Jan Heggenes

Habitat selection by brown trout (Salmo trutta) and young atlantic salmon (S. salar) in streams : Static and dynamic hydraulic modelling

Brown trout and young Atlantic salmon in streams are selective in their habitat use, which is partially determined by hydro-physical conditions. Habitat selection may be quantified in models and combined with hydraulic models to evaluate instream habitat suitability. Fish occupancy of habitat depends on the fish species and size. Brown trout prefer deep stream areas with moderate to low water velocities and rocky substrates, whereas young Atlantic salmon chose more fast flowing and often shallower areas. Habitat selection has been quantified in static selection models which should be based on measures of habitat usage and availability (preferences) and combined with data on hydro-physical conditions to build predictive habitat hydraulic models. Such models assess habitat availability and capacity rather than discharge–biomass relationships. Limitations of static models in fish habitat studies are (1) the relevant hydro-physical variables are not included, (2) the interaction terms are difficult to quantify and not incorporated, (3) the hydraulic models may not operate on a spatial scale that is relevant to fish, (4) the models include spatial but only to a limited extent temporal heterogeneity in habitat conditions and (5) biotic factors are not included. Streams may be extremely heterogeneous ecosystems, both spatially and temporally, which may influence habitat selection and modelling. In response to varying habitat availabilities (stream size and structure, water flows) habitat selection in brown trout and young Atlantic salmon is dynamic and relatively flexible. Furthermore, changes in temperature may result in seasonal and daily niche shifts. Therefore unless the dynamic aspects of habitat selection are incorporated into the habitat models, long-term predictive power in habitat–hydraulic modelling is unlikely. However, habitat–hydraulic modelling is a useful tool in a ‘no net loss of habitat’ management strategy regardless of these shortcomings.

Flexible Summer Habitat Selection by Wild, Allopatric Brown Trout in Lotic Environments

Abstract Spatial and temporal hydraulic heterogeneity influence distributional patterns of species in streams. Ecological theory suggests flexible habitat selection strategies are favored in such unstable environments. The effects of varying hydraulic conditions on habitat selection by brown trout Salmo trutta in summer were studied in eight streams in Norway and Scotland. At normal summer flows, brown trout averaging 16 cm total length (SD = ±5 cm, range = 3-43 cm) were selective in habitat use. The selection window was relatively narrow for focal water velocity (mean = 14 cm/s, median = 10 cm/s, 60.1% of observations ≤14 cm/s). Trout favored slower flowing pool areas, but selection ranges were wide (mean water column velocity = 24 ± 21 cm/s, range = 0-142 cm/s; mean depth = 69 ± 29 cm, range = 9-305 cm). Larger fish used deeper habitats; other variables did not correlate with size. Great overlaps in spatial niche used by the studied size-classes of trout indicated versatility in habitat selection (e.g.,...

IMPROVED WORK ABILITY AND RETURN TO WORK FOLLOWING VOCATIONAL MULTIDISCIPLINARY REHABILITATION OF SUBJECTS ON LONG-TERM SICK LEAVE

OBJECTIVE To evaluate a vocational multidisciplinary rehabilitation programme for patients on long-term sick leave with respect to their work ability and return to work. METHODS A multidisciplinary rehabilitation programme was administered to an intervention group of 183 patients on long-term sick leave (mean 12.2 months). Effects of the treatment were compared with a control group (n = 96) recruited from the national sickness insurance record of patients on sick leave of 6-12 months duration (mean 11.5 months). Perceived work ability, return to work, background factors and psychosocial aspects of work were assessed on the basis of questionnaires at baseline and after 4 months. RESULTS Perceived work ability of the intervention group improved significantly after 4 months compared with the control group (p < 0.01). In the intervention group, 80% had returned to work compared with 66% in the control group (p = 0.06). Return to work after 4 months was predicted by good work ability at baseline, improved work motivation, improved work ability at follow-up and increased rumours of change in the workplace (R2 26.1-38.6%, p < 0.05). CONCLUSION This multidisciplinary rehabilitation programme significantly improved perceived work ability compared with treatment as usual.

Molecular responses to toxicological stressors: profiling microRNAs in wild Atlantic salmon (Salmo salar) exposed to acidic aluminum-rich water.

Atlantic salmon (Salmo salar) is among the most sensitive organisms toward acidic, aluminum exposure. Main documented responses to this type of stress are a combination of hypoxia and loss of blood plasma ions. Physiological responses to stress in fish are often grouped into primary, secondary and tertiary responses, where the above mentioned effects are secondary responses, while primary responses include endocrine changes as measurable levels of catecholamines and corticosteroids. In this study we have exposed young (14 months) Atlantic salmon to acid/Al water (pH ≈ 5.6, Al(i) ≈ 80 μg L⁻¹) for 3 days, and obtained clear and consistent decrease of Na⁺ and Cl⁻ ions, and increases of glucose in blood plasma, hematocrit and P(CO₂) in blood. We did not measure plasma cortisol (primary response compound), but analyzed effects on microRNA level (miRNA) in muscle tissue, as this may represent initial markers of primary stress responses. miRNAs regulate diverse biological processes, many are evolutionarily conserved, and hundreds have been identified in various animals, although only in a few fish species. We used a novel high-throughput sequencing (RNA-Seq) method to identify miRNAs in Atlantic salmon and specific miRNAs as potential early markers for stress. A total of 18 miRNAs were significantly differentially expressed (FDR<0.1) in exposed compared to control fish, four down-regulated and 14 up-regulated. An unsupervised hierarchical clustering of significant miRNAs revealed two clusters representing exposed and non-exposed individuals. Utilizing the genome of the zebrafish and bioinformatic tools, we identified 224 unique miRNAs in the Atlantic salmon samples sequenced. Additional laboratory studies focusing on function, stress dose-responses and temporal expression of the identified miRNAs will facilitate their use as initial markers for stress responses.

Population connectivity: dam migration mitigations and contemporary site fidelity in arctic char

BackgroundAnimal feeding and spawning migrations may be limited by physical barriers and behavioral interactions. Dam constructions (e.g. hydropower) commonly include gateways for fish migrations to sustain ecological connectivity. Relative genetic impacts of fish passage devices versus natural processes (e.g. hybrid inferiority) are, however, rarely studied. We examined genetic (i.e. microsatellite) population connectivity of highly migrating lake-dwelling Arctic char (Salvelinus alpinus), introduced 20 generations ago, across and within two subalpine lakes separated by a dam with a subterranean tunnel and spill gates after 7 generations. Due to water flow regime, the time window for fish migration is highly restricted.ResultsChar populations, with similar genetic structuring and diversity observed across and within lakes, were admixed across the dam with fishways during feeding. For spawning, however, statistically significant, but very low population differentiation (θ; 0.002 - 0.013) was found in nine out of ten reproductive site comparisons, reflecting interactions between extensive migration (mean first generation (F0) = 10.8%) and initial site fidelity. Simulations indicated that genetic drift among relatively small effective populations (mean Ne = 62) may have caused the observed contemporary differentiation. Novel Bayesian analyses indicated mean contributions of 71% F0 population hybrids in spawning populations, of which 76% had maternal or paternal native origin.ConclusionsEcological connectivity between lakes separated by a dam has been retained through construction of fishways for feeding migration. Considerable survival and homing to ancestral spawning sites in hybrid progeny was documented. Population differentiation despite preceding admixture is likely caused by contemporary reduced reproductive fitness of population hybrids. The study documents the beginning stages of population divergence among spatial aggregations with recent common ancestry.