Fish stocks composed of several populations are considered to have more stable productivity than stocks containing only one or few populations. This stability is attributed to complementary or independent dynamics among the populations within the stock—the so-called portfolio effect. Declines of populations within stocks that have delayed recovery potentially increase risk to productivity and local extinctions. Portfolio effects may be relevant in the Baltic Sea, where autumn-spawning herring was the dominant herring ecotype until the early/mid-20th century. The current fishery assessment and management in the area assumes that the abundance of autumn spawning herring has been negligible since the 1970s; the share of spring spawning herring has become dominant and is considered to be the only ecotype. Data from a multi-annual ichthyoplankton survey in the southern Baltic Sea (Bornholm Basin) during autumn 2002–2019 show that abundance and spatial distribution of the smallest larval stages have increased significantly. This pattern could be due to an increase in autumn spawners in the area. Genetic studies confirm that these larval herring are offspring from true autumn spawners. Preserving intraspecific diversity is critical for a species’ future abilities to adapt to and survive in changing environmental conditions. Thus, our results not only provide new insights to the temporal dynamics of herring ecotypes and challenge the current understanding of central Baltic herring stock processes in general, but are also important in the context of monitoring, assessment, and spatial management of herring in the Baltic Sea.

The management of the herring fishery in the Skagerrak-Kattegat and Western Baltic is challenging because of the complex dynamics of several herring populations with different migration patterns and population dynamics and a complex fleet structure fishing for herring. To address these complexities and policy issues related to management areas and EU borders, management has become increasingly complex and non-transparent. The Case Study (CS) explores how things could be simplified and rationalised by developing a Multi-Annual Management Plan (MAMP – previously referred to as Long-Term Management Plan (LTMP)) that could provide predictability and stability. Industry stakeholders from two Advisory Councils (the Pelagic and Baltic Sea ACs), representatives from management, from national governments and the EU, and scientists collaborated to improve stock management by developing a robust MAMP. A common understanding of relevant scientific and political issues is a prerequisite for the successful formulation and implementation of a MAMP. The CS focused on getting all relevant stakeholders involved and successfully engaged the European fishing industry through the ACs and, to some extent, the management bodies involved within the EU. The two ACs have only limited overlap in their membership. Until this CS came about, there was very little collaboration in providing advice on Western Baltic Spring Spawning (WBSS) herring management. With the opportunity to collectively formulate management objectives for the fishery, the two ACs, science partners and management representatives narrowed the gaps between stakeholders. In this chapter, we review the achievements of the project and analyse the effectiveness of the collaborative process and how it affected the individual endeavours of the scientific and stakeholder groups. The chapter describes the process of creating an arena where a management framework and procedures could be discussed by all involved so as to establish a communication platform for setting objectives, management clauses and evaluation criteria for the requested MAMP. We also reflect on the concept of the 'GAP Method' and how such science-management-stakeholder collaboration can contribute to overall fisheries governance.

Forage fish occupy a central position in marine food-webs worldwide by mediating the transfer of energy and organic matter from lower to higher trophic levels. The lesser sandeel (Ammodytes marinus) is one of the ecologically and economically most important forage fish species in the North-east Atlantic, acting as a key prey for predatory fish and sea birds, as well as supporting a large commercial fishery. In this case study, we investigate the underlying factors affecting recruitment and how these in turn affect productivity of the North Sea sandeel using long-term data and modelling. Our results demonstrate how sandeel productivity in the central North Sea (Dogger Bank) depends on a combination of external and internal regulatory factors, including fishing and climate effects, as well as density dependence and food availability of the preferred zooplankton prey (Calanus finmarchicus and Temora longicornis). Furthermore, our model scenarios suggest that while fishing largely contributed to the abrupt stock decline during the late 1990s and the following period of low biomass, a complete recovery of the stock to the highly productive levels of the early 1980s would only be possible through changes in the surrounding ecosystem, involving lower temperatures and improved feeding conditions. To that end, we stress the need for ecosystem-based management accounting for multiple internal and external factors occurring within the broader context of the ecosystem in which forage fish species, such as sandeel, play an important and integral part.

