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1.
Movement and recaptures of two hatchery-reared brown trout, Salmo trutta L., stocks and landlocked salmon, Salmo salar L., released at different sites in regulated Lake Oulujärvi, were studied in relation to release site. Five groups of fish from each stock were released in approximately equal numbers. Most of the fish released in June and July were recaptured within 3 months, whereas the majority of the fish released in early winter (October and November) were caught the following spring, about 7–9 months after stocking. The release site had a significant effect on recapture rate. The results showed that fishing restrictions targeted mainly at gill net fishing are needed to preserve the stocked fish from overfishing. Significantly fewer recaptures were observed from the landlocked salmon stocking compared with brown trout. The recaptures from the landlocked salmon stocking indicated more active movement and less clumping compared with the two brown trout stocks.  相似文献   

2.
Abstract Lake-to-lake variation in brown trout, Salmo trutta m. lacustris L., yield from stocking was examined in 34 lakes in northern Finland. The trout were mainly stocked as 2–3-year-old fish. Catch statistics were compiled with information on water quality, water level fluctuations, fishing effort and lake geomorphology. Absolute brown trout yields (kgha-1) increased with increasing stocking rate, but there was an indication of non-linearity at higher stocking densities. Relative yields (kg per thousand trout released) were highest at low stocking rates. Stepwise multiple regression analysis was used to determine the best predictive model for lake-to-lake variability in brown trout yields. Seventeen measured regressands were used initially, and then replaced with scores obtained in a principal component analysis of highly correlated water quality variables and species-specific fish yields. Three major determinants of brown trout yields in these lakes were found in both analyses: fish community, stocking rate and fishing effort. Brown trout yields from stocking were higher in lakes with proportionally high yields of vendace or vendace and whitefish and proportionally low yields of pike.  相似文献   

3.
Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., fry were point and scatter stocked in the early part of June at densities of 63–263 fry 100 m−2 per species in the River Viantienjoki, a small river in northern Finland, and their population densities were assessed in late summer. Both species were always stocked together in similar quantities. Point stocking was used in the first 2 years and scatter stocking in the following 2 years. In point stocking, there was no correlation between the distance from the stocking sites (maximum = 250 m) and parr density in census sites ( r = −0.013 and 0.019 for brown trout and Atlantic salmon, respectively). The stocking density of fry did not influence parr density in August by either method or by species. Stocking density explained only from 11% to 23% of the parr survival depending on the species or stocking method. The mean densities of Atlantic salmon and brown trout parr did not differ significantly from each other at any fishing site ( P > 0.05). Both point and scatter stocking appear to be suitable methods for use in small rivers. The parr densities depend more on the other factors (e.g. habitat quality) than the stocking method, and the choice between methods could be based on the time and labour available.  相似文献   

4.
Abstract  Recaptures of adult, hatchery-reared, brown trout, Salmo trutta L., and fishing time from anglers were used to evaluate the benefits of stocking programmes with repeated releases of adult brown trout. The recapture rate varied between 17% and 29%. The time between stocking and capture (referred to as residence time) varied between 1 and 160 days (median 3–49 days). Between 67% and 84% of trout caught in the river were recently released fish. Fishing effort increased after stocking, thereby increasing the impact of angling on wild stocks. Stocking with adult brown trout decreases the impact of angling on wild trout only if the time spent fishing by all anglers is kept stable. Furthermore, because of the short residence time of stocked trout, long-term impacts through competition for space and food, or genetic impact through introgression, are limited.  相似文献   

5.
Abstract Rate of recapture (gill netting), habitat use, and diet of three strains of stocked brown trout, Salmo trutta L., were compared with resident brown trout in a Norwegian lake. The strains originated from an alpine lake, from a boreal lake, and from the native brown trout population in the lake. Overall recapture rate was 5–8% for all strains. The low recapture rate could be due to the relatively small size at stocking; mean fish length varied between 13.1 and 14.5 cm with strain and stocking method. Two years after release, the frequency of the different strains decreased from about 12% in the first year to stabilize at about 1%. The alpine strain showed the highest overall recapture rate, whereas the native strain was recaptured at an intermediate rate. The overall recapture rate of scatter-planted brown trout was higher than that of spot-planted brown trout. Immediately after being stocked, introduced fish ate less and had a less-varied diet than resident trout; however, stocked fish adopted a natural diet within the first summer. The distribution of trout between the pelagic and the upper epibenthic habitat was similar for both the resident and the stocked brown trout. Results indicate that the habitat use of stocked brown trout is adaptive and becomes similar to that of indigenous fish.  相似文献   

