Stock Assessment Form

Small Pelagics

Reference Year: 2016

Reporting Year:2017

The results of the a4a stock assessment method for the anchovy stock in the Greek

part of GSA 22 are presented.

1

Stock Assessment Form version 1.0 (January 2014)

Uploader: Giannoulaki Marianna

Stock assessment form

Contents 1 Basic Identification Data ........................................................................................................ 3

2 Stock identification and biological information .................................................................... 4

2.1 Stock unit ........................................................................................................................ 4

2.2 Growth and maturity ...................................................................................................... 4

3 Fisheries information .......................................................................................................... 6

3.1 Description of the fleet ................................................................................................... 6

3.2 Historical trends .............................................................................................................. 7

3.3 Management regulations ............................................................................................... 9

3.4 Reference points ........................................................................................................... 10

4 Fisheries independent information ..................................................................................... 11

4.1 Direct method: Acoustics .............................................................................................. 11

4.1.1 Brief description of the chosen method and assumptions used ............................ 11

4.1.2 Spatial distribution of the resources ...................................................................... 13

4.1.3 Historical trends ...................................................................................................... 13

5 Ecological information ......................................................................................................... 14

5.1 Protected species potentially affected by the fisheries ................................................ 14

6 Stock Assessment................................................................................................................. 15

6.1 Statistical catch-at-age: a4a .......................................................................................... 15

6.1.1 Model assumptions ................................................................................................. 15

6.1.2 Scripts ...................................................................................................................... 15

6.1.3 Input data and Parameters ..................................................................................... 15

6.1.4 Tuning data ............................................................................................................. 19

6.1.5 Results ..................................................................................................................... 20

6.1.6 Robustness analysis ................................................................................................ 22

6.1.7 Retrospective analysis, comparison between model runs, sensitivity analysis, etc.

.......................................................................................................................................... 22

6.1.8 Assessment quality.................................................................................................. 23

7 Stock predictions ................................................................................................................. 24

2

8 Draft scientific advice........................................................................................................... 25

8.1 Explanation of codes ..................................................................................................... 26

3

1 Basic Identification Data

Scientific name: Common name: ISCAAP Group:

Engraulis encrasicolus European anchovy [Small gregarious pelagic - 35]

1st Geographical sub-area: 2nd Geographical sub-area: 3rd Geographical sub-area:

[GSA_22] Aegean Sea

4th Geographical sub-area: 5th Geographical sub-area: 6th Geographical sub-area:

1st Country 2nd Country 3rd Country

[Greece] [Country_2] [Country_3]

4th Country 5th Country 6th Country

Stock assessment method: (direct, indirect, combined, none)

Indirect: a4a

Authors:

Giannoulaki Marianna, Athanassios Machias

Affiliation: Hellenic Centre for Marine Research, Institute of Marine Biological Resources and Inland

Waters

The ISSCAAP code is assigned according to the FAO 'International Standard Statistical Classification

for Aquatic Animals and Plants' (ISSCAAP) which divides commercial species into 50 groups on the

basis of their taxonomic, ecological and economic characteristics. This can be provided by the GFCM

secretariat if needed. A list of groups can be found here:

http://www.fao.org/fishery/collection/asfis/en

http://www.fao.org/fishery/collection/asfis/en

4

2 Stock identification and biological information

The assessment covers the Greek part of GSA22, Aegean Sea. The Greek part of Aegean Sea

does not correspond to a complete stock unit. Anchovy distribution extends also to the

Turkish part of GSA 22. However, this analysis is based on data coming from the EU DCF as

well as information derived from HCMR projects and surveys.

2.1 Stock unit

2.2 Growth and maturity

Incorporate different tables if there are different maturity ogives (e.g. catch and survey). Also incorporate figures with the ogives if appropriate. Modify the table caption to identify the origin of the data (catches, survey). Incorporate names of spawning and nursery areas and maps if available.

Table 2.2-1: Maximum size, size at first maturity and size at recruitment.

Somatic magnitude measured

(LT, LC, etc)

Units

Sex Fem Mal Combined Reproduction season

Late spring-summer-

early autumn

Maximum

size

observed

176

Recruitment

season

Late autumn-winter

Size at first

maturity Spawning area Shelf and upper

Recruitment

size to the

fishery

9 cm

Nursery area Shelf and upper

*Maximum size observed corresponds to the maximum size ever observed in the MEDIAS acoustic

campaign

*Size at first maturity was calculated based on samplings in July of the last few years.

