Showing papers in "Fish and Fisheries in 2015"

Energy acquisition and allocation to egg production in relation to fish reproductive strategies

Abstract: Oogenesis in fishes follows a universal plan; yet, due to differences in the synchrony and rate of egg development, spawning frequency varies from daily to once in a lifetime. Some species spawn and feed in separate areas, during different seasons, by storing energy and drawing on it later for reproduction (i.e. capital breeding). Other species spawn using energy acquired locally, throughout a prolonged spawning season, allocating energy directly to reproduction (i.e. income breeding). Capital breeders tend to ovulate all at once and are more likely to be distributed at boreal latitudes. Income breeding allows small fish to overcome allometric constraints on egg production. Income breeders can recover more quickly when good-feeding conditions are re-established, which is a benefit to adults regarding bet-hedging spawning strategies. Many species exhibit mixed capital- and income-breeding patterns. An individual's position along this capital–income continuum may shift with ontogeny or in relation to environmental conditions, so breeding patterns are a conditional reproductive strategy. Poor-feeding environments can lead to delayed maturation, skipped spawning, fewer spawning events per season or fewer eggs produced per event. In a few cases, variations in feeding environments appear to affect recruitment variability. These flexible processes of energy acquisition and allocation allow females to prioritize their own condition over their propagules' condition at any given spawning opportunity, thereby investing energy cautiously to maximize lifetime reproductive value. These findings have implications for temporal and spatial sampling designs, for measurement and interpretation of fecundity, and for interpreting fishery and ecosystem assessments.

The seascape nursery: a novel spatial approach to identify and manage nurseries for coastal marine fauna

Abstract: Coastal marine and estuarine ecosystems are highly productive and serve a nursery function for important fisheries species. They also suffer some of the highest rates of degradation from human impacts of any ecosystems. Identifying and valuing nursery habitats is a critical part of their conservation, but current assessment practices typically take a static approach by considering habitats as individual and homogeneous entities. Here we review current definitions of nursery habitat and propose a novel approach for assigning nursery areas for mobile fauna that incorporates critical ecological habitat linkages. We introduce the term 'seascape nurseries' which conceptualizes a nursery as a spatially-explicit seascape consisting of multiple mosaics of habitat patches that are functionally connected. Hotspots of animal abundances/productivity identify the core area of a habitat mosaic, which is spatially constrained by the home ranges of its occupants. Migration pathways connecting such hotspots at larger spatial and temporal scales, through ontogenetic habitat shifts or inshore–offshore migrations, should be identified and incorporated. The proposed approach provides a realistic step forward in the identification and management of critical coastal areas, especially in situations where large habitat units or entire water bodies cannot be protected as a whole due to socio-economic, practical, or other considerations.

The ways in which fish use estuaries: a refinement and expansion of the guild approach

Abstract: This study refines, clarifies and, where necessary, expands details of the guild approach developed by Elliott et al. (2007, Fish and Fisheries 8: 241-268) for the ways in which fish use estuaries. The estuarine usage functional group is now considered to comprise four categories, that is, marine, estuarine, diadromous and freshwater, with each containing multiple guilds. Emphasis has been placed on ensuring that the terminology and definitions of the guilds follow a consistent pattern, on highlighting the characteristics that identify the different guilds belonging to the estuarine category and in clarifying issues related to amphidromy. As the widely employed term 'estuarine dependent' has frequently been imprecisely used, the proposal that the species found in estuaries can be regarded as either obligate or facultative users of these systems is supported and considered in the guild context. Thus, for example, species in the five guilds comprising the diadromous category and those in the guilds containing species or populations confined to estuaries are obligate users, whereas those in the marine and freshwater estuarine-opportunistic guilds are facultative users.

Large reservoirs as ecological barriers to downstream movements of Neotropical migratory fish

Abstract: Most large rivers in South America are fragmented by large dams, and a common management strategy to mitigate impacts has been construction of fish passes. Recent studies, however, indicate that downstream passage of adults and young fish is nil or minimal. Better understanding of this phenomenon is needed if fishways are to provide any tangible conservation value in South America. We propose, in this article, that large reservoirs impose a different kind of barrier to migrating fish: impoundments create a diffuse gradient of hydraulic/limnological conditions that affects fish behaviour and functions as an extensive environmental filter that discourages downstream movements. To develop this idea, we characterize the barriers created by dams and reservoirs by describing their distinct nature, the effects on fish migration and potential solutions. We show, for example, that dams generally prevent upstream movements, whereas reservoirs impede mainly downstream movements. In this context, we explain how fish passes, in some instances, can partially mitigate fragmentation caused by dams, but there is no technical solution to solve the barrier effect of reservoirs. In addition, we present a body of empirical evidence that supports the theory that large reservoirs are important barriers to fish migration in South America, we offer an overview of the size of reservoirs to show that impoundments typically have large dimensions, and we discuss the significance of this theory for other regions. Based on current and proposed river regulation scenarios, we conclude that conservation of Neotropical migratory fish will be much more complicated than previously believed.

