Daily Vertical Migration Research Articles

An Unprecedented Bloom of Oceanic Dinoflagellates (Karenia spp.) Inside a Fjord within a Highly Dynamic Multifrontal Ecosystem in Chilean Patagonia.

At the end of summer 2020, a moderate (~105 cells L-1) bloom of potential fish-killing Karenia spp. was detected in samples from a 24 h study focused on Dinophysis spp. in the outer reaches of the Pitipalena-Añihue Marine Protected Area. Previous Karenia events with devastating effects on caged salmon and the wild fauna of Chilean Patagonia had been restricted to offshore waters, eventually reaching the southern coasts of Chiloé Island through the channel connecting the Chiloé Inland Sea to the Pacific Ocean. This event occurred at the onset of the COVID-19 lockdown when monitoring activities were slackened. A few salmon mortalities were related to other fish-killing species (e.g., Margalefidinium polykrikoides). As in the major Karenia event in 1999, the austral summer of 2020 was characterised by negative anomalies in rainfall and river outflow and a severe drought in March. Karenia spp. appeared to have been advected in a warm (14-15 °C) surface layer of estuarine saline water (S > 21). A lack of daily vertical migration patterns and cells dispersed through the whole water column suggested a declining population. Satellite images confirmed the decline, but gave evidence of dynamic multifrontal patterns of temperature and chl a distribution. A conceptual circulation model is proposed to explain the hypothetical retention of the Karenia bloom by a coastally generated eddy coupled with the semidiurnal tides at the mouth of Pitipalena Fjord. Thermal fronts generated by (topographically induced) upwelling around the Tic Toc Seamount are proposed as hot spots for the accumulation of swimming dinoflagellates in summer in the southern Chiloé Inland Sea. The results here provide helpful information on the environmental conditions and water column structure favouring Karenia occurrence. Thermohaline properties in the surface layer in summer can be used to develop a risk index (positive if the EFW layer is thin or absent).

Daily Fluctuation of Planktons Abundance in Percut Sei Tuan Waters, Deli Serdang Regency, North Sumatera

Plankton is an aquatic biota that lives following the currents in the water. The life of plankton is highly dependent on the water quality in those aquatic environments. The constantly changing physical and chemical conditions of water lead to fluctuations in the abundance of plankton in a water. This study aims to analyze fluctuations in plankton abundance and its correlation with water quality in Percut Sei Tuan Waters. The study was conducted in February and March 2023. Filtration method at 3 stations is the Sampling technique used in this study. The sampling period is carried out in the morning, afternoon, and evening. Data analysis to determine the relationship between variables using Pearson correlation in SPSS version 26. Based on the research results, 42 genera of phytoplankton and 16 genera of zooplankton were found. The highest abundance of phytoplankton was 4.635 Ind/L during the afternoon. The highest abundance of zooplankton was obtained at evening, which was 1.049 Ind/L. This is due to the daily vertical migration of zooplankton and their negative phototactic behavior, while phytoplankton require light for photosynthesis. The research results indicate that the abundance of phytoplankton has a very strong correlation with temperature, light intensity, salinity, TSS, pH, DO, and Nitrate. The abundance of zooplankton is highly correlated with water flow velocity, light intensity, salinity, TSS, TDS, pH, DO, Nitrate, and Phosphate.

Suspected evening fish chorusing sounds detected in deep waters off Kauai, Hawaii

Noise analyses are crucial to understanding passive acoustic monitoring for marine mammals and their behavioral responses to natural and anthropogenic noises. Suspected biological sounds in the ambient noise data from hydrophones at the Pacific Missile Range Facility (PMRF), Kauai, Hawaii have been found. The sounds are suspected to be chorusing associated with the Deep Scattering Layer (DSL) upward daily vertical migration given they peak around 2 hours after sunset. They have been observed occurring daily including a period in January 2017 when high ambient noise levels during a storm was associated with baleen whale cessation of calling. The sounds occur from 1.4 to 1.8 kHz with the peak near 1650 Hz. They are detectable on multiple broadband hydrophones (21 to 68 km offshore) in deep water (1.5 to 4.7 km), suggesting a large spatial extent. The maximum spectrum level in the 1.6 kHz 1/3rd octave band observed to date was 71 dB re 1 μPa2/Hz. Individual sounds have not been identified to date given the geometries involved and the large spatial extent sensed using deep water hydrophones. These results have similarities to related chorusing research which has suggested a potential link with Myctophidae fishes.

