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1.
Abstract –  A genetic survey was carried out on recently emerging fry to investigate interbreeding between anadromous and freshwater resident brown trout in La Roche Brook, a major spawning tributary of the Oir River system (Normandy, France). Emerging fry were sampled at three different sites in spring 2002 and 2003. Stable isotope analysis (SIA) allowed the classification of each individual as the progeny of resident ( N  = 76) or anadromous ( N  = 58) female trout. Microsatellite DNA analysis showed that genetic diversity between fry samples can be explained by microgeographical (various sampling sites) and temporal (2 years of sampling) variations rather than maternal origin (anadromous vs. freshwater resident). We conclude that a high level of gene flow exists between the two morphs when anadromous adults have access to the spawning grounds of residents. We highlight the relevance of using SIA in conjunction with genetic analysis to study interactions between the two morphs.  相似文献   

2.
Partial migration, in which some individuals of a population migrate while other individuals remain resident, is generally associated with ontogenetic shifts to better feeding areas or as a response to environmental instability, but its underlying mechanisms remain relatively unknown. Brown trout (Salmo trutta) exhibit partial migration, with some individuals remaining in freshwater (freshwater resident) while others undertake an anadromous migration, where they spend time at sea before returning to breed in freshwater (migrant). We reared full‐sibling groups of offspring from freshwater‐resident and anadromous brown trout from the same catchment in the laboratory under common garden conditions to examine potential differences in their early development. Freshwater‐resident parents produced eggs that were slower to hatch than those of anadromous parents, but freshwater‐resident offspring were quicker to absorb their yolk and reach the stage of exogenous feeding. Their offspring also had a higher conversion efficiency from the egg stage to the start of exogenous feeding (so were larger by the start of the fry stage) than did offspring from anadromous parents despite no difference in standard metabolic rate, maximal metabolic rate or aerobic scope. Given these differences in early development, we discuss how the migration history of the parents might influence the migration probability of the offspring.  相似文献   

3.
We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily with distance from the sea forming a spatial continuum in migration strategies which is probably maintained by the combination of several factors such as divergent availability of food resources, variable migration costs and genetic differences. These within‐catchment differences in migration strategies should be taken into account in fisheries management practices.  相似文献   

4.
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   

5.
Bull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ‘to ensure the long‐term persistence of self‐sustaining bull trout populations’. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization.  相似文献   

6.
Spawning runs of brown trout Salmo trutta L., and rainbow trout, Oncorhynchus mykiss Walbaum, were compared in three tributaries of two lakes for timing, numbers and redd characteristics. Redd characteristics for the two species in four other streams were examined. No significant differences in redd characteristics between the two species were observed, but in all lake tributaries the possibilities of superimposition of spring spawning rainbow trout on redds of brown trout were examined. A common feature was the high ratio of numbers of spawners to the area of preferred spawning gravel, and it was concluded that in the lake tributaries, superimposition resulted in increased mortality of brown trout eggs, and in one case elimination of the brown trout population. Management possibilities for control of the species proportions in comparable situations are discussed.  相似文献   

7.
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8.
Habitats modify the population ecology of species. Here, we show how low water level influences abundance and size of adult anadromous brown trout (Salmo trutta) entering a small, South Norwegian stream for spawning. After smolting, the fish appear chiefly to feed within 10 km of the home stream. In the autumn, South Norwegian streams typically flood because of heavy rainfall, when the anadromous brown trout entered from the sea. Mean annual duration of the upstream migration period was 34 days and ended when the flooding ended and the water temperature dropped to below 4°C. During most of the migration period, on average two trout ascended the river per day. The sexes entered the spawning area concurrently, and the male:female ratio of the anadromous trout was 1.27. No fish entered when the water depth just downstream of the spawning area was below 5 cm, and mean number of fish increased with increasing water depth to ca. 30 cm, but not at higher flows when the ascent gradually decreased. Mean and maximum size of the entering spawners increased with water depth between 5 and 16 cm. Among those that had been to sea, most were recaptured in the home stream, 4% in other streams, but only two of the strays were caught close to spawning time. The present results illustrate that population traits of anadromous brown trout from a small stream differ from those in larger rivers, probably because of selection associated with water flow.  相似文献   

