Phenotypic and social effects on behavioural trade-offs in Eurasian perch

Trading between conflicting demands is a fundamental part in how animals interact with its environment and social surrounding. Knowledge of what factors that are affecting behavioural decisions is central in our understanding of animal adaptation and ecology. This thesis summarizes a series of behavioural experiments investigating how animals compromise behaviours depending on environmental background and context. The focus is on within- and between-population variation in risk-taking and social trade-offs in young of the year and one year old Eurasian perch. Perch behaviour was quantified by observational studies in aquaria, using standardized assays that captured perch boldness and sociability. Perch from different predation backgrounds were compared in common garden experiments, as well as in multi-year inter-population comparisons, to study influence of predation experience on risk-taking phenotype. Results demonstrate predation as an important factor underlying how perch balance risk. Variation in risk-taking phenotype could to a large extent be explained by individual differences in experience of predation, rather than by fixed inherited responses caused by divergent selection. Experience of predation had long lasting effects on perch boldness, but perch were also able to quickly adjust phenotype in response to current conditions, indicating temporal flexibility in how experience shape behaviour. Social context influenced behaviour, with fish being bolder in larger group, and showing higher behavioural conformity. Occurrence of consistent individual variation in risk-taking and social behaviour could be established, confirming the existence of a personality dimension in perch behaviour. The thesis concludes that variation in how perch trade-off conflicting behaviours exists at multiple levels, from population to individual. Behavioural plasticity, even in strongly fitness related traits, is evident, although potential behavioural constraints in the form of consistent individuality is also present

Ponds as experimental arenas for studying animal movement: current research and future prospects

Animal movement is a multifaceted process that occurs for multiple reasons with powerful consequences for food web and ecosystem dynamics. New paradigms and technical innovations have recently pervaded the field, providing increasingly powerful means to deliver fine-scale movement data, attracting renewed interest. Specifically in the aquatic environment, tracking with acoustic telemetry now provides integral spatiotemporal information to follow individual movements in the wild. Yet, this technology also holds great promise for experimental studies, enhancing our ability to truly establish cause-and-effect relationships. Here, we argue that ponds with well-defined borders (i.e. "islands in a sea of land") are particularly well suited for this purpose. To support our argument, we also discuss recent experiences from studies conducted in an innovative experimental infrastructure, composed of replicated ponds equipped with modern aquatic telemetry systems that allow for unparalleled insights into the movement patterns of individual animals

Guiding downstream migrating Atlantic salmon Salmo salar and brown trout Salmo trutta of different life stages in a large river using bubbles

Salmonid repeat spawners are precious individuals for wild populations due to their high fecundity and previous spawning experience, making them important in environmental policy. However, repeat spawners rarely exist above hydropower dams in regulated rivers as the mortality of post-spawners (kelts) when passing through turbines during downstream migration is very high. To mitigate this problem, there are different technical solutions that potentially guide fish toward available fishways. Bubble barriers represent one alternative to costly physical guiding structures, but the efficiency of bubbles for guiding downstream migrating kelts has not been tested. In this study, we evaluate a 100 m long bubble barrier in guiding salmonids-both smolts and kelts-away from the main current and toward an alternative fishway in Ume River, a large regulated river in northern Sweden. We used both acoustic telemetry and sonar to measure the guiding effect of the bubble barrier for downstream migrating fish. We found that more than twice as many salmonids chose the alternative fishway when the bubble barrier was turned on. This was true both for smolts and kelts, suggesting that bubble barriers can be used to guide salmonids of different life stages in rivers with flow rates over 500 m(3) s(-1). Indeed, our study indicates that bubble barriers are low-cost structures that could be rapidly applied in many regulated rivers to support salmonid migration

Dispersal of brown trout (Salmo trutta L.) fry in a low gradient stream - implications for egg stocking practices

Stocking of eggs is a common strategy to support declining or reintroduce extirpated salmonid populations. Data on how juveniles disperse from stocking points is crucial to be able to design efficient stocking programs. Detailed information of dispersal is limited for many salmonids, for example, brown trout. In this study, dispersal distance was measured at the end of the first growing season in a low gradient (0.7%) stream in Sweden where the trout population had been depleted. Eggs from 17 separate sets of parents were stocked as eyed eggs in March. During the following fall fry were sampled throughout the stream. The majority of the fry dispersed downstream and remained within a distance of 200 m from the stocking point with no difference between sizes of fry and the presence of a competing cohort or not. There was no dissimilarity in dispersal distances across offspring originating from different parents indicating absence of genetic influence. Our results suggest that, in streams similar to our study site, stocking points should be separated by approximately 330 m in order to avoid overlap in habitat use of fry from different stocking points and that the presence of competing cohorts, fry size and within population variability in dispersal can be neglected

