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Home , Coregonus albula, Coregonus hoyi, Stenodus

14th International Coregonid Fishes Symposium Jyväskylä, , 22–26 June 2020

A generic recipe for modelling lake food web dynamics: case studies on life-history changes, environmental stochasticity, stocking and invasive

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 ’s Lake Whitefish ( 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 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. 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 (), 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 () 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 at the larval stage

1 2 3 4 5 6 ∗Hannah Lachance , Amanda Ackiss , Wes Larson , Verena Lucke , Mark Vinson , Jason Stockwell 1University of Vermont/USGS/NOAA, USA 2Wisconsin Cooperative Fishery Research Unit, University of Wisconsin Stevens Point, USA 3Wisconsin Cooperative Fishery Research Unit, University of Wisconsin Stevens Point;, USA 4University of Vermont/Woods Hole Oceanographic Institution, USA 5USGS, USA 6University of Vermont, USA Coregonines, including (), (Coregonus kiyi), and bloater (), are a focus for preyfi sh restoration efforts throughout the Great Lakes. However, fundamental questions about coregonine ecology remain. For example, we have limited knowledge about how to identify different species from one another during the early life stages, which makes coregonine species difficult to study at the egg and larval stage. To increase the probability for success in restoration efforts, current and future research need to integrate traditional and novel approaches to better understand coregonine populations at each life stage. Therefore, we sampled larval coregonines throughout the Apostle Islands of from hatch in May until late July 2018. We used genomic sequencing to identify 197 larvae as either cisco, bloater, or kiyi. There was a temporal difference in estimated hatch dates for each species yet no significant spatial differences in where each species was found. The larval demographic characteristics of each species was assessed and revealed that length ranges, growth rates, yolk sac condition, and effective population size varied among species. Genetic diversity within each species appears high. The results from our study help advance our understanding of the important early life stages of coregonines. Biology, ecology & population dynamics Poster session

Tendency for two-year cyclicity (2YC) in Finnish vendace (Coregonus albula) populations: a robust meta-analysis

1 2 ∗Timo J. Marjomäki , et al. 1University of Jyväskylä, Finland 2JYU, Finland Significant support for the hypothesis of two-year cyclicity in vendace abundance has been found in in time series from certain Finnish vendace abundance indices. Yet, doing correlative analysis for several individual data sets separately is prone to risk offi nding coincidental spurious correlations. To gain further understanding on the veracity of the 2YC hypothesis, a simple meta-analysis was performed by combining the data sets from different Finnish lakes, developing a robust indicator for 2YC and applying Fisher’s combined probability test fro hypothesis testing. Significant (p < 0.05) support for the tendency for two-year cyclicity in vendace abundance was found. The potential reasons for this tendency are discussed. Biology, ecology & population dynamics Oral presentation

Lifting the vendace (Coregonus albula) on the table: mortality, growth and reproduction in different life-stages at low and high population densities

1 2 1 ∗Timo J. Marjomäki , Pentti Valkeajärvi , Juha Karjalainen 1University of Jyväskylä, Finland 2Not applicable, Finland The life-cycle of vendace is analysed in life-table context. The level of mortality of immature and mature sub- population as well as growth and reproductive output of females required for population stability are determined for both high and low population densities. The capability of real populations for the required compensatory change in these population parameters at low spawner density is discussed based on the data from populations that have experienced long periods of low density. The implications of the results forfi sheries management and risk of due to anthropogenic stressors, such as increased predation due to warming or extensive stocking, are discussed. Biology, ecology & population dynamics Oral presentation

Impact of the invasive three-spined stickleback (Gasterosteus aculeatus) on the native pelagic whitefish (Coregonus wartmanni) spawners in Upper Lake Constance

∗Roland Roesch, Tyrell DeWeber, Mark Schumann, Jan Baer Fisheries Research Station Baden-Württemberg, A massive increase in the pelagic population of non-endemic three-spined sticklebacks, Gasterosteus aculeatus L. in Lake Constance has coincided with drastic declines infi shery yields. Data from monthly monitoring of pelagic whitefish (Coregonus wartmanni Bloch, 1784) and the annual spawningfi shery were used to compare weight-at-age, abundance, gonadosomatic index, spawner catch and egg mass during spawning season for years before (< 2013) and after the invasion (2013–2019). In addition, the yearly energy content of spawners after the invasion was measured. Nearly all parameters showed a negative trend, implying direct effects of stickleback presence on pelagic whitefish, including interspecific competition for food leading to reduced growth, energy, survival and egg quality. In conclusion, this study shows that the invasion of sticklebacks had significant effects on the population structure of the economically important whitefish, resulting in reduced yield and a hard future for the last remainingfi shermen. Biology, ecology & population dynamics Oral presentation

