Behaviour of adult sea trout in a regulated lake

Masteroppgave i biologiBIO399MAMN-BIOMAMN-HAVS

Behaviour of anadromous brown trout (Salmo trutta) in a hydropower regulated freshwater system

Many Norwegian rivers and lakes are regulated for hydropower, which afects freshwater ecosystems and anadromous fish species, such as sea trout (Salmo trutta). Lakes are an important feature of many anadromous river systems. However, there is limited knowledge on the importance of lakes as habitat for sea trout and how hydropower afects the behaviour of sea trout in lakes. To investigate this, we conducted an acoustic telemetry study. A total of 31 adult sea trout (532±93 mm total length) were captured by angling in river Aurlandselva, Norway, and tagged between July 20 and August 12, 2021. The tags were instrumented with accelerometer, temperature, and depth sensors, which provided information on the sea trout’s presence and behaviour in lake Vassbygdevatnet. Our results indicate that there was a large prevalence of sea trout in the lake during the spawning migration, and that the sea trout were less active in the lake compared to the riverine habitats. An increase in activity of sea trout in the lake during autumn might indicate that sea trout spawn in the lake. However, the discharge from the high-head storage plant into the lake did not afect the depth use or activity of sea trout in the lake. Furthermore, the large prevalence of spawners in the lake during autumn will likely cause an underestimation of the size of the sea trout population in rivers with lakes during annual stock assessment. In conclusion, our results could not fnd evidence of a large impact of the discharge on the behaviour of sea trout in the lake. Biologging, Anadromous brown trout, Hydropower, Lake ecology, AccelerationpublishedVersio

Predation research with electronic tagging

Predation is a fundamental aspect of ecology that drives ecosystem structure and function. A better understanding of predation can be facilitated by using electronic tags that log or transmit positions of predator or prey species in natural settings, however, there are special considerations that must be made to avoid biased estimates. We provide an overview of the tools available for studying predation with electronic tags including the tag types and analytical tools that can be used to identify where, when and how prey are killed by predators. We also discuss considerations for experimental design when studying predation using electronic tags, including how to minimize effects of capture and tagging procedures. Ongoing innovation and integration of sensors for tags will provide more detailed data about the performance of tagged predators and the fate of tagged prey. Where analysts can effectively resolve the timing of predation using state-of-the-art tags and analytical tools, we foresee exciting advances in our understanding of animal demographics, evolutionary trajectories and management systems. Prospects to develop new tools and approaches for tracking predation while designing studies to more effectively limit bias are an important frontier for understanding ecosystems and addressing human–wildlife conflicts. Given great uncertainties about environmen-tal change and intensifying conflicts between humans and predators, effective study designs integrating electronic tagging to study predation have a promising future in fundamental and applied ecologypublishedVersio

Effects of tag type and surgery on migration of Atlantic salmon (Salmo salar) smolts

Tagging salmon smolts to provide information about the timing of outmigration has been a common approach to monitor phenology and model the risk of encountering stressors. However, the validity of tagging has come under scrutiny because of the sensitivity of this parameter in various management systems. We studied the probability of migration, timing of migration and growth during migration for Atlantic salmon smolts tagged with three different tags in the River Dale, western Norway. Two groups were tagged with passive integrated transponder (PIT) tags via a small ventral nonsurgical incision, either a 12 mm or a new 16 mm PIT tag. Two groups were subjected to surgical implantation of either a dummy acoustic transmitter or a 12 mm PIT tag (a sham surgery). Overall, 71% of the tagged smolts were recaptured at the downstream Wolf trap. Smolts from the sham tagged group were recaptured most frequently (78%) compared to dummy acoustic transmitters and 16 mm PIT tags (both 68%), but the differences were not significant. Results agree with prior assessments that longer smolts migrated earlier, with about half a day earlier migration for each millimetre total length of the smolt, but did not suggest any difference in time of migration among the tag types. Growth in length was evident from release to recapture, with smaller smolts exhibiting greater growth and no effect of tagging treatment. Our findings suggest that inferences about the timing of outmigration for salmon smolts based on acoustic tagging should be made cautiously because of the relationship among tag size, suitable fish size and the timing of a tagged individual's migration.publishedVersio

Effects of tag type and surgery on migration of Atlantic salmon (Salmo salar) smolts