9.
Variation in brown trout (Salmo trutta L.) population recruitment and structure is related to migratory patterns, which should depend on ease of access to habitats providing increased opportunity for growth. We quantified the number of young of year (YOY) as a proportion of the total number of brown trout at 24 locations on 11 streams within the Taieri catchment, New Zealand, including back calculated growth rates and emergence dates from otoliths. Locations with high absolute and relative abundance of YOY fish were related to elevation and distance from the river mainstem (habitat used by migratory fish), fish density, and the interaction between invertebrate food biomass, distance and elevation. Hatch date and growth were not related to the proportion of YOY fish, though growth was negatively correlated to total fish density. We suggest landscape features play a large role in determining recruitment and population structure. Locations at lower elevations have a high YOY density, high competition and lower growth, likely prompting out‐migration. These conditions could be created by successful return migration and spawning of large fecund fish resulting in YOY densities exceeding the habitat carrying capacity. Environmental factors, such as food availability, also played a role in determining population structure. These results provide an example of how population structure and recruitment might be controlled by local conditions and access to high growth environments in wild populations of introduced brown trout across a catchment.  相似文献   

10.
Abstract –  Life history strategies and migratory patterns of 71 adult radio-tagged bull trout, Salvelinus confluentus , were studied in the Secesh River watershed within the South Fork Salmon River (SFSR) sub-basin in west-central Idaho, USA during 2003 and 2004. In both years, upstream migrations occurred during late June and early July, migrations into two spawning tributaries during late July and early August, spawning from mid-August through mid-September, and rapid downstream (postspawning) migrations from late August to mid-September. Primary over-wintering areas were Loon Lake, the lower Secesh River (downstream of Loon Creek), and the lower SFSR (downstream of the confluence with the Secesh River). Loon Lake evidently provides sufficient production to allow the adfluvial life history strategy to persist and predominate in the Secesh River, while the fluvial life history strategy was previously found to predominate in the nearby East Fork SFSR. Adfluvial, nonconsecutive-year migrations were the predominant life history strategy. Only seven fish made consecutive-year migrations to Lake Creek; however, only one of these fish, a female, utilised a spawning tributary in both years and showed spawning tributary fidelity. Three consecutive-year migrants and three in-season migrants showed over-wintering site fidelity by returning to Loon Lake in September, 2004. The life history variations observed for bull trout in the Secesh River watershed are similar to those observed for bull trout throughout their range and to those of other charr species worldwide, yet the development of distinct migration patterns demonstrate the adaptability of the species to a range of available habitats.  相似文献   

11.
Abstract –  Human-induced habitat alteration is one of the main causes of the decline of freshwater fish populations. The watershed of the River Bidasoa (Spain) is an example of heavily fragmented habitat. The local brown trout ( Salmo trutta L.) population is disturbed, with evidence of poor recruitment as well as low adult densities in the main stem. Forty male and female adult migratory trout were tagged with external or internal radio transmitters and released. Fixed stations with data loggers and mobile antennae were used with daily surveys to track fish movements during the migration and spawning period (3 months). Migration distances did not exceed 10 km, and half of the fish never entered a tributary in the study area. Fragmentation because of weirs on the main stem apparently prevented fish from reaching their spawning destination. Fish that entered the tributaries were first confronted with an accessibility problem because of low discharge. However, each fish chose one tributary, without making attempts to run up in other tributaries. Once in the tributary, fish were restrained in their upstream movements by dams. The study area appeared to be isolated from the vast upper part of the watershed. Within the study area, upper parts of tributaries also seemed strongly disconnected from the main stem. This study illustrates the negative impact of river fragmentation on S. trutta migration pattern. Population sustainability can be directly affected through the low availability of spawning grounds for migratory fish. Long-term effects of fragmentation may cause reproductive isolation within watersheds, which in the case of trout also means isolated phenotypic population units.  相似文献   

