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ICES WKSIBCA REPORT 2014 ICES ADVISORY COMMITTEE

ICES CM 2014/ACOM:62

REF. ACOM, SCICOM

Report of the Workshop on Scoping for Integrated Baltic Cod Assessment (WKSIBCA)

1–3 October 2014

Gdynia, Poland

International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer

H. C. Andersens Boulevard 44–46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk [email protected]

Recommended format for purposes of citation:

ICES. 2014. Report of the Workshop on Scoping for Integrated Baltic Cod Assessment (WKSIBCA), 1–3 October 2014, Gdynia, Poland. ICES CM 2014/ACOM:62. 51 pp.

For permission to reproduce material from this publication, please apply to the Gen-eral Secretary.

The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council.

© 2014 International Council for the Exploration of the Sea

ICES WKSIBCA REPORT 2014 | i

Contents

Executive summary ................................................................................................................ 1

1 Opening of the meeting ................................................................................................ 3

2 ToRs.................................................................................................................................. 4

3 Subgroups ....................................................................................................................... 6

3.1 Age and stock identity ......................................................................................... 6 3.1.1 Age ............................................................................................................. 6 3.1.2 Stock mixing ............................................................................................. 7

3.2 Mortality and growth ......................................................................................... 10 3.2.1 Mortality.................................................................................................. 10 3.2.2 Workplan for the benchmark (short term) and later work

(mortality) ............................................................................................... 11 3.2.3 Growth .................................................................................................... 11 3.2.4 Workplan benchmark (short term) and later work (Growth–

weight, length, condition) ..................................................................... 12 3.3 Recruitment ......................................................................................................... 12

3.3.1 Recruitment related actions suggested ............................................... 12 3.4 Integrated assessment ........................................................................................ 13

Annex 1: List of participants ................................................................................ 17

Annex 2: Agenda .................................................................................................... 23

Annex 3: Abstracts of presentations ................................................................... 27

Annex 4: Recommendations ................................................................................ 46

ICES WKSIBCA REPORT 2014 | 1

Executive summary

The ICES Workshop on Scoping for Integrated Baltic Cod Assessment (WKSIBCA), chaired by Marie Storr-Paulsen, Denmark, and Maciej Tomczak, Sweden, met in Gdy-nia, Poland, 1–3 October 2014 with 42 participants and six countries represented. The objective of WKSIBCA was to review data used in the single-stock assessment, to come up with a timeline for how to improve the assessment and to discuss how an integrated assessment could be implemented for the two Baltic cod stocks; the cod in SD 22–24 and cod in SD 25–32. Participants in the workshop were a large group with diverse background representing the industry, fisheries, NGOs, managers and scientists.

The single-stock analytic assessment of the eastern Baltic stock was not accepted by this year’s assessment working group (WGBFAS) due to severe problems with the in-put data. The advice for the eastern Baltic cod was, therefore, based on the ICES ap-proach for data-limited stocks. As an outcome ICES decided to establish a benchmark for both cod stocks and to scope an integrated assessment for the Baltic cod stocks. This meeting (WKSIBCA) was therefore meant to introduce the intercessional work con-ducted since the assessment working group in April 2014, and to reach some conclu-sions on how to proceed both in the short term (Benchmark in March 2015) and longer term (2–3 years).

It was recognized that four main issues had to be covered during this workshop. Alt-hough there was some overlap between the topics, it was decided to have subgroups on: 1) age and stock identification; 2) mortality and growth; 3) recruitment; and 4) on the process of integrated assessment and advice leading to ecosystem-based approach for fisheries management.

Presentations on the progress were made by scientists within these four main topics and on the 2nd and 3rd day of the workshop, four subgroups were formed based on the same topics listed above. In these groups, all participants were asked to produce a timetable with a detailed description on the work that has to be conducted, responsible person(s) and time of deliverable.

The report’s structure is in line with the four subgroups and the respective output. Abstracts of all presentation are available the end of the report.

Main outputs from the workshop were

From the age and stock mixing group:

• Analysis of an otolith exchange showed that traditional age reading of the eastern cod stock is subject to substantial bias leading to low accuracy and precision (SD 24–32). WKSIBCA recommends a review process of the docu-ments presented at the meeting. The review should take place before the benchmark to draw conclusions if the current age reading should be aban-doned.

• Analysis for alternative assessment independent of age readings should be carried out simultaneously. A data call on historic length-based data (2000-2013) has to be sent out before the benchmark, and as soon as possible after WKSIBCA, to be able to compare length and age-based assessment outputs.

• In SD 24 a large part of the stock is currently belongs to the eastern Baltic cod. It was decided to split the catches and survey data in SD 24 according to the proportion on eastern and western cod found in the area. Different methods for splitting were suggested (see Section 3.1.2).

2 | ICES WKSIBCA REPORT 2014

From the mortality and growth subgroup:

• Infection of cod with the seal associated cod worm and liver worm has been increasing in later years. Analyses are needed to quantify the potential par-asite-related mortality and the effects on cod growth (by length class/group) and performance.

• The grey seal population has increased since the beginning of the 2000s. This has likely increased the predation mortality on cod but need to be quantified by size.

• Discards apparently increased in the last years. Further investigation of the effect of gear selection on cod discards is needed.

• Body condition of cod has declined during the last decade. However, the mortality caused by the decrease in condition has to be quantified. The rea-sons for the decline in condition are currently not fully understood, but is likely a combination of several factors such as density-dependent effects, food availability, anoxic areas and parasites.

From the recruitment subgroup:

• Since the middle of the 2000s the recruitment of eastern Baltic cod has in-creased. However, the most recent ichthyoplankton surveys indicate a low larval abundance. Until the benchmark in March 2015 an egg production estimates from ichthyoplankton surveys in 2011–2014 should be prepared. On a longer time-scale, a study relating growth and condition with fecun-dity and viability of offspring is needed.

From the integrated assessment subgroup:

• There is a need for additional data time-series to explain and understand the development in growth and mortality. These dataset should be spatially dis-aggregated and include biomass and abundance of species (macrobenthos, marine mammals, fish eating birds) and consumption rates (marine mam-mals and birds).

• For short-term prediction a feasibility of an ecosystem-based recruitment model should be investigated, thereby giving indications on new year clas-ses at a much earlier stage than at present.

• For defining reference points in an ecosystem context, regime shift and man-agements objectives should be considered.

• In the longer term a development of assessment methods ensemble model-ling approach (many models are used together) need to be investigated.

• Ways to integrate ecological knowledge into advisory process need to be tested.


1 Opening of the meeting

The meeting was opened October 1st at 10am by Director Dr Tomasz B. Linkowski from the National Marine Fisheries Research Institute (NMFRI). Participants were hereafter introduced. The chairs went through the ToRs, explained the role of the par-ticipants and the expected outcome of the meeting. The agenda was adopted and the list of participants and the agenda are presented in Annexes 1 and 2, respectively. The first two presentations were “Introduction to the issues with cod assessments” by Ma-rie Storr-Paulsen and “DEMOnstration exercise for Integrated Ecosystem Assessment and Advice of Baltic Sea fish stocks” by Maciej T. Tomczak. The former explained the challenges and knowledge faced by WGBFAS when conducted this year’s assessment and the outcome of discussions on the knowledge gaps that lead to this workshop with the goal of improving the data input to an analytical assessment. The second talk fo-cused on understanding of integrated assessment, what is meant by integrated assess-ment and how can we incorporate this in our single-stock assessment or in the advice. Hereafter, all participants were asked to formulate important issues to be considered by the workshop on small yellow stickers and to group them within four main topics. These inputs were then used as basis for the subgroup work on the 2nd and 3rd day.

Figure 1. Board with the four topics addressed at WKSIBCA, where participants identified im-portant issues to be considered during the workshop and future work (yellow stickers).


2 ToRs

The Workshop on Scoping for Integrated Baltic Cod Assessment (WKSIBCA), chaired by Ma-rie Storr-Paulsen, Denmark, and Maciej Tomczak, Sweden, will be established and will meet in Gdynia, Poland, 1–3 October 2014 to:

a ) Collate revised data for the single-species stock assessments agreed at the most recent benchmark (WKBALT, 2013) following intersessional work out-lined by the Baltic Fisheries Assessment Working Group (WGBFAS, 2014); this includes revised age-reading data, considerations of potential catchabil-ity changes and increased discard rates. Examine the results and identify additional work, as required;

b ) Present a status report of relevant work from the Working Group on Inte-grated Assessment of the Baltic Sea (WGIAB) and connected activities (in particular, results from the meeting on the assessment of the Baltic cod, sprat and herring environment, held in Sweden in August 2014);

c ) Identify ecosystem processes that explain the recent changes detected in the Baltic cod stocks (i.e. especially reduced growth, spatial distribution, stock mixing);

d ) Identify which ecosystem information (related to processes, parameters and data) can be included in an integrated assessment of the Baltic cod stocks and the fisheries, and how;

e ) Identify potential gaps in information and knowledge necessary to derive an assessment, and how they can be closed;

f ) Set up a process to ensure the transfer of existing science into WGBFAS (in-cluding a plan of work to be conducted in the remainder of 2014 and in early 2015).

WKSIBCA will report by 15th October 2014 for the attention of the ACOM and SCICOM.


Supporting information

Priority The current activities of this workshop are in line with the ICES strategic plan to progress towards integrated ecosystem assessments.

This initiative was triggered by the problems detected on the previously benchmarked assessment of Eastern Baltic cod (developed at the benchmark WKBALT, 2013) at the WGBFAS 2014 meeting. The latter meeting identified the need for a more comprehensive benchmark assessment that considers ecosystem aspects, as well as the need to review the available data. Consequently, these activities are considered to have a very high priority.

Scientific justification The workshop will: (i) Examine the revised data following from the intersessional work outlined by WGBFAS 2014; (ii) identify available ecosystem knowledge, and how to incorporate the knowledge into an integrated assessment for the cod stocks and the fisheries in the Baltic Sea.

Resource requirements

The research programmes which provide the main input to this group are already underway, and resources are already committed. The additional resource required to undertake additional activities in the framework of this group is negligible.

Participants Experts on integrated assessment, fish stock assessment models and Baltic Sea ecosystem. The workshop is open to observers.

Secretariat facilities None.

Financial No financial implications.

Linkages to advisory committee

There are close links with ACOM and SCICOM.

Linkages to other committees or groups

There is a very close working relationship with the ACOM/SCICOM Benchmarking Steering Group (BSG), WGIAB, WGBFAS, SGSPATIAL and other groups (WGISDAA, WGFTFB, WGSAM, WGMM,…) holding information about the Baltic Sea System.

Linkages to other organizations

HELCOM, BSAC


3 Subgroups

Four main themes were planned in advance of the work-shop, however due to the out-come of the participants input on yellow sticks on the first day the pre-planned groups were reorganized to include all relevant input. The group work was still clustered within four main topics and although there was some overlap between the topics it was decided to have subgroups on 1) age and stock identification 2) mortality and growth 3) recruitment and 4) on the process of integrated assessment.

Participants gave their scientific input as talks during plenary sessions. Talks have been grouped in relation to the subject and included in the report as an abstract (Annex 3).

