Habitat use by a Midwestern U.S.A. riverine fish assemblage: effects of season, water temperature and river discharge

The hypothesis that temperate stream fishes alter habitat use in response to changing water temperature and stream discharge was evaluated over a 1 year period in the Neosho River, Kansas, U.S.A. at two spatial scales. Winter patterns differed from those of all other seasons, with shallower water used less frequently, and low‐flow habitat more frequently, than at other times. Non‐random habitat use was more frequent at the point scale (4·5 m²) than at the larger reach scale (20–40 m), although patterns at both scales were similar. Relative to available habitats, assemblages used shallower, swifter‐flowing water as temperature increased, and shallower, slower‐flowing water as river discharge increased. River discharge had a stronger effect on assemblage habitat use than water temperature. Proportion of juveniles in the assemblage did not have a significant effect. This study suggests that many riverine fishes shift habitats in response to changing environmental conditions, and supports, at the assemblage level, the paradigm of lotic fishes switching from shallower, high‐velocity habitats in summer to deeper, low‐velocity habitats in winter, and of using shallower, low‐velocity habitats during periods of high discharge. Results also indicate that different species within temperate river fish assemblages show similar habitat use patterns at multiple scales in response to environmental gradients, but that non‐random use of available habitats is more frequent at small scales.     

New modelling of complex fish migration by application of chaos theory and neural network

Rules or patterns of movement or migration were still vague even for the main commercial fishes due to different routs in scale or in different, times resulting from complex environments to complex behaviour concept. The quantitative model of fish migration has been investigated using chaos theory to mimic more realistic fish movements by time steps from environmental and biological stimuli. The model uses three steps within a model neural network such as input stimuli, central decision‐making and response output in fish movements. The stimuli in the first step include the main physical (temperature, salinity, light, flow etc .) and biotic factors (prey, predator, life cycle etc .) which could be quantified as intensity parameters which were then normalized as ratios. The decision‐making process can be generated available signals for motor neuron using Lorenz chaos equations by the relevant stimuli. The response of fish movements from the output signal representing speed and direction can be re‐regulated as object‐oriented migration depending on physiological state or life cycle by third response filtering. The simulation results seen as 2‐dimensional seasonal migration for demersal fishes in the southern sea of the Korean Peninsula represented more realistic meandering tracks than the interpolated tracks in previous reports.     

Using stable isotope analysis with telemetry or mark-recapture data to identify fish movement and foraging

Information about animal movements has often been inferred from stable isotope analysis (SIA), but is dependent on animals assimilating site-specific isotopic signatures via diet. This potential weakness in ecological interpretation can be overcome by using other investigative tools that provide precise information about individual movement patterns. In this paper, we demonstrate the value of combining SIA with telemetry or mark-recapture data from trapping, electrofishing and remote detection of individuals to study the movement and feeding ecology of fishes in different habitats. In a fjord lake system in Newfoundland, Canada, juvenile Atlantic salmon delayed downstream migration (smolts) or actively moved into a large lake (parr) where they foraged for periods reflecting different life history strategies. In the Miramichi River (New Brunswick, Canada), SIA provided evidence of distinct foraging habitats (tributary versus large river). By tracking fish implanted with passive integrated transponder (PIT) tags, we distinguished between movements related to foraging versus seeking cool water refugia during high temperature events. Finally, site fidelity and limited mobility of slimy sculpin, a small benthic fish, was established where δ¹³C in muscle tissue showed a progressive enrichment downstream and where a median displacement of <10 m was estimated for sculpin tagged with PIT tags. Technological improvements have permitted non-destructive tissue sampling of wild fishes for SIA, and the tagging and remote detection of animals smaller than was previously possible. These advancements and the combination of investigative tools promise new insights into animal ecology.     

