Cyprinids in Estonian Small Lakes: Comparison between Main Water Basins
Anu Palm (1) amd Teet Krause (1), Ain Järvalt(1), Maidu Silm (1) (1) Estonian University for Life Sciences, Centre for Limnology at PKI, Tartu, Estonia
Abstract
In last 16 years, we sampled slightly over a hundred small lakes in Estonia with Nordic type of multimesh gillnets for cyprinids. We captured 15 cyprinid species out of 18 considered as natural of origin in Estonian inland waters. Rheophilic riffle minnow (Alburnoides bipunctatus) and minnow (Phoxinus phoxinus) in addition to stocked carp (Cyprinus carpio) never occurred in samples, whereas vimba bream (Vimba vimba) and piscivorous asp (Aspius aspius) occurred twice. Extremely rare in samples were also chub (Leuciscus cephalus), gudgeon (Gobio gobio), dace (L. leuciscus), and ide (L. idus). The gibel carp (Carassius gibelio), crussian carp (Carassius carassius), and tench (Tinca tinca) were caught mostly in coastal and closed lakes. Open lakes with in- and outlet were preferred by bream (Abramis brama), bleak (Alburnus alburnus), and white bream (Blicca bjoerkna). Numbers of cyprinid species co-increased with the numbers of individuals in a sample both either water basins or lake types along the water course were compared; coastal lakes were the only exception. We consider the ratio numbers of cyprinid individuals per cyprinid species to indicate directly the pressure of piscivory and hence indirectly the quality of lake water.
Keywords: Cyprinidae, lake type, multimesh gill net, water quality
Introduction
The fish distribution of Northern Europe is described as a outcome of postglacial dispersal (Mooi, Gill, 2002) in the long-lasting processes of retreat southwards by ice formation and recolonization of ice- free areas (Paaver, Lõugas, 2003). Nowadays boreal Estonian fresh inland waters are inhabited by ten orders of bone fish (Pihu, Turovski, 2001) of which the order of Cypriniformes is represented by two families one of which is the Cyprinidae also known as cyprinids. According to M. Kottelat (Mooi, Gill, 2002) cyprinids as an order include mostly freshwater species inhabiting only the Northern Hermisphere and are considered to contribute about 36 % of the species diversity in the Palearctic.
Most cyprinids of Estonia are moderately cold-tolerant either earlier invaders or later on adapted to temperate conditions; some species like asp Aspius aspius, sunbleak Leucaspius delineatus, and vimba bream Vimba vimba are considered to be thermophilic freshwater species, whereas carp Cyprinius carpio and gibel carp Carassius auratus are released into Estonian fresh waters by man.
From the habitat point of view several cyprinid species like bleak prefer pelagial waters, while species like tench and bream are mostly caught in benthic regions. The wide range in the diversity of habitat is also highlighted by feeding customs as usual bottom dwellers consume on benthic animals and pelagial species prefer plankton as a food. According to classical standpoints the share of cyprinids in the whole fish assemblage tends to increase alongside with the load of nutrients in the water (Colby et al.,1972; Svärdson, 1976; Leach et al., 1977; Reshetnikov, 1980; Moss,1998). In this study we try to find differences in cyprinid species composition between and alongside the four major water basins of Estonia and point out the species characterizing lakes with different runoff conditions.
Material and methods
Study site Estonia (45,226 km2 in area) lies between 21.5o to 28.1oE and 57.3o to 59.5oN on the east European plain bordered on the Republic of Latvia in south, and the Russian Federation in north (Fig. 1) and has cool to cold temperate climate. Its mainland is flat - one fifth of it described as mire lowland. Four major drainage basins empty into the Gulf of Riga (GR), the Baltic Proper (BP), and either straight or through Lake Peipsi (LP) and the Narva River into the Gulf of Finland (GF). Waters are drained from catchments areas of 10,421 km2 (GR), 8017 km2 (BP), 10,314 km2 (GF), and 14,743 km2 (LP).
