Effects of Lake Productivity on Density and Size Structure of Pelagic Fish Estimated by Means of Echosounding in 17 Lakes in Southeast Norway

Density estimation of pelagic fish was performed by means of single beam echosounding in 17 lakes within a period of 34 years, from 1985 to 2018. Surveys were performed repeatedly (two to fourteen times) in five lakes. The density estimates ranged from 34 to 4720 fish/ha and were significantly correlated with total phosphorus concentration. The high density in relatively phosphorus rich lakes (TP > 10 µg/L) was comprised of small fish (<20 cm) and was partly due to the higher number of pelagic fish species. The number of pelagic species varied from one, Arctic charr, in the most elevated and oligotrophic lakes, and whitefish dominated in less elevated oligotrophic lakes. In lowland lakes characterized as mesotrophic or tending to mesotrophy, smelt, vendace, and two to three cyprinids comprised the pelagic fish stock. These fish species predate zooplankton effectively, and species composition and body size of planktonic cladocerans was affected by fish density. Large species of Daphnia were lacking in lakes with high fish density, and body size of present species, D. galeata, D. cristata, and Bosmina spp. were negatively correlated with pelagic fish density.publishedVersio

Climate Change and Monitoring of Temperate Lakes

Provided the predicted 2°C temperature increase during this century, lake ecology will go through dramatic changes, and this must be addressed in fish management in purpose of exploitation as well as in species preservation. In temperate lakes with fish communities dominated by cold-water and cool water fish, temperature increase will affect the species dominance. Extended growth season will benefit recruitment of less cool adapted species, total fish density may increase and growth will decrease of some species. Lakes dominated by salmonid fish may become dominated by cyprinids and percids. Primary production will increase due to extended growth season and increased precipitation. This can reduce the oxygen level in the deep layer of lakes when the organic matter decomposes, whereas the upper layer is too warm for cold-water species. In addition, increased density of small plankton feeding fish will reduce the algae feeding zooplankton. Lakes should be monitored by means of modern and sophisticated methods, monitoring lakes from satellites and in situ loggers, and pelagic fish may be counted by echosounding. To counteract increasing density of plankton feeding fish, fish biomass removal is a possible measure, though the effect is limited in time

Genetic Diversity in Small Populations

The chapter focuses on animal populations of low genetic diversity, among which some have low population size and are, or have been, threatened by extinction. Genetic diversity is regarded as a must for a species to be able to adapt to environmental challenges, but despite this, several species, also among advanced animal groups like birds and mammals, seem to thrive well with low genetic diversity. Some species are assumed to have done so for thousands of years. Other species have low genetic diversity resulting from heavy bottleneck events, in some cases very close to extinction, caused by human activities. Although some species live with surprisingly low genetic diversity, being prone to further loss of genetic variation, this may be retarded due to sexual selection and fitness superiority of heterozygotes. Simulations with population size N = 25 showed that a homozygote fitness of 0.75 compared to fitness = 1.0 of the heterozygote resulted in exclusion of a p = 0.10 frequency allele in <10% of 50 simulation over 50 generations, whereas fitness 1.0 of all genotypes resulted in exclusion of the p = 0.10 allele in 78% of 50 simulations

The interactions of abiotic and biotic factors influencing perch Perca fluviatilis and roach Rutilus rutilus populations in small acidified boreal lakes

Four small, acidified boreal lakes, all sustaining populations of perch Perca fluviatilis, roach Rutilus rutilus and pike Esox lucius, were studied in four successive years. Three lakes were moderately acidified (mean pH of 5·61–5·83), while the fourth was more acidic (mean pH of 5·16) and had a sparse population of R. rutilus. Perca fluviatilis density was higher in this lake (1004 ha−1) than in the other three (355–717 ha−1), where R. rutilus dominated in terms of numbers (981–2185 ha−1). Large, potentially predatory, P. fluviatilis were most abundant in the lake with clearest water, and these seemed to have a negative effect on P. fluviatilis density. Perca fluviatilis mean mass was negatively correlated with R. rutilus biomass and was highest in the most acidic lake with the sparse R. rutilus and the highest P. fluviatilis density. Perca fluviatilis mass correlated positively with pH in two lakes (with the highest fish biomass), suggesting that low pH affected P. fluviatilis mass negatively. Perca fluviatilis growth correlated positively with summer (July to August) air temperature in the lake with sparse R. rutilus, thus differing from P. fluviatilis and R. rutilus growth in the other three lakes. The mean age of P. fluviatilis was generally lower than that of R. rutilus and was lowest in the two lakes with the highest fish biomass, indicating that adult mortality was affected by density-induced factors

