Patch selection by mottled sculpin (Pisces: Cottidae) in a southern Appalachian stream

1. We examined the effects of prey abundance on patch selection by a benthic fish, the mottled sculpin ( Cottus bairdi ), in a fourth order, southern Appalachian stream (North Carolina, U.S.A.). This habitat is a mosaic of small (i.e. < 0.5 m²), relatively discrete patches.
2. Patches were characterized in terms of physical habitat variables, detritus (coarse particulate organic matter, CPOM) and macroinvertebrate abundance (number and biomass). We quantified patch selection by comparing the characteristics of patches utilized by sculpin with those of locally available patches. Locally available patches were selected using a constrained random sampling design (i.e. randomly selected within a 2 m radius from each fish). We also examined the relationship between macroinvertebrate abundance, CPOM and the physical characteristics of available patches.
3. Patches selected by sculpin contained significantly higher macroinvertebrate abundances (both number and biomass) than locally available patches in five out of six seasonal samples. Sculpin also occupied patches with significantly higher amounts of CPOM in three out of five seasonal samples. Patches utilized by sculpin, however, could not be consistently differentiated from locally available patches on the basis of physical variables. In addition, macroinvertebrate abundance was not consistently related to physical habitat variables or CPOM during the course of the study.
4. Our results suggest that sculpin are able to assess patch quality on the basis of prey abundance and select patches that potentially maximize energy gain. This behaviour may produce an increase in individual fitness, especially when prey distributions are not consistently related to habitat variables. Quantifying patch use in relation to prey abundance may help elucidate the causal factors determining habitat use by benthic fishes in other lotic systems.     

Patch selection by mottled sculpin (Pisces: Cottidae) in a southern Appalachian stream

1. We examined the effects of prey abundance on patch selection by a benthic fish, the mottled sculpin ( Cottus bairdi ), in a fourth order, southern Appalachian stream (North Carolina, U.S.A.). This habitat is a mosaic of small (i.e. < 0.5 m²), relatively discrete patches.
2. Patches were characterized in terms of physical habitat variables, detritus (coarse particulate organic matter, CPOM) and macroinvertebrate abundance (number and biomass). We quantified patch selection by comparing the characteristics of patches utilized by sculpin with those of locally available patches. Locally available patches were selected using a constrained random sampling design (i.e. randomly selected within a 2 m radius from each fish). We also examined the relationship between macroinvertebrate abundance, CPOM and the physical characteristics of available patches.
3. Patches selected by sculpin contained significantly higher macroinvertebrate abundances (both number and biomass) than locally available patches in five out of six seasonal samples. Sculpin also occupied patches with significantly higher amounts of CPOM in three out of five seasonal samples. Patches utilized by sculpin, however, could not be consistently differentiated from locally available patches on the basis of physical variables. In addition, macroinvertebrate abundance was not consistently related to physical habitat variables or CPOM during the course of the study.
4. Our results suggest that sculpin are able to assess patch quality on the basis of prey abundance and select patches that potentially maximize energy gain. This behaviour may produce an increase in individual fitness, especially when prey distributions are not consistently related to habitat variables. Quantifying patch use in relation to prey abundance may help elucidate the causal factors determining habitat use by benthic fishes in other lotic systems.     

Mechanosensory based orienting behaviors in fluvial and lacustrine populations of mottled sculpin ( Cottus bairdi )

We compared prey-orienting and rheotactic behaviors in a fluvial (Coweeta Creek) and lacustrine (Lake Michigan) population of mottled sculpin. Blinded sculpin from both populations exhibited unconditioned, mechanosensory based rheotaxis to low velocity flows. Whereas Lake Michigan sculpin generally showed increasing levels of positive rheotaxis to increasing velocities, Coweeta Creek sculpin show varying levels of positive rheotaxis at low to intermediate velocities and often reduced positive rheotaxis or even negative rheotaxis at the highest velocities (12?cm?s^?1). Blinded Lake Michigan, but not Coweeta Creek mottled sculpin exhibited an orienting response to a small (3?mm diameter) artificial prey (50?Hz vibrating sphere). In conclusion, the two populations differed in the strength and polarity of the rheotactic response at higher velocities and in their responsiveness to mechanosensory cues from epibenthic prey sources. These behavioral differences have most likely arisen from different learning experiences in different habitats and from the greater importance of visual cues to the Coweeta Creek mottled sculpin and mechanosensory cues to Lake Michigan mottled sculpin in the sensory guidance of orienting behaviors.     