Tagging salmon smolts to provide information about the timing of outmigration has been a common approach to monitor phenology and model the risk of encountering stressors. However, the validity of tagging has come under scrutiny because of the sensitivity of this parameter in various management systems. We studied the probability of migration, timing of migration and growth during migration for Atlantic salmon smolts tagged with three different tags in the River Dale, western Norway. Two groups were tagged with passive integrated transponder (PIT) tags via a small ventral nonsurgical incision, either a 12 mm or a new 16 mm PIT tag. Two groups were subjected to surgical implantation of either a dummy acoustic transmitter or a 12 mm PIT tag (a sham surgery). Overall, 71% of the tagged smolts were recaptured at the downstream Wolf trap. Smolts from the sham tagged group were recaptured most frequently (78%) compared to dummy acoustic transmitters and 16 mm PIT tags (both 68%), but the differences were not significant. Results agree with prior assessments that longer smolts migrated earlier, with about half a day earlier migration for each millimetre total length of the smolt, but did not suggest any difference in time of migration among the tag types. Growth in length was evident from release to recapture, with smaller smolts exhibiting greater growth and no effect of tagging treatment. Our findings suggest that inferences about the timing of outmigration for salmon smolts based on acoustic tagging should be made cautiously because of the relationship among tag size, suitable fish size and the timing of a tagged individual's migration

Migratory contingents of brown trout reveal variable exposure to anthropogenic threats along a fjord-river continuum

Brown trout is a partially migratory salmonid that makes use of diverse habitats to maximise growth and fitness. One of the most substantial threats to brown trout is infection with pathogens from open net-pen fish farming, which creates hotspots for pathogen reproduction and transmission. Western Norway is a global hotspot for both fish farming and wild salmonids, which generates conflicts due to the impacts of the farms on the behaviour, survival, and fitness of salmonids that overlap with farming activities. In this study, we tagged adult brown trout (>35 cm) at two spatiotemporal intervals that corresponded to two different life history stages: springtime in the river when trout were completing overwintering and summer in the fjord when trout were in their marine feeding phase. The tagging revealed three different behaviours, fish that remained in freshwater, fish that migrated between freshwater and the fjord, and fish that remained in the estuary. Although some trout moved >100 km to the outer fjord areas, most trout remained relatively close to the river. Depth sensor transmitters in a subset of trout also revealed that the trout remained in the upper water column. Most of the horizontal and vertical movements therefore resulted in spatial overlap with fish farming for the migratory trout, but not for resident trout that remained in the estuary or in freshwater. Findings reveal the challenges of managing a fish with such behavioural plasticity but the urgency of recognising how important inner fjord habitats are for migratory brown trout.publishedVersio

Vurdering av overlevelsen til laksesmolt i Modalselva ved bruk av telemetri

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A comparative study of the alternative life history of iteroparous salmonids

The kelt phase of anadromous iteroparous salmonid life history remains mysterious, particularly aspects of their habitat use and factors influencing survival. Atlantic salmon and sea-run brown trout were captured in the estuary during their return migration to the Vosso River, Norway, tagged with acoustic transmitters, and tracked in the watershed and estuary in three different years (2020–2023). We found a relatively narrow window of river exit timing among trout that survived overwinter, whereas salmon tended to leave during a more protracted period. Trout preferred overwintering in lakes within the river system, which provided for lower locomotor activity than fish that overwintered in pools in the river according to data from tri-axial accelerometer transmitters. In contrast, Atlantic salmon tended to spend surprisingly little time in lakes even though the energy expenditure in this habitat is was seemingly lower for salmon that did overwinter in the lake. Our results demonstrate different use of habitat during overwintering and could suggest that measures to protect iteroparous life history strategies of salmonids will differently impact these two iteroparous salmonids.publishedVersio

PigghåFRI – Hvordan unngå problemer med pigghå?

This study has mapped the impact of interaction of spiny dogfish (Squalus acanthias) with aquaculture installations in Norway and studied the behavior of spiny dogfish, in laboratory and field studies, in response to sensory cues for possible development of an anti-shark measure for fish farms. Electromagnetic pulse and smell of dead conspecific (skin extract) induce aversive response without inducing chronic stress in spiny dogfish; orca sound has no effect as repellent against spiny dogfish behaviour. This suggests a promising approach in development of technology based on electromagnetic pulse stimulation and aversive chemical cues to keep spiny dogfish away from fish farms.PigghåFRI – Hvordan unngå problemer med pigghå?publishedVersio

Tracking aquatic animals to understand a world increasingly shaped by a changing climate and extreme weather events

Despite great promise for understanding the impacts and extent of climate change on aquatic animals, their species, and ecological communities, it is surprising that tracking tools, like biotelemetry and biologging devices, have not been extensively used to understand climate change or develop and evaluate potential interventions that may forestall or mitigate its effects. In this review, we provide an overview of methodologies and study designs that leverage available tracking tools to investigate aspects of climate change on aquatic ecosystems. Key interventions to protect aquatic life from the impacts of climate change, including habitat restoration, protected areas, conservation translocations, mitigations against interactive effects of climate change, and simulation of future scenarios can all be greatly facilitated by using electronic tagging and tracking. We anticipate that adapting study designs (e.g. use of replicated ponds, randomized control trials, physiologging) to effectively use tracking will greatly enhance our understanding of climate change and its impacts on aquatic ecosystems, hopefully also facilitating research into effective solutions and interventions against the most extreme and acute impacts