VARIABILITY OF LENGTH AND WEIGHT GROWTH RATES IN THE VENDACE Coregonus albula (L.) FROM SOME WESTERN POMERANIAN LAKES

Acta Sci. Pol., Piscaria 6 (34) 2007, 1332 VARIABILITY OF LENGTH AND WEIGHT GROWTH RATES IN THE VENDACE Coregonus albula (L.) FROM SOME WESTERN POMERANIAN LAKES Przemysław Czerniejewski, Wawrzyniec Wawrzyniak, Katarzyna Stepanowska Agricultural University of Szczecin, Poland Abstract. Individual weight, total length, condition, and growth rate was determined in the vendace caught in spring, summer, and autumn of 19992000 from 4 Western Pomeranian lakes: Miedwie, Ińsko, Woświn, and Glinno, the lakes differing in their trophic status and morphometry. The vendace caught in the mesotrophic lakes Miedwie and Ińsko showed better condition and higher length and weight growth rates, compared to those parameters revealed by the vendace from the eutrophic lakes Woświn and Glinno. Key words: age structure, condition, Glinno, growth rate, Ińsko, lakes, Miedwie, vendace, Woświn INTRODUCTION Despite its small size, the vendace Coregonus albula (L., 1758) is of commercial importance in cold, clean, and well-oxygenated lakes of Norway [Grudniewski 1970, Sandlund 1992], Sweden [Svärdson 1979], and Finland [Viljanen 1988, Mutenia and Salonen 1992] as well as in more eutrophic lakes of Poland and Germany [Bauch 1961, Bernatowicz and Radziej 1974, Czerniejewski and Wawrzyniak 2006]. The species' importance stems mostly from its biological traits. Under the climatic conditions of Poland, it takes the vendace a short time only (most often 23 years [Ciepielewski 1974a]) to grow to the commercial size. The species has a relative fast growth rate [Marciak 1970] and lives in schools, which facilitates harvesting. In addition, due to the high quality of the vendace meat, the species is enjoyed and sought after by consumers. The advantageous biological traits of the vendace notwithstanding, the 1990s witnessed a decline in the species' abundance in Polish lakes, most likely due to eutrophication progressing in numerous lakes and due to management changes resulting from economic transformation of fisheries; as a result, vendace catches dropped by more than a half [Wołos and Mickiewicz 1998]. In the Province of Western Pomerania, the vendace occurs in 44 out of 1575 lakes [Filipiak and Raczyński 2000], commercial vendace fishery being carried out in only in 23 of them Corresponding author Adres do korespondencji: Dr inŝ. Przemysław Czerniejewski, Department of Fisheries Management in Open Waters, Agricultural University of Szczecin, K. Królewicza 4, 71-550 Szczecin, Poland, e-mail: zgl@fish.ar.szczecin.pl

14 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska [Czerniejewski and Filipiak 2001]. The commercially exploited vendace populations occur in, i.a., the Miedwie, Glinno, Ińsko, and Woświn, which differ both in their morphometry and trophic status (Table 1). The commercially exploited vendace populations in those lakes are strengthened by stocking operations. The Miedwie and the Glinno are stocked with fish produced by broodstocks obtained from the Miedwie, while the Woświn and Ińsko are stocked with newly hatched individuals and/or juveniles descending from the broodstock obtained from both lakes. In view of the necessity to rationally use the vendace resources in various lakes, it seems mandatory to analyse some biological traits of the populations exploited. The present study was aimed at assessing the dynamics of individual weight and length growth as well as the condition of the vendace in different fishing seasons (spring, lake, and autumn) in lakes Miedwie, Ińsko, Woświn, and Glinno, and at determining and comparing age structure as well as length and weight growth rates of those populations. Table 1. Basic morphometric and trophic information on lakes studied Tabela 1. Podstawowe dane morfometryczne i troficzne badanych jezior Morphometric data (according to Freshwater Fisheries Institute, Olsztyn) Dane morfometryczne (według IRS Olsztyn) Lake Jezioro surface, ha powierzchnia, ha volume, thou. m 3 objętość, tys. m 3 maximum depth, m głębokość max, m mean depth, m głębokość średnia, m elongation index wskaźnik wydłuŝenia shore complexity index wskaźnik rozwoju linii brzegowej Trophic status* trofia* Miedwie Ińsko Woświn Glinna 3527.0 486.6 809.1 75.6 681672.4 65182.0 75840.8 6238.7 43.8 41.7 28.1 16.4 19.3 11.1 9.4 8.2 5.1 2.6 4.7 3.4 1.80 3.19 2.59 2.20 mezotroficzne mezotroficzne eutroficzne eutroficzne * according to Szlauer [1999], Jurkowska et al. [2000], Cydzik et al. [2000], unpublished data of Provincial Environmental Inspection Centre, Szczecin. * według: Szlauer [1999], Jurkowska i in. [2000], Cydzik i in. [2000], dane niepublikowane WIOŚ, Szczecin. MATERIAL AND METHODS The vendace used in the study were obtained during nocturnal fishing, with 24 mm mesh size gill nets, in spring, autumn, and summer of 19992000 in lakes Miedwie, Ińsko, Woświn, and Glinno. The lakes differ in their morphometry and trophic status (Table 1). The numbers of individuals examined are reported in Table 2. After capture, each fish was weighed (to 0.1 g, on an Axis electronic scales) and measured (total length measured to 0.1 mm with an electronic callipers). The fish condition was expressed with the Fulton (K F ) and Clark (Kc) condition coefficients [Bolgier and Acta Sci. Pol.

