Brown trout Salmo trutta express different morphometrics due to divergence in the rearing environment

Variation in the body morphology of juvenile brown trout Salmo trutta was studied for both wild and hatchery-reared individuals from the same gene pool. The thin-plate spline (TPS) method by pointing landmarks was used to characterize juveniles from their natal environment, the River Kuusinkijoki in eastern Finland, and from wild parents raised in a hatchery environment. Differences were found in the morphometrics of juvenile S. trutta from the two different environments. Wild S. trutta are characterized by a longer head and shorter anterior part of the trunk compared to hatchery S. trutta. Stocked to their natal river with wild S. trutta, the hatchery fish became characterized with more similar morphometrics to their wild counterparts. The characteristics of the body form are explained by the differing environmental conditions in the wild and hatchery. It is concluded that a simple hatchery environment may delay the development of morphological characteristics important in a natural river environment.     

Testing for temporal coherence across spatial extents: the roles of climate and local factors in regulating stream macroinvertebrate community dynamics

Temporal coherence or spatial synchrony refers to the tendency of population, community or ecosystem dynamics to behave similarly among locations through time as a result of spatially‐correlated environmental stochasticity (Moran effect), dispersal or trophic interactions. While terrestrial studies have treated synchrony mainly as a population‐level concept, the majority of freshwater studies have focused on community‐level patterns, particularly in lake planktonic communities. We used spatially and temporally hierarchical data on benthic stream invertebrates across six years, with three seasonal samples a year, in 11 boreal streams to assess temporal coherence at three spatial extents: 1) among regions (watersheds), 2) among streams within a region, and 3) among riffles within a stream, using the average of correlation coefficients for stream/riffle pairs across years. Our results revealed the primacy of strongly synchronized climatic factors (precipitation, air temperature) in inducing temporal coherence of macroinvertebrate assemblages across geographically distinct sites (i.e. Moran effect). Coherence tended to decrease with increasing spatial extent, but positive coherence was detected for most biological variables even at the largest extent (about 350 km). The generally high level of coherence reflected the strong seasonality of boreal freshwater communities. A hydrologically exceptional year enhanced the synchrony of biological variables, particularly total macroinvertebrate abundance. Regionally low precipitation in that year led to a substantial decrease in benthic densities across a broad spatial extent, followed by a rapid post‐drought recovery. Coherence at the among‐riffle (within‐stream) extent was lower than expected, implying that local‐scale habitat filters determine community dynamics at smaller spatial extents. Thus, temporal coherence of stream benthic communities appears to be controlled by partly different processes at different spatial scales.     

Species–environment relationships of fish and map‐based variables in small boreal streams: Linkages with climate change and bioassessment

Species–environment relationships were studied between the occurrence of 13 fish and lamprey species and 9 mainly map‐based environmental variables of Finnish boreal small streams. A self‐organizing map (SOM) analysis showed strong relationships between the fish species and environmental variables in a single model (explained variance 55.9%). Besides basic environmental variables such as altitude, catchment size, and mean temperature, land cover variables were also explored. A logistic regression analysis indicated that the occurrence probability of brown trout, Salmo trutta L., decreased with an increasing percentage of peatland ditch drainage in the upper catchment. Ninespine stickleback, Pungitius pungitius (L.), and three‐spined stickleback, Gasterosteus aculeatus L., seemed to benefit from urban areas in the upper catchment. Discovered relationships between fish species occurrence and land‐use attributes are encouraging for the development of fish‐based bioassessment for small streams. The presented ordination of the fish species in the mean temperature gradient will help in predicting fish community responses to climate change.     

Intra- and Interspecific Competition in Hatchery Landlocked Salmon and Brown Trout in Semi-Natural Streams

I studied inter- and intraspecific competition in two hatchery stocks: landlocked salmon with long-hatchery background and a heterogenic brown trout stock. These species are potential competitors in the natural environment when landlocked salmon is being restored to wild by stocking hatchery juveniles. Behavioural responses were studied in four indoor laboratory flumes (400 cm long and 37 cm wide) and habitat use in six semi-natural outdoor streams (26 m long and 1.5 m long). Video recordings were used to monitor fish behaviour and electrofishing for fish positioning in the outdoor channels. The study design included five treatments: two densities of brown trout and salmon in solitary and both species together. The results of the study demonstrated that juvenile brown trout changed their behaviour in laboratory streams in response to presence of the landlocked salmon and the density of the conspecifics also tended to alter the habitat use by brown trout in semi-natural streams. Landlocked salmon juveniles showed no response to treatments. I conclude that possible poor adaptive ability to conditions outside hatchery by the hatchery salmon together and more competitive brown trout stocks may limit the success of management action in restoring landlocked salmon back to their natural streams of stocking.     