As a starting point each subgroup had the outcome of the scientific talks presented under their theme as well as the stickers produced by all participants during the first day. All subgroups were asked to report back on a) main challenges within their area, b) suggestions to how to solve the challenges, c) who is going to do the work, and d) timeline or road map for the process. Three different time perspective were considered by the subgroups. Short term is in this respect meant to be before the next benchmark (early March 2015), the next important time-step is the assessment working group (WGBFAS) to be conducted in April 14–21 2015, to allow new information to be con-sidered in the single-stock advice for 2016. Medium term and long term are in the next two to three years.

3.1 Age and stock identity

3.1.1 Age

This subgroup focused on discussing and identifying ways forward in relation to two issues that were raised at the meeting. First, the presentation of “Review of Age Read-ing problems in Baltic cod”, by Karin Hüssy suggested that only a smaller part of the otoliths from the eastern Baltic cod (around 25%) are every year forming annual ring structures that can be detected by the age readers. This together with productions of false rings make traditional age readings suffer from a high lack of precision and accu-racy. In the exchange study presented at the workshop the between and within reading consistency was very low. A second study included known age up to age 3 with 100 ototliths and showed a high degree of lack of detection of the true age structure.

The analyses presented demonstrated significant differences between and within read-ers, showing that traditional age reading of the eastern stock is subject to extensive bias in accuracy and precision. The task of the group was to come up with suggestions and a workplan for ways towards developing an alternative assessment not using tradi-tional age readings. The participants were asked to write down their ideas for activities to be carried out, after which these were discussed and placed on a time-scale to dif-ferentiate between the activities that can be carried out until the benchmark in 2015, or which activities need longer term efforts. Also, the suggested activities were ranked according to how promising the group felt these were, in terms of leading to an ac-ceptable assessment and solving the identified issues with age reading. The activities discussed are listed in Table 3.1.2.2 below, including timelines. A general pattern that emerged from this process was that several activities were suggested that can be car-ried out by the time of benchmark, however the confidence that these will solve the problem for an analytical assessment was generally medium-low. In contrast, the ac-


tivities that were considered to be more promising in terms of delivering useful out-comes (e.g. otolith microchemistry, tagging) will need longer time before these results can be obtained and will also depend on finances.

Decisions: Before drawing firm conclusions on abandoning the current age reading practice of EB cod for assessment purposes, the group felt the need to have a closer look at the materials and analyses presented that suggested that the eastern Baltic cod otoliths do not comply with basic criteria to be useful for age reading in traditional way as done today. Thus, it was recommended to carry out a review process of the pre-sented materials before benchmark, involving external experts with expertise in age reading and stock assessment and have a meeting afterwards including the national laboratories of the Baltic Sea countries. At the same time, the identified activities (shown in Table 3.1.2.1) towards an alternative assessment approach (i.e. not using tra-ditional age readings) should be continued.

Further, it was decided to send out a data call on historic length-based data (2000–2013) to be able to conduct an alternative assessment to an age-based assessment.

3.1.2 Stock mixing

The second issue, addressed by this group was mixing of eastern and western popula-tions in SD 24 (current management area of the western cod). The presentation on stock mixing (“Stock mixing of eastern and western Baltic cod“, presented by Karin Hüssy), showed that a large part of the cod in SD 24 belongs to the eastern population, and this tendency has increased in recent years. Presently, there is now evidence of western Baltic cod appearing in large quantity in SD25 however, if future data are identifying this as an issue a similar approach should be applied for in SD 25. The group discussed different options for dealing with SD 24 in stock assessment as follows:

1 ) Keep 22–24 as one management unit; 2 ) 22–23 as one unit, 24–32; 3 ) 22–23; 24 separately; 25–32; 4 ) 22–23–24W; 24E–32; 5 ) 22–23; 25–32 + splits of 24 (plan A using otolith flags; plan B using otolith

shape).

Decision: The group agreed that the best option would be to split the catches (and survey) in SD 24 according to the proportion on eastern and western cod found in the area (option 5).

Different options for splitting the data were discussed; the simplest one would be using the otolith readability as an indicator whether it is an eastern or western cod, since experienced age readers usually comment that eastern Baltic cod otoliths are more dif-ficult and complex than the ones from the western stock. When performing age read-ing, the readability of the otolith is registered in the laboratories in Germany and Denmark and therefore it is only a matter of compiling the information. However, ap-plicability of this method to identify the stock needs to be validated with the available genetic information. Alternatively, otolith shape analyses could be used. This also needs to be validated with the available genetic information, before adoption as the main tool. The options and steps that were discussed are shown in the table below. Technicalities involved in this split were discussed but due to time constraints, exact splitting scheme and procedures was not developed at the meeting. Thus, this process will continue intersessionally. A workplan is included in Table 3.1.2.2.


Table 3.1.2.1. Work-plan for the age reading issues.

AREA CHALLENGE SOLUTION COMMENTS RESPONSIBLE TIMELINE TO

APPLICATION

24–32 Consensus on abandoning traditional age reading

Daily increment method review: Send around literature and method description

Karin Hüssy

1/11/2014

Age reading WebGR: Include Russians, LV

Karin Hüssy

1/11/2014

External review of applicability of traditional age readings of Eastern Baltic cod

Relevant only if consensus on abandoning traditional ageing not reached

Cristina Morgado

Length–frequency analysis

Restricted to <3 years old -> Not applicable to solve assessment in 2015

Rainer Oeberst

Case study 1/02/2015

Microchemistry: Case study to evaluate present otoliths Validation of element signals via tagging Application to catch data

Karin Hüssy

After April 2015 >2 years >2–3 years

Tagging (fish + otolith) (GER experiment starting in 2014 SD22/24) Provide Call for tender text to EU

Input as validation for elemental signals

MSP/KH et al.

>3 years 7/11/2014

Approach evaluation to derive age from length: Back-calculation of fish size at hyaline zone formation to identify sizes with higher frequency alternative age estimate

Not applicable to solve assessment in 2015

Rainer Oeberst

Case study 1/02/2015

Data Data call on Length data in catch (2000–2013)

Marie Storr-Paulsen

15/10/2014

Assessment methods

Stock-production models

Jan Horbowy

1/02/2015

Length-based SAM? Uncertain outcome

Anders Nielsen

1/02/2015

Exploration of age-reading uncertainty in SAM

Uncertain outcome

Noél Holmgren

SS3 Uncertain outcome

Max Cardinale

1/02/2015

Exploration of different ALK: Is it possible to

Relevant only if consensus on

Joachim Hjelm

1/02/2015


apply only the most consistent country’s ALK Cohort analysis: If cohorts can be followed (BUT: Need to borrow data; ALK from one country not necessarily applicable to others)

abandoning traditional ageing not reached

22, 23 Age reading

Compare length distributions of catch: DK sends data to GER and vice versa

Marie Storr-Paulsen /Uwe Krumme

1/11/2014

Compare mean age at length between countries for survey and submit methodology description to other countries

Rainer Oeberst

15/10/2014

Application of Rainers mean-length-at –age-methodology to catch data

Margit Eero (DK data)

1/11/2014

(Compare otolith size distribution of a cohort from age 0 to 1 (Q1) with identified otolith structure)

Different trends in otolith exchange, age structures survey and catch

Uwe Krumme

1/11/2014


Table 3.1.2.2. Workplan for stock identification of Baltic cod.

3.2 Mortality and growth

The subgroup on mortality and growth had contributions from four industry persons and three scientists. The group work used the yellow sticks as starting point for the discussions as well as the presented talks within this topic. The discussion was initiated by having each group member state what they though was the most important factor for the increased mortality of large cod. The industry placed the major responsibility of the increased mortality on (direct and indirect) effects of seals, arguing that is was also why they did not catch last year’s quota. Consequently, various potential effects of the seals and their parasites were discussed, with general consensus that especially parasites have major impact. Discard and present selectivity was also evaluated as being potential (partly) explanations of the increased mortality, and likewise was the presence/absence of sprat discussed. Finally, the impact of recreational fishery was talked through, however with uncertainties regarding available (national) data for fur-ther analysis.

3.2.1 Mortality

It has been speculated that mortality is not, as assumed in the assessment, constant in time anymore. The reason for the change in mortality is not known, however, there are several hypotheses:

1 ) Parasites 1.1 ) Estimate how parasitic infection effects food conversion efficiency

(growth, condition) 1.2 ) Estimate cost associated with parasite infection 1.3 ) Estimate effects of parasites on cod performance (swimming, ability

to escape from net) 2 ) Diseases other than parasites

Challenge Solution Comments Responsible Timeline to application Method validation

Correlate genetic/shape/readability KH sends selection of genotyped otoliths to Uwe

Karin/Uwe 30/11/2014

Approach - Plan A: 2007-2013, split derived from otolith readability. Split provided by GER and DK.

- Plan B: 2007, 2010, 2013, split derived from otolith shape. Split provided by GER, DK. By 1/02/2015

- Plan C: Keep 24 separate

Proceeding 1. Step: initiation of splitting process with available methods

2. Step: Validation exercise using 300 otoliths

3. Step: Stock split of catch using quality flags for 2007-2013

4. Step: Set up sampling protocol for 2015 involving also genetic samples (starting with catches Q1 and Q4) – timeline before 1/01/2015

Catch and survey splitting

1) Apply constant stock mix until 2006

2) Otolith readability based stock mix 2007-2013

3) Otolith shape based stock mix 2007, 2010, 2013 (starting with 2013, moving back in time)

Rainer (survey) Uwe (catch)

1) 1/02/2015 2) After 1/02/2015

Historic stock mixing: Tagging database After April 2015


3 ) Dynamics in natural mortality (due to predation or other factors, such as condition).

3.2.2 Workplan for the benchmark (short term) and later work (mortality)

1 ) Mortality of larger cod from recreational fishery 1.1 ) This fishery (Polish example) in weight constitutes up to 10% of total

catches, but it is to some extent large fish, thus may induce marked mortality on larger cod; to be estimated from existing databases (WGRFS)

1.2 ) Length distributions to be compared from trawl and recreational catches (for the benchmark in March 2015)

2 ) Mortality which may be induced by parasitic infection 2.1 ) Jan Horbowy to work on the way of estimating it (short-term work

for the benchmark in March) 2.2 ) Jane Behrens to conduct experimental work (long-term work, appli-

cation for funds needed) 3 ) Mortality by direct seal predation (include also damaged fish). A working

document on recommendation to Integrated Assessment Baltic Group for seals effect on cod, was presented by Jane Behrens.

4 ) Mortality through increased discard; the lower cod weight under TAC lim-itation may lead to increased discard due to highgrading. A work on possi-ble effects of different codends on size selection and hence on discards (Uwe Krumme and Daniel Stepputtis) was presented. Further work on dis-card will be conducted by Uwe Krumme and Joakim Hjelm and presented to the benchmark.

5 ) Change in catchability was presented by Margit Eero. A change in catcha-bility can be modelled. Depending on the final model chosen to the bench-mark this exercise could be reanalysed with length data instead as present including age data.