Gender and small-scale fisheries: a case for counting women and beyond

Abstract: Marine ecosystem–scale fisheries research and management must include the fishing effort of women and men. Even with growing recognition that women do fish, there remains an imperative to engage in more meaningful and relevant gender analysis to improve socio-ecological approaches to fisheries research and management. The implications of a gender approach to fisheries have been explored in social approaches to fisheries, but the relevance of gender analysis for ecological understandings has yet to be fully elaborated. To examine the importance of gender to the understanding of marine ecology, we identified 106 case studies of small-scale fisheries from the last 20 years that detail the participation of women in fishing (data on women fishers being the most common limiting factor to gender analysis). We found that beyond gender difference in fishing practices throughout the world, the literature reveals a quantitative data gap in the characterization of gender in small-scale fisheries. The descriptive details of women’s often distinct fishing practices nonetheless provide important ecological information with implications for understanding the human role in marine ecosystems. Finally, we examined why the data gap on women’s fishing practices has persisted, detailing several ways in which commonly used research methods may perpetuate biased sampling that overlooks women’s fishing. This review sheds light on a new aspect of the application of gender research to fisheries research, with an emphasis on ecological understanding within a broader context of interdisciplinary approaches.

Examining common assumptions about recruitment: A meta-analysis of recruitment dynamics for worldwide marine fisheries

Abstract: Assumptions about the future productivity of a stock are necessary to calculate sustainable catches in fisheries management. Fisheries scientists often assume the number of young fish entering a population (recruitment) is related to the biomass of spawning adults and that recruitment dynamics do not change over time. Thus, managers often use a target biomass based on spawning biomass as the basis for calculating sustainable catches. However, we show recruitment and spawning biomass are not positively related over the observed range of stock sizes for 61% of 224 stocks in the RAM Legacy Stock Assessment Database. Furthermore, 85% of stocks for which spawning biomass may not drive recruitment dynamics over the observed ranges exhibit shifts in average recruitment, which is often used in proxies for target biomasses. Our results suggest that the environment more strongly influences recruitment than spawning biomass over the observed stock sizes for many stocks. Management often endeavours to maintain stock sizes within the observed ranges, so methods for setting management targets that include changes within an ecosystem may better define the status of some stocks, particularly as climate changes.

Managing fisheries for human and food security

Abstract: We evaluate the current status of the global marine fisheries using the frameworks of conflict, food security and vulnerability. Existing trends suggest that there is likely to be greater food insecurity and fisheries conflicts due to issues such as: declining fishery resources; a North–South divide in investment; changing consumption patterns; increasing reliance on fishery resources for coastal communities; and inescapable poverty traps creating by low net resource productivity and few alternatives. Consequently, managing fisheries from a food security perspective will become increasingly necessary, and we therefore briefly review fisheries from the perspective of food security and evaluate it using a vulnerability framework. Specifically, we describe three key components of vulnerability (exposure, sensitivity and adaptive capacity) for selected fisheries. This is followed by proposals to build the adaptive capacity of fisheries and recommendations to avoid future conflicts. Adaptive capacity attributes include assets, social flexibility and organization attributes, and learning. We present some key ways to build these aspects of the fishery to reduce the many potential environmental and social threats that increase the vulnerability of fisheries. Recommendations include fewer subsidies, reduced capital investment, precautionary management to minimize risks of ecosystem collapse, conservation of remaining resources, diversified portfolios of production and markets, and greater equity in contracts and distribution. Further, we recommend a contextual diagnostic and environmental justice framework to assess a range of options for fishery governance.

Ocean's eleven: a critical evaluation of the role of population, evolutionary and molecular genetics in the management of wild fisheries

Abstract: Significant changes have occurred in the well-established partnership between fisheries managers and geneticists over the last 50 years. It is therefore timely to review and recalibrate the ways in which genetic technologies can assist the fishing industry to maintain productive and sustainable harvests. Our objective is to contribute to the mutual understanding of all stakeholders in the genetics–management partnership. Genetic technologies that are relevant to fisheries management are grouped into eleven themes, which are described in plain language for a non-specialist audience. The role that the genetic information plays in fisheries management is explained, along with an assessment of the challenges and barriers that may be preventing the uptake of the information into the fisheries management process. The compelling conclusion is that genetics offers a diverse collection of versatile and useful tools for informing fisheries managers about issues that have a biological basis. Presently, mainstream use of genetic tools focuses on a narrow set of fisheries management issues, but the diversity of genetic tools and the novel issues they can address indicates that uptake will grow, particularly as communication between geneticists and end-users improves.

