Eastern Baltic cod in distress: biological changes and challenges for stock assessment

Eero, Margit; Hjelm, Joakim; Behrens, Jane; Buchmann, Kurt; Cardinale, Massimiliano; Casini, Michèle; Gasyukov, Pavel; Holmgren, Noél; Horbowy, Jan; Hüssy, Karin; Kirkegaard, Eskild; Kornilovs, Georgs; Krumme, Uwe; Köster, Friedrich; Oeberst, Rainer; Plikshs, Maris; Radtke, Krzysztof; Raid, Tiit; Schmidt, Jörn O.; Tomczak, Maciej; Vinther, Morten; Zimmermann, Christopher; Storr-Paulsen, Marie

doi:10.1093/icesjms/fsv109

Cited by 131 publications

(133 citation statements)

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“…The finding that smaller cod remain uninfected or merely lightly infected until they reach a TL of 30 cm may have implications for the ecology of this fish species in the eastern Baltic Sea. During the last decade, a high survival rate and increasing numbers have been recorded for small cod (TL < 30 cm) whereas the population of larger cod (TL > 38 cm) has exhibited a drastic and unexpected decline (Eero et al 2015). Direct predation on cod by seals has been suggested to have caused a reduction in Canadian fish stocks (Chouinard et al 2005, Swain & Chouinard 2008, Swain & Benoit 2015, and predation may play a role for the Baltic cod as well.…”

Section: Discussionmentioning

confidence: 99%

“…These pinnipeds are final hosts for both C. osculatum and P. decipiens (Marcogliese et al 1996, McClelland 2002, Mattiucci & Nascetti 2008, Skrzypczak et al 2014, Lunneryd et al 2015. Eero et al (2015) suggested that heavy C. osculatum liver infections may partly explain the distress of the eastern population of Baltic cod, where juveniles (< 30 cm total length [TL]) perform successfully but larger cod (> 38 cm TL) show increased mortality. However, so far no parasitological studies on the infection of juvenile stages of Baltic cod are available, and it is therefore important to address this question.…”

Section: Introductionmentioning

confidence: 99%

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Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

Zuo

Huwer²,

Bahlool

et al. 2016

Dis. Aquat. Org.

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A significant increase in the infection level of Baltic cod Gadus morhua with the anisakid nematode larvae Contracaecum osculatum and Pseudoterranova decipiens has been recorded during recent years due to the expanding local population of grey seals Halichoerus grypus, which act as final hosts for these parasites. Here, we report from an investigation of 368 cod (total length [TL] 6−49 cm; caught in ICES Subdivision 25) that the infection level of juvenile cod (TL 6−30 cm) with larvae of C. osculatum and P. decipiens is absent or very low, whereas it increases drastically in larger cod (TL 31−48 cm). A third nematode Hysterothylacium aduncum was rarely found. The study indicates that the prey animals for large cod act as transport hosts for the parasite larvae. Analyses of stomach contents of cod caught in the same area (2007−2014) showed that small benthic organisms (including polychaetes Harmothoë sarsi) are preferred food items by small cod, the isopod Saduria entomon is taken by all size classes, and sprat Sprattus sprattus are common prey items for cod larger than 30 cm. Parasitological investigations (microscopic and molecular analyses) of H. sarsi (100 specimens) and S. entomon (40 specimens) did not reveal infection in these invertebrates, but 11.6% of sprat (265 specimens examined) was shown to be infected with 1−8 C. osculatum third stage larvae per fish. Analyses of sprat stomach contents confirmed that copepods and cladocerans are the main food items of sprat. These observations suggest that the C. osculatum life cycle in the Baltic Sea includes grey seals as final hosts, sprat as the first transport host and cod as second transport host. It may be speculated that sprat obtain infection by feeding on copepods and/or cladocerans, which could serve as the first intermediate hosts. One cannot exclude the possibility that the size-dependent C. osculatum infection of cod may contribute (indirectly or directly) to the differential mortality of larger cod (> 38 cm) compared to smaller cod (< 30 cm) recently recorded in the Baltic cod population.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

Zuo

Huwer²,

Bahlool

et al. 2016

Dis. Aquat. Org.

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“…F MSY was estimated as the fishing mortality, with a given fishing pattern, that gives the longterm maximum yield. The definition of stock targets turned difficult in 2014, due to a regime shift in the Baltic ecosystem (Möllmann et al, 2009) in combination with input data quality concerns (Eero et al, 2015). Because of that, advice on harvest opportunities is recently based on a combined biomass index from two surveys, used as proxy for spawning stock biomass (ICES, 2015b).…”

Section: Introductionmentioning

confidence: 99%

Ecological-Economic Fisheries Management Advice—Quantification of Potential Benefits for the Case of the Eastern Baltic COD Fishery

Voss¹,

Quaas²,

Stoeven³

et al. 2017

Front. Mar. Sci.

