David MillerWageningen IMARES

� The assessment(s)

� Data used (and not used):◦ Catch data

◦ Surveys

� Biological reference points

� The 2010 assessment

� Potential issues/uncertainties in the assessment

� Way forward?

� WGWIDE examines 3 models:◦ TISVPA: separable selection (>1994)◦ XSA: non-separable - assumes perfect catch data◦ SMSSMSSMSSMS: Stochastic Multi-species Model (separable)

� All analytical age-structured assessments◦ Ages 1-10+ (age 10 is a plusgroup)

� No benchmark assessment◦ Based on previous evaluations and comparisons,

SMS has been chosen as the final assessment for the last 5 years

� Catch values are provided to ICES by the member nations fishing the stock

� Estimates are considered to be reliable

Catch data

Constant selection pattern for the

catch

2 periods:

1981–1999,1999–2009

First age with age independent catchability

8

Age groups with the same variance 1, 2, 3–6, 7–10

� International Blue Whiting Spawning Stock Survey International Blue Whiting Spawning Stock Survey International Blue Whiting Spawning Stock Survey International Blue Whiting Spawning Stock Survey

� Norway, Russia, the Faroe Islands and the EU

� Spawning grounds west of the British Isles

� March-April (peak of spawning)

International blue whiting

spawning stock ground survey , ages 3–8

2004-2010

First age with age independent catchability

5

Age groups with the same variance 3–8, min std 0.4

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4

Longitude

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

Lat

itud

e

Tridens

Celtic Explorer

G.O. Sars

Vimus

Magnus Heinason

Cruise tracks

50.0°

51.0°

52.0°

53.0°

54.0°

55.0°

56.0°

57.0°

58.0°

59.0°

60.0°

61.0°

62.0°

63.0°

-20° -19° -18° -17° -16° -15° -14° -13° -12° -11° -10° -9° -8° - 7° -6° -5° -4° -3° -2° -1°

200m

500m

1000m

Faroes

Netherlands

Ireland

Norway

Russia

Current survey plan Proposed plan for 2011

� Primary source of information about the current state of the stock

� Covers a large area◦ Not always well standardised

◦ Limited time

◦ Migrations occur during the survey

◦ Weather conditions often unfavourable

� Short time series◦ ‘catchability’ estimates still variable

◦ In a transition phase, should stabilise in the future

� International Ecosystem Survey in the Nordic International Ecosystem Survey in the Nordic International Ecosystem Survey in the Nordic International Ecosystem Survey in the Nordic SeasSeasSeasSeas

� EU, Norway, the Faroe Islands and Russia� Barents Sea, north & central Norwegian Sea

and southwestern Norwegian Sea (Faroese and Icelandic Zones)

� May

International ecosystem survey in

the Nordic Seas, ages 1–2

2000-2010

First age with age independent

catchability

2

Age groups with the same variance 1,2

Trawls Stations

� Blue Whiting is not the primry target of the survey

� Generally small and loose registrations of blue whiting

� Used as an index of recruitment (incoming year-class strength)

� Norway

� Spawning grounds west of the British Isles

� Precursor for IBWSSS

� 1991-2006◦ 2004-2006 incorporated in IBWSSS

◦ 2007 onwards: Norwegian contribution to IBWSSS changed

Norwegian spawning ground

survey, ages 3–8 1993–2003

First age with age independent catchability

5

Age groups with the same variance 3–4, 5–6, 7–8

� Norway, some years in co-ordination with Russia

� Barents Sea

� late January‐early March

� Only used in forecastOnly used in forecastOnly used in forecastOnly used in forecast◦ Coverage on edge of the distribution area

◦ Considered first reliable indication of year-class strength (recruitment)

� NOT USED IN THE CURRENT ASSESSMENTNOT USED IN THE CURRENT ASSESSMENTNOT USED IN THE CURRENT ASSESSMENTNOT USED IN THE CURRENT ASSESSMENT

� Only representative for a small part of the stock:◦ Spanish bottom trawl survey◦ Portuguese bottom trawl survey

� Patchy temporal coverage / not updated:◦ Norwegian Sea summer survey (1981–2001, 2005–2007)

◦ Faroes plateau spring bottom trawl survey (1996–2008)

◦ Faroes plateau autumn bottom trawl survey (1994–2008)

� Spanish pair trawls CPUE ◦ 1983-2003

◦ Discontinued because fleet only represents a small part of the landings in a small part of the distribution area

� Norwegian CPUE◦ 1982-2003

◦ Not updated

◦ Not considered representative of the development of the stock

Type Name Year range Age range Variable from year

to year

Yes/No

Caton Catch in tonnes 1981 – 2009 1-10 Yes

Canum Catch at age in

numbers

1981 - 2009 1-10 Yes

Weca Weight at age in the commercial catch

1981 – 2009 1-10 Yes

West Weight at age of the

spawning stock at spawning time.

