Forhold for overlevelse av Gyrodactylus salaris i Oslofjorden

Prosjektleder: André StaalstrømI denne rapporten har modellkjøringer med FjordOs-modellen blitt kalibrert mot målinger av saltholdighet i overflatelaget i Oslofjorden. Disse modellresultatene er brukt for å vurdere muligheten for at vandrende laks kan overføre parasitten Gyrodactylus salaris fra elv til elv via sjøen. Det er en mulighet for G.salaris kan overføres fra Drammenselva til Aulivassdraget, selv om sannsynligheten for at dette skjer er liten. I en ekstrem flomsituasjon i fjordsystemet slik som den i juni 1995, vil det være stor sannsynlighet for at parasitter ville overleve på fisk hvis de hadde vandret mellom Glomma og Aulivassdraget, eller motsatt.Vestfold og Telemark fylkeskommunepublishedVersio

Vertebrates...and the conflicts in public image

The author explores human perceptions, as influenced by words and the images they conjure in the human brain. People worldwide have formed strong images relating to our environment, both positive and negative: beauty and splendor vs. struggle, plague, and ills. Such a conflict is just beginning between two opposing philosophies concern vertebrates: one, their management completely for the benefit of man; the other, quoting civilization’s threat to the beauty and even existence of high animals. Both viewpoints are unacceptable. When these two viewpoints meet, pest control will be under the giant floodlights of public opinion

Migratory passage structures at hydropower plants as potential physiological and behavioural selective agents

publishedVersio

Genetic differences between wild and hatchery-bred brown trout (Salmo trutta L.) in single nucleotide polymorphisms linked to selective traits

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2017 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.publishedVersio

Behavioural response of brown trout (Salmo trutta) to total dissolved gas supersaturation in a regulated river

Total dissolved gas supersaturation from dams and power stations is a chronic freshwater pollutant that is toxic to animals with aquatic respiration. Laboratory ecotoxicology experiments have revealed capacity for captive fishes to saturoregulate by moving deeper, but field ecotoxicology research is largely lacking. We instrumented 94 brown trout in the Rysstad basin of the Otra River, Norway, with depth sensor acoustic transmitters and monitored their movements for 10 months. We found that the depths used by the trout largely protected them from the effects of total dissolved gas supersaturation, which ranged from 96% to 133% total gas pressure during the study. The depth use of fish was affected by sun position, lunar phase and spatial position in the river (i.e., available depth), and there was an extremely weak effect of total dissolved gas supersaturation that was counterintuitive (i.e., positive slope, movement toward surface). Depth traces of the fish revealed that nine fish died during the study, mostly coinciding with the first wave of supersaturation, consistent with observations of untagged dead fish with signs of gas bubble trauma found on the river bottom during this period (May-June). Overall, tagged trout exposure to total dissolved gas supersaturation depended on their use of depth, but responses to waves of extreme supersaturation at supraphysiological levels were weak and biologically insignificant, with individual variation and spatial position in the river most important in the model. Exposure to total dissolved gas supersaturation was mediated by individual differences in habitat use, which may be linked to activity and other traits that determine overall vulnerability to exposure to total dissolved gas supersaturation.publishedVersio

Influence of dense macrophyte vegetation and total gas saturation on the performance of acoustic telemetry

Acoustic telemetry is widely used as a method for high resolution monitoring of aquatic animal movement to investigate relationships between individual animals and their environment. In shallow freshwater ecosystem, aquatic macrophytes are common and their presence increases habitat complexity and baffles sound propagation. These properties may be likely to affect the performance of acoustic telemetry, however, to date this issue has received little attention, when studying the ecology of movements of fishes in and around the important macrophyte habitats. Here, we conducted a range-test study in a freshwater riverine ecosystem, with mass development of the aquatic macrophyte Juncus bulbosus (L.), to assess how dense macrophytes impact detection probability, detection range, and performance of a three-dimensional receiver positioning system. Supersaturation of gas frequently occurs at the study site as a by-product of upstream hydroelectric power generation and gave a unique opportunity to investigate how total gas saturation affects the performance of acoustic telemetry. We also investigated the influence of environmental conditions (i.e., day-of-year, time of day, average water level above J. bulbosus) on detection probability together with vertical position of transmitters and location inside or outside macrophytes. The detection probability and range were generally low for transmitters in and outside J. bulbosus stands, with mean hourly detection probabilities ranging from 1.18 to 5% and detection ranges between 17.26 m ± 0.74. The interaction between total macrophyte biomass and distance to receiver reduced the detection probability and detection range substantially. Detection probability further decreased with increasing total gas saturation, and transmitters positioned near the sediment and close to the surface also had lower detection probabilities compared to receivers in the middle of the water column. Finally, the low detection probability affected position estimates, where only 23% of the detections could be positioned using the average positioning estimation method and positional accuracy and precision were low ranging from 1.48 to 164.8 m and 0 to 50.1 m, respectively

Increased precision of growth data gained by reading multiple scales from each individual of Atlantic salmon (Salmo salar)

The precision of growth estimates based on fish scales often remains uncertain because of withinindividual variation in scale size and scale patterns, and also due to measurement errors. Based on scale readings of Atlantic salmon, we show that errors decreased with number of times and number of scales read per fish. The annual number of scale circuli was not constant, but positively correlated with annual specific growth rates. Number of circuli deposited after the last winter correlated positively with sampling date. There was no significant relationship between mean inter-circuli distance and the total circuli number during the first and second year at sea. For growth estimation in scientific studies, we recommend the use of 4-5 scales per fish. Consideration should be given to both circuli number and inter-circuli distances when estimating growth rate instead of relying on inter-circuli distances only

