Advice June Sole in Division IIIa and Subdivisions (Skagerrak, Kattegat, and the Belts)

Transcription

1 Advice June 2014 ECOREGION STOCK North Sea Sole in Division IIIa and Subdivisions (Skagerrak, Kattegat, and the Belts) Advice for 2015 ICES advises on the basis of the MSY approach that catches in 2015 should be no more than 211 tonnes. If discard rates do not change from last year (2013), this implies landings of no more than 205 tonnes. Stock status MSY (FMSY) Precautionary approach (Fpa,Flim) MSY (Btrigger) Precautionary approach (Bpa,Blim) F (Fishing Mortality) Above target Harvested sustainably SSB (Spawning-Stock Biomass) Below trigger Reduced reproductive capacity Figure Sole in Division IIIa and Subdivisions Summary of stock assessment (weights in tonnes). 95% confidence limits indicated for recruitment, fishing mortality, and spawning-stock biomass. Predicted values are shaded. Top right: SSB and F over the years. SSB has decreased since 2006 and is below B lim since Fishing mortality has been relatively stable and above F MSY since The last strong year class was the 2000 year class; since then recruitment has decreased to a historical low.. Management plans No specific management objectives are known to ICES. ICES Advice 2014, Book 6 1

2 Biology Sole is a nocturnal predator and therefore more susceptible to capture by fisheries at night than in daytime. Sole is a long lived flatfish species. The main spawning takes place in the second quarter in coastal areas close to the nurseries. The main diet of sole consists of worms and small soft-shelled bivalves. As for many other flatfish species sole has a sexual dimorphism, i.e. females reach older ages and bigger sizes than males. The fisheries Sole is taken in a mixed trawl fishery with Nephrops, plaice, and cod, the main season being in autumn winter. In addition there is a directed gillnet fishery for sole, mainly in Skagerrak in spring and summer. Catch distribution Total catch (2013): 342 t, where 332 t were official/estimated landings (44% demersal trawl), 56% gillnets), and 10 t discards. Quality considerations Sampling of landings is complicated by the low total landings which are dispersed spatially. This affects the quality of the input data, including the weight-at-age. Historically, the assessment has overestimated SSB and underestimated fishing mortality. Discard rates in recent years are around 2% in weight and not included in the assessment but this does not impact the quality of the assessment. The main indicator of recruitment, the cooperative Fishermen DTU Aqua sole survey, ceased in 2011 and this has deteriorated the quality of the assessment and advice. The lack of the survey and the use of commercial cpue data only with changes in gear regulations in the fishery (cod avoidance) make the estimation of the recent year classes more uncertain. The reinstatement of the survey would likely improve the accuracy of the assessment and the advice. Figure Sole in Division IIIa and Subdivisions Historical assessment results (final year recruitment estimates included). Scientific basis Stock data category 1 (ICES, 2014a) Assessment type Age-based analytical stochastic assessment (SAM). Input data Commercial catches (international landings, ages and length frequencies from catch sampling), one survey index (Fishermen DTU Aqua ),three commercial indices (trawlers m, mm (1994 present), private logbook gillnetters ( ), private logbook trawlers ( )); fixed maturity; and fixed natural mortality (0.1) for all age groups. Discards and bycatch Used to provide advice, but not included in the assessment. Discard information available since 2000, average discard rates from main fleets are 2%. Indicators None. Other information Stock benchmarked in 2010 (WKFLAT 2010; ICES, 2010). Reference points benchmarked in 2014 (WKMSYREF2, ICES, 2014b). Working group Baltic Fisheries Assessment Working Group (WGBFAS). 2 ICES Advice 2014 Book 6

