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1.
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   

2.
Abstract –  We compared the growth and prey consumption of juvenile hatchery and wild brown trout of similar genetic origin in 12 wire mesh cages in a natural river in North-Eastern Finland. Wild trout started feeding shortly after the start of the experiment, and clearly earlier than novel hatchery trout, but ate less in the presence of hatchery trout. When accompanied with wild trout, novel hatchery trout started to feed earlier, consumed more live prey, and lost less weight than when in allopatry. Hatchery trout grew more slowly than wild trout. To our knowledge, this is the first study to show that hatchery trout benefit from the presence of wild, experienced trout in a complex semi-natural environment. However, our results also indicate that the benefits to hatchery fish are not transferred to wild fish, and ultimately that care should be exercised in management actions when using hatchery trout to supplement wild populations. On the other hand survival potential of the novel hatchery brown trout could be better in the wild when also undomesticated trout are present.  相似文献   

3.
Brown trout populations of three headwater streams in the Northern Limestone Alps of Austria were supplemented by three‐month‐old hatchery‐reared parr from a wild and locally adapted strain and a nonresident domesticated hatchery strain. Growth and survival were monitored with three surveys over a period of 16 months after stocking. Fish descending from the wild reared origin strain demonstrated higher survival rates than the hatchery strain. Differences in growth were found among the investigated streams but not among the investigated strains. The differing temperature regimes of the streams were considered as the primary factor causing those disparities. We conclude that stocking measures had little or no additive effect on successful natural reproduction, as the resident wild brown trout performed significantly better than the stocked fish.  相似文献   

4.
Predation after release is one of the major concerns of hatchery fish propagation. However, size-specific interaction between predator and prey on the survival of hatchery-released salmonid fish is largely unknown. To understand the size-selective predation risk, 24-h predation experiments were conducted on masu salmon Oncorhynchus masou in tanks. Four ranges of fork length (FL) were examined for masu salmon as a prey, in combination with three ranges of FL for white-spotted charr Salvelinus leucomaenis as a predator. The results show that not only predator and prey sizes, but also interaction between prey size and predator size, strongly affected the survival rate of masu salmon. Predation on masu salmon with the FL exceeding 40% of the FL of white-spotted charr was rare in the experiment. A logistic regression suggests that 37% relative FL of masu salmon to white-spotted charr results in the 50% survival of masu salmon. Our results suggest that adjusting relative size of hatchery fish to the size of local fish predators at the time of hatchery release will have a significant impact on the survival of hatchery fish in the wild. From this perspective, site-specific, adaptive management might be important to improve the effectiveness of hatchery fish propagation.  相似文献   

5.
Abstract. Hatchery-reared brown trout, Salmo trutta L., yearlings were captured shortly (3h to one week) after their release in a Norwegian stream. The feeding of recaptured hatchery fish was compared with that of wild brown trout. The investigations were carried out during three different periods (May, July and October). Investigations of drift fauna indicated that food availability was best in May. Most hatchery-reared brown trout started feeding shortly after their release in all three periods. Hatchery fish went through a learning process with respect to feeding. This was most clearly demonstrated by the amounts of plant fragments in their stomachs, which were always greater in hatchery fish than in wild fish but which decreased with time after release in hatchery fish stomachs in all three periods. By about a week after release, hatchery trout appeared to be feeding on wild prey nearly as well as did wild fish, but they achieved this better in May than in October.  相似文献   

6.
Abstract. Counts were made of cormorants, Phalacrocorax carbo (L.), feeding on the River Bush. County Antrim. Northern Ireland during the post-dawn period on three occasions. Two of the counts during May 1986 indicated that up to 264 birds may have been feeding at least once per day throughout the catchment during the salmon, Salmo salar L., smolt run. The number of feeding birds had dropped to an estimated 61 by the time of the third count on 1 July 1986. Stomach samples from shot birds showed that upstream feeding was concentrated on wild smolts and brown trout. Salmo trutta L. However, cormorant predalion downstream from the salmon hatchery at Bushmills was restricted solely to hatchery smolts. Estimates of the total daily predation rates were calculated at 653–1214 wild smolts. 107–231 hatchery smolts and 422–785 brown trout. The possible impact of this level of predation on the salmonid stocks of the river was assessed.  相似文献   

