Sustainability of deep-sea fisheries

As coastal fisheries around the world have collapsed, industrial fishing has spread seaward and deeper in pursuit of the last economically attractive concentrations of fishable biomass. For a seafood-hungry world depending on the oceans' ecosystem services, it is crucial to know whether deep-sea fisheries can be sustainable.The deep sea is by far the largest but least productive part of the oceans, although in very limited places fish biomass can be very high. Most deep-sea fishes have life histories giving them far less population resilience/productivity than shallow-water fishes, and could be fished sustainably only at very low catch rates if population resilience were the sole consideration. But like old-growth trees and great whales, their biomass makes them tempting targets while their low productivity creates strong economic incentive to liquidate their populations rather than exploiting them sustainably (Clark's Law). Many deep-sea fisheries use bottom trawls, which often have high impacts on nontarget fishes (e.g., sharks) and invertebrates (e.g., corals), and can often proceed only because they receive massive government subsidies. The combination of very low target population productivity, nonselective fishing gear, economics that favor population liquidation and a very weak regulatory regime makes deep-sea fisheries unsustainable with very few exceptions. Rather, deep-sea fisheries more closely resemble mining operations that serially eliminate fishable populations and move on.Instead of mining fish from the least-suitable places on Earth, an ecologically and economically preferable strategy would be rebuilding and sustainably fishing resilient populations in the most suitable places, namely shallower and more productive marine ecosystems that are closer to markets.     

Thermal regimes in a large upland salmon river: a simple model to identify the influence of landscape controls and climate change on maximum temperatures

Temperature observations at 25 sites in the 2000 km² Dee catchment in NE Scotland were used, in conjunction with geographic information system (GIS) analysis, to identify dominant landscape controls on mean monthly maximum stream temperatures. Maximum winter stream temperatures are mainly controlled by elevation, catchment area and hill shading, whereas the maximum temperatures in summer are driven by more complex interactions, which include the influence of riparian forest cover and distance to coast. Multiple linear regression was used to estimate the catchment‐wide distribution of mean weekly maximum stream temperatures for the hottest week of the 2‐year observation period. The results suggested the streams most sensitive to high temperatures are small upland streams at exposed locations without any forest cover and relatively far inland, while lowland streams with riparian forest cover at locations closer to the coast exhibit a moderated thermal regime. Under current conditions, all streams provide a suitable thermal habitat for both, Atlantic salmon and brown trout. Using two climate change scenarios assuming 2·5 and 4 °C air temperature increases, respectively, temperature‐sensitive zones of the stream network were identified, which could potentially have an adverse effect on the thermal habitat of Atlantic salmon and brown trout. Analysis showed that the extension of riparian forests into headwater streams has the potential to moderate changes in temperature under climate change. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing the performance of a physically based hydrological model using a proxy‐catchment approach in an agricultural environment

Physically based models are useful frameworks for testing intervention strategies designed to reduce elevated sediment loads in agricultural catchments. Evaluating the success of these strategies depends on model accuracy, generally established by a calibration and evaluation process. In this contribution, the physically based SHETRAN model was assessed in two similar U.K. agricultural catchments. The model was calibrated on the Blackwater catchment (18 km²) and evaluated in the adjacent Kit Brook catchment (22 km²) using 4 years of 15 min discharge and suspended sediment flux data. Model sensitivity to changes in single and multiple combinations of parameters and sensitivity to changes in digital elevation model resolution were assessed. Model flow performance was reasonably accurate with a Nash–Sutcliffe efficiency coefficient of 0.78 in Blackwater and 0.60 in Kit Brook. In terms of event prediction, the mean of the absolute percentage of difference (μAbs_diff) between measured and simulated flow volume (Qv), peak discharge (Qp), sediment yield (Sy), and peak sediment flux (Sp) showed larger values in Kit Brook (48% [Qv], 66% [Qp], 298% [Sy], and 438% [Sp]) compared with the Blackwater catchment (30% [Qv], 41% [Qp], 106% [Sy], and 86% [Sp]). Results indicate that SHETRAN can produce reasonable flow prediction but performs less well in estimation of sediment flux, despite reasonably similar hydrosedimentary behaviour between catchments. The sensitivity index showed flow volume sensitive to saturated hydraulic conductivity and peak discharge to the Strickler coefficient; sediment yield was sensitive to the overland flow erodibility coefficient and peak sediment flux to raindrop/leaf soil erodibility coefficient. The multiparameter sensitivity analysis showed that different combinations of parameters produced similar model responses. Model sensitivity to grid resolution presented similar flow volumes for different digital elevation model resolutions, whereas event peak and duration (for both flow and sediment flux) were highly sensitive to changes in grid size.     