Assessment of the ecological status of regulated lakes: stressor-specific metrics from littoral fish assemblages

Although in situ sediment capping is frequently used to reduce internal loading of contaminants and nutrients, post-application assessment rarely includes the potential undesirable short-term effects on plankton species composition. We hypothesised that a modified zeolite (Z2G1) application as a sediment capping agent in Lake Okaro, New Zealand, could cause significant undesirable shifts in species composition of both zooplankton and phytoplankton due to burial of resting stages or interference with feeding for the zooplankton. Alternatively, we predicted that the capping agent might have no effect due to, for example, the coarse grain size of the material (1–3 mm). We used multidimensional scaling (MDS) and analysis of similarity (ANOSIM) to identify any adverse effects of Z2G1 on zooplankton and phytoplankton species composition (i.e. shifts in community structure, including species loss) by comparing the community structure before and after the Z2G1 application. We found no significant differences in species composition before and after the Z2G1 application at the depths investigated (surface and 9 m). However, all of the analyses showed statistically significant differences among seasons, indicating seasonal variations in plankton composition far outweigh those that may have resulted from the Z2G1 application. Coarse particle size, low dose rate and a restricted area where the sediment capping agent was applied were considered to be the factors limiting potential adverse effects on plankton species. Considerations of finer-grained material to increase coverage and efficacy of phosphorus adsorption require assessment for their effects on zooplankton, however, and a direct mode of application into the hypolimnion is recommended to minimise effects on zooplankton and phytoplankton communities.     

Predation Threat Affects Behaviour and Habitat Use by Hatchery Brown Trout (Salmo Trutta L.) Juveniles

The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juveniles were studied in four indoor and six outdoor experimental channels. Northern pike (Esox lucius L.) was used as a predator. Brown trout were more active during the night compared to day, but in the presence of pike the increase in activity was less than in treatments without predator. Aggressive interactions between trout were higher during the day when pike was absent. In the presence of pike trout tended to use more coarse substrate classes as subdominant habitat suggesting increased use of cover and also higher or lower water depths. Our results increase knowledge of the effects of predation threat on habitat selection and behaviour by brown trout.     

Intercohort competition causes spatial segregation in brown trout in artificial streams

When together in a flume, 13-cm L _s (age-1) trout appeared to increase their activity and behaved more aggressively, whereas 10-cm L _s (age-0) trout tended to move less and were rarely aggressive in the presence of the larger size class. Both size classes were less mobile and preferred lower water velocities in winter than in summer, and increased their use of instream cover in winter. When both size classes were present, only small trout decreased their use of low water velocities and cover. The results indicate that intercohort competition may cause spatial segregation among size groups of brown trout, especially in winter when trout attempt to minimize their maintenance costs.     

Response of fish assemblages to water quality in boreal rivers

The relationship between fluvial fish assemblages and environmental variables including water quality was studied by nonmetric multidimensional scaling (NMS) and generalised regression neural network (GRNN). Fish assemblages in the studied boreal rivers in Central Finland showed a higher response to water quality than to other environmental variables such as altitude and river width. Of the water quality parameters, total phosphorus, oxygen saturation in winter and solids had the highest influence on fish assemblages. Brown trout (Salmo trutta L.) responded to water quality strongly by favouring pristine waters. Among other fish species, the responses were lighter, and the relative contribution of environmental variables varied. Percentage of fishless sites, i.e. no catch in electrofishing, was 4.4% when pH ≥ 6, and 38.2% when pH < 6. However, the most effective way to influence the fish assemblage composition, and to raise the fish-based FIFI integrity index value, would be to reduce loading of solids and phosphorus, rather than depressing acidification.     

Habitat preference by grayling (Thymallus thymallus) in an artificially modified, hydropeaking riverbed: a contribution to understand the effectiveness of habitat enhancement measures

This paper describes a case study to rehabilitate habitat for adult European grayling (Thymallus thymallus L.) in a large river reservoir in northern Finland. A channelled river reach was restored by building small islands and reefs as well as cobble and boulder structures for grayling. The total area of the restored stretch was 1.0 ha. The physical habitat was mapped using an echosounder, Doppler device, tachometer and scuba diving, and modelled with a 2D hydraulic model. The mean water velocity in the modelled stream section was 0.28 m s^?1 during 110 m³ s^?1 flow and 0.43 m s^?1 during 300 m³ s^?1 flow. Twelve adult grayling, tagged with transmitters, were released into the area and tracked for a maximum period of 30 days. The grayling largely stayed in the restored area and tended to avoid the unchanged channel of the river. The range of daily movement was from stationary to 2700 m per day. The adult grayling preferred water velocities between 0.20 and 0.45 m s^?1, water depths between 0.20 and 1.55 m and coarse substrate. The study provides a small part of the information needed in habitat restoration for grayling.     

Effect of fluctuating flow and temperature on cover type selection and behaviour by juvenile brown trout in artificial flumes

Brown trout Salmo trutta in a flume used cover more often and were more aggregated at low water temperatures in winter compared with summer. Cover combinations providing the most cover (overhead, visual and velocity cover) were preferred in winter whereas velocity refuges were preferred in late summer; and brown trout rarely used any of these cover structures in early summer. Flow affected cover use especially in winter, when most of the trout moved to shelters during the first high flow period. Movements by brown trout were most frequent in early summer. The much higher aggression rate in summer compared with winter decreased during the first period of high flow in both summer experiments. The results indicate seasonal changes in cover habitat and cover type preferences suggesting that habitat complexity is important, and availability of cover is particularly important during different seasons and fluctuating flow.