Fish predation pressure on zooplankton in a large northern temperate lake : impact of adult predators versus juvenile predators

In recent decades, a marked decrease in planktivorous fish (Osmerus eperlanus eperlanus m. spirinchus Pallas and Coregonus albula (L.)) in Lake Peipsi has stimulated research into the potential effect of fish predation on zooplankton. The abundance of planktivorous fish and the abundance and biomass of zooplankton were studied from 1986 to 2014, and the diet of plankton-eating fish was analysed from 2007 to 2013. A linear regression model was used to establish possible trends in the zooplankton assemblages (biomass, abundance, mean weight of individuals) and in the abundance of zooplankton-eating fish. The ANOVA test was used to evaluate differences in the zooplankton assemblages and in fish consumption in the years with large and small fish cohorts. Despite the collapse of the smelt and vendace populations, the abundance of plankton-eating fish remained high due to an increase in the abundance of juvenile fish. Fish juveniles consumed as much as or even more zooplankton than adult planktivores. Since 1986, a significant decrease was observed in the cladoceran and copepod biomass and in the mean body weight of cladocerans. Large cladocerans such as Leptodora kindtii (Focke) and Bythotrephes longimanus Leydig were rare in zooplankton samples and the biomass of Bosmina spp. decreased. Changes in the structure of the zooplankton community were most likely caused by the feeding of juvenile fish as the calculated consumption by fish was high, especially in years with particularly large fish cohorts.The research was supported by the Estonian target financed project SF0170006s08. We gratefully acknow- ledge Ester Jaigma for the linguistic editing of the manuscript, Marina Haldna for assistance in statistical analyses, and Dr Peeter Kangur for data collection. The publication costs of this article were covered by the Estonian Academy of Sciences.The research was supported by the Estonian target financed project SF0170006s08. We gratefully acknow- ledge Ester Jaigma for the linguistic editing of the manuscript, Marina Haldna for assistance in statistical analyses, and Dr Peeter Kangur for data collection. The publication costs of this article were covered by the Estonian Academy of Sciences

A shift in the regional climate regime strongly affects Peipsi fish : [poster]

Fish populations in northern latitude lakes are strongly impacted by climate warming. This is particularly evident in L. Peipsi (Fig. 1), as climate change favour warm-water species such as pikeperch (Sander lucioperca) or bream (Abramis brama), and inhibit the survival of cool-water species such as vendace (Coregonus albula), Peipsi whitefish (C. lavaretus maraenoides) and burbot (Lota lota). At the turn of the 1980-1990 decade, a significant shift in the Peipsi fish community took place (Fig. 2), which coincided with a recorded shift in the regional climate regime in Europe, including Estonia (Jaagus et al., 2017).The presentation took place at the 11th International Shallow Lakes Conference.Külli Kangur was supported by the Estonian Research Council (PRG 1266).This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963.Külli Kangur was supported by the Estonian Research Council (PRG 1266).This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963

Weather conditions influencing phosphorus concentration in the growing period in the large shallow Lake Peipsi (Estonia/Russia)

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Citizen science shows systematic changes in the temperature difference between air and inland waters with global warming

Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (Tw-Ta) as a proxy for sensible heat flux (QH). If QH is directed upward, corresponding to positive Tw-Ta, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative Tw-Ta across small ponds, lakes, streams/rivers and the sea shore (i.e. downward QH), with Tw-Ta becoming increasingly negative with increasing Ta. Further examination of Tw-Ta using high-frequency temperature data from inland waters across the globe confirmed that Tw-Ta is linearly related to Ta. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative Tw-Ta with increasing annual mean Ta since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative Tw-Ta, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere

Slaughter weight rather than sex affects carcass cuts and tissue composition of Bisaro pigs

Carcass cuts and tissue composition were assessed in Bisaro pigs (n=64) from two sexes (31 gilts and 33 entire males) reared until three target slaughter body-weights (BW) means: 17 kg, 32 kg, and 79 kg. Dressing percentage and backfat thickness increased whereas carcass shrinkage decreased with increasing BW. Slaughter weight affected most of the carcass cut proportions, except shoulder and thoracic regions. Bone proportion decreased linearly with increasing slaughter BW, while intermuscular and subcutaneous adipose tissue depots increased concomitantly. Slaughter weight increased the subcutaneous adipose tissue proportion but this impaired intramuscular and intermuscular adipose tissues in the loin primal. The sex of the pigs minimally affected the carcass composition, as only the belly weight and the subcutaneous adipose tissue proportions were greater in gilts than in entire males. Light pigs regardless of sex are recommended to balance the trade-offs between carcass cuts and their non-edible compositional outcomes.Work included in the Portuguese PRODER research Project BISOPORC – Pork extensive production of Bísara breed, in two alternative systems: fattening on concentrate vs chesnut, Project PRODER SI I&DT Medida 4.1 “Cooperação para a Inovação”. The authors are grateful to Laboratory of Carcass and Meat Quality of Agriculture School of Polytechnic Institute of Bragança ‘Cantinho do Alfredo’. The authors are members of the MARCARNE network, funded by CYTED (ref. 116RT0503).info:eu-repo/semantics/publishedVersio

