Forgotten fishes: What is the future for small threatened freshwater fish? Population risk assessment for southern pygmy perch,Nannoperca australis

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Habitat suitability modelling for sardine juveniles (Sardina pilchardus) in the Mediterranean Sea

Identification of potential juvenile grounds of short‐lived species such as European sardine (Sardina pilchardus) in relation to the environment is a crucial issue for effective management. In the current work, habitat suitability modelling was applied to acoustic data derived from both the western and eastern part of the Mediterranean Sea. Early summer acoustic data of sardine juveniles were modelled using generalized additive models along with satellite environmental and bathymetry data. Selected models were used to construct maps that exhibit the probability of presence in the study areas, as well as throughout the entire Mediterranean basin, as a measure of habitat adequacy. Areas with high probability of supporting sardine juvenile presence persistently within the study period were identified throughout the Mediterranean Sea. Furthermore, within the study period, a positive relationship was found between suitable habitat extent and the changes in abundance of sardine juveniles in each study area.     

Modelling sea lice dispersion under varying environmental forcing in a Scottish sea loch

The spread of infectious larval sea lice, Lepeophtheirus salmonis (Krøyer, 1838), between wild salmonids and farmed Atlantic salmon, Salmo salar , remains a contentious area of uncertainty. However, as laboratory and field experiments increase our knowledge of sea lice behaviour under environmental forcing, numerical modelling tools can be used to predict the spread of infectious sea louse larvae from a point source. A three-dimensional numerical model has been developed and recently validated within Loch Torridon, a fjordic sea loch on the west coast of Scotland. Output from the numerical model is used to drive a particle tracking model which follows statistical representations of sea lice through the planktonic stages of a louse life cycle. By including maturation and mortality, the models can be used to predict the dispersion and transport of infectious sea lice from a point source and can be used to produce maps of infectivity under varying environmental conditions. Results highlight the importance of the wind-driven circulation for larval lice transport and suggest that local environmental conditions have considerable impact on the probability of sea lice infection spreading between wild and farmed fish populations.     

Prey abundance, channel structure and the allometry of growth rate potential for juvenile trout

Abstract  The application of a drift-foraging bioenergetic model to evaluate the relative influence of prey abundance (invertebrate drift) and habitat (e.g. pool frequency) on habitat quality for young-of-the-year (YOY) and yearling juvenile cutthroat trout, Oncorhynchus clarki (Richardson) is described. Experiments and modelling indicated simultaneous limitation of fish growth by prey abundance and habitat, where depth and current velocity limit the volume of water and prey flowing through a fish's reactive field as well as swimming costs and prey capture success. Predicted energy intake and growth increase along a depth gradient, with slower deeper pool habitat generating higher predicted growth for both YOY and yearling trout. Bioenergetic modelling indicated that fish are constrained to use progressively deeper habitats to meet increasing energy requirements as they grow. Sensitivity of growth to prey abundance identified the need to better understand how variation in invertebrate drift and terrestrial drop affects habitat quality and capacity for drift-feeding fishes.     

Quantifying allowable harm in species at risk: application to the Laurentian black redhorse (Moxostoma duquesnei)

• 1. When a species is identified for conservation, often the only way to effect recovery is to reduce the harm imposed by stressors threatening the survival of the species. Ideally all threats would be removed; however, this is often not feasible or practical. Within this context, a demographic approach is presented to assess how much human‐induced harm could be allowed without impairing the persistence of the species. Harm is defined as a negative perturbation that can target one or more vital rates and life stages simultaneously.
• 2. Allowable harm, defined as a level of harm that will not jeopardize survival or recovery, will be a function of the vital rates affected by human actions, the sensitivity of population growth to changes in these vital rates (their elasticities), the population growth rate prevailing before harm occurs, and the set of demographic parameters considered safe for long‐term persistence. This life‐history based approach requires minimal data, can link demography with habitat‐explicit information, is flexible enough to encompass complex life histories, and follows a precautionary approach.
• 3. Quantification of allowable harm could be applied to any species at risk. This approach is introduced by applying it to a Canadian population of a freshwater fish, the black redhorse (Moxostoma duquesnei), demonstrating that in the absence of habitat constraints population dynamics of this species are most sensitive to the survival of young adults, but population fitness is particularly sensitive to the loss of habitat used by young‐of‐the‐year fish under current levels of habitat supply.

Copyright © 2009 John Wiley & Sons, Ltd.     

How fast can the European eel (Anguilla anguilla) larvae cross the Atlantic Ocean?

The migration duration of European eel ( Anguilla anguilla ) larvae (leptocephali) from the spawning areas in the Sargasso Sea to the European continental shelf remains highly controversial, with estimates varying from 6 months to more than 2 yr. We estimated the fastest migration period and the shortest distance travelled by eel larvae by simulating Lagrangian particles released in the Sargasso Sea and by simulating a range of larval behaviours (fixed-depth drift, vertical diurnal migration and active-depth selection to maximize current velocity). This enabled us to compute (i) a passive drift speed, and (ii) a hypothetic swimming speed needed for European eel larvae to cross the Atlantic in 6 months (i.e., the migration duration estimated from otolith daily growth increments). Our results show that the minimum travel time for an eel larva that is passively drifting was 10 months and 3 days. Active behaviours (vertical diurnal migration and rheotaxis) paradoxically increased the migration period. We found that for leptocephali to cross the Atlantic Ocean in 6 months, they would need to swim a minimum of 3.4 body lengths per second for 8200 km. No larvae have been observed with such swimming capabilities. These results provide evidence that leptocephali cannot cross the Atlantic in 6 months.     

