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PERCIS II
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Preface. — Ann. Zool. Fennici 33: 303–304. (Abstract not available).
Preface. — Ann. Zool. Fennici 33: 303–304. (Abstract not available).
PERCIS II
Second International Percid Fish Symposium, Vaasa, Finland, 21–25 August 1995.
Working group reports
Rösch, R., Kangur, A., Kangur, K., Krämer, A., Rab, R., Schlechta, V., Tapaninen, M. & Treasurer, J. 1996: Minutes of the Percis II working group. Ruffe (Gymnocephalus cernuus). — Ann. Zool. Fennici 33: 305–308. (Abstract not available).
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Kjellman, J., LeCren, D., Smith, P. & Green, D. M. 1996: Minutes of the Percis II working group. Population dynamics of percid fish. — Ann. Zool. Fennici 33: 309–312. (Abstract not available).
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Loew, E., Egloff, M. & Wahl, C. 1996: Minutes of the Percis II working group. Early life stages of percid fishes. — Ann. Zool. Fennici 33: 313–314. (Abstract not available).
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Neuman, E., Roseman, E. & Lehtonen, H. 1996: Minutes of the Percis II working group. Determination of year-class strength in percid fishes. — Ann. Zool. Fennici 33: 315–319. (Abstract not available).
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Early life stages
Frankiewicz, P., Dabrowski, K. & Zalewski, M. 1996: Mechanism of establishing bimodality in a size distribution of age-0 pikeperch, Stizostedion lucioperca (L.) in the Sulejow Reservoir, Central Poland. — Ann. Zool. Fennici 33: 321–327.
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Urho, L. 1996: Habitat shifts of perch larvae as survival strategy. — Ann. Zool. Fennici 33: 329–340.
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Roseman, E. F., Taylor, W. W., Hayes, D. B., Haas, R. C., Knight, R. L. & Paxton, K. O. 1996: Walleye egg deposition and survival on reefs in Western Lake Erie (USA). — Ann. Zool. Fennici 33: 341–351.
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Mehner, T., Schultz, H., Bauer, D., Herbst, R., Voigt, H. & Benndorf, J. 1996: Intraguild predation and cannibalism in age-0 perch (Perca fluviatilis) and age-0 zander (Stizostedion lucioperca): Interactions with zooplankton succession, prey fish availability and temperature. — Ann. Zool. Fennici 33: 353–361.
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Kjellman, J., Hudd, R. & Urho, L. 1996: Monitoring 0+ perch (Perca fluviatilis) abundance in respect to time and habitat. — Ann. Zool. Fennici 33: 363–370.
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Karås, P. 1996: Basic abiotic conditions for production of perch (Perca fluviatilis L.) young-of-the-year in the Gulf of Bothnia. — Ann. Zool. Fennici 33: 371–381.
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Hudd, R., Kjellman, J. & Urho, L. 1996: The increase of coincidence in relative year-class strengths of coastal perch (Perca fluviatilis L.) stocks in the Baltic Sea. — Ann. Zool. Fennici 33: 383–387.
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Population dynamics
Sarvala, J. & Helminen, H. 1996: Year-class fluctuations of perch (Perca fluviatilis) in Lake Pyhäjärvi, Southwest Finland. — Ann. Zool. Fennici 33: 389–396.
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Machiels, M. A. M. & Wijsman, J. 1996: Size-selective mortality in an exploited perch population and the reconstruction of potential growth. — Ann. Zool. Fennici 33: 397–401.
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Jansen, W. A. 1996: Plasticity in maturity and fecundity of yellow perch, Perca flavescens (Mitchill): comparisons of stunted and normal-growing populations. — Ann. Zool. Fennici 33: 403–415.
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Dubois, J.-P., Gillet, C., Bonnet, S. & Chevalier-Weber, Y. 1996: Correlation between the size of mature female perch (Perca fluviatilis L.) and the width of their egg strands in Lake Geneva. — Ann. Zool. Fennici 33: 417–420.
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Lappalainen, J., Lehtonen, H., Böhling, P. & Erm, V. 1996: Covariation in year-class strength of perch, Perca fluviatilis L. and pikeperch, Stizostedion lucioperca (L.). — Ann. Zool. Fennici 33: 421–426.
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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.
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Karjalainen, J., Lehtonen, H. & Turunen, T. 1996: Variation in the relative year-class strength of pikeperch, Stizostedion lucioperca (L.), in two Finnish lakes at different latitudes. — Ann. Zool. Fennici 33: 437–442.
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Interactions
Rudstam, L. G., Green, D. M., Forney, J. L., Stang, D. L. & Evans, J. T. 1996: Evidence of interactions between walleye and yellow perch in New York State lakes. — Ann. Zool. Fennici 33: 443–449.
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Salonen, S., Helminen, H. & Sarvala, J. 1996: Feasibility of controlling coarse fish populations through pikeperch (Stizostedion lucioperca) stocking in Lake Köyliönjärvi, SW Finland. — Ann. Zool. Fennici 33: 451–457.
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Winfield, I. J., Adams, C. E. & Fletcher, J. M. 1996: Recent introductions of the ruffe (Gymnocephalus cernuus) to three United Kingdom lakes containing Coregonus species. — Ann. Zool. Fennici 33: 459–466.
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Rösch, R. & Schmid, W. 1996: Ruffe (Gymnocephalus cernuus L.), newly introduced into Lake Constance: preliminary data on population biology and possible effects on whitefish (Coregonus lavaretus L.). — Ann. Zool. Fennici 33: 467–471.
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Kangur, K. & Kangur, A. 1996: Feeding of ruffe (Gymnocephalus cernuus) in relation to the abundance of benthic organisms in Lake Võrtsjärv (Estonia). — Ann. Zool. Fennici 33: 473–480.
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Peltonen, H., Rita, H. & Ruuhijärvi, J. 1996: Diet and prey selection of pikeperch (Stizostedion lucioperca (L.)) in Lake Vesijärvi analysed with a logit model. — Ann. Zool. Fennici 33: 481–487.
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Radke, R. J. & Eckmann, R. 1996: Piscivorous eels in Lake Constance: can they influence year class strength of perch?. — Ann. Zool. Fennici 33: 489–494.
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Van Densen, W. L. T., Ligtvoet, W. & Roozen, R. W. M. 1996: Intra-cohort variation in the individual size of juvenile pikeperch, Stizostedion lucioperca, and perch, Perca fluviatilis, in relation to the size spectrum of their food items. — Ann. Zool. Fennici 33: 495–506.
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Boisclair, D. & Rasmussen, J. B. 1996: Empirical analysis of the influence of environmental variables associated with lake eutrophication on perch growth, consumption, and activity rates — Ann. Zool. Fennici 33: 507–515.
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Rask, M., Järvinen, M., Kuoppamäki, K. & Pöysä, H. 1996: Limnological responses to the collapse of the perch population in a small lake. — Ann. Zool. Fennici 33: 517–524.
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Fish stock management
Lehtonen, H., Hansson, S. & Winkler, H. 1996: Biology and exploitation of pikeperch, Stizostedion lucioperca (L.), in the Baltic Sea area. — Ann. Zool. Fennici 33: 525–535.
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Smith, P. A., Leah, R. T. & Eaton, J. W.: Removal of pikeperch (Stizostedion lucioperca) from a British Canal as a management technique to reduce impact on prey fish populations. — Ann. Zool. Fennici 33: 537–545.
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Setälä, J., Salmi, P., Muje, P. & Käyhkö, A. 1996: The commercial utilization of small perch (Perca fluviatilis L.) in Finnish inland fisheries. — Ann. Zool. Fennici 33: 547–551.
