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The giant red sea cucumber ( Apostichopus californicus) fishery in BC, Canada, is considered sustainable by managers but not by many harvesters. In 1997, the Kitasoo/Xai'xais First Nation began experimental fishing areas (EFAs) at Tolmie Channel and Laredo Inlet to test the effects of different exploitation rates on sea cucumber populations and determine what harvest levels are sustainable. These EFAs were annually surveyed by dive transects and subsequently harvested from 1998 to 2018. Bayesian surplus production models developed in 2011 indicated that the fishery was sustainable, after which the fishery changed from annual to 3-year rotational harvests. Here, we develop updated models to estimate the sustainability of the fishery using all currently available EFA data, including direct estimates of unfished biomass. Our models suggest that the fishery is likely to persist for 175 years at the current harvest rate annually or rotationally, though such long-term projections are likely inaccurate. We present methodology to generate scientific advice for the process of determining a maximum sustainable exploitation rate in the form of crash rate analysis.

Marine fisheries have a long history of exploitation, with the potential to shape many life history traits, particularly those that are heritable, such as age and size at maturity. Here, we analyze 43 marine fish stocks, using prewhitened cross-correlations, to examine the relationship between past levels of fishing mortality ( F) and resulting shifts in age structure. Significant cross-correlations between F and age structure were evident in 88% of stocks examined. For 37% of stocks, changes in age structure followed changes in F, whereas in 39% of cases age structure preceded changes in F. Sensitivity and response time varied widely, likely a result of management, past exploitation, and life history. The efficacy of our method was tested empirically by simulations, revealing that certain time-series properties (e.g., high variance and low strength correlation) have potential to obscure underlying associations. Methods that allow for the identification of sensitivity and response time to pressures such as fishing contribute to the development of stock-specific management measures that can protect, or rebuild, age structure.

Wild-caught fish provide an irreplaceable source of essential nutrients in food-insecure places. Fishers catch thousands of species, yet the diversity of aquatic foods is often categorized homogeneously as ‘fish’, obscuring an understanding of which species supply affordable, nutritious and abundant food. Here, we use catch, economic and nutrient data on 2,348 species to identify the most affordable and nutritious fish in 39 low- and middle-income countries. We find that a 100 g portion of fish cost between 10 and 30% of the cheapest daily diet, with small pelagic fish (herring, sardine, anchovy) being the cheapest nutritious fish in 72% of countries. In sub-Saharan Africa, where nutrient deficiencies are rising

Injustices are prevalent in food systems, where the accumulation of vast wealth is possible for a few, yet one in ten people remain hungry. Here, for 194 countries we combine aquatic food production, distribution and consumption data with corresponding national policy documents and, drawing on theories of social justice, explore whether barriers to participation explain unequal distributions of benefits. Using Bayesian models, we find economic and political barriers are associated with lower wealth-based benefits; countries produce and consume less when wealth, formal education and voice and accountability are lacking. In contrast, social barriers are associated with lower welfare-based benefits; aquatic foods are less affordable where gender inequality is greater. Our analyses of policy documents reveal a frequent failure to address political and gender-based barriers. However, policies linked to more just food system outcomes centre principles of human rights, specify inclusive decision-making processes and identify and challenge drivers of injustice.

International audience; The sustainability of coral reef fisheries is jeopardized by complex and interacting socio-ecological stressors that undermine their contribution to food and nutrition security. Climate change has emerged as one of the key stressors threatening coral reefs and their fish-associated services. How fish nutrient concentrations respond to warming oceans remains unclear but these responses are probably affected by both direct (metabolism and trophodynamics) and indirect (habitat and species range shifts) effects. Climate-driven coral habitat loss can cause changes in fish abundance and biomass, revealing potential winners and losers among major fisheries targets that can be predicted using ecological indicators and biological traits. A critical next step is to extend research focused on the quantity of available food (fish biomass) to also consider its nutritional quality, which is relevant to progress in the fields of food security and malnutrition. Biological traits are robust predictors of fish nutrient content and thus potentially indicate how climate-driven changes are expected to impact nutrient availability within future food webs on coral reefs. Here, we outline future research priorities and an anticipatory framework towards sustainable reef fisheries contributing to nutrition-sensitive food systems in a warming ocean.

Alteration of benthic reef habitat after coral bleaching and mortality induces changes in fish assemblages, with implications for fisheries. Our understanding of climate impacts to coral reef fisheries is largely based on fish abundance and biomass. The rates at which biomass is produced and replenished (productivity and turnover) are also important to sustaining fisheries, yet the responses of these metrics following bleaching are largely unknown. Here, we examine changes in fish productivity and turnover after mass coral bleaching events in Seychelles, on reefs that were recovering to coral-dominated habitats and those that shifted to macroalgae-dominated regimes. Productivity of fish assemblages increased on all recovering reefs, particularly on fished reefs resulting in levels similar to protected reefs 19 years after bleaching. Herbivore-detritivores, such as scraping and excavating parrotfish, appeared to drive biomass production through increased abundance on recovering reefs. Productivity on regime-shifted reefs remained stable at 1994 levels in fished areas, with increases observed on protected reefs. Large increases in browser productivity (particularly on protected reefs), combined with increases for invertivores, maintained post-bleaching productivity on macroalgal reefs. For all diet groups, net turnover was generally higher on fished regime-shifted reefs than on recovering reefs, suggesting fish biomass is more readily replenished on macroalgal reefs. Reef structural complexity was a positive predictor of productivity for all diet groups. These findings indicate that post-bleaching reef fish productivity is strongly influenced by benthic recovery trajectories, and demonstrates the importance of herbivore and invertivore species in sustaining small-scale inshore fisheries following climatic disturbances.

Wild-caught fish are a bioavailable source of nutritious food that, if managed strategically, could enhance diet quality for billions of people. However, optimising nutrient production from the sea has not been a priority, hindering development of nutrition-sensitive policies. With fisheries management increasingly effective at rebuilding stocks and regulating sustainable fishing, we can now begin to integrate nutritional outcomes within existing management frameworks. Here, we develop a conceptual foundation for managing fisheries for multispecies Maximum Nutrient Yield (mMNY). We empirically test our approach using size-based models of North Sea and Baltic Sea fisheries and show that mMNY is predicted by the relative contribution of nutritious species to total catch and their vulnerability to fishing, leading to trade-offs between catch and specific nutrients. Simulated nutrient yield curves suggest that vitamin D, which is deficient in Northern European diets, was underfished at fishing levels that returned maximum catch weights. Analysis of global catch data shows there is scope for nutrient yields from most of the world's marine fisheries to be enhanced through nutrient-sensitive fisheries management. With nutrient composition data now widely available, we expect our mMNY framework to motivate development of nutrient-based reference points in specific contexts, such as data-limited fisheries. Managing for mMNY alongside policies that promote access to fish could help close nutrient gaps for coastal populations, maximising the contribution of wild-caught fish to global food and nutrition security.