6 ) Relation (dependence) of mortality on condition. This topic needs further investigations. Some progress were presented by Michele Casini, and it was recommended to be further explored to the benchmark meeting (March 2015).

3.2.3 Growth

Regarding growth, much of the same exercise as for mortality was performed. How-ever, effects of anoxic areas was an additional aspect here, and more emphasis was put onto effects of limited food supply and changes in benthic fauna. Overall, the following aspects were identified as being relevant to explain recent changes in cod condition and growth (Eero et al., 2012; Svedäng et al., 2014):

1 ) Changes in food in recent years has impacted on cod condition; 2 ) Oxygen poor areas, has impacted on growth. Anoxic areas in the Baltic have

increased; 3 ) Size matching of predator and prey. Work to compare area specific size

spectra of cod and clupeids, would help on understanding the predator- prey relation and food availability for cod;


4 ) Some studies indicate that cod growth depends more on herring than sprat. Further work to explore this should be undertaken (Noel Holmgren’s model);

5 ) Potential effects of selectivity (mesh size) on growth ; 6 ) Length distribution from BITS do not suggest big changes in growth in

length (Rainer Oeberst), this should be compared with the other data avail-able that suggest the opposite.

3.2.4 Workplan benchmark (short term) and later work (Growth–weight, length, condition)

The following work was presented in relation to this subject:

1 ) Dependence of growth (weight, length, condition) on environmental factors (density-dependent effects, food availability, anoxic areas). Michele Casini to provide analysis and equations, working doc (see abstract);

2 ) Do we really have marked decline in growth? (Rainer Oeberst to provide length distribution from BITS and analyses on this, see abstract);

3 ) Dependence of cod condition on parasites. Jane Behrens, see abstract).

This work should be further explored and available for the benchmark (March 2015).

3.3 Recruitment

Our state of knowledge of processes affecting recruitment and recent changes observed in the central Baltic system affecting reproductive success of the Eastern Baltic cod were reviewed, based on results from hydrographic, ichthyoplankton and spawning stock surveys.

3.3.1 Recruitment related actions suggested

Short term (until benchmark)

Estimate egg production of stock (at least SD 25) per egg stage from ichthyoplankton surveys (data from May and August 2011–2014 need to be analysed).

• Indication whether individual egg production has been reduced over time • Whether mortality in egg stage has changed since 1986

Recruitment estimate for 2015 and 2016, based on:

• Larval abundance March–November 2014 (November survey to be 2014 in-cluded)

• BITS survey in Q4 (age 0 and 1 separated by length compared to 2001–2013)

Predation on cod eggs by clupeids in SD 25

• Quantification of predation 2004–2008 compared to 1990s

Within 2015

Estimating spawning–stock size via egg production, requires

• Above total egg production from ichthyoplankton surveys • Individual fecundity (TI has recent data from SD 24 and 25 needs analysis

also with respect to point1.)


• Sex ratios and sex specific maturity ogives (need updates)

Cannibalism (results from stomach tender, data from AtlantNiro)?

• Demo and MS WG?

Longer term

Study on impact of condition/growth on individual egg production and survival of offspring (BIO-C3 project).

Quantifying egg production, survival and fate in SD 24 based on:

• Egg production based on distribution of adults during spawning time (problem: covering trawl surveys only outside spawning area available, ich-thyoplankton surveys not regularly conducted)

• Buoyancy of eggs and oxygen related egg survival (available) • Analysis of drift model output (runs conducted)

Predation on cod eggs by clupeids in SD 24

• Importance in SD 24 (not quantified, but observed), however, sampling of stomachs too limited, rather analysis of hydroacoustic survey

3.4 Integrated assessment

Subgroup of Integrated assessment of the cod stock composed of seven persons repre-sents stakeholders (industry, fisheries and NGO) and six scientists.

The subgroup dealing with “integrated assessment” discussed what “integrated as-sessment” means and what we understand in terms of the cod stock assessment in the Baltic. General conclusion was that integrated approach needs to include: i) fisheries assessment integrated with environmental/ecosystem factors, ii) integrated ecosystem assessment – indicators approach, iii) fisheries advice supported by integrated ecosys-tem assessment, iv) socio-economical perspective and v) involvement of fishermen into the process (see the reference fleets example). The subgroup identified main challenges and possible action in related for integrated assessment and advice for Baltic cod stock (Table 3.4.1). Subgroup members recognized a need for new datasets related to other trophic/functional groups as: marine mammals, fish eating birds and benthic macro fauna. Identified important data should be spatially disaggregated and include bio-mass and abundance of species (macrobenthos, marine mammals, fish eating birds) and consumption rates for species (marine mammals and birds).

Due to the lack of relevant expertise within the subgroup, a preparation of data call by related ICES EG was requested.

One of the points during subgroup discussion was related to the integrated fisheries assessment method. As an “integrated assessments methods” participants meant: spa-tially disaggregated models and integration of environmental factors into models and multispecies approach. One of the conclusions was that there is a need of including ecological processes (i.e. growth or predation) in to the modelling. As a first step par-ticipant regarded the application of environmentally sensitive stock–recruitment rela-tionships in to short-term prediction as a basis for advice and performing spatially disaggregated assessment. Participants agreed that one model do not answer all the questions and an option to consider, in future assessment method improvement, could be an ensemble modelling approach using different models to investigate stock status


and to integrate modelling types. Contaminants effect on fish and ecosystem was dis-cussed as one of the future direction to improve assessment methods and to improve model parameterization.

Integration of ecosystem indicators (see i.e. DEMO results) was discussed also in rela-tion to the ICES advisory system. To deliver the reliable advice, reference points are necessary and evaluation of existing reference points using multispecies approach is recommended, based on already existing models and data. The main obstacle recog-nized was the lack of defined objectives for multispecies and ecosystem approach for fisheries management and socio-economic perspective. Subgroup suggested to ad-dress those question to the relevant ICES EGs (e.g. WGRISCO, WGIMM, WGMARS).

Project “DEMOnstration exercise for Integrated Ecosystem Assessment and Advice of Baltic Sea fish stocks”, led by Maciej T. Tomczak (Stockholm University) and Christian Möllmann (Hamburg University), was discussed in a framework of integrating ecosys-tem information into the ICES advice. Subgroup agreed that DEMO results (end of 2015) need to be tested as a pilot project (parallel with existing advice) at ICES in years 2016–2017. DEMO ideas was suggested to be a contribution to the Terms of References of newly established WGDEMO (WG on DEMOnstration of Integrated Ecosystem As-sessment and Advice of Baltic Sea fish stocks) closely interacting with WGIAB, WGRISCO, and WGIMM.


Table 3.4.1. Table is showing the work-plan for the further work to be conducted in respect to the integrated assessment.

CHALLENGE SOLUTION COMMENT RESPONSIBLE TIMELINE

Availability of benthic food components

Develop a database with benthos data

Ask WGBENTHOS to prepare the data call Data call for benthos data member countries (national programmes)

Jörn Schmidt 25/10/2014

Incorporate the data in the ICES DataCenter

Communication with DataCenter


Analyse changes in growth and mortality

Use existing environmental data to analyse the effect

DEMO2, Anna Gårdmark and Michele Casini

30/11/2014

Effect of changes in distribution of sprat, herring on cod growth

Analyse existing datasets

SGSPATIAL, Michele Casini

30/11/2014

Spatially explicit SMS

Stefan Neuenfeldt ?

Are the reference points still valid? (see also objective setting in a multispecies or even ecosystem context)

Evaluation of existing reference points (ensemble modelling approach??)

Multispecies models

Noel Holmgren, Niclas Norrström

01/03/2015

Morten Vinther, Stefan Neuenfeldt

Rudi Voss, Jörn Schmidt

Production models

Jan Horbowy

Effect of environment on recruitment

Environmental sensitive stock–recruit relationships

Based on literature and DEMO1 results - Piotr Margonski

March 2015

Dynamic stock modelling

DEMO3, March 2015, and Martin Lindegren

April 2015

Consumption of Marine mammals and birds

Calculate consumption rates

Request to WGMME, WGSE

Cristina Morgado 08/10/2014

Effect of contaminants on mortality, recruitment and growth

Calculate rates for different contaminants

Thünen Institute for Fish Ecology? Propose Baltic workshop on this topic?


CHALLENGE SOLUTION COMMENT RESPONSIBLE TIMELINE

Effect of environmental indicators on TAC level

Using Ecosystem Indicators to inform the advice

Provide information on ecosystem indicator that could be use in the 2016 advice (advice for 2017)

DEMO4, August 2015, Maciej Tomczak and Christian Möllmann

September 2015

Expert Group to continue DEMO activities - Create WG DEMOnstration of Integrated Ecosystem Assessment and Advice of Baltic Sea fish stocks.

Maciej T. Tomczak and Christian Möllmann WGIAB 2015/DEMO 2015

After DEMO and WGIAB 2015 long term To disscuss within WGIAB not to overlap.

Valuable information from fisherfolk and other sources is not taken into account

Include fisherfolks knowledge; include them in the observing framework

Example of Norwegian reference fleets draft a proposal for Baltic

Staffan Larsson and Henrik Loveby

15/11/2014

Data for the science groups is distributed and difficult to assemble; often only available in excel sheets

Incorporate the data in the ICES DataCenter and formalize the data stream request to PGDATA and the data center

Prepared and update consistant dataset of enviromental and fisheries data for SCICOM EG (i.e WGIAB)


The objectives in a multispecies or even ecosystem context are not clear

Define a process of defining objectives with advice recipients

WKRISCO, November 2014, Mark Dickey-Collas, Jörn Schmidt

15/12/2014

Integration of the socio-economic perspective into the advisory framework

Explore options WGIMM, March 2015, Rasmus Nielsen, Eric Thunberg, Jörn Schmidt

WGMARS, December 2014, Dorothy Dankel

Long Term


Annex 1: List of participants

NAME ADDRESS PHONE/FAX E-MAIL

Michael Andersen

Danish Fishermen’s Association Fredericia Nordensvej 3 Taulov 7000 Fredericia Denmark

Phone +45 70 10 9645 Cell: +45 4026 5040

[email protected]

Jane Behrens DTU Aqua - National Institute of Aquatic Resources Section for Ocean Ecology and Climate Jægersborg Allé 1 2920 Charlottenlund Denmark

Phone +45 35883429 Cell: +45 23296863

[email protected]

Michele Casini

Swedish University of Agricultural Sciences Institute of Marine Research Turistgatan 5 453 30 Lysekil Sweden

Phone +46 10 478 4016 Fax +46 523 13977

[email protected]

Sally Clink Baltic Sea Advisory Council H.C. Andersens Boulevard 37, 3rd Floor 1553 Copenhagen K Denmark

Phone +45 21677248 Fax +45 33 93 50 09

[email protected]

Anna Dębicka Marine Stewardship Council Rakowiecka Street 34 m 51 02-532 Warsaw Poland

Phone +48 502 44 77 34 Fax +48

[email protected]

Margit Eero DTU Aqua - National Institute of Aquatic Resources Charlottenlund Slot Jægersborg Alle 1 2920 Charlottenlund Denmark

