Atypical size selection of captive school prawns,Metapenaeus macleayi,by three recreational fishing gears in south‐eastern Australia

Three manipulative experiments were done to estimate the selectivity of conventional and new sizes and configurations of mesh for school prawns, Metapenaeus macleayi, in three south‐eastern Australian recreational fishing gears (haul, push, and scoop nets). The treatment meshes examined were: (1) conventional‐sized, diamond‐shaped mesh used in all gears (20 mm in scoop nets and 30 mm in push and haul nets); (2) 30 mm in scoop nets; and (3) 40‐mm diamond‐ and (4) 23‐mm square‐shaped mesh in all gears. In all experiments, known quantities of school prawns (6–24 mm carapace length (CL)) were placed in purpose‐built enclosures, monitored to ensure no experimental‐induced stress (as measured by changes in L‐lactate in their haemolymph) and the replicate treatments of the various gear configurations deployed. Escapees from the various treatment nets were collected from the enclosures using fine‐meshed nets. Logistic selection curves were derived for all treatment nets and specific comparisons made within and among gears. All nets had 50% retention lengths (L₅₀) comparable to other penaeid‐catching gears with similar mesh sizes, but most had selection ranges (SRs) that were atypically inflated. The large SRs were attributed to a combination of factors that included the mesh geometry and towing speed of the gears and the behaviour of school prawns. The 20‐mm scoop net had the smallest selection parameters, retaining >99% of individuals larger than 13 mm CL. Mesh size in this gear would need to be increased to at least 30 mm to allow some maturing prawns (>18 mm CL) to escape.     

Large-scale traveling atmospheric disturbances (LSTADs) in the thermosphere inferred from CHAMP,GRACE, and SETA accelerometer data

Densities derived from accelerometer measurements on the GRACE, CHAMP, and Air Force/SETA satellites near 490, 390, and 220 km, respectively, are used to elucidate global-scale characteristics of traveling atmospheric disturbances (TADs). Several characteristics elucidated in numerical simulations are confirmed in this study, namely: (1) propagation speeds increase from the lower thermosphere to the upper thermosphere; (2) propagation to the equator and even into the opposite hemisphere can occur; (3) greater attenuation of TADs occurs during daytime and at higher levels of solar activity (i.e., more wave activity during nighttime and solar minimum), presumably due to the greater influence of ion drag. In addition, we find that the occurrence of significant TAD activity emanating from the auroral regions does not reflect a clear relation with the level of planetary magnetic activity as measured by Kp. There is also evidence of waves originating in the tropics, presumably due to convective sources; to some extent this may contribute to the Kp and solar flux relationships noted above. Further elucidation of local time, season, and altitude dependences of TAD propagation characteristics may be forthcoming from density measurements from the GOCE and Swarm missions.     

Shaking‐table tests of flat‐bottom circular silos containing grain‐like material

According to Eurocode 8, the seismic design of flat‐bottom circular silos containing grain‐like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents. Copyright © 2015 John Wiley & Sons, Ltd.     

Graphical methods of river profile analysis to unravel drainage area change,uplift and erodibility contrasts in the Central Range of Taiwan

To reveal river channel steepness patterns and variance in settings with significant variation in rock uplift rate, rock erodibility and moving water divides, we present a series of graphical methods to interpret channel profiles. To complement Cartesian χ plots, longitudinal profiles and mapping methods, we introduce a new method based on a radial coordinate system. We map each basin onto polar coordinates in which the radial dimension is χ and the azimuthal coordinate, ?, is calculated with an increment (Δ?) scaled to the distance to neighboring channel heads. The elevation is contoured on this mapping. Average channel steepness is estimated by fitting a conical surface to the elevation. The graph simplifies the comparison of χ and elevation between channels that share a divide, and helps identify spatial changes in drainage area and patterns of erodibility. We apply this approach to derive the uplift pattern in the eastern and southern Central Range of Taiwan, where the high tectonic convergence and uplift rates combined with sub‐tropical climate and frequent typhoons results in high exhumation rate, and well‐developed, detachment‐limited river networks. Additionally, the tectonic activity leads to drainage basin reorganization. We identify examples of divide migration, discrete river capture as well as anomalous steepness that we attribute to local variability in rock erodibility. Estimated basin‐average steepness values show the highest and a near constant value from Hsinwulu basin to Liwu basin in the center of the Island. To the north and south of this region, the values gradually decrease. These estimates show good correlation with the topography of the Central Range and erosion rates derived from in situ ¹⁰Be concentrations in river‐borne quartz. We conclude that the basin steepness reflects systematic differences in rock uplift rate and erosion rate. Copyright © 2016 John Wiley & Sons, Ltd.     

