Timing of migration and changes in age structure of Atlantic salmon, Salmo salar L., in the River Frome, a Dorset chalk stream, over a 24-year period

During the last 24 years, the number of Atlantic salmon, Salmo salar L., migrating up the River Frome has varied between < 1000 and > 4000 fish per annum. Most parr become smolts at age 1+ and there are three main sea ages of salmon returning to the river. Each sea age shows a bimodal pattern of migration in the river. Primary migration times for 3-sea-winter (3SW) fish are spring and autumn, with 2SW fish and grilse (1SW) peaking in summer and autumn. Some 28.4% of 3SW and 6.9% of 2SW fish are previous spawners. Multi-sea-winter fish historically passed over the counter in all months of the year, but recently, their numbers have declined, as have total numbers of fish of all ages. There has been a fundamental change in the age structure of the population, with grilse increasing in proportion over the study period. Photographs of fish, taken for validation of the counter, showed a significant decrease in mean length of grilse, but an increase in mean length for 2SW and 3SW fish. Rod catch data support these findings.     

Stream habitat use and diet of juvenile (0+) brown trout and grayling in sympatry

Abstract – Electrofishing survey data and experiments carried out in a semi-natural stream were used to test the hypothesis that interactions between underyearling (0+) trout and grayling during their first summer affect habitat use and diet. The survey data revealed a general difference in habitat use, with 0+ grayling being more common than 0+ trout in large streams and deeper sections. It was also found that in the presence of trout, finer substrate and shallower sections were utilised more by grayling. Field experiments were carried out with three treatments; trout alone, grayling alone and the two species together. In both the July and September experiments grayling tended to occupy deeper sections than trout. Trout abundance was higher in shallow areas in sympatry, while no such difference was found in allopatry. The rate of disappearance of grayling from the study sections was significantly higher in sympatry in July, while no difference was found in September. In July the size difference between species and the degree of dietary overlap were small and non-significant, respectively, indicating that the two species were strongly competing. ^Note     

The effects of an underwater fish observation technique on stream macroinvertebrates at two spatial scales

Abstract – We examined the effects of snorkeling, a commonly used fish observation technique, on the distribution and abundance of benthic macroinvertebrates at both the reach (i.e., 10 m) and patch scale (i.e.,< 1 m) within a southern Appalachian stream (North Carolina, USA). At the reach scale, we quantified increases in macroinvertebrate drift rates associated with snorkeling and used these values to calculate the percentage of the macrobenthos that drifted out of snorkeled reaches. We also used a simple decay model of macroinvertebrate drift to quantify patch scale effects of snorkeling. The model incorporated size specific macroinvertebrate settling rates to estimate the total number of benthic macroinvertebrates that entered the drift in response to snorkeling disturbance. We found that snorkeling consistently produced significant increases in the number of drifting macroinvertebrates. Nevertheless, these increases comprised a very small percentage (<1%) of the total number of organisms in the benthos, suggesting that snorkeling probably did not strongly affect macroinvertebrate assemblages at either the reach or patch scale. However, our analyses also indicated that snorkeling had a disproportionate effect on the drift of small ephemeropterans (4–5% entered the drift in response to snorkeling) relative to other macroinvertebrate taxa. Consequently, the microdistribution of early instar mayflies may have been altered within snorkeled reaches. We conclude that snorkeling related disturbance to the benthos should have a minimal effect on the behavior and distribution of most stream fishes at either the reach or patch scale. However, because snorkeling had a substantial effect on the drift of small mayflies, snorkeling may influence the behavior of fishes that depend on early instar mayflies as a primary food resource. ^Note     

The onset of downstream movement of juvenile Atlantic salmon, Salmo salar L., in a chalk stream

The downstream movements of wild Atlantic salmon, Salmo salar L., from their established feeding territories in the River Itchen, Hampshire, UK, were logged continuously over an 11-month period using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. Initial downstream movement of smolts in April was correlated with the onset of darkness, at which time salmon moved from their established feeding territories alone. No relationship was found between the number of smolts migrating and river flow or maximum daily water temperature. The timing of downstream movement of parr between October and March was random with regard to sunset and time of maximum daily water temperature, suggesting the environmental cue that initiates movement may be different outside the spring smolt period.     

