Managing conflicts arising from fisheries enhancements based on non‐native fishes in southern Africa

Southern Africa has a long history of non‐native fish introductions for the enhancement of recreational and commercial fisheries, due to a perceived lack of suitable native species. This has resulted in some important inland fisheries being based on non‐native fishes. Regionally, these introductions are predominantly not benign, and non‐native fishes are considered one of the main threats to aquatic biodiversity because they affect native biota through predation, competition, habitat alteration, disease transfer and hybridization. To achieve national policy objectives of economic development, food security and poverty eradication, countries are increasingly looking towards inland fisheries as vehicles for development. As a result, conflicts have developed between economic and conservation objectives. In South Africa, as is the case for other invasive biota, the control and management of non‐native fishes is included in the National Environmental Management: Biodiversity Act. Implementation measures include import and movement controls and, more recently, non‐native fish eradication in conservation priority areas. Management actions are, however, complicated because many non‐native fishes are important components in recreational and subsistence fisheries that contribute towards regional economies and food security. In other southern African countries, little attention has focussed on issues and management of non‐native fishes, and this is cause for concern. This paper provides an overview of introductions, impacts and fisheries in southern Africa with emphasis on existing and evolving legislation, conflicts, implementation strategies and the sometimes innovative approaches that have been used to prioritize conservation areas and manage non‐native fishes.     

Predicting introduction, establishment and potential impacts of smallmouth bass

Aim The introduction of non‐indigenous species has resulted in wide‐ranging ecological and economic impacts. Predictive modelling of the introduction and establishment of non‐indigenous species is imperative to identify areas at high risk of invasion to effectively manage non‐indigenous species and conserve native populations. Smallmouth bass (Micropterus dolomieu), a warm water fish species native to central North America has negatively impacted native fish communities, including cyprinids and salmonid populations, as a result of intentional introductions. We predicted the introduction risk; species establishment based on habitat suitability; identified lakes at high risk of invasion; and finally assessed the consequential impacts on native salmon, trout and cyprinid populations. Location Ontario and British Columbia, Canada. Methods Classification tree and logistic regression models were developed and validated to predict the introduction and establishment of smallmouth bass for thousands of lakes. Results Densely human populated areas and larger lake surface areas successfully identify lakes associated with the introduction of smallmouth bass (introduction model) in British Columbia. Climate, lake morphology and water chemistry variables were the driving environmental parameters to define suitable smallmouth bass habitat (establishment model). A combination of the introduction and establishment model identified 138 lakes that are currently at risk in British Columbia to the introduction and establishment of smallmouth bass. Of these 138 high‐risk lakes, 95% of them contain at least one species of salmon, trout or cyprinid, thereby increasing the potential impact of an invasion by smallmouth bass. Main conclusions Our framework can be applied to other terrestrial and aquatic species to obtain a better understanding of the potential risk posed by a non‐indigenous species to an ecosystem. Furthermore, our methodology can be used to focus management efforts on areas at higher risk (e.g. number of potential releases, more favourable habitats) to control future introductions of non‐indigenous species, thereby conserving native populations.     

Freshwater fish introductions in mediterranean‐climate regions: are there commonalities in the conservation problem?