Summary Climate change is transforming coral reefs, threatening supply of essential dietary micronutrients from small-scale fisheries to tropical coastal communities. Yet the nutritional value of reef fisheries and climate impacts on micronutrient availability remain unclear, hindering efforts to sustain food and nutrition security. Here, we measure nutrient content in coral reef fishes in Seychelles and show that reef fish are important sources of selenium and zinc and contain levels of calcium, iron, and omega-3 fatty acids comparable with other animal-source foods. Using experimental fishing, we demonstrate that iron and zinc are enriched in fishes caught on regime-shifted macroalgal habitats, whereas selenium and omega-3 varied among species. We find substantial increases in nutrients available to fisheries over two decades following coral bleaching, particularly for iron and zinc after macroalgal regime shifts. Our findings indicate that, if managed sustainably, coral reef fisheries could remain important micronutrient sources along tropical coastlines despite escalating climate impacts., Highlights • Coral reef fishes are important sources of essential dietary nutrients • Nutrients available to fisheries increased after mass coral bleaching • Iron and zinc were higher in reef fishes caught on macroalgal habitats • Coral reefs can remain key sources of nutritious food despite climate impacts, Science for society Tropical small-scale fisheries supply nutritious and affordable seafood to hundreds of millions of people, including catches from coral reefs that are vulnerable to marine heatwaves. Climate changes therefore threaten seafood supply in places where food insecurity is most prevalent, but what is the nutrient value of climate-impacted coral reefs? We analyzed nutrient content of 43 tropical reef fish species in Seychelles and found that coral reef fish contain similar levels of iron, selenium, and zinc as chicken, pork, and beef and higher levels of calcium and omega-3 fatty acids. By integrating nutrient data with fish surveys collected before and after mass coral bleaching, we show that high post-bleaching fish biomass led to greater nutrient supply for fisheries, particularly for iron and zinc. Sustainable management of reef fisheries can therefore continue to support tropical food and nutrition security, despite climate impacts to reef ecosystems., Marine heatwaves are transforming coral reefs, yet the nutritional value of reef fisheries and climate impacts on micronutrient availability remain unclear. We show that reef fish contain levels of calcium, iron, selenium, zinc, and omega-3 fatty acids equivalent to or greater than other animal-source foods. Using monitoring data from Seychelles, we also find nutrient availability to fisheries increased after mass coral bleaching, due to greater herbivore productivity. Sustainably managed reef fisheries can support food and nutrition security along climate-impacted tropical coastlines.

Atlantic mackerel or Amalamaq (Scomber scombrus) has been subject to diverse fishing pressures in Atlantic Canada for commercial, bait, recreational, and Indigenous food-social-ceremonial (FSC) fisheries, resulting in its substantial social and cultural significance in the region. Recent stock declines have led to closures of the commercial and bait mackerel fisheries, while recreational and FSC harvesters retain respectively the ability or right to fish. Here we assess the human dimensions of the recreational mackerel fishery through administration of a voluntary questionnaire shared at wharfs and through online/social media channels. A total of 285 responses were received, with results providing a rich picture of this poorly-engaged stakeholder community. The operational dimensions of this fishery and benefits derived from recreational fishing are explored. While recommendations for conservation and management measures were not solicited explicitly, many respondents shared comments and suggestions regarding management of the stock. Engaging more actively with recreational mackerel anglers may allow for enhanced assessments of the fishery and foster local stewardship toward more effective fisheries management.

Sustainably managing fisheries requires regular and reliable evaluation of stock status. However, most multispecies reef fisheries around the globe tend to be data-poor and lack research and monitoring capacity (e.g., long-term fishery data), preventing the estimation of sustainable reference points against which stocks can be assessed. Here, combining fish biomass data for more than 2000 coral reefs with catch estimates from 99 jurisdictions, we estimate site-specific sustainable reference points for coral reef fisheries and use these to assess the status of coral reef fish stocks. We reveal that more than half of jurisdictions with available information have stocks of conservation concern, having failed at least one fisheries sustainability benchmark. We quantify the trade-offs between biodiversity, mean fish length, and ecosystem functions relative to key benchmarks and highlight the ecological benefits of increasing sustainability. Our approach yields multispecies sustainable reference points for coral reef fisheries using environmental conditions, a promising means for enhancing the sustainability of the world’s coral reef fisheries.TeaserA global assessment of the sustainability of multispecies reef fisheries indicates that more than half of jurisdictions have failed at least one of two key sustainability benchmarks.

Fish are an important source of bioavailable micronutrients and essential fatty acids, and capture fisheries have potential to substantially reduce dietary deficiencies. Vigorous debate has focused on trade and fishing in foreign waters as drivers of inequitable distribution of volume and value of fish, but their impact on nutrient supplies from fish is unknown. We analyze global catch, trade, and nutrient composition data for marine fisheries to quantify distribution patterns among countries with differing prevalence of inadequate nutrient intake. We find foreign fishing relocates 1.5 times more nutrients than international trade in fish. Analysis of nutrient flows among countries of different levels of nutrient intake shows fishing in foreign waters predominantly (but not exclusively) benefits nutrient-secure nations, an outcome amplified by trade. Next, we developed a nutritional vulnerability framework that shows those small island developing states and/or African nations currently benefiting from trade and foreign fishing, and countries with low adaptive capacity, are most vulnerable to future changes in nutrient supplies. Climate change exacerbates vulnerabilities for many nations. Harnessing the potential of global fisheries to address dietary deficiencies will require greater attention to nutrition objectives in fisheries’ licensing deals and trade negotiations.

Ecologists often rely on observational data to understand causal relationships. Although observational causal inference methodologies exist, predictive techniques such as model selection based on information criterion (e.g. AIC) remains a common approach used to understand ecological relationships. However, predictive approaches are not appropriate for drawing causal conclusions. Here, we highlight the distinction between predictive and causal inference and show how predictive techniques can lead to biased causal estimates. Instead, we encourage ecologists to valid causal inference methods such as the backdoor criterion, a graphical rule that can be used to determine causal relationships across observational studies.

Ecologists often rely on observational data to understand causal relationships. Although observational causal inference methodologies exist, model selection based on information criterion (e.g., AIC) remains a common approach used to understand ecological relationships. However, such approaches are meant for predictive inference and is not appropriate for drawing causal conclusions. Here, we highlight the distinction between predictive and causal inference and show how model selection techniques can lead to biased causal estimates. Instead, we encourage ecologists to apply the backdoor criterion, a graphical rule that can be used to determine causal relationships across observational studies.

