70 research outputs found
Movement and Activity Patterns of Non-Native Wels Catfish (Silurus glanis Linnaeus, 1758) at the Confluence of a Large River and Its Colder Tributary
The establishment and proliferation of non-native fish species can have a range of effects
within the local ecosystem, including alteration of food webs, nutrient cycling, pathogen dynamics
and predation, sometimes also resulting in changed behavior and distribution of native fish species.
Knowledge about movements and activity patterns is important to understand the dynamics of
non-native animals in their new environment. The Wels catfish (Silurus glanis Linnaeus, 1758) is
considered an invasive species in many places in Western Europe, and regional control programs
are in place. Here, using radiotelemetry, we study the movements and activity patterns of invasive
Wels catfish at an invasion front within the Po River (Italy); namely, at the confluence between the
main river, where the species is abundant, and a colder tributary, the Dora Baltea River, where it is
absent. In addition, we also investigate potential spatiotemporal overlap betweenWels catfish and
native and endangered marble trout (Salmo marmoratus Cuvier, 1829) in the area. A total of nine Wels
catfish and eight marble trout were tagged. The Wels catfish showed a very high degree of residency
within the study area in the Po River, close to the mouth the colder tributary. Despite this, only one
catfish entered the lower reaches of the tributary and did so only occasionally during August. No
catfish moved further upstream in the tributary. It is likely that lower temperatures in combination
with more challenging hydrodynamic conditions made the tributary unattractive to the catfish. The
catfish were active during all times of the day but substantially more so during evenings and at
nights. Some, but not all, tagged catfish moved to areas in the main stem upstream of the confluence
with the tributary. A large proportion of the tagged marble trout made occasional or longer visits
to the Po River, with several individuals becoming resident, but without apparent mortality, in the
tagged catfish home range. The high residency of theWels catfish suggests that removal efforts may
do well to initially focus on areas close to the habitats of species under conservation concern
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Evaluation of Intake Rack Solutions for Downstream Fish Passage Using a Large Scale Fish Flume
Survival and swimming performance of a small-sized Cypriniformes (Telestes muticellus) tagged with passive integrated transponders
Italian riffle dace (Telestes muticellus, Bonaparte 1837) is a small-bodied Leuciscidae native to the Italian Peninsula, of which little is known about the ecology and individual movements in nature. Passive Integrated Transponder (PIT) telemetry is used to track fish movements and behaviour. The basic assumption is that the PIT-tagged organism's performances do not differ considerably from their natural behaviour. Here we present the first evaluation of potential tagging effects in the genus Telestes. The survival rate and tag retention were compared between two different tag implantation methods â injector gun and scalpel incision - and pit-tagging effects on swimming performance were evaluated. Five weeks after tagging, Italian riffle dace demonstrated high survival rates in all treatments: 94.8% for fish tagged with injector gun (n=58), 100% for scalpel incision method (n=58), and 98.3% for controls (n=58). The tag retention was 96.6% for gun treatment and 100% for scalpel treatment. Prolonged swimming performance, tested 22-23 days after tagging, showed a reduction in endurance (time-to-fatigue) for scalpel treatment (n=22) compared to the control group (n=21), while no difference in maximum swimming velocity was observed. We conclude that PIT tagging is a suitable technique for Italian riffle dace, showing high survival and PIT retention and no effect on maximum swimming speed. Significantly lower prolonged swimming performance, although likely less ecologically important, shows that tagging is not without costs. Potential biases need to be evaluated on a study-by-study basis, and future studies should explore behavioural tagging effects in nature
Survival and swimming performance of a small-sized Cypriniformes (Telestes muticellus) tagged with passive integrated transponders
Italian riffle dace (Telestes muticellus, Bonaparte 1837) is a small-bodied Leuciscidae native to the Italian Peninsula, of which little is known about the ecology and individual movements in nature. Passive Integrated Transponder (PIT) telemetry is used to track fish movements and behaviour. The basic assumption is that the PIT-tagged organismâs performances do not differ considerably from their natural behaviour. Here we present the first evaluation of potential tagging effects in the genus Telestes. The survival rate and tag retention were compared between two different tag implantation methods â injector gun and scalpel incision - and pit-tagging effects on swimming performance were evaluated. Five weeks after tagging, Italian riffle dace demonstrated high survival rates in all treatments: 94.8% for fish tagged with injector gun (n=58), 100% for scalpel incision method (n=58), and 98.3% for controls (n=58). The tag re-tention was 96.6% for gun treatment and 100% for scalpel treatment. Prolonged swimming performance, tested 22-23 days after tagging, showed a reduction in endurance (time-to-fatigue) for scalpel treatment (n=22) compared to the control group (n=21), while no difference in maximum swimming velocity was observed. We conclude that PIT tagging is a suitable technique for Italian riffle dace, showing high survival and PIT retention and no effect on maximum swimming speed. Significantly lower prolonged swimming performance, although likely less ecologically important, shows that tagging is not without costs. Potential biases need to be evaluated on a study-by-study basis, and future studies should explore behavioural tagging effects in natur
A unifying hypothesis for the spawning migrations of temperate anguillid eels