The increased efficiency of fish swimming in a school

Abstract: There is increasing evidence that fish gain energetic benefits from the hydrodynamic interactions when they swim in a school. The most recent indications of such benefits are a lower tail (or fin) beat at the back of a school and reduced oxygen consumption in schooling fish versus solitary ones. How such advantages may arise is poorly understood. Current hydrodynamic theories concern either fish swimming side by side or in a diamond configuration and they largely ignore effects of viscosity and interactions among wakes and individuals. In reality, however, hydrodynamic effects are complex and fish swim in many configurations. Since these hydrodynamic effects are difficult to study empirically, we investigate them in a computer model by incorporating viscosity and interactions among wakes and with individuals. We compare swimming efficiency of model fish (based on shapes of mullets of 126 mm) travelling solitarily and in schools at several interindividual distances in four different configurations (diamond, rectangular, phalanx and line). We show that these fish always swim more efficiently in a school than alone (except in a dense phalanx). We indicate how this efficiency may emerge from several kinds of interactions between wakes and individuals. As individuals in our simulations are not even intending to exploit the wake, gains in efficiency are obtained more easily than previously thought.

Fuel consumption of global fishing fleets: current understanding and knowledge gaps

Abstract: Compared to a century ago, the world's fishing fleets are larger and more powerful, are travelling further and are producing higher quality products. These developments come largely at a cost of high-fossil fuel energy inputs. Rising energy prices, climate change and consumer demand for ‘green’ products have placed energy use and emissions among the sustainability criteria of food production systems. We have compiled all available published and unpublished fuel use data for fisheries targeting all species, employing all gears and fishing in all regions of the world into a Fisheries and Energy Use Database (FEUD). Here, we present results of our analysis of the relative energy performance of fisheries since 1990 and provide an overview of the current state of knowledge on fuel inputs to diverse fishing fleets. The median fuel use intensity of global fishery records since 1990 is 639 litres per tonne. Fuel inputs to fisheries vary by several orders of magnitude, with small pelagic fisheries ranking among the world's most efficient forms of animal protein production and crustaceans ranking among the least efficient. Trends in Europe and Australia since the beginning of the 21st century suggest fuel use efficiency is improving, although this has been countered by a more rapid increase in oil prices. Management decisions, technological improvements and behavioural changes can further reduce fuel consumption in the short term, although the most effective improvement to fisheries energy performance will come as a result of rebuilding stocks where they are depressed and reducing over-capacity.

Rethinking length-based fisheries regulations: the value of protecting old and large fish with harvest slots

Abstract: Managing fisheries using length-based harvest regulations is common, but such policies often create trade-offs among conservation (e.g. maintaining natural agestructure or spawning stock biomass) and fishery objectives (e.g. maximizing yield or harvest numbers). By focusing harvest on the larger (older) fish, minimumlength limits are thought to maximize biomass yield, but at the potential cost of severe age and size truncation at high fishing mortality. Harvest-slot-length limits (harvest slots) restrict harvest to intermediate lengths (ages), which may contribute to maintaining high harvest numbers and a more natural age-structure. However, an evaluation of minimum-length limits vs. harvest slots for jointly meeting fisheries and conservation objectives across a range of fish life-history strategies is currently lacking. We present a general age- and size-structured population model calibrated to several recreationally important fish species. Harvest slots and minimum-length limits were both effective at compromising between yield, numbers harvested and catch of trophy fish while conserving reproductive biomass. However, harvest slots consistently produced greater numbers of fish harvested and greater catches of trophy fish while conserving reproductive biomass and a more natural population age-structure. Additionally, harvest slots resulted in less waste in the presence of hooking mortality. Our results held across a range of exploitation rates, life-history strategies and fisheries objectives. Overall, we found harvest slots to represent a valuable option to meet both conservation and recreational fisheries objectives. Given the ubiquitous benefits of harvest slots across all life histories modelled, rethinking the widespread use of minimum-length limits is warranted.

