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1.
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   

2.
Abstract. Analysis of 4 years’ club records shows that, on average, the anglers fishing for brown trout in the lower River Don, Aberdeenshire, Scotland made 9 trips/y of 4 hours duration, caught 0·8 fish/trip at the rate of 0·2 fish/h, making a total of 7 fish/season, having an average weight of 350g. There was, however, considerable variation in the results. Guests tended to fish for longer, and to catch less, than regular members. Most (95%) of the fish were caught by only 30% of the anglers, who accounted for 80% of the fishing effort. Angler efficiency increased with the number of seasons spent fishing the club waters during the period; it decreased with increase in water temperature and flow and, early in the season, tended to decrease slightly with increase in catch in the preceding month.  相似文献   

3.
Legal-sized trout stocked in spring in three lakes in Wisconsin U.S.A. provided a short-term, popular, sport fishery. Frequently, half or more of the stocked fish were caught in the first month of the Fishing season, and few were caught thereafter. Separate estimates of the percentage of numbers (and weight) returned in the first month of the fishing season were 46 (47), 73 (76), 62 (113), and 31 (22) for rainbow trout (Salmo gairdneri) and 64 (81) for brook trout (Salvelinus foutinalis). Most anglers interviewed at two of the lakes were fishing primarily for trout, including in one case 95% of the anglers interviewed over the 9-month season, even though the trout fishery persisted for less than 2 months. Fishing pressure also was highest at the opening of the angling season and declined exponentially thereafter. Of an estimated total of 7,906 angler-hours in one lake, 67% occurred in the first month of the season and 79% in the first 2 months. Because the trout were harvested rapidly, relatively little of the productive capacity of the lakes were channelled into production of trout flesh. Therefore, the stocked trout provided a put-and-take fishery at tittle expense to the existent warmwater fishery.  相似文献   

4.
Hatchery-reared brown trout Salmo trutta L. (length 23–26 cm) were stocked in the Afon Taf, South Wales. The effects of ‘spot-’ and ‘scatter-planting’ and of stocking at 1 and 4 weeks prior to the start of the angling season were investigated. Data on the percentage recapture and post-stocking movements of the trout were obtained from tag returns. Higher percentage recaptures were recorded for ‘spot-plantings’ (65% and 31%) than for ‘scatter-planting’ (16%). Stockings made 1 week before the start of the angling season yielded better returns (17.1%) than those made 3 weeks earlier (2.2%). Neither ‘spot-’ nor ‘scatter-planting’ resulted in stocked fish contributing to the catch for an appreciably longer period of time. The majority of trout stocked were caught in the area of stocking irrespective of the method or time of planting.  相似文献   

5.
The operation of a put-and-take trout fishery at Toft Newton reservoir is analysed from detailed studies of the 1978 and 1979 seasons. Toft Newton is only a small reservoir but the large number of anglers that utilize the fishery mean that the stocking rates per hectare of water have to be very high. As a result of these high densities and a short average residence time in the reservoir, rainbow trout which were the predominantly stocked species do not grow after release. Brown trout, however, which were stocked at lower densities do grow after release. The success rate of the 8–9% of anglers not returning their catch data was examined using a postal survey. Partial correlation analysis indicated that the numbers of fish in the reservoir, the number of anglers fishing and the number of hours of sunshine significantly affected the catch rate. A regression between catch rate and number of fish in the reservoir only explained 35% of the variability but the addition of the other two factors did not significantly improve the accuracy of the model. The market area of the fishery was studied from the register of anglers. Most anglers attending Toft Newton travel a considerable distance to the fishery, the peak number driving from 98–129 km (61–80 miles) round trip. The present and future management policy of the fishery is discussed in the light of this analysis and many of the recommendations may also apply to other small put-and-take trout fisheries.  相似文献   

