Article

Night, day, sunrise, sunset: Do fish under snow and ice recognize the difference?

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Abstract

1. Although boreal lakes are ice-covered for several months annually, little is known about the behaviour of fish under ice. To consider the reasons for diel vertical migrations (DVM) it is important to compare periods under ice as opposed to under open water. Echosounding provides a tool for non-intrusive continuous monitoring of fish, even in winter. 2. Changes in the vertical distribution of fish through six 48-h periods were monitored using a stationary, mounted echosounder that beamed vertically either from the bottom up or from the surface down from February to April, 2003. The up-beaming and down-beaming transducers were run alternately for 24 h each over the 48-h period. Standard echo analysis software was used to detect fish traces and estimate the vertical and temporal distribution of fish abundance. Fish were sampled with a winter seine. 3. Prominent diel vertical migration in response to changing light level was detected throughout the study period (late winter to spring). Fish were highest in the water column at sunset and sunrise. In daylight, most detected fish were well below 10-m depth. The number of fish detected was greatest during the night when they occurred throughout almost the whole water column, sometimes with a considerable number very close to the ice. Fish were mostly vendace and whitefish. 4. It became evident from data from the up-beaming transducer that at night fish may occupy the layer closest to the surface. These fish would not have been detected if we had only used the down-beaming transducer. The overall pattern of DVM in winter was very similar to that in summer. The results support the suggestion that DVM is a genetically fixed behavioural trait responding to the contemporary level of illumination.

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... В данных условиях оптимальной стратегией зимнего выживания будет являться компромисс определенной степени между риском смертности от голода или хищничества [18], который возможно «регулировать» [3], миграциями в более коротких временных и пространственных масштабах, чем при более длительных и протяженных сезонных миграциях. Такое перемещение рыб называют «суточной вертикальной миграцией -СВМ» (Diel vertical migration -DVM) [3,19,20], при которой рыба мигрирует вверх и вниз в толще воды; данная закономерность встречается у ряда видов пресноводных рыб. При этом основным непосредственным триггером СВМ у них является резкое изменение интенсивности света [3,19,20], которое в сумерках запускает подъем рыб в толщу воды, а на рассвете -погружение ко дну. ...
... Такое перемещение рыб называют «суточной вертикальной миграцией -СВМ» (Diel vertical migration -DVM) [3,19,20], при которой рыба мигрирует вверх и вниз в толще воды; данная закономерность встречается у ряда видов пресноводных рыб. При этом основным непосредственным триггером СВМ у них является резкое изменение интенсивности света [3,19,20], которое в сумерках запускает подъем рыб в толщу воды, а на рассвете -погружение ко дну. Основные причины СВМ -поддержание эффективности биоэнергетических трат, кормление и избегание хищников, однако ни один из этих факторов сам по себе не может объяснить СВМ во всех случаях [3,20], в связи с этим данную особенность необходимо рассматривать на основе сложной многофакторной гипотезы, включающей в себя совокупность представленных факторов, сила каждого из которых может варьировать в различных местообитаниях [3]. ...
... В [19] показано, что водоемах Финляндии модель поведения рыб в естественной среде, обусловленная сменой дня и ночи, сохраняется в водах в условиях развитого ледового покрытия и снега, как и в нашем исследовании: в светлое время суток освоение акватории ямы более локальное, в темное -с бόльшим охватом площади исследуемой акватории. Таким образом, СВМ является генетически фиксированной [19], обусловленной внутренним циркадным ритмом животных. ...
Article
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To study the dynamics of the spatial distribution of fish under ice cover the research was carried out in the water area of the riverbed depression located in the lower reaches of the Irtysh River (Western Siberia, Tyumen region). The research was conducted by using the hydroacoustic method based on a computerized hydroacoustic software-hardware complex. It was found that, in the diurnal aspect, throughout the entire observation period (December - April), the number of fish in the riverbed increases during the dark period of the day, and during the light period it decreases. The dominant groups of fish change with the change of the period of the day: December - cyprinids prevail in the dark period of the day, in March and April - in the light period of the day, the rest of the time the group of percids predominated. With an increase in water temperature from December to April from 3.7 to 6.5 °C, it was noted that the density of fish decreases from 184 to 8 sp/hect. in the daytime and from 2157 to 91 sp/hect. at night (dark period), respectively. Fish explore the horizons of the water column of the riverbed depression during the day and night from the surface to the bottom with the highest density indicators near the surface, except - the daytime in December. With increasing density of fish at nightfall at the same time, there was an increase used water area of riverbed depression. In the vertical aspect, cyprinids avoid predators (pike, in-connu, burbot) in the diurnal dynamics; the distribution of cyprinids has a significant negative cor-relation with the distribution of the second group of fish. Thus, the features of the vertical and hori-zontal distribution of fish in the diurnal dynamics throughout the entire observation period are the strategy of their survival: for prey - escape from predators, for predators - search for food objects
... Считается, что динамика суточной активности и вертикальных перемещений гидробионтов связана в первую очередь с интенсивностью света [1,5,6,11], пространственно-временным компромиссом между перемещением за кормовыми объектами и избеганием хищников [2,4,[6][7][8]11], гидростатическим давлением [2] и температурой воды [2,12]. Изучение вертикального распределения рыб, их суточ-ной активности в пресноводных экосистемах в зимний период выполнено преимущественно в лимнических водоемах [2,6,13] и мелководных водотоках [14,15], что в свою очередь повышает актуальность изучения распределения рыб и их вертикальной миграции в глубоководной зимовальной русловой яме Нижнего Иртыша, играющего важную роль в формировании и сохранении водных биологических ресурсов Обь-Иртышского бассейна. ...
... Существенная суточная активность рыб установлена [13] в бореальных озерах в условиях наличия ледового покрытия значительными по длительности исследованиями -шестью 48-ми часовыми наблюдениями. В результате выполненной работы установлено, что вертикальная суточная миграция в ответ на изменение уровня освещенности происходит на протяжении всего зимне-весеннего периода исследования [13]. ...
... Существенная суточная активность рыб установлена [13] в бореальных озерах в условиях наличия ледового покрытия значительными по длительности исследованиями -шестью 48-ми часовыми наблюдениями. В результате выполненной работы установлено, что вертикальная суточная миграция в ответ на изменение уровня освещенности происходит на протяжении всего зимне-весеннего периода исследования [13]. Рыба была самой многочисленной в толще воды на закате и восходе солнца, при дневном свете большинство обнаруженных рыб были значительно ниже 10-метровой глубины, а их количество максимально в течение ночи, когда они регистрировались почти во всей толще воды, иногда в значительном количестве возле льда [13]. ...
Article
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Работа выполнена в акватории Горнослинкинской русловой зимовальной ямы Нижнего Иртыша в зимний период с помощью компьютеризированного гидроакустического комплекса. Съемка выполнена в светлое время суток при «высоком» солнце и вечером в темное время. Установлено, что рыбы различных экологических и размерных групп в акватории русловой ямы в суточно-световом аспекте демонстрируют статистически достоверную динамику плотности, степень ос-воения горизонтов водной толщи. Плотность рыб по горизонтам водной толщи (поверхностный, пелагический, придонный) в светлое и темное время суток составила 18, 105, 61 и 1378, 368, 411 экз/га соответственно. В светлое время рыбы осваивают придонные и пелагические горизонты с меньшими глубинами, ближе к берегам, в темное-наиболее интенсивно осваивают поверх-ностный горизонт, а пелагический и придонные в срединной более глубоководной части ямы. Вертикальное распределение таксономических и размерных групп рыб в пределах одной фазы суток и в суточно-световой динамике отражает оборонительное поведение мирных и хищных видов рыб-избегание риска хищничества и каннибализма. Карповые распределяются в гори-зонтах с меньшим относительным числом особей групп окуневых и сиговых-щуковых рыб, для окуневых характерна дифференциация по размерному признаку. Установлена статистически значимая разница в выборе рыбами вертикальных горизонтов водной толщи и их батиметриче-ских характеристик (глубин) в зависимости от световой фазы суток. Вертикальная миграция рыб в отсутствии световых ориентиров отражает генетически фиксированную реакцию животных на уровень освещения реализуемую посредством циркадного ритма. Ключевые слова: вертикальная миграция, зимние перемещения рыб, русловая зимовальная яма, Обь-Иртышский бассейн, избегание риска хищничества, динамика зимних скоплений рыб, циркадный ритм. Работа выполнена в рамках темы ФНИ: «Оценка состояния зимовальных русловых ям как элемент стратегии сохранения популяций сиговых и осетровых рыб Обь-Иртышского бассейна», № государственной регистрации 116020510083.
