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1.
Brown trout Salmo trutta L. parr were sampled from 21 Estonian and three Finnish streams to investigate whether national sea trout parr surveys sample the progeny of anadromous or resident maternal parents. Otolith Sr:Ca core values were used and validated as a tool for distinguishing between the progeny of the two forms. In Estonia (n = 283), 92% of the parr were the progeny of anadromous maternal parents, and 8% were the progeny of resident maternal parents, whereas in Finland (n = 24), the respective proportions were 79% and 21%. Variation in the maximum otolith Sr:Ca core values among progeny of anadromous maternal parents indicated that some adult females may enter fresh waters several months before spawning. It was concluded that easily accessible locations situated up to 30 km from the sea largely contain progeny of sea trout, whereas sites with poor connectivity with the sea can be dominated by progeny of resident trout. This study demonstrated that the method applied provided an effective means to distinguish between the progeny of sea trout and resident brown trout.  相似文献   

2.
Landlocked Atlantic salmon (ouananiche, Salmo salar) spawning migration timing varies throughout its range and is influenced by a variety of environmental variables. This study examined the spawning migration time of landlocked Atlantic salmon in a small (4 ha) constructed stream linked to a large reservoir (32,600 ha) in Newfoundland, Canada. Salmon use of the stream was passively monitored using Passive Integrated Transponder (PIT) Tags from 2006 to 2012. Of the salmon tagged throughout the reservoir, 48% entered the stream during the spawning season and remained there for 18–36 days from late September to November before they returned to the reservoir. Most fish entered the stream at dusk (32%). The lunar cycle influenced the timing of migration each year. Mean stream discharge (cubic metres per second) influenced migration timing in some years, and water temperature appeared to have minimal impact on migration timing. Twenty per cent of fish migrated to the stream in multiple years and 51% of these individuals appeared to use the stream on a biennial or alternate year cycle. These results demonstrate that small constructed streams can attract salmon from throughout a large reservoir and can provide valuable habitat in areas where spawning habitat is limited.  相似文献   

3.
The first evidence of proliferative kidney disease (PKD) in an Austrian river (the River Kamp) was documented in 2016, and no information on the PKD infection status of trout in other rivers was available. Since then, brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) have been collected from rivers in Upper and Lower Austria for different diagnostic purposes. In this study, we summarize the recent findings of a first survey concerning the distribution of Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), from these samples. Between September 2015 and October 2017, a total of 280 brown trout and 39 rainbow trout were collected from 21 rivers in the provinces of Upper and Lower Austria. T. bryosalmonae was detected by PCR of kidney tissue in 17 of 21 sampled rivers and in 138 of 280 brown trout as well as in 11 of 39 rainbow trout. Pathological signs of PKD (e.g., hypertrophy of the kidney) were observed in 33 analysed brown trout and six rainbow trout samples. No correlations between fish infected by T. bryosalmonae and the parameters size and age class, condition factor, geological origin of the streams and distribution within the river course were found, while positively tested fish are significantly increased at sampling sites exceeding water temperatures of 15°C for median periods of 115 days. The prevalence within the affected streams or stream sections is highly variable, and in single rivers, infection rates of up to 90% are confirmed.  相似文献   