Variability of length and weight growth 15 Connolly 1989], and was assessed by analysing parameters a and b of the total length (L)-weight (W) relationship (L-W) [Szypuła et al. 2001]: W = al b where: W individual weight (g), L total length (mm), a, b species (population) specific parameters determined from empirical data. Table 2. Vendace sample sizes (individuals) analysed in 19992000 Tabela 2. Zestawienie liczebności prób sielawy (osob.) pozyskanej do analiz badań w latach 19992000 Number of individuals Liczba osobników Lake Jezioro spring (MarchMay) okres wiosenny (marzecmaj) summer (JulyAugust) okres letni (czerwiecsierpień) autumn (OctoberNovember) okres jesienny (wrzesieńlistopad) Total Razem Miedwie 208 478 396 1082 Ińsko 208 406 241 855 Woświn 411 421 832 Glinno 100 111 44 255 Total Razem 516 1406 1102 3024 The fish age was assessed from scales; scales were also used to obtain data necessary for the length and weight growth rate assessment. Scales were collected as recommended by Bernatowicz [1952]. After collection, the scales were cleaned from mucus by rinsing with ammonia solution, and prepared for readings. Age readings and scale radius measurements were performed on the oral part of a scale, using the MultiScan image analysis software (measurements taken to 0.001 mm). The total fish length (L)-scale radius (R) relationship revealed a curvilinear increase of the scale radius. The equations describing the relationship, developed using the so-called standard, i.e., the length at which scales form (30 mm in the vendace 30 mm [Grudniewski 1970]), were as follows: 0.713 2 Lake Miedwie: L = 30+122.736R R = 0.9760, 0.6740 2 Lake Ińsko: L = 30+128.6884R R = 0.9826, Lake Woświn: L = 30+116.5069R 0.7534 R 2 = 0.9710, 0.6778 2 Lake Glinno: L = 30+130.1691R R = 0.9850. Owing to the curvilinearity of the R-L relationship, back readings were taken using the Vovk method as described by Szypuła et al. [2001]. On the outset, the curve equation was fitted to the data points using power function; subsequently, scale radius Piscaria 6 (34) 2007

16 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska measurements were corrected so that fish lengths in consecutive years of life could be calculated correctly. The empirical data thus obtained were used for theoretical representation of length and weight growth rates of the vendace with the mathematical growth model based on the von Bertalanffy equation [Szypuła et al. 2001]. Significance of differences in the total length, mean individual weight, and condition coefficients (K F and Kc) between the vendace populations from different lakes was tested with analysis of variance (ANOVA), followed by Duncan s multiple range test applied post hoc. Testing of the null hypothesis of no significant difference between the respective means was preceded by testing for the normality of distribution (the Shapiro- Wilk test) and for homogeneity of variance (the Levene test) [Stanisz 1998]. RESULTS Age and sex Except in Lake Glinno, the vendace populations sampled were clearly dominated by fish aged 2+, which contributed 75.4489.83% to the population in individual lakes (Table 3). In contrast, the Glinno population was dominated by the fish aged 3+ (155 inds; 60.78%), while the contribution of the fish aged 2+ was as low as 12.55% (32 inds). Table 3. Age and sex structure of vendace populations in lakes studied Tabela 3. Struktura wieku i płci sielawy z badanych jezior Age Wiek Lake Jezioro 1+ 2+ 3+ 4+ 5+ 6+ 7+ females samice Sex Płeć males samce Miedwie 16 972 81 11 2 618 464 Ińsko 36 645 116 31 10 12 5 413 442 Woświn 103 678 48 3 482 350 Glinno 32 155 16 4 170 85 The sex structure, summarised in Table 3, showed females to have contributed more to the Miedwie, Woświn, and Glinno populations (from 57.12 to 66.67%) than males; these were more numerous (51.7%) than females in Lake Ińsko. Length and weight Mean lengths and weights of the fish caught in individual lakes are shown in Tables 4 and 5, respectively. In spite of fairly selective fishing gear used (24 mm mesh size gill nets), the mean lengths and weights varied considerably between the lakes, the differences between the populations being significant (P < 0.05). The Woświn vendace had the significantly lowest total length and individual weight. Acta Sci. Pol.