Satellittovervåking av innsjøer - en metode for framtida?

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Registrering av salamanderforekomster i Hamar og Stange kommuner 2015-2017: Med vekt på forekomster i kunstig gravde dammer

Det ble satt ørekyteruser i 2 dammer i Hamar, i 39 dammer i Stange og i en dam i Løten kommuner i mai-juni i 2015-2017 for å fange salamandere. Det ble registrert småsalamander (Lissotriton vulgaris) i 40 dammer og storsalamander (Triturus cristatus) i 17 av disse dammene. Det ble også registrert storsalamander larver (med håv) i en dam i tillegg til disse. De fleste av de undersøkte dammene er kunstig gravd, og mange av disse ligger vest og sør i Stange kommune, og i de aller fleste (13 av 16) ble det fanga storsalamander. Begge artene synes utbredt i området vest for E 6 og begrenses sannsynligvis av sommervannstanden i dammene. Storsalamander begrenses i større grad enn småsalamander av fisk (dam nr. 26 ved Skava), men den kan leve med karuss (Carassius carassius)(dam nr. 7 ved Rå). Storsalamander ble registrert i dammer med pH ned mot 5,5, som var den laveste pH målt i noen av dammene. pH synes derfor ikke å være begrensende i de undersøkte dammene. I de 13 dammene som ble undersøkt øst for E 6, fra Ådalsbruk til Tangen, ble det bare registrert småsalamander. Dette er i samsvar med tidligere undersøkelser, men det er vanskelig å forklare.English: Minnow traps were set in two ponds in Hamar, in 39 ponds in Stange and in one dam in Løten municipalities in May – June in 2015-2017 to sample newts. The smooth newt (Lissotriton vulgaris) was detected in 40 ponds and crested newt (Triturus cristatus) in 17 of these ponds. There was also registered crested newt larvae (with dip net) in one pond in addition to these. Most of the investigated ponds are artificially excavated, and most of them are in the southwestern part of Stange municipality, and in the vast majority of them (13 out of 16), the crested newt was present. Both species appear widely in the area west of E 6 and are probably limited by water levels in the summer. Crested newt is limited by fish more than smooth newt is (pond 26 at Skava), but can live with crucian carp (Carassius carassius)(pond no 6 at Rå). Crested newt was recorded in ponds with pH down to 5.5, which was the lowest pH measured in any of the ponds. The pH therefore does not appear to be limiting in the examined ponds. In the 13 ponds examined east of E 6, from Ådalsbruk to Tangen, only smooth newt was registered. This is consistent with previous surveys, but it is, nevetheless, difficult to explain.Norsk Ornitologisk Forening, avdeling Hedmark med økonomisk støtte fra Miljødirektorate

Genetic diversity of hatchery-bred brown trout (Salmo trutta) compared with the wild population: Potential effects of stocking on the indigenous gene pool of a Norwegian reservoir

This study was conducted in Lake Savalen in southeastern Norway, focusing on genetic diversity and the structure of hatchery-reared brown trout (Salmo trutta) as compared with wild fish in the lake and in two tributaries. The genetic analysis, based on eight simple sequence repeat (SSR) markers, showed that hatchery bred single cohorts and an age structured sample of stocked and recaptured fish were genetically distinctly different from each other and from the wild fish groups. The sample of recaptured fish showed the lowest estimated effective population size Ne = 8.4, and the highest proportion of siblings, despite its origin from five different cohorts of hatchery fish, counting in total 84 parent fish. Single hatchery cohorts, originating from 13–24 parental fish, showed Ne = 10.5–19.9, suggesting that the recaptured fish descended from a narrow group of parents. BayeScan analysis indicated balancing selection at several loci. Genetic indices of wild brown trout collected in the lake in 1991 and 2010 suggested temporal genetic stability, i.e., the genetic differentiation (FST) was non-significant, although the Ne, the number of alleles per locus and the number of private alleles were lower in the 2010 sample. artificial breeding; effective population size; genetic diversity; siblings; bottleneck events; genetic structurepublishedVersio