Phone +45 21314880/35 88 33 18 Fax +45 33963333

[email protected]

Pavel Gasyukov

AtlantNIRO 5 Dmitry Donskogo Street RU-236000 Kaliningrad Russian Federation

Phone +7 4012 225 257 Fax +7 4012 219 997

[email protected]



Kim Kær Hansen

Danish Fishermen’s Association Fiskeriforening Øst Lendemarkhovedgade 32 DK-4780 Stege Denmark

Phone +45 40 891 381 Fax +45

[email protected]

Karin Hüssy DTU Aqua - National Institute of Aquatic Resources Jægersborg Allé 1 2920 Charlottenlund Denmark

Phone +45 Fax +45

[email protected]

Piotr Gruszka Polish Ecological Club West Pomerian Branch, Krolewicza Kazimierza 4 71-550 Szczecin Poland

Phone +48 914 23 10 61 Fax +48

[email protected]

Joakim Hjelm Swedish University of Agricultural Sciences Institute of Marine Research PO Box 4 453 21 Lysekil Sweden

Phone +46 523 18751 Fax +46 523 13977

[email protected]

Noél Holmgren

University of Skövde School of Life Sciences PO Box 408 541 28 Skövde Sweden

Phone +46 500 448607 Fax +46

[email protected]

Jan Horbowy National Marine Fisheries Research Institute ul. Kollataja 1 81-332 Gdynia Poland

Phone +48 609 421 687 Fax +48 587-356-110

[email protected]

Stanislovas Jonusas

European Commission Directorate for Maritime Affairs and Fisheries 200 rue de la Loi Unit E2, J-79 05/04 B-1049 Brussels Belgium

Phone +32 2 298 01 55 Fax +32

[email protected]

Zbigniew Karnicki

National Marine Fisheries Research Institute ul. Kollataja 1 81-332 Gdynia Poland

Phone 58 735 6232

[email protected]



Eskild Kirkegaard

DTU Aqua – National Institute of Aquatic Resources Jægersborg Allé 1 2920 Charlottenlund Denmark

Phone +45 35 88 30 10 Fax +45

[email protected]

Georgs Kornilovs

Institute of Food Safety, Animal Health and Environment (BIOR) 8 Daugavgrivas Str. Fish Resources Research Department 1048 Riga Latvia

Phone +371 676 76 027 Fax +371 6761 6946

[email protected]

Fritz W. Köster

DTU Aqua - National Institute of Aquatic Resources Section for Fisheries Advice Charlottenlund Slot Jægersborg Alle 1 2920 Charlottenlund Denmark

Phone 45 35 88 30 00 Fax 45 33 96 33 33

[email protected]

Uwe Krumme Thünen Institute vTI -OSF Rostock Rostock Germany

Phone +49 Fax +49

[email protected]

Staffan Larsson

Swedish Cod Fishermen’s Producer Organisation Tofta Sörhagen 10 442 75 Lycke Sweden

Phone +46 703 64 04 11 Fax +46

[email protected]

Sebastian Linke

University of Gothenburg PO Box 100 SE-405 30 Gothenburg Sweden

Phone +46 735736703 Fax +46

[email protected]

Henrik Loveby

Sveriges Fiskares Riksförbund Fiskhamnsgatan 33 414 58 Gothenburg Sweden

Phone +46 Fax +46

[email protected]

Anna Luzenczyk


Phone +48 58 735 62 74 Fax +48 58 735 6110

[email protected]



Piotr Margonski


Phone 48 58 735 6134

[email protected]

Ewa Milewska

World Wildlife Fund Poland ul. Wisniowa 38 02-520 Warszawa Poland

Phone +48 22 849 84 69 Fax +48 22 646 36 72

[email protected]

Cristina Morgado

International Council for the Exploration of the Sea H. C. Andersens Boulevard 44-46 1553 Copenhagen V Denmark

Phone +45 33 38 67 21 Fax +45 33 63 42 15

[email protected]

Stefan Neuenfeldt

DTU Aqua - National Institute of Aquatic Resources Section for Fisheries Advice Charlottenlund Slot Population Ecology and Genetics Kavalergården 6 2920 Charlottenlund Denmark

Phone +45 35883402

[email protected]

Alex Olsen A. Espersen A/S Fiskerivej 1 3700 Rønne, Bornholm Denmark

Phone +45 5690 6010/+45 2015 4259 Fax +45 5690 6001

[email protected]

Niclas Norrström

University of Skövde PO Box 408 541 28 Skövde Sweden

Phone +46 500 448653 Fax +46

[email protected]

Rainer Oeberst

Thünen Institute Institute for Baltic Sea Fisheries Alter Hafen Süd 2 18069 Rostock Germany

Phone +49 381 811 6125 Fax +49 381 811 6199

[email protected]

Konstantin Podgornyy

AtlantNIRO 5 Dmitry Donskogo Street RU-236000 Kaliningrad Russian Federation

[email protected]

mailto:[email protected]



Piotr Predki World Wildlife Fund Poland ul. Wisniowa 38 02-520 Warszawa Poland

Phone +48 22 849 84 69 Fax +48

[email protected]

Krzysztof Radtke


Phone +48 587356223 Fax +48 58 7356 110

[email protected]

Jörn Schmidt Christian-Albrechts-University of Kiel Department of Economics Wilhelm-Seelig-Platz 1 24118 Kiel Germany

Phone +49 431 880 5632

[email protected]

Olle Schuschel

Fishermen’s Federation for Small-Scale Fishery in Sweden Nätgatan 17 38062 Mörbylånga Sweden

Phone +46 4854 1548 Fax +46

[email protected]

Krzysztof Stanuch

National Vhamper of Fish Producers Krajowa Izba Producentów Bohaterow Westerplatte 4A 76-270 Ustka Poland

Phone +45 Fax +45

[email protected]

Marie Storr-Paulsen Chair

DTU Aqua - National Institute of Aquatic Resources Section for Fisheries Advice Charlottenlund Slot Jægersborg Alle 1 2920 Charlottenlund Denmark

Phone +45 35 88 34 41 Fax +45 3396 3333

[email protected]

Andreas Sundelöf

Swedish Agency for Marine and Water Management PO Box 11930 40439 Göteborg Sweden

Phone +46 Fax +46

[email protected]



Thomas Thomsen

Fishermen’s Association of Bornholm and Christiansø Øernes Kaj 2 3700 Rønne, Bornholm Denmark

Phone +45 56957360 Fax +45

[email protected]

Maciej Tomczak Chair

Baltic Sea Center Stockholm University SE-106 91 Stockholm Sweden

[email protected]

Irek Wojcek Polish Association of Fishermen of Sea PO National Marine Fisheries Research Institute ul. Kollataja 1 81-332 Gdynia Poland

Phone +48 58 7356 219 Fax +48

[email protected]

Christopher Zimmermann

Thünen Institute Institute for Baltic Sea Fisheries

Alter Hafen Süd 2

18069 Rostock

Germany

Phone (0) 381 8116-115 / mobile (0) 1712777464

Fax (0) 381 8116-101

[email protected]


Annex 2: Agenda

Agenda Workshop on Scoping for Integrated Baltic Cod Assessment Purpose of the meeting: see TORs Use of the results of the meeting: Preparation for benchmark in 2015 and scoping further work on integrated Baltic cod assessment

Information on the meeting: Date: 1-3 October, 2014

Location: NMFRI, Gdynia (see info in the SharePoint under 01.tors and general information)

To prepare: Data to be used in assessment for cod,

To bring along:

Agenda item: Process and outcome: Responsible: Duration

OCTOBER 1st START: 10 am Welcome Introduction Challenges with cod assessments Introduction of DEMO Discussion/brainstorm Adjusting agenda

Seating the scene Welcoming words Presentation of participants. Chairs orientate on general background of the meeting, what is an integrated assessment, what is the expected outcome of the meeting Orientate on the main issues encountered in eastern and western cod assessments, to have a common understanding of the challenges where solutions are needed. Inform participants on the DEMO initiative and the idea behind. Challenges for ecosystem assessment and advice Possibility for all to express general views of the main issues with the assessments (incl. stakeholder perspectives Go through agenda, add if needed

Dir.Tomasz Linkowski; ACOM chair Eskild Kirkegard; Maciej Tomczak, Marie Storr-Paulsen Marie Storr-Paulsen Maciej Tomczak All Maciej Tomczak Marie Storr-Paulsen,

15 min 15 min 30 min 20 min 30 min 15 min



12.15 AGE READING: Inconsistencies in age readings Effect of age readings on assessment Lunch 13.15-14.00 Selectivity model Model issues related to size at age: catchability Discussion ECOSYSTEM AND ENVIRONMENT: Intro/DEMO RECRUITMENT Discussion

Presentation of the results from otolith exchange between countries Presentation of assessment analyses for eastern and western cod, testing sensitivity of the results to age readings Cod assessment with CAGEAN effects of varying selectivity and natural mortality estimates Presentation of possibilities to implement time varying catchability at age in assessment model, given changes in growth Generate ideas and conclude on ways forward in relation to aging problem, alternatives for age based assessment. The outcome of this discussion serves as input to the workplan for benchmark Processes - recruitment Presentation of the results of DEMO1 workshop concerning integrating ecosystem and environmental data in assessment and advice Presentation of processes/variables affecting recruitment Discussion of whether and how envir. information could be included in assessment/advice concerning recruitment

Karin Hüssy Margit Eero (western cod); Joachim Hjelm (eastern cod) Jan Horbowy Margit Eero All Maciej Tomczak Fritz Köster All

25 min 30 min 15 min 15 min 60 min 15 min 15 min 30 min



OCT0BER 2, START: 9 AM GROWTH/MORTALITY: Growth effects Food base Seals/ Parasites Discussion MORTALITY: Fisheries catch German discard Discussion, industry input Lunch 13.15-14.00

Potential explanations for the change in growth (prey composition, oxygen) Presentation of the new stomach analyses to elucidate potential changes in food base Presentations on the developments in seals, parasites and related potential effects on cod growth and mortality. Conclude on whether cod growth has changed and why. How can we integrate ecosystem information on growth/mortality in stock assessment /forecast/advice Identify the research needed, input to workplan for benchmark Presentation of analyses of discard data German discard rates 2009-2014 Can discard mortality potentially be higher than anticipated in the assessment? Conclude on work needed, input to work plan for benchmark

Michele Casini Stefan Neuenfeldt Jane Behrens; Jan Horbowy All Joachim Hjelm Uwe Krumme All

15 min 15 min 30 min 15 min 20 min 30 min



OTHER ISSUES: Stock ID Discussion Work plan for benchmark Process for EBFM OCTOBER 3, START: 10 am Summing up/ Discussion Discussion/brainstorm Workplan for benchmark and long term activities Closing of the meeting 15.00

Presentation of results of genetics/otolith form analyses of mixing of eastern and western cod in SD 24 How do we deal with this in assessment/advice. Work needed, input to workplan for benchmark Sub-groups, writing specific workplan for benchmark using outputs from earlier discussions Start up discussions and work plan for ecosystem based fisheries management and advice for the Baltic stocks (study group?) Group work – summing up Sum up and agree on conclusions from the earlier discussion points: i_)which processes can explain recent changes on growth/mortality ii_)which information can be included in analytical assessment of the Baltic cod and how iii_)where are gaps and how can they be closed Where challenges are today related to information transfer from other groups to WGBFAS and/or Advice. How can these be overcome? Go through and agree on the workplan for benchmark, responsibilities, time lines etc (short time) and roadmap for EBFM (long term)

Karin Hüssy All All All Marie Storr-Paulsen, Maciej Tomczak All All

20 min Until the end of the day 90 min 60 min 60 min


Annex 3: Abstracts of presentations

Introduction to the issues with cod assessments by Marie Storr-Paulsen (DTU Aqua, Denmark)

The age-based analytic assessment of the eastern Baltic cod stock was not accepted by ICES this year (2014). There were several factors that have changed the prerequisite of the present assessment with the most important being the decrease of larger cod the last two years although the recruitment level has been at a historic high level. This resulted in an advice based on ICES data-limited approach. This approach are using the numbers of cod above 30 cm (as a proxy for SSB) from the survey were the two last datapoints are divided with the average of the three earlier years.

