Juvenile Migration Research Articles

The Core Story: Intertwined Maternal and Progeny Signatures Enclosed in the Otolith

Analytical imaging via synchrotron analysis was used to study sagittal otoliths of four freshwater pipefish species exhibiting amphidromous or freshwater resident lifestyles. We undertook a hyperfine elemental scanning of a 25 μm diameter length area centred on the core, namely the pre-hatch zone, corresponding to the sagitta formed during embryogenesis. We analysed calcium (Ca), strontium (Sr), manganese (Mn), chromium (Cr), cobalt (Co), nickel (Ni) and sulphur (S), with the latter serving to count growth increments. Whatever the species, a Ca pit consistently marked the core; the amphidromous species exhibited Mn enrichment at the core and the sagitta formed a week before hatching. These results illustrate common otolith formation mechanistic processes. Sr and heavy metals’ signals in the pre-hatch zone were compared to their signal in the edge of the otolith, an area encompassing the adult freshwater (adFW) environmental signature. We found that Co and Ni otolith signals had no relation to environmental conditions, but it is worth looking into Cr as a marker of early-life environment. While we caution against the use of a Sr:Ca ratio for life history interpretations at the core because of the Ca pit, the Sr signal analysis uncovered possible variations in the parental behaviour that potentially trigger newly-hatched juvenile migration to sea or residency. Finally, our results demonstrate that the microchemistry of otolith formation during early development is a melting of maternal signal during egg yolk elaboration, of the environmental signal during egg incubation, and of individual physiology during early growth.

Spectral absorbance changes in the photoreceptors of the juvenile masked greenling, Hexagrammos octogrammus (Pisces, Hexagrammidae).

When changing habitat during migration or ontogenesis, fish encounter changes of the visual environment, among which the most important is the spectral composition of light and turbidity. This leads to changes in the behavior, morphology, and physiology of the visual system, in particular, spectral sensitivity, which is determined by the properties of visual pigments. The masked greenling Hexagrammos octogrammus has an additional factor that shapes effective spectral sensitivity-the presence of densely bright orange cornea which reversibly changes its density depending on the state of light/dark adaptation. However, it is unknown to what extent the properties of visual pigments are matched to spectral properties of the developing cornea at the final stage of metamorphosis during migration of juveniles from pelagic to coastal environments. The findings of this microspectrophotometric study show that the range of the spectral sensitivity of rods and cones in juveniles is much wider than in adults, with a shift in the sensitivity of a significant part of the cells to shorter wavelengths. The reason for this is the large variation in the ratio of chromophores A1:A2 in the pigment mixture in each cell and possible expression of new opsins. This also indicates the asynchrony of pigment transformations in different types of photoreceptors and the incompleteness of these transformations on the eve of the transition to bottom life in shallow water.

Revisiting Perdeck's massive avian migration experiments debunks alternative social interpretations.

Whether avian migrants can adapt to their changing world depends on the relative importance of genetic and environmental variation for the timing and direction of migration. In the classic series of field experiments on avian migration, A.C. Perdeck discovered that translocated juveniles failed to reach goal areas, whereas translocated adults performed 'true-goal navigation'. His translocations of > 14 000 common starlings (Sturnus vulgaris) suggested that genetic mechanisms guide juveniles into a population-specific direction, i.e. 'vector navigation'. However, alternative explanations involving social learning after release in juveniles could not be excluded. By adding historical data from translocation sites, data that was unavailable in Perdeck's days, and by integrated analyses including the original data, we could not explain juvenile migrations from possible social information upon release. Despite their highly social behaviour, our findings are consistent with the idea that juvenile starlings follow inherited information and independently reach their winter quarters. Similar to more solitarily migrating songbirds, starlings would require genetic change to adjust the migration route in response to global change.

On monitoring the downstream and spawning migrations of Pacific salmon on the Paramushir Island (Northern Kuriles) in 2023

The purpose: The main goal of the work is to study the conditions of migration of juveniles on the control Savushkina River and describe the state of Pacific salmon migrating off the coast of the Paramushir Island in 2023.Methods used: Research work was carried out using standard generally accepted methods.Result: During the research work, data were obtained on the timing and dynamics of migration of juvenile Pacific salmon. The results of monitoring the approaches of Pacific salmon producers are presented. Shown are data on the size-mass characteristics and age composition of chum salmon, sockeye salmon, coho salmon and pink salmon.Practical significance: The results of the research work carried out will be used in the preparation of materials for the projected volume of production (catch) of Pacific salmon for 2024 and subsequent years for the North Kuril subzone.