Threats from climate change and other human pressures have led to widespread concern for the future of Australia's Great Barrier Reef (GBR). Resilience of GBR reefs will be determined by their ability to resist disturbances and to recover from coral loss, generating intense interest in management actions that can moderate these processes. Here we quantify the effect of environmental and human drivers on the resilience of southern and central GBR reefs over the past two decades. Using a composite water quality index, we find that while reefs exposed to poor water quality are more resistant to coral bleaching, they recover from disturbance more slowly and are more susceptible to outbreaks of crown-of-thorns starfish and coral disease-with a net negative impact on recovery and long-term hard coral cover. Given these conditions, we find that 6-17% improvement in water quality will be necessary to bring recovery rates in line with projected increases in coral bleaching among contemporary inshore and mid-shelf reefs. However, such reductions are unlikely to buffer projected bleaching effects among outer-shelf GBR reefs dominated by fast-growing, thermally sensitive corals, demonstrating practical limits to local management of the GBR against the effects of global warming.

[Extract] Shark sanctuaries, defined as national prohibitions on the commercial fishing and trade of sharks, provide globally important refuges for some shark species. The Maldives has earned international acclaim for being a sanctuary and reaps considerable economic benefit from shark dive tourism. Despite its success in shark conservation, the country may repeal or weaken its sanctuary legislation based on the desire to benefit economically from shark fishing and perceptions of increased conflict between fishers and sharks due to depredation (when sharks take or damage catches). Although recent pandemic-related disruption of tourism likely fueled this initiative, it may have been inevitable given that revenue generated from shark tourism does not directly benefit communities that once fished sharks and now experience depredation.

Biotic connectivity between ecosystems can provide major transport of organic matter and nutrients, influencing ecosystem structure and productivity1, yet the implications are poorly understood owing to human disruptions of natural flows2. When abundant, seabirds feeding in the open ocean transport large quantities of nutrients onto islands, enhancing the productivity of island fauna and flora3,4. Whether leaching of these nutrients back into the sea influences the productivity, structure and functioning of adjacent coral reef ecosystems is not known. Here we address this question using a rare natural experiment in the Chagos Archipelago, in which some islands are rat-infested and others are rat-free. We found that seabird densities and nitrogen deposition rates are 760 and 251 times higher, respectively, on islands where humans have not introduced rats. Consequently, rat-free islands had substantially higher nitrogen stable isotope (δ15N) values in soils and shrubs, reflecting pelagic nutrient sources. These higher values of δ15N were also apparent in macroalgae, filter-feeding sponges, turf algae and fish on adjacent coral reefs. Herbivorous damselfish on reefs adjacent to the rat-free islands grew faster, and fish communities had higher biomass across trophic feeding groups, with 48% greater overall biomass. Rates of two critical ecosystem functions, grazing and bioerosion, were 3.2 and 3.8 times higher, respectively, adjacent to rat-free islands. Collectively, these results reveal how rat introductions disrupt nutrient flows among pelagic, island and coral reef ecosystems. Thus, rat eradication on oceanic islands should be a high conservation priority as it is likely to benefit terrestrial ecosystems and enhance coral reef productivity and functioning by restoring seabird-derived nutrient subsidies from large areas of ocean.

Fish are rich in bioavailable micronutrients, such as zinc and iron, deficiencies of which are a global food security concern.1,2 Global marine fisheries yields are threatened by climate change and overfishing,3,4 yet understanding of how these stressors affect the nutrients available from fisheries is lacking.5,6 Here, using global assessments of micronutrient content2 and fisheries catch data,7 we investigate how the vulnerability status of marine fish species8,9 may translate into vulnerability of micronutrient availability at scales of both individual species and entire fishery assemblages for 157 countries. We further quantify the micronutrient evenness of catches to identify countries where interventions can optimize micronutrient supply. Our global analysis, including >800 marine fish species, reveals that, at a species level, micronutrient availability and vulnerability to both climate change and overfishing varies greatly, with tropical species displaying a positive co-tolerance, indicating greater persistence to both stressors at a community level.10 Global fisheries catches had relatively low nutritional vulnerability to fishing. Catches with higher species richness tend to be nutrient dense and evenly distributed but are more vulnerable to climate change, with 40% of countries displaying high vulnerability. Countries with high prevalence of inadequate micronutrient intake tend to have the most nutrient-dense catches, but these same fisheries are highly vulnerable to climate change, with relatively lower capacity to adapt.11 Our analysis highlights the need to consolidate fisheries, climate, and food policies to secure the sustainable contribution of fish-derived micronutrients to food and nutrition security.

Ecosystems are becoming vastly modified through disturbance. In coral reef ecosystems, the differential susceptibility of coral taxa to climate-driven bleaching is predicted to shift coral assemblages towards reefs with an increased relative abundance of taxa with high thermal tolerance. Many thermally tolerant coral species are characterised by low structural complexity, with reduced habitat niche space for the small-bodied coral reef fishes on which piscivorous mesopredators feed. This study used a patch reef array to investigate the potential impacts of climate-driven shifts in coral assemblages on the trophodynamics of reef mesopredators and their prey communities. The ‘tolerant’ reef treatment consisted only of coral taxa of low susceptibility to bleaching, while ‘vulnerable’ reefs included species of moderate to high thermal vulnerability. ‘Vulnerable’ reefs had higher structural complexity, and the fish assemblages that established on these reefs over 18 months had higher species diversity, abundance and biomass than those on ‘tolerant’ reefs. Fish assemblages on ‘tolerant’ reefs were also more strongly influenced by the introduction of a mesopredator (Cephalopholis boenak). Mesopredators on ‘tolerant’ reefs had lower lipid content in their muscle tissue by the end of the 6-week experiment. Such sublethal energetic costs can compromise growth, fecundity, and survivorship, resulting in unexpected population declines in long-lived mesopredators. This study provides valuable insight into the altered trophodynamics of future coral reef ecosystems, highlighting the potentially increased vulnerability of reef fish assemblages to predation as reef structure declines, and the cost of changing prey availability on mesopredator condition.