Green Crab Larval Retention in Willapa Bay,Washington: An Intensive Lagrangian Modeling Approach

The European green crab (Carcinus maenas) is invasive on the U.S. West Coast. This study uses a high-resolution circulation model to determine the likelihood that green crab larvae spawned in Willapa Bay, Washington could be retained by circulation and behavior long enough to reach maturity and resettle within the bay. A particle-tracking method (the “diffusive Lagrangian return map”) is presented that makes it possible to track the dispersion of hundreds of thousands of model larvae—each subject to three-dimensional advection, vertical turbulent diffusion, and imposed vertical migration behavior—over their full 30–50 days development time with modest computational resources. Larvae spawned in summer show significant retention (5–40%) in the southern and western portions of the bay, including the Stackpole shoals near the mouth, the area most likely to be colonized by late-stage megalopae arriving from the coastal ocean. Larvae spawned in spring show much less retention throughout the bay because of (1) increased flushing caused by increased river input relative to summer conditions and (2) longer development times caused by lower water temperatures. The role of larval swimming behavior is secondary to hydrodynamics in setting these spatial and seasonal patterns of retention.     

Strip Transect Sampling to Estimate Object Abundance in Homogeneous and Non-homogeneous Poisson Fields: a Simulation Study of the Effects of Changing Transect Width and Number

This paper investigates the use of strip transect sampling to estimate object abundance when the underlying spatial distribution is assumed to be Poisson. A design-based rather than model-based approach to estimation is investigated through computer simulation, with both homogeneous and non-homogeneous fields representing individual realizations of spatial point processes being considered. Of particular interest are the effects of changing the number of transects and transect width (or alternatively, coverage percent or fraction) on the quality of the estimate. A specific application to the characterization of unexploded ordnance (UXO) in the subsurface at former military firing ranges is discussed. The results may be extended to the investigation of outcrop characteristics as well as subsurface geological features.     

Differences in throughfall drop size distributions in the presence and absence of foliage

ABSTRACT

Throughfall drop size distributions (DSDs) are important for plant–soil interactions. This is the first known study to quantify differences in throughfall DSDs with the presence and absence of foliage. Employing a disdrometer, three parameters solely representing throughfall drip were measured and calculated: maximum drop diameter (D_MAX), median volume diameter of drops (D₅₀D_R) and relative volume percentage of drops (pD_R). Beneath Liriodendron tulipifera L. in Maryland (USA), D_MAX, D₅₀D_R and pD_R were substantially larger when the canopy was unfoliated. In fact, the presence or absence of foliage was one of the primary factors affecting all three throughfall DSDs along with air temperature, according to the boosted regression tree analysis. Experimental results were attributed to differing physical properties of intercepted water between foliated and unfoliated periods and differential water behavior on leaves and bark. Future work should examine the effects of concentrated drip points on the development of throughfall-induced hot spots.

Editor M.C. Acreman; Associate editor F. Hattermann     

Locating day-labor employment: toward a geographic understanding of day-labor hiring site locations in the San Diego metropolitan area

Day-labor hiring sites are common features of the contemporary North American landscape. These are public and semi-public spaces where mostly male residents congregate daily in hopes of being hired for short-term work. Research on contemporary day-labor markets in the United States to date tends to be policy-oriented, intended to reduce the injustices that are a common part of life as a day laborer. Unfortunately, very little is understood about the spatial organization of day-labor markets. Drawing on more than five years of mixed-methods research in the San Diego Metropolitan Area (SDMA), this paper takes two important steps toward a spatial understanding of day-labor hiring sites. First, it demonstrates that informal hiring sites are established in locations that maximize laborers’ chances of finding employment. Second, it establishes a geo-spatial typology of hiring sites for the SDMA that can be used to better tailor day-labor support efforts and policy to site-level context.     

An experimental study of a minette from the Milk River area, southern Alberta, Canada

Buhlmann et al. (Can J Earth Sci 37: 1629–1650, 2000) studied the minettes and xenoliths from the Milk River area of southern Alberta, Canada. Based on previous work, they hypothesized that the minettes were derived from a source containing phlogopite?+?clinopyroxene?±?olivine, at pressures ≥1.7?GPa. To test this hypothesis, liquidus experiments were performed on a primitive minette between 1.33 and 2.21?GPa and between 1,300 and 1,400?°C to constrain the mineralogy of its source region. We found a multiple saturation point along the liquidus at 1.77 GPa and 1,350?°C, where the liquid coexists with orthopyroxene and olivine. Neither phlogopite nor clinopyroxene were found to be liquidus phases, which is inconsistent with Buhlmann et al.’s hypothesis. We suggest that our minette is not primary, but had re-equilibrated with harzburgitic mantle subsequent to formation. In such a scenario, partial melting of a veined source containing mica and clinopyroxene occurred at or near the base of the Wyoming craton (~200?km). Minimal heating or the introduction of hydrous fluids into the source would be required to induce partial melting. Rapid ascent rates, coupled with slow cooling rates, of the “primary minette magma” would preserve the high temperature observed in our experiments. At ~58?km, our “primary minette magma” likely stalled and re-equilibrated with the harzburgite surroundings.