Article

Effects of a large northern European no-take zone on flatfish populations

Journal of Fish Biology

October 2013
83(4):939-962

DOI:10.1111/jfb.12097

Source
PubMed

Authors:

Ann-Britt Florin

Swedish University of Agricultural Sciences

Ulf Bergström

Swedish University of Agricultural Sciences

Didzis Ustups

Institute of Food Safety, Animal Health and Environment “BIOR”

Karl Lundström

Swedish University of Agricultural Sciences

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In March 2006, a 360 km(2) no-take zone (NTZ) was established north of Gotland in the central Baltic Sea, with the purpose to scientifically evaluate the effects of a fishing ban on flatfish populations. A monitoring programme was set up to study the populations in the NTZ and in a reference area east of Gotland where the fishing pressure was high. The programme included fishing with multimesh survey nets, modelling of potential larval export and estimation of fish consumption by large marine predators. Overall, the results showed a clear positive effect of the NTZ on turbot Scophthalmus maximus, with higher densities in the closed area compared with the fished area and also higher densities after closure compared with before. The NTZ also had older individuals and a more even sex ratio. This, in combination with a high potential for larval export from the NTZ to Gotland, shows that the marine reserve may be important for maintaining a viable S. maximus stock at Gotland. Also, for flounder Platichthys flesus, the densities were higher in the NTZ compared to the reference area and there was a net larval export to the fished area. For both species, density-dependent growth was evident, with a lower length at age in the closed area. Potential predation by grey seal Halichoerus grypus and great cormorant Phalacrocorax carbo sinesis on flatfishes, that could hamper the evaluation of the marine reserve, was also addressed. Taken together, the results show that there are clear benefits of the fishing ban for both flatfish species within the NTZ, while the net effects on fisheries are difficult to quantify.

Environmental Impacts of Offshore Wind Farms in the Belgian Part of the North Sea: Progressive Insights in Changing Species Distribution Patterns Informing Marine Management.

Book

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Jan 2024

This report, targeting marine scientists, marine managers and policy makers, and offshore wind farm developers, presents an overview of the scientific findings of the Belgian offshore wind farm environmental monitoring programme (WinMon.BE), based on data collected up to and including 2022.

Påverkansanalys fisk till åtgärdsprogram för havsmiljön

Technical Report

Full-text available

Dec 2021

The purpose of this report is to describe the current state of knowledge of the most important factors influencing fish in Swedish marine waters in preparation for the update of the program of measures in 2021 within the Swedish implementation of the Marine Strategy Framework Directive (MSFD). The objective of the MSFD is to achieve or maintain good environmental status in the marine environments. For ecosystem components such as fish where the status is poor, an analysis of the key impacting pressures can contribute with knowledge to support management in directing and prioritizing measures required to achieve the goals. This review is divided into the two Swedish assessment areas of the MSFD, the North Sea and the Baltic Sea, and makes a division into coast and open sea in terms of describing the evidence for pressures affecting the fish fauna. The report presents literature support available during the autumn 2019 for the impact of pressures on fish from fishing, climate, eutrophication, habitat loss and food-web interactions. In addition, the significance of other pressures for which knowledge is more limited such as pollutants, pharmaceutical residues, marine litter including micro plastics, underwater noise, vitamin deficiency, as well as parasites and diseases are presented in short. A qualitative synthesis of the results shows that several pressures are likely to have a major impact on fish in the coastal and offshore ecosystems both in the Baltic Sea and in the North Sea. These pressures are a combination of direct and indirect human impact, as well as of altered food-web interactions. Direct impact from fishing on target and by-catch species is important in all management areas and habitats. The number of significantly influencing factors appears somewhat lower in the North Sea (especially in the open sea), compared to the Baltic Sea. However, there also seems to be less information on other impacts in the North Sea, where fishing has been the dominant pressure for a long period. Climate, eutrophication and habitat loss are significant pressures for the status of fish in both administrative areas. However, there is a general lack of knowledge about the importance of climate on the status of stocks in the North Sea, as well as the importance of food-web interactions in all areas and habitats, including how increasing populations of seals and cormorants interact with fish. This report concludes that a quantitative estimate of the relative importance of different pressures for fish would be desirable, including studies of the cumulative effects of several pressures that act simultaneously. Cumulative effects are poorly understood and studied, but are likely significant for the development of the fish populations and fish communities in our marine waters. Given the wide plethora of potentially impacting pressures, a more precautionary and ecosystem based approach to management is advocated in the current and future management of fish stocks, populations and communities in Swedish marine waters.

Rapid effects of a fishing closure on whitefish (Coregonus maraena) in the northern Baltic Sea

Article

Full-text available

Jun 2021
BOREAL ENVIRON RES

Areas closed to fishing year-round (no-take zones, NTZs) or during spawning time (spawning closures) are used as a management tool to increase declining fish populations. We evaluated the effects of a 147 km2 NTZ and a 3980 km2 spawning closure on whitefish populations in the northern Baltic Sea, and also accounted for fish consumption by seals and cormorants. Fish monitoring with multimesh gillnets in 2011–2016 showed a significant increase in catch per unit effort (CPUE) of mature whitefish (> 30 cm) both in the spawning closure and the NTZ compared with the reference area open to fishing. The rate of increase was significantly higher in the NTZ than in the spawning closure. Our results suggest that NTZs may strengthen coastal fish populations in temperate regions and that also seasonal closures under a critical period of the life cycle may benefit the populations.

Viktig miljöinformation finns i fiskars hårda vävnader

Technical Report

Full-text available

Dec 2020

Summary Fish is an important indicator in monitoring and assessment of Swedish environmental goals and international directives and agreements. Several indicators describing recruitment, growth and age structure are based on age determination of fish. Age determination is done by reading growth zones on different hard structures from fish, e.g. otoliths, operculum bones, wing bones and scales. When the fish grows changes in its environment are also reflected in fish's hard structures. Age samples of fish are taken in many ongoing monitoring programs, and at SLU there are also large archives of age samples from many older surveys. In this report, we evaluate how age determination and other analyses of hard structures in fish might complement and strengthen knowledge about the structure and function of fish populations and fish communities in environmental monitoring in Swedish freshwaters and along the Baltic coast. Different types of age-based indicators are needed in assessment according to the Water Framework Directive, the Marine Strategies Framework Directive, the Species and Habitats Directive and as a basis for ecosystem-based fisheries management. It deals with different metrics of age structure, recruitment, growth and mortality, all of them calculated from aged fish. We describe collected age samples from test-fished coastal areas and lakes, and give both published and new examples of using age data in environmental and fisheries management. We also give examples of how analyses based on the shape and chemical composition of otoliths can be used. The recruitment of fish varies more or less between years, depending on natural conditions and human impact. Recruitment indices based on fish age provide more specific information than uncertain interpretation based on fish size alone. We show variation in recruitment index and relative year-class strength for several fish species in both smaller and larger lakes and along the coast. Environmental changes also affect fish growth. We give examples of age-based analyses of growth, for individuals and stocks, with and without use of growth models. Knowledge of survival and mortality is needed to understand what affects the development of fish stocks, and is therefore an important basis for ecosystem-based management. We provide several new examples of how mortality can be estimated based on ageing for some coastal fish species that are of interest for commercial and recreational fishing, and on how fishing mortality is used in new stock models for vendace in Lake Vänern and the Gulf of Bothnia. We also show comparisons between age and length structure, illustrating that fish age cannot be correctly estimated from its length. New and previously collected age samples are stored in SLU's biological archive. The samples can be used for more analyses than was originally planned when collecting the samples within environmental monitoring and other surveys. We show examples of how collected age samples can be used to identify different stocks of fish. There are different methods based on the shape of otoliths, chemical composition of otoliths and scales, and genetic analysis of scales.

Status of coastal fish communities in the Baltic Sea during 2011-2016 – the third thematic assessment

Technical Report

Full-text available

Nov 2018

Coastal fish, the fish assemblages in relatively near-shore and shallow (< 20 m depth) coastal areas, in the Baltic Sea harbour a mixture of species with marine and freshwater origins. Typical species are perch, pikeperch, pike, roach and breams, which are of freshwater origin and confined to coastal areas, as well as marine species like flounder, cod and herring, which often have seasonal migrations between nearshore and outer sea areas. Coastal fish populations and communities provide important ecosystem services, contributing to ecosystem functioning and high socio-economic and cultural values. They represent key elements for assessing environmental status in relation to environmental objectives within the Baltic Sea Action Plan (BSAP) and the Marine Strategy Framework Directive (MSFD). The main aim of this report is to provide a comprehensive assessment of the status of coastal fish in the Baltic Sea during 2011-2016, in support of the second holistic assessment of HELCOM (HOLAS II). The results are included in summary in the State of the Baltic Sea report. The report contains the latest status assessment of coastal fish in the Baltic Sea using two Baltic-wide CORE indicators and an agreed assessment approach (Chapter 3). The report also includes a review of major pressures acting on coastal fish communities (Chapter 2), and of potential measures to restore and support coastal fish communities in the Baltic Sea (Chapter 4). The report ends with future recommendations for continued work on coastal fish monitoring and assessment in the Baltic Sea in relation to the BSAP and MSFD (Chapter 5). The status assessments presented in this report includes data from Finland, Estonia, Latvia, Lithuania, Poland, Denmark and Sweden. Experts from Russia and Germany have also participated in the HELCOM work on coastal fish during recent years, but data from these countries are not included in the current assessment. Status is assessed based on the two HECLOM core indicators ‘Abundance of key species’ and ‘Abundance of key functional groups’, of which the latter is composed of a component assessing the abundance of piscivores and one on the abundance of Cyprinids/mesopredators. The results show that the status of the coastal fish communities varies between areas, regions and indicators, but the general status based on the two core indicators appears weak. Only approximately half of the assessed areas and assessment units are classified as being in good status. The more northern areas, where perch is used as the key species, are more often assessed to be in good status than more southern areas, where flounder is recognised as the key species. For the two functional group indicators, the status of piscivores follows a similar pattern of the key species indicator, with relatively better status in more northern areas. The other important functional group, cyprinids, shows insufficient status also in more north-eastern areas of the Baltic Sea as a result of too high abundances. The current monitoring network for coastal fish is rather extensive, but does still only support an assessment in half or less than half of the 42 listed assessment units for coastal fish in the Baltic Sea. The confidence of the assessment is moderate to low, depending on area and indicator, mainly as a result of short time-series, poor spatial representation, and data quality issues. The review of pressures acting on coastal fish communities show that a multitude of natural and human-induced pressures potentially affect coastal fish communities simultaneously. These include for example fishing, habitat exploitation, climate change, eutrophication and natural interactions within the coastal food-web. Whereas a few pressures are strong and often explain a large proportion of the variation in fish abundance and distribution, the effects of others can only be observed locally or under certain conditions and vary across areas and among communities. The potential for generalizations across areas is hence limited, and evaluations of which pressure is of key importance should be undertaken for each individual case separately considering the ambient local conditions in each area together with the range of potential human induced pressures. As a result, measures to restore and protect coastal fish communities should also be developed with a local perspective, and different measures might be relevant in different geographic areas. In general, however, scientific evidence on the effectiveness of different measures is poor, as only few thorough evaluations of implemented measures have been undertaken in the Baltic Sea. The few measures that have been scientifically evaluated with proven effects includes actions aimed at reducing the mortality of fish (e.g. no take areas). There is also partial support for temporary fishing closures and gear and catch restrictions. Among measures that aim at improving the production of fish, habitat protection and restoration have proven to be effective. For many other potential measures there is a general lack of scientific support, including biomanipulation, nutrient and substance abatement, as well as stocking of hatchery-reared fish. The assessment results and reviews presented in this report show that coastal fish assessments and monitoring in the Baltic Sea have taken noteworthy steps forward since the last thematic assessment. For example, Baltic-wide CORE indicators on coastal fish have been agreed on, as well as a regionally agreed concept for assessing the status of coastal fish communities. Knowledge has improved on the key pressures impacting on coastal fish communities, and on measures that are potentially most effective for supporting and restoring coastal fish communities. In spite of this, there are still several knowledge gaps and development needs, which should be considered in the future. There is a need to safeguard existing monitoring programs and to initiate new monitoring programs for coastal fish in geographic areas that are currently poorly covered or not possible to assess at all. There is also a need to continue harmonizing assessment approaches to enable comparisons across monitoring programs and data sources, and to further develop common indicators and assessment methods. This concerns the further evaluation and development of current indicators, as well as the development of new generic indicators, focusing on aspects of size-structure in the assessed fish communities. Finally, it is clear that initiatives to strengthen the evaluation measures must be undertaken. It is recommended that the results presented in this report should be used as the basis for following up on the objectives of the BSAP and MSFD, as well as for the development of national management plans and coastal fish assessments in the Baltic Sea.