TO THE QUESTION OF INFLUENCE OF ABIOTIC AND ANTHROPOGENIC FACTORS ON THE DAILY VERTICAL MIGRATION ACTIVITY ON THE AQUATIC ORGANISMS OF LAKE BAIKAL

Daily vertical migration (DVM) of aquatic organisms is a widespread phenomenon in both small and large water bodies. It is observed, including in the deepest lake in the world – Baikal. Unique Baikal amphipods and lower crustaceans (Cladocera, Copepoda, Ostracoda) are the main representatives of the nocturnal migratory complex. As part of this study, it was found that artifi cial lighting and changes in the lake water level can aff ect the nighttime migratory activity of aquatic organisms.

Model estimates of metazoans' contributions to the biological carbon pump

Abstract. The daily vertical migrations of fish and other metazoans actively transport organic carbon from the ocean surface to depth, contributing to the biological carbon pump. We use an oxygen-constrained, game-theoretic food-web model to simulate diel vertical migrations and estimate near-global (global ocean minus coastal areas and high latitudes) carbon fluxes and sequestration by fish and zooplankton due to respiration, fecal pellets, and deadfalls. Our model provides estimates of the carbon export and sequestration potential for a range of pelagic functional groups, despite uncertain biomass estimates of some functional groups. While the export production of metazoans and fish is modest (∼20 % of global total), we estimate that their contribution to carbon sequestered by the biological pump (∼800 PgC) is conservatively more than 50 % of the estimated global total (∼1300 PgC) and that they have a significantly longer sequestration timescale (∼250 years) than previously reported for other components of the biological pump. Fish and multicellular zooplankton contribute about equally to this sequestered carbon pool. This essential ecosystem service could be at risk from both unregulated fishing on the high seas and ocean deoxygenation due to climate change.

Swimbladder Function in the European Eel Anguilla anguilla

Eels use the swimbladder for buoyancy control. The ductus pneumaticus connecting the esophagus with the swimbladder is closed soon after initial opening of the swimbladder in the glass eel stage, so that eels are functionally physoclist. Subsequent filling of the swimbladder is achieved by activity of gas gland cells in the swimbladder epithelium and countercurrent concentration in the rete mirabile. Gas gland cells produce and release lactic acid and CO2. In blood, acidification induces a release of oxygen from the hemoglobin (Root effect). The resulting increases in PO2 and PCO2 provide diffusion gradients for the diffusion of oxygen and CO2 into the swimbladder, the main gases secreted into the swimbladder. In addition, the partial pressure of these two gases remains elevated in venous blood leaving the swimbladder epithelium and returning to the rete mirabile. Back-diffusion from venous to arterial capillaries in the rete results in countercurrent concentration, allowing for the generation of high gas partial pressures, required for filling the swimbladder under elevated hydrostatic pressure. The transition of the yellow eel to the silver eel stage (silvering) is accompanied by a significant improvement in swimbladder function, but swimbladder volume cannot be kept constant during the daily vertical migrations silver eels perform during their spawning migration back to the spawning grounds in the Sargasso Sea. Infection of the swimbladder with the nematode Anguillicola crassus significantly impairs the function of the swimbladder as a buoyancy organ.