Coeffects of temperature and photoperiod on the age-related timing of spring migration of Whooper swans via satellite tracking

Extrinsic and endocrine factors are important mechanisms influencing the timing of spring bird migration. Whooper swans (Cygnus cygnus), including 122 adults and subadults over one year old and 98 juveniles under one year old, were satellite tracked to obtain detailed locational data at a wintering ground from 2015 to 2020. We assessed the effects of temperature, wind, photoperiod, available food resources, and sex hormones on age-related timing of spring migration. Our results suggested that both photoperiod and temperature had the greatest impacts on the timing of spring migration of adults, subadults and juveniles when food resources and wind conditions were favourable. With increasing photoperiod and temperature, the peak sex hormone concentrations of adults and subadults occurred one month earlier than that of juveniles, which corresponded to the peak of their departure time. Our study showed the synergistic impact of photoperiod and temperature and their variation among adults, subadults and juveniles on the initiation of spring migration. Compared with juveniles, adults and subadults with spring migration experience and reproductive needs could adjust their behaviours more quickly before departure based on changes in environmental conditions.

Vertical Migration of Second-stage Juveniles of Meloidogyne enterolobii as Influenced by Temperature and Host.

Infective second-stage juveniles (J2) of Meloidogyne spp. migrate towards host roots, which depends on several factors, including root exudates and soil temperature. Although Meloidogyne enterolobii is a highly virulent nematode that affects major agricultural crops worldwide, there is limited ecological data about it. The objective of this study was to determine the J2 migration pattern vertically in 14-cm long segmented soil columns towards tomato (Solanum lycopersicum) and marigold (Tagetes patula) roots, each grown at two soil temperatures (20 or 26ºC). Bottomless cups with tomatoes or marigolds were attached to the top of each column; cups with no plants were used as untreated controls. Juveniles (1,000/column) were injected into a hole located 1 cm from the bottom of each column. The apparatuses were placed in growth chambers at 20 or 26ºC, and J2 were allowed to migrate for 3, 6, 9, or 12 days after injection (DAI). At each harvest, J2 were extracted from each ring of the columns and counted to compare their distribution, and root systems were stained to observe root penetration. M. enterolobii migrated over 13 cm vertically 3 DAI regardless of temperature, even without plant stimuli. The vertical migration was greater at 26ºC, where 60% of active J2 were found at distances >13 cm at 12 DAI. Temperature did not affect root penetration. Overall, a greater number of J2 was observed in tomato roots, and root penetration increased over time.

Evaluation of survival estimates generated from tracking downstream migrating juvenile sea lamprey (Petromyzon marinus) with a miniature acoustic telemetry tag

Fish that undertake juvenile migration pass through habitats that vary in mortality risk. The ability to identify regions of persistently low survival would improve fishery management. We conducted a field study combined with predictive modeling of survival in downstream migrating juvenile sea lamprey using a new micro-acoustic telemetry tag designed for implantation into small, slender-bodied fishes. Detection data were collected from eight receivers placed across a coastal riverine–wetland–lake complex. Juvenile sea lamprey initiated downstream movement near nautical twilight, stopped frequently, and were more likely to move during high river discharge. Estimated survival was highest in the riverine reach, declined through the river–wetland complex, and dropped precipitously in the drowned rivermouth lake. However, the high transmission rate and resulting short battery life of the microtransmitters (as configured) likely resulted in missed detections in the lower reaches. Simulation analyses suggested survival estimation could be improved by increasing the number of tagged lamprey and staggering release locations. We offer practical recommendations for the use of this new transmitter in field studies with small anguilliform fish.

The structure of the scales of juvenile sockeye salmon of Nachikinskoe Lake (Western Kamchatka)

Analysis of biometric data of juvenile sockeye salmon caught during the run to sea in the channel from Nachikinskoe Lake was carried out in order to clarify the question of the minimum possible number of sclerites on the scales to the 1st annual ring. For the first time, the study of the features of the scale structure of juvenile sockeye salmon of different ages was carried out. The differences revealed between groups of individuals of different age categories are highly reliable not only in weight and length, but also in the total circuli number in the freshwater zone and circuli number to the first annual ring (6.0 ± 0.1 in yearlings, 3.9 ± 0.3 in two-year-olds); physiological explanation for these differences is proposed. On the basis of the scleritograms constructed, a comparison of other features of the scale structure of the juvenile migrants of different ages was carried out. The key characteristics obtained are recommended as clarifying criteria in reading the freshwater age of juvenile sockeye salmon in Nachikinskoe Lake.