Förvaltningsmål för nationellt förvaltade fiskbestånd

Technical Report

Full-text available

May 2016

Örjan Östman

Fish and shellfish stocks with distributions mainly restricted within Swedish national waters are also mainly governed nationally and to some extent by regional or local authorities and organizations. Such stocks are often, in contrast to species that are subject to international exploitation and management, utilized by several different stakeholders (e.g. commercial and recreational fisheries). The needs and long-term management objectives of these stakeholders may sometimes differ and in the worst cases be in direct conflict with each other (e.g. large yield vs. large individuals). There is often limited data available for these stocks, and consequently they often lack quan-titative management objectives, resulting in a less effective management. The aim of this report is to provide an overview of available management targets and associated methods and instruments suitable for assessing if the exploitation of nationally man-aged fish and shellfish stocks are sustainable in the long term. There are three broad categories of quantitative management targets: 1) Targets to achieving long-term sus-tainable yield, which require detailed data from many different sources. 2) Targets of biomass or abundance index, or a ratio between catch and abundance/biomass index, which requires reliable monitoring, catch or effort data. 3) Targets of the demo-graphic structure of a stock or of the life-history characters of a stock, to achieve a “natural like” or “desirable” stock structure which requires data of trait distributions (e.g. size, age, maturity) in stocks. All three categories have their merits and draw-backs. For example, sustainable yield and abundance-index goals do not consider size-structure, and vice versa, and different objectives require different types of input data. In addition we therefore review which objectives may be suitable for different types of nationally managed fish and shellfish stocks. At the current stage data are generally too limited to propose specific targets for most stocks that can be consid-ered for national management. Rather, we stress the importance of using several dif-ferent management targets or indicators of exploitation instead of relying on a single target/indicator to facilitate sustainable use of aquatic resources taking into account the demands of different stakeholders. In addition, there is no clear definition of what a local stock is and when national and/or local management should be enforced. Therefore it is important that management objectives are set such that they can reflect nationally or locally enforced measures.

Light and Shade in Marine Conservation Across European and Contiguous Seas

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Nov 2018

As a response to increasing human pressures on marine ecosystems, the legislation aimed at improving the conservation and management of marine coastal areas in European and Contiguous Seas (ECS) underwent crucial advances. ECS, however, still remain largely affected by increasing threats leading to biodiversity loss. Here, by using emblematic case studies and expert knowledge, we review current conservation tools, comparing their application in different areas to assess their effectiveness, potential for synergies, and contradictions. Despite regional differences in their application, the existing legislative frameworks have the potential to regulate human activities and to protect marine biodiversity. However, four challenges remain to be addressed to fully achieve environmental policy goals: (1) Lack of shared vision representing a limitation in transboundary collaboration. Although all EU countries are committed to fulfil EU Directives and other binding international legislative acts, a remarkable heterogeneity exists among countries in the compliance with the common legislation on conservation and in their degree of implementation. (2) Lack of systematic procedures for the selection of protected marine sites. Regional and national approaches in designating Natura 2000 sites and nationally designated marine protected areas (MPAs) reflect varying conservation targets and importance of conservation issues in political agendas. (3) Lack of coherent ecological networks. Natura 2000 sites and other MPAs are still far from reaching the status of effective networks in all considered case studies. (4) Hotspot of conflicts with private economic interests prevailing over conservation aims. Recommendations are given to overcome the fragmented approach still characterizing the conservation and management of coastal marine environments. Holistic, integrated, ecosystem-based, cross-cutting approaches can avoid conflicts among institutions so as to provide effective and timely solutions to current and future challenges concerning the conservation and management of marine ecosystems and associated goods and services.

When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area

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Jan 2023

This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Castellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and size structure of demersal finfish and shellfish and on the proportion of different commercial categories of fish. Data were collected by experimental trawl surveys conducted in the GCAST and in two trawled areas before and after 1990. The biomass of the total assemblage and of a number of selected species was significantly higher in the GCAST after the ban. Highly commercial species had the largest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen. The results from size-based indicators were not as clear-cut as those from biomass though. Although the length frequency distributions obtained in the GCAST were significantly different from the other gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Our results suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomass recovery but only partial size structure recovery of the fish populations subject to trawl exclusion, at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example of an effective ecosystem-based fisheries management tool that offers the potential for fish stock rebuilding and for the economic sustainability of artisanal, small-scale fisheries.

Offshore wind farms affect the spatial distribution pattern of plaice Pleuronectes platessa at both the turbine and wind farm scale

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Jun 2022

We investigated how the distribution of plaice Pleuronectes platessa, a typical soft-sediment fish species, has been affected by the introduction of hard substrate [turbines and scour protection layer (SPL)] at both turbine and wind farm scale in two Belgian offshore wind farms (OWFs). Diving transects (40 m) at 11 monopiles revealed four times higher plaice abundances on the sandy patches of the SPL (average radius 16.5 m) compared to the surrounding sand. We suggest that the configuration of the SPL, i.e. an open rock field, offering increased food and shelter opportunities, with sandy patches in between, facilitating the natural burrowing behaviour of plaice, forms the basis for the increased plaice abundances at the turbine scale. At the wind farm scale, beam trawl catches in between the turbines and in reference zones revealed significantly increased plaice abundances in one OWF, which suggests that wind farms can act as refuge areas for plaice, at least under specific conditions. Differences in environmental conditions, turbine foundation type, and surrounding fishing pressure may explain the equivocal findings between both OWFs, whereas low statistical power could have hampered the detection of general refuge effects. Next to the integration of different spatial scales (turbine/wind farm) within one study, longer-term monitoring and including extra life history parameters (e.g. length and sex ratio) might enhance the detectability of potential refuge effects.

Ecological connectivity of the marine protected area network in the Baltic Sea, Kattegat and Skagerrak: Current knowledge and management needs

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Dec 2021

Marine protected areas (MPAs) have become a key component of conservation and fisheries management to alleviate anthropogenic pressures. For MPA networks to efficiently promote persistence and recovery of populations, ecological connectivity, i.e. dispersal and movement of organisms and material across ecosystems, needs to be taken into account. To improve the ecological coherence of MPA networks, there is hence a need to evaluate the connectivity of species spreading through active migration and passive dispersal. We reviewed knowledge on ecological connectivity in the Baltic Sea, Kattegat and Skagerrak in the northeast Atlantic and present available information on species-specific dispersal and migration distances. Studies on genetic connectivity are summarised and discussed in relation to dispersal-based analyses. Threats to ecological connectivity, limiting dispersal of populations and lowering the resilience to environmental change, were examined. Additionally, a review of studies evaluating the ecological coherence of MPA networks in the Baltic Sea, Kattegat and Skagerrak was performed, and suggestions for future evaluations to meet management needs are presented.

Scophthalmus maximus 10.2305 IUCN.UK.2021-2.RLTS.T198731A144939322.en

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Dec 2021

Cemal Turan

The IUCN Red List of Threatened Species,Scophthalmus maximus, Turbot

Scophthalmus maximus, Turbot

Technical Report

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Nov 2021

The proportion of flatfish recruitment in the North Sea potentially affected by offshore windfarms

Article

Full-text available

Feb 2020

Understanding the influence of man-made infrastructures on fish population dynamics is an important issue for fisheries management. This is particularly the case because of the steady proliferation of offshore wind farms (OWFs). Several flatfish species are likely to be affected because areas with OWFs in place or planned for show a spatial overlap with their spawning grounds. This study focuses on six commercially important flatfish species in the North Sea: common sole (Solea solea), European plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), brill (Scophtalmus rhombus), European flounder (Platichthys flesus), and common dab (Limanda limanda). We used a particle-tracking model (Larvae&Co) coupled to a 3D hydrodynamic model to assess the effects of spatial overlap of OWFs with the species’ spawning grounds on the larval fluxes to known nursery grounds. An important overlap between planned areas of OWFs and flatfish spawning grounds was detected, with a resulting proportion of settlers originating from those areas varying from 2% to 16%. Our study suggests that European plaice, common dab, and brill could be the most affected flatfish species, yet with some important local disparities across the North Sea. Consequently, the study represents a first step to quantify the potential impact of OWFs on flatfish settlement, and hence on their population dynamics.

Modelling of larval dispersal of Baltic flounder (Platichthys solemdali) revealed drifting depth as a major factor determining opportunities for local retention vs large-scale connectivity

Article

Jun 2019
FISH RES

For flatfishes, transportation of larvae to nursery areas is regarded a key mechanism for recruitment, with adaptations in larval behaviour to reach a suitable habitat. Here we model different possibilities of larval drifting of coastal spawning Baltic flounder Platichthys solemdali (recently identified as a species from European flounder P. flesus) to reveal opportunities for local retention vs large-scale dispersal to ensure settling in coastal nursery areas. Drifting depth, duration of drifting and effects of year and time during season were modelled using 1) a high-resolution local dispersal model, and 2) a large-scale connectivity database. The outcome revealed drifting depth as a major factor affecting larval dispersal. Drift at 10-22 m depth involved retention along the coast with the majority of larvae (≥94% or 69-93% according to 1 and 2, respectively) with end points ≤20 km from the coast enabling further successful migration to nursery habitats. Contrary, larval drift close to the surface resulted in advection with end points in the open sea (72-76%), i.e. loss of larvae, but with a small fraction (5-12%) displaying cross-basin connectivity. The results suggest, in agreement with depth distribution of spawning, a larval behaviour promoting drift in the lower part of the water mass, favouring retention close to coastal nursery areas. Obtained dispersal patterns may sustain both local recruitment but also connectivity with other areas, potentially explaining the low genetic diversity between areas for P. solemdali. Low inter-annual variability in dispersal patterns when drifting at 10-22 m depth suggests that larval drift is not a major bottleneck explaining recruitment variability in P. solemdali in the area. The study highlights the differences in life-history strategies of the species pair of flounder in the Baltic Sea; P. flesus spawning in the deep basins with extensive larval dispersal, and coastal spawning P. solemdali with, according to the model outcome, mainly local larval dispersal for sustaining a viable population, i.e. request for different management strategies.

