Diet patterns and ontogenetic diet shift of pikeperch, Sander lucioperca (L.) fry in lakes Peipsi and Võrtsjärv (Estonia)

Abstract

Pikeperch is a major predator in the pelagic zone of eutrophic waters, such as the large north-temperate lowland lakes Võrtsjärv (Estonia) and Peipsi (Estonia/Russia). The size and structure of the pikeperch population is strongly influenced by their success at the juvenile stage. Therefore, we investigated the diet and prey selection of pikeperch fry caught in the ice-free period in lakes Peipsi and Võrtsjärv in 2007 and 2008. We analysed the stomach contents of 635 pikeperch from Lake Peipsi and 202 pikeperch from Lake Võrtsjärv, and compared our findings with similar data from the 1950s (Erm, About Biological and Morphological Differences of Pikeperch. Hydrobiological Researches II (in Estonian), 1961). Analysing 4-20 cm long fry, we studied differences in prey size, seasonal diet patterns and the ontogenetic diet shift. In both lakes, 0? pikeperch feed mostly on large predatory zooplankters. However, in Lake Peipsi the stomach content weight and the average number of food items in stomach were higher, and the food spectrum was wider than in Lake Võrtsjärv. There was also a difference in the type of food that dominated fry's stomach content (calculated by weight) in the two lakes. In Lake Peipsi, chironomids larvae, as well as zooplankters Daphnia galeata and Bythotrephes longimanus dominated, while in Lake Võrtsjärv zooplankters Mesocyclops leuckarti and Leptodora kindti. Seasonal analysis showed that cladocerans dominated in pikeperch fry stomach content in summer and at the beginning of September, but copepods were dominant in autumn and spring. In contrast to the studies carried out from 1952 to 1958

Indices of zooplankton community as valuable tools in assessing the trophic state and water quality of eutrophic lakes: long term study of Lake Võrtsjärv

“…Scarce occurrence of adult copepods (particularly large egg-carrying females) indicates the pressure of fish. In a recent study (Ginter et al, 2011) on the stomach content of pikeperch fry, the Ivlev selectivity index revealed high positive selection for adult M. leuckarti. The calanoid copepod E. gracilis is a species of lower trophy (Chapman, 1969;Gulati, 1984;Shumka, 2001;May and O'Hare, 2005;Vǣrvågen and Nilssen, 2010) and was numerous in the 1950s (Shönberg, 1958) and even in the 1960s.…”

Consequences of size-selective harvesting and changing climate on the pikeperch Sander lucioperca in two large shallow north temperate lakes

“…Our previous investigations (Ginter et al, 2011(Ginter et al, , 2012a have shown that mismatches in predator and prey sizes have triggered a postponement of the shift to a piscivory diet among the pikeperch in Lakes Peipsi and Võrtsjärv. However, recently, winters have become milder, and juvenile pikeperch are now capable of surviving the first winter at smaller sizes and without shifting to a piscivory diet in these Estonian lakes.…”

Shifts in Prey Selection and Growth of Juvenile Pikeperch (<i>Sander lucioperca</i>) over Half a Century in a Changing Lake Võrtsjärv

“…However, the prey-predator length relationship decreased towards autumn and pikeperch was able to shift to piscivory in spring, being 7.6 -8.5 cm in length [13]. In 2007 and 2008 the average autumn length (± standard deviation) of pikeperch fry was 6.2 ± 0.8 cm and 6.1 ± 0.9 cm, respectively [17]. In 2009 and 2010 it was 5.5 ± 1.1 cm and 5.6 ± 0.8 cm, respectively ( Table 3 In the recent period, the first fishes eaten by pikeperch were ruffe and pikeperch.…”

“…The diet and growth of juvenile pikeperch have been studied several times since 1920 in a large shallow Lake Võrtsjärv [12][13][14][15][16][17]. Moreover, the probability of major shifts in the feeding modes of fish is especially high in shallow lakes [11] such as Lake Võrtsjärv.…”

“…In addition, an attempt was made to identify possible factors influencing the success of the pikeperch population in large shallow lakes. Therefore, studies since 1920 [12][13][14][15][16][17] on the diet, ontogenetic diet shift and growth of juvenile pikeperch were analysed to understand the long-term nature of pikeperch fry diet. This investigation concentrated on four different time periods: the 1920s, 1950s, 1960s-1970s and 2007-2010, as there have been significant shifts in living conditions and food supplies of juvenile pikeperch during those time periods.…”