14th International Coregonid Fishes Symposium Jyväskylä, Finland, 22–26 June 2020 A generic recipe for modelling lake food web dynamics: case studies on life-history changes, environmental stochasticity, stocking and invasive species Keynote presentation Anna Kuparinen anna.k.kuparinen@jyu.fi University of Jyväskylä, Finland Over the past two decades, community ecologists have successfully solved many long-standing ques- tions regarding the structure, stability and complexity of food web dynamics using the allometric trophic network modelling approach (ATN). Later, ATN has also proven successful to describe sea- sonal plankton dynamics in Lake Constance (Bodensee). In my talk, I will describe the fundamental biological foundation of the ATN approach and a generic way to parameterize complex feeding inter- actions. The theory will be followed by case studies that illustrate how the modelling tool can be used to explore ecosystem consequences of fish life-history changes, enhanced whitefish stocking and the ways in which environmental noise affect the food web dynamics. I will also demonstrate how the same modelling approach has been applied to another lake system, to study the ecosystem impacts of an invasive species. ∗Presenting author Biology, ecology & population dynamics Oral presentation Identifying the early-life history survival bottleneck in Lake Erie’s Lake Whitefish (Coregonus clupeaformis) population 1 1 2 1 3 ∗Zachary Amidon , Robin DeBruyne , Edward Roseman , Christine Mayer , Alexis Sakas 1University of Toledo, USA 2United States Geological Survey Great Lakes Science Center, USA 3The Nature Conservancy, USA In recent years Lake Erie’s Lake Whitefish commercial landings have declined with few new recruits (age-3) in thefi shery. To narrow down the life stage where a survival bottleneck may be occurring, Lake Whitefish were sampled for abundance at egg, larval, and juvenile stages. In the fall of 2016, 2017, and 2019, eggs were sampled at 35 locations throughout the western basin. Post-hatch pelagic larvae were collected weekly from 2017-2019 at 27 locations and abundances compared with similar data from 1995-1998. Fall age-0, age-1, and age-2 juvenile abundances from 1990-2019 were taken from the Ohio Department of Natural Resource fall trawl surveys. Eggs were collected throughout the western basin, indicating that available spawning habitat is likely not limited. Larval abundances in 2017-2019 were of the same magnitude as 1995-1998, a time when adult Lake Whitefish were recruiting to thefi shery, indicating that contemporary Lake Whitefish embryos survived to the pelagic larval stage with potential to recruit to older age classes. Comparisons of juvenile abundances suggests that cohort strength may be set by fall age-0. Our results suggest a recruitment bottleneck likely occurs during or after the pelagic larval stage and before fall age-0. 14th International Coregonid Fishes Symposium Jyväskylä, Finland, 22–26 June 2020 Shift from plankton to benthos in the diet of vendace, Coregonus albula, in northern regions ∗Nadezhda Berezina 1, Elena Zubova 2, Alexandra Strelnikova 3, Alexey Borovskoy 4 [email protected] 1Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia 2Institute of the Industrial Ecology Problems of the North KSC RAS, Apatity, Russia 3Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok, Russia 4Polar Branch of the Federal State Budgetary Institution ”VNIRO”, Arkhangelsk, Russia The diet of vendace, Coregonus albula (10-25 cm of the total length), was studied in subarctic lakes: small Lake Krivoe and a large Lake Imandra in 2011-19 and compared with its feeding habits in bo- real Lake Pleshcheevo and Rybinsk Reservoir. Vendace from lakes Krivoe and Imandra preferred to consume benthic macroinvertebrates, but their contribution to the diet varied seasonally and related to fish length. In Lake Krivoe, amphipods contributed >50% in the total mass of the stomach content during summer, but up to 50% for mollusks and 25% of cladocerans in autumn. In Lake Imandra vendace fed on chironomids (75% for >15-cm fish) and bivalve and gastropod mollusks. The diet of another northern form, C. sardinella marisalbi (15-21 cm), from the Pechora River basin based on insect adults (Simulidae, 73%) and larvae (Trichoptera, 24%). In contrast to the northern areas, plank- tonic crustaceans (Copepoda, Cladocera) were the main food items for C. albula in boreal lakes while benthic animals occurred occasionally. In the Rybinsk Reservoir, pelagic vendace fed on planktonic cladocerans, but the coastal part of the fish population consumed also amphipods. Study confirms a high importance of omnivory in vendace diet with increasing contribution of benthic sources in northern lakes. ∗Presenting author