Mitigating unaccounted fishing mortality from gillnets and traps

Abstract: Gillnets and traps often are considered to have fewer holistic environmental impacts than active fishing gears. However, in addition to the targeted catches, gillnets and traps still cause unwanted mortalities due to (i) discarding, (ii) ghost fishing of derelict gear, (iii) depredation, (iv) escaping or dropping out of gear, (v) habitat damage, and potentially (vi) avoiding gear and predation and (vii) infection of injuries sustained from most of the above. Population-level concerns associated with such ‘unaccounted fishing mortalities’ from gillnets and traps have been sufficient to warrant numerous attempts at mitigation. In this article, we reviewed relevant research efforts, locating 130 studies in the primary literature that concomitantly quantified mortalities and their resolution through technical modifications, with the division of effort indicating ongoing concerns. Most studies (85) have focused on discard mortality, followed by ghost-fishing (24), depredation (10) and escape (8) mortalities. The remaining components have been poorly studied (3). All problematic mortality components are affected by key biological (e.g. species), technical (e.g. fishing mechanisms) and/or environmental (e.g. temperature) factors. We propose that these key factors should be considered as part of a strategy to reduce impacts of these gears by first assessing modifications within and then beyond conventional configurations, followed by changes to operational and handling practices. Justification for this three-tiered approach is based not only on the potential for cumulative reduction benefits, but also on the likely ease of adoption, legislation and compliance.

Evaluating the relative conservation value of fully and partially protected marine areas

Abstract: The establishment of marine protected areas (MPAs), particularly of no-take areas, is often viewed as a conflict between conservation and fishing. Partially protected areas (PPAs) that restrict some extractive uses are often regarded as a balance between biodiversity conservation and socio-economic viability. Few attempts have been made to generalize the ecological effects of PPAs. We synthesized the results of empirical studies that compared PPAs to (i) no-take reserves (NTRs) and (ii) to open access (Open) areas, to assess the potential benefits of different levels of protection for fish populations. Response to protection was examined in relation to MPA parameters and the exploitation status of fish. Our syntheses suggest that while PPAs significantly enhance density and biomass of fish relative to Open areas, NTRs yielded significantly higher biomass of fish within their boundaries relative to PPAs. The positive response to protection was primarily driven by target species. There was a large degree of variability in the magnitude of response to protection, although the size of the PPA explained some of this variability. The protection regime within the PPA provided useful insights into the effectiveness of partial MPAs. We conclude that MPAs with partial protection confer advantages, such as enhanced density and biomass of fish, compared to areas with no restrictions, although the strongest responses occurred for areas with total exclusion. Thus, MPAs with a combination of protection levels are a valuable spatial management tool particularly in areas where exclusion of all activities is not a socio-economically and politically viable option.

Measuring and monitoring compliance in no‐take marine reserves

Abstract: No-take marine reserves are increasingly popular tools for conservation and fisheries management. While much attention has been paid to evaluating the effects of design aspects (size, location, etc.) in achieving reserve objectives, less emphasis has been placed on the role of stakeholder compliance. Therefore, the first aim of this study was to evaluate the state of compliance literature and examine the methods used to measure compliance in reserves. The state of compliance literature is limited, although publications with compliance information have increased sixfold in the last decade. However, most studies containing compliance information (63%) fail to provide quantitative estimates. Furthermore, most (95%) quantitative estimates of compliance were reported using a single method, which is problematic because each method has biases and limited applicability. Methods used to indicate compliance include (i) direct observation; (ii) indirect observation; (iii) law enforcement records; (iv) direct questioning; (v) expert opinion; and (vi) modelling. Our second aim was to empirically demonstrate the critical role of compliance in reserve outcomes by comparing a mixed-effects model on compliance data synthesized from 63 marine reserves to that of a null model. The model of best fit demonstrated a negative relationship between non-compliance and target species biomass response ratios. Thus, without incorporating any aspects of reserve design, compliance data predicted reserve response ratios of fish biomass. Accordingly, researchers should explore ways to better understand and measure non-compliance. Therefore, future research should triangulate multiple sources of quantitative compliance data collected using standardized techniques and conduct baseline surveys before reserve implementation.

Overlooked impacts and challenges of the new European discard ban

Abstract: Discards are the portion of animal and plant material in the catch that is dumped back at sea. The Common Fisheries Policy plan proposed by the European Commission for 2014–2020 presents a controversial goal: to enforce the landing of fishing discards as a measure to encourage their reduction. This historical and political decision will shape the future of the fishing exploitation in European Seas. Discards generated by European fleets are not negligible, and its reduction is an ecological, socioeconomical and moral imperative. However, it must be achieved through the reduction in discards at source and the promotion of selective and non-destructive gears. We argue it is doubtful that this discard ban will result in an effective reduction of discards. The proposed measure may, in fact, negatively affect ecosystems at all levels of biological hierarchy by disregarding the Ecosystem-Based Approach to Fisheries and the Precautionary Principle. It could negatively impact several species by increasing fishing mortality, also commercial species if discards are not accounted in the total allowable catch. Communities preying on discards will likely be affected. The role discards currently play in the energy turnover of current ecosystems will be modified and should be fully evaluated. The landing of discards will likely generate new markets of fishmeal due to the growing demands for marine living resources. The ban will require substantial public investment to deal with technical problems on board and to control and enforce. Therefore, this measure should be only implemented after rigorous scientific and technical studies have been developed.