7.
Habitat use, food composition and growth of stocked and native brown trout, Salmo trutta L., were studied in the subarctic Lake Muddusjärvi in northern Finland. Stocked brown trout and native brown trout preferred littoral and pelagic areas. Trout were stocked in October. In June stocked trout fed primarily on invertebrates while native fish were piscivorous. From July onwards the composition of the diet of both stocked and native trout was similar and consisted almost entirely of small‐sized whitefish. Brown trout were already piscivorous at a length of about 20 cm. The mean length of prey consumed was about 12 cm. Mean length‐at‐age was similar from the second year in the lake despite of the larger size of stocked fish during the first year in the lake.  相似文献   

8.
We explored potential negative effects of exotic brown trout (Salmo trutta) on native sculpin (Cottus sp.) on the Logan River, Utah, USA by (i) examining factors most strongly correlated with sculpin abundance (e.g., abiotic conditions or piscivory?), (ii) contrasting the extent of brown trout predation on sculpin with that by native cutthroat trout (Oncorhynchus clarkii utah) and (iii) estimating the number of sculpin consumed by brown trout along an elevational gradient using bioenergetics. Abundance of sculpin across reaches showed a strong (r ≥ 0.40) and significant (P < 0.05) correlation with physical variables describing width (positive) and gradient (negative), but not with abundance of piscivorous brown trout or cutthroat trout. In mainstem reaches containing sculpin, we found fish in 0% of age‐1, 10% of age‐2 and 33% of age‐3 and older brown trout diets. Approximately 81% of fish consumed by brown trout were sculpin. Despite a similar length–gape relationship for native cutthroat trout, we found only two fish (one sculpin and one unknown) in the diets of native cutthroat trout similar in size to age‐3 brown trout. Based on bioenergetics, we estimate that an average large (> 260 mm) brown trout consumes as many as 34 sculpin per year. Nevertheless, results suggest that sculpin abundance in this system is controlled by abiotic factors and not brown trout predation. Additional research is needed to better understand how piscivory influences brown trout invasion success, including in‐stream experiments exploring trophic dynamics and interactions between brown trout and native prey under different environmental conditions.  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.
Conservation of migratory salmonids requires understanding their ecology at multiple scales, combined with assessing anthropogenic impacts. We present a case‐study from over 100 years of data for the endemic landlocked Atlantic salmon (Salmo salar, Salmonidae) and brown trout (Salmo trutta, Salmonidae) in Lake Vänern, Sweden. We use this case‐study to develop life history‐based research and monitoring priorities for migratory salmonids. In Vänern, small wild populations of salmon and trout remain only in the heavily regulated Rivers Klar (Klarälven) and Gullspång (Gullspångsälven), and commercial and sport fisheries are maintained by hatchery stocking. These populations represent some of the last remaining large‐bodied (up to 20 kg) landlocked salmon stocks worldwide. We found that one of four stocks of wild fish has increased since 1996; the other three remain critically low. Hatchery return rates for three of four stocks appear stable at roughly 1% and annual fisheries catch is roughly 75 metric tons, with an estimated 7.5% of hatchery smolts being recruited to the fishery; this also appears relatively stable since 1990. Our analysis reveals much uncertainty in key data requirements, including both river return and fisheries catch rates, estimates of wild smolt production and survival, and hatchery breeding and genetics protocols. These uncertainties, coupled with a lack of information on their riverine and lacustrine ecology, preclude effective management of these unique populations. We conclude with a framework for a life history‐based approach to research and monitoring for Vänern salmon and trout, which should be applicable for all endemic, migratory salmonid populations.  相似文献   

11.
Abstract– To assess the levels of gene introgression from cultured to wild brown trout populations, four officially stocked locations and four nonstocked locations were sampled for one to three consecutive years and compared to the hatchery strain used for stocking. Allozyme analysis for 25 loci included those previously described as providing allelic markers distinguishing hatchery stocks and native populations. Different levels of hybridization and introgression with hatchery índividuals were detected in stocked drainages as well as in protected locations. These findings indicate that new policies for stocking and monitoring hatchery fish are needed if gene pools of wild Spanish brown trout populations are to be preserved.  相似文献   