6.
Although freshwater fish stocking is widely used by managers, quantitative assessments of stocking practices are lacking in many countries. The general objective of the present study was to determine the quantity and characteristics of fish stocking in metropolitan France. Using a survey-based approach, stocking practices for 2013 by recreational angling clubs in France were quantified, which represented the bulk of fish stocking undertaken in that year. Stocking was found to be practiced by 88.6% of angling clubs in France, representing, on average, 65% of their annual budget. Overall, 22 species were stocked, including 13 native and nine non-native species, with strong variations among species in terms of life stages and body sizes used for stocking. Using Bayesian modelling, a total biomass of 2.029 t, representing approximately 90 million fishes, was estimated to be stocked in France in 2013. In terms of biomass, the most widely stocked species were rainbow trout Oncorhynchus mykiss (Walbaum), brown trout Salmo trutta L., roach Rutilus rutilus (L.), common carp Cyprinus carpio L. and northern pike Esox lucius L. A stocking volume of approximately 60 fishes or 1.5 kg of fish biomass per angler per year seems commonplace in industrialised countries for which data are available.  相似文献   

7.
Abstract –  This study aimed to evaluate otter predation on stocked trout. Large hatchery-reared trout (16–30 cm) were stocked into two Danish rivers with different fish populations. Otter diet before and after trout stocking was determined by analysing 685 spraints, collected regularly during the 35-day study period. Fish composition in the rivers before stocking was assessed by electrofishing. In River Trend, a typical trout river, the proportion of trout in the otter diet increased from 8% before stocking to 33% a few days after stocking. Moreover, trout lengths in the diet changed significantly towards the lengths of stocked trout, indicating that newly stocked trout were preferred to wild trout. In River Skals, dominated by cyprinids, there was no change in otter diet after stocking of hatchery trout, i.e., these were ignored by otter. Otter predation should be taken into account together with fish and bird predation, when stocking is used as a measure for conserving endangered salmonid populations.  相似文献   

8.
Lake Veere (1750–2050 ha), a brackish water lake in south‐west Netherlands, is a former branch of the Oosterschelde. The lake was closed off by the construction of two dams in 1961. Since the early 1970s Lake Veere has been regularly stocked for recreational and commercial fisheries with rainbow trout, Oncorhynchus mykiss (Walbaum), brown trout, Salmo trutta L., and glass eel, Anguilla anguilla (L.). Between May and September 1996 an experimental stocking of 18 054 trout of sea trout parentage (15–16 cm; 776 kg) was carried out to study their potential for recreational fisheries. The growth and mortality of the stocked trout were estimated from recaptures in eel fyke nets. The production and consumption of the stocked trout were estimated with a bioenergetics model. After 3.5 years (May 1996–November 1999) the stocked trout measured between 50 and 70 cm. The estimated annual total mortality was 84%. During the winter of 1996–1997, the biomass of the stocked trout reached a maximum of about 1800 kg. By November 1999 the biomass was estimated to be 100 kg. The maximum daily consumption by the trout population was 60 g ha?1 in October 1996 and in June 1997. The total consumption of the stocked trout population over the 3.5‐year period was estimated as 54 244 kg. The analysis suggested that the stocked trout used about 0.2% of the average annual primary production of the lake system. Although the growth and initial production of the population are attractive from the perspective of a recreational fishery, the high mortality and infestation with the salmon louse, Lepeophtheirus salmonis (Krøyer), are serious drawbacks for a future stocking programme with trout in Lake Veere.  相似文献   