5

Table 2-2.2: M vector and proportion of matures by size or age

Size/Age Natural mortality (Unsexed) Proportion of matures (Females)

0 1.55 0.5

1 0.89 0.99

2 0.72 1

3 0.66 1

4 0.5 1

Table 2-3: Growth and length weight model parameters

Sex

Units female male Combined Years

Growth model

L∞ cm 19.1

K 0.385

t0 -1.559

Data source

Length weight

relationship a 2E-06 2016

b 3.2068 2016

M

(scalar)

sex ratio

(% females/total)

6

3 Fisheries information

3.1 Description of the fleet

Description of the purse seine fleet targeting anchovy in the Greek part of GSA 22 is based on

EU DCF data. Data concerning the Turkish part of GSA 22 were provided by Dr Ercan Erdem

to the GFCM WKSASP.

Table 3-1: Description of operational units exploiting the stock

Country

GSA

Fleet Segment

Fishing Gear

Class Group of Target Species

Species

Operational Unit

1* [Greece] [GSA22] [Fleet

Segment1] PS [Small gregarious

pelagic - 35]

ANE

Operational Unit

1* [Turkey] [GSA22] [Fleet

Segment1] P-11 [Small gregarious

pelagic - 35] ANE

Operational Unit

2* [Turkey] [GSA22] [Fleet

Segment2] S-3 [Small gregarious

pelagic - 35] ANE

Operational Unit

3* [Turkey] [GSA22] [Fleet

Segment1] S-4 [Small gregarious

pelagic - 35] ANE

7

Table 3.1-2: Catch, bycatch, discards and effort by operational unit in the reference year

Operational Units*

Fleet (n°

of

boats)*

Catch (T or kg

of the species

assessed)

Other species

caught

(names and

weight )

Discards

(species

assessed)

Discards

(other

species

caught)

Effort

(units)

[Operational Unit

1-Greek part of

GSA22]

205 12480.18 PIL 0 6664417

(Days at

Sea)

[Operational Unit

1-Turkish part of

GSA22]

35 1884.02 PIL

[Operational Unit

2-Turkish part of

GSA22]

24 3768.04 PIL

[Operational Unit

3-Turkish part of

GSA 22]

45 3768.04 PIL

Total 309 21900.28

3.2 Historical trends

The observed trends in landings and fishing effort concerning anchovy in the Greek part of

GSA 22 are shown below.

Reported discards are very low for the purse seine fleet regarding anchovy in GSA 22 and

reported as zero for 2016 (reference year). Discards data were reported to STECF EWG 17-09

through the DCF. Age structure of the discards is missing for all the years and gears. Discards

although very low, they were taken into account for the assessment as a 2% percentage to

reported landings. The fishery is multispecies and fishermen tend to avoid schools of

undersized anchovies due to sorting difficulties (blocking of the mess) and low price,

practically by using nets of bigger mesh size, targeting mostly mackerels or horse mackerels.

8

Figure 3.1. Anchovy DCF landings by the Greek fleet in GSA 22. Years 2007 and 2009-2012 are

missing, while data from 2013 and 2015 come only from the fourth quarter.

Fig 3.2. Anchovy landings as reported by GFCM for the entire part of GSA22.

9

Figure 3.2. Nominal effort (days at sea) of purse seines in the Greek part of GSA 22 as reported by DCF.

Figure 3.3 Effort (gt * days at sea) of purse seines in the Greek part of GSA 22 as reported by DCF.

3.3 Management regulations

Sardine (Sardina pilchardus) is one of the most important target species for the purse seine

fishery in GSA 22. Sardine is being exploited only by the purse seine fishery. Pelagic trawls are

banned and benthic trawls are allowed to fish small pelagics in percentages less than 5% of

their total catch. Commonly sardine is caught from shallow waters about 30 m to 100 m

depth. Regarding the management regulations enforced in the Greek part of GSA 22 they

concern a closed period from the mid December till the end of February and technical

measures such as minimum distance from shore (300m), minimum bottom depth (30 m), gear

and mesh size, engine, GRT restrictions etc. There is also a minimum landing size at 11 cm.

