Analysis of bycatch in the South African midwater trawl fishery for horse mackerel Trachurus capensis based on observer data     

JR Reed  SE Kerwath  CG Attwood 《African Journal of Marine Science》2017,39(3):279-291

The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme.  相似文献   

Mars reconnaissance lander: Vehicle and mission design     

H.R. Williams  J.C. Bridges  R.M. Ambrosi  M.-C. Perkinson  J. Reed  L. Peacocke  N.P. Bannister  S.D. Howe  R.C. O'Brien  A.C. Klein 《Planetary and Space Science》2011,59(13):1621-1631

There is enormous potential for more mobile planetary surface science. This is especially true in the case of Mars because the ability to cross challenge terrain, access areas of higher elevation, visit diverse geological features and perform long traverses of up to 200 km supports the search for past water and life. Vehicles capable of a ballistic ‘hop’ have been proposed on several occasions, but those proposals using in-situ acquired propellants are the most promising for significant planetary exploration. This paper considers a mission concept termed Mars Reconnaissance Lander using such a vehicle. We describe an approach where planetary science requirements that cannot be met by a conventional rover are used to derive vehicle and mission requirements.The performance of the hopper vehicle was assessed by adding estimates of gravity losses and mission mass constraints to recently developed methods. A baseline vehicle with a scientific payload of 16.5 kg and conservatively estimated sub-system masses is predicted to achieve a flight range of 0.97 km. Using a simple consideration of system reliability, the required cumulative range of 200 km could be achieved with a probability of around 80%. Such a range is sufficient to explore geologically diverse terrains. We therefore plot an illustrative traverse in Hypanis Valles/Xanthe Terra, which encounters crater wall sections, periglacial terrain, aqueous sedimentary deposits and a traverse up an ancient fluvial channel. Such a diversity of sites could not be considered with a conventional rover. The Mars Reconnaissance Lander mission and vehicle presents some very significant engineering challenges, but would represent a valuable complement to rovers, static landers and orbital observations.  相似文献   

Encounters with an unearthly mudstone: Understanding the first mudstone found on Mars          下载免费PDF全文

Juergen Schieber  David Bish  Max Coleman  Mark Reed  Elisabeth M. Hausrath  John Cosgrove  Sanjeev Gupta  Michelle E. Minitti  Kenneth S. Edgett  Mike Malin 《Sedimentology》2017,64(2):311-358

The Sheepbed mudstone forms the base of the strata examined by the Curiosity rover in Gale Crater on Mars, and is the first bona fide mudstone known on another planet. From images and associated data, this contribution proposes a holistic interpretation of depositional regime, diagenesis and burial history. A lake basin probably received sediment pulses from alluvial fans. Bed cross‐sections show millimetre to centimetre‐scale layering due to distal pulses of fluvial sediment injections (fine‐grained hyperpycnites), fall‐out from river plumes, and some aeolian supply. Diagenetic features include mineralized synaeresis cracks and millimetre‐scale nodules, as well as stratiform cementation. Clay minerals were initially considered due to in situ alteration, but bulk rock chemistry and mineralogy suggests that sediments were derived from variably weathered source rocks that probably contained pre‐existing clay minerals. X‐ray diffraction analyses show contrasting clay mineralogy in closely spaced samples, consistent with at least partial detrital supply of clay minerals. A significant (ca 30 wt%) amorphous component is consistent with little post‐depositional alteration. Theoretical modelling of diagenetic reactions, as well as kinetic considerations, suggest that the bulk of diagenetic clay mineral formation occurred comparatively late in diagenesis. Diagenetic features (synaeresis cracks and nodules) were previously thought to reflect early diagenetic gas formation, but an alternative scenario of synaeresis crack formation via fabric collapse of flocculated clays appears more likely. The observed diagenetic features, such as solid nodules, hollow nodules, matrix cement and ‘raised ridges’ (synaeresis cracks) can be explained with progressive alteration of olivine/glass in conjunction with centrifugal and counter diffusion of reactive species. Anhydrite‐filled fractures in the Sheepbed mudstone occurred late in diagenesis when fluid pressures built up to exceed lithostatic pressure. Generating fluid overpressure by burial to facilitate hydraulic fracturing suggests a burial depth of at least 1000 m for the underlying strata that supplied these fluids.  相似文献   

Relating groundwater to seasonal wetlands in southeastern Wisconsin, USA     

John D. Skalbeck  Donald M. Reed  Randall J. Hunt  Jamie D. Lambert 《Hydrogeology Journal》2009,17(1):215-228

