The fish fauna in selected rivers of the Mazovian Lowland

A bstrac t: In 1999-2003, investigations o f the fish fauna were carried out in selected rivers o f the Mazovian Lowland. Electrofishing was used to investigate species diversity and abundance at 35 sampling sites. In total, 8618 fish representing 29 species were caught, weighing in total 77.9 kg. 13 to 22 species o f fish and lamprey were registered. The highest number o f species was identified in the Świder River (22), dominated in abundance by roach (35.1%) and stone loach (34.9%), and in the Rządza River (20), dominated by gudgeon (33.4) and roach (24.9%). Ten-spined stickleback dominated in the Długa River (45.5%), roach in the Klusówka river (27.0%), and gudgeon (48.4%) and sunbleak (30.0%) in the U trata River. 9 reophilic species were identified in particular rivers, accounting for 8.6% to 61.0% o f total abundance. The abundance o f pike, the major predator o f small lowland rivers accounted for 0.1% in the Utrata River to 1.3% in the Rządza River. The highest abundance o f fish in terms o f numbers and the biomass per 1 km o f river course were found in the Klusówka River and the Długa River.

So far, studies of the fish fauna of the Mazovian river have been carried out in the Jeziorka River, which flows into the Vistula River near Wilanów and the Czarna Struga River, the tributary of the Dluga River in the Narew River basin (Rembiszewski 1964), the Bzura River and its right tributary the Utrata River, the Wkra River, which flows into the Narew River below the Dębe dam, left tributaries of the Narew River, some of which are located in the Mazovian region, as well as the Pilica basin (Penczak 1968, Zalewski & Penczak 1981, Penczak et al. 1991, 1995, 2001).Also the Liwiec River, left tributary of the Bug River in the eastern part of the Mazovian voivodeship was investigated within the boundaries of two macroregions: the South Podlasie Lowland and the Central Mazovian Lowland as well as the Skrwa River (Marszal et al. 2004(Marszal et al. , 2006)).Infonnation on fish can also be found in the study on the fauna conservation strategy in the Mazovian Lowland (Kot & Dombrowski 2001).
In 1999-2003, experimental catches were conducted in selected five small rivers of the Mazovian Lowland, characterised by varied size, river bed morphology and coastal zone structure.Catches were conducted in the following rivers: the Dluga River, the Klusówka River, the Utrata River, the Świder River and the Rządza River.They are typical lowland rivers, with a morphology of foothill rivers in some parts.Varied géomorphologie parameters of these rivers are responsible for species composition of fish communities, composed both by species typical for lowland rivers, as well as those characteristic for upland streams (Starmach 1964, Lassleben 1977).A common feature of these rivers is the close vicinity of the Warsaw agglomeration and therefore particular risk of anthropopression.Flowing through highly urbanized areas of the most densely populated Mazovian voivodeship (Baranowski 1999), the rivers in this region collect municipal, agricultural and industrial waste water and are exploited by anglers and recreation.
The purpose of this investigation was to assess the state of the ichthyofauna and species richness in small, lowland rivers, flowing in the vicinity of a big agglomeration.