Electrofishing and salmonid movement: reciprocal effects in two small montane streams

The effects of electrofishing on salmonid movement and of salmonid movement on electrofishing‐derived abundance estimates were studied in two streams in western Montana, U.S.A. Electrofishing increased emigration of salmonids from study reaches for 1 day, but not for succeeding days, whereas immigration to study reaches was unaffected. Movement of most emigrating fishes was downstream. On these small streams, electrofishing did not appear to cause fishes to flee during sampling. Numbers of salmonids migrating between mark and recapture runs were small relative to the fish abundance estimates in study reaches, usually much less than the 95% CL for those estimates, thus disregarding movements of marked fishes from the study reaches would have produced small positive biases in abundance estimates. Overall, for this suite of salmonid species in mid‐summer in these streams, the effects of electrofishing on fish movement and of fish movement on abundance estimates were minor.     

Movements of Macquaria ambigua, in the Murray River, south‐eastern Australia

A 2 year (2000–2001) radio‐tagging study was undertaken to investigate the movements of 51 golden perch Macquaria ambigua in the Murray River at Nyah in north‐western Victoria, Australia. During the winter of both years, golden perch did not undertake movements >5 km and displayed strong home range fidelity. In the first year of the study there was an increase in the distance of golden perch movement during late spring which coincided with increasing water temperature and river discharge. Nineteen golden perch were tracked during this period, of which 10 travelled downstream between 11 and 290 km. Seven of these fish moved to an area below the junction of the Murray and Wakool Rivers. Five golden perch travelled upstream between 13 and 35 km, four of which travelled to an area around the junction of the Murray River and Speewa Creek. The remaining four golden perch undertook localized movements of <5 km. Many of the long distance movements undertaken in spring 2000 were rapid and 53% of these golden perch returned to within 3 km of their release locations, indicating homing behaviour. Given that the rapid movements of golden perch in spring coincided with the known spawning season of this species, these long distance movements may be associated with reproductive strategy.     

Summer use of a small stream by fish and crayfish and exchanges with adjacent lentic macrohabitats

1. Movements between a stream reach and two adjacent lentic macrohabitats, a beaver pond and a lake, were followed for the Appalachian crayfish and two fish species, brook charr and brown bullhead, over an 85‐d period from early June to late August, and were analysed in relation to water level, maximum water temperature, photoperiod length, lunar luminosity, and age, by use of time‐series regressions. 2. Brook charr showed strong net immigration to the stream reach for underyearling (age class 0+) fish but net emigration for 1+ fish. Both immigration and emigration were positively related to water level and temperature; migratory responses to temperature were age‐specific. 3. Brown bullhead used the stream primarily as a corridor for downstream migration from the beaver pond to the lake. As with brook charr, water level and temperature had a positive effect on movement and responses were stronger in younger individuals. 4. Crayfish emigrated from the stream during the summer. Movements were positively related to increases in water level and temperature, with responses of 1+ crayfish much stronger than those of older individuals. 5. The results indicate that the stream tributary played different roles for brook charr (nursery), brown bullhead (dispersal corridor) and Appalachian crayfish (early summer refuge), and suggest that variation in water level or temperature resulting from climatic change or local anthropogenic activities might modify connectivity between macrohabitats, particularly for younger individuals.     

Variation in brook and brown trout survival within and among seasons, species, and age classes

The Program MARK was used to generate and test a plausible set of survival models for brook trout Salvelinus fontinalis and brown trout Salmo trutta to determine whether survival differed by season, species or age class. Apparent survival varied with time and age, but not by species. For the older (1999) age class, survival was lowest during the autumn of their age 1+ year whereas survival was lowest for the younger (2000) age class during the early summer of their age 1+ year. Additionally, estimates of survival for the younger age class exceeded those of the older age class in all but one interval (early summer 2001) but significant differences were observed in only one of these intervals (autumn 2000). To determine whether the observed seasonal differences in survival were related to seasonal differences in movement rates, multi‐strata spatial models were used within Program MARK to determine the probability of moving for each interval. In‐site movement rates were found to be low regardless of season (average for all cohorts combined was 5%). The ability of the multi‐strata modelling approach to detect temporal variability in movement, however, was potentially limited by spatial scale of the study reach ( c . 1 km). Differences in survival between different aged fishes could lead to selection acting on age at maturity or reproductive effort at a given age.     

Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22–30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.     

Mismatch between fishway operation and timing of fish movements: a risk for cascading effects in partial migration systems

Habitat fragmentation is a growing problem worldwide. Particularly in river systems, numerous dams and weirs hamper the movement of a wide variety of species. With the aim to preserve connectivity for fish, many barriers in river systems are equipped with fishways (also called fish passages or fish ladders). However, few fishways provide full connectivity. Here we hypothesized that restricted seasonal opening times of fishways can importantly reduce their effectiveness by interfering with the timing of fish migration, for both spring‐ and autumn‐spawning species. We empirically tested our hypothesis, and discuss the possible eco‐evolutionary consequences of affected migration timing. We analyzed movements of two salmonid fishes, spring‐spawning European grayling (Thymallus thymallus) and autumn‐spawning brown trout (Salmo trutta), in Norway's two largest river systems. We compared their timing of upstream passage through four fishways collected over 28 years with the timing of fish movements in unfragmented river sections as monitored by radiotelemetry. Confirming our hypothesis, late opening of fishways delayed the migration of European grayling in spring, and early closure of fishways blocked migration for brown trout on their way to spawning locations during late autumn. We show in a theoretical framework how restricted opening times of fishways can induce shifts from migratory to resident behavior in potamodromous partial migration systems, and propose that this can induce density‐dependent effects among fish accumulating in lower regions of rivers. Hence, fragmentation may not only directly affect the migratory individuals in the population, but may also have effects that cascade downstream and alter circumstances for resident fish. Fishway functionality is inadequate if there is a mismatch between natural fish movements and fishway opening times in the same river system, with ecological and possibly evolutionary consequences for fish populations.     

Temporal variability of pelagic fish assemblages around fish aggregation devices: biological and physical influences

Pelagic fishes were counted around four fish aggregation devices (FADs) moored between 3 and 10 km offshore on the continental shelf off Sydney, Australia. Visual counts were made at FADs on 81 days periodically from April 1999 to April 2002. Surface water temperature and current speed were also measured at the FADs. Assemblages of fishes at FADs followed a seasonal pattern, however, biological and physical variables influenced seasonal structure greatly. Abundances at FADs were greatest in spring due to the appearance of large schools (100s to 1000s) of juvenile Trachurus sp. In contrast, diversity was far greater in summer and autumn, principally due to the appearance of schools (10s to 100s) of juvenile Coryphaena hippurus (Coryphaenidae), and other warm water species from January to May when water temperatures were >20° C. Short‐term variability differed among species; C. hippurus fluctuated greatly among counts separated by 2–3 days, while Seriola lalandi (Carangidae) and Alutera monoceros (Monacanthidae) abundances were more stable, indicating greater residence times at FADs for these two species. Marked differences in fish assemblages occurred between times when predators were present and absent, with few small fishes being observed when piscivorous predators occurred at FADs, regardless of season. Furthermore, abundances of C. hippurus and A. monoceros were correlated with current speed, with greatest abundances observed when currents were strong and weak, respectively. The results indicated that much of the temporal variability in fish assemblages at moored FADs could be explained by biological and physical factors.     