Historically, drier types of wetlands have been difficult to characterize and are not well researched. Nonetheless, they are considered to reflect the precipitation history with little, if any, regard for possible relation to groundwater. Two seasonal coastal wetland types (wet prairie, sedge meadow) were investigated during three growing seasons at three sites in the Lake Michigan Basin, Wisconsin, USA. The six seasonal wetlands were characterized using standard soil and vegetation techniques and groundwater measurements from the shallow and deep systems. They all met wetland hydrology criteria (e.g., water within 30 cm of land surface for 5% of the growing season) during the early portion of the growing season despite the lack of appreciable regional groundwater discharge into the wetland root zones. Although root-zone duration analyses did not fit a lognormal distribution previously noted in groundwater-dominated wetlands, they were able to discriminate between the plant communities and showed that wet prairie communities had shorter durations of continuous soil saturation than sedge meadow communities. These results demonstrate that the relative rates of groundwater outflows can be important for wetland hydrology and resulting wetland type. Thus, regional stresses to the shallow groundwater system such as pumping or low Great Lake levels can be expected to affect even drier wetland types.  相似文献   

Between the devil and the deep blue sea: Florida��s unenviable position with respect to sea level rise     

Reed F. Noss 《Climatic change》2011,107(1-2):1-16

This paper introduces and summarizes a series of articles on the potential impacts of sea level rise on Florida??s natural and human communities and what might be done to reduce the severity of those impacts. Most of the papers in this special issue of Climatic Change were developed from presentations at a symposium held at Archbold Biological Station in January 2010, sponsored by the Florida Institute for Conservation Science. Symposium participants agreed that adaptation to sea level rise for the benefit of human communities should be planned in concert with adaptation to reduce vulnerability and impacts to natural communities and native species. The papers in this special issue discuss both of these categories of impacts and adaptation options. In this introductory paper, I place the subject in context by noting that that the literature in conservation biology related to climate change has been concerned largely about increasing temperatures and reduced moisture availability, rather than about sea level rise. The latter, however, is the most immediate and among the most severe impacts of global warming in low-lying regions such as Florida. I then review the content of this special issue by summarizing and interpreting the following 10 papers. I conclude with a review of the recommendations for research and policy that were developed from group discussions at the Archbold symposium. The main lesson that emerges from this volume is that sea level rise, combined with human population growth, urban development in coastal areas, and landscape fragmentation, poses an enormous threat to human and natural well-being in Florida. How Floridians respond to sea level rise will offer lessons, for better or worse, for other low-lying regions worldwide.  相似文献   

Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow's goldeneyes to residual Exxon Valdez oil     

Esler D  Ballachey BE  Trust KA  Iverson SA  Reed JA  Miles AK  Henderson JD  Woodin BR  Stegeman JJ  McAdie M  Mulcahy DM  Wilson BW 《Marine pollution bulletin》2011,62(3):609-614

We examined hepatic EROD activity, as an indicator of CYP1A induction, in Barrow’s goldeneyes captured in areas oiled during the 1989 Exxon Valdez spill and those from nearby unoiled areas. We found that average EROD activity differed between areas during 2005, although the magnitude of the difference was reduced relative to a previous study from 1996/1997, and we found that areas did not differ by 2009. Similarly, we found that the proportion of individuals captured from oiled areas with elevated EROD activity (?2 times unoiled average) declined from 41% in winter 1996/1997 to 10% in 2005 and 15% in 2009. This work adds to a body of literature describing the timelines over which vertebrates were exposed to residual Exxon Valdez oil and indicates that, for Barrow’s goldeneyes in Prince William Sound, exposure persisted for many years with evidence of substantially reduced exposure by 2 decades after the spill.  相似文献   

An Equation of State for Hypersaline Water in Great Salt Lake,Utah, USA     

David L. Naftz  Frank J. Millero  Blair F. Jones  W. Reed Green 《Aquatic Geochemistry》2011,17(6):809-820

Great Salt Lake (GSL) is one of the largest and most saline lakes in the world. In order to accurately model limnological processes in GSL, hydrodynamic calculations require the precise estimation of water density (ρ) under a variety of environmental conditions. An equation of state was developed with water samples collected from GSL to estimate density as a function of salinity and water temperature. The ρ of water samples from the south arm of GSL was measured as a function of temperature ranging from 278 to 323 degrees Kelvin (^oK) and conductivity salinities ranging from 23 to 182 g L⁻¹ using an Anton Paar density meter. These results have been used to develop the following equation of state for GSL (σ = ± 0.32 kg m⁻³):