Variability of length and weight growth 17 Table 4. Mean length (mm) of vendace in lakes studied Tabela 4. Średnia długość sielawy (w mm) z badanych jezior Lake Jezioro Sex Płeć Mean Średnia Range Zakres Standard deviation Odchylenie standardowe Median Mediana Lower quartile Q25 Dolny kwartyl Q25 Upper quartile Q75 Górny kwartyl Q75 Miedwie 226.3 220.4 223.8 181.5284.0 183.0289.0 181.5289.0 14.93 13.53 14.63 226.0 220.0 222.8 216.0 212.6 214.7 235.0 227.5 232.1 Ińsko 220.1 215.5 217.7 171.0341.0 172.2304.9 171.0341.0 25.10 18.83 22.19 213.2 214.0 213.5 205.4 204.3 204.7 228.3 226.0 227.8 Woświn 200.2 193.4 197.3 169.0246.0 163.4223.6 163.4246.0 13.30 11.51 13.01 199.4 192.1 195.8 191.0 185.0 188.3 209.7 200.9 205.7 Glinno 220.7 209.0 216.8 199.9245.9 189.8235.6 189.8245.9 9.19 10.31 11.03 221.1 207.6 217.6 214.9 201.9 208.4 228.3 215.9 225.3 Table 5. Mean weight (g) of vendace in lakes studied Tabela 5. Średnia masa sielawy (g) z badanych jezior Lake Jezioro Sex Płeć Mean Średnia Range Zakres Standard deviation Odchylenie standardowe Median Mediana Lower quartile Q25 Dolny kwartyl Q25 Upper quartile Q75 Górny kwartyl Q75 Miedwie 103.8 90.5 98.1 52.8236.5 55.2181.8 52.8236.5 21.18 15.19 19.95 100.7 89.4 94.6 90.7 80.7 86.0 112.9 98.6 108.6 Ińsko 97.1 86.2 91.4 39.0331.1 33.6227.7 33.6331.1 40.29 21.65 32.48 85.8 83.9 84.6 75.1 73.7 74.3 103.9 95.6 99.3 Woświn 72.1 60.3 67.1 43.5130.0 39.190.1 39.1130.0 14.10 11.51 14.33 71.2 58.4 65.9 61.7 52.0 56.1 80.2 67.4 76.3 Glinno 89.2 75.4 84.6 63.4113.7 57.6101.4 57.6113.7 10.27 10.92 12.35 88.7 72.7 84.9 82.6 66.8 74.7 95.9 82.4 92.8 Piscaria 6 (34) 2007

18 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska Figure 1 illustrates changes in total length of the vendace caught in different seasons. The populations showed a distinct pattern whereby the total length and individual weight were increasing in spring-summer and, due to reasons difficult to explain, declined in autumn. Acta Sci. Pol.

Variability of length and weight growth 19 cont. Fig. 1 cd. rys. 1 Fig. 1. Dynamics of changes in total lenght (mm) and individual weight (g) of vendace from lakes Miedwie (A), Ińsko (B), Woświn (C) and Glinno (D) Rys. 1. Dynamika zmian długości całkowitej (mm) i masy jednostkowej (g) sielawy z jeziora Miedwie (A), Ińsko (B), Woświn (C) i Glinno (D) Piscaria 6 (34) 2007

20 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska Condition and seasonal changes in condition coefficients As already mentioned, fish condition was assessed by analysing the Fulton (K F ) and Clark (Kc) coefficients and parameters of the total length (l.t.) individual weight (W) relationships. The condition coefficients given in Table 6 varied only slightly. The lowest Fulton coefficients were observed in the Lake Glinno vendace, the mean coefficient being by 4.60% lower than that in the Miedwie fish, which showed the best condition. The lower condition of the Glinno fish is evidenced also by the location of the relevant length-weight curve in Fig. 2. Although the parameter b in the Glinno fish equation (b = 0.0002) was slightly higher than that in the Ińsko (b = 0.00001), the curve described by the first equation is in Fig. 2 located below that describing the Ińsko vendace due to the parameter a, responsible for the curvilinearity of the function, being clearly lower in the first equation (a = 2.4438 and 2.8752, respectively). Table 6. Vendace condition coefficients in lakes studied Tabela 6. Wartości współczynników kondycji sielawy z badanych jezior Lake Jezioro Sex Płeć Fulton (K F) Współczynnik Fultona K F range zakres mean+s średnia+s Clark (Kc) Współczynnik Clark Kc range zakres mean+s średnia+s (KKc)+S Miedwie Ińsko Woświn Glinno 0.631.23 0.651.24 0.89+0.07 0.84+0.09 0.460.97 0.591.08 0.74+0.09 0.76+0.07 0.15+0.06 0.08+0.03 0.631.24 0.87+0.08 0.461.08 0.75+0.09 0.12+0.06 0.521.13 0.651.12 0.88+0.07 0.85+0.08 0.380.98 0.461.03 0.75+0.09 0.78+0.07 0.12+0.06 0.07+0.04 0.521.13 0.86+0.08 0.381.03 0.77+0.08 0.09+0.06 0.641.18 0.581.05 0.89+0.07 0.83+0.07 0.410.94 0.480.96 0.72+0.09 0.75+0.07 0.17+0.09 0.08+0.03 0.581.18 0.86+0.08 0.410.96 0.73+0.08 0.13+0.09 0.691.07 0.700.98 0.83+0.08 0.82+0.07 0.601.00 0.620.92 0.74+0.08 0.0.75+0.08 0.09+0.03 0.07+0.02 0.691.07 0.83+0.07 0.601.00 0.75+0.08 0.08+0.02 Acta Sci. Pol.