Diet specificity is likely to be the key predictor of a predator's vulnerability to changing habitat and prey conditions. Understanding the degree to which predatory coral reef fishes adjust or maintain prey choice, in response to declines in coral cover and changes in prey availability, is critical for predicting how they may respond to reef habitat degradation. Here, we use stable isotope analyses to characterize the trophic structure of predator–prey interactions on coral reefs of the Keppel Island Group on the southern Great Barrier Reef, Australia. These reefs, previously typified by exceptionally high coral cover, have recently lost much of their coral cover due to coral bleaching and frequent inundation by sediment‐laden, freshwater flood plumes associated with increased rainfall patterns. Long‐term monitoring of these reefs demonstrates that, as coral cover declined, there has been a decrease in prey biomass, and a shift in dominant prey species from pelagic plankton‐feeding damselfishes to territorial benthic algal‐feeding damselfishes, resulting in differences in the principal carbon pathways in the food web. Using isotopes, we tested whether this changing prey availability could be detected in the diet of a mesopredator (coral grouper, Plectropomus maculatus). The δ13C signature in grouper tissue in the Keppel Islands shifted from a more pelagic to a more benthic signal, demonstrating a change in carbon sources aligning with the change in prey availability due to habitat degradation. Grouper with a more benthic carbon signature were also feeding at a lower trophic level, indicating a shortening in food chains. Further, we found a decline in the coral grouper population accompanying a decrease in total available prey biomass. Thus, while the ability to adapt diets could ameliorate the short‐term impacts of habitat degradation on mesopredators, long‐term effects may negatively impact mesopredator populations and alter the trophic structure of coral reef food webs.

Shifting prey distributions due to global warming are expected to generate dramatic ecosystem-wide changes in trophic structure within Arctic marine ecosystems. Yet a relatively poor understanding of contemporary Arctic food webs makes it difficult to predict the consequences of such changes for Arctic predators. Doing so requires quantitative approaches that can track contemporary changes in predator diets through time, using accurate, well-defined methods. Here we use fatty acids (FA) to quantify differences in consumer diet using permutational multivariate analysis of variance tests that characterize spatial and temporal changes in consumer FA signatures. Specifically we explore differences in Greenland shark (Somniosus microcephalus) FA to differentiate their potential trophic role between Svalbard, Norway and Cumberland Sound, Canada. Greenland shark FA signatures revealed significant inter-annual differences, probably driven by varying seal and Greenland halibut responses to environmental conditions such as the NAO, bottom temperature, and annual sea-ice extent. Uncommon FA were also found to play an important role in driving spatial and temporal differences in Greenland shark FA profiles. Our statistical approach should facilitate quantification of changing consumer diets across a range of marine ecosystems.

Shifts in size structure have been documented for many commercially exploited marine fish stocks, thought to be attributed to size-selective harvesting practices coupled with changing oceanic conditions. Northwest Atlantic monkfish (Lophius americanus) is a commercially valued species in the United States that is commonly caught as bycatch in Canadian scallop and groundfish fisheries. This uniquely positioned stock is bisected by the Canadian–American jurisdictional boundary, with considerable differences in exploitation and management across its range. The status of this species was assessed two decades ago (2000) in the Maritimes region of Canada and more recently (2016) in the United States, with both countries reporting considerable decreases in the average and maximum size attained by fish. A comprehensive understanding of the magnitude of this size decrease and the drivers underlying these changes across this species’ range is lacking. Here, using 55 years of fishery-independent survey data, we apply a linear mixed effects model to quantify temporal changes in monkfish length frequencies. Widespread decreases were evident in both countries, with a 48% reduction in historic body length, indicating that the large fish once prevalent in the 1970s have become uncommon. Length varied significantly as a function of seasonality and bottom temperature. Discrepancies exist in the average observed size between countries when controlling for year, season, and area; with monkfish observed by the United States trawl survey 6 cm larger on average than those observed by the Canadian trawl survey. The implications of this difference should be considered when combining fish length data from multiple surveys. Irrespective of survey differences, the truncation of size structure in Northwest Atlantic monkfish is significant and understanding how these drivers, among others hypothesized to affect size structure (e.g. fishing mortality, density dependence), are associated with population viability will be necessary to ensure its long-term sustainability.

Micronutrient deficiencies account for an estimated one million premature deaths annually, and for some nations can reduce gross domestic product

In the face of increasing cumulative effects from human and natural disturbances, sustaining coral reefs will require a deeper understanding of the drivers of coral resilience in space and time. Here we develop a high-resolution, spatially explicit model of coral dynamics on Australia's Great Barrier Reef (GBR). Our model accounts for biological, ecological and environmental processes, as well as spatial variation in water quality and the cumulative effects of coral diseases, bleaching, outbreaks of crown-of-thorns starfish (Acanthaster cf. solaris), and tropical cyclones. Our projections reconstruct coral cover trajectories between 1996 and 2017 over a total reef area of 14,780 km(2), predicting a mean annual coral loss of -0.67%/year mostly due to the impact of cyclones, followed by starfish outbreaks and coral bleaching. Coral growth rate was the highest for outer shelf coral communities characterized by digitate and tabulate Acropora spp. and exposed to low seasonal variations in salinity and sea surface temperature, and the lowest for inner-shelf communities exposed to reduced water quality. We show that coral resilience (defined as the net effect of resistance and recovery following disturbance) was negatively related to the frequency of river plume conditions, and to reef accessibility to a lesser extent. Surprisingly, reef resilience was substantially lower within no-take marine protected areas, however this difference was mostly driven by the effect of water quality. Our model provides a new validated, spatially explicit platform for identifying the reefs that face the greatest risk of biodiversity loss, and those that have the highest chances to persist under increasing disturbance regimes.

To understand the effects of predator removal in marine ecosystems requires accurate estimates of trophic position and trophic structure that have been difficult to obtain to date. For example, most sharks are classified as diet generalists that feed around trophic position 4, but this classification contradicts observations of diverse feeding behaviour among large species, suggesting that trophic structure has been oversimplified among upper trophic level species. To test this assumption, bulk δ 15 N and δ 13 C values of 13 shark species constituting the large shark assemblage off southern Africa were integrated into (i) a hierarchical Bayesian model, accounting for body size and variable sample sizes among species, and (ii) a dietary δ 15 N-dependent enrichment model to quantify individual and assemblage-wide trophic position and structure. Compound specific isotopic analysis of amino acids (CSIA-AAs) for a subset of species was used to verify results. Although discrepancies occurred between methods, overall these data confirm that large sharks, including several globally threatened species, feed at markedly higher trophic positions and across a broader trophic range than is currently assumed. This identifies a lower degree of functional equivalence among the assemblage. Such complex trophic structure among large sharks suggests that cascading effects from species-specific removals in food webs may be weaker but more pervasive than currently assumed. Reassignment of the trophic structure of large marine predators has important consequences for any potential regulatory and stabilizing roles in marine food webs.

