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1.
Widespread fish introductions have led to a worldwide decline in the number of fishless lakes and their associated communities. Studies assessing effects of fish stocking on native communities in historically fishless lakes have been limited to high-elevation headwater lakes stocked with non-native trout. Little is known about the effect of fish stocking in historically fishless and hydrologically isolated lowland kettle lakes. We compared the effects of introduced fish on macroinvertebrate communities in kettle lakes stocked with centrarchids, salmonids, and cyprinids, and headwater lakes stocked with brook trout (Salvelinus fontinalis) in Maine, USA. Fish had significant effects on macroinvertebrate community structure in both lake types, with reduced species richness and abundances of taxa characteristic of fishless lakes. The effects of introduced fish were more pronounced in headwater lakes despite a less diverse fish assemblage than in kettle lakes. We attribute this to abundant submerged vegetation providing refuge from fish predation and reduced stocking frequency in kettle lakes. We assessed effects of stocking duration on macroinvertebrates in a subset of headwater lakes with known dates of trout introduction. Species richness and abundance of most taxa declined within 3 years following trout introduction; however, richness and abundance were least in lakes with long stocking histories (?40 years). Macroinvertebrates previously identified as fishless bioindicators were absent from all stocked lakes, indicating that trout rapidly eliminate these sensitive taxa. Conservation of this historically undervalued ecosystem requires protecting remaining fishless lakes and recovering those that have been stocked.  相似文献   

2.
Populations living on the periphery of a species range are subjected to intense habitat pressures that stress their vulnerability to threats. South Iberian brown trout (Salmo trutta) populations are located on the southwestern boundary of the species range in Europe. This region has been described as a contact zone between Atlantic and Mediterranean populations in other fish species, and allozyme data detected natural hybridization between native Atlantic and Mediterranean brown trout in this area. Nevertheless, native pattern of populations relationships are threatened by hybridization with exogenous hatchery fish. Allozyme data and complete mtDNA control region sequences were used to analyse the ongoing processes of human mediated hybridization between native and hatchery brown trout in this region. Estimates of the persistence of hatchery genes detected a high level of introgression in some of the sampled locations (hatchery ancestry more than 25% in GF-1, GF-2 and GF-3), but results differed from both kinds of markers. The low intrapopulation diversity (Hs = 0.051) indicated that genetic drift could explain discrepancies between markers. At individual level, the complementary use of both markers detected more hatchery origin fish than those detected by the use of a single technique. Based on these results, the importance of considering a large number of genetic markers to evaluate introgression accurately is emphasized. The ability of the current management policies to the protection and conservation of marginal populations that retain complex and special evolutionary histories such as those studied is also questioned.  相似文献   

3.
The presence of introduced brown trout (Salmo trutta) on the distribution of native crayfish (Paranephrops planifrons), native galaxiid fishes (Galaxias spp.) and invertebrate fauna was investigated in 18 West Coast New Zealand streams (8 with trout and 10 without trout) differing in chemical characteristics. Gut contents of trout, crayfish and eels were also examined to evaluate whether competition or predation could be linked to the patterns found. Abundances of crayfish and galaxiids were significantly lower in streams with trout, but in streams without trout, substrate size was one of the most important factors determining crayfish abundance. In contrast to crayfish, other macroinvertebrates were more abundant in trout streams than streams without trout and significantly more taxa were found in streams with trout. Macroinvertebrate abundance was related to environmental factors, such as pH, substrate, depth and total nitrogen. Gut content analysis showed an overlap in diet (mostly invertebrates) between trout and eels. Crayfish, however, had a more omnivorous diet where detritus was the most frequently occurring food material. Differences in chemical characteristics marked the streams with and without trout. Thus, trout were not present in streams with pH < 6.0. Crayfish and galaxiids were present in streams with pH ranging from 4.1 to 7.9, and those with pH < 6.0 may function as trout-free refuges where larger populations of these species may persist. However, other macroinvertebrate taxa may be more negatively affected by acidification than by trout. By protecting naturally acidic, brown water streams, New Zealand crayfish and galaxiid fish populations can be conserved within geographic areas where trout are present.  相似文献   