Light and Shade in Marine Conservation Across European and Contiguous Seas

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Nov 2018

Light and Shade in Marine Conservation Across European and Contiguous Seas

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Light and Shade in Marine Conservation Across European and Contiguous Seas

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Ekologiska effekter av fiskefria områden i Sveriges kust- och havsområden

Technical Report

Full-text available

Nov 2016

This report describes the ecological effects of fishing closures (no-take areas) in Swedish marine and coastal waters. In 2005 the Swedish Board of Fisheries (now the Swedish Agency for Marine and Water Management) was commissioned by the government to establish a number of areas where all fishing was prohibited and to evaluate the effects of these closures. Five such no-take areas were established in 2009-2011. The effects on fish populations, and in some cases also on other components of the ecosystem, were monitored until 2015. This report gives a summary of biological effects of these no-take areas, focusing on fish populations and ecosystems. When these five new fishing closures had been established in 2011, the total area of no-take areas in Swedish marine and coastal waters amounted to 1 200 km2. This corresponds to less than 1 % of the Swedish sea area, but two thirds of the total areal extent of no-take areas in Europe. Hence, the monitoring and evaluation of the Swedish areas makes an important contribution also to the general knowledge base regarding no-take areas for European fisheries management. The geographical areas and target species of the evaluation were: • European whitefish in the Bothnian Sea • Pikeperch, pike and perch in the Stockholm archipelago, central Baltic Sea • Cod in the Kattegat • European lobster and predatory fish in the Gothenburg archipelago, Skagerrak • Cod, turbot and plaice in the Swedish fjords of Skagerrak More detailed results for each of the study areas are given in supplementary reports, whereas overall results are synthesized here. Abundance and body size of target species increased in most of the no-take areas, as compared to nearby reference areas where fishing was continued. The results show that the earlier fishing pressure in the no-take areas had been large enough to influence both fish abundance and size structure. The responses in abundance and body size were seen both for populations that had been targeted primarily by commercial fisheries, such as cod in Kattegat, and for coastal species where recreational fisheries dominated the catches, for example whitefish in the Bothnian Sea, pikeperch in Stockholm archipelago and European lobster in the Gothenburg archipelago. Despite the relatively short evaluation period of 5 years, substantial positive effects on the populations were evident in four of the five no-take areas, illustrating the utility of no-take areas for strengthening vulnerable fish populations. In one area, Havstensfjorden in Skagerrak, no positive effects have so far been seen in the target species cod, plaice and turbot. This is most probably explained by previous recruitment overfishing on local populations, leading to slow recovery. In addition to the studies on target fish populations, effects on fish communities and benthic fauna were studied in some of the areas, showing changes also in these ecosystem components. These observations were likely due to a combination of direct effects of excluding fisheries on target and bycatch species, and indirect effects of the increase in large predatory fish and European lobster leading to increased predation on prey species. Thus, the studies suggest that no-take areas may contribute to re-establishment of ecosystem functions by increasing the abundances of large predators. Such changes in food web function may also counterbalance other processes, such as the increased production of fast-growing algae in eutrophicated areas, through trophic cascades. Another effect of no-take areas is the cessation of bottom trawling leading to improved conditions for benthic fauna sensitive to physical disturbance. In most cases, the introduction of the no-take areas has likely decreased the total fishing effort rather than displacing it to adjacent areas. In the Kattegat no-take area, however, the purpose was explicitly to displace an unselective coastal mixed bottom-trawl fishery targeting Norway lobster and flatfish to areas where the bycatches of mature cod were smaller. The mixed fishery has continued in the buffer zones and the open areas of Kattegat, and total catches of Norway lobster and flatfish have been maintained but with substantially less bycatches of adult cod than before the introduction of the measures. The report also reviews the general scientific knowledge base on no-take areas, including also experiences from previously studied no-take areas in Swedish waters. The effects observed in these other Swedish no-take areas are consistent with the ones reported here, showing increases in population sizes and size structures, and an increase in the reproduction potential. The results also generally agree with international studies in terms of the effects no-take areas on target species for fisheries. The Swedish examples generally lack specific empirical studies on ecosystem effects of the closures. However, knowledge on the effects of large predatory fish on ecosystem functioning, including their role in trophic cascades, is available from other research projects in Sweden. As the population density and body size of fish and lobsters increase, the reproduction potential also increases, which may generate positive effects also outside the closed areas through spillover. The magnitude of such spillover effects, through export of eggs and larvae and migration of adult fish, are however not easily estimated. Apart from spillover effects, there are also other potential benefits from no-take areas. By keeping a part of the fish populations protected from fishing, the risk for stock collapse due to otherwise inadequate management decreases, whereby the no-take areas may act as an insurance policy. No-take areas may also counteract genetic impoverishment due to selective fishing on large, fast-growing individuals, and may hence mitigate a decrease in fish productivity due to genetic effects, and may support biological variation and resilience against environmental change. In the present evaluation, the net effects were quantified for the Kattegat no-take area, showing a positive effect on the cod population in the Kattegat management area as a whole, while catches of other commercial species had not decreased. In a longer-term perspective, the recovery will likely provide increased opportunities for a cod fishery, as a substantial part of the population is found outside of the no-take area after the spawning period. No-take areas can, if they are adequately designed, give rise to positive population effects and may be a useful complement to other fisheries management instruments. In many cases, the desired results can potentially also be achieved by a combination of other measures, such as gear or catch restrictions in space and time. The experiences from the current evaluation show that no-take areas can be an important tool for fisheries management especially for mixed fisheries and local coastal fish populations, as well as in cases where there is a need to counteract adverse ecosystem effects of fishing. Marine protected areas where the protection of both fish and their habitats is combined may be an important instrument for ecosystem-based management. In this context, no-take areas are also needed as reference for marine environmental management, as well as for understanding of the effects of fishing on fish populations and ecosystems in relation to other pressures.

Spatial structure of body size of European flounder (Platichthys flesus L.) in the Baltic Sea

Article

May 2017
FISH RES

The spatial structure of fish species is important for stock identification and management. The European flounder (Platichthys flesus L.) shows morphological differences across the Baltic Sea Proper. However, it is not known whether flounders cluster into several distinct areas based on morphological characters, indicating discrete sub-populations, or whether they show continuous morphological variation along space indicating a more continuous population structure. Here, we study the spatial structure of body length and length-at-age distributions of the European flounder (Platichthys flesus L.) across the Baltic Sea Proper (International Council for the Exploration of the Sea (ICES) subdivisions 25–28) using high spatial resolution data (ICES rectangles) from fishery independent surveys 2008–2014. Our results are in agreement with genetic data suggesting a continuous gradient of decreasing body length from south-west to north-east. Further, we observed distance decay in the spatial synchrony of temporal changes in the length distributions, such that the temporal trends were correlated among adjacent ICES rectangles but independent across the whole study area. Length-at-age and maturity patterns that were calculated for each subdivision also showed a consistent spatial difference where SD 28 was significantly different from SD 25 and 26. Our results indicate that the European flounder in the Baltic Sea consists of several loosely defined sub-populations, which may warrant a reconsideration of assessment models, management targets and regulations across subdivisions.

Inferring spatial structure from population genetics and spatial synchrony in demography of Baltic Sea fishes: Implications for management

Article

Full-text available

Sep 2016
FISH FISH

The spatial structure of species is important for their dynamics and evolution, but also for management and conservation. There are numerous ways of inferring spatial structures, and information from multiple methods is becoming more common to examine how different processes shape the spatial structures of species to improve fish management. Here, we investigate the spatial structure of a suite of Baltic Sea fish species based on the following: (i) spatial (presumably neutral) genetic differentiation, reviewed from the literature, and (ii) spatial synchrony in abundance changes from time series of fishery-independent surveys, which we currently find to be underused given the amount of data available. For each of these two methods, species were classified as having a distinct, continuous or no/weak spatial structure. In addition, based on each source of information, we estimated the spatial scale of management units for species. The results show that only among species confined to the coastal zone the two sources of information yielded a congruence of the spatial structure (displaying a continuous spatial structure). In contrast, offshore species show weak spatial genetic structure but stronger spatial structure of synchrony in abundance. Based on this, we suggest that population genetic structure and synchrony in abundance should be used as complementary information as they reflect different spatial processes and suggest that management actions should differ with respect to scale depending on the management targets applied. We propose similar analysis should be applied to areas outside the Baltic Sea, and other stock identification methods, to improve management of fish resources.

Beneath the blades: Marine wind farms support parts of local biodiversity - a systematic review

Article

Full-text available

May 2024
SCI TOTAL ENVIRON

Offshore wind energy developments in European waters are rapidly expanding to meet the increasing global demand for renewable energy. These developments provide new substrates for species colonisation, but also introduce changes in electromagnetic fields, noise levels, and hydrological conditions. Understanding how these man-made structures affect marine biodiversity across various species groups is crucial, yet our knowledge in this field remains incomplete. In this synthesis paper, based on 14 case studies conducted in northeastern Atlantic (North, Irish and Baltic seas), we aggregated species-level data on abundance, biomass, and other quantity proxies spanning the entire food chain from invertebrates to mammals, and compared these variables between wind farms and nearby control sites. Overall, our analysis revealed that in wind farm areas, species tend to occur at higher quantities than in control areas. Additionally, we noticed a slight trend where the positive effect of wind farms was more pronounced in newly established ones, gradually diminishing as wind farms aged. None of the tested covariates (depth, distance from coastline, years in commission) nor species' characteristics (habitat and spawning types, trophic level) showed statistical significance. When examining species groups individually, there was a tendency for wind farm areas to harbour higher quantities of polychaetes, echinoderms and demersal fishes. These findings suggest that wind farms contribute to the so-called reef-effect, providing shelter and food supplies to their inhabitants and acting as no-take-zones. Our results support the idea that wind farms could serve as zones of increased local biodiversity, potentially facilitating spillover effects to nearby areas for certain species groups. Further studies are necessary to gain a more comprehensive understanding of the adverse effects of wind farms on associated biodiversity, while also exploring avenues to amplify their positive impacts.

UPPFÖLJNING AV MILJÖÅTGÄRDERS EFFEKTER PÅ KUST OCH HAV

Technical Report

Full-text available

Oct 2022

Havsmiljöinstitutet genomförde under 2021 ett projekt där aktuell information om uppföljning av effekter av fysiska åtgärder och områdesbaserade åtgärder sammanställdes. Resultaten presenteras i denna rapport. Informationen har hämtats från databaser, rapporter och artiklar om uppföljning av effekter av åtgärder samt samtal med forskare och utredare på myndigheter som på olika sätt arbetar med genomförande, uppföljning eller tilldelning av medel för åtgärder. Samtalen fokuserade på personernas erfarenheter av uppföljning av åtgärder, befintligt kunskapsläge om effekter av åtgärder, och för utredare även hur arbetet med uppföljning av åtgärder organiseras på myndigheten. Från det inhämtade underlaget och samtalen framkom en samsyn kring flera brister i uppföljning av åtgärder i Sverige, bland annat: brister i kunskap om effekter för flera vanligt förekommande åtgärdstyper som genomförs för att förbättra tillståndet eller minska påverkan på kust och hav, ett behov av en tydligare systematik och långsiktighet i uppföljning av åtgärder, brister i data och information om genomförda åtgärder, beträffande såväl tillgänglighet som fullständighet och ändamålsenlig form.

Protecting Europe's Future Seas

Thesis

Full-text available

Dec 2022

George Hoppit

Problems of climate change and marine conservation occur across many aspects of social-ecological systems. Addressing these challenges requires the use of interdisciplinary research techniques. Marine Protected Areas (MPAs) are a common mechanism to support marine conservation and livelihoods but are often created without regard to climate change impacts. Understanding how climate change will impact MPAs, how existing MPAs can be modified considering climate, and where current institutional practices enable climate change adaptation are all needed to support future seas. Meta-analysis of available experimental work examining European benthic organism responses to ocean acidification and warming suggests that calcifying organisms are likely to experience decreases in growth, reproductive capacity, and survival. Meta-analysis also shows European fleshy algae are resilient to end of century projected conditions. Underlying MPA ecological conditions are therefore likely to change based on current emission pathways. Examination of UK MPA case studies shows that existing conservation mechanisms can be adjusted to enhance resilience to climate change in marine social-ecological systems. Ways to achieve this include adopting adaptive management approaches, ecosystem-based management approaches, enhanced recognition of climate change in primary legislation used to support MPAs, and improved site monitoring. Doctrinal analysis of key conservation legislation supporting English MPAs and semi-structured interviews with individual’s familiar using said legislation reveals that there is large scope for adaptive governance in response to climate change in inshore waters. Current legislation has supported ecosystem-based management approaches and large-scale habitat restoration efforts. However, practical capacity issues of insufficient resourcing for key marine governance organisations prevents effective monitoring of MPAs, researching challenges within inshore regions, and enforcing conservation agreements.

Increased food availability at offshore wind farms affects trophic ecology of plaice Pleuronectes platessa

Article

Full-text available

Dec 2022
SCI TOTAL ENVIRON

Offshore wind farms (OWFs) and their associated cables, foundations and scour protection are often constructed in soft sediment environments. This introduction of hard substrate has been shown to have similar effects as artificial reefs by providing food resources and offering increased habitat complexity, thereby aggregating fish around the turbines and foundations. However, as most studies have focused their efforts on fish species that are typically associated with reef structures, knowledge on how soft sediment species are affected by OWFs is still largely lacking. In this study, we analysed the trophic ecology and condition of plaice, a flatfish species of commercial interest, in relation to a Belgian OWF. The combination of a stomach and intestine content analysis with the use of biomarkers (i.e. fatty acids and stable isotopes) identified a clear shift in diet with increased occurrences of typical hard substrate prey species for fish in the vicinity of the foundations and this both on the short and the long term . Despite some condition indices suggesting that the hard substrate provides increased food availability, no clear increases of overall plaice condition or fecundity were found. Samples from within the wind farm, however, contained larger fish and had a higher abundance of females compared to control areas, potentially indicating a refuge effect caused by the cessation of fisheries activities within the OWF. These results suggest that soft sediment species can potentially benefit from the presence of an OWF, which could lead to fish production. However, more research is still needed to further elucidate the behavioral ecology of plaice within OWFs to make inferences on how they can impact fish populations on a larger spatial scale.