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 1 Drainage divides between basins are mostly plateaus: lower (ca 80 m.a.s.l.) and marshy in north, higher in south (exceeding 190 m.a.s.l.). The vast majority of lakes locate in the south Estonia in the water basins LP (Table 1) and GR, whereas shallow still freshwaters are common at the coasts of the
Gulf of Finland
Narva River Baltic Proper
59 Lake Peipsi °
R U S S I A N Federation
L.Võrtsjärv
58 °
Republic of L A T V I A Gulf of Riga
022° 027°
Fig. 1. Schematic map of still waters in four main catchments sampled for cyprinid fish. Location on a tributary is denoted according to Arukaevu (1986), water basins according to Ojaveer and co- authors (2003).
Baltic Sea and Lake Peipsi. Most still waters neighbour fen or bog, few are based on only sand and peel. Mud-covered base and densely vegetated littoral are common, whereas pebble and sand as sole base are rare. The history of replenishment still freshwaters with hatchery reared fish goes back to the 19th century (Mäemets, 1977). According to OECD (2009) of cyprinids the release of larvae or yearlings of T. tinca has been funded by the state.
Lakes were ranked according to their location at the watercourse (Table 1; first suggested by Riikoja (1934) using also data published by Mäemets (1977) and Loopmann (1984)) ranging from closed to open and coastal waters. Coastal still freshwaters are extremely shallow, closely adjacent to the Baltic Sea or Lake Peipsi and located at the altitude less than 4 m.a.s.l. Our study covered the time period when water budget in all studied drainage basins was at their depression over the last thirty years of period (Jaani, Kullus 1999). Low water levels were in mild winters, in cold winters with snow cover was deep and vernal floods higher than an average. Neither serious summer nor winter fish kills were recorded in surveyed small lakes throughout the study period.
Sampling
Between 1995 and 2011, in total 121 lakes were sampled for fish numbers (NPUE) with ‘Nordic’ multimesh gill nets (N = 1557) according to CEN 14757 (2005), with an exception that each individual was separately measured for total length (TL) to the nearest 1 mm. Multimesh gill nets were set in all depth ranges of a lake but those measured to be anoxic. Gill nets were set overnight for 12 hours including dusk and dawn. Dissolved oxygen content (mg l-1) in water was measured with microprocessor ‘Marvet Junior’ (Estonia) in pelagial at the depth gaps of 1 m.
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 2 Table 1. Average lake area (km2) (Loopmann, 1984; Mäemets, 1977, Tamre, 2006) describing still freshwaters sampled for fish species with multimesh gill nets.
N Lake Peipsi Gulf of Riga Gulf of Finland Baltic Proper Lake type Mean Range Mean Range Mean Range Mean Range Closed 7 0,08 0,01-0,1 3,5 3.5 0,04 0,04-0,2 1,4 1,4 Open with runoff 62 1,1 0,02-7,2 1,4 0,06-4,6 0,9 0,1-3,5 1,3 0,1-3,4 Open with inlet 33 1,2 0.08-6,0 1,1 0,2-2,3 3,4 0,3-9,4 0,7 0,1-1,6 and runoff Coastal 19 1,7 0,86-2,8 3,1 0,8-5,3 2,1. 1,3-3,5 0,9 0,07-2,9 All studied lakes 121 1,1 0,01-7,2 1,7 0,01-5,3 1,7 9,94-9,4 1 0,06-3,4 N 61 30 15 15
Statistics
To compare water basins and lake types, data collected only in August and September were used (in total 1469 ‘Nordic’ gill nets). Calculations were performed in MS Excel environment. For mean cyprinid NPUE values the catch within a single lake was treated as a single sample (Appelberg 2000) to calculate among-type variation. F-Test Two-Sample for Variances was used to estimate deviations. Correlation coefficient k was calculated to follow similarity in data.