9.
Two strains of hatchery-reared adult brown trout, Salmo trutta L., [208–334 mm total length (TL); n =  591] were individually marked and released into a limestone stream. The estimated survival after one month (86%; n =  508) was comparable to that for resident brown trout and rainbow trout, Oncorhynchus mykiss (Walbaum), (89%; n =  771), but declined to 14% ( n =  83) after 8 months compared with 52% ( n =  451) for resident trout. The movement of resident trout out of stocked stretches was higher (14%) than from control sites (5%), but the population size in both individual sites and the overall study area were unaffected. The growth of resident brown trout was unaffected by stocking, but rainbow trout showed lower growth rates in stocked versus unstocked stretches both one and 8 months after stocking ( P <  0.002).  相似文献   

10.
Hatchery-reared, juvenile European grayling, Thymallus thymallus (L.), and brown trout, Salmo trutta L., were each stocked six times into an area of a semi-natural stream. The order in which the two species were released was switched after every second experimental stocking. Temporal and spatial post-stocking dispersal, effects of previously stocked species, feeding behaviour and the influences of sex and size were studied. During each 48-h experimental release period, some fish were recaptured in a trap situated 200 m downstream from the stocking site, and fish remaining in the stream after each experimental release were caught by electric fishing. Significantly more grayling than trout moved downstream and left the semi-natural stream. Proportions of stocked grayling recaptured in the trap within 2 h and from 2 to 48 h post stocking in the stream were 36.4% and 10.0%, respectively. Corresponding recapture rates for brown trout were both 1.5%. Most of the grayling and brown trout that did not leave the stream early were recaptured in deep, slow-moving water at low velocities in the release area. The presence of grayling at the time that the brown trout were stocked resulted in significantly fewer brown trout staying in the upper part of the stream. Within 48 h of their release, 33.3% and 22.8% of the grayling and brown trout, respectively, had eaten natural food items. The mean length of brown trout recaptured in the upper part of the stocking area was significantly lower than that of fish recaptured in the lower part and in the trap. Among brown trout, males showed a significantly greater propensity to eat and to stay in the upper part of the stream near the stocking site compared with females . Brown trout with natural food items in their stomachs had significantly lower mean length than trout without such items. No sex- or size-related differences were found in the spatial distribution or feeding activity of grayling.  相似文献   

11.
Enhancement stocking is a widespread but rarely evaluated practice in German vendace, Coregonus albula L. fisheries, which is precautionarily carried out to buffer yield fluctuations. However, it is assumed that stocking of larval vendace can elevate year‐class strength only in the presence of substantial reproductive deficits, which so far cannot be detected prior to the spring time period when stocking is conducted by fisheries managers. Simple measures for the early quantification of natural reproduction were tested, and the efficiency of larval enhancement stocking in a lake with strong reproduction deficits was analysed. Analysis in four lakes over 3 years revealed a significant positive correlation between standardised catches of vendace larvae caught with pump‐driven illuminated traps in spring and the abundance of young‐of‐year (YoY) vendace in the following autumn, whereas standardised catches of spawners were insufficient to forecast YoY recruitment. In a lake with low natural vendace reproduction, stocked vendace contributed 73–100% of year‐class strength and fisheries yield. Accordingly, enhancement stocking can efficiently compensate for reproduction deficits, and the simple larvae sampling method may facilitate early detection of these deficits, which would allow fisheries managers to respond accordingly through larvae stocking.  相似文献   

12.
One-year-old hatchery brown trout, Salmo trutta L., ( n  = 16 520) from a sea-run, local brood stock were marked and released (scatter-planted) into the River Laisälven in northern Sweden. Eight different groups were created using Alcian blue and Visible Implant Elastomer tags. Half the fish were kept in small enclosures in four stocking areas for 6 days before release. The other half were released just after transportation. To evaluate the effect of acclimatization on post-stocking performance, the areas were electric fished 2 months later. During the electric fishing survey, a higher number of the acclimatized hatchery fish were recaptured than those released immediately. The growth rate of stocked fish differed significantly between stocking areas and fish held in enclosures grew more than those released directly. The rate of recapture of hatchery fish varied between stocking areas (6.4–17.4%). Movements of juveniles within and between the stocking areas were low, and only 3.6% of the recaptured fish were found in an area not originally stocked. These results showed that acclimatization of fish before release increases the number and size at recapture within a stocking area.  相似文献   