4.
Abstract– Habitat is important in determining stream carrying capacity and population density in young Atlantic salmon and brown trout. We review stream habitat selection studies and relate results to variable and interacting abiotic and biotic factors. The importance of spatial and temporal scales are often overlooked. Different physical variables may influence fish position choice at different spatial scales. Temporally variable water flows and temperatures are pervasive environmental factors in streams that affect behavior and habitat selection. The more frequently measured abiotic variables are water depth, water velocity (or stream gradient), substrate particle size, and cover. Summer daytime, feeding habitats of Atlantic salmon are size structured. Larger parr (>7 cm) have a wider spatial niche than small parr. Selected snout water velocities are consistently low (3–25 cm. s?1). Mean (or surface) water velocities are in the preferred range of 30–50 cm. s?1, and usually in combination with coarse substratum (16–256 mm). However, salmon parr demonstrate flexibility with respect to preferred water velocity, depending on fish size, intra- and interspecific competition, and predation risk. Water depth is less important, except in small streams. In large rivers and lakes a variety of water depths are used by salmon parr. Summer daytime, feeding habitat of brown trout is also characterized by a narrow selection of low snout water velocities. Habitat use is size-structured, which appears to be mainly a result of intraspecific competition. The small trout parr (<7 cm) are abundant in the shallow swift stream areas (<20–30 cm depths, 10–50 cm. s?1 water velocities) with cobble substrates. The larger trout have increasingly strong preferences for deep-slow stream areas, in particular pools. Water depth is considered the most important habitat variable for brown trout. Spatial niche overlap is considerable where the two species are sympatric, although young Atlantic salmon tend to be distributed more in the faster flowing and shallow habitats compared with trout. Habitat use by salmon is restricted through interspecific competition with the more aggressive brown trout (interactive segregation). However, subtle innate differences in behavior at an early stage also indicate selective segregation. Seasonal changes in habitat use related to water temperatures occur in both species. In winter, they have a stronger preference for cover and shelter, and may seek shelter in the streambed and/or deeper water. At low temperatures (higher latitudes), there are also marked shifts in habitat use during day and night as the fish become nocturnal. Passive sheltering in the substrate or aggregating in deep-slow stream areas is the typical daytime behavior. While active at night, the fish move to more exposed holding positions primarily on but also above the substrate. Diurnal changes in habitat use take place also in summer; brown trout may utilize a wider spatial niche at night with more fish occupying the shallow-slow stream areas. Brown trout and young Atlantic salmon also exhibit a flexible response to variability in streamflows, wherein habitat selection may change considerably. Important topics in need of further research include: influence of spatial measurement scale, effects of temporal and spatial variability in habitat conditions on habitat selection, effects of interactive competition and trophic interactions (predation risk) on habitat selection, influence of extreme natural events on habitat selection use or suitability (floods, ice formation and jams, droughts), and individual variation in habitat use or behavior.  相似文献   

5.
Abstract – Strontium (Sr) content of eggs collected from redds were used to determine the spawning contribution of resident and anadromous female brown trout in the Taieri River, New Zealand and were analysed on the catchment and tributary scale. At the catchment scale, analysis of Sr showed differences between eggs collected above and below the Taieri River Gorge. Samples collected above the gorge all had low‐Sr concentrations similar to levels found in an entirely resident brown trout population. Samples collected below the gorge exhibited a broad range in Sr concentrations, ranging from levels comparable to the known anadromous samples to levels comparable to the known freshwater‐resident samples. This suggests that the gorge prevents upstream migration by anadromous brown trout in the Taieri River. At the tributary scale, this pattern of anadromous brown trout spawning downstream of freshwater‐resident fish was repeated in one of the two tributaries located downstream of the gorge. Energetic cost of migration is the most likely explanation for the observed patterns in catchment and tributary scale distribution of spawning by resident and anadromous brown trout. It is concluded that the use of Sr concentrations in eggs collected from redds is a cost‐effective and reliable method to investigate the spawning contribution by anadromous brown trout.  相似文献   

6.
The temperatures of stream water and hyporheic water were monitored in spawning areas of an upland stream (Girnock Burn) and a degraded lowland stream (Newmills Burn). Both streams are located in North-east Scotland and are spawning streams for Atlantic salmon, Salmo salar L., and brown trout, S. trutta L. Monitoring between the spawning and hatching of ova revealed significant differences in the thermal regimes of the two sites. Whilst temperatures in stream and hyporheic water were similar in the Girnock, notable attenuation in the Newmills Burn resulted in increasing moderation of thermal regime with hyporheic depth. This probably reflects contrasting groundwater–surface water interactions in the two systems. In the Girnock an open gravel stream bed and lack of groundwater influence resulted in stream water downwelling through the gravel. In contrast, fine bed sediments and local groundwater inputs resulted in more complex stratification of temperatures in Newmills Burn. However, even in the conditions of the Newmills Burn, temperature based salmonid embryo development models predicted that egg burial depth has an insubstantial effect on ova development.  相似文献   

7.
In‐stream wood can increase shelter availability and prey abundance for stream‐living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in‐stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small‐sized trout. In a laboratory stream experiment, we tested the behavioural response of young‐of‐the‐year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four‐fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others.  相似文献   

8.
Gathering information on both individual movement and gene flow is rarely possible when studying dispersal among populations in fish species. It is, however, possible to assess both at a reasonable cost in Salmo trutta L. on the Atlantic coast of Europe where the facultative anadromous species is composed of discrete populations of brown trout residents occupying distinct river systems, but exchanging phenotypically distinguishable sea trout migrants. We performed two kinds of genetic analyses using individual microsatellite genotypes: the stock identification of sea trout entering each corridor and the estimates of effective dispersal through each corridor. We observed that individual movement (nonlocal individuals of each source population ranging from 4% to 35% of the sea trout run) never translates into effective dispersal except in one of four migratory corridors examined. The likely origin of this uniquely detected gene flow event is discussed in the light of well‐documented migratory fish management actions undertaken in the past in the studied area.  相似文献   

