Past and present state of the ichthyofauna of Lake Lugano

The evolution of the ichthyofauna of Lake Lugano (Lago di Lugano) during the past 120 years is characterized by the introduction of eight new fish species and by the possibly natural addition of the blenny (Blennius fluviatilis) in recent years. Introduced Salmonids such as charr (Salvelinus alpinus) and whitefish (Coregonus sp.) have established strong populations during the first half of this century, but have declined drastically thereafter. Likewise, the population of the native shad (Alosa fallax lacustris) has diminished significantly. A hydroacoustic survey of the pelagic fish stock of Lake Lugano in 1989 revealed the presence of a dense bleak (Alburnus albidus) population at 0 to 14 m depth. No other fish were found to be present in the pelagic zone. Oxygen and temperature distributions seem to confine the bleak to the uppermost layer in summer. In winter, very few fish were located by echosounding. Growth of bleak and roach (Rutilus rubilio) was difficult to interpret since data for comparison are lacking. Growth of perch (Perca fluviatilis) in the littoral zone was found to be slower than in other eutrophic lakes, for no obvious reason. Possible ways of restructuring the pelagic fish community are discussed.     

Failure of swim bladder inflation of perch,Perca fluviatilis L. found in natural populations

Perch suffering from swim bladder inflation failure (sinkers) are reported from wild populations of Lakes Constance, Geneva, Lucerne, Sempach, and Zurich in central Europe. Sinkers were found at all 7 locations considered in a survey. Relative abundance of sinkers varied from 0.1% to 7.9% of local perch populations. Sinkers from wild populations and sinkers reared in the laboratory showed similar behaviour and malformations. Information on sinker syndrome in 26 physoclistous species is compiled. It is found to be a widespread problem in aquaculture, but is reported here for the first time from natural populations.     

Effects of larval density and salinity on the development of perch larvae (Perca fluviatilis L.)

We performed two experiments, one to test whether survival and initial swim bladder inflation of perchPerca fluviatilis are affected by population density (4 or 16 larvae 1^–1) or salinity (0, 0.6 and 1.2), and the second to test the salinity tolerance of larvae. In experiment 1, survival was higher at low larval densities and at salinities of 0.6 and 1.2 rather than in fresh water. Initial swim bladder inflation was not affected by salinity or density. Average survival of fry 24 days after hatching varied from 29.6% to 86.3%, but only an average of 19.2% of the hatched larvae had grown into viable fish with an inflated swim bladder. In experiment 2, survival varied from 19% to 49%, but was not significantly affected by salinities of up to 4.8. At a salinity of 9.6, only 2 out of 344 larvae survived.     

Influence of submerged aquatic vegetation on size class distribution of perch (Perca fluviatilis) and roach (Rutilus rutilus) in the littoral zone of Lake Geneva (Switzerland)

The abundance of different size classes of perch and roach in the littoral zone of Lake Geneva was compared between submerged aquatic vegetation and unvegetated zones. Samples were taken with gillnets during four periods between June and October 1993. During the vegetation period (June to September), perch 9 cm and roach 10 cm were more abundant in vegetation whereas roach > 20 cm were more abundant in open water. Perch larger than 18 cm and medium roach were equally distributed in both habitats whatever the period, whereas medium perch distribution fluctuated according to the period. In October, after the decline of the vegetation, no more differences in fish distribution were observed except for small roach, which were always more abundant in the vegetated sites.     

Zur Ökologie des Brachsen (Abramis brama (L.)) im Bodensee

The reactions of the bream,Abramis brama, to the ecological changes due to man-made eutrophication of Lake Constance were investigated. It could be demonstrated that the bream adapted only to a negligible amount. Likely due to its largeness, structure of the body and population composition the bream is more conservative than perch, roach and whitefish. The only reactions to the changed environment are modificated vertical and horizontal distribution and partly plancton feeding in summer.      