Mechanosensory based orienting behaviors in fluvial and lacustrine populations of mottled sculpin (Cottus bairdi)

We compared prey-orienting and rheotactic behaviors in a fluvial (Coweeta Creek) and lacustrine (Lake Michigan) population of mottled sculpin. Blinded sculpin from both populations exhibited unconditioned, mechanosensory based rheotaxis to low velocity flows. Whereas Lake Michigan sculpin generally showed increasing levels of positive rheotaxis to increasing velocities, Coweeta Creek sculpin show varying levels of positive rheotaxis at low to intermediate velocities and often reduced positive rheotaxis or even negative rheotaxis at the highest velocities (12 cm s^-1). Blinded Lake Michigan, but not Coweeta Creek mottled sculpin exhibited an orienting response to a small (3 mm diameter) artificial prey (50 Hz vibrating sphere). In conclusion, the two populations differed in the strength and polarity of the rheotactic response at higher velocities and in their responsiveness to mechanosensory cues from epibenthic prey sources. These behavioral differences have most likely arisen from different learning experiences in different habitats and from the greater importance of visual cues to the Coweeta Creek mottled sculpin and mechanosensory cues to Lake Michigan mottled sculpin in the sensory guidance of orienting behaviors.     

Life-history variations in the fluvial sculpin, Cottus nozawae (Cottidae), along the course of a small mountain stream

Life-history variations in male and female fluvial sculpins, Cottus nozawae, were studied in a small mountain stream in Hokkaido, Japan, primarily by using capture-mark-recapture methods. At three study areas established along the stream course, the majority of marked sculpins were recaptured in their original location over one or more years, indicating their long-term occupation of each restricted habitat area. Sculpin densities increased toward the upstream habitats, whereas individual growth rates were more rapid downstream. In both sexes, sculpins distributed downstream matured at a larger body size and later in life than upstream sculpins, clearly demonstrating a clinal variation in these respects. A comparison of life-history variations in C. nozawae with those in amphidromous C. hangiongensis suggests that intrapopulational life-history variations in the former might be environmentally induced, and that one of the most important determinants for the variations in Cottus species might be population density.     

Riffles as barriers to interpool movement by three cyprinids (Notropis boops,Campostoma anomalum and Cyprinella venusta)

1. The effects of riffles as barriers to movement of stream fish was investigated in a set of eight large outdoor artificial streams. Pools were 183 cm in diameter and 45 cm deep; riffles were 183 cm long and 43 cm wide. Rates of movement of three species of minnows (Cyprinidae) (Campostoma anomalum, Cyprinella venusta and Notropis boops) among pools were measured at four riffle current velocities (0, 15, 30 and 45 cm s^–1), three thalweg depths (10, 50 and 100 mm), two riffle lengths (183 and 549 cm), and with and without the threat of predation. Visual observation and video cameras were used to quantify movement rate. 2. Mean movement rate (percentage of fish crossing a riffle each 30 min) was 18.1% at 0 cm s^–1 and only 1.8 at 45 cm s^–1. Movement rate was 7.2% with no predators present and 20.2% with caged predators in pools. Notropis boops had a lower rate of movement than C. venusta or C. anomalum across all trials. The mean group size (number of individuals crossing a riffle together) was 1.2 fish overall, indicating most movement was by individuals and not groups. Group size was significantly greater only with shallow riffles or under the threat of predation. 3. Overall biotic and abiotic factors in these artificial streams do influence movement rates and may affect movement among pools in natural streams.     

