Stock Assessment of Pacific bluefin tuna (PBF) International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean

Transcription

1 Stock Assessment of Pacific blefin tna (PBF) International Scientific Committee for Tna and Tna-like Species in the North Pacific Ocean

2 Otline Back gronds Catch information Fishery data pdates Specification of model Stock assessment reslts Stock stats Ftre projection Conservation advise

3 Back gronds ISC PBF working grop is in charge of the stock assessment of Pacific blefin tna Crrent (Jly 2013~) WG chair Ziro Szki (Japan) Scientists from IATTC, Mexico, Taiwan, USA, Korea and Japan are active members of the WG

4 ISC s stock assessment working model ISC does not have its own scientific staff to condct stock assessments ISC employs a working model to condct stock assessment by the team of scientists from members inclding IATTC staff Usally model development and data preparation inclding data selection for stock assessment will be done throgh intercessional species grop meeting between stock assessments. Active participations from members are essential for sccess of the stock assessment.

5 Distribtion of PBF PBF starts spawning in Sothern portion of Sea of Japan in Jne- Ag. 80% of age 3(abot 30kg) is matre in SOJ(Tanaka 2006) Above 60 kg (over 150 cm FL, age 5+ ) PBF spawn in waters adjacent to the Ryky Islands in Japan to the east of Taiwan, exploited by JLL and TWLL A part of yong blefin make trans-pacific migration to EPO

6 The 2014 stock assessment pdate The latest fll stock assessment was done in Nov 2012 with data throgh Jne The 2013 ISC Plenary decided to condct a stock assessment pdate throgh pdates of fishery data with additional two years (Jly 2011-Jne 2013) The ISC Plenary proposed work plans for the assessment. The latest stock assessment were completed in Febrary 2014 at the SWSFC in La Jolla, USA.

7 Work plans for stock assessment pdate in Feb by ISC(ISC13 Plenary Report) 1. Condct model rn with an additional two years (2011 and 2012) of data sing the same SS model (ver. 3.23b from the 2012 stock assessment) for the stock assessment platform and sing the same model strctre and parameters as the representative rn (base-case rn) from the 2012 stock assessment. 2. The stock assessment time period will be from Jly 1952 to Jne The WG will not change the fishery data (qarterly catch, size composition) from (Jly 1952-Jne 2011) that was sed in 2012 stock assessment. 4. In the case of CPUE time series, de to the natre of the CPUE standardizations method, the whole time series will need to be restandardized with the additional 2 years data.

8 Expected merits of pdating stock assessment pdate (ISC13 Plenary Report) 1. With the additional 2 years (or optionally 3 years) of recritment estimates, the WG can provide more accrate estimates of the immediate risk of declining SSB below the historically lowest observed SSB. 2. The 2012 stock assessment only evalated the stock stats before management measres were introdced (2011 by WCPFC, 2012 by IATTC) and this pdate will evalate stock stats since CMMs were introdced. 3. These additional 2 years of stock size and recritment strength estimates enables the WG to address actal fishing mortalities nder management (Fs in 2011 and 2012), recognizing that ncertainties still remain.

9 Catch information

10 PBF catch by year and by contry ( ) PBF were caght by fleets from Japan, Korea, Chinese Taipei, United States and Mexico. Total catch in 2012 was 15,270 t (18,146 t in 2011). In EPO, US caght a lot PBF ntil 1980s, Mexico increased catch after 2000s. US SPO catches certain amont(93~617t, in recent 5 years) of PBF

11 PBF catch by year and by gear ( ) Prse seine fleets (inclding USA, Mexico, Korea and Japan) contined dominant fisheries in the total catch throghot the stock assessment period( ). Jpn PS in SOJ (age 3+), Jpn LL in waters off Nansei Islands (age 5+) and TW LL in waters soth of JPN LL fishing grond (older than PBF caght by JLL) are the fisheries caght spawners

12 PBF catch at age ( ) Predominately composed of jvenile PBF Since the early 1990s, the catch of age 0 PBF has increased significantly

