Non-native and translocated freshwater fish species in Turkey

1  SUMMARY Turkey is a hotspot of freshwater fish diversity and endemism, holding a unique ichthyofauna containing distinct European and Asian elements. Currently, 78 endemic species are recognised from Turkey, 65 of which are classified as Critically Endangered or Endangered. Habitat degradation, pollution, and the introduction of non-native fishes are the greatest threats to this unique ichthyofauna. We compiled data on the introduction and distribution of freshwater fishes in Turkey, both nonnative and translocated, based on historical accounts and recent surveys. Thirty fish species have been introduced, 11 of which are translocations within Turkey. The overall establishment success was 64% (44% for non-natives and 100% for translocated species). New species continue to be introduced at a rate of 4.8 species per decade, of which 3.1 species establish per decade. Fisheries and aquaculture are two main vectors of deliberate introduction, but the contaminant of stockings is the primary pathway for secondary spread, in particular for Carassius gibelio, Pseudorasbora parva and Lepomis gibbosus. Natural dispersion of species introduced into neighbouring countries through trans-boundary river systems is highlighted as the most likely pathway for future species introductions. We discuss the management options available and outline how these can be incorporated into freshwater fish conservation and non-native fish management programmes. Education, public awareness and information are central components to reduce current rate of fish introductions in Turkey.


INTRODUCTION
Freshwater ecosystems are particularly affected by non-native species introductions (Stiassny, 1998;Dudgeon et al., 2006), yet freshwater fish continue to be introduced despite their documented ecological and economic impacts (Cambray, 2003;Lintermans, 2004;Cucherousset & Olden, 2011;García-Berthou & Moyle, 2011). These introductions are strongly associated with international shipping, ornamental fish trade, aquaculture, biological control of mosquitoes and water plants, development of new fisheries, irrigation schemes, and inter-basin transfers (Allan & Flecker, 1993;Maitland, 1995;Ruesink, 2005;Jeschke & Strayer, 2006;Stohlgren et al., 2006;Rahel, 2007;Tricarico, 2012). Although a small proportion of non-native species may have neutral, or even beneficial, effects on native biota and ecosystems (Cope & Winterbourn, 2004;Johnson et al., 2009), others become invasive and establish spreading populations that negatively impact the recipient environment and its biota (Mack et al., 2000). Freshwater fish are the most frequently introduced aquatic animal group (Gozlan, 2008), exhibiting higher establishment rates than many other taxa (Jeschke & Strayer, 2006), with introductions generally being irreversible (Cucherousset & Olden, 2011). Further, current technologies available to eradicate established populations can detrimentally impact the native species (Myers et al., 2000) with relatively few long-term success stories. Understanding the multi-faceted process of aquatic invasions is important for the management and conservation of freshwater ecosystems. Identifying the primary vectors and pathways for species introductions is therefore key to reduce the risk of future introductions (Simberloff et al., 2005;Hulme, 2006) and manage the secondary spread of species already present (Vander Zanden & Olden, 2008).
Turkey is a hotspot of freshwater fish diversity and endemism (Fricke et al., 2007), having a distinct ichthyofauna that contains unique elements from both Europe and Asia (Balık, 1995;Smith & Darwall, 2006;Cuttelod et al., 2009). In Turkey, 11 freshwater ecoregions sensu Abell et al. (2008) are recognised incorporating three major habitat types: xeric and endorheic basins with large and small lakes and small streams (Central Anatolia and Lake Vansaline and soda lakes), temperate floodplain rivers and wetlands (Upper Dicle (Tigris) and Fırat (Euphrates) and Kura -Southern Caspian Drainages) and temperate coastal rivers (Trakya (Thrace), Western Anatolia, Southern Anatolia, Northern Anatolia, Western Transcaucasia and Asi (Orontes)). The temperate coastal rivers vary between the large meandering rivers of Northern and Western Anatolia to the shorter steep rivers of Southern Anatolia and Asi (Orontes). Northern Anatolia also has fewer lakes than Western and Southern Anatolia. Most rivers, streams, wetlands and lakes in Turkey are heavily polluted and/or eutrophic (Fricke et al., 2007) with numerous dams having been constructed creating artificial lakes (reservoirs), particularly in the major river systems. Additional threats to freshwater habitats include the draining of wetlands, construction of dams, weirs and barrages, over abstraction of water and gravel extraction from river beds (Balık, 1995;Fricke et al., 2007).