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Ruuhijärvi, J., Salminen, M. & Nurmio, T. 1996: Releases of pikeperch (Stizostedion lucioperca (L.)) fingerlings in lakes with no established pikeperch stock. — Ann. Zool. Fennici 33: 553–567.
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Nyberg, P., Degerman, E. & Sers, B. 1996: Survival after catch in trap-nets, movements and growth of the pikeperch (Stizostedion lucioperca) in Lake Hjälmaren, Central Sweden. — Ann. Zool. Fennici 33: 569–575.
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Johnson, B. M., Vogelsang, M. & Stewart, R. S. 1996: Enhancing a walleye population by stocking: effectiveness and constraints on recruitment. — Ann. Zool. Fennici 33: 577–588.
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Colby, P. J. & Baccante, D. A. 1996: Dynamics of an experimentally exploited walleye population: sustainable yield estimate. — Ann. Zool. Fennici 33: 589–599.
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Baccante, D. A. & Colby, P. J. 1996: Harvest, density and reproductive characteristics of North American walleye populations. — Ann. Zool. Fennici 33: 601–615.
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Saura, A. 1996: Use of hot branding in marking juvenile pikeperch (Stizostedion lucioperca) — Ann. Zool. Fennici 33: 617–620.
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Turunen, T. 1996: The effects of twine thickness on the catchability of gillnets for pikeperch (Stizostedion lucioperca (L.)). — Ann. Zool. Fennici 33: 621–625.
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Aquaculture
Steffens, W., Geldhauser, F., Gerstner, P. & Hilge, V. 1996: German experiences in the propagation and rearing of fingerling pikeperch (Stizostedion lucioperca). — Ann. Zool. Fennici 33: 627–634.
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Tamazouzt, L., Dubois, J.-P., Fontaine, P., Capdeville, B. & Terver, D. 1996: Zootechnical performance and body composition of Perca fluviatilis pelleted diet in a floating cage:Effect of daily ration. — Ann. Zool. Fennici 33: 635–641
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Mélard, C., Baras, E., Mary, L. & Kestemont, P. 1996: Relationships between stocking density, growth, cannibalism and survival rate in intensively cultured larvae and juveniles of perch (Perca fluviatilis). — Ann. Zool. Fennici 33: 643–651.
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Grignard, J. C., Mélard, C., Baras, E., Poirier, A., Philippart, J. C. & Bussers, J. C. 1996: Occurrence and impact of Heteropolaria sp. (Protozoa, Ciliophora) on intensively cultured perch (Perca fluviatilis). — Ann. Zool. Fennici 33: 653–657.
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Morphology, behaviour, physiology, stress indicators
Urho, L. 1996: Identification of perch (Perca fluviatilis), pikeperch (Stizostedion lucioperca) and ruffe (Gymnocephalus cernuus) larvae. — Ann. Zool. Fennici 33: 659–667.
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Neuman, E., Thoresson, G. & Sandström, O. 1996: Swimming activity of perch, Perca fluviatilis, in relation to temperature, day-length and consumption. — Ann. Zool. Fennici 33: 669–678.
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Eckmann, R. & Imbrock, F. 1996: Distribution and diel vertical migration of Eurasian perch (Perca fluviatilis L.) during winter. — Ann. Zool. Fennici 33: 679–686
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Vetemaa, M. & Saat, T. 1996: Effects of salinity on the development of fresh-water and brackish-water ruffe Gymnocephalus cernuus (L.) embryos. — Ann. Zool. Fennici 33: 687–691.
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Saat, T. & Veersalu, A. 1996: The rate of early development in perch Perca fluviatilis L. and ruffe Gymnocephalus cernuus (L.) at different temperatures. — Ann. Zool. Fennici 33: 693–698
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Billington, N. 1996: Geographical distribution of mitochondrial DNA (mtDNA) variation in walleye, sauger, and yellow perch. — Ann. Zool. Fennici 33: 699–706
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Nikolic, V. P. & Simonovic, P. D. 1996: Occurrence of parasitic ciliates (Protozoa) on perch (Perca fluviatilis) in Lake Vlasinsko. — Ann. Zool. Fennici 33: 707–710.
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Krpo-Cetkovic, J. & Stamenkovic, S. 1996: Morphological differentiation of the pikeperch Stizostedion lucioperca (L.) populations from the Yugoslav part of the Danube. — Ann. Zool. Fennici 33: 711–723.
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Frankiewicz, P., Dabrowski, K. & Zalewski, M. 1996: Mechanism of establishing bimodality in a size distribution of age-0 pikeperch, Stizostedion lucioperca (L.) in the Sulejow Reservoir, Central Poland. — Ann. Zool. Fennici 33: 321–327.
The distribution and food of age-0 pikeperch were investigated in the lowland Sulejow Reservoir in Central Poland. Samples were taken weekly, from mid June to mid August 1994, both in pelagic and littoral zones. Up to mid-July, age-0 pikeperch were found to be divided into two distinguished groups. The first group was located in the pelagic zone and consisted of planktivorous specimens; the second group seemed to be restricted to the littoral zone and were predominantly piscivorous already at a very small size (TL ~30 mm). These differences in feeding between the two groups of age-0 pikeperch were due to prey fish availability and resulted in a slower growth of pelagic fish, as compared with that of littoral fish. In mid-July, after reaching mean length of about 50 mm, pelagic pikeperch invaded the littoral zone, but they were not able to shift from planktivory to piscivory, as available prey fish were already too big. As larger littoral pikeperch continued foraging on fish, previously established size differences were further strengthened.
Urho, L. 1996: Habitat shifts of perch larvae as survival strategy. — Ann. Zool. Fennici 33: 329–340.
Perch (Perca fluviatilis L.) spawn in lakes, rivers and estuaries and even in the brackish water of the Baltic Sea. In the outer archipelago of the Baltic the selection of unexposed spawning sites can be explained by the genetic component in larval dispersal and the return to inshore waters. The larvae were found to be active, at least in initiating the dispersal. Nevertheless, currents probably aid in the dispersal process. Although the shift back inshore has been documented in all lakes studied, it was here noted to be a gradual process. The timing of the return to littoral areas varies somewhat from one lake to another, and it may also depend on the size and trophic state of the lake. Perch thus appears to be adapted to variable environments. It is suggested that the shift may be a sensitive period in the formation of year-class strength, since the 0+ perch are then more exposed to predator pressure. The dispersal strategies of roach and perch larvae differed, and only after perch returned to the littoral did the distribution area of 0+ perch overlap with that of 0+ roach.
Roseman, E. F., Taylor, W. W., Hayes, D. B., Haas, R. C., Knight, R. L. & Paxton, K. O. 1996: Walleye egg deposition and survival on reefs in Western Lake Erie (USA). — Ann. Zool. Fennici 33: 341–351.
Variation in egg survival has been suspected to be a major source of walleye (Stizostedion vitreum) recruitment variability in Lake Erie. We sampled walleye eggs and larvae in western Lake Erie in 1994–95. Densities of eggs and larvae were higher in 1994 than 1995. Egg survival for depths and reefs pooled averaged 37% in 1994 and 13% in 1995. We found white perch (Morone americana) to consume large numbers of walleye eggs on reefs in 1995. Mean density of larvae from the date of first hatch through the end of May was 14 times higher in 1994 than 1995. Relatively slow water warming rates and frequent intense winds contributed to the low density and survival of eggs on reefs in 1995 by prolonging incubation periods and increasing the vulnerability of eggs to predation and severe wind events.