Aim To compare patterns and drivers of freshwater fish introductions across five climatically similar regions and evaluate similarities and differences in the non‐native species introduced. Location Five mediterranean‐climate regions: California (USA), central Chile, south‐western Australia, the Iberian peninsula (Spain and Portugal) and the south‐western Cape (South Africa). Methods Species presence–absence for native and non‐native fishes were collated across the regions, and patterns of faunal change were examined using univariate and multivariate statistical approaches. Taxonomic patterns in freshwater fish introductions were evaluated by comparing the number of species introduced by order to the numbers expected from binomial probabilities. Factors influencing multiple introductions of freshwater fish species in mediterranean regions were determined using generalized linear modelling. Results High levels of endemism (70–90%) were revealed for south‐western Cape, south‐western Australia and Chile. Despite their high rates of endemism, all regions currently have more non‐native species than endemic species. Taxonomic selection was found for five orders, although this was only significant for Salmoniformes across regions. The average increase in regional compositional similarity of fish faunas resulting from non‐native fish introductions was 8.0%. Important factors predicting multiple introductions of a species include previous introduction success and mean latitude of its distribution Main conclusions The mediterranean‐climate regions of the world, separated by vast distances, originally had a few fish species in common but are now more similar, owing to species introductions, illustrating the extent and importance of taxonomic homogenization. Introductions are largely driven by taxonomically biased human interests in recreational fisheries, aquaculture and ornamental pet species.     

Antarctica: The final frontier for marine biological invasions

Antarctica is experiencing significant ecological and environmental change, which may facilitate the establishment of non‐native marine species. Non‐native marine species will interact with other anthropogenic stressors affecting Antarctic ecosystems, such as climate change (warming, ocean acidification) and pollution, with irreversible ramifications for biodiversity and ecosystem services. We review current knowledge of non‐native marine species in the Antarctic region, the physical and physiological factors that resist establishment of non‐native marine species, changes to resistance under climate change, the role of legislation in limiting marine introductions, and the effect of increasing human activity on vectors and pathways of introduction. Evidence of non‐native marine species is limited: just four marine non‐native and one cryptogenic species that were likely introduced anthropogenically have been reported freely living in Antarctic or sub‐Antarctic waters, but no established populations have been reported; an additional six species have been observed in pathways to Antarctica that are potentially at risk of becoming invasive. We present estimates of the intensity of ship activity across fishing, tourism and research sectors: there may be approximately 180 vessels and 500+ voyages in Antarctic waters annually. However, these estimates are necessarily speculative because relevant data are scarce. To facilitate well‐informed policy and management, we make recommendations for future research into the likelihood of marine biological invasions in the Antarctic region.     

Pathways of ornamental and aquarium fish introductions into urban ponds of Epping Forest (London,England): the human vector*

To examine the role of humans in the non‐native fish introductions, we measured the frequency of occurrence and density of non‐native fishes in ponds (Epping Forest, Essex, England) that had been restored (drained of water and voided of fish or treated with rotenone) on a known date and into which no piscivorous or non‐native fishes had subsequently been stocked intentionally. For each pond, the period of time since pond restoration, pond area, distance to nearest residential housing, distance to nearest footpath, distance to nearest water body or stream, and the proportion of pond vegetated were measured. The occurrence of both non‐native and unexpected native fish species was non‐random, and the number of ornamental varieties was found to increase as pond distance from the nearest road decreased. Variety richness of each of three categories of fish (non‐native, goldfish Carassius auratus and native) was significantly correlated with at least two of the following variables: distance from nearest road, nearest footpath and nearest pond. The rate of non‐native fish introductions (adjusted variety richness per year) could also be estimated from pond distance to the nearest road, being about 3.5 ornamental varieties introduced per year in ponds adjacent to roads, but the rate appears to be much greater in ponds that had recently (<1.5 years) undergone restoration. Implications for conservation and management, as well as the potential role of societal issues such as recreational activities, cultural and religious practices, are discussed.     

Understanding invasion history: genetic structure and diversity of two globally invasive plants and implications for their management