4.
Muscle tissue from stocked lake trout (Salvelinus namaycush) from lakes near the smelters at Sudbury, Canada was analyzed for Al, Cu, Fe, Hg, Mn, Ni, and Zn. Metals in tissue were not abnormally high compared with fish from lakes farther away from the smelters. Tissue concentrations of Al, Fe, Mn, and Zn declined significantly after stocking. Because metal concentrations were lower in hatchery water than the study lakes, this decline in tissue metal suggests that diet plays a prominent role in the uptake of these metals in lake trout. Only Hg showed evidence of accumulation to levels that might be harmful for human consumption, and then only in a few older, larger trout. In contrast, tissue Mn and Zn were inversely correlated with trout weight. Fluctuations, independent of age, body weight or time of year, were observed in tissue concentrations of Al, Cu, and Zn. Annual cycles, independent of pH and alkalinity were observed in tissue concentrations of Fe, Hg, Mn, and Ni. Bioaccumulation of metal proved to be an unfounded concern for the rehabilitation of fish populations in lakes near Sudbury.  相似文献   

5.
In Slovenia, the Adriatic basin inhabited by native marble trout (S. marmoratus), and the Danubian basin inhabited by native Danubian lineage of brown trout (S. trutta) have been intensively affected by stocking with non-native trout strains. In order to assess spread of non-native strains and their introgression with native trout, a population study based on five microsatellite loci was applied across ten marble and ten brown trout populations, ranging from allegedly non-introgressed to heavily managed. On the basis of correspondence analysis, which revealed three clear groupings consisting of the Danubian and Atlantic lineages of brown trout and the marble trout, the alleles, characteristic of each grouping were identified and used for estimating genetic composition of each population according to the three possible origins. Among the wild populations, five marble and one brown trout populations were found to be pure; all the others were introgressed with exotic alleles (Atlantic and marmoratus alleles in the Danubian basin and Atlantic and Danubian in the Adriatic basin) that markedly dominate in intensively managed populations. As revealed by non-significant FIS values, panmixia between native and introduced fishes has for the most part already been reached. Our research showed that it is not only marble trout whose identity is endangered in Slovenia but also the existence of autochthonous Danubian brown trout is critically compromised, which is new information to be taken into account for local trout conservation.  相似文献   

6.
Hyperpredation occurs when non-native prey facilitate invasive predators, which then suppress native prey. Direct impacts of introduced fish on amphibians are well studied, but the role of fish in supporting shared predators has not been considered. We present evidence for indirect effects of trout on amphibians through snake predation. Analyses of the diet, distribution and density of the Pacific coast aquatic garter snake (Thamnophis atratus) relative to the sympatric common garter snake (Thamnophis sirtalis) in the Klamath Mountains of California suggest that trout introductions facilitated expansion of T. atratus by providing alternative prey. T. atratus diet included trout and amphibians whereas T. sirtalis preyed solely upon amphibians. The distribution and density of T. atratus matched that of introduced trout instead of native amphibians. Populations of T. atratus could reach high densities in the absence of high densities of amphibians. When the snakes opportunistically prey upon amphibians whose numbers are already directly impacted by trout, they can cause significant additional declines. When T. atratus was present in lake basins, native Cascades frogs (Rana cascadae) were rarer than in basins without T. atratus. This case differs from other hyperpredation studies because the two prey species also interact via intraguild predation. Given the worldwide practice of stocking fish into aquatic habitats, it is important to understand the consequences of the practice on food-web structure and ecosystem functioning. Bottom-up impacts of introduced predators should be considered as well as top-down so that managers can incorporate the range of ecosystem-level effects into conservation goals and decisions.  相似文献   