Mehner, T., Schultz, H., Bauer, D., Herbst, R., Voigt, H. & Benndorf, J. 1996: Intraguild predation and cannibalism in age-0 perch (Perca fluviatilis) and age-0 zander (Stizostedion lucioperca): Interactions with zooplankton succession, prey fish availability and temperature. — Ann. Zool. Fennici 33: 353–361.
The preconditions for the ontogenetic diet shift from planktivory to piscivory in age-0 perch and age-0 zander were examined in the long-term biomanipulated Bautzen reservoir (Germany). Early piscivory already was observed in age-0 zander of approximately 20 mm total length, but occurred only in the largest (> 40 mm TL) perch specimens during early summer. The onset of piscivory was triggered by high water temperatures in late spring which enhanced the growth rates of the predators relative to their prey, and by the drastic decline in zooplankton abundances during that time. Due to the lack of other prey fish, cannibalism and mutual intraguild predation dominated in piscivorous zander and perch. Early piscivory in both species was additionally favoured by the biomanipulation experiment in Bautzen reservoir due to (1) an abundant Daphnia population in spring which increased the growth rates of the predators, and (2) the coexistence of perch and zander in high densities which is uncommon in naturally-structured waters.
Kjellman, J., Hudd, R. & Urho, L. 1996: Monitoring 0+ perch (Perca fluviatilis) abundance in respect to time and habitat. — Ann. Zool. Fennici 33: 363–370.
The episodic acidification of the river Kyrönjoki decreased from 1980 to 1994. During this time 0+ perch (Perca fluviatilis) abundance showed a homogeneously increasing trend in the whole estuary. Every year the 0+ perch abundances showed a clear but often uneven decrease throughout July. The decrease was frequently significant in the middle of the month. It was also evident that the habitat affected the abundance pattern. In the beginning of July most 0+ perch were found in shallow waters. In late July 0+ juveniles were more frequent in vegetated than in nonvegetated areas, where perch were also smaller. The homogeneity of sampling stations allows us to reduce the number of sampling stations when monitoring the relative abundance of 0+ perch, but then the time and habitat should be standardised more tightly.
Karås, P. 1996: Basic abiotic conditions for production of perch (Perca fluviatilis L.) young-of-the-year in the Gulf of Bothnia. — Ann. Zool. Fennici 33: 371–381.
A recruitment model for perch (Perca fluviatilis L.) was used to predict relative abundances of young-of-the-year in habitats with different degrees of exposure to the open sea in the Gulf of Bothnia. The model describes the most basic conditions influencing the recruitment process, namely the influence of day-length and temperature on consumption affecting the growth potential. First year growth in these waters is positively correlated with year-class strength, thus, the size at the end of the first growth season is in the model used as an index of recruitment. The predictions were compared with observations during surveys regarding growth, distribution and abundance. As verified by the survey results, recruitment success should be very low in the most exposed habitats due to a low potential for first-year growth. Only sheltered bays and archipelagos, estuaries and small freshwaters provide favourable conditions for production of recruits in the Gulf of Bothnia. As predicted by the model, recruitment areas with the highest basic quality, the highest temperatures, had the widest extensions in the archipelagos.
Hudd, R., Kjellman, J. & Urho, L. 1996: The increase of coincidence in relative year-class strengths of coastal perch (Perca fluviatilis L.) stocks in the Baltic Sea. — Ann. Zool. Fennici 33: 383–387.
The year-class strengths of four perch populations (Perca fluviatilis L.) in the Northern Quark of the Baltic Sea were compared using a relative year-class strength index. As a result of this it was found that, of the four coastal populations, the three that were reproducing in rivers or estuaries tended to have coinciding year-class fluctuations. Concerning the river and estuary spawning populations, it was discovered that acidification overrules the temperature conditions normally affecting the year-class formation of perch. In the estuaries of the Northern Quark the year-class strengths were more extreme and diverged from the general pattern in the Baltic Sea. In recent years of less acidified conditions, the year-class strength of estuarine perch corresponded more closely to the general pattern in the Baltic Sea.
Sarvala, J. & Helminen, H. 1996: Year-class fluctuations of perch (Perca fluviatilis) in Lake Pyhäjärvi, Southwest Finland. — Ann. Zool. Fennici 33: 389–396.
Year-class variation of perch (Perca fluviatilis), a potentially important predator of larval and juvenile vendace (Coregonus albula), was assessed in Lake Pyhäjärvi, based on a two-stage sampling of the winter seine net catches in 1989–1995. From these data, we could estimate relative abundances of perch year-classes for the years 1986–1993. During this period, the year-classes of 1988 and possibly 1992 were strong. The year-class 1988 dominated numerically in catches from 1990 to 1993 and the year-class 1992 in 1994 and 1995. Year-class strength of perch was positively associated with the June-August temperature sum.
Machiels, M. A. M. & Wijsman, J.: Size-selective mortality in an exploited perch population and the reconstruction of potential growth. — Ann. Zool. Fennici 33: 397–401.
This study assesses the extent of size-selective mortality exerted on perch cohorts recruited to the commercial gillnet fishery in Lake IJssel. The size distribution of the 1985 cohort was surveyed with bottom trawling before and after the winter commercial gillnet fishery, from 1985 till 1990. Ageing and reconstruction of individual growth was done, using opercular bones from fish collected during the surveys and scales sampled from the commercial gillnet catch. The reconstructed potential average size of the 1985 cohort showed that the size reached after five summers could have been 26.9 cm, whereas average length observed in the population was 25.3 cm. Correlations between population size and back-calculated size were highest for back-calculations for the previous year. When earlier back calculations were considered, the correlations became poor or even insignificant. These findings stress the large individual differences in growth history within a cohort and show that the size selective mortality of perch can only be proven over relatively short growth trajectories of less than one year.
Jansen, W. A. 1996: Plasticity in maturity and fecundity of yellow perch, Perca flavescens (Mitchill): comparisons of stunted and normal-growing populations. — Ann. Zool. Fennici 33: 403–415.
Maturity, fecundity, and egg size of a stunted (mean length at age 5: 13.5 cm) and normal-growing (21.8 cm) population of yellow perch (Perca flavescens Mitchill) were studied in central Alberta, Canada. Stunted perch matured at a younger age and at a much smaller size than normal perch. Minimum size at initial maturation in stunted females was the smallest recorded in the literature for either perch (Perca) species. Relative fecundity, the slope of the fecundity-weight regression, and the gonado-somatic index were significantly higher in stunted perch. Mean dry weight of eggs, percentage connective tissue, gonad energy content, and gonad weight specific fecundity were similar for perch from both populations. Reproductive parameters of stunted perch are discussed in the context of life-history theory.
Dubois, J.-P., Gillet, C., Bonnet, S. & Chevalier-Weber, Y. 1996: Correlation between the size of mature female perch (Perca fluviatilis L.) and the width of their egg strands in Lake Geneva. — Ann. Zool. Fennici 33: 417–420.
The size of the mature perch females were estimated from the width of the egg strands that were laid on their spawning grounds. By separately sampling egg strands and mature females in 1992–1995, general relationships were established for perch in Lake Geneva. Because of the high variability in the ova content of smallest perch, this relationship could be applied to perch with a total length 150–350 mm.
Lappalainen, J., Lehtonen, H., Böhling, P. & Erm, V. 1996: Covariation in year-class strength of perch, Perca fluviatilis L. and pikeperch, Stizostedion lucioperca (L.). — Ann. Zool. Fennici 33: 421–426.