Temporal and Spatial Habitats of Anadromous Brook Charr in the Laval River and its Estuary

Anadromy in brook charr occurs across the species’ range, but few studies have examined contiguous seasonal movements and habitat utilization of freshwater and estuarine environments. We used acoustic telemetry to track movements of anadromous brook charr for 1 year in the Laval River, Quebec. Fish entered the marine environment in May and June, inhabited shallow (<1.7 m), near-shore areas (<500 m from shore), and rarely ventured beyond the headlands of the bay. They were found where salinities were 1–34 ppt and temperatures 5–18°C. There was a strong tidal periodicity to observed movements with fish running up into bays as they became inundated at high tide and then returning to deep river channels in the bays at low tide. Between late July and early September, the charr returned to freshwater and spawned in the middle and upper sections of the river in October and November. Winter habitats were dispersed over 22 km of the river including two lakes. These detailed observations are an important contribution to our understanding of the evolutionary significance of anadromy in this species. The salinity and temperature co-tolerance provides insights into the species’ post-glacial dispersal, present-day distribution, and potential habitat maps for conservation, restoration, and enhancement programmes.     

Fish, climate and the Gulf Stream: the influence of abiotic factors on the recruitment success of cyprinid fishes in lowland rivers

1. Climatic effects are increasingly being recognised as an important factor causing inter‐annual variability in organism abundances in aquatic and terrestrial ecosystems. This study investigated the relationships between water temperature (cumulative degree‐days >12 °C), river discharge (cumulative discharge‐days above basal discharge rate), the position of the North Wall of the Gulf Stream (NWGS), and the 0+ growth (September mean length) and recruitment success (year‐class strength, YCS) of three species of cyprinid fishes in two contrasting English lowland rivers, using a 21‐year dataset. 2. Contrary to the majority of studies on 0+ fishes, growth in the Yorkshire Ouse was most significantly correlated with river discharge, with water temperature of less importance. By contrast, temperature was more influential than discharge in the River Trent, possibly because of its regulated hydrological regime, although none of the relationships were statistically significant for this river. 3. Year‐class strength of roach (Rutilus rutilus) was positively correlated with the position of the NWGS, and there was evidence of synchrony in recruitment success between rivers, but the relationships were poorer for chub (Leuciscus cephalus) and dace (Leuciscus leuciscus). The strongest relationships between YCS and discharge during specific time periods were for when the fish were in their early (especially larval) developmental stages, although none of the relationships were statistically significant because of inter‐annual variations in river discharge relative to the timing of fish hatching. 4. Fishes are key predators in the majority of aquatic ecosystems and, as such, fluctuations in their abundances can have implications for ecosystem functioning as a whole. This study has demonstrated an underlying influence of broad‐scale climatic effects on the recruitment of riverine fishes, in spite of local variations in biotic and abiotic conditions. The relative importance of various abiotic factors on the recruitment success of riverine cyprinid populations varies spatially and temporally. For example, river discharge is likely to be of relatively greater importance in poorly‐structured rivers or those that are prone to large and rapid fluctuations in flow, while temporal variations occur because of inter‐annual differences in river discharge relative to the timing of fish hatching. Biotic factors may also be important determinants of fish recruitment success, especially in rivers with stable and predictable flow regimes.     

The upstream migratory behaviour of salmonids in the River Frome, Dorset

Data on the migratory behaviour of salmonids were collected at a gauging weir by means of a restivity fish-counter which triggered a motor-driven 35 mm still camera to provide photographic records of passing fish. A clear bimodal seasonal pattern of movement was observed in three consecutive years with peaks during June–August and October–December. Daily variations in the rate of movement could not be correlated with changes in discharge or temperature. Salmonids tended to move at discharges lower than those generally available. This contrasts with other published work and was attributed to the more equitable flow-pattern of chalk rivers. There was no optimal temperature associated with movements. Some evidence suggested that the largest fish moved earlier in the year but this was not marked. In clear water most movement occurred during the hours of darkness but during floods, when the river was turbid, the diurnal pattern tended to be reversed with greatest movement during the hours of daylight. Most fish negotiated the weir close to the bottom, well below mean velocity, and took a central path through the flume. Although analysis of upstream migratory behaviour was hindered by the lack of data on the numbers of fish available below the counting point it was concluded that the basic pattern of migration is established by time (season). Changes in discharge, light intensity and other parameters may then play a secondary role in modifying the details of the pattern but attention is drawn to records of movements in regulated flows where a remarkably constant pattern is shown from year to year.     