Results obtained
Among surveyed waters lakes with only cyprinid species occurred as well as those with no cyprinid species at all. Although no clear lake-type pattern was found, lakes that lacked cyprinids started usually a brook or river i.e. had only runoff (table 2), while lakes with only cyprinid species were usually closed. In total, fifteen cyprinid species where caught, whereas the number of cyprinid species per lake averaged at 3,86 (range between 0 and 10). Most of the lakes harboured roach (90,98 %), about half of lakes were inhabited by rudd (52,46 %), bream (50,00 %), and bleak (46,08 %) followed by sunbleak (40,16 %) and a species widely released into the Estonian small lakes – tench (38,52 %). Approximately one third of studied waters were inhabited by white bream (31,97 %), while one fifth contained crussian carp (24,59 %). Significantly less lakes harboured gibel carp (9,84 %) and ide (4,92 %). Of the most sparse amongst cyprinids: gudgeon, and dace both inhabited 2,46 % of lakes, whereas chub and asp were both caught from only two lakes (1,64 %) that locate in the water basin of Lake Peisi. (Fig. 2). Vimba bream was fished from two water basins GR and GF (one lake in both). Only two water basins – LP and GR harboured gudgeon and ide. In total, LP harboured all but one of caught cyprinid species, lakes of GR lacked chub, asp, and gibel carp, while the rarest cyprinids in Estonian lakes - gudgeon, ide, chub, and asp were absent from lakes of GF. Lakes of BP harboured only approximately half of cyprinid species, lacking even a bream.
Table 2. Share of cyprinid fish per unique effort of a Nordic type of gillnet in four main water basins and lake types with different runoff conditions.
Lake Type N Lake Peipsi Gulf of Riga Gulf of Finland Baltic Proper Mean Range Mean Range Mean Range Mean Range Closed 7 0,83 0,44-1 0,09 0,09 0,71 0,42-1 0,48 0,48 Open with runoff 62 0,62 0-0,96 0,65 0-0,98 0,68 0-1 0,44 0,27-0.62 Open with inlet and runoff 33 0,80 0,36-0,98 0,77 0,41-0,99 0,6 0,32-0,82 0,53 0,53 Coastal 19 0,47 0,25-0,61 0,43 0,38-0,55 0,46 0,13-0,70 0,68 0,08-0.99 N 61 30 15 15
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 3 Three species – roach, sunbleak and rudd - out of fifteen as a total occurred almost evenly in all four lake types with different runoff conditions (Fig. 3). As an opposite, asp and vimba bream were caught only in two lake types. All caught cyprinid species inhabited open lakes with both inlet and runoff. Both coastal and open lakes with only runoff i.e. started a brook or river lacked one species: first ones chub and the second ones asp. Closed lakes harboured the least number of species – six. The average number of cyprinid species per a closed lake was 2,75 (Fig. 4), one of species inhabiting this lake type was commonly roach. The number of species per lake in distinct water basins ranged between 3.1 and 4.1. The average numbers of cyprinid individuals per unique effort ranged a lot more
100%
75%
50%
25%
0%
Tinca tinca Gobio gobio Vimba vimba Rutilus rutilus Aspius aspius Blicca bjoerknaAbramis brama Leuciscus idus Carassius gibelio Alburnus alburnus Carassius carassius Leuciscus leuciscus Leuciscus cephalus Leucaspius delineatus
Scardinius erythrophthalmus
Baltic Proper L. Peipsi Gulf of Riga Gulf of Finlamd
Fig. 2. Occurence of cyprinids in four main water basins of Estonia.