A no-take zone and partially protected areas are not enough to save the Kattegat cod, but enhance biomass and abundance of the local fish assemblage

Article

Full-text available

Sep 2022

To supplement catch and effort regulations with the purpose to rebuild the cod (Gadus morhua) stock in Kattegat, Sweden and Denmark established a large (426 km2) year-round no-take zone (NTZ) surrounded by partially protected areas (PPAs) in 2009. The purpose of these spatial regulations was to prohibit cod fishing on the spawning grounds and to displace fisheries bycatch of cod from areas where mature cod aggregate in the Kattegat. The aim of this study is to evaluate the effects of the established NTZ and PPAs on the local fish assemblage, including cod. Based on a spatially high-resolution bottom trawl survey in the Kattegat (covering 2008–2021), multivariate analyses revealed significant shifts in the fish assemblage. A closer analysis indicated that six to seven fish species, including cod increased in the NTZ relative to control areas depending on if abundance or biomass was used as dependent variable. Univariate analysis showed that two flatfish species dab (Limanda limanda) and lemon sole (Microstomus kitt), and Norway lobster (Nephrops norvegicus) significantly increased in biomass in the NTZ, and turbot (Scophthalmus maximus) in the PPA relative to the control areas. These results suggest that the NTZ protected even relatively mobile species in an open sea system, such as the Kattegat. However, neither cod abundance nor biomass showed a significant increase as an effect of the NTZ and PPA despite two relatively strong year classes in 2012 and 2013, which possibly would have helped the recovery of the cod stock. As assessed by the International Council for the Exploration of the Sea in 2022, Kattegat cod continuously suffer from being severely overfished with low recruitment, and high discard rates in the mixed N. norvegicus fishery, is considered the major driver behind the reinforced depletion of the stock.

Are marine protected areas an adaptation measure against climate change impacts on coastal ecosystems? A UK case study

Article

Full-text available

Dec 2022

Climate change is impacting marine seascapes against a backdrop of multiple anthropogenic stressors. These current impacts are projected to increase in the future with increasing warming, acidification, oxygen loss, and sea level rise. Marine Protected Areas (MPAs) have been established to protect features in the ocean, traditionally with a focus to reduce fishing pressures and infrastructure placements. These MPAs are static in nature and are rarely considering climate change; therefore, their potential adaptation effectiveness as local adaptation measures for conservation in response to climate change are not clear. Here we discuss the challenges to Marine Protected Areas as conservation tools and for adaptation to climate change threats. We use two case studies from the UK to ask how climate change resilience could be included in MPA management to future-proof these conservation measures. We conclude that the resilience of MPAs to climate change would be better supported when adaptive management measures and an ecosystem-based approaches are adopted. We emphasise the need to increase the recognition in the primary legislation of MPAs and the monitoring of sites to better understand climate change as it becomes more pronounced, and impacts emerge.

Attraction of an artificial reef: a migratory demersal flounder remains in shallow water under high temperature conditions in summer

Article

Sep 2021

Offshore manmade structures, termed artificial reefs (e.g., wind farms, oil platforms, and manmade islands), affect the movement and migration of wild migratory marine animals. Certain types of migratory pelagic and benthic fish are known to utilize artificial reefs as feeding areas, for spatial reference (landmarks for their navigation), or as meeting points. However, little is known about the impact of artificial reefs on the migratory behavior of demersal flatfish. The marbled flounder (Pseudopleuronectes yokohamae), an important commercial flatfish species, exhibits seasonal migration between shallow water for spawning in winter and deeper water to avoid high water temperatures in summer. In this study, 39 tagged marbled flounders were released in the shallow water of the inner Osaka Bay area in June 2016, and then actively tracked, predominantly in deeper waters (100–140 m), from a fishing boat every week until mid-September 2016. Our active tracking detected no tagged fish in the deeper waters, whereas 36% of the fish were detected in the shallow water (10–15 m) around an artificial reef (offshore manmade island) at a high water temperature (26 °C). We suggest that a portion of the marbled flounder population did not show seasonal migration but remained in the shallow water around the artificial reef, even though the water temperature was high in summer. We suggest that this is related to the abundant food supply associated with the artificial reef.

Demographic responses to protection from harvesting in a long-lived marine species

Article

Full-text available

Apr 2021
BIOL CONSERV

Marine protected areas (MPAs) are usually considered to have positive effects on the recovery of over-exploited populations. However, resolving the extent to which MPAs function according to their conservation goals requires that essential demographic information such as individual survival and population size are quantified. To this end, we analyzed a 16-year replicated mark-recapture study on European lobster (Homarus gammarus, n = 8793) conducted at several protected and unprotected sites in southern Norway, quantifying the impact of MPAs on local population dynamics by means of a “before-after control-impact” study approach (BACI). Lobster survival and abundance were estimated by applying mu lti-state and robust design models to the mark-recapture data. These models revealed underlying positive responses to protection. Annual survival rates and population abundances reached higher values in the MPAs, compared to the unprotected sites (abundance range: MPAs = 96–1172, control areas = 92–747). In general, female survival was higher than male survival (range of survival: male = 0.13–0.75, female = 0.37–0.85), while larger males benefited more from protection compared to smaller males (range of increase in survival after protection: big = 100–125%, small = 55–101%). We also detected regional differences in demographic responses to protection, as not all MPAs showed the same changes in abundance over time. Our results show that MPAs can reach conservation goals by increasing the local survival and abundance of lobster, but they also highlight demographic differences between sexes and geographic areas that are worth considering for the management and design of both current and future MPAs.

Diet overlap between Cod (Gadus morhua) and European Flounder (Platichthys flesus) in the central Baltic Sea

Thesis

Full-text available

Jan 2018

The Baltic Sea is a frontrunner in ecosystem analysis and assessment, which have been used also in multispecies fisheries management advice. In the Baltic Sea, the multispecies assessment and management advice have been focused on the pelagic interactions between cod (Gadus morhua), sprat (Sprattus sprattus) and herring (Clupea harengus), by virtue of their well-known ecology. However, the fish interactions occurring in the benthic habitat are largely unknown. This study investigates, for the first time, the feeding interactions between the most important demersal fish species, cod and flounder (Platichthys flesus), in three areas of the eastern Baltic Sea. In this study I use stomach data from 2015 and 2016, collected in the ICES subdivisions 25 – 28 by the Swedish University of Agricultural Sciences, Department of Aquatic Resources. The diet of cod differs between the areas but, overall, shows an ontogenetic shift with a decrease of benthic prey and an in-crease of fish preys with size. In the coastal area the amount of benthic prey is al-ways > 50% irrespective of predator size, while in the offshore areas the amount of fish prey increase > 50% with increasing cod size. Conversely, the diet of flounder is relatively constant between sizes and areas. Cluster analyses revealed similarity between the diet of flounder and small-medium size cod in the offshore areas. A significant diet overlap was found between cod < 30 cm and flounder > 20 cm in the offshore area in SD 25, which is mainly driven by similar benthic prey, especially Saduria entomon, in the diet of both predators. These results point to a food competition between cod and flounder, likely augmented by recent increased abundance of Baltic flounder stocks. This competition could decrease the availability of benthic prey for cod, which, in turn, can lead to low condition factor, a reduction of cod growth and ultimately accentuate the negative effects of hypoxia on cod. Because of all of these reasons, cod and flounder competition could be an-other factor explaining the current bad status of the Eastern Baltic Cod stock.

POPULATION DYNAMICS OF FLOUNDERS IN THE NORTHERN BALTIC SEA -DECLINES, CRYPTIC SPECIES AND ENVIRONMENTAL DRIVERS

Thesis

Full-text available

Jun 2020

Henri Jokinen

Initiated by signs of drastic declines of once abundant flounders in the northern Baltic Sea, this thesis characterised/quantified these declines and studied their potential reasons. Multiple approaches were used to describe population trends, reveal intricacies in stock structure, and assess links to key environmental drivers. The results from the thesis verified clear negative trends in both adult and juvenile flounders in the northern Baltic Sea over the last 2–4 decades. Genetics revealed well-defined genetic structure and evidence for far gone speciation among Baltic Sea flounders, leading to the recognition of two instead of one flounder species, one of which was recently described as the only endemic fish species known to the region. Contrary to previous belief, flounders on the coast of Finland in the northern Baltic Sea were shown to be a mixed assemblage of this cryptic species pair. The thesis further showed that temporal variability in local species composition of the flounder assemblage explained some of the observed stock decline and was related to changing local and regional environmental conditions, of which reproductive volume, salinity, temperature and eutrophication were identified as potentially important factors. Finally, the thesis presented a new method for modelling environmental suitability for long-term population maintenance of the newly described Baltic flounder. The knowledge obtained has great value for how we understand and investigate stock composition and population dynamics of Baltic Sea flounders, and relates to issues of source-sink mechanisms, population connectivity, biological traits, resilience to exploitation and environmental change, among others. The results are likely important for future management and conservation of these fishes in the changing environment of the Baltic Sea.

Recruitment variability in Baltic flounder (Platichthys solemdali) – Effects of salinity with implications for stock development facing climate change

Article

Full-text available

May 2020
J SEA RES

The brackish water Baltic Sea is strongly influenced by irregular saline water inflows. Fewer inflow events since the 1980s have resulted in a decrease in salinity, and will according to predicted climate change continue to decrease. The newly described Baltic flounder Platichthys solemdali has adapted to reproduction at low salinity conditions since it colonized the Baltic Sea 7000 years BP; in the area studied (ICES SD 3d 28.2) spawning occurs at 3–20 m depth at ca 7 psu. Here we monitored variability in year-class strength as newly settled 0-gr fish in three coastal nursery areas, and compared obtained recruitment indices with prevailing temperature and salinity conditions. 0-gr abundance indices varied considerably between years, from 1 to 90, 10–296 and 17–86 at the respective sampling site, and showed strong accordance with the age structure of the adult stock. Variability in temperature showed no effect, but stronger and weaker year-classes respectively were related to variability in salinity in the range 6.6–7.1 psu with stronger year-classes at >6.8 psu. This coincides with variability in spermatozoa motility, fertilization rates and early egg development at different salinities and suggests that the year-class strength may be set already at the egg stage. Thus, only small changes in salinity at spawning may affect reproductive success and ultimately stock development. The potential effects on stock abundance and distribution facing climate change call for changes in future fishing patterns as well as adaptations in management to prevent stock collapse.

Sizing up the role of predators on Mullus barbatus populations in Mediterranean trawl and no-trawl areas

Article

Feb 2019
FISH RES

Fishing leads to drastic changes in ecosystems with a net loss of predatory biomass. This issue has been evidenced from historical ecological studies and from the evaluation of the effects of effective and large marine protected areas. In two fishery reserves off the northern Sicily coast the red mullet Mullus barbatus underwent an impressive biomass increment and a few piscivores fish species recovered after a trawl ban. The red mullet, more than 20% of all demersal fish in the untrawled areas, represented a huge food resource to its potential predators. By contrasting two trawled and two untrawled gulfs we figured out predator-prey relationships through the use of a combined approach based on trophic niche, stable isotopes data and biomass. We show that the white grouper Epinephelus aeneus and the black-bellied anglerfish Lophius budegassa are the most important predators of the red mullet with higher biomass in the untrawled areas. We also found a potential re-establishment of the trophic role for white grouper inside the untrawled areas. Our study highlights some of the benefits obtained from the use of large offshore marine protected areas as a tool for ecosystem restoration.