A fish-based typology of small temperate rivers in the northeastern lowlands of Germany

Fish assemblage data from 69 brooks and small streams were analysed to derive a fish-based typology of small lowland streams in the “Central Plains” ecoregion of northeastern Germany. Altogether 32 native, 1 non-native fish species and 2 lamprey species were detected in the lowland rivers studied. Species number and diversity varied significantly according to mean summer water temperatures and size of the watercourses. Summer-cold brooks contained on average 3-5 species, brooks with higher summer temperatures 5-8 species and small lowland rivers around 10-14 species. Small lowland brooks contained a significantly higher number of fish species when they flowed into or out of lakes: typically around 8-12.In the northeastern German lowlands the following three different river types were distinguished according to their fish assemblages: (1) The “lowland trout brook”, where brown trout (Salmo trutta L.) are reference species and accompanied by stone loach (Barbatula barbatula (L.)), brook lamprey (Lampetra planeri (Bloch)), three-spined stickleback (Gasterosteus aculeatus L.), ten-spined stickleback (Pungitius pungitius (L.)) and gudgeon (Gobio gobio (L.)); (2) The “perch- and roach-dominated lowland brook”, where perch (Perca fluviatilis L.) and roach (Rutilus rutilus (L.)) are reference species, accompanied by pike (Esox lucius L.), three-spined stickleback and gudgeon; and (3) The “lowland lake connected brook” inhabited by higher numbers of fish species, with higher proportions of cyprinid fishes, and higher proportions of limnophilic fish. Apart from perch and roach, bleak (Alburnus alburnus (L.)), common bream (Abramis brama (L.)), silver bream (Blicca bjoerkna (L.)) and rudd (Scardinius erythrophthalmus (L.)) also occurred frequently.Further two observed fish-based types were not considered: The potential stone loach-dominated brook was not sufficiently represented in this study to be verified, and the stickleback brook was considered to represent degradation of lowland trout brooks.The correspondence between the fish-based typology and the morphology-based German stream typology was rather weak and requires further investigation.     

The influence of egg size and thermal conditions of incubation on the body length and the yolk sac volume of vendace (Coregonus albula L.) eleutheroembryos

Eggs of C. albula were incubated at 1.5 ° and acclimated for different times to 10 °. This procedure caused a varying delay in their hatching. The percentage of normal hatch and the eleutheroembryos' body length and yolk sac dimensions (height and length) were measured, and the yolk sac volume was calculated. The number of days of hatching delay was positively correlated with the total length of embryos and inversely correlated with their yolk sac volume. Dimensions of vendace embryos emerging from eggs of different size were compared. Larger eggs produced longer embryos equipped with larger yolk sacs, and differences in the yolk sac volume were far more pronounced than differences in the body length.     

Predicting Diel,Diurnal and Nocturnal Dynamics of Dissolved Oxygen and Chlorophyll‐a Using Regression Models and Neural Networks

Human‐induced and natural interruptions with continuous streams of observational data necessitate the development of gap‐filling and prediction strategies towards better understanding, monitoring and management of aquatic systems. This study quantified the efficacy of multiple non‐linear regression (MNLR) versus artificial neural network (ANN) models as well as the temporal partitioning of diurnal versus nocturnal data for the predictions of chlorophyll‐a (chl‐a) and dissolved oxygen (DO) dynamics. The temporal partitioning increased the predictive performances of the best MNLR models of diurnal DO by 45% and nocturnal DO by 4%, relative to the best diel MNLR model of diel DO ($r_{{\rm adj}}^{2} = 68.8\%$ ). The ANN‐based predictions had a higher predictive power than the MNLR‐based predictions for both chl‐a and DO except for diurnal DO dynamics. The best ANNs based on independent validations were multilayer perceptron (MLP) for diel chl‐a, generalized feedforward (GFF) for diurnal and nocturnal chl‐a, MLP for diel DO, GFF for diurnal DO, and MLP for nocturnal DO.     

Perch larvae (Perca fluviatilis L.) survive better in dilute sea water

Larvae of perch (Perca fluviatilis L.) reared in tanks for 27 days survived better in lake water to which 2% of artificial sea water had been added (46.6% average survival rate) than in lake water only (13.5% survival). One week after hatching, over 90% of the larvae had their guts filled in all tanks. During the following week the populations divided into floaters (fish with an inflated swimbladder) and sinkers (fish apparently lacking a functional swim-bladder). Although they continued feeding, sinkers remained smaller than floaters and most of them died.     

