8.4.3 Advice May 2013 ECOREGION STOCK. Baltic Sea Cod in Subdivisions (Eastern Baltic Sea)

Transcription

1 8.4.3 Advice May 2013 ECOREGION STOCK Baltic Sea Cod in Subdivisions (Eastern Baltic Sea) Advice for 201 ICES advises on the basis of the EU management plan (EC 1098/2007) a TAC of tonnes in This is conditional on the discard rates remaining unchanged from the average of the last three years. Stock status Figure Cod in Subdivisions Summary of stock assessment (weights in thousand tonnes). Predicted values are shaded. Top right: SSB and F for the time-series used in the assessment. Management target fishing mortality cannot be displayed due to the difference in reference F age range compared to the current assessment. The SSB has increased in recent years and is now estimated to have been above B pa since Fishing mortality has declined and is now estimated to be below F MSY, since The abundance of the year classes is above the average of the last 20 years. Management plans EU has agreed on a multi-annual plan for cod in the Baltic Sea in 2007 (EC No. 1098/2007). ICES has evaluated the management plan in 2009 and considers it to be in accordance with the precautionary approach. It should be noted that there is a large difference between the FMSY and the target F in the management plan, regardless of the different reference age.

2 Biology Cod is the main predator on sprat and herring, and given the recent increase in the eastern Baltic cod stock the natural mortality of the pelagic stocks is likely to be affected,and an increase in cannibalism may be expected. However, at present, the geographical overlap between cod and the pelagic stocks is reduced. Consistent with declining availability of sprat and herring and an increasing cod stock in the current main distribution area of cod (Subdivision 25, and to a lesser extent Subdivision 26), the mean weight of larger cod has sharply declined in recent years. Environmental influence on the stock Eastern Baltic Cod recruitment is mainly driven by hydrological factors. At present, successful reproduction of the eastern Baltic cod occurs only in the Bornholm Basin (Subdivision 25). The distribution of cod is currently mainly confined to Subdivision 25, to a lesser degree Subdivision 26, and with very low abundance in northern areas (Subdivisions 27 32). The fisheries The demersal fisheries for cod in the eastern Baltic have bycatch of flounder which are mainly discarded. Catch distribution Total catch (2012) is 57.8 kt, where 88% are landings (16% by gillnetters and longliners, 84% by trawlers) and 12% discards. Effects of the fisheries on the ecosystem Because sprat and herring are the major prey for cod, the cod fishery can indirectly affect the sprat and herring stocks by changing predation mortality on these species. Furthermore, the fishery for sprat and herring in the distribution area of cod can influence the available food base for cod. Quality considerations Ageing problems are a concern for the quality of the assessment. Collection of cod stomach contents data has been sampled in 2012 and 2013 and will greatly improve the basis for application of multispecies stock assessment models. Data are needed to quantify the amount of mixing of cod between eastern and western the Baltic Sea areas. Stock identification studies are required. Figure Cod in Subdivisions Historical assessment results (final-year recruitment estimates included). This stock was benchmarked in Fishing mortality before the 2013 assessment year had a different F reference age range (i.e. 4 7). Scientific Basis Assessment type Stock data category Input data Discards and bycatch Indicators Other information Expert Group report Age-based analytical assessment (SAM). Category 1 Commercial catches (international landings, age and length frequencies from catch sampling); two survey indices (BITS Q1_ and BITS Q1 (since 2001); BITS Q4); one commercial index (Danish_Trawlers_>105 mm); maturity data constant (since 1998 from surveys); natural mortalities constant (0.2 for all ages). Discards are included in the assessment. None. This stock was benchmarked in 2013 (WKBALT; ICES, 2013a). WGBFAS

3 8.4.3 Supporting information May 2013 ECOREGION STOCK Baltic Sea Cod in Subdivisions (Eastern Baltic Sea) Reference points Type Value Technical basis MSY Approach MSY B trigger B pa. F MSY 0.46 Based on stochastic simulations using stock recruitment data from Multispecies F MSY 0.55 Multispecies model (SMS). Precautionary B lim B loss in Approach B pa B lim*1.4. F lim Undefined. Undefined. Management Plan Outlook for 2014 F pa SSB MGT F MGT 0.30 (Changed in 2013, WKBALT (ICES, 2013a)). Undefined. EU management plan based on stochastic simulations (reference F age range 4 7). Basis: F(2013) = Fsq = 0.37 (Fbar ages 4 6, mean of the last 3 years, scaled to F2012) ; SSB (2014) = ; commercial landings (2013) = ; discards (2013) = 5 800; R(2013) = ; R (2014, 2015) = (geometric mean 15 years) millions. Weights in thousand tonnes. 1) SSB 2015 relative to SSB ) Commercial landings 2014 relative to the 2013 EU TAC+ Russian autonomous quotas. 3) Reference F range age 4 7. Discard proportions in the projections were assumed to be the average proportions discarded per age in (fishing pattern partitioned in landings and discards and taken as an average ).