A total of 248 native freshwater fish species have been recorded from Turkey, comprised mostly of the families Cyprinidae, Balitoridae and Cobitidae (Fricke et al., 2007). Of these, 78 species are endemic (31.5 % of the total native freshwater fish fauna), 51 % of which are classified as Critically Endangered and 32 % as Endangered (Fricke et al., 2007). Turkey's geographical location and large trans-boundary river systems increases the risk of introduction of non-native fishes from both Asia and Europe (Fig. 1). Despite recent recognition of the impacts of non-native species on native fish communities in Turkey (Gaygusuz et al., 2007;Aydın et al., 2011;Tarkan et al., 2012b), information on the introduction vectors and distribution pathways of nonnative fishes remains limited, or buried in obscure reports. The major vectors for the introduction of non-native fishes to Turkey have been government authorized aquaculture and stocking programmes to establish and support cage aquaculture, and commercial fisheries (Innal & Erk'akan, 2006). In addition, native species have been translocated within Turkey, many of which may have exerted detrimental impacts on the recipient fish (Innal & Erk'akan, 2006).
To date, only two studies have examined the introduction and translocation of freshwater fishes in Turkey; Innal and Erk'akan (2006) and Innal (2012). However, these works contain contentious data and lack analysis of the distribution, introduction history, success and spread of nonnative and translocated species. This study aims to fill these gaps by: (i) providing an updated record of non-native and translocated freshwater fishes in Turkey; (ii) determining the major vectors and pathways for the introduction and secondary spread of non-native and translocated fish species; and (iii) proposing a management framework to provide adequate protection for the native fishes and permit the utilization of non-native and translocated species while limiting the risk of future introductions and the secondary spread of introduced species.

METHODS
A history of freshwater fish introductions in Turkey was compiled from published (e.g. Anonymous (DSI), 1988(DSI), , 2001Wildekamp et al., 1997;Van Neer et al., 1999;Çıldır, 2001;Innal and Erk'akan, 2006;Innal, 2012) and grey literature (e.g. reports, unpublished manuscripts, theses, and books), supported by personal communications with fellow researchers (See supplementary Appendix A for a full list of references used). In Turkey, government authorized freshwater fish introductions are controlled by the Ministry of Agriculture and Rural Affairs and the General Directorate of State Hydraulic Works. Both bodies independently collect and report fish stocking and occurrence data at a national level. Native species recorded outside their historical distribution ranges were considered to be translocated. Translocated spe-cies, although strictly non-native where introduced, were treated separately from the non-native species because they are native at a national level. Translocated species are, however, included in the overall analysis of introduced species.
For both non-native and translocated species, their present status in Turkey was assessed to determine whether the introduction had been successful. The success of the introductions were evaluated following the categorization scheme of Blackburn et al. (2011): C0 -Individuals released into the wild (i.e. outside of captivity or cultivation) in location where introduced, but incapable of surviving for a significant period; C1 -Individuals surviving in the wild in location where introduced, no reproduction; C2 -Individuals surviving in the wild in location where introduced, reproduction occurring, but population not self-sustaining; C3 -Individuals surviving in the wild in location where introduced, reproduction occurring, and population self-sustaining; D1 -Selfsustaining population in the wild, with individuals surviving a significant distance from the original point of introduction; D2 -Selfsustaining population in the wild, with individuals surviving and reproducing a significant distance from the original point of introduction; and E -Fully invasive species, with individuals dispersing, surviving and reproducing at multiple sites across a greater or lesser spectrum of habitats and extent of occurrence. An introduction was considered to have been successful where the species had recruiting populations in the recipient environment, i.e. classification C2 or higher. We excluded species that had been imported into Turkey by aquaculture research stations at universities and research hatcheries, but never released into the natural environment e.g. Acipenser baeri and Ictalurus punctatus; the latter incorrectly reported as released into the wild by Innal and Erk'akan (2006). Copp et al. (2009)  stocks (Hulme et al., 2008). Each species introduced into the freshwaters of Turkey was allocated to the most probable vectors for the introduction. The success of each vector was determined by whether the species established in the recipient water body.