Continuing degradation of coral reef ecosystems has generated substantial interest in how management can support reef resilience(1,2). Fishing is the primary source of diminished reef function globally(3-5), leading to widespread calls for additional marine reserves to recover fish biomass and restore key ecosystem functions(6). Yet there are no established baselines for determining when these conservation objectives have been met or whether alternative management strategies provide similar ecosystem benefits. Here we establish empirical conservation benchmarks and fish biomass recovery timelines against which coral reefs can be assessed and managed by studying the recovery potential of more than 800 coral reefs along an exploitation gradient. We show that resident reef fish biomass in the absence of fishing (B-0) averages similar to 1,000 kg ha(-1), and that the vast majority (83%) of fished reefs are missing more than half their expected biomass, with severe consequences for key ecosystem functions such as predation. Given protection from fishing, reef fish biomass has the potential to recover within 35 years on average and less than 60 years when heavily depleted. Notably, alternative fisheries restrictions are largely (64%) successful at maintaining biomass above 50% of B-0, sustaining key functions such as herbivory. Our results demonstrate that crucial ecosystem functions can be maintained through a range of fisheries restrictions, allowing coral reef managers to develop recovery plans that meet conservation and livelihood objectives in areas where marine reserves are not socially or politically feasible solutions.

Collaborative management arrangements are increasingly being used in fisheries, yet critical questions remain about the conditions under which these are most successful. Here, we conduct one of the first comprehensive tests of Elinor Ostrom's diagnostic framework for analyzing social–ecological systems to examine how 16 socioeconomic and institutional conditions are related the livelihood outcomes in 42 co-management arrangements in five countries across the Indo-Pacific. We combine recent developments in both theory and modeling to address three key challenges among comparative studies of social–ecological systems: the presence of a large number of explanatory mechanisms, variables operating at multiple scales, and the potential for interactions among socio-economic and institutional factors. We find that resource users were more likely to perceive benefits from co-management when they are more involved in decisions, were aware that humans are causal agents of change in marine systems, were wealthier, were not migrants, were in villages with smaller populations and older co-management arrangements, and had clearly established boundaries. Critically, we quantify a number of key interactions between: wealth, dependence on marine resources, involvement in decision-making, and population size that have strong implications for co-management success in terms of livelihood benefits. This study demonstrates that context plays a critical but identifiable role in co-management success.

The common scientific and media narrative in fisheries is one of failure: poor governance, collapsed stocks, and vanishing livelihoods. Yet, there are successful fisheries – instances where governments and/or communities have maintained or rebuilt stocks, where fishers have robust livelihoods, and where institutions are strong. Scientists and managers alike are becoming increasingly interested in moving beyond the doom-and-gloom stories of fisheries failures toward cumulative knowledge for making fisheries governance more successful. Recent literature has attempted to determine what separates the successes from the failures and better understand how lessons learned for effective fisheries governance can be cumulatively compiled. In this special issue, we present a range of fisheries studies from around the world – Latin America, The Pacific, and East Africa. The studies look at varying fisheries outcomes, including sustainability, cooperation, self-governance, and sustaining livelihoods. The contributions in this special issue all tackle the challenge of exploring, testing, and refining the Diagnostic Framework for Analyzing Social-Ecological Systems developed by Elinor Ostrom as a way to cumulate knowledge on the potential conditions that could be causing a problem or creating a benefit in the governance of small-scale marine fisheries. These articles successfully explore the applicability and contributions of the framework while providing important theoretical refinements for small-scale fisheries.

Meta-analysis and decision analysis are underpinned by well-developed methods that are commonly applied to a variety of problems and disciplines. While these two fields have been closely linked in some disciplines such as medicine, comparatively little attention has been paid to the potential benefits of linking them in ecology, despite reasonable expectations that benefits would be derived from doing so. Meta-analysis combines information from multiple studies to provide more accurate parameter estimates and to reduce the uncertainty surrounding them. Decision analysis involves selecting among alternative choices using statistical information that helps to shed light on the uncertainties involved. By linking meta-analysis to decision analysis, improved decisions can be made, with quantification of the costs and benefits of alternate decisions supported by a greater density of information. Here, we briefly review concepts of both meta-analysis and decision analysis, illustrating the natural linkage between them and the benefits from explicitly linking one to the other. We discuss some examples in which this linkage has been exploited in the medical arena and how improvements in precision and reduction of structural uncertainty inherent in a meta-analysis can provide substantive improvements to decision analysis outcomes by reducing uncertainty in expected loss and maximising information from across studies. We then argue that these significant benefits could be translated to ecology, in particular to the problem of making optimal ecological decisions in the face of uncertainty.

Reference points are specific values related to the state of a resource to which targets and limits for harvest management can be set. Although reference points evolved within fisheries science, they are likely to be widely applicable across a range of ecosystems and environments, as the principles behind their development and implementation apply to any harvested system. This special issue ofEnvironmental Conservationtakes a critical look at the ways in which reference points have been used previously, including the political, scientific and management contexts that have hindered and enabled their implementation. Through these experiences, a range of recommendations are made, highlighting the importance of social context in which biological reference points are developed and in favour of approaches that deal explicitly with uncertainty. When implemented without qualification, reference points have proven effective at preventing fisheries collapse and rebuilding depleted stocks; where they have not, management failures have occurred. Given the social-ecological complexity of fisheries management, the papers in this special issue provide a strong argument for the application of reference points across a range of resource management problems.

Summary 1. In light of the continuing biodiversity crisis, the need for high-resolution, broad-scale ecological data is particularly acute. The expansive scale of volunteer data collection programmes provides an opportunity to address this challenge, however, protocols used to collect such data are typically less standardized than those used by professional scientists. Although previous studies have established that different protocols can lead to different results, it remains unclear how relevant these differences are to specific study goals, such as biodiversity assessment. 2. This study uses both null model and Bayesian occupancy approaches to examine the capacity of a widely used volunteer survey protocol, the roving diver transect, to detect patterns of marine fish diversity. Richness estimates are compared with those obtained using the conventional belt transects favoured in many peer reviewed studies, examining the power of both protocols to detect statistically significant differences between survey sites and quantifying differences in detectability. 3. Pairwise site comparisons of a-diversity (i.e. within site diversity) were consistent between protocols, particularly for species totals. 4. The roving diver transect protocol detected a substantially larger number of species than the belt transect protocol, due to notably higher detectability, even after controlling for confounding factors. Both protocols detected the same species pool, although the species richness among observations was higher for the belt protocol at certain sites. 5. The significance of pairwise site b-diversity (i.e. differentiation between sites) comparisons differed between the protocols and care should be exercised, when using either protocol, when studying variation in species composition. 6. These results provide vital information for managers and researchers considering the use of volunteer data or protocols for the purpose of biodiversity assessment in aquatic systems, helping to quantify the value of thousands of existing survey records. The larger number of species detected by the volunteer protocol suggests this protocol may be advantageous with regards to the completion of taxonomic lists.