The reasons for the distrust of the present assessment can be found in several different challenges with the data. The first indication that data are giving conflicting results are the retrospective analysis indicating that every year the SSB is largely overesti-mated and F largely underestimated. At the assessment time there were several hy-potheses for the discrepancy in data a) Missing large cod, despite a lot of recruits b) Age reading problems c) Changed growth d) Changed catchability e) Unaccounted mortality (Natural / Fishing).

The biomass of cod larger and smaller than 38 cm. from the combined survey.

It was during the WGBAS realized that there were severe differences between coun-tries in the length-at-age data. This was highlighted by the comparison between Danish and Polish age-by-length data. However, even if ages were not included in the analysis there was documentation for a large decrease in the condition in cod over time. The decrease was largest in SD 25. It was also shown that the mortality could have changed in recent years due to increase in parasite infection, increase in numbers of cod with a very bad condition and/ or an increase in discard rates.

For the western Baltic cod stock some of the same challenges were recognized as for the eastern Baltic cod stock. In SD 24 however, there were also an issue on stock mixing between the eastern and western stock and the age readings in this area is therefore also thought to be problematic. In the western Baltic cod stock the biomass in the two


main areas the SD 22 and SD 24 seems to have developed a different pattern which could indicate a change in mixing rate in recent years.

DEMOnstration exercise for Integrated Ecosystem Assessment and Advice of Baltic Sea fish stocks by Maciej T. Tomczak (Baltic Sea Center, Stockholm Univ., Sweden)

A major goal of ecosystem-based fisheries management (EBFM) is to manage fishing pressure on target species in the context of the overall state of the system, habitats and non-target species. Although ecosystem-based approaches are now central to living marine resource policies worldwide, the implementation of EBFM in Europe still ig-nores ecosystem context. One reason for the slow implementation of EBFM is a lack of a coherent strategy. The DEMO project will develop such a strategy applying the Inte-grated Ecosystem Assessment (IEA) concept with the goal to complement and improve the present single species advice and management of Baltic Sea fish stocks.

Reliable assessments of present and future states is crucial to a sustainable manage-ment of commercially exploited fish stocks. Uncertainties in fish stock assessments and management are not only detrimental for the fish stocks themselves but especially for the social communities depending on them. How uncertainty in advice and manage-ment can result in conflicts between stakeholders is demonstrated currently by the case of Eastern Baltic cod that after a period of apparent recovery is found to be in an unclear state. Uncertainties in the cod stock assessments have now resulted in the application of more precautionary assessment approaches which result in reduced catch quotas for the fishery.

A way to complement and improve the currently still dominating single-species ap-proaches to assessment and management of commercially exploited fish stocks is to apply ecosystem-based management (EBM) principles. Core to EBM approaches for fisheries (EBFM) is either to account for the ecosystem consequences of the exploitation of single fish stocks, but as well to reduce the uncertainty in fish stock assessments by accounting for the present and potential future states of the environment. However, EBFM needs detailed knowledge and more complex modelling tools in order to be successful. But most importantly it requires a strategy for practical implementation into the existing scientific and institutional procedures for fish stock assessment, advice and management.

A strategy to implement EBFM is offered by the concept of Integrated Ecosystem As-sessments (IEAs), a formal synthesis tool to quantitatively analyse information on rel-evant natural and socio-economic factors, in relation to specified EBM objectives (Levin et al., 2009; 2014). IEAs provide a strategy to overcome the still prevailing single-species and single-sector approaches, they organize science in order to inform decisions in ma-rine EBM at multiple scales.

The DEMO project has the goal to demonstrate the potential of implementing EBFM for the Baltic Sea based on an IEA approach developed by the ICES/HELCOM Working Group on Integrated Assessments (Möllmann et al., 2014). At DEMO we focus on pro-cess focuses on integrated advice for the three commercially important Baltic Sea fish stocks cod, herring and sprat. It integrates elements of traditional single species with multispecies fish stock assessments, management strategy evaluations and im-portantly assessments of the state of the environment.


Assessing the environment in support of management advice for the Eastern Baltic cod stock was the focus of the first of four meetings of the DEMO project. The work will result in a portfolio of environmental indicators that show the state of the Baltic Sea ecosystem in relation to the potential reproductive success of the cod stock. The indi-cator portfolio has been developed based on indicator screening and selection using expert knowledge and extensive statistical analyses and has a large potential to im-prove the currently unclear apprehension of this fish stock of socio-economic im-portance.

The assessment of the environment in relation to the cod stock is the first step towards developing and testing a full EBFM approach to be developed by DEMO. The IEA ex-ercise of the project will demonstrate the feasibility of developing traditional single-species approaches into EBFM based on the case of the Baltic Sea. The project members are however convinced that such an approach is needed to improve the present scien-tific advice.


Review of Age Reading problems in Baltic cod by Karin Hüssy (DTU Aqua, Denmark)

Age reading of eastern Baltic cod has traditionally been considered difficult. Over the last four decades a number of expert groups have focused on revealing the extent of the problem, to standardize age interpretation through calibration exchanges and eval-uating new approaches. The expert groups concluded that significant differences in age interpretation existed between (and within) readers. Of the alternative methods examined daily increment patterns are very consistent, providing the best method for accurate age estimation in fish <3 years of age. However all approaches tested suffer from validation through “known age” samples. WKBFAS (2014) observed a strong di-vergence in age structure of catches and survey data suggesting an increase in ageing inconsistencies, which triggered a new age reading exchange.

The objective of the 2014 exchange: This exchange was to 1) Examine the extent of the problems 2) Identify where the problems are (i.e. first winter ring and/or subsequent rings), and 3) To provide a validation through daily increment analysis.

Materials and methods

General exercise: Based survey samples of BITS-1, 2014 and covering SDs 22, 24 and 25. Samples were selected to cover the entire length distribution and individuals with dif-ferent somatic condition. 100 otoliths were used, each represented with two identical images where length information was available only for one image. All countries con-tributing to the age–length keys in the respective SDs were involved in the exchanges.

Validation exercise: Based survey samples of BITS-2, 2013 and covering SD 25 only. The objective was to validate the first 2–3 winter rings, therefore the size range was limited to fish <30 cm. 100 otoliths were used and were annotated by all age readers. In the same exercise the position of the true winter ring was marked following examination of the otoliths for daily increment patterns.

The tool and analyses: The Internet-based platform WebGR (http://webgr.azti.es) was used for the exchange. Following annotation by the readers, data on the estimated age and distance between structures interpreted as winter rings are available. Based on these distances growth curves were established for each fish and reader individually. These growth curves allow for detailed examination of where the main problems with age interpretation are. Age estimates were compared using Friedman rank sum test and post hoc pairwise comparison with Wilcoxon signed rank test. The growth curves were analysed using Linear Mixed Effects Models with reader as fixed effect and indi-vidual fish as random effects with post hoc comparison using Tukey Contrasts for mul-tiple comparisons. While the age data provide information on whether the age readers agree in age estimates, the growth data can identify specifically where the problems are, i.e. differences in intercept only are attributable to problems with the first winter ring, while differences in slope indicate a general inconsistency in structures used for age estimation.

Results

General exercise - SD 22: Participants: GER, DK. Significant differences were found be-tween the Danish and German readers, in that the Danish reader estimated fish to be one year older. Within reader differences were not significant. This inconsistency was exclusively attributable to the interpretation of the first winter ring.

General exercise - SD 24: Participants: GER, DK, SE. Significant differences in age esti-mates between readers were found, where interpretation problems were associated with both the first and subsequent winter rings. Within reader inconsistency was much

http://webgr.azti.es/


higher compared to SD 22, but without systematic differences in age readings with/without fish length.

General exercise - SD 25: Participants: GER, DK, PL, SE (LTV and Russia are participat-ing currently). Significant differences in age estimates between readers were found, where interpretation problems were associated with both the first and subsequent win-ter rings. Within reader inconsistency was even higher than in SD 24 (up to ±3 years on the identical images), but without systematic differences in age readings with/without fish length. Closer inspection of the annotations in WebGR showed that although read-ers may estimate a fish to the same age, they do not identify the same structures as annual growth zones. Fish somatic condition was found to have no effect on agreement in age interpretation.

Validation exercise - SD 25: Validation of true age was possible in >90% of all individuals <25 cm, while only 68% of 25–30 cm (fish older than two years) could be validated. This exercise confirmed the results of the general exercise: Variation in structures inter-preted differed significantly between readers, and did on average not correspond to the true winter ring for any of the readers. Structures identified as winter rings seemed predominantly to be formed during summer. Between the second and third true winter ring, all readers except one identified two structures as winter rings. No within reader consistency check was carried out in this exercise. Closer inspection of which structures were identified by the readers showed that many of these seemed translucent zones associated with migrations of several days (with clearly defined daily increments) into warmer water, followed by a return to colder water. True winter rings may or may not be associated with a translucent zone.

Conclusions

Conclusion: The basic requirements for using otolith patterns for age reading are that the structures used show strong seasonality, occur in all individuals across the entire age/size range and be consistent over the years. Easter Baltic cod otoliths do not comply with these requirements. Given the significant differences between and particularly within readers, these results document that traditional age reading of the eastern stock is subject to extensive bias in accuracy and precision.

Other approaches: Two suggestions for alternative approaches to derive age estimates are 1) Tag/release programmes with chemical marking of the otolith and external marking of the fish, and 2) Otolith microchemistry signals corresponding to seasonal variations in trace element incorporation.

Reference

Hüssy, K. 2010. Why is age determination in Baltic cod (Gadus morhua L.) so difficult? ICES J. mar. Sci. 67, 1198–1205.

Hüssy, K., Hinrichsen, H.H., Fey, D.P., Walther, Y., Velasco, A. 2010. The use of otolith micro-structure to estimate age in adult Eastern Baltic cod (Gadus morhua L.). J. Fish. Biol. 76, 1640–1654.