9.
The anadromous, or sea‐going, life history form of brown trout, or sea trout ( Salmo trutta), may lead to potential mixing of populations while foraging at sea. In this article, we assess the potential that multiple populations are using common semi‐enclosed estuaries and quantify the potential levels of straying (i.e. dispersal) of foreign‐produced individuals into populations by using otolith chemical signatures as natural ‘tags’. To do so, we created a database of juvenile fish otolith chemistry (a marker of freshwater production) from four rivers and compared the chemistry of harvested fish in two estuaries important to anglers, the Renews River and Chance Cove Brook, to the database. A discriminant function analysis revealed significant differences in the otolith chemistry of juvenile fish inhabiting the four rivers with a 97% cross‐validated accuracy when classifying individual juveniles to their natal river, indicating our baseline was robust. When assigning adults caught over 3 years (2007–2009) in the recreational fishery in the Renews River estuary, it was determined that over 95% of the fish caught each year originated from Renews River. In contrast, harvested fish in Chance Cove during 2009 were disproportionately comprised of fish produced in Renews River, suggesting the potential for source‐sink population dynamics in Newfoundland. Taken as a whole, these results indicate limited population mixing in nearshore estuaries of this region, but also highlight the potential for some populations to subsidise the harvest by anglers in different areas.  相似文献   

10.
Timing of spawning, habitat use and egg burial depths of brown trout were studied in seven Swiss (alpine and prealpine) rivers, which differed in size, altitude and flow regime. In general, we observed brown trout spawning activity between the end of October and the beginning of January. The spawning duration differed significantly, however, between rivers, ranging from 28 to 72 days. Analysis of environmental parameters for their influence on spawning activity revealed mean water temperature and altitude as the most explanatory variables. Detailed investigation of redd characteristics based on water velocity, water depth and substrate size clearly showed differences between positions on the redd. Brown trout in Alpine rivers preferred to use velocities of 30–40 cm·s?1, water depths of 10–20 cm and substrates of 16–32 mm for spawning. It has to be noted, however, that recorded values cover almost the whole range of data on spawning habitats that has been reported in literature so far. A special focus of this study was on egg burial depths, which were surprisingly not found to differ significantly between the rivers despite their different flow regimes. Recorded egg burial depths were, however, found to be distinctly lower (mean burial depth: 3.8 cm) than reported by almost any study so far. We see this observation of low burial depths in Alpine rivers as useful in the context of scouring effects, especially when evaluating the influence of scouring on fish populations.  相似文献   

11.
This study evaluated the importance of the environment and spatial distribution of juvenile fish for the adoption of alternative migratory tactics in a partially anadromous population of rainbow trout (Oncorhynchus mykiss) from the Santa Cruz River. We captured young‐of‐the‐year fish along the river during autumn 2009, 2010 and spring 2010 and determined their maternal origin (anadromous vs. resident) using strontium to calcium ratios in the otolith core. Relative proportion of anadromous offspring, modelled with logistic regression, increased towards headwaters and in areas with deeper channels and larger substrate composition. Body length, modelled with linear multiple regression, varied positively with site depth, water velocity, substrate size and anadromous maternal origin. Based on evidence for limited juvenile movements (<25 km), the spatial extent of this study (240 Rkm) and the identification of large, contrasting reaches along the river, it is likely that the observed spatial distribution of juveniles and their association to sites with coarse substrate composition reflects maternal spawning activity. Results further indicate that anadromous females breed predominantly in middle and upper river sections in areas with coarse substrate. Given that body size in this system has been positively related to propensity for anadromy, we propose that female spawning choice affects their offspring's spatial distribution, providing the adequate physical template for anadromous offspring to reach or maintain larger body sizes and display anadromy themselves. Relevance of this study is also discussed in the context of alterations in response to future dam construction in one of the latest free‐flowing rivers sustaining anadromous O. mykiss.  相似文献   