Active flux seasonality of the small dominant migratory crustaceans and mesopelagic fishes in the Gulf of California during June and October

The biological carbon pump is the process that transports carbon vertically out of the mixed layer in the ocean. Besides the sinking flux of organic particles, active flux due to the daily vertical migration of zooplankton and micronekton promotes a significant carbon transport not fully accounted for or understood in the world’s oceans. The diversity and abundance of epipelagic and mesopelagic species in the Gulf of California has been extensively studied, but the role of micronekton in carbon export has not yet been investigated. We studied the carbon flux promoted by juvenile and adult mesopelagic fishes and crustaceans (Decapoda and Euphausiidae) during the transition from the cold to warm period (June) and the onset of the warm season (October) in 2018. We provide the first estimation of migrant biomass and respiratory flux of the most abundant migratory species of mesopelagic fishes, decapods and euphausiids in the Gulf of California. The micronekton species collected accounted for a large biomass of mesopelagic fishes and pelagic crustaceans. The average migrant biomass estimates were 151.5 ± 101.2 mg C·m−2 during June and 90.9 ± 75.3 mg C·m−2 during October. The enzymatic activity of the electron transfer system (ETS) was measured as an estimate of their respiratory rates. Average specific ETS activity was significantly different between fishes and decapods, and between fishes and euphausiids (p < 0.05). The respiratory flux of fishes was predominant in the Gulf of California, followed by pelagic decapods and euphausiids. Seasonal changes in respiratory flux were observed for fishes (June: 6.1 ± 1.5 mg C·m−2·d−1; October: 3.2 ± 1.8 mg C·m−2·d−1) and decapods (June: 0.4 mg C·m−2·d−1; October: 0.7 ± 0.05 mg C·m−2·d−1). Respiratory flux estimation by crustaceans (decapods and euphausiids) and fishes together was 6.86 mg C·m−2·d−1 during June, and 4.21 mg C·m−2·d−1 during October 2018, suggesting a functional role of this large micronektonic fauna in the biological carbon export in this region.

Construction of the fitness function depending on a set of competing strategies based on the analysis of population dynamics

The purpose of this work is to construct a fitness function that depends on the set of coexisting competing hereditary elements based on population dynamics in the “predator– prey” model with the logistic growth of prey. Materials and methods. The work uses the generalized Volterra model. The planktivorous fish plays the role of a predator. Many different species of zooplankton are considered as prey, which differ from each other in the hereditary strategies of daily vertical migrations. The model takes into account the intraspecific competition of prey. The peculiarity of the model consists of the presence of pairs of hereditary strategies in which the carriers of the first can displace the carriers of the second and vice versa — the carriers of the second can displace the carriers of the first, depending on the set of competing strategies in which they coexist. To restore the fitness function, the ranking method is used, which is reduced to the classification of ordered pairs of hereditary strategies into two classes “the first strategy displaces the second” and “the second displaces the first”. Results. The article presents a new methodology for constructing the fitness function. The technique involves two stages. First, the fitness function is reconstructed for a certain finite subset of elements on the basis of processing data on the long-term dynamics and comparing their competitive advantages. At the second stage, the form of the fitness function is derived for an arbitrary set of elements. It uses the features of interspecies interaction reflected in the model. With the help of the constructed fitness function, an evolutionarily stable regime of daily vertical migrations of zooplankton is modeled by numerically solving the minimax problem. Conclusion. The proposed method for constructing a fitness function that depends on a set of competing strategies is quite general and can be applied to a wide range of models of population dynamics. The strategy of diel vertical migrations of zooplankton constructed as a result of modeling is in good agreement with empirical data.

Quantification of deep sound scattering layers using a moored upward-looking broadband split-beam echosounder

Distinct deep sound scattering layers are prevalent throughout the ocean mesopelagic zones (200–1000 m depths). These deep sound scattering layers are often characterized by daily vertical migration, in which many of the inhabitants of the ocean mesopelagic communities migrate to shallow waters during the night to feed, and descend during the day to avoid predators. And yet little is known about the impact of mesoscale physical oceanography, such as warm core rings or Gulf stream meanders, on the patterns of daily vertical migration or on the small-scale spatial distribution, or patchiness, of the deep sound scattering layers. To address these questions, an upward-looking broadband split-beam echosounder (36 kHz–44 kHz) has been moored at 580 m depth in the slope waters south of the New England shelf break in a location in which warm core rings are a prevalent feature. Data from a 3-day test deployment are analyzed in terms of target density, spectral characterization, patchiness and timing of the migrations. The calibrated broadband spectra of individual targets are used to determine the number of swimbladdered fish in the deep sound scattering layers. Meanwhile, two other methods, including echo-counting and echo-statistics, are also applied to give target density estimation.