4 Management plan Following the agreed EU Management plan implies fishing at an F (4 7) of 0.3, which results in a TAC in 2014 of tonnes. This is conditional on the discard rates remaining unchanged from the average of the last three years. This is expected to lead to an increase in SSB to tonnes in MSY approach Following the ICES MSY approach implies fishing mortality should be no more than 0.46, resulting in catches of no more than tonnes in This is expected to lead to an SSB of tonnes in 2015, above MSY B trigger. If discard rates do not change from the average of the last three years, this implies landings of no more than tonnes. No transition is needed as F in 2012 is below F MSY. Precautionary approach As there is no Fpa defined for this stock, the catch corresponding to the precautionary approach cannot be calculated. B pa is tonnes, and all options in the outlook will result in an SSB above B pa in Multispecies considerations Cod multispecies F MSY given as one value does not exist in a multispecies context, as the natural mortality of cod depends on the population size of the other stocks in the Baltic Sea. Long-term yields of cod (estimated from the SMS model) are similar for F in the range of ; however, the biomass will differ significantly. Fishing on the prey stocks herring and sprat will influence the food availability for cod and thereby the level of cod cannibalism and cod yield. However, the actually applied F for the prey species (in the range ) will only marginally affect the long-term yield of cod. See Section for details on how the multispecies F MSY used in the outlook table was derived. Fishing at multispecies F MSY = 0.55 would give catches in 2014 of tonnes and SSB in 2015 at tonnes. Additional considerations Management considerations ICES has revised the single-species F MSY this year. A range of values were considered (0.27 to 0.54). Based on the perception of the current status of productivity, growth and natural mortality of this stock, the value chosen (0.46) is considered the most appropriate. This value is closer to the multispecies F MSY values for cod than the previous single-species value, which was similar to the F target for the management plan. Earlier work (STECF, 2011) suggests that mean yield for cod may be expected to change by around 5% over the range of F = ; however, the biomass would be very different. The current FMSY does not include estimation uncertainty, and higher F values will have higher risks to the stock. All the proposed values are considered precautionary. In considering target Fs for single- or multispecies management plans, managers might like to consider the risks and potential benefits that are associated with different candidate values. The candidate multispecies F MSY value is estimated slightly higher (0.55) than the F MSY of 0.46 set for this stock. This is mainly due to cannibalism being taken into account in multispecies F MSY estimates while natural mortality is kept constant for all ages and years in the single-stock assessment. The present distribution pattern implies that an increase in F on cod will not necessarily result in increasing Baltic-wide clupeid stock sizes, and conversely a decrease in F on cod will not necessarily result in a decrease of the Baltic clupeid stock size if it is not accompanied by a cod expansion to northern areas. However, cod cannibalism will be higher, and slower cod growth due to food deprivation will be a bigger problem. On the other hand, a reduction of clupeid F in Subdivision 25 will likely improve the growth and condition of cod as well as reduce cannibalism. An increase in clupeid F in northern areas (Subdivisions 27 32) will likely not have a negative effect on cod, since this will not affect the stock component distributed in southern areas (Subdivisions 25 26). Furthermore, a higher F on clupeids in northern areas would likely reduce density dependence and improve the growth and condition of clupeid stocks. Increasing F on cod would not result in a substantial increase in yield. There are indications that discards in general have increased recently and particularly of older age groups, probably due to poorer condition. To optimize the growth potential and yield of cod, sprat, and herring, a spatially explicit management plan needs to be developed. Changes in fishing technology and fishing patterns Cod in the eastern Baltic are taken primarily by trawlers and gillnetters. There was a substantial increase in the use of gillnets in the 1990s. In 2012, gillnet catches accounted for about 15% of the total catch. Regulations and their effects The fishery is managed through TAC, effort, seasonal fisheries restrictions, and technical measures. The Baltic cod management plan (EC Regulation 1098/2007) inter alia called for a reduction in fishing effort (10% annually in terms of number of fishing days per year) until the target F has been reached. The maximum number of fishing days for the Subdivisions was fixed at 160 in 2010, and kept at 160 days in 2011, 2012, and Since 2012, EU Member States have been allowed to allocate additional days absent from port to vessels if an equal amount of days absent from port is withdrawn from other vessels. The number of