Smoltutvandring i Nidelva 2014-Utprøving av tiltak for nedvandrende smolt ved Rygene kraftverk

Antall pre-smolt oppstrøms Rygene, 3546 (3083-4214), er lavere en hva en kunne forvente utfra antall oppvandrende gytefisk og egnet gyte- og oppvekstareal i elva. I tillegg estimeres et betydelig tap av smolt under nedvandring. Sistnevnte skyldes antagelig to forhold; predasjon fra gjedde og vandring gjennom kraftverksturbinen på Rygene. Det ble i 2014 PIT-merket smolt ved Rygene som ble satt ut oppstrøms. Modellene som er tilpasset merke-gjenfangstdataene tilsier en overlevelse på i størrelsesorden 70 % fra utsetting og ned til Rygene dam. Hypotesen er at oppdemmingen ved Rygene påvirker smolten negativt ved å forsinke den under utvandring og dermed gjøre den tilgjengelig for predasjon over et lengre tidsrom, samtidig som oppdemmingen begunstiger gjedda i dette området. Fra 2013 er det åpnet en fluktrute (isluke) ved inntaket til turbinen ved Rygene. I størrelsesorden 50 % av smolten bruker denne utvandringsveien istedenfor turbinen. Økende smoltlengde og vannføring i fluktruten har en positiv effekt på andelen smolt som benytter tiltaket. Tiltaket kan og bør forbedres. I første omgang ved å øke vannhøyden og/eller vannføringen i isluka. Samtidig er tapet til gjedde stort og bestanden bør kartlegges nærmere med tanke på tiltak. Registrering av tilbakevandrede gytelaks merket som smolt i Storelva indikerer en høy feilvandring til Nidelva. Flere år med data vil kunne si oss mer om dette.Agder Energi Vannkraft A

Influence of dense macrophyte vegetation and total gas saturation on the performance of acoustic telemetry

Acoustic telemetry is widely used as a method for high resolution monitoring of aquatic animal movement to investigate relationships between individual animals and their environment. In shallow freshwater ecosystem, aquatic macrophytes are common and their presence increases habitat complexity and baffles sound propagation. These properties may be likely to affect the performance of acoustic telemetry, however, to date this issue has received little attention, when studying the ecology of movements of fishes in and around the important macrophyte habitats. Here, we conducted a range-test study in a freshwater riverine ecosystem, with mass development of the aquatic macrophyte Juncus bulbosus (L.), to assess how dense macrophytes impact detection probability, detection range, and performance of a three-dimensional receiver positioning system. Supersaturation of gas frequently occurs at the study site as a by-product of upstream hydroelectric power generation and gave a unique opportunity to investigate how total gas saturation affects the performance of acoustic telemetry. We also investigated the influence of environmental conditions (i.e., day-of-year, time of day, average water level above J. bulbosus) on detection probability together with vertical position of transmitters and location inside or outside macrophytes. The detection probability and range were generally low for transmitters in and outside J. bulbosus stands, with mean hourly detection probabilities ranging from 1.18 to 5% and detection ranges between 17.26 m ± 0.74. The interaction between total macrophyte biomass and distance to receiver reduced the detection probability and detection range substantially. Detection probability further decreased with increasing total gas saturation, and transmitters positioned near the sediment and close to the surface also had lower detection probabilities compared to receivers in the middle of the water column. Finally, the low detection probability affected position estimates, where only 23% of the detections could be positioned using the average positioning estimation method and positional accuracy and precision were low ranging from 1.48 to 164.8 m and 0 to 50.1 m, respectively

Smoltutvandring i Nidelva 2014-Utprøving av tiltak for nedvandrende smolt ved Rygene kraftverk

-Antall pre-smolt oppstrøms Rygene, 3546 (3083-4214), er lavere en hva en kunne forvente utfra antall oppvandrende gytefisk og egnet gyte- og oppvekstareal i elva. I tillegg estimeres et betydelig tap av smolt under nedvandring. Sistnevnte skyldes antagelig to forhold; predasjon fra gjedde og vandring gjennom kraftverksturbinen på Rygene. Det ble i 2014 PIT-merket smolt ved Rygene som ble satt ut oppstrøms. Modellene som er tilpasset merke-gjenfangstdataene tilsier en overlevelse på i størrelsesorden 70 % fra utsetting og ned til Rygene dam. Hypotesen er at oppdemmingen ved Rygene påvirker smolten negativt ved å forsinke den under utvandring og dermed gjøre den tilgjengelig for predasjon over et lengre tidsrom, samtidig som oppdemmingen begunstiger gjedda i dette området. Fra 2013 er det åpnet en fluktrute (isluke) ved inntaket til turbinen ved Rygene. I størrelsesorden 50 % av smolten bruker denne utvandringsveien istedenfor turbinen. Økende smoltlengde og vannføring i fluktruten har en positiv effekt på andelen smolt som benytter tiltaket. Tiltaket kan og bør forbedres. I første omgang ved å øke vannhøyden og/eller vannføringen i isluka. Samtidig er tapet til gjedde stort og bestanden bør kartlegges nærmere med tanke på tiltak. Registrering av tilbakevandrede gytelaks merket som smolt i Storelva indikerer en høy feilvandring til Nidelva. Flere år med data vil kunne si oss mer om dette