1. Stable isotopes of nitrogen and carbon are widely used in the evaluation and understanding of trophic interactions, and especially so in aquatic food‐webs. However, differences among tissues which occur in consumers such as fish may confound resolution of these ecological relationships, and greatly affect dietary compositions calculated through mass‐balance equations. 2.δ13C and δ15N were determined for homogenized whole fry (≈ 2·7 g) and particular tissues (white muscle, red muscle, liver and heart) of juveniles (≈ 20·6 g) of Rainbow Trout Oncorhynchus mykiss. 3. Differences in δ13C and δ15N were observed among tissues; removal of lipid resulted in these tissues becoming statistically indistinguishable but more variable in δ13C, particularly in tissues with higher lipid content. Differences in δ15N among tissues may be related to the relative composition of ‘essential’ and ‘non‐essential’ amino acids. 5. Acidification, which is used to reduce variability caused by the presence of inorganic carbonate, had a significant effect on δ15N, while having a non‐significant effect on the δ13C. This was the case for whole ground fish‐fry, which contained 22·6% inorganic carbonates in the form of bones and scales, and for individual fish tissues which contained only very small amounts of inorganic carbonate. 6. White muscle was found to be less variable in δ13C and δ15N than all other tissues, and is probably the best tissue for use in ecological work. Red muscle, which is often closely associated with white muscle, is more variable in δ13C and may constitute a source of significant error in source material identification and dietary overlap.

It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types.

An important principle of environmental science is that changes in single components of systems are likely to have consequences elsewhere in the same systems. In the sea, food web data are one of the few foundations for predicting such indirect effects, whether of fishery exploitation or following recovery in marine protected areas (MPAs). We review the available literature on one type of indirect interaction in benthic marine ecosystems, namely trophic cascades, which involve three or more trophic levels connected by predation. Because many indirect effects have been revealed through fishery exploitation, in some cases we include humans as trophic levels. Our purpose is to establish how widespread cascades might be, and infer how likely they are to affect the properties of communities following the implementation of MPAs or intensive resource exploitation. We review 39 documented cascades (eight of which include humans as a trophic level) from 21 locations around the world; all but two of the cascades are from shallow systems underlain by hard substrata (kelp forests, rocky subtidal, coral reefs and rocky intertidal). We argue that these systems are well represented because they are accessible and also amenable to the type of work that is necessary. Nineteen examples come from the central-eastern and north-eastern Pacific, while no well-substantiated benthic cascades have been reported from the NE, CE or SW Atlantic, the Southern Oceans, E Indian Ocean or NW Pacific. The absence of examples from those zones is probably due to lack of study. Sea urchins are very prominent in the subtidal examples, and gastropods, especially limpets, in the intertidal examples; we suggest that this may reflect their predation by fewer specialist predators than is the case with fishes, but also their conspicuousness to investigators. The variation in ecological resolution amongst studies, and in intensity of study amongst systems and regions, indicates that more cascades will likely be identified in due course. Broadening the concept of cascades to include pathogenic interactions would immediately increase the number of examples. The existing evidence is that cascade effects are to be expected when hard-substratum systems are subject to artisanal resource exploitation, but that the particular problems of macroalgal overgrowth on Caribbean reefs and the expansion of coralline barrens in the Mediterranean rocky-sublittoral will not be readily reversed in MPAs, probably because factors other than predation-based cascades have contributed to them in the first place. More cascade effects are likely to be found in the soft-substratum systems that are crucial to so many large-scale fisheries, when opportunities such as those of MPAs and fishing gradients become available for study of such systems, and the search is widened to less conspicuous focal organisms such as polychaetes and crustaceans.

Rijnsdorp, A. D., Peck, M. A., Engelhard, G. H., Möllmann, C., and Pinnegar, J. K. 2009. Resolving the effect of climate change on fish populations. – ICES Journal of Marine Science, 66: 1570–1583. This paper develops a framework for the study of climate on fish populations based on first principles of physiology, ecology, and available observations. Environmental variables and oceanographic features that are relevant to fish and that are likely to be affected by climate change are reviewed. Working hypotheses are derived from the differences in the expected response of different species groups. A review of published data on Northeast Atlantic fish species representing different biogeographic affinities, habitats, and body size lends support to the hypothesis that global warming results in a shift in abundance and distribution (in patterns of occurrence with latitude and depth) of fish species. Pelagic species exhibit clear changes in seasonal migration patterns related to climate-induced changes in zooplankton productivity. Lusitanian species have increased in recent decades (sprat, anchovy, and horse mackerel), especially at the northern limit of their distribution areas, while Boreal species decreased at the southern limit of their distribution range (cod and plaice), but increased at the northern limit (cod). Although the underlying mechanisms remain uncertain, available evidence suggests climate-related changes in recruitment success to be the key process, stemming from either higher production or survival in the pelagic egg or larval stage, or owing to changes in the quality/quantity of nursery habitats.