Application of environmental DNA (eDNA) analysis has attracted the attention of researchers, advisors and managers of living marine resources and biodiversity. The apparent simplicity and cost‐effectiveness of eDNA analysis make it highly attractive as species distributions can be revealed from water samples. Further, species‐specific analyses indicate that eDNA concentrations correlate with biomass and abundance, suggesting the possibility for quantitative applications estimating abundance and biomass of specific organisms in marine ecosystems, such as for stock assessment. However, the path from detecting occurrence of an organism to quantitative estimates is long and indirect, not least as eDNA concentration depends on several physical, chemical and biological factors which influence its production, persistence and transport in marine ecosystems. Here, we provide an overview of basic principles in relation to eDNA analysis with potential for marine fisheries application. We describe fundamental processes governing eDNA generation, breakdown and transport and summarize current uncertainties about these processes. We describe five major challenges in relation to application in fisheries assessment, where there is immediate need for knowledge building in marine systems, and point to apparent weaknesses of eDNA compared to established marine fisheries monitoring methods. We provide an overview of emerging applications of interest to fisheries management and point to recent technological advances, which could improve analysis efficiency. We advise precaution against exaggerating the present scope for application of eDNA analysis in fisheries monitoring, but also argue that with informed insights into strengths and limitations, eDNA analysis can become an integrated tool in fisheries assessment and management.

Forage fish populations support large scale fisheries and are key components of marine ecosystems across the world, linking secondary production to higher trophic levels. While climate-induced changes in the North Sea zooplankton community are described and documented in literature, the associated bottom-up effects and consequences for fisheries remain largely unidentified. We investigated the temporal development in forage fish productivity and the associated influence on fisheries yield of herring, sprat, Norway pout and sandeel in the North Sea. Using principal component analysis, we analysed 40 years of recruitment success and growth proxies to reveal changes in productivity and patterns of synchroneity across stocks (i.e. functional complementarity). The relationship between forage fish production and Calanus finmarchicus (an indicator of climate change) was also analysed. We used a population model to demonstrate how observed shifts in productivity affected total forage fish biomass and fisheries yield. The productivity of North Sea forage fish changed around 1993 from a higher average productivity to lower average productivity. During the higher productivity period, stocks displayed a covariance structure indicative of functional complementarity. Calanus finmarchicus was positively correlated to forage fish recruitment, however, for growth, the direction of the response differed between species and time periods. Maximum sustainable yield (MSY) and the associated fishing mortality (Fmsy) decreased by 33%–68% and 26%–64%, respectively, between the higher and lower productivity periods. Synthesis and applications. The results demonstrate that fisheries reference points for short-lived planktivorous species are highly dynamic and respond rapidly to changes in system productivity. Furthermore, from an ecosystem-based fisheries management perspective, a link between functional complementarity and productivity, indicates that ecosystem resilience may decline with productivity. Based on this, we advise that system productivity, perhaps monitored as forage fish growth, becomes an integral part of management reference points; in both single species and ecosystem contexts. However, to retain social license of biological advice when fish catch opportunities are reduced, it is crucial that shifts in productivity are thoroughly documented and made apparent to managers and stakeholders.

Fish and FisheriesVolume 19, Issue 3 p. 573-574 BOOK REVIEW Management Science in Fisheries Review by Lotte W. Clausen Head of Advisory Support, ICES, Copenhagen, GBP 95.00, USD 145.00. Lotte W. Clausen, Corresponding Author Lotte W. Clausen lotte.worsoe.clausen@ices.dk orcid.org/0000-0003-1503-6092 ICES, Copenhagen, DenmarkEmail: lotte.worsoe.clausen@ices.dkSearch for more papers by this author Lotte W. Clausen, Corresponding Author Lotte W. Clausen lotte.worsoe.clausen@ices.dk orcid.org/0000-0003-1503-6092 ICES, Copenhagen, DenmarkEmail: lotte.worsoe.clausen@ices.dkSearch for more papers by this author First published: 23 February 2018 https://doi.org/10.1111/faf.12274Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue3May 2018Pages 573-574 RelatedInformation