Drivers of year-class variation of vendace (Coregonus albula (L.)) revisited: roles of density-dependent and density-independent factors in Lake Pyhäjärvi in 1971-2018

1 2 ∗Jouko Sarvala , Harri Helminen 1Department of Biology, University of Turku, Finland 2Centre for Economic Development, Transport and the Environment for Southwest Finland, Finland Widefl uctuations in year-class strength are typical for most populations of the small coregonid vendace (Core- gonus albula). A number of density-dependent and density-independent factors causing this variation have been identified. Long-term data (1971-2018) of the vendace population in Lake Pyhäjärvi, southwest Finland, have been useful in evaluating the importance of different factors. In 1971-1986, time series analysis of ven- dace recruitment in Pyhäjärvi showed a two-year cycle of alternating strong and weak year-classes, consistent with the hypothesis of asymmetric intraspecific competition between age groups, abundant young-of-the-year leading to inferior egg quality of the adults. Exceptional weather conditions disrupted the two-year cycle, causing recruitment failures, and from 1990 to 1999 year-classes remained small because spawning stock was kept reduced by overfishing. From 2000 onwards the oscillations were re-established, but with different phase and at lower mean level. Throughout the time series, unpredictable weather conditions caused confounding variation through multiple paths, affecting several life stages. During the two-year cycle, vendace recruitment in Pyhäjärvi was predictable from the abundance of the previous year-class, water temperature in spring, and abundance of predators. Here we compare predictions from this model with observed year-class strength, and explore which factors and mechanisms might explain the deviations. Biology, ecology & population dynamics Oral presentation

Vendace (Coregonus albula) 50 years in Lake Inari – What has changed

∗Erno Salonen Luke Inari, Finland Lake Inari is a subarctic, oligotrophic, regulated lake in northern Finland, connected via the River Pasvik to the Arctic Ocean. A new coregonid species, vendace (Coregonus albula), was introduced into the watershed in the 1960’s and gradually established a population in the lake. Hence during the last 50 years the vendace has been included in the lake ecosystem. The vendace has shown boom and bust development, with the annual catch reaching 300 tonnes in 1989. Compared to this peak level the vendace catch has declined and stabilized to a very low level already during the last 25 years’. In this speech, I will review some of the huge changes and impacts happened both independently and dependently of the vendace presence in the lake: i) Climatic and hydrological changes ii) Lake ecosystem changes – due to vendace iii) Fishing culture changes – due to vendace iv) Role of vendace: catch itself and prey for predatoryfi shes and v) Life history changes of vendace itself Biology, ecology & population dynamics Oral presentation

Spawning behavior of whitefish

∗Sergey Semenchenko, Natalya Smeshlivaya Tyumen Branch of VNIRO, Coregonus migratorius, C., C.tugun, C.pidschian, C. have been used for visual observation, pho- tography, video and audiorecording of spawning in facilities for gathering eggs by ecological method. Spawn- ing of each species takes place in autumn for 2-3 weeks every day in nighttime. The following phases can be distinguished in the spawning process: courtship, an act of spawning and rest, which are frequently repeated during night. Spawning is an act for a couple, in combination male-female or male-male, taking place either in water depth or on surface. Males are initiators. Spawning act is a rhythmic impingement offi sh bodies with parallel movement and synchronous excretion of reproductive products. Vertical, horizontal and com- bined types of spawning can be distinguished in terms of prevailing couple motion. Frequency of such types is species-specific. Once the act of spawning is over,fi sh can swim up and topple over on the surface. A male in the pair is shifted ahead of a female for one head length. Male hits its tail stalk in the back of female abdomen. Depending onfi sh size, spawning act continues for 0.3-3sec with a path of 0.3-2m. One female participates in 20-80 spawning acts for 1-3 nights. Eggs cannibalism has been noticed. Biology, ecology & population dynamics Oral presentation

Recovering Inconnu, leucichthys, on Great Slave Lake: The effectiveness of marine protected areas, harvest control rules, habitat management and non- quota limitations in the rehabilitation of depleted resources.