Where the species had arrived in Turkey through more than one vector, the vectors of subsequent introductions were noted.
We then evaluated the most probably pathways for the secondary spread of species in Turkey. Species that were recorded from more than one locale were classified according to three pathways for secondary spread: deliberate introductions, contaminants of deliberate introductions, and accidental introductions (mostly the release of unwanted ornamental fish).

RESULTS
We recorded 30 freshwater fish species introduced into Turkish freshwaters including 11 of which have been translocated within Turkey (making the assumption that Cyprinus carpio were native to some portion of Turkey). Nineteen of the introduced species have established selfsustaining populations (Table 1, Fig. 2), although ten of these have restricted ranges, found at ten or fewer locations, have not expanded beyond their point of introduction, or become abundant there. The oldest recorded introduction was Gambusia holbrooki, introduced for the biological control of mosquitos in the 1930s (Geldiay & Balık, 1988), with the most recent recorded introduction Heteropneustes fossilis, first recorded in Turkish headwaters of Fırat River (Euphrates) in 2011 (Ünlü et al., 2011) putatively from introductions in neighbouring countries. Cyprinus carpio, Carassius gibelio, G. holbrooki and Pseudorasbora parva are the most widespread introduced species, followed by Atherina boyeri and Lepomis gibbosus (Fig. 3).  Checklist of non-native (n) and translocated (t, in bold)) fish species presently occurring in Turkish inland waters summarising the decade initial introduction, vectors for introduction and secondary spread, and establishment success according to Blackburn et al. (2011) -  Although limited knowledge is available on the detrimental effects of most of the wide-spread non-native fishes in Turkey (Tarkan et al., 2012b), the number of species successfully introduced into Turkey is steadily increasing. The average rate of introduction of new fish species to Turkey since the 1930s is 4.1 species per decade (R 2 = 0.97), but increases to 4.8 species per decade (R 2 = 0.99) for the period 1950-2010 (Fig. 4). The average rate of new species establishment in Turkey since the 1930s is 2.8 species per decade (R 2 = 0.98), but also increases for the period 1950-2010 to 3.1 species per decade (R 2 = 0.98) (Fig. 4). The rate of secondary spread of established species is approximately ten new water bodies per decade (Aydın et al., 2011). The overall establishment rate of non-native and translocated fish in Turkey was found to be 64%, 44% for the 19 non-native species and 100% for the 11 translocated species (Table 1). This figure is in line with estimates from similar studies for Greece 52% (Economidis et al., 2000), other European countries 63% (García-Berthou et al., 2005), and worldwide 64% (Ruesink, 2005). For freshwater fish, 63% of intentional introductions are successful whereas <30% of all introduction pathways are successful (García-Berthou et al., 2005). Intentional introductions have higher establishment success (Hulme et al., 2008) largely as a result of the higher propagule numbers and climate matching used in intentional stockings (Lockwood et al., 2005). The high introduction success highlights the role of deliberate introductions in Turkey.