Competition for the fish

Article

Aug 2018

Maria Ovegård

European flounder - Report of the Working Group on Data Limited Diadromous Species

Technical Report

Full-text available

Aug 2019

The European flounder is a demersal species present along the NE-Atlantic Ocean, from Norway to Portugal, both in coastal and estuarine ecosystems (Nielsen, 1986). It is also present in the adjacent seas - Baltic, North, White, Mediterranean, and Black seas (Nielsen, 1986; Figure 5.2.2-1, Table 5.2.2-2). The species was introduced in North America through ballast water; however, the last record dates back to 2000 (Erling Holm, personal communication). The European flounder has been considered a strict catadromous species. However, there is some controversy about classifying flounder as catadromic, semi-catadromic, estuarine migrant, marine-estuarine opportunistic, or even as an estuarine resident species (Elliott & Dewailly, 1995; Elliott et al., 2007). Recent works revealed that flounder is not an estuarine resident species (Daverat, Martin, Fablet, 2011, & Pécheyran, 2011a; Morais, Dias, Babaluk, & Antunes, 2011), despite using estuarine habitats for extended periods of time (Jagger, 1998; Marchand, Tanguy, Laroche, Quiniou, & Moraga, 2003).

Characterizing and predicting the distribution of Baltic Sea flounder ( Platichthys flesus ) during the spawning season

Article

Jul 2017
J SEA RES

Identification of essential fish habitats (EFH), such as spawning habitats, is important for nature conservation, sustainable fisheries management and marine spatial planning. Two sympatric flounder (Platichthys flesus) ecotypes are present in the Baltic Sea, pelagic and demersal spawning flounder, both displaying ecological and physiological adaptations to the low-salinity environment of this young inland sea. In this study we have addressed three main research questions: 1) What environmental conditions characterize the spatial distribution and abundance of adult flounder during the spawning season? 2) What are the main factors defining the habitats of the two flounder ecotypes during the spawning season? 3) Where are the potential spawning areas of flounder? We modelled catch per unit of effort (CPUE) of flounder from gillnet surveys conducted over the southern and central Baltic Sea in the spring of 2014 and 2015 using generalized additive models. A general model included all the stations fished during the survey while two other models, one for the demersal and one for the pelagic spawning flounder, included only the stations where each flounder ecotype should dominate. The general model captured distinct ecotype-specific signals as it identified dual salinity and water depth responses. The model for the demersal spawning flounder revealed a negative relation with the abundance of round goby (Neogobius melanostomus) and a positive relation with Secchi depth and cod abundance. Vegetation and substrate did not play an important role in the choice of habitat for the demersal ecotype. The model for the pelagic spawning flounder showed a negative relation with temperature and bottom current and a positive relation with salinity. Spatial predictions of potential spawning areas of flounder showed a decrease in habitat availability for the pelagic spawning flounder over the last 20 years in the central part of the Baltic Sea, which may explain part of the observed changes in populations' biomass. We conclude that spatiotemporal modelling of habitat availability can improve our understanding of fish stock dynamics and may provide necessary biological knowledge for the development of marine spatial plans.

Modelling the abundance and size-based indicators of cod and flounder stocks in the Baltic Sea using newly standardized trawl survey data.

Article

Feb 2017

Standardized indices of abundance and size-based indicators are of extreme importance for monitoring fish population status. The main objectives of the current study were to (i) combine and standardize recently performed trawl survey with historical ones, (ii) explore and discuss the trends in abundance, and (iii) the trends in maximum length (Lmax) for cod (Gadus morhua) and flounder (Platichthys flesus) stocks in the Baltic Sea. Standardization of catch per unit of effort (CPUE) from trawl surveys from 1978 to 2014 to swept area per unit of time was conducted using information on trawling speed and horizontal opening of the trawls. CPUE data for cod and flounder stocks were modelled using generalized additive models (GAMs) in a delta modelling approach framework, while the Lmax data were modelled using ordinary GAMs. The CPUE time series of the Eastern Baltic cod stock closely resembles the spawning stock biomass trend from analytical stock assessment. The results obtained furnish evidence of the cod spill-over from Subdivisions (SD) 25–28 to SD 24. The decline of Lmax in recent years was evident for both species in all the stocks analysed indicating that the demersal fish community is becoming progressively dominated by small individuals. It is concluded that the standardization of long time series of fisheries-independent data constitutes a powerful tool that could help improve our knowledge on the dynamics of fished populations, thus promoting a long-term sustainable use of these marine resources.

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Article

Full-text available

Mar 2016

Down-regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d. total length of the sampled fish was 32·7 ± 3·1 cm and mean ± s.d. age was 6·2 ± 1·5 years. Measurements of atresia were performed using the 'profile method' with the intensity of atresia adjusted according to the 'dissector method' (10·6% adjustment; coefficient of determination was 0·675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down-regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.

Long term changes in the status of coastal fish in the Baltic Sea

Article

Feb 2016

Demographic effects of full vs. partial protection from harvesting: Inference from an empirical before-after control-impact study on Atlantic cod

Article

Jul 2015

In recent years, marine protected areas ( MPA s) excluding all or some fishing activities have become widely applied as a tool to rebuild marine ecosystems and fisheries, but still, our knowledge of the effects of MPA s on the demography of harvested populations remains scarce, especially in cases where partly protected areas are still supporting some fishing activities. Here, we investigated the influence of partial protection – excluding fixed gears such as gillnets and traps but still allowing a hook and line fishery – on the demography of A tlantic cod G adus morhua along the N orwegian S kagerrak coast. To do so, we applied novel multi‐event models to a 9‐year data set containing both live recaptures and dead recoveries of marked fish of different sizes collected before and after the implementation of an MPA , also including several unprotected sites. At the MPA site, the annual proportion of deaths due to fishing decreased from 0·59 before MPA implementation to 0·32 after MPA implementation. As a result, annual survival increased by 167% (from 0·09 to 0·24) for small (16–44 cm) and 83% (from 0·23 to 0·42) for big (45–97 cm) cod, respectively. Average survival was lower in unprotected areas, and annual fishing mortality was higher, representing almost 100% of the total mortality of large‐sized cod in some years. Annual emigration rates (i.e. spillover from the MPA ) increased in the last years of the study, but no differences in body growth were detected between sites. Closure of the fishery within the MPA would further increase the annual survival of smaller individuals by 100% (from 0·24 ± 0·07 to 0·48 ± 0·11) and that of larger individuals by 44% (from 0·42 ± 0·05 to 0·60 ± 0·09). Synthesis and applications . Our study reveals how current marine protected areas (MPA s) function and provides important insights for guiding a future adaptive management process. Given that harvested populations will not be able to sustain annual survival rates consistently below 30%, as found here; our results underscore the urgency of effective management measures such as no‐take zones in areas where local populations are particularly reduced or in dire need of demographic rescue.

Spatial Segregation in Eastern North Pacific Skate Assemblages

Article

Full-text available

Oct 2014
PLOS ONE

Skates (Rajiformes: Rajoidei) are common mesopredators in marine benthic communities. The spatial associations of individual species and the structure of assemblages are of considerable importance for effective monitoring and management of exploited skate populations. This study investigated the spatial associations of eastern North Pacific (ENP) skates in continental shelf and upper continental slope waters of two regions: central California and the western Gulf of Alaska. Long-term survey data were analyzed using GIS/spatial analysis techniques and regression models to determine distribution (by depth, temperature, and latitude/longitude) and relative abundance of the dominant species in each region. Submersible video data were incorporated for California to facilitate habitat association analysis. We addressed three main questions: 1) Are there regions of differential importance to skates?, 2) Are ENP skate assemblages spatially segregated?, and 3) When skates co-occur, do they differ in size? Skate populations were highly clustered in both regions, on scales of 10s of kilometers; however, high-density regions (i.e., hot spots) were segregated among species. Skate densities and frequencies of occurrence were substantially lower in Alaska as compared to California. Although skates are generally found on soft sediment habitats, Raja rhina exhibited the strongest association with mixed substrates, and R. stellulata catches were greatest on rocky reefs. Size segregation was evident in regions where species overlapped substantially in geographic and depth distribution (e.g., R. rhina and Bathyraja kincaidii off California; B. aleutica and B. interrupta in the Gulf of Alaska). Spatial niche differentiation in skates appears to be more pronounced than previously reported.

Age and Growth

Chapter

Nov 2007

Age and growth studies of flatfish form some of the oldest contributions to the scientific literature. Age-estimation methods are based mostly on reading otolith annuli, however, scales are used for some species. A variety of age validation studies have been pursued, using direct methods and radiometric techniques. The growth of flatfish larvae is better understood for aquaculture species than for wild species and there seems to be a propensity for high individual variability. Growth slows during metamorphosis in many species studied. On the nursery grounds growth is influenced by food availability and temperature but also shows patterns of density dependence and compensatory growth, and counter- and co-gradient variation in species with wide latitudinal ranges. Flatfishes can reach considerable ages and in general there is a sexual dimorphism where females are larger than males.

Konnektivitet och fysisk påverkan i kustvatten – en sammanställning över kunskapsläget och förslag till revidering av bedömningsgrund

Technical Report

Full-text available

May 2024

Connectivity in coastal waters is described as the ability of animals, plants, sediments and organic material to spread freely between the open sea and coast, along the coastline and between coastal areas and inland waters. Since connectivity has an important and pivotal role regarding the biological, physicochemical, and hydromorphological conditions in aquatic systems, it is included as a quality element when estimating ecological status of surface waters in the coastal zone. The description of connectivity and how it should be evaluated is deficient in the regulations provided by the Swedish Agency for Marine and Water Management, SwAM (HVMFS 2019:25). As such, the Department of Aquatic Resources at the Swedish University of Agricultural Sciences (SLU Aqua) was assigned to give suggestions on what information on the biological connectivity concerning plants and animals that could be included in a revised version of these regulations. The assignment also included to provide a knowledge base on connectivity and physical disturbance in the coastal zone. In addition, the assignment included analysing physical disturbance on the connectivity of fish in the coastal areas of the Skagerrak, Kattegat and the Baltic Sea. When revising the regulations, it was noted that information on the biological aspects of connectivity, and at what scales it operates, are missing. The current regulations do not account for connectivity being either active, through migrations of young and adult organisms, or passive, through transport of eggs, larvae, spores, seeds or fragments by currents (Chapter 2.1.2). This is important to keep in mind, since physical disturbance caused by jetties, piers, noise, boat traffic, etc. has different effects depending on what type of connectivity is in focus. The different dispersal types also occur over different time scales, where active migrations often occur on a seasonal basis and between different life stages, while passive dispersal generally occurs over days or weeks as larvae and spores develop in the free water column before settling on suitable habitat. There are also species that live their entire lives in open waters, such as phytoplankton, which is also included as a biological quality element to be assessed. Within the assessment process, it is essential to distinguish between typical home ranges and maximum migration and dispersal distances, as home ranges are relevant for population dynamics, while maximum migration and dispersal distances have a greater impact on genetic variation between populations. It is also important to consider how connectivity may be affected by a changing climate. Fish play a central role in marine ecosystems, and therefore connectivity of fishes – both between the coast and sea, within coastal areas and between the coast and freshwater – become crucial determinants of ecological status, both in freshwater and in coastal waters. As it is mainly fish that undertake migration between coastal and freshwater areas and the coast and sea, it is difficult to classify parameter 8.3 Connectivity between coastal waters and transitional waters and coastal land areas in the regulations (HVMFS 2019:25) without including fish. Fish should therefore also be included as a biological quality element in the regulations for coastal waters (Chapter 2.1.3). Fish are included in the assessment of ecological status in the Marine Strategy Framework Directive (MSFD), which geographically overlaps with the Water Framework Directive (WFD) in the coastal zone. On the other hand, the MSFD does not include connectivity as a criterion in ecological status assessments. This means that connectivity in the coastal zone, especially for fish, is currently overlooked and coordination between the directives is therefore required to address this. As connectivity is primarily a biological function linked to fish and other organisms, it is also worth considering whether connectivity should be included among the biological quality elements instead of the hydromorphological ones. Summary To our knowledge, Sweden seems to be one of the countries in the EU that has come furthest in terms of assessment of connectivity within the Water Framework Directive. The other EU countries seem to focus on the other two hydromorphological quality elements hydrographic condition and morphological condition in their assessments. This may be due to the fact that connectivity is not included in the Water Framework Directive, but that Sweden has chosen to include it as a separate quality factor in the regulations on status assessment in Swedish coastal waters. Connectivity is mentioned in some contexts in other EU countries, but is then most often linked to freshwater systems with a focus on migratory fish and barriers in the form of hydropower and other physical structures that interfere with the flow of water. Interest in developing the hydromorphological quality element, including connectivity, has grown in the EU and a number of reports and scientific articles are available on the subject (Chapter 2.1.4). Connectivity can be measured in different ways and at different spatial scales. In Chapter 3, we summarise this information in a knowledge base for assessing connectivity in the coastal zone. Measuring and analysing the distribution of species in coastal and marine areas is a challenging task, and therefore knowledge in this area is still limited. Spatial analyses based on habitat maps and information on the dispersal distance of species have been used to analyse and assess active migration, especially in the Baltic Sea and the Skagerrak, as well as tagging studies and combinations of methods. To investigate passive dispersal, a combination of empirical data and hydrodynamic models have mainly been used to investigate dispersal routes and nursery habitats of different marine organisms and to identify key areas of connectivity such as sources and sinks. Chapter 3 also summarises the connectivity patterns of some biologically important groups of organisms and information on natural barriers such as salinity, depth and temperature that affect the dispersal of organisms and organic matter. Few studies have examined the effects of physical disturbance on connectivity, both within Europe and other parts of the world. Chapter 4.2 describes the studies that have been carried out in Swedish waters, regarding the effects of physical disturbance on passive dispersal and active migration, and Chapter 4.3 summarises information on physical disturbance and connectivity on some key habitats. Chapter 5 describes the results of new analyses of physical disturbance on fish along the Swedish west coast that are part of the current assignment. The results of these studies show that physical disturbance can have a significant impact on connectivity, especially for those species that depend on shallow and wave-sheltered areas for their reproduction. This type of habitat is particularly sensitive to physical impacts, with a noticeable reduction in connectivity. These areas are also the most affected by loss of connectivity due to their high degree of coastal development, including jetties, buoys and marinas. In addition, the results from the modelling studies showed that macroalgae and macrophytes are strongly affected by physical changes. These findings underscore the importance of carefully considering and managing physical disturbance on species and habitats in the coastal zone in order to conserve and protect vulnerable marine ecosystems and the services they provide. The results are important for decision-makers and planners working on conservation measures and management of these environments. There are significant knowledge gaps on connectivity and physical disturbance in coastal waters. Chapter 6 lists these knowledge gaps, including the need for high-resolution spatial data on the distribution of both organisms and pressures, as well as the relationships between these, both for the biological quality elements benthic fauna, macroalgae, marine plants and phytoplankton and for fish, which are not included as biological quality elements in the coastal zone. There is also a need for increasing the knowledge base on the effects of a changing climate and of various types of restoration measures on connectivity.