Aim Resolving the origin of invasive plant species is important for understanding the introduction histories of successful invaders and aiding strategies aimed at their management. This study aimed to infer the number and origin(s) of introduction for the globally invasive species, Macfadyena unguis‐cati and Jatropha gossypiifolia using molecular data. Location Native range: Neotropics; Invaded range: North America, Africa, Europe, Asia, Pacific Islands and Australia. Methods We used chloroplast microsatellites (cpSSRs) to elucidate the origin(s) of introduced populations and calculated the genetic diversity in native and introduced regions. Results Strong genetic structure was found within the native range of M. unguis‐cati, but no genetic structuring was evident in the native range of J. gossypiifolia. Overall, 27 haplotypes were found in the native range of M. unguis‐cati. Only four haplotypes were found in the introduced range, with more than 96% of introduced specimens matching a haplotype from Paraguay. In contrast, 15 haplotypes were found in the introduced range of J. gossypiifolia, with all invasive populations, except New Caledonia, comprising multiple haplotypes. Main conclusions These data show that two invasive plant species from the same native range have had vastly different introduction histories in their non‐native ranges. Invasive populations of M. unguis‐cati probably came from a single or few independent introductions, whereas most invasive J. gossypiifolia populations arose from multiple introductions or alternatively from a representative sample of genetic diversity from a panmictic native range. As introduced M. unguis‐cati populations are dominated by a single haplotype, locally adapted natural enemies should make the best control agents. However, invasive populations of J. gossypiifolia are genetically diverse and the selection of bio‐control agents will be considerably more complex.     

Do non‐native fish as prey favour the conservation of the threatened indigenous Eurasian otter?

1. Biological invasions are considered a major threat to biodiversity. Most research has focused on the distribution, biology and impacts of non‐native species on native fauna and flora. However, few studies have explored their role as prey for native predators of conservation concern. 2. To assess the incidence and intensity of predation by the Eurasian otter Lutra lutra on established non‐native fish species, data were collated from the published literature. To be selected, studies had to cover at least 1 year, analyse more than 100 spraints and report the study period and percentage relative frequency (%RF) of all prey fish species. 3. To permit reliable, time‐related comparisons with %RF of non‐native fishes in otter diet, we also reviewed available information about both the distribution of non‐native fishes and history of their introductions to European countries, revealing a decrease with longitude in the number of naturalised non‐native fishes taken (ranging between 5 and 34) and their percentage in each fish assemblage. 4. Our selective criteria were met by 30 dietary studies from 44 study areas in 15 European countries during 1970–2010. The extent to which otters rely on non‐native fishes was almost negligible (mean %RF = 4.8), with the number of non‐native fishes preyed upon by otters decreasing with both latitude and longitude. 5. The %RF of non‐native fish in the diet increased slightly with time, with otters preying significantly more on non‐native fish in study areas where alterations of the fish assemblage had been highlighted in the reference papers. No relationship was found between otter diet breadth and the occurrence of non‐native fishes in their diet. 6. The current role of non‐native species in otter diet suggests that effective otter conservation management plans should focus on the maintenance and/or enhancement of native fish assemblages.     

To be,or not to be,a non‐native freshwater fish?

We examine the evolving concept of what constitutes a non‐native (or alien) freshwater fish. In an attempt to distinguish between biogeographical and socio‐political perspectives, we review the patterns in the introduction and dispersal of non‐native fishes in Europe and North America, and especially the recent expansion of Ponto‐Caspian gobies in Europe. We assess patterns in the development of national policy and legislation in response to the perceived threat of non‐native fish introductions to native species and ecosystems. We review, and provide a glossary of, the terms and definitions associated with non‐native species. Finally, we discuss perspectives as regards the future treatment of naturalized species.     

Non-native fish species in Slovak waters: origins and present status

Freshwater fishes recorded in the territory of Slovakia include 95 fish species. As many as one third of these are allochthonous fish species belonging to 14 families, among which several have not occurred in Slovakia recently. Historically, there were three main periods of introduction: the first is the beginning of the 20^th century, the second includes two decades between 1955 and 1975 and the third period is from the year 1990 up to the present time. The origins of the exotic species seen in Slovakia are the four continents — Africa (3), North America (7), Central America (3), and Asia (13) and ten of them are from different regions in Europe. The purpose of intentional introductions of non-native species was to occupy vacant ecological niches in the ecosystems reshaped by human activities, fish stocking, angling or fish farming. Some of these species spread from their original ranges or they penetrated spontaneously from the adjacent countries via the river network system. At the present time, 76 fish species in total form populations in Slovakia. There are 54 autochthonous and 22 allochthonous species, 14 of them are exotic fishes. The invasive characters in 13 fish species were considered, the recent native/total fish ratio is 0.71.     