5 receiving vessels may not exceed 10% of the total number of vessels. For 2014, the provisions of the plan call for a reduction of F (as F F MP) and thus a 10% reduction in days-at-sea, corresponding to 144 days-at-sea in 2014 (days-at-sea current year 0.9). It should be noted that the plan would have allowed for an increase in the number of days-at-sea in the last three years (EC 1098/2007, Art 8 Para 5), when the perceived F was below F MP. This was however not implemented. The cod fisheries in the eastern Baltic are also regulated by a seasonal closure from 1 July to 31 August. A closure of a central part of the main spawning area in the Bornholm Deep has been implemented since the mid-1990s for all fisheries. A year-round area closure for all fisheries in specific areas of the Bornholm Deep, the Gotland Basin, and the Gdansk Deep was introduced in 2005 aimed at reducing fishing mortality. Since 2006, area closures have been implemented from 1 May to 31 October. The plan was designed to protect the spawning aggregation. However, STECF's evaluation (STECF, 2011) of the impact of the present spawning closures on the stocks and the fisheries concluded that the effect "is unclear but the measures are unlikely to have had a limiting effect on the overall fishing mortality. Spawning closures are not required to meet the biological objectives of the management plan as long as the TACs are effective in limiting the fishing mortalities as intended. Highgrading has been prohibited since 1 January 2010 in all Baltic Sea fisheries. Data from observer schemes indicate that highgrading is a minor problem. To decrease discards, a "Bacoma" codend with a 120 mm mesh was introduced by the International Baltic Sea Fisheries Commission (IBSFC) in 2001 in parallel with an increase in diamond mesh size to 130 mm in traditional codends. The expected effect of introducing the "Bacoma" 120 mm exit window was nullified by compensatory measures in the industry. This was to some extent explained by the mismatch between the selectivity of the 120 m "Bacoma" trawl and the minimum landing size. In October 2003, the regulation was changed to a 110 mm "Bacoma" window. This was expected to enhance the compliance and to be in better accordance with the minimum landing size, which was changed from 35 to 38 cm in the same year. On 1 March 2010 the "Bacoma" 120 mm was re-introduced along with an extended "Bacoma" window (5.5 m) to further decrease discarding, and the minimum landing size was kept at 38 cm. The fishery Cod in the eastern Baltic are taken primarily by trawlers and gillnetters. There was a substantial increase in the use of gillnets in the 1990s. In 2012, gillnet catches accounted for about 20% of the total catch. Information from the fishing industry Some of the information on historical mis- and underreporting came from industry sources, indicating that the estimates used in the assessment are minimum values. From 2010 the mis- and underreporting has been negligible. The increase in flatfish abundance interferes with the selectivity of the Bacoma codend, and discarding of cod has increased in 2011 and Environmental conditions Cod distribution in the Baltic is affected by environmental conditions, specifically lack of oxygen. As a consequence, two (the Gotland and the Gdansk basins) out of three spawning areas have ceased to significantly contribute to the reproduction of the eastern Baltic cod. In recent years, even though the stock has increased in Subdivision 25 and to a lesser extent Subdivision 26, and is apparently suffering from food limitation, there is no strong northwards expansion (ICES, 2012; Figure ). This could potentially be related to a number of conditions including, continued poor hydrographic conditions in the northeastern areas of the Baltic Sea or year class strengh. In the 2000s, salinity conditions have been reasonably good, which corresponds to relatively strong year classes formed since However, the estimates of reproductive volume have been variable by year. Data and methods Substantial underreporting of catches occurred in , and also from 2000 to In this situation, ICES chose to include misand non-reported landings in the assessment. Estimates of the amount of misreporting are available from the national industries and control agencies, and indicated that total catches during were about 32 45% higher than the reported figures. This information is highly uncertain and incomplete, and no data were available for some countries where misreporting was suspected to occur. ICES considers that the enforcement of fishing control in 2008 and 2009 led to a significant reduction in non-reporting; the available information suggests that unreported landings in 2009 were only 6% of the reported landings. Since 2010 the unreported landings are assumed to be zero. Although the adjusted landings values in previous years derived by ICES are the best possible estimates, they are likely to be minimum estimates. Discard data have been available since 1996 and are applied in the assessment as yearly proportions of discards per age group. For , an average proportion discarded per age group, estimated for , was applied. From 2004 onwards, annual estimates of discards have been derived from the biological sampling of catches. The season and area coverage of discard sampling still requires improvement. Due to changes in technical regulations (e.g. increase in minimum landing size, the introduction of different codend sizes, highgrading ban, and various fishery closures), discard rates have been variable. In 2013, a revision of mean weights-at-age in surveys was made. In the 2013 assessment, the mean weights in the stock for ages 2 and 3 were taken from the bottom trawl survey (BITS Q1). The weights for ages 4+ were calculated from commercial catches. Uncertainties in the assessment and forecast In the current assessment SSB has been consistently overestimated and F underestimated in the recent years. The reason for this is still

