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

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Mac

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l

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rin

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Sca

llop

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d

Bro

wn

Cra

b

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bst

ers

Hak

e

Qu

een

Sca

llop

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Had

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ck

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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

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90

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110

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140

1994

1995

1996

1997

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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

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7

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9

10

1994

1995

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2001

2002

2003

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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)