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1.
Abstract Catch returns are often analysed as a means of inferring the status of salmon stocks. One aspect of such analyses is the problem of grilse error (the misreporting of one-sea-winter salmon as multi-sea-winter salmon), which may have important consequences for the management of salmon stocks. Reported catches from two estates on the River Spey between 1982 and 1992 were compared with the sea ages of the fish determined from scale reading. Weight was an important factor in determining the reported sea age of salmon in catch returns; the relationship between weight and sea age in the reported catch remained relatively constant throughout the angling season. Analysis of the scale sample data, however, indicated that the relationship between weight and actual sea age changed through the angling season, grilse accounting for increasing proportions of all weight classes up to 10 lbs (4.5 kg) as the season progressed. Grilse error was an identifiable problem at both estates, resulting in grilse catches being underreported by over 20%.  相似文献   

2.
Reared salmon smolts have been released into the Burrishoole river system since 1957. From 1970 it has been possible to record all adult returns. Survival of reared smolts to adult, as measured by numbers of fish returning to fresh water, has averaged 2.1% cf. 8.4% for wild smolts. A number of factors contributing to the comparatively poor returns of reared smolts are outlined. The behaviour of reared adults on return to fresh water is described and it is concluded that once past their homing point, their contribution to the rod and line fishery diminishes. Thus, the exploitation rate of reared grilse below their homing point (L. Furnace) exceeds that above (L. Feeagh). In confirmation, whilst a positive correlation exists between total stock and total catch of reared grilse on L. Furnace, no significant correlation exists between stock and catch on L. Feeagh. In the Burrishoole system, the exploitation rate of wild grilse usually exceeds that of reared and it is only in L. Furnace that reared grilse make a significant contribution to the total rod catch. The mean exploitation rate obtained for Burrishoole reared grilse is low (10.8%) when compared with those recorded for salmon in other systems. The comparable exploitation rate of Burrishoole wild grilse is 14.3%.  相似文献   

3.
Smolts of coho salmon (Oncorhynchus kisutch) were exposed to 5 × 10?5 mg·l?1 morpholine for 15 days and released into the Salmon River along with an unexposed control group. During the following two autumns, morpholine was introduced into the hatchery's fish ladder on various days and the return of experimental fish was recorded. The returns of morpholine-exposed and control fish were not statistically different. With morpholine present in the fish ladder, control fish were not repelled, and with morpholine absent from the ladder, morpholine-exposed fish returned as readily as control fish.  相似文献   

4.
Information on marine and freshwater survival and exploitation of River Bush salmon was developed into a model illustrating the potential ranges of grilse production per 1000 smolts. Values were attributed to the grilse 'crop' at each of three potential production stages – commercial landings, angler catches and fertilized egg production – using both published and derived valuations. Using the model, a range of values per wild smolt was calculated for grilse production on the River Bush.  相似文献   

5.
Infectious salmon anaemia (ISA) is a highly virulent viral disease of Atlantic salmon that causes massive economic losses to infected aquaculture operations. Our goal was to detect and map quantitative trait loci (QTL) that confer resistance to ISA in an admixed commercial strain of Atlantic salmon that was largely founded from the Saint John River (SJR) in North America. Full‐sibling families were challenged with a virulent strain of ISA virus. Mortality was tracked during two annual trials with individual fish that survived to the end of the trial being classified as ‘resistant’, and those that died were classified as ‘susceptible’. Ten families with intermediate levels of mortality and an average size of 54.2 individuals were chosen for genotyping with a 50K SNP array designed for the SJR strain. Single nucleotide polymorphisms that were segregating within families were first used to make a composite 11K female linkage map that was then used to find the positions of QTL for ISA resistance using a half‐sib model. The dam‐based HS model detected a total of three QTL for ISA resistance including an experiment‐wide significant QTL on Ssa25 that accounted for 8.3% of the phenotypic variance and chromosome‐wide significant QTL on Ssa03 and on Ssa04 that accounted for 6.0% and 6.6% respectively. We conclude that classic linkage mapping within families continues to be an important method of detecting QTL for oligogenic traits in strains founded from multiple populations. Single nucleotide polymorphisms with moderate trait effects are being used to select within families for more ISA‐resistant strains of Atlantic salmon.  相似文献   