Challenges in the conservation,rehabilitation and recovery of native stream salmonid populations: beyond the 2010 Luarca symposium

Abstract – In May 2010, I chaired a session on challenges to salmonid conservation at the international symposium ‘Advances in the population ecology of stream salmonids’ in Luarca, Spain. I suggested that in addition to scientific challenges, a major challenge will be improving the links between ecologists, conservationists and policy makers. Because the Luarca symposium focused mainly on ecological research, little time was explicitly devoted to conservation. My objective in this paper is to further discuss the role of ecological research in informing salmonid conservation. I begin with a brief overview of research highlights from the symposium. I then use selected examples to show that ecological research has already contributed much towards informing salmonid conservation, but that ecologists will always be faced with limitations in their predictive ability. I suggest that conservation will need to move forward regardless of these limitations, and I call attention to some recent efforts wherein ecological research has played a crucial role. I conclude that ecologists should take urgent action to ensure that their results are available to inform resource managers, conservation organisations and policy makers regarding past losses and present threats to native, locally‐adapted salmonid stocks.     

Effects of exotic salmonids on juvenile Atlantic salmon behaviour

Abstract –  We examined the effects of two salmonid species, chinook salmon ( Oncorhynchus tschwaytscha ) and brown trout ( Salmo trutta ), both exotic species to Lake Ontario, on behaviour and foraging success of juvenile Atlantic salmon ( S. salar ), a native species to Lake Ontario, in an artificial stream. We found that both exotic species have effects on Atlantic salmon behaviour, but that neither had an effect on foraging success. These results may explain why the Atlantic salmon re-introduction programme in Lake Ontario has had little success, as more than 3 million exotic salmonids are released in Lake Ontario streams annually.     

Density of juvenile brown trout and Atlantic salmon in natural and man-made riverine habitats

The density of juvenile brown trout (Sulmo trutta L.) and Atlantic salmon (Salmo salar L.) was significantly higher along river bank areas protected against erosion than along natural river banks in the River Gaula, Central Norway. A habitat shift appeared in Atlantic salmon, and a behavioural shift was demonstrated by brown trout from August October. The effect of habitat on densities of juvenile salmonids should be taken into account as mitigation measures on eroded river banks and when assessing fish production in rivers.     

The effects of stream substratum composition on the emergence of salmonid fry

Sternecker K, Geist J. The effects of stream substratum composition on the emergence of salmonid fry.
Ecology of Freshwater Fish 2010: 19: 537–544. © 2010 John Wiley & Sons A/S Abstract – Salmonid fishes are target species for the conservation of freshwater habitats, but their natural reproduction is often insufficient. The emergence of fry is a crucial phase in the life cycle of salmonids and the stream substratum is the key habitat which regulates the emergence success. In this study, brown trout (Salmo trutta) and Danube salmon (Hucho hucho) eggs were exposed to different sediment textures and the emergence and the postemergence survival and growth were observed under constant water chemical conditions in the laboratory. In both species, textural effects on emergence rate, chronology of emergence, survival rate after emergence and growth after emergence were detected. Fine‐textured substratum (5–8 mm) formed a physical barrier to the posthatch migration of salmonids from the interstitial zone to the open water. The time period between the first and the last emerged fish was shorter in treatments with fine texture compared with coarse substratum. The survival rate was higher in treatments of coarser sediment. The effects of different textures on the growth of fry after emergence differed between brown trout and Danube salmon, which can be explained by different life history strategies. These results suggest that physical characteristics of substratum texture can have strong effects on salmonid emergence, and ultimately on the persistence of salmonid populations. They also suggest that biodiversity conservation in stream ecosystems can greatly benefit from an inclusion of the physical characteristics of the stream bed into catchment‐based management plans.     

Survival and bioenergetic responses of juvenile Atlantic salmon along a perturbation gradient in a natural stream

Abstract – We tested the effects of a pollution gradient on the survival and energetic responses of Atlantic salmon fry stocked in Onondaga Creek, a historic but highly polluted nursery stream. A relatively unperturbed reference stream provided similar physical and thermal gradients that co-varied longitudinally with the pollution gradient in Onondaga Creek, and macroinvertebrate communities provided indices of water quality degradation. Survival, cohort biomass, instantaneous growth rate and growth index of Atlantic salmon were inverse functions of water quality in the perturbed stream. Generally, survival and energetic parameters of Atlantic salmon responded differently to longitudinal gradients in the two streams, indicating that water quality, rather than habitat variation, exerted the strongest control over salmon. Effects were more pronounced during the early summer, possibly because tolerance to such perturbations increases with age or body size. Energetics-related parameters were more sensitive to water quality than were survival-related parameters, indicating that sub-lethal effects of pollution may be detected and quantified by examining energy balances of individuals.     