The use of acoustic cameras in shallow waters: new hydroacoustic tools for monitoring migratory fish population. A review of DIDSON technology

Abstract: European Union legislation, through the Water Framework Directive (2000/60/ EC), as well as national legislation, such as the ‘Grenelle Environnement’ (2007) in France, requires restoration of ecological connectivity in streams to improve free circulation of migratory fish. Different methods (e.g. capture by trap or net, telemetry, hydroacoustics) are used to evaluate the efficiency of fish passes to estimate the migratory species abundance and analyse changes in their within-river distributions. Among these methods, hydroacoustics is non-intrusive, allowing long-term observation and description of fish populations based on physical properties of sound in water. However, the main limit to hydroacoustic tools is their difficulty in identifying species. Initially designed for military purposes, dual-frequency identification sonar (DIDSON) has been used in environmental management for a decade. This acoustic camera uses higher frequencies and more sub-beams than common hydroacoustic tools, which improves image resolution and then enables observation of fish morphology and swimming behaviour. The ability to subtract static echoes from echograms and directly measure fish length improve the species-identification process. However, some limits have been identified, such as automatic dataset recording and the low range of the detection beam, which decreases accuracy, but efficient tools are now being developed to improve the accuracy of data recording (morphology, species identification, direction and speed). The new technological properties of acoustic cameras, such as the video-like visualization of the data, have greatly improved monitoring of diadromous fish populations (abundance, distribution and behaviour), helping river and fisheries managers and researchers in making decisions.

Real-time spatial management approaches to reduce bycatch and discards: experiences from Europe and the United States

Abstract: Spatial management measures are currently being used to manage bycatch and discards, given the spatial heterogeneity of fish distributions. However, permanent fishing closures are often poorly implemented, unresponsive to stock dynamics and do not achieve their management objectives. Recently, real-time spatial management tools for managing bycatch and discards implemented under either a comanagement or self-governance approach have been introduced in Europe and the US. Real-time catch and discard information is shared among fishers to incentivise and encourage vessels to leave areas of high bycatch. Here, the similarities and differences, in governance, implementation and management of ten real-time spatial management systems from across Europe and the US are reviewed. A framework is developed to characterize the attributes associated with voluntary, private and regulatory real-time spatial management tools. Challenges and management practices in the different case studies are reviewed providing insights for designing these spatial management tools. The results illustrate that real-time spatial management approaches can create incentives for fishers to develop, use and share information and technology to avoid undesired catch. Compared with Europe, the US has developed spatial management tools with more truly real-time mechanisms and with greater involvement of the fishing industry in designing and operating the tools.

The food limitation hypothesis for juvenile marine fish

Abstract: Coastal zones are productive areas that serve as nursery grounds for a large number of marine species. However, the processes involved in survival success during the juvenile phase are not well-known. Some authors suggest that the availability of prey is important to support the production of pre-recruit fish whose fitness is enhanced through optimal feeding conditions. Accordingly, recruitment is limited by the carrying capacity of the nursery habitat. In contrast, other authors state that the carrying capacity of the nursery grounds is not fully exploited, suggesting that there is no effect of food limitation. This study combines an overview of the literature, focused on flatfish that are especially dependent on coastal and estuarine nursery grounds, an extension to other marine fishes and a modelling approach on growth and survival of juvenile fish to explore the controversy of food limitation in their nursery grounds. We demonstrate that the relative lack of growth limitation observed for young marine fishes at the individual scale is related to an observational bias: fish have been affected by size-selective mortality linked to food limitation, but only surviving individuals are observed. As the population is skewed towards the faster-growing juveniles, the growth of survivors remains close to optimal, even when food resources are limited. Food limitation is of major influence in determining the carrying capacity of the nursery habitat. To sustain marine fish populations and related fisheries, management action is needed to protect coastal and estuarine areas and maintain or restore nursery productivity.