12.
Brown trout Salmo trutta were first introduced into Japan in 1892, and they currently naturally reproduce in several rivers in Honshu and Hokkaido, Japan. Although negative impacts of brown trout introductions on native salmonid fishes have been documented in some Hokkaido rivers, studies of ecological interactions between brown trout and native salmonid fishes on Honshu are limited. In this study, we describe the longitudinal distribution patterns of introduced brown trout, white-spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou in a 4 km stretch of a stream in central Honshu. Underwater observations were conducted in all pools within upstream, middle and downstream sections (190–400 m in length) of this stretch in order to estimate the densities of these species. Only white-spotted charr was observed in the upstream section, while brown trout and masu salmon were observed in the middle and downstream sections. Masu salmon densities, however, were much lower than brown trout densities. In the downstream section, white-spotted charr was absent. These results are consistent with results from previous studies of Hokkaido rivers, where it was found that white-spotted charr in low-gradient areas tend to be displaced by brown trout.  相似文献   

13.
Pacific salmon and trout (Oncorhynchus spp., Salmonidae) of the Puget Sound region of Washington State, USA, have experienced recent and longer‐term (multidecadal) variability in abundance while supporting robust fisheries. As part of the post‐season salmon management process, population‐specific estimates of total adult abundance to Puget Sound (Strait of Juan de Fuca) for pink (O. gorbuscha), chum (O. keta), coho (O. kisutch), sockeye (O. nerka), and Chinook (O. tshawytscha) salmon and steelhead trout (O. mykiss) are calculated annually. We compiled annual estimates of body mass, abundance and survival of hatchery‐ and naturally produced salmon from 1970 to 2015 to compare spatial and temporal patterns across species. Average weights of adult salmon and steelhead returning to Puget Sound, with the exception of coho salmon, have decreased since the 1970s. Temporal trends in abundance, survival and productivity varied by species and origin (hatchery vs. naturally produced). Generally, abundance and survival rates of natural‐origin species decreased whereas those of hatchery‐produced species did not, which is in contrast with other studies' general conclusions of decreasing survival among Puget Sound salmonids. Species diversity has decreased in recent years, with salmonids that rely on a short freshwater rearing phase in the natural environment (hatchery‐produced fish and naturally produced pink and chum) representing >90% of total returns in most years. This new information reveals patterns of body size, abundance, survival and productivity across species, life history and rearing type over the past 45 years and, in doing so, demonstrates the strength in multidecadal, multifactor time series to critically evaluate salmonid species.  相似文献   

14.
Although non‐native species can sometimes threaten the value of ecosystem services, their presence can contribute to the benefits derived from the environment. In the Great Lakes, non‐native brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) support substantial recreational fisheries. With current efforts underway to restore once‐native Atlantic salmon (Salmo salar) to Lake Ontario, there is some concern that Atlantic salmon will impede non‐native contributions to the recreational fishery because Atlantic salmon exhibit niche overlap with brown trout and rainbow trout, particularly during the juvenile life stage. We therefore examined competition and growth of juvenile Atlantic salmon, brown trout and rainbow trout in semi‐natural streams. We found that brown trout were the most dominant and had the greatest growth rate regardless of what other species were present. Rainbow trout were more dominant than Atlantic salmon and consumed the most food of the three species. However, in the presence of brown trout, rainbow trout fed less frequently and exhibited negative growth as compared to when the rainbow trout were present with only Atlantic salmon. These data suggest that, outside of density‐dependent effects, Atlantic salmon will not impact stream production of brown trout and rainbow trout.  相似文献   

15.
Abstract – The possibility to increase the proportion of migrating hatchery‐reared smolts by reducing their food ration was studied. Lake‐migrating, hatchery‐reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish‐farming industry, or reduced (15–20%) rations. They were released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.  相似文献   