Ocean warming under climate change threatens coral reefs directly, through fatal heat stress to corals and indirectly, by boosting the energy of cyclones that cause coral destruction and loss of associated organisms. Although cyclone frequency is unlikely to rise, cyclone intensity is predicted to increase globally, causing more frequent occurrences of the most destructive cyclones with potentially severe consequences for coral reef ecosystems. While increasing heat stress is considered a pervasive risk to coral reefs, quantitative estimates of threats from cyclone intensification are lacking due to limited data on cyclone impacts to inform projections. Here, using extensive data from Australia's Great Barrier Reef (GBR), we show that increases in cyclone intensity predicted for this century are sufficient to greatly accelerate coral reef degradation. Coral losses on the outer GBR were small, localized and offset by gains on undisturbed reefs for more than a decade, despite numerous cyclones and periods of record heat stress, until three unusually intense cyclones over 5 years drove coral cover to record lows over >1500 km. Ecological damage was particularly severe in the central-southern region where 68% of coral cover was destroyed over >1000 km, forcing record declines in the species richness and abundance of associated fish communities, with many local extirpations. Four years later, recovery of average coral cover was relatively slow and there were further declines in fish species richness and abundance. Slow recovery of community diversity appears likely from such a degraded starting point. Highly unusual characteristics of two of the cyclones, aside from high intensity, inflated the extent of severe ecological damage that would more typically have occurred over 100s of km. Modelling published predictions of future cyclone activity, the likelihood of more intense cyclones within time frames of coral recovery by mid-century poses a global threat to coral reefs and dependent societies.

Coral reef fisheries support the livelihoods of millions of people but have been severely and negatively affected by anthropogenic activities. We conducted a systematic review of published data on the biomass of coral reef fishes to explore how the condition of reef fisheries is related to the density of local human populations, proximity of the reef to markets, and key environmental variables (including broad geomorphologic reef type, reef area, and net productivity). When only population density and environmental covariates were considered, high variability in fisheries conditions at low human population densities resulted in relatively weak explanatory models. The presence or absence of human settlements, habitat type, and distance to fish markets provided a much stronger explanatory model for the condition of reef fisheries. Fish biomass remained relatively low within 14 km of markets, then biomass increased exponentially as distance from reefs to markets increased. Our results suggest the need for an increased science and policy focus on markets as both a key driver of the condition of reef fisheries and a potential source of solutions.

Cost-effective proxies of biodiversity and species abundance, applicable across a range of spatial scales, are needed for setting conservation priorities and planning action. We outline a rapid, efficient, and low-cost measure of spectral signal from digital habitat images that, being an effective proxy for habitat complexity, correlates with species diversity and requires little image processing or interpretation. We validated this method for coral reefs of the Great Barrier Reef (GBR), Australia, across a range of spatial scales (1 m to 10 km), using digital photographs of benthic communities at the transect scale and high-resolution Landsat satellite images at the reef scale. We calculated an index of image-derived spatial heterogeneity, the mean information gain (MIG), for each scale and related it to univariate (species richness and total abundance summed across species) and multivariate (species abundance matrix) measures of fish community structure, using two techniques that account for the hierarchical structure of the data: hierarchical (mixed-effect) linear models and distance-based partial redundancy analysis. Over the length and breadth of the GBR, MIG alone explained up to 29% of deviance in fish species richness, 33% in total fish abundance, and 25% in fish community structure at multiple scales, thus demonstrating the possibility of easily and rapidly exploiting spatial information contained in digital images to complement existing methods for inferring diversity and abundance patterns among fish communities. Thus, the spectral signal of unprocessed remotely sensed images provides an efficient and low-cost way to optimize the design of surveys used in conservation planning. In data-sparse situations, this simple approach also offers a viable method for rapid assessment of potential local biodiversity, particularly where there is little local capacity in terms of skills or resources for mounting in-depth biodiversity surveys.

In an effort to deliver better outcomes for people and the ecosystems they depend on, many governments and civil society groups are engaging natural resource users in collaborative management arrangements (frequently called comanagement). However, there are few empirical studies demonstrating the social and institutional conditions conducive to successful comanagement outcomes, especially in small-scale fisheries. Here, we evaluate 42 comanagement arrangements across five countries and show that: ( i ) comanagement is largely successful at meeting social and ecological goals; ( ii ) comanagement tends to benefit wealthier resource users; ( iii ) resource overexploitation is most strongly influenced by market access and users’ dependence on resources; and ( iv ) institutional characteristics strongly influence livelihood and compliance outcomes, yet have little effect on ecological conditions.

Sustainably managing ecosystems is challenging, especially for complex systems such as coral reefs. This study develops critical reference points for sustainable management by using a large empirical dataset on the coral reefs of the western Indian Ocean to investigate associations between levels of target fish biomass (as an indicator of fishing intensity) and eight metrics of ecosystem state. These eight ecological metrics each exhibited specific thresholds along a continuum of fishable biomass ranging from heavily fished sites to old fisheries closures. Three thresholds lay above and five below a hypothesized window of fishable biomass expected to produce a maximum multispecies sustainable yield ( B MMSY ). Evaluating three management systems in nine countries, we found that unregulated fisheries often operate below the B MMSY , whereas fisheries closures and, less frequently, gear-restricted fisheries were within or above this window. These findings provide tangible management targets for multispecies coral reef fisheries and highlight key tradeoffs required to achieve different fisheries and conservation goals.

With rapidly increasing rates of contemporary extinction, predicting extinction vulnerability and identifying how multiple stressors drive non-random species loss have become key challenges in ecology. These assessments are crucial for avoiding the loss of key functional groups that sustain ecosystem processes and services. We developed a novel predictive framework of species extinction vulnerability and applied it to coral reef fishes. Although relatively few coral reef fishes are at risk of global extinction from climate disturbances, a negative convex relationship between fish species locally vulnerable to climate change vs. fisheries exploitation indicates that the entire community is vulnerable on the many reefs where both stressors co-occur. Fishes involved in maintaining key ecosystem functions are more at risk from fishing than climate disturbances. This finding is encouraging as local and regional commitment to fisheries management action can maintain reef ecosystem functions pending progress towards the more complex global problem of stabilizing the climate.