Daily vertical distribution of zooplankton in two oligo-mesotrophic north Patagonian lakes (39° S, Chile).

The zooplankton communities often exhibit daily vertical migrations to avoid natural ultraviolet radiation and/or fish predation. However there is no information on this topic in Chilean North Patagonian lakes up to date. Therefore, this study deals with a first characterization of plankton crustacean daily vertical migration in two temperate, oligotrophic lakes (Villarrica and Panguipulli lakes, 39°S) in Southern Chile. Zooplankton were collected at different depths intervals (0-10m, 10-20 m, 20-30m, 30-40m) at early morning, middle day, evening and night in the studied site. The results revealed that zooplankton species (Daphnia pulex, Ceriodaphnia dubia, Neobosmina chilensis, Mesocyclops araucanus, and Tropocyclops prasinus) are abundant in surface zones at night, early morning and evening, whereas at middle day the zooplankton abundances are high at deep zones. The results agree with observations for Argentinean and North American lakes where these daily migration patterns in crustacean zooplankton species were reported due mainly natural ultraviolet radiation exposure, whereas for northern hemisphere lakes the vertical migration is due to combined effect of natural ultraviolet radiation and fish predation exposure.

Global optimisation in Hilbert spaces using the survival of the fittest algorithm

Global optimisation problems in high-dimensional and infinite-dimensional spaces arise in various real-world applications such as engineering, economics and finance, geophysics, biology, machine learning, optimal control, etc. Among stochastic approaches to global optimisation, biology-inspired methods are currently very popular in the literature. Bio-inspired approaches imitate natural ecological and evolutionary processes and are reported to be efficient in a large number of practical study cases. However, many bio-inspired methods can possess some vital drawbacks. For example, due to their semi-empirical nature, convergence to the globally optimal solution cannot always be guaranteed. Another major obstacle is that the existing methods often struggle with higher dimensionality of the space of parameters, which results in a slow convergence. Moreover, it is often difficult to adjust the dimensionality of the space of parameters in the corresponding computer code for a practical realisation of the optimisation method. Here, we present a bio-inspired global stochastic optimisation method applicable in Hilbert function spaces. The proposed method is an evolutionary algorithm inspired by the Darwin’s famous idea of survival of the fittest and is, therefore, referred to as the ‘Survival of the Fittest Algorithm’ (SoFA). Mathematically, the convergence of SoFA is a consequence of the fundamental property of localisation of probabilistic measure in a Hilbert space and we rigorously prove the convergence of the introduced algorithm for a generic class of functionals. The approach is simple in terms of practical coding. As an insightful, real-world problem, we apply our method to find the globally optimal trajectory for the daily vertical migration of zooplankton in the ocean and lakes, this phenomenon is considered to be the largest synchronised movement of biomass on Earth. We maximise fitness in a function space derived from a von-Foerster stage-structured population model with biologically realistic parameters. We show that for problems of fitness maximisation in high-dimensional spaces, SoFA provides better performance as compared to some other stochastic global optimisation algorithms. We highlight the links between the new optimisation algorithm and natural selection processes in ecosystems occurring within a population via gradual exclusion of competitive con-specific strains.