16.
Abstract. Shortly after their release in two Norwegian lakes (3 hours to 3 weeks), hatchery-reared brown trout, Salamo trutta L., yearlings were recaptured, and their feeding was compared with that of wild brown trout. Investigations were conducted during three different periods (June, August and September). In all three periods most of the hatchery-reared fish started feeding immediately after their release. The amounts of exuviae from Ephemeroptera larvae and Chironomidae pupae found in the stomachs of hatchery-reared trout decreased with time, indicating that their feeding habits were influenced by a learning process. However, within one week of their release, hatchery trout appeared to be feeding on wild prey as well as did wild fish.  相似文献   

17.
1. Brown trout (Salmo trutta) is an important conservation resource in the Iberian Peninsula. The Atlantic is considered the most hydrologically stable region for the species, although inner Galicia (NW Spain) shows Mediterranean (unstable) climatic conditions. The Galician region, threatened by past releases of brown trout individuals from central European origin, harbours two native lineages, one of them endemic to the Iberian Peninsula. These populations are thus highly valuable for conservation, as well as being important for recreational fisheries. 2. In total, 546 individuals from 16 sampling sites (15 natural locations from inner Galicia and one from a central European hatchery stock) were genotyped for 11 nuclear markers (10 microsatellite loci and the LDH‐C* locus) to analyse genetic variability, population structure and introgression impact from stocking in order to assess the conservation status of brown trout in the region. Moreover, correlation among hatchery introgression and environmental variables relevant for species population dynamics was also investigated. 3. Genetic variability was within the range of Iberian brown trout (He = 0.500–0.600). Stocking impact was higher than previously reported values for the Atlantic region and was related to environmental instability. Highly significant native population differentiation was observed in the whole region (FST = 0.283), at least four main genetic groups being detected across the geographic distribution studied. 4. Conservation strategies at local level (including the creation of genetic refuges and temporal monitoring of genetic composition) are suggested to agencies and administrations for the sustainable management of brown trout.  相似文献   

18.
Abstract –  The swimming performance of wild and hatchery-reared smolts of two salmonid species was investigated. Wild Atlantic salmon smolts (WS) and brown trout smolts (WT) of equal size were caught in fish traps during migration. Hatchery-reared smolts of both species (HS and HT for salmon and trout respectively) were first generation offspring from wild broodstock. The swimming performance of individual smolts from the four groups (WS, HS, WT, HT) was tested three consecutive times using a swimming flume with water flowing at a start rate of 0.16 m·s−1 and a constant acceleration rate of 0.167 cm·s−2 (10 cm·s−1·min−1). Wild caught smolts of both species performed significantly better than those reared in hatchery conditions. The WS group were observed to maintain an average swimming speed ( U burst) that was 30% faster than the HS group, whereas the wild trout smolts were superior to HT by approximately 25%. Repeated measures revealed species-specific exhaustion patterns. Brown trout smolts maintained consecutive U burst indicating significant stamina compared with Atlantic salmon smolts that were found to be exhausted by the initial trial.  相似文献   

19.
Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey‐switching hypothesis); (ii) salmon foraging behaviour (refuge‐dispersion hypothesis); and (iii) salmon size and growth (size‐refuge hypothesis). Two facultative planktivorous fishes, Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important. Our prey‐switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0.2 g m?3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge‐dispersion hypothesis was supported by data indicating a five‐fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size‐refuge hypothesis was supported by data indicating that size‐ and growth‐dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery‐reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process.  相似文献   

20.
Migration timing, speed, survival and effects of environmental parameters on migration, between wild and hatchery produced Atlantic salmon, Salmo salar L., smolts in the River Lærdalselva were studied. Hatchery‐reared (n = 40) and wild pre‐smolts (n = 40) were tagged with acoustic tags, and an array of receivers along the migration route was deployed. In all, 77 and 85% of the fish from the two groups, respectively, were recorded as migrating smolts, that is, predation rate and/or numbers of fish opting to remain in the river were low. Hatchery‐reared smolts showed a migration pattern, speed and migration route similar to wild smolts, even though the time period between river release and onset of migration was relatively short. Both groups of smolt showed high migration speed through both the river and the fjord compared with other studies.  相似文献   

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