10

3.4 Reference points

For anchovy stock in the Greek part of GSA 22, the number of years of S-R data is very limited and it is not possible to carry out full evaluations of MSY, because the stock-recruit

relationships cannot be established. For the same reason no Biomass related reference

point can be proposed and evaluated. An alternative approach endorsed by STECF (STECF

2017) explored the estimation of an alternative proxy for FMSY for small pelagics. An

alternative approach is the choice of a target value at F=0.667M (where M is the natural

mortality) as an empirical target for management of small pelagic fish. This target was

calculated by Patterson (1992), who analysed the historical behaviour of 27 exploited small

pelagic fish stocks. Patterson (1992) defined an exploitation rate (E=F/Z, the ratio between

fishing mortality and total mortality) of 0.4 as an appropriate upper limit to the exploitation

rate for small pelagic stocks. STECF (STECF 2017) evaluated the Stock-Recruit and

Exploitation rate methods and concluded that E=0.4 (equivalent to F=0.667M) is the best

method for estimating FMSY for small pelagic stocks such as those in the Mediterranean.

This EWG has continued with this practice and has provided estimates of catch/landings F

based on F=0.667M (equivalent to E-0.4) as target values for stocks with age based

assessments.

Table 3.3-1: List of reference points and empirical reference values previously agreed (if any)

Indicator

Limit

Reference

point/emp

irical

reference

value

Value

Target

Reference

point/empi

rical

reference

value

Value

Comments

B

SSB

F

F at E=0.4 or equivalent

F=0.667M

0.467

Fbar for ages 1 to 3

Y

CPUE

Index of

Biomass at

sea

11

4 Fisheries independent information

4.1 Direct method: Acoustics

4.1.1 Brief description of the chosen method and assumptions used

Acoustic echoes were registered continuously along 74 pre-defined transects in the Aegean Sea

during June 2016 with a Simrad ES38-10, 38 kHz split-beam echo sounder transducer. The size of the

Elementary Distance

Sampling Unit (EDSU) was one nautical mile. The acoustic survey in GSA 22 is part of the

Mediterranean Acoustic Survey (MEDIAS) since 2008 and follows the MEDIAS protocol. Echo trace

classification was applied based on a) echogram visual scrutinisation and direct allocation of school

marks that characterise anchovy as well as b) allocation on account of representative fishing stations

that were held along transects (Simmonds and MacLennan, 2005). Acoustic survey covered a total

area of 32599 Km2 in Aegean Sea. In order to estimate anchovy’s and sardine’s biomass, the weight-

length relationship is required as well as species length frequency distribution per area. Therefore, 40

pelagic trawls were held along transects in the positions of high fish concentrations. While all

frequencies were visualized during sampling and helped deciding when to conduct a trawl, only the

energies from the 38kHz channel were used to estimate fish biomass. Acoustic data were preliminary

treated with Echoview software in order to perform bottom corrections and to attribute echotraces

to different echotypes and estimate NASC values per EDSU.

12

Table 4.1-1: Acoustic cruise information.

Date June 2016 to July 2016

Cruise MEDIAS AEGEAN R/V PHILIA

Target species ANCHOVY, SARDINE

Sampling strategy Parallel transect spaced 10 nm, zig zag in gulfs

Sampling season June-July

Investigated depth range (m) 20-600 m

Echo-sounder SIMRAD EK 80, 38 KHz for assessment

120, 200 used as complementary frequency

Fish sampler Pelagic trawl

Cod –end mesh size as opening (mm) 8 mm

ESDU (i.e. 1 nautical mile) 1 nautical mile

TS (Target Strength)/species -71.2

Software used in the post-processing Echoview

Samples (gear used) Pelagic trawl

Biological data obtained Length-Weight relationship, Age, Sex, Maturity, Fat content

Age slicing method Otolith

Maturity ogive used L50

Table 4.1-2: Acoustic results by age class

Biomass in metric tons

fish numbers Nautical Area Scattering Coefficient

Indicator

… Indicator

…

Age 0 9.79 4 602 312

Age 1 75 876 14 839 527 721

Age 2 1 644 163 711 022

Age 3 0.64 30 440

Age 4

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4.1.2 Spatial distribution of the resources

Figure 4.1.2.1. The distribution of anchovy biomass (t) per EDSU in the Greek part of GSA 22 (Aegean

Sea) during June 2016.