Five species (C. carpio, G. holbrooki, A. boyeri, C. gibelio and P. parva) have established extensive populations and are considered invasive and problematic (Fig.  3). A further three species, Clarias gariepinus (Küçük & İkiz, 2004;Emiroğlu, 2011), L. gibbosus (Özcan, 2007;Top, 2011) and Tinca tinca (Balık et al., 1997), have established widespread populations in their introduced range and dominate communities in these areas. Coptodon zilli (formerly Tilapia zilli), however, have established a widespread population but do not dominate communities (Balma et al., 1995). Carassius auratus (İzci, 2004), Oreochromis niloticus (Dikel, 1995;Mert & Çiçek, 2010), Sander lucioperca (Ekmekçi & Erk'akan, 1997) and Knipowitschia caucasica (Van Neer et al., 1999) have established self-sustaining recruiting populations and could potentially start expanding their ranges. Similarly, Silurus glanis, Perca fluviatilis and Aphanius mento (Balma et al., 1995) have established recruiting populations and could become self-sustaining in time, although S. glanis and P. fluviatilis populations have declined as a result of overfishing. Some species have only been recorded once from a single watershed, e.g. Pterygoplichthys disjunctivus (Yalçın Özdilek, 2007) and H. fossilis (Ünlü et al., 2011), while others are maintained through escapees from cage aquaculture and fishery stocking programmes, e.g. Oncorhynchus mykiss (Anonymous (DSI), 1988). Other species (e.g. Salvelinus fontinalis, Morone hybrid) are now only found in aquaculture facilities and research facilities at universities, having been extirpated in the wild whereas others (Ctenopharyngodon idella and Hypophthalmichthys molitrix) appear to have failed to establish self-sustaining populations or have not expanded from their original introduction. Cichlid species were introduced by universities as part of government authorized research programmes, however great uncertainty persists regarding their identification with some authors have reporting several different cichlid species being introduced at a single locality (e.g. Innal and Erk'akan, 2006) when they were, in fact, a single species C. zilli (Akın et al., 2005).
Contrary to expectation, we found that introduction and establishment decreased with increasing watershed size (Table 2). A power relationship was found for both introduction and establishment densities (introduction = 5.318 A 0.755 (R 2 = 0.912) and establishment = 4.835 A 0.784 (R 2 =0.917), where A is the watershed area in 1000 km 2 ). The watersheds recording the highest introduction densities were in southern and western Turkey. These regions have Mediterranean climates and higher population densities than the central, northern and eastern Turkey.

Cumulative number of non-native fish
Most species translocations have been carried out legally by the government agencies for the "enhancement" of fisheries, mostly resulting in successful established populations e.g. S. lucioperca, T. tinca, S. glanis, P. fluviatilis (Anonymous (DSI), 1988). However, A. boyeri has been dispersed illegally into natural lakes and manmade reservoirs due to its economic value, establishing viable populations in most of them, some of which are expanding rapidly from the introduction locations and becoming invasive (Gençoğlu, 2010).
The two most important pathways for the secondary spread of non-native fishes were identified as the deliberate release of aquaculture and fishery species and the contamination of fishery or aquaculture stockings ( Table 1). The remaining pathway identified was the accidental release of ornamental species.

DISCUSSION
In Turkey, the majority of non-native fishes introductions have been intentional (Wildekamp et al., 1997;Aydın et al., 2011), mostly as part of government-sponsored stocking programmes of reservoirs (Tarkan et al., 2012a). As in other Mediterranean countries, the building of reservoirs to provide irrigation, industrial and domestic water provides new opportunities for the establishment of non-native fishes (Collares-Pereira & Cowx, 2004). Recent studies have confirmed that non-native fishes are more successful in artificial water bodies than natural lakes or rivers (Clavero & Hermoso, 2011;Tarkan et al., 2012a;Clavero et al., 2013). Freshwater fish species introductions aimed at improving commercial fisheries in reservoirs have resulted in 80% of the species introduced establishing recruiting populations (Fig. 5). However, all the species that became established as a result of this vector are native to Turkey whereas the two species that failed to establish are both non-native, O. mykiss and Coregonus lavaretus (Özuluğ et al., 2005), most likely due to their cold water adaptations. Overfishing has, however, resulted in the decline of introduced S. glanis and P. fluviatilis and  (Rad & Rad, 2012).

Non-native and translocated freshwater fish species in
Overfishing is a major threat to freshwater biodiversity (Allan et al., 2005), especially larger species (Olden et al., 2007). Many commercial fisheries are reliant on stocking programmes to sustain the harvest (Petr, 1997;Cowx, 1999) although C. carpio is the only species exploited by inland capture fisheries in Turkey that is regularly stocked.