13 Fishery data pdates

14 Smmary table of fishery data pdates Fleet Region Fishery Catch Size CPUE F1 Jpn LL Updated Updated Updated F2 SPelPS Updated Updated - F3 TnaPSJS Updated Updated - F4 TnaPSPO Updated Updated - F5 JpnTroll Updated Updated Updated F6 WCPO JpnPL Updated Not sed - F7 Updated Updated - F8 Updated Updated - JpnSetNet F9 Updated Updated - F10 Updated Updated - F11 TWLL Updated Updated Updated F12 EPOPS Updated Updated - EPO F13 EPOSports Updated Not sed - F14 WCPO Others Updated Updated -

15 Temporal coverage of catch, abndance indices and size composition data F1 JLL F2 SPelPS F3 TnaPSJS F4 TnaPSPO F5 JpnTroll F6 JpnPL F7 JpnSetNetNOJWeight F8 JpnSetNetNOJLength F9 JpnSetNetOALength Q1-3 F10 JpnSetNetOAJLength Q4 F11 TWLL F12 EPOPS F13EPOSP F14 Others S1 JpCLL S2 JpnDWLLFjiokaRevto74 S3 JpnDWLLYokawaRevfrom75 S4 TPSJO S5 JpnTrollChinaSea S6 JpnTrollPacific S7 JpnTRKochi S8 JpnTRWakayama S9 TWLL S10 USPSto82 S11 MexPSto06 F1 JLL F2 SPelPS F3 TnaPSJS F4 TnaPSPO F5 JpnTroll F6 JpnPL F7 JpnSetNetNOJWeight F8 JpnSetNetNOJLength F9 JpnSetNetOALength Q1-3 F10 JpnSetNetOAJLength Q4 F11 TWLL F12 EPOPS F13EPOSP F14 Others In EPO, USA(~1950s) and IATTC contined effort on size sampling In WPO size sampling of JLL (F1) was rich ~1960s ntil when Jpn DWLL change their fishing grond to tropical, EPO, Atlantic oceans In Japan, extensive size sampling started from 1990s

16 Specification of model

17 Data and model Inpt data Fishing year applied, starting from Jly and ending to Jne. Qarterly catch Qarterly size composition Standardized CPUE Japanese longline (JpnLL) for adlt Taiwanese longline(twll) for adlt Japanese troll (JpnTroll) for age-0 Period: (Jly 1952-Jne 2013) No. of fleets: 14 Stock assessment model Stock Synthesis v3.23b

18 Model settings Almost all model settings were same as the model sed in the 2012 fll assessment. Single stock and single spatial area inclding WCPO and EPO. Essentially stock is expected to be mixed very well even between WPO and EPO Implicit assmption that selex =gear selex and availability Maximm age is 20. Steepness is fixed to Smaller h is contradict to be the recent catch amont. Monte Carlo simlation from life history parameters (Mangel s method, Iwata 2012) spported.

19 Growth crve Used externally determined VBGF parameters determined from otolith data with adjstment of observed length at age 0 from length comps L1=21.5cm at age=0 (Jly 1 st ) L2= at age=3 k=0.157 Linf=254.4 CV_yong (CV@L1): estimated CV_old=0.05:fixed(CV@L2)

20 Natral mortality Externally inpt age specific natral mortality Age-0 M=1.6 Determined from tag recaptre data Age-1 M=0.38 mimics SBT s M (determined from tagging) of same size Age-2 and older M =0.25 from life history consideration

21 Matrity Schedle Age specific inpt matrity at age. Age 0-2: 0 Age 3: 0.2 Age 4: 0.5 Age 5+: 1 Rational : 80% of age 3 caght by JPN PS in SOJ was matre (Tanaka 2006) In EPO, age 3 is also exploited by PS bt no spawning in EPO was recorded Yong spawners (age 3,4) are not exploited by longline

22 Stock assessment reslts

23 Spawning stock biomass The crrent (2012) spawning stock biomass was 26,324 mt, near historically low levels. Depletion ratio (SSB 2012 /Unfished SSB) was

24 Recritment Recritment level in 2012 was relatively low (the 8 th lowest in 61 years) Mean recritment for the last five years was likely to be below the historical average level.