A Contraction Based Solution for the Improvement of Fish Ladder Attraction Flow

A new, potentially cost efficient, concept for improving the attraction flow to a fish ladder has been investigated in a case study. For the upstream migrating Atlantic salmon to reach the fish ladder and by-pass the case study hydropower plant, it must be able to localize the attraction flow where it enters the main flow from the tailrace of the hydropower plant in the so-called confluence area. Here the comparatively small and limited attraction flow from the old river channel must be improved in order to be able compete with the substantially larger main flow. The objective of the present study is to investigate the feasibility of a new concept for further improvement of the attraction flow using guiding walls forming a contraction channel. Field measurements were performed tracing tagged fish in the confluence area downstream of the case study hydropower plant in order to understand the movement pattern of the fish. Based on the results, and results from bathymetry measurements in the same area, a physical scale model was constructed where it was experimentally demonstrated that it is hydraulically feasible to construct guiding walls, forming a contraction, which accelerate the attraction flow and generate a concentrated turbulent jet with a higher velocity, while keeping the flow rate unchanged. The attraction flow penetrates about half-way (70 m) into the main flow and reaches the position where most fish are positioned according to fish position measurements and therefore potentially has a good ability to attract upstream migrating fish. There is no negative impact on the water level in the confluence area and thereby not on electricity production. It was shown that the results can be scaled up to prototype conditions and the strategy can presumably be generalized to similar flow situations, existing at other hydropower plants, allowing for improved upstream fish migration in coexistence with a sound hydropower production

Validation of Francis–Kaplan Turbine Blade Strike Models for Adult and Juvenile Atlantic Salmon (Salmo Salar, L.) and Anadromous Brown Trout (Salmo Trutta, L.) Passing High Head Turbines

The negative effects of hydroelectric power (HEP) on salmonid populations has long been recognized and studied. Downstream passage through turbines may potentially constitute a significant source of mortality for both juvenile and adult fish in regulated rivers. Numerical models have been developed to calculate turbine passage mortality based on the probability of collision with the turbine blades, but although widely used in management and conservation, their performance is rarely validated in terms of the accuracy and bias of the mortality estimates. In this study, we evaluated commonly used blade strike models for Kaplan and Francis turbines by comparing model predictions with observed passage mortalities for juvenile 13-27 cm and adult 52-94 cm Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) acquired by acoustic telemetry. Predictions made for juveniles aligned closer with observed mortality for both Kaplan and Francis turbines (within 1-3% percentage points). However, the model severely underestimated the mortality of adult fish passing through Francis turbines, with up to 50% percentage points difference between predicted and observed mortalities. Furthermore, the model did not capture a clear negative correlation between mortality and discharge observed for salmon between 50-60 cm (grilse). We concluded that blade strike models are a useful tool for quantifying passage mortality for salmonid smolts passing large, high-head turbines, but that the same models should be used with care when trying to estimate the passage mortality of kelts in iteroparous populations. We also concluded that the major cause of passage mortality for juveniles is injury by collision with the turbine blade, but that other factors seem to contribute substantially to the passage mortality of kelts. Our study reports low mortality for smolts up to 27 cm passing through Kaplan and Francis turbines (0-12%), but high mortality for salmon over 50 cm passing though Francis turbines (56-81%)

