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1.
Introduced and translocated fish species in the inland waters of Greece   总被引:5,自引:0,他引:5  
Over the last 7 decades, 23 exotic fish species have been introduced into the inland waters of Greece. Some introductions were deliberately planned to take advantage of particular ecological or economic qualities of the species concerned. These include rainbow trout, Oncorhynchus mykiss (Walbaum), Pacific salmon, Oncorhynchus sp., vendace, Coregonus lavaretus (L.), grass carp, Ctenopharyngodon idella (Valenciennes), and silver carp, Hypophthalmichthys molitrix (Valenciennes). Other introductions, such as that of pumpkinseed, Lepomis gibbosus (L.), and false rasbora, Pseudorasbora parva (Temminck & Schlegel), were unintentional. Further transfers were made of species between various basins within the country, including common carp, Cyprinus carpio L., tench, Tinca tinca (L.), crucian carp, Carassius auratus gibelio (Bloch), bitterling, Rhodeus amarus (Bloch), and Aristotle's catfish, Silurus aristotelis Garman. Some species have become fully acclimatized and have built up important populations. In other cases, the transfers and introductions have had considerable negative impacts, particularly where introduced species have outcompeted native forms, as in the cases of the mosquito fish, Gambusia affinis (Baird & Girard), versus Greek toothcarp, Valencia letourneuxi (Sauvage), in the western Greek marshes, and of Aristotle's catfish versus the wels, Silurus glanis L., in Lake Volvi.  相似文献   

2.
  • 1. The topmouth gudgeon Pseudorasbora parva Schlegel, 1842, a south-east asian cyprinid, was introduced accidentally in the Danube Delta in Romania in the 1960s and has now achieved a pan-Danubian distribution. P. parva has been introduced into other countries, such as Greece, usually inadvertently included with other species imported for fish farming. In 1984–85, during a study of the fish populations of Lake Mikri Prespa (north-west Greece), several topmouth gudgeon were caught. Our aim was to study the changes in the population size of P. parva over nearly 10 years, to study its life history traits and to assess its potential impacts on native fish species.
  • 2. The catch per unit effort (CPUE) in spring increased significantly between 1984 and 1992. We found evidence that P. parva has established a breeding population in the lake. P. parva combines many characteristics likely to favour a successful colonization (resistance to harsh climatic conditions, early sexual maturity, extended breeding season, broad dietary spectrum). Growth in Lake Prespa, where the oldest individuals captured were 3 years old, is very similar to that observed within its native range.
  • 3. There is evidence for dietary overlap between P. parva and three endemic species: Paraphoxinus epiroticus prespensis, Cobitis meridionalis and Alburnoides bipunctatus ohridanus. No decline in the populations of these three species has yet been demonstrated. Other possible impacts are discussed. The successful colonization by P. parva was certainly favoured by the absence of a true piscivorous fish in the lake and by the isolation and high level of endemism of fish communities.
  • 4. The conservation of the many endemic species in the lake should be a priority and the introduction of exotic species should be banned.
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3.
Introduced fishes may have major impacts on community structure and ecosystem function due to competitive and predatory interactions with native species. For example, introduced lake trout (Salvelinus namaycush) has been shown to replace native salmonids and induce major trophic cascades in some North American lakes, but few studies have investigated trophic interactions between lake trout and closely related native Arctic charr (S. alpinus) outside the natural distribution of the former species. We used stomach content and stable isotope analyses to investigate trophic interactions between introduced lake trout and native Arctic charr in large subarctic Lake Inarijärvi in northern Finland. Both salmonids had predominantly piscivorous diets at >280 mm total length and were mainly caught from the deep profundal zone. However, lake trout had a more generalist diet and showed higher reliance on littoral prey fish than Arctic charr, whose diet consisted mainly of pelagic planktivorous coregonids. According to length at age and condition data, lake trout showed slightly faster growth but lower condition than Arctic charr. The results indicate that introduced lake trout may to some extent compete with and prey upon native Arctic charr, but currently have only a minor if any impact on native fishes and food web structure in Inarijärvi. Future monitoring is essential to observe potential changes in trophic interactions between lake trout and Arctic charr in Inarijärvi, as well as in other European lakes where the two salmonids currently coexist.  相似文献   