Variability of length and weight growth 21 Fig. 2. Total length-weight relationship of vendace in lakes studied Rys. 2. ZaleŜność pomiędzy długością całkowitą a masą sielawy z badanych jezior Table 7 illustrates seasonal changes in the condition coefficients in the whole samples and in males and females separately. The mean K F and Kc indicate a clearly better condition of the vendace caught in springsummer, compared to the autumn catches. It should be pointed out that the Fulton and Clark coefficients in females caught in autumn were significantly higher (P < 0.05) and significantly lower (P < 0.05), respectively, than those in males. The differences resulted from the female vendace getting ready to spawn, whereby their abdominal region was expanded by the developed gonads. Table 7. Seasonal changes in vendace condition coefficients in lakes studied Tabela 7. Sezonowe zmiany wartości współczynników kondycji sielawy z badanych jezior Month of collection Sex Płeć Lake Miedwie Lake Ińsko Lake Woświn Lake Glinno Jezioro Miedwie Jezioro Ińsko Jezioro Woświn Jezioro Glinno K F+S Kc+S K F+S Kc+S K F+S Kc+S K F+S Kc+S May 2000 Maj 2000 July 1999 Lipiec 1999 August 2000 Sierpień 2000 0.93+0.05 0.84+0.05 0.95+0.06 0.86+0.06 0.88+0.08 0.90+0.07 0.78+0.07 0.81+0.07 0.89+0.07 0.89+0.06 0.82+0.06 0.83+0.05 0.94+0.05 0.85+0.06 0.89+0.08 0.79+0.07 0.89+0.07 0.82+0.06 0.87+0.06 0.75+0.05 0.86+0.05 0.75+0.05 0.88+0.05 0.86+0.05 0.81+0.05 0.81+0.06 0.86+0.04 0.86+0.05 0.77+0.04 0.77+0.05 0.78+0.04 0.78+0.05 0.70+0.04 0.70+0.05 0.87+0.05 0.75+0.05 0.87+0.06 0.81+0.06 0.86+0.04 0.77+0.04 0.78+0.05 0.70+0.04 0.90+0.05 0.79+0.04 0.86+0.06 0.76+0.05 0.90+0.07 0.89+0.06 0.81+0.06 0.81+0.06 0.89+0.06 0.87+0.07 0.80+0.05 0.79+0.06 0.86+0.06 0.80+0.07 0.88+0.06 0.77+0.05 0.90+0.07 0.81+0.06 0.88+0.07 0.80+0.06 0.86+0.06 0.80+0.07 Piscaria 6 (34) 2007

22 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska cont. Table 7 cd. tabeli 7 October 2000 Październik 2000 November 1999 Listopad 1999 0.85+0.06 0.64+0.05 0.79+0.05 0.74+0.06 0.84+0.05 0.76+0.05 0.63+0.04 0.71+0.05 0.87+0.07 0.75+0.06 0.62+0.06 0.69+0.06 0.83+0.07 0.67+0.07 0.80+0.07 0.67+0.06 0.83+0.09 0.65+0.07 0.89+0.08 0.65+0.07 0.75+0.05 0.69+0.04 0.88+0.06 0.79+0.05 0.71+0.04 0.72+0.05 0.95+0.06 0.82+0.05 0.68+0.05 0.73+0.05 0.79+0.04 0.77+0.04 0.66+0.04 0.72+0.04 0.82+0.10 0.67+0.06 0.81+0.07 0.72+0.04 0.88+0.09 0.71+0.05 0.78+0.04 0.68+0.05 Fish length and growth rates The fish growth rates in the lakes sampled, as determined from back readings, are shown in Fig. 3. The fastest length growth rate was typical of the first year of life (mean length increments in the lakes ranged within 138.79148.92 mm), the increments in the second and third year of life being 23 times lower, compared to those in the respective preceding year. Among the populations analysed, the best growth rates were typical of the Miedwie and Ińsko vendace which, in their third year of life, showed the total length to be by about 10% higher than in the fish in the remaining lakes. The differences in the vendace growth resulted, most probably, from differences in environmental conditions and food resources. It seems that the mesotrophic lakes Miedwie and Ińsko offer better conditions for a faster growth of the vendace, compared to the eutrophic lakes Woświn and Glinno. Fig. 3. Vendace lenght growth rate, as determined by back readings, in lakes studied Rys. 3. Tempo wzrostu długości sielawy określone metodą odczynów wstecznych z badanych jezior Acta Sci. Pol.

Variability of length and weight growth 23 The lengths, determined with back readings, were used to develop parameters of the mathematical model of fish growth, based on the von Bertalanffy equation. The models are as follows: 0.5242(t+0.2923) Lake Miedwie: Lt = 298.1[1e ], 0.2444(t+1.0696) Lake Ińsko: Lt = 368.8[1e ], Lake Woświn: Lt = 300.8[1e 3.247(t+1.09073) ], 0.4476(t+0.8251) Lake Glinno: Lt = 257.0 [1e ]. The highest theoretical maximum length (L ) was found in the vendace caught in Lake Ińsko (L = 368.8 mm), while the Glinno population showed as little as 257.0 mm. Similar L values were determined for the vendace caught in the Miedwie and Woświn (298.1 and 300.8 mm, respectively). The strongest curvilinearity (the highest k) is seen in the growth curve describing the Miedwie vendace (k = 0.5242). Noteworthy is the fact that the mean absolute differences between the empirical (from back readings) and theoretical (from the von Bertalanffy model) data were 5.1, 2.2, 0.4, and 0.7 mm in the Ińsko, Miedwie, Woświn, and Glinno populations, respectively. The small differences, particularly in the last three populations, evidence a good fit of the mathematical growth model to the empirical data. The weight growth rate of vendace in the lakes studied was estimated from the modified von Bertalanffy equation; the equation parameters are given in Fig. 4. In their first year of life, the fish from different lakes showed similar weight growth rates. However, as early as in the second year, the Miedwie vendace became distinct in having clearly higher weight increments. In the fourth year of life, the Glinno population was markedly different on account of the fish weight that was by as much as 31.63% lower than that in the Miedwie vendace. Fig. 4. Comparison of vendace weight growth rates in lakes studied Rys. 4. Porównanie tempa wzrostu masy sielawy z badanych jezior Piscaria 6 (34) 2007