... There is broad consensus for several fish genera (Oncorhynchus, Coregonus, Lota, Osmerus) that the decline in illumination at dusk stimulates ascent, whereas the increasing illumination at dawn induces descent to the hypolimnion (Appenzeller & Leggett, 1995;Scheuerell & Schindler, 2003;Busch & Mehner, 2009;Probst & Eckmann, 2009). Further support for the triggering effect of light cycles has been gained by studies at high latitude in summer and on fish under ice (Steinhart & Wurtsbaugh, 1999;Jurvelius & Marjomäki, 2008;Gjelland et al., 2009;Kahilainen, Malinen & Lehtonen, 2009). In all these examples, migrations only occurred where there were diel phases of rapid changes in illumination, but stopped when the difference between day and night was low (as it is typical for Polar summer). ...
... Avoidance of predation by the deepwater form of lake trout [siscowet, Salvelinus namaycush siscowet (Walbaum)] might also explain DVM in deepwater coregonids [bloater; kiyi, C. kiyi (Koelz); lake herring, C. artedi Lesueur] in Lake Superior Jensen et al., 2006). Although predation risk has been discussed as an important ultimate explanation in many other case studies on freshwater fish DVM (Scheuerell & Schindler, 2003;Hardiman et al., 2004;Gjelland et al., 2009;Kahilainen et al., 2009), it has been noted that the often low densities of pelagic predators presumably impose only a slight direct predation risk and thus the selective value of DVM is not obvious (Narver, 1970;Mehner et al., 2007;Jurvelius & Marjomäki, 2008). ...
Article
1. Diel vertical migrations (DVM) are typical for many cold-water fish species such as Pacific salmons (Oncorhynchus spp.) and coregonids (Coregonus spp.) inhabiting deep lakes. A comprehensive recent overview of DVM in freshwater fish has not been available, however. 2. The main proximate trigger of DVM in freshwater fish is the diel change in light intensity, with declining illumination at dusk triggering the ascent and the increase at dawn triggering the descent. Additional proximate cues are hydrostatic pressure and water temperature, which may guide fish into particular water layers at night. 3. Ultimate causes of DVM encompass bioenergetics efficiency, feeding opportunities and predator avoidance. None of these factors alone can explain the DVM in all cases. Multi-factorial hypotheses, such as the ‘antipredation window’ combined with the thermal niche hypothesis, are more likely to explain DVM. It is suggested that planktivorous fish move within a layer sufficiently well illuminated to capture zooplankton, but too dark for predators to feed upon the migrating fish. In complete darkness, fish seek layers with a temperature that optimises bioenergetics efficiency. The strength of each factor may differ from lake to lake, and hence system-specific individual analyses are needed. 4. Mechanistic details that are still poorly explored are the costs of buoyancy regulation and migration, the critical light thresholds for feeding of planktivorous and piscivorous fish, and predator assessment by (and size-dependent predation risk of) the prey fish. 5. A comprehensive understanding of the adaptive value of DVM can be attained only if the behaviour of individual fish within migrating populations is explicitly taken into account. Size, condition and reproductive value differ between individuals, suggesting that migrating populations should split into migrants and non-migrants for whom the balance between mortality risk and growth rate can differ. There is increasing evidence for this type of partial DVM within populations. 6. Whereas patterns of DVM are well documented, the evolution of DVM is still only poorly understood. Because experimental approaches at realistic natural scales remain difficult, a combination of comprehensive data sets with modelling is likely to resolve the relative importance of different proximate and ultimate causes behind DVM in fish.
... DVM in coregonids has been reported from several lakes (Dembinski 1971;Hamrin 1986;Hrabik et al. 2006;Stockwell et al. 2010). Ascent and descent are proximately triggered by the change of illumination threshold during dusk and dawn (Jurvelius and Marjomäki 2008;Busch and Mehner 2009). The ultimate causes of coregonid DVM have been widely discussed with some controversy, but most researchers suggest that fish leave the well-lit near-surface layers during daytime to avoid visually oriented predators (Hrabik et al. 2006;Gjelland et al. 2009). ...
... Interestingly, however, evidence for high predation risk of coregonids in shallower layers of lakes could rarely be found, because the density of piscivores was in most cases surprisingly low (Hrabik et al. 2006;Stockwell et al. 2010;Mehner et al. 2010a). Therefore, a genetically fixed migration has been discussed as a response to the 'ghost of predation past' (Mehner et al. 2007b;Jurvelius and Marjomäki 2008). ...
Article
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Systematic comparisons of the ecology between functionally similar fish species from freshwater and marine aquatic systems are surprisingly rare. Here, we discuss commonalities and differences in evolutionary history, population genetics, reproduction and life history, ecological interactions, behavioural ecology and physiological ecology of temperate and Arctic freshwater coregonids (vendace and ciscoes, Coregonus spp.) and marine clupeids (herring, Clupea harengus, and sprat, Sprattus sprattus). We further elucidate potential effects of climate warming on these groups of fish based on the ecological features of coregonids and clupeids documented in the previous parts of the review. These freshwater and marine fishes share a surprisingly high number of similarities. Both groups are relatively short-lived, pelagic planktivorous fishes. The genetic differentiation of local populations is weak and seems to be in part correlated to an astonishing variability of spawning times. The discrete thermal window of each species influences habitat use, diel vertical migrations and supposedly also life history variations. Complex life cycles and preference for cool or cold water make all species vulnerable to the effects of global warming. It is suggested that future research on the functional interdependence between spawning time, life history characteristics, thermal windows and genetic differentiation may profit from a systematic comparison of the patterns found in either coregonids or clupeids.
... There is broad consensus for several fish genera (Oncorhynchus, Coregonus, Lota, Osmerus) that the decline in illumination at dusk stimulates ascent, whereas the increasing illumination at dawn induces descent to the hypolimnion (Appenzeller & Leggett, 1995;Scheuerell & Schindler, 2003;Busch & Mehner, 2009;Probst & Eckmann, 2009). Further support for the triggering effect of light cycles has been gained by studies at high latitude in summer and on fish under ice (Steinhart & Wurtsbaugh, 1999;Jurvelius & Marjomäki, 2008;Gjelland et al., 2009;Kahilainen, Malinen & Lehtonen, 2009). In all these examples, migrations only occurred where there were diel phases of rapid changes in illumination, but stopped when the difference between day and night was low (as it is typical for Polar summer). ...
... Avoidance of predation by the deepwater form of lake trout [siscowet, Salvelinus namaycush siscowet (Walbaum)] might also explain DVM in deepwater coregonids [bloater; kiyi, C. kiyi (Koelz); lake herring, C. artedi Lesueur] in Lake Superior Jensen et al., 2006). Although predation risk has been discussed as an important ultimate explanation in many other case studies on freshwater fish DVM (Scheuerell & Schindler, 2003;Hardiman et al., 2004;Gjelland et al., 2009;Kahilainen et al., 2009), it has been noted that the often low densities of pelagic predators presumably impose only a slight direct predation risk and thus the selective value of DVM is not obvious (Narver, 1970;Mehner et al., 2007;Jurvelius & Marjomäki, 2008). ...
Conference Paper
Diel vertical migrations (DVM) of freshwater organisms have traditionally been described as population-wide behaviour. Evolutionary explanations for DVM in fish consider predation avoidance, feeding opportunities and bioenergetics, all of these processes being sensitive to phenotypical differences between individuals within a population, for example with respect to size, sex, or reproductive status. The unit of selection is likewise the individual, and therefore we have to expect that the selective forces causing the evolution of DVM are individual-specific. Consequently, I predict that highly variable migration patterns and trajectories coexist in populations performing DVM. In this keynote lecture, I will show conceptual models on how the adaptive value of DVM is shaped by phenotypic variance within populations, and how individuals may modify their migrations to achieve highest relative fitness. I will combine the models with empirical evidence of individual migration trajectories and partial migration patterns. I will close the presentation by highlighting a few promising research questions which will foster understanding of the evolutionary origin of DVM.