Effect of habitat type on growth and diet of brown trout, Salmo trutta L., in stream enclosures

The effect of habitat on the growth and diet of brown trout, Salmo trutta L., stocked at the same densities in nine stream enclosures, comprising three habitat types of different quality, were tested. The habitats, which were created based on microhabitat preference data, were a shallow water habitat lacking cobbles (habitat 1), a deeper, mixed cobble-bottomed (128-384 mm diameter) habitat (habitat 2) and a large cobble-bottomed (256-384 mm) habitat of intermediate depth (habitat 3). Brown trout were found to have greater increases in total biomass in habitats 2 and 3 than in habitat 1. The pattern for length did not follow that of biomass as trout had greater increases in total length in habitat 2 than in the other two habitats. Biomass of food in trout diets reflected habitat-specific fish biomass changes, with a greater total biomass of prey as well a greater biomass of the leech, Erpobdella, in habitats 2 and 3 than in habitat 1. There were no habitat-specific differences in the biomass of benthic or drifting invertebrates in the enclosures, with the exception of a tendency for an effect of habitat on the biomass of Erpobdella. Although there may have been habitat-specific differences in food resources that were not detected, it is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.     

渔洞水库大型无脊椎动物群落结构及其与环境关系的初步调查

于2009年12月、2010年3月、6月和9月共4次对渔洞水库的大型无脊椎动物进行了调查,共采集到动物19个分类单元,隶属于3门3纲5科16属。其中,寡毛类、水生昆虫及软体动物等主要类群分别记录6种(占总物种数的31.6%)、12种(63.2%)和1种(5.3%)。大型无脊椎动物密度优势类群主要为霍甫水丝蚓(Limnodrilus hoffmeisteri Claparède)、前突摇蚊(Procladius sp.)和长跗摇蚊(Tanytarsus sp.)。渔洞水库的大型无脊椎动物在冬春季的现存量较夏秋季高,库湾的多样性高于主体库区。多余度分析(RDA)显示,水深和溶氧是影响渔洞水库无脊椎动物群落分布的关键环境因子。4次调查中寡毛类密度均未超过1 000 ind./m2,水质属轻度污染。     

Population size in stream-living juveniles of lake-migratory brown trout Salmo trutta L.: the importance of stream discharge and temperature

Abstract –  Based on the analysis of 17 successive year-classes, this investigation attempted to identify the factors determining year-to-year variation in population size of the stream-living juveniles of Lake Hald-dwelling brown trout Salmo trutta L. Population size appeared to be influenced chiefly by annual recruitment that in turn, was determined by stream discharge and temperature. These patterns matched those previously highlighted for a resident population located >2500 km apart and emphasised the importance of environmental (climatic) variability as a major regulating agent of population size in stream brown trout. However, distinctly shaped recruitment–discharge relationships between the two populations suggested different mechanisms in response to environmental variability and thus to persist in time.     

Qualitative and quantitative effects of reintroduced beavers on stream fish

Reintroduction of beaver (Castor spp) may facilitate rehabilitation of freshwater habitats providing a cost‐effective sustainable means of improving ecological conditions. Despite extensive research, debate and consultation, a general consensus on the impact of beaver on fishes has proven elusive because of variability in biological response. This paper provides a systematic review of the impacts of beaver dams on fishes and fish habitat based on a meta‐analysis of the literature and expert opinion. Research is regionally biased to North America (88%). The most frequently cited benefits of beaver dams were increased habitat heterogeneity, rearing and overwintering habitat and flow refuge, and invertebrate production. Impeded fish movement because of dams, siltation of spawning habitat and low oxygen levels in ponds were the most often cited negative impacts. Benefits (184) were cited more frequently than costs (119). Impacts were spatially and temporally variable and differed with species. The majority of 49 North American and European experts considered beaver to have an overall positive impact on fish populations, through their influence on abundance and productivity. Perceived negative effects related to the movement of aquatic organisms in tributary streams, including upstream and downstream migrating salmonids, and the availability of suitable spawning habitat.     