24 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska DISCUSSION The vendace is harvested in Poland with gill nets and trawls. The latter, although more advantageous under specific conditions (e.g., in lakes situated in very popular tourist locations), are being replaced by more selective gill nets [Bernatowicz et al. 1974]. For example, as reported by Czerniejewski and Wawrzyniak [2006], 83% of the gear used to catch the vendace in the Western Pomeranian lakes are gill nets; they are most frequently made of 24 mm mesh size netting. This mesh size selects for fish that are 17.824.2 cm long, 21.0 cm long individuals being harvested with the maximum efficiency [Ciepielewski 1974b]. This explains the relative homogeneity of total length and individual weight of the fish examined in this study. A wider range of total lengths, found in this study, compared to data reported by Ciepielewski [1974b] seems to have been caused by the fact that about 10% of the fish caught were large individuals that were stuck in the net because their abdominal, pectoral, and dorsal fins got entwined in the meshes. Assessment of fish condition is an important component of studies on different fish populations. According to Bolgier and Connolly [1989], variability of fish condition is studied with length-weight relationship [Winfield et al. 1996] and mathematical formulae supplied by Fulton and Clark (referred to by Ritterbusch-Nauwerck [1995]). The length-weight relationship is usually a power function. The function exponent depends, i.a., on fish body shape; in the "slender", fish the exponent is lower than 3 and becomes higher in the "stout" fish [Wootton 1996]. The exponent in the vendace amounts to about 3 [Sandlund 1992, Christianus 1995, Czerniejewski and Filipiak 2002], thus indicating an isometric growth of the species. In some crustacean plankton-rich lakes, the exponent is close to 3.5 [Winfield et al. 1996], but it may drop below 2.5 in the lakes characterised by environmental conditions that are not advantageous for the vendace growth [Czerniejewski and Filipiak 2002]. The mean values of the coefficient b of the length-weight relationship of the vendace from the Miedwie, Ińsko, Woświn, and Glinno were similar to data reported by the authors referred to above. It is noteworthy that the exponent b in the Glinno vendace was the lowest (b = 2.44), which indirectly indicated the population being in poor condition. It seems that the poor condition resulted from unfavourable physical and chemical conditions in the lake (the dissolved oxygen content at the depth of 6 m drops to below 1 mg dm 3 during the summer stagnation) and a too low amount of the planktonic food during the period of intensive feeding [Chojnacki et al. 2001]. Knowledge on sex ratio, age structure, and growth rate of a population is an important component of rational fisheries management. Sex ratios in the vendace samples analysed were variable and depended on fish age, females dominating in older age groups. Similar observations were reported by Viljanen [1988] who is of the opinion that males and females contribute equally to the abundance of young age classes, populations consisting of older fishes being dominated by females. For example, as reported by Lehtonen [1981], in the Bothnian Bay vendace population, age groups 2+ 8+ were dominated by females, males being dominant in the age group 1+ only. The samples obtained from lakes Acta Sci. Pol.

Variability of length and weight growth 25 Miedwie, Woświn, and Glinno in different seasons were dominated by females, a slight domination of males (51.7%) being observed in the materials collected from Lake Ińsko. Analysis of the vendace samples collected from lakes Ladoga and Belozero, reported by Koskova [1977], showed a clearly higher contribution of males than females (sex ratio of 1:3). A similar sex ratio, particularly in autumn, was reported Ustyugov [1976] and Vyšegorodcev [1977] in the vendace (Coregonus albula sardinella) from Siberian lakes. Lehtonen [1981] is of the opinion that contribution of males in autumn catches might be only apparently higher than that of females owing to the fact that males stay in the spawning ground longer and thus are more prone to being caught, although their true contribution to the population size is in fact lower. Lehtonen's [1981] observations are confirmed by the testes histology which allows to conclude that the vendace males are capable of multiple ejaculation, and therefore stay longer in the spawning ground [Backiel 1952]. The vendace is generally regarded as a pelagic species which is relatively short lived; individuals aged 1+ to 3+ make up 8090% of commercial catches [Viljanen 1988, Christianus 1995, Czerniejewski and Filipiak 2002]. As suggested by Leopold [1972], individuals aged 2+ should be harvested at the maximum intensity, due to the short life span of the species. Therefore, in accordance with those suggestions, the vendace in the Miedwie, Ińsko, and Woświn were caught with 24 mm mesh size gill nets, which resulted in the fish aged 2+ contributing 89.83, 75.44, and 81.49% to the entire catch, respectively. The high proportion of individuals aged 2+ in the catches resulted from the fact that the vendace grows at the highest intensity during the first three years of life [Bernatowicz et al. 1975]. However, due to changes in fish growth, the use of the same fishing gear or cessation of fishing in a lake may lead to ageing of the exploited part of the population [Ciepielewski 1974a, Winfield et al. 1996]. It seems that the slow-down of vendace growth in Lake Glinno contributed to the unfavourable age structure, observed in the lake (a low proportion 12.55% of the vendace aged 2+ and high proportions of the fish aged 3+ and 4+, 60.78 and 26.67%, respectively). Vendace feeding and growth intensity should be taken into account when planning exploitation of the resources. According to Svärdson [1979] (quoted by Viljanen [1988]), the highest vendace growth increments in Swedish lakes were recorded from March to August, the best growth period in the Finnish lakes being narrowed down to MayJuly [Lehtonen 1981]. On the other hand, Marciak [1962] showed vendace feeding and growth in Polish lakes to be at their highest from April to October, about 70% of the annual increment being obtained within JuneJuly (during the summer stagnation). A seasonal pattern in the vendace length and weight growth was observed also in this study in the Western Pomeranian lakes Miedwie, Ińsko, Woświn, and Glinno. The seasonality is most likely a result of a higher abundance of crustacean zooplankton, dominated by the easily caught cladocerans [Marciak 1962]. Reduction of length and weight increments in autumn is related to a lower feeding intensity and gonad development [Backiel 1952, Marciak 1962]. According to Dąbrowski [1985], the vendace allocates less than 1% of the energy supplied by food to gonad development in Piscaria 6 (34) 2007