FIGURE 5.
Number of non-native fish species introduced into Turkey by introduction vector. Black bars represent species that have successfully established, white bars species that failed to establish, and grey bars species whose establishment is currently uncertain.
The contribution of freshwater species in aquaculture in Turkey has steadily increased from 30% in 1996 to about 65% in 2009 (Rad & Rad, 2012). Aquaculture is the leading vector of aquatic species introductions worldwide (Casal, 2006), with more than 50% non-native species having been intentionally introduced for aquaculture (Casal, 2006;Cook et al., 2008;Gozlan, 2008 Today, C. carpio constitutes the bulk of both aquaculture production and stocking programs in Turkey. The spread of P. parva and C. gibelio across Europe has been linked to contamination of hatchery stocks (Copp et al., 2005a;Gozlan et al., 2010a).
The contamination of C. carpio stockings could result from two scenarios: contaminated hatcheries or stocking from compromised wild populations, both of which can be managed by implementing of a stock audit programme (Davies et al., 2013).
As a country industrializes, there is a decrease in the importance of commercial fishing with inland water bodies increasingly, or exclusively, being used as recreational/sport fisheries (Cowx et al., 2010); e.g. Greece, Zenetos et al. (2009). Across Europe, non-native species for sport angling have been introduced with devastating impacts on native faunal biodiversity e.g. S. glanis (Copp et al., 2009a), P. fluviatilis and S. lucioperca (Cowx, 1997;Copp et al., 2005a;Küçük, 2012). Once introduced, non-native species are subsequently illegally spread by anglers to neighbouring watershed (García-Berthou et al., 2005). An increase in the popularity of recreational angling could result in an increase in the illegal introduction of popular angling species (Cowx et al., 2010), such as North American Micropterus sp., or the translocation of aggressive and large native species e.g. S. glanis, S. lucioperca, E. lucius. Recreational angling groups have requested E. lucius introductions for recreational angling, but Turkish authorities have refused such requests having adopted a policy of not introducing piscivorous species. Adoption of stringent policies regarding recreational angling could result in the illegal introduction of "recreational" species, seriously compromising both existing fisheries and conservation programmes (Johnson et al., 2009;Gozlan et al., 2010b).
The translocation of native fish species has been very successful with all 11 species introduced establishing selfsustaining populations. One translocated species reported to have failed to establish, A. tarichi a deep-water species endemic to Lake Van, was introduced into Lake Burdur, one of the largest and deepest lakes in Turkey (Akşıray, 1982;Yıldırım et al., 2009). The introduction appeared to be successful until pollution from lakeside factories reduced deep-water oxygen levels (Akşıray, 1982;Yıldırım et al., 2009), resulting in the extirpation of A. tarichi. Pollution, rather than biotic or natural environmental factors, resulted in this species failing to establish. However, a second introduction of A. tarichi in Lake Erçek in 1990's has been successful (Çetinkaya, 2006).
