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1.
Abstract – The morphologies of sympatric juvenile Atlantic salmon Salmo salar parr and brown trout Salmo trutta parr were compared between Irish rivers with contrasting hydraulic environments – a high‐gradient and a low‐gradient tributary from the River Barrow catchment, south‐east Ireland and a high‐gradient river from the Burrishoole catchment, west of Ireland. The two catchments differ markedly in mean annual precipitation (849.0 mm year?1 and 1370.3 mm year?1 for the Barrow and Burrishoole catchments, respectively). Parr of both species demonstrated morphological variation between and within catchments. Changes in metrics such as pectoral fin length, body depth and body length between and within catchments suggest that hydraulic forces were a major determinant of morphological variation. Both species from the Burrishoole catchment had relatively larger pectoral fins, longer heads, larger eyes and shallower bodies than conspecifics from the Barrow catchment. In rivers subject to frequent rainfall‐driven high discharges, such as those in the Burrishoole catchment, a more fusiform body and head shape coupled with larger pectoral fins may reduce the energetic cost of maintaining position in the water column, as well as increase stability and manoeuvrability. The larger eyes in both parr species in the Burrishoole catchment could further be a response to the lower visibility of the more turbid and peat‐stained waters or to the reduced prey availability. The results of this study demonstrate that local adaptation to flow conditions can yield morphologically distinct populations and that multiple species can exhibit parallel phenotypic responses to changing environmental conditions.  相似文献   

2.
Abstract Dense riparian tree canopy is generally found to have a negative effect on salmonid populations. Canopy can affect fish both directly via trophic impacts and its effects as cover, and indirectly via its effects on the distribution of instream vegetation. This study examined the impact of riparian canopy on the ecology of juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in south‐west Ireland. Riparian canopy reduced the density, length and gut contents of juvenile salmon, but not brown trout. The negative relationship between canopy cover and fish size and feeding was strongly influenced by the abundance of instream macrophytes, which in turn varied as a function of catchment water chemistry. As a management strategy, the reduction of dense riparian canopy is unlikely to have the same effect on juvenile salmonids on all streams within an ecoregion because of differences in catchment‐wide factors.  相似文献   

3.
Many studies have documented that hatchery‐reared salmonids generally have inferior survival after being stocked compared with wild conspecifics, hatchery and wild salmonids have been observed to differ in their antipredator responses. The response of brown trout (Salmo trutta) juveniles (0+) of differing backgrounds to a live predator was compared in two experiments. First, the antipredator behaviour of predator‐naïve hatchery‐reared brown trout and wild‐exposed brown trout were assessed in behavioural trials which lasted for eight days. Second, predator‐naïve and predator‐conditioned hatchery‐reared brown trout were assessed in identical behavioural trials. Brown trout were ‘predator‐conditioned’ by being held in a stream‐water aquarium with adult Atlantic salmon (Salmo salar) and adult brown trout for two days prior to behavioural trials. Predator‐conditioned hatchery‐reared brown trout spent more time in shelters in the trial aquaria than predator‐naïve hatchery‐reared fish, but did not differ in time spent in the predator‐free area. Predator conditioning may account for the increased time spent in the shelter, but does not appear to have affected time spent in the predator‐free area. However, even if significant alteration in behaviour can be noted in the laboratory, the response might not be appropriate in the wild.  相似文献   

4.
This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.  相似文献   

5.
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   

6.
Abstract Population genetic studies can be useful for informing conservation and management. In Atlantic salmon, Salmo salar L., population structuring frequently occurs between river systems, but contrasting patterns occur within rivers, highlighting the need for catchment‐specific studies to inform management. Here, population structure of Atlantic salmon was examined in the River Tamar, United Kingdom, using 12 microsatellite loci. Gene diversity and allelic richness ranged from 0.80 to 0.84 and from 8.96 to 10.24, respectively. Some evidence of genetic structure was found, including significant genetic differentiation between samples in different subcatchments (pairwise θ and tests of genic differentiation), results from assignment tests and a pattern of isolation by distance. Conversely, structure revealed only one population cluster, and an analysis of molecular variance showed no significant variation between subcatchments. Evidence of population bottlenecks depended on the mutation model assumed and is discussed with reference to catchment‐specific studies of stock abundance. Implications for implementing management actions are considered.  相似文献   