Variability of a cyprinid lake ecosystem with special emphasis on the native fish fauna under intensive fisheries management including common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix)

The lake investigated (Lake Heiliger See near the town of Angermünde, North-East Germany) is small (10.2 ha) but deep (z_max = 12 m, ? = 6.5 m). During summer the thermocline is at a depth of 4-5 m, and the hypolimnion is filled with H₂S already by mid-June, making 60-75% of the bottom area inaccessible to fish. The native fish fauna is dominated by planktivorous roach (Rutilus rutilus). A test stocking of silver carp (Hypophthalmichthys molitrix) together with an unplanned and erroneous stocking of common carp (Cyprinus carpio), coupled with an incorrectly calculated strong stocking of eel (Anguilla anguilla), which assumed that the total lake area yielded fish food organisms, brought about a strong depression of the food biomass available to native fish. Both silver carp and common carp showed a pattern of behaviour which only partly agreed with results obtained in experimental ponds prior to lake stocking. At least for 10 years there was a very low zooplankton biomass (mostly below 1 mg/l fresh weight) caused by silver carp and a strongly reduced benthos biomass (frequently below 1 g/m² fresh weight) caused by common carp and eel on H₂S-free bottom areas. Despite this extreme situation, which lasted for 20 years and is rarely found in lakes elsewhere, it was not possible to demonstrate negative effects on the native fish fauna comprising 16 species. Also the dominance pattern seems uninfluenced in the long run. A strong decline of the catchable roach stock was observed for some years, but the stock reappeared soon in comparable quantity. During the time of roach stock depression the individual growth of roach (and common carp) was particularly low. Nevertheless, roach succeeded in reproduction during this time in spite of the reduced zooplankton and detritus concentrations. Fry numbers per year ranged from 500-15 000 individuals/ha. The pike perch (Stizostedion lucioperca) was perhaps the most endangered species of all those living at small population numbers in the lake, since its fry is confined to the limnion where competition from silver carp and adult roach and perhaps predation by roach is highest. However the pike perch stock remained unchanged at the low level of 1950, the time prior of carp and eel stocking. All other rare species of Lake Heiliger See spawn in the littoral zone where fry survival conditions were less impacted. In summary, we present more evidence that the fish fauna of cyprinid lakes is more robust than in salmonid lakes. The regulation capacity of fish communities of eutrophic lakes seems to be able to offset even severe direct and indirect influences of fisheries management.     

Diurnal dynamics of streamflow in an upland forested micro‐watershed during short precipitation‐free periods is altered by tree sap flow

Diurnal variations in streamflow are becoming acknowledged as a way of analysing how changing climatic conditions and land use affects watersheds but also as a way to understand watersheds as a whole. Yet not many studies from uplands below 900 mm mean annual precipitation zone are available from European countries. During the 2012 growing season, a sampling campaign took place in an upland forested micro‐watershed, Czech Republic (65 ha). Tree sap flow, rainfall and temperature were measured continuously, while streamflow at the discharge point and soil moisture were estimated from short‐term measurements. Short precipitation‐free periods lasting several days were identified for evaluation of trends in diurnal dynamics of both sap flow and streamflow. The results demonstrated that during these periods, the main factor altering streamflow was almost exclusively tree sap flow. A decrease in streamflow was observed during the day and an increase at night. The decline in sap flow after sunset was accompanied by a continuous increase in streamflow throughout the night up to its initial maximum in the morning. The amplitude in diurnal variations reached 18%. The observed time lag between the diurnal variations of sap flow and streamflow was approximately 2 h. Relatively low changes in diurnal dynamics of streamflow pointed out a strong regulatory role of the forest in buffering water discharge from the catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of prolonged darkness on the relative pigment content of cultured diatoms and green algae