4.
Periodicity and timing of opaque zone formation in otoliths of introduced redbelly tilapia, Tilapia zillii (Gervais), in Crater Lake Nkuruba, Uganda, were validated using marginal increment. Age and growth were assessed through readings of biannuli in thin‐sectioned sagittal otoliths. Deposition of opaque zone formation in T. zillii otoliths was bimodal (March–May and September–November), corresponding to two seasonal peaks of precipitation characteristic of this equatorial region. Ages of T. zillii ranged from 2 to 8 years, with fish gillnetted offshore having a faster growth and attaining larger size‐at‐age than fish captured inshore in minnow traps, suggesting that use of multiple gears is needed when estimating the growth of T. zillii. Total instantaneous mortality (Z), estimated using catch curve analysis, was 0.74 for gillnetted fish and 0.71 for trapped fish. These estimates were at the low end of the total mortality reported for other tilapia species. Natural mortality (M) was estimated as 0.52–0.54 by applying Rikhter and Efanov's maximum age at maturity and Hoenig's maximum age methods, respectively. Fishing mortality (F) in Lake Nkuruba was 0.17–0.22, indicating a low exploitation level in the lake.  相似文献   

5.
A popular species for food and sport, the European catfish (Silurus glanis) is well‐studied in its native range, but little studied in its introduced range. Silurus glanis is the largest‐bodied freshwater fish of Europe and is historically known to take a wide range of food items including human remains. As a result of its piscivorous diet, S. glanis is assumed to be an invasive fish species presenting a risk to native species and ecosystems. To assess the potential risks of S. glanis introductions, published and ‘grey’ literature on the species’ environmental biology (but not aquaculture) was extensively reviewed. Silurus glanis appears well adapted to, and sufficiently robust for, translocation and introduction outside its native range. A nest‐guarding species, S. glanis is long‐lived, rather sedentary and produces relatively fewer eggs per body mass than many fish species. It appears to establish relatively easily, although more so in warmer (i.e. Mediterranean) than in northern countries (e.g. Belgium, UK). Telemetry data suggest that dispersal is linked to flooding/spates and human translation of the species. Potential impacts in its introduced European range include disease transmission, hybridization (in Greece with native endemic Aristotle’s catfish [Silurus aristotelis]), predation on native species and possibly the modification of food web structure in some regions. However, S. glanis has also been reported (France, Spain, Turkmenistan) to prey intensively on other non‐native species and in its native Germany to be a poor biomanipulation tool for top‐down predation of zooplanktivorous fishes. As such, S. glanis is unlikely to exert trophic pressure on native fishes except in circumstances where other human impacts are already in force. In summary, virtually all aspects of the environmental biology of introduced S. glanis require further study to determine the potential risks of its introduction to novel environments.  相似文献   

6.
  1. Wetlands in the Lake Victoria basin serve as structural and hypoxic refugia for some native fishes against predation by introduced Nile perch (Lates niloticus); however, little is known about the fine‐scale patterns of distribution and abundance of these refuge inhabitants.
  2. This study sought to quantify wetland ecological gradients and determine where peaks in native fish abundance and richness (‘peak refugia’) occurred using Lake Nabugabo, Uganda as a model system.
  3. Extensive wetland transects were sampled between June and August, 2011 to measure ecological variation over distance from the lake–wetland edge.
  4. Wetlands were characterized by strong clines in water temperature, pH, dissolved oxygen (DO), depth and vegetation density, and narrow peak refugia were found precisely at the lake–wetland edge. Community richness and diversity tended to be greater in areas with higher DO and lower temperature, pH, and vegetation density. It is interesting that areas encroached upon by a native emergent macrophyte (hippo grass, Vossia cuspidata) had more extreme physico‐chemical conditions and supported fewer native fish species.
  5. These results demonstrate the importance of wetland edges in the maintenance of native fish fauna in the Lake Victoria basin, and suggest that the continued expansion of hippo grass may reduce the accessibility of wetlands as refugia.
  6. We recommend that the use of spatially explicit management approaches such as the development of secure buffer zones surrounding wetland edges to protect peak refugia, and the need for hippo grass control to minimize its effects on this important refuge.
Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
The invasion of non‐indigenous freshwater fish species is one of the most important threats to aquatic biodiversity. Similar to other Mediterranean countries, Greece is considered a hot spot for freshwater biodiversity, with many range‐restricted endemics of high conservation concern. The aim of this study was to undertake a risk screening assessment to evaluate the invasive potential of non‐native, translocated and traded aquarium fishes in Greece by applying the Fish Invasiveness Screening Kit (FISK). In total, 73 freshwater fish species were evaluated by two assessors. FISK was able to discriminate reliably between invasive and non‐invasive species with a threshold of 15.25. Based on mean scores, 30 species were classified as ‘high risk’, of which 17 as ‘moderately high risk’, six as ‘high risk’ and seven as ‘very high risk’. There was a high coincidence rate for the species categorisation between the two assessors, but significant differences in certainty. The results suggest that FISK is a useful tool for assessing risks posed by non‐native, translocated and traded aquarium fish species in Greece.  相似文献   

