Stock Assessment Form of Hake (M. Merluccius) in Combined GSA 12-16

Stock Assessment Form of Hake (M. merluccius) in combined GSA 12-16

Reference year: 2007-2017

Reporting year: 2018

Merluccius merluccius, is an important demersal target species of the commercial fisheries in the cenral Mediterranean Sea (GFCM-GSA12-16). In this area, European hake is fished by 5 fishing fleet components: Italian coastal trawlers, Italian distant trawlers, Tunisian trawlers, Maltese trawlers, Tunisian and Italian artisanal vessels. Annual landings of hake for 2013-2017 was over 1200 t from Italian and about 1800 t from Tunisian trawlers. Hake is the main commercial by-catch species of deep water shrimp fisheries and a target species for vessels using longlines and gillnets. Trawlers catching hake exploit a highly diversified species assemblage, the main other commercial species being deep water rose shrimp (Parapenaeus longirostris, generally main target species), striped mullet (Mullus surmuletus) and red mullet (Mullus barbatus). Size structures of hake catches range mostly between 8 and 70 cm total length (TL), the minimum landing size is 20 cm total length (TL). The assessment, performed by extended survivor analysis (XSA) tuned with trawl survey data, showed a state of High Overfishing with relative low level of stock SSB.

Uploader: Vita Gancitano

Stock assessment form 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 ...... 7 3.1 Description of the fleet ...... 7 3.2 Historical trends ...... 9 3.3 Management regulations ...... 10 3.4 Reference points ...... 12 4 Fisheries independent information ...... 13 4.1 MEDITS Trawl Survey ...... 13 4.1.1 Brief description of the direct method used...... 13 4.1.2 Historical trends ...... 22 5 Stock Assessment...... 25 5.1 Extended Survivor Analysis (XSA) ...... 25 5.1.1 Model assumptions ...... 25 5.1.2 Scripts ...... 25 5.1.3 Input data and Parameters ...... 25 5.1.4 Results ...... 28 5.1.5 Robustness analysis...... 34 5.1.6 Retrospective analysis ...... 35 5.1.7 Assessment quality ...... 36 6 Stock predictions ...... 37 6.1 Short term predictions (XSA) ...... 37 7 Draft scientific advice...... 38 7.1 Explanation of codes ...... 39

1 Basic Identification Data

Scientific name: Common name: ISCAAP Group:

Merluccius merluccius [European hake] [HKE]

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

[GSA_12] [GSA_13] [GSA_14]

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

[GSA_15] [GSA_16]

1st Country 2nd Country 3rd Country

[TUNISIA] [ITALY] [MALTA]

4th Country 5th Country 6th Country

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

Indirect Method: XSA analysis tuned with MEDITS data from GSAs 15 and 16

Authors:

V. Gancitano1, S. Ben Meriem2, R. Micallef3, F. Colloca1, G. Milisenda5, L. Ceriola4, O. Ben Abdallah2, M. Gambin3, H. Farrugia3, O. Jarboui2, E. Arneri4, F. Fiorentino1 Affiliation:

1 IRBIM-CNR Mazara del Vallo, Italy;

2 Institut National des Sciences et Technologies de la Mer (INSTM), Tunisia; 3MSDEC, Malta, 4Food and Agriculture Organization of the United Nations (FAO), MedSudMed Project, Viale delle Terme di Caracalla, 00153 Rome, Italy. 5Stazione Zoologica Anton Dohrn (Napoli)

3 2. Stock identification and biological information

2.1 Stock unit

The European hake (Merluccius merluccius, L. 1758) has a wide distribution from the coastal grounds to the high depth (up to 1000m), the larger individuals preferring the deepest waters. The stock structure of hake in the Strait of Sicily (south-central Mediterranean Sea) is still under investigation. Levi et al., (1994) compared the growth of M. merluccius from several Mediterranean areas and found a similar pattern in individuals from the northern side of the Strait of Sicily (GSA15 and 16) and those caught in the Gulf of Gabès (GSA 14). Ben Meriem and Gharbi (1996) indicated a similar historical trend in CPUE in north and south Tunisia (GSA 12, 13 and 14). Lo Brutto et al., (1998) have also found no evidence of genetic subdivisions or significant differences in allelic frequencies, between samples near Sicily and those from the north Tunisia. More recently, Levi et al., (2004) applied electrophoretic, morphometric and growth analyses to test the hypothesis of the existence of a unique stock of hake in the south-central Mediterranean, which includes part of the North African continental shelf off the Tunisian coast and the shelf off the southern Sicilian coast. Milano et al., (2014), working with genetic markers able to identify fine population structure (SNPs), found a main difference between hake inhabiting Western, Central and Eastern Mediterranean. According to the multidimensional definition of stock followed in the STOCKMED project (Fiorentino et al., 2015), European hake of the Strait of Sicily would belong to a single a population unit, extending from the Ligurian-North Tyrrhenian Sea (GSA 9) to eastern Ionian (GSA19). According to the decision adopted in the benchmark assessment of 2015, DPS living in the GSAs 12, 13, 14, 15 and 16 were considered belonging to a stock units.