To determine some of the environmental effects that influence the relative proportions of pigments in algae, high pressure liquid chromatographic (HPLC) analysis was employed to determine the relative amounts of common photosynthetic pigments in batch cultures of the diatoms,Fragilaria crotonensis andThalassiosira pseudonana, and the green algae,Scenedesmus abundans, andHaematococcus pluvialis, illuminated for 12 hours each day. Similar analyses were conducted in five-day experiments during which cultures ofF. crotonensis andS. quadricauda were kept in continuous darkness. Comparing the results to those for controls continuing to receive the daily illumination indicated that the diatoms and green algae react similarly to light deficiency. The relative amounts of the main accessory pigment in the diatoms, fucoxanthin, and that in the green alga, apparently lutein, decreased as a reaction to a lack of illumination, while the total chlorophyll level in algae of both groups remained nearly constant. Quantitative differences induced by the experimental conditions were considerably less that those observed among different species of diatom or among the different green algae, however. Finally, cultures ofS. quadricauda were analyzed and then kept for 43 days without the addition of any nutrients. A proportion of the culture was kept for this period in perpetual darkness while another continued to receive 12 hours of illumination. The results show that considerable changes occur as the cultures age, and that these changes occur more slowly in the darkness. Some consequences of these findings for phytoplankton production studies based on analyses of photosynthetic pigments are discussed.     

The effects of UVR irradiance and spectral composition on yellow perch (<Emphasis Type="Italic">Perca flavescens</Emphasis>) larvae survival

The purpose of this study was to determine experimentally the effects of the quality (UV-A/UV-B ratio) and quantity (irradiance) of natural ultraviolet radiation (UVR) on the survival of yellow perch (Perca flavescens) larvae and on the oxidative stress in their cytoplasm, estimated by the activity of the superoxide dismutase (SOD). We also estimated the potential accumulation of photodamage in DNA by using UV dosimeters. Freshly-hatched yellow perch and UV dosimeters were incubated in controlled conditions under a factorial combination of selective and non-selective filters offering different levels of UVR protection and exposed to natural solar light. Larval survival was inversely related to the UVR intensity gradient, and responded similarly to the presence of both UV-A and UV-B or UV-A only. In contrast, the responses of SOD activity and UV dosimeter were stronger in the presence of both UV-A and UV-B than UV-A only, leading to a partial mismatch with the results on survival. Our results, obtained under natural solar light, suggest that incident UV-A radiation, despite its lower energy per unit photon than UV-B, could be a serious threat for yellow perch larvae. They also show that UV dosimeters and SOD activity predict only some components of UVR risk for yellow perch larvae. The partial mismatch between UV dosimeters results and larval survival cautions against the use of UV dosimeters alone as a proxy for UVR risk in the field.     

基于多源遥感数据的震后恢复评估——以四川长宁MS6.0地震为例

通过植被指数和灯光指数定量评估地震发生后灾区的恢复情况,对灾区经济建设和生态恢复的评估具有重要科学意义。以2019年6月17日四川省宜宾市长宁县M_S6.0地震灾区为研究区,对月度NPP-VIIRS数据、MODIS-EVI数据和统计年鉴数据进行预处理后获得4种灯光指数和增强型植被指数(EVI),分别建立NPP-VIIRS数据和MODIS-EVI数据的非线性回归预测模型,预测地震年份的灯光指数和植被指数;通过预测数据和实际数据的对比分析,评价震后的恢复情况。结果表明：地震发生后灯光总强度(TNL)和EVI均明显下降,与震中距离越近的乡镇下降越明显;EVI数据的下降具有滞后性和持续性,夜间照明恢复优于植被恢复情况;地震对TNL的影响高于EVI,且随着距离的增加地震的影响程度逐渐减小。文章从经济和环境两个方面开展研究,对地震救援和震后恢复评价均有一定的应用价值。     

基于NPP-VIIRS数据的夜间灯光指数变化分析——以夏河MS5.7地震为例

夜间灯光数据具有反映人类活动的特点,其数据变化与电力设施运行情况、建筑物和其他发光物体息息相关,因此近年来被广泛应用于各类科学研究中。本文从夜间灯光数据特点出发,以夏河M_S5.7地震灾区为研究区,利用多时相NPP-VIIRS夜间灯光数据,经过数据预处理后获得三种灯光指数,从而分析灾区的夜间灯光变化,为地震应急救援工作提供一种震后灾情信息获取的途径和方法,为甘肃县级尺度的地震应急工作提供另一种思路。     

Artificial macrophytes as fish habitat in a Mediterranean reservoir subjected to seasonal water level disturbances

