Seasonal and diurnal patterns of larval and juvenile fish drift were investigated in the Marchfeldkanal, a man-made side branch of the Danube River near Vienna, Austria. A clear seasonal pattern with peak densities in mid-June was found. Species composition varied over time, showed a site specific pattern and was dominated by tubenose goby Proterorhinus marmoratus. Water temperature was the main factor responsible for the increase of drift densities until the median drift date and repeated occurrence of early larval stages in drift indicated repeated spawning for many species. Significant differences in drift densities between different time periods of the day (day, dusk, night and dawn) were found for common bream Abramis brama, barbel Barbus barbus, chub Leuciscus cephalus, tubenose goby and roach Rutilus rutilus. The highest drift rates occurred at night (2200-0400 hours), with 86% of all larvae drifting during the hours of darkness. Fish larvae of different lengths drifting at different phases of the day were found for common bream, bleak Alburnus alburnus and chub, with largest larvae drifting during dusk (chub) and day (bleak and common bream). For bleak, all gudgeon species Gobio spp., tubenose goby, roach and for all cyprinid species combined, one 2 h night sample was found to be sufficient to predict the total 24 h drift. # 2004 The Fisheries Society of the British Isles

A total of 10 649 larval and juvenile fishes of 24 species were caught in the drift at Marchfeldkanal, a man-made side branch of the Danube River near Vienna, Austria, with tubenose goby Proterorhinus marmoratus being the dominant species. Distinct differences in inter-and intraspecific drift patterns among different sampling stations along the course of the channel were found. The percentage of the rheophilic and rheoparous ecological guild was highest at the inlet of the channel, where it is directly fed with water from the Danube. For individual species, significant differences in drift densities among sites were found for tubenose goby, barbel Barbus barbus, ide Leuciscus idus, roach Rutilus rutilus and for the two most abundant percids, the pike-perch Sander lucioperca and zingel Zingel zingel combined. The occurrence of larval and juvenile fishes in the drift was related to certain developmental stages and differed between species and sites. Most species (common bream Abramis brama, bleak Alburnus alburnus, gudgeon species Gobio spp., chub Leuciscus cephalus, ide and roach) occurred with highest densities at the earliest developmental larval stage, but some species (e.g. common bream and roach) were also found abundantly in drift at later developmental stages. Application of Ivlev's index of electivity as a drift index describing the propensity of the different species to drift, yielded the highest indices for the gudgeon species, common bream and bleak and the lowest for perch Perca fluviatilis, Prussian carp Carassius auratus gibelio and rudd Scardinius erythrophthalmus. # 2004 The Fisheries Society of the British Isles

Magnesium is generally considered to be one of the most attractive base materials for biodegradable implants, and many magnesium alloys have been optimized to adjust implant degradation. Delayed degradation, however, generates prolonged presence in the organism with the risk of foreign body reactions. While most studies so far have only ranged from several weeks up to 12months, the present study provides data for complete implant degradation and bone regeneration until 24months, for two magnesium alloys (ZX50, WZ21) with different degradation characteristics. μCT monitoring, histological staining and LA-ICP-MS illustrate the distribution of the elements in the neighboring bony tissues during implant degradation, and reveal in particular high concentrations of the rare-earth element Yttrium.

The potential to discriminate between wild and hatchery trout [Salmo trutta f. fario L. and Oncorhynchus mykiss (Walbaum)] by chronological microchemical patterns of different otolith regions was tested. Central and rim regions of otoliths were analysed for life stage specific elemental patterns of strontium (Sr), sodium (Na) and calcium (Ca) as well as of 87 Sr/ 86 Sr ratios using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Classification to life stage specific habitats was achieved with 100% accuracy by 88 Sr/ 43 Ca, 23 Na/ 43 Ca and 87 Sr/ 86 Sr ratios resulting in a discrimination of hatchery fish from wild fish. 87 Sr/ 86 Sr ratios and Sr concentration in otoliths were positively correlated with the ratio and amount in the water. Na content in otoliths did not directly reflect the concentration in the water, although the 23 Na/ 43 Ca ratio in otoliths contributed to the discrimination. Clear differences in otolith chemistry were found for fish experiencing different geological units or a groundwater-fed environment in a hatchery. Natural chronological microchemical patterns in otoliths proved to be a valuable tool for discriminating wild and hatchery fish without the necessity to use marking methods. LA-ICP-MS is well suited for this application because of its limited need for sample preparation, its potentially high sample throughput and the possibility of simultaneous measurement of multiple elemental and isotopic fingerprints. K E Y W O R D S : hatchery fish, laser ablation, management, natural chemical mark, otolith microchemistry.