Electrotrawling: a promising alternative fishing technique warranting further exploration

Abstract: In trawl fisheries, beam trawls with tickler chains, chain mats or bobbin ropes are used to target flatfish or shrimp. High fuel consumption, seabed disturbance and high discard rates are well-known disadvantages of this fishing technique. These shortcomings are increasingly gaining international public and political attention, especially with the upcoming discard ban in Europe. The most promising alternative fishing technique meeting both the fisherman's aspirations, and the need for ecological progress is pulse fishing with electrotrawls. Here, the mechanical stimulation by tickler chains or bobbins is replaced by electrical stimulation resulting in reduced bottom contact, fuel costs and discards. Although a significant amount of research has been done on electrotrawls and their impact on marine organisms, most data were published in very diverse sources ranging from local non-peer-reviewed reports with a limited distribution to highly consulted international peer-reviewed journals. Therefore, there is a clear need for a comprehensive yet concise and critical overview, covering and summarizing all these data and making these available for the scientific community. This article aims to meet the above goals by discussing the working principle of electric fields, the history of electrotrawls and their current application in the North Sea and impact on marine organisms. It is concluded by elaborating on the opportunities and challenges for the further implementation of this alternative fishing technique.

Managing inequality or managing stocks? An ethnographic perspective on the governance of small‐scale fisheries

Abstract: A growing volume of recent research on small-scale fisheries governance has a focus on local perspectives and priorities of small-scale fisherfolk. This paper develops from this local perspective a novel focus on what is a fundamental priority of many small-scale fishers: concerns about inequality. The paper begins with a critical review of the literature on small-scale fisheries governance and suggests how a focus on inequality can make a useful contribution. The paper uses case-studies of small-scale fisheries in Papua New Guinea (PNG) and the Philippines to highlight local priorities about inequality and the implications for small-scale fisheries governance. PNG and the Philippines have very different social, political and environmental contexts, yet in both cases, local inequalities were a key pre-occupation of fisherfolk and posed major challenges for fisheries governance. While in both of the case-studies, fishers were aware of and keen to act on resource sustainability, this concern was overridden by concerns over: who obtained benefits from the fishery; who was responsible for resource degradation; and who should bear the costs of regulation. We conclude by discussing how our emphasis on the importance of inequality at a local level can potentially be integrated within many influential approaches to small-scale fisheries governance.

Size structure, not metabolic scaling rules, determines fisheries reference points

Abstract: Impact assessments of fishing on a stock require parameterization of vital rates: growth, mortality and recruitment. For ‘data-poor’ stocks, vital rates may be estimated from empirical size-based relationships or from life-history invariants. However, a theoretical framework to synthesize these empirical relations is lacking. Here, we combine life-history invariants, metabolic scaling and size-spectrum theory to develop a general size- and trait-based theory for demography and recruitment of exploited fish stocks. Important concepts are physiological or metabolic scaled mortalities and flux of individuals or their biomass to size. The theory is based on classic metabolic relations at the individual level and uses asymptotic size W∞ as a trait. The theory predicts fundamental similarities and differences between small and large species in vital rates and response to fishing. The central result is that larger species have a higher egg production per recruit than small species. This means that density dependence is stronger for large than for small species and has the consequence that fisheries reference points that incorporate recruitment do not obey metabolic scaling rules. This result implies that even though small species have a higher productivity than large species their resilience towards fishing is lower than expected from metabolic scaling rules. Further, we show that the fishing mortality leading to maximum yield per recruit is an ill-suited reference point. The theory can be used to generalize the impact of fishing across species and for making demographic and evolutionary impact assessments of fishing, particularly in data-poor situations.

Adverse consequences of stock recovery: European hake, a new “choke” species under a discard ban?

Abstract: Many commercial fish stocks are beginning to recover under more sustainable exploitation regimes. In this study, we document the temporal and spatial changes in one remarkable example of stock recovery: northern European hake (Merluccius merluccius). Analysing data from several scientific surveys, we document a dramatic increase in estimates of biomass between 2004 and 2011 throughout the larger area now occupied by the stock. The largest increase occurred in the North Sea, where hake have been largely absent for over 50 years. Spatio-temporally resolved commercial landings show that high densities occur in the North Sea only between April and September, suggesting a density-dependent seasonal habitat expansion to suitable temperature and depth conditions. These changes have implications for the management of the stock which are discussed. Notably, if discards are banned as part of management revisions, the relatively low quota for hake in the North Sea will be a limiting factor (the so-called ‘choke’ species) which may result in a premature closure of the entire demersal mixed fishery in the North Sea, jeopardizing many commercial fisheries in the region. This example of the unforeseen consequences of improved stewardship highlight the need for a more holistic, regional and responsive approach to managing our marine ecosystems.