A recent literature review reported negative relationships between diet discrimination factors (DDFs = X(fish) - X(food) ; X = δ(15) N or δ(13) C) and the values of δ(15) N and δ(13) C in the food of wild organisms but there has been no laboratory-based confirmation of these relationships to date. Laboratory reared guppies (Poecilia reticulata) fed a series of diets with a range of δ(13) C (-22.9 to -6.6‰) and δ(15) N (6.5 to 1586‰) values were used to magnify diet-tissue dynamics in order to calculate DDFs once the fish had achieved equilibrium with each of the diets. Values of DDFs range widely for δ(15) N (7.1 to -849‰) and δ(13) C (1.1 to -7.0‰) and showed a strong negative correlation with the stable isotope value in the food for δ(15) N (slope = -0.59 ± 0.02, r(2) = 0.95) and δ(13) C (slope = -0.56 ± 0.02, r(2) = 0.94). Based on these relationships, the magnitude of DDF change over environmentally relevant values of δ(15) N or δ(13) C would be significant and could confound the interpretation of stable isotopes in the environment. Using highly enriched experimental diets, our study adds to a growing number of studies that undermine the consistent trophic enrichment paradigm with results that demonstrate the currently poor mechanistic understanding of how DDFs arise. The results of our study highlight that the magnitude of the stable isotope values in prey must be considered when choosing DDF values. Future laboratory studies should therefore be directed at uncovering the mechanistic basis of DDFs and, like others before, we recommend the determination of diet-dependent DDFs under laboratory conditions before modeling dietary proportions or calculating trophic positions.

Changes from coral to macroalgal dominance following disturbances to corals symbolize the global degradation of coral reefs. The development of effective conservation measures depends on understanding the causes of such phase shifts. The prevailing view that coral–macroalgal phase shifts commonly occur due to insufficient grazing by fishes is based on correlation with overfishing and inferences from models and small-scale experiments rather than on long-term quantitative field studies of fish communities at affected and resilient sites. Consequently, the specific characteristics of herbivorous fish communities that most promote reef resilience under natural conditions are not known, though this information is critical for identifying vulnerable ecosystems. In this study, 11 years of field surveys recorded the development of the most persistent coral–macroalgal phase shift (>7 years) yet observed on Australia’s Great Barrier Reef (GBR). This shift followed extensive coral mortality caused by thermal stress (coral bleaching) and damaging storms. Comparisons with two similar reefs that suffered similar disturbances but recovered relatively rapidly demonstrated that the phase shift occurred despite high abundances of one herbivore functional group (scraping/excavating parrotfishes: Labridae). However, the shift was strongly associated with low fish herbivore diversity and low abundances of algal browsers (predominantly Siganidae) and grazers/detritivores (Acanthuridae), suggesting that one or more of these factors underpin reef resilience and so deserve particular protection. Herbivorous fishes are not harvested on the GBR, and the phase shift was not enhanced by unusually high nutrient levels. This shows that unexploited populations of herbivorous fishes cannot ensure reef resilience even under benign conditions and suggests that reefs could lose resilience under relatively low fishing pressure. Predictions of more severe and widespread coral mortality due to global climate change emphasize the need for more effective identification and protection of ecosystem components that are critical for the prevention of coral reef phase shifts.

Stable isotopes of nitrogen and carbon (δ15N and δ13C) provide an important tool to examine diet, trophic position and movement/migration of both aquatic and terrestrial animals. Over the past 10 years, there have been repeated calls to tighten up basic assumptions when applying stable isotopes, one of the most important being the application of accurate, species-specific diet-tissue discrimination factors (DTDFs). Taxa- or species-specific DTDFs are required for (i) predicting dietary sources to a consumer using stable isotope mixing models and (ii) for estimating trophic position relative to primary consumers or known base species. Logan & Lutcavage (2010) recently presented data on stable isotope dynamics in elasmobranch fishes and concluded that DTDFs for teleost fish were suitable for elasmobranch fish, endorsing the generally applied value of 3.4‰. When considering (i) a recent study which found that DTDFs were lower for large sharks than teleost fish (Hussey et al., 2010) and (ii) that the Logan and Lutcavage study did not experimentally address the issue of DTDFs, we would argue that this conclusion is misleading. We demonstrate this point by estimating the proportion of prey items of a captive shark with a known diet history by modelling the δ15N values of the shark and its prey. The often repeated implication of inaccurate DTDFs is clear, with model results highly variable depending on the selected DTDF. In addition, model results for the standard teleost DTDF of 3.4‰ provided erroneous estimates of prey consumption. The suggestion that DTDFs for teleost fish are suitable for elasmobranchs may mislead investigators to choose DTDFs which are likely not applicable to their study species. Caution is therefore warranted in advocating this approach. Continued experimental work to examine stable isotopes in sharks is required and recommendations are made.

Ecological monitoring programs typically aim to detect changes in the abundance of species of conservation concern or which reflect system status. Coral reef fish assemblages are functionally important for reef health and these are most commonly monitored using underwater visual surveys (UVS) by divers. In addition to estimating numbers, most programs also collect estimates of fish lengths to allow calculation of biomass, an important determinant of a fish’s functional impact. However, diver surveys may be biased because fishes may either avoid or are attracted to divers and the process of estimating fish length could result in fish counts that differ from those made without length estimations. Here we investigated whether (1) general diver disturbance and (2) the additional task of estimating fish lengths affected estimates of reef fish abundance and species richness during UVS, and for how long. Initial estimates of abundance and species richness were significantly higher than those made on the same section of reef after diver disturbance. However, there was no evidence that estimating fish lengths at the same time as abundance resulted in counts different from those made when estimating abundance alone. Similarly, there was little consistent bias among observers. Estimates of the time for fish taxa that avoided divers after initial contact to return to initial levels of abundance varied from three to 17 h, with one group of exploited fishes showing initial attraction to divers that declined over the study period. Our finding that many reef fishes may disperse for such long periods after initial contact with divers suggests that monitoring programs should take great care to minimise diver disturbance prior to surveys.

Aim Quantifying and predicting change in large ecosystems is an important research objective for applied ecologists as human disturbance effects become increasingly evident at regional and global scales. However, studies used to make inferences about large-scale change are frequently of uneven quality and few in number, having been undertaken to study local, rather than global, change. Our aim is to improve the quality of inferences that can be made in meta-analyses of large-scale disturbance by integrating studies of varying quality in a unified modelling framework that is informative for both local and regional management. Innovation Here we improve conventionally structured meta-analysis methods by including imputation of unknown study variances and the use of Bayesian factor potentials. The approach is a coherent framework for integrating data of varying quality across multiple studies while facilitating belief statements about the uncertainty in parameter estimates and the probable outcome of future events. The approach is applied to a regional meta-analysis of the effects of loss of coral cover on species richness and the abundance of coral-dependent fishes in the western Indian Ocean (WIO) before and after a mass bleaching event in 1998. Main conclusions Our Bayesian approach to meta-analysis provided greater precision of parameter estimates than conventional weighted linear regression meta-analytical techniques, allowing us to integrate all available data from 66 available study locations in the WIO across multiple scales. The approach thereby: (1) estimated uncertainty in site-level estimates of change, (2) provided a regional estimate for future change at any given site in the WIO, and (3) provided a probabilistic belief framework for future management of reef resources at both local and regional scales.

