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Arch. Pol. Fish. (2011) 19: 259-265DOI 10.2478/v10086-011-0032-5 RESEARCH ARTICLE
Marking and return method for evaluating the effects of stocking larval
vendace, Coregonus albula (L.), into Lake Wigry in 2000-2001
Received – 12 April 2011/Accepted – 10 October 2011. Published online: 30 December 2011; Inland Fisheries Institute in Olsztyn, Poland Pawe³ Poczyczyñski, Krzysztof Koz³owski, Jacek Koz³owski, Andrzej Martyniak
Abstract. In 2000 and 2001, larval vendace, Coregonus
Introduction
albula (L.), were marked and released into Lake Wigry. Thelarvae were immersed in alizarin red S. Of the 19.2 million Marking and return studies are one of the best methods vendace larvae released in 2000, 2 million were marked(10.4% of the overall number of fish released), and in 2001 of for investigating various aspects of the biology of many the 18.8 million fish released, 7 million were marked (47.8%).
fish species. They are particularly useful for identifying In subsequent years, otoliths were excised from caught population dynamics, migration research, and deter- vendace and the number of them with alizarin marks was mining stocking effectiveness (Everhart et al. 1975, determined. It was assumed that all unmarked specimens Mills and Beamish 1980, Babaluk and Cambell 1987, came equally from natural spawning and stocking assuming Hilborn et al. 1990, Meunier 1994, Secor and Houde that survival is equal in both forms of recruitment. It wasconfirmed that 82.4% of the vendace caught from the 2000 1995). Techniques for marking fish have improved generation originated from stocking, while this figure was vastly in the past fifty years. Earlier methods (e.g., clip- 64.2% of all specimens caught from the 2001 generation.
ping fins, freezing, attaching external tags) are increas- Lake Wigry hosts the most abundant vendace population in ingly being replaced by more modern methods such as Poland, and this stock spawns on a massive scale annually.
attaching PIT or microtags with binary or alphanumeric Even so, the study described herein provides evidence of just codes. However, these methods cannot be used to mark how important systematic stocking is to the maintenance ofthe vendace population in this lake.
larval fish because of their small sizes. Evaluating theeffects of stocking larvae was basically impossible until Keywords: vendace, otoliths, alizarin red S, marking and
a method was developed for marking juvenile fish on return method, marking coefficient, stocking a mass scale using, among other methods, chemicalagents or thermal shock. Marking is the only methodthat provides reliable data on the success of reinforcingnatural reproduction through stocking in a given basin(Koz³owski 2007). Intense research into marking fishusing chemicals was the begun in the 1960s. Two dis-tinctively different methods were developed. One ofthese methods uses strontium chloride. As strontium is P. Poczyczyñski [+], K. Koz³owski, J. Koz³owski, A. Martyniak a calcium analogue, it is built into the bone structures Department of Fish Biology and Pisciculture of fish (Ophell and Judd 1968, Bagenal et al. 1973).
Faculty of Environmental Sciences and Fisheries Otoliths are analyzed using atomic mass spectrometry University of Warmia and MazuryOczapowskiego 5, 10-719 Olsztyn, Poland (AMS) and atomic absorption spectrometry (AAS). The Tel. +48 89 523 32 62, e-mail: k.kozlowski@uwm.edu.pl second, far more popular marking method is to use fluorochromes, which form chelate complexes with cal- on March 10, 2000. Alizarin red S, was used to mark cium ions that are built into skeletal and otolith struc- two-day-old larvae. The fish were immersed in an tures. Markings are visible under ultraviolet light since alizarin solution (Tsukamoto 1988, Nagiêæ et al.
the calcium-fluorochrome complexes emit fluorescent 1995). The water supply was shut off to a tank with light (Beverander and Goss 1962, Monaghan 1993).