... An interesting finding of the present study was long-distance movements of three individuals in midwinter, when water temperature was only few tenths of a degree over the freezing point and light levels were extremely low. In general, little is known about fish behavior under ice cover (Jurvelius and Marjomäki 2008), and even less of fishes living in large rivers (Huusko et al. 2007). The common belief is that under these conditions, fish reduce movement, activity, aggression, and feeding (Huusko et al. 2007). ...
Article
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In the Koitajoki River, Eastern Finland, there exists a self-sustaining population of river-spawning densely rakered whitefish (Coregonus lavaretus pallasi). The population has been classified as near-threatened due to overexploitation and possible hybridization with the lake-spawning sparsely rakered whitefish form. Thus, knowledge of habitat use, movements, and migrations is important for threat assessment and management decisions. We employed conventional tagging and acoustic telemetry to provide information on movements and home range of the Koitajoki River whitefish. We tagged mature individuals at their spawning areas and followed fish movements by tag recoveries and continuously recording fixed receiving stations. The maximum movement distances were 40–50 km both upstream and downstream from the releasing site. There were indications of a clear seasonal migration pattern and spawning-site fidelity; riverine habitats were mainly occupied for spawning and overwintering, while feeding and growth mainly took place in lacustrine environments within several lakes of the river system. Due to their migratory nature, whitefish is vulnerable to environmental disturbances and overfishing in a large geographic area.
... It reduces the amplitude of the short daylong night light regime. However, in northern streams and lakes this do not seem to change diel behavior patterns in local fish fauna (Jurvelius and Marjomaki 2008;Linnansaari et al. 2008;Strand et al. 2008;Linnansaari and Cunjak 2013). Juveniles may even be more active under surface ice, compared to more unstable periods with sub-surface ice or steep channels with more dynamic ice formation (Linnansaari et al. 2008;Stickler et al. 2008a;Linnansaari and Cunjak 2013;Watz et al. 2015). ...
Article
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Winter is an ecologically challenging season for ectothermic cold-water fish in natural streams because of reduced flow and freezing. Hydropower regulation in many northern rivers increase winter stream flow and temperatures, and reduce ice formation and surface ice cover. From a background review of knowledge about e.g. Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) winter survival strategies, we explore responses to hydropower impacts as a basis for adaptive management, mitigating strategies, and future research. Winter intensity and duration, hydrologic conditions and channel characteristics drive complex ice processes which become more complex and pervasive in smaller, high-gradient streams. Stream ice formation may be divided into the dynamic period ‘freeze-up’ in early winter with sub-surface ice, more stable ‘mid-winter’ with surface ice, and the ecologically challenging ‘ice break-up’ in winter-spring with potential mechanical ice runs and scouring. The characteristics of periods vary depending on climate and hydropower regulation. In reaches downstream of power-plant outlets water temperature may increase and reduce surface ice formation. The mid-winter period destabilize or become absent. In bypass reaches flows decrease and facilitate freezing and ice production. Knowledge about longitudinal water temperature changes is limited. Hydro-peaked systems may aggravate high-low flow effects. A basic winter survival strategy in salmon and trout is energy storage, but also reduced metabolism, tolerance and starvation effected by quiescence. Energy storage may depend on local conditions, but there is little indication of adaptation to local thermal climates. Intraspecific phenotypic plasticity is important. The main behavioural strategy is risk-reducing sheltering in the substratum or deep areas, and nocturnal activity. Local movements between daytime refuges and nighttime slow-current activity areas are usually limited to meters. Larger fish may move more and aggregate in restricted suitable deep-slow refuge habitats such as pools and deep glides. Fish cope with ordinary thermal ice phenomena, and do not appear to become trapped in ice. Surface ice may reduce fish metabolism, but other factors, e.g. availability of substrate shelter, may override this effect. Mechanical ice break-ups and less surface ice may reduce survival. An adaptive mitigating strategy may be higher regulated flows in winter which increase rearing and/or resting habitat and survival, but studies are few and knowledge is limited. However, higher regulated flows also affect temperature regime. Low flows increase ice formation, reduce and fragment available habitat, and may reduce egg and fish survival. Influx of ground water may mitigate these impacts, as will stabilize minimum flows. Sudden drops in regulated water discharge should be avoided. Fish may strand, in particular at low temperatures in the daytime when fish are less mobile and seek shelter. The challenging winter season is understudied, and important management considerations and future research areas for better adaptive management are suggested.
... Although the sampling was performed only in September, the previous seasonal open water datasets of zooplankton and niche utilization of whitefish morphs and vendace support the observed patterns in this study (Bøhn and Amundsen 1998, 2001; Kahilainen et al. 2004, 2005; Gjelland et al. 2009). However, there is a need for winter sampling during ice cover when zooplankton community is certainly different due to lack of cladocerans (Tolonen 1998) and niche utilization of coregonids may also differ (Jurvelius and Marjomäki 2008). In this study, we found that zooplankton body size and density decreased with increasing coregonid diversity, a pattern commonly observed in zooplankton communities when the number of specialized planktivorous fish species increases (Nilsson and Pejler 1973; Post et al. 2008; Amundsen et al. 2009). ...
Article
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Gill raker divergence is a general pattern in adaptive radiations of postglacial fish, but few studies have addressed the adaptive significance of this morphological trait in foraging and eco-evolutionary interactions among predator and prey. Here, a set of subarctic lakes along a diversifying gradient of coregonids was used as the natural setting to explore correlations between gill raker numbers and planktivory as well as the impact of coregonid radiation on zooplankton communities. Results from 19 populations covering most of the total gill raker number gradient of the genus Coregonus, confirm that the number of gill rakers has a central role in determining the foraging ability towards zooplankton prey. Both at the individual and population levels, gill raker number was correlated with pelagic niche use and the size of utilized zooplankton prey. Furthermore, the average body size and the abundance and diversity of the zooplankton community decreased with the increasing diversity of coregonids. We argue that zooplankton feeding leads to an eco-evolutionary feedback loop that may further shape the gill raker morphology since natural selection intensifies under resource competition for depleted prey communities. Eco-evolutionary interactions may thus have a central role creating and maintaining the divergence of coregonid morphs in postglacial lakes. KeywordsEcological speciation–Foraging trait–Polymorphism–Vendace–Whitefish morphs
... In northern latitudes, the light regime shifts markedly throughout the year. The response in DVM behaviour of fishes has been documented during the long periods of day length associated with sub-Arctic summers (Gjelland et al., 2009;Kahilainen et al., 2009), as well as during the long-term darkness of the under-ice environment (Steinhart & Wurtsbaugh, 1999;Jurvelius & Marjomäki, 2008). In addition, advancements in animal tracking technology have made it possible to discover daily and seasonal patterns of fish movement in relation to their physical environment in ways that were previously impossible (Cooke et al., 2004). ...
Article
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Determining the habitat use and movements by fish is critical to our understanding of aquatic ecosystem function. The objective of this study was to assess the diel movements of Burbot (Lota lota) over the open water season. We employed a high-resolution acoustic telemetry positioning system to track the movements and activity of four Burbot during the ice-free season (between June and September) in a sub- Arctic lake. Burbot underwent diel bank migration (DBM), a benthic form of diel vertical migration, where depths are transitioned in close association with the bottom rather than through the water column. During daytime, Burbot occupied deeper water, at the transition of soft, low complexity substrates and ascended along the rocky bottom lake banks to shallower water habitats at night. Increased activity rates during shallow water forays suggest active feeding events. DBM was low at the start of summer with nearly 24 h of daylight, but increased towards the mid-summer with a more pronounced night cycle, coalescing towards the fall. The DBM of Burbot is dynamic, with proximate triggers of light and temperature, and ultimate causes likely being foraging opportunities, bioenergetics gain and predator avoidance.
... Lake Superior experiences an average maximum ice coverage of 63% annually and rarely experienced [ 90% ice coverage (ten times since 1973; Wang et al., 2018). DVM is known to occur under lake ice (Jurvelius & Marjomaki, 2008) and thickness of ice, ice clarity and snow cover can drastically affect light penetration (Bolsenga, 1978;Roulet & Adams, 1986). For the Great Lakes, light extinction coefficients of k = 0.25 m -1 , and 0.5 m -1 are common for ice. ...