6.
Abstract. Stock and catch statistics for a small (5–5ha) lowland put-and-take trout fishery have been used to investigate the relative catchability of brown, Salmo trutta L., and rainbow, Oncorhynchus mykiss (Walbaum), trout. Brown trout were consistently less vulnerable to fly fishing than rainbows, and were particularly difficult to catch between mid-June and September. As a consequence, the turn-over of rainbow trout stock was more rapid than that of brown trout, but eventual recapture levels of both species were similar at around 90% of the fish stocked. In these circumstances, brown trout could be regarded as a long-term investment for fishery managers, with rainbows providing more'instant'sport.  相似文献   

7.
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   

8.
Tagging experiments are described where hatchery over-yearlings and similar sized wild brown trout were spring-stocked in two small angling lakes. This was followed in the autumn with a stocking of hatchery fingerlings and wild fish. The spring-stocked hatchery fish gave the best return to anglers of 9.3% over the first two seasons, while the autumn-stocked hatchery fish apparently suffered heavy over-winter mortality — giving a return of only 1.3% over a comparable time period. Wild fish gave low return rates of 2.9 and 2.0% from spring and autumn stockings respectively, although netting exercises indicated that these survived longer in the lake than hatchery fish. Analysis of the methods of capture indicated that hatchery fish were more liable to be caught by bait fishing whereas fly fishing was the most successful for wild fish. Estimates were made of the relative cost effectiveness of the various types of fish in terms of returns to the angler.  相似文献   

9.
Abstract. Stock, catch and fishing effort statistics for a 12·5-ha lowland pul-and-lake trout fishery have been used to compute the ‘catchability’ of rainbow trout, Salmo gairdneri Richardson, during the fishing seasons 1980–1983. Seasonal trends in the fishes’ susceptibility to capture by fly-fishing are apparent but there was no indication that, in this fishery, newly stocked fish were more vulnerable than the longer-term residents. This consistency of recapture rates of rainbow trout, relative to the population available, is a function both of the fish's behaviour and that of the anglers themselves, and it is suggested that for management purposes the latter must be taken into account. In the fishery studied rainbow trout grew well at fish densities below 60 kg ha?1, but even with overall recapture levels exceeding 80% the yield of the fishery was less than the weight of fish stocked. The selection of strains of rainbow trout which satisfy the requirements of sport fisheries is discussed.  相似文献   

10.
Abstract Small amounts of radioactivity in liquid effluent are discharged under authorization into Lake Trawsfynydd in north Wales. MAFF inspectors from the Directorate of Fisheries Research (DFR) advise the Welsh Office on the terms of authorization and on the power station operators' compliance with them. DFR also has the responsibility for environmental monitoring, including fish caught for consumption. Trout angling is particularly popular in Lake Trawsfynydd, and because of angling pressure, additional brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), need to be introduced. An important factor in determining the concentration of radionuclides in these fish is the length of time that they spend at liberty. During the fishing season, samples of these stocked trout were tagged and released to assess the average residence time. This was found to be 6 days for rainbow trout and 10 days for brown trout. Less than 7% of the recaptured stocked trout of either species had a residence time of more than 20 days. Radiocaesium concentrations in recaptured trout were very low. Trout which avoided recapture and overwintered in the lake were found to have radiocaesium concentrations similar to those of indigenous trout sampled at the same time.  相似文献   

11.
Apart from some irregularities reflecting changes in permit costs (1975) and the effects of drought (1976), there were increases in angler-visits, catch per angler-visit and number of fish caught during the first 5 years of the fishery. Thereafter, there were about 1000–1500 angler-visits per season, a mean catch of 1.0–1.2 trout per angler-visit and an annual catch of 1200–1800 trout. Between 1971 and 1980 the mean weight of the fish caught fell from 472 to 349 g. During the period 1976–1980 the mean catch per angler-visit was 1.2 fish. This compares favourably with results from a selection of upland and lowland British reservoirs. The mean weight of individual trout caught was 362 kg and this value is typical of both stocked and unstocked upland reservoirs. The mean annual catch during 1976–1980 was about 2 kg ha?1. This is similar to the values observed in other unstocked upland reservoirs. The gross yield from such reservoirs can be increased by stocking but the limited data available suggest that at stocking rates above about 5 kg ha?1 the net yield (i.e. weight caught — weight stocked) becomes negative.  相似文献   

12.
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   

13.