7.
In this paper we document the effects of acidification on fish populations in lakes in Sør-Varanger near the Russian border in northern Norway. We used questionnaires in order to assess the current status and distribution of different fish species, and conducted test-fishing to determine relative abundance (CPUE-T) and age structure. Acidification of surface waters in this area is due to emissions of SO2 from smelters on the Kola Peninsula in Russia (Nikel and Zapoljarnij) between 10 and 30 km from the Norwegian border. Sulphur deposition in Sør-Varanger ranges from 0.6 to 2.0 g S m-2 yr-1, which is similar to levels in the most acidified areas in southern Norway. However, a dominant fraction of the acidic deposition reaches the ground in particulate form during summer and autumn. Coastal areas in Sør-Varanger receive small amounts of precipitation; the annual mean is 580 mm. We obtained fish status from 401 lakes, about 40% of all lakes larger than 3 ha, which were inhabited by 236 and 293 populations of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta), respectively. The extent of fish damage was small as only three populations of Arctic charr were lost, while three populations of Arctic charr and eight populations of brown trout were at various stages of reduction. Damaged and lost fish populations were identified in smaller lakes at relatively high elevations (172–349 m) in six areas in the Jarfjord Mountains, covering a land area of 30.0 km2. Most of the damage probably occurred during the 1970s and 1980s. In lakes that supported or had supported Arctic charr and brown trout, we found a significant relationship between CPUE-T, and acid neutralizing capacity (ANC) and pH, and also between alkalinity and the concentration of inorganic Al for brown trout. In both species, the catch of fish in age groups 1+ and 2+ (CPUE-R) increased significantly with CPUE-T. Affected populations typically exhibited irregular age composition, and age-classes were missing, indicating that reductions in fish populations were due to recruitment failure. The limited fish damage is related to relatively good catchment resistance to acidic inputs, small amounts of wet deposition as well as precipitation. These conditions result in low accumulation of acidic compounds, producing less acidic run-off waters and few episodes of unfavourable water quality.  相似文献   

8.
Nonnative fishes have been introduced into naturally fishless mountain lakes worldwide, often with negative consequences for native fauna. In this study, I used data collected during a census of native herpetofauna, nonnative trout, and habitat characteristics at all lentic water bodies in Yosemite National Park (n=2655) to quantify the effect of trout introductions and habitat on the distribution of four amphibian species and two reptile species. Impacts of trout on amphibians and reptiles were characterized using generalized additive models that included as predictor variables fish presence/absence, amphibian presence/absence (only in models for the two reptile species), elevation, water depth, littoral zone and shoreline substrate composition, relative survey date, and location. All species showed significant associations with habitat characteristics, and elevation and water depth appeared particularly important in influencing distributions. In addition, distributions of the mountain yellow-legged frog (Rana muscosa) and Pacific treefrog (Hyla regilla) were strongly negatively associated with the presence of nonnative trout while those of the Yosemite toad (Bufo canorus) and Sierra newt (Taricha torosa sierrae) were unrelated to trout presence. The distribution of the mountain garter snake (Thamnophis elegans elegans) was strongly negatively associated with the presence of nonnative trout and positively associated with the presence of native amphibians. Regression results for the Sierra garter snake (Thamnophis couchi couchi) were similar except that the direct effect of nonnative trout was considerably weaker. Together, these results indicate that trout introductions have resulted in considerable alteration of Yosemite's herpetofauna. Long-term studies will be necessary to determine whether removal of nonnative trout populations, where possible, would allow these impacts to be partially reversed.  相似文献   