Biology, ecology & population dynamics Oral presentation Density-dependence and human activities as key drivers of whitefish growth in Lake Geneva ∗Chloé Goulon, Jean Guillard, Orlane Anneville UMR CARRTEL INRAE-University of Savoie Mont Blanc, France Whitefish (Coregonus lavaretus), autochtonous in Lake Geneva, play an important role in the cultural heritage, local economy and in the ecosystem functioning. Eutrophication greatly reduced whitefish catches in the mid- dle of 20th century; with the improvement of water quality, population started to recover in the middle of 1990s. Catches reached a record level of over 900 tons in 2014 then dropped significantly. The understanding of populationfl uctuations is a central goal of population ecology andfi sh management. Individual growth is a key demographic parameter and variability can be driven throw density-dependent processes and environ- mental conditions, including temperature that increased during the recent decades. The objective of this study is to analyse long-term whitefish growth dynamics and to identify the main factors involved in the observed changes. The relative importance of density-dependent (i.e competition) and density-independent processes (water temperature, trophic resources and interspecies interaction) in the observed evolution was analysed. From the beginning of the population recovering to the middle of the 2000s, temperature mainly contributed in growth changes; thereafter, competition became the main driver. Our results indicate that density-dependent processes and human activities are important drivers in whitefish growthfl uctuation and consequently in white- fish dynamics in Lake Geneva. Biology, ecology & population dynamics Poster session Bet-hedging trait of multiple-batch spawning underfi shing pressure 1 2 1 ∗Sara Hocevar , Jeffrey A. Hutchings , Anna Kuparinen 1University of Jyväskylä, Finland 2Dalhousie University, Canada Under variable environmental conditions, natural selection tends to favour the evolution of risk-managing life- history strategies. These are essential for populations to endure uncertainties and maximize individualfi tness. One of these evolved strategies is multiple-batch spawning, a trait common tofi shes that ’hedge their bets’, by distributing the risk to their offspring on a temporal and spatial scale. Given that thefi tness benefits of the trait increase with female body size, size-selectivefi shing pressure could hinder the security that bet-hedging, in the form of multiple-batch spawning provides, and may strip the population of its security mechanism. By applying an empirically and theoretically motivated eco-evolutionary mechanistic model, we simulated multiple-batch and single-batch spawning phenotypes and exposed them to varying levels of environmental andfi shing stochasticity. We explored whetherfi shing mortality alters the life-history traits andfi tness of each spawning strategist and, if so, how these alterations might affect population dynamics. Ourfi ndings illustrate how the feedbacks of a bet-hedging strategy illuminate the necessity of accounting for spawning strategy when managing broadcast-spawningfi sh stocks. Biology, ecology & population dynamics Oral presentation Vendace disperse eggs widely during spawning ∗Juha Karjalainen, Markus Tuloisela, Kristiina Nyholm, Timo J Marjomäki University of Jyväskylä, Finland Depending on their reproductive strategy, different fishes aggregate or disperse eggs and larvae in their re- productive habitat. Vendace (Coregonus albula) yolk-sac larvae are known to occur widely around the lake after hatching, but it has been unclear, where are exact spawning and egg incubation locations in the boreal lakes. Egg and larval densities of vendace were studied in Lake Konnevesi, Finland, to clarify the lake-wide spawning strategy of this commercially important species. In October 2019, 1-2 weeks prior to spawning 500 egg samplers were installed according to stratified sampling design to the potential spawning areas around the study lake. Sampling plots were same as the regular monitoring plots of newly-hatched larvae of coregonids in the lake. Fertilized vendace eggs were found in 18 of the 20 sampling plots. The mean fertilization rate was 84.2% (SD 24.5) and the mean density of eggs 70.8 (SD 110.8) eggs per square metre. The results confirm the hypothesis that vendace disperse their offspring lake-widely already during spawning. High egg densities in autumn have observed in the same areas as the high larval densities in spring. The reproduction strategy of vendace aim to stabilise the high environmental and temporal fluctuation in their habitats. Biology, ecology & population dynamics Oral presentation Who’s Who? Identifying three coregonine species