Despite its relatively small stock size and economic value, Western Baltic spring spawning herring (WBSS) is managed in a highly complex governance scheme, with demanding scientific challenges and an elaborate political process of resource allocation among fishing fleets. WBSS herring spawns in the western Baltic Sea, where it is exploited by several EU fishing fleets. It migrates into the Kattegat, Skagerrak and eastern North Sea areas, where it mixes with North Sea autumn spawning herring (NSAS), in an age and season ‐ dependent pattern with high variability, and where it is exploited by both EU and non ‐ EU fleets. For the two separate management areas, TACs are set at different times in the yearly TAC ‐ setting process, and this can result in conflicts over quota allocations to individual fleets. Industry stakeholders of two Regional Advisory Councils – the Pelagic and Baltic Sea RACs – and scientists involved in the FP7 JAKFISH project engaged in collaboration, aiming to improve stock management through joint development of a robust Long ‐ Term Management Plan. A common understanding of relevant scientific and political issues developed and used to conduct Management Strategies Evaluations in an interactive process.

Maximising the long term average catch of single stock fisheries as prescribed by the globally-legislated MSY objective is unlikely to ensure ecosystem, economic, social and governance sustainability unless an effort is made to explicitly include these considerations. We investigated how objectives to be maximised can be combined with sustainability constraints aiming specifically at one or more of these four sustainability pillars. The study was conducted as a three-year interactive process involving 290 participating science, industry, NGO and management representatives from six different European regions. Economic considerations and inclusive governance were generally preferred as the key objectives to be maximised in complex fisheries, recognising that ecosystem, social and governance constraints are also key aspects of sustainability in all regions. Relative preferences differed between regions and cases but were similar across a series of workshops, different levels of information provided and the form of elicitation methods used as long as major shifts in context or stakeholder composition did not occur. Maximising inclusiveness in governance, particularly the inclusiveness of affected stakeholders, was highly preferred by participants across the project. This suggests that advice incorporating flexibility in the interpretation of objectives to leave room for meaningful inclusiveness in decision-making processes is likely to be a prerequisite for stakeholder buy-in to management decisions.

The population structure of Atlantic herring (Clupea harengus) from 13 local, coastal and offshore areas of the North Sea, Skagerrak, Kattegat and western Baltic (northeast Atlantic) was studied using biological and environmental data from 1970-2015. The objective was to identify distinct populations by comparing variability in the temporal and spatial phenotypic characteristics and evaluate the potential for mixing of populations in time and space. The populations varied in biological characteristics such as mean vertebral counts (VS), growth and maturity ogives. Generalized additive models indicated temporally stable VS in the North Sea and western Baltic, whereas intra-annual temporal variation of VS occurred in other areas. High variability of VS within a population was not affected by environmental factors such as temperature and salinity. Consequently, seasonal VS variability can be explained by the presence or absence of herring populations as they migrate between areas. The three main populations identified in this paper correspond to the three managed stocks in this area: Norwegian spring spawners (NSS), western Baltic spring spawners (WBSS) and North Sea autumn spawners (NSAS). In addition, several local populations were identified in fjords or lakes along the coast, but our analyses could not detect direct mixing of local populations with the three main populations. Our results highlight the importance of recognizing herring dynamics and understanding the mixing of populations as a challenge for management of herring.