Dennard, S. T., MacNeil, M. A., Treble, M. A., Campana, S., and Fisk, A. T. 2010. Hierarchical analysis of a remote, Arctic, artisanal longline fishery. – ICES Journal of Marine Science, 67: 41–51. This is the first paper to explore trends in catch per unit effort (cpue) through time of a Greenland halibut Reinhardtius hippoglossoides stock targeted by an artisanal, winter fishery in Cumberland Sound on southern Baffin Island, Canada. We modelled cpue data from 1987 to 2003, looking at two questions: what factors have driven cpue trends, and is cpue an accurate index of a stock's abundance? In the context of limited data availability, we used generalized linear models (GLMs) and hierarchical models to assess important predictors of cpue. Hierarchical models with multiple fixed environmental effects contained fishing location or individual fisher as random effects. A month effect showed greatest catch rates during February and March; the monthly North Atlantic Oscillation index was positively associated with catch rates; and a change from decreasing to increasing cpue after 1996 was linked to reduced fishery participation following a large storm. The best Akaike's information criterion-ranked GLM identified a negative relationship of cpue with shark bycatch. Although data limitations precluded conventional stock assessment, our models implicated the environment and fisher behaviour as drivers of cpue trends. Additionally, using multiple hierarchical models to predict cpue provided a more informative analysis for understanding trends in cpue than a GLM alone.

MacNeil, M. A., Carlson, J. K., and Beerkircher, L. R. 2009. Shark depredation rates in pelagic longline fisheries: a case study from the Northwest Atlantic. – ICES Journal of Marine Science, 66: 708–719. A suite of modelling approaches was employed to analyse shark depredation rates from the US Atlantic pelagic longline fishery. As depredation events are relatively rare, there are a large number of zeroes in pelagic longline data and conventional generalized linear models (GLMs) may be ineffective as tools for statistical inference. GLMs (Poisson and negative binomial), two-part (delta-lognormal and truncated negative binomial, T-NB), and mixture models (zero-inflated Poisson, ZIP, and zero-inflated negative binomial, ZINB) were used to understand the factors that contributed most to the occurrence of depredation events that included a small proportion of whale damage. Of the six distribution forms used, only the ZIP and T-NB models performed adequately in describing depredation data, and the T-NB and ZINB models outperformed the ZIP models in bootstrap cross-validation estimates of prediction error. Candidate T-NB and ZINB model results showed that encounter probabilities were more strongly related to large-scale covariates (space, season) and that depredation counts were correlated with small-scale characteristics of the fishery (temperature, catch composition). Moreover, there was little evidence of historical trends in depredation rates. The results show that the factors contributing to most depredation events are those already controlled by ships' captains and, beyond novel technologies to repel sharks, there may be little more to do to reduce depredation loss in the fishery within current economic and operational constraints.

Assessments of the biodiversity and structure of coral reef fish communities are often plagued by inadequate sampling and biases inherent in commonly used Underwater Visual Census (UVC) methods. Of these biases, heterogeneity in the detectability of reef-fish species is often ignored, even though it may have substantial effects on biodiversity estimates. Using highly repli- cated UVC sampling of all fish species at 4 sites in Tanzania, East Africa, we show that detectability varies greatly across species and is affected by traits such as body size and schooling behaviour, and that detectability of reef fishes can be readily accounted for by the application of Capture-Mark- Recapture (CMR) models. Based on our results, we recommend that approximately 24 point counts are necessary to assess full reef-fish species richness at sites in the Western Indian Ocean.

Epistemology, the theory of how knowledge arises, is an issue that ecologists and environmental scientists may not often consider in their work. However, beliefs about epistemology play a direct role in how they conduct research and, consciously or not, the conclusions made through analysis reflect some form of epistemology. I argue that the Popperian epistemology by which most environmental scientists are trained is generally incompatible with research on observational data and that observation-based studies can be improved by modifying Popper's notion of falsification.

Diet-tissue fractionation factors and metabolic turnover rates of delta15N and delta13C were assessed in laboratory-reared black fly (Simulium vittatum IS-7) larvae fed isotopically distinct diets. Five treatments consisted of using food with different delta15N signatures throughout the experiments (19-26 days), a sixth shifted from a low to high delta15N signature diet (uptake) on day 14, and the last shifted from a high to low delta15N signature diet (elimination) on day 14. In the larvae, diet-tissue fractionation factors for delta13C, which were in steady state with food, ranged from -0.61 to 2.0, with a median of 1.87. The delta15N diet-tissue fractionation factors were mostly negative, ranging from +2.85 to -24.96 per thousand, with a single positive value from the elimination treatment in which larval delta15N did not achieve steady state with the food. Diet-tissue fractionation factors also had a significant negative relationship (r2 = 0.98) with delta15N values in the food suggesting that nitrogen diet-tissue fractionation factors are 15N concentration-dependent. The delta15N of shed head capsules and feces were enriched in 15N and could be mechanisms for elimination of 15N by the larvae. For delta15N, metabolic turnover values based on the Hesslein model were highly consistent (0.40 to 0.43 delta15N*day(-1)) between uptake and elimination phases and across experiments and were an order of magnitude greater than growth rates. The rapid turnover of nitrogen in black fly larvae, which was orders of magnitude greater than measured in vertebrates, makes them an excellent indicator of short-term changes in nitrogen inputs to aquatic systems.

Stable isotope analysis (SIA) is recognized as a powerful analytical tool with numerous ecological applications. This has been highlighted by the increase in popularity of the isotope ratio mass spectrometry (IRMS) technique and the large number of studies reporting isotopic data. Comparisons of new isotopic data with previously published results and the use of large volumes of isotopic ratios in meta-analyses to explain isotopic variance are commonplace. Such data often originate from different IRMS instruments and are assumed to be readily comparable as all instruments are calibrated to International Atomic Energy Agency (IAEA) standards. To test the validity of this assumption, we analyzed a single ecological sample (homogenized cod muscle, Gadus morhua) on eight anonymous IRMS instruments and found significant variation in both δ15N and δ13C. We used a one-way analysis of variance (ANOVA) with random effects to estimate the average variability of laboratory results within and among instruments. Overall, 74% of variation in δ15N and 35% of variation in δ13C of a single ecological sample was explained by differences in the IRMS instrument used. In light of these findings, researchers are encouraged to submit their own sample reference to provide an independent check on variation between runs and between instruments; consistent discrepancies between instruments should be corrected through linear regression. Comparisons of data obtained from multiple instruments should acknowledge inter-instrument variation as a potential source of error.