12.
SUMMARY: The objective of this study was to reveal the spawning grounds and reproductive characteristics of anadromous and resident pond smelt, Hypomesus nipponensis , coexisting in Lake Ogawara. Life history styles of females shedding in spawning grounds in the lake and its inflowing rivers were differentiated by otolith increment analysis. Size, dry weight, and water content of mature oocytes and fecundity of fish were compared between resident and anadromous fish. Both anadromous and resident fish spawned in the lake. In contrast, no resident fish were found in any of the inflowing rivers, where only anadromous fish spawned. Regression of fecundity against standard length was discontinuous with an inflection point at 63.8 mm, which is the body size that differentiates large anadromous spawning groups from small resident spawning groups. Mean oocyte diameters were not significantly different between resident and anadromous fish. The eggs of resident fish had significantly more water content and a significantly lower dry weight than those of anadromous fish. These differences might influence the growth and developmental processes of progeny.  相似文献   

13.
Abstract – Salmon and trout have been introduced to many ecosystems worldwide, yet the ecological impacts of salmonid introductions remain poorly understood. We investigated the effects of introduced Pacific salmon on stream‐resident fish in the Great Lakes basin by monitoring the movements of passive integrative transponder (PIT)‐tagged brook trout in a Lake Michigan tributary receiving a salmon spawning run and in a nearby stream not receiving salmon. Coincident with the September arrival of salmon, an estimated 52% of resident brook trout moved >200 m, while no such movements were detected in the nonsalmon stream. After 3–4 days, however, brook trout movement patterns became similar in the two streams, suggesting that salmon effects on brook trout movements were short‐lived. Movements in the salmon stream were predominantly upstream in direction, with 50% of the tagged brook trout travelling from below to above the stationary PIT tag readers during the study. Declining water temperatures with the onset of fall coincided with low levels of brook trout movement at both sites, likely due to relocation for spawning. Increased brook trout movements coincident with the arrival of salmon spawners could be driven by a combination of interference competition and egg consumption. Using a bioenergetics model, we estimated that the energy lost to movement was likely compensated by the energy obtained from consuming salmon eggs. We conclude that salmon spawners can substantially increase brook trout movement, but in our study, these effects were short‐lived and likely negligible from a bioenergetics perspective.  相似文献   

14.
The population dynamics of Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) were compared in a small tributary of the River Scorff (Brittany, France) from spawning time to the beginning of the third growing season. The spawning and fry emergence of the two species took place at approximately the same time. In the first autumn, the densityof 0+ juveniles and settling rate from the egg stage were much higher in trout than in salmon. The emigration rate from 0+ population was much higher in trout than in salmon. The size of resident and migrating fish was always smaller in salmon than in trout, whatever the age. The low level of salmon production in the brook, compared with trout, was the result of low survival from egg to 0+ stage in autumn, combined with the small proportion of juveniles migrating after the first growing season. This was not compensated by a high number of migrants the next year. The role of physical habitat, inter-and intraspecific competition, predation and migration dependence on size and early sexual maturity is discussed. Indications are that small tributaries of the type studied are of great value for recruitment in trout but not very productive for juvenile salmon.  相似文献   