Long-term effects of no-take zones in Swedish waters

Technical Report

Full-text available

Jan 2023

Marine protected areas (MPAs) are increasingly established worldwide to protect and restore degraded ecosystems. However, the level of protection varies among MPAs and has been found to affect the outcome of the closure. In no-take zones (NTZs), no fishing or extraction of marine organisms is allowed. The EU Commission recently committed to protect 30% of European waters by 2030 through the updated Biodiversity Strategy. Importantly, one third of these 30% should be of strict protection. Exactly what is meant by strict protection is not entirely clear, but fishing would likely have to be fully or largely prohibited in these areas. This new target for strictly protected areas highlights the need to evaluate the ecological effects of NTZs, particularly in regions like northern Europe where such evaluations are scarce. The Swedish NTZs made up approximately two thirds of the total areal extent of NTZs in Europe a decade ago. Given that these areas have been closed for at least 10 years and can provide insights into long-term effects of NTZs on fish and ecosystems, they are of broad interest in light of the new 10% strict protection by 2030 commitment by EU member states. In total, eight NTZs in Swedish coastal and offshore waters were evaluated in the current report, with respect to primarily the responses of focal species for the conservation measure, but in some of the areas also ecosystem responses. Five of the NTZs were established in 2009-2011, as part of a government commission, while the other three had been established earlier. The results of the evaluations are presented in a synthesis and also in separate, more detailed chapters for each of the eight NTZs. Overall, the results suggest that NTZs can increase abundances and biomasses of fish and decapod crustaceans, given that the closed areas are strategically placed and of an appropriate size in relation to the life cycle of the focal species. A meta-regression of the effects on focal species of the NTZs showed that CPUE was on average 2.6 times higher after three years of protection, and 3.8 times higher than in the fished reference areas after six years of protection. The proportion of old and large individuals increased in most NTZs, and thereby also the reproductive potential of populations. The increase in abundance of large predatory fish also likely contributed to restoring ecosystem functions, such as top-down control. These effects appeared after a 5-year period and in many cases remained and continued to increase in the longer term (>10 years). In the two areas where cod was the focal species of the NTZs, positive responses were weak, likely as an effect of long-term past, and in the Kattegat still present, recruitment overfishing. In the Baltic Sea, predation by grey seal and cormorant was in some cases so high that it likely counteracted the positive effects of removing fisheries and led to stock declines in the NTZs. In most cases, the introduction of the NTZs has likely decreased the total fishing effort rather than displacing it to adjacent areas. In the Kattegat NTZ, however, the purpose was explicitly to displace an unselective coastal mixed bottom-trawl fishery targeting Norway lobster and flatfish to areas where the bycatches of mature cod were smaller. In two areas that were reopened to fishing after 5 years, the positive effects of the NTZs on fish stocks eroded quickly to pre-closure levels despite that the areas remained closed during the spawning period, highlighting that permanent closures may be necessary to maintain positive effects. We conclude from the Swedish case studies that NTZs may well function as a complement to other fisheries management measures, such as catch, effort and gear regulations. The experiences from the current evaluation show that NTZs can be an important tool for fisheries management especially for local coastal fish populations and areas with mixed fisheries, as well as in cases where there is a need to counteract adverse ecosystem effects of fishing. NTZs are also needed as reference for marine environmental management, and for understanding the effects of fishing on fish populations and other ecosystem components in relation to other pressures. MPAs where the protection of both fish and their habitats is combined may be an important instrument for ecosystem-based management, where the recovery of large predatory fish may lead to a restoration of important ecosystem functions and contribute to improving decayed habitats. With the new Biodiversity Strategy, EUs level of ambition for marine conservation increases significantly, with the goal of 30% of coastal and marine waters protected by 2030, and, importantly, one third of these areas being strictly protected. From a conservation perspective, rare, sensitive and/or charismatic species or habitats are often in focus when designating MPAs, and displacement of fisheries is then considered an unwanted side effect. However, if the establishment of strictly protected areas also aims to rebuild fish stocks, these MPAs should be placed in heavily fished areas and designed to protect depleted populations by accounting for their home ranges to generate positive outcomes. Thus, extensive displacement of fisheries is required to reach benefits for depleted populations, and need to be accounted for e.g. by specific regulations outside the strictly protected areas. These new extensive EU goals for MPA establishment pose a challenge for management, but at the same time offer an opportunity to bridge the current gap between conservation and fisheries management.

Fisk- och skaldjursbestånd i hav och sötvatten 2021: Resursöversikt

Technical Report

Full-text available

Mar 2022

Report on stock status & management advice for fish & shellfish species in Swedish waters (Report In Swedish). The resource overview for fish and shellfish stocks describes conditions and trends for commercial and recreational fishing's most relevant stocks of fish and shellfish in the sea and the four great lakes: Lake Vänern, Lake Vättern, Mälaren and Hjälmaren. The report is published annually and for the 2022 report, 48 species divided into more than a hundred different populations are described. For each stock, catch advice is given with the aim of keeping the stock within biological safe borders. The advice does not consider social or economic aspects of fishing. For nationally managed stocks the Swedish University of Agricultural Sciences, Department of Aquatic Resources (SLU Aqua) develops and gives the biological catch advice, and for stocks managed by the EU, advice is based on the International Council for the Exploration of the Sea (Ices) relevant catch advice. About 50 researchers from SLU Aqua participate in Ice's advisory work. SLU Aqua's advice is worked out in a process with an internal review, partly by species-specifically selected experts, partly in the form of joint seminars. Citation: Sundelöf, A., Florin, A., Rogell, B. and Bolund, E. V., F; Sundblad, G; Strömberg, H; Bergendahl, IA, Sundin, J; Lundström, K; Wikström, K; Magnusson, K; Fetterplace, L; Wennström, L; Ogonowski, M; Bergenius, M; Holmgren, N; Kaljuste, O; Bohman, P; Fredriksson, R; Eiler, S; Larsson, S; Axenrot, T; Östman, Ö. (2022). Havs-och vattenmyndigheten.

Fisk- och skaldjursbestånd i hav och sötvatten 2020: Resursöversikt

Technical Report

Full-text available

Feb 2021

Report on stock status & management advice for fish & shellfish species in Swedish waters (In Swedish). Open Access in DiVA - http://havochvatten.diva-portal.org/smash/record.jsf?pid=diva2%3A1531416&dswid=9443

Competition for the fish - Fish extraction from the Baltic Sea by humans, aquatic mammals, and birds

Article

Full-text available

Dec 2017

Populations of fish eating mammals (primarily seals) and birds have increased in the Baltic Sea and there is concern that their consumption reduces fish stocks and has negative impact on the fishery. Based primarily on published data on fisheries' landings and abundances, consumption and diets of birds and seals around year 2010, we compare consumption of commercial fish species by seals (1*10 5 metric tons per year) and birds (1*10 5 tons) to the catch in the commercial and recreational fishery (7*10 5 tons), and when applicable at the geographical resolution of ICES subdivisions. The large populations of herring (Clupea harengus), sprat (Sprattus sprattus) and cod (Gadus morhua), primarily inhabit offshore areas and are mainly caught by the fishery. Predation by birds and mammals likely has little impact on these stocks. For these species, seals and birds may be negatively impacted by competition from the fishery. In the central and southern Baltic, seals and birds consume about as much flatfish as is caught by the fishery and competition is possible. Birds and seals consume 2-3 times as much coastal fish as is caught in the fishery. Many of the coastal species are not much targeted by the fishery (e.g. eelpout Zoarces viviparus, roach Rutilus rutilus and ruffe Gymnocephalus cernua), while other species used by wildlife are important to the fishery (e.g. perch Perca fluviatilis and whitefish Coregonus spp.) and competition between wildlife and the fishery is likely, at least locally. Estimated wildlife consumption of pike (Esox lucius), sea trout (Salmo trutta) and pikeperch (Sander lucioperca) varies among ICES subdivisions and the degree of competition for these species will likely differ among areas. Our results indicate that competition between wildlife and fisheries need to be addressed in basic ecosystem research, management and conservation. This requires improved quantitative data on wildlife diets, abundances and fish production.

Coastal fish indicators response to natural and anthropogenic drivers –variability at temporal and different spatial scales

Article

Full-text available

Oct 2016

Ecological indicators are increasingly used in marine and freshwater management but only few are developed towards full operationalization with known patterns of variability and documented responses to natural and anthropogenic environmental drivers. Here, we evaluate potential sources of indicator variability at two different spatial scales in three coastal fish-based indicators of environmental status in the Baltic Sea; abundance of cyprinids, abundance of perch and the proportion of larger perch. The study was performed on a data set covering 41 monitoring areas subject to different levels of anthropogenic impact, at a latitudinal range of 56–66°N and a salinity range of 2–8. Interannual variation was clearly minor relative to spatial variation. Small-scale spatial variation was related to water depth, wave exposure and water temperature. The remaining variation was assessed in relation to differences in natural and anthropogenic drivers between monitoring areas. Cyprinids showed a clear inverse relationship to water transparency, which was used as a proxy for eutrophication, indicating increased abundances in nutrient enriched areas. None of the indicators showed an expected negative relationship to the level of coastal commercial fisheries catches. Rather, a positive relationship for Perch suggested that the coastal fisheries were concentrated to areas with strong perch populations in the studied areas. The effect of salinity and climate (temperature during the growth season) among monitoring areas were small. The results emphasize the importance of assigning area-specific boundary levels to define good environmental status in the coastal fish indicators, in order to account for natural sources of variability. Further, although long-term monitoring in reference areas is crucial for obtaining a historical baseline, our results suggest that the status assessment of coastal fish would generally gain precision by increasingly including spatially based assessments. We propose that similar analytical approaches could be applied to other ecosystem components, especially in naturally heterogenic environments, in order to separate indicator variability attributed to potential anthropogenic impact.