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Using siscowet lake charr (Salvelinus namaycush siscowet) as an example organism, we modeled visual foraging habitat in relation to: (i) daily solar and lunar intensity, (ii) seasonal changes in maximum solar and lunar altitude, (iii) foraging for pelagic or benthic prey, and (iv) increased turbidity that may occur with climate change. Siscowet foraging success increased with light intensity and was higher for pelagic prey than benthic prey. Daily and seasonal siscowet foraging patterns were similar for benthic and pelagic prey types. Predicted day-time foraging depths were deepest in summer and shallowest in winter (range 172–233 m for pelagic prey and 210–283 m for benthic prey), and night-time foraging depths were deepest in winter and shallowest in summer (range 25–32 m for pelagic prey and 63–81 m for benthic prey). Within the Lake Superior basin, extreme precipitation events and associated sediment plumes can cause localized declines in light attenuation. Increases in turbidity associated with these sediment plumes can reduce predicted foraging depths by 65% and 80%, when compared to normal lake attenuation values. The model can be applied to predict how solar and lunar patterns influence foraging patterns in any aquatic organism that displays light-mediated behavior.
... If fish have reduced their movement, passive equipment will catch less fish than active equipment. Data on fish activity, aggregation, and behavior can be obtained qualitatively using remotely operated vehicles or a simple "inverted periscope" (Magnuson and Karlen 1970), or quantitatively using an acoustic telemetry array (e.g., Hanson et al. 2008) or echosounder (e.g., Jurvelius and Marjomäki 2008;Ahrenstorff and Hrabik 2016). Minnows traps can be placed on the lake bottom or suspended in the water column to investigate fish distributions and collect specimens (Magnuson et al. 1985). ...
... The notion of an inactive ecosystem, combined with the logistic and methodological challenges involved in winter field studies, has implicated that the general knowledge on lake winter ecology is limited (Salonen et al. 2009). However, evidence is mounting that lake winter ecology is not static, at least regarding the activity and behaviour of the fish (e.g., Jurvelius & Marjomaki 2008;Amundsen & Knudsen 2009;Salonen et al. 2009). ...
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Temperate lakes can be ice covered for several months each year, yet little is known about the behaviour and activity of the fish during the cold season. As northern pike represents the top of the food web in many northern temperate lakes and may structure the ecosystem both directly and indirectly, a detailed understanding of the behaviour of this species during winter is important. We continuously monitored the activity of adult northern pike (Esox lucius) in a small temperate lake from late summer to winter for two consecutive years using an automatic acoustic positional telemetry system. Four subsample periods representing different temperature regimes from each year were chosen for further investigation. The results revealed that pike activity was similar between seasons. In all periods, a distinct diel pattern, showing increased activity during day as compared to night, was evident. Our findings indicate that the fish component of temperate lentic ecosystems can be more active during the cold season than previously assumed. This may have implications for the structuring effect of pike on the lower trophic levels.
... Fish living at high latitudes with severe winters and short days seem capable of detecting very low light levels. For example, studies of several species in both Norway (Strand et al. 2008) and Finland (Jurvelius and Marjomaki 2008) have shown that diel behaviour patterns driven by day-night cycling continue unimpeded in waters covered by thick layers of ice and snow. Successful feeding in reduced light can be achieved by improving vision or by employing other senses that do not depend on light (e.g. ...
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Thermal preference and performance provide the physiological frame within which fish species seek strategies to cope with the challenges raised by the low temperatures and low levels of oxygen and food that characterize winter. There are two common coping strategies: active utilization of winter conditions or simple toleration of winter conditions. The former is typical of winter specialist species with low preferred temperatures, and the latter is typical of species with higher preferred temperatures. Reproductive strategies are embodied in the phenology of spawning: the approach of winter conditions cues reproductive activity in many coldwater fish species, while the departure of winter conditions cues reproduction in many cool and warmwater fish species. This cuing system promotes temporal partitioning of the food resources available to young-of-year fish and thus supports high diversity in freshwater fish communities. If the zoogeographic distribution of a species covers a broad range of winter conditions, local populations may exhibit differences in their winter survival strategies that reflect adaptation to local conditions. Extreme winter specialists are found in shallow eutrophic lakes where long periods of ice cover cause winter oxygen levels to drop to levels that are lethal to many fish. The fish communities of these lakes are simple and composed of species that exhibit specialized adaptations for extended tolerance of very low temperatures and oxygen levels. Zoogeographic boundaries for some species may be positioned at points on the landscape where the severity of winter overwhelms the species' repertoire of winter survival strategies. Freshwater fish communities are vulnerable to many of the shifts in environmental conditions expected with climate change. Temperate and northern communities are particularly vulnerable since the repertoires of physiological and behavioural strategies that characterize many of their members have been shaped by the adverse environmental conditions (e.g. cool short summers, long cold winters) that climate change is expected to mitigate. The responses of these strategies to the rapid relaxation of the adversities that shaped them will play a significant role in the overall responses of these fish populations and their communities to climate change.
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Visually foraging planktivorous fish are prey of visual predators, and their foraging behaviour may be affected by light levels both in terms of gain and risk. The large seasonal change in day length throughout a subarctic summer at 69 degrees N was used to show the influence of light on diel vertical migration (DVM) and shoaling patterns in a planktivorous fish assemblage consisting of two species (Coregonus lavaretus and Coregonus albula). Under the midnight sun in June, night and daytime behaviour was similar, with extensive shoaling and limited DVM. With increasingly darker nights towards autumn, the fish dispersed during the dark hours and showed more extensive DVM. Throughout the changing light regime of both the day and the season, the planktivores consistently chose depths with light levels compatible with visual foraging and reduced predation risk as revealed from reactive distance modelling of coregonids and their salmonid predators. The findings support the hypothesis that behavioural decisions are based on a trade-off between foraging rate and predation risk, and increased predator avoidance behaviour towards autumn suggests that this trade-off is state-dependent.
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Winter has traditionally been considered as an ecologically insignificant season and, together with technical difficulties, this has led winter limnology to lag behind summer limnology. Recently, rapidly expanding interest in climate warming has increased water research in winter. It has also become clear that neither winter conditions of lakes nor under-ice communities are as static as often supposed. Although interannual differences in water temperature are small, close to the maximum density temperature, they may have profound effect on under-ice hydrodynamics. Thus, stochastic variations in weather, particularly those preceding the time of freezing and ice melting, may have important consequences for hydrodynamics which then affect the distributions and conditions of microorganisms and probably further to higher trophic levels. Even fish distributions can be dictated by under-ice conditions and their activities as well as behavior can sometimes approach those in summer. Life in freshwater ice is one of the least studied aspects of winter limnology and recent studies suggest that a thorough evaluation is needed. Altogether there are strengthening signs that winter should be considered as an integral part in the functioning and dynamics of lakes affecting quantitative and qualitative characteristics of aquatic communities in summer. There are great prospects that more thorough understanding of the prevailing limnological conditions in winter will improve our understanding of lake ecosystems in their entirety, and there is no doubt that such an approach requires multidisciplinary and long- term studies at different spatial scales.
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1. Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. 2. Undertaking a large-scale field experiment in a thermally stratified, canyon-shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. 3. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < 0.001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (depth >3.0 m) reaching a maximum amplitude of 13 m. 4. Hydroacoustic recordings by the echosounder SIMRAD EK 60 (120 and 400 kHz) showed that during the experiment, when the surface was covered with a large black non-transparent foil (2500 m 2 ; simulated conditions of complete and constant darkness), the regular vertical movement of the bathypelagic perch early juveniles was interrupted and the community occupied the epilimnion constantly for 24 hr. 5. Immediately after the foil was removed at midday, the bathypelagic perch early juveniles were exposed to a steep increase in light intensity (from <1 LUX to >100 000 LUX) and they escaped into the hypolimnion where they were safe from visual predation which took place in the bright surface layers (epilimnion particularly). Our findings imply that occupying a deep, dark refuge in the daytime is essential for the survival of perch in their early life stage. See also supplementary Appendixes S1-S5.