13.
The predation impact of recently stocked triploid brown trout, Salmo trutta L., on migrating wild Atlantic salmon, Salmo salar L., smolts was investigated in two field‐based experiments. The first experiment employed a unique experimental facility to monitor 57 wild S. salar smolts through an enclosure containing a known density of stocked S. trutta to determine a predation rate. None of these smolts were preyed upon by the stocked S. trutta. The second experiment investigated the diet of free‐ranging stocked triploid S. trutta in a chalk stream during the spring. Although at least 6% of the free‐ranging stocked triploid S. trutta became piscivorous on Phoxinus phoxinus (L.), the results suggest that large, recently stocked, triploid S. trutta with a high condition factor do not represent a predation threat to wild S. salar smolts. However, it is recommended that a precautionary approach is maintained and the findings are not generalised until further investigation permits explicit management advice to be developed, and that the stocking of large triploid S. trutta is avoided before May/ June (regional variations to apply) each calendar year, where this can reasonably be achieved.  相似文献   

14.
Weirs and traps were used to monitor the movement of two strains of stocked brown trout, Salmo trutta L. Within 24 h of stocking, 15% ( n  = 13) of a Danish strain and 21% ( n  = 19) of a hybrid strain moved at least 100 m from their release site. In the following 5–6 days, no further movement was found for Danish fish, but hybrid fish continued to move, totaling 32% ( n  = 29) of the fish stocked. During this same period, 36 wild brown trout (≈ 3.5% of the population) were captured, moving over the weirs. Two weeks later, and one week after a flood, 70% ( n  = 59) of the Danish strain were recovered within their release sites and 89% ( n  = 76) were recovered during an electric fishing survey within the 3.5-km-long experimental area. In contrast, 43% ( n  = 31) of the hybrid strain were recaptured in their release sites and 49% ( n  = 45) within the experimental area. The total recapture of wild adult fish was only 16% ( n  = 41). The flooding event was insignificant in comparison with strain-specific behaviours in determining patterns of movement and residency.Austria, brown trout, floods, movement, stocking.  相似文献   

15.
During 1985-88, a total of 17500 under-yearling (0+) brown trout. salmo trutta L., were released in Låktabäcken Creek in Swedish Lapland. Of these, 15500 had been reared in a pond adjacent to the creek during their first summer, where they fed on natural prey. The other 2000 were conventionally reared hatchery fish fed dry food pellets. All fish were released in the autumn (size 6O-70mm) at the confluence of the pond outlet and the creek. Electrofishing revealed that the stocked fish gradually spread downstream from the point of release at the expense of the resident wild trout population. In 1989, stocked fish accounted for 70-90% and 30-50% of the trout population in the upper and lower stretches of the creek respectively. No long-term changes in total trout densities or standing crop occurred as a result of stocking. First-year survival of fish released in the creek varied between 15 and 30% over the 4 years. After 3 years, 5% of the stocked fish remained in the creek. Planted fish grew less rapidly than wild fish during the first year in the creek. Pond fish had a higher survival rate than hatchery fish and showed a greater propensity to disperse from the point of release.  相似文献   

16.
Embryonic mortality, egg production and the spawning stock biomass of Pacific anchovy, Engraulis japonicus , off Southern Korea during 1983–1994, and their biological response to oceanographic features in spring and summer, were analysed. The instantaneous mortality rate (IMR) of embryonic stages decreased in spring and increased in summer, with a range of 0.33–1.23 day–1 in spring and 0.78–1.69 day–1 in summer. Egg production in summer was three times that during spring and production was low in the late 1980s. Mean lengths of yolk-sac larvae and adult females were greater in spring than in summer, whereas spawning fraction and spawning stock ratio (spawning biomass:adult biomass) were lower in spring than summer. Estimated mean spawning stock biomass ranged from 141 × 103 to 380 × 103 MT in spring and from 221 × 103 to 557 × 103 MT in summer. Statistically, the seasonal and long-term trends of embryonic mortality, egg production and spawning stock biomass of Pacific anchovy can be explained largely by spring warming, summer cooling and by less abundant zooplankton in the late 1980s.  相似文献   