Summary1. Body size determines rates of respiration and production, energy requirements, mortality rates, patterns of predation and vulnerability to mortality. Body size distributions are often used to describe structure and energy flux in communities and ecosystems. 2. If clear relationships can be established between body size and trophic level in fishes, they may provide a basis for integrating community and ecosystem analyses based on size spectra, food webs and life histories. 3. We investigated relationships between the body sizes (weight and length) of northeast Atlantic fishes and their trophic level. The abundance of 15 N, as determined by stable isotope analysis, was used as an index of trophic level. 4. Cross-species and comparative analyses demonstrated that body size was unrelated or weakly related to trophic level. Thus allometric relationships between body size and trophic level could not be used to predict the trophic structure of fish communities. 5.The results of the cross-species analyses contrasted with patterns in the size and trophic structure of entire fish communities. When fish communities were divided into size classes, there were strong positive relationships between size class and trophic level. The slope suggested a mean predator : prey body mass ratio of 80 : 1. 6. Our results suggest that body size does not provide a useful surrogate of trophic level for individual species, but that body size is an excellent predictor of trophic level within the community, providing an empirical basis for integrating community analyses based on models of trophic structure and body size distributions.

Aquatic food security: insights into challenges and solutions from an analysis of interactions between fisheries, aquaculture, food safety, human health, fish and human welfare, economy and environment AbstractFisheries and aquaculture production, imports, exports and equitability of distribution determine the supply of aquatic food to people. Aquatic food security is achieved when a food supply is sufficient, safe, sustainable, shockproof and sound: sufficient, to meet needs and preferences of people; safe, to provide nutritional benefit while posing minimal health risks; sustainable, to provide food now and for future generations; shock-proof, to provide resilience to shocks in production systems and supply chains; and sound, to meet legal and ethical standards for welfare of animals, people and environment. Here, we present an integrated assessment of these elements of the aquatic food system in the United Kingdom, a system linked to dynamic global networks of producers, processors and markets. Our assessment addresses sufficiency of supply from aquaculture, fisheries and trade; safety of supply given biological, chemical and radiation hazards; social, economic and environmental sustainability of production systems and supply chains; system resilience to social, economic and environmental shocks; welfare of fish, people and environment; and the authenticity of food. Conventionally, these aspects of the food system are not assessed collectively, so information supporting our assessment is widely dispersed. Our assessment reveals trade-offs and challenges in the food system that are easily overlooked in sectoral analyses of fisheries, aquaculture, health, medicine, human and fish welfare, safety and environment. We highlight potential benefits of an integrated, systematic and ongoing process to assess security of the aquatic food system and to predict impacts of social, economic and environmental change on food supply and demand.Keywords Ethics, food safety, food security, food system, health, sustainability F I S H and F I S H E R I E S , 2016, 17, 893-938Received 16 Nov 2015 Accepted 21 Jan 2016 Introduction 894The aquatic food system 898Wild-capture fisheries 898Aquaculture production 899Critical elements of food security 900 Sufficient food supply 901Sufficiency of UK supply: production and consumption 901Global production and consumption 903Safe food supply 904 Biological hazards 904Pathogens of human concern 904Marine biotoxins 906 Chemical hazards 906 Contaminants and veterinary residues 906Radiation hazards 908 Sustainable food supply 908Wild-capture fisheries 909Aquaculture production 914Relative impacts of fishing and aquaculture 915Processing 915 Drivers of sustainability 916Shockproof food supply 917Risks to wild-capture production 917Risks to aquaculture production 919Risks to supply chains 920 Sound food supply 921Social welfare and ethics 922Environmental welfare and ethics 924Animal welfare and ethics 925 Food authenticity 926Conclusions 927Acknowledgements 931References 931 IntroductionFood f...

Metabarcoding has been used in a range of ecological applications such as taxonomic assignment, dietary analysis and the analysis of environmental DNA. However, after a decade of use in these applications there is little consensus on the extent to which proportions of reads generated corresponds to the original proportions of species in a community. To quantify our current understanding, we conducted a structured review and meta‐analysis. The analysis suggests that a weak quantitative relationship may exist between the biomass and sequences produced (slope = 0.52 ± 0.34, p < 0.01), albeit with a large degree of uncertainty. None of the tested moderators, sequencing platform type, the number of species used in a trial or the source of DNA, were able to explain the variance. Our current understanding of the factors affecting the quantitative performance of metabarcoding is still limited: additional research is required before metabarcoding can be confidently utilized for quantitative applications. Until then, we advocate the inclusion of mock communities when metabarcoding as this facilitates direct assessment of the quantitative ability of any given study.

In this paper we demonstrate that low level 'artisanal' fishing can dramatically affect populations of slow-growing, late-maturing animals and that even on remote oceanic islands, stocks have been depleted and ecosystems degraded for millennia. Industrialised fisheries have developed during different decades in different regions of the world, and this has almost always been followed by a period of massive stock decline. However, ecosystems were not pristine before the onset of industrial fishing and it is difficult to assess the 'virgin' state of a population given that it may have been subject to moderate or even high levels of fishing mortality for many centuries.A wide range of information is available to help define or deduce historic marine population status. These include 'traditional' written sources but also less conventional sources such as archaeological remains, genetic analyses or simple anecdotal evidence. Detailed information, collected specifically for the purpose of determining fish stock biomass tends to exist only for recent decades, and most fishery assessments around the world (and thus time-series of biomass estimates), are less than 30 years long. Here we advocate using a wider range of multidisciplinary data sources, although we also recognise that it can be difficult to separate natural variability associated with changing climatic conditions from human-induced changes through fishing. We consider whether or not recovery of degraded ecosystems is ever possible and discuss a series of one-way ratchet like processes that can make it extremely difficult to return to a former ecosystem state.