2.2 Growth and maturity

M. merluccius is considered a long living species reaching at least 25 year old (Vitale et al., 2016). Hake growth is still a matter of active debate in fishery biology, with some Authors proposing the so called low growth and other the fast growth. On the basis of a preliminary validation of age at size with bomb radiocarbon analysis (Vitale et al., 2016), the so-called low growth hypothesis is considered as the most reliable for the species in the south-central Mediterranean.

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

Somatic magnitude measured Units (TL in cm)

Reproduction all the year round Sex Fem Mal Combined season peak winter

Maximum Recruitment size 90 58 season all the year round observed Size at first Outer shelf and 28.35 Spawning areas maturity upper slope

Recruitment size to the 8 Nursery areas Identified in the fishery north sector 4

Table 2-2.2: M vector from Prodbiom (Abella et al., 2009) and proportion of matures by age (sex combined).

Size/A Natural mortality Proportion of matures ge 0 1.38 0.01

1 0.56 0.16

2 0.27 0.61

3 0.22 0.93

4 0.19 0.98

5 0.18 1.00

6 0.17 1.00

7 0.16 1.00

8+ 0.16 1.00

Table 2-3: Growth and length weight model parameters.

Sex

Units female male Combined Years

L∞ cm 100

K 0.116 Growth model t0 -0.6

Data source Tunisian and Italian data

Length a 0.004 weight b 3.15 relationship M 0.20 (scalar)

sex ratio (% females/total) 0.48

6 3 Fisheries information

3.1 Description of the fleet

European hake, Merluccius merluccius, is an important demersal species for commercial fisheries in the Strait of Sicily (GFCM-GSAs12-16, south-central Mediterranean Sea). It is the main accessory species of trawling targeting deep water rose shrimp as well as an important target species for artisanal vessels using longlines and gillnets on the outer shelf and upper slope. In the south-central Mediterranean, European hake is exploited by 6 main fishing fleet segments: Italian coastal trawlers, Italian distant trawlers, Tunisian trawlers, Maltese trawlers, Italian and Tunisian vessels using fixed nets. Sicilian coastal trawlers (length overall, LOA, between 12 and 24 m) operate mainly on short-distance fishing trips, which range from 1 to 2 days at sea, and fishing taking place on the outer shelf and upper slope. With 276 registered vessels, this is the largest component of the fleet fishing deep water rose shrimp in 2017. Sicilian trawlers over 24 m in length perform longer fishing trips, which may last up to 4 weeks. These vessels operate offshore, in both Italian and international waters of the south-central Mediterranean. Due to the progressive shift in target species of such trawlers from deep water rose shrimps and Norway lobster to red shrimps, about 75 out 107 can be considered as mainly targeted on P. longirostris in 2017. In Maltese Islands small vessels measuring 12 to 24 m in length target rose shrimp very close to land (around 6 km from the coast) at a depth of around 200 m. The number of trawlers targeting rose shrimp decreased from 13 in 2011 to 10 in 2015. The activity is mainly carried out in winter, when the weather does not allow to fish in deeper waters. Tunisian trawl vessels which target rose shrimp measure around 24 m in length, and operate primarily in Northern Tunisia where 90% of the country’s total P. longirostris catches originate. The great majority of these catches are landed in the town of Bizerte and Kelibia. The number of Tunisian trawlers based in GSAs 12 and 13 mainly targeting rose shrimp has increased from 40 in 1996 to about 77 in 2017. Furthermore about 100 trawlers move seasonally from GSA 14 to fish DPS in GSAs 12 and 13.

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

Fishing Gear Group of Target Country GSA Fleet Segment Class Species Species

Operational Unit Demersal slope 1* ITA 16 T11 - Trawls OTB species HKE

Demersal slope Operational Unit 2 ITA 16 T12 - Trawls OTB species HKE

Demersal slope Operational Unit 3 TUN 12-13-14 T12 - Trawls OTB species HKE

Operational Unit 4 TUN 12-13-14 P-07 GTR Demersal species HKE

Demersal slope Operational Unit 5 MLT 15 T11 - Trawls OTB species HKE

Table 3.1-2: Catch and effort by operational unit in 2017.

Other Hake Hake Discards Fleet (n Catch species caught discards Effort of boats) (names and (other species (units) (in tons) weight ) (tons) caught)

Operational Unit 1* 290 617.8 60.9 tons

Operational Unit 2 123 240.2 tons

Operational Unit 3 1358.94 tons

Operational Unit 4 41.76 tons

Operational Unit 5 10 11.90 tons

Total 2270.6 60.9

3.2 Historical trends

Time series analysis with figures showing the observed trends in landings and LFD.

