Migration of eels tagged in the Baltic Sea and Lake Mälaren—in the context of the stocking question

Eels (Anguilla spp.) are in decline worldwide, and the signs of reduced recruitment have been observed in continental Europe since the early 1970s. To aid recovery of the European eel, stocking is used by many European countries as a management option. In this study, tagging experiments were conducted to follow eel migration from Lake Mälaren and four sites along the Swedish east coast in the Baltic Sea. The recaptured tagged eels were retrieved from fishermen, allowing for the opportunity to investigate their origin (brackish water, stocked in freshwater or a mix in between) by otolith microchemistry and to assess for morphological differences after tagging. Several changes took place; for example, eye index increased while weight and condition decreased with migrated distance and time until recapture. In Lake Mälaren, the majority of tagged eels did not migrate out of the outlets, irrespective of their origin. Most of them were caught in the opposite direction and continued to be caught in the lake 1–3 years after tagging, with significant weight losses. Overall, overwintering is suggested to be an inferior option, but it is uncertain whether this is a natural behaviour or a result of translocation and restocking. For coastal eels, origin had no effect on migratory behaviour; a majority of the tagged eels migrated towards the outlet of the Baltic Sea. Interestingly, a minority of the recaptured eels originated from stocked fish. Instead, recaptures were dominated by natural immigrants that had spent most of their lives in brackish waters.     

Biomass conversion factors (density and carbon concentration) by decay classes for dead wood of Pinus sylvestris, Picea abies and Betula spp. in boreal forests of Sweden

For estimating the amount of carbon (C) in dead wood, conversion factors from raw volume per decay class to dry weight were developed using three different classification systems for the species Norway spruce (Picea abies L. Karst), Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth and B. pubescens Ehrh) in Sweden. Also the C concentration in dead wood (dry weight) was studied. About 2500 discs were collected from logs in managed forests located on 289 temporary National Forest Inventory (NFI) sample plots and in 11 strips located in preserved forests. The conversion factors were based on an extensive data compilation with a wide representation of different site-, stand-, species- and dead wood properties and were assumed to represent the population of fallen dead wood in Sweden. The density decreased significantly by decay class and the range in density for decay classes was widest for the NFI decay classification system, suggesting this to be the most suitable. The C concentration in dead wood biomass increased with increasing decay class and in average Norway spruce (P. abies) showed a lower C concentration than Scots pine (P. sylvestris). The average dead wood C store of Swedish forests was estimated to 0.85 Mg C/ha.     

Integration of word meaning and world knowledge in language comprehension

Although the sentences that we hear or read have meaning, this does not necessarily mean that they are also true. Relatively little is known about the critical brain structures for, and the relative time course of, establishing the meaning and truth of linguistic expressions. We present electroencephalogram data that show the rapid parallel integration of both semantic and world knowledge during the interpretation of a sentence. Data from functional magnetic resonance imaging revealed that the left inferior prefrontal cortex is involved in the integration of both meaning and world knowledge. Finally, oscillatory brain responses indicate that the brain keeps a record of what makes a sentence hard to interpret.     

A numerical study of the shape stability of sawn timber subjected to moisture variation Part 1: Theory

A three-dimensional theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed, assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate and the mechano-sorption strain rate. Wood is assumed to be an orthotropic material with large differences between the longitudinal, radial and tangential directions in the properties found. The influence of the growth rings, the spiral grain and the conical shape of the log on the orthotropic directions in the wood is taken account of in the model. A finite element formulation is used to describe the deformation process and the stress development during drying.The research presented in this paper is a part of the national research programme in Sweden concerning wood physics and drying. It was financially supported by the Research Foundation of Swedish Sawmills and the Swedish Council for Forestry and Agricultural Research.     

A numerical study of the shape stability of sawn timber subjected to moisture variation

Summary Numerical simulations were performed to investigate how the annual ring orientation affects the shape stability of sawn timber. The influence of radial variations in the basic properties and the spiral grain is also studied. The knowledge obtained can contribute to more effective use of the raw material through allowing boards having properties that would yield bad shape stability to be sorted out. Possibilities for improving shape stability through gluing pieces of wood together are examined as well. Received 24 April 1997     

Functions for estimating aboveground biomass of birch in Norway

A suite of regional allometric aboveground biomass functions were derived for Betula pubescens and Betula pendula for Norwegian conditions. The data consisted of 67 trees sampled throughout Norway. A total of 14 component functions were developed for total aboveground, total stem, stemwood, stem bark, live crown, live branch, leaf, and dead branch biomass using combinations of diameter at breast height and height as predictor variables. Application of the derived functions to existing local southern Norwegian mountain birch and regional Swedish biomass datasets indicated an overall good predictive ability of the developed functions. However, the functions produced slight underestimates, suggesting that the respective birch populations had differing biomass allocation patterns. When the developed functions were applied to Norwegian National Forest Inventory data, they produced slightly higher biomass stock and stock change estimates than what is obtained using existing Swedish functions. The higher estimates were evident in the north, central, and western part of Norway, while estimates were similar in southeastern Norway where growing conditions are most similar to Swedish conditions. The analysis indicates that the derived functions are the best available for regional birch biomass stock and stock change estimation in Norway.     