Sound production through the substrate during reproduction in the mottled sculpin,Cottus bairdi (Cottidae)

Synopsis During reproduction maleCottus bairdi defend cavities beneath stones and perform defense and reproductive displays. Using a geophone to detect substrate vibrations under dark conditions (infrared viewing), we recorded three types of sounds. Knocks are produced during head nods and an acoustically similar sound is produced when the fish slaps the head to the substrate. A third sound, the drum roll appears to be a fast repetition of several knocks followed by a head slap. We argue that these signals traveling through the substrate are of greater importance than sounds traveling through the water because (1) the substrate vibration attenuates at a much lesser rate than the water vibration and, (2) even near riffles, which generate much water vibration, the background noise in the substrate is low enough for the fish to detect such sounds.     

Factors influencing the longitudinal distribution of larval Hydropsychidae (Trichoptera) in a southern Appalachian stream system (U.S.A.)

The influence of physical habitat variables and suspended particulate organic matter (seston) on the distribution and production of eight species of larval Hydropsychidae was studied along a 6.4 km section of a southern Appalachian stream. Samples were collected at six stations encompassing stream orders 1–4 and an elevation range of 610 m. Multivariate analysis of covariance (using time as the covariable) and discriminant function analysis were used to examine habitat differences between the sampling stations due to the following variables: current velocity; coarse benthic detritus; substrate composition (by particle size); substrate heterogeneity; degree-days; and diel temperature fluctuation. The associations of these variables with the abundance (and production) of larval hydropsychids was also examined using the same statistical procedures. The six sampling stations represented three or four distinct habitats based on patterns of change in the variables along the stream continuum. Diel temperature fluctuation, median substrate particle size, the proportion of sand substrate, and substrate heterogeneity were most closely associated with the overall difference between the sampling stations. Hydropsychid species distribution along the stream system followed subfamily lines, i.e., Arctopsychinae and Diplectroninae were more abundant and productive in the upper 4.5 km of the stream, while Hydropsychinae were dominant in the lower 1.9 km. Diel temperature fluctuation was the habitat variable most highly correlated with patterns of hydropsychid abundance and production. The longitudinal pattern of species distribution, i.e., larger particle feeding Arctopsychinae being replaced downstream by smaller particle feeding Hydropsychinae, also coincided with the distribution of seston particle size classes along the stream. Mean seston particle size generally declined downstream, as particles <42 µm increased in relative abundance while those between 43 µm and 5 mm decreased. Temperature, seston, and substrate composition all undoubtedly exerted an important influence on the distribution and production of Hydropsychidae and other filter feeding insects in this stream. The validity and generality of these results depend upon the scope of the sampling effort. Conclusions drawn from data collected over the entire range (and limits) of a species' distribution are more sound than those based on data from a limited area.     

Diet and growth of a leaf-shredding caddisfly in southern Appalachian streams of contrasting disturbance history

Diet and growth of leaf-shredding caddisfly larvae, Pycnopsyche spp.,were examined in streams draining a reference catchment and a 16-year-oldclear-cut (disturbed) catchment at Coweeta Hydrologic Laboratory insouthwestern North Carolina, USA. The objective was to explain why shredderproduction is higher in the disturbed streams despite the larvae having lessfood (i.e., leaves) available. We predicted larvae would grow faster onfast-decaying leaf material representative of the disturbed streams. Larvaeconsumed mostly leaf detritus in three streams draining each catchment overthree seasons (fall, winter, and spring), which showed larvae did notconsume higher quality foods (e.g., algae and animal material) in disturbedstreams. When fed 2-month-old conditioned black birch (Betula lenta L.) (afast-decaying leaf species) and white oak (Quercus alba L.) (a slow-decayingleaf species) leaves in the laboratory, larvae grew significantly faster onthe birch leaves. However, when larvae were fed the same leaf types after3-months conditioning, larvae grew significantly faster on oak leaves. Afield growth experiment conducted for 42 d using mixed-species leaf dietsrepresentative of each catchment and initially conditioned for 2 monthsfound that Pycnopsyche grew significantly better on the diet representativeof the reference catchment. The reference diet contained more oak leaveswhich apparently became a more acceptable food as the experiment proceeded.High shredder production in the disturbed streams could not be explained byhigh Pycnopsyche growth rates on fast-decaying leaves. Instead, larvae grewbetter on leaves that were apparently conditioned optimally regardless ofconditioning rate.     