The evolution of a discard policy in Europe

Abstract: Ocean sustainability is a widespread public concern in Europe, and the issue of fisheries discards is one that is now widely known. With this increase in public awareness comes the need to adapt fisheries management policies to manage issues like fisheries discards that were not previously taken into account. In this context, this study analyses the evolution of the European Union's discard policy since its inception in 2006 until the present day and the events that shaped its current format. It analyses the policy's advantages and disadvantages, and its political, environmental and scientific consequences. It argues that an increase in public awareness, due to public campaigns against fisheries discards, has focused managers' attention onto a symptom of fisheries mismanagement, rather than on its underlying causes of over-exploitation and lack of fisheries control. This has distorted the discussion of the reform of the Common Fisheries Policy and potentially undermined its provisions relating to discards.

Approaches to fully documented fisheries: practical issues and stakeholder perceptions

Abstract: The Common Fisheries Policy (CFP) reform sets out a move to a land-all catch policy in European Union waters with a requirement for full reporting of fishing and on-board processing activity. We explore the merits, stakeholder perceptions and applicability of different technology and approaches to the full documentation of fisheries that might be considered in the context of implementing the CFP reform. While recent efforts have focused on demonstrating how remote electronic monitoring (REM) systems can be utilized in fully documented fisheries (FDF), other technologies and approaches such as reference fleet and self-sampling exist that could contribute to delivering FDF. Perceptions of fishers show that they would prefer using a reference fleet or self-sampling to REM systems as a future method of implementing FDF. In general, there is support from the fishing industry for data collection and enhancement, but there remains some mistrust concerning the use of the data. Findings show that the most appropriate means and methods of FDF will depend on the circumstances and objectives for full documentation whether in enforcing a discard ban, documentation of total catch or data enhancement. We conclude that any technology or approach that will be used to deliver the monitoring requirements for FDF needs to make practical and commercial sense at the fishing vessel level.

Recruitment ecology of pelagic‐broadcast spawning minnows: paradigms from the ocean advance science and conservation of an imperilled freshwater fauna

Abstract: Pelagic-broadcast spawning is a dominant mode of fish reproduction in the oceans and is associated with Fundamental Triad (i.e. nutrient enrichment, nutrient concentration, propagule retention) and Loophole (i.e. disruption of larval competition and predation) processes that are mediated by water currents. Pelagic-broadcast spawning is uncommon in freshwater, but is employed by an evolutionarily convergent spawning guild in rivers on the Great Plains, North America. We reviewed ecological studies of pelagic-broadcast spawning minnows to evaluate whether Fundamental Triad and Loophole concepts explain the adaptive significance of this behaviour. Pelagic-broadcast spawning minnows exhibit spawning periodicity dependent on floods. Nutrient enrichment, nutrient concentration and propagule retention are enhanced during flood recession. Retention is also enhanced by high fecundity and rapid development of pelagic-broadcast propagules. Predation and competition threats are relatively low in temporary, patchily distributed nurseries present during flood recession. Extended spawning periods and diffusive spread of juveniles and adults ensure annual recruitment despite the unpredictable and often harsh conditions in rivers on the plains. Over the last century, pelagic-broadcast spawners have suffered declines due to dewatering, flood control and sediment deprivation that disrupt natural Fundamental Triad and Loophole processes. We propose that restoration of conditions necessary for Fundamental Triad and Loophole processes to operate will be most successful at stopping decline and extinction of pelagic-broadcast spawning minnows of the Great Plains.

Prioritization of knowledge needs for sustainable aquaculture: a national and global perspective

Abstract: Aquaculture is currently the fastest expanding global animal food production sector and is a key future contributor to food security. An increase in food security will be dependent upon the development and improvement of sustainable practices. A prioritization exercise was undertaken, focusing on the future knowledge needs to underpin UK sustainable aquaculture (both domestic and imported products) using a ‘task force’ group of 36 ‘practitioners’ and 12 ‘research scientists’ who have an active interest in sustainable aquaculture. A long list of 264 knowledge needs related to sustainable aquaculture was developed in conjunction with the task force. The long list was further refined through a three stage process of voting and scoring, including discussions of each knowledge need. The top 25 knowledge needs are presented, as scored separately by ‘practitioners’ or ‘research scientists’. There was similar agreement in priorities identified by these two groups. The priority knowledge needs will provide guidance to structure ongoing work to make science accessible to practitioners and help to prioritize future science policy needs and funding. The process of knowledge exchange, and the mechanisms by which this can be achieved, effectively emerged as the top priority for sustainable aquaculture. Viable alternatives to wild fish-based aquaculture feeds, resource constraints that will potentially limit expansion of aquaculture, sustainable offshore aquaculture and the treatment of sea lice also emerged as strong priorities. Although the exercise was focused on UK needs for sustainable aquaculture, many of the emergent issues are considered to have global application.