6.
Abstract. In order to assess the accuracy and reliability of automated fish counters for counting adult Atlantic salmon, Salmo salar L., a 'Logie' resistivity counter was installed in late June 1989 in the control dam above the fishway in Northeast River, Placentia, Newfoundland, Canada. The counter was in operation for 26 days (1–26 July). The accuracy of daily counts recorded by the counter was verified by visual counts of Atlantic salmon released from a trap located downstream of the counter and immediately above the fishway. All the fish released from the trap had to pass over the counter. A total of 517 salmon (mainly grilse) was released from the trap and the net number of upstream migrants recorded by the counter was also 517. This is the first test and use of an open-channel counter in eastern Canada. The results suggest that some counting fences and fishways may be easily adapted for installation of automated counters and that counters offer a cost-effective means of counting adult Atlantic salmon.  相似文献   

7.
The upstream migration of 17 radio-tagged adult Atlantic salmon, Salmo salar L., past hydroelectric developments on the River Nidelva, Southern Norway, was examined. Salmon migrated quickly from the site of release in the lower part of the river up to the tunnel outlet of Rygene power station, but were substantially delayed at the outlet. The salmon stayed in the outlet area for 0–71 days (median = 20), and mainly took up a position inside the dark power station tunnel. Water discharge in the tunnel was 57–176 m3 s−1, while residual flow in the river between the outlet and the dam 2.5 km further upstream was 3 m3 s−1. Ten salmon passed the outlet and entered the residual flow stretch, but none passed the dam. Six of the 10 salmon returned to the tunnel outlet. No major migration barriers were identified in the residual flow stretch, suggesting lack of motivation among the salmon to migrate due to either low water discharge compared with the main river, or several minor migration barriers along the river stretch.  相似文献   

8.
Investigations were conducted on the effects of oceanic variations (as indicated by sea temperatures) and catches of the Faroese, Norwegian Sea and West Greenland salmon fisheries on the sea-age composition of Atlantic salmon (Salmo salar L.) from 22 Icelandic north-coast rivers. Catches of grilse in rivers were strongly correlated among the 22 rivers, as were the ratios of grilse caught to two-sea winter (2SW) salmon caught the next year. Four of the 22 rivers showed increasing ratios over time and three of these rivers, all in the northeast, had significantly higher mean ratios after the expansion of the Faroese fishery than before (P < 0.05). No evidence was found from ratios for the other 18 rivers to suggest that Faroese fishing was significantly depleting those stocks, even though 13 micro-tagged north-coast salmon had been recovered in the fishery in the 1988–1989 season. No evidence was found that Norwegian Sea or West Greenland fisheries affected stock composition. The mean April–May sea temperature prior to when the smolts enter the sea was significantly and positively related to ratios in eight of the 22 rivers. This result, along with frequent significant correlations in ratios among rivers, indicated that more rapid growth of smolts in their first summer may have increased grilse to 2SW salmon ratios on several rivers.  相似文献   

9.
During the last 24 years, the number of Atlantic salmon, Salmo salar L., migrating up the River Frome has varied between < 1000 and > 4000 fish per annum. Most parr become smolts at age 1+ and there are three main sea ages of salmon returning to the river. Each sea age shows a bimodal pattern of migration in the river. Primary migration times for 3-sea-winter (3SW) fish are spring and autumn, with 2SW fish and grilse (1SW) peaking in summer and autumn. Some 28.4% of 3SW and 6.9% of 2SW fish are previous spawners. Multi-sea-winter fish historically passed over the counter in all months of the year, but recently, their numbers have declined, as have total numbers of fish of all ages. There has been a fundamental change in the age structure of the population, with grilse increasing in proportion over the study period. Photographs of fish, taken for validation of the counter, showed a significant decrease in mean length of grilse, but an increase in mean length for 2SW and 3SW fish. Rod catch data support these findings.  相似文献   

