首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
In fish hormones are released into the nutritive yolk sac during oogenesis in quantities that mirror female plasma levels, thus implying a potential for the maternal endocrine state at spawning to affect offspring characteristics. In the present study, mature female Atlantic salmon, Salmo salar, were given intraperitoneal cortisol implants to investigate potential impacts of simulated stress on offspring ontogeny. Maternal cortisol levels reduced fertilization success and affected several offspring characters: lowered initial survival rates, impaired growth early in life and increased prevalence of morphological abnormalities in adult individuals. In addition, offspring from cortisol administered females displayed increased locomotor activity in an acute confinement test. These results suggest that developmental trajectories of salmon offspring can be considerably altered if their mothers experience severe stress during the final stages of gametogenesis. The present findings may have conceptual and applied ramifications as they demonstrate a mechanism that links the maternal environment to subsequent viability of the progeny.  相似文献   

2.
Abstract Spawning adult Atlantic salmon, Salmo salar L., were sampled in five tributaries of the River North Esk, Scotland, during the winters 1989/90 and 1990/91. The fish furthest upriver had higher sea- and smolt-ages and the one-sea-winter fish were smaller and more coloured than those spawning further downstream. These differences indicate that the uppermost tributaries are populated by fish which enter the river early in the year and the lowest tributaries by fish entering late in the year. Exactly why such a structure exists is not clear, but it is suggested that these differences may be adaptive and that selection effects may continually be modifying these populations.  相似文献   

3.
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   

4.
Run timing of escaped farmed Atlantic salmon Salmo salar vs. wild fish was compared by the use of video camera surveillance in 15 rivers over several years, covering 1600 km of the Norwegian coastline (from 58°N to 69°N). Annual runs of wild salmon varied among rivers from <200 fish to more than 10 000. During the surveillance period that for most rivers extended from late May to early October, larger‐sized salmon (fish ≥ 65 cm) generally entered the rivers earlier than small fish. The percentage of salmon identified as escaped farmed fish ranged from 0.1% to 17% across rivers with an average of 4.3%. Estimates of escapees are, however, assumed to represent minimum values because an unknown number of farmed fish passing the video cameras may have been misclassified as wild fish. By the use of a linear mixed model and generalised additive mixed models, it was found that the relationship between run timing and fish length differed significantly between farmed and wild salmon. While small‐sized farmed and wild fish (<65 cm) entered the river at about the same time, wild large salmon returned on average 1–2 weeks earlier than similarly sized escapees. The proportion of large‐sized farmed escapees also increased until late August and decreased thereafter. In contrast, there was a relatively constant and lower proportion of small‐sized escapees throughout the season. Within the surveillance period, there was no evidence of any exceptionally late runs of fish classified as escaped farmed salmon.  相似文献   

5.
The migration patterns of wild and released farmed Atlantic salmon, Salmo salar L., were studied by radio-telemetry during migration from entering a river to after spawning. The wild salmon were caught during return migration in bagnets and the farmed salmon were produced in a near by fish farm. Both groups were tagged and released at sea near the river mouth of the River Alta, North Norway. A pronounced individual variation in migration pattern was observed. No significant differences was found between wild and farmed salmon in the distance from entering the river mouth to the place of the first stop (recorded in the same pool for 5 days or longer) and the days from entering the river mouth to arrival at the first stop. For both wild and farmed salmon, mean migration speed was 2.6 km day1, varying from 0.4 to 11.0 km day-1. A larger proportion of farmed salmon distributed to the upper part of the river at spawning; mean distances from the river mouth were 30.1 and 19.1 km. respectively. Farmed salmon spent a significantly longer time from entering the river to reaching the area occupied during spawning.  相似文献   

6.
A monitoring program for the prevalence and intensity of sea lice infestations of wild and escaped farmed salmon has been underway on the Magaguadavic River since 1992. Fish are screened in a fish ladder trap located in freshwater a short distance above the head of tide. No trends with time were evident in observed sea lice burdens, and in all years the majority of salmon, both wild and escapees, had no or low levels of infestation with sea lice. In the spring of 2002, 23 landlocked salmon moving to sea from the Magaguadavic River were acoustically tagged. Two fish returned to the river after a brief period of residence in Passamaquoddy Bay, with significant dermal damage from sea lice. These fish were tracked to areas close to commercial salmon farms.  相似文献   

