6,160 research outputs found
Managing fisheries in a changing climate
No need to wait for more information: industrialized fishing is already wiping out stocks
What catch data can tell us about the status of global fisheries
The only available data set on the catches of global fisheries are the official landings reported annually by the Food and Agriculture Organization of the United Nations (FAO). Attempts to detect and interpret trends in these data have been criticized as being both technically and conceptually flawed. Here, we explore and refute these claims. We show explicitly that trends in catch data are not an artifact of the applied method and are consistent with trends in biomass data of fully assessed stocks. We also show that, while comprehensive stock assessments are the preferred method for evaluating single stocks, they are a biased subsample of the stocks in a given area, strongly underestimating the percentage of collapsed stocks. We concur with a recent assessment-based analysis by FAO that the increasing trends in the percentage of overexploited, depleted, and recovering stocks and the decreasing trends in underexploited and moderately exploited stocks give cause for concern. We show that these trends are much more pronounced if all available data are considered
Breakdown of Quasilocality in Long-Range Quantum Lattice Models
We study the nonequilibrium dynamics of correlations in quantum lattice models
in the presence of long-range interactions decaying asymptotically as a power
law. For exponents larger than the lattice dimensionality, a Lieb-Robinson-
type bound effectively restricts the spreading of correlations to a causal
region, but allows supersonic propagation. We show that this decay is not only
sufficient but also necessary. Using tools of quantum metrology, for any
exponents smaller than the lattice dimension, we construct Hamiltonians giving
rise to quantum channels with capacities not restricted to a causal region. An
analytical analysis of long-range Ising models illustrates the disappearance
of the causal region and the creation of correlations becoming distance
independent. Numerical results obtained using matrix product state methods for
the XXZ spin chain reveal the presence of a sound cone for large exponents and
supersonic propagation for small ones. In all models we analyzed, the fast
spreading of correlations follows a power law, but not the exponential
increase of the long-range Lieb-Robinson bound
Marine diversity shift linked to interactions among grazers, nutrients and propagule banks
Diverse coastal seaweed communities dominated by perennial fucoids become replaced by species-poor turfs of annual algae throughout the Baltic Sea. A large-scale field survey and factorial field experiments indicated that grazers maintain the fucoid community through selective consumption of annual algae. Interactive effects between grazers and dormant propagules of annual algae, stored in a 'marine seed bank', determine the response of this system to anthropogenic nutrient loading. Nutrients override grazer control and accelerate the loss of algal diversity in the presence but not in the absence of a propagule bank. This implies a novel role of propagule banks for community regulation and ecosystem response to marine eutrophication
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