100%
75%
50%
25%
0%
Tinca tinca Gobio gobio Rutius rutilus Vimba vimbaAspius aspius Blicca bjoerknaLeuciscus idus Abramis brama Carassius gibelio Alburnus alburnus Carassius carassius Leuciscus leuciscus Leuciscus cephalus Leucaspius delineatus
Scardinius erythrophthalmus
Closed Open with outlet Open with in- and outlet Coastal
Fig. 3. Occurence of cyprinids in lakes with different runoff conditions widely from 21,2 in the lakes of BP to 49,2 in the lakes of LP, but in the similar pattern (k = 0,95) as the numbers of species. The number of individuals per species increased as follows: GF 6,9, BP 7,7, GR 10,3, and LP 12,1. Runoff conditions separated lake types more clearly. Average numbers of
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 4 species per lake were the lowest in closed lakes (2,75), increased from 3,5 for lakes with runoff, to 4,3 in lakes with inlet and runoff to 4,9 for coastal lakes. The highest significant difference (p < 0,001) appeared to be between the two open lake-types (lakes with only runoff and lakes having both inlet and runoff).
A Species NPUE 5 60
4 50 40 3 30 2 of of species 20 Average NPUE Average Average nunber Average 1 10
0 0 Baltic Proper L Peipsi Gulf of Riga Gulf of Finland Water basin
B Species NPUE 6 60
5 50
4 40
3 30 species 2 20 Average NPUE Average
Average number of Average 1 10
0 0 Closed Open with Open with Coastal runoff runoff and outlet Lake type
Fig. 4. Average numbers of cyprinid species in a lake and individuals per unique effort in four main water basins of Estonia (A) and in lakes with different runoff conditions (B).
Average numbers of individuals per unique effort increased following the same pattern (k = 0,48), but dropped approximately twice from 56,1 (open lakes with inlet and runoff) to 31,5 (coastal lakes). The most significant difference (p < 0,001) was again between the two types of open lakes. Numbers of individuals per species increased as follows: closed lakes 7,9; lakes with outlet 10,8; lakes with in- and outlet 13,0 and dropped abruptly to 6,4 for coastal lakes grazed by piscivores of adjacent large water body.
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 5 Discussion
According to species richness of freshwater fish Estonia belongs to the bio geographical region of Central Europe (Reyjol et al., 2006). Inside this region cyprinids are the strongest dominant with more than half of all species. Our study area located slightly eastward from the mid-point of the Central Europe bio geographical region and the richness of cyprinid species followed highly the latitudinal pattern (Sale, 1980). In comparison with the southernmost area of this Central Europe region the ’Central Plains’ (Mehner et al., 2007; Diekmann et al., 2005) the numbers of cyprinid species were in Estonian small lakes lower by four to five species, but interestingly in the lakes of Central Plains ide and chub are missing. In comparison with more close northward areas of southern Finland (Olin et al., 2002) Estonian lakes contained six more species with one species – blue bream Abramis ballerus – absent. Blue bream is occasionally fished in the Gulf of Riga and has been rare in Latvian lakes (Pihu, 1993). Bitterling Rhodeus amarus occurring in the ’Central Plains’ lakes was absent in Estonian small lakes, but is common in the Gulf of Riga alongside with ziege Pelecus cultratus. Southward from Estonia, in Latvia, tench and bream are more widely spread in small lakes (Pihu, 1993). Compared with the occurrence of cyprinid species in Estonian lakes two decades ago only two species missed our catches – minnow and common carp. The first of these two species characterizes more the running waters and is usually considered to be a rheophilic species.
Of thermophilic cyprinids only sunbleak was ubiquitous being absent from only closed lakes, whereas asp and vimba bream were extremely rare. Vimba bream is considered to be more numerous in the bays of the Estonian coast of the Baltic Sea (Saat, Ojaveer, 2005) We also caught this species from two lakes both connected to the Baltic Sea. Another species widely spread alongside the Estonian Baltic Sea coast since mid-1990s gibel carp (Vetemaa et al., 2005) was surprisingly missed from only lakes of GR. Of cyprinid species recorded to occur in the Matsalu Bay (BP) neither dace, chub, ide, nor vimba bream (Vetemaa et al., 2006) never occurred in the catches from the lakes of BP. Even gudgeon frequent in the coastal waters of the Gulf of Riga was only caught a few times in the lakes of GR. From one point of view all above mentioned species are described to prefer faster-flowing habitats that provide prey at a higher rate (Tyler and Gilliam, 1995). Freshwater fish communities are shown to change along with the hydraulic characteristics of environment (Blanck et al., 2007). On the other hand, gill nets as gear are described to be highly selective (Prchalová et al., 2009) and at least such littoral dwellers like gudgeon, sunbleak, large rudd, and tench are considered to be underestimated if fished by gill nets (Diekmann et al., 2005).