Feeding ecology of a vertebrate assemblage inhabiting a stream of NW Spain (Riobo; Ulla basin)

The food resource use of a stream in NW Spain by fish (Salmo trutta L. and Anguilla anguilla L.), birds (Cinclus cinclus L. and Motacilla cinerea L.) and mammals (Galemys pyrenaicus G. and Neomys anomalus C.) was studied. Data on seasonal diets and stream benthos prey were used to determine prey selection patterns.Caddisfly larvae are the main resource for Cinclus and Galemys, but these predators also consumed other benthic prey. Salmo fed on a wide range of benthic invertebrates, emergent pupae and terrestrial prey, whereas Anguilla consumed primarily benthic invertebrates, especially Lumbricids. Neomys fed mainly on terrestrial prey (Gasteropods and Lumbricids), but also consumed aquatic prey. Motacilla captured aquatic insects both in larval and aerial stages, as well as terrestrial prey.Both prey availability and selection led to seasonal differences in the use of food resources. All species showed a marked prey selection of aquatic taxa. Prey size plays an important role in this selection, most species consuming the largest of available prey sizes. In spite of the fact that all species feed upon freshwater invertebrates, substantial resource partitioning was observed in all seasons. This partitioning may be attributable to morpholological and physiological differences. Nevertheless, Anguilla and Galemys, two quite different animals, did feed on the same prey much of the time.     

Prioritising the rehabilitation of fish passage in a regulated river system based on fish movement

Environmental rehabilitation budgets are often limited, and management actions need to be prioritised to achieve the best outcomes. Prioritisation can best be done when evidence informs the decision‐making process. We acoustically tagged twenty Golden Perch (Macquaria ambigua) in the Loddon River, Australia, and tracked their movements to gain an understanding on the requirements for fish passage at a major regulating structure, the Box Creek regulator. The movements of these fish were monitored through a network of receivers located throughout the lower Loddon River and Pyramid Creek system. Five fish moved 50–120 km upstream, four of which reached the Box Creek regulator before moving back downstream to the entrance of the Kerang Lakes system. Most long distance upstream movements were associated with an increase in river discharge. The remaining 15 fish moved <20 km, with all fish being detected at least once. This pilot study indicates that Box Creek regulator is acting as a barrier for some fish within the Loddon River system. Movement data also indicate that Golden Perch migration pathways may be influenced by river discharge. The management implications of this work includes the need to reinstate fish passage at Box Creek regulator and the potential use of environmental flows to enhance colonisation of native fish species throughout the Murray Darling Basin.     

Forecasting fish distribution along stream networks: brown trout (Salmo trutta) in Europe

Aim

Species inhabiting fresh waters are severely affected by climate change and other anthropogenic stressors. Effective management and conservation plans require advances in the accuracy and reliability of species distribution forecasts. Here, we forecast distribution shifts of Salmo trutta based on environmental predictors and examine the effect of using different statistical techniques and varying geographical extents on the performance and extrapolation of the models obtained.

Location

Watercourses of Ebro, Elbe and Danube river basins (c. 1,041,000 km²; Mediterranean and temperate climates, Europe).

Methods

The occurrence of S. trutta and variables of climate, land cover and stream topography were assigned to stream reaches. Data obtained were used to build correlative species distribution models (SDMs) and forecasts for future decades (2020s, 2050s and 2080s) under the A1b emissions scenario, using four statistical techniques (generalised linear models, generalised additive models, random forest, and multivariate adaptive regression).

