Application of the weight-of-evidence approach to assess the decline of brown trout ( Salmotrutta ) in Swiss rivers

Abstract.: To assess potential causes for the decline in catch of brown trout and their impaired health status in Switzerland, a 5-year multidisciplinary research project was conducted. Multiple causal hypotheses were postulated and investigated in a variety of laboratory and field studies. We present here the application of a weight-of-evidence analysis to evaluate the results of these studies and to assess the causes for decline in brown trout abundance. Based on human health epidemiological criteria, the method considers the exposure situation, the correlation between causes and effects, specificity of effects, and amelioration due to removal. For our evaluation, we concentrated on four test rivers and included data on fish health and population density, water quality, and habitat parameters. Our results showed that proliferative kidney disease (PKD) caused by a parasite and clinical outbreak supported by other factors is a very probable single parameter for the decline of brown trout abundance at the sites of the test rivers where it occurs. Elevated levels of nitrogen compounds may also be posing a serious risk at several sites, in particular those downstream of sewage treatment plants. Several habitat parameters, such as large width, low percentage of riffles or elevated winter temperatures, were identified as factors likely contributing to impaired health, recruitment, and abundance at single sites. At most sites, more than one factor must be acting jointly to cause the observed decline in brown trout abundanc

Master's degree in sustainable development in Switzerland, the first master course comprising three faculties

Sustainable development has become a key aspect in society, economics and environment. Therefore, experts dealing with questions relating to people, the environment and its resources are more and more requested. This paper presents the concept and first experiences of a specialised Master's Degree in Sustainable Development (MSD). This is a pioneer course as it is equally anchored in three faculties (Human science, Natural science, Business and Economy) at the University of Basel, Switzerland. It aims to transmit knowledge, teach methodology and enable practical work experience in the field of sustainable development. This interdisciplinary master's degree is composed of several modules. At first, the attendance of modules providing a basic understanding in the disciplines not yet covered by the former Bachelor degree, is mandatory. In optional modules, the acquired knowledge of the compulsory modules is further enhanced, focussing on four different topics and are titled as: Agglomeration and Ecosystems; Conservation and Utilisation of Natural Resources; Environment, Values, Societal Transformation and Health; and Environmental Problems in a Globalised World. In another optional module, students may complete an internship in which they can apply theoretical and thematic knowledge. To work independently on a problem in the context of, interdisciplinary projects are a central request in the MSD. Finally, the master thesis has to be planned and realized by applying the scientific methods and skills acquired in the previous modules. Since the beginning of the programme in the winter of 2005/2006, 45 students have enrolled. They received degrees at 25 different universities, 13 of which are from abroad. Some already have several years of working experience, while others have only just completed their Bachelor's degrees. A analysis has shown that the graduates will have excellent chances in the employment market, since they are well qualified to take over sought-after positions in the business world, in administration, in consultancy, national or international organisations, or to follow academic career

Round gobies in the third dimension - use of vertical walls as habitat enables vector contact in a bottom-dwelling invasive fish

Sessile invasive species often efficiently exploit anthropogenic structures, such as harbour walls and pontoons, which can lead to increased vector contact (i.e. contact with boats), and therefore spread rate. The round goby (Neogobius melanostomus) is a bottom-dwelling invasive fish species which was never documented on boats or habitats near the water surface. In this study, we wanted to find out if this fish makes use boat hulls and other vertical anthropogenic structures, which could act as invasion beachheads. We inspected boats close to harbour walls in the river Rhine in Basel, Switzerland, to search for gobies on them and documented the position of the boat and the ways the gobies could have reached the hull. We observed round goby presence on three different boats, with up to 28 goby sightings on one boat hull in the course of 45 minutes. Additionally, we recorded gobies on walls between one and five meters above the ground. Based on these observations, we investigated the behaviour of round gobies using vertical walls as habitat and compared the observed behaviours to those exhibited by gobies on the bottom. Gobies used the habitat along a wall in a generally similar fashion to the habitat on the bottom. However, they sat still for less time and moved more on walls than on the bottom, while feeding activity was similar in both habitats. The results raise questions about the drivers for using vertical structures as habitat in the usually bottom-dwelling round gobies and the plasticity of this behaviour. Our study documents round gobies in direct contact with boats for the first time. Potentially, gobies could find hiding places or suitable structures to nest on boats. This study therefore provides support for the theory that boat hulls are potential vectors for the translocation of round gobies. Our observations should lead to an increased awareness about fish and their eggs on boat hulls and stimulate efforts to implement measures like the check-clean-dry routine for commercial as well as private boats