∗Ross Tallman, M. Yamin Janjua, Melanie Van Gerwen Toyne, Lauren Wiens Fisheries and Oceans Canada, Canada Inconnu, , stocks have been subject to commercial and subsistencefi shing on Great Slave Lake, Canada from the late 1940s to the present. They are part of larger multispeciesfi shery principally focussed on Lake Whitefish, Coregonus clupeaformis and , Salvelinus namaycush. Inconnu are considered the most valuable Coregonid per kilogram harvested and conservation is an important concern. Some stocks have been extirpated while others such as the Buffalo River stock hover close to collapse. To conserve Inconnu a variety of measures have been implemented including mesh size changes, marine protected areas, and formal and informal quota regulations. Recently, genetic techniques such as micro-satellite mixed stock analysis and environmental DNA have been applied to determine the status of stocks. We review the effectiveness of the management measures and note directions for the future. In general, closed areas have been moderately effective in recovering Inconnu stocks but it also appears that market forces may overwhelm non-quota restrictions applied to thefi shery. Biology, ecology & population dynamics Oral presentation

FISHING TRIGGERS TROPHIC CASCADE IN TERMS OF VARIATION, NOT ABUNDANCE

∗Silva Uusi-Heikkilä, Tommi Perälä, Anna Kuparinen University of Jyväskylä, Finland Trophic cascade studies that rely on linear food chains may not realistically represent complex food webs. Further, trophic cascades are almost exclusively measured as biomass averages whereas measures of biomass variation have remained unexplored. We adopt a multi-dimensional view on trophic cascades by modeling them propagating across a complex food web and include a measure of biomass variation in addition to a measure of biomass average. We examined whether two differentfi shing strategies removing different predatory species from the ecosystem induce trophic cascades and whether the cascades differ from each other. The two different fishing strategies did not trigger a traditional trophic cascade propagating across the food web, as measured in biomass averages. Instead, bothfi shing strategies triggered a variation cascade that propagated across the food web includingfi sh, and phytoplankton. Infi sheries that removed a large amount of top-predatory and cannibalisticfi sh, the biomass oscillations started to decrease shortly afterfi shing was started while in fisheries that mainly targeted large planktivorous whitefish, the biomass oscillations did not show any sign of stabilizing. Predicting under whatfi shing strategy and at what rate trophic cascades might occur could help us to anticipate, and potentially prevent, the cascading effects offi shing. Biology, ecology & population dynamics Oral presentation

Drift of whitefish (Coregonus lavaretus L.) larvae in a tributary river of the Hallstättersee

∗Josef Wanzenböck, Tobias Grossgasteiger Research Department for Limnology Mondsee, University of Innsbruck, Austria Thefi sh community of Hallstättersee is dominated by European whitefish (Coregonus lavaretus). Besides the commonly used spawning habitats within lakes, mostly in shallow littoral areas, potamodromous spawning migrations are also known in several (sub-) populations of whitefish, e.g. in Hallstättersee. We investigated the drift of newly hatched larvae of whitefish in the major tributary of Hallstättersee during seven weeks in spring 2019 using drift nets. We used known numbers of larvae marked with alizarin red to spike larvalfi sh drift and to improve quantitative assessments. Furthermore, the distribution of larvae within the lake was investigated using an established push net method. Driftnet catches of larval whitefish were generally lower compared to similar catches done in 1999. The diel and seasonal (February, March, April) patterns of larval drift were analyzed. Biology, ecology & population dynamics Oral presentation

Whitefish Coregonus lavaretus in the upper reaches of the Pasvik River (Murmansk Region, Russia)

∗Zubova Elena, Kashulin Nikolay, Terentjev Petr Institute of the Industrial Ecology Problems of the North of the Kola Scienсe Center of the Russian Academy of Sciences, Russia The ichthyofauna in the upstream of the Pasvik River was investigated. Whitefish dominated in catches and was represented by individuals with the number of gill rakers from 19 to 34. It is known that the whitefish of the Inari-Pasvik system has from 16 to 40 gill rakers with a pronounced bimodal distribution according to this feature, which makes it possible to distinguish sparsely- and densely-rakered morphs. However, whitefish in the upstream of the Pasvik have no bimodal distribution. In appearance the rakers on thefi rst branchial arch are difficult to attribute to an individual in some form. The relative length of the largest gill raker in the whitefish did not depend on the number of rakers on the branchial arch and varied from 8.9 to 18.8%. Research in the agricultural district of Rayakoski in 2002-2004 showed a wider range of the number of whitefish rakers without bimodality in their distribution. Perhaps the convergence of the trait is associated with the hybridization of whitefish in the upper reaches of the Pasvik River. The hybridization reasons are: migration restriction due to dam construction; reduction of whitefish habitats, due to the vendace introduction, which actively displaces the densely-rakered whitefish from the pelagial.