Diurnal stream habitat use of juvenile Atlantic salmon, brown trout and rainbow trout in winter

Abstract  The diurnal winter habitat of three species of juvenile salmonids was examined in a tributary of Skaneateles Lake, NY to compare habitat differences among species and to determine if species/age classes were selecting specific habitats. A total of 792 observations were made on the depth, velocity, substrate and cover (amount and type) used by sympatric subyearling Atlantic salmon, subyearling brown trout and subyearling and yearling rainbow trout. Subyearling Atlantic salmon occurred in shallower areas with faster velocities and less cover than the other salmonid groups. Subyearling salmon was also the only group associated with substrate of a size larger than the average size substrate in the study reach during both winters. Subyearling brown trout exhibited a preference for vegetative cover. Compared with available habitat, yearling rainbow trout were the most selective in their habitat use. All salmonid groups were associated with more substrate cover in 2002 under high flow conditions. Differences in the winter habitat use of these salmonid groups have important management implications in terms of both habitat protection and habitat enhancement.     

Restoration of dead wood in Basque stream channels: effects on brown trout population

Abstract – Streams in the Aiako Harria Natural Park (Basque Country, Spain) have excellent water quality, but are physically impoverished after centuries of snagging. In an attempt to restore channel complexity and ecosystem functioning, especially in‐channel retention of sediments and organic matter, large woody debris (LWD) was introduced into four mountain streams (channel width 3–13 m) following a before/after, control/impact (BACI) design. Logs were introduced by means of hand‐held machinery and located uncabled, mimicking the natural amount and disposition of LWD in streams. Floods disrupted most of the structures at the large stream, but caused little damage to those in the small ones. Only minnow and brown trout inhabit in the area. Before wood addition, trout densities were fairly high in the small streams, low in the large one, where recruitment seemed very poor. In the small tributaries, trout populations showed a strong imbalance towards young fish, adults being only found in the spawning season. Wood addition produced some interesting trends in trout, although statistical significance was low as a result of large environmental variability. Fish densities showed small changes, but biomass increased, especially in the spawning season. Also, there was a trend towards more aged 2⁺ or larger, thus suggesting wood addition improved adult habitat. Although restoring LWD is extremely unusual in Spain, the changes in physical habitat and the trends in fish populations detected in the present project suggest it is worth making more experiments, at least in safe settings where there is no risk of flooding or damaging properties.     

Growth and digestibility effects of soya lecithin and choline chloride on juvenile Atlantic salmon

Atlantic salmon, Salmo salar L., fingerlings with a mean weight of 1.5 g were fed one of four casein-gelatine-based purified diets supplemented with soya lecithin (LC) and choline chloride (CH) for 84 days. The diets were supplemented with either: 0 g kg⁻¹ CH and 0 g kg⁻¹ LC, 0 g kg⁻¹ CH and 30 g kg⁻¹ LC, or 5 g kg⁻¹ CH and 0 g kg⁻¹ LC, or 5 g kg⁻¹ CH and 30 g kg⁻¹ LC. The same diets were also fed to 100-g salmon to assess the effects of LC and CH supplementation on digestibility. Fingerlings fed the diet with neither LC nor CH (0 g kg⁻¹ LC and 0 g kg⁻¹ CH) grew at a significantly slower rate than fish fed the supplemented diets. There were significant effects on growth of supplementation of both LC and CH. The results indicate that the choline requirement of Atlantic salmon fingerlings is satisfied by 4 g kg⁻¹ inclusion in a gelatine-casein-based diet, and that dietary soya lecithin can fully replace choline chloride. The digestibility study with the larger fish indicated a beneficial effect of lecithin on the digestibility of both protein and energy.     