Turkey has four major transboundary river systems (Meriç, Asi (Orontes), Dicel-Fırat (Tigris-Euphrates), Kura-Aras and Çoruh: Fig. 1), all of which could allow species introduced into neighbouring countries to naturally extend their ranges into Turkish waters. There is evidence that fish species have entered Turkey via transboundary river systems from Eastern Europe (via Meriç River shared by Bulgaria, Greece, and Turkey) in the northwest (Aydın et al., 2011) and the Middle East (via Asi (Orontes) and Dicle-Fırat (Tigris-Euphrates) rivers) in the south and southeast (Yalçın Özdilek, 2007; Ünlü et al., 2011). Four species (G. holbrooki, C. gibelio, L. gibbosus, and P. parva) have entered Turkish waters via Greece and Bulgaria through natural expansion of their introduced ranges in the Meriç River system (Wildekamp et al., 1997;Ekmekçi & Kırankaya, 2006). High numbers of nonnative fish species are present in Greece and Bulgaria are high, 25 and 26 species respectively (Economidis et al., 2000;Economou et al., 2007;Uzunova & Zlatanova, 2007), some of which have not previously been recorded in Turkish waters. Similarly, several species have been introduced into Syria, Iran, Iraq, Georgia, Armenia and Azerbaijan that have not previously been recorded in Turkish waters (Coad, 1993;Coad & Abdoli, 1993;Coad, 1996;Gabrielyan, 2001;Coad, 2010Coad, , 2013Salmanov et al., 2013). Recently H. fossilis was recorded in the Turkish headwaters of the Fırat (Euphrates) River after having been first recorded in the lower reaches of the Dicle-Fırat (Tigris-Euphrates) River system in the 1950s (Al-Hassan & Muhsin, 1986;Ünlü et al., 2011). It is too soon to determine whether this species has established a recruiting Non-native and translocated freshwater fish species in Turkey DOI: 10.29094/FiSHMED.2015.003 population in Turkey, but it may represent the first of many introductions from countries south and east of Turkey. The majority of the species introduced into neighbouring countries have already been introduced into Turkish freshwaters, or are native to Turkey (see Table 3). The species that could have greatest impact in Turkish waters are Hemiculter leucisculus and Percottus glenii, because both species have detrimentally impacted native fish assemblages elsewhere (Reshetnikov, 2003;Jurajda et al., 2006;Grabowska et al., 2009;Wang et al., 2013).

Although both Micropterus salmoides and
Lepomis macrochirus have been recorded as introduced into Iran and Iraq including the Tigris-Euphrates (Coad, 1993;Coad & Abdoli, 1993;Coad, 1996), these species do not appear on recent checklists of introduced fish from either country (Coad, 2010(Coad, , 2013. Both species have been successfully introduced into other Mediterraneanclimate regions (Marr et al., 2010(Marr et al., , 2013, significantly impacting native fish assemblages and should be considered as highly undesirable species. Management of transboundary river systems is a complex balance of water rights, pollution, species introductions, Turkish water policy, and trans-boundary agreements (see Kramer et al. 2011). The foundations for developing agreements regarding the introduction of non-native fishes in shared river systems could be developed along the guidelines used to establish the trans-boundary programme between Greece and Bulgaria for the Nestos River (Economidis et al., 2009).
The extent of ornamental fish releases is frequently underestimated (Welcomme, 1992) with about 6% of USA aquarists having admitted to releasing unwanted fish (Gertzen et al., 2008;Strecker et al., 2011). Because of the widespread dispersal of ornamental fish to homes and businesses, these fish can be released into all freshwater habitats (Padilla & Williams, 2004;Copp et al., 2005d;. Three species of ornamental fish have been introduced in Turkey. The majority of ornamental species are from tropical climates and should not be able to reproduce in Turkish conditions. There are, however, a number of ornamental species that have established in Mediterranean Europe (e.g. Misgurnus anguillicaudatus) that may establish in Turkey if released in sufficient numbers.