12.
Beaded streams are prominent across the Arctic Coastal Plain (ACP) of Alaska, yet prey flow and food web dynamics supporting fish inhabiting these streams are poorly understood. Arctic grayling (Thymallus arcticus) are a widely distributed upper‐level consumer on the ACP and migrate into beaded streams to forage during the short 3‐month open‐water season. We investigated energy pathways and key prey resources that support grayling in a representative beaded stream, Crea Creek. We measured terrestrial invertebrates entering the stream from predominant riparian vegetation types, prey types supporting a range of fish size classes, and how riparian plants and fish size influenced foraging habits. We found that riparian plants influenced the quantity of terrestrial invertebrates entering Crea Creek; however, these differences were not reflected in fish diets. Prey type and size ingested varied with grayling size and season. Small grayling (<15 cm fork length (FL)) consumed mostly aquatic invertebrates early in the summer, and terrestrial invertebrates later in summer, while larger fish (>15 cm FL) foraged most heavily on ninespine stickleback (Pungitius pungitius) throughout the summer, indicating that grayling can be insectivorous and piscivorous, depending on size. These findings underscore the potential importance of small streams in Arctic ecosystems as key summer foraging habitats for fish. Understanding trophic pathways supporting stream fishes in these systems will help interpret whether and how petroleum development and climate change may affect energy flow and stream productivity, terrestrial–aquatic linkages and fishes in Arctic ecosystems.  相似文献   

13.
Abstract –  Anthropogenic barriers that may interfere or prevent fish migration are commonly found in streams throughout the distribution of salmonids. Construction of fish passages in streams is a common solution to this problem. However, the goal with fish passages is often, at least in Scandinavia, to allow Atlantic salmon ( Salmo salar L.) and migratory brown trout ( S. trutta L.) to get access to spawning areas above these barriers. Hence, the fish passages may often only be open during the spawning migration of salmonids (late summer to autumn). We present data, on wild brown trout migration, from two trapping systems in two Scandinavian streams showing that intra- and interstream migrations are common throughout the summer and autumn. Moreover, differences in size were found between trap-caught trout and electrofished trout where trapped trout were generally larger than electrofished trout. We suggest that the current regime with fish passages only open parts of the year can have negative effects on populations by depriving trout from the possibility to perform migrations throughout the year.  相似文献   

14.
The relative proportions of mature wild and stocked brown trout in four Irish lakes were compared with their subsequent occurrence in spawning runs. Data indicate that stocked trout, of two strains, did not run the streams to spawn in significant numbers. Considerable stocks of introduced fish, which had shed their milt or eggs, were present in these lakes in springtime. The failure of brown trout stocked in lakes to run spawning streams subsequently has not been recorded previously.  相似文献   

15.
Many investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s?1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m2 over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.  相似文献   

16.
The accuracy of drift diving surveys of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L., was evaluated by comparing the abundance and size distribution with catches in a fish trap over 6 years in the River Etneelva, western Norway. The population count from drift diving accounted for on average 96.3% of the salmon in the trap after accounting for the catches during fishing. Size structure registered during drift diving corresponded with trap catches of salmon, but the number of small salmon (<3 kg) appeared to be somewhat underestimated, while large salmon (>7 kg) were overestimated in drift diving. For sea trout, the match between drift diving counts and trap registrations was poorer (average 76.3%), but may have been affected by the surveys being performed too late with regards to sea trout spawning time. The study illustrates the utility of drift counting for estimating the entire population of anadromous salmonids in a river.  相似文献   

17.
Piscivory by birds can be significant, particularly on fish in small streams and during seasonal low flow when available cover from predators can be limited. Yet, how varying amounts of cover may change the extent of predation mortality from avian predators on fish is not clear. We evaluated size‐selective survival of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in replicated semi‐natural stream sections. These sections provided high (0.01 m2 of cover per m2 of stream) or low (0.002 m2 of cover per m2 of stream) levels of instream cover available to trout and were closed to emigration. Each fish was individually tagged, allowing us to track retention of individuals during the course of the 36‐day experiment, which we attributed to survival from predators, because fish had no other way to leave the streams. Although other avian predators may have been active in our system and not detected, the only predator observed was the belted kingfisher Megaceryle alcyon, which is known to prey heavily on fish. In both treatments, trout >20.4 cm were not preyed upon indicating an increased ability to prey upon on smaller individuals. Increased availability of cover improved survival of trout by 12% in high relative to low cover stream sections. Trout also survived better in stream sections with greater shade, a factor we could not control in our system. Collectively, these findings indicate that instream cover and shade from avian predators can play an important role in driving survival of fish in small streams or during periods of low flow.  相似文献   