Covariation in the year-class strengths of perch, Perca fluviatilis L., and pikeperch Stizostedion lucioperca (L.), were studied among ten populations in Baltic coastal areas and three pikeperch populations in lakes. Within the studied periods in 1974–1981 and 1980–1987 the covariations in the year-class strength were similar between populations of the same species and between species. When the variations in year-class strength in several populations were compared annually between species no statistically significant differences were found during the 16 examined years. Despite the covariations, correlation coefficients in year-class strength between populations were lower for greater distances. About half (18 cases out of 35) of the correlation coefficients were statistically significant when the distance between populations was less than 300 km. Some rather high correlation coefficients were also found at distances between 300 and 900 km, but only one was statistically significant.
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.
This study was carried out in the oligotrophic lake Munksjøen in South-East Norway. The lake is situated 569 m above sea level, its surface area is 48 ha and maximum depth 10 m. The fish fauna consists of perch, roach (Rutilus rutilus L.), pike (Esox lucius L.) and sparse populations of brown trout (Salmo trutta L.) and burbot (Lota lota L.). The water quality was poor due to acidification, with a pH level of about 5.0 until the summer of 1991 when 23 tonnes of limestone powder were added. Afterwards, pH > 6.0 was maintained, except for snowmelt periods when the pH dropped to 5.8. Liming was expected to improve recruitment, and to avoid overcrowding and stunting, the most numerous species, perch and roach, have been heavily fished with traps and gillnets annually since 1992. Density of the perch population was determined with the mark recapture experiment, and biomass and production in the period 1992–1994 were simulated by modelling. Biomass of perch was estimated to 9.5 kg/ha before the mass removal and to 2.8 kg/ha afterwards. The biomass reduction led to increased growth rate, and based on the model, 1–1.5 kg/ha of perch with a mean weight of 100 g may be caught annually.
Karjalainen, J., Lehtonen, H. & Turunen, T. 1996: Variation in the relative year-class strength of pikeperch, Stizostedion lucioperca (L.), in two Finnish lakes at different latitudes. — Ann. Zool. Fennici 33: 437–442.
The catch per unit effort (CPUE), total catch and growth data of pikeperch, Stizostedion lucioperca (L.), from two Finnish lakes, Lake Lohjanjärvi and Lake Pyhäselkä, were gathered between 1979 and 1994. The growth rate of pikeperch in southern Lake Lohjanjärvi was faster than in northern Lake Pyhäselkä. The variation in the year-class index was higher in Lake Lohjanjärvi. We concluded that the shorter growing season and lower temperatures in northern areas weakened the variation in the relative strength of the year-classes.
Rudstam, L. G., Green, D. M., Forney, J. L., Stang, D. L. & Evans, J. T. 1996: Evidence of interactions between walleye and yellow perch in New York State lakes. — Ann. Zool. Fennici 33: 443–449.
We believe that the population dynamics of walleye (Stizostedion vitreum vitreum) and yellow perch (Perca flavescens) are strongly affected by biotic interactions: abundant walleye populations limit perch recruitment, resulting in fast perch and slow walleye growth rates; sparse walleye populations allow for strong perch recruitment resulting in slow yellow perch and fast walleye growth rates. If these mechanisms are important, we would expect a negative correlation between perch and walleye growth rates. Mean length at age 4 for walleye and yellow perch in 23 New York waters were negatively correlated. Further, changes over time in length at age of both species as walleye populations increased in Canadarago and Silver Lakes follow the regression from the whole data set. This indicates a strong interaction between these two percid species in New York waters. The residuals were affected by lake productivity, but not lake area or mean depth. Waters with very low productivity had smaller walleye and yellow perch than expected from the regression.
Salonen, S., Helminen, H. & Sarvala, J. 1996: Feasibility of controlling coarse fish populations through pikeperch (Stizostedion lucioperca) stocking in Lake Köyliönjärvi, SW Finland. — Ann. Zool. Fennici 33: 451–457.
In order to create a new equilibrium fish community, in which fish consumption by piscivorous fish equals the production of prey fish, mass removal of unwanted fish and intensified stocking of young-of-the-year pikeperch has been performed in Lake Köyliönjärvi. A revised bioenergetics model of walleye (Stizostedion vitreum vitreum) was used for pikeperch to calculate consumption rates from the growth rate, fish population size and ambient temperature. According to model calculations, food consumption of pikeperch alone is insufficient to control production of prey fish in Lake Köyliönjärvi. Combinations of fishing restrictions, removal of unwanted fish and intensified stocking are needed to enhance the pikeperch population and its predatory effect.
Winfield, I. J., Adams, C. E. & Fletcher, J. M. 1996: Recent introductions of the ruffe (Gymnocephalus cernuus) to three United Kingdom lakes containing Coregonus species. — Ann. Zool. Fennici 33: 459–466.
Although a native of the United Kingdom fish fauna, the distribution of the ruffe (Gymnocephalus cernuus) was, until recently, largely restricted to lowland England. However, it has now been introduced, probably by anglers fishing with ruffe as bait, to numerous localities elsewhere in the UK. This expansion has provoked concern because it has included introductions to lakes containing nationally-rare Coregonus albula or C. lavaretus. This paper documents the history of these introductions to Loch Lomond (Scotland), Llyn Tegid (Wales) and Bassenthwaite Lake (England), describes pertinent aspects of the local ecology of ruffe, and discusses implications for the continued survival of the coregonids.
Rösch, R. & Schmid, W. 1996: Ruffe (Gymnocephalus cernuus L.), newly introduced into Lake Constance: preliminary data on population biology and possible effects on whitefish (Coregonus lavaretus L.). — Ann. Zool. Fennici 33: 467–471.
In 1987, ruffe (Gymnocephalus cernuus L.) was recorded for the first time in Lake Constance, Germany. Since then its population has increased dramatically. This species is now (1995) found in high numbers throughout the lake from inshore areas to depths up to 100 m. In autumn 1994, the ruffe population consisted of fish of an age of 0+ to 3+. Maximum body length was 16 cm. At the end of the first year ruffe attained an average body length of 7.6 ± 0.9 cm (mean ± S.D.), at the end of the second year 10.4 ± 1.1 cm. During the growing season ruffe were bottom feeders, preying mainly on chironomids and detritus. However, during the spawning season of whitefish (Coregonus lavaretus L.) in December ruffe switched to whitefish eggs as a main prey. In December 1993, high numbers of eggs were found in the stomachs of all ruffe investigated with a maximum of 322 eggs in a ruffe of 16 cm body length and 60.1 g body wet weight. In December 1994, ruffe started predation on whitefish eggs at the end of the spawning period, but the percentage of ruffe preying on whitefish eggs did not exceed 60%. Due to this egg predation, negative impacts on the natural reproduction of nearshore spawning whitefish are to be expected. There is also a possibility of interactions during the growing season with the commercially important perch (Perca fluviatilis L.) population.
Kangur, K. & Kangur, A. 1996: Feeding of ruffe (Gymnocephalus cernuus) in relation to the abundance of benthic organisms in Lake Võrtsjärv (Estonia). — Ann. Zool. Fennici 33: 473–480.