15.
Exotic species present a great threat to native fish conservation; however, eradicating exotics is expensive and often impractical. Mechanical removal can be ineffective for eradication, but nonetheless may increase management effectiveness by identifying portions of a watershed that are strong sources of exotics. We used mechanical removal to understand processes driving exotic brown trout (Salmo trutta) populations in the Logan River, Utah. Our goals were to: (i) evaluate the demographic response of brown trout to mechanical removal, (ii) identify sources of brown trout recruitment at a watershed scale and (iii) evaluate whether mechanical removal can reduce brown trout densities. We removed brown trout from 2 km of the Logan River (4174 fish), and 5.6 km of Right Hand Fork (RHF, 15,245 fish), a low‐elevation tributary, using single‐pass electrofishing. We compared fish abundance and size distributions prior to, and after 2 years of mechanical removal. In the Logan River, immigration to the removal reach and high natural variability in fish abundances limited the response to mechanical removal. In contrast, mechanical removal in RHF resulted in a strong recruitment pulse, shifting the size distribution towards smaller fish. These results suggest that, before removal, density‐dependent mortality or emigration of juvenile fish stabilised adult populations and may have provided a source of juveniles to the main stem. Overall, in sites demonstrating strong density‐dependent population regulation, or near sources of exotics, short‐term mechanical removal has limited effects on brown trout populations but may help identify factors governing populations and inform large‐scale management of exotic species.  相似文献   

16.
Abstract –  Scotland is a stronghold for Arctic charr, with about 200 freshwater, wholly loch-resident populations, most of which have yet to be studied. To date, no anadromous populations or individual sea-run charr, have been reported. In Scotland, most Arctic charr spawn in stillwater, during autumn and early winter (September to January), with only one population spawning in spring. Spawning in running water does occur, but has been regarded as rare. This paper examines the status of stream spawning of charr in Scotland, describing instances from 10 populations, although two of these are now extinct. Most stream-spawning charr migrate relatively short distances to running water and construct redds in gently flowing water. The longest recorded migration occurs in Loch Insh, Speyside, with fish travelling 15 km within the River Spey. Information on the extent of stream spawning is essential to help conserve the rich phenotypic and genetic diversity of our remaining charr populations.  相似文献   

17.
Abstract – The evolution of parental care depends on the sex‐dependent resolution of a trade‐off between present and future reproduction. In salmonids, the mating systems are often characterised by fierce male–male competition, and the absence of paternal care is widely admitted in these species. However, the fact that brown trout eggs can be cannibalised by peripheral individuals just after spawning suggests that dominant males would benefit from protecting their offspring by keeping cannibals away from the nest. We used 77 field observations of brown trout spawning to document the defensive behaviour of dominant males towards peripheral individuals before and after spawning, and test whether this behaviour was related to the probability of the clutch being cannibalised. We showed that dominant males stayed on the nest and chased peripherals even after the eggs were laid and fertilised. The number of chases performed by dominant males during the 2 min following spawning was negatively correlated to the probability of egg cannibalism. This result indicates that brown trout males can provide direct benefits to females through protection against egg cannibalism by peripheral individuals.  相似文献   

18.
In 2017, a PCR‐based survey for Piscine orthoreovirus‐3 (PRV‐3) was conducted in wild anadromous and non‐anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR‐positive, with Ct‐values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR‐negative. Neither non‐anadromous trout (brown trout) nor landlocked salmon were PRV‐3 positive. Altogether, these findings suggest that in Norway PRV‐3 is more prevalent in the marine environment. In contrast, PRV‐3 is present in areas with intensive inland farming in continental Europe. PRV‐3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted.  相似文献   

19.
Abstract A severe fish kill event caused by agricultural pollution impacted 2.4 km of the River Blackwater, Northern Ireland, in August 2007. A post‐kill monitoring programme sampled existing monitoring sites in the fish kill zone as well as upstream and downstream control sites. Post‐kill monitoring in combination with historical background data facilitated an assessment of the extent and severity of the disturbance episode on local salmonid populations. Subsequent recovery patterns indicated that total salmonid abundance returned to control levels within 1 year. Total salmonid biomass recovered within 2 years, whereas brown trout age structure took up to 3 years to return to background levels. Recovery dynamics were dominated by large‐scale directional migrations rather than random local movements. This included an initial autumnal immigration of 0+ age class brown trout, Salmo trutta L., in late 2007 followed by spawning migrations of adult migratory salmonids. The significance of relatively rapid natural recovery patterns is discussed in the context of potential management options such as restocking.  相似文献   

20.
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   

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