8.
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   

9.
1. Seventy-two per cent of the Flathead River catchment (22 241 km2) is federally designated and protected as wilderness or national park. Thus, the catchment remains one of the more pristine areas of its size in the temperate latitudes of the world. 2. Discharge in the downstream reaches of the river system outside the protected areas is regulated by three dams for flood control and hydropower production. These dams have blocked natural migration of native fish from Flathead Lake (496 km2) and isolated populations in sub-catchments. Temperature and erratic flow fluctuations have altered phenologies of river zoobenthos and fish, and in dam tailwaters aquatic biodiversity is drastically reduced in comparison to unregulated segments. 3. Ecological problems caused by changing water quality conditions, altered land-use patterns and introductions of non-native biota are interactive with the impacts of stream and lake level regulation, thereby emphasizing the complexity of this river–lake ecosystem. 4. Mitigation of the effects of regulation is compromised by differing management priorities and regulatory mandates of County, State, Tribal, and Federal agencies responsible for natural resource management within the catchment. Moreover, economic and ecological interests outside the Flathead influence the way flows are regulated within the catchment. 5. The most pervasive influences of stream and lake regulation can be ameliorated by retrofitting the hypolimnial release dam with a selective depth outlet structure to allow temperature control, and by controlling changes in flow rates to create a more natural hydrograph in the tailwaters of the large dams. Allowing fish passage by construction of fish ladders is problematic because upstream passage will commingle native species that were isolated upstream by construction of the dams with non-native species that were introduced subsequently below the dams. Cascading food web interactions elicited by invasions of non-native biota may offset any advantage to native stocks gained by passage and/or augmentation with hatchery stocks. 6. Mitigation must be adaptive in the sense that unanticipated effects and interactions with other management objectives can be documented and alternative action can be implemented. 7. This case history of the effects of stream and lake level regulation, and the approaches to management reviewed in this paper, should serve as a lesson in river conservation.  相似文献   

10.
Abstract –  We examined the relative contribution of environmental heterogeneity and dispersal limitation on freshwater fish community composition in 18 Greek protected lakes and reservoirs. Environmental heterogeneity was measured by spatial pattern metrics (calculated by digital map processing, e.g., patch richness density, area-weighted mean patch area), altitude, maximum lake depth and trophic status. Dispersal limitation was measured by straight-line distances among lake centres. Ecosystems were clustered according to species composition. We examined the correlation of similarity in species composition among ecosystems with that of environmental heterogeneity and with straight-line distances, for the entire dataset, as well as for the occurring clusters. Fish species richness increased with ecosystem area and decreased with altitude. The clusters identified (aquatic ecosystems of Northern vs. ecosystems of Western Greece), implied an underlying biogeographical pattern as defined, with Pindus range acting as a natural barrier. Between ecosystems similarity, based on fish species composition, showed a weak to insignificant correlation with environmental heterogeneity, but was significantly correlated to dispersal limitation for the entire dataset as well as within each occurring cluster. Thus, natural barriers, species biogeography and dispersal limitation played a more significant role in shaping freshwater fish communities than environmental heterogeneity.  相似文献   

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