The Characteristics of Feeding Migrations of Hatchery-Reared Pacific Salmon Juveniles in the Sea of Okhotsk Basin and Adjacent Pacific Waters in the Autumn–Winter Period (Regional Identification, Abundance, Distribution of Catches, Biological Characteristics, and Mortality Rate Estimates)

The Characteristics of Feeding Migrations of Hatchery-Reared Pacific Salmon Juveniles in the Sea of Okhotsk Basin and Adjacent Pacific Waters in the Autumn–Winter Period (Regional Identification, Abundance, Distribution of Catches, Biological Characteristics, and Mortality Rate Estimates)

Icelandic Whimbrel first migration: Non‐stop until West Africa, yet later departure and slower travel than adults

Migratory behaviour in young individuals is probably developed by using a complex suite of resources, from molecular information to social learning. Comparing the migration of adults and juveniles provides insights into the possible contribution of those developmental factors to the ontogeny of migration. We show that, like adults, juvenile Icelandic Whimbrel Numenius phaeopus islandicus fly non‐stop to West Africa, but on average depart later, follow less straight paths and stop more after reaching land, resulting in slower travel speeds. We argue how the variation in departure dates, the geographical location of Iceland and the annual migration routine of this population make it a good model to study the ontogeny of migration.

Are street children juvenile migrants? Discoveries from their earning, spending and saving practices (Ouagadougou, Burkina Faso)

ABSTRACT In Ouagadougou, capital of Burkina Faso, the so-called street children and youth I worked with usually preferred to describe themselves as juvenile migrants, ‘searching money’ in order to support themselves and their family and, some day, build their own future. Could they indeed be considered as participating to a form of juvenile migration? I addressed this hypothesis as an anthropologist by looking empirically at their economic practices. The analysis of the daily budget of dozens of bakoroman revealed that their desire to appear as providers for their family was not simply delusional: it materialised in routine saving practices and remittances to their family. But these practices varied significantly from one group and from one individual to another. These variations revealed that they navigated between norms of juvenile labour migration, which entailed redistribution to kin, and that of a deviant street ethos, which is based on a rugged individualism.

Characteristics of feeding migrations of hatchery juveniles of pacific salmon in the basin of Okhotsk Sea and adjacent Pacific waters in the autumn-winter period (regional identification, abundance and distribution of catches, bio-logical indices, estimates of mortality)

Long-term data on feeding migrations of hatchery pacific salmon (pink and chum salmon) in the Okhotsk Sea and adjacent Pacific waters in the autumn-winter of 2011–2021 are generalized. The study is based on materials (otolith samples, biological indices) collected in the trawl surveys conducted by TINRO, as well as on international statistics on releases and tagging of pacific salmon at the Russian and Japanese hatcheries. The main patterns of intraspecific structure, migration routes, spatial distribution, and volumes of catch are determined for these species, as well as the size-weight parameters of fish originated from different regions. Natural mortality of salmon juveniles at the stage of migration from the coastal zone to the open sea is estimated at systemic level for the first time.

The using of data on the moult progress in the study of migration periods of the annual cycle of passerines

Using trapping and ringing of birds for studying the ecology and the demographic parameters of populations is necessary to determine as accurately as possible in which period of the annual cycle each individual was caught. The first-year passerine birds undergo juvenile migration (usually in form of postfledging dispersal) and postmoulting (autumn) migration in summer-autumn period. These stages of annual cycle are difficult to identify in trapping birds by calendar dates because the timing of migration seasons can significantly overlap in the same location. The study of moult at the Ladoga Ornithological Station made it possible to determine the states of plumage that mark juvenile and postmoulting migrations in first-year birds. The article presents two examples of the use of moult progress in the study of bird migrations. The first one is an analysis of the ratio of the terms of departure and passage in three long-distant and three short-distant migrants of passerines. It has been shown that the timing of the departure of local birds is earlier than the timing of the passage of other populations in all studied species, while the last local individuals in long-distance migrants are recorded long before the end of the passage of the species, and in short-distance migrants they can be found until its end. As another example, an analysis of long-term trends in the timing of summer-autumn movements in the Garden Warbler was performed. It is shown that for almost a fifty-year observation period, neither the timing of juvenile migration nor the timing of postmoulting migration of first-year birds has changed. At the same time, the timing of the spring passage of the species shifted to earlier. As a result, the duration of stay of the Garden Warbler in the Ladoga region has increased.