An eDNA Assay to Monitor a Globally Invasive Fish Species from Flowing Freshwater

Ponto-Caspian gobies are a flock of five invasive fish species that have colonized freshwaters and brackish waters in Europe and North America. One of them, the round goby Neogobius melanostomus, figures among the 100 worst invaders in Europe. Current methods to detect the presence of Ponto-Caspian gobies involve catching or sighting the fish . These approaches are labor intense and not very sensitive. Consequently, populations are usually detected only when they have reached high densities and when management or containment efforts are futile. To improve monitoring, we developed an assay based on the detection of DNA traces (environmental DNA, or eDNA ) of Ponto-Caspian gobies in river water. The assay specifically detects invasive goby DNA and does not react to any native fish species . We apply the assay to environmental samples and demonstrate that parameters such as sampling depth, sampling location, extraction protocol, PCR protocol and PCR inhibition greatly impact detection. We further successfully outline the invasion front of Ponto-Caspian gobies in a large river, the High Rhine in Switzerland, and thus demonstrate the applicability of the assay to lotic environments. The eDNA assay requires less time, equipment, manpower, skills, and financial resources than the conventional monitoring methods such as electrofishing, angling or diving. Samples can be taken by untrained individuals, and the assay can be performed by any molecular biologist on a conventional PCR machine. Therefore, this assay enables environment managers to map invaded areas independently of fishermen's' reports and fish community monitorings

Reproductive health of brown trout inhabiting Swiss rivers with declining fish catch

Abstract.: In recent years, brown trout catches have been declining in many Swiss rivers. One hypothesis is that this declining catch is linked to environmental estrogens, known to have the potential to adversely affect fish reproduction. In order to assess if the reproductive health of brown trout is impaired, we sampled fish at three sites along four rivers with a well documented catch decline. These rivers are affected by inputs of treated sewage effluent. The sampling was conducted during two years; we measured plasma vitellogenin (Vtg) concentrations and surveyed gonadal histology. Analysis of plasma Vtg revealed elevated concentrations (up to 8 µg/mL) in only 10 out of 197 males. Furthermore, there were no site specific patterns to this induction. These results indicate that the exposure to estrogenic compounds is low. Also the incidence of ovarian atresia was low and we found no male intersex fish. In contrast to males, females caught along two rivers had spermatogenic activity in ovarian tissue. However, this intersex condition does not appear to be connected to exposure to environmental estrogens. At one of 12 sites there was a high incidence of gonadal parasites in ovarian tissue, which may affect reproductive output but was not a general problem across sites. In conclusion, the exposure to estrogenic compounds does not appear to significantly affect the reproductive parameters we investigated in Swiss brown trou

Status of young-of-the-year brown trout ( Salmo trutta fario ) in Swiss streams: factors influencing YOY trout recruitment

Abstract.: As part of the Swiss Fischnetz project (network for declining fish yields in Switzerland) studies were carried out to investigate the decline in catches of brown trout. Insufficient YOY (young-of-the-year) recruitment of brown trout due to different abiotic and/or biotic factors was hypothesized as a potential cause of this decline. Quantitative assessments of fish ecology parameters and habitat measurements were carried out at 97 river sites over a two-year period. The main objectives of this study were to document the occurrence and abundance of naturally reproduced YOY trout and to develop an understanding of environmental factors responsible for the observed YOY density. A general linear model (GLM) was used to analyse the influence of selected environmental abiotic and biotic parameters on YOY density. Successful recruitment of YOY trout was observed in all but three of the sites studied. Abundance was correlated with abiotic and biotic factors, such as river width, slope, altitude, substratum condition, and the occurrence of proliferative kidney disease (PKD). The results highlight the importance of small streams for natural YOY recruitment of brown trout and their function as a source of individuals for downstream river section

Movement patterns and shelter choice of spiny-cheek crayfish (Orconectes limosus) in a large lake’s littoral zone

he study of individual movement patterns and habitat choice is a fundamental step to assess an invasive species’ range extension and to inform possible management options. The spiny-cheek crayfish is an invasive species currently spreading in Europe and also in Lake Constance. This is of concern because the greater Lake Constance area still holds refugial populations of native crayfish that might be endangered by the invader. In invasive crayfish, individual movement patterns and the availability of suitable shelters can predict an invasive population’s spread. In a radio telemetry and mark-recapture study and in semi-natural outdoor experiments, we investigated movement patterns and shelter choice of spiny-cheek crayfish. In the field, radio-tagged and marked crayfish moved distances up to 1200 m within 4 and 13 days, respectively and mostly prevailed within the littoral zone at less than 3 m depth. Tracked crayfish resided close to artificial structures such as boat harbours in the study area. In the outdoor experiments spiny-cheek crayfish used litter as daytime shelter but also chose natural stones and macrophytes. We provide the first large- lake telemetry data on crayfish movement and our results suggest that spiny-cheek crayfish will expand its range within the lake moving along the shoreline. Artificial structures such as boat harbours and litter might facilitate this spread by providing suitable shelters. Our results can help to inform the implementation of countermeasures against the spread of invasive crayfish populations