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We observed small schools of vendace (Coregonus albula (L.)) which occasionally crossed the thermocline and migrated into the exceptionally warm (22 to 23 °C) epilimnion of a large Finnish lake in August 2010. This is against previous observations regarding diel vertical migration (DVM) in this species. The ascending schools were detected for a short period of time about an hour after sunset. The findings were based on data gathered with a 120 kHz echo sounder, an Acoustic Doppler Current Profiler, a Laser Optical Plankton Counter, a MultiNet plankton sampler and a mid-water trawl for the experimental sampling of pelagic fish. The study emphasises the importance of examining DVM with different kinds of samplers simultaneously. We are unable to state the ultimate reason why some vendace migrated from cool to warm water, but we can state that there was a lot of food for them in the epilimnion around sunset. It would have been impossible to detect the phenomenon using only mean or maximum abundances of fish, and we had to use very fine scales to detect the phenomenon on echograms. The ascension of macrozooplankton, mostly Chaoborus flavicans (Meigen), followed a rhythm described by a third order polynomial function. Vendace were feeding in the evening near sunset within the ascending anti-predation window in which there was enough light for detecting zooplankton and shelter against predators, while during daytime the majority of stomachs of vendace (63%) and smelt (Osmerus erperlanus (L.)) (50%) were empty in mid-water depth layers of the lake where the main pelagic fish populations were detected. Based on our observations on fish movements during thermal stratification in August, we conclude that vendace has a potential to tolerate by behavioural means warm water up to 23 °C.
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Acoustic estimation of fish abundance requires knowledge of the target strength (TS) distribution associated with the fish present. We measured the TS distribution at 70 kHz for five size-groups of alewives Alosa pseudoharengus (mean total length = 68-138 mm) swimming freely in a large net-cage. Although the mean and mode of the distributions were significantly related to fish length, the TS range obtained from each length-class was over 25 decibels (dB). The TS distributions were negatively skewed and had a tendency toward bimodality. The TS distributions at 70 and 123 kHz were similar for one alewife size-group that was measured with both frequencies. Small but inconsistent differences were found between day and night for the same groups of fish. Shapes of the TS distributions were similar when centered on the mode, and we derived a probability density function (PDF) for TS at 70 kHz as a function of fish length to describe these distributions. We used this PDF to predict TS distributions based on alewife gill-net catch from six lake surveys and compared predictions with in situ TS distributions from each acoustic survey. Observed and predicted distributions were similar for TS values greater than −50 dB, but the observed number of small TS values exceeded the predicted number for several of the surveys. Some of these smaller TS values were probably from invertebrates or smaller fish or were indicative of noise. Estimates of alewife density from lake surveys were highly affected by inclusion or exclusion of these smaller targets. We used the predicted TS distribution derived either from catch data or from the TS values greater than −50 dB to calculate the proportion of smaller TS values that were probably from alewives. Both methods resulted in similar abundance estimates, which were higher than estimates based on an existing TS-length regression for alewives.
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In winter, the role of wintering riverbed depressions is reduced to the usual wintering of various fish species. In this regard, currently relevant questions are: functioning of riverbed depressions in the period of open water, relationship of fish in the predator-prey system, and dependence of horizontal and vertical distribution of fish of different families in river areas and their value. The aim of this work was to reveal the patterns of vertical and horizontal distribution of fish in the wintering riverbed depression on the Irtysh river in the period of open water. We conducted a research during the summer period (June 23, 2015) in the Gornoslinkinskaya wintering riverbed depression situated on the Irtysh river in the territory of Uvatsky district, Tyumen region, 58°43'35,58''N, 68°41'45,75''E. The maximum depth is more than 41 m. To determine the average density of fish and their number, we performed hydroacoustic surveys by the ''PanCor'' complex, which is based on the sonar ''Furuno'', analog-digital converter and GPS-location. On the investigated water area, we used a boat to move along a grid of tacks (zigzagging). We processed the hydroacoustic survey files in the laboratory using special applications: ''PanCor'', ''Taxonomy''. For analysis, the water column was conventionally divided into 4 horizons: surface-pelagic (<10 m), 2 pelagic (10-20, 20-30 m) and bottom-pelagic (> 30 m). To analyze the correlations of fish distribution of different taxonomic groups, the nonparametric method, Spearman rank correlation, was used. The degree of statistical significance of differences in the distribution of fish in the different horizons of the water column was carried out using the sign test. In the distribution of representatives of percidae and coregonidae, which were represented only by predatory fish species in the area of our research, we found regularity: their proportion increased with depth for percidae from 15.07 to 35.89%, for coregonidae from 4.6 to 9.26% from the surface to horizons of 20-30 m; at the depth of more than 30 m the proportion of corigonidae remained about the same - 8.09% (See Figure 1). Cyprinidae dominated throughout the entire water column of the investigated water area, in terms of numbers: at the depth of less than 10 m - 77.64%, 10-20 m -64.70%, 20-30 m - 59.77%, at the depth of more than 30 m, their proportion was the lowest - 51.31% (See Figure 1). From cyprinidae in all horizons of the water column, juvenile fish with body length up to 15 cm dominated. From the surface to the bottom, the proportion of these fish in the layers of water was decreasing. For percidae, the maximum distribution values for the majority of the size groups of fish characterized the 1-st pelagic layer. The distribution of coregonidae and not identified fish was similar to that of percidae. The distribution of fish is determined by the dominance of juvenile cyprinidae in the surface-pelagic horizon, and fish of other families, predominantly carnivorous, in the 1-st pelagic layer, which is the window of ''anti-predation'' in the watercourse - a strategy of defensive behavior and survival (See Figure 2). In the vertical aspect, a significant correlation (high and moderate) is revealed between individuals of the same family and representatives of predators and prey in the conjugated horizons of the water column, reflecting the mechanism of proportional distribution of some species and simultaneous reduction of their intra - and interspecific competition, as well as trophic behavior, which is also noted in the horizontal aspect - in fish of different families. (See Tables 1, 2). The article contains 2 Figures, 2 Tables and 36 References.
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Floating solar photovoltaics, or floatovoltaics (FPV), are a relatively new form of renewable energy, currently experiencing rapid growth in deployment. FPV decarbonises the energy supply while reducing land-use pressures, offers higher electricity generating efficiencies compared to ground-based systems and reduces water body evaporation. However, the effects on lake temperature and stratification of FPV both sheltering the water’s surface from the wind and limiting the solar radiation reaching the water column are unresolved, despite temperature and stratification being key drivers of the ecosystem response to FPV deployment. These unresolved impacts present a barrier to further deployment, with water body managers concerned of any deleterious effects. To overcome this knowledge gap, here the effects of FPV-induced changes in wind speed and solar radiation on lake thermal structure were modelled utilising the one-dimensional process-based MyLake model. To resolve the effect of FPV arrays of different sizes and designs, observed wind speed and solar radiation were scaled using a factorial approach from 0% to 100% in 1% intervals. The simulations returned a highly non-linear response, dependent on system design and coverage. The responses could be either positive or negative, and were often highly variable, although, most commonly, water temperatures reduce, stratification shortens and mixed depths shallow. Modifications to the thermal dynamics of the water body may subsequently drastically alter biogeochemical processes, with fundamental implications for ecosystem service provision and water treatment costs. The extreme nature of response for particular wind speed and solar radiation combinations results in impacts that could be comparable to, or more significant than, climate change. As such, depending on how they are used, FPV have the potential to mitigate some of the impacts of climate change on water bodies and could be a useful tool for water body managers in dealing with changes to water quality, or, conversely, they could induce deleterious impacts on standing water ecosystems. These simulations provide a starting point to inform the design of future systems that maximise ecosystem service and environmental co-benefits from this growing water body change of use.
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To evaluate the consistency of mobile and vertical echosounding results from the 1980s to the 2000s, fish density (fish ha−1) and target strength (TS, dB) estimates of single (70 and 200 kHz) and split (38 and 120 kHz) beam echo sounders were compared under varying light conditions. Acoustic estimates were compared with trawling results. During daytime hauls, the catch per swept area (CSA) of vendace and smelt were high at 10–15 m depth and low at 15–30 m depth. Around sunset, vendace and to some degree also smelt were concentrated at some meters above the thermocline. Around midnight, the CSA showed that smelt occupied higher water layers than vendace. Under different light conditions, both single and split beam echo sounders were in good agreement regarding the general level of fish density. In dusk and darkness, density estimates from echosounding and trawling as well as the TS-distribution between the single and split beam sounders were more consistent than those in daylight. We conclude that in boreal lakes single and split beam echosoundings outline, in comparable light conditions, consistent time series from the 1980s up to the year 2010. Darkness gives the best condition for estimating fish density and acoustic fish size.