9.
The introduction of lake trout (Salvelinus namaycush) to Yellowstone Lake in Yellowstone National Park has contributed to a significant decline in the endangered Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri), leading to concern over the persistence of this subspecies but also to piscivorous predators in this community. We assessed the impact of lake trout on a key piscivore, the river otter (Lontra canadensis) in two lakes in Yellowstone National Park. Yellowstone Lake continues to support a native cutthroat trout population, although the recent introduction of lake trout has dramatically impacted the cutthroat trout population. Nearby Lewis Lake has an entirely introduced fish fauna of lake trout, brown trout (Salmo trutta), and Utah chub (Gilia atraria) but lacks cutthroat trout. Analysis of otter scat from Yellowstone Lake implicated trout (lake or cutthroat trout) as a major prey item (57% of scat), whereas stable isotopes identified longnose suckers (Catostomus catostomus) as the primary prey there (58% of diet). By contrast, scat from Lewis Lake implicated minnows, presumably Utah chub, as the primary prey for otters occupying that lake (86%), while stable isotopes implicated brown trout (64%) over both lake trout and Utah chub (36% combined). Our data establish the importance of alternative prey to otters and suggest that lake trout-induced reductions in cutthroat trout may not be catastrophic for otter populations here. These data do not necessarily exonerate lake trout, as their impact on other species, most notably grizzly bears (Ursus arctos) and piscivorous birds, has been documented to be substantial, and further data on the nutritional value of alternate prey are required to confirm or refute a working hypothesis that otter populations will continue to thrive in the face of the lake trout invasion.  相似文献   

10.
Reintroduction of extirpated populations creates a unique context that can exacerbate the effects of interactions among species. Thus, reintroduced populations may be particularly vulnerable to predators and competitors, including native species with which they historically coexisted. In this study, we evaluated the effect of native fishes on survival of reintroduced Atlantic salmon (Salmo salar) in the Connecticut River basin, where the native salmon population is extinct. Juvenile salmon are stocked annually in many Connecticut River tributaries. We sampled salmon reintroduction sites across tributaries with different fish communities to determine whether native fish reduce the success of salmon reintroductions (N = 19 site-years). Increased density of slimy sculpin (Cottus cognatus), a native generalist predator, was associated with reduced recruitment of reintroduced salmon. Salmon first-summer survival declined with increased sculpin density across sites, and low first-summer survival led to reduced densities of overyearling salmon the subsequent year. Hierarchical partitioning analysis showed that the negative relationship between sculpin and salmon was independent of potentially confounding variation in other fish community or habitat characteristics. Negative effects of native, historically-sympatric species, particularly generalist predators, can impede restoration of extirpated populations.  相似文献   

11.
We have examined populations of brown trout in low-conductivity mountain lakes (5.0?C13.7 ??S/cm and 0.14?C0.41 mg/l Ca) in southwestern Norway during the period 2000?C2010. Inlets to the lakes were occasionally even more dilute (2007; conductivity?=?2.9?C4.8 ??S/cm and Ca?=?0.06?C0.17 mg/l). The combination of pH and conductivity was the best predictor to fish status (CPUE), indicating that availability of essential ions was the primary restricting factor to fish populations in these extremely diluted water qualities. We suggest that conductivity <5 ??S/cm is detrimental to early life stages of brown trout, and subsequently that there are lakes in these mountains having too low conductivity to support self-reproducing trout populations. Limited significance of alkalinity, Ca, Al, and color suggests that effects of ion deficit apparently overruled the effects of other parameters.  相似文献   

12.
The mountain yellow-legged frog (Rana muscosa) was once a common inhabitant of the Sierra Nevada (California, USA), but has declined precipitously during the past century due in part to the introduction of nonnative fish into naturally fishless habitats. The objectives of the current study were to describe (1) the effect of fish removal from three lakes (located in two watersheds) on the small, remnant R. muscosa populations inhabiting those lakes, and (2) the initial development of metapopulation structure in each watershed as R. muscosa from expanding populations in fish-removal lakes dispersed to adjacent habitats. At all three fish-removal lakes, R. muscosa population densities increased significantly following the removal of predatory fish. The magnitude of these increases was significantly greater than that observed over the same time period in R. muscosa populations inhabiting control lakes that remained in their natural fishless condition. Following these population increases, R. muscosa dispersed to adjacent suitable (but unoccupied) sites, moving between 200 and 900 m along streams or across dry land. Together, these results suggest that large-scale removal of introduced fish could result in at least partial reversal of the decline of R. muscosa. Continued monitoring of R. muscosa at the fish-removal sites will be necessary to determine whether the positive effects of fish eradication are sustained over the long-term, especially in light of the increasingly important role played by an emerging infectious disease (chytridiomycosis, caused by Batrachochytrium dendrobatidis) in influencing R. muscosa populations.  相似文献   