7.
This study investigated interactions between eco‐hydromorphological state, riparian vegetation cover, water temperature and fish community composition in lowland rivers in Ireland. Physical habitat modification of study sites corresponded with degraded eco‐hydromorphological state (degree of ecological and physical modification) and reduced thermal buffering capacity (greater temperature fluctuation and increased frequency of extreme temperature events). This impact was reflected in the fish community, with a shift from a brown trout‐dominated (Salmo trutta L.) fish assemblage to predominance of the more thermally plastic minnow, Phoxinus phoxinus (L.), and stone loach, Barbatula barbatula (L.). Eco‐hydromorphological state may be a central factor affecting the ability of temperate rivers to resist temperature change in a warming climate and to maintain suitable conditions for salmonids and other cold‐water biota. Strategies aimed at climate change proofing of temperate rivers should focus on preserving or re‐establishing the eco‐hydromorphological processes that create habitat complexity and buffer stream temperature.  相似文献   

8.
Recruitment of salmonids is a result of density‐dependent factors, specifically egg production in the previous year, and density‐independent environmental processes driven by discharge and temperature. With the plethora of knowledge on major drivers of Atlantic salmon Salmo salar and brown trout Salmo trutta recruitment, there is a requirement to explore less known species, such as European grayling Thymallus thymallus, whose postemergence time coincides with period of increasing temperature and low discharge. This study assessed drivers of grayling recruitment in a southern English chalk stream, a system vulnerable to discharge and temperature alterations under future climate change predictions. The analyses explored age 0+ grayling survival in relation to conspecific and heterospecific densities and discharge‐ and temperature‐derived factors. The final mixed‐effects model revealed a positive relationship between age 0+ grayling survival and incubation temperature anomaly and age 0+ trout abundance. Similarly, postincubation temperature anomaly had a positive effect on 0+ grayling survival, but only up to a threshold temperature of 13.5°C, beyond which it had a negative effect. In contrast, increasing number of days with low discharge postincubation negatively influenced age 0+ grayling survival, with no evidence of an effect of elevated discharges following spawning. Our results emphasise the importance of maintaining natural discharge regimes in salmonid rivers by tackling multiple stressors operating at the catchment scale, including land and water use to mitigate for predicted climate driven changes. In addition, further research on recruitment drivers in less stable, rain‐fed systems, is required.  相似文献   

9.
Competitive interactions with non‐native species can have negative impacts on the conservation of native species, resulting in chronic stress and reduced survival. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (Sebago and LaHave) that are being used for reintroduction into Lake Ontario were placed into semi‐natural stream tanks with four non‐native salmonid competitors that are established in Ontario streams: brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha) and coho salmon (O. kisutch). Brown trout and rainbow trout reduced the survival and fitness‐related traits of Atlantic salmon, whereas Chinook salmon and coho salmon had no impact on these traits. These data support theories on ecological niche overlap and link differences in observed aggression levels with competitive outcomes. Measurements of circulating hormones indicated that the Atlantic salmon were not chronically stressed nor had a change in social status at the 10‐month time point in the semi‐natural stream tanks. Additionally, the Sebago population was better able to coexist with the non‐native salmonids than the LaHave population. Certain populations of Atlantic salmon may thus be more suitable for some environments of the juvenile stream phase for the reintroduction into Lake Ontario.  相似文献   

10.
Johnston P, Bergeron NE. Variation of juvenile Atlantic salmon (Salmo salar) body composition along sedimentary links.
Ecology of Freshwater Fish 2010: 19: 187–196. © 2010 John Wiley & Sons A/S Abstract – The objective of this study was to determine the proximate body composition of juvenile Atlantic salmon along the sequence of aquatic habitat types created by longitudinal changes in the riverbed substrate of two rivers (i.e., sedimentary links units). Interesting trends in the body composition were observed but our initial hypothesis, that fish of the upstream sections have higher energy content, was nevertheless not verified. No common longitudinal pattern was detected in the body composition (water, lipid, energy density) along the studied rivers. Trends in the body constituents were different between age‐classes and rivers, whereas they were highly variable within‐ and among‐samples. There was however a common trend in the pattern of variations, with the coefficient of variations increasing in the downstream direction for almost all constituents, age‐classes and rivers. Potential abiotic and biotic factors that might have contributed to these observations are discussed.  相似文献   

11.
Salmonid eggs were collected from spawning redds in the Norwegian rivers Alta, Gaula, and Driva in 1982. Their phosphoglucoisomerase (PGI; E.C. No. 5.3.1.9) patterns, as revealed by isoelectric focusing and histochemical staining, were compared to standard zymograms produced by Atlantic salmon (Salmo salar L.) and trout (S. trutta L.) white skeletal muscle extracts, and to the zymogram in salmon eggs of known origin. In salmon, the egg zymogram was identical with that of muscle. Two types of zymograms, identical with either salmon or trout muscle zymograms and thus regarded as species-determinants, were observed among the eggs from wild fish. Their proportions in the three rivers were as expected from current knowledge of species composition. The present findings are related to previous reports on PGI expression in salmonids. The PGI zymograms are probably diagnostic keys to species for eggs from Norwegian stream-dwelling salmonids, including Arctic char (Salvelinus alpinus L.). Some managemental implications of the present results are briefly discussed.  相似文献   