Microplastic ingestion by Atlantic horse mackerel (Trachurus trachurus) in the North and central Moroccan Atlantic coast between Larache (35°30′N) and Boujdour (26°30′N)

Horse mackerel is a semi-pelagic species found in abundance in the Moroccan coasts and occupies the first ranks in the catches landed by the coastal fleet. In this study, we investigated the ingestion of Polyamide, Acrylic and Polystyrene by Atlantic horse mackerel, in the Moroccan Atlantic coastal area located between Larache (35°30′N) and Boujdour (26°30′N). The objective is to map the spatial distribution of horse Mackerel containing microplastics (MPs) in their stomachs and identify hot spot areas. We also aim to verify the most ingested polymer by this fish characterized by significant daily vertical migrations. The results show that the three studied polymers were detected in the stomach contents of more than 73% of studied fishes. The hot spot areas are located more in the northern part where urbanization and fishing activity are important. Polyamide, the densest polymer, is the most abundant (86% of cases), followed by acrylic. These two polymers were found in association in 47% of cases. No correlation between the presence of MPs in the stomach contents and the size of the individual fishes was noted. Interestingly, the group of mature specimens ingested more MPs than the immature group.

Abundance and ecology of Myctophidae fishes in the Gulf of Alaska in winter season

Distribution and abundance of myctophid fish species in the upper epipelagic layer are analyzed based on results of surveys in the Gulf of Alaska in winters of 2019 and 2020. A common myctophid community driven by blue lanternfish Tarletonbeania crenularis was revealed that occupied likely the entire eastern part of the Subarctic Front zone eastward from 150ºW. Abundance and biomass of four mass myctophid species were generally comparable between the northeastern and northwestern Pacific. Small-sized juveniles prevailed among northern lampfish Stenobrachius leucopsarus, which were likely transported by the Subarctic Current and could be recruited to the Bering Sea stock. Patterns of daily vertical migrations are discussed for the mass myctophid species. New observations confirm general understandings on the myctophid species input to functioning of fish community.

Summer phytoplankton 24-hours dynamics in the lake Svetloyar (Nizhny Novgorod region)

In this research the information of structural parameters of algocenoses (species richness, proportions of leading groups, abundance, biomass) in the photosynthetic zone of a unique karst lake Svetloyar (Nizhny Novgorod region) is provided according to the data for the summer of 2012. During the studied 24-hours period the main components of plankton were coccoid green and diatom algae, colonial and filamentous cyanobacteria, whose daily vertical migration was poorly expressed. The maximum of abundance and biomass of these species were noted at the afternoon (the period from 13:30 to 16:30) and in the most heated layer (0–4 m). Motile algae (mainly from phylum Dinophyta) were characterized with more noticeable daily activity. They were present in the algocenoses only in the daytime and evening hours and moved at night and in the morning below the photosynthetic zone. The daily dynamics of the species richness of algae demonstrated was similar with the indicators of quantitative development, while the number of dominant species remained stable during the day (amounting to 1–4 taxa in the sample).

Seasonal and annual variability in daily vertical migration observed from acoustic Doppler current profiler derived backscatter at the Mid-Atlantic Bight shelf break

75 kHz ADCPs stationed near the 450-meter isobath within the Ocean Observatories Initiative Coastal Pioneer Array capture consistent patterns indicative of daily vertical migration (DVM) in depth profiles of both mean volume backscatter (MVB) and the vertical component of velocity (w). While the presence of DVM patterns is consistent throughout 2018 and 2019, attributes of MVB and w profiles are subject to variability within and across different seasons and years. This variability may be influenced by abiotic factors characteristic of the Mid-Atlantic Bight region such as the disruption of typical spring time temperature-salinity structures via frontal instability or the episodic introduction of warm-core rings. Additionally, biological community composition in the region may be reflected in MVB and w profiles given zooplankton survey data and knowledge of seasonal biophysical dynamics in the region, along with measured variability of other environmental properties observed by the Pioneer Array including dissolved oxygen concentration, chlorophyll-a concentration, and photosynthetically available radiation. Linking all of these factors, driven by long-term, stationary acoustical observations, can provide a useful framework for more directly assessing the impacts of aberrational physical phenomena on regional biological patterns.