S t u d y A r e a
The rivers under investigation flow in the Mazovian Lowland, within a few dozen kilometres from the Warsaw agglomeration (Fig. 1).The Dluga River has its source at 165 meters above sea level, east of Mińsk Mazowiecki.Its waters flow to the Żerań canal, connecting the Vistula River to the Zegrze Reservoir.The upper part of the Dluga River has disappeared.The river appears again in Halinów and its watercourse is visible below the carp ponds.The Czarna Struga River, which starts in the Wołomin forest district, is the only bigger tributary of the Dluga River.
The sources of the Klusówka River are located at 115 m above sea level, in the forests close to Żabiczyn.It flows into the Zegrze Reservoir above Wierzbica.Its entire watercourse has a natural, unregulated waterbed.
The Utrata River is the right tributary of the Bzura River, into which it flows at its 25.6 km.It starts from northern slopes of Wysoczyzna Rawska, near Żelechów.
The Świder River has its sources in Wysoczyzna Sądecka, near the town of Stoczek Łukowski, and its mouth at 490 km of the Vistula River, near the town of Świdry Wielkie.In 1978, a landscape reserve "Świder" with an area of 238 ha, covering 41 km of the middle and lower river course was created to ensure river protection.The protected area covers the riverbed and 20 m wide strip of the embankments (Monitor Polski No. 4, 1978).This reserve is part of the Mazovian Landscape Park, created in 1986(Official Journal of Mazovian Voivodeship No. 13, 2001).
The Rządza River ends its course in the Zegrze Reservoir.The river sources are located close to the Wiśniew locality, at the altitude of 185 m above sea level.The river meanders, splits into branches and flows through a wide valley with a marshy bed.In its upper and middle course, the river flows within the boundaries of the Mińsk Area of the Protected Landscape created in 1986 under the Regulation of the Governor of the Mazovian Voivodeship (Regulation No. 39).
Basic information on the investigated rivers can be found in Table 1.35 sampling sites were established in the studied rivers.Diversity of riverbed and its embankments as well as the closest vicinity were taken into account in selecting the sampling sites (Buras & Gasiński 2000).Site characteristics is presented in Table 2.
Depending on the river size, two methods were used to conduct catches.In watercourses deeper than 0.8 m, catches were conducted from a boat going downstream close to one of the banks, with a 2.5 kW electrical generator.In sampling sites located in smaller watercourses (depth up to 0.8m) catches were conducted by wading upstream across the entire width of the waterbed.In both cases, 230 V full wave direct current supplied by a 1.5 kW Honda backpack generator was used.Fish were caught in a hand bucket with anode in a form of metal rim with a knotiess net of 5mm mesh size.The cathode was made of a 4 meters long copper intertwined wire.Fish caught in sampling sites were first identified, then counted and weighed.Species were classified in ecological reproductive guilds, according to Kryzhanovsky (1948) and Balon (1975), as well as in habitat guilds, according to Schiemer & Waidbacher (1992).Stability of occurrence was evaluated by the following index: C, = n/Nx 100, where: w, is the number of sites where an "i" species was caught, N is the number of all investigated sites (Głowaciński 1996).The species conservation status was assessed by: AP -active protection (Journal of Laws 2004, No. 220, item 2237); HD.AII -species listed in Annex II of Habitat Directive (Journal of Laws L 206, 22.7.1992, item 7); PRLLF.-Polish Red List of Lamprey and Fish (Witkowski et al. 2009criteria andcategories IUCN 2001 of the native fish and lamprey species of Poland (PL): EXextinct; EW -extinct in the wild; CR -critically endangered; EN -endangered; VU -vulnerable; NT -near threatened; LC -least concern; DD -data deficient); RIF -Regulation on Inland Fishing (Journal of Laws 2001, No. 138, item 1559 with amendments).

Site
River The ichthyofauna of the studied rivers was represented by 29 fish and lamprey species belonging to 10 families (Table 3).Representatives of a majority of ecological reproductive guilds found in Polish inland waters were registered in the catches.Lithophylic fish group was represented by four species, namely chub, spirlin, brown trout and the Ukrainian brook lamprey.These species require fast flow and hard bottom for spawning and their populations are not very dense in the investigated rivers.Their biggest share in the catches was noted in Klusówka River where they accounted for 10.5 % of the total abundance.In the Rządza and the Świder Rivers, the share of lithophylic species in fish communities was respectively 8.5 and 5.2%.Lithophylic fish species were not registered in the Dluga and the Utrata Rivers.In the Dluga River phytophylic ten-spined stickleback and lithophylic perch, whereas in the Utrata River psammophylic gudgeon and phytophylic sunbleak dominated in the catches.
No  In all studied rivers, the group of predatory fish was scarcely represented.The percentage share of pike in the total community abundance amounted to 0.1% in the Utrata River up to 1.3% in the Rządza River, whereas representatives of this species were not observed in the Klusówka River.This major predator of lowland rivers appeared at half of the sampling sites.Facultative predator, perch was more often discovered in electrofishing (Table 4).This species accounted for 1.6% of the abundance in the Świder River up to 17.1% in the Dluga River.The invertebrate-eating species dominated among non-predatory fish (Table 3).They were characterised by the highest frequency of occurrence; stone loach was found at 28 sampling sites, gudgeon at 25 sites and three-spined stickleback at 21 sites.Bream, rudd and ruff, and also carp and two invasive species, goad goby and stone morocco were the most rare species at sites (Table 4).The highest number of species, namely 22, was registered in the Świder River.The eurytopic roach and psammophylic stone loach were the dominant species but the reophilic species, namely dace, ide, gudgeon, chub, spirlin, brown trout, stone loach and lamprey constituted in total 50.3% in terms of abundance and 32.1% of the total biomass of fish caught in the watercourse.In the Rządza River, 20 species were registered and the average share of reophilic species in the total abundance and catch weight amounted to 54.9 and 47.7% respectively.In the Utrata River, 13 fish species were registered, however, the share of reophilic species was the highest.A high share of reophilic fish species was noted in the Klusówka River.They constituted 43.4% of the abundance and 49.3% of the weight of fish.In the Dluga River, reophilic fish constituted 8.6% in terms of the abundance and 10.2% in terms of weight.Ten-spinned stickleback and eurytopic perch dominated in the catches (Table 5).
The lowest value of fish abundance at a sampling site per kilometre of a river course, 1395 individuals km"1 was noted in the Rządza River, and the highest one, 4173 individuals km"1 in the Klusówka River.The biomass also varied in particular rivers.The highest biomasses, 34,6 kg km"1 and 32,3 kg km"1 were noted respectively in the Dluga River and the Klusówka River.In the Świder River and the Rządza River the biomass was twice lower.The lowest biomass, namely 11,4 kg km_1was registered in the Utrata River, where gudgeon and sunbleak dominated (Table 5).