13.
Up to 1978 51% of brown trout populations and 27% of perch populations in the four southernmost counties of Norway were lost. During 1983 the fish status of lakes in the two southernmost counties which in the period 1974 to 1978 still had fish were updated. During the period 1978 to 1983, 30% of the remaining brown trout populations and 12% of the perch populations were lost. By 1983 71% of brown trout populations and 43% of perch populations in this area have been lost. In October 1983, 623 (77%) of the lakes were sampled for analyses of water quality. The status and change in fish populations during the period from 1974–78 to 1983 were highly related to water quality status.  相似文献   

14.
Fish communities in four lakes sampled over several years were compared against a reference data set of forty-nine lakes in south-central Ontario. Two of the temporal-comparison lakes (Crosson and Grindstone) exhibit significant changes in their fish communities relative to the reference set. This was due to the extirpation of various fish species (white sucker Catostomus commersoni, lake trout Salvelinus namaycush, and blacknose shiner Notropis heterolepis) during the intervening years. A control lake in the temporal comparison (Poorhouse) showed little change in species composition over time and no loss of species. The fourth temporal lake, Plastic Lake, also showed little change likely as a consequence of the previously documented extinctions in this lake. White suckers within Crosson Lake have demonstrated intermittent recruitment and a 89% reduction in population abundance due to acid-induced reproductive constraints in their spawning stream. Similar conditions contributed to the loss of sucker populations and additional species in Grindstone and Plastic Lakes also. Various species in many of the lakes represent metapopulations. Given the barriers imposed by outflow drainage conditions, these accelerated rates of local extinctions have not been balanced by colonizations from other lakes within the watershed. As a consequence the underlying fish communities have been changed and will remain so without active rehabilitation.  相似文献   

15.
Netting surveys of lakes varying in pH (4.4–7.1) showed that lake trout (Salvelinus namaycush) populations fail to recruit at pH <5.5 and are lost from lakes with pH<5.2. Brook trout (S. fontinalis) were extirpated in lakes with pH <5.0. In regional chemical surveys of Ontario lakes, it was found that 2% of sampled brook trout lakes and 2.5% of lake trout lakes were acidified (alkalinity <0 uEq L?1). Threshold pH levels determined from fisheries assessments were used to estimate that 1% of lake trout and brook trout populations have been lost due to acidification.  相似文献   

16.
This study presents data concerning long-term trends after neutralization of four acidified lakes in two regions on the Swedish west coast. Neutralization was achieved by a di-Ca-silicate with 52% CaO and about 11.5% MgO. Between 61 and 74% of the spread lime product dissolved during a 5 to 7 yr period. The liming increased pH, from a range of 4.5 to 5.2 to near neutral and restored alkalinity in the range of 0.2 to 0.3 meq l?1 and the Ca-content became 3 to 4 times higher than before liming. In two lakes transparency decreased significantly presumably due to changed phytoplankton composition. These changes successively declined due to dilution and continuous acid loading. The changes in water chemistry and development of stocked brown trout (Salmo trutta) populations initiated biotic changes. Phyto- and zooplankton communities reacted both instantly and later with successions in species composition. Changes of benthic macroinvertebrate species occured over several years, but some pelagic species, e.g. corixids were rapidly reduced due to predation of fish. Observed changes were predominantly due to expanding populations of species present at very low abundances even during acid state of the lakes. Some organisms found during preacid state of the lakes did not establish new populations and this process may need a prolonged time with favorable conditions. Reacidification towards the end of the study period significantly stressed the brown trout population and also favored expansion of the filamentous algaMougeotia sp. andSphagnum sp. that almost vanished during the first year after liming. Decreasing concentration of total P was not influenced by neutralization and may be mostly dependent on negative changes in the soils surrounding the lakes. If generally valid, this process may be an important factor for the oligotrophication of lakes in areas where acid deposition is high.  相似文献   