Microplastics profile along the Rhine River

Microplastics result from fragmentation of plastic debris or are released to the environment as pre-production pellets or components of consumer and industrial products. In the oceans, they contribute to the ‘great garbage patches’. They are ingested by many organisms, from protozoa to baleen whales, and pose a threat to the aquatic fauna. Although as much as 80% of marine debris originates from land, little attention was given to the role of rivers as debris pathways to the sea. Worldwide, not a single great river has yet been studied for the surface microplastics load over its length. We report the abundance and composition of microplastics at the surface of the Rhine, one of the largest European rivers. Measurements were made at 11 locations over a stretch of 820 km. Microplastics were found in all samples, with 892,777 particles km −2 on average. In the Rhine-Ruhr metropolitan area, a peak concentration of 3.9 million particles km −2 was measured. Microplastics concentrations were diverse along and across the river, reflecting various sources and sinks such as waste water treatment plants, tributaries and weirs. Measures should be implemented to avoid and reduce the pollution with anthropogenic litter in aquatic ecosystems

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

Background, aim, and scope: Catch decline of freshwater fish has been recorded in several countries. Among the possible causes, habitat change is discussed. This article focuses on potentially increased levels of fine sediments going to rivers and their effects on gravel-spawning brown trout. Indications of increased erosion rates are evident from land-use change in agriculture, changes in forest management practices, and from climate change. The latter induces an increase in air and river water temperatures, reduction in permafrost, changes in snow dynamics and an increase in heavy rain events. As a result, an increase in river sediment is likely. Suspended sediment may affect fish health and behaviour directly. Furthermore, sediment loads may clog gravel beds impeding fish such as brown trout from spawning and reducing recruitment rates. To assess the potential impact on fine sediments, knowledge of brown trout reproductive needs and the effects of sediment on brown trout health were evaluated. Approach: We critically reviewed the literature and included results from ongoing studies to answer the following questions, focusing on recent decades and rivers in alpine countries. Have climate change and land-use change increased erosion and sediment loads in rivers? Do we have indications of an increase in riverbed clogging? Are there indications of direct or indirect effects on brown trout from increased suspended sediment concentrations in rivers or from an increase in riverbed clogging? Results: Rising air temperatures have led to more intensive precipitation in winter months, earlier snow melt in spring, and rising snow lines and hence to increased erosion. Intensification of land use has supported erosion in lowland and pre-alpine areas in the second half of the twentieth century. In the Alps, however, reforestation of abandoned land at high altitudes might reduce the erosion risk while intensification on the lower, more easily accessible slopes increases erosion risk. Data from laboratory experiments show that suspended sediments affect the health and behaviour of fish when available in high amounts. Point measurements in large rivers indicate no common lethal threat and suspended sediment is rarely measured continuously in small rivers. However, effects on fish can be expected under environmentally relevant conditions. River bed clogging impairs the reproductive performance of gravel-spawning fish. Discussion: Overall, higher erosion and increased levels of fine sediment going into rivers are expected in future. Additionally, sediment loads in rivers are suspected to have considerably impaired gravel bed structure and brown trout spawning is impeded. Timing of discharge is put forward and is now more likely to affect brown trout spawning than in previous decades. Conclusions: Reports on riverbed clogging from changes in erosion and fine sediment deposition patterns, caused by climate change and land-use change are rare. This review identifies both a risk of increases in climate erosive forces and fine sediment loads in rivers of alpine countries. Increased river discharge and sediment loads in winter and early spring could be especially harmful for brown trout reproduction and development of young life stages. Recently published studies indicate a decline in trout reproduction from riverbed clogging in many rivers in lowlands and alpine regions. However, the multitude of factors in natural complex ecosystems makes it difficult to address a single causative factor. Recommendations and perspectives: Further investigations into the consequences of climate change and land-use change on river systems are needed. Small rivers, of high importance for the recruitment of gravel-spawning fish, are often neglected. Studies on river bed clogging are rare and the few existing studies are not comparable. Thus, there is a strong need for the development of methods to assess sediment input and river bed clogging. As well, studies on the effects to fish from suspended sediments and consequences of gravel beds clogging under natural conditions are urgently neede