14.
Routine statistics have been analysed from a varied selection of 18 British reservoir fisheries The numbers and weights of fish caught have been compared with the numbers and weights stocked. In lowland reservoirs the “put and take” system of management is used and annual stocking rates of 40–60 fish ha-1 (c 12 kg ha-1) give catches of 20–30 fish ha-1 (c 20 kg ha-1). Higher stocking rates lead to greater catches numerically but to relatively little increase in the weight of catch per unit area. In general, the recapture of rainbow trout is greater than that of brown trout, relative to the numbers stocked. The management of upland reservoirs is complicated by the presence of indigenous trout, poorer growing conditions and lack of research into the population dynamics of fish populations in such places. A wide variety of management possibilities exist in upland reservoirs and these are worthy of thorough investigation. Stocking at rates comparable to those used in lowland reservoirs takes negligible advantage of the potential for natural trout growth in upland reservoirs and the economics of this practice would repay closer analysis.  相似文献   

15.
In an attempt to increase fish standing crop and improve angler-catch, stocking was undertaken in the middle reaches of the River Derwent in Derbyshire using four cyprinid species. Each fish was marked with a dyespot, and nearly 2000 fish were introduced before the 1980–81 fishing season began. Bankside observations and catch return sheets were used to collect information on the number of marked and unmarked fish taken by angling. The percentage of captured fish that were marked reached 50% during summer 1980, although this was lower during winter 1980–81. A relatively small proportion of the fish caught were taken in angling matches. Anglers reported that the fishing had improved from‘poor’to‘good', and catches by a single angler in one day exceeded 20 kg. It is thought that the success of the operation was due to the fact that the stock fish were obtained from local rivers, were of a large size (> 20 cm) and were introduced when the river was at normal level. The implications of the results on management options are considered, and it is suggested that the quality of sport demanded by anglers in rivers of this type may be most easily sustained by periodic stocking with suitable fish.  相似文献   

16.
Abstract Since the mid‐1980s, water quality has improved in German rivers, and fisheries have recovered. However, it is unsure whether the improvements are sufficient to maintain stocks and angling yield without supplementary stocking. This study examined the development in the local brown trout, Salmo trutta L., stocks and angling yield in the River Wutach following cessation of stocking in 2001, using electric fishing and an angler questionnaire. Natural reproduction was recorded in each year between 2001 and 2007, and a stable stock of trout >20 cm was found. Trout catches by anglers increased after stocking ceased and approximately 60% of the anglers were convinced that stocking was unnecessary to maintain the brown trout stocks or angler catch satisfaction.  相似文献   

17.
Abstract. Takeable-sized (25-61 cm total length), hatchery-reared brown trout, Salmo trutta L., were released in early July from 1982 to 1984 in the sub-alpine River Sjoa in southern central Norway.
Of those recovered during the same season that they were stocked, 67-73% were caught within 10 days. Mean exploitation and survival rates in the same season of release ranged from 0 41 to 0-54 and 005 to 0.11, respectively. No tagged fish were caught 2 years after stocking.
The frequency of capture increased significantly with fish length. The length at stocking of those fish recovered after one winter in the river was greater than those caught in the same season as released. The migrant fish (n = 20) were significantly larger than stationary fish (n=434).
Between 87.5 and 95-6% of the fish with known capture sites caught during the first year (n=180) were recovered in the release area. The highest fraction of migrants was obtained in the year with the highest stocking density; the water discharge was also higher that year. The migrants (n=17) were caught 1.0 - 6.0km downstream, with the exception of one fish which moved 2.0 km upstream. The year after stocking, 63% (n=8) of the remainder were caught in the release area, while the migrants (n = 3) were caught 2.0-6.0km downstream.  相似文献   

18.
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   

19.
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   

20.
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   

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