Invasion of the Hawaiian Islands by a parasite infecting imperiled stream fishes

Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co‐introduction of parasites with non‐native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent parasite of at‐risk native stream fishes. In this study, we evaluated the prevailing hypothesis that C. cotti entered the Hawaiian Islands with poeciliid fishes from the Americas, and spread by translocation of poeciliid hosts across the archipelago for mosquito control. We also considered the alternative hypothesis of multiple independent co‐introductions with host fishes originating from Asia. We inferred conduits of introduction and spread of C. cotti across the archipelago from geographic patterns of mtDNA sequence variation and allelic variation across 11 newly developed microsatellite markers. The distribution of haplotypes suggests that C. cotti spread across the archipelago following an initial introduction on O'ahu. Approximate Bayesian Computation modeling and allelic variation also indicate that O'ahu is the most likely location of introduction, from which C. cotti dispersed to Maui followed by spread to the other islands in the archipelago. Evidence of significant genetic structure across islands indicates that contemporary dispersal is limited. Our findings parallel historical records of non‐native poeciliid introductions and suggest that remediating invasion hotspots could reduce the risk of infection in native stream fishes, which illustrates how inferences on parasite co‐introductions can improve conservation efforts by guiding responses to emerging infectious disease in species of concern.     

Occurrence of non‐native fishes in the Danube east of Vienna (Austria) and potential interactions of invasive gobiids with native fishes

Non‐native fish species pose a major threat to local fish populations and aquatic ecosystems in general. Invasive gobies are a particular focus of research, but with partly inconsistent results. While some studies reported severe detrimental impacts on native species, others have concluded less serious or neutral effects. We provide results from a large‐scale, multi‐annual fish monitoring program on the occurrence and abundance of non‐native fishes in the main stem of a free‐flowing section of the Austrian Danube. Special emphasis was placed on identifying positive or negative interactions of invasive gobies with native species. Whereas most non‐native species occurred too sporadically or were too few in number to infer a direct threat on the local fish community, invasive gobies were among the most common fishes throughout all sampling years. Co‐occurrence analyses revealed species‐ and mesohabitat type‐specific associations of gobies with native species, which were primarily positive. Notably, native predators such as asp, burbot, or perch probably benefit from the ubiquitous gobies. Two characteristic fluvial fishes revealed negative associations with invasive gobies, namely barbel (Barbus barbus) and Danube whitefin gudgeon (Romanogobio vladykovi): they appear to avoid habitats occupied by gobies. Accordingly, high abundances of round and bighead goby most likely resulted in population losses of barbel and whitefin gudgeon, respectively. Overall, our results indicate a limited negative impact of non‐native species in the sampling area. This is because only two out of 51 occurring species were found to be adversely affected by gobies, the share of co‐occurrences with native species was high, and other non‐native species were generally rare. Nevertheless, invasions are highly dynamic, and new non‐native species are likely to occur in the Austrian Danube, calling for continued monitoring and awareness.     