a volume of 800 dm3 in which there were 2 million The abundance of the family Coregonidae in Po- larval vendace; then 170 g of alizarin was dissolved land has been dependent on stocking for many years, in the water (concentration 200 ppm). The water and until a certain time, the number of lakes in which temperature was 5.3°C. During marking, which these fish occurred increased as a result of the imple- lasted for 4 hours, the amount of dissolved oxygen in mentation of various management strategies. In the the water was monitored systematically. After 2 1958-1969 period, the number of coregonid lakes hours, the oxygen concentration decreased to 43.8%, reached 420, which comprised 62% of the total sur- which is why the water in the tank was supplemented face area of Polish lakes. Later, disadvantageous en- to a volume of about 1000 dm3. After four hours of vironmental changes, decreased stocking intensity, immersion, water flow was restored in the tank. No changes in management strategies, and intense fish- increased mortality was noted during marking. It can eries led to smaller Coregonidae populations, and take up to 14 days for alizarin to chelate with calcium even their extinction in some basins (Bniñska 1998, ions. To verify the effectiveness of the marking and Wo³os 1998a, 1998b, Wo³os and Mickiewicz 1998, determine its quality, 100 vendace larvae were reared for two weeks in an aquarium. Then otolithswere excised from 36 fish, mounted with Entellan Lake Wigry, with a surface area of 2186.7 ha, is Neu, and viewed under a Nikon OPTIPHOT 2 in the tenth largest lake in Poland. It is of a mixed UV-B at a magnification of 800x. The markings were trough–morena origin, with a highly varied shoreline legible on all of the otoliths viewed. A second mark- and bottom topography. There are 18 islands in the ing was performed in the same hatchery on March 19 lake with a total surface area of 68.4 ha. The maxi- and 20, 2001 when 9 million vendace larvae were mum depth is 73 m, which makes Lake Wigry the marked. Because of the large number of larvae and fifth deepest lake in Poland. The population of ven- the oxygen deficit in the water that occurred in the dace, Coregonus albula (L.), in Lake Wigry is proba-bly the most abundant in Poland. Its biomass is previous year, this time marking was performed in estimated at 222 kg ha-1 (Œwierzowski 1999). Cur- two rounds and in a greater number of tanks. On the rently, annual catches range from 10 to 20 tons. The first day, marking was conducted in two tanks, one aim of the present study was to evaluate the effects of with a volume of 650 dm3 and the second with a vol- stocking Lake Wigry in 2000 and 2001 with marked ume of 450 dm3. The water temperature was 5.9°C.
larvae using the stocking-return method. In order to Again, alizarin S was used at a concentration of 225 perform calculations, the marking coefficient (MC), ppm. Marking was completed after three hours. The which is described in the Materials and methods sec- oxygen content during the procedure did not de- crease below 9.0 mg dm-3, which was about 74% sat-uration. On the second day, marking was performedin one tank with a volume of 650 dm3 and in threewith a volume of 450 dm3. The water temperature Materials and Methods
was 6.3°C. Immersion time in the alizarin solution ata concentration of 200 ppm was three hours. The The stocking material originated from vendace concentration of oxygen in the water remained above spawners caught in Lake Wigry. The eggs were incu- 71%. After the conclusion of marking, 100 vendace bated at a hatchery (Wigierski National Park, Po- larvae from each tank were held for rearing. After 16 land). The first marking of larvae vendace was done days the otoliths were excised and examined using Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).
the same procedures applied to the fish in 2000.
required introducing the marking coefficient param- Brightly shiny marks were confirmed in all 124 of the eter (P), which expresses the ratio of fish marked to otoliths examined. In 2000, Lake Wigry was stocked all vendace produced through artificial breeding and with 19.2 million vendace larvae, of which 10.4% released into a given lake. In 2000 this parameter had been marked. In the following year, 18.8 million was 9.61 (100%:10.4%), while in 2001 it was 2.09 larval vendace were released, of which 47.8% were Assuming that mortality in marked and un- The material analyzed came from commercial marked hatch is equal (Czerkies 1998), it was possi- and experimental catches conducted in 2002-2005 ble to calculate the percentage of catches that originated from stocking. To do this, the marking co- efficient was multiplied by the share of marked fish Number of otoliths obtained from the 2000 and 2001 Of the total number of fish stocked into Lake Wigryin 2000, otoliths from 312 specimens were read, The otoliths examined came from fish of the while in 2001, the otoliths from 346 vendace speci- 2000 and 2001 generations. The age of the fish was determined based on scale readings. The otoliths chosen for examination were mounted on glass slides Number of otoliths analyzed microscopically from vendace with Entellan Neu. After a week they were, polished from the 2000 and 2001 generations by age groups with fine-grade 1000 and 1200 waterproof sandpa-per. One-sided polishing was applied to the otoliths of young fish aged 1+ to 3+. The otoliths of older fish were polished on both sides. During polishing, the otoliths were examined under a light microscope at a magnification of 400x. Polishing was stopped oncethe center of the otolith, where the mark had been re- The best quality marks were noted in fish aged corded, was exposed. Processing the material re- 1+. In older fish, while the marks on the otoliths were quired precision and great care since the otoliths are less visible, they were still distinct enough to exclude fragile and are easily damaged. Additionally, the identification error. Among the 312 otoliths exam- otolith center is convex, and excessive polishing can ined from the 2000 generation, 27 (8.6%) had dis- cause it to collapse. During polishing, 112 otoliths tinct alizarin marks, with the most (22) noted in the were damaged, including all of those from fish aged 2+ age group. This comprised 9% of the otoliths ana- 5+, 15 from fish aged 4+, 12 from fish aged 3+, and lyzed in this age group. Among the fish aged 1+ and 72 from fish aged 2+. Of the remaining 734 otoliths, 2+ examined, marked otoliths were noted in 2 and 3 76 were illegible, thus 658 otoliths were used to ana- fish or in 1.8 and 5.8%, respectively (Table 2). Of the lyze the alizarin marks in legible otolith centers. The 346 otoliths examined from the 2001 generation, prepared materials were examined under a Nikon 109 alizarin marks were confirmed (31.5%). Simi- OPTIPHOT 2 microscope in UV-B at a magnification larly, the most marks were noted in fish aged 2+ (85 individuals, which was 37.9% of the whole sample).