4500 140

4000 120 3500

Malta&TUN_NET 100 3000 2500 80

2000 60

1500 40 1000 20 500 0 0 2006 2008 2010 2012 2014 2016 2018 ITA TUN Total MLT TUN_net

Figure 3.2.1 - Catch of HKE from 2007 to 2017 in the Strait of Sicily, Central Mediterranean (GSA 12,13,14,15 and 16) by fleet (Italian coastal and distant trawlers, Tunisian trawlers and gill nets, Maltese coastal trawlers) and country.

2500 600

inthousand Malta&TUN_NET number Mean 500 2000

400 1500 300 1000 200

Meannumber thousand in 500 100

0 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 ITA COAST ITA DIST TUN TRAWL TUN NET MALTA

Figure 3.2.2 - LFD (2007-2017) of catch data by fleet and country, combined sex.

3.3 Management regulations

In the south-central Mediterranean, as in other Mediterranean areas, fishery management is based on control of capacity (number of fishing licenses), fishing effort (days at sea, number of vessels), and technical measures (cod-end mesh size for trawlers, temporary or permanent area closures and fish- size limits). A multiannual management plan (IMAP) for 2008-2013 has been agreed for Italian trawlers in the Strait of Sicily. The plan was mainly based on a fleet reduction of 25% of the capacity obtained in two steps. The first (12.5%) from 2008 to 2010, and the second (12.5%) from 2011 to 2013. The IMAP adopted also a trawling ban is, normally implemented in late summer early autumn. Although the IMAP foresees an interruption of fishing for 45 consecutive days, the effective duration of the ban was 30 days per year. The IMAP was updated in January 2018. The new IMAP based regulation mainly on reduction of fishing effort of 5 % and 10 % of fishing days in 2018. In addition, the Mediterranean Regulation EC 1967 of 21 December 2006 fixed a minimum harvest size of 20 cm TL and a minimum mesh size of 40 mm square or 50 mm diamond for EU bottom trawling vessels (i.e. Italian and Maltese trawlers). In 2015, Malta had 14 trawlers that operated on a full-time basis. A preliminary analysis of the capacity of the fleet in the Sub-regional Committee report for the Central Mediterranean (SRC_CM) showed that there was a 39% reduction from 2011 to 2015 (7 permanent and 2 temporary). Fishing effort and capacity in the 25 nautical miles fisheries management zone are being managed by limiting vessel sizes, as well as total vessel engine powers (EC 813/2004; EC 1967/2006). Trawling is allowed within this designated conservation area, however only by vessels not exceeding an overall length of 24m and only within designated areas. Such vessels fishing in the management zone hold a special fishing permit in accordance with Article 7 of Regulation (EC) No 1224/2009, and are included in a list containing their external marking and vessel's Community fleet register number (CFR) to be provided to the Commission annually by the Member States concerned (EC 813/2004). In Tunisia, fisheries management targets trawlers generally setting a number of measures affecting also hake related fisheries. Trawling is not permitted within 3 nautical miles of the coast and at less than 50m depth in GSAs 12-14. Moreover, in GSA 14, a three-month closed season for trawling (from July to September) is in place. The objective of the measure is to protect recruits of a large number of species. In addition, a trawling ban of 11 months is in place in the Gulf of Tunis (GSA 12) and trawling in this area is allowed only during July. Also, minimum landing size of 20 cm total length in Tunisia has been established.

10 The GFCM in 2015 adopted a recommendation to protect juvenile European hake in the entire Mediterranean Sea (REC.CM-GFCM/40/2016/5 establishing a minimum conservation reference size for European hake in the Mediterranean Sea). In addition, owing to the importance of the fisheries for the costal countries in the area, the GFCM adopted a series of recommendations targeting deep water rose shrimp and hake fisheries: i) REC.CM-GFCM/39/2015/2 on the establishment of a set of minimum standards for bottom trawling fisheries of demersal stocks in the Strait of Sicily, pending the development and adoption of a multiannual management plan; ii) REC.CM- GFCM/40/2016/4 establishing a multiannual management plan for the fisheries exploiting European hake and deep-water rose shrimp in the Strait of Sicily (GSA 12 to 16); and iii) REC.CM-GFCM/41/2017/8 on an international joint inspection and surveillance scheme outside the waters under national jurisdiction of the Strait of Sicily (geographical subareas 12 to 16).

In order to protect juveniles, three Fishery Restricted Areas (FRAs) where bottom trawling is prohibited were established in the northern sector of the Strait of Sicily (GSA 15 and 16) based on the REC.CM-GFCM/40/2016/4. Periodic scientific studies assessing the effectiveness of the measure. More studies should be carried out to identify nursery areas of hake in GSAs other than 15 and 16, in order to evaluate the possibility of proposing additional FRAs to protect nursery areas throughout the subregion.