10.
Abstract Variations in the age structure and number of Atlantic salmon, Salmo salar L., running into the River Eo in northern Spain were assessed from catch records of sport fisheries for the period 1949 to 1991. The analysis focused on two periods (1951–1960 and 1981–1991) for which more complete data on fish number, size and age were available. Over the whole period, no evidence for a decline in the total salmon run was found, but the last few years revealed significant changes in both the number and age structure of salmon caught. The catches were mainly composed of multi-sea-winter salmon, and this did not change from the 1950s to the 1980s as the proportion of grilse remained unchanged. However, since 1980, there was a marked decline in both the proportion of 3-sea-winter salmon (versus 2-sea-winter fish) and the frequency of previous spawners among the multi-sea-winter salmon. These changes were probably linked because most of the previous spawners re-entered the river as 3-sea-winter or older salmon. River age of salmon caught in the 1950s was low and constant (about 90% of the catch had smolted at one year) but the mean age of smolting increased in the 1980s.  相似文献   

11.
本报道绥芬河开展大麻哈鱼人工繁殖与孵化放流试验。1989、1991、1993年共采捕利用亲鱼674尾，其中雌亲鱼365尾， 采卵101．6万粒，雌亲鱼利用率为81．3％，受精率为95．6％，孵化率为96．3％，稚鱼饲养成活率为92．5％，放流稚鱼共92．2万尾。本项试验为该水系大麻哈鱼大规模殖放流提供必要的技术参数。  相似文献   

12.
Abstract. Paired subgroups of fish were derived in January from each of two parent sea-cages of Atlantic salmon, Salmo salar L. The proportion of fish which later became sexually mature in each parent group, after one winter (as grilse) and under commercial rearing density, was determined. Maturity rates in the subgroups, reared in sea-cages at lower density, were significantly greater than in the parent groups. Rearing at reduced density was associated with increased growth in some, hut not all, comparisons. Periodic anaesthesia, handling and sampling of blood for steroid hormone determinations did not consistently affect maturation rate or growth among fish in one of each pair of subgroups. Sexual development was assessed by determining levels of the steroid hormones 11-oxotestosterone or 17β-oestradiol in samples of blood serum taken monthly from individually marked fish in one of each pair of subgroups. Between February and April specific growth rates in maturing male grilse were significantly higher than in fish subsequently shown to have remained immature. Growth rates in maturing female grilse differed similarly between March and April. Between July and August, however, growth rates of non-maturing salmon exceeded those of grilse.  相似文献   

13.
Abstract – Understanding population regulation in juvenile salmonids requires distinguishing the effects of intrinsic (size, behaviour) and extrinsic (food, competition) factors. To examine the relative influence of these variables on juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Salmon River drainage (ID, USA), we examined diel differences in foraging microhabitats, behaviour and consumption in two areas with consistent differences in parr‐to‐smolt survival. In lower Big Creek (LBC, high‐survival area) and upper Big Creek (UBC, low‐survival area), we observed fish by snorkelling, recording length, behaviour (foraging rate and aggression) and physical (depth, velocity, cover, temperature) and biotic (density, size and species of neighbouring fish) microhabitat features. Stomach contents were extracted to estimate consumption. Depth and temperature were greater in LBC, where Chinook salmon were significantly larger and present at lower densities. Fish in LBC exhibited higher foraging activity during the day than night, but there were no size differences between day and night foragers. In UBC, a higher density area, foraging behaviour did not change between day and night, although the smallest size classes did not forage nocturnally. Regression models that integrated physical and biotic variables suggested that physical factors influenced foraging in both areas, but competition also affected foraging in UBC. Our results demonstrate that fish from low‐ and high‐survival populations in Big Creek are exposed to different physical and biological influences during their first growth season, which are reflected in different diel foraging behaviours.  相似文献   