Hüssy K., Mosegaard H., Nielsen B., Worsøe Clausen L. 2009. Using data storage tags to link otolith macrostructure in Baltic cod (Gadus morhua L.) with environmental conditions. Mar. Ecol. Prog. Ser., 378: 161–170.


Effect of differences in age structure on the assessment of western Baltic cod; by Margit Eero (DTU Aqua, Denmark).

Since 2007, pronounced differences in age structure in German and Danish cod catches in the western Baltic became apparent. This was considered as possibly due to incon-sistent age readings. To test the effect of this in the assessment, sensitivity analyses where conducted applying scenarios using either only German or only Danish age in-formation for years since 2007. For commercial landings, either GER or DK relative age structure (in pct.) by year, quarter, SD and gear (active/passive) was applied to the total international catch (tons) taken in given strata. For BITS survey, for scenario with GER age information, GER age–length key by SD and survey was applied for cpue from 2007 onwards. For the scenario with DK age information, two versions of BITS data were produced, where ALK for SD 24 originated either from SD 25 (a) or from SD 22 (b). This is because surveys in SD 24 are mainly conducted by GER and DK ALK is not available. The commercial tuning fleet used in the assessment used either GER or DEK ALK in the scenarios performed. This resulted in scenarios 1 (GER age data) and scenarios 2a and b (DK age data, where the difference between a and be is only related to the source of age information for SD 24 in BITS survey).

Fishing mortalities from the scenarios were compared. The result showed pronounced differences in F trajectories between scenarios 1 and 2 (Figure 1). Retrospective anal-yses indicated reduced retrospective bias in scenarios 2a and b, compared to the latest ICES assessment. Further, in scenarios 1 and 2a, the signals from different tuning indi-ces concerning fishing mortality were more similar compared to the latest ICES assess-ment.

Two types of age-independent information on fishing pressure in the western Baltic were investigates, i.e. fishing effort (kw days) and relative harvest rate. Effort was based on based on demersal trawlers and gillnetters, i.e. the main segments catching cod. Relative harvest rate used biomass indices from both Q1 and Q4 survey, combined via geometric mean, and included cod over 30 cm in length. Relative harvest rate was then calculated as a ration between commercial landings and relative biomass.

The two age-independent information sources both indicate reduction in fishing pres-sure approximately by a half or more since 2000. The ICES assessment shows less re-duction in F in this period compared to age independent information. Comparison of age-independent information on fishing pressure with F from sensitivity runs shows that part of age information included in ICES assessment is pointing at much different F trajectory in recent period that indicated by age-independent information (Figure 2).

In conclusion, the assessment was found to be sensitive to differences in age infor-mation by countries. Further, part of the inconsistencies observed in ICES assessment (retrospective bias, different signals in different tuning indices) were found to be re-lated to age information. Thus, solving age-readings issues or alternative age-inde-pendent assessment methods are needed. Age reading is considered a large problem in SD 24 compared to SD 22–23. Thus, in the more western areas, current age-based methods can potentially be continued, which should be further investigated at bench-mark.


Figure 1. Fishing mortality from scenario 1 (grey line) compared to scenario 2a (black line, left panel) and to scenario 2b (black line, right panel).

Figure 2. Fishing effort (kwdays) and relative harvest rate compared to trends in fishing mortality (F) from current ICES assessment and from the sensitivity runs using age information from either GER or DK. All data are presented relative to values in 2000.

Eastern Baltic cod: Assessment sensitivity 2007-2013; by Joakim Hjelm (SLU-Aqua, Sweden)

Age readings

To explore the sensitivity of the SPALY assessment, two scenarios were constructed, one with only Polish age readings (Polish ALK) and one with only Danish age readings (Danish ALK). In both scenarios, the commercial tuning fleet was discarded due to it only contains Danish vessels. As the weights were not corrected in this analysis, the comparison was only made for differences in fishing mortality (F, numbers).

The comparison showed that by using the Polish ALK created much higher fishing mortalities (approximately F=1.5) then the SPALY assessment in recent years. Using only the Danish ALK also created higher fishing mortalities (approximately F=1.0) then


the SPALY run but much lower than the run with the Polish ALK. Both scenarios cre-ated somewhat better retrospective pattern compared to the SPALY run.

In order to compare the different runs with different ALKs with the pattern in other measures of exploitation rate, the relative change the last years where constructed. It shows that biomass, fishing mortality based on the Danish ALK and possibly fishing effort is hump shaped with a maximum around 2011. Harvest rate has been relatively stable since 2009 but the fishing mortality based on the Polish ALK suggests an in-crease.

Increased natural mortality

To explore the effect of natural mortality (using the standard ALK), the natural mor-tality was adjusted as a function of condition (Fulton), i.e. lower condition resulted in a higher natural mortality per age group during the period 2007–2013. The results show a higher natural mortality results in a similar spawning biomass but a much higher fishing mortality compared to the SPALY run.

Catchability

To explore the effect of the different trends in catchability observed in the commercial tuning fleet and surveys, two scenarios were explored. On scenario with no commer-cial tuning fleet and one scenario with no commercial catches from 2005. The scenario with no commercial tuning fleet suggested that spawning biomass is relatively low and comparable with the SPALY run whereas fishing mortality is much higher. The second scenario, with no commercial catches, suggested that spawning biomass is much higher relatively to the SPALY run whereas fishing mortality is higher. Both runs shows a better retrospective pattern compared to The SPALY run.

Conclusions

It has been suggested that the problems experienced with the current assessment is either due to, problems with the age readings, increased natural mortality or a change in catchability (or a combination all these). These runs suggest that the assessment of eastern Baltic cod shows a high sensitivity in all these parameters.

Cod assessment with CAGEAN – effects of varying selectivity and natural mortality on estimates by Jan Horbowy (National Marine Fisheries Research Institute, Poland)

The CAGEAN model (Deriso et al., 1985) was used to assess eastern cod stock devel-opment under different assumptions on selectivity and natural mortality. So far, within WGBFAS cod assessments was performed with SAM as primary method and the XSA as secondary method. In both cases constant from year to year selectivity and natural mortality were assumed.

Recent changes in biological situation of cod (e.g. declining growth rate, lack of older cods) require new parameterization of existing models or perhaps even new assess-ment methodology. The advantage of CAGEAN model is that it may be easily imple-mented in a spreadsheet, and its structural equations may be modified or new implemented to simulate processes observed (test assumptions) in the cod stock. Thus, the CAGEAN approach was applied to:

a ) model selectivity as dependent on weight; b ) model natural mortality as dependent on weight.


The CAGEAN model is an integrated, age-structured approach in which fishing mor-tality F is separated into age and year effects Fa,y = saFbary, where s is age-dependent selectivity and FBAR is year effect of F. Other equations are the same as in traditional VPA i.e. exponential decay of year-class numbers, Baranov catch equation. The model was fitted by minimization of Sum of Squared differences, SS, between observed and modelled catch in numbers and indices of stock size (log scale).

2,,

,

2

,,,1990 ]ln)[ln()ln(ln),,,,( yaya

yaa

yayaya UNqCobsCqRNFbarsSS −+−= ∑∑ λ

where C is catch in numbers, U is index of stock size (survey and/or commercial cpue), λ is weight of information. The model was fitted to data from 1990–2014 and for index of stock size the estimates from two BITS surveys (1st and 4th quarter) and Danish Commercial Fleet were used. Variables/parameters estimated within the model were vectors of initial stock numbers, N1990, recruitment in 1990–2013, R, yearly F effect, selectivity, and catchability, q.

The following options were considered and implemented in CAGEAN approach:

1 ) OptionStandard: Standard approach, i.e. selectivity and natural mortality constant from year to year;

2 ) OptionSelectivity: Selectivity related to weight-at-age (from 2007 onwards, linear relation assumed);

3 ) OptionM: Natural mortality increasing with declining weight (from 2007 onwards, hyperbolical relation assumed);

4 ) OptionSelectivity & M: Selectivity related to weight, natural mortality in-creasing with declining weight.

Parameters of selectivity and M dependence on weight were estimated within the model.

Results for standard approach are presented in Figure 1a–1b. Generally, SSB estimated with CAGEAN shows similar estimates to SSB obtained with SAM in 2013 assessment. Retrospective pattern is somewhat better in recent three years but in previous years shows similar variation as in case of SAM assessment. Catch residuals show marked trends in 2000–2007 (Figure 1b). Inclusion or exclusion of Danish commercial fleet did not have bigger effect on the results.

Implementation of the weight-dependent selectivity did not improve the model fit in terms of residuals distribution or retrospective pattern (Figure 2).

Including weight-dependent natural mortality into the model, markedly improved both retrospective pattern and distribution of catch residuals (Figures 3a–3b). How-ever, the model fitted very high values for M at ages 6 and 7 (Figure 3c), high even in light of expected marked increase of M due to poor condition and increasing parasitic infection of cod.

The analysis under option 4 did not perform better than the analysis under option 3.

References

Deriso, R.B., Quinn, T.J.,II, and Neal, P.R. 1985. Catch-at-age analysis with auxiliary information. Can. J. Fish. Aquat. Sci. 42: 815–824.


Figure 1a. Biomass estimates and retrospective analysis for CAGEAN with constant selectivity and M. For comparison SAM biomass obtained in 2013 is presented.

Figure 1b. Residuals for CAGEAN with constant selectivity and M.

Figure 2. Retrospective analysis for CAGEAN (SSB and F) with selectivity dependent on weight and constant M.


Figure 3a. Retrospective analysis (SSB and F) for CAGEAN with constant selectivity and weight dependent M.

Figure 3b. Residuals for CAGEAN with constant selectivity and weight dependent M.

Figure 3c. The dynamics of M in time as fitted in option 3 (OptionM).

0

0.5

1

1.5

2

2006 2008 2010 2012 2014

M

2

3

4

5

6

7


Can we and should we allow for time varying catchabilities in SAM by Margit Eero (DTU Aqua, Denmark) and Anders Nielsen (DTU Aqua, Denmark)

Observations of catch per unit of effort that used for tuning the assessment are related to stock size through catchability. Catchability is usually assumed to be constant with time. There are good reasons for doing so, as the time-series of surveys and other tun-ing indices are aimed at being consistent and standardized accordingly. However, the assumption of constant catchability in time may be invalid in situations where there are pronounced changes in size of the fish at-age, as in the age-based model (SAM, in the case of EB cod) is estimating catchabilities by age. If the size of fish at a given age has changed over time, there are reasons to believe that the catchability of fish at given age has changed as well. This may be the case for the Eastern Baltic cod, where reduc-tion in condition and possibly also in mean weight/length-at-age (conditional of age interpretation) has occurred.

Thus, SAM model was modified to include deviance to the catchability parameter that is allowed to either increase or decrease with time. The possibility for time-varying catchability was implemented as Random Walk approach, which is consistent with the rest of the model and allows detecting trends or changes from one level to another.

The results showed large increase in catchability in second half of 2000s for all ages for both Q1 and Q4 survey time-series and a decline again in recent years for Q1 (Figure 1). It should be noted, that the catchability was estimated to have increased by up to factor 5 in some cases, which can be considered unrealistic. Further, the catchabilities were estimated with large confidence intervals. This subsequently increased the un-certainty in the assessment results.