Spawning migration of salmon and sea trout in the Tornionjoki river

In this collaborative project between the Natural Resources Institute (Luke) and the Swedish Agricultural University (SLU), the migratory behaviour and survival of Tornionjoki (Torneälv in Swedish) salmon and sea trout were studied between 2018‒2021 by the means of radiote-lemetry. Altogether, 227 and 92 salmon were tagged at the Tornionjoki estuary and in the river, respectively. 114 sea trout were tagged in the river. Scale samples and fin clips for age-ing and genetic identification were taken from all the tagged specimens. The external condi-tion of the tagged specimen was also documented (wounds, skin colour, degree of haemor-rhage etc.). Moreover, a separate follow-up of the external condition of salmon caught in trap nets was conducted in 2020‒2021 at sea near the river mouth. The post-release behaviour of salmon tagged at the estuary was markedly different from that normally expected: a large majority (61% and 83% in 2018 and 2019, respectively) of the salmon which ascended the river after tagging aborted their riverine migration on the lower river and returned to the sea during the summer (i.e., before spawning season). Those salmon which stayed in the river until spawning time predominantly stayed on the lowermost 100 km of the river. More varying migration patterns were observed among the salmon tagged in the river. All specimens caught and tagged during the early summer of 2018 and 2019 started to drift downstream after their release and none of them was alive in the river at spawning time. However, about half of the specimens tagged in the river in early summer 2020 and 2021 continued their upstream migration and were alive in the river at spawning time. Salmon tagged in late summer 2018‒2020 stayed alive in the river and almost half of them also moved further upstream by spawning time. A large majority of salmon overwintered in the river after spawning and returned to the sea in spring. The majority of the salmon caught in the estuary had various external damages (wounds, scale losses, fin damages, and skin haem-orrhage). Most of the damages, however, were regarded as minor. No correlation between the occurrence of damages and the post-tagging behaviour of salmon could be detected. Based on the data obtained from tagged sea trout, two distinct groups of trout were recog-nised: (1) non-mature trout which ascended the river in autumn and returned to the sea in spring after overwintering in river, and (2) maturing trout which ascended the river in autumn, overwintered in the river, and continued their upstream spawning migration the following summer. Specimens belonging to either of these groups typically overwintered in the same short lowermost stretch of the river, although some of the maturing trout overwintered fur-ther upstream. At spawning season, tagged trout were located both on the main stem (Torni-onjoki and Muonionjoki rivers) and in several tributaries (Naamijoki, Äkäsjoki, Parkajoki, Paka-joki and Merasjoki rivers). After spawning time, trout which were observed in the tributaries usually moved back to the main stem where they overwintered and descended to the sea the next spring. Both the immature and the maturing overwintering trout descended to the sea at almost the same time in spring. The results of the project highlight the sensitivity of salmon to handling at/around the time of their river ascent in early summer. This sensitivity is likely linked to the recent health problems observed among Tornionjoki salmon and may have induced the unexpected (and seemingly maladaptive) migratory behaviour of salmon observed in the study. The in-river and sea to river movements observed for the Tornionjoki sea trout provides very useful information for efforts to protect this species and strengthen its stock status. In general, mature Tornionjoki sea trout have a two year in-river migratory cycle in connection with spawning, and hence spend a large majority of their life in the river, which underlines the need for good management of the riverine environment and river fisheries

Immune priming using DC- and T cell-targeting gene therapy sensitizes both treated and distant B16 tumors to checkpoint inhibition

Immune checkpoint inhibitors have revolutionized the treatment of metastatic melanoma, but most tumors show resistance. Resistance is connected to a non-T cell inflamed phenotype partially caused by a lack of functional dendritic cells (DCs) that are crucial for T cell priming. Herein, we investigated whether the adenoviral gene vehicle mLOAd703 carrying both DC- and T cell-activating genes can lead to inflammation in a B16-CD46 model and thereby overcome resistance to checkpoint inhibition therapy. B16-CD46 cells were injected subcutaneously in one or both flanks of immuno-competent C57BL/6J mice. mLOAd703 treatments were given intratumorally alone or in combination with intraperitoneal checkpoint inhibition therapy (anti-PD-1, anti-PD-L1, or anti-TIM-3). Tumor, lymph node, spleen, and serum samples were analyzed for the presence of immune cells and cytokines/chemokines. B16-CD46 tumors were non-inflamed and resistant to checkpoint blockade. In contrast, mLOAd703 treatment led to infiltration of the tumor by CD8(+) T cells, natural killer (NK) cells, and CD103(+) DCs, accompanied by a systemic increase of pro-inflammatory cytokines interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin-27 (IL-27). This response was even more pronounced after combining the virus with checkpoint therapy, in particular with anti-PD-L1 and anti-TIM-3, leading to further reduced tumor growth in injected lesions. Moreover, anti-PD-L1 combination also facilitated abscopal responses in non-injected lesions

Comparison of triploid and diploid rainbow trout (Oncorhynchus mykiss) fine-scale movement, migration and catchability in lowland lakes of western Washington

Fisheries managers stock triploid (i.e., infertile, artifcially produced) rainbow trout Oncorhynchus mykiss in North American lakes to support sport fsheries while minimizing the risk of genetic introgression between hatchery and wild trout. In Washington State, the Washington Department of Fish and Wildlife (WDFW) allocates approximately US $3 million annually to stock hatchery-origin rainbow trout in>600 lakes, yet only about 10% of them are triploids. Many lakes in Washington State drain into waters that support wild anadromous steelhead O. mykiss that are listed as threatened under the U.S. Endangered Species Act. As a result, there is a strong interest in understanding the costs and benefts associated with stocking sterile, triploid rainbow trout as an alternative to traditional diploids. The objectives of this study were to compare triploid and diploid rainbow trout in terms of: (1) contribution to the sport fshery catch, (2) fne-scale movements within the study lakes, (3) rate of emigration from the lake, and (4) natural mortality. Our results demonstrated that triploid and diploid trout had similar day-night distribution patterns, but triploid trout exhibited a lower emigration rate from the lake and lower catch rates in some lakes. Overall, triploid rainbow trout represent a viable alternative to stocking of diploids, especially in lakes draining to rivers, because they are sterile, have comparable home ranges, and less often migrat