Results

The SDMs showed an excellent performance. Climate was a better predictor than stream topography, while land cover characteristics were not necessary to improve performance. Forecasts predict the distribution of S. trutta to become increasingly restricted over time. The geographical extent of data had a weak impact on model performance and gain/loss values, but better species response curves were generated using data from all three basins collectively. By 2080, 64% of the stream reaches sampled will be unsuitable habitats for S. trutta, with Elbe basin being the most affected, and virtually no new habitats will be gained in any basin.

Main conclusions

More reliable predictions are obtained when the geographical data used for modelling approximate the environmental range where the species is present. Future research incorporating both correlative and mechanistic approaches may increase robustness and accuracy of predictions.

     

Longitudinal patterns of production, food consumption, and seston utilization by net-spinning caddisflies (Trichoptera) in a southern Appalachian stream (USA)

Larval production of ten species of Hydropsychidae and Philipotamidae was studied at six stations along 6.4 km of a southern Appalachian stream, encompassing stream orders 1–4 and a 600 m elevation change. Species-specific production estimates ranged from 23–983 mg AFDM m^?2 yr^?1 These low values are attributed to the paucity of nutrients in these undisturbed headwater streams which reduces detrital food quality, algal growth, and production of smaller invertebrates eaten by hydropsychids. Animal food supported the majority of hydropsychid production (72%); philopotamids relied primarily on fine detritus (80%) and diatoms (15%). The contribution of animal food to caddisfly production decreased downstream, while the relative importance of filamentous algae and diatoms increased. These changes reflect the downstream decline of more carnivorous species, as well as increased primary production which accompanies the shift in lotic community metabolism from heterotrophy towards autotrophy with increasing stream order. Net-spinning caddisflies had a minor impact on seston quantity, consuming only 0.0003%-0.005% of the total seston (including invertebrate drift) passing over a m² of substrate annually. In contrast, the percentage of invertebrate drift consumed was, on the average, > 400 × higher than total seston consumption. These insects influence seston quality rather than quantity. The percentage of total seston and animal drift consumed declined downstream, indicating that turnover lengths of these materials increase with stream order. Longer turnover lengths or “spirals” result from changes in the physical characteristics of the stream, i.e., increasing discharge and stream power and decreasing numbers of retention devices (i.e., organic debris dams), which increase the downstream transport velocity of seston. Higher transport velocities reduce the rates at which these filter feeding caddisflies can process the organic inputs to a given reach of stream. Small streams (orders 1–3) appear to be most responsible for efficient processing of a stream's energy inputs.     

Evidence for non-random spatial positioning of migrating smolts (Salmonidae) in a small lowland stream

1. The ontogenetic development of anadromous salmonids includes downstream emigration of immature individuals from freshwater towards the marine environment. Although this migration of juvenile salmonids (smolts) may be associated with severe mortalities, only limited attention has been paid to the spatial positioning of smolts in small streams. 2. Using a novel approach, this study examined the vertical and horizontal positioning of brown trout and Atlantic salmon smolts while performing downstream migration in a small lowland stream. 3. Pre‐smolts of indigenous and hatchery‐reared (F1) brown trout (Salmo trutta), and two different populations of Atlantic salmon (S. salar), were tagged with passive integrated transponder (PIT) tags and subsequently released upstream of an antenna array consisting of five circular swim‐through PIT antennas. Antennas were positioned in order to determine whether the migrating smolts were bottom or surface oriented, and if they were oriented towards the mid‐channel or the stream bank. 4. During the smolt emigration period, data describing both the detection of the migrating fish and the amount of water passing through the antennas were collected. This was accomplished in order to determine if the fish were performing active positioning behaviour independently of the vertical and horizontal discharge distributions in the stream. 5. The results showed that the smolts migrated in a non‐random spatial pattern independently of the stream discharge distributions. Vertically, the indigenous brown trout and the Atlantic salmon demonstrated a preference for the bottom orientated positions. In contrast, the distribution of the F1 brown trout was not different from the discharge distribution. The latter observation suggests random vertical positioning, which may be indicative of inferior migratory performance. Horizontally, all tested smolt populations strongly preferred the mid‐channel positions. 6. The discharge‐corrected preferences for certain spatial positions suggest that smolt emigration is not entirely a matter of passive displacement in lowland streams. 7. Anthropogenically altered channels may inhibit or delay downstream emigration of smolts resulting in increased mortalities. Given that the smolts in this study actively selected spatial positions in the mid‐channel and near the bottom, it is suggested that deep, mid‐channel furrows may be used to help guide migrating smolts past adverse habitats in lowland streams.     