Selected Papers from the Sixth World Fisheries Congress

Article

Oct 2013
J FISH BIOL

Towards marine landscapes in the Baltic Sea

Technical Report

Full-text available

Jan 2007

Nursery area utilization by turbot (Psetta maxima) and flounder (Platichthys flesus) at Gotland, central Baltic Sea

Article

Full-text available

Feb 2011
BOREAL ENVIRON RES

To reveal the temporal and spatial utilization of a preferred nursery ground habitat by 0-group turbot and flounder in the Baltic Sea, sampling was conducted in six sandy bays in early-mid-July to early-mid-September 2003-2005 off the coast of Gotland (ICES SD 27 & 28-2). Settlement and peak abundance of turbot occurred from late July-early August to early September and from mid-August to early September, respectively. Settlement of flounder occurred from early-mid-July with decreasing numbers over time, except in 2005. Peak abundance of 0-group flounder occurred in late July-early August to mid-September, suggesting a considerable temporal overlap with 0-group turbot. 0-group turbot and flounder also overlapped in respect to depth with preference for 0.2 and 0.6 m over 1 m. The spatial and temporal overlap of the species was verified by a logistic regression analysis; the probability of sampling 0-group flounder when 0-group turbot was caught in a haul was 0.84 (0.80-0.87, 95% CI).

BaltiX V 1.1 : A 3D Ocean Modelling Configuration for Baltic & North Sea Exchange Analysis

Technical Report

Full-text available

Jan 2013

Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates?

Article

Full-text available

Jun 2012

Gårdmark, A., Östman, Ö., Nielsen, A., Lundström K., Karlsson O., Pönni, J., and Aho, T. 2012. Does predation by grey seals (Halichoerus grypus) affect Bothnian Sea herring stock estimates? – ICES Journal of Marine Science, 69: . Mortality of small pelagic fish due to marine mammals is generally considered to be low compared with other sources of mortality. With recent recoveries of marine mammal predators worldwide, this may no longer hold. The grey seal (Halichoerus grypus) population in the Bothnian Sea has increased fivefold since 1985. Its main prey, herring (Clupea harrengus), is a key species for fisheries in the region. Yet, current stock assessments assume constant natural mortality, leading to a risk of biased stock estimates with increasing predation and misleading analyses of herring population dynamics. We estimated grey seal predation from diet data and reanalysed herring spawning stock biomass (SSB) during 1973–2009. Accounting for predation increased the herring SSB 16% (maximum 19%), but this was within the confidence intervals when ignoring predation. Although mortality in older individuals was inflated when accounting for seal predation, this did not change the conclusions about drivers of herring dynamics. Accounting for grey seal predation is important for abundance estimates of old herring, but currently not for SSB estimates, given the great uncertainties in the standard assessment. The grey seal impact on Bothnian Sea herring will need to be reassessed if stock age composition, grey seal feeding preferences, or total stock development change.

Both predation and feeding opportunities may explain changes in survival of Baltic salmon post-smolts

Article

Full-text available

May 2012

Mäntyniemi, S., Romakkaniemi, A., Dannewitz, J., Palm, S., Pakarinen, T., Pulkkinen, H., Gårdmark, A., and Karlsson, O. 2012. Both predation and feeding opportunities may explain changes in survival of Baltic salmon post-smolts. – ICES Journal of Marine Science, 69: 1574–1579. The survival of wild and hatchery-reared post-smolts of salmon (Salmo salar) in the Baltic Sea has declined since the 1990s. Direct observations of the processes affecting survival are, however, lacking. Here, the importance of food availability and predation in regulating post-smolt survival is analysed. Based on previous studies, the following explanatory variables were selected: (i) availability of herring (Clupea harengus membras) recruits in the Gulf of Bothnia (Bothnian Sea, Bothnian Bay) in the northern Baltic Sea; (ii) sprat (Sprattus sprattus balticus) and herring abundance in the southern Baltic Sea; and (iii) abundance of grey seal (Halichoerus grypus) along the post-smolt migration route. Bayesian analysis was used to estimate the relative probability of each of the 32 combinations of these variables and revealed that the model including grey seal abundance and herring recruits per post-smolt had the highest posterior probability and a high coefficient of determination. The results suggest that the declining trend in post-smolt survival is explained by the increased number of grey seals, whereas the annual variation in survival coincides with variation in the recruitment of Bothnian Sea herring. However, it remains uncertain whether the observed correlations arise from direct causalities or other mechanisms.

Egg production of turbot, Scophthalmus maximus, in the Baltic Sea

Article

Full-text available

Nov 2013
J SEA RES

In the brackish water Baltic Sea turbot spawn at ~ 6-9 psu along the coast and on offshore banks in ICES SD 24-29, with salinity influencing the reproductive success. The potential fecundity (the stock of vitellogenic oocytes in the pre-spawning ovary), egg size (diameter and dry weight of artificially fertilized 1-day-old eggs) and gonad dry weight were assessed for fish sampled in SD 25 and SD 28. Multiple regression analysis identified somatic weight, or total length in combination with Fulton's condition factor, as main predictors of fecundity and gonad dry weight with stage of maturity (oocyte packing density or leading cohort) as an additional predictor. For egg size, somatic weight was identified as main predictor while otolith weight (proxy for age) was an additional predictor. Univariate analysis using GLM revealed significantly higher fecundity and gonad dry weight for turbot from SD 28 (3378-3474 oocytes/g somatic weight) compared to those from SD 25 (2343 oocytes/g somatic weight), with no difference in egg size (1.05 ± 0.03 mm diameter and 46.8 ± 6.5 μg dry weight; mean ± sd). The difference in egg production matched egg survival probabilities in relation to salinity conditions suggesting selection for higher fecundity as a consequence of poorer reproductive success at lower salinities. This supports the hypothesis of higher size-specific fecundity towards the limit of the distribution of a species as an adaptation to harsher environmental conditions and lower offspring survival probabilities. Within SD 28 comparisons were made between two major fishing areas targeting spawning aggregations and a marine protected area without fishing. The outcome was inconclusive and is discussed with respect to potential fishery induced effects, effects of the salinity gradient, effects of specific year-classes, and effects of maturation status of sampled fish.

Estimates of the Size of the Baltic Grey Seal Population Based on Photo-Identification Data

Article

Full-text available

Jan 2007

The size of the year 2000 summer population of grey seals in the Baltic Sea was estimated using identification of individual seals from photographs taken over a period of 6 years. Photos were taken at haul-out sites within all major grey seal areas in the semi-closed Baltic Sea. The point estimate is 15,631, based on a value for annual survival of identification markings of 0.904, which was also estimated using the photo-id data, with 95% confidence limits from 9,592 to 19,005. The estimate is subject to an unknown, but probably small, upward bias resulting from the risk of failure to identify all individuals in the photographs used for the analysis. An estimated min- imum of 15,950 seals were counted at moulting haul-outs in 2003, which thus provides a low- er bound on the population size in that year and represents 80% of the photo-id point estimate. Hiby, L., Lundberg, T., Karlsson, O., Watkins, J., Jüssi, M., Jüssi, I. and Helander, B. 2007. Estimates of the size of the Baltic grey seal population based on photo-identification data. NAMMCO Sci. Publ. 6:163-175.

Estimation of grey seal (Halichoerus grypus) diet com- position in the Baltic Sea

Article

Full-text available

Jan 2005

We examined the digestive tract contents from 145 grey seals (Halichoerus grypus) collected be- tween 2001 and 2004 in the Baltic Sea. We compensated for biases introduced by erosion of otoliths, both by using additional hard-part structures other than otoliths, and species-specific size and nu- merical correction factors. In the absence of numerical correction factors based on feeding experi- ments for some species, we used correction factors based on a relationship between otolith recovery rate and otolith width. A total of 24 prey taxa were identified but only a few species contributed substantially to the diet. The estimated diet composition was, independently of the prey number estimation method and diet composition estimation model used, dominated by herring (Clupea harengus), both by numbers and biomass. In addition to herring, common whitefish (Coregonus lavaretus) and sprat (Sprattus sprattus) were important prey, but cyprinids (Cyprinidae), eelpout (Zoarces viviparus), flounder (Platichtys flesus) and salmon (Salmo salar) also contributed sig- nificantly. Our results indicated dietary differences between grey seals of different age as well as between seals from the northern (Gulf of Bothnia) and the southern (Baltic Proper) Baltic Sea. Lundström, K., Hjerne, O., Alexandersson, A. and Karlsson O. 2007. Estimation of grey seal (Halichoerus grypus) diet composition in the Baltic Sea. NAMMCO Sci. Publ. 6:177-196.

Salinity requirements for successful spawning of Baltic and Belt Sea cod and the potential for cod stock interactions in the Baltic Sea

Article

Full-text available

Jun 1997

The brackish water of the Baltic Sea, with decreasing salinity from the west to the east and from the south to the north, is a borderline area for cod Gadus morhua. The major stock, the eastern Baltic cod, has decreased substantially during the last decade. A discussion concerning the possibility of immigration of cod and the potential of stock interactions has evolved. The present study was conducted in order to elucidate if differences in salinity requirements for successful spawning exist between the eastern Baltic cod and the western Belt Sea cod, and if adaptation to ambient salinity is possible. Activation of the spermatozoa occurred at greater than or equal to 11 to 12 psu (practical salinity units) for Baltic cod and at greater than or equal to 15 to 16 psu for Belt Sea cod. Neutral egg buoyancy was obtained at 14.5 +/- 1.2 psu and at 20 to 22 psu respectively. Transfer of fish from marine to brackish water conditions showed that these characteristics remained essentially the same; activation of spermatozoa occurred at greater than or equal to 14 to 15 psu and neutral egg buoyancy at 19 to 21 psu. The results suggest that these characteristics are specific to populations. Regarding hydrographic conditions in the spawning areas of cod in the Baltic, the results suggest that stock interactions may be possible in the western Baltic spawning areas where salinity requirements for both stocks are fulfilled, but not in the eastern spawning areas as low salinity prevents successful spawning of Belt Sea cod. Salinity and oxygen conditions in the Baltic vary with highly irregular saline water inflows. Periods of stagnation without inflows may, due to decreasing salinity, e.g. <15 psu during the last stagnation period, act as an ecological barrier separating the stocks.

Energy requirements of breeding Great Cormorants Phalacrocorax Carbo Sinensis

Article

Full-text available

May 1995

Cormorants and humans are purported to compete for fish resources. Recent increases in cormorant populations in western Europe have led to new conflicts between fishermen and nature conservationists, a situation which has stimulated research into the food requirements of these seabirds. However, most dietary studies are based on stomach content or pellet analysis. Both these methods are biased. We used a time-budget model to calculate the energy requirements of great cormorants Phalacrocorax carbo sinensis breeding in Schleswig-Holstein, Germany. The time budgets of the birds were recorded for different breeding phases and the energetic costs of the different activities determined through respirometric measurements or by using values derived from the literature. The food requirements of great cormorants during incubation were calculated to be 238 g adult(-1) d(-1). These requirements rise to 316 g d(-1) during the rearing of young chicks and to 588 g d(-1) during rearing of downy chicks. Human disturbance causing great cormorants to fly off their nests entails an additional consumption of 23 g fish per bird or ca 23 kg per disturbance event for a typical colony.

The impact of marine reserves: Do reserves work and does reserve size matter?