26 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska summer, while the amount of energy allocated to gonad development in August- November increases to 1.737.4%. At the same time, the vendace stop feeding during spawning [Czerniejewski and Rybczyk 2002], the energy expenditures being covered by lipids stored in the body [Bernatowicz et al. 1975]. In view of those findings, as well as because the highest protein and lipid contents in the vendace body are typical of July- September [Dąbrowski 1983], the species should be exploited in the period of late summer-early autumn. Vendace populations from various lakes differ greatly in their growth rates. Viljanen [1988], maintains that latitude increases the length of vendace caught in subsequent years of life clearly diminishes, which is probably the result of lower production in these lakes. Bauch [1961], too, suggested that specific environmental conditions play a major role in vendace growth; the highest increments and the longest age are usually found in those lakes rich in crustacean plankton. This opinion was confirmed by studies of Radziej [1973] who stocked Lake Wierzbiczany (maximum depth 21.6 m; good oxygen conditions and abundant food resources) with vendace originating from a slowly growing population of the Masurian Lake Narie. The growth rate of the Wierzbiczany population's first generation was higher than that in Lake Narie. In addition to abundance of the zooplankton, the vendace growth depends also on lake size [Marciak 1970], depth, water transparency and oxygenation during the summer stagnation [Bernatowicz et al. 1975], and the vendace population size. In his overview, Christianus [1995] stated that the highest growth rate is usually typical of the vendace living in small lakes (28120 ha), 2142.5 m deep, that are highly transparent. Growth rates of the Western Pomeranian vendace populations analysed were evaluated with a set of criteria given by Szczerbowski [1978], presented in Fig. 5 against the backdrop of border values of individual growth classes. Among the four populations, it was only the Miedwie and Ińsko vendace that grew fast, while growth of the remaining populations may be considered as mediocre. At the same time, it has to be stressed that the Miedwie vendace aged 2 and 3 grew very fast. Smaller lengths attained in the consecutive years of life by the Glinno and Woświn vendace resulted most probably from unstable and adverse chemical conditions prevailing in those lakes in summer when the fish would usually attain the highest increments. Acta Sci. Pol.

Variability of length and weight growth 27 Total lenght, cm Długość calkowita, cm Fish age Wiek ryb Fig. 5. Assessment of vendace growth rate (according to scale developed by Szczerbowski [1978]) Rys. 5. Ocena tempa wzrostu sielawy (według skali Szczerbowskiego [1978]) Piscaria 6 (34) 2007

28 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska CONCLUSIONS 1. The total length and individual weight of the fishes examined were typical of the vendace caught by 24 mm mesh size gill nets, the ranges of the respective means being 197.3223.8 mm and 67.1103.8 g). 2. The fish population samples obtained from lakes Miedwie, Ińsko, and Woświn showed an advantageous age structure (domination of the fish aged 2+: 89.83; 75.44; and 81.49%, respectively, of all the vendace caught); the Lake Glinno sample was dominated (60.78%) by the fish aged 3+. 3. Condition coefficients and parameters of the length-weight relationship of fish from the lakes studied were similar to those reported in the literature from other vendace lakes. The Lake Miedwie vendace showed the highest, among the population analysed, Fulton condition coefficients and the highest parameters n and K of the total length-individual weight relationship. 4. The vendace population sampled were find to differ greatly in their length and weight growth rates. Judging by the criteria developed by Szczerbowski [1978], the Miedwie and Ińsko vendace showed fast to very fast growth rate, while the growth rates of the Woświn and Glinno vendace were intermediate between medium fast to slow. All the vendace showed very large increments in the first year of life, the increments in the second and third years being much lower and were dropping markedly in the subsequent years. 5. The better growth rate and condition of the vendace in the mesotrophic lakes Miedwie and Ińsko show the lakes to be more amenable to the "vendace management model" than the eutrophic lakes Woświn and Glinno the hypolimnion and metalimnion of which being affected by a considerable oxygen deficiency. REFERENCES Backiel T., 1952. Rozwój gruczołów płciowych sielawy (Coregonus albula) w cyklu rocznym [Development of gonads in the vendace (Coregonus albula) during the year]. Rocz. Nauk. Rol. 64, 271295 [in Polish]. Bauch G., 1961. Die einheimischen Sősswasserfische. Neuman- Verlag. Radebaul und Berlin. Bernatowicz S., 1952. Zagadnienie trafności oznaczania wieku i przyrostu sielawy na podstawie łusek z róŝnych okolic [The problem of reliability of using scales for age and increment determination in the vendace from various areas]. Rocz. Nauk Rol. 65, 311335 [in Polish]. Bernatowicz S., Dembiński W., Radziej J., 1975. Sielawa [The vendace]. PWRiL, Warszawa [in Polish]. Bernatowicz S., Radziej J., 1974. Rozsiedlenie sielawy Coregonus albula (L.) w jeziorach Polski [Distribution of vendace (Coregonus albula (L.)) in Polish lakes]. Acta Hydrobiol. 16 (2), 209219 [in Polish]. Bolgier T., Connolly P.L., 1989. The selection of suitable indices for the measurement and analysis of fish condition. J. Fish. Biol. 34, 171182. Acta Sci. Pol.