Pike -Esox lucius (L., 1758)
The main predator in the investigated rivers.Its occurrence stability index amounted to 49%.Its presence was noted at 17 sites; it was absent from sapling sites in the Klusówka river.Conservation status: RIF (catégorie LC in PL & Vistula basin).

Perch -Perea fluviatilis (L., 1758)
This species had, similarly to stone loach, the highest occurrence stability index.In the Dluga, the Klusówka and the Utrata Rivers it appeared at all sampling sites, in the Świder River at 8 sites and in the Rządza River it did not appear only in the river sector close to the source.Conservation status: PRLLF (catégorie LC in PL & Vistula basin).

Carp -Cyprinus carpio (L., 1758)
It was registered in the Dluga River, at sampling site No. 4. Probably, it was an escapee from fish ponds in Halinów farm; Occurrence stability index: 3%.Conservation status: alien species.

Sunbleak -Leaucaspius delineatus (Heckel, 1843)
It was recorded at all sites in the Dluga and the Utrata Rivers.In the Utrata River, sunbleak together with the dominant gudgeon accounted for 78% of the abundance.It appeared at 2 sites in the Świder River and at 1 site in the Klusówka River, in total at 11 sampling sites.Occurrence stability index: 31%.It was not recorded in catches in the Rządza River.Conservation status: PRLLF (catégorie LC in PL & Vistula basin).

Bitterling -Rhodeus sericeus (Pallas, 1776)
In the Dluga and the Utrata Rivers it appeared at single sites.It was more often registered in the Świder River where it appeared at 7 sampling sites and accounted for 0.5% up to 15.7% of total abundance.It was not registered in the Klusówka and the Rządza Rivers.In total, it appeared at 9 sites.Occurrence stability index: 23%.Conservation status: AP, HD.AII, PRLLF (catégorie VU AI in PL and VUA2 in Vistula basin).

Gudgeon -Gobio gobio (L., 1758)
It was recorded in all investigated rivers.In the Klusówka and the Utrata, it was noted at all sampling sites.At many sites it was considered as dominant species in terms of abundance.In total, it appeared at 25 sites.Occurrence stability index 71%.Conservation status: PRLLF (catégorie LC in PL & Vistula basin).