17.
Abstract The timing of the smolt run in the Dale River in western Norway was monitored from 2002 to 2007 after annual stocking in late autumn 2000 to 2005 with 5000–10800, 11–16 g, Atlantic salmon, Salmo salar L., parr. The releases yielded an annual smolt production of 1000–2000 individuals, mainly 1+ smolts. Almost 5700 stocked smolts were trapped during smolt migration and 60% of these were genotyped for family identification. The date for 50% descent varied by 14 days from year to year. For the most part, however, the 2+ stocked smolts and the majority of the wild smolts left the river in May, while the 1+ stocked smolts migrated 23–26 days later in June. It was concluded that the strategy of stocking large parr in late autumn may conflict with the natural timing of smolt migration the following spring.  相似文献   

18.
Abstract. During the period June 1982-84 hatchery-reared brown trout, Salmo trutta L., fry were Stocked into stretches of the Owendoher. a trout nursery stream on the east coast of Ireland. These experiments were designed to examine the survival of stocked fry and to estimate the carrying capacity of the system. During the first year fry were stocked into sectors already supptorting wild fish at densities normal for the system. In the following year fry numbers were artificially reduced prior to stocking with the hatchery-reared fish. Mortality of the stocked fry was high after release with less than 33% of the fish surviving beyond the first 3 weeks. No stocked fish survived after October 1982. In the second year, however, 2-9% of the fish survived. The best survival rates were achieved where wild fry numbers were lowest. Regardless of the initial stocking density the various experiments yielded autumn fry densities (0.07-0.7 fish/m2) similar to those at unstocked sites (0.1-0.62 fish/m2).
Stocking did not increase recruitment to the 1+ group and again 1+ densities (0.15-0.35 fish/m2) similar to unstocked sites (0.07-0.39 fish/m2) were obtained at the end of each year. These results suggest that spawning and recruitment in the Owendoher yield population densities approaching the maximum carrying capacity of the stream. The system appears to support a maximum summer fry density in the region of 1 fish/m2 and a maximum autumn density of 0.7 fish/m2.  相似文献   

19.
Abstract –  The population density of brown trout ( Salmo trutta ) in a small natural system was manipulated in six equal-length stream sections by stocking hatchery-reared 1+ brown trout (unstocked, tripled and quintupled) over two consecutive years. The results showed that hatchery-reared trout grew more slowly and were more mobile than resident trout, and that their growth was inversely density dependent. In contrast, growth of the resident trout was density independent. The recapture of 1+ resident and hatchery-reared trout was inversely density dependent. This is most likely a consequence of increased competition. However, after a single winter the population density returned to its base level prior stocking and older resident trout showed no density-dependent recapture. Thus, the advantage of stocking, here higher biomass, may have the detrimental effect of decreasing resident stocks of the same size class during summer.  相似文献   

20.
Habitat use, growth and food composition of native and stocked Arctic charr, Salvelinus alpinus (L.), were studied in the subarctic Lake Muddusjärvi, northern Finland, to investigate reasons for poor stocking success. Samples were collected with pelagic and epibenthic gill nets. Stocked and native charr occurred in similar epibethic habitats, whereas pelagic habitat was avoided. Native charr grew fast after shifting to piscivory. Growth rate of stocked charr was slow because only a small proportion of stocked fish became piscivorous during the first year after stocking. During the first lake year, stocked charr divided into slow-growing planktivores and fast-growing piscivores. Piscivorous stocked and native charr consumed only whitefish, Coregonus lavaretus (L.), as their prey. Small-sized (<10 cm) whitefish were preferred when shifting to piscivory.  相似文献   

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