25 Fishing mortality by age Fs in relative to (the base period for the crrent WCPFC Conservation and Management Measre ) show 19%, 4%, 12%, 31%, 60%, 51% and 21% increases for ages 0-6, respectively, and 35% decrease for age 7+. There were apparent decreases of Fs in relative to at ages of 1,2 and 3

26 F at age by gear Age 0 Age 1 Age Age 3 Age 4 Age F Age 6 Age Year Others (F14) EPO_Sports (F13) EPO_COMM (F12) TW_LL (F11) Set_net (F7-10) Troll_PL (F5-6) Jpn_TnaPS (F3-4) Kor_SPelPS (F2) Jpn_SPelPS (F2) Jpn_LL (F1)

27 Biological Reference Points No target or limit reference points have been established for the PBF stock nder the aspices of the WCPFC and IATTC. Crrent F (F ) was above all BRPs except for F loss. Therefore, overfishing is occrring and the stock is overfished. F Max F 0.1 F Med F loss F 10% F 20% F 30% F 40% F F F Note: Vales above 1.0 mean overfishing.

28 Stock stats

29 Impact on SSB by fisheries Catching a high nmber of smaller fish can have an greater impact on ftre spawning stock biomass than catching the same weight of larger matre fish.

30 Two examples of Kobe plot F/Fmed SSB med and F med SSB 20% and SPR 20% (1-SPR)/(1-SPR_20%) SSB/SSBmed SSB/SSB_20% For illstrative prposes, two examples of Kobe plots were presented. Becase no reference points for PBF have yet been agreed to, these versions of the Kobe plot represent alternative interpretations of stock stats in an effort to prompt frther discssion.

31 Smmary of stock stats The crrent (2012) spawning stock biomass was 26,324 mt, near historically low levels. Mean recritment for the last five years may have been below the historical average level. Overfishing is occrring and the stock is overfished.

32 Model fitting problem Poor fit to CPUEs and length compositions from longline fisheries of Japan and Chinese Taipei targeting adlt PBF Inconsistent year trends of CPUE between JpnLL and TWLL inevitable becase of different target age class or model is too simple Or One of two is wrong? Availability difference hypothesis is not enogh? Sensitivity rns were condcted to examine effects of pdates of CPUE and length comp. data for JpnLL and TWLL

33 Specification of 4 sensitivity rns JpnLL TWLL Rn # 1 (Base case) Latest 2 yrs CPUE Latest 2 yrs length comp. Latest 2 yrs CPUE Latest 2 yrs length comp. Updated Updated Updated Updated 2 Updated Updated Not sed Not sed 3 Not sed Not sed Updated Updated 4 Not sed Not sed Not sed Not sed

34 Reslts of sensitivity rns - 1 For rns has similar declining SSB trends. After 2005, there were slight divergences among Rns 1-4. Recritment estimates were robst across the rns.

35 Reslts of sensitivity rns - 2 F Max F 0.1 F Med F loss F 10% F 20% F 30% F 40% Depletion ratio F Rn Rn Rn Rn F Rn Rn Rn Rn F Rn Rn Rn Rn

36 Smmary of sensitivity rns All rns indicated that SSB in recent years were close to historical lowest level, althogh there were slight divergences among 4 rns. All rns indicated that stock is overfished and overfishing is occrring. Reslts of sensitivity analysis are consistent to the conclsion of stock stats from base case rn.

37 Ftre projection

38 Crrent(2014) management measres in EPO and WCPO WCPFC: Redce all catches of jveniles (age 0 to 3-(less than 30 kg)) by at least 15% below the annal average levels, maintain the total fishing effort below the annal average levels. IATTC: Catch limit of 5000 t with an additional 500 t for commercial fisheries for contries with catch history.

39 Reqests from WCPFC NC9 1. Provide range of historical variation in recritment or other appropriate measres, specifically, information for the low recritment period dring the 1980s, and for the last 10 years. 2. Condct ftre projection based on 7 harvesting scenarios proposed by NC9.