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This review assessed the status and scope of freshwater hydroacoustic fisheries research in global aquatic ecosystems with emphasis on i) geographical and spatial scope, ii) taxonomic range at the species and family levels (restricted to bony fishes of the Actinopterygii and Sarcopterygii), and iii) temporal scope. Hydroacoustic measures have been used by ecologists and managers of freshwater systems for several decades, with major progress in technology and methods in recent years. A literature review indicated 296 research contributions that employed hydroacoustics to study freshwater fisheries in 294 different aquatic ecosystems. Spatially, hydroacoustics research in freshwater systems have thus far been concentrated in developed countries, particularly in North America and Northern and Central Europe (83% of the studies reviewed here). Most studies were small in spatial scale and short-term, with 80% including only a single body of water and 63% conducted over a single year or season (75% spanning less than two years). In addition, effects of fish morphology and behavior on acoustic target strength (TS) and taxonomic identification are not well parameterized, with only 21 species receiving empirical study of TS. Despite progress, the present study reveals gaps in the knowledge needed for wider applications to management. These include larger biogeographical and temporal scales of study and further empirical research on TS and taxonomic identification. Recent advances in size rather than species-based methods and theory offer potential solutions to this issue but require further investigation. We conclude with recommendations for systematic hydroacoustic research to enable more effective monitoring, management, and conservation of fisheries and freshwater ecosystems.
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The diel vertical distribution of nutrients, phytoplankton, zooplankton and fish were studied simultaneously at two pelagial stations in Lake Ladoga in August 1995. At one site (Valaam) cryptophyceans dominated in phytoplankton, while at the other (Konevits) diatoms were more common. In Valaam the algae were distributed unevenly, mainly in the surface layers, while in Konevits the algae were distributed evenly throughout the entire 0-20 m layer. In Valaam a clear diel migration pattern was observed by most of studied zooplankton taxa, while in Konevits only large Cyclops and Limnocalanus migrated. The peak total density of pelagic fish was more than twice as high in Konevits as in Valaam, while the zooplankton density was three times lower in Konevits than in Valaam. In Valaam the clear surface maximum of cryptophyceans probably affected the migration pattern of most species of herbivorous zooplankton. In Konevits the lower temperature in the metalimnion, where the daytime zooplankton maximum occurred, and evenly distributed food resources may have limited zooplankton migration, despite the existing predation pressure.
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The distribution of fishes is influenced by a host of physico-chemical and biological variables, including temperature and oxygen, prey abundance, feeding or assimilation rates, and predation risk. We used hydroacoustics and midwater trawls to measure the vertical distribution of pelagic fishes during a series of research cruises on Lake Superior's western arm in 2001 and 2004. Our objective was to assess vertical structuring in the fish assemblage over varying light levels. We observed variability in vertical structuring of both ciscoes (Coregonus spp.) and their primary predator, the siscowet (Salvelinus namaycush siscowet). Our results indicate that deepwater predators and prey migrate extensively over a diel cycle. This migration pattern is most consistent with changes in the distribution of prey resources for siscowet and diel variability in predation risk controlled by changing light levels for ciscoes. The magnitude of vertical migration in ciscoes increased with higher abundance of siscowets, supporting predation risk as a driver of cisco distribution. This study describes the extent of vertical migration in each group of fish, provides a statistical description of the pattern, and discusses the implications for trophic interactions in the Lake Superior food web.
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A large block of unpublished information from the late 1960s on the interactive ecology of two highly zooplanktivorous fishes - vendace (Coregonus albula) and smelt (Osmerus eperlanus)- in Lambarfjärden of Lake Mälaren, Sweden, was used to demonstrate quantitatively diel and seasonal changes in their limnetic feeding distribution, to compare their trophic structures, and to examine their selective use of some 20 different zooplanktonic taxa with those pelagically present by species, size, abundance and vertical distribution. Although there were significant differences in gillraker number, as well as spacing and structure between vendace and smelt, these did not seem to be strongly reflected in selection or use of major zooplanktonic prey taxa during the summer – autumn seasons. Schoener's overlap indices were high for both vertical distribution and prey taxa use by the two species, suggesting the possibility of strong competitive interaction between their planktivorous stages, though alternative explanations are explored. Their joint use of pelagic space and prey, changing seasonally, may offer a partial explanation for the marked year class fluctuations and periodic failures of vendace recruitment known to occur in Lambarfjärden, and other lakes where the two species coexist. In addition, the comparisons support the image of the environmentally cul-de-sac position of vendace as an extreme zooplankton specialist, with a very narrow diet spectrum and habitat range, whereas smelt seem to express a more opportunistic ecology.
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We studied the swimming speed and vertical distribution of fish under ice from March to April and in open water in August. Fish were surveyed with a downward facing stationary 120 kHz split beam echo-sounder in a boreal lake. A commercial trace tracking software was used to estimate the depth, speed and size of fish. Most fish in the study area were smelt (Osmerus eperlanus) and vendace (Coregonus albula). In March and April, fish were detected under the ice around the clock, whereas in August only a few fish were detected during daytime. Fish were typically detected between 12 and 19 m depth and they swam from 5 to 50 cm s-1 i.e. 0.5 to 3 body lengths s-1. The effect of sunrise and sunset on the under-ice swimming depth and speed became more marked with increasing day length. In summer, the effect on depth was not so evident. In March-April there was a shift towards day activity, which persisted in August. Changing illumination seemed to account for most variation in the swimming depth and speed of fish.
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As a consequence of a local disagreement between commercial fishermen and local fishing-right owners, we estimated the size of a vendace (Coregonus albula) stock in a southern boreal lake in Finland in March 2000. We applied a mobile under-ice echo-survey and catch sampling from winter seining. The sounder with a tape recorder was placed in a shuttle and towed under ice from hole to hole with a rope. The mean fish density was 4270 fish ha-1. Vendace biomass was estimated to be ca. 36 tonnes. Commercial fishing started on a restricted scale after the completion of the assessment. The vendace yield was ca. 6 tonnes in the area during the remainder of the winter-seining season. The total winter seining catch amounted to ca. 40% of the initial vendace stock size in January 2000.
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The abundance of fish in three contrasted Norwegian freshwater lakes (different species, depth, habitat) was measured in August and September 1999 by echo sounding. All three lakes were surveyed by day and night with the echo sounder acoustic beam oriented both vertically and horizontally. Vertical beaming, due to the hydroacoustic blind-zone, detected little fish activity close to the surface of the lakes. When beaming horizontally, particularly at night, large number of fish were observed near the surface of all the lakes. The range obtained when beaming horizontally was 50–100 m. Vertical beaming was shown to underestimate the presence of fish by 20–100%, supporting the conclusion that horizontal beaming is a critical factor in compiling accurate fish stock assessments in lakes. Echo sounding data were in agreement with catch data with respect to vertical distribution and fish density. Other valuable information was obtained on diurnal and nocturnal fish distribution and noise masking of fish echoes due to shallow water and wind.
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Hydroacoustics is a suitable method for estimating the stock size and spatial distribution of pelagic fish species with low fishing mortality. Pelagic three-spined stickleback (Gasterosteus aculeatus) is such a species. Its spatial distribution and abundance were studied by hydroacoustics and trawling in the Gulf of Bothnia in August 1991. Upward and downward looking transducers were used in this round-the-clock survey. Sticklebacks were in the surface layers at night, and during the day they migrated down to 10–20 m depth. The thermocline was at a depth of 13 m. Sticklebacks had a very patchy horizontal distribution, with the highest biomass densities being found just north of the Quark area (up to 14–28 t NM−2) and the lowest in the southern parts of the Bothnian Sea. The areal density of sticklebacks was lowest in the southern Bothnian Sea (124 × 103 specimens NM−2) and highest in the Bothnian Bay (3000 × 103 specimens NM−2). The estimated total biomass of three-spined stickleback was about 25 000 tons in the pelagic areas of the Gulf of Bothnia.
