Putting the principles of the Sustainable Livelihoods Approach into fisheries development policy and practice

The Sustainable Livelihoods Approach (SLA) combines a conceptual framework with a set of operational principles to provide guidance on policy formulation and development practice. The SLA has been widely used in coastal and fisheries development research and has informed the design of development programmes but experience of operationalising it remains largely undocumented. In the Sustainable Fisheries Livelihoods Programme, which involves 25 West African countries, the SLA has helped to align fisheries policy with wider poverty reduction initiatives and to identify means of contributing to poverty reduction that do not directly increase pressure on fully or over-exploited fish resources.     

Sewage diversion effects on the water column of a subtropical estuary

A study of the phytoplankton community and water column chemistry in Kaneohe Bay, Oahu, Hawaii, before and after the diversion of secondary treated sewage from the bay has shown that changes in total nutrient concentrations in the water column cannot be accurately predicted without taking into account water column-benthos interactions. During the first year after sewage diversion, the decomposition of about 400 tonnes of benthic organisms, primarily filter feeders, resulted in water column dissolved organic nitrogen and phosphorus concentrations roughly an order of magnitude higher than those expected in the absence of such interactions. The biomass of phytoplankton appears to have been N limited both before and after sewage diversion, with internal nutrient recycling accounting for 70–99% of phtyoplankton nutrient uptake. Both the biomass and growth rate of the phytoplankton declined as a result of the sewage diversion, with post-diversion growth rates evidently well below nutrient-saturated values. Since the principal stresses on the bay's coral reef community as a result of the sewage discharges appear to have resulted from the elevated concentrations of plankton in the water, various measures of seston concentration appear to be the most ecologically significant indicators of nutrient enrichment in this system.     

Small Scale Field Study of an Ocean CO<Subscript>2</Subscript> Plume

We have carried out a small-scale (∼20 l) CO₂ sequestration experiment off northern California (684 m depth, ∼5°C, background ocean pH ∼7.7) designed as an initial investigation of the effects of physical forcing of the fluid, and the problem of sensing the formation of a low pH plume. The buoyant CO₂ was contained in a square frame 1.2 m high, exposing 0.21 m² to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO₂ pool was also equipped with two recording pH electrodes. An additional pH electrode was held in the ROV robotic arm to probe the fluid interface. Local water velocities of up to 40 cm sec⁻¹ were encountered, creating significant eddies within the CO₂ box, and forcing wavelets at the fluid interface. This resulted in rapid CO₂ dissolution, with all CO₂ being depleted in a little more than 2 days. The pH record from the sensor closest (∼10 cm) to the CO₂ showed many spikes of low pH water, the extreme value being ∼5.9. The sensor 1 m immediately below this showed no detectable response. The electrodes placed 1.9 m distant from the source also recorded very small perturbations. The results provide important clues for the design of future experiments for CO₂ disposal and biogeochemical impact studies. These include the need for dealing with the slow CO₂ hydration kinetics, better understanding of the fluid dynamics of the CO₂-water interface, and non-point source release designs to provide more constant, controlled local CO₂ enrichments within the experimental area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure and Stability of Non-Transform Discontinuities on the Mid-Atlantic Ridge between 24° N and 30° N

Observations of the median valley within the 24–30° N area ofthe Mid-Atlantic Ridge (MAR), using the IOSDL high resolutionside-scan sonar instrument TOBI, image four separate areas of themedian valley, containing part or all of nine spreading segments, and fivenon-transform discontinuities between spreading segments (NTDs).These high resolution side scan images were interpreted in parallel withmultibeam bathymetry (Purdy et al., 1990), giving a greater degree ofstructural precision than is possible with the multibeam data alone. Threedistinct types of NTD were identified, corresponding in part to typespreviously identified from the multibeam bathymetric survey of the area.Type 1 NTDs are termed septal offsets, and are marked by a topographic ridgeseparating the two spreading segments. The offset between the spreadingsegments ranges from 9 to 14 km. These can be further subdivided into Type1A in which the septa run parallel to the overall trend of the MAR and Type1B in which the septa lie at a high angle to the bulk ridge trend. Type 1ANTDs are characterised by overlap of the neovolcanic zones of the segmentson each side, and strong offaxis traces, while Type 1B NTDs show no overlapof neovolcanic zones, and weak offaxis traces. Type 2 NTDs arebrittle/ductile extensional shear zones, marked by oblique extensionalfractures, and associated with rotation of tectonic and volcanic structuresaway from the overall trend of the MAR. Type 3 NTDs are associated withoffsets of less than 5 km, and show no sign of any accommodating structure.In this type of NTD, the offset zone is covered with undeformed volcanics.The type of NTD developed at any locality along the ridge axis appears todepend on the amount of segment offset and segment overlap, the overalltrend of the mid-ocean ridge, the width of the zone of discontinuity, themedian valley offset and the longevity of the offset. These factorsinfluence the mechanical properties of the lithosphere across thediscontinuity, and ultimately the tectonic style of the NTD that can besupported. Thus brittle/ductile extensional shear zones are long-livedstructures favoured by large segment offsets, and small or negative segmentoverlaps. Septa can be short or long lived, and are associated with largesegment offsets. Segment overlaps vary from negative (an along axis gap) tozero, for Type 1B septal offsets, or positive to zero for Type 1A septaloffsets. Non-tectonised NTDs are generally short lived structures,characterised by small segment offsets and zero or positive overlaps.     