Loss of genetic diversity and increased embryonic mortality in non‐native lizard populations

Many populations are small and isolated with limited genetic variation and high risk of mating with close relatives. Inbreeding depression is suspected to contribute to extinction of wild populations, but the historical and demographic factors that contribute to reduced population viability are often difficult to tease apart. Replicated introduction events in non‐native species can offer insights into this problem because they allow us to study how genetic variation and inbreeding depression are affected by demographic events (e.g. bottlenecks), genetic admixture and the extent and duration of isolation. Using detailed knowledge about the introduction history of 21 non‐native populations of the wall lizard Podarcis muralis in England, we show greater loss of genetic diversity (estimated from microsatellite loci) in older populations and in populations from native regions of high diversity. Loss of genetic diversity was accompanied by higher embryonic mortality in non‐native populations, suggesting that introduced populations are sufficiently inbred to jeopardize long‐term viability. However, there was no statistical correlation between population‐level genetic diversity and average embryonic mortality. Similarly, at the individual level, there was no correlation between female heterozygosity and clutch size, infertility or hatching success, or between embryo heterozygosity and mortality. We discuss these results in the context of human‐mediated introductions and how the history of introductions can play a fundamental role in influencing individual and population fitness in non‐native species.     

Non‐native fishes and climate change: predicting species responses to warming temperatures in a temperate region

1. Temperate regions with fish communities dominated by cold‐water species (physiological optima <20 °C) are vulnerable to the effects of warming temperatures caused by climate change, including displacement by non‐native cool‐water (physiological optima 20–28 °C) and warm‐water fishes (physiological optima >28 °C) that are able to establish and invade as the thermal constraints on the expression of their life history traits diminish. 2. England and Wales is a temperate region into which at least 38 freshwater fishes have been introduced, although 14 of these are no longer present. Of the remaining 24 species, some have persisted but failed to establish, some have established populations without becoming invasive and some have become invasive. The aim of the study was to predict the responses of these 24 non‐native fishes to the warming temperatures of England and Wales predicted under climate change in 2050. 3. The predictive use of climate‐matching models and an air and water temperature regression model suggested that there are six non‐native fishes currently persistent but not established in England and Wales whose establishment and subsequent invasion would benefit substantially from the predicted warming temperatures. These included the common carp Cyprinus carpio and European catfish Silurus glanis, fishes that also exert a relatively high propagule pressure through stocking to support angling and whose spatial distribution is currently increasing significantly, including in open systems. 4. The potential ecological impacts of the combined effects of warming temperatures, current spatial distribution and propagule pressure on the establishment and invasion of C. carpio and S. glanis were assessed. The ecological consequences of C. carpio invasion were assessed as potentially severe in England and Wales, with impacts likely to relate to habitat destruction, macrophyte loss and increased water turbidity. However, evidence of ecological impacts of S. glanis elsewhere in their introduced range was less clear and so their potential impacts in England and Wales remain uncertain.     

Widespread primary,but geographically restricted secondary,human introductions of wall lizards,Podarcis muralis

Establishing the introduction pathways of alien species is a fundamental task in invasion biology. The common wall lizard, Podarcis muralis, has been widely introduced outside of its native range in both Europe and North America, primarily through escaped pets or deliberate release of animals from captive or wild populations. Here, we use Bayesian clustering, approximate Bayesian computation (ABC) methods and network analyses to reconstruct the origin and colonization history of 23 non‐native populations of wall lizards in England. Our analyses show that established populations in southern England originate from at least nine separate sources of animals from native populations in France and Italy. Secondary introductions from previously established non‐native populations were supported for eleven (47%) populations. In contrast to the primary introductions, secondary introductions were highly restricted geographically and appear to have occurred within a limited time frame rather than being increasingly common. Together, these data suggest that extant wall lizard populations in England are the result of isolated accidental and deliberate releases of imported animals since the 1970s, with only local translocation of animals from established non‐native populations. Given that populations introduced as recently as 25 years ago show evidence of having adapted to cool climate, discouraging further translocations may be important to prevent more extensive establishment on the south coast of England.     

