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Current and future prospects for successfully rebuilding global fisheries remain debated due to uncertain stock status, variable management success, and disruptive environmental change. While scientists routinely account for some of this uncertainty in population models, the mechanisms by which this translates into decision-making and policy are problematic and can lead to unintentional overexploitation. Here, we explicitly track the role of measurement uncertainty and environmental variation in the decision-making process for setting catch quotas. Analyzing 109 well-sampled stocks from all oceans, we show that current practices may attain 55% recovery on average, while richer decision methods borrowed from robotics yield 85% recovery of global stocks by midcentury, higher economic returns, and greater robustness to environmental surprises. These results challenge the consensus that global fisheries can be rebuilt by existing approaches alone, while also underscoring that rebuilding stocks may still be achieved by improved decision-making tools that optimally manage this uncertainty.

While the physical dimensions of climate change are now routinely assessed through multimodel intercomparisons, projected impacts on the global ocean ecosystem generally rely on individual models with a specific set of assumptions. To address these single-model limitations, we present standardized ensemble projections from six global marine ecosystem models forced with two Earth system models and four emission scenarios with and without fishing. We derive average biomass trends and associated uncertainties across the marine food web. Without fishing, mean global animal biomass decreased by 5% (±4% SD) under low emissions and 17% (±11% SD) under high emissions by 2100, with an average 5% decline for every 1 °C of warming. Projected biomass declines were primarily driven by increasing temperature and decreasing primary production, and were more pronounced at higher trophic levels, a process known as trophic amplification. Fishing did not substantially alter the effects of climate change. Considerable regional variation featured strong biomass increases at high latitudes and decreases at middle to low latitudes, with good model agreement on the direction of change but variable magnitude. Uncertainties due to variations in marine ecosystem and Earth system models were similar. Ensemble projections performed well compared with empirical data, emphasizing the benefits of multimodel inference to project future outcomes. Our results indicate that global ocean animal biomass consistently declines with climate change, and that these impacts are amplified at higher trophic levels. Next steps for model development include dynamic scenarios of fishing, cumulative human impacts, and the effects of management measures on future ocean biomass trends.

Human beings are the dominant top predator in the marine ecosystem. Throughout most of the global ocean this predation is carried out by industrial fishing vessels, that can now be observed in unprecedented detail via satellite monitoring of Automatic Identification System (AIS) messages. The spatial and temporal distribution of this fishing effort emerges from the coupled interaction of ecological and socio-economic drivers and can therefore yield insights on the dynamics of both the ecosystem and fishers. Here we analyze temporal variability of industrial fishing effort from 2015-2017 as recorded by global AIS coverage, and differentiated by fishing gear type. The strongest seasonal signal is a reduction of total deployed effort during the annual fishing moratorium on the numerically-dominant Chinese fleet, which occurs during boreal summer. An additional societally-controlled reduction of effort occurs during boreal winter holidays. After accounting for these societal controls, the total deployed effort is relatively invariant throughout the year for all gear types except squid jiggers and coastal purse seiners. Despite constant deployment levels, strong seasonal variability occurs in the spatial pattern of fishing effort for gears targeting motile pelagic species, including purse seiners, squid jiggers and longliners. Trawlers and fixed gears target bottom-associated coastal prey and show very little overall seasonality, although they exhibit more seasonal variation at locations that are further from port. Our results suggest that societal controls dominate the total deployment of fishing effort, while the behavior of pelagic fish, including seasonal migration and aggregation, is likely the most prominent driver of the spatial seasonal variations in global fishing effort.