Seasonal changes in morphometric and biochemical endpoints in northern pike (Esox lucius), burbot (Lota lota) and slimy sculpin (Cottus cognatus)

1. Morphometric and biochemical endpoints were used to assess growth and energetics in young‐of‐the‐year (YOY) northern pike (Esox lucius), YOY burbot (Lota lota) and slimy sculpin (Cottus cognatus) collected upstream and downstream of a uranium mining operation in northern Saskatchewan, Canada. 2. Water sampled at sites downstream of uranium mining and milling effluent discharge was higher in certain trace metals (arsenic, molybdenum), ions (conductivity, hardness, ammonia and sulphate) and total dissolved solids compared with ecologically similar reference sites. 3. Overwinter survival potential was estimated by determining total body lipids and total body triglycerides in fishes collected in late autumn and early spring. Two‐factor anova indicated no site or season differences in total body lipids or triglycerides in YOY northern pike. In spring, burbot collected from the exposure site were higher in total body lipids and triglycerides compared with the previous autumn and compared with fish collected from the reference site. Slimy sculpin from both exposure and reference sites had lower total body lipid and triglyceride content in spring compared with the previous autumn. In addition, sculpin from the exposure site had lower total body lipids and triglycerides in spring compared with fish collected from the reference site. 4. Biochemical estimates of fish growth (muscle RNA/DNA ratio and muscle protein concentration) exhibited clear seasonal differences, with consistent decreases in this endpoint for all fish species in spring relative to the previous autumn at both exposure and reference sites. 5. Results for total body lipids and triglycerides were inconclusive and inconsistent between species and exposure scenarios. However, all species exhibited a similar seasonal decrease in muscle protein and to a lesser extent, muscle RNA/DNA ratio.     

Reproductive ecology of Dendrocoelum lacteum (Turbellaria) in a rapid stream in southern Sweden and comparisons with a lake population

Rapid streams in southern Sweden are often inhabited by the triclad Dendrocoelum lacteum. Outside Fennoscandia, this species is mainly restricted to lentic habitats. The normal food refuge for D. lacteum, the isopod Asellus aquaticus, is seldom found in the stream habitats, and probably the prey here is the amphipod Gammarus pulex. With respect to spatial and trophic niche components, it seems that D. lacteum has taken the place of Crenobia alpina in southern Sweden.Two parameters of reproduction, namely production of cocoons and of hatchlings, both peaked approximately one month later in a stream than in an adjacent lake. This difference was attributed to a low temperature regime in the stream. Number of hatchlings per cocoon and cocoon sterility were higher in the stream than in the lake. Similar cocoon and hatchling output per adult was found in the two habitats, indicating a similar reproductive effort for the two triclad populations. I suggest that D. lacteum, by virtue of its choice of microhabitat, viz., under stones, is not so vulnerable to the more severe stream environment.     

Fish assemblage of a Pampasic stream (Buenos Aires,Argentina): temporal variations and relationships with environmental variables

In the Argentine Pampa fertile soils were originally covered by grasslands, but at present are intensively cultivated. We assessed the specific composition of the fish assemblage of El Pescado stream and compared it with that recorded in 1991–1993, when land use in the watershed consisted in natural pastures. The persistence of the fish assemblage between the two studies was rather high: 0.76. Abundance, biomass and species richness were higher during drought periods. Connectivity with the huge Río de la Plata hydrographic system seems the most important contribution to the high and stable species richness of El Pescado stream.     