Variability of length and weight growth 29 Chojnacki J.C., Turkiewicz J., Śliwińska B., 2001. Zoocenozy planktonowe podszczecińskich jezior Binowo i Glinno (w: Materiały Zjazdowe z okazji jubileuszu 50-lecia Wydziału Rybactwa Morskiego i Technologii śywności. Szczecin 2829 czerwca 2001 [Planktonic communities in the lakes Binowo and Glinno near Szczecin (in: Proceedings of Conference Commemorating 50 Years of the Faculty of Sea Fisheries and Food Technology)]. Szczecin 2829 June 2001. AR, Szczecin [in Polish]. Christianus J., 1995. Age and growth of selected vendace (Coregonus albula L.) populations in Poland. Arch. Hydrobiol. Spec. Issues Adv. Limnol. 46, 97102. Ciepielewski W., 1974a. Względne liczebności roczników sielawy w jeziorze Maróz [Relative abundance of vendace year classes in Lake Maróz]. Rocz. Nauk Rol. 96 H (1), 3147 [in Polish]. Ciepielewski W., 1974b. Selektywność wontonów sielawowych [Selectivity of vendace gill nets]. Rocz. Nauk. Rol. 96 H (1), 1729 [in Polish]. Cydzik D., Kudelska D., Soszka H., 2000. Atlas stanu czystości jezior Polski badanych w latach 19941998 [An Atlas of Water Quality of Polish Lakes Monitored in 19941998]. Bibl. Monit. Śr. IOŚ, Warszawa [in Polish]. Czerniejewski P., Filipiak J., 2001. Występowanie sielawy (Coregonus albula L.) w jeziorach Pomorza Zachodniego [The occurrence of vendace (Coregonus albula L.) in lakes of Western Pomerania]. Kom. Ryb. 5, 37 [in Polish]. Czerniejewski P., Filipiak J., 2002. Biological and morphological characteristics of vendace, Coregonus albula L, from lakes Drawsko and Pełcz. Acta Ichthyol. Piscat. 32 (1), 5369. Czerniejewski P., Rybczyk A., 2002. OdŜywianie się sielawy (Coregonus albula L.) w okresie jesiennym [Feeding of vendace (Coregonus albula L.) in autumn]. Kom. Ryb. 5, 710 [in Polish]. Czerniejewski P., Wawrzyniak W., 2006. Management of vendace (Coregonus albula (L.)) in the lakes of North West Poland in the late twentieth and early twenty-first centuries. Arch. Pol. Fish. 14 (1), 105121. Dąbrowski K., 1983. A note on the energy transformation in body and gonad of Coregonid fish. Arch. Hydrobiol. 97 (3), 406414. Dąbrowski K., 1985. Energy budget of coregonid (Coregonus spp.) fish growth, metabolism and reproduction. OIKOS 45, 358364. Filipiak J., Raczyński M., 2000. Jeziora Zachodniopomorskie. Zarys faktografii [Western Pomeranian Lakes. A Book of Facts]. Wydaw. AR Szczec. [in Polish]. Grudniewski C., 1970. Zakładanie się łusek u sielawy (Coregonus albula L.) [The establishment of scales in vendace (Coregonus albula L.)]. Rocz. Nauk Rol. 92 H (4), 1725 [in Polish]. Jurkowska K., Wierzchowska E., Złoczowska J., 2000. Woda (w: Raport o stanie środowiska w województwie zachodniopomorskim w roku 1999 [Water (in: Report on the status of natural environment in the Province of Western Pomerania)]. M. Landsberg-Uczciwek (ed.). Bibl. Monit. Śr. WIOŚ, Szczecin [in Polish]. Koskova L.A., 1977. Bielozerskaja rjapuška Coregonus sardinella vessicus Drjagin v Saratovskom vodochranilišče [Lake Beloye cisco, Coregonus sardinella vessicus Drjagin in Saratov reservoir]. Vopr. Ikchtiol. 17 (3), 545548 [in Russian]. Lehtonen H., 1981. Biology and stock assessments of Coregonids by the Baltic coast of Finland. Finn. Fish. Res. 3, 3183. Leopold M., 1972. Metodyka prognozy i oceny połowów ryb o krótkim cyklu Ŝyciowym w jeziorach polskich (na przykładzie sielawy Coregonus albula L.) [Methodology of forecasting and assessment of short-lived fish catches in Polish lakes (on the example of vendace, Coregonus albula L.)]. Rocz. Nauk. Rol. 94 H (4), 198 [in Polish]. Marciak Z., 1962. Sezonowe zmiany w odŝywianiu się i wzroście sielawy (Coregonus albula L.) z jez. Pluszne [Seasonal changes in feeding and growth of vendace (Coregonus albula L.) in Lake Pluszne]. Rocz. Nauk. Rol. 81 B (2), 335357 [In Polish]. Piscaria 6 (34) 2007