In response to fisheries declines and delayed population recoveries, many management agencies globally are integrating alternative strategies that incorporate precautionary and ecosystem considerations, increasingly focusing on climate variability and change. Here, we quantitatively evaluate how these themes have been incorporated into the science and management plans for Canada's fisheries by analyzing the content of 905 research and management documents published by the Fisheries and Oceans Canada (DFO) for the Atlantic and Eastern Arctic regions. We found that the precautionary approach was mentioned much more frequently (44%) than climate change (11%) or ecosystem approaches to fisheries management (1%). Of research documents that mentioned climate change, 61% contained only a single reference to it, suggesting that it is not quantitatively evaluated in the science that informs the advisory and decision-making processes. Most references to climate change in the DFO research documents expressed high uncertainty of how climate change would impact the stock dynamics. We propose explanations for this and discuss approaches for increasing the incorporation of these themes into Canada's fishery management. En reponse aux declins des ressources halieutiques et a la lenteur du retablissement des populations, de nombreuses agences de gestion a l'echelle mondiale integrent des strategies nouvelles qui incorporent des considerations ecosystemiques et de prevention, en mettant de plus en plus l'accent sur la variabilite et les changements climatiques. Nous avons realise une evaluation quantitative de la maniere dont ces themes ont ete incorpores aux plans de recherche et de gestion visant les ressources halieutiques canadiennes en analysant le contenu de 905 documents de recherche et de gestion publies par le ministere des Peches et des Oceans du Canada (MPO) pour les regions de l'Atlantique et de l'est de l'Arctique. Nous constatons que l'approche de prevention est mentionnee beaucoup plus frequemment (44 %) que l'approche axee sur les changements climatiques (11 %) ou l'approche ecosystemique (1 %) de gestion des peches. Des documents de recherche qui mentionnent les changements climatiques, 61 % ne le font qu'une seule fois, ce qui indiquerait que ces changements ne font pas l'objet d'une evaluation quantitative dans la recherche servant a eclairer les processus decisionnels et de formulation d'avis. La plupart des references aux changements climatiques dans les documents de recherche du MPO expriment une grande incertitude quant a l'incidence des changements climatiques sur la dynamique des stocks. Nous proposons des raisons pour expliquer cette situation et discutons d'approches permettant d'accroitre l'incorporation de ces themes dans la gestion des ressources halieutiques du Canada. [Traduit par la Redaction], Introduction Quantitative approaches to fisheries management, rooted in population modelling, serve as the foundation for current fisheries management practices in Canada and elsewhere. Traditionally, these models focused on fishing mortality [...]

Strong decreases in greenhouse gas emissions are required to meet the reduction trajectory resolved within the 2015 Paris Agreement. However, even these decreases will not avert serious stress and damage to life on Earth, and additional steps are needed to boost the resilience of ecosystems, safeguard their wildlife, and protect their capacity to supply vital goods and services. We discuss how well-managed marine reserves may help marine ecosystems and people adapt to five prominent impacts of climate change: acidification, sea-level rise, intensification of storms, shifts in species distribution, and decreased productivity and oxygen availability, as well as their cumulative effects. We explore the role of managed ecosystems in mitigating climate change by promoting carbon sequestration and storage and by buffering against uncertainty in management, environmental fluctuations, directional change, and extreme events. We highlight both strengths and limitations and conclude that marine reserves are a viable low-tech, cost-effective adaptation strategy that would yield multiple cobenefits from local to global scales, improving the outlook for the environment and people into the future.

Here, we identify the extant species of marine megafauna (>45 kg maximum reported mass), provide a conceptual template for the ways in which these species influence the structure and function of ocean ecosystems, and review the published evidence for such influences. Ecological influences of more than 90% of the 338 known species of extant ocean megafauna are unstudied and thus unknown. The most widely known effect of those few species that have been studied is direct prey limitation, which occurs through consumption and risk avoidance behavior. Consumer-prey interactions result in indirect effects that extend through marine ecosystems to other species and ecological processes. Marine megafauna transport energy, nutrients, and other materials vertically and horizontally through the oceans, often over long distances. The functional relationships between these various ecological impacts and megafauna population densities, in the few well-studied cases, are characterized by phase shifts and hysteresis.

New technologies could revolutionize ocean observation

Over the past two decades, sharks have been increasingly recognized among the worldÕs most threatened wildlife and hence have received heightened scientific and regulatory scrutiny. Yet, the effect of protective regulations on shark fishing mortality has not been evaluated at a global scale. Here we estimate that total fishing mortality increased from at least 76 to 80 million sharks between 2012 and 2019, ~25 million of which were threatened species. Mortality increased by 4% in coastal waters but decreased by 7% in pelagic fisheries, especially across the Atlantic and Western Pacific. By linking fishing mortality data to the global regulatory landscape, we show that widespread legislation designed to prevent shark finning did not reduce mortality but that regional shark fishing or retention bans had some success. These analyses, combined with expert interviews, highlight evidence-based solutions to reverse the continued overexploitation of sharks. [ABSTRACT FROM AUTHOR]

Large animals are severely depleted in many ecosystems, yet we are only beginning to understand the ecological implications of their loss. To empirically measure the short-term effects of removing large animals from an ocean ecosystem, we used exclosures to remove large fish from a near-pristine coral reef at Palmyra Atoll, Central Pacific Ocean. We identified a range of effects that followed from the removal of these large fish. These effects were revealed within weeks of their removal. Removing large fish (1) altered the behavior of prey fish; (2) reduced rates of herbivory on certain species of reef algae; (3) had both direct positive (reduced mortality of coral recruits) and indirect negative (through reduced grazing pressure on competitive algae) impacts on recruiting corals; and (4) tended to decrease abundances of small mobile benthic invertebrates. Results of this kind help advance our understanding of the ecological importance of large animals in ecosystems.