Anguillid eels grow in freshwater but spawn in the open ocean. The cues that guide eels over long distances to the spawning area are unknown. The Earth's magnetic field can provide directional and positional information and is likely used by catadromous eels during their spawning migration; as magnetosensitivity and compass orientation have been reported in eels. To test whether this is theoretically possible, we compared the migratory routes of five species of temperate eels that undertake long migrations with the geomagnetic field of their distribution/spawning areas. We found that, regardless of the species and although routes are different between life stages, larvae of those species always drift along paths of increasing magnetic inclination and intensity, while adults follow reverse gradients. This is consistent with an imprinting/retracing hypothesis. We propose a general navigation mechanism based on larvae imprinting on a target magnetic intensity (or inclination) at the hatching area and on the intensity (or inclination) gradient during larval drift. Years later, adults retrace the magnetic route by following the gradient of decreasing total intensity (or inclination) values that occurs towards lower latitudes. As they reach the target value, adults switch to compass orientation to stay on the target isoline and reach the spawning area. The proposed mechanism fits for all temperate eels examined. Knowledge about navigational strategies of eels is important to evaluate the effectiveness of management strategies that involve stocking of juveniles displaced from one area to another to rebuild local populations.publishedVersio
Magnetic fields generated by submarine power cables have a negligible effect on the swimming behavior of Atlantic lumpfish (Cyclopterus lumpus) juveniles
Submarine power cables carry electricity over long distances. Their geographic distribution, number, and areal coverage are increasing rapidly with the development of, for example, offshore wind facilities. The flow of current passing through these cables creates a magnetic field (MF) that can potentially affect marine organisms, particularly those that are magnetosensitive. The lumpfish (Cyclopterus lumpus) is a migratory species that is widely distributed in the North Atlantic Ocean and Barents Sea. It migrates between coastal spawning grounds and pelagic offshore feeding areas. We tested whether lumpfish respond to MFs of the same intensity as those emitted by high voltage direct current (HVDC) submarine power cables. Laboratory experiments were conducted by placing juvenile lumpfish in an artificial MF gradient generated by a Helmholtz coil system. The intensity of the artificial MF used (230 ”T) corresponded to the field at 1 m from a high-power submarine cable. The fish were filmed for 30 min with the coil either on or off. Swimming speeds, and presence in the different parts of a raceway, were extracted from the videos and analyzed. Juvenile lumpfish activity, defined as the time that the fish spent swimming relative to stationary pauses (attached to the substrate), and the distance travelled, were unaffected by exposure to the artificial MF. The swimming speed of juvenile lumpfish was reduced (by 16%) when the coil was on indicating that the fish could either sense the MF or the induced electric field created by the movement of the fish through the magnetic field. However, it seems unlikely that a 16% decrease in swimming speed occurring within 1 m of HVDC cables would significantly affect Atlantic lumpfish migration or homing.publishedVersio
Havforskningsinstituttets rÄdgivning for menneskeskapt stÞy i havet: seismikk, elektromagnetiske undersÞkelser og undersjÞiske sprengninger
publishedVersio
Spawning Atlantic cod (Gadus morhua L.) exposed to noise from seismic airguns do not abandon their spawning site
Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustic telemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test site and 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during the spawning periods of 2020â2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey 5â>40 km away. Residency and survival of tagged cod were analysed with captureâmarkârecapture models fitted to the detection and recapture data. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survival nor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at received SEL of up to âŒ145 dB re 1 ÎŒPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawning grounds.publishedVersio
Visioner om de svenska vattenfallen : Ett statligt vattenkraftsprojekt i Ălvkarleby under 1900-talet
De svenska statliga vattenkraftsprojekten i början av 1900-talet speglar en förhoppning om ett starkt industriellt Sverige nĂ„got som tidigare forskning har pĂ„pekat. Syftet med den hĂ€r uppsatsen Ă€r att undersöka relationen mellan statliga tekniksatsningar och förestĂ€llningar om nationen. Jag vill belysa att det Ă€r viktigt att sĂ€tta sĂ„dana projekt i relation till förestĂ€llningar om vad som Ă€r bra och efterstrĂ€vansvĂ€rt, riskfyllt och hotfullt för nationen. Begreppet sociotechnical imaginaries (sociotekniska förestĂ€llningar) relaterar den âkollektivt förestĂ€llda idĂ©nâ om nationen till teknikutveckling, dĂ€r tekniken ofta representerar verktyg för att nĂ„ den efterstrĂ€vade visionen. Med förestĂ€llningar om vattenkraften i centrum mĂ„las det tredje statliga vattenkraftsprojektet i Ălvkarleby upp med början vid bildandet av en statlig vattenkraftsproducent fram till den första fasen i elnĂ€tets utbredning. Jag visar att sociotekniska förestĂ€llningar underbygger argumenten i det politiska beslutsfattandet och operationaliseras i den ingenjörsmĂ€ssiga praktiken.
Time management challenges of major refurbishment projects : An analysis of 20 hydropower outages at Fortum
While most western hydropower sites are already developed or protected by legislation, the aging hydropower park requires refurbishment actions. Especially to tackle the challenges of an increased fluctuation at the grid coming from the expansion of other renewable energy sources such as wind power. The company Fortum is carrying out a number of major refurbishment projects every year and want to enhance their time performance during the outage. Delayed projects are resulting in unexpected costs and production losses. By investigating 20 historical refurbishment outages from a project manager perspective, the delays are related to different sections of the outage time. These sections are referred to as work packages, meaning a set of activities related to a functional part of the plant. The material is based on interviews and project documentation. The outages are divided into three groups depending on the amount of delay and some additional set of factors are used in a comparison. The results are discussed from a time management and a multi-project perspective. The study can be viewed as an initial study to address time management challenges in a company. The methodology proves to be an efficient way to get time management challenges at a company to the surface. The results displays late manufacturing deliveries and overruns of assembly and erection durations as the most common reasons of delay. A number of potential success/failure factors are suggested. It is also pointed out that small projects are at risk being more delayed compared to larger ones.
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