introduced into Bulgarian and Greece (Economidis et al., 2000;Economou et al., 2007;Uzunova & Zlatanova, 2007) Pangasius sp. recently reported from Iraq (Coad, 2010) Perccottus glenii introduced into Bulgaria (Uzunova & Zlatanova, 2007) Oryzias latipes introduced into Azerbaijan (Salmanov et al., 2013)  In 2004, the General Directorate of Protection and Control Department of the Ministry of Food, Agriculture and Livestock instituted penalties for the transport and introduction of non-native species into new environments and the Department of Agriculture and Rural Affairs have declared C. gibelio as dangerous species (Circular No: 37/2), promoting its capture throughout the year. These are promising signs but conservation of the unique and highly endangered native fish fauna of Turkey should be prioritized and the precautionary principle applied to all future stockings. Tarkan et al. (2014) identified 17 of the 35 species evaluated as having a high risk of potential invasiveness (very high -C. auratus, C. gibelio, C. carpio, Gambusia affinis, G. holbrooki, I. punctatus; high -Amerius melas, C. gariepinus, C. idella, H. molotrix, L. gibbosus, Liza haematocheila, Oreochromis mossambicus, Oreochromis niloticus, P. parva; and medium high -Oreochromis aureus and P. disjunctivus). Of these, Gambusia affinis, I. punctatus; Amerius melas, Liza haematocheila, Oreochromis mossambicus, Oreochromis niloticus, and Oreochromis aureus have not been recorded as introduced in Turkey whereas C. idella and H. molotrix have been released into natural waters but have not established in Turkey to date. This study did not include species such as E. lucius, Micropterus sp. and Misgurnus anguillicaudatus that have been widely introduced in Europe. The omission of E. lucius is regrettable since the introduction of this species has been requested by recreational anglers. Interestingly, species we highlight as potentially invasive (H. leucisculus, H. fossilis and P. glenni) were all classified as medium risk species. This paper has focussed on nonnative and translocated fishes but it should be noted that these are not the only threats to the native fishes of Turkey. Other factors such as pollution, habitat degradation, and unsustainable water abstraction, amongst others, all threaten native fish populations. An example of extreme habitat degradation is the draining of Lake Amik in southern Anatolia from the 1940s to the 1970s resulting in the loss of the entire fish assemblage (Balık, 1995). In contrast, pollution in the Asi (Orontes) River is threatening the endemic species of this unique freshwater ecoregion (Erk'akan and Ekmekçi, 2000). To date, two global extinctions have been reported from Turkey: Alburnus akili Battalgil, 1942 andPseudophoxinus handlirschi (Pietschmann, 1933) in Central Anatolia, both the result of the introduction of piscivorous S. lucioperca (Küçük, 2012). Further studies are required to distinguish between the threats exerted by pollution, habitat destruction, and non-native/translocated fish on the native fish populations.

MANAGEMENT MEASURES
Although the presence of non-native species poses a threat to native fish assemblages, it is acknowledged that non-native and translocated fishes are the mainstay of Turkey's freshwater aquaculture and commercial fisheries. A balance must therefore be maintained between the conservation of native taxa and the management of nonnative fish (Chadderton, 2003). The management of non-native fishes requires a clear goal to direct the efforts of implementing authorities, funding agencies, and stakeholders towards an agreed outcome (Bomford & Tilzey, 1997;Wittenberg & Cock, 2001;Hulme, 2006). Once a goal has been established management options can be identified and the most appropriate strategies selected to achieve the goal (Bomford & Tilzey, 1997;Wittenberg & Cock, 2001;Hulme, 2006).
Prevention of future introductions is the most effective way of addressing invasion by non-native species (Saunders et al., 2002;Britton et al., 2011a) Council Regulation 708/2007/EC requires an assessment to identify and evaluate the potential risks associated with existing and future nonnative species according to their potential to become invasive by instituting adequate decision support tools and risk assessment metrics (Britton et al., 2011a, b), e.g. the Fish Invasiveness Screening Kit (FISK) (Copp et al., 2005c, b). FISK was developed Non-native and translocated freshwater fish species in Turkey DOI: 10.29094/FiSHMED.2015.003 to provide a screening tool for freshwater fish introductions can become a tool to aid decision-and policy-makers in assessing and classifying freshwater fishes according to their potential invasiveness (Copp et al., 2009b). FISK was recently applied for both non-native and translocated freshwater fish species in Turkey; see Tarkan et al., (2014). Many potentially harmful non-native species have established populations in Turkey, but may be far from achieving their potential geographic distribution. Preventing, or slowing, the secondary spread of known and established non-native species requires different set of goals, strategies, and target audiences than measures required to restrict the import of new species (Vander Zanden & Olden, 2008). Implementation of a stock audit procedure, sensu Davies et al. (2013), and employing adequate effort by experienced fisheries officials may reduce the extent of stock contamination by undesirable fish species such as L. gibbosus, P. parva and C. gibelio. Capacity at relevant levels (i.e. law enforcement, taxonomic expertise and communication) is critical for prevention programmes to be effective.