11 3.4 Reference points

Table 3.4-1: List of reference points and empirical reference values in 2017.

Limit Target

Reference Reference point/empirical point/empirical Indicator Value Value Comments reference value reference value

SSB

F Range of values obtained at the last F0.1 0.2 benchmark assessment of HKE held in 2015

CPUE

Index of Biomass at sea

4 Fisheries independent information

4.1 MEDITS Trawl Survey

In order to collect fisheries independent data, which is a requirement of the EU DCF (Council Regulation 199/2008, Commission Regulation 665/2008, Commission Decision EC 949/2008 and Commission Decision 93/2010), the MEDITS international trawl survey is carried out in GSAs 15 & 16 on an annual basis. In July 2011 an inter-calibration experiment was carried out to standardize MEDITS indices from GSAs 15-16 with those of Tunisian surveys.

4.1.1Brief description of the direct method used

Distribution, abundance and demographic information of the stock at sea derived from data collected during the standard bottom trawl surveys carried out annually in the northern sector of the Strait of Sicily from 1994 to 2017 in spring/early summer within the MEDITS (MEDiterranean International Bottom Trawl-Surveys) program, included in the European Data Collection Framework (DCF). A total of 45 hauls in GSA 15 and 120 hauls in GSA 16 were performed yearly. The bottom trawl surveys covered an area of about 10,600 km2 in GSA 15 and 31,400 km2 in GSA 16 within a depth-range 10-800 m in both areas. The sampling design is random stratified with allocation of hauls proportional to strata extension (depth strata: 10-50 m, 51-100 m, 101-200 m, 201-500 m, 501-800 m). Roughly the same haul positions were kept each year. A GOC 73 gear is used with mesh size in the cod-end 20 mm opening and the vertical opening of the mouth of 2.4- 2.9 m. More details on the MEDITS protocol is reported in the MEDITS-Handbook. Version n. 9 (2017).

Direct methods: trawl based abundance indices

Table 4.1-1: Trawl survey basic information.

Survey MEDITS Trawler/RV TRAWLER

Sampling season MAY-JULY

Sampling design Stratified with number of haul by stratum proportional to stratum surface (see MEDITS-Handbook. Version n. 9, 2017, MEDITS Working Group: 106 pp.)

Sampler (gear used) Bottom trawl made of four panels (IFREMER reference GOC 73)

Cod –end mesh 10 mm mesh size, which corresponds to ~ 20 mm of mesh opening size as opening in mm Investigated depth 10-800m range (m)

Table 4.1-2: Trawl survey sampling area and number of hauls (GSAs 15&16).

Trawlable Number Number of Total surface Total surface Swept area Stratum surface of hauls hauls GSA (km2) GSA15 (km2) GSA16 (km2) (km2) GSA 15 16 a 152 2979 na na 11 b 1473 5943 na na 23 c 3076 5563 na na 21 d 3353 6972 na na 27 e 2526 9927 na na 38 Total 10428 31384 na na 45 120

Figure 4.1.1 - Map of hauls positions in the Strait of Sicily (GSA 16).

Figure 4.1.2 - Map of hauls positions in GSA 15.

Table 4.1-3: Trawl survey abundance and biomass results (GSAs 15&16)

CV CV CV CV Depth Kg/km2 N/km2 Kg/km2 N/km2 Kg/km2 N/km2 Kg/km2 N/km2 Stratum (GSA 16) (GSA 16) (GSA 16) (GSA 16) (GSA 15) (GSA 15) (GSA 15) (GSA 15) 10-800 m 1994 34.9 20.4 1249 45.2 na na na na 1995 26.3 27.6 549 42.2 na na na na 1996 15.4 21.8 334 25.8 na na na na 1997 21.9 24.3 927 33.2 na na na na 1998 15.8 16.8 355 28.5 na na na na 1999 17 23.6 432 37.4 na na na na 2000 24.5 22.4 710 27.6 na na na na 2001 18 17.8 333 24.7 na na na na 2002 20.6 22.8 427 28.8 na na na na 2003 21.7 29.3 804 49.8 na na na na 2004 28.8 27.1 613 29.9 na na na na 2005 49.1 34.2 1635 42.3 38.5 na 462.66 na 2006 37 21 1258 43 31.8 na 432.29 na 2007 35.2 22.1 1586 38.3 44.1 19.08 559.8 18.16 2008 38.4 38.6 928 32.3 51.6 13.86 949.2 24.63 2009 35 27.2 1172 31.7 46.3 12.83 807.9 35.5 2010 38.7 26.2 507 27.3 25.2 12.92 275.3 19.94 2011 30.6 28.8 826 38.7 31.9 14.07 820 40.31 2012 46.5 21 1795 30.9 41 15.54 897.3 16.52 2013 54.3 23.8 995.6 27.8 42.3 14.18 777.3 21.06 2014 44.37 31.4 1001 50 49.3 14.24 906.6 17.54 2015 31.47 30.93 729 43 33.8 13.52 465.6 22.19 2016 25.7 30.2 492 27 28.65 13.06 743.6 19.14 2017 19.4 24.33 289 25 24.9 18.8 454 19.89

Direct methods: trawl based length/age structure of population at sea

Slicing method

Length structure was sliced by knife edge approach.