17.
Although the decline in fish populations due to acidicwater in Norway started as early as in the 1920's the most rapid losses appeared during the 1960–70's. Until 1978, the populations of Atlantic salmon had disappeared from the southernmost part of Norway, and in these areas, more than half of the brown trout populations had been lost. Today, in spite of no increase in acid depositions, the fishery problems seems to continue at the same speed. Data based on interviews of the local fish authority shows that lakes still holding a fish population in the late 70's, have experienced a 30% loss of brown trout populations and a 12% loss of perch in the period 1978–1983. This trend have been confirmed by testfishing in lake systems having long data series. Salmon rivers on the western coast of Norway have experienced several episodes of fish kills due to rapid changes in water quality. These fish kills have mainly affected smolts of Atlantic salmon. Spawning migrating salmon on entering their acidified home river have also been affected. In Sweden, several salmon populations along the western coast have been lost due to acidification with no positive trends so far in the 1980's. Areas in central Sweden and in some high mountain areas are still experiencing a continuous and increasing acidification with detrimental effects on invertebrates and fish. In Finland, an increase in acidic deposition during the last decades have occurred, leading to acidification in the most sensitive freshwater systems. Although some acidified freshwater lakes are reported to have lost their fish stocks, few data on fish population effects are available.  相似文献   

18.
Many southern populations of the common loon (Gavia immer) face threats from lead and methylmercury contamination, lake acidification, shoreline development and human recreation. It is now clear that the task of conserving loon populations will depend upon mitigating these varied threats. In a controlled experiment, we examined the efficacy of using floating nest platforms to increase reproductive success of loons and thus help sustain local populations. Platforms were attractive nesting sites both on lakes that had consistently hatched chicks from natural sites and on lakes where chick production had been sporadic. When compared to natural nest sites, platforms increased hatching success by 69% and fledging success by 32%, apparently through reduction in mammalian egg predation. A well-managed effort to introduce nesting platforms might be a viable strategy to help sustain threatened populations.  相似文献   

19.
Despite a slight reduction in the level of acidic deposition in Norway, acidification of lakes and rivers continues. The Norwegian Liming Project (1979–84) demonstrated that lime treatment can be an effective measure against acidification of watercourses given appropriate adaptation to local conditions. Liming in Norway is difficult because of (1) large amounts of precipitation, (2) short retention time of lakes, and (3) episodic changes in water chemistry. In 1988 NOK 14 mill. has been allocated to operational liming and research. We report here on chemical and biological responses from lime treatment of a lake, a river and a catchment. Lake Store Hovvatn was limed in 1981 and successfully stocked with brown trout. Before reliming in 1987, fish growth had ceased, but increased post liming. The River Audna has been continuously limed since 1985. Sea trout fisheries have improved, and the stocking of Atlantic salmon smolts at the mouth of the river in 1986 has already resulted in the return of spawners. Liming of the entire terrestrial catchment to the pond Tjønnstrond in 1983 by helicopter was also successful; stocked brown trout have survived to the present.  相似文献   

20.
Acid deposition has led to acidification and loss of fish populations in thousands of lakes and streams in Norway. Since the peak in the late 1970s, acid deposition has been greatly reduced and acidified surface waters have shown chemical recovery. Biological recovery, in particular fish populations, however, has lagged behind. Long-term monitoring of water chemistry and fish populations in Lake Langtjern, south-eastern Norway, shows that around 2008, chemical recovery had progressed to the point at which natural reproduction of brown trout (Salmo trutta) reoccurred. The stocked brown trout reproduced in the period 2008–2014, probably for the first time since the 1960s, but reproduction and/or early life stage survival was very low. The results indicate that chemical thresholds for reproduction in this lake are approximately pH?=?5.1, Ali?=?26 μg l?1, ANC?=?47 μeq l?1, and ANCoaa?=?10 μeq l?1 as annual mean values. These thresholds agree largely with the few other cases of documented recovery of brown trout in sites in Norway, Sweden, and the UK. Occurrence and duration of acidic episodes have decreased considerably since the 1980s but still occur and probably limit reproduction success.  相似文献   

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