Microscale Variability in Biomass and Photosynthetic Activity of Microphytobenthos During a Spring-Neap Tidal Cycle

Carbon fixation by microphytobenthic algae of intertidal flats often dominates the total primary production of turbid, temperate estuaries. Whilst remote sensing can accurately measure the spatial distribution of photosynthetic biofilms at the mesoscale (1-300 m), variability at smaller scales requires in-situ investigation. Here, changes in biomass and photosynthetic activity of microphytobenthos (MPB) at the micro-scale (<1 m) were investigated. Biomass of MPB was estimated from repeated high resolution spectral measurements carried out at intervals along a short transect. Whilst the mean concentration of MPB remained constant over time, considerable variability in the spatial and temporal dimensions was measured. The biofilm grew and diminished along the transect over time, and net growth and loss rates could be established under natural conditions. Daily vertical migration was observed for the first time in an undisturbed sediment, and was modelled as a function of solar elevation and tidal angle. Top down factors such as grazing, or physical disturbance, play an important role in the changes in biomass. Photosynthetic activity was measured with portable fluorometers: one device used an artificial light source, the other measured the effective photosystem-II quantum efficiency (ΔF/Fm’) in-situ with solar irradiance. No evidence was found for photoinhibition, with Fv/Fm values consistently high, indicating an ability of the diatom biofilm to remain productive under periods of high irradiance. The maximum rate of photosynthesis reached artificial light was rarely achieved in-situ, even with full solar exposure. There was however a very good agreement between the predicted rate at ambient irradiance, and that actually measured. Composite photosynthesis-irradiance curves over the whole experimental period were similar, and showed the same initial slopes, but the maximum rate of relative photosynthetic electron transport (rETRm) based on the in-situ measurement was lower. When total depth-averaged primary production during low tide was calculated, the differences between methods varied between 5-13%, and were smallest when surface irradiance values were higher. These results show that the protocol used to measure the photosynthetic activity of the MPB had only minor importance on the overall productivity estimate compared to accurate knowledge of photosynthetically-active biomass and irradiance.

Representatives of the genus Eurytemora Giesbrecht, 1881 (Calanoida, Temoridae) in aquatic ecosystems of Belarus

Abstract The main biological features of two species of the genus Eurytemora have been studied: the relict E. lacustris (Poppe, 1887) and the alien E. velox (Lilljeborg, 1853), which can be found in natural environments on the territory of the Republic of Belarus. The relict species E. lacustris has been found only in two mesotrophic dimictic lakes belonging to the Baltic Sea basin: Volchin (maximum depth 32.9 m) and Vecheliye (35.9 m). E. velox has now colonized the main rivers of the south of Belarus and their accessory reservoirs belonging to the basins of the Baltic and Black seas. E. lacustris is characterized by an uneven distribution in the water column and location in deep water layers with temperatures below 13°C. Seasonal and daily vertical migrations have been established for E. lacustris. With age, the amplitude of migrations increases, reaching values of more than 10 m of depth for adults. E. velox is recorded in the coastal biotopes of watercourses and shallow water bodies. In the recent two years, the average density of E. lacustris in Lake Vecheliye has been established as about 2000 ind./m3, while their percentage in the zooplankton was 6%. In Lake Volchin, its density has been 2-5 times lower in the same period, and there this species’ percentage in the plankton did not exceed 2%. The density of E. velox varies from 20 to 12 000 ind./m3, their average density is 1631 ind./m3, and their percentual share in the zooplankton does not exceed 1%. For E. lacustris, the body length at all stages of development has been determined. It has been established that males have a greater body length in comparison with females, due to the relatively longer male abdomen, which is not typical for other species of freshwater planktonic copepods. In Belarus, E. lacustris is a bicyclic species, whereas E. velox is polycyclic.