40 # 7 harvesting scenarios proposed by WCPFC NC9 WCPO EPO COMM Fishing effort Jvenile catches* Adlt catches Catches avg avg avg avg avg avg. 7 15% redction from avg. 15% redction from avg. 15% redction from avg. 15% redction from avg. 15% redction from avg. 25% redction from avg. 50% redction from avg. 25% redction from avg. 15% redction from avg. 15% redction from avg. 5,500 mt/yr 5,500 mt/yr 4,675 mt/yr 4,675 mt/yr 4,125 mt/yr 2,750 mt/yr 4,125 mt/yr *Jvenile corresponds to fish of ages 0 throgh 3 (less than 30 kg)

41 Specifications of ftre projection Each simlation starts from F at age and N at age in 2012 is taken from 300 parametric bootstrap SS rns. For each bootstrap replicate, 20 simlations condcted with resampled recritment in Ftre recritment were set based on the historical variation stochastic simlations by 2028 with 7 harvesting scenarios proposed by WCPFC NC9. EPO : annal qota for commercial fleet, average F

42 Harvest scenario condition i. Fishing effort is interpreted as fishing mortality, i.e., e.g. fishing effort of level is translated into average F in ii. iii. iv. 14 fisheries in the stock assessment model reorganized into 6 fleets, approximately each fishery represent a contry s fishery. If redction of jvenile catch is reqired to certain level, F of ages 0-2 (<30kg) is assmed to be redced to meet necessary jvenile catch redction reqirement. If, in addition, redction of adlt catch is reqired, F of ages 3 and older is assmed to be redced.

43 Definition of jvenile (Poplation dynamics vs management simlation) The ISC-PFBWG has noted differences in the definition of jveniles by NC9 and stock assessment (if it is recognized as non matre individals) those specified in the stock assessment model. NC9 Jvenile : fish of ages 0 throgh 3 ( (and) less than 30 kg) Poplation dynamics in stock assessment (inclding ftre projections) Jvenile : non-matre individals (age 0 age 2 :100%, age 3 : 80%, age 4 50%) Therefore, the PBFWG recognized that jvenile catch redction, inclding all non-matre individals, shold be considered in management decisions. However, how we can actally redce jvenile catch of age 3 by 50% withot changing catch of matred individals of age 3, which are indistingishable virtally from jveniles? Need more direction if it is the what we want to do.

44 Historical variation in recritment (Ishida et al. 2014, ISC/14/PBFWG-1/06) Recritment from 1980 to 2012 There were two break points between 1993 and 1994, and between 2008 and Recritments in and were significantly lower than the historically average recritments. Dration of different prodctivity phase may be on the order of 14 or 15 years.

45 Ftre recritment For recritments in 2012 and 2013 which has already occrred, re-sampling was condcted from the recritment in Years of were the lowest 3 years of recritment in Two definitions of ftre recritment Average recritment scenario Re-sampled from the whole stock assessment period ( ). Low recritment scenario Re-sampled from the period of Recritment scenario # From Low Low 2 Low Average 3 Average Average

46 SSBrecent,F=0 A dynamic SSB F=0 was calclated by projecting setting F=0 with randomly drawing from recent 10 years ( ) recritments Average recritment ( ) is abot same as average of whole stock assessment period =630KT

47 Recritment, SSB and total catch nder recritment scenario 1 (Low for initial 10 yrs and low for sbseqent 5 yrs Recritment SSB If the low recritment in recent years contines, the risk of SSB below its historical lowest wold increase. Only the harvest scenario 6 achieved increase of SSB above at least historical median more than 80% within 10 yrs from Total catch

48 Recritment, SSB and total catch nder recritment scenario 2 (Low for initial 10 yrs and average for sbseqent 5 yrs Only the harvest scenario 6 achieved increase of SSB above historical median more than 50% within 10 yrs from Recritment SSB Total catch