4.1.3 Historical trends

European Anchovy time series of abundance and biomass indices from acoustic surveys in

GSA 22 are shown and described in the following figure.

Figure 4.1.3.1 Acoustic survey abundance index of anchovy in the Greek part of GSA 22 as reported by DCF and used for assessment. No survey was carried out in 2007, 2009-2011 and 2015. The survey

was carried out in June/July except from 2012 when it was carried out in December and 2013 when it

was carried out in September.

14

Figure 4.1.3.2 Age frequency distribution of the acoustic survey abundance index of anchovy in the

Greek part of GSA 22 as reported by DCF and used for assessment. No survey was carried out in 2007,

2009-2011 and 2015. The survey was carried out in June/July except from 2012 when it was carried

out in December and 2013 when it was carried out in September.

5 Ecological information

5.1 Protected species potentially affected by the fisheries

No protected species should be affected by small pelagic fisheries.

15

6 Stock Assessment

In this section there will be one subsection for each different model used, and also different

model assumptions runs should be documented when all are presented as alternative

assessment options.

6.1 Statistical catch-at-age: a4a

6.1.1 Model assumptions

A statistical catch-at-age analysis method was used for this stock. Such methods utilize catch-

at- age data to derive estimates of historical population size and fishing mortality. However,

unlike VPA, model parameters estimated using catch-at-age analysis are done so by working

forward in time and analyses do not require the assumption that removals from the fishery

are known without error. Data typically used are: catch, abundance index, statistical sample

of age composition of catch and abundance index. Specifically, for anchovy stock in GSA 22

we used the Assessment for All Initiative (a4a) (Jardim et al., 2015). Assessment was

performed with version 1.1.2 of FLa4a, together with version 2.6.4 of the FLR library (FLCore).

A single tuning fleet was used in both methods based on the biomass at age estimates from

summer acoustic surveys conducted in the Greek part of GSA 22 (2003 to 2016 with gaps in

2007, 2009-2013 and 2015) as reported in the DCF.

The analysis was carried out for the ages 0 to 4. Concerning the Fbar, the age range used was

1-3 age groups.

For the years 2007, 2009-2012 where no EU DCF was carried out in Greece catch numbers at

age were NA.

6.1.2 Scripts

The assessment was carried out within the framework of the STECF EWG 1709. The R script

used will be available through the respective depository.

6.1.3 Input data and Parameters

Input data for the assessment are presented below: Catch (in tons), Catch at age (in thousands) and weight at age in the catch. As discards are very low for the specific fishery and length structure information is missing, discards were added as 2% in the landings information to obtain catch.

The time series of total PS landings for the Greek part of GSA 22 as estimated in the STECF EWG 16-14 (2016) was used for the period 2000-2014 (Figure 6.10.3.3.1). For 2013 and 2015 the DCF reported landings referred only to the last trimester thus the HELSTAT officially reported landings to FAO GFCM were used. The DCF reported landings were used for 2016.

16

Catch (in tons)

2000 9776

2001 8581

2002 8579

2003 14013

2004 16114

2005 16376

2006 22355

2007 21558

2008 24565

2009 20746

2010 15139

2011 10451

2012 10548

2013 10437

2014 14386

2015 13058

2016 12736

17

Catch-at

Year -age

(thousands)