7.
The timing of smolt migration is a key phenological trait with profound implications for individual survival during both river descent and the subsequent sea sojourn of anadromous fish. We studied relationships between the time of smolt migration, water temperature and light intensity for Atlantic salmon (Salmo salar) and sea trout (Salmo trutta). During 2006–2012, migrating smolts descending the southern Norway River Storelva were caught in a rotary screw trap located at the river mouth. The date of 50% cumulative smolt descent correlated significantly with the date when the river temperature exceeded 8°C for both Atlantic salmon and sea trout smolts. In 2010, smolts of both species were passive integrated transponder (PIT)‐tagged, and the diel timing of their migration was precisely documented. The degree of night migration decreased in both species as the river temperature rose, and at temperatures above 12–13°C, more smolts migrated during day than during night. A multinomial model was fitted for estimating temperature and species effects on probabilities of migration during night, daytime, dusk and dawn. Atlantic salmon smolts preferred migrating under lower light intensities than sea trout smolts during early, but not late spring when both species migrated during bright daylight. In accordance with the early‐season tendency to migrate at night, Atlantic salmon smolts migrated more during darker hours of the day than sea trout. In both species, smaller smolts migrated under dark conditions than during light conditions. Most of the findings on thermal, light and temporal effects on the observed smolt migration pattern can be explained as adaptations to predation avoidance.  相似文献   

8.
Supportive breeding of Atlantic salmon (Salmo salar) is commonly employed to maintain numbers of fish where the species has become locally endangered. Increasingly, one of the main aims of population management is the preservation of natural genetic diversity. If the stocks employed in supportive breeding exhibit reduced variation they can alter the natural pattern of genetic variation observed in wild populations. In northern Spain, wild adult salmon are caught every year from local rivers and artificially crossed in order to create supportive stocks. The offspring are hatchery reared until the juvenile stage, then released into the same river where their parents were caught. In the current study, our findings demonstrate that although adult broodstock exhibit a pattern of variation similar to the wild populations, variability at microsatellite loci was drastically reduced in the juveniles released into one of three rivers analyzed. The contribution of broodstock to this juvenile stock was examined by pedigree analysis. A restricted number of females contributing to the hatchery stock was identified as the main cause of loss in genetic variation, possibly due to overmaturity of some multi-sea-winter females. We suggest that better monitoring and control of parental contribution will help in solving the problem of loss of genetic diversity in hatchery populations.  相似文献   

9.
The migratory behaviour of adult wild and escaped farmed Atlantic salmon, Salmo salar L., before, during after spawning in the River Namsen, Norway, was analysed using radio telemetry. The fish were caught, radio tagged and released into the fjord between 7 and 25 km from the river mouth. A significantly higher proportion of wild (74%) than farmed (43%) salmon was subsequently recorded in the river. Wild salmon (33%) were more frequently captured in the sea and in rivers than farmed salmon (14%). The migration speed from release to passing a data logger 11 km upstream from the river mouth was not significantly different between wild (20.6 km day?1) and farmed (19.8 km day?1) salmon. Wild salmon tagged when water flow in the river was increasing had a significantly higher migration speed than wild salmon tagged when water flow was decreasing. This was not true for farmed salmon. Farmed salmon were distributed significantly higher up the river than wild salmon during spawning, although both types of fish were found together in spawning areas. Thus, there was no geographical isolation to prevent spawning between wild and escaped farmed salmon. Farmed salmon had significantly more and longer up- and downstream movements than wild salmon during the spawning period. Unlike farmed salmon, the number of riverine movements by wild salmon increased significantly when variation in water flow increased. A smaller proportion of wild (9%) than farmed (77%) salmon survived through the winter after spawning.  相似文献   

10.
Interactive segregation has been suggested as the ruling competition mechanism determining niche and niche segregation between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Results from allopatry–sympatry observations of habitat use in both nature and in experiments were contrary to predictions derived from the interactive segregation hypothesis. Habitat use parameters under natural conditions such as distance to shore for Atlantic salmon parr were nearly identical in allopatric (mean ± SD; 3.2 ± 1.4 m) and sympatric (3.3 ± 1.4 m) situations. Occupied water depths largely reflected available water, but water depths <15 cm were avoided by salmon parr. Under experimental conditions, habitat use of allopatric salmon was density independent and salmon size had only minor effects, with smaller fish being more likely to occur in the shallow. Habitat use of salmon in sympatry with trout did not differ from allopatric salmon habitat use, and only salmon size had minor effects on depth choice – occurrence of trout or fish density had no effect. Allopatric trout was in general more frequent in the shallow habitat than salmon. Habitat use of sympatric trout was affected by the occurrence of salmon and trout size, resulting in a higher use of the shallow habitats for small trout. To conclude, selective segregation has a dominant role in salmon habitat use (not affected by trout occurrence), whereas a mixed situation occurs in trout habitat use with elements of interactive segregation when competing with Atlantic salmon (affected by salmon occurrence).  相似文献   

