Cyprinids in Estonian Small Lakes: Comparison Between Main Water Basins
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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.