From May till November 1994 the diet of ruffe was investigated in the shallow eutrophic Lake Võrtsjärv (South Estonia). 187 ruffes of standard length (SL) of 4.3–12.0 cm were examined. Ruffe of SL over 4.5 cm (age 1+ and older) were typical benthophagous fishes consuming mainly chironomid larvae and pupae (over 95% of the weight of food). Chironomus plumosus (91%), Einfeldia carbonaria (36%) and Microchironomus tener (31%) had the highest frequency of occurrence. The most important food item was C. plumosus (about 98% of the chironomid biomass in stomachs). The biomass of C. plumosus in the profundal mud bottom corresponded to its proportional amount in stomachs of ruffe. The diet of ruffe was compared with that of eel (Anguilla anguilla) and bream (Abramis brama). Overlap in their diets appeared mostly in respect of C. plumosus larvae and pupae.
Peltonen, H., Rita, H. & Ruuhijärvi, J. 1996: Diet and prey selection of pikeperch (Stizostedion lucioperca (L.)) in Lake Vesijärvi analysed with a logit model. — Ann. Zool. Fennici 33: 481–487.
Diet and prey selection of piscivorous pikeperch (Stizostedion lucioperca (L.)) was studied with a multicategory logit model. Statistically significant (log-likelihood statistics, p < 0.05) differences were found in the proportions of pikeperch feeding on different fish species at different seasons and at various weights. The differences among the two sampling years were found non-significant. The proportion of pikeperch feeding on perch (Perca fluviatilis L.) increased as the abundance of perch increased in the sampling area. It can be concluded that pikeperch are positively selective for perch. The logistic approach was found useful in order to analyse the feeding pattern of pikeperch.
Radke, R. J. & Eckmann, R. 1996: Piscivorous eels in Lake Constance: can they influence year class strength of perch?. — Ann. Zool. Fennici 33: 489–494.
Research on predator-prey relationships in the littoral zone of Lake Constance showed that eels (Anguilla anguilla (L.)) were the most numerous piscivorous predators in the shallow water zones up to 3-metres depth in 1992. From July on fish was the most important component of the diet of eels. Perch (Perca fluviatilis L.), burbot (Lota lota (L.)) and bream (Abramis brama (L.)) were thwe most frequently consumed fish. As 61% of all identifiable fish the eels had consumed were perch, an attempt was made to estimate the impact of eel predation on the young-of-the-year (y-o-y) of the perch population. Consumption by the total eel population never exceeded the amount of perch fry consumed by adult, cannibalistic perch estimated in other studies, but it seems possible that eel predation could have an adverse influence on weak year classes. Further reoligotrophication of the lake might lead to even higher fish consumption by the eels due to declining benthic production and consequent increased predation pressure.
Van Densen, W. L. T., Ligtvoet, W. & Roozen, R. W. M. 1996: Intra-cohort variation in the individual size of juvenile pikeperch, Stizostedion lucioperca, and perch, Perca fluviatilis, in relation to the size spectrum of their food items. — Ann. Zool. Fennici 33: 495–506.
Size distributions of cohorts of pikeperch and perch originating from three lakes in the Netherlands were compared to test the hypothesis that skewness or bimodality within cohorts of pikeperch and perch develops especially in environments with a discontinuous size distribution of their potential food items. In older, more eutrophic lake ecosystems like Tjeukemeer and IJsselmeer, where macro-invertebrates occur in low densities, 0-group pikeperch generally exhibit differential growth of fast-growing piscivores and slow-growing zooplanktivores. The size distributions of such cohorts become positively skewed during their first summer and often become bimodal at the end of the growing season with modes at ca. 10–15 cm and 6–8 cm, respectively. The size attained by zooplanktivorous 0-group perch in these systems is relatively small (6–9 cm) and is positively related to summer temperature. Cohorts of perch in these systems shift to piscivory, partially or totally, in their second or third summer. The differential growth of zooplanktivorous and piscivorous perch of the same cohort can cause a broadening and a positive skewness in the cohort size distribution, but never results in a bimodal size distribution. In the recently freshened, mesotrophic Volkerak ecosystem, the initial high availability of the macro-invertebrate Neomysis integer, in the first couple of years enabled 0-group pikeperch and perch to reach similar large sizes of 12–14 cm and to both switch to piscivory in their second summer. After ca. 5 years Volkerak became more eutrophic, the stock biomass of cyprinids increased, the size distribution of 0-group pikeperch became bimodal and the 0-group perch stayed small (< 10 cm), as in the older, more eutrophic systems. It is postulated that more productive systems with a higher fish biomass, but with lower biomasses of macro-invertebrates and less large-sized zooplankton probably have stronger selection mechanisms for recruiting percids.
Boisclair, D. & Rasmussen, J. B. 1996: Empirical analysis of the influence of environmental variables associated with lake eutrophication on perch growth, consumption, and activity rates — Ann. Zool. Fennici 33: 507–515.
We developed a series of relationships between components of fish bioenergetic model and environmental variables using data for twenty-six combinations of three age classes and eleven perch populations. Perch growth decreased as total fish numerical abundance increased. Growth, consumption, and activity rates decreased with the increase of the percent contribution of small prey to the invertebrate community. Furthermore, consumption and activity rates were negatively related to the biomass of the total invertebrate community but positively related to water transparency. Our analyses offer a more quantitative framework to the suggestion that perch growth and consumption rates may be negatively affected by eutrophication.
Rask, M., Järvinen, M., Kuoppamäki, K. & Pöysä, H. 1996: Limnological responses to the collapse of the perch population in a small lake. — Ann. Zool. Fennici 33: 517–524.
Several limnological responses were recorded after an almost total collapse of the population of perch, Perca fluviatilis, in the control basin of the limed Lake Iso Valkjärvi in autumn 1992. Increases in hypolimnetic concentrations of dissolved organic carbon and ammonium-nitrogen were the most striking changes in water chemistry. After a few months, high densities of ciliates were recorded in the hypolimnion, suggesting an increased microbial activity in the decomposition of fish carcasses. Correspondingly, hypolimnetic bacterial biomasses in summer 1993 were higher than earlier. In crustacean zooplankton: the densities of planktonic cladocerans were lower in the fishless side of the lake in summer 1993 than before the fish kill in the previous summer. The decline in cladocerans was probably due to predation by the rapidly increased numbers of Chaoborus larvae and corixids after the disappearance of fish. The mean biomass of zoobenthos also increased following the fish kill. The remaining perch in the control basin started to grow very rapidly. Instead of the normal length increase of 1–2 cm per year, they grew 5–7 cm in the summer of 1993 and their weight increased ten times more than that of perch of the limed basin of the lake. The mercury concentrations and radioactivity of the perch showed a 50% decrease, probably due to the growth dilution. A behavioural change in the golden-eye, Bucephala clangula, was also recorded. The breeding individuals continued to use both basins of L. Iso Valkjärvi, but the brood clearly preferred the control basin after the collapse of the perch population.
Lehtonen, H., Hansson, S. & Winkler, H. 1996: Biology and exploitation of pikeperch, Stizostedion lucioperca (L.), in the Baltic Sea area. — Ann. Zool. Fennici 33: 525–535.
In the Baltic Sea, there are considerable environmental gradients from north to south and from littoral areas to the open sea. These gradients include both abiotic (e.g. salinity and temperature) and biotic parameters (e.g. prey and predator abundances). The Baltic Sea thus forms a variable, and with respect to salinity, extreme, environment for a typical limnetic and warm water species like pikeperch. It is forced to spawn in shallow inlets, estuaries and bays where salinity is lower and temperature higher than in exposed areas. Pikeperch occur mainly in eutrophicated archipelagoes and bays where the spring and summer temperatures are high. It has expanded its distribution in recent decades, in response to increased coastal eutrophication. Pikeperch is also favoured by high summer temperatures, as shown by a positive correlation between temperature and year-class strength. Pikeperch populations are heavily affected by human disturbances and exploitation. In many areas it is economically the most important species. The effects of intensive fishery on pikeperch populations are largely unknown, as is the ecological significance of pikeperch as a piscivorous predator.