49 Performance table of 7 harvesting scenarios proposed by NC9 Scenario # No.1 No.2 No.3 No.4 No.5 No.6 No.7 Ftre recrit level (10years) From 2024 Within 10 years from 2014 Within 15 years from 2014 Probability achieving reference level at least one year Probability achieving reference level at least one year 62KT (10%SSB 0 ) 93KT (15%SSB 0 ) 124KT (20%SSB 0 ) 155KT (25%SSB 0 ) Historical Median(43KT) 62KT (10%SSB 0 ) 93KT (15%SSB 0 ) 124KT (20%SSB 0 ) 155KT (25%SSB 0 ) Historical Median(43KT) Mean yield in Low Low 0% 0% 0% 0% 4% 1% 0% 0% 0% 7% 13,665 Low Average 0% 0% 0% 0% 4% 3% 0% 0% 0% 14% 16,321 Average Average 48% 24% 10% 4% 69% 76% 50% 29% 15% 90% 22,932 Low Low 1% 0% 0% 0% 5% 2% 0% 0% 0% 9% 13,456 Low Average 1% 0% 0% 0% 5% 4% 0% 0% 0% 17% 15,818 Middle Average 53% 30% 16% 8% 72% 80% 59% 40% 26% 92% 17,572 Low Low 1% 0% 0% 0% 9% 4% 0% 0% 0% 18% 13,380 Low Average 1% 0% 0% 0% 9% 8% 1% 0% 0% 29% 15,447 Average Average 60% 36% 20% 10% 79% 87% 67% 48% 31% 96% 17,019 Low Low 1% 0% 0% 0% 2% 1% 0% 0% 0% 5% 13,186 Low Average 1% 0% 0% 0% 2% 2% 0% 0% 0% 9% 15,834 Average Average 48% 27% 13% 5% 64% 77% 57% 37% 20% 87% 23,565 Low Low 3% 0% 0% 0% 16% 8% 1% 0% 0% 32% 14,196 Low Average 3% 0% 0% 0% 16% 16% 2% 0% 0% 46% 16,225 Average Average 70% 43% 22% 10% 87% 92% 75% 52% 32% 98% 24,219 Low Low 51% 12% 2% 0% 85% 84% 39% 9% 2% 98% 17,056 Low Average 51% 12% 2% 0% 85% 90% 51% 17% 4% 99% 18,768 Average Average 96% 83% 61% 38% 99% 100% 98% 91% 77% 100% 27,454 Low Low 6% 1% 0% 0% 31% 18% 2% 0% 0% 59% 14,454 Low Average 6% 1% 0% 0% 31% 30% 4% 0% 0% 73% 16,502 Average Average 77% 49% 26% 13% 92% 96% 81% 59% 38% 99% 23,317 Note: SSB 0 was calclated sing the most recent 10 years recritment. Scenario 6 performs best across the three recritment scenarios.

50 Smmary of ftre projections Stats qo (contination of measres in 2014 in the following years, Scenario 1) is not expected to increase SSB, if recent low recritment contines. No scenario except for Scenario 6, the strictest one, demonstrates increase of SSB assming the crrent low recritment contines. Probability in the table above is calclated as nmber of simlation which reach a target SSB at least once dring specific years (10 years or 15 years)

51

52 Conservation Advise from ISC The crrent (2012) PBF biomass level is near historically low levels and experiencing high exploitation rates above all biological reference points except for F loss. Based on projection reslts, the recently adopted WCPFC CMM ( ) and IATTC resoltion for 2014 (C-13-02) if contined in to the ftre, are not expected to increase SSB if recent low recritment contines.

53 Conservation Advise from ISC In relation to the projections reqested by NC9, only Scenario 6, the strictest one, reslts in an increase in SSB even if the crrent low recritment contines (Figre 11). Given the reslt of Scenario 6, frther sbstantial redctions in fishing mortality and jvenile catch over the whole range of jvenile ages shold be considered to redce the risk of SSB falling below its historically lowest level. If the low recritment of recent years contines, the risk of SSB falling below its historically lowest level observed wold increase. This risk can be redced with implementation of more conservative management measres.

54 Conservation Advise from ISC Based on the reslts of ftre projections reqested at NC9, nless the historical average level ( ) of recritment is realized, an increase of SSB cannot be expected nder the crrent WCPFC and IATTC conservation and management measres, even nder fll implementation (Scenario 1) If the specifications of the harvest control rles sed in the projections were modified to inclde a definition of jveniles that is more consistent with the matrity ogive sed in the stock assessment, projection reslts cold be different; for example, rebilding may be faster. While no projection with a consistent definition of jvenile in any harvest scenario was condcted, any proposed redctions in jvenile catch shold consider all non-matre individals. Given the low level of SSB, ncertainty in ftre recritment, and importance of recritment in inflencing stock biomass, monitoring of recritment shold be strengthened to allow the trend of recritment to be nderstood in a timely manner.

55 Next stock assessment The next fll stock assessment of PBF by ISC is planed to condct early in 2016.