12.
Whether territoriality regulates population size depends on the flexibility of territory size, but few studies have quantified territory size over a broad range of densities. While juvenile salmonids in streams exhibit density‐dependent mortality and emigration, consistent with space limitation, there has been relatively little study of how territory size and individual growth rate change over a broad range of densities, particularly in field experiments. Consequently, we manipulated the density (range = 0.25–8 m?2) of young‐of‐the‐year (YOY) Atlantic salmon (Salmo salar) in mesh enclosures erected in a natural stream to test whether (i) territory size is fixed, decreases continuously or decreases towards an asymptotic minimum size as density increases; and (ii) individual growth rate decreases as a negative power curve with density as in observational field studies. Territory size decreased with increasing density, consistent with an asymptotic minimum size of about 0.13 m2 for a 5‐cm fish. Individual growth rate also decreased with density, although the magnitude of decrease was steeper than in observational studies. Our results suggest a limit to how small territories can be compressed, which will set the upper limit to the local density in a habitat. The density‐dependent changes in territory size and individual growth rate will both play a role in the regulation of stream salmonid populations.  相似文献   

13.
Abstract– The utilization of lakes, and inlet and outlet streams by juvenile Atlantic salmon ( Salmo salar L.), brown trout ( Salmo trutta L.) and Arctic charr ( Salvelinus alpinus (L.), were investigated in 16 watercourses northern Norway, all known to inhabit salmon stocks. In lakes, fish were caught by small mesh size gill nets, while in rivers fish were caught electrofishing. In the shallow littoral (0-3 m depth) there were juvenile salmon in 15 of 19 investigated lakes, juvenile trout in 17 and juvenile charr in seven. Trout dominated significantly in numbers in the shallow littoral of seven lakes, while salmon and charr dominated in three lakes each. When trout and salmon were frequent in the shallow littoral, charr was usually not present in this habitat, but were found in the profundal zone in most of the lakes. Atlantic salmon parr utilized both shallow and deep lakes, and used both stones and macrophytic vegetation as shelter. The utilization of lakes by salmon parr seemed to be closely related to utilization of small inlet streams for spawning. In most inlet and outlet streams salmon dominated over trout in numbers, while charr were absent. This is the first documentation of lake-use by naturally occurring salmon parr in Scandinavia.  相似文献   

14.
A total of 21 acidified Norwegian rivers are now being limed to re‐establish or restore Atlantic salmon, Salmo salar L., stocks. Natural reproduction of Atlantic salmon was evident 1 year after the first year of liming in all rivers that had lost their native stocks (n = 9) except for one river. The density of fry (age 0+) developed significantly more rapidly in rivers that supported remnant stocks than in rivers that had lost their stocks, based on data 5 years after treatment. Nine of the study rivers were supplied with hatchery‐reared salmon, mainly unfed fry. Of the rivers with lost stocks, those which were supplied with fish had significantly higher densities than those that were not enhanced. On the other hand, rivers with remnant stocks that were supplied with fish had significantly lower densities of salmon fry than those that did not undergo such mitigation measures. In 2001, all limed rivers yielded 41.9 t of salmon.  相似文献   

15.
Despite long‐standing interest in foraging modes as an important element of animal space use, few studies document and compare individual foraging mode differences among species and ecological conditions in the wild. We observed and compared foraging modes of 61 wild Arctic charr, Salvelinus alpinus, 42 brown trout, Salmo trutta, and 50 Atlantic salmon, Salmo salar, in their first growing season over a range of habitats in 10 Icelandic streams. We found that although stream salmonids typically sit‐and‐wait to ambush prey from short distances, Arctic charr were more mobile during prey search and prior to prey attack than Atlantic salmon, whereas brown trout were intermediate. In all three species, individuals that were mobile during search were more likely to be moving when initiating attacks on prey, although the strength and the slope of this relationship differed among species. Arctic charr also differed from salmon and trout as more mobile individuals travelled longer distances during prey pursuits. Finally, coupled with published data from the literature, salmonid foraging mobility (both during search and prior to attack) clearly decreased from still water habitats (e.g., brook charr), to slow‐running waters (e.g., Arctic charr) to fast‐running waters (e.g., Atlantic salmon). Hence, our study suggests that foraging mode of young salmonids can vary distinctly among related species and furthers our understanding of the behavioural mechanisms shaping the geographical distribution of wild salmonids.  相似文献   