Table 4.1-4: Hake MEDITS abundance index (n km-2/100) by age class (GSAs 15&16).

N (Total or Year sex combined)

by Age class 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 in thousand 0 42.44 19.64 27.55 7.21 20.80 47.50 16.78 19.68 22.65 19.19

1 4.67 8.18 6.51 5.91 3.38 5.52 11.88 10.06 6.93 9.83

2 0.75 1.16 1.24 2.04 0.77 1.18 1.57 1.06 2.36 1.23

3 0.22 0.26 0.31 0.36 0.27 0.26 0.39 0.25 0.42 1.64

4 0.11 0.08 0.11 0.11 0.10 0.08 0.12 0.09 0.26 0.65

5 0.04 0.03 0.04 0.04 0.06 0.04 0.06 0.06 0.14 0.19

6 0.02 0.02 0.02 0.01 0.03 0.01 0.02 0.04 0.04 0.11

7 0.01 0.02 0.00 0.01 0.02 0.00 0.02 0.01 0.04 0.08

8+ 0.00 0.01 0.00 0.01 0.01 0.00 0.01 0.02 0.02 0.04

Total 48.27 29.40 35.77 15.70 25.44 54.60 30.86 31.26 32.86 31.76

Table 4.1-5 Sex ratio by length class in mm of hake from MEDITS in GSA 16. All year combined.

TL (mm) Sr TL (mm) Sr

100 0.94 460 0.99

120 0.42 480 0.99

140 0.46 500 1.00

160 0.48 520 1.00

180 0.48 540 1.00

200 0.48 560 1.00

220 0.47 580 1.00

s la

c 240 0.51 600 1.00

h h

ng e

201 260 0.51 620 1.00

o by by o 1994

i 280 0.65 640 1.00

r x x

e 300 0.75 660 1.00 S

320 0.80 700 1.00

340 0.87 720 1.00

360 0.85 740 1.00

380 0.91 760 1.00

400 0.93 780 1.00

420 0.88 800 1.00

440 0.98

Direct methods: trawl based Recruitment analysis (GSA 16)

Table 4.1-6 Trawl surveys; recruitment analysis summary

Survey MEDITS Trawler/RV TRAWLER

Survey season May-July

Cod –end mesh size as opening in mm 20

Investigated depth range (m) 10-800

Recruitment season and peak All year around (months) Age at fishing-grounds recruitment 0

Length at fishing-grounds recruitment 6 cm TL

Table 4.1-7: Trawl surveys; recruitment analysis results.

Area in N of Years recruit CV km2 per km2 1994 952 50 1995 366 55 1996 220 34 1997 762 36 1998 242 35 1999 308 46 2000 556 32 2001 198 34 2002 198 35 2003 607 57 2004 373 35 2005 1115 43 2006 901 58 2007 1331 43 2008 557 34 2009 854 38 2010 197 37 2011 582 44 2012 1306 36 2013 371 41 2014 445 46 2015 419 37 2016 306 34 2017 78 34

4.1.2 Spatial distribution of the resources

The spatial distribution of main Essential Fish Habitats in terms of stable nursery areas in the northern sector of the Strait of Sicily are well known (Fiorentino et al., 2003; Abella et al., 2008; Garofalo et al., 2011; Colloca et al., 2015) Data collected during MEDITS trawl survey were used to map the distribution of stable nurseries in GSA 15 and 16.

Fig. 4.1.2.1- Temporal persistence of nursery areas of hake in GSAs 15-16, from MEDISEH - MAREA project (from Colloca et al., 2015).

A contribution to the identification of the spatial distribution of potential nurseries in the southern Strait of Sicily (SoS) was given by niche (Druon et al., 2015) and habitat (Garofalo et al, 2018) modelling. The probabilistic occurrence of recruits in the entire Strait of Sicily, according to GAM using depth and seafloor features as predictors, obtained by Garofalo et al. (2018) is reported in figure 4.1.2.2. This potential distribution, which was preliminary verified by Local Ecological Knowledge of high sea trawlers of Mazara del Vallo, needs to be validated by an ad hoc trawl survey program.

Fig. 4.1.2.2- Probabilistic occurrence of Hake recruits according to GAM using depth and seafloor features as predictors (from Garofalo et al., 2018).

