richard briggs (agri-food & biosciences institute) – the assessment of nephrops stocks in the...
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The Assessment of Nephrops Stocks in the Irish Sea
Dr Richard Briggs
Probably not Nephrops
Overview
1. Biology and Fishery
2. Stock Assessment
3. UWTV Method
4. The 2010 Assessment
5. ICES Advice (International Council for the Exploration of the Sea)
6. Conclusions
Dublin Bay prawn(Nephrops norvegicus)
Cod(Gadus morhua)
1. BiologyNephrops in NOT a fish!!
Phylum: Arthropoda
Class: Crustacea
Order: Decapoda
Super Family: Nephropsidea
Characteristics
Hard exoskeleton which is periodically shed (ecdysis) and growth is discernable (the only time). No hard structures with growth rings
Kidney shaped eye (from the Greek nephros = kidney and op = eye)
Live within burrows in seabed sediment which they build.
Females remain in burrows whilst incubating eggs (9 months)
Planktonic larval stage
Juveniles (0-group) remaining burrowed for at their 1st year
Life Cycle
The FisheryCaptured by otter trawls (single or multiple) or by creels
Value of top 15 species in 2009
Value of all species = £21.5 millions
0
2
4
6
8
10
12
14
Nep
hro
ps
Mac
kere
l
Her
rin
g
Sca
llop
s
Co
d
Bro
wn
Cra
b
Lo
bst
ers
Hak
e
Qu
een
Sca
llop
s
Had
do
ck
Ho
rse
Mac
kere
l
Mo
nks
or
An
gle
rs
Vel
vet c
rab
Co
ckle
s
Tu
rbo
t
Val
ue
(£m
) Northern Ireland Marine Fisheries
12
3
4
56
7
8
91 0
1 1
1 21 3
1 41 51 6 1 7
1 8
1 9 2 0 - 2 2
2 32 4
2 5
2 6
2 7
2 82 9 3 0
3 1
3 2
3 3
3 4
3 5
3 63 7 3 8
3 9 4 0
4 1
2. Stock AssessmentFunctional Units as defined by ICES
Irish Sea Nephrops TAC: Sub-Area VII
MA FU
J 14 15
L 16 17 18 19
M 20 21 22
Sub Area VII
- 1 8 . 0 0 - 1 6 . 0 0 - 1 4 . 0 0 - 1 2 . 0 0 - 1 0 . 0 0 - 8 . 0 0 - 6 . 0 0 - 4 . 0 0 - 2 . 0 0 0 . 0 0 2 . 0 04 8 . 0 0
4 9 . 0 0
5 0 . 0 0
5 1 . 0 0
5 2 . 0 0
5 3 . 0 0
5 4 . 0 0
5 5 . 0 0
1 5 1 4
2 0 - 2 21 9
1 7
1 8
1 6
Western Irish Sea = FU15
Assessment Methods
(2) Larval Production
Using fecundity data to back calculate the number of females required to produce the amount of larvae observed in surveys. Labour intensive and costly. Done as a one off.
(1) Catch Data
a) Length Cohort analysis b) Size compositions sliced to ages, VPA and XSA models used similar to Fin-fish methods (used until 2005).
(3) Camera Surveys*Underwater video used to count Nephrops burrow clusters
*Adopted by ICES since 2005
3. UWTV Method Adults inhabit burrows in
offshore sediment from which they only emerge to feed and to mate.
Research in Scotland suggests that one adult Nephrops occupies a single burrow cluster and unoccupied burrows are quickly filled by sediment.
By counting burrow clusters over a known area it is possible to provide a fishery independent index of Nephrops abundance and to map the Nephrops grounds.
Nephrops burrows
Resin CastingPolyester resin pours underwater rather
like treacle in air and when mixed with catalyst cures to produce high quality casts of burrows like this burrow of Nephrops norvegicus (Scale bar 20cm)
RV Corystes
RV Celtic Voyager
The ShipsAFBI have performed collaborative UWTV
Nephrops surveys with the Irish Marine Institute since
2003. Now 7 years data
The AFBI camera sledge Deploying the camera
Camera Surveys (AFBI/Marine Institute initiative but now includes CEFAS to cover eastern Irish Sea stocks (FU14)
The Stations
• 3.5km apart
• Camera towed for 10
mins at each station
Eastern Irish Sea (FU14) Stations
UWTV survey extended since2007 and used for the
assessment in 2010
Joint survey with CEFAS/AFBI and Marine Institute
Western Irish Sea (FU 15) abundance estimate
5.3
6.3 6.3
4.9
6.26.55.9
0
1
2
3
4
5
6
7
2003 2004 2005 2006 2007 2008 2009
Survey Year
Bil
lio
n b
urr
ow
clu
ster
s
4. The 2010 Assessment Western Irish Sea (FU15)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
6040000 2003
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
6040000 2004
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
6040000 2005
300000 320000 340000 360000 380000
5920000
5940000
5960000
5980000
6000000
6020000
6040000 2006
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
6040000 2007
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
6040000 2008
300000 320000 340000 360000 380000
5940000
5960000
5980000
6000000
6020000
60400002009
Contour plots of burrow densities using geostatistics (2003 – 2009)
0.45
0.29 0.29
0.49
0.69
1.21
1.47
0.84
1.6
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Farn
Deep
s
Fla
den
Mo
ray F
irth
No
rth
Min
ch
Cly
de
So
un
d o
f Ju
ra
W. Ir
ish
Sea
Aru
n G
rou
nd
s
Galw
ay B
ay
Clu
ste
rs m
-2
Burrow densities from different areas
Summary of data analysis Landings
Bias Adjusted Burrow Count
Harvest Ratesfrom Model
Predicted Landings
Size distribution
Mean Nephrops weight in
Catch Option Table
Catch Data Growth and