Non-native fish in aquaculture and sport fishing in Brazil: economic benefits versus risks to fish diversity in the upper River Paraná Basin

Brazil has a highly diverse freshwater fish fauna and their freshwaters provide valuable provisioning ecosystem services in aquaculture and sport angling, especially in the developed regions in the south. Non-native fish now comprise a substantial proportion of the total aquaculture production and value, contributing at least $US 250?million in 2008 (63% of the total value of freshwater fish aquaculture) according to the Fish and Agriculture Organisation. Much of this aquaculture activity is centred in Central and Southern Brazil, such as impounded sections of the upper River Paraná. The non-native fishes used tend to feed at relatively low trophic levels, with the most prominently species being Cyprinus carpio and Oreochromis niloticus. Ecological risk assessment suggests these species are potentially highly invasive and deleterious to the native fish diversity of invaded water bodies. Fishes introduced for the creation of sport fisheries tend feed higher trophic levels through piscivory, such as the peacock basses (Cichla species) from Amazonia. Their introductions have generally resulted in establishment and invasion, which tends to be followed by significant and rapid declines in native fish diversity as a consequence of increased predation pressure. Thus, whilst non-native fish in the upper Paraná River support provisioning ecosystem services of substantial economic value, the principal species used represent high risks to fish diversity and conservation. It is recommended local management should concentrate on reducing these risks through use of more appropriate species in these ecosystem services, with these decisions derived using risk assessment and precautionary principles.     

Impact on indigenous species biodiversity caused by the globalisation of alien recreational freshwater fisheries

One of the most insidious threats to fish conservation around the world is deliberate or accidental introduction of fish species. The impact of alien invasive sport fish is for the most part unpredictable in time and space, with the introduction of relatively few species having resulted in many extirpations of indigenous fish species worldwide. More nations need to quantify biodiversity loss caused by alien sport fishes. The spread of alien invasive fishes does not respect political boundaries. Therefore total global costs to aquatic biodiversity and ecosystem functioning resulting from these introductions need to be assessed. The global invasive species database of the Global Invasive Species Programme, highlights eight fish species among the one hundred `World's Worst Invasive Alien Species'. Three of these fish species (two trout and one bass species) were introduced solely for sport. Historically the social value of recreational fishing was usually more important than conserving biodiversity. Globalisation of alien fish species for sport is best illustrated by rainbow trout – now in 82 countries, and still spreading, along with the associated expensive angling gear, magazines and accommodation infrastructure. Such sport species have become part of the global consumer society. The nature and extent of the globalisation phenomenon is addressed with regard to how introduction of alien fish for recreational angling has impacted on biodiversity; trophic cascades at a local level and the unassessed total cumulative global trophic cascades; and some of the motives that underlie promotion of this sport within the complexity of globalisation as we know it today. Alien invasive recreational fish species are now recognised as a global environmental degradation problem resulting in loss of biodiversity and therefore require a global solution. Parallel trends such as globalisation of environmental education and the internet must be encouraged to counteract the damage caused and reverse the trend. This globally concerted campaign requires utilizing environmental education forums aimed at the angling community, general public and policy makers; networking with existing alien invasive groups; legislation; better understanding of processes; development of environmental economic evaluation tools; international bio-invasion control; wider use of the precautionary approach and utilization of the present globalisation of ecological thought.     

A call for an end to calls for the end of invasion biology

Calls for the end of invasion biology are misguided. There is no evidence that modern invasion biology has progressed slowly in its short life. Although some aspects of biological invasions fit comfortably in the framework of ecological succession, many others do not. Some native species, particularly in the wake of various anthropogenic impacts, behave like invasive non‐native species, but the probability and degree of harmful impact are greater for non‐native than for native species. Neither native nor non‐native species suffer lack of attention and research by virtue of the fact that invasion biology focuses on the latter. Basing management solely on current observed impact is highly risky because impacts may be subtle but nonetheless important, and impacts often change, as they are contingent on the physical or biotic environment. The known harmful impacts of many non‐native species suggest that recent introductions warrant attention even if impacts are not evident. Neither is the focus of modern invasion biology on non‐native species motivated by xenophobia. Rather, it reflects the recognition of their likelihood of harmful impact. A related call for the end of traditional restoration ecology shares many features with calls to terminate invasion biology, not least because management of invasive non‐native species is a key component of restoration ecology. Such species are a dominant element in generating the ‘novel ecosystems’ that are said to render traditional restoration ecology obsolete. The argument that both invasion management and traditional restoration are largely futile endeavors is contradicted by substantial and growing successes in both fields.     