Petrologic and experimental evidence for the movement and heating of the pre-eruptive Minoan rhyodacite (Santorini, Greece)

Hydrothermal experiments combined with petrologic observations form the basis for a new two-stage model for the evolution of the pre-eruption Minoan magma chamber at Santorini, Greece. Ninety-nine percent of the erupted volume is two-pyroxene, rhyodacitic magma that had been stored at a temperature of ∼885 °C, based on magnetite-ilmenite and QUILF geothermometry. The rest of the volume is basaltic to andesitic magma, which occurs as <10 cm scoria clasts and as small inclusions in rhyodacite pumices. Petrologic observations show that these magmas mixed at different scales and at different times (i.e., multiple batches of mafic magma). Hydrothermal experiments were carried out on samples of rhyodacite and a mafic scoria in order to determine magma storage conditions and the mixing history of the two magmas. At 885 °C, the rhyodacite must have been stored at water-saturated pressures of ∼50 MPa, based on its phase assemblage, matrix-glass composition, and crystal content. However, glass inclusions inside rhyodacitic plagioclase phenocrysts contain more than 6 wt% H₂O, indicating they formed at pressures >200 MPa. In addition, the composition of the plagioclase hosts (An_{56 ± 6}) of the inclusions require temperatures of 825 ± 25 °C at pressures >200 MPa. This demonstrates that the Minoan rhyodacitic magma underwent a two-stage evolution, first crystallizing at ∼825^∘C and >200 MPa, and then rinsing to a shallow ∼50 MPa storage region with a concomitant rise in temperature to ∼885 °C. We suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption. Phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region. Thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years. Preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption, perhaps triggering the event. Received: 30 September 1997 / Accepted: 5 October 1998     

Spatial and temporal variability in the responses of Arctic terrestrial ecosystems to environmental change

This paper compares the responses of two contrasting Arctic ecosystems to climate change simulations: a polar semi-desert (in Svalbard) and a dwarf shrub heath (at Abisko, northern Sweden). These ecosystems are located close to the northern-and southernmost extremes of the Arctic region, respectively. Inmacts of simulated climatic changes were determined through factorial perturbation experiments, where growing season temperature, nutrient availability and water supply were manipulated. The results are compared with the impact of interannual variation in climate on the growth of a keystone moss species, Hylocomium splendens , from the wider circumpolar area. The perturbation studies revealed that current interannual variability in temperature and the temperate tolerance of many species may exceed predicted changes in mean summer temperature over the next century. Arctic ecosystems differed in their responses to environmental manipulations, with the structure of the dwarf shrub health being affected through shifts in competitive hierarchy, potentially leading to lower biodiversity, and the polar semi-desert being affected through invasion, potentially leading to higher diversity. H. splendens showed negative responses to perturbation at the sub-Arctic site, in contrast to the positive relationship between temperature and growth observed in the natural environment. This apparent discrepancy may result from: (i) artefacts arising from the perturbations, such as lower atmospheric relative humidity; (ii) non-equilibrium responses during the relatively short-term perturbation studies and/or (iii) ecotypic variation in the moss population. Thus, caution should be employed when extrapolating from perturbations studies to both longer time-scales and different ecosystems within the Arctic.     

Ascent and eruption of a lunar high-titanium magma as inferred from the petrology of the 74001/2 drill core

Abstract— An analysis of the orange glasses and crystallized beads from the 68 cm deep 74001/2 core has been conducted to understand the processes occurring during ascent and eruption of the Apollo 17 orange glass magma. Equilibrium between melt and metal blebs (Fe₈₅Ni₁₄Co₁) within the core, along with Cr contents in olivine phenocrysts, suggest there was an oxidation of C and a reduction of the melt at an O fugacity of IW-1.3 and 1320 °C to form CO gas at 200 bars or ～4 km depth. This was followed by development of more oxidized conditions during ascent. Also during ascent, there was formation of euhedral, homogeneous Fo₈₁ olivine crystals and spinel crystals with higher Al and Mg contents than the smaller spinels in the crystallized beads. Both the metal blebs and Al-rich spinels were trapped inside the Fo₈₁ olivine phenocrysts as they grew prior to eruption. The composition of the orange glasses are homogeneous throughout the core, except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking. A few glassy melt inclusions of orange glass composition trapped in the Fo₈₁ phenocrysts contain 600 ± 100 ppm S and ～50 ppm Cl compared to the 200 ppm S and 50 ppm Cl in the orange glass melt when quenched. These inclusions therefore document the addition of 400 ppm S to the CO-rich volcanic gas during the eruption. The size and distribution of different volcanic beads in the Apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster. Progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume. The development of a brown texture in the orange glasses at the bottom of the core, where the black beads dominate, is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface. The change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time, which consequently would increase the plume optical density and favor slower cooling rates.     