Age 0

Age 1

Age 2 Age 3 Age 4

2000 16809 393648 269681 6314 159

2001 49053 534410 274400 870 301

2002 5838 364072 279518 14323 700

2003 4676 348900 513289 41899 3881

2004 16315 342761 521446 57843 8527

2005 14523 498088 591543 43454 3003

2006 21930 766824 863957 57795 6472

2007 NA NA NA NA NA

2008 75828 892863 866883 64421 2531

2009 NA NA NA NA NA

2010 NA NA NA NA NA

2011 NA NA NA NA NA

2012 NA NA NA NA NA

2013 113852 452365 347589 129636 2778

2014 56614 493287 367377 150936 2836

2015 40146 379892 448035 229898 31589

2016 33377 311680 422004 232698 39932

18

Weight-at-age (in kg) Year Age

0 Age 1 Age 2 Age 3 Age 4

2000 0.0060 0.0132 0.0161 0.0210 0.0270

2001 0.0040 0.0100 0.0110 0.0170 0.0250

2002 0.0060 0.0110 0.0150 0.0230 0.0250

2003 0.0055 0.0140 0.0160 0.0180 0.0350

2004 0.0029 0.0146 0.0184 0.0204 0.0338

2005 0.0036 0.0135 0.0147 0.0185 0.0334

2006 0.0095 0.0122 0.0136 0.0160 0.0180

2007 0.0090 0.0125 0.0139 0.0170 0.0220

2008 0.0095 0.0120 0.0138 0.0171 0.0258

2009 0.0092 0.0121 0.0140 0.0152 0.0245

2010 0.0092 0.0124 0.0141 0.0153 0.0245

2011 0.0105 0.0115 0.0133 0.0144 0.0246

2012 0.0080 0.0092 0.0106 0.0114 0.0193

2013 0.0080 0.0095 0.0106 0.0115 0.0193

2014 0.0097 0.0117 0.0150 0.0164 0.0280

2015 0.0067 0.0096 0.0119 0.0135 0.0224

2016 0.0064 0.0102 0.0123 0.0140 0.0224

19

6.1.4 Tuning data

Numbers-at-age (thousands) based on acoustics were used for tuning

Numbers of individuals (thousands)

2003 1144350 1395617 636108

2004 1953979 1323299 10920

2005 2008764 1013061 20625

2006 5583451 1335320 63922

2007 NA NA NA

2008 4469332 2495923 95920

2009 NA NA NA

2010 NA NA NA

2011 NA NA NA

2012 NA NA NA

2013 NA NA NA

2014 2688671 40491 7193

2015 NA NA NA

2016 14839527 163711 30440

20

6.1.5 Results

Different a4a models were performed (combination of different f, q). The best model

(according to a combination of AIC, BIC and residuals) included:

f~s(replace(age, age>2,2), k=2)+s(year, k=4)+s(year, k = 4, by = as.numeric(age==0))

q~factor(age)

sr~geomean(CV=0.5)

Figure 6.1.5.1 Stock summary from the a4a model for anchovy in GSA 22, recruits, SSB (Stock

Spawning Biomass), catch (model output for catch and landings) and harvest (fishing mortality for

ages 1 to 3).

21

Figure 6.1.5.2 Stock summary from the SAM model for anchovy in GSA 22, recruits, SSB (Stock

Spawning Biomass), catch (model output for catch and landings) and harvest (fishing mortality for

ages 1 to 3).

Based on the a4a results, the anchovy SSB fluctuated over the time period examined (2000-

2016) from 23333 tons (in 2000) to 74802 tons in 2016. A drop in SSB was observed in the

years 2009 to 2013. This is generally in accordance with the SAM results that estimate SSB at

67546 tons in 2016. The assessment shows an increasing trend in the number of recruits

between 2001 and 2007. The recruitment (age 0) reached a maximum of 26.5 million

individuals in 2016 and a minimum value of 9.4 million individuals in 2000. Fbar (1-3) shows a

decreasing trend since 2000, presenting an average around 1.092 for the period 2007 to 2013.

Since 2013, F is decreasing with a value at 0.46 in 2016.

22

6.1.6 Robustness analysis

6.1.7 Retrospective analysis, comparison between model runs, sensitivity

analysis, etc.

The retrospective analysis was applied up to 3 years back. Models results were quite stable (Figure 6.1.7.1).

Figure 6.1.7.1 European anchovy in GSA 22. Restrospective analysis output for the a4a model.

23

Figure 6.1.7.2 European anchovy in GSA 22. Stock summary of the simulated and fitted data for the

a4a model.

6.1.8 Assessment quality

Τhe output of this model was suitable to provide an indication of the current status of the stock.

However due to the lack of surveys and catch-at-age data for a big part of the time series since 2009

the EWG 17-09 agreed not to provide forward projections and catch advice based on this assessment.

