Faculty of Social and Life Sciences Biology Arne N. Linløkken Population ecology of perch (Perca fluviatilis) in boreal lakes DISSERTATION Karlstad University Studies 2008:21 Arne N. Linløkken Population ecology of perch (Perca fluviatilis) in boreal lakes Karlstad University Studies 2008:21 Arne N. Linløkken. Population ecology of perch (Perca fluviatilis) in boreal lakes DISSERTATION Karlstad University Studies 2008:21 ISSN 1403-8099 ISBN 978-91-7063-180-1 © The Author Distribution: Faculty of Social and Life Sciences Biology 651 88 Karlstad 054-700 10 00 www.kau.se Printed at: Universitetstryckeriet, Karlstad 2008 Population ecology of perch (Perca fluviatilis) in boreal lakes This thesis is based on the following eight papers, which are referred to by their Roman numerals. List of papers/publications I. Linløkken, A. 2003. Temperature dependence of Eurasian perch (Perca fluviatilis). pp 75-76. In: T.P. Barry, and J. A. Malison (eds.) Percis III: The Third International Percid Fish Symposium, University of Wisconsin Sea Grant Institute, Madison Wisconsin. II. Linløkken, A. & Haugen, T. 2006. Density and temperature dependence of gill net catch per unit effort for perch, Perca fluviatilis, and roach, Rutilus rutilus. Fisheries Management and Ecology, 13: 261-269. III. Linløkken, A., Bergman, E. & Greenberg, L. (2008). Effect of temperature and group size on swimming speed and capture rate of perch (Perca fluviatilis) and roach (Rutilus rutilus). Manuscript IV. Linløkken, A. 1988. Vertical distribution of brown trout (Salmo trutta) and perch (Perca fluviatilis) in an acidified lake. Water, Air, and Soil Pollution 40: 203-213. V. Linløkken, A., Kleiven, E. & Matzow, D. 1991. Population structure, growth and fecundity of perch (Perca fluviatilis) in an acidified river system in southern Norway. Hydrobiologia 220: 179-188. VI. Linløkken, A. & Seeland, P. A. H. 1996. Growth and production of perch (Perca fluviatilis L.) responding to biomass removal. Ann. Zool. Fennici 33: 427-435. VII. Linløkken, A., Bergman, E. & Greenberg, L. (2008) Environmental correlates of population variables of perch (Perca fluviatilis) in boreal lakes. Environmental biology of fishes (in press). VIII. Linløkken, A. & Hesthagen, T. (2009) Environmental effects on size and growth of perch (Perca fluviatilis) and roach (Rutilus rutilus) in four small boreal lakes. Manuscript Abstract I studied the effects of temperature, pH, competition and predation on Eurasian perch (Perca fluviatilis) in 30 lakes in Norway during 1981-2001. The study lakes were situated in two different areas in southern Norway; four lakes in Aust- Agder county in southernmost Norway were explored during 1981-1984 and 26 lakes in Hedmark county in south-eastern Norway were investigated during 1992-2001. The study lakes varied considerably in pH, temperature, fish species composition, and perch abundance and size composition. In addition to field surveys, behavioural studies of perch were conducted at Karlstad University in 2006-2007. The field studies revealed that temperature affected recruitment of perch as strong year-classes of perch generally occurred in summers with high temperatures. Temperature also affected perch behaviour as indicated by the low gillnet catches (CPUE) of perch at low temperature. This effect on CPUE was also supported by results from the aquaria experiments, where swimming and feeding activity of perch was low at low temperature. In a study of four lakes, growth was positively related to August air temperature in the lake with an allopatric perch population, but not in three lakes where perch occurred sympatrically with roach. pH also affected recruitment. In the four lakes in Aust-Agder, one strong year- class of perch occurred in all lakes in a year with especially high pH in spring and early summer. Adult mortality was also affected by pH, as old perch were less abundant in lakes with late spring pH=5.5-5.8 than in lakes with pH<5.5 and pH>5.8. The size and growth of adult perch were negatively affected by low pH, whereas abundance of large, potentially predatory perch was positively related to pH. The field studies indicated that roach influence perch populations. When coexisting with roach, perch were mainly littoral. In lakes where roach dominated (by number), there was no growth – temperature correlation, but there was such a correlation in a lake without roach. In lakes with sympatric roach, age-specific weight of perch and the growth of 2+ perch were negatively related to the proportion of roach in the gillnet catches. In the aquaria experiments, swimming and feeding activity of perch were lower than that of roach at all temperatures tested, and the difference was most pronounced at 4 and 8 °C. The aquaria experiments indicated that