Article

Full-text available

Feb 2003

Benjamin Halpern

Marine reserves are quickly gaining popularity as a management option for marine conservation, fisheries, and other human uses of the oceans. Despite the popularity of marine reserves as a management tool, few reserves appear to have been created or designed with an understanding of how reserves affect biological factors or how reserves can be designed to meet biological goals more effectively (e.g., attaining sustainable fish populations). This shortcoming occurs in part because the many studies that have examined the impacts of reserves on marine organisms remain isolated examples or anecdotes; the results of these many studies have not yet been synthesized. Here, I review the empirical work and discuss the theoretical literature to assess the impacts of marine reserves on several biological measures (density, biomass, size of organisms, and diversity), paying particular attention to the role reserve size has in determining those impacts. The results of 89 separate studies show that, on average, with the exception of invertebrate biomass and size, values for all four biological measures are significantly higher inside reserves compared to outside (or after reserve establishment vs. before) when evaluated for both the overall communities and by each functional group within these communities (carniv- orous fishes, herbivorous fishes, planktivorous fishes/invertebrate eaters, and invertebrates). Surprisingly, results also show that the relative impacts of reserves, such as the proportional differences in density or biomass, are independent of reserve size, suggesting that the effects of marine reserves increase directly rather than proportionally with the size of a reserve. However, equal relative differences in biological measures between small and large reserves nearly always translate into greater absolute differences for larger reserves, and so larger reserves may be necessary to meet the goals set for marine reserves. The quality of the data in the reviewed studies varied greatly. To improve data quality in the future, whenever possible, studies should take measurements before and after the creation of a reserve, replicate sampling, and include a suite of representative species. Despite the variable quality of the data, the results from this review suggest that nearly any marine habitat can benefit from the implementation of a reserve. Success of a marine reserve, however, will always be judged against the expectations for that reserve, and so we must keep in mind the goals of a reserve in its design, management, and evaluation.

Biological Effects Within No-Take Marine Reserves: A Global Synthesis

Article

Full-text available

May 2009

The study and implementation of no-take marine reserves have increased rapidly over the past decade, providing ample data on the biological effects of reserve protection for a wide range of geographic locations and organisms. The plethora of new studies affords the opportunity to re- evaluate previous findings and address formerly unanswered questions with extensive data synthe- ses. Our results show, on average, positive effects of reserve protection on the biomass, numerical density, species richness, and size of organisms within their boundaries which are remarkably simi- lar to those of past syntheses despite a near doubling of data. New analyses indicate that (1) these results do not appear to be an artifact of reserves being sited in better locations; (2) results do not appear to be driven by displaced fishing effort outside of reserves; (3) contrary to often-made asser- tions, reserves have similar if not greater positive effects in temperate settings, at least for reef ecosystems; (4) even small reserves can produce significant biological responses irrespective of lati- tude, although more data are needed to test whether reserve effects scale with reserve size; and (5) effects of reserves vary for different taxonomic groups and for taxa with various characteristics, and not all species increase in response to reserve protection. There is considerable variation in the responses documented across all the reserves in our data set — variability which cannot be entirely explained by which species were studied. We suggest that reserve characteristics and context, par- ticularly the intensity of fishing outside the reserve and inside the reserve before implementation, play key roles in determining the direction and magnitude of the reserve response. However, despite considerable variability, positive responses are far more common than no differences or negative responses, validating the potential for well designed and enforced reserves to serve as globally important conservation and management tools.

Flatfi shes in the Baltic Sea - a review of biology and fi shery with a focus on Swedish conditions

Article

Full-text available

Jan 2005

Ann-Britt Florin

Density dependence in marine protected populations: A review

Article

Full-text available

Jun 2000

The cessation or reduction of fishing in marine protected areas (MPAs) should promote an increase in abundance and mean size and age of previously exploited populations. Thus density-dependent changes in life-history characteristics should occur when populations are allowed to recover in MPAs. In this review, we synthesize the existing information on resource limitation in marine ecosystems, densitydependent changes in life-history traits of exploited populations and evidence for biomass export from MPAs. Most evidence for compensatory changes in biological variables has been derived from observations on populations depleted by high fishing mortality or on strong year classes, but these changes are more evident in juveniles than in adults and in freshwater rather than in marine systems. It is unclear if adults of exploited marine populations are resource limited. This may suggest that exploited populations are controlled mainly by density-independent processes, which could be a consequence of the depleted state of most exploited populations. MPAs could be a useful tool for testing these hypotheses. If we assume that resources become limiting inside MPAs, it is plausible that, if suitable habitats exist, mobile species will search for resources outside of the MPAs, leading to export of biomass to areas which are fished. However, it is not possible to establish from the available data whether this export will be a response to resource limitation inside the MPAs, the result of random movements across MPA boundaries or both. We discuss the implications of this process for the use of MPAs as fisheries management tools.

A comparison of frameworks and objectives for implementation of marine protected areas in Northern Europe and in Southeast Asia

Article

Full-text available

Jul 2009

A proliferation of marine protected areas around the world, including Europe and Southeast Asia, is evidence of a growing global concern for the marine environment and its living resources. While marine protected areas in Europe on a wider scale have generally been considered a tool for either nature conservation or a technical measure in management of fisheries, overall management objectives of marine protected areas in Southeast Asian countries have varied more significantly between countries and sites due to differences in societal needs and opportunities, spatial scales, environmental conditions and varying threats. These differences have resulted in different approaches to marine protected area development and management. Management of the Northern European marine environment and its living resources is highly sectoral and largely determined by central directives and policies stemming from the European Union, such as the Habitats Directive and the Common Fisheries Policy. This paper however, will touch upon an ongoing evolution within the European Union from a strictly sectoral approach to marine protected areas and marine management, towards a more integrated, ecosystem approach to management of fisheries and the marine environment. In Southeast Asia, marine protected area development is usually determined by individual governments, municipalities and coastal communities, based upon specific needs and settings. Examples of such marine protected areas in Vietnam and the Philippines will be described, including their underlying institutional frameworks and objectives such as tourism, management of artisanal fisheries, etc. Examples of differences and similarities between Northern European and Southeast Asian marine protected areas will be presented and areas in which regions might learn from one another identified. For instance, where Southeast Asian protected areas have addressed the inevitable interdependency between healthy ecosystems and sustainable coastal fisheries for decades, marine protected areas in Northern Europe usually address either large scale management of stocks of individual fish species or nature conservation. Tourism has long been an overarching driving force in marine protected area implementation in SE Asia, while in Northern Europe especially this has only had little influence on overall objectives pertaining to the marine environment.

Density dependence in marine protected populations: a review

Article

Full-text available

Jun 2000
ENVIRON CONSERV

The cessation or reduction of fishing in marine protected areas (MPAs) should promote an increase in abundance and mean size and age of previously exploited populations. Thus density-dependent changes in life-history characteristics should occur when populations are allowed to recover in MPAs. In this review, we synthesize the existing information on resource limitation in marine ecosystems, density-dependent changes in life-history traits of exploited populations and evidence for biomass export from MPAs. Most evidence for compensatory changes in biological variables has been derived from observations on populations depleted by high fishing mortality or on strong year classes, but these changes are more evident in juveniles than in adults and in freshwater rather than in marine systems. It is unclear if adults of exploited marine populations are resource limited. This may suggest that exploited populations are controlled mainly by density-independent processes, which could be a consequence of the depleted state of most exploited populations. MPAs could be a useful tool for testing these hypotheses. If we assume that resources become limiting inside MPAs, it is plausible that, if suitable habitats exist, mobile species will search for resources outside of the MPAs, leading to export of biomass to areas which are fished. However, it is not possible to establish from the available data whether this export will be a response to resource limitation inside the MPAs, the result of random movements across MPA boundaries or both. We discuss the implications of this process for the use of MPAs as fisheries management tools.

Environmental management of marine protected areas

Article

Full-text available

Jan 2009
ICES J MAR SCI

Simon Jennings

Jennings, S. 2009. The role of marine protected areas in environmental management. – ICES Journal of Marine Science, 66: 16–21. Marine protected areas (MPAs) are one of several tools used to meet management objectives for the marine environment. These objectives reflect political and societal views, and increasingly reconcile fishery and conservation concerns, a consequence of common high-level drivers, such as the World Summit on Sustainable Development. The contribution of MPAs to meeting objectives should be assessed in conjunction with other tools, taking account of the management systems of which they are part. Many of the same factors determine the success of MPAs and other management tools, such as quality of governance and the social and economic situation of people using marine goods and services. Diverse legislation governs MPA designation. Designation could be simplified by prearranged and prenegotiated agreements among all relevant authorities. Agreements could specify how to make trade-offs among objectives, interpret scientific advice, ensure effective engagement among authorities and stakeholders, deal with appeals, and support progressive improvement. The jurisdiction and competence of fishery management authorities mean that they are well placed to contribute to the design, designation, and enforcement of MPAs. Their strengths include well-established procedures for accessing scientific advice, the capacity to work across multiple jurisdictions, experience with MPA management, and access to vessels and personnel for enforcement.

Density and temperature dependence of gill net catch per unit effort for perch, Perca fluviatilis, and roach, Rutilus rutilus

Article

Full-text available

Jul 2006
FISHERIES MANAG ECOL

Abstract The densities of perch, Perca fluviatilis L., and roach, Rutilus rutilus (L.), were estimated in six and three lakes, respectively, using mark–recapture and ranged from 25–1064 perch ha−1 and 865–2749 roach ha−1. Effects of fish density, net type and water temperature on catch-per-unit-effort (CPUE) were analysed by generalised linear models (GLM) and generalised additive models (GAM). GAMs were fitted to estimate the simultaneous linear and nonlinear effects of temperature and density on CPUE. These models showed significant nonlinear effects of density on CPUE – mostly for perch, and also for both species at high densities. The models also revealed that both species had distinct density–temperature criteria of expected maximum CPUE and zero CPUE values. Because of the nonlinear relationship between CPUE and density, it was concluded that CPUE should be used with caution as a proxy of density.

Development and intercalibration of methods in Nordic freshwater fish monitoring

Article

Full-text available

Dec 1995

The awareness of the effects of transboundary pollution has increased the necessity to use comparable methods and to initiate joint studies between countries in environmental monitoring. In freshwater fish monitoring a number of different methods have been used, strongly reducing the possibilities to comparative assessments between countries. In 1990, a workshop on freshwater fish sampling was initiated in order to develop and intercalibrate methods used in freshwater fish studies in the Nordic countries. During a three year period, a new type of multi-mesh gillnet to be used for fish monitoring in Norway, Finland and Sweden have been developed. Comparative studies and gillnet-selectivity assessments show that these new multi-mesh gillnets better describe the actual population structure of European perch (Perca fluviatilis), roach (Rutilus rutilus) and Arctic char (Salvelinus alpinus) than do the traditional gillnet series used in the Nordic countries. Ageing of fish is central in most environmental studies, however, the comparability of analyses performed at different laboratories may be low. Comparative age analyses between the three countries have been performed for a number of fish species. The results of ageing E. perch, whitefish (Coregonus sp.) and roach indicate that differences between laboratories can be reduced by intercalibration. In the future, the workgroup will be focused on a further development of joint methods within studies of freshwater fish and on joint intemordic assessments on species distribution, abundance and life history characteristics in relation to airborne pollutants and liming.

Benefits Beyond Boundaries: The Fishery Effects of Marine Reserves

Article

Full-text available

Sep 2003
TRENDS ECOL EVOL

Marine reserves are areas of the sea where fishing is not allowed. They provide refuges where populations of exploited species can recover and habitats modified by fishing can regenerate. In some places, closed areas have been used for fisheries management for centuries [1] and, until recently, natural refugia also existed, inaccessible through depth, distance or adverse conditions. Developments in technology have left few areas of fishing interest beyond our reach. Recently, the idea of marine reserves as fisheries management tools has re-emerged with developing interest in ecosystem-based management, and observations of incidental fisheries benefits from reserves established for conservation. In light of new evidence, we argue that, by integrating large-scale networks of marine reserves into fishery management, we could reverse global fishery declines and provide urgently needed protection for marine species and their habitats.

The Structure of Mediterranean Rocky Reef Ecosystems across Environmental and Human Gradients, and Conservation Implications

Article

Full-text available

Feb 2012
PLOS ONE

Enric Sala

Effects of a large northern European no-take zone on flatfish populations

Abstract

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