Integrating biophysical and socio‐economic aspects of soil conservation on the Loess Plateau,China. Part II. Productivity impact and economic costs of erosion

Using the simulation model described in Part I, this paper examines the impact of erosion on soil productivity, how the impact varies according to initial soil conditions and organic matter management and the economic cost of erosion measured as net present value. The reference crop is winter wheat grown in Chunhua in the southern Loess Plateau. Biomass yield is plotted over 100 years for four erosion scenarios represented by 0, 9, 27 and 47 per cent slopes, three initial soil conditions indicated by 0·5, 1 and 2 per cent organic matter, and two management levels determined by high or low levels of reincorporation of organic residues. Calculations of soil productive half‐life (time to half initial yield) and whole‐life (to equilibrial yield) are presented. The principal findings are that decline in soil productivity is caused by both erosion and insufficient return of organic matter. By increasing organic matter input, erosion damage is offset and soil productive life prolonged, but this is a costly strategy. If yield decline caused by erosion is isolated, erosion control is more important on a high organic matter input system. A maximum soil productive half‐life of 600 years is achieved with no erosion, high initial organic matter and return of organic residues; minimum half‐life of 10 years is with high erosion, low initial organic matter and little return of residues. In between, there are complicated interactions that significantly affect the economic cost of erosion and hence the decisions farmers make in investing in conservation practices. Copyright © 2000 John Wiley & Sons, Ltd.     

膨化机三维参数化设计系统的研究

详细介绍了基于机械自动化设计软件Solidworks研制的膨化机三维参数化设计系统的功能结构、人机界面和关键技术的处理方法。该系统完全被封装在Solidworks的一个菜单项下,通过简单的人机交互,输入功率、转速等设计参数后,它就能自动完成整台膨化机的结构设计,包括膨化腔、带轮传动和减速箱传动的全部设计过程,具有一定的智能化,然后根据用户选择输出零件或者装配体的三维实体模型和工程图。零件自动三维造型的实现采用了以尺寸驱动为主,程序驱动为辅的编程思想,并建立相应的膨化机模板零件库。整个系统程序使用VisualC 语言开发,以动态链接库的形式嵌入Solidworks系统,实现了与Solidworks软件的无缝结合。配合Solidworks强大的三维造型、设计和装配功能,极大地提高了膨化机设计的效率、精度和质量。     

A conceptual framework for guiding the participatory development of agricultural decision support systems

Scientists develop decision support systems (DSSs) to make agricultural science more accessible for farmers and extension officers. Despite the growing use of participatory approaches in agricultural DSS development, reflection on this endeavour has largely focused on the ‘doing’ of participation or the ‘problem of implementation’ when DSSs have not been adopted by stakeholders. There has been little reference to relevant theoretical approaches to the social processes involved in ‘participation’ or ‘implementation’. However, if DSS use is to reach its full potential, a more conceptually informed understanding of how stakeholders collaborate in the participatory development of DSSs is required. To contribute to this conceptualisation, we developed a framework based on three concepts drawn from the field of science and technology studies: technological frames, interpretative flexibility and boundary objects. The framework highlights the importance and value of social learning for participatory DSS development, which relies upon exploring the participating parties’ different perspectives on the agricultural system represented in the DSS. Our framework provides a broad definition of success for participatory DSS development, placing greater weight on learning during the participatory process compared with subsequent use of the DSS by farmers and/or advisors. Two case studies of stakeholder collaboration to develop an irrigation scheduling DSS for sugarcane production were used to explore the relevance of the framework. The concepts in the framework were clearly displayed during the case studies. At the conclusion of the studies there were contrasting outcomes for the DSS. One group of farmers was keen to apply it in their ongoing irrigation management, while another saw little relative advantage in use of the DSS. In both instances co-learning occurred amongst case study participants, so the participatory process was clearly a success.     

Salinization,alkalinization and sodification in Punjab (Pakistan): characterization of the geochemical and physical processes of degradation

Evidence of soil degradation impeding soil tillage and irrigation in cultivated soils in Pakistan is identified, described and represented in a general process of degradation. Based on a chemical analysis of soil characteristics, it is shown that a more general geochemical degradation process may occur in these soils. Two paths of salinization, i.e. neutral salinization and alkalinization inducing a process of sodification, are identified. The wide range of chemical properties of soils and corresponding geochemical processes can be explained by the great diversity of quality in irrigation water that is taken either from the canal or from the groundwater. The basic module of a geochemical model AQUA (Vallès and DeCockborne, 1992) is calibrated with the help of a study of the soil geochemical properties (identification of minerals, characterization of exchanges) and then used to assess the effect of four different water qualities on sandy and loamy soils. Based on these scenarios, the salinity, alkalinity and sodicity hazard of irrigation water is assessed by taking into account simultaneously the electrical conductivity and the residual alkalinity (calcite-residual alkalinity, residual sodium carbonates) or irrigation water and the soil cation exchange capacity: these three indicators appear the most relevant in the context of the study. Copyright © 1999 John Wiley & Sons, Ltd.