Loach -M isgurnus fo ssilis (L., 1758)
In the investigated rivers, loach was rare, only at site No. 2 (in the Dluga River) it accounted for 24.5% of abundance.In the Świder and the Utrata Rivers it was registered at 2 sites and in the Rządza River at 4 sites.It was not registered in the Klusówka River.Occurrence stability index: 26%.Conservation status: AP, HD.AII, PRLLF (catégorie VU AI in PL, NT in Vistula basin).
In analysing the relation between the river size and the fish species diversity in a river on the basis of the published data, Wiśniewolski (2002) concluded that in lowland rivers of different length and with a different degree of modifications, ranging from 60 to 90 km, with different degree of transformations, even 26 fish species, including 14 exploited species could be expected to exist.The number of species registered in the investigated rivers was lower than expected, although in the Klusówka River, a relatively small, 20 kilometres long river 15 species were recorded, with the species potentially attractive for anglers accounting for almost 50% of the total abundance.The occurrence of carp in the Dluga River, probably escapees from the stocking centre in Halinów (Stolarz & Sędkiewicz 1995) disturbed the natural composition of fish communities in this river.
Among all species registered in the investigated rivers, there are 20 limnophilic and eurytopic species and their abundance in particular rivers ranged from 43.7% to 91.4% of the total abundance of fish.Such composition of fish communities in rivers reflects the unfavourable changes that occur in the aquatic environment.(Rolik & Rembiszewski 1987, Błachuta et al. 1993, Penczak et al. 1991, Schrimer & Waidbacher 1992).
Species covered by legal protection were also registered in the catches, namely the Ukrainian lamprey, spined loach, loach, spirlin, bitterling and stone loach (Journal of Laws 2004No. 220, item. 2237).According to the IUCN classification, spirlin is classified as endangered species (EN).Notwithstanding the shift from the category of endangered species in 1999 (EN) to the category of vulnerable species in 2009 (VU), the Ukrainian lamprey, bitterling and loach have remained on the list of species under the highest extinction risk (Witkowski et al. 2009) and are listed in the Red List of Threatened Species (Głowaciński 2001).The Ukrainian lamprey, bitterling and loach are protected in the framework of the European network "Natura 2000" (Annex II to the EU Habitat Directive).Each of the abovementioned species has specific, narrow-spectrum, environmental requirements.These elsewhere rare fish occurred at 6-13 sampling sites and usually accounted for a small percentage of the total abundance of investigated fish communities.
Two species alien to the local ichthyofauna were caught in the Klusówka and the Utrata Rivers, namely goad goby belonging to the Black Sea basin and stone morocco, originating from the Amur River basin.The occurrence of the first species is a result of a natural migration from the East through the Bug River system, whereas the second species is an example of unintentional introduction.The expansion of these alien species, competing with local fish fauna in rivers which lack strong populations of predatory species, can be very fast and significant.(Witkowski 1991, 1996, Danilkiewicz 1996, Grabowska et al. 2010).
During spawning, different fish species require not only adequate water temperature and oxygenation, but also specific bottom substrate, in which they lay the eggs (Kryzhanovsky 1948, Balon 1975).Species from all reproductive ecological guilds occurring in the Polish fish fauna were registered in the studied ecosystems, whereas the group of phytophylic and psammophylic species group visibly dominated in every river.It could therefore be concluded that, notwithstanding their transformations, the studied ecosystems are still diversified in terms of the existing ichthyofauna, although some river sections with the morphology characteristic for upland streams, with fast current and rocky bottoms are not fully inhabited by ichthyofauna.This is confirmed by the low occurrence of lithophylic species, especially trout in the ichthyofauna of the Św ider, the Rządza and the Dluga Rivers (Buras & Gasiński 2000).
The greatest species diversity was recorded in the Świder River flowing into the Vistula River and the Rządza River which is part of the Zegrze Reservoir drainage basin.The smallest number of species were registered in the Dluga River ending its course in the Żerań canal and the Utrata River, belonging to the Bzura River basin.The Bzura River is highly transformed (Penczak et al. 2000).Already in 1963-1966, Penczak estimated the fish resources in the Bzura River, apart from its upper segment close to the source, to be completely destroyed and the ichthyofauna of most of its tributaries as very poor both in terms of quality and quantity (Penczak 1968(Penczak , 1969)), although some parts of the Utrata River were abundant in fish (Zalewski & Penczak 1981).The Dluga River is also highly transformed and polluted (Buras & Gasiński 2000), whereas both the Świder River and the Rządza River are relatively less transformed and have preserved their natural character.Large segments of the Świder River and the Rządza River flow through the landscape parks, established also to preserve the natural character of these rivers.
The small share of predatory fish observed in all studied rivers is alarming.Pike occurred only at 17 sampling sites, mainly in the Dluga River and the Rządza River.Its abundance was low in all studied rivers and accounted for 0.7 up to 10.0% (Table 4).Low frequency of occurrence may be a result of high angling and poaching pressure in easily accessible rivers located in the vicinity of Warsaw.At the same time, excessive flow in canalized parts and even, often shallow river bed worsens the living conditions for all fish, including the phytophylic species, notwithstanding the presence of vegetation on the river bottom.Fish do not find adequate hiding places, feeding and wintering grounds.Also unregulated sewage management in river basins and the resulting bad water quality cause the disappearance of more sensitive species (Backiel 1958, Wajdowicz 1979, Bless 1985, Backiel 1993).

Fig. 1 .
Fig. 1.Location o f electrofishing sites in the investigated rivers.

Table 1 .
Characteristics o f the investigated rivers.

Table 4 .
The dom inant fish species at particular sites and abundance o f fish species in some o f ecological guilds http://rcin.org.plhttp://rcin.org.pl

Table 5 .
Characteristics o f the investigated rivers based on fish fauna and some average values o f community indices.