perch had a lower feeding efficiency and that they generally occupied positions closer to the bottom than roach. Introduction Understanding the distribution and abundance patterns of fish has been the focus of much research in population ecology. The limits of distribution often indicate where environmental conditions are becoming too difficult for the organisms to survive. By environmental conditions we generally refer to abiotic factors like temperature, acidity and salinity (Begon et al. 1996), which are to be distinguished from biotic factors like competition and predation, which can affect the distribution and abundance of species as well. The distribution patterns of freshwater fishes are also related to the abilities of fish to invade new areas. The purpose of this dissertation is to identify biotic and abiotic factors that are affecting the abundance, activity and growth of perch. Specifically, I concentrate on four factors, temperature, pH, density and roach. Distribution of perch Eurasian perch is widely distributed in the temperate zone of Eurasia, from the British Isles to east Siberia in Russia. The distribution is in part limited by perch’s low tolerance for salinity, which makes it dependent on freshwater passages to be able to increase its distribution. Nevertheless, the Eurasian perch has a broad distribution, much broader than either the congeneric North American yellow perch (Perca flavescens , Mitchill) or the Asian Balkhash perch (Perca schrenki, Kessler) (Craig 2000). In Norway, perch is found in two geographic regions, the south-east and the north-east (Huitfeldt - Kaas 1918). Perch entered both regions from the east, from present-day Sweden to the south-eastern area, and from present-day Finland to the north-eastern area. Because perch cannot live in marine environments, it was never able to enter the river systems in western Norway. Perch from the Ancylus Sea, which covered the present-day Baltic Sea, entered river systems running south and east in south-eastern Norway. In Sweden, perch is the most common freshwater fish species (Lundberg 1899), often coexisting with pike (Esox lucios) and roach (Rutilus rutilus) within its natural distribution. Perch has, like several other fish species, received help from humans to enter lakes and tarns outside their natural distribution, and in Norway it is found in high elevation lakes, up to 1000 m a. s.l., often coexisting with brown trout (Salmo trutta) (Huitfeldt - Kaas 1918). Perch is a popular species for angling and ice-fishing (Aas 1996), but exploitation is often low compared to its reproductive capacity. Many lakes are densely populated with small stunted individuals that seldom exceed 20 cm (Alm 1946, LeCren 1947). Growth may increase after removal of perch, due to reduced intraspecific competition (LeCren 1958, Craig 1980). Growth and biomass of perch are also negatively affected by total fish biomass and by the presence of other species, especially roach, suggesting that interspecific interactions negatively affect growth, recruitment and survival of perch (Persson 1997, Byström et al. 1998, Holmgren & Appelberg 2001). As poikilothermic organisms, metabolic processes in fish are strongly dependent on external temperature (Evans & Claiborne 2006), which in turn affects swimming and feeding activity. The optimum temperature for perch growth is 23 °C (Melard et al. 1996), although growth relationships with temperature may vary geographically due to local adaptation (Mandiki et al. 2004). Both perch growth and recruitment have been shown to be positively related to temperature (LeCren 1958, Neuman 1976, Tolonen et al. 2003), and negatively related to latitude (Heibo et al. 2005), the latter relationship undoubtedly related to the shorter annual period with temperature suitable for growth at high latitudes. Year-class strength has been shown to be regulated by first winter survival, which is positively related to first summer growth (Karås 1996). Perch activity is low at low water temperature, and Neuman (1979) found that perch activity had a stronger relationship with temperature than the activity of roach in the Baltic Sea. Since the 1960s airborn pollution has affected freshwater habitats through acid precipitation in large areas in Norway (Drabløs & Tollan 1980, Sevaldrud & Muniz 1980) and elsewhere in Fennoscandia (Appelberg et al. 1989, Rask et al. 1995a, Tammi et al. 2003), reducing and even exterminating populations of freshwater fish (Hesthagen 1986, Rosseland et al. 1986, Hesthagen et al. 1999) as well as some of their invertebrate prey (Fjellheim & Raddum 2001, Halvorsen et al. 2001). The highest depositions of acid components in precipitation are received in the southernmost and in south-eastern Norway, one of the regions where