24

7 Stock predictions

The Empirical Reference point corresponding at Exploitation rate 0.4 (Patterson 1992) as

suggested by the STECF SG-MED 09-02 is used as a proxy for MSY and has been used to define

stock status. The F equivalent to E=0.4 is estimated as 0.464 from the M and fishery selection

at age in the a4a assessment.

Given the uncertainty associated with the models fit no short term forecast and catch

options were carried out for anchovy stock in GSA 22.

25

8 Draft scientific advice

Based on Indicator Analytic al

reference

point

(name and

value)

Current value

from the

analysis

(name and

value)

Empirical

reference value

(name and

value)

Trend

(time

period)

Status

Fishing

mortality Fishing

mortality 0.463 (a4a)

0.345 (SAM)

F at E=0.4,

estimated as

0.467

D SL

Fishing effort

Catch D

Stock

abundance Biomass I OH

SSB 74802 (a4a)

67567

(SAM)

I

Recruitment I

Final Diagnosis Sustainably exploited

Assessment is based on analytical stock assessment methods and the empirical reference

point for F (Patterson 1992) to assess stock status. Results give an indication that the stock

is sustainably exploited based on the empirical reference point for F (Patterson 1992,

Exploitation rate=0.4), assessment is verified but considered as uncertain due to the GAPs in

the DCF and both assessment models fit. We should note that total biomass estimates

deviate more than twice to the acoustic estimates that make model output uncertain. No

short term or medium term forecast was made based on this. In addition, the short length

of time series and stock behavior does not allow to set a Blim reference point.

26

8.1 Explanation of codes

Trend categories

1) N - No trend

2) I - Increasing

3) D – Decreasing

4) C - Cyclic

Stock Status Based on Fishing mortality related indicators

1) N - Not known or uncertain – Not much information is available to make a judgment;

2) U - undeveloped or new fishery - Believed to have a significant potential for expansion in

total production;

3) S - Sustainable exploitation- fishing mortality or effort below an agreed fishing mortality or

effort based Reference Point;

4) IO –In Overfishing status– fishing mortality or effort above the value of the agreed fishing

mortality or effort based Reference Point. An agreed range of overfishing levels is provided;

Range of Overfishing levels based on fishery reference points

In order to assess the level of overfishing status when F0.1 from a Y/R model is used as LRP,

the following operational approach is proposed:

• If Fc*/F0.1 is below or equal to 1.33 the stock is in (OL): Low overfishing

• If the Fc/F0.1 is between 1.33 and 1.66 the stock is in (OI): Intermediate overfishing

• If the Fc/F0.1 is equal or above to 1.66 the stock is in (OH): High overfishing

*Fc is current level of F

5) C- Collapsed- no or very few catches;

27

Based on Stock related indicators

1) N - Not known or uncertain: Not much information is available to make a judgment

2) S - Sustainably exploited: Standing stock above an agreed biomass based Reference Point;

3) O - Overexploited: Standing stock below the value of the agreed biomass based Reference

Point. An agreed range of overexploited status is provided;

Empirical Reference framework for the relative level of stock biomass index

• Relative low biomass: Values lower than or equal to 33rd percentile of biomass index in the time series

(OL)

• Relative intermediate biomass: Values falling within this limit and 66th percentile

(OI)

• Relative high biomass: Values higher than the 66th percentile (OH)

4) D – Depleted: Standing stock is at lowest historical levels, irrespective of the amount of fishing

effort exerted;

5) R –Recovering: Biomass are increasing after having been depleted from a previous period;

Agreed definitions as per SAC Glossary

Overfished (or overexploited) - A stock is considered to be overfished when its abundance is

below an agreed biomass based reference target point, like B0.1 or BMSY. To apply this

denomination, it should be assumed that the current state of the stock (in biomass) arises

from the application of excessive fishing pressure in previous years. This classification is

independent of the current level of fishing mortality.

Stock subjected to overfishing (or overexploitation) - A stock is subjected to overfishing if the

fishing mortality applied to it exceeds the one it can sustainably stand, for a longer period. In

other words, the current fishing mortality exceeds the fishing mortality that, if applied during

a long period, under stable conditions, would lead the stock abundance to the reference point

of the target abundance (either in terms of biomass or numbers)