Geophysical inversion with a neighbourhood algorithm—I. Searching a parameter space

This paper presents a new derivative-free search method for finding models of acceptable data fit in a multidimensional parameter space. It falls into the same class of method as simulated annealing and genetic algorithms, which are commonly used for global optimization problems. The objective here is to find an ensemble of models that preferentially sample the good data-fitting regions of parameter space, rather than seeking a single optimal model. (A related paper deals with the quantitative appraisal of the ensemble.)
  The new search algorithm makes use of the geometrical constructs known as Voronoi cells to derive the search in parameter space. These are nearest neighbour regions defined under a suitable distance norm. The algorithm is conceptually simple, requires just two 'tuning parameters', and makes use of only the rank of a data fit criterion rather than the numerical value. In this way all difficulties associated with the scaling of a data misfit function are avoided, and any combination of data fit criteria can be used. It is also shown how Voronoi cells can be used to enhance any existing direct search algorithm, by intermittently replacing the forward modelling calculations with nearest neighbour calculations.
  The new direct search algorithm is illustrated with an application to a synthetic problem involving the inversion of receiver functions for crustal seismic structure. This is known to be a non-linear problem, where linearized inversion techniques suffer from a strong dependence on the starting solution. It is shown that the new algorithm produces a sophisticated type of 'self-adaptive' search behaviour, which to our knowledge has not been demonstrated in any previous technique of this kind.     

Physiological responses of juvenile and adult shore crabs Carcinus maenas (Crustacea: Decapoda) to pyrene exposure

This study measured aspects of the physiology of juvenile [(<35mm carapace width (CW)] and adult (>60mm CW) Carcinus maenas to test the hypothesis that these different life-history stages exhibit different sensitivities to environmental contamination. Newly-collected juveniles had significantly (P<0.05) lower immunocompetence (phagocytosis and cellular integrity), lower metabolic energy (haemolymph glucose) and increased scope for growth compared with adults. Seven day exposure to a sub-lethal concentration (200microgL(-1)) of pyrene significantly (P<0.01) reduced immunocompetence, elevated basal heart rate and decreased respiration (at rest) for juveniles but had no overall impact on adult crab physiology. Results confirm that physiological differences exist between juvenile and adult shore crabs, and cause juveniles to be more susceptible to the effects of pyrene exposure than adults. Such differences in sensitivity to contamination between life-cycle stages of the same species have to be taken into account during the risk assessment process.     

Six decades of ecohydrological research connecting landscapes and riverscapes in the Girnock Burn,Scotland: Atlantic salmon population and habitat dynamics in a changing world

Long-term data are crucial for understanding ecological responses to climate and land use change; they are also vital evidence for informing management. As a migratory fish, Atlantic salmon are sentinels of both global and local environmental change. This paper reviews the main insights from six decades of research in an upland Scottish stream (Girnock Burn) inhabited by a spring Atlantic salmon population dominated by multi-sea-winter fish. Research began in the 1960s providing a census of returning adults, juvenile emigrants and in-stream production of Atlantic salmon. Early research pioneered new monitoring techniques providing new insights into salmon ecology and population dynamics. These studies underlined the need for interdisciplinary approaches for understanding salmon interactions with physical, chemical and biological components of in-stream habitats at different life-stages. This highlighted variations in catchment-scale hydroclimate, hydrology, geomorphology and hydrochemistry as essential to understanding freshwater habitats in the wider landscape context. Evolution of research has resulted in a remarkable catalogue of novel findings underlining the value of long-term data that increases with time as modelling tools advance to leverage more insights from “big data”. Data are available on fish numbers, sizes and ages across multiple life stages, extending over many decades and covering a wide range of stock levels. Combined with an unusually detailed characterization of the environment, these data have enabled a unique process-based understanding of the controls and bottlenecks on salmon population dynamics across the entire lifecycle and the consequences of declining marine survival and ova deposition. Such powerful datasets, methodological enhancements and the resulting process understanding have informed and supported the development of fish population assessment tools which have been applied to aid management of threatened salmon stocks at large-catchment, regional and national scales. Many pioneering monitoring and modelling approaches developed have been applied internationally. This history shows the importance of integrating discovery science with monitoring for informing policy development and assessing efficacy of management options. It also demonstrates the need to continue to resource long-term sites, which act as a focus for inter-disciplinary research and innovation, and where the overall value of the research greatly exceeds the costs of individual component parts.