Genotype by environment interaction for length of productive life in Swedish Red and White dairy cattle

In this study the amount of genotype by environment interaction (G×E) for length of productive life of Swedish Red and White dairy cattle was studied. The environmental variables used were the herd-year averages of number of first parity cows, peak yield, protein yield, and productive life. Data were analysed using multi-trait models (using low and high quartile herds) and reaction norm models (using the whole continuous scale). Considerable G×E was found for the trait productive life between environments (herds) with short or long average productive life, and a genetic correlation of 0.74 was found. For productive life in relation to herd size, G×E was negligible, and the genetic correlation was 0.95. For productive life in relation to herd-year average of peak yield or protein yield some G×E was indicated by the reaction norm model, especially between extreme environments. The G×E between herds with short or long average productive life should be studied further and might need to be considered in breeding programmes for dairy cattle.     

Clostridium difficile in faeces from healthy dogs and dogs with diarrhea

Background

This study was conducted to evaluate the faecal occurrence and characterization of Clostridium difficile in clinically healthy dogs (N = 50) and in dogs with diarrhea (N = 20) in the Stockholm-Uppsala region of Sweden.

Findings

Clostridium difficile was isolated from 2/50 healthy dogs and from 2/20 diarrheic dogs. Isolates from healthy dogs were negative for toxin A and B and for the tcdA and tcdB genes. Both isolates from diarrheic dogs were positive for toxin B and for the tcdA and tcdB genes. The C. difficile isolates from healthy dogs had PCR ribotype 009 (SE-type 6) and 010 (SE-type 3) whereas both isolates from dogs with diarrhoea had the toxigenic ribotype 014 (SE-type 21). One of the isolates from healthy dogs was initially resistant to metronidazole.

Conclusions

This study revealed presence of toxigenic C. difficile in faecal samples of diarrheic dogs and low number of non- toxigenic isolates in healthy dogs from Uppsala-Stockholm region in Sweden. However, more comprehensive studies are warranted to investigate the role of C. difficile in gastrointestinal disease in dogs.     

Heavy loads of parasitic freshwater pearl mussel (Margaritifera margaritifera L.) larvae impair foraging,activity and dominance performance in juvenile brown trout (Salmo trutta L.)

The life cycle of the endangered freshwater pearl mussel (Margaritifera margaritifera) includes a parasitic larval phase (glochidia) on the gills of a salmonid host. Glochidia encystment has been shown to affect both swimming ability and prey capture success of brown trout (Salmo trutta), which suggests possible fitness consequences for host fish. To further investigate the relationship between glochidia encystment and behavioural parameters in brown trout, pairs (n = 14) of wild‐caught trout (infested vs. uninfested) were allowed to drift feed in large stream aquaria and foraging success, activity, agonistic behaviour and fish coloration were observed. No differences were found between infested and uninfested fish except for in coloration, where infested fish were significantly darker than uninfested fish. Glochidia load per fish varied from one to several hundred glochidia, however, and high loads had significant effects on foraging, activity and behaviour. Trout with high glochidia loads captured less prey, were less active and showed more subordinate behaviour than did fish with lower loads. Heavy glochidia loads therefore may negatively influence host fitness due to reduced competitive ability. These findings have implications not only for management of mussel populations in the streams, but also for captive breeding programmes which perhaps should avoid high infestation rates. Thus, low levels of infestation on host fish which do not affect trout behaviour but maintains mussel populations may be optimal in these cases.     

Comparison of different site preparation techniques: quality of planting spots,seedling growth and pine weevil damage

In northern Europe, there are high risks of severe pine weevil (Hylobius abietis) damage to newly planted conifer seedlings. Site preparation is one of the most important measures for reducing these risks and as several studies have shown the damage is highly dependent on the amount of pure mineral soil around the seedlings. We investigated effects of three site preparation techniques: (1) disc trenching with a conventional Bracke T26, (2) MidiFlex unit and (3) soil inversion with a Karl Oskar unit on characteristics of the planting spots, growth and pine weevil damage and survival rates of untreated and insecticide treated planted Norway spruce (Picea abies) seedlings. All three site preparation techniques reduced pine weevil damage in comparison with no site preparation, and the proportion of spots with pure mineral soil they created was inversely related to the rate of mortality caused by pine weevil. The results indicate that the quality of the planting spots depends on the technique used. In areas where pine weevil is the major threat to seedling survival, the amount of mineral soil in the planting spots is the most important factor in order to protect the seedling from damage. Without site preparation most planting spots consisted of undisturbed humus. Generally, the Karl-Oskar created the most spots with pure mineral soil, but on very stony soils the Bracke T26 created more mineral soil spots than other methods. Site preparation is a valuable tool in order to improve survival in regeneration areas and it is of great importance to make the right choice of technique depending on the particular circumstances on the actual site.