14.
In 1972 a hybridization experiment with salmonids was initiated at the Fish Breeding Experimental Station, Sunndalsøra. The purpose of this experiment was to study the viability, performance traits and the fertility of hybrids. Hybrids were produced from the following members of the salmon family: Salmon (Salmo salar), sea trout (Salmo trutta), brown trout (Salmo trutta), rainbow trout (Salmo gairdneri) and arctic char (Salvelinus alpinus). All crosses attempted, except those involving the rainbow trout, were relatively successful. Considerable differences in the hatching rates of the different hybrids were observed. All crosses with the arctic char were heavier than the better pure bred specimens at 11 months. In all other crosses the hybrids were lighter than the purebred specimens. The experiment is continuing, it is evident that more research is necessary before the potential value of these hybrids for fish farming can be properly assessed.  相似文献   

15.
The microhabitat selection of the ectoparasite Gyrodactylus salaris (Lærdalselva strain, Norway) was investigated concurrently with studies on the parasite population growth on five strains of Atlantic salmon, Salmo salar L., and a strain of Danish rainbow trout, Oncorhynchus mykiss (Walbaum). The salmon used were hatchery‐reared parr of East Atlantic strains [River Conon (Scotland), River Storå (western Denmark) and River Ätran (western Sweden)] and Baltic strains [Lule and Ume (eastern Sweden)]. The location and numbers of parasites were recorded on anaesthetized fish once a week from week 0 to week 8. The mean abundance of G. salaris steadily increased to high levels on the River Conon, Storå and Ätran strains until the end of the experiment. The mean abundance of G. salaris on the two Baltic strains (River Lule älv and River Ume älv) initially increased but after 4–7 weeks the growth of the parasite infrapopulations decreased markedly. The Danish rainbow trout strain showed the lowest abundances of all the fish species and strains. Gyrodactylus salaris preferentially selected the fins and head region when colonising the hosts (all species and strains). Increasing percentages of G. salaris on the tail fins of the East Atlantic strains and rainbow trout were found during the course of infection, whereas the two Baltic salmon strains experienced a decreasing percentage of parasites in this microhabitat.  相似文献   

16.
Abstract  For a number of rivers in Newfoundland, Atlantic salmon, Salmo salar L., is managed in relation to river-specific conservation spawning requirements. One such river is the Gander River, where between 1989 and 1999, the escapement of Atlantic salmon, a major factor in assessing the status of stock, was determined using a fish counting fence. In 2000, the counting fence was discontinued and alternative means of calculating total returns were explored. Regression and simulation methods, using relationships between total returns and salmon counts at an upstream tributary during 1989–99, formed the basis for estimates of returns for 2000, and the uncertainty around estimates. The accuracy of methods is evaluated by retrospective comparisons with actual total returns between 1989 and 1999. Estimates of total returns deviated from the actual by as much as 50–60%, depending on the method. Management implications of the approach are discussed.  相似文献   

17.
In August 2008 the Kasatoshi volcano in the Aleutian archipelago erupted. Prevailing winds carried volcanic ash to the Gulf of Alaska, where its soluble iron dissolved and initiated a widespread phytoplankton bloom. Two years later, the abundance of sockeye salmon (Oncorhynchus nerka) returning to spawn in the Fraser River was larger than any observed since 1913. Kasatoshi's influence on growth and survival has been proposed as the ultimate cause of the abundant return. However, when relevant data are brought to bear on the hypothesis, it shows that: (1) survival of the abundant sockeye salmon cohort was unremarkable when compared with the historical record; (2) without an accompanying volcano, survival of the returns in 2011 was about the same as in 2010; (3) parental abundance that spawned the abundant return in 2010 was the sixth largest since 1948; (4) during their first summer at sea, sockeye salmon are not known to migrate in the offshore region where the anomalous chlorophyll bloom occurred; (5) an older cohort that was likely exposed to the chlorophyll bloom had the second lowest productivity on record when it returned in 2009; (6) immature sockeye salmon do not feed on diatoms, so any trophodynamic benefit derived from excess chlorophyll in mid‐to late August 2008 would have to have found a rapid trophic pathway to sockeye salmon on the continental shelf; and (7) no other populations of sockeye salmon or other species of salmon that are known to rear in the same region had unexpectedly high returns.  相似文献   