In conclusion, technically it is possible to implement time varying catchability in SAM. However, this option should be carefully considered before implemented as the impact on the assessment can be substantial. It should be kept in mind that in case of the EB cod, the potential catchability at-age issues are interlinked to inconsistencies in age readings. Thus, issues with age reading should be solved first. In general, ensuring consistency and standardization of input data should be preferred, rather than trying to fix for inconsistencies in input data in the assessment model.


Figure 1. Estimated catchability by age (columns) for BITS Q1 (upper panel) and BITS Q4 (middle panel) surveys and commercial tuning fleet (lower panel), when allowing for time-varying catcha-bility in SAM model.

Variations in cod growth: potential explanations by Michele Casini (SLU-Aqua, Sweden)

The mean body size (weight-at-age, length-at-age and condition) of the Eastern Baltic cod has decreased from the early 1990s in all the SDs of the central Baltic Sea (SDs 25–28), as shown by time-series of BITS data.

Preliminary analyses covering the whole central Baltic Sea (SDs 25–28) have shown that the changes in cod mean body size are mainly correlated to the changes in the area with anoxic conditions (oxygen concentration <2 ml/l), where the cod are considered not to reside. Density-dependence (cod abundance) and food limitation (prey abun-dance) were also significantly correlated to cod mean body size, confirming previous investigations (Eero et al., 2012), although these correlations were much weaker than the correlation with hypoxic areas. The strong statistical relationship between cod body size and hypoxic areas can be explained by different mechanisms, not mutually exclu-sive, such as increased density-dependence (same or higher amount of fish concen-trated in a more restricted area, increasing competition), decrease in benthic food, reallocation of cods into the pelagic water mass, and direct physiological effects.

Feeding basics for Eastern Baltic (ICES SD 25) cod at 30 cm to 40 cm length: Then and Now by Stefan Neuenfeldt & Niels Gerner Andersen (DTU Aqua, Denmark)

Cod in ICES Subdivision 25 have shown a considerable decrease in weight-at-length since 2007. We used newly available data from an EU financed stomach sampling scheme to investigate, if cod between 30 cm and 40 cm total length consuming less food nowadays, and if yes, the difference a possible cause for stunned growth. Using first a stochastic stomach content model, we found that average meal intensity (number of meal per day if searching for food) increased, but that average daily food consumption decreased by about 35%. The ratio of fish compared to benthos in the stomachs de-creased since 2009, but is on the same level as in the 1980s, when there was no poor condition observed in cod of the investigated size group. Second, we applied a bio-energetic model in order to investigate, if the cod between 30 cm and 40 cm total length consumed enough energy to support somatic growth. The alternative estimate of daily


consumption was considerably lower than the one derived by the stochastic mode, im-plying that the assumption of lognormally distributed meal sizes in the stochastic model has probably been misleading. Daily consumption, estimated based on food in-take of benthos and fish with different energy densities, ranged in the new collected stomachs between 10.7 kJ/day in 2012, and 18.6 kJ/d in 2008. These values are in line with literature values, but at the lower end of consumption rates supporting somatic growth. Accounting for the food conversion, and cost of activity, the excess energy was about 20%, i.e. the consumed energy was ca. 20% than the estimated standard meta-bolic rate. This energy excess has to be distributed over somatic growth, and matura-tion, and is possibly compromised by the increasing degree of infection with parasites. The results will be further investigated, including all available data, within the frame of ICES SGSPATIAL and the DEMO2 workshop. A possible inclusion of these findings on a more general level into multispecies stock assessment will be discussed at WGSAM.

Occurrence of seal associated parasites in cod from the Baltic Sea, SD25 by Jane Behrens (DTU Aqua, Denmark) & Kurt Buchmann (Copenhagen University, Denmark)

Grey seals have, except for few short occurrences, been presented in small numbers in the Baltic Sea. During recent years however, they have recovered in numbers, currently reaching a high of 40 000 individuals, including a colony establish a decade ago east of Bornholm by Christiansø (SD25), now counting more than 400 individuals. Seals act as final host for the parasites cod worm (Pseudoterranova decipiens) and liver worm (Con-tracaecum osculatum), while crustaceans/polychaetes and cod are first and second transport hosts, respectively. Due to the large numbers of seals, infection of cod in this area was possible and prompted field investigation between 2011 and 2014. We here provide evidence of increasing infestation (prevalence and intensity) during this pe-riod, also when comparing to the early 1980s where Baltic seal numbers were low. More specifically, cod worm prevalence was 2% (1–4 worms per fish) in 2011, as com-pared to nil in 1982/1983. Prevalence had increased to 29% and intensity to 5 in 2013/2014, with both prevalence and intensity being significantly higher in cod ≥50 cm and with a significant negative correlation between infection intensity and condition factor. Liver worms were present in all size ranges except the smallest in 1982/1983, mean prevalence being 22%. Intensity was however low with on average four worms. In 2012, prevalence was 55% and intensity 20. Notably, opposite to expectations inten-sity was lower in 70–80 cm cod as compared to 60–70 cm cod, suggesting increased mortality of the largest, most heavily infested individuals. In 2013/2014 all investigated livers had worms (i.e. 100% prevalence) with up to 320 worms per liver, small livers with many parasites being haemorrhagic. Mean condition factor for all fish in 2013/2014 (0.7) was significantly lower than for fish from the same area in 1982/1983 (0.82–0.95). There are also direct effects of seals; an adult grey seal eats 4.4 kg fish per day, and assuming that the 400 individuals by Christiansø eat solely cod, ‘worst case scenario’ will be a yearly cod consumption of 642 t in SD25. In summary, there has been a marked increase of infection levels from 1982 to 2014 for cod worm and liver worm and these infections clearly reflect the high seal population east of Bornholm, which in itself may have effects on the Baltic cod stock. There are indications for worm effects on condition factor, physiology, food intake and liver integrity in cod and par-asite infection is likely part of the explanation of under-nourished cod east of Born-holm. From field data it nevertheless extremely difficult to disentangle effects of e.g. food abundance/quality and abiotic factors (temperature and oxygen) from effects of parasite burden, why the issues relating to parasite infestation should be investigated


under controlled laboratory conditions, before any firm conclusions on effects on con-dition and mortality are drawn.

References

Buchmann and Kania. 2012.

HELCOM. 2013.

Galitus and Olsen. 2014.

Harder et al. 2014.

Mehrdana et al. 2014.

Effects of parasitic infection on cod condition and natural mortality by Jan Horbowy, Magdalena Podolska & Katarzyna Nadolna (National Marine Fisheries Research Institute, Poland)

Samples of cod for parasitic infection were collected in 2011–2013 in the Polish waters in the southern Baltic. The presence of Anisakis simplex and Contracaecum osculatum in fish liver was recorded and number of parasites were counted. In addition, standard biological parameters were recorded.

For statistical analysis of the data generalized linear models (GLM) were used.

The Fulton Condition Factor, FCF, was significantly dependent on infection (infected or not) and number of parasites. Fact of being infected reduced FCF by ca. 2% and each 35 parasites reduced FCF by additional 1% (the largest number of nematodes observed in the liver was close to 400; in such a case FCF is lower than for non-infected fish by 14%).

Prevalence and intensity of infection increased significantly in considered years and the highest levels were at Bornholm Basin. Both prevalence and intensity increased with length but at length of over 60 cm started to decline (parabolic shape of the de-pendence with significant quadratic term). This decline may suggest that fish at higher length undergo higher natural mortality than non-infected cod.

Discard rates of Eastern Baltic cod in the German trawl fisheries by Uwe Krumme & Daniel Step-puttis (Thünen Institute of Baltic Sea Fisheries, Germany)

Discard estimates are a central element in ICES stock assessments for demersal fish. Discard rates of Eastern Baltic cod reported by Member States to ICES and WGBFAS have not raised major concerns although there was evidence of increased discard rates in the recent past. Personal communication with German fishermen suggests that dis-card rates in 2014 partly exceeded 50%, which is much higher than the “usual” 10–20%.

Therefore, we analysed the original discard data of the German DCF at-sea observer and self-sampling programme in the Baltic Sea from 2009 to 2014. For any given haul, the discard rate was calculated as: raised discard weight /(landings weight + raised discard weight). In addition, between-year changes in the frequency distribution of discard ratios were explored. The relative frequency of discard events was determined in discard classes of 5% for each year from 2009–2014.

Discard ratios of Eastern Baltic cod from the German self-sampling and at-sea observer programme were very similar from 2009–2012 (approximately 10%). In 2013, discard ratios increased to 22%. In 2014, the self-sampling programme yielded a mean discard ratio of 24%, the only observer trip yielded 48% discards. This observer trip in 2014 was the first evidence that the high discard ratios reported by the fisheries really occur.


Hauls with high discard ratios were recorded in 2013 and 2014, both in the self-sam-pling and at-sea observer programme. The only at-sea observer trip in 2014, consisting of six sampled hauls, reported discard rates close to 50%. The greatest discard ratio from a self-sample in 2014 was near 45%.

This exercise showed that discard rates in the German trawl fisheries on Eastern Baltic cod increased enormously in the last two years. Hauls of observer trips in 2013 and 2014 witnessed high discard ratios near 50% that confirmed the anecdotal information from the fishermen. It would be extremely important to assess whether the pattern reflect discard patterns observed by other countries and to critically evaluate the con-sistency and reliability between the national discard sampling programmes. Evidence of staunching of the codend continues to be anecdotal but if it occurs on a regular basis, available discard ratios are likely underestimates, causing severe negative bias in the stock assessment. It is likely that the DCF discard estimates are rather minimum esti-mates and it may be advisable to carry out sensitivity analyses involving different lev-els of discards. Further information from the industry on discard rates may be required; the sources could be kept confidential as the amounts of illegal removals from the same stock in former years.

Selection experiments suggested that the introduction of BACOMA 120 in 2010 re-duced overall catches and drove the fishing pressure towards larger sizes (STECF, 2010). The most abundant length classes above 38 cm would be over-proportionally reduced in the catch when using BACOMA 120 mm so that the total landings per trip would be significantly reduced. Consequently, fishermen would have to increase the number of trips to catch their quota. This would result in overall increased discards. We will have a closer look into the potential effect of fishing gear-induced changes in selectivity on landings and discard patterns due to the introduction of BACOMA 120. Since no such discards patterns were detected in Western Baltic cod despite the use of BACOMA 120, the effect of different changes in environmental conditions on cod will also be investigated.

Fishing effort and Discard trends 2009–2013 in the Eastern Baltic Sea, by Joakim Hjelm (SLU-Aqua, Sweden)

Trends in effort

The effort (KwDays) showed a hump shaped pattern with highest effort in 2012. To explore the difference in effort in the western and eastern of Subdivision 25 (SD25), the discard rates were divided in east and west. The pattern in effort is not so clear when exploring effort in the eastern and western SD25, but it is clear that the effort is higher in the western part of SD25 compared to the eastern part.

Trends in discards

The number of samplings occasions per year has generally decreased since 2009. The reason why is unclear but for some countries it’s related to difficulties to get permission to sample on board. The discard sampling rate is not correlated to effort.