3 Supporting information June 2014 ECOREGION STOCK North Sea Sole in Division IIIa and Subdivisions (Skagerrak, Kattegat, and the Belts) Reference points Type Value Technical basis MSY MSY B trigger 2000 t. Lowest observed SSB, excluding low SSBs in (ICES, 2010). Approach F MSY 0.32 Equilibrium scenarios constrained by prob(ssb<b lim)<5% w. stochastic recruitment (WKMSYREF2, ICES, 2014b). B lim 1200 t. B loss and segmented regression (WKMSYREF2 2014, ICES, 2014b). Precautionary B pa 2000 t B lim e 1.645σ, σ=0.30 (WKMSYREF2 2014, ICES, 2014b). Approach F lim 0.92 F lim replacement line. Consistent with B lim (WKMSYREF2 2014, ICES, 2014b). F pa 0.49 B pa replacement line. Consistent with B pa and F lim (WKMSYREF2 2014, ICES, 2014b). (Last changed in: 2014). Outlook for 2015 Basis: F 2014 = mean F ( ) = 0.389; SSB (2015) = 1232; R (age 2 in 2014) = GM ( ) = millions; landings (2014) = 329 t. Rationale Catches (2015) a) Landings (2015) Basis F (2015) SSB (2016) %SSB change b) %TAC change c) MSY F MSY SSB 2015/MSY B trigger % -42% approach Precautionary 0 0 SSB 2016 >B pa % -100% approach Zero catch 0 0 F= % -100% Other options F % -45% F % +3% F MSY % -15% % TAC (F ) % -15% No change in TAC % 0% (F ) % TAC (F ) % +15% F pa (F ) % +25% Weights in tonnes. a) Catches are calculated based on landings and 3% discard rate (in weight), the same as 2013 discard rate. b) SSB 2016 relative to SSB c) Landings 2015 relative to TAC MSY approach Following the ICES MSY approach implies fishing mortality to be reduced to 0.20(lower than F MSY because SSB in the beginning of 2015 is 38% below MSY B trigger), which implies catches of no more than 211tonnes in If discards rates do not change from last year (2013), this implies landings of no more than 205 tonnes. This is expected to lead to an SSB of 1590 tonnes in Precautionary approach Even a zero catch in 2015 is not expected to result in SSB reaching B pa in ICES Advice 2014, Book 6 3

4 Additional considerations Management considerations New fishing and biomass reference points were defined in 2014 (ICES, 2014b) and adopted for the stock (see text table above). F MSY (0.32) was estimated lower than the previous estimate (0.38). The cod stock in the Kattegat is depleted and any bycatches of cod in the mixed fishery for sole should be avoided. The assessment of short-term stock dynamics is highly dependent on having an estimate of recruitment that used to be provided by the cooperative Fishermen DTU Aqua sole survey for sole. Re-instating the survey would improve the assessment and the forecast.. Changes in fishing technology and fishing patterns The SELTRA trawl was introduced in 2011 to protect cod. This trawl is likely less efficient on sole compared to previous trawl types; catch rates of sole are therefore expected to decrease with the SELTRA trawl. In 2013 a SELTRA trawl was introduced in Skagerrak. Also changes in the regulations for the protection of cod in the Nephrops fishery, with the introduction of a sorting grid system in the trawls since 2004, may have resulted in smaller bycatch of sole. These changes in regulations that likely have caused a significant change in selectivity for the smaller sole were not taken into account by the assessment model. Spatial and temporal fishing area closures were implemented in the Kattegat in January 2009 to reduce fishing mortality on cod. Although most of these areas are outside the main fishing areas for sole, the closures may influence the effort distribution on sole, and effects on the sole stock are unclear. Regulations and their effects The management area includes Division IIIa plus the Belts (Subdivisions 22 24). Danish vessel quota shares cover the whole management area and there is therefore no incentive to misreport sole between Division IIIa and the Belts. Data and methods The stochastic analytical assessment (SAM) includes cpue data from three commercial tuning series (reference fleets) and one scientific survey series along with catch-at-age information. However, only one commercial tuning fleet is available since 2012; the two remaining commercial fleets ceased in 2007 and 2008 and the survey ceased in Discard data are not included in the assessment, but used to provide advice on catches. Sampling of landings is complicated by the small total landings which are dispersed spatially. This affects the quality of the input data. Uncertainties in assessment and forecast The discontinuation of cooperative Fishermen DTU Aqua sole survey in 2012 increased the assessment uncertainty especially with regard to recruitment estimations. The survey was the only source for recruitment observations. Landings port information does not provide reliable information for recruitment estimation, due to significant change in selectivity. Comparison of the basis of previous assessment and advice The basis for the assessment has not changed from last year. The basis for the advice this year is the same as last year: the MSY approach. 4 ICES Advice 2014 Book 6