ON NIGHTTIME VERTICAL MIGRATIONS OF AMPHIPODS IN LAKE LADOGA

Daily vertical migrations (DVM) of amphipods is a widespread phenomenon both in rivers and lakes, and in seas. The leader among freshwater bodies in terms of the number of amphipod species and the intensity of DVM is the ancient Lake Baikal. Lake Ladoga is also inhabited by several species of these crustaceans, and some of them are invaders from Lake Baikal. Therefore, the aim of this study was to check whether amphipods in Lake Ladoga perform nighttime vertical migrations. To test this assumption, we used a combination of video equipment (a video system consisting of a metal frame, a GoPro 4 video camera, 3 lighting elements, and an iButton temperature logger), a plankton net, and a bottom grab. Co-application of these methods did detect vertical nighttime migrations in amphipods in Lake Ladoga, but their intensity was extremely low and they were observed only in invasive species from Lake Baikal, Gmelinoides fasciatus and Micruropus possolskii . A comparison of depth-specific intensities of vertical nighttime migrations revealed no significant variation. In addition to amphipods, the nighttime migrants community in Lake Ladoga includes representatives of such groups as fish, chironomids, water bugs, opossum shrimps, and predatory cladocera Leptodora kindtii (Focke, 1844) .

Суточная динамика вертикального распределения и доля осетровых рыб в русловой яме в летне-осенний период

The article presents the results of studying the fish distribution in the water column of the riverbed depression using remote echometric sounding with a software-hardware acoustic system with a vertical view. The study was conducted in the lower reaches of the Irtysh River. In the appointed period (July-October) under a decrease in the level regime and water temperature the increasing density of fish in the water area of the riverbed depression is explained by fish gathering in the period preceding wintering. The share of sturgeons varied from 5.46 to 10.28% of the total fish density, the indicators of which were in the range 1.70-5.05 thousand sp/ha in the daytime, 2.78-6.77 thousand sp/ha in the night. There has been stated the daily vertical migration of sturgeons, which is more uniform throughout the water column in the night, including the near-surface and near-bottom water horizons. In the dark near-surface water horizons are most intensively explored by large fish (25-30, 30-35, &gt; 35 cm). The trigger of the daily vertical migration of sturgeons is supposed to be the light brightness, despite the poor eyesight of the fish under study, i.e. changing vertical position of sturgeons occurs due to endogenous circadian rhythms, as in many hydrobionts. The recorded features of sturgeon distribution because of preference of the direction and intensity of various factors can contribute to the optimization of bioenergy losses in hard turbulent conditions of riverbed depressions.

Global satellite-observed daily vertical migrations of ocean animals.

Every night across the world's oceans, numerous marine animals arrive at the surface of the ocean to feed on plankton after an upward migration of hundreds of metres. Just before sunrise, this migration is reversed and the animals return to their daytime residence in the dark mesopelagic zone (at a depth of 200-1,000m). This daily excursion, referred to as diel vertical migration (DVM), is thought of primarily as an adaptation to avoid visual predators in the sunlit surface layer1,2 and was first recorded using ship-net hauls nearly 200years ago3. Nowadays, DVMs are routinely recorded by ship-mounted acoustic systems (for example, acoustic Doppler current profilers). These data show that night-time arrival and departure times are highly conserved across ocean regions4 and that daytime descent depths increase with water clarity4,5, indicating that animals have faster swimming speeds in clearer waters4. However, after decades of acoustic measurements, vast ocean areas remain unsampled and places for which data are available typically provide information for only a few months, resulting in an incomplete understanding of DVMs. Addressing this issue is important, because DVMs have a crucial role in global ocean biogeochemistry. Night-time feeding at the surface and daytime metabolism of this food at depth provide an efficient pathway for carbon and nutrient export6-8. Here we use observations from a satellite-mounted light-detection-and-ranging (lidar) instrument to describe global distributions of an optical signal from DVM animals that arrive in the surface ocean at night. Our findings reveal that these animals generally constitute a greater fraction of total plankton abundance in the clear subtropical gyres, consistent with the idea that the avoidance of visual predators is an important life strategy in these regions. Total DVM biomass, on the other hand, is higher in more productive regions in which the availability of food is increased. Furthermore, the 10-year satellite record reveals significant temporal trends in DVM biomass and correlated variations in DVM biomass and surface productivity. These results provide a detailed view of DVM activities globally and a path for refining the quantification of their biogeochemical importance.