Behavioral effects of invaders: alien crayfish and native sculpin in a California stream

Invasive crayfish have been shown to have negative impacts on a range of taxa, though the mechanisms for those effects have not always been evaluated. Signal crayfish (Pacifastacus leniusculus) in Sagehen Creek were associated with reduced growth rates and gut fullness of Paiute sculpin (Cottus beldingi) in earlier experiments. This paper assesses potential behavioral mechanisms of competition between the two species. I conducted experiments to determine crayfish effects on sculpin behavior and habitat use in a stream observation facility at the Sagehen Research Station, California, USA. Sculpin reduced their use of refuges and pools, shifted into higher-velocity microhabitats, and spent more time fleeing in the presence of crayfish. Crayfish used refuges, pools, and low-velocity habitats more than sculpin in either treatment. Both species were notably nocturnal, with most activity at dusk and night observations, although crayfish were more strongly so than sculpin. Detailed field surveys of lower Sagehen Creek found that potential refuges (unembedded rocks) were closely associated with total crayfish and sculpin numbers, suggesting that cover is at least sometimes limiting under natural conditions. By displacing sculpin from refuges and pools and increasing their activity rate, crayfish may increase the likelihood of predation on sculpin. Behavioral shifts in sculpin appear to be at least partly responsible for the reduced growth rates of sculpin in the presence of crayfish.     

Seasonal and temperature‐related movement of Colorado River cutthroat trout in a low‐elevation,Rocky Mountain stream

Mobile species will migrate considerable distances to find habitats suitable for meeting life history requirements, and stream‐dwelling salmonids are no exception. In April–October 2014, we used radio‐telemetry to examine habitat use and movement of 36 Colorado River cutthroat trout Oncorhynchus clarkii pleuriticus (CRCT) in a 14.9‐km fragment of Milk Creek, a relatively low‐elevation stream in the Rocky Mountains (Colorado). We also used a network of data loggers to track stream temperature across time and space. Our objectives were to (1) characterize distribution and movement of CRCT, (2) evaluate seasonal differences in distribution and movement of CRCT, and (3) explore the relationship between stream temperature and distribution and movement of CRCT. During the course of our study, median range of CRCT was 4.81 km (range = 0.14–10.94) and median total movement was 5.94 km (range = 0.14–26.02). Median location of CRCT was significantly further upstream in summer than in spring, whereas range and movement of CRCT were greater in spring than in summer. Twenty‐six of the 27 CRCT tracked through mid‐June displayed a potamodromous (freshwater migratory) life history, migrating 1.8–8.0 km upstream during the spring spawning season. Four of the seven CRCT tracked through July migrated >1.4 km in summer. CRCT selected relatively cool reaches during summer months, and early‐summer movement was positively correlated with mean stream temperature. Study fish occupied stream segments in spring and fall that were thermally unsuitable, if not lethal, to the species in summer. Although transmitter loss limited the scope of inference, our findings suggest that preferred habitat is a moving target in Milk Creek, and that CRCT move to occupy that target. Because mobile organisms move among complementary habitats and exploit seasonally‐unsuitable reaches, we recommend that spatial and temporal variability be accounted for in delineations of distributional boundaries.     

River flow, Atlantic salmon (Salmo salar L.) movement and rod catch in the Aberdeenshire Dee

The relationship between river flow and rod and net catches of salmon and grilse have been analysed for four of the major fisheries on the Aberdeenshire Dee. On the lower two fisheries there is a good correlation between the rod catch and the average flow on the day of the catch and the preceding 3 days but there is no such correlation at the highest fishery. There is also a good correlation between the annual flow during the rod season and the total annual rod catch at the lowest fishery, while there is an inverse correlation between the flow during the rod season and the net catch. When the nets are off there is no longer any correlation between river flow and rod catch at the lowest fishery.