Portable spectroscopic instruments are an interesting alternative for in-field and on-line measurements. However, the practical implementation of visible-near infrared (VIS-NIR) portable sensors in the forest sector is challenging due to operation in harsh environmental conditions and natural variability of wood itself. The objective of this work was to use spectroscopic methods as an alternative to visual grading of wood quality. Three portable spectrometers covering visible and near infrared range were used for the detection of selected naturally occurring wood defects, such as knots, decay, resin pockets and reaction wood. Measurements were performed on wooden discs collected during the harvesting process, without any conditioning or sample preparation. Two prototype instruments were developed by integrating commercially available micro-electro-mechanical systems with for-purpose selected lenses and light source. The prototype modules of spectrometers were driven by an Arduino controller. Data were transferred to the PC by USB serial port. Performance of all tested instruments was confronted by two discriminant methods. The best performing was the microNIR instrument, even though the performance of custom prototypes was also satisfactory. This work was an essential part of practical implementation of VIS-NIR spectroscopy for automatic grading of logs directly in the forest. Prototype low-cost spectrometers described here formed the basis for development of a prototype hyperspectral imaging solution tested during harvesting of trees within the frame of a practical demonstration in mountain forests.

The effect of restoring connectivity for fish by the construction of 11 fish ladders in the Pielach and Melk rivers, both tributaries to the Danube in Austria, was monitored using electric fishing and fish traps between 1999 and 2004. In order to assess the efficiency of connectivity rehabilitation measures pre-and post-project data combining electric fishing and trap catch data were analyzed by means of three fish-based assessment methods: a MUlti-Level concept for a Fish-based, river-typespecific Assessment of ecological integrity (MUL-FA), the Fish Index Austria (FIA) and the European Fish Index (EFI). The effect of adding qualitative trap catch data to electric fishing data on metrics and indices was also tested and the magnitude of the effect was related to the distance of the sites from the river mouth. The results clearly demonstrated the significant contribution of connectivity rehabilitation measures to the ecological integrity of rivers like the River Pielach where morphological conditions are good, whereas remaining channelization still limits the success of connectivity measures in the River Melk. Trap catch data were found to represent an essential source of additional information to assess the efficiency of connectivity measures shortly after their implementation. The negative correlations of the magnitude of the effect of different indices and metrics with the distance of assessment sites from river mouths obviously underline the importance of the river Danube as a source for the re-colonization process. While the indices tested were found to have limited ability to reflect short-term response of fish assemblages to continuum rehabilitation, guild metrics were able to detect improvements of the ecological status shortly after the implementation of connectivity measures. Six metrics showed significant differences between pre and post-project data reflecting the expected increase of the ecological integrity: (1) Fish Region Index (FRI; FIA, MULFA), (2) number of subdominant species and (3) number of flow-guilds (FIA), (4) number of type specific species (MULFA), (5) number of benthic species and (6) number of potamodromous species (EFI); the FRI differences were only significant when trap catch data were added. The EFI indicated a decline of ecological integrity through increases in the density of omnivorous species and the relative number of tolerant species as well as a decrease in the relative number of intolerant species. Significantly decreasing responses with the distance from the river mouth were documented by the EFI and MULFA-index, the FRI (FIA,

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Articles AI MAGAZINE Modeling is regarded as fundamental to human cognition and scientific inquiry (Schwarz and White 2005). It helps learners express and externalize their thinking, visualize and test components of their theories, and make materials more interesting. Particularly, the importance of learners constructing conceptual interpretations of system behavior has been pointed out many times (Mettes and Roossink [1981], Elio and Sharf [1990], Ploetzner and Spada [1998], Frederiksen andWhite [2002]). Modeling environments can thus make a significant contribution to the improvement of science education.A new class of knowledge construction tools is emerging that uses logic-based (symbolic, nonnumeric) representations for expressing conceptual systems knowledge (