Maturity Parameters
FU Area Edge EffectDetection
RateSpecies
IdentificationBurrow
OccupancyCumulative
bias6 Farn Deeps 1.30 0.85 1.05 1 1.207 Fladen 1.45 0.90 1.00 1 1.358 Firth of Forth 1.23 0.90 1.05 1 1.189 Moray Firth 1.31 0.90 1.00 1 1.21
11 North Minch 1.38 0.85 1.10 1 1.3312 South Minch 1.37 0.85 1.10 1 1.3213 Clyde 1.19 0.75 1.25 1 1.1915 Irish Sea West 1.24 0.75 1.15 1 1.1417 Aran 1.35 0.90 1.05 1 1.30
Bias estimates introduced by ICES Benchmark Assessment 2009
Bias Adjusted Count = Count X Bias
Catch Option Table
RationaleHarvest
ratio
Landings
2011
(tonnes)
MSY framework 17.10% 8,724
MSY transition 17.80% 9,104
F2009 18.00% 9,199
F0.1 (combined) 11.00% 5,612
F35% (combined) 13.40% 6,832
Fmax (combined) 17.10% 8,724
Justification for choice of Harvest Rate
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
1
2
3
4
Fmult
yie
ldFmax
F0.1
F2009
Maximum Sustainable Yield (MSY): now forming ICES advice basis. Not possible to estimate directly for Nephrops as no age or SSB data. MSY proxy therefore established
Evidence for Harvest Rate at Fmax as Proxy for MSY
Landings - International
0
3000
6000
9000
12000
15000
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Land
ings
(to
nnes
)
International Landings
UK - All gears
Rep. of Ireland - All gears
Effort - Different fleets
0
50
100
150
200
250
1980 1985 1990 1995 2000 2005 2010
Effo
rt (
'000
hou
rs tr
awlin
g)
UK Northern Ireland Nephrops trawlers
Rep. of Ireland
LPUE - Different fleets
0
10
20
30
40
50
60
70
80
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
CP
UE
or
LPU
E (
kg/h
our
traw
ling)
Rep. of Ireland - LPUE
UK Northern Ireland - LPUE
Mean sizes - Different fleets
20
22
24
26
28
30
32
34
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Mea
n si
ze (
mm
car
apac
e le
ngth
)
ROI - Catch - MalesROI - Catch - FemalesUK NI - Catch - MalUK NI - Catch - Fem
Commercial Fishery Data: ie fished sustainably for many years above Fmax
12
78
10
1517
20
30
35
101
102
103104
105
106
107
108
109
200
207
208209
210
6 .4 W 6 .2 W 6 .0 W 5 .8 W 5 .6 W 5 .4 W 5 .2 W 5 .0 W 4 .8 W 4 .6 W
5 3 .4 N
5 3 .6 N
5 3 .8 N
5 4 .0 N
5 4 .2 N
5 4 .4 N
5 4 .6 N
5 4 .8 N
36
E4 E5E3
37
38
35
F ig u re 1 : W este rn Irish S ea N ep h ro p s s ta tio n s
Trawl Survey Data
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Kg
per
nm
August
April
Aug mean
Apr mean
Trawl Surveys: catch rates
0
10
20
30
40
50
60
70
80
90
100
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Perc
enta
ge fem
ale
s (
%)
Mean percentage females in August(error bars = SD)
Mean carapace length from Q3 surveys(error bars = SD)
10
15
20
25
30
35
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
cara
pace
leng
th (m
m)
August males
August females
0
1
2
3
4
5
6
7
8
9
10
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
Bill
ion
s (
UW
TV
)UWTV Survey
Trawl Survey Scaled
Btrigger
5 year mean = Btrigger
Trawl survey data scaled to UWTV survey abundance index
Other Data
• Examination of historical data from 1960s when the fishery was in its
infancy shows little change in size composition of catches
• Larval production studies have shown that in 1995 440 x 109 Nephrops
larvae were produced suggesting high recruitment potential
• The Irish Sea Gyre (whirlpool effect) retains both larvae and sediment
enhancing recruitment success
5. ICES Advice
Benchmark Workshops
Data compilation +
External review
32
Expert Groups
Stock annex
Review Group
Advice Drafting Groups
1st draft of advice
ACOMweb conference
Final Advice
Update assessments
Benchmark Workshops
Data compilation +
External review
Stock annex
Benchmark Workshops
Data compilation +
External review
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Advice Drafting Groups
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Advice Drafting Groups
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
ACOMweb conference
Advice Drafting Groups
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
ACOMweb conference
Advice Drafting Groups
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops
Data compilation +
External review
Final Advice
ACOMweb conference
Advice Drafting Groups
1st draft of advice
Review Group
Expert Groups
Stock annex
Benchmark Workshops(2009 for Nephrops)
Data compilation +
External review
STEC and EU
6. Conclusions• Since 2005 Nephrops stock assessment based on UWTV surveys
• The 2010 assessment of W. Irish Sea (FU15) stocks advises
Landings at Fmax as an MSY proxy ie near to 2009 tonnage.
• Management should be at Functional Unit level as components of the
TAC area (VIIa) have different states of exploitation eg FU 17
(Porcupine Bank) are over fished and the advice is zero catch.
This drags the TAC downwards
----- The End ----
CEFAS - AFBI – MI(Jon Elson, Richard Briggs, Colm Lordan)
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