGCSE 
Date   6 Feb 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 in-
cluded 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 connectivi-
ty) on adult sole populations in the Northeast Atlantic area. Major large-scale diffe-
rentiation was detected between three distinct regions (Baltic transition area, North 
Sea, Irish/Celtic Seas) with both types of markers. The assignment success of individ-
uals to their collection location was much higher based on otolith edge microchemi-
stry 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 microchemistry, whereas this region 
demonstrated high genetic self-assignment scores (ca 60% of 91 individuals) suggest-
ing 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, 
demonstrating mainly local recruitment and limited movement of sole outside the 
management areas (Horwood et al., 1993). Therefore, the management unit is consi-
dered 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% respectively of the sole landings. The Netherlands and France take the remain-
der. Approximately 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 to-
wards the posterior of the net for at least 30 meshes and constructed of diamond-
meshed netting material of 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 
ICES WKFLAT REPORT 2011 |  233 
 
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 re-
covery 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 spawn-
ing 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 concerning 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 composition 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 ob-
tain an aggregated age composition. 
Catch weights were obtained from the combined AWK (UK(E&W), Belgium and Ire-
land 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 informa-
tion) estimates of natural mortality. Therefore, annual natural mortality (M) is as-
sumed 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 infor-
mation for this stock: 
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 displaying much 
reduced rates of growth after reaching maturity, whereas females continue to grow. 
234  | ICES WKFLAT REPORT 2011 
 
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; 520  N to 550 N; 30 W to 60 30’ W. 
Target species 
Flatfish species, particularly juvenile plaice and sole. Length data recorded for all fin-
fish 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 dura-
tion 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 ar-
eas. 
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 stra-
tum 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 mean cpue values are simple totals divided by distance in metres (or hours 
fished). Population number estimates derived using stratum areas as weighting fac-
tors. 
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 incom-
ing years classes. 
ICES WKFLAT REPORT 2011 |  235 
 
B.4. Commercial cpue 
Cpue and effort-series were available from the Belgium beam trawlers, UK(E&W) 
beam and otter trawlers, and the Irish otter trawlers and from two UK beam trawl 
surveys (September 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 un-
til the late eighties. Since then Belgian beam trawl effort has declined over the nine-
ties, increased 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 fluctuated around a lower level than the late eighties, and dropped dur-
ing 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 demonstrated in WGNSDS 2002 (Table 12.2.2). High abun-
dance 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. 
236  | ICES WKFLAT REPORT 2011 
 
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 
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 
ICES WKFLAT REPORT 2011 |  237 
 
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 
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 thor-
ough investigation 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 recruit-
ment (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 
238  | ICES WKFLAT REPORT 2011 
 
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 
detected) 
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 
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 corre-
sponding 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 
random number generator 
• Initial stock size: Lognormal distribution, LOGNORM(mean, standard de-
viation), with mean as in the short-term projections and standard deviation 
calculated 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 re-
ICES WKFLAT REPORT 2011 |  239 
 
cruitment 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. 
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 re-
scaling 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, Copen-
hagen, Denmark. ICES CM 2010/ACOM:12. 1435pp. 


Stock Annex: Irish Sea sole VIIa

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