The discard rates per haul were generally higher for Sweden compared to the other countries, but there is strong positive trend over time irrespectively of country. To ex-plore if there was a difference in discard rates in the west and east of SD25, the discard rates were divided in east and west. The results suggested that discard rates were higher in west of SD25 compared to east SD25, but still a positive trend irrespectively


of area. The analysis also revealed that Denmark has only sampled the eastern part of SD25.

The discard rates by haul has generally increased over time as well as the standard deviation (variation discard rate) suggesting that there are more sampling occasions with really high discard rates. Standard deviation in discard rates per area suggests that the standard deviation is higher in the western part of SD25 compared to the east-ern part, but there is no trend over time.

It is also apparent, from the collected discard data that Poland has been sampling the pelagic fishery and a suggestion would be to compile that information and analyse its effect on the cod stock.

Conclusions

• Fishing effort is not uniformly distributed suggesting that… • Discard rates vary between countries and area • Discards are increasing • A positive trend in standard deviation

Recruitment of eastern Baltic cod, acting processes and changes during most recent ten years by Fritz Köster (DTU Aqua, Denmark)

Our state of knowledge of processes affecting recruitment and recent changes observed in the central Baltic system affecting reproductive success of the Eastern Baltic cod were reviewed, based on results from hydrographic, ichthyoplankton and spawning–stock surveys conducted by DTU Aqua, GEOMAR, NMFRI, BIOR, TI-OSF, Uni Kiel and Uni Hamburg.

First order controlling factors of cod recruitment were identified by a series of EU framework projects (CORE 1994–1997, STORE 1998–2003 and BECAUSE 2004–2007) as 1) loss of two out of three spawning areas in the 1980s caused by lack of major Baltic inflows and eutrophication, i.e. reduced salinity and oxygen, with the result that suc-cessful spawning is largely confined to the Bornholm Basin (e.g. Köster et al., 2009) and 2) reduced prey availability for first-feeding larvae, i.e. decline in marine copepods during the 1990s, caused by reduced salinity and predation by the increasing sprat population (Hinrichsen et al., 2002; Möllmann et al., 2005).

Second order regulating factors were identified as 3) egg predation by sprat and her-ring, depending on salinity/oxygen and timing of spawning defining vertical and hor-izontal overlap between predator and prey, respectively (Köster et al., 2005), 4) prey availability for sexually maturing and adult cod affecting egg production (Kraus et al., 2002) and 5) cod cannibalism, depending on transport of juveniles, temperature and oxygen defining horizontal overlap to adults as well as abundance of alternative prey (e.g. Neuenfeldt and Köster, 2000; Uzars and Plikshs, 2000).

Above factors cannot explain the increased reproductive success of the cod stock from 2007–2013, as the period is characterized by a continued absence of large-scale Baltic inflows and prevailing anoxic conditions in the bottom water of the deep Baltic basins (Lehman et al., 2014; Plikshs et al., 2014), expected to impact negatively on egg and larval survival through processes 1–2) and partly 3). However, it was also realized that a reduction of the sprat population in Subdivision 25 from mid-1990s to early 2000s should have a positive effect on processes 2) and 3), but potentially a negative effect on processes 4) and 5).


Compiling evidence from hydrographic and ichthyplankton surveys from 2003–2014 suggest the following processes being responsible for an increased reproductive suc-cess: 1) minor inflows in the Bornholm Basin (Lehmann et al., 2014) enhancing egg sur-vival, 2) utilization of the Arkona Basin for spawning by the eastern stock (Hüssy, 2011), 3) an extended spawning season (April to November) with high larval survival in different months (spreading risk), 4) improved nutritional condition/growth of lar-vae in certain years and areas (Huwer et al., 2011 and 2014) and 5) a decline in cod egg predation by sprat and herring (Neumann et al., 2014). Process 2) needs quantification, e.g. estimates of egg production and survival in the Arkona Basin as well as destination of recruits, and process 4) needs validation, while process 5) is currently quantified for 2004–2008 compared with earlier period.

Three out of four ichthyoplankton surveys conducted in 2014 yielded far below aver-age (1986–2013) larval abundances, which together with a statistically significant rela-tionship between larval abundance and recruitment-at-age 2 (r2 = 0.61), may indicate declining recruitment, potentially due to density-dependent processes (poor condition and growth) affecting fecundity and offspring quality, including egg buoyancy and viability of larvae. To test this hypothesis, requires i) to prepare the egg production estimates from ichthyoplankton surveys in 2011–2014 and ii) to conduct a study relat-ing growth and condition with fecundity and viability of offspring. While the former analysis can be done until the benchmark for the stock in 2015, the latter requires an entire seasonal sampling and should be planned for 2015. In addition, the importance of stock structure, i.e. the size and age composition in the stock, for egg survival will be further investigated (Hinrichsen et al., submitted).

Finally, it is suggested to test whether the egg production method can be used to de-liver a fishery-independent estimate of spawning–stock size as suggested by Kraus et al. (2012).

References

Hinrichsen, H.-H., Möllmann, C., Voss, R., Köster, F.W., and Kornilovs, G. 2002b. Biophysical modelling of larval Baltic cod (Gadus morhua L) growth and survival. Canadian Journal of Fisheries and Aquatic Sciences, 59: 1858–1873.

Hinrichsen, H.-H., von Dewitz, B., Dierking, J., Haslob, H., Makarchouk, A., Petereit, C. and Voss, R. (submitted). Stock-structure dependent spatial extent of the Eastern Baltic cod spawning environment.

Hüssy, K. 2011. Review of western Baltic cod (Gadus morhua) recruitment dynamics. – ICES J. Mar. Sci. 68: 1459–1471.

Huwer, B., Clemmesen, C., Grønkjær, P. and Köster, F.W. 2011. Vertical distribution and growth performance of Baltic cod larvae - Field evidence for starvation-induced recruitment regu-lation during the larval stage? Progr. Oceanogr. 91: 382–396.

Huwer, B., Hinrichsen, H.H., Böttcher, U., Voss, R. and Köster, F.W. 2014. Characteristics of ju-venile survivors reveal spatio-temporal differences in early life stage survival of Baltic cod. Mar. Ecol. Progr. Ser. 511: 165–180.

Köster, F.W., Möllmann, C., Hinrichsen, H.-H., Tomkiewicz, J., Wieland, K., Kraus, G., Voss, R., MacKenzie, B.R., Schnack, D., Makarchouk, A., Plikshs, M. and Beyer J.E. 2005. Baltic cod recruitment–the impact of climate and species interaction. ICES J. Mar. Sci., 62: 1408–1425.

Köster, F.W., M. Vinther, B.R. MacKenzie, M. Eero, and Plikshs, M. 2009. Environmental effects on recruitment and implications for biological reference points of eastern Baltic cod (Gadus morhua). J. Northw. Atl. Fish. Sci., 41: 205–220.


Kraus, N., Tomkiewicz, J., and Köster, F.W. 2002. Egg production of Baltic cod in relation to variable sex ratio, maturity and fecundity. Can. J. Fish. Aquat. Sci. 59: 1908–1920.

Kraus, G., Hinrichsen, H.-H., Voss, R., Teschner, E., Tomkiewicz, J. and Köster, F.W. 2012. Ro-bustness of egg production methods as a fishery independent alternative to assess the East-ern Baltic cod stock (Gadus morhua callarias L.). Fish. Res. 117–118: 75–85.

Lehmann, A., Hinrichsen, H. H., Getzlaff, K. and Myrberg, K. 2014. Quantifying the heterogene-ity of hypoxic and anoxic areas in the Baltic Sea by a simplified coupled hydrodynamic-oxygen consumption model approach J. Mar. Syst. 134: 20–28.

Möllmann, C., Kornilovs, G., Fetter, M. and Köster, F. W. 2005. Climate, zooplankton and pelagic fish growth in the Central Baltic Sea. ICES J. Mar. Sci., 62: 1270–1280.

Neuenfeldt, S., and Köster, F.W. 2000. Trophodynamic control on recruitment success in Baltic cod: the influence of cannibalism. ICES Journal of Marine Science, 57: 300–309.

Neumann, V., Köster, F.W., Schaber, M., and Eero, M. 2014.Recovery in eastern Baltic cod: is increased recruitment caused by decreased predation on early life stages? ICES Journal of Marine Science, 71: 1382–1392.

Plikshs, M. 2014. Impact of environmental variability on year class strength of Baltic cod (Gadus morhua callarias L.). Doctoral Thesis. University of Latvia, 49 pp.

Uzars, D. and Plikshs, M. 2000. Cod (Gadus morhua callarias L.) cannibalism in the Central Baltic: interannual variability and influence of recruitment abundance and distribution. ICES J. Mar. Sci., 57: 324–329.


Annex 4: Recommendations

RECOMMENDATION ADRESSED TO

1. To establish a workshop under WGBIOP to look into age estimating of Baltic cod

WGBIOP (see proposal)

2. To review the presented data on WKSIBCA on age quality. To detemine if present age data can be used in stock assessment. Two reviewers with the knowledge of; age readings, stock assessment and data quality assurance should be contacted

ICES Secretariat

3. Spatial abundance information on grey seal population in the Baltic Sea, with consumption information (species, amount and size). Information on target distance.

HELCOM seal group

4. Time-series on benthic data in the Baltic? BEWG

5.


Workshop on Age Estimation of Baltic Cod (WKEABCod)

The Workshop on Age Estimation of Baltic Cod (WKAEBCod), chaired by Karin Hüssy, Denmark, will be established and will meet in XX, XXX, XXX 2015 to:

a ) Review existing methods to derive age information; b ) Test the applicability of different methods to the eastern Baltic cod case; c ) Design a protocol for future proceedings.

WKAEBCod will report by DATE for the attention of the ACOM and SCICOM.

Supporting information

Priority This work is considered with high priority to support decision on age data for the two Baltic cod stocks assessmenst.

Scientific justification

Term of Reference a) The aim of the workshop is to review existing methods of deriving age compositions based on other approaches than traditional age reading, test the applicability of these approaches and to design a protocol for optimal procedures of Eastern Baltic cod. Term of Reference b) The trace element composition of otoliths has for some years served as tool to infer stock identity and migration patterns in anadromous fish species. Recently, targeted experiments have suggested a close copling between elemental concentrations and specific life-history events. Longitudinal analysis of elemental concentrations (from nuclues to the edge of otolith) will therefore provide information of fish migration, habitat occupation, growth and spawning periodicity. Other methods to derive growth estimates and age structures are based on tag–recapture programmes with concurrent marking of otolith and fish and length–frequency analysis. The usefulness of these approaches for the easter Baltic cod stock will also be explored.

Resource requirements

XX

Participants Expert on age estimation. It is desireable that an external expert on age estimation/ validation and the use of ages information in stock assessmet attend the meething.

Secretariat facilities None.

Financial No financial implications.

Linkages to advisory committees

ACOM, WGBFAS, SSGIEOM, WGPATA, WGBIOP.

Linkages to other committees or groups

SCICOM

Linkages to other organizations

None.

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