Is the breeding success of the White-throated Dipper Cinclus cinclus in Hedmark, Norway influenced by acid rain?

The aim of this study was to investigate if the White-throated Dipper Cinclus cinclus in Hedmark has problems related to acidification of its habitat. Thirty-three breeding attempts were found in the study area in 1998 and water samples were taken at 29 localities and bottom samples at 20. The number of young in the nest at day 8-10 after hatching was used as a proxy of breeding success and 26 breeding attempts were successful. There was found a significant positive correlation between number of young in the nest and the parameters pH, alkalinity and calcium concentration at the locality. At least one unsuccessful breeding was probably related to low calcium

Assessing Evolutionary Significant Units (ESU) of the Endangered Freshwater Pearl Mussel (Margaritifera margaritifera) in Southeast Norway on the Basis of Genetic Analysis

A total of 312 specimens of freshwater pearl mussel (Margaritifera margaritifera) were sampled from 11 populations, located in four different river systems in Southeast Norway, and analyzed for 11 simple sequence repeat (SSR) (microsatellite) markers. All study populations have landlocked brown trout (Salmo trutta) as the only possible host. Several populations had experienced recruitment failure, probably due to low pH (about 6.0) and calcium concentration. STRUCTURE clustering analysis revealed two genetic clusters, of which one cluster occurred mainly in the western river systems, and totally dominated in one population (Fallselva (A-FAL)) that had higher genetic diversity than the others. Cluster 2 completely dominated in the populations of the eastern river systems, and all of them had low genetic diversity. Bottleneck events were indicated in all populations and the inbreeding coefficient FIS was significant in all populations, except for the southernmost population (Sørkedalselva (B-SØR)), which was the only population with genotypes in Hardy–Weinberg equilibrium. FIS were especially high in the populations of the eastern river systems, and maximum shell length was negatively correlated to FIS. If artificially breeding and stocking should become necessary for future preservation, it should be based on single populations; alternatively, the eastern populations should be based on cross-breeding of populations within the cluster to increase their genetic diversity.publishedVersio

Predicting Habitat Properties Using Remote Sensing Data: Soil pH and Moisture, and Ground Vegetation Cover

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Remote sensing data comprise a valuable information source for many ecological landscape studies that may be under-utilized because of an overwhelming amount of processing methods and derived variables. These complexities, combined with a scarcity of quality control studies, make the selection of appropriate remote sensed variables challenging. Quality control studies are necessary to evaluate the predictive power of remote sensing data and to develop parsimonious models underpinned by functional variables, i.e., cause rather than solely correlation. Cause-based models yield superior model transferability across different landscapes and ecological settings. We propose two basic guidelines for conducting such quality control studies that increase transferability and predictive power. The first is to favour predictors that are causally related to the response. The second is to include additional variables controlling variation in the property of interest and testing for optimum processing method and/or scale. Here, we evaluated these principles in predicting ground vegetation cover, soil moisture and pH under challenging conditions with forest canopies hindering direct remote sensing of the ground. Our model using lidar data combined with natural resource maps explained most of the observed variation in soil pH and moisture, and somewhat less variation of ground vegetation cover. Soil pH was best predicted by topographic position, sediment type and site index (R 2 = 0.90). Soil moisture was best predicted by topographic position, radiation load, sediment type and site index (R 2 = 0.83). The best model for predicting ground vegetation cover was a combination of lidar-based estimates for light availability below canopy and forest type, including an interaction between these two variables (R 2 = 0.65).publishedVersio