Prey size,prey abundance,and temperature as correlates of growth in stream populations of cutthroat trout

Growth and maximum size of stream fishes can be highly variable across populations. For salmonid fishes in streams, individuals from populations confined to headwater streams often exhibit small size at maturity in comparison to populations with access to main-stem rivers. Differences in prey size, prey availability, and metabolic constraints based on temperature may explain patterns of maximum size and growth. In this study, cutthroat trout from headwater stream populations that were isolated above a waterfall were compared to individuals from populations in similar sized streams without a movement barrier and from large main-stem rivers. Cutthroat trout from smaller streams with or without a movement barrier were significantly smaller at a given age than fish from main-stem rivers, where individuals were able to achieve a much larger maximum size. Comparisons of invertebrate drift abundance and size in the three types of streams revealed that drift size did not differ between stream categories, but was highest per volume of water in large main-stem rivers. Across all stream types, prey abundance declined from summer to fall. Temperature declined over the course of the season in a similar manner across all stream types, but remained relatively high later in the season in main-stem river habitats. Prey availability and temperature conditions in main-stem rivers may provide more optimal growing conditions for fish as individuals increase in size and become constrained by prey availability and temperature conditions in small streams. Maintaining connectivity between small spawning and rearing tributary streams and main-stem river habitats may be critical in maintaining large-bodied populations of stream salmonids.     

Comparison of brook trout reproductive success and recruitment in an acidic adirondack lake following whole lake liming and watershed liming

Limestone applications to the catchment of one tributary to Woods Lake were highly effective in reducing stream acidity and stabilizing seasonal fluctuations in pH. The resulting improvement in stream water quality also led to a dramatic shift in reproductive strategy of the Woods Lake brook trout population. Prior to catchment liming, brook trout in Woods Lake were restricted to spawning on poor quality near shore substrate with limited ground water seepage. Reproductive success was limited by high mortality of eggs and larvae and recruitment from in lake spawning was not successful. Spawning brook trout did not utilize the tributary for spawning prior to watershed liming. Mitigation of acidity in the tributary, by catchment liming, effectively extended the spawning habitat available to the Woods Lake brook trout population and one year following treatment brook trout spawned successfully in the tributary for the first time in 6 years of observation. Significant recruitment of young trout into the lake population occurred from 1991 through 1993, although the absolute number of fish captured was relatively small. In the fall of 1993, four year classes of naturally spawned brook trout were present in the lake. Although reproductive success was enhanced by improving tributary spawning habitat in the Woods Lake basin, self maintenance of the population may be limited by low recruitment rates of young trout, due to high levels of summer mortality resulting from predation. Mitigation of this constraint would require substantially higher levels of fry production than were observed in Woods Lake and/or enhanced refugia for young trout. The results of this experiment suggest that re-establishment of tributary spawning populations of brook trout may be possible, with future reductions in acidic deposition, in acidic Adirondack lakes with limited in-lake spawning habitat.     

Movement patterns of the round stingray Urobatis halleri(Cooper) near a thermal outfall

Fine‐scale movements and site fidelity of round stingrays Urobatis halleri at Seal Beach California, U.S.A., were examined using acoustic telemetry. Actively tracked fish generally exhibited limited nearshore movement, with greater distances travelled at night when the tide was ebbing than during the day with ebbing tides. Increases in round stingray activity were associated with increases in ambient temperature. Passively tracked fish showed seasonal patterns in their presence at Seal Beach. Males left Seal Beach during the autumn, returned the following spring, and remained in the area until the following autumn. Females spent far less time at Seal Beach, remaining in the area for a few weeks during June and July. Passively tracked round stingrays were recorded more often in the warm waters of the San Gabriel River mouth (the location of a thermal outfall from an electric‐generating station) than adjacent beaches, with fish often returning to Seal Beach after periods of absence. Anthropogenic effects resulting from coastal development may have created environmental conditions ( i.e . warmer water and finer sediments) that influence the movements and site fidelity of round stingrays.     