5 Sources ICES Report of the Benchmark Workshop on Flatfish (WKFLAT), 25 February 4 March 2010, Copenhagen, Denmark. ICES CM 2010/ACOM: pp. ICES Report of the Baltic Fisheries Assessment Working Group (WGBFAS), April 2013, Copenhagen, Denmark. ICES CM 2013/ACOM:10. ICES. 2014a. Advice basis. In Report of the ICES Advisory Committee, ICES Advice 2014, Book 1, Section 1.2. ICES. 2014b. Report of the Workshop to consider reference points for all stocks (WKMSYREF2), 8-10 January 2014, ICES Headquarters, Copenhagen, Denmark. ICES CM 2014/ACOM: pp. ICES. 2014c. Report of the Baltic Fisheries Assessment Working Group (WGBFAS), 3-10 April 2014, Copenhagen, Denmark. ICES CM 2014/ACOM:10. Figure Sole in Division IIIa and Subdivisions Stock recruitment (left) and yield-per-recruit analysis plot (right). The vertical lines represent biological reference points. ICES Advice 2014, Book 6 5

6 Table Sole in Division IIIa and Subdivisions ICES advice, management, and landings. Year ICES Advice Predicted catch corresp. to advice Predicted landings corresp. to advice Weights in thousand tonnes. a) TAC applies to Division IIIa and the EC waters of Divisions IIIb and IIIc, d. b) Landings include Division IIIa and Subdivisions c) Discard estimates not available for all year. d) Uncertain. e) No more than 461 t in Division IIIa. f) Discard assumed to be negligible. Agreed TAC a ICES landings b ICES discards c TAC - < Precautionary TAC TAC d TAC d TAC at recent catch levels d No advice due to uncertain catches No advice No advice No advice No advice No increase in F No increase in F No increase in F F below F pa F below F pa F below F pa No increase in F F below F pa Limit catches to average F below F pa F below F pa F below F pa See scenarios MSY framework e MSY framework MSY approach f MSY approach ICES Advice 2014 Book 6

7 Table Sole in Division IIIa and Subdivisions Official landings (tonnes) and ICES corrections. For Sweden there is no information available between 1962 and Year Denmark Sweden Germany Belgium Netherlands Working Group Kattegat Skagerrak Belts Skag+Kat Kat+Belts Skagerrak Skagerrak Corrections Norway Considerable non-reporting assumed for the period Catches from Skagerrak were reduced by these amounts because of misreporting from the North Sea. The subtracted amount has been added to the North Sea sole catches. Total landings for these years in Division IIIa have been reduced by the amount of misreporting. 3 Assuming misreporting rates at 50%, 100%, 100%, and 20% in , respectively. Total ICES Advice 2014, Book 6 7

8 Table Sole in Division IIIa and Subdivisions Summary of stock assessment (weights in tonnes). Estimated recruitment (age 2, in thousands), spawning-stock biomass (SSB), and median fishing mortality for ages 4 to 8 (Mean F Ages 4 8). Low = lower limit and High = higher limit of 95% confidence interval. Year Recruitment High Low SSB High Low Landings Mean F High Low Age 2 (tonnes) (tonnes) Ages 4-8 (thousands) a) 1072 Average a) Geometric mean ( ). 8 ICES Advice 2014 Book 6