Smith, P. A., Leah, R. T. & Eaton, J. W.: Removal of pikeperch (Stizostedion lucioperca) from a British Canal as a management technique to reduce impact on prey fish populations. — Ann. Zool. Fennici 33: 537–545.
Pikeperch in a British canal have been depleted for a period of 16 years in an attempt to reduce their abundance. For the first 11 years, the intensity of removal was low but was then increased. Initially, two dominant cohorts followed each other with a gap of four years. After intensifying removal, there have been no further dominant cohorts. Total pikeperch biomass did not decrease after the change in removal rate, but numbers increased and mean length decreased. It is suggested that in this case, removal of pikeperch increased the intensity of predation on prey fish.
Setälä, J., Salmi, P., Muje, P. & Käyhkö, A. 1996: The commercial utilization of small perch (Perca fluviatilis L.) in Finnish inland fisheries. — Ann. Zool. Fennici 33: 547–551.
A total of 89 fish-processing companies were interviewed to determine their attitude towards the use of under-utilized fresh-water fish species, their methods and the problems involved in processing. Small perch were used by 17 companies. The product groups were traditional Finnish fish pasty kalakukko (4 processors), other ready meals (2), canned fish (4), fish meat (3), fillets (2) and smoked fish products (2). The main reason why companies are not using small perch is the unreliable supply of raw material. According to the interviews, inland fisheries appear poorly organized and inefficient.
Ruuhijärvi, J., Salminen, M. & Nurmio, T. 1996: Releases of pikeperch (Stizostedion lucioperca (L.)) fingerlings in lakes with no established pikeperch stock. — Ann. Zool. Fennici 33: 553–567.
One-summer-old pikeperch (Stizostedion lucioperca (L.)) fingerlings (4–8 cm) were released in ten small and medium-sized (175–3 600 ha) Finnish lakes with no permanent pikeperch stock in five successive years. Mean stocking density ranged 10–40 fingerlings/ha. In the following 5–7 years, data were collected to estimate the growth and survival rates of the fish and to assess the total yield and profitability of the releases in each lake. Catch samples were obtained from co-operating local fishermen. Fishing statistics were obtained by mailed fishing questionnaires. Reference data on growth and survival were collected from the two parent populations, which belong to the most abundant in Finland. Large annual and between-lake variation was found in the growth and survival rates of the fish released. In most year-classes, the stocked fish were smaller than one-year-old pikeperch in the parent populations. In two lakes, subsequent growth rates were faster than in the parent populations. Similarities in year-class patterns in parent populations and annual survival patterns of stocked fish suggest that common factors contribute to the variation in both cases. Year-class indices for the parent populations were, however, not correlated with summer mean temperatures or with the mean size of one-year-old fish. The yield of the releases varied in different lakes from 0.1 to 34 kg per thousand fingerlings (mean 11.5 kg). In two lakes, the estimated economic output exceeded the direct costs of the releases. An onset of natural reproduction was recorded in two other lakes. In an attempt to explain the variable results, the quality of the stocking material, the limnological features of the lakes, as well as the differences in the fish communities and in the fisheries are considered.
Nyberg, P., Degerman, E. & Sers, B. 1996: Survival after catch in trap-nets, movements and growth of the pikeperch (Stizostedion lucioperca) in Lake Hjälmaren, Central Sweden. — Ann. Zool. Fennici 33: 569–575.
Lake Hjälmaren is a shallow eutrophic lake with an intense commercial fishery. The pikeperch is the most important species from an economical point of view. A total of 2 299 individuals with a total length of 22–39.5 cm were marked with Dart tags during late June-early August 1990. The fish were caught in commercial trap-nets, measured, marked and released immediately at the place of capture. In total 1 900 recaptures were recorded and the number of recaptured individuals were 887 (38.6%). Six individuals were recaptured 20 times and one fish 39 times in trap-nets, before it was caught and killed in a gill-net. These figures show that the fishing is intense. 48% of the fish that were recaptured once and released were recaptured also a second time. They also show that the young pikeperch tolerate capture in trap-nets and also survive post-capture handling before the release quite well. The pikeperch showed a very stationary behaviour during the growth season and many individuals were captured repeatedly in the same trap-net, both during the season of tagging and following seasons. On average pikeperch smaller than 30 cm were caught less than 2 km from the point of release, whereas fish 35–39 cm on average were caught 4–5 km away during summer. In the autumn the pikeperch moved from shallower areas to the deeper central part of the lake and were caught in gill-nets in the winter-fishery. The average rate of growth of pikeperch in the size 25–30 cm at the time of marking was 51 mm/365 days until they reached 40 cm (legal size limit). After that, the size selective gill-net fishery significantly affected the average growth rate, by catching and removing the most fast growing individuals.
Johnson, B. M., Vogelsang, M. & Stewart, R. S. 1996: Enhancing a walleye population by stocking: effectiveness and constraints on recruitment. — Ann. Zool. Fennici 33: 577–588.
A long term project to evaluate the potential for food web manipulation to improve water quality in Lake Mendota, Wisconsin began in 1987. Intensive walleye Stizostedion vitreum stocking and harvest regulations were used to enhance walleye biomass. Over 60 million walleye fry and 2.4 million 50-mm walleye fingerlings were stocked during 1987–1992. Fry survival was negligible; mark-recapture estimates of small (< 275 mm) walleye abundance showed first year survival of stocked fingerlings to be variable but always <= 10%. Direct (predator consumption) and indirect (prey abundance, predator biomass) evidence suggested predation to be a major constraint to augmenting walleye recruitment by stocking.
Colby, P. J. & Baccante, D. A. 1996: Dynamics of an experimentally exploited walleye population: sustainable yield estimate. — Ann. Zool. Fennici 33: 589–599.
Savanne Lake, Ontario is one of five lakes that have been closed to public fishing since 1969 to study the effects of exploitation on walleye. The study has four phases: pre-harvest (1972–79), harvest phase I (1980–85) simulating an angling fishery at an annual mean harvest level approximating 1.78 kg/ha, as recommended by the Ontario Provincial Guidelines, harvest phase II (1986–89) where the recommended mean harvest level was exceeded (1.95 kg/ha) in conjunction with a protected slot of 45 to 55 cm total length, and a recovery phase 1990 to the present. Prior to exploitation the adult walleye population density was averaging about 15/ha, then reduced to 10.5/ha in phase I, and 9.1/ha after phase II. Production and biomass also decreased. There was little change in the mean age of the population, declining slightly from 7 to 6.2 years. There were no significant changes in growth rates but condition factor and fecundity increased. Strong year classes were evident about every 4 to 6 years. About 78 percent of the strongest year-classes occurred in even-numbered years. We hypothesized that the pulse production of the mayfly (Hexagenia limbata), a major food item for walleye in Savanne, in even-numbered years enhances year-class strength of walleye. Year-class strength was positively correlated to young-of-the-year (YOY) abundance. The protected slot appeared to be ineffective in protecting the walleye biomass and production. Northern pike abundance was also reduced, although no cause-effect relationship has been established, considering that northern pike were not harvested. We suggest that an annual harvest of about 1.0 kg/ha, which is below the annual production of 1.39 kg/ha calculated for the unexploited population, can be sustained while providing a fishing experience approximating a remote unexploited lake. Harvest levels exceeding those recommended by our guidelines can quickly reduce population density, biomass and production, and have de-stabilizing effects on the community. This study shows that fish populations in small unproductive lakes can be impacted very quickly when harvest exceeds allowable levels. This study reaffirms the importance of long-term research to assess impacts of regulations on fish populations.