Giants' shoulders 15 years later: lessons, challenges and guidelines in fisheries meta-analysis

Abstract: Meta-analysis has been an integral tool for fisheries researchers since the late 1990s. However, there remain few guidelines for the design, implementation or interpretation of meta-analyses in the field of fisheries. Here, we provide the necessary background for readers, authors and reviewers, including a brief history of the use of meta-analysis in fisheries, an overview of common model types and distinctions, and examples of different goals that can be achieved using meta-analysis. We outline the primary challenges in implementing meta-analyses, including difficulties in discriminating between alternative hypotheses that can explain the data with equal plausibility, the importance of validating results using multiple lines of evidence, the trade-off between complexity and sample size and problems associated with the use of model output. For each of these challenges, we also provide suggestions, such as the use of propensity scores for dealing with selection bias and the use of covariates to control for confounding effects. These challenges are then illustrated with examples from diverse subfields of fisheries, including (i) the analysis of the stock–recruit relationship, (ii) fisheries management, rebuilding and population viability, (iii) habitat-specific vital rates, (iv) life-history theory and (v) the evaluation of marine reserves. We conclude with our reasons for believing that meta-analysis will continue to grow in importance for these and many other research goals in fisheries science and argue that standards of practice are therefore essential.

Squaring the circle: reconciling fishing and conservation of aquatic ecosystems

Abstract: Size-at-entry regulations in fisheries cause major disruption to aquatic ecosystems, including truncation of age- and size-structures, destabilization of fish stocks, directional selection on phenotypic traits and a by-catch of unwanted species and sizes. Here, we use simple dynamic models of size-spectra to examine an alternative, so-called balanced harvesting. Balanced harvesting helps in retaining the approximate power-law size-structure of natural ecosystems, whereas size-at-entry regulations do not. Balanced harvesting is less likely to destabilize steady states than size-at-entry regulations set close to the size at maturation. Surprisingly, our numerical results suggest that steady-state biomass yield can be substantially increased by switching from size-at-entry to balanced harvesting. On the basis of these results, we argue that the goals of conservation and of greater yields seem less difficult to reconcile than have previously been thought. However, to work towards these goals require a change in our approach to fishing.

Ending overfishing while catching more fish

Abstract: The world's seas and oceans are a vital source of animal protein from fishing and a major contributor to global food security. It has been argued that global wild-catch production has reached its limit, and there is concern that many species are overfished. Concerns are also mounting about the state of marine ecosystems and the ecological impacts of fishing on them, with increasing efforts to protect marine biodiversity. Fisheries appear to be at an impasse – demand for seafood is rising but so is concern about the impacts of fishing. However, through a simple analysis, we show that global exploitation rates are well below long-term sustainable levels at a whole ecosystem level. The oceans can support considerably higher sustainable catch than currently harvested. Overfishing has happened but only to a small fraction of species as a result of intensive and selective fishing. Shifting fishing effort away from highly targeted stocks towards currently underutilized species would reduce pressure on overfished species, result in fewer adverse ecosystem effects of fishing and increase overall fisheries production. This shift requires significant changes to our views about seafood, particularly in the developed world. We suggest ways in which this paradigm shift could happen and the range of expertise that would be required to achieve higher global yields with less ecological impact.

Using scenarios to project the changing profitability of fisheries under climate change

Abstract: Over-exploitation and economic underperformance are widespread in the world's fisheries. Global climate change is further affecting the distribution of marine species, raising concern for the persistence of biodiversity and presenting additional challenges to fisheries management. However, few studies have attempted to extend bioclimatic projections to assess the socio-economic impacts of climate-induced range shifts. This study investigates the potential implications of changes in relative environmental suitability and fisheries catch potential on UK fisheries by linking species distribution modelling with cost-benefit analyses. We develop scenarios and apply a multimodel approach to explore the economic sensitivity of UK fisheries and key sources of uncertainty in the modelling procedure. We projected changes in maximum potential catch of key species and the resulting responses in terms of net present value (NPV) over a 45-year period under scenarios of change in fuel price, discount rate and government subsidies. Results suggest that total maximum potential catch will decrease within the UK EEZ by 2050, resulting in a median decrease in NPV of 10%. This value decreases further when trends of fuel price change are extrapolated into the future, becoming negative when capacity-enhancing subsidies are removed. Despite the variation in predictions from alternative models and data input, the direction of change in NPV is robust. This study highlights key factors influencing future profitability of UK fisheries and the importance of enhancing adaptive capacity in UK fisheries.