11.
    相似文献   

12.
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   

13.
Total aggression and individual behavioural traits of equal-sized juveniles of farmed Atlantic salmon Salmo salar L. selected for five generations in the Norwegian Breeding Programme for Salmonids and a wild strain originating from the River Rauma, Norway, were compared in pure (10 fish) and mixed (5 + 5 fish) groups. Total aggression was defined as the sum of the following five offensive behaviour patterns: intentional movements, lateral display, frontal display, charge and bite. Experiments were carried out in 2-m2 tanks with either a grey fibreglass substrate (pure and mixed groups) or diagonally divided into a fibreglass and river cobble substrate (mixed groups only). In mixed groups kept on a fibreglass substrate, the aggressive behaviour directed by wild salmon towards farmed salmon was more frequent than the reverse (84.2 and 27.0 aggressive acts h–1, respectively, P < 0.025). Total aggression was not significantly different between wild and farmed juveniles in tanks with divided substrate. The aggressive behaviour of wild and farmed salmon was significantly increased when kept in tanks with fibreglass substrates (437%, P < 0.005, and 296%, P < 0.05 respectively). Pure groups of either wild or farmed salmon kept on a fibreglass substrate exhibited similar frequencies of total aggression (85.7 and 101.6 0 aggressive acts h–1, respectively, P > 0.1) and single behaviour patterns. The aggressive behaviour of farmed offspring was not influenced by vertical distribution in the tanks with a fibreglass substrate. Farmed salmon tended to position pelagically (78%) and used the water column more frequently than wild salmon (19%), whereas wild salmon hid more. It is concluded that social interactions among groups of juvenile Atlantic salmon are influenced by substrate.  相似文献   

14.
Closure of the Newfoundland commercial Atlantic salmon, Salmo salar L., fishery in 1992 was the most restrictive measure introduced to help rebuild depressed local stocks of salmon. Here, the effects of the closure are evaluated by analysing trends in abundance since 1984, and estimates of survival in both freshwater and marine environments derived from enumeration of salmon at fish counting facilities. While freshwater production of smolts generally has been maintained, marine survival rates remain low (2–10%), and highly variable. Overall, total stock size differs little from that prior to the closure of the commercial salmon fishery. Spawning escapements have increased by a factor of 2 or 3 in some rivers, but in other areas total returns are lower on average than those prior to the fishery closure. Factors other than exploitation are contributing to lack of stock recovery, resulting in continued conservation concerns.  相似文献   

15.
The level of genetic diversity in a cultured Atlantic salmon (Salmo salar) population from Tasmania, Australia was examined at 11 microsatellite loci and compared with that in its progenitor population from the River Philip in Nova Scotia, Canada. The reference progenitor population consisted of archived scales collected from wild River Philip salmon in 1971 and 1972, not long after salmon from this river were imported into Australia in the mid‐1960s. The Tasmanian hatchery stock had a significant reduction in the mean number of alleles (31–43%) and mean allelic richness (28–39%) across all microsatellite loci compared with the wild Canadian population. Mean heterozygosity levels remained unchanged. Estimates of per‐generation effective population sizes for the Tasmanian population, based on allele frequency temporal variance with the wild progenitor population, ranged from 102–207 individuals and reflected hatchery records.  相似文献   

16.
Grimardias D, Merchermek N, Manicki A, Garnier J, Gaudin P, Jarry M, Beall E. Reproductive success of Atlantic salmon (Salmo salar) mature male parr in a small river, the Nivelle: influence of shelters.
Ecology of Freshwater Fish 2010: 19: 510–519. © 2010 John Wiley & Sons A/S Abstract – The breeding activity of a small population of Atlantic salmon (Salmo salar L.) was monitored on the Nivelle River in southwest France to estimate the overall contribution of mature male parr and the numbers involved in egg fertilisation. In the twelve redds sampled, 563 eggs were collected for parental assignment and the physical habitat was characterised to investigate the possible relationship between parr reproductive success and habitat complexity. The overall contribution of mature male parr was particularly high (87%, one of the highest estimates ever reported). Concerning habitat complexity, granulometry and shelter diversity were correlated with the number of parr breeders contributing to egg fertilisation in each redd. A complex habitat increased multiple paternity, which could affect the effective size and genetic variability of small salmon populations.  相似文献   