4.1.2 Historical trends

The trends in biomass and density of European hake (HKE) during the MEDITS survey in GSA 15 and GSA 16 showed large fluctuations (Fig. 4.1.3.1). The current relative stock biomass (kg km-2) is below the 66° percentile of the time series (Fig. 4.1.3.2).

Figure 4.1.3.1 – a) Medits Density Index (DI) in GSA 15&16. b) Medits Biomass Index (BI) in GSA 15 & 16. Sex combined. (Both indices were weighted per stratum).

The length structures of hake in MEDITS 2007-2017 are shown in Fig. 4.1.3.4

Trawl survey Medits GSA 15 2007-2017

250

200

150

LFD in % 100

TL (cm) 0 0 10 20 30 40 50 60 70 80 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Trawl survey Medits GSA 16 2007-2017 25

in LFD % 10

5 TL (cm) 0 0 10 20 30 40 50 60 70 80 90 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Figure 4.1.3.2 – a) Length frequency distributions (LFD) from MEDITS survey in GSA 15. b) Length frequency distributions LFD from MEDITS survey in GSA 16. Sex combined.

24 5 Stock Assessment

An Extended Survivor Analysis (XSA) assessment was carried out using official trawl catch data (landings and discards, EU data collection framework) collected in GSAs 15-16 and GSAs 12-14 (Tunisia) in the period 2007 - 2017. The XSA was tuned using Medits survey data (2007-2017) from GSA 15 and GSA 16. The natural mortality M was estimated by Prodbiom’s method. The annual size of the landings, as well as Medits data was converted into the number at age by knife edge slicing.

5.1 Extended Survivor Analysis (XSA)

5.1.1 Model assumptions

Darby and Flatman (1994) outlined the XSA algorithm as performing the following steps: (1) a cohort analysis of the total catch-at-age data to produce estimates of population abundance-at-age, and total fishing mortalities; (2) adjustment of the CPUE values for the period of fishing defined using the alpha and beta parameters in the fleet tuning file, into CPUE values that would have been recorded if the fleet had fished only at the beginning of the year. The adjusted values are directly comparable with the population abundances at the beginning of the year; (3) calculation of fleet-based estimates of population abundance-at-age from the adjusted CPUE values and fleet catchabilities; (4) calculation of a least squares estimate (weighted mean) of the terminal population (survivors at the end of the final assessment year) for each cohort in the tuning range using the fleet-derived estimates of population abundance-at-age. These terminal populations are used to initiate the Cohort analysis in the next iteration. The process iterates until the convergence criteria described for ad hoc tuning are achieved. Various options are available for catchability analysis, time series weighting and shrinkage of the weighted estimates.

5.1.2 Scripts

The scripts are available to the WG

5.1.3 Input data and Parameters

For analytical models: catch matrix in ages. Discard is included.

25 Table 5.1.3.1 - Catch matrix by year and age in thousands.

0 1 2 3 4 5 6 7 8

2007 320.1 31537 6279 1181 241 86 83 17 14

2008 237.4 23829 6109 1297 224 62 48 16 13

2009 1029.9 29922 6007 1180 367 176 154 47 21

2010 663.6 21690 6678 1448 345 251 140 47 20

2011 709.7 20992 4192 1119 250 157 82 32 17

2012 1754.3 15839 7351 1821 431 171 92 94 77

2013 1890.3 15479 8129 2002 498 189 87 88 74

2014 2930.4 18641 9657 2426 602 236 121 137 122

2015 2354.8 13657 7403 2288 556 634 310 100 158

2016 600.1 10650.6 6983 1845 717 658 380 138 162

2017 409.9 18123.7 9014.6 2054.7 275.4 214.7 123.5 9.7 6.0

Table 5.1.3.2 - Catch weight in kg matrix by year and age.

0 1 2 3 4 5 6 7 8 2007 0.013 0.050 0.148 0.357 0.651 1.061 1.447 1.975 2.634 2008 0.013 0.055 0.154 0.369 0.653 0.981 1.452 1.987 2.895 2009 0.011 0.042 0.133 0.304 0.562 0.872 1.232 1.622 2.235 2010 0.011 0.048 0.142 0.322 0.593 0.893 1.325 1.703 2.188 2011 0.011 0.042 0.132 0.290 0.540 0.794 1.194 1.544 2.142 2012 0.008 0.047 0.130 0.287 0.524 0.821 1.205 1.535 1.851 2013 0.009 0.049 0.133 0.296 0.541 0.824 1.221 1.545 1.836 2014 0.009 0.050 0.134 0.290 0.535 0.826 1.237 1.553 1.827 2015 0.009 0.044 0.135 0.298 0.553 0.819 1.206 1.654 1.857 2016 0.014 0.040 0.086 0.225 0.299 0.337 0.509 0.725 0.754 2017 0.007 0.033 0.096 0.210 0.394 0.609 0.875 1.788 0.030

Table 5.1.3.3 – Tuning data by year and age in thousands. Density indices were raised to the whole GSAs 15 and 16 areas assuming the same catchability.