1981 – 2009 1-10 Yes

Mprop Proportion of natural

mortality before spawning

1981 – 2009 1-10 No

Fprop Proportion of fishing

mortality before spawning

1981 - 2009 1-10 No

Matprop Proportion mature

at age

1981 - 2009 1-10 No

Natmor Natural mortality 1981 - 2009 1-10 No

Tuning data:

Type Name Year range Age range

Tuning fleet 1 Norwegian Acoustic Survey 1991-2003 3-8

Tuning fleet 2 International Ecosystem Survey 2000 - 2010 1-2

Tuning fleet 3 International Spawning Stock Survey 2004 - 2010 3-8

� History:◦ SGPA 1998:

� Blim = 1.5 million t (~lowest observed at the time)� Flim=Floss=0.32� Bpa (2.25 Mt) and Fpa (0.21) arbitrarily calculated up from these� Simulations suggested in absence of clear stock-recruit

relationship

◦ ACFM 1998� Fpa=0.32 (avg. F, no apparent neg. effects on rec.)� Flim raised to 0.51

◦ SGPRP 2003:� Bloss=1.2 Mt, similar to current Blim, assessments still unstable

– no change

� History:◦ ACFM 2006� Using Bpa as a trigger expected to lead to a >5% risk

of SSB dropping below Blim� Suggests Bpa should be higher

◦ WKREF 2007� In the period of low recruitment there seems to be no

sign of reduced recruitment at low SSB� In the period of high recruitment no apparent trend in

recruitment over the range of biomass� May be no need for different Blim values in different

productivity regimes

� History:◦ MP simulation evaluation 2008

� high risk of stock collapse for F > 0.3

� F0.1=0.18, low risk to stock

� Current BRPs:Reference Point Blim Bpa Flim Fpa

Value 1.5 mill t 2.25 mill t 0.51 yr-1 0.32 yr -1

Basis Bloss Blim*exp(1.645* σ)

With σ = 0.25

Floss Fmed

� WGWIDE – assessment working group on widely distributed and highly migratory stocks

� Vigo, Spain

� Aug/Sep 2010

� Participants include scientists from almost all countries fishing the stock

Catch proportion at age for Blue whiting

year

age

2

4

6

8

10

1980 1985 1990 1995 2000 2005 2010

all

Area

Season

� Deviations from pre-agreed survey plan:◦ Temporal: Russian component 2 weeks late

� Excluded from survey (risk of ‘double counting’)

◦ Spatial: Dutch component incomplete due to poor weather� Gap in area coverage occurred in an area of concentrated

fishing effort and thus likely to have contained a high but unununun----quantifiedquantifiedquantifiedquantified biomass

� Interpolated (estimated) from surrounding surveyed areas

� WGNAPES considered the revised estimate to be robust and recommended WGWIDE to use these values

-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4

Longitude

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

Lat

itud

e

Tridens

Celtic Explorer

G.O. Sars

Vimus

Magnus Heinason

Planned Realised

� 2010 mean acoustic density the lowest observed since 2004 ◦ 50% decrease in stock biomass compared to the 2009

survey

50°

54°

60°

62°

58°

52°

56°

0°12°20° 4°4°8°16°

sA - values

0 - 100 100 - 500 500 - 10001000 - 141000

2009 2010

� Largest coordinated coverage in the Norwegian Sea and surrounding waters in summer ever

� Small and loose registrations of blue whiting

� Generally colder in the Norwegian Sea, but extremely warm Atlantic water masses in the southern and southwestern part of Iceland

# International Norweigian Sea ecosystem survey 2000-2009# Effort and catch numbers age 1 age 248927 3133 #2000 85772 25110 #200115251 46656 #200235688 21487 #200349254 22086 #200454660 19904 #2005

570 18300 #2006 21 552 #200729 75 #20080 14 #20090 0 #2010

Recruitment (age 1 yr)

0

10

20

30

40

50

60

70

1980 1983 1986 1989 1992 1995 1998 2001 2004 2007

Re

crui

ts, *

10

^9

SMS

TISVPA

XSA

Fishing mortality

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1980 1983 1986 1989 1992 1995 1998 2001 2004 2007

F 3

-7

Spawning stock biomass

0

1

2

3

4

5

6

7

8

1980 1983 1986 1989 1992 1995 1998 2001 2004 2007

SS

B (

mill

ion

t)

� Close agreement in 3 models:

1980 1985 1990 1995 2000 2005 2010

0.0

0.2

0.4

0.6

mea

n F

1980 1985 1990 1995 2000 2005 2010

020

0040

0060

0080

00

SS

B (

1000

t)

1980 1985 1990 1995 2000 2005 2010

020

000

4000

060

000

Rec

ruitm

ent (

10^6

)

� SMS estimated Stock development with uncertainty bounds (95%)

Norw. Spawning Stock Surv.