A review of the research on introduced freshwater fishes: new perspectives,the need for research,and management implications

Although freshwater fishes have a long history of human-induced introduction, recent globalization has accelerated worldwide introduction events even more, and those introduced fish species are now perceived to be a major threat to ecosystems. Over the last two decades, numerous studies have been published on introduced fish species; however, it has been challenging for researchers to understand the magnitude of the impact and the underlying mechanism of invasions. Recently, new perspectives in understanding invasive freshwater fish biology have been presented in a number of studies, which can be largely attributed to advances in analytical techniques and also to a growing need for proactive analysis in management strategies. The aim of this paper is to summarize new ecological perspectives, the need for research, and/or management implications with emphasis on technological advances in, for example, statistics, molecular analysis, modeling techniques, and landscape analysis addressed under the following five categories: introduction pathways, predicting spatial patterns, biotic homogenization, hybridization, and control and eradication. The conservation of native fish fauna and the management of introduced fish species will benefit from combining these new perspectives with fundamental studies such as those on life history and population biology.     

外来养殖鱼类的入侵风险评估及防控对策——以尼罗罗非鱼为例

[目的]筛选合适的指标建立一套外来养殖鱼类的生物入侵风险评估体系,并对外来养殖鱼类的生物入侵防控提出对策建议。[方法]通过文献资料的收集和整理,对外来养殖鱼类中典型入侵物种的入侵过程、影响危害和入侵生物学特性进行分析和归纳,从适应能力、繁殖能力、扩散能力3方面指示其入侵性;从对生物的影响和对环境的影响2方面指示其生态影响;从自然因素和人为因素2方面指示环境可入侵性,以上述3方面为框架进行评估体系构建。[结果]筛选20个指标构建了外来养殖鱼类的生物入侵风险评估体系,并举例说明该评估体系的应用。从法规政策、科学研究、治理技术和公众参与等4个方面针对性地提出外来养殖鱼类生物入侵风险防控对策。[结论]防范和治理入侵生物是一个系统工程。对于外来养殖鱼类的管理,既不能只考虑经济效益而置生态风险于不顾,也不能片面放大外来养殖良种的入侵风险。科学管控的关键在于完善制度建设、加强风险评估、发展防治手段、促进公众参与,使外来鱼类养殖业在严格受控的前提下发挥其经济效益,将其潜在的生态危害效应降到最低。     

Mechanisms structuring stream fish assemblages: Are there lessons from introduced species?

Synopsis Stream fish faunas are being increasingly subjected to non-native fishes. Successful establishment of non-native forms varies widely between geographic regions (38–77%), but is generally greater in areas that are either altered by man or initially depauperate in fish species. While such introductions have generally had undesirable effects on native fish species, they show no signs of decreasing. Thus, this essay is an attempt to determine if the introduction of non-native fishes may provide insights into processes structuring stream fish assemblages. There are, unfortunately, few detailed ecological studies documenting the response of stream fish assemblages to introduced fishes. Of the 31 studies included in my analysis, the majority (77%) documents a decline in native fishes following the introduction of exotic or transplanted forms. Only 10 studies examined shifts in resource use, of which 5 documented or suggested shifts in habitat. Overall, the responses of native stream fish assemblages to non-native fishes suggest that biotic interactions are important in structuring the impacted assemblages, being implicated in 62% of the studies. Proposed or demonstrated mechanisms are divided equally between competition and predation. Unfortunately, pre-disturbance data are generally lacking so that processes important in structuring native fish assemblages cannot be determined.