Tuning data at age 0 1 2 3 4 5 6 7 8

2007 42.439 4.67 0.752 0.221 0.107 0.043 0.018 0.012 0.003

2008 19.643 8.178 1.162 0.264 0.077 0.028 0.022 0.017 0.011

2009 27.549 6.505 1.236 0.31 0.106 0.041 0.018 0 0.001

2010 7.212 5.91 2.038 0.356 0.107 0.042 0.014 0.013 0.008

2011 20.8 3.382 0.765 0.274 0.101 0.056 0.031 0.018 0.009

2012 47.496 5.524 1.179 0.259 0.084 0.037 0.013 0.004 0.004

2013 16.782 11.877 1.569 0.389 0.123 0.064 0.02 0.021 0.011

2014 19.68 10.058 1.061 0.252 0.092 0.055 0.035 0.01 0.017

2015 22.65 6.93 2.36 0.42 0.26 0.14 0.04 0.04 0.02

2016 19.19 9.83 1.64 0.65 0.19 0.11 0.08 0.04 0.03

2017 8.35 8.38 1.47 0.34 0.14 0.08 0.07 0.02 0.01

Table 5.1.3.4 – Natural Mortality at age estimated by Prodbiom method.

Group 0 Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 1.38 0.56 0.27 0.21 0.19 0.18 0.17 0.16 0.16

Table 5.1.3.5 – Proportional of maturity specimens by age.

Group 0 Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 0.01 0.16 0.61 0.93 0.98 1.0 1.0 1.0 1.0

27 5.1.4 Results

XSA was run using different setting of shrinkage on fishing mortality (0.5, 1.0, 1.5 and 2.0), rage (0, 1), qage (1, 2, 3, 4), shk.age (2,3), shk.years (3). The XSA run results with shrinkage = 1 and catchability = 1 years, was adopted as final model (Fig. 5.1.4.1) based on both residuals and retrospective analysis. The settings reflect the settings adopted on occasion of the GFCM Benchmark assessment carried out in 2015.

Setting parameters of the best model

xsa_control <- FLXSA.control (x=NULL, tol=1e-09, maxit=30, min.nse=0.3, fse=1, rage=0, qage=1, shk.n=TRUE, shk.f=TRUE, shk.yrs=3, shk.ages=3, window=100, tsrange=20, tspower=3, vpa=FALSE)

In table 5.1.4.1 are reported the XSA results in terms of spawning stock biomass (SSB) and annual recruitment. SSB seems to be stable from 2006 to 2011, increases until 2014 and then decreases. Recruitment varies with no clear trend.

Figure 5.1.4.1 - Final XSA model for European hake in GSAs 12-16.

28 Table 5.1.4.1 – XSA estimates of spawning stock biomass (SSB) and recruitment (REC).

2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 SSB (tons) 3013.9 3075.6 3079.7 3221.4 2679 3720.3 4456.4 5269.7 5439.4 2841.9 2621.8

REC (in 195.5 232.7 179.6 211.4 194.1 199.8 187.8 163.8 167 208.8 187.7 milions)

Fishing mortality values at age are reported in table 5.1.4.2. Fbar (1-5) fluctuates without any trend. The average Fbar (1-5) of the last three year (2015-2017) was 0.91.

Table 5.1.4.2 – F at age by XSA.

F at age 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 0 0.003 0.002 0.011 0.006 0.007 0.018 0.02 0.036 0.029 0.006 0.004 1 1.222 1.031 1.132 1.029 0.746 0.566 0.536 0.761 0.606 0.423 0.614 2 1.16 1.213 1.166 1.241 0.747 0.886 0.897 1.107 1.156 1.037 1.126 3 1.023 0.862 0.875 1.14 0.747 0.958 0.685 0.807 0.949 1.182 1.154 4 0.957 0.536 0.644 0.698 0.6 0.745 0.774 0.451 0.429 0.94 0.535 5 0.694 0.687 1.111 1.364 0.805 1.127 0.876 1.099 1.28 1.44 0.825 6 0.694 0.687 1.111 1.364 0.805 1.127 0.876 1.099 1.28 1.44 0.825 Fbar(1-5) 1.01 0.87 0.99 1.09 0.73 0.86 0.75 0.84 0.88 1 0.85

6000.0

5000.0

4000.0 2

3000.0

BIkm tons 2000.0

SSB_XSA SBB33 percentile SBB66 percentile 1000.0

0.0

2006

2008

2010

2012

2014 2016 2018

Figure 5.1.4.2 - Trend of SSB (2007-2017) in GSA 12-16 estimated by XSA, the value in the last year is lower than 33th percentile - Relative low biomass.

5.1.5 Robustness analysis

Residuals at age of the Medits survey are reported in fig. 51.5.1.

Figure 5.1.5.1 - Residual at age of Medits survey.