1990 1995 2000 2005 2010

3

4

5

6

7

8

1.92

Intl. Surv. in Nord. Seas.

1990 1995 2000 2005 2010

1

2

3.29

IBWSSS

1990 1995 2000 2005 2010

3

4

5

6

7

8

0.69

� Residuals

� Retrospective fits

1980 1985 1990 1995 2000 2005 2010

02

000

4000

600

0

Retrospective anlysis: 2007 - 2009

SS

B

1980 1985 1990 1995 2000 2005 2010

0.0

0.1

0.2

0.3

0.4

0.5

F

010

000

300

0050

000

recr

iuts

10

^6

OverOverOverOverestimate?

UnderUnderUnderUnderestimate?

� IBWSSS 2010◦ Conclusion: The

2010 estimate is likely to be an underestimateunderestimateunderestimateunderestimateof the SSB

◦ However this is the only survey only survey only survey only survey available covering the spawning stock

◦ 2010 observations are importantimportantimportantimportant for the assessment.

Bl. whiting

BW 2009 final runBW 2010, no IBWSSS 2010BW 2010 all data

1985 1990 1995 2000 2005 2010

010

2030

4050

60

Recruits

(bill

ions

)

1985 1990 1995 2000 2005 2010

0.0

0.1

0.2

0.3

0.4

0.5

F

1985 1990 1995 2000 2005 2010

020

0040

0060

00

SSB

(100

0t)

� IBWSSS 2010◦ Residuals

without 2010:

◦ Residuals with 2010:

IBWSSS

1990 1995 2000 2005 2010

3

4

5

6

7

8

0.45

IBWSSS

1990 1995 2000 2005 2010

3

4

5

6

7

8

0.69

� IESNS

Bl. whiting

a) as inputb) 0 to lowest observedc) survey excluded

2006 2007 2008 2009 2010

01

23

45

6

Recruits

(bill

ions

)

2006 2007 2008 2009 2010

0.0

0.1

0.2

0.3

0.4

F

2006 2007 2008 2009 2010

010

0030

0050

00

SSB

(100

0t)

� 2010 assessment should be considered:◦ uncertainuncertainuncertainuncertain with respect to the absolute estimatesabsolute estimatesabsolute estimatesabsolute estimates of stock

metrics

◦ certaincertaincertaincertain in the conclusion on the steep declinesteep declinesteep declinesteep decline in both SSB and recruitment in the most recent years

� The devil is in the datadatadatadata...◦ Assessment results highly dependent on the quality of the

only survey that covers the spawning stock (IBWSSS)

◦ Errors in the surveys may give misleading estimates of stock abundance

◦ Could attempt model formulations that better handle errors in the data, or identify and ignore data that lead to wrong results

� IBWSS is still short, at times inconsistent, leading to high annual variability in assessment models fit to the data◦ Hopefully estimates of catchability will improve as

the series lengthens, reducing fluctuations of estimates in the terminal year

� Two main areas of uncertainty:◦ TimingTimingTimingTiming: aimed for peak of spawning, but this may

vary over years (e.g. due to temperature)◦ CoverageCoverageCoverageCoverage: earlier migration of the stock northwards

can affect distribution at time of survey◦ More robust design for 2011 to try ensure complete

coverage

� It is difficult to estimate the exact level of recruitment in recent years, but there is no doubt that recruitment has been very low since 2006

� IESNS recruit survey may no longer be indicative of the strength of incoming year classes ◦ In the most recent years there is a mismatch

between survey indices and the amounts caught from these year classes later on

◦ Potentially small year classes may grow up elsewhere

� Benchmark assessment requested for the start of 2012◦ Not 2011 because time is needed to prepare work and

source potential new inputs or methods to present valid alternatives

◦ Good platform to bring about assessment reforms

� Industry information:◦ WGWIDE 2010 report: “No comprehensive information

has been received from the fishing industry this year”� How can industry contribute data or information to make the

assessment more robust?� Industry data to help improve our knowledge of the location of

juvenile fish?� Inform on center of abundance/timing of northward migration?