Prey densities are reduced by piscivorous species (Hixon, 1991) in Estonian waters first and foremost by pike Esox lucius, pikeperch Sander lucioperca and probably by widely stocked eel Anguilla anguilla (Järvalt et al., 2010; Dörner, Benndorf, 2003). Although stocking predators as a tool to improve water quality can easily fail (Skov, Nilsson, 2007), piscivores still decrease effectively the numbers of their prey (Juanes et al., 2002). On the other hand it is widely known that trophic structure, species richness, and biodiversity are mostly explained by the changes along a nutrient load gradient (Jeppesen et al., 2000). This seemed to apply to lake types with different runoff conditions as both the numbers of individuals per unique fishing effort and the numbers of species per lake increased along the watercourse until the species richness achieved its maximum in coastal lakes well connected to larger water bodies (the Baltic Sea or L. Peipsi). The significant difference in species numbers between two open lake-types seemed surprising as frequently the distance between the two lakes is not that long and only two cyprinid species – asp and vimba bream were absent from lakes with slower rate of water flow. Asp and vimba bream are also recorded as highly rare in the lakes of neighbouring inland areas (Pihu, 1993) as well as in L. Peipsi (Saat, Vaino, 2010). Asp should be more numerous in Estonian southernmost rivers adjacent to Latvia (Järvekülg, 2001).
Foraging modes of fish comprize planktivore, molluscivore and piscivore (Mittelbach, 2002) all practised by cyprinides, hence using all suitable habitats that cover the whole water body despite its area and volume. As predators are shown to stabilize in numbers not extinct their prey (Evans et al., 1987), the ratio numbers of cyprinid individuals per species should indicate the nutrient load in a water body and hence the water quality.
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 6 Conclusions
• The survey of 121 lakes of four main water basins in Estonia conformed the occurrence of fifteen cyprinid species with three species absent as compared with previously published data. Two of missed species – minnow and riffle minnow are rheophilic, the third – common carp has been released into the wild by man. In an average 3,9 cyprinid species were caught per lake (ranging from zero to ten). • Closed lakes harboured only those of cyprinid species that prefer slow-flowing either shallow or deep habitats. All cyprinid species preferring fast-flowing habitats except bream, white bream and bleak were highly rare; two species - asp and vimba bream occurred only in open lakes with in- and outlet in addition to coastal lakes. • Fish fauna did differ from water basin to water basun. Approximately half of cyprinid species (15 as total fished from Estonian small lakes) were absent in the extremely shallow lakes of Baltic Proper (linked with the coastal waters of the Suur Väin Strait and Väinameri). In contrast, all cyprinid species but vimba bream were recorded in the largest studied water basin of Lake Peipsi (connected via Narva River with the Gulf of Finland). Four species (gudgeon, ide, dace and asp, all preferring fast-flowing habitats) were absent from the lakes of the Gulf of Finland. Three species – dace, asp and a man-released gibel carp (that prefer slow-running habitats) were absent from the lakes of GR. • The numbers of cyprinid individuals per species increased along the watercourse (following the increasing gradient of nutrient load) and dropped abruptly in coastal lakes (grazed by piscivores of adjacent large water bodies).
BALWOIS 2012 - Ohrid, Republic of Macedonia – 27 May, 2 June 2012 7 References
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