r- r0 = 184.0 10 6 2 + 1.0 4 70 8*\textS - 1. 2 10 6 1*\textT + 3. 1 4 7 2 1 \textE - 4*\textS 2 +  0.00 1 9 9 \textT 2 - 0.00 1 1 2*\textS*\textT, \rho - \rho^{0} = { 184}.0 10 6 2 { } + { 1}.0 4 70 8*{\text{S}} - 1. 2 10 6 1*{\text{T }} + { 3}. 1 4 7 2 1 {\text{E}} - 4*{\text{S}}^{ 2} + \, 0.00 1 9 9 {\text{T}}^{ 2} - 0.00 1 1 2*{\text{S}}*{\text{T}},  相似文献    58. Vulnerability of population and transportation infrastructure at the east bank of Delaware Bay due to coastal flooding in sea-level rise conditions   总被引：1，自引：1，他引：0   Han Song Tang  Steven I-Jy Chien  Marouane Temimi  Cheryl Ann Blain  Qu Ke  Liuhui Zhao  Simon Kraatz 《Natural Hazards》2013,69(1):141-163 Catastrophic flooding associated with sea-level rise and change of hurricane patterns has put the northeastern coastal regions of the United States at a greater risk. In this paper, we predict coastal flooding at the east bank of Delaware Bay and analyze the resulting impact on residents and transportation infrastructure. The three-dimensional coastal ocean model FVCOM coupled with a two-dimensional shallow water model is used to simulate hydrodynamic flooding from coastal ocean water with fine-resolution meshes, and a topography-based hydrologic method is applied to estimate inland flooding due to precipitation. The entire flooded areas with a range of storm intensity (i.e., no storm, 10-, and 50-year storm) and sea-level rise (i.e., current, 10-, and 50-year sea level) are thus determined. The populations in the study region in 10 and 50 years are predicted using an economic-demographic model. With the aid of ArcGIS, detailed analysis of affected population and transportation systems including highway networks, railroads, and bridges is presented for all of the flood scenarios. It is concluded that sea-level rise will lead to a substantial increase in vulnerability of residents and transportation infrastructure to storm floods, and such a flood tends to affect more population in Cape May County but more transportation facilities in Cumberland County, New Jersey.  相似文献    59. Stock Origins of Subadult and Adult Atlantic Sturgeon, Acipenser oxyrinchus, in a Non-natal Estuary, Long Island Sound      John R. Waldman  Tim King  Tom Savoy  Lorraine Maceda  Cheryl Grunwald  Isaac Wirgin 《Estuaries and Coasts》2013,36(2):257-267 The anadromous acipenserid Atlantic sturgeon Acipenser oxyrinchus was listed in 2012 under the U.S. Endangered Species Act as having four endangered and one threatened distinct population segment (DPS) in American waters. Anthropogenic activities outside of natal estuaries, particularly bycatch, may hinder the abilities of some populations to rebuild. Most Atlantic sturgeon are residential for their first 2–6 years within their natal estuaries, whereas older subadults and adults may migrate to non-natal estuaries and coastal locations. Previous studies demonstrated that subadults and adults aggregate during summer at locations in Long Island Sound (LIS) and its tributary, the Connecticut River; however, the population origin of these fish is unknown. Because of its geographic proximity and relatively robust population, we hypothesized that the LIS and Connecticut River aggregations were almost solely derived from the Hudson River. We used microsatellite nuclear DNA analysis at 11 loci and mitochondrial DNA control region sequence analyses to estimate the relative contributions of nine Atlantic sturgeon populations and the five DPS to these aggregations using individual-based assignment tests and mixed-stock analysis. From 64 to 73 % of specimens from LIS were estimated to be of Hudson origin. Similarly, 66–76 % of specimens from the Connecticut River were of Hudson origin. However, moderate numbers of specimens were detected from distant spawning populations in the southeastern DPS and from two populations once thought to be extirpated or nearly so, the James River (6–7.3 %), and the Delaware River (7.6–12 %). Additionally, specimens were detected from all five DPS in both the LIS and Connecticut River collections. These results highlight the difficulty of evaluating the status of individual Atlantic sturgeon populations because of the propensity of subadults and adults to migrate for extended duration to distant sites where they may be vulnerable to anthropogenic disturbances.  相似文献    60. A Recent Full-Depth Survey of the Alaskan Stream      R.K. Reed  P.J. Stabeno 《Journal of Oceanography》1999,55(1):79-85 We examine results from a cruise in May 1997. CTD casts to near the bottom were made south of the Aleutian Islands, across Amchitka Pass, and north of the islands. We computed a westward geostrophic speed of 123 cm s–1 at 173.5°W in the Alaskan Stream. The computed volume transport there, referred to the bottom, was 25×106m3s–1. On other similar sections, transports were 8–15 × 106 m3s–1. Various complex variations in geopotential height along the Stream apparently altered the cross-stream gradients, and hence the transports. Rotational tendencies were also present. Northward inflow through Amchitka Pass was quite strong (6 × 106 m3s–1). Data north of the islands supported the existence of a zero-velocity reference level of variable depth.  相似文献    [首页] « 上一页 [1] [2] [3] [4] [5] 6 [7] [8] [9] [10] [11] 下一页 » 末  页»