18.
Between 1979 and 1991, hatchery-reared 1+ and 2+ rainbow trout were released in May and June in the Boknafjord at the mouth of the River Imsa, and from April to June in the Oslofjord, southern Norway. The fish were recaptured in the fjords of release, in rivers emptying there and from rivers and sea further along the Norwegian coast. Of the total recaptures, 35.6% ascended rivers in the year of release. Some fish released at the River Imsa returned to the area of release after spending 1 to 3 years at sea. Among those that were recaptured in rivers, 11.9% were recaptured in other rivers than the Imsa. The growth rate of the fish varied inversely with size at release. The growth rate was higher in the Oslofjord than in the Boknafjord, and in both areas the growth rate decreased with time after release. Rainbow trout that had escaped from local fish farms entered the River Imsa between March and December. Adults ascending in spring remained a shorter time in the river (37 days) than those ascending in autumn (200 days). Fish entering in autumn decreased more in weight during their river stay than those ascending in spring, and females more than males. Spawning took place in April-May. The monthly mean river stay of juvenile entrants ranged from 2 weeks to 6 months. In total, 27.8% of the rainbow trout escaped from fish farms and captured in the Imsa strayed to other rivers for repeat spawning. There is no evidence for continuing survival of escaped Norwegian rainbow trout in the wild.  相似文献   

19.
  • 1. The lacustrine brown trout (Salmo trutta) is endangered and of high conservation importance. In the only spawning habitat of the population in the Bavarian Lake Walchensee, the River Obernach, a substantial decrease in spawning runs has been reported. In this study, the present ecological state of the spawning stream was analysed with the objective of identifying life‐stage specific limitations to successful recruitment attributable to deficiencies in (i) spawning migration, (ii) spawning habitat quality, and (iii) habitat quality for juveniles.
  • 2. Structural stream analysis showed that discharge and several migration barriers — particularly near the river outlet into the lake — prevent successful spawning migrations at normal water levels. Migration barriers are probably the main limiting factor for reproduction of lacustrine brown trout, whereas structural variability of the Obernach meets the habitat requirements of both spawners and juveniles.
  • 3. Spawning site quality was suitable for trout, as indicated by stream substratum texture and high exchange rates between free‐flowing water and the interstitial zone in physico‐chemical parameters (redox potential, dissolved oxygen, pH, temperature and conductivity).
  • 4. Analyses of fish community structure revealed dominance of lithophilic species, in particular of riverine brown trout (Salmo trutta). Its density and intact demographic population structure suggest that spawning and juvenile habitat quality for salmonids is not limiting. Recapture of stocked lacustrine trout juveniles also indicates habitat suitability for the juvenile stage.
  • 5. In conclusion, the results show that the methodology used in this study is suitable for the identification of life‐stage specific habitat deficiencies in lacustrine brown trout and other fish species. Availability of habitat data throughout the species' distribution range is a first crucial step for the development of an effective recovery plan. Copyright © 2009 John Wiley & Sons, Ltd.
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20.
Non‐native predators may interfere with conservation efforts for native species. For example, fisheries managers have recently become concerned that non‐native brown trout may impede efforts to restore native salmon and trout in California's Trinity River. However, the extent of brown trout predation on these species is unknown. We quantified brown trout predation on wild and hatchery‐produced salmon and trout in the Trinity River in 2015. We first estimated the total biomass of prey consumed annually by brown trout using a bioenergetics model and measurements of brown trout growth and abundance over a 64‐km study reach. Then, we used stable isotope analysis and gastric lavage to allocate total consumption to specific prey taxa. Although hatchery‐produced fish are primarily released in the spring, hatchery fish accounted for most of the annual consumption by large, piscivorous brown trout (>40 cm long). In all, the 1579 (95% CI 1,279–1,878) brown trout >20 cm long in the study reach ate 5,930 kg (95% CI 3,800–8,805 kg) of hatchery fish in 2015. Brown trout predation on hatchery fish was ca. 7% of the total biomass released from the hatchery. Brown trout only ate 924 kg (95% CI 60–3,526 kg) of wild fish in 2015, but this was potentially a large proportion of wild salmon production because wild fish were relatively small. As large brown trout rely heavily on hatchery‐produced fish, modifying hatchery practices to minimise predation may enhance survival of hatchery fish and potentially reduce the abundance of predatory brown trout.  相似文献   

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