Chenier plain development in northern Sierra Leone, West Africa

The coast of northern Sierra Leone, between the Scarcies and Mellacoree estuaries, forms a prograding muddy Holocene plain comprising two separate, as yet undated, clusters of sand cheniers. The general coastal morpho-stratigraphy and available data on regional climatic and sealevel history suggest that alternations between muddy progradation and chenier cluster formation have been controlled by a probable conjunction of several factors, including the local geomorphic framework, a climatically induced change in mud supply, and relative sealevel oscillations since the middle Holocene. The inner chenier cluster was apparently elaborated under conditions of efficient wave action over a deep, largely unfilled Mellacoree estuary and at a time of reduced mud availability. It peters out seaward, probably in response to several factors, including an increase in mud supply from the upland, a negative sealevel pulse resulting in higher rates of mud export from accreted inner tidal flats, increased muddy sedimentation over a shallower nearshore zone, and attenuated wave action as a result of energy capture by accreted estuarine shoals. The outer cluster, which partly fringes the coast, was formed in a mayor embayment representing the terminus of longshore sand drift. It is suggested that its formation may have been favoured by a higher sealevel resulting in efficient winnowing of sands from subtidal muds, a greater propensity for accretion of tidal flats landwards and, consequently, a lower mud supply to the foreshore.

Although the timing of muddy progradation and chenier formation has not been determined, the foregoing interpretation suggests a complex sequence of events, reflecting as much the influence of local morphodynamic factors as external factors.     

Kinematic dynamo action with helical symmetry in an unbounded fluid conductor: Part 2. Further development of an explicit solution for the prototype case of lortz

Abstract

An explicit example of a steady prototype Lortz dynamo is elaborated in terms of a previously derived illustrative, exact, closed form solution to the nonlinear dynamo equations. The eigenvalue character of the dynamo problem is now introduced which simplifies the solution. The magnetic field lines, which lie on circular cylinders, and velocity streamline pattern are then displayed and discussed. Analysis of the magnetic energy balance by way of the Poynting flux reveals the existence of a finite critical cylinder across which zero net magnetic energy flows, thereby proving that the material inside is a self-excited dynamo, despite the fact that the total magnetic energy is unbounded.     

Reports from the Smithsonian’s Global Volcanism Network, May 2010

Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 35, no. 5, May 2010 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations.     

Ecological Risk Assessment for seabird interactions in Western and Central Pacific longline fisheries

The risk of seabird–fishery interactions in the Western and Central Pacific Ocean (WCPO) was examined by analysing the overlap of seabird distributions with tuna and swordfish pelagic longline fisheries managed by the Western and Central Pacific Fisheries Commission (WCPFC) and its constituent members. The study used spatially-explicit Productivity–Susceptibility Analysis (PSA). Key data inputs were species productivity, fishing effort, likelihood of capture and species density by region. The outputs tailored results to the needs of fisheries- and wildlife-managers, indicating areas of greatest risk of species interactions, species of greatest concern for population impacts, and the flags or fisheries most likely to contribute to the risk. Large albatross species were found to be most likely to suffer population effects when exposed to longline fishing activity, followed by the larger petrels from the genuses Procellaria, Macronectes and Pterodroma. A mixture of coastal states with nesting seabird populations in their Exclusive Economic Zones (New Zealand, Australia and United States of America), distant water fishing nations (Japan, Taiwan) and flags of convenience (Vanuatu) contributed 90% of the risk to seabird populations. Recommendations include enhancing the level of fisheries observer monitoring in areas indicated as high to medium risk for seabird interactions, and consideration of spatial management tools, such as more intensive or more stringent seabird bycatch mitigation requirements in high- to medium-risk areas. The methods used, and similar studies conducted in the Atlantic Ocean could lead to improved targeting of monitoring resources, and greater specificity in the needs for seabird-mitigation measures. This will assist in reducing seabird mortality in longline fishing operations and with more effective use of resources for fishery managers in both domestic fisheries and RFMOs.     

Rapidly varying accretion and AGN feedback

Accretion rates on to active galactic nuclei (AGNs) are likely to be extremely variable on short time-scales; much shorter than the typical cooling time of X-ray emitting gas in elliptical galaxies and galaxy clusters. Using the Langevin approach it is shown that, for a simple feedback system, this can induce variability in the AGN power output that is of much larger amplitude, and persists for longer time-scales, than the initial fluctuations. An implication of this is that rich galaxy clusters are expected to show the largest and longest-lived fluctuations. Stochastic variations in the accretion rate also mean that the AGN injects energy across a wide range of time-scales. This allows the AGN to maintain a much closer balance with its surroundings than if it was periodically activated. The possible non-linear correlation between Bondi accretion rate and jet power, found by Allen et al., can be explained if the instantaneous accretion rate, scaled by jet power, varies log-normally. This explanation also implies that the duty cycle of AGN activity increases with the radiative losses of the surroundings, in qualitative agreement with Best et al.