No matter how effective the prevention programmes, there is a high probability that further non-native species will be introduced. The precautionary principle requires that action be taken to control or eradicate potentially invasive species as soon as they are detected (Wittenberg & Cock, 2001). Detection of new introductions at low population levels is often difficult, especially in aquatic systems (Collares-Pereira & Cowx, 2004;Mehta et al., 2007) and the costs associated with detection programmes are high (Finnoff et al., 2007). Further, there is often a substantial time lag between introduction and detection. In principle, early detection and rapid response should be straightforward. In practice, for all but economic pests and vectors of disease, the required rapid response is often very slow. Rapid response management includes an assessment of the ecological and economic risks once an introduced species has been detected. An effective rapid response system requires enabling legislation, a sound scientific basis, tools and protocols, and resources to implement appropriate actions (Thomas et al., 2009). For fish introduction into river networks, early detection is unlikely, or highly improbably (Collares-Pereira & Cowx, 2004). The modular approach outlined by Britton et al. (2011a) could be modified for application in Turkey.
Where non-native species have already established, active management needs to focus on reducing their impacts and preventing further spread (Saunders et al., 2002;Britton et al., 2011a). Eradication is more cost-effective than long-term mechanical control (Bomford & O'Brien, 1995;Bomford & Tilzey, 1997;IUCN, 2000), particularly for recent introductions, or where the species has been spatially constrained (Britton et al., 2011a). Eradication of non-native fishes is achieved by chemical treatments, e.g. piscicides, or by draining water-bodies (Collares-Pereira & Cowx, 2004;Finlayson et al., 2005;Britton et al., 2011a). However, the use of piscicides on the Anatolian Peninsula of Turkey needs to be carefully evaluated because the karst formations and ground water systems are susceptible to pesticides. Sustained mechanical removal has been successful only in enclosed systems (small lakes or headwater streams) at small scales (Britton et al., 2011a). Eradication should, however, only be attempted where it is ecologically feasible and has financial and political support (IUCN, 2000). Where eradication is not feasible, control is the next best alternative. Control programmes using mechanical removal techniques (e.g. electrofishing or netting) are generally effective in suppressing population abundance and reducing their recruitment (Britton et al., 2011a). Eradication and control of nonnative fishes remain constrained by their lack of selectivity, and the challenges of treating large spatial scales effectively (Britton et al., 2011a).
Many non-native fishes have established widespread populations and threaten native species. While large-scale eradication of non-native fish is difficult, and rarely implemented, small-scale projects to eradicate non-native fish from priority reaches of small rivers can be successfully completed with currently available technologies. For example, a piscicide and barrier based conservation management strategy, such as those proposed for the control of non-native fish in the lower Colorado River (Clarkson et al., 2005) and the Cape Floristic Region (Marr et al., 2012), could be implemented. The risk of the illegal release of non-native fish into treated areas must be minimised and new introductions prevented. Education and publicity initiatives with local landowners and angling bodies could be established, in conjunction with simple and inexpensive monitoring protocols to detect nonnative species in restored reaches, to ensure long-term success of conservation programmes (Clarkson et al., 2005). A freshwater fish lobby group similar to the Desert Fish Council (Pister, 1990(Pister, , 1991 could be established for the conservation of the freshwater fishes of Turkey. The responsibilities of this group would be to identify research needs of freshwater ecosystems in Turkey, detect areas of weakness in freshwater ecosystem conservation, and providing assistance in compensating for bureaucratic inadequacies, and enhancing government conservation programmes. and B. Yoğutçuoğlu for providing species and pond pictures. SMM acknowledges the financial support of the University of Limpopo and the VLIR-IUC (Vlaamse Interuniversitaire Raad -University Development Cooperation) Funding Programme (Belgium).

AUTHOR CONTRIBUTIONS
AST and FGE developed the initial concepts of the first draft with all authors contributing to the final manuscript