USING AN EXPERIMENTAL IN SITU FISHWAY TO PROVIDE KEY DESIGN CRITERIA FOR LATERAL FISH PASSAGE IN TROPICAL RIVERS: A CASE STUDY FROM THE MEKONG RIVER,CENTRAL LAO PDR

Fish passage through an experimental vertical‐slot fishway was assessed at a floodplain regulator on the Mekong River in Central Laos between April and July 2009. Experiments were conducted to investigate the influence of fishway floor slope (1v:15h or 1v:7.5h) on fish passage success with a view to developing a series of optimal design criteria for the construction of vertical‐slot fishways at other barriers to fish passage in the Lower Mekong Basin. A total of 14 661 fish from 73 species were captured during the experiments. Catches were dominated by riverine (white) (n = 51; 69% of total) and floodplain (black) species (n = 15; 20%) which represented 19 families in total. The work demonstrated that fish were actively attempting upstream passage from the Mekong River to an adjacent floodplain and displayed strong migratory behaviour during river level rises. Migratory activity was greatest during sharp rises in water level but reduced substantially when river level fell. Fish community composition varied greatly among the two fishway floor slopes and the control group. More fish species were collected from control samples, but the most fish and species were collected when the fishway was configured on a moderate hydraulic slope (1v:15h). A range of size classes were also collected from control and moderate‐slope groups, but steeper‐gradient catches were dominated by larger fish. This study demonstrated that vertical‐slot fishways could provide passage for a biodiverse fish community where fish move laterally onto floodplains. The construction of fishways which consider the local fish ecology and hydrology may therefore represent a valuable management tool to help restore important movement pathways for tropical freshwater fish. Copyright © 2011 John Wiley & Sons, Ltd.     

Genetic diversity and structure of lake whitefish (Coregonus clupeaformis) 100 years after closure of the commercial fishery

In small, inland fisheries even small perturbations to the ecosystem can quickly influence population abundance, size and age distribution, and genetic structure and diversity. In Lake Champlain, lake whitefish (Coregonus clupeaformis) experienced extensive commercial harvest from the mid-1800 s to1918 and habitat fragmentation due to the construction of multiple causeways between 1850 and 1899. We evaluated the influence these environmental perturbations had on lake whitefish population genetics 120 years later. We used historic catch records to determine whether fishing pressure could have been strong enough to reduce lake whitefish population abundance, and used genotype data from eight microsatellite loci to look for genetic signatures of population-sub structure and bottleneck. Catch records indicate lake whitefish were being harvested in Lake Champlain at a similar magnitude to the Great Lakes, and simulations suggest genetic diversity may have been lost as a result of harvest. However, we were unable to detect significant evidence of a genetic bottleneck, but we cannot conclusively suggest that harvest of lake whitefish did not result in a genetic bottleneck. Additionally, we found only slight evidence of population sub-structure among isolated basins, suggesting that either some gene flow among basins is possible, or that populations are just beginning to diverge and therefore differences in allele frequency were too small to detect. These data provide a perspective on effects of an inland lake commercial fishery that was closed prior to population collapse, and offer a comparison to the Laurentian Great Lakes where lake whitefish are still being harvested.     

Controlled Lagrangians and the stabilization of mechanical systems.I. The first matching theorem

We develop a method for the stabilization of mechanical systems with symmetry based on the technique of controlled Lagrangians. The procedure involves making structured modifications to the Lagrangian for the uncontrolled system, thereby constructing the controlled Lagrangian. The Euler-Lagrange equations derived from the controlled Lagrangian describe the closed-loop system, where new terms in these equations are identified with control forces. Since the controlled system is Lagrangian by construction, energy methods can be used to find control gains that yield closed-loop stability. We use kinetic shaping to preserve symmetry and only stabilize systems module the symmetry group. The procedure is demonstrated for several underactuated balance problems, including the stabilization of an inverted planar pendulum on a cart moving on a line and an inverted spherical pendulum on a cart moving in the plane     

Some magnetic and mechanical properties of fibre-reinforced nickel and nickel-iron alloys

Composites containing tungsten wires reinforcing nickel and nickel-iron alloy matrices have been fabricated by a filament winding-electroplating technique and a considerable improvement in the tensile strength was achieved relative to the unreinforced matrix. The presence of the fibres was found to have a significant influence on the magnetic properties of the composites measured in the direction of the fibre axes. In composites having a matrix with a negative magnetostriction, the maximum permeability decreased with increasing volume fraction, V _f, and was also dependent on the fibre diameter and the magnitude of the magnetostriction. In cases where the matrix had a positive magnetostriction the maximum permeability was observed to increase with increasing V _f, reaching a peak value at V _f0.1. It was suggested that the presence of stresses induced in the matrix during cooling from the heat-treatment temperature, due to the difference in the thermal expansion between the fibre and matrix, could explain this magnetic behaviour. By theoretical considerations, the peak was shown to coincide approximately with the volume fraction at which the maximum, uniaxial elastic stress was expected to form in the matrix. Above this volume fraction the uniaxial and transverse stresses became sufficiently high to cause plastic deformation in the entire matrix leading to the observed fall in the maximum permeability, although in all cases the value remained above that shown by the unreinforced matrix.     