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We used stationary hydroacoustics and measures of environmental conditions (water temperature, dissolved oxygen, light levels, and zooplankton) to determine what factors, foraging or predation risk, influenced die! vertical migrations of Oncorhynchus nerka during winter in three high-mountain lakes. The Sawtooth Valley lakes are deep, oligotrophic, glacial lakes located in central Idaho, U.S.A., and historically contained populations of anadromous O. nerka. In general, low light intensities limited foraging opportunities of O. nerka under ice, especially at night. In Stanley Lake, O. nerka underwent diel vertical migrations to exploit available light to feed. Oncorhynchus nerka occupied shallow water at night, where there was still sufficient light to feed, but were found in deep water during the day. It is unknown whether O. nerka occupied deep depths during the day to feed on high densities of zooplankton or to avoid predators. In Alturas Lake, O. nerka remained in the top 25 m both day and night to feed high densities of zooplankton found near the surface. In Redfish Lake, O. nerka also showed little migration: O. nerka stayed in shallow water both day and night and occupied the same depths with the highest zooplankton densities. The vertical distribution of O. nerka during the winter appears to be determined by available food and light, but the deep daytime distribution found in Stanley Lake is still unexplained.
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To determine how moonlight and daylight affect hydroacoustic estimates of fish abundance, we used a dual-beam transducer and echo integration to survey pelagic fish (primarily Bonneville ciscoes Prosopium gemmifer) in Bear Lake, Utah and Idaho. During the new moon, the fish were dispersed (not schooling) below the thermocline, chiefly at the depths of 10–20 m. At full moon, they were dispersed but much closer to the bottom, where they were difficult to detect. Acoustic estimates offish density and biomass during full moons were approximately 50% of values derived during new moons. A diel survey during a new moon indicated that fish were widely dispersed in the water column at night, but formed schools at dawn. Our study indicated that light conditions must be standardized to insure consistent and comparable population estimates of some pelagic fishes.
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The effects of the timing of hydroacoustic surveys on the accuracy and precision of smelt (Osmerus eperlanus) density estimate were studied by comparing four day and night surveys in the eutrophic and clay-turbid Lake Hiidenvesi. The acoustic surveys were supplemented by trawling in the surface "blind" zone of the echo sounder. We hypothesised that due to acoustic shadowing, day surveys should result in lower density estimates than night surveys, unless a noticeable portion of the stock ascends to the surface blind zone at night. The effect of acoustic shadowing on the accuracy of density estimates was negligible, probably due to the sparser and smaller schools, as well as the smaller fish, in Lake Hiidenvesi compared to those study areas where shadowing has been previously documented. Similarly, the effect of diel vertical migration was small, because densities also remained rather low in the surface blind zone at night. Surprisingly, the highest densities in the blind zone were found during daytime in November. Both day and night surveys revealed a decreasing trend of density, probably due to high natural mortality. Based on the coefficients of variance for acoustic data, night sampling yielded more precise density estimates than day sampling. However, because the overlap with vertical distributions of 0+ and older smelt was clearly higher at night, making determination of unbiased size distribution more laborious, we found day surveys slightly more appropriate for smelt stock assessment in Lake Hiidenvesi.
Article
The density and movements of fish under ice were studied with single-beam mobile surveys and fixed location split-beam surveys, as well as exploratory fishing in winter-seining areas of two shallow Finnish lakes during winter 1999. Fish schooled near the bottom during the day but the schools dispersed and fish ascended at night. Single and split-beam target strength distributions corresponded fairly closely with the length distribution of seine catch samples. Estimated fish densities were greater at night than in daylight. The swimming speed of smelt (Osmerus eperlanus) was 0.18 m·s–1 in daylight and 0.36 m·s–1 at night. The corresponding figures for vendace (Coregonus albula) were 0.11–0.17 and 0.05–0.08 m·s–1. Nights immediately before and after fishing were the best periods to estimate the effect of seining on fish density. The hydroacoustic fish density estimates at night corresponded closely with seine catches. We conclude that it is possible to estimate the effects of winter-seining by mobile under-ice echo-surveys and catch samples.
Article
SYNOPSIS. Studies on the relation of temperature to tolerance, preference, metabolic rate, performance, circulation, and growth of sockeye salmon all point to a physiological optimum in the region of 15°C. Natural occurrence is limited in time and space at temperatures above 18°C despite being able to tolerate 24°C. Forms of physiological inadequacy can be demonstrated which account for such restrictions in distribution. Predictive power for locating and accounting for concentrations of young fish in thermally stratified lakes appeared to provide "proof" for the controlling influence of the physiological optimum temperature. Early literature on the ecology of sockeye supported this view. Recent studies using midwater trawls and sonar detection reveal a diurnal behavior pattern which points to a more subtle interaction of biotic andabiotic factors governing vertical distribution in which the controlling force appears to be bioenergetic efficiency. It is concluded that a mechanism of behavioral thermoregulation has evolved which favorably balances daily metabolic expenditures in order to conserve energy when food is limited.
Article
Diel migrations between habitats containing different levels of food abundance is a common phenomenon among marine organisms, both vertebrate and invertebrate. We hypothesize that in many cases this behavior constitutes a response to diel changes in the relationship between potential feeding rates and predation risks in the different habitats. For planktivores that locate their prey by sight (such as juvenile sockeye salmon) and that in turn are subject to predators that use sight to locate them, the diel time profiles of potential feeding rate and predation risk in near-surface waters may be determined largely by the relative densities of prey at the two trophic levels. A simple model of aquatic predation leads us to hypothesize the existence of brief "antipredation windows" for feeding at dawn and dusk. If this hypothesis is valid, then the optimal behavior for pelagic planktivores is to migrate into surface waters to feed during these two daily windows and to migrate to deeper, less illuminated waters ...
Article
Patterns of limnetic feeding behavior (vertical movement, schooling, diel feeding chronol- ogy, zooplankton prey selectivity) of Lake Washington juvenile sockeye salmon are described. A general hypothesis to explain the relative fitness of alternative behaviorial decisions is presented. The limnetic feeding behavior of the salmon appears to minimize their vulnera- bility to predation by the visual piscivore, northern squawfish. Seasonal variation indicates that sockeye feeding behavior is a short term optimization process involving foraging success and encounters with northern squawfish. Lake Washington sockeye salmon can afford to spend a large amount of their time engaged in antipredator behavior at the expense of foraging success because Lake Washington is comparatively zooplankton-rich and the energy demands of the fish can be met in short foraging periods. Sockeye in other less productive systems show a more aggressive exploitation of the zooplankton.
Article
Diel vertical distribution of juvenile and adult vendace, Coregonus albula, was studied acoustically and by gill netting during summer in thermally stratified lakes in southern Sweden. Daytime distribution of adult vendace was restricted to hypolimnion (minimum 5 °C). During nocturnal vertical migrations, adults moved into the metalimnion, but temperatures greater than 18 °C were avoided. In contrast, juvenile vendace were often found in the warmer and more shallow water of the metalimnion during the day. At night, the juveniles experienced a temperature change of 10° as they migrated into the epilimnion. All age classes had a nocturnal/crepescular diel rhythm. The diel vertical distribution of vendace is interpreted as a response to temperature stratification and to diel changes in light intensities. The different responses of the age classes are influenced by ontogenetic changes in temperature and light preferences as well as by size-related intraspecific interactions.
Article
Evolutionary hypotheses for diel vertical migrations (DVM) of aquatic animals include foraging opportunity, predator avoidance, and bioenergetics efficiency. Here we test which hypothesis predicts DVM in the small planktivorous coregonids vendace, Coregonus albula, and Fontane Cisco, Coregonus fontanae, in a deep oligotrophic lake. Densities and population depths of young-of-the-year and larger coregonids were determined by hydroacoustics during day and night over 10 consecutive months. Depth distributions of predator-like fishes and zooplankton resources were recorded as well. Furthermore, Secchi depth, water temperature, oxygen concentrations, and pH values were determined at each sampling month. A DVM of the coregonids was observed in all months. Population depths during the night were significantly correlated to water temperatures, oxygen concentrations, and pH values. In contrast, the vertical distributions of predators or resources were not correlated with the coregonid depth distribution. These results do not correspond to the feeding opportunity or predator avoidance hypotheses of DVM, but support in part the bioenergetics efficiency hypothesis. However, the stable migration pattern of fishes over all months despite substantial changes in biotic and abiotic conditions suggests that diel migrations in the coregonids are a genetically fixed behavioral trait to minimize the anticipated potential predation risk in the illuminated water layers during daytime.