Estimating the effects of stocking during which The number of marked otoliths from fish aged 1+ only a portion of the material released was marked and 3+ was 22 and 2, which was 30.8 and 16.7%, Koz³owski 2007), which is nearly twice the average amount of stocking material released other Polish lakes at 3860 larvae per ha-1 (Wo³os 1998b). Larval vendace were released into Lake Wigry systemati- cally, and the stocking frequency coefficient was 1, which indicates annual stocking. According to data published by Leopold (1998a), coefficient values above 0.7 were noted in only 2.6% of the lakes ana- The statistical analysis of vendace stocking and catches in Lake Wigry did not indicate significant de- Figure 1. Share (%) marked larval vendace in the entire sample pendencies between these variables (Koz³owski 2007). In this study, the analyses of correlations be-tween stocking and catches one and two years follow- respectively, of the analyzed individuals in these age ing stocking did not exhibit any significant statistical correlations between these variables. No statistically The proportions between the share of marked significant dependencies in the analysis of correla- larvae released into the lake and the share of marked tions between stocking, taking into consideration the otoliths in the material collected were similar. In the two and three year moving variables, and catches generation from 2000, the share of marked larvae were noted. While the lack of statistically significant was 10.4%, and the share of marked otoliths was dependencies between stocking and catches of ven- 8.6%. Based on the proportion of marked fish to the dace have been confirmed in many lakes, this does number of fish caught, 82.4% of the vendace caught not provide evidence that stocking is ineffective. The came from stocking. In the 2001 generation, marked lack of correlations can be explained by the greatvariability in the amounts of stocking material re- larvae comprised 47.8%, and the share of marked leased, breaks in stocking, the application of various otoliths was 31.5%. The share of vendace from the kinds of stocking materials, the success of natural spawning, and, as is the case in Lake Wigry, low lev-els of exploitation (Koz³owski 2007). According toa study by Leopold (1998b) conducted on 60 ven- Discussion
dace lakes in Poland, the mean number of larvae re-leased that corresponded to 1 kg of commercial Stocking Polish lakes with coregonids has been the vendace ranged from 720 to 2,138 individuals de- focus of many studies of the effectiveness of this mea- pending on the basin. During this study period, Lake sure as well as the general principles for the manage- Wigry, with 1,273 larvae released per kg of vendace ment of these species (Falkowski 1998). In Poland, caught, was classified as a lake with medium stock- the most common type of vendace stocking material is freshly-hatched larvae. The share of vendace sum- Applying fluorescent markers using the immer- mer fry in stocking is slight and, according to Wo³os sion technique is a relatively simple procedure that is (1998a) it comprises barely 0.4% of all the stocking possible to perform in virtually any hatchery. Its ad- material released into 123 basins that he analyzed.
vantages include the low cost and the possibility of Lake Wigry has been and continues to be stocked ex- marking large numbers of fish in early developmen- clusively with larvae. The average number of larvae tal stages. While the marking procedure is performed released into this lake in the 1977-2004 period was without any great difficulty, reading fish otoliths re- 15.8 million larvae annually (7241 larvae ha-1; quires sacrificing the fish and specialist equipment Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).