Effects of ambient acidity on chemosensory learning: an example of an environmental constraint on acquired predator recognition in wild juvenile Atlantic salmon (Salmo salar)

Abstract –  In many prey fish species, learning the identity of novel predators may be facilitated when novel predator cues and an aversive stimulus are presented together. Damage-released chemical alarm cues are typically released from the skin of prey individuals following mechanical damage and are known to mediate the learned recognition of novel predators. While such chemically mediated acquired predator recognition can provide increased survival benefits to prey, environmental constraints impeding learning may exist. For example, in several fish species the ability to detect chemical alarm cues is impaired in under acidic conditions and as such, inhibits this chemically mediated learning. In this experiment, we studied in two streams of different mean acidity level (pH c . 6.0 and 7.0), to assess if wild juvenile Atlantic salmon ( Salmo salar ) had the ability to acquire the recognition of a novel lemon essence odour when paired with conspecific chemical alarm cues. Our results demonstrate that under acidic conditions, no learned recognition of the novel odour occurred. In neutral conditions, however, salmon recognised the novel odour as a predation threat. This result suggests that ambient acidity creates an environmental constraint on chemically mediated learned recognition of a novel cue.     

The effects of riparian management and physicochemistry on macroinvertebrate feeding guilds and community structure in upland British streams

1. Patterns in the community structure and feeding guild composition among macroinvertebrates in the margins and riffles of 66 streams in upland Wales and Scotland were appraised and related to site chemistry, physiography and riparian management. We aimed to assess the effectiveness of riparian strips of broadleaves and moorland/grassland in protecting stream communities and their trophic function during commercial forestry. 2. The composition of macroinvertebrate communities in margins and riffles most strongly reflected stream pH and aluminium concentrations; acidic riffles contained fewest species of all major macroinvertebrate groups. However, the character of marginal habitats had some influence on communities in stream margins through the presence of broadleaf trees or moorland/grassland vegetation in the riparian zone. Even at low pH, streams with moorland riparian zones had different macroinvertebrates from those with pure conifer. 3. Stream chemistry was important in explaining patterns among feeding guilds. Species richness and abundances of grazers and filterers were reduced at acidic sites with high aluminium concentrations. The number of shredder species was significantly lower in riffles at low pH than at high pH. 4. In contrast, marginal habitat structure was of overriding importance in explaining patterns among collectors and predators. These functional groups were most abundant at sites with riparian zones of moorland and grassland, but scarce in streams where the bankside vegetation consisted of coniferous or broadleaved trees. Total grazer abundances were lowest at sites with riparian zones of pure conifer. 5. We conclude that riparian management can modify effects of forestry on the trophic dynamics and structure of the macroinvertebrate communities of upland streams, but the effect operates within a strong gradient due to acidity. Thus, the array of macroinvertebrates which may benefit from riparian management in forest streams is liable to be restricted by low pH. 6. We discuss the wider ramifications of riparian management for the conservation of streams during commercial forestry. In particular we assess if management proposals set out by the forestry industry are supported. We also discuss the problem of scale when considering measures implemented for stream conservation, emphasizing that the control of problems such as acidification may only be possible at a regional level.     

Effect of predation and habitat quality on growth and reproduction of a stream fish

Billman EJ, Tjarks BJ, Belk MC. Effect of predation and habitat quality on growth and reproduction of a stream fish.
Ecology of Freshwater Fish 2011: 20: 102–113. © 2010 John Wiley & Sons A/S Abstract – Anthropogenic disturbances are rarely independent, requiring native fishes to respond to multiple factors to persist in changing environments. We examined the interaction of predation environment (presence of introduced brown trout, Salmo trutta) and habitat quality on growth and reproduction of southern leatherside chub, Lepidomeda aliciae, a small‐bodied stream fish native to central Utah, USA. Southern leatherside chub were sampled from four streams representing a complete two‐factor cross of predation environment and habitat quality. Growth was estimated using increment analysis of annuli on otoliths, and reproductive traits were measured for both sexes. Southern leatherside chub growth was greater in high‐quality than in low‐quality habitats, and greater in predator than in nonpredator environments. However, fish exhibited a greater growth response to presence of brown trout in low‐quality habitats. Southern leatherside chub growth followed predictions of plastic responses to resource availability based on habitat quality and predation environment (lethal vs. nonlethal effects). Reproductive allocation (gonad wet mass) was significantly greater in low‐quality versus high‐quality habitats, but was unaffected by predation environment. Other female life‐history traits were affected either by both effects or their interaction. Reproductive responses to habitat quality and predation environment were consistent with predictions based on differential mortality. Southern leatherside chub growth and reproduction responded differently to the combination of habitat quality and predation environment, thus demonstrating the importance of assessing interacting effects of anthropogenic disturbances to more fully comprehend impacts on native species and to appropriately manage, recover and restore these species and their habitats.