Chapter 23 Impacts of Climate Change on Pelagic Fish and Fisheries Barbara Muhling, Princeton University Program in Atmospheric and Oceanic Science, Forrestal Campus/Sayre Hall, Princeton, USA NOAA Geophysical Fluid Dynamics Laboratory, Princeton, USASearch for more papers by this authorMartin Lindegren, DTU AQUA, National Institute of Aquatic Resources, Centre for Ocean Life, Technical University of Denmark, Charlottenlund, DenmarkSearch for more papers by this authorLotte Worsøe Clausen, DTU AQUA, National Institute of Aquatic Resources, Section for Marine Living Resources, Technical University of Denmark, Charlottenlund, DenmarkSearch for more papers by this authorAlistair Hobday, CSIRO Oceans and Atmosphere Flagship, Hobart, AustraliaSearch for more papers by this authorPatrick Lehodey, Collecte Localisation Satellites (CLS), Ramonville Saint-Agne, FranceSearch for more papers by this author Barbara Muhling, Princeton University Program in Atmospheric and Oceanic Science, Forrestal Campus/Sayre Hall, Princeton, USA NOAA Geophysical Fluid Dynamics Laboratory, Princeton, USASearch for more papers by this authorMartin Lindegren, DTU AQUA, National Institute of Aquatic Resources, Centre for Ocean Life, Technical University of Denmark, Charlottenlund, DenmarkSearch for more papers by this authorLotte Worsøe Clausen, DTU AQUA, National Institute of Aquatic Resources, Section for Marine Living Resources, Technical University of Denmark, Charlottenlund, DenmarkSearch for more papers by this authorAlistair Hobday, CSIRO Oceans and Atmosphere Flagship, Hobart, AustraliaSearch for more papers by this authorPatrick Lehodey, Collecte Localisation Satellites (CLS), Ramonville Saint-Agne, FranceSearch for more papers by this author Book Editor(s):Bruce F. Phillips, Department of Environment and Agriculture, Curtin University AustraliaSearch for more papers by this authorMónica Pérez-Ramírez, Centro de Investigaciones Biológicas del Noroeste S.C.-CONACYT, MexicoSearch for more papers by this author First published: 20 September 2017 https://doi.org/10.1002/9781119154051.ch23Citations: 2 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Summary Pelagic fishes support some of the highest yield fisheries worldwide, but the impacts of climate change on the distribution, recruitment and sustainability of these species remain largely uncertain. Several projected changes to the world's oceans are highly relevant to pelagic fishes, including warming, changes in circulation patterns and altered pelagic foodwebs. These are likely to drive changes in species distributions, spawning and migration behaviors, early life survival and recruitment. In many marine ecosystems, climate change will result in environmental conditions which are beyond the range of variability experienced since the advent of industrialized fishing. In recent years, modeling studies have begun to project potential impacts of climate change on pelagic fishes through a variety of methods, ranging from simple correlative models to more complex mechanistic models. As global climate models improve and computing power increases, bounds of uncertainty around these projections will decrease. However some significant gaps remain in our understanding of basic mechanistic drivers of distribution and population dynamics of many species. Climate change will also influence the availability of target species to fishing fleets as fish distributions shift, as well as sustainable harvest rates as stock dynamics change. Management strategies will likely need to be more adaptive, flexible and environmentally explicit in the future if populations are to be sustainably managed, and the communities and livelihoods that they support are to be preserved. This chapter reviews the current state of knowledge regarding potential climate change impacts on pelagic fish and fisheries, including biogeochemical drivers, ecological responses and economic consequences. Citing Literature Climate Change Impacts on Fisheries and Aquaculture: A Global Analysis, I RelatedInformation

from practical reconcile mismatches Recent advances in the application of stock identification methods have revealed inconsistencies between the spatial structure of biological populations and the definition of stock units used in assessment and management. From a fisheries management perspective, stocks are typically assumed to be discrete units with homogeneous vital rates that can be exploited independently of each other. However, the unit stock assumption is often violated leading to spatial mismatches that can bias stock assessment and impede sustainable fisheries management. The primary ecological concern is the potential for overexploitation of unique spawning components, which can lead to loss of productivity and reduced biodiversity along with destabilization of local and regional stock dynamics. Furthermore, ignoring complex population structure and stock connectivity can lead to misperception of the magnitude of fish productivity, which can translate to suboptimal utilization of the resource. We describe approaches that are currently being applied to improve the assessment and management process for marine fish in situations where complex spatial structure has led to an observed mismatch between the scale of biological populations and spatially-defined stock units. The approaches include: (i) status quo management, (ii) “weakest link” management, (iii) spatial and temporal closures, (iv) stock composition analysis, and (v) alteration of stock boundaries. We highlight case studies in the North Atlantic that illustrate each approach and synthesize the lessons learned from these real-world applications. Alignment of biological and management units requires continual monitoring through the application of stock identification methods in conjunction with responsive management to preserve biocomplexity and the natural stability and resilience of fish species.

Targets and limits for long-term management are used in fisheries advice to operationalize the way management reflects societal priorities on ecological, economic, social and institutional aspects. This study reflects on the available published literature as well as new research presented at the international ICES/Myfish symposium on targets and limits for long term fisheries management. We examine the inclusion of ecological, economic, social and institutional objectives in fisheries management, with the aim of progressing towards including all four objectives when setting management targets or limits, or both, for multispecies fisheries. The topics covered include ecological, economic, social and governance objectives in fisheries management, consistent approaches to management, uncertainty and variability, and fisheries governance. We end by identifying ten ways to more effectively include multiple objectives in setting targets and limits in ecosystem based fisheries management.