16.
There is concern that expanding beaver (Castor fiber) populations will negatively impact the important economic, recreational and ecological resources of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) populations in Europe. We studied how beaver dams influenced habitat, food resources, growth and movement of juvenile Atlantic salmon and trout on three paired beaver-dammed and beaver-free (control) tributaries of important salmon rivers in central Norway. Lotic reaches of beaver-dammed and control sites were similar in habitat and benthic prey abundance, and ponds were small (<3,000 m2). Though few juvenile salmonids were detected in ponds, trout and salmon were present in habitats below and above ponds (comprising 9%–31% and 0%–57% of the fish collected respectively). Trout dominated control sites (79%–99%), but the greatest proportion of Atlantic salmon were upstream of beaver ponds (0%–57%). Growth rates were highly variable, with no differences in growth between lotic reaches of beaver-dammed and control sites. The condition and densities of juvenile salmon and trout were similar in lotic reaches of beaver-dammed and control sites, though one beaver-dammed site with fine sediment had very few juvenile salmonids. Beaver dams did not block the movement of juvenile salmonids or their ability to use upstream habitats. However, the degree of repeated movements and the overall proportion of fish moving varied between beaver-dammed and control sites. The small scale of habitat alteration and the fact that fish were able to move past dams makes it unlikely that beaver dams negatively impact the juvenile stage of salmon or trout populations.  相似文献   

17.
Salmonid fishes may reside within or migrate between stream and lake habitats, or undergo anadromous migrations between freshwater and the ocean. While the degree of anadromy of salmonids has been thoroughly compared, no analogous review has examined the degree of lake use. To assess the extent of reliance on lake habitat in this family, we considered 16 species of salmon, trout and charr from the genera Oncorhynchus, Salmo and Salvelinus, comparing their (a) use of lakes as spawning habitat, (b) rearing strategies in lakes, and (c) occurrence and diversity of lacustrine trophic polymorphism. In identifying the primary life‐history patterns of each species and exploring the lesser‐known lacustrine behaviours, we found that the extent of reliance on lakes exhibits a negative association with the degree of anadromy. Oncorhynchus rely least on lakes, Salmo to an intermediate level and Salvelinus the most, opposite of the general prevalence of anadromy among these genera. Lakes are critical to adfluvial and lake‐resident salmonids, but they also support anadromous and fluvial life histories by providing spawning, rearing, overwintering and/or summer refuge habitat. Adfluviality, although a non‐anadromous life history, consists of similar migration‐related traits and behaviours as anadromy, including the parr–smolt transformation, sex‐biased patterns of migration and residency, and the presence of precocious males. Lakes support life‐history variants, reproductive ecotypes and trophic morphs unique to lacustrine habitat. Therefore, conservation of salmonids is dependent on maintaining the diversity and quality of their habitats, including lakes.  相似文献   

18.
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.  相似文献   

19.
Abstract – After release to the wild, captive reared salmon have shown lower foraging rates on natural prey and impaired ability to avoid natural predators and thus lower survival compared with wild‐born conspecifics. Here, we examine whether captive breeding influences learning of foraging on natural prey and how enriched rearing methods may improve foraging on natural prey by Atlantic salmon (Salmo salar) parr. We reared offspring of hatchery or wild salmon of the same population in either a standard or enriched environment at production‐scale densities. The enriched environment featured submerged overhead shelter, varying water current, depth and direction and consequently alterations in food dispersion. Parr reared in the enriched environment expressed higher feeding rates, and parr of wild origin started to forage earlier on natural prey. The enriched method promoted foraging of hatchery reared parr on natural prey and is easily applicable to commercial production of salmonids for reintroduction or stock enhancement purposes.  相似文献   

20.
Intraspecific hybridisation may result in hybrid offspring exhibiting superior (heterosis) or inferior (outbreeding depression) fitness relative to their parental populations. As both have been demonstrated in salmonids, consequences of interbreeding between divergent populations are relevant to their conservation. Atlantic salmon Salmo salar L. were extirpated from Lake Ontario by the late 19th Century due to anthropogenic causes. Multiple allopatric populations of hatchery‐reared Atlantic salmon are being stocked in an effort to re‐establish a self‐sustaining population. This study evaluated whether interbreeding between Sebago Lake (Maine) and LaHave River (Nova Scotia) individuals will result in heterosis or outbreeding depression in juveniles. This was accomplished through full‐factorial 2 × 2 mating crosses between the strains and comparing multiple fitness‐related traits between the cross types. Hybrid juveniles displayed no signs of outbreeding depression nor heterosis. Further studies on comparative fitness of backcross and F2 hybrids are recommended to assess potential consequences for this and similar restoration efforts.  相似文献   

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