Crack growth and development of fracture zones in plain concrete and similar materials

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Are perch (Perca fluviatilis L.) getting larger or smaller in Swedish lakes?

Space-for-time approaches are often used to indicate current or future changes over time. A European gillnet standard facilitates spatial-scale comparisons of fish communities in European lakes. Fish size was generally lower and densities higher in warmer lakes, but less is known about trends over decadal time scales. We analysed the size of European perch (Perca fluviatilis L.) in 2121 Swedish lakes sampled during 1996–2021. The aim was to test whether size changed over time, and whether trends were similar in southern and northern regions. We analysed mean length and occurrence or relative abundance of size classes from the smallest

Long term trends of fish after liming of Swedish streams and lakes

AbstractThousands of Swedish acidified lakes and streams have been regularly limed for about 30 years. Standard sampling of fish assemblages in lakes and streams was an important part of monitoring the trends after liming, i.e. sampling with multi-mesh gillnets in lakes (EN 14757) and electrofishing in streams (EN 14011). Monitoring data are nationally managed, in the National Register of Survey test-fishing and the Swedish Electrofishing Register. We evaluated long-term data from 1029 electrofishing sites in limed streams and gillnet sampling in 750 limed lakes, along with reference data from 195 stream sites and 101 lakes with no upstream liming in their catchments. The median year of first liming was 1986 for both streams and lakes. The proportion of limed stream sites with no fish clearly decreased with time, mean species richness and proportion of sites with brown trout (Salmo trutta) recruits increased. There were no consistent trends in fish occurrence or species richness at non-limed sites, but occurrence of brown trout recruits also increased in acid as well as neutral reference streams. Abundance of brown trout, perch (Perca fluviatilis) and roach (Rutilus rutilus) increased significantly more at limed sites than at non-limed reference sites sampled before and after 1986. The mean species richness did not change consistently in limed lakes, but decreased in low alkalinity reference lakes, and fish abundance decreased significantly in limed as well as in non-limed lakes

Failed protective effort of ex situ conservation of River Vistula trout (Salmo trutta) in Sweden

Ex situ conservation comprises some of the oldest and best-known conservation methods and it has been applied for different fish stocks. This study describes attempts undertaken to preserve the long-migrating River Vistula (Poland) brown trout by a sea-ranching programme in the River Dalalven (Sweden). This focal strain was threatened in its native river and a major reason for selecting the River Dalalven was that its river mouth faces north as does that of the River Vistula. In the Swedish river, the Vistula trout in the 1970s and early 1980s returned early in the autumn and were generally large-sized (compared to the native strain of the River Dalalven). Over the study period (1978-2012), the size of returning adult fish declined, the return date becoming later in the year, and the number of spawners also declined. The reasons for these changes were probably caused by several interacting factors: (1) the most likely being high mortality of early returning fish which were held for longest in captivity before being used in the artificial spawning process; (2) the fact that the hatchery process was adapted to the Dalalven strain and not the Vistula one; (3) that the Vistula fish were marked by removing both pelvic fins (possible reducing subsequent survival); and (4) low genetic variation (as a result of few returning individuals). Thus, for several reasons, this ex situ conservation attempt for Vistula trout in Sweden is thought to have failed

Assessing Measurements for Feed-Forward Control

A method is presented for assessing disturbances in SISO loops.The method indicates if the SISO loop under consideration will benefit from an addition of feed forward control from a measured disturbance. The method uses minimal process knowledge and is based on measurement from normal operation

Cormorant predation effects on fish populations: A global meta-analysis

This paper provides the results from the first meta-analysis to examine the impact of cormorant (Phalacrocoracidae) predation on fish. It is based on a systematic search of literature, covering studies using significance-based hypotheses tests on the relation between fish parameters and cormorant abundance. The results show that extensive research on cormorant diet exists, but few studies use statistical hypotheses testing to examine the effect on fish populations. In total, 603 publications were identified from titles and abstracts, to include the interaction between cormorants and fish. From these, 27 articles tested fish population parameters against cormorant predation, whereof 22 could be included in analyses. The effect size was defined negative in cases when cormorant numbers or presence reduced fish numbers or biomasses, or when individual fish sizes decreased, and vice versa for a positive effect. In a hierarchical dependence model, the combined effect of cormorant predation on fish was negative, but the overall effect was not significant at the 95% confidence level (-0.169, 95% C.L. -0.505 to 0.167, p = .256, df = 5.26). A covariate analysis revealed a difference in predatory effects between fish prey taxa (p = .006, df = 5.73), but no difference in effect sizes between study type, foraging habitat, or response variable measured. The meta-analysis reveals a complex interaction between cormorants and fish, but adds to the consensus on the importance of considering cormorant predatory effects in research, conservation actions, ecosystem-based management, and environmental monitoring