MSY principles for marine fisheries management reflect a focus on obtaining continued high catches to provide food and livelihoods for humanity, while not compromising ecosystems. However, maintaining healthy stocks to provide the maximum sustainable yield on a single-species basis does not ensure that broader ecosystem, economic, and social objectives are addressed. Weinvestigate how the principles of a "pretty good yield" range of fishing mortalities assumed to provide.95% of the average yield for a single stock can be expanded to a pretty good multispecies yield (PGMY) space and further to pretty good multidimensional yield to accommodate situations where the yield from a stock affects the ecosystem, economic and social benefits, or sustainability. Wedemonstrate in a European example that PGMY is a practical concept. As PGMY provides a safe operating space for management that adheres to the principles ofMSY, it allows the consideration of other aspects to be included in operational management advice in both data-rich and data-limited situations. PGMYfurthermore provides away to integrate advice across stocks, avoiding clearly infeasible management combinations, and thereby hopefully increasing confidence in scientific advice.

Information on stock identification and spatial stock structure provide a basis for understanding fish population dynamics and improving fisheries management. In this study, otolith shape analysis was used to study the stock structure of blue whiting (Micromesistius poutassou) in the northeast Atlantic using 1693 samples from mature fish collected between 37°N and 75°N and 20°W and 25°E. The results indicated two stocks located north and south of ICES Divisions VIa and VIb (54°5N to 60°5N, 4°W to 11°W). The central area corresponds to the spawning area west of Scotland. Sampling year effects and misclassification in the linear discriminant analysis suggested exchanges between the northern and southern stocks. The results corroborate previous studies indicating a structuring of the blue whiting stock into two stocks, with some degree of mixing in the central overlap area.

A multi-disciplinary study was conducted to clarify stock identity and connectivity patterns in the populations of European plaice (Pleuronectes platessa) in the Skagerrak-Kattegat transition area between the Eastern North Sea and the Baltic Sea. Five independent biological studies were carried out in parallel. Genetic markers suggested the existence of different genetic populations in the transition area. Growth backcalculation with otoliths resulted in significant although limited differences in growth rates between North Sea and Skagerrak, indicating weak differentiation or important mixing. Hydrogeographical drift modelling suggested that some North Sea juveniles could settle along the coast line of the Skagerrak and the Kattegat. Tagging data suggested that both juveniles and adult fish from the North Sea perform feeding migrations into Skagerrak in summer/autumn. Finally, survey data suggested that Skagerrak also belongs to the area distribution of North Sea plaice. The outcomes of the individual studies were then combined into an overall synthesis. The existence of some resident components was evidenced, but it was also demonstrated that North Sea plaice migrate for feeding into Skagerrak and might constitute a large share of the catches in this area. The mixing of different populations within a management area has implications for stock assessment and management. Choice must be made to either lump or split the populations, and the feasibility and constraints of both options are discussed. The outcomes of this work have directly influenced the management decisions in 2015.

Regulations on the exploitation of populations of commercially important fish species and the ensuing consumer interest in sustainable products have increased the need to accurately identify the population of origin of fish and fish products. Although genomics-based tools have proven highly useful, there are relatively few examples in marine fish displaying accurate origin assignment. We synthesize data for 156 single-nucleotide polymorphisms typed in 1039 herring, Clupea harengus L., spanning the Northeast Atlantic to develop a tool that allows assignment of individual herring to their regional origin. We show the method's suitability to address specific biological questions, as well as management applications. We analyse temporally replicated collections from two areas, the Skagerrak (n = 81, 84, 66) and the western Baltic (n = 52, 52). Both areas harbour heavily fished mixed-origin stocks, complicating management issues. We report novel genetic evidence that herring from the Baltic Sea contribute to catches in the North Sea, and find support that western Baltic feeding aggregations mainly constitute herring from the western Baltic with contributions from the Eastern Baltic. Our study describes a general approach and outlines a database allowing individual assignment and traceability of herring across a large part of its East Atlantic distribution.

5th International Otolith Symposium (IOS2014), 20-24 October 2014, Mallorca, Balearic Islands Spain.-- 2 pages