34 5.1.6 Retrospective analysis

Retrospective analyses showed rather consistent results with no major pattern in the data (Fig. 5.1.6.1).

Figure 5.1.6.1 - Retrospective analysis.

35 5.1.7 Assessment quality

Based on Medits residuals and retrospective analysis the XSA results appear consistent and in line with the XSA assessment carried out in 2017 (Fig. 5.1.7.1).

Figure 5.1.7.1 - Final XSA model obtained in 2017 for hake in GSA 12-16.

36 6 Stock predictions

6.1 Short term predictions (XSA)

A deterministic short term prediction for the period 2017 to 2020 was performed using the FLR routines provided by JRC and based on the results of the XSA assessment done during the GFCM WG. The input parameters were the same used for the XSA stock assessment. An average of the last three years has been used for weight at age, maturity at age and F at age. Recruitment (age 0) has been estimated from the population results as geometric mean of the last 3 years (190 million individuals). To achieve FMSY hake catch in 2020 should not exceed 1451 tons.

Table 6.1.1 – GSA 12-16 HKE - Short term forecast in different F scenarios.

Change_SSB_2018- Change_Catch_ Ffactor Fbar Catch_2018 Catch_2019 Catch_2020 SSB_2018 SSB_2019 SSB_2020 2020(%) 2018-2020(%)

0 0.000 4658.753 4859.060 0.000 0.000 5432.973 12322.190 126.804 100.000 0.1 0.091 4658.753 4859.060 697.159 1291.310 5432.973 11299.840 107.986 85.036 0.2 0.182 4658.753 4859.060 1333.125 2288.117 5432.973 10373.150 90.930 71.385 0.3 0.273 4658.753 4859.060 1913.747 3049.046 5432.973 9532.715 75.460 58.921 0.4 0.364 4658.753 4859.060 2444.289 3621.542 5432.973 8770.084 61.423 47.533 0.5 0.455 4658.753 4859.060 2929.492 4043.972 5432.973 8077.656 48.678 37.119 0.6 0.547 4658.753 4859.060 3373.628 4347.342 5432.973 7448.598 37.100 27.585 0.7 0.638 4658.753 4859.060 3780.545 4556.677 5432.973 6876.765 26.575 18.851 0.8 0.729 4658.753 4859.060 4153.709 4692.153 5432.973 6356.629 17.001 10.841 0.9 0.820 4658.753 4859.060 4496.249 4770.012 5432.973 5883.215 8.287 3.488 1 0.911 4658.753 4859.060 4810.986 4803.305 5432.973 5452.049 0.351 -3.268 1.1 1.002 4658.753 4859.060 5100.464 4802.496 5432.973 5059.099 -6.882 -9.481 1.2 1.093 4658.753 4859.060 5366.980 4775.954 5432.973 4700.736 -13.478 -15.202 1.3 1.184 4658.753 4859.060 5612.609 4730.352 5432.973 4373.691 -19.497 -20.475 1.4 1.275 4658.753 4859.060 5839.225 4670.990 5432.973 4075.017 -24.995 -25.339 1.5 1.366 4658.753 4859.060 6048.523 4602.059 5432.973 3802.061 -30.019 -29.831 1.6 1.457 4658.753 4859.060 6242.032 4526.855 5432.973 3552.426 -34.614 -33.985 1.7 1.549 4658.753 4859.060 6421.139 4447.953 5432.973 3323.953 -38.819 -37.830 1.8 1.640 4658.753 4859.060 6587.098 4367.349 5432.973 3114.694 -42.671 -41.392 1.9 1.731 4658.753 4859.060 6741.043 4286.573 5432.973 2922.888 -46.201 -44.696 2 1.822 4658.753 4859.060 6884.004 4206.781 5432.973 2746.947 -49.439 -47.765 0.21 0.200 4658.753 4859.060 1450.848 2453.842 5432.973 10202.290 87.785 68.858

7 Draft scientific advice

The ratio Fcurr/F0.1 is above to 1.66 (F0.1 = 0.2). Hence the stock is in High Overfishing status with Relative low Spawning stock biomass (SSB). To improve the stock status a reduction of fishing effort and catches of undersized shrimps is recommended.

Based on Indicator Analytical Current Empirical Trend Stock reference value from reference (2007- Status point the analysis value 2017)

Fishing Fishing F0.1 = 0.20 Fcurr =0.91 N OH mortality mortality

Catch N

Stock 3032 33th percentile N OL

abundance SSB (tons) 3533 66th percentile (XSA)

2622 SSBcurrent

Recruitment 187.7 Rec 2017

5523 million

Final Diagnosis The ratio Fcurr/F0.1 is above to 1.66 (F0.1 = 0.2). Hence the stock is in High Overfishing status with Relative low Spawning stock biomass (SSB).

7.1 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;

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

39 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)