Lake Peipsi fishery data 1986 and 1990-2007 (test trawling samples)

For Lake Peipsi, experimental trawling has been conducted since 1986. Test trawling was conducted in the Estonian side of Lake Peipsi s.s. in autumn 1986 and from 1990 to 2007 using the bottom trawl (height 2 m, width 12 m, knot-to-knot mesh size at the cod-end 10 to 12 mm). The trawl was towed by a ship for 15-30 min per haul at speed of 5.5–6.2 km h–1. Test trawling was carried out monthly at noon from August until November in the pelagic zone of the Estonian side of Lake Peipsi s.s. On each sampling occasion, several hauls were made at multiple locations of the lake. All fish were identified, and their standard lengt (SL) was measured to the nearest mm. Moreover, the catches per unit effort (CPUE, individual per trawl-hour and kg per trawl-hour) of trawl samples taken in autumn were calculated for the main fish species (i.e., lake (dwarf) smelt (Osmerus eperlanus), vendace (Coregonus albula), Peipsi whitefish (Coregonus lavaretus maraenoides), Northern pike (Esox lucius), roach (Rutilus rutilus), common bleak (Alburnus alburnus), common bream (Abramis brama), burbot (Lota lota), Eurasian perch (Perca fluviatilis), pike-perch (Sander lucioperca), ruffe (Gymnocephalus cernuus) and total catch

How Did the Late 1980s Climate Regime Shift Affect Temperature-Sensitive Fish Population Dynamics: Case Study of Vendace (Coregonus albula) in a Large North-Temperate Lake

The population dynamics of fish in northern lakes is strongly influenced by climatic factors. In this study, we investigated whether there is a link between the late 1980s climate regime shift in Europe and the collapse of vendace (Coregonus albula) population at the same time in Lake Peipsi. Until the end of the 1980s, vendace was very abundant in the lake, but then its catches sharply declined. This decline inspired investigations into the extreme weather events preceding the vendace collapse using data on daily water temperatures and ice phenology together with commercial fishery statistics since 1931 and test catch data since 1986. We identified using advanced statistical methods that the hot summer of 1988, which was accompanied by a severe cyanobacterial bloom and extensive fish kill, and the subsequent non-permanent ice cover and early ice-offs in 1989 and 1990 in Lake Peipsi were the main reasons for the disappearance of vendace from catches in 1991. Moreover, a negative correlation appeared between catches of the predatory pikeperch (Sander lucioperca) and vendace. Predation pressure as well as fish habitat degradation caused by lake eutrophication may contribute to the instability of the vendace population too. Our study showed that extreme weather events such as heat waves in summer and non-permanent ice-cover in winter in consecutive years may have long-lasting harmful effects on the population abundance of cool-water fish species such as vendace whose eggs usually develop under an ice cover in north-temperate lakes

Long-term effects of extreme weather events and eutrophication on the fish community of shallow Lake Peipsi (Estonia/Russia)

The fish kill in lake Peipsi (Estonia/Russia) during the extraordinarily hot summer of 2010 evoked an investigation into the effects of environmental extremes and long-term eutrophication on the fish community of the lake. Current data on lake Peipsi indicate that temperature extremes and synergistic interactions with eutrophication have led to a radical restructuring of the fish community. Commercial landings of lake smelt, <em>Osmerus eperlanus eperlanus</em> m. <em>spirinchus</em> (Pallas), the previous dominant species of the fish community, have decreased dramatically since the 1930s, these declines being coupled with summer heat waves coinciding with low water levels. Gradual decline in smelt stock and catches was significantly related to a decline of near-bottom oxygen conditions and to a decrease in water transparency. The first documented fish kill in 1959 occurred only in the southern, most shallow and eutrophic lake (lake Pihkva). Recently, summer fish kill have become more frequent, involving larger areas of the lake. In addition to the cold-water species, <em>e.g. </em>smelt and vendace <em>Coregonus albula </em>(L.), the abundance of bottom-dwelling fishes such as ruffe <em>Gymnocephalus cernuus</em> (L.) and juvenile fish have significantly decreased after the 2010 heat wave probably due to hypoxia and warm water temperatures. This study showed that fish community structure in large shallow lakes may be very vulnerable to water temperature increases, especially temperature extremes in combination with eutrophication

Lake Peipsi 2004 (Phytoplankton samples) 

DatasetMethod: Phytoplankton samples were preserved in Lugol’s (acidified iodine) solution and counted under an inverted microscope (Utermöhl, 1958). 3 ml of preserved sample was settled overnight and counted in random fields or transects. Biovolumes of algal cells, colonies and/or filaments were calculated using assigned geometric shapes dimensions, and converted to biomass assuming the specific density of 1 g cm-3 in accordance with Edler (1979). Approved by CEN on 14 July 2006 “Water quality - Guidance standard on the enumeration of phytoplankton using inverted microscopy (Utermöhl technique)” (CEN 15204, 2006) European Standard EN 15204:2006 Utermöhl, H., 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitteilungen der Internationale Vereinigung für Theoretische und Angewandte Limnologie 9, 1- 38. Edler, L. (ed.), 1979. Recommendations on methods for marine biological studies in the Baltic Sea. Phytoplankton and chlorophyll. Baltic Marine Biologists WG 9