Baccante, D. A. & Colby, P. J. 1996: Harvest, density and reproductive characteristics of North American walleye populations. — Ann. Zool. Fennici 33: 601–615.
A synopsis of walleye population characteristics from North American lakes is presented. Harvest, density and reproductive data from the primary literature, agency reports and personal communications were summarized, and include: sport fishing harvests, exploitation rates, population densities, relative fecundity, and age to 50% maturity. Empirical relationships between yield, population size, lake area, relative fecundity, age to maturity and growing degree-days are described. Factors affecting these empirical relationships are also discussed. Quartiles were used to describe the frequency distributions of harvest, yield and density parameters. Managers can use these empirical relationships and descriptive statistics as comparative diagnostic tools for interpreting the status of their walleye fishery. We feel this is a useful approach because managers are often having to make decisions regarding their fishery with minimal information. The interpretive value of minimal data can be enhanced when comparative information is available.
Saura, A. 1996: Use of hot branding in marking juvenile pikeperch (Stizostedion lucioperca) — Ann. Zool. Fennici 33: 617–620.
Hot branding methods used for adult fish are generally considered harmful to juveniles. Use of a very thin electrically heated metal (nichrome) wire to impress a mark on the scales of the fish is a fairly gentle procedure compared with the traditional method of branding. The thin metal filament can easily be shaped to form code symbols. About 200 000 one-summer-old pikeperch (Stizostedion lucioperca) juveniles (mean weight 2.5–5.5 g) were branded with this method during 1986–1995 and stocked in two lakes in southern Finland. No mortality or physiological responses caused by the branding were observed and the marks were readily identified on adult fish several years after application. This method is very economical. Branding instruments cost about FIM 600 and one person can mark up to 500–1 000 fish per hour. The method is suitable for pikeperch and other species with fairly small and firmly attached scales.
Turunen, T. 1996: The effects of twine thickness on the catchability of gillnets for pikeperch (Stizostedion lucioperca (L.)). — Ann. Zool. Fennici 33: 621–625.
The effect of twine (monofilament) thickness (0.15 and 0.20 mm in diameter) in six mesh sizes (30 to 55 mm, knot to knot length) on the catchability of pikeperch (Stizostedion lucioperca (L.)) in the gillnet fishery of Lake Pyhäselkä, eastern Finland, was examined. The study was carried out mainly during two winter seasons (i.e. under-ice conditions) in 1992–1993 and 1993–1994. The mean length of pikeperch in the catches was 38 cm (range 22–51 cm, S.D. = 4.6) and the mean weight 490 g (range 70–1 440 g, S.D. = 190). In the mesh size range of 30–45 mm, a 5 mm increase caused the modal length of the pikeperch catch to rise by 3–5 cm, while in the sparser mesh sizes such an increase caused the modal length to rise by 1–2 cm. Any given mesh size captured fish mainly within a length range of 10–15 cm. The effects of twine thickness on the catchability of gillnets was significant: the thinner twine caught on average 1.9 times as many pikeperch as the thicker twine.The size composition of the catches was the same for both twine thickness. A large proportion of the fish in the experimental catches were undersized. However, the twine thickness did not effect the proportion of undersized individuals.
Steffens, W., Geldhauser, F., Gerstner, P. & Hilge, V. 1996: German experiences in the propagation and rearing of fingerling pikeperch (Stizostedion lucioperca). — Ann. Zool. Fennici 33: 627–634.
Three different procedures have been used to propagate pikeperch in Germany, all requiring spawners that have been reared in ponds at favourable nutritional conditions. The simplest method of propagation is to spawn pikeperch in ponds. Semi-artificial reproduction is possible in cages or basins. Good results are obtained by inducing spawning after hypophysation and artificial insemination. Egg adhesiveness must be neutralized and eggs incubated in Zug jars at water temperatures of about 16–18°C. It is advisable to use well-prepared nursing ponds for advanced fry rearing. To produce one-summer-old fingerlings in polyculture, the proper food supply in the pond is very important. An adequate density of prey fish is a prerequisite for the harvest of large fingerlings in autumn which are well suited for a successful stocking in natural waters.
Tamazouzt, L., Dubois, J.-P., Fontaine, P., Capdeville, B. & Terver, D. 1996: Zootechnical performance and body composition of Perca fluviatilis pelleted diet in a floating cage:Effect of daily ration. — Ann. Zool. Fennici 33: 635–641
Mass rearing performances and body composition of perch Perca fluviatilis (25 g) fed on a pellet diet in floating cages were studied during July to September 1993. At the end of this period, they weighed 48 to 49 g and the survival rates were 70 to 79%. The feeding rates (3 or 4%) had no direct influence on the zootechnical potentialities or body composition. In September the gonadosomatic index increased, particularly for males. Sexual maturity triggered a regression of hepatosomatic index and a modification of fish body composition. In comparison with perch bred in a closed system at 22.0°C, the fish in cages had a higher protein and a lower lipid and energy content. Triacylglycerol fractions and phospholipids evolve reversely as function of the rearing system.
Mélard, C., Baras, E., Mary, L. & Kestemont, P. Relationships between stocking density, growth, cannibalism and survival rate in intensively cultured larvae and juveniles of perch (Perca fluviatilis). — Ann. Zool. Fennici 33: 643–651.
The influence of stocking density on the dynamics of growth, cannibalism and survival (GCS) was investigated in cultured larvae (0–44 day old fish, 500–4 000 fish m– 2, 20–23°C) and juveniles (60–143 day old fish, 95–2 380 fish m– 2, 23°C) of perch Perca fluviatilis. High stocking density granted significantly (P < 0.01) more homogeneous growth patterns within the cultured stocks that decreased the overall mortality rate and emergence of cannibals. The impact of cannibalism was proportionally decreased when fish grew more slowly. Weaned juvenile perch showed higher growth at high stocking density (P < 0.05). Cannibalism was suppressed by size-sorting after 24 days of rearing and was most intense at intermediate densities till this moment (P < 0.01).
Grignard, J. C., Mélard, C., Baras, E., Poirier, A., Philippart, J. C. & Bussers, J. C. 1996: Occurrence and impact of Heteropolaria sp. (Protozoa, Ciliophora) on intensively cultured perch (Perca fluviatilis). — Ann. Zool. Fennici 33: 653–657.
This study describes the occurrence and the impact of Heteropolaria sp. in intensively cultured perch (Perca fluviatilis). Heteropolaria sp., in association with Aeromonas sp., form a symbiotic complex which may induce severe pathology in intensively cultured perch. This colonial ciliate is most frequently detected in winter when it colonizes the spiny dorsal fin of young perch and spreads all over the body in older individuals. High population density favours the propagation of Heteropolaria sp.: the infestation frequency in 40 g perch after two months of rearing at 23°C was 10, 50 and 91%, at stocking densities of 303, 602 and 1 974 fish m– 3, respectively. High temperatures and repeated handling (e.g. sorting) also increase the risks of infestation.
Urho, L. 1996: Identification of perch (Perca fluviatilis), pikeperch (Stizostedion lucioperca) and ruffe (Gymnocephalus cernuus) larvae. — Ann. Zool. Fennici 33: 659–667.