Article
Abstract –  Hydroacoustic surveys are an important tool for assessing the abundance of Arctic charr (Salvelinus alpinus (L.)) in lakes, the requirement for which is increasing because of new environmental legislation. Consequently, survey demand is now such that assessments must be undertaken with the minimum of effort compatible with scientific validity. One major complication is seasonal variability in abundance, with which surveyors have attempted to deal by defining somewhat arbitrary seasonal sampling windows. The definition of more objective windows was pursued by analysing variations in the seasonal abundance of Arctic charr in Windermere, UK, recorded using day and night hydroacoustic surveys at monthly intervals from 1991 to 2001. Two alternative sampling windows for night surveys free of significant internal seasonal effects were revealed, i.e., December to September and September to December. It was also found that day surveys gave a useful, although lower, estimate of abundance as compared with night surveys.
Article
Abstract– Studies were performed with both a mechanical and a photosensory arrangement of the experimental tanks. Silver (migratory) eels were more active than yellow (stationary) eels. Comparison of pooled data on yellow eels tested under natural geomagnetic field conditions with those on eel tested under unnatural ones prcded no evidence of difference in activity. Silver and yellow eels showed stronger activity during the 6 days around new moon compared with the phase around full moon as well as a peak before new moon and a smaller peak before full moon. Under each kind of unnatural field condition, the activity relationships reversed or were cancelled. The directional choice of eels under natural conditions (controls) pointed to magnetic NW and mostly also in the opposite direction. When the magnetic north was changed by 90°, the tested yellow eels followed this change to about the same degree. The additional change of both the inclination (from 68° or 45° or 30°) and total intensity (by a reduction to 31% of the natural field) resulted in a change of the preferences of about 90° relative to magnetic north. Reversal of magnetic north by 180°, which is identical to a change of the inclination from 68° to 112°, also resulted in a change of the preferences by about 90°. Three experiments using compensation of both the horizontal and the vertical geomagnetic field led to circular directional preferences at random in two cases and in one case to about NW of the residual field magnetic north. The navigational abilities of the eel, on the basis of its magnetic sensitivity, are discussed.
Article
Studies on the vertical distribution of vendace Coregonus albula (L.), smelt Osmerus eper-tanus (L.) and bleak Alburnus alburnus (L.) in lakes have been carried out with the application of an echo sounder and then compared with control catches of fish and plankton, Methods and results have been discussed. Some remarks have been made on taking these species of fish.
Article
An acoustic estimate of the number and biomass of a vendace stock (age >2 + years) in a deep basin of Lake Karjalan Pyhäjärvi was made in August 1985. The acoustic data were collected at night during the summer stagnation. The vendace were on the lake bottom during the day and rose by midnight to the hypolimnion; they did not rise to the thermocline or water layers above it. In the research area the mean number of vendace was 1900 fish ha −1 and the mean biomass was 76 kg ha −1. Total vendace biomass was 151 in the whole 200-ha research area.
Article
Abstract –  Diel vertical migration (DVM) is a widespread behavioural pattern in populations of aquatic animals. Its adaptive value is explained by a trade-off between the protection against visually feeding predators in the dark hypolimnion during daytime, and a higher food uptake in the upper food-rich layers during the night. Whereas vertical migration patterns of entire populations have been frequently described, less is known with respect to individual variability of DVM within fish populations. Here, individual migration patterns of European vendace (Coregonus albula) are described, obtained by stationary vertical hydroacoustics in Lake Stechlin (Germany) during the dusk and dawn phases of 2 months in 2004. The variability of speeds of depth change was high, with only a few fish rising or falling faster than 1 cm s−1. Swimming activity was not dependent on fish size. There was some evidence that variability of echo strengths was highest in those fish which showed the greatest three-dimensional swimming distances which might indicate a limited swimbladder compensation during vertical migrations. However, migration seems to be performed mainly in a saltatory mode with vertical swimming always interrupted by phases of constant depth. It is suggested that these phases are used for pressure compensation by fish with the consequence that overall the frequency distribution of target strengths deviates only slightly between the start and the end of the recordings. Stationary hydroacoustics proved to be a useful tool for studying individual fish swimming behaviour.
Article
Based on the analysis of data of many-year actinometric observations, a considerable temporal (interannual, seasonal, synoptic, and diurnal) and spatial variability of the albedo of the snow-and-ice cover of a shallow lake is shown. The ranges of variations in the albedo of snow and ice for a wide spectrum of the state of surface and weather conditions are presented. The variability of the thickness and structure of snow-and-ice cover is analyzed for different periods in winter. The results of field experiments aimed to determine the degree of absorption of solar radiation by snow and ice are presented. The effective coefficients of absorption of solar radiation by snow and ice are determined. The comparison of the observed and calculated values of the under-ice radiation has shown that the determined coefficients adequately describe the absorption of solar radiation by snow-and-ice cover.
Article
This paper describes under-ice observations on the diurnal dynamics of the distribution and behaviour of roach in Lake Glubokoe in March, 1983, and in March, 1984. It presents data on the reactions of fish to external stimuli. Some factors influencing the distribution of fish in the winter period are discussed.
Article
Hydro-acoustic stock assessment and exploratory sampling with small mesh-sized trawls and seines have sometimes suggested that the importance of smelt (Osmerus eperlanus) in pelagic fish communities might be greater than sampling from commercial fishery and gillnetting indicate. We studied the proportion of smelt in the total fish density (fish ha−1) and biomass (kg ha−1) of pelagic fish with echo sounding and trawling in five southern boreal lakes. Fish density varied between 460 and 2000 fish ha−1 in the study lakes. Smelt and vendace (Coregonus albula) accounted for more than 95% of the exploratory trawl-catches. The total fish biomass in the study areas varied between 3 and 13 kg ha−1. In four lakes the proportion of smelt was more than 60%. In one lake the proportion of vendace was over 85%. These estimates indicate the importance of smelt in the study lakes. Studies of the co-occurrence of smelt with other fish species in the pelagic area of boreal lakes are needed to get a less biased picture of the fish community. This underlines the need for relevant sampling methods for the species involved.
Article
Five ecologically different whitefish forms were stocked in Lake Vuokalanjärvi in eastern Finland to establish dense populations and to analyse competition between different forms. Altogether, 213 253 whitefish were tagged with coded wire tags (microtags) injected into their snouts in 1987–1988. The morphologically highly similar whitefish forms have different gill-raker count distributions, but distributions overlap. In 1989–1992, 12 755 tagged whitefish were recaptured and the codes of the microtags were identified. In this study a growth model was applied to analyse and compare growth rates of different whitefish forms. The model was based on annual length increments. Differences in both the length increments in the youngest age-group and also the annual decline in length increments of different forms were statistically significant (F-test, p<0.0001). Whitefish forms with dense gill-rakers had the greatest growth rates.
Article
This paper demonstrates the advantages of echo surveys carried out by means of scanning sonar during the ice period of Lake Glubokoe. Using an FS 3300 sonar, data were obtained on the vertical and horizontal fish distribution over a 24 h period in the central deep-water portion of the lake. During daylight the fish formed shoals of different size, structure, shape and density recorded at a depth of 8–16 m. The trajectories of movement and disintegration of some shoals were traced. At night the shoals broke up and the pelagic distribution of fish in the lake was patchy. Fish ascended to a depth of 4–8 m. The use of an FS 3300 scanning sonar to study the behaviour of fish and to assess the surface density of their aggregations is investigated.
Fisheries Acoustics, 325 p
  • D N Maclennan
  • E J Simmonds
MacLennan D.N. & Simmonds E.J. (1995) Fisheries Acoustics, 325 p. Chapman & Hall, Fish and Fisheries Series 5, London, UK.
Influence of moon phase on acoustic estimates of the abundance of fish performing daily horizontal migration in a small oligotrophic lake
  • Gaudreu
Gaudreu N. & Boisclair D. (2000) Influence of moon phase on acoustic estimates of the abundance of fish performing daily horizontal migration in a small oligotrophic lake. Canadian Journal of Fisheries and Aquatic Sciences, 57, 581-590.
Zooplankton studies in the lake Lngelmvesi, south Finland
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Hakkari L. (1969) Zooplankton studies in the lake Längelmävesi, south Finland. Annales Zoologici Fennici, 6, 313-326.
Instruction manual. EP500 Echo processing system. Simrad
  • Simrad
Simrad (1995) Instruction manual. EP500 Echo processing system. Simrad, Horten, Norge AS.
Principles of Animal Physiology
  • D W Wood
Wood D.W. (1970) Principles of Animal Physiology, 332 p. Edward Arnold (Publishers) Ltd., London. (Manuscript accepted 06 June 2008)