Studies of the migration of juvenile Pacific salmon in the Savushkina river (Paramushir Island, Northern Kuriles) in 2022

The purpose of the research is to form scientific basis of effective management of salmon fisheries in the Russian Far East.Applied methods: research work was carried out in accordance with standard methods used in fisheries research.Scientific novelty: data on qualitative and quantitative composition of juvenile Pacific salmon migrating from the Savushkina River for rearing in marine waters in May-July 2022. Based on qualitative heterogeneity of juveniles, presence of eco-temporal groups within chum salmon and coho salmon was supposed.Result: data on timing and dynamics of seaward migration of Pacific salmon juveniles, as well as their qualitative and quantitative patterns.Practical relevance: Results of the research would be used in forecasting of commercial catch of Pacific salmon in the Northern Kurils.

Disentangling Population Level Differences in Juvenile Migration Phenology for Three Species of Salmon on the Yukon River

Migration phenology influences many important ecological processes. For juvenile Pacific salmon, the timing of the seaward migration from fresh to marine waters is linked to early marine survival and adult returns. Seaward migration phenology is determined by interactions between the intrinsic attributes of individual species and environmental factors that are acting upon them. Temperature and discharge are two factors of the freshwater environment that have been shown to influence intra- and interannual variation in juvenile salmon phenology, but these factors may affect the migrations of sympatric species differently. Understanding how variations in phenology change with environmental heterogeneity is a critical first step in evaluating how the future climate may affect salmon. This is especially crucial for high-latitude rivers, where the pace of climate change is nearly twice as rapid as it is for more temperate areas. This research investigates the influence of river conditions on the seaward migration phenology of Chinook, chum, and coho salmon in the Yukon River. The results identified species-specific differences in the factors affecting migration duration, concentration, and skew and provide a starting point for a more detailed examination of how phenological variability may affect the temporal matching of juvenile salmon with biological resources and environmental conditions for optimal survival.

Diversity in freshwater life history in spring and summer Chinook Salmon from the Fraser River, Canada

AbstractObjectiveWe describe juvenile migration tactics for spring/summer‐run populations of Chinook Salmon Oncorhynchus tshawytscha that spawn in tributaries of the Fraser River, Canada.MethodsWe trapped juveniles migrating from tributaries, and sampled juvenile Chinook salmon rearing in the Fraser River.ResultIn four tributaries, we found two dominant life history types within each population: a natal‐stream‐rearing variant in which juveniles spend a year in their natal stream before migrating to the sea as yearling smolts; and a fry migrant variant in which juveniles disperse downstream from spawning areas to the Fraser River main stem soon after emergence. In a fifth tributary, where flows are regulated, juveniles migrated as parr later in the spring. Juveniles colonized the Fraser River main stem in spring and were distributed throughout the accessible length of the main stem. Their relative density in nearshore habitats was similar to that observed in other rivers. Migrants spend up to a year in the main stem before smolting as yearlings.ConclusionThe extensive year‐round use of the Fraser River main stem appears to be unique among Chinook Salmon‐producing watersheds, likely due to favorable environmental conditions in the main stem during the spring and summer months. The diversity of habitats used by these populations is an important consideration for the design of conservation programs that are intended to maintain or improve freshwater productivity.

Age-related changes in migratory behaviour within the first annual cycle of a passerine bird.

First time migrants (juveniles hereafter) of many species migrate without specific knowledge of non-breeding locations, but experience may aid adults in timing and route decisions because they can migrate more efficiently to their previous non-breeding sites. Consequently, we expect a transition to more efficient migratory behaviour with age, but when and how this happens is little known. We used light-level geolocator data from Cyprus wheatears Oenanthe cypriaca to compare migration timing and route directness between juveniles and adults, and repeatability of their timing and non-breeding locations. We predicted that juveniles would depart and arrive later than adults for both autumn and spring migration; that duration of migration would be greater for juveniles; that routes taken by juveniles would be less direct than those for adults; and that autumn and spring departure timing, and non-breeding locations, would be more repeatable for adults between two years than for juveniles between their first and subsequent migration. We found that juveniles departed significantly later than adults in autumn but there was no difference in arrival timing, and although spring departure timings did not differ, juveniles arrived on the breeding grounds later than adults. Nevertheless, we found no significant age-related difference in the duration of migration in autumn or spring. Yet, juvenile migrations were less direct than those of adults in autumn, but not spring. We found evidence that spring departure timing and non-breeding locations were repeatable for adults but not juveniles. Our findings show that age-related changes in migratory behaviour begin to occur during the first annual cycle demonstrating the potential for early adaptation to environmental variability within an individual’s life.