17.
Variations in space (geographical location) and time (year) of phenotypic traits linked to life-history (size, growth, condition and sexual maturation) were analysed within the population of Atlantic salmon (Salmo salar L.) 1 + parr of Little Codroy River (southwest Newfoundland). The hydrographic system was divided into 10 zones: 4 for the mainstem and 6 for the tributaries. Despite the small size of the river studied, a highly significant spatial heterogeneity was observed. Within the mainstem, size, growth and rate of maturation of males tended to decrease when progressing upstream. When compared with the tributaries as a whole, the mainstem had smaller salmon juveniles, both at the end of the first winter (mainstem: 67.6 mm; tributaries: 73.3 mm) and at 1 + age (mainstem: 80.6 mm; tributaries: 88.3 mm), and the proportion of maturing fish among 1 + males was lower (mainstem: 48.6%; tributaries: 74.2%). According to the feature considered, from 20% to 70% of the spatial effect was due only to differences between the mainstem and the tributaries as a whole. A strong year effect was also revealed. Life-history traits seemed to fluctuate over time independently from one tributary to another, whereas patterns in their yearly variations were basically consistent among zones in the mainstem. The potential role of genetic and environmental factors in explaining changes in space and time of biological characteristics of parr is discussed. Within a small system such as Little Codroy River, spatio-temporal life-history variations of Atlantic salmon juveniles were most likely driven by environment.  相似文献   

18.
This study explores the ecological and economic impacts of interactions between escaped farmed and wild Atlantic salmon (Salmo salar, Salmonidae) over generations. An age‐ and stage‐structured bioeconomic model is developed. The biological part of the model includes age‐specific life‐history traits such as survival rates, fecundity and spawning successes for wild and escaped farmed salmon, as well as their hybrids, while the economic part takes account of use and non‐use values of fish stock. The model is simulated under three scenarios using data from the Atlantic salmon fishery and salmon farming in Norway. The social welfare is derived from harvest and wild salmon while the economic benefits of fishing comprise both sea and river fisheries. The results reveal that the wild salmon stock is gradually replaced by salmon with farmed origin, while the total social welfare and economic benefit decline, although not at the same rate as the wild salmon stock.  相似文献   

19.
Thermal habitat was recorded by data storage tags (DSTs) applied to Atlantic salmon (Salmo salar L.) kelts during their seaward migration in the spring of 1998 at enumeration facilities in Highlands River, Humber River, Western Arm Brook, and Campbellton River, Newfoundland. In total, 139 DSTs were applied and data were downloaded from eleven of the recovered tags. The recovered tags had been applied at Highlands, Campbellton and Western Arm rivers and recovered in the coastal waters of Newfoundland and Québec and at the enumeration facilities at Highlands and Campbellton rivers. Water temperatures experienced by the fish were recorded for periods of 62–118 days at resolutions of 15–30 min. The data from the sea record on the DSTs were analysed for temperature patterns in relation to migration behaviour and diurnal movement of the fish. A variety of patterns were exhibited on the temperature records suggesting that the fish were behaving in various ways at different times. For Campbellton and Highlands fish over the course of some 24 h periods, night‐time temperatures changed little and were among the highest daily temperatures experienced by the fish, whereas daytime temperatures often showed dramatic and frequent shifts in temperature presumably as the fish rapidly and frequently changed depth. For the Western Arm Brook fish, rapid fluctuations in temperature occurred sometimes during the day and night without a consistent diurnal pattern. We also considered large‐scale aspects of the data by examining oceanographic conditions in relation to the temperatures recorded by the tags.  相似文献   

20.
The straying rate of ranched Atlantic salmon, Salmo salar L., into rivers in Iceland was estimated on the basis of coded wire tag recoveries. Out of a total of 15 158 recaptured tagged salmon from the releases between 1987 and 1992, 189 fish (1.3%) strayed into 25 out of the 79 salmon rivers observed. Most of the strayers were found in neighbouring rivers to the ranching stations. There were no significant differences in straying rate between different age classes of salmon returning from the same smolt year class. Generally, there was a delay of 26-27 days in running time between strayers in rivers and salmon returning to the ranching station. Higher straying rates were observed for ranching stations using riverine traps than for stations using estuary traps. By close inspection of seven key rivers in Iceland and assuming a 50% exploitation rate (fishing effort) in the rivers, on average, 2.1% of the returning salmon in ranching were estimated to stray to native salmon rivers over the years. A limitation of using these numbers to estimate geneflow between ranching stocks and wild populations is discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号