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Fishing is a social and economic activity, and consequently socio-economic considerations are important for resource management. While this is acknowledged in the theory of Ecosystem-Based Management (EBM) and its sector-specific development Ecosystem-Based Fisheries Management (EBFM), currently applied fishery management objectives often ignore economic considerations. Year-to-year management, however, implicitly responds to short-term economic interests, and consequently, regularly resorts to tactical short-term rather than strategic long-term decisions. The aim of this article is to introduce a new way of estimating management advice referred to as an "ecologically-constrained Maximum Economic Yield" (eMEY) strategy, which takes into account ecological criteria as well as short-to medium-term economic costs. We further illustrate what net cost reductions per year are possible applying the eMEY strategy compared with the existing way of setting total allowable catches (TACs). The eMEY approach aims at maximizing the economic benefits for the fishery as well as society (consumers), while safeguarding precautionary stock sizes. Using an age-structured optimization model parameterized for the Eastern Baltic cod case study, we find that application of eMEY advice results in more stability in catch advice. Quantification and visualization of the costs of deviating from eMEY advice offers a transparent basis for evaluating decision-making outcomes. The costs of overfishing are mainly borne by the commercial fishery, while fishing less than optimal is particularly costly for the processing industry and consumers. To foster the uptake of our eMEY approach in current advice given by the International Council for the Exploration of the Sea (ICES) and the EU fishery management system, we suggest an easy-to-implement scheme of providing integrated advice, also accounting for economic considerations.

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“…An example of this was the case of the Eastern Baltic cod stock in 2014 when an ICES assessment failed to provide adequate feedback on the present stock of cod (cf. Eero et al 2015 ). The uncertainty challenge has therefore been and is still high on the agenda of both scientists and politicians, particularly because the TAC system in general has not been able to resolve the problems of overfi shing and resource depletion Villasante et al 2011).…”

Section: Uncertainty As a Key Challengementioning

confidence: 99%

“…Epistemic uncertainty on the other hand stems from a lack of knowledge of dynamics or phenomena within the fi eld. Although extended data gathering and research might decrease both aleatory and epistemic uncertainties, with dynamic systems such as marine environments, uncertainty often prevails and can even increase as a consequence of further research as it happened in 2014 with the failure of ICES' Eastern Baltic cod assessment (Eero et al 2015 ).…”

Section: Dealing With Uncertainty In Assessment-management Interactionsmentioning

confidence: 99%

Fisheries: A Case Study of Baltic Sea Environmental Governance

Sellke

Dreyer

Linke

2016

MARE Publication Series

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This chapter analyses environmental governance through a case study of fi sheries management in the Baltic Sea and investigates the problems, challenges and opportunities for improving sustainability in this sector. Fisheries management in the Baltic Sea is politically and culturally complex, institutionally fragmented and confronted with serious environmental problems, such as recent shifts in cod stocks. The central challenge is therefore to establish a regionally based, ecologically sustainable and socio-economically viable fi sheries governance system for the Baltic Sea. Our analysis is focused on how past and current reform processes of fi sheries management in the Baltic Sea have been able to move away from the pathdependent and highly ineffective management system linked to EU's Common Fisheries Policy towards new regional arrangements and procedures that address environmental problems in the Baltic on par with the social and economic challenges. We fi rst describe existing governance structures for fi sheries management in the Baltic Sea and their role in procedures of knowledge production, policy advice and decision-making. We then examine how the different governance actors (i.e. scientists, stakeholders, policymakers) address key issues such as the framing of the 'overfi shing problem', the handling of uncertainty in the interactions of risk assessment and risk management and the role of stakeholder participation and communication. The chapter concludes by emphasising the need for an improved understanding of how scientifi c developments and connected uncertainty problems, policy constraints and stakeholder perspectives can be brought together for improving the biological, ecological and socio-economic sustainability of Baltic Sea fi sheries governance.

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Eastern Baltic cod in distress: biological changes and challenges for stock assessment

Cited by 131 publications

References 46 publications

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences

Ecological-Economic Fisheries Management Advice—Quantification of Potential Benefits for the Case of the Eastern Baltic COD Fishery

Fisheries: A Case Study of Baltic Sea Environmental Governance

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