such as a fluorescent microscope. Preparing the oto- was stocked with two types of vendace stocking mate- liths is also a labor-intensive task. Additionally, oto- rial: hatch (300,000 individuals) and summer fry liths are often damaged while being polished, which (15,000 individuals). The larvae were marked with excludes them from further analysis. While prepar- alizarin, while the summer fry were marked with tetra- ing 423 otoliths for analysis, Czerkies (1997, 1998) cycline. Of the 170 fish caught, the author confirmed discarded 233 as damaged ones with illegible cen- alizarin marks in 4.5% of the individuals, while no ters; this comprised more than 50% of the material marks were noted in the other individuals, which was that had been collected. The number of damaged explained by the strong autofluorescent, amphoric otoliths in the current study was significantly lower; otolith centers. However, these did fish exhibit daily because the likelihood that the otolith would be dam- increment patterns on their otoliths that are typical of aged was high, the second otolith was always col- stocking and which indicated that they originated In experiments with marking fish later released Stocking larval vendace marked with alizarin red into open basins, an important issue is the perma- S into Lake Werbellin (Germany) showed how effec- nence of the markings. The results of the current study tive natural spawning is there (Eckmann et al. 1998).
indicate that alizarin marks remain visible in fish oto- Among the 1072 individuals examined, only 1.3% of liths for many years. Tsukamoto (1995) observed in the fish had marked otoliths. In the studies in Lake Pagrus major (Temminck and Schlegel) marks five Wigry indicated quite the opposite situation. The years after marking, while in grayling, Thymallus share of marked fish was higher at 8.6% in the 2000 thymallus (L.), marks were confirmed to be at least generation and 31.5% in the 2001 generation, which, two years old, and brown trout, Salmo trutta L., re- when recalculated, indicated a high share of fish tained otolith marks for three years (Nagiêæ et al.
1995). In the case of vendace from lake Wigry, otolith from stocking in the catches at 82.4% and 64.2%.
marks were noted in fish aged 3+, but it is plausible The results of the study described above clearly that the marks remain visible for at least four years.
confirm the view that the occurrence of vendace in Studies conducted to date on fish markings indi- Polish lakes is mainly because of stocking programs.
cate that as time passes the marks in a certain num- Even the exceptionally abundant population of this ber of fish fade. According to Muth and Bestegen species in Lake Wigry, despite its effective natural re- (1991) this phenomenon occurs in the youngest fish production, is supported largely by stocking pro- and is linked to ultraviolet solar radiation. However, grams. It is plausible that if stocking were Eckmann et al. (1996), in a study of larval vendace discontinued, vendace would disappear from this marked with alizarin did not report the subsequent loss of marks, and in a control group of vendace heldfor a year, all of the fish retained markings.
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Marking and return method for evaluating the effects of stocking larval vendace, Coregonus albula (L.).
Streszczenie
Zastosowanie metody znakowanie – zwroty do oceny efektów zarybieñ jeziora Wigry
larwami sielawy, Coregonus albula (L.) w latach 2000-2001
W roku 2000 i 2001 przeprowadzono znakowanie w alizary- naturalnego tar³a, jak i z zarybieñ, przyjmuj¹c podobn¹ prze- nie S larw sielawy, Coregonus albula (L.), przeznaczonych do ¿ywalnoœæ ryb z obu Ÿróde³ rekrutacji. Stwierdzono, ¿e zarybienia jeziora Wigry. Spoœród 19,2 mln larw sielawy w od³owach sielaw z pokolenia 2000 ryby z zarybieñ stano- w 2000 roku poznakowano 2 mln (10,4% ca³kowitej iloœci wi³y 82,4%, a z pokolenia 2001 64,2% wszystkich od³owio- wpuszczonych ryb) a w roku nastêpnym z 18,8 mln ryb, po- nych osobników. Jezioro Wigry jest zbiornikiem o najwiêkszej znakowano 7 mln (47,8%). W kolejnych latach od wszystkich liczebnie populacji sielawy w Polsce, w którym co roku odby- od³owionych sielaw pobierano otolity i ustalano ile z nich po- wa siê jej masowe tar³o. Jednak wyniki opisywanych badañ siada³o znaczek alizarynowy. Za³o¿ono, ¿e wszystkie osobniki œwiadcz¹ o niezbêdnoœci systematycznych zarybieñ dla utrzy- niepoznakowane pochodz¹, w równym stopniu, tak z

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