A quick way to distinguish between percids at the early yolk sac stage is to count the myomeres from yolk to anus, 2 to 3 for ruffe, 4 to 6 for perch and 7 to 9 for pikeperch. Reliable identification of later larvae involves more laborious myomere counting. Ruffe has only 13 to 16 preanal myomeres whereas perch and pikeperch have at least 17. The number of postanal myomeres is higher in pikeperch (27–31) than in perch (23–26) and ruffe (22–24). In perch less than 15 to 20 mm in size, the most useful feature is the characteristic line-shaped melanophore pattern between the myomeres. The melanophores may, however, be weak or lacking in perch from turbid waters, and in clear waters thin melanophores may also exist in pikeperch. The position of the mouth and the length of jaws can be used for identifying percids after they have attained a total length of 12 mm. The number of fin rays in the anal and second dorsal fin can be counted by the time the fish are 16–18 mm in size.
Neuman, E., Thoresson, G. & Sandström, O. 1996: Swimming activity of perch, Perca fluviatilis, in relation to temperature, day-length and consumption. — Ann. Zool. Fennici 33: 669–678.
The swimming activity of a Baltic population of perch Perca fluviatilis was studied by gillnet fishing during a 13 year period in an experimental enclosure receiving cooling water from a nuclear power plant. A distinct seasonal rhythm was observed, correlated with temperature and day-length except for a peak during the spawning period in spring. The timing of the spring activity peak was not affected by the large differences in temperature between years and seemed to be more synchronized by day-length. Swimming activity was strongly related to consumption predicted by a bioenergetics model. The hypothesis that fish abundance may influence the cost of swimming through social interactions could not be supported by the studies, as growth rate remained unchanged although fish abundance increased considerably.
Eckmann, R. & Imbrock, F. 1996: Distribution and diel vertical migration of Eurasian perch (Perca fluviatilis L.) during winter. — Ann. Zool. Fennici 33: 679–686.
The distribution and migration patterns of overwintering perch were studied by hydroacoustics and gill netting in Lake Constance, central Europe. In autumn, perch left the littoral and moved to deeper waters for over-wintering. They lived at temperatures below 6°C for about six months. In January, perch were present between the 42 and 69 m depth contours. Their distribution then shifted to increasingly shallower depths by 0.25 m per day, and they returned to the littoral in early May where adults spawned in late May. During winter, perch performed diel vertical migrations, resting on the bottom during day and swimming up to 25 m off the bottom during night. Light was the proximate cause of this regular vertical migration. Perch did not gain an energetic advantage by migrating in a homothermal water column, but they may have gained access to copepods in addition to their main diet of benthic invertebrates. It is hypothesized that predator avoidance is the ultimate cause of diel migration in overwintering perch which avoid piscivorous birds by resting on the bottom during day and avoid burbot by swimming off the bottom during night.
Vetemaa, M. & Saat, T. 1996: Effects of salinity on the development of fresh-water and brackish-water ruffe Gymnocephalus cernuus (L.) embryos. — Ann. Zool. Fennici 33: 687–691.
Eggs of ruffe inhabiting a fresh-water (FW) lake and a brackish-water (BW) Baltic bay were inseminated and reared in sea water of different salinity. Normal prelarvae hatched at salinities up to 9 ppt in the BW ruffe and 6 ppt in the FW ruffe. The duration of incubation until hatching in the BW ruffe remained constant at 0–8 ppt but increased in the FW ruffe at salinity > 2 ppt. The maximum length of prelarvae in the BW ruffe was observed at higher salinity than in the FW ruffe. These differences indicate an adaptive increase in embryonic salinity tolerance of ruffe inhabiting brackish water.
Saat, T. & Veersalu, A. 1996: The rate of early development in perch Perca fluviatilis L. and ruffe Gymnocephalus cernuus (L.) at different temperatures. — Ann. Zool. Fennici 33: 693–698
The time (minutes from fertilization) when perch and ruffe embryos reached the 4 and 16 blastomere stage (tII and tIV, respectively) was recorded, and the duration of one synchronous cell cycle t0 = (tIV – tII)/2 and the rate of development R = 1/t0 x 10– 4 was calculated at different temperatures. R was higher for ruffe than for perch. The range of optimal temperatures for early development (determined from logt0-temperature plots according to Mazin and Dettlaff, 1985) was 8–18°C (Ropt = 13°C) for perch and 9–21°C (Ropt = 15°C) for ruffe. R and Ropt in perch and ruffe are higher than in salmonids and coregonids, and less than in warm-water cyprinids and cobitids.
Billington, N. 1996: Geographical distribution of mitochondrial DNA (mtDNA) variation in walleye, sauger, and yellow perch. — Ann. Zool. Fennici 33: 699–706
To assess its usefulness for stock identification and resolving post-Pleistocene recolonization events, mtDNA variation was examined in three economically important North American percids: walleye, sauger and yellow perch. Forty-two walleye mtDNA haplotypes were identified which could be divided into five groups that showed distinct geographic distributions. Sauger showed very little genetic variation with only four haplotypes being found across the species´ range. Thirteen yellow perch mtDNA haplotypes were identified, with one haplotype predominating in all populations examined. These results suggest that mtDNA analysis will be useful for stock identification in walleye, but less so in sauger and yellow perch.
Nikolic, V. P. & Simonovic, P. D. 1996: Occurrence of parasitic ciliates (Protozoa) on perch (Perca fluviatilis) in Lake Vlasinsko. — Ann. Zool. Fennici 33: 707–710.
In the sample of 83 specimens of the perch (Perca fluviatilis L., 1758), caught on eight different sampling sites at the Vlasinsko Lake reservoir, in April–October 1993, 25 infested specimens were found. They were infested with the following species of parasitic ciliates: Trichodinella epizootica, Apiosoma robustum, Apiosoma piscicolum ssp. perci, Ichthyophthirius multifiliis, Chilodonella cyprini and Chilodonella hexasticha. The most intensive infestation with all quoted parasitic ciliates was registered in April. Only Ichthyophthirius multifiliis infested the perch intensively in July. Trichodinella epizootica and Apiosoma robustum revealed both the highest prevalence and intensity of infestation. Regarding the localization of the parasitic species, Trichodinella epizootica and Apiosoma robustum had a much stronger affinity for the gills than for the skin of the perch.
Krpo-Cetkovic, J. & Stamenkovic, S. 1996: Morphological differentiation of the pikeperch Stizostedion lucioperca (L.) populations from the Yugoslav part of the Danube. — Ann. Zool. Fennici 33: 711–723.
In order to analyse the intra- and interpopulation homogeneity/heterogeneity of the pikeperch (Stizostedion lucioperca), the phenotypic variability of morphological characters was estimated on the basis of a biometric analysis of 31 morphometric and 10 meristic characters in 284 specimens collected at four different sections along the Yugoslav sector of the Danube, during 1986–1989. An ANCOVA of morphological characters, with fish size as a covariate, was performed for analysed samples and between males/females and adults/juveniles respectively. Comparison was also made with the pikeperch samples from the Dnepr and the West Dvina (Zhukov 1965). The results were tested with a GT2-method for multiple unplanned comparison of means, or with a t-test where appropriate. The differentiation between populations from three geographically distinct and isolated areas (Danube–Dnepr–Dvina) is much greater than between the four samples from the Danube. The results of the variability analysis of morphological characters and known pikeperch habits (first of all having in mind the so-called “homing” effect — returning to the same spawning place from year to year), suggest that the four samples from the Yugoslav part of the Danube most probably represent four distinct populations. The presence of reproductive isolation still has to be proved through experimental marking. Since this analysis takes into account only the phenotypic variation, it would be necessary to study the genetic differentiation between populations, as well, by biochemical or DNA-sequencing methods.