18.
The numbers of particular prey in stomach samples of juvenile chinook salmon varied between sites, months and years in two controlled flow demonstration channel sites and the mainstem lower Waitaki River. During 4 growing seasons, 1982–1986, Deleatidium, Aoteapsyche, Hydroptilidae, Elmidae, Chironomidae and Amphipoda were important components of the diet. Salmon also ate a variety of other items of aquatic and terrestrial origin. Diets were quite similar and tended to change in the same way in all sites simultaneously, perhaps in response to discharge. Smaller prey (Chironomidae, Hydroptilidae and early instar Aoteapsyche) were more numerous in stomach samples in seasons of lower, more stable, discharge. Fewer but larger prey were consumed during high flows. The salmon sampled in March 1986 originated from the high egg deposition of 1985 and grew during a season of low discharge. They were exceptionally small and their diet consisted of large numbers of small prey. There was no evidence of progressive annual changes in the habitat or the diet of salmon in the demonstration channels. However, it would be prudent to arrange for flow fluctuations that would be sufficient to flush finer substrate sediments in a controlled flow residual river, thus maintaining the diversity of prey for juvenile salmon.  相似文献   

19.
Abstract –  We examined the site fidelity of spawning adult sockeye salmon ( Oncorhynchus nerka ) by tagging and releasing fish in the same stream reach (controls) and displacing them among different but nearby sites ( c . 50 m away). Three sites – two above a stream junction ('upper' reach and 'pond') and one below ('lower' reach) – allowed us to compare the behavior of salmon in the presence and absence of olfactory cues and habitat similarity. Most controls of both sexes (90%) remained in the immediate vicinity of the tagging and release site. When displaced downstream, where the odors of both the upper reach and the pond were detectable, most salmon returned to their former site (65%). Displaced sockeye were more likely to return to the pond from the lower reach than from the upper one ( P  = 0.05), consistent with olfactory orientation and the hypothesis that salmon prefer certain habitats. Salmon displaced from the upper to the lower reach were much more likely to return than those displaced to the pond ( P  < 0.01), consistent with the role of odors in orientation and inconsistent with the habitat choice hypothesis.  相似文献   

20.
Our objective was to detect single nucleotide polymorphisms (SNPs) associated with resistance to the salmon louse in the Saint John River aquacultural population of North American Atlantic salmon using estimated breeding values (EBVs) and 6K genotypes from the parent‐generation and lice count phenotypes from the challenged, but ungenotyped, offspring‐generation. In 2011 and 2012, we challenged recent smolts with approximately 100 copepodids each. Fish were euthanized once the lice reached the chalimus stages and lice count, sex, tank and salt water weight were recorded. We used a multiple trait model to estimate breeding values for the parent‐generation using their own fresh water weights and the salt water weights and lice counts of the offspring‐generation. Salmon lice count heritability for untransformed and transformed data was 0.17 and 0.29 respectively. Two different genome‐wide association study methods were compared: (i) forward multiple linear regression and (ii) a mixed linear model using principal components to correct for population stratification as implemented in the egscore function of GenABEL. The two methods detected different SNPs located on different chromosomes. The multiple regression method incorporated 70 SNPs found on chromosomes 2, 7, 9, 12, 14, 15, 21, 22, 1p/23, 24. Many SNPs entered into the forward multiple regression are likely to be false positives from not correcting for the observed population stratification and cryptic relatedness. In contrast, the mixed linear model identified only two SNPs, one on chromosome 1p/23 (6.9%) and one on chromosome 1q (6.1%) consistent with louse‐resistance being a quantitative trait.  相似文献   

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