Artificial macrophytes were experimentally deployed in Boadella Reservoir (NE Spain) and assessed for fish use throughout the first 3 months of the 2007 summer drawdown. In total, 1,832 individuals of seven fish species were recorded through visual censuses, with introduced perch Perca fluviatilis being the prevalent species. Fish richness and abundance were significantly higher in artificial macrophytes than in rocky shores and sandy beaches, displaying a unimodal variation through time. P. fluviatilis, Rutilus rutilus and Abramis brama were significantly more abundant in artificial macrophytes than in the other two naturally submersed habitats, where no individuals of these species were recorded. The abundances of Squalius laietanus, Lepomis gibbosus, Micropterus salmoides and Cyprinus carpio were overall greater in artificial macrophytes than in rocky shores but displayed significant habitat × time interactions. A decrease in predation risk was apparently the key-factor of the intensive use of artificial macrophytes by small fish (≤100 mm TL) in Boadella Reservoir, since most species reduced drastically or completely the use of submerged structures when body size increased. This study demonstrates that adding artificial structures mimicking aquatic macrophytes can be an interesting tool to mitigate the adverse effects of water level fluctuations on fish assemblages in structure-less and homogeneous ecosystems, and to understand the mechanisms affecting habitat use and species replacement.     

Competitive effects of fish in structurally simple habitats: perch,invertebrates, and goldeneye in small boreal lakes

We determined the associations between Eurasian perch Perca fluviatilis, invertebrates, and common goldeneye Bucephala clangula in boreal lakes. Our aim was to test the hypothesis that perch play a controlling role in small, oligotrophic, acidic, and poorly vegetated boreal lakes, affecting both invertebrate numbers and community structure. In addition, we predicted that perch impact lake usage by goldeneye. In the observational part of our study, we first explored the association between perch, invertebrates and goldeneye (pairs and broods per shore km) in 18 boreal, poorly vegetated lakes. Perch densities were associated negatively with invertebrate abundance and lake usage by goldeneye broods. In the experimental part in three fish-free lakes, we found that upon successful perch introductions, the number and biomass of invertebrates, the proportion of large dytiscids, and lake usage by goldeneye broods significantly decreased. We conclude that perch apparently plays a key role as a predator of invertebrates in boreal lakes with few aquatic macrophytes. It is evident that perch can strongly affect their prey populations and communities, and this predation may have an indirect effect on species, e.g. goldeneye, that consume the same prey.     

Daily availability of nutrients and metals in a eutrophic meso-tidal coastal lagoon (Óbidos lagoon, Portugal)

This baseline reports daily variations of physico-chemical parameters, nutrients and metals in water of two sites [eutrophic conditions (BB) versus reference (LL)] in Óbidos coastal lagoon (Portugal). Dissolved oxygen in BB varied between 40% saturation levels (night) and 190% (daylight). , and ratios to Al of Mn, Fe and Pb in suspended particulate matter increased during the period of lower oxygenation, indicating exportation of nutrients and metals from the sediment to water at night. At LL, O₂ values oscillated always around 100%. and Mn/Al ratio at LL were always lower than at BB and no increases were found during the night. The input of and Mn provided from the sediment at BB during the night could surpass the contribution of freshwater discharges. PCA confirmed the separation of most samples from BB and LL. These results pointed to the importance of assessing chemical conditions over day-night cycles.     

Diurnal Variations in the Rate of Gas Exchange between Lake Baikal and the Atmosphere

The diurnal course of gas exchange between Lake Baikal and the atmosphere during the summer warming up is calculated using the data of continuous 102-hour observations in August 2000 and the published materials of individual diurnal measurements of the dissolved gases concentrations made in different years. The diurnal course of the rate of gas exchange in both the coastal and open parts of the lake is found to be due to the fact that slow gas-exchange processes fail to compensate fast changes in the partial pressures of gases dissolved in the upper water layer. The changes are associated with the diurnal dynamics of the hydrometeorological conditions and the intensity of the production–destruction processes. It is found that under light winds, the contribution of biological factors to the formation of short-period variations in the CO₂ and O₂ fluxes through the lake water surface makes about 80% and that of abiotic factors, 20%. Considerable aperiodic changes in the diurnal course of hydrometeorological conditions are found to essentially distort the normal diurnal course of the gas-exchange processes.