6 not fully understood. In addition the unexplained overestimation of SSB and underestimation of F uncertainties in the assessment are also due to historical underreporting, discarding, and inconsistencies in age-reading. Sampling intensity for discards is insufficient and raising procedures have been problematic in the recent past. Large inconsistencies exist in age determinations for the eastern Baltic cod stock owing to the lack of clear growth rings in the otoliths. ICES attempted to resolve the inconsistencies in age determinations for this stock, but no consensus was reached on the age determinations. An EU-funded study initiated in 2007 (project DECODE) has taken a different approach to delivering validated aging data for the assessment, but this method is not fully validated from tagging studies. Removals of cod in recreational fisheries in the Baltic Sea are currently not consistently and completely sampled, and are therefore not included in the assessment. Mixing of the eastern and western Baltic cod stocks is considered to have increased in recent years. This affects the quality of the assessment. Problems with the commercial tuning fleets have been identified (e.g. spatial coverage of the commercial tuning fleet) in the recent benchmark, but has not been resolved yet (ICES, 2013a). Comparison with previous assessment and advice The stock was benchmarked this year, with a revision of the reference F age range. The current perception of the status of the eastern Baltic cod stock in terms of trends is similar to that of the 2012 assessment. However, the expected increase in SSB has been downgraded, partly because of the lower stock weight-at-age used for the last years. The basis for the advice is the same as last year, the management plan (EC 1098/2007 ). Sources ICES Report of the Study Group on Spatial Analyses for the Baltic Sea (SGSPATIAL). Lysekil, 6 8 November ICES CM 2012/SSGRSP: pp. ICES. 2013a. Report of the Benchmark Workshop on Baltic Multispecies Assessments (WKBALT 2013). 4 8 February 2013, Copenhagen, Denmark. ICES CM 2013/ACOM:43. ICES. 2013b. Report of the Baltic Fisheries Assessment Working Group (WGBFAS). ICES Headquarters, April ICES CM 2013/ACOM:10. STECF Impact Assessment of Baltic cod multi-annual plans (STECF 11-05). Edited by John Simmonds. EUR Scientific and Technical Research series ISSN pp. Figure Cod in Subdivisions (Eastern Baltic Sea). Stock (tonnes) and recruitment (thousands, age 2) plot.

7 Table Cod in Subdivisions ICES advice, management, and landings. Year ICES Advice Predicted landings corresp. to advice Agreed TAC 1 ICES landings (25 32) 1987 Reduce towards F max TAC TAC TAC TAC Lowest possible level No fishing TAC ICES landings (22 32) % reduction in fishing effort from level % reduction in fishing effort from level % reduction in fishing mortality from 1995 level % reduction in fishing mortality from 1996 level 1999 Proposed F pa ( = 0.6) % reduction in F from level Fishing mortality of No fishing % reduction in F See option table % reduction in F < * 2005 No fishing * 2006 Develop Management plan < * 2007 No fishing * 2008 No fishing * 2009 Limit (total) landings to t * 2010 Follow management plan * 2011 See scenarios * 2012 Follow management plan * 2013 Follow management plan Follow management plan 70.3 Weights in thousand tonnes. 1 For total Baltic until and including The reported landings in and are likely to be minimum estimates due to incomplete reporting. 3 TAC is calculated as EU + Russian autonomous quotas. * Separate management for western and eastern Baltic cod since 2004.

8 Table Cod in Subdivisions Total landings (tonnes) by country. Year Denmark Estonia Finland German Germany, Latvia Lithuania Poland Russia Sweden USSR Faroe Norway Unallo- Total Dem.Rep. 2 Fed. Rep. Islands 4 cated

9 , Provisional data. The actual total landings are tonnes. The difference is due to problems in the upload of the catches from Finland and Lithuania in InterCatch. 2 Includes landings from October to December 1990 of Fed. Rep. Germany. 3 Working group estimates. No information available for years prior to For 1997 landings not officially reported, estimated by the WG.

10 Table Cod in Subdivisions Summary of stock assessment (weights in tonnes). Recruits (age 2, in thousand ind.), Low = 2.5% confidence limit, High = 97.5% confidence limit. F4 6 = Fbar 4 6 ages. Recruitment (thousands) TSB (tonnes) SSB (tonnes) F (ages 4 6) F (ages 4 7) Year Medium Low High Medium Low High Medium Low High Medium Low High Medium Low High

11 Figure Cod in Subdivisions (Baltic Sea). Distribution from bottom trawl surveys (BITS) during (left) the 4th quarter 2012 (Subdivisions South) and (right) the 1st quarter 2013 (Subdivisions 25 28). Figure Distribution of Baltic sprat from the acoustic survey (BIAS) in the 4th quarter in 2012 (in Subdivisions 22 30) (left panel); herring in Subdivisions 25 to 29 and 32, excluding the Gulf of Riga from the BIAS survey (BIAS) in the 4th quarter in 2012 (in Subdivisions and 32) (middle panel); Eastern Baltic Sea cod (Subdivisions 25 32) from bottom trawl survey (BITS) in the 4th quarter in 2012 (in Subdivisions South) (right panel).