Feeding of mass fish species by natural and farmed juveniles of pacific salmons on example of the Obutonai River (Sakhalin Island)

Feeding of mass fish species caught in the Obutonai River (Sakhalin, Nevelsk district) was examined in May-July 2021, in the time of downstream migration of natural pink salmon Oncorhynchus gorbuscha juveniles and release of chum salmon O. keta juveniles from a fish hatchery. Three fish species capable to predate on salmon juveniles were presented in the catches in significant number, as whitespotted char Salvelinus leucomaenis, pacific redfin Tribolodon brandtii, and juveniles and dwarf males of masu salmon O. masou. These species occurred in different lower reaches of the river. Whitespotted char fed by both pink and chum juveniles, but was relatively few in number (single mass catch). Two-year-olds and dwarf males of masu salmon fed less intensively and pacific redfin fed exceptionally rarely on the migrating pink salmon juveniles of natural origin, but both these species consumed actively the chum juveniles released from a hatchery. The masu salmon juveniles had the maximum abundance in early June, then their number decreased. The pacific redfin abundance had complicated dynamics because of migrations both from the upper part of the river and from the sea; pacific redfin spawned in late June when ate exclusively eggs of the same species.

A life cycle model for evaluating estuary residency and recovery potential in Chinook salmon

Understanding the spatial and temporal habitat use of a population is a necessary step for recovery planning. For Chinook salmon (Oncorhynchus tshawytscha), variation in their migration and habitat use complicate predicting how restoring habitats could impact total recruitment. To evaluate how juvenile life history variation affects a population’s response to potential restoration, we developed a stage-structured model for a Chinook salmon population in a northern California river with a seasonally closed estuary. We modeled the timing of juvenile migration and estuarine use as a function of freshwater conditions and fish abundance. We used the model to evaluate the sensitivity of the population to different estuary and freshwater restoration scenarios that could affect population parameters at different life stages. The population’s run size increased most in response to freshwater restoration that enhanced spawning productivity (egg and fry survival), followed by spawner capacity. In contrast, estuary restoration scenarios affected only a subset of Chinook salmon (average 15%), and as a result, did not have a large impact on the total recruitment of a cohort. Under current condition, estuary rearing fish were over six times less likely to survive than fish that migrate to the ocean in the spring or early summer before estuary closure. Because estuary residents experienced low survival in the estuary and in the ocean, improvements to both estuary survival and growth would be needed to increase their total survival. When life cycle monitoring data is available, life cycle models such as ours generate predictions at scales relevant to conservation and are an advantageous approach to managing and conserving anadromous salmon that use multiple habitats throughout their life cycle.

Changes in Dendritic Spine Morphology and Density of Granule Cells in the Olfactory Bulb of Anguilla anguilla (L., 1758): A Possible Way to Understand Orientation and Migratory Behavior.

Simple SummaryThe olfactory bulb can process odour cues through granular cells (GCs) and dendritic spines, changing their synaptic plasticity properties and their morphology. The GCs’ dendritic spines density and morphology were analysed in Anguilla anguilla, considering the olfaction as a driver involved in fish orientation and migration. For the head and neck morphology, spines were classified as mushroom, long thin, stubby, and filopodia. Spines’ density decreased from juvenile migrants to no-migrant stages and increased in the adult migrants. Spines’ density was comparable between glass and silver eels as an adaptation to migration, while at non-migrating phases, spines’ density decreased. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb. Considering the role of olfaction in the orientation and migration of A. anguilla, the modification of environmental stimuli (ocean alterations and climate change) could represent contributing factors that threaten this critically endangered species.Olfaction could represent a pivotal process involved in fish orientation and migration. The olfactory bulb can manage olfactive signals at the granular cell (GC) and dendritic spine levels for their synaptic plasticity properties and changing their morphology and structural stability after environmental odour cues. The GCs’ dendritic spine density and morphology were analysed across the life stages of the catadromous Anguilla anguilla. According to the head and neck morphology, spines were classified as mushroom (M), long thin (LT), stubby (S), and filopodia (F). Total spines’ density decreased from juvenile migrants to no-migrant stages, to increase again in the adult migrant stage. Mean spines’ density was comparable between glass and silver eels as an adaptation to migration. At non-migrating phases, spines’ density decreased for M and LT, while M, LT, and S density increased in silver eels. A great dendritic spine development was found in the two migratory phases, regressing in trophic phases, but that could be recreated in adults, tracing the migratory memory of the routes travelled in juvenile phases. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb as an index of synaptic plasticity involved in the modulation of olfactory stimuli. If olfaction is involved in the orientation and migration of A. anguilla and if eels possess a memory, these processes could be influenced by the modification of environmental stimuli (ocean alterations and rapid climate change) contributing to threatening this critically endangered species.