Occurrence Patterns,Habitat Associations,and Potential Prey of the River Dolphin,Inia geoffrensis,in the Cinaruco River,Venezuela1

The distribution, habitat association, group size, population structure, and prey availability of river dolphins (Inia geoffrensis) were studied from November 1993-June 1994 in the Cinaruco River, a tributary of the Orinoco River that forms the southern boundary of Venezuela's Santos Luzardo National Park. Dolphins were sampled from a boat using modified strip-width transects, for a total of 418 h. The study area was 1.67 km², and contained 20 km of water courses. Like other rivers of this region, the Cinaruco River undergoes a seasonal flood cycle. Dolphins were seen most often during the period of falling water (41% of total sightings) and least often during the rising water period (24% of total sightings). Dolphins were seen most often in confluence areas (35% of total sightings) and were seldom seen in side channels (13% of total sightings). The presence of rocks or sandbanks was associated with a greater frequency of dolphin sightings, and sightings increased with habitat heterogeneity. Average group size for the 8-mo study was 2.0 (±1.0) and was largest during the rising water period. Calves were first sighted during the end of the dry season and became more common during the early flood season. Six individuals were photo-identified and resighted with one sighted eight times over 186 d. The fish diversity of the study area was high, with 161 species documented in our samples. The stomach of one Inia contained 15 fishes representing at least 4 species.     

澜沧江梯级开发下鱼类支流生境替代效果

作为干流高坝水电开发导致鱼类生境丧失的一种补偿措施,支流替代生境近年来被广泛应用于受工程影响河段的土著鱼类保护,但替代支流发挥怎样的保护效果及干流对其的影响仍不清楚。以实施了澜沧江梯级生境替代的支流基独河与罗梭江为研究对象,并选择了邻近的对照支流,通过对鱼类调查数据的分析对比,揭示了各支流鱼类种类组成与群落结构的差异特征,初步阐明了梯级开发下鱼类支流生境替代效果以及干流工程建设对其的影响。结果表明：澜沧江支流替代生境对干流鱼类具有明显的保护作用,支流生境修复后鱼类物种丰富度明显提高,罗梭江土著鱼类、特有鱼类物种数分别增加了12种、7种,基独河则是7种、2种,替代生境能为澜沧江土著鱼类、部分濒危特有鱼类和洄游鱼类提供完成生活史的关键栖息地。干流对支流生境替代保护有着重要影响,罗梭江、基独河与邻近干流鱼类群落的Bray-Curtis相似性分别为21.76%、10.73%,支流河口段保持“河相”是支流生境替代保护效果可持续的关键。综合考虑生境替代保护的效益与投入,建议今后开展此类保护措施时优先选择库尾河相区的支流。     

Abundance and movement patterns of age-0 juvenile lake sturgeon in the Peshtigo River,Wisconsin

In Great Lakes tributaries, age-0 juvenile lake sturgeon Acipenser fulvescens use riverine nursery habitats during their first summer of life and migrate to adjacent lakes after a seasonal decline in water temperature. We used mark-recapture data collected during this river-residency phase to monitor patterns in juvenile abundance and movement in the Peshtigo River, Wisconsin, during 2006 and 2007. Jolly-Seber and multistate models were used to estimate abundance and describe the probability of movement between river sections. Juvenile abundance was higher in 2007 than in 2006; however, in both years, abundance at the end of the sampling season was lower than at the beginning. Downstream movements were observed more frequently than upstream movements, and the probability of a downstream movement was higher than the probability of an upstream movement. The lower abundance later in the sampling season and propensity for downstream movements suggests that some age-0 juvenile lake sturgeon may leave the natal river before a seasonal decline in water temperature.