An energy-stable mixed formulation for isogeometric analysis of incompressible hyperelastodynamics

We develop a mixed formulation for incompressible hyperelastodynamics based on a continuum modeling framework recently developed in the work of Liu and Marsden and smooth generalizations of the Taylor-Hood element based on nonuniform rational B-splines (NURBSs). This continuum formulation draws a link between computational fluid dynamics and computational solid dynamics. This link inspires an energy stability estimate for the spatial discretization, which favorably distinguishes the formulation from the conventional mixed formulations for finite elasticity. The inf-sup condition is utilized to provide a bound for the pressure field. The generalized-α method is applied for temporal discretization, and a nested block preconditioner is invoked for the solution procedure. The inf-sup stability for different pairs of NURBS elements is elucidated through numerical assessment. The convergence rate of the proposed formulation with various combinations of mixed elements is examined by the manufactured solution method. The numerical scheme is also examined under compressive and tensile loads for isotropic and anisotropic hyperelastic materials. Finally, a suite of dynamic problems is numerically studied to corroborate the stability and conservation properties.     

Optimal pollution mitigation in Monterey Bay based on coastal radar data and nonlinear dynamics

High-frequency (HF) radar technology produces detailed velocity maps near the surface of estuaries and bays. The use of velocity data in environmental prediction, nonetheless, remains unexplored. In this paper, we uncover a striking flow structure in coastal radar observations of Monterey Bay, along the California coastline. This complex structure governs the spread of organic contaminants, such as agricultural runoff which is a typical source of pollution in the bay. We show that a HF radar-based pollution release scheme using this flow structure reduces the impact of pollution on the coastal environment in the bay. We predict the motion of the Lagrangian flow structures from finite-time Lyapunov exponents of the coastal HF velocity data. From this prediction, we obtain optimal release times, at which pollution leaves the bay most efficiently.     

Water quality in Scotland: the view of the regulator

Water quality in Scotland has progressively improved over the past 50 years as the environmental damage, which resulted from the industrial revolution, has been addressed. This paper provides an overview of current water quality in rivers, lochs, estuaries and coastal waters and describes the limited information available on groundwater. The main factors affecting water quality are reviewed, with sewage, diffuse agricultural pollution, acidification and urban drainage identified as the most important. Trends in pollution pressure and levels of investment in pollution control have been used to predict the condition of Scotland's surface water over the next 10 years. Major improvements are expected. However, progress will be slowed by the increased relative importance of diffuse sources of pollution, which are less amenable to legislative controls. Future changes in environmental monitoring are also expected to move the emphasis away from point source pollution. The current freshwater classification schemes are based upon a relatively narrow measure of water quality and are expected to expand to include a wider range of ecological parameters. This will result in an increase in the waters defined as impacted as the effects of other environmental pressures are taken into account. Finally the implications of these changes for the future management of the aquatic environment are assessed.     

Digital free-space optical interconnections: a comparison of transmitter technologies

We investigate the performance of free-space optical interconnection systems at the technology level. Specifically, three optical transmitter technologies, lead-lanthanum-zirconate-titanate and multiple-quantum-well modulators and vertical-cavity surface-emitting lasers, are evaluated. System performance is measured in terms of the achievable areal data throughput and the energy required per transmitted bit. It is shown that lead-lanthanum-zirconate-titanate modulator and vertical-cavity surface-emitting laser technologies are well suited for applications in which a large fan-out per transmitter is required but the total number of transmitters is relatively small. Multiple-quantum-well modulators, however, are good candidates for applications in which many transmitters with a limited fan-out are needed.     

HypEs: an architecture for hypermedia-enabled expert systems

Expert systems and hypermedia constitute two important technologies for organizations to create, store, and manage information products. The purpose of our research is to develop an architectural blueprint for the construction of hypermedia-enabled expert systems. We propose an architecture termed HypEs (Hypermedia-enabled Expert System) for the development of media-rich expert systems. The integration of hypermedia technologies and expert systems can provide significant potential benefits by enabling the storage and manipulation of non-textual knowledge, enhancing the effectiveness of both knowledge acquisition from the sources of expertise and knowledge transfer to non-expert users. An experimental analysis that contrasts the hypermedia-enabled and text-restricted expert systems provides results that underscore the usefulness of hypermedia techniques in enhancing the effectiveness of expert systems in practical applications.     

Spatial and seasonal comparisons of growth of wild and stocked juvenile lake trout in Lake Champlain

After 42 years of stocking in Lake Champlain, recruitment of wild juvenile lake trout (Salvelinus namaycush) was first observed in 2015. Abundance of wild lake trout juveniles was spatially heterogeneous. Recruitment of wild fish to age-1 and subsequent survival are likely related to growth including overwinter growth. We hypothesized that growth potential or growth-related mortality of wild and stocked fish may explain spatial differences in abundance. We collected juvenile (age-0 to 3) lake trout by bottom trawling in the central, north, and south Main Lake every 2–4 weeks during the ice-free season, 2015–2018. The percentage of wild juveniles increased from 27.8% of the total catch in 2015 to 65.7% in 2018. Rates of growth in length and change in condition were compared in wild versus stocked lake trout, among sampling areas, and between seasons (sampling season relative to winter). Wild juveniles grew equally or faster in length than stocked juveniles at the same age, but changed more slowly in condition. There was a higher percentage of wild juveniles in the central sampling area than the north and south, but no differences in growth among sampling areas. Wild and stocked fish grew in length over winter, but most cohorts (6 of 7) maintained or increased condition. Results indicate high growth potential of wild juvenile lake trout and progress toward population restoration.