30 P. Czerniejewski, W. Wawrzyniak, K. Stepanowska Marciak Z., 1970. Podstawa przyrodnicza gospodarki sielawowej (w: Zagospodarowanie jezior sielawą, część II) [Biological basis of vendace management (in: Vendace management in lakes, part II)]. Broszura IRŚ, Olsztyn 39, 813 [in Polish]. Mutenia A., Salonen E., 1992. The vendace (Coregonus albula L.) a new species in the fish community and fisheries of lake Inari. Pol. Arch. Hydrobiol. 39, 797805. Radziej J., 1973. Wpływ środowiska na wolnorosnącą sielawę (Coregonus albula L.) wsiedloną z jeziora Narie do jeziora Wierzbiczany [Environmental effects on the short-lived vendace (Coregonus albula L.) stocked in Lake Wierzbiczany from Lake Narie]. Rocz. Nauk. Rol. 95 H (1), 129146 [in Polish]. Ritterbusch-Nauwerck B., 1995. Condition or corpulence, fitness or fatness: a discussion of terms. Arch. Hydrobiol. Spec. Issues Adv. Limnol. 46, 109112. Sandlund O.T., 1992. Differences in the ecology of two vendace population separated in 1895. Nordic. J. Freshw. Res. 67, 5260. Stanisz A., 1998. Przystępny kurs statystyki w oparciu o program STATISTICA PL na przykładach z medycyny [A STATISTICA PL-based accessible course on medical examples]. Statsoft Polska sp. z o.o., Kraków [in Polish]. Svärdson G., 1979. Speciation of Scandinavian Coregonus. Rep. Inst. Freshw Res. Drottningholm 57, 195. Szczerbowski J.A., 1978. Ocena tempa wzrostu sielawy, siei, leszcza, płoci i sandacza jako podstawy określania wymiaru gospodarczego [Assessment of growth rate of vendace, whitefish, bream, roach, and zander as a basis for commercial size determination]. IRŚ, Olsztyn, 111 [in Polish]. Szlauer B., 1999. Zooplankton-based assessment of the lake Miedwie (North-Western Poland) trophic status. EJPAU, Fisheries 2 (1), www.ejpau.media.pl/fisheries. Szypuła J., Więski K., Rybczyk A., 2001. Ćwiczenia z biologii ryb z wykorzystaniem arkusza MS Excel [Practicals in Fish Biology, using an MS Excel worksheet]. Wydaw. AR Szczec. [in Polish]. Ustyugov A.F., 1976. On the origin of two ecological forms of the Siberian cisco Coregonus albula sardinella from the Yenisey basin. J. Ichthyol. 16 (5), 701711. Viljanen M., 1988. Population dynamics of vendace (Coregonus albula L.) in Finland. University of Joensuu. Publ. Sci. 12, 119. Vyšegorodcev A.A., 1977. Sibirskaja rjapuška Coregonus albula sardinella (Valenciennes) reki Juribej (Bassejn Gydanskogo Zaliva) [The Siberian cisco, Coregonus albula sardinella, from the Yuribej River (Gyda Bay Basin)]. Vopr. Ikchtiol. 17 (1), 1726 [in Russian]. Winfield I.L., Cragg- Hine D., Fletcher J.M., Cubby P.R., 1996. The consvervation ecology of Coregonus albula and C. lavaretus in England and Wales, UK. Conservation of Endangered Freshwater Fish in Europe, 213223. Wołos A., Mickiewicz M., 1998. Charakterystyka jezior oraz gospodarki sielawą i sieją (w: Gospodarka Koregonidami. Uwarunkowania i efektywność) [Lake characteristics and vendace and whitefish management (in: Coregonid management. Conditions and efficiency]. IRŚ, Olsztyn [in Polish]. Wootton R.J., 1996. Ecology of Teleost Fishes. Chapman and Hall, London. ZRÓśNICOWANIE SZYBKOŚCI WZROSTU DŁUGOŚCI I MASY SIELAWY Coregonus albula (L.) Z WYBRANYCH JEZIOR POMORZA ZACHODNIEGO Streszczenie. Sielawy pozyskano w okresie wiosennym, letnim i jesiennym w latach 19992000 z 4 zachodniopomorskich jezior: Miedwie, Ińsko, Woświn i Glinno, róŝniących się poziomem trofii i cechami morfometrycznymi. Określono zróŝnicowanie masy jednostkowej, długości Acta Sci. Pol.

Variability of length and weight growth 31 całkowitej, kondycji oraz tempa wzrostu ryb z poszczególnych akwenów. Sielawy z mezotroficznych jezior: Miedwie i Ińsko charakteryzowały się korzystniejszymi parametrami kondycji i wyŝszym tempem wzrostu długości i masy w porównaniu do sielaw ze zeutrofizowanych jezior: Woświn i Glinno. Słowa kluczowe: jeziora: Glinno, Ińsko, Miedwie, Woświn, kondycja, sielawa, struktura wieku, tempo wzrostu Accepted for print Zaakceptowano do druku: 25.07.2008 Piscaria 6 (34) 2007