Elevated river discharge enhances the immigration of juvenile catadromous and amphidromous fishes into temperate coastal rivers

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22–30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.     

Evidence of putative sensory receptors from snout and tongue in an upstream amphihaline migratory fish hilsa <Emphasis Type="Italic">Tenualosa ilisha</Emphasis>

Epidermal sensory structures of adults and juveniles of amphihaline migratory fish hilsa Tenualosa ilisha were studied from two habitats, i.e., freshwater (FW) and marine water (MW). Every year, adults and sexually mature hilsa migrate upstream from marine habitat to riverine freshwater habitat for breeding. This report provides evidences of chemoreception on their upstream migration through several characteristic features on their body, especially on the head and oral cavity. Scanning electron microscopy (SEM) reveals that freshwater adult hilsa (FH) has abundant solitary chemosensory cells (SCCs) on the snout epidermis (around the openings of the epidermal pit) and upper lip, whereas marine water adult hilsa (MH) moderately possesses such sensory structures. The juveniles returning to marine water completely lack SCCs. Immunohistochemical studies revealed the expression of PLC β2 on the snout of FH and tongue of both FH and MH. Further analysis (immunofluorescence, immunoblot and densitometry) of the epidermis confirms the presence of chemosensory structures through strong expression and localization of G-proteins (Gαq and Gα s/olf) from the snout as well as tongue in freshwater hilsa. The SEM also confirms the presence of two types of taste buds in FH, viz. type I (TB I) and type III (TB III). Whereas TB I and TB III are observed on the upper palatine and lips, most of the TB III are located on the tongue region of freshwater and marine hilsa. The juvenile hilsa are devoid of such structures. The presence of dense and rich SCCs and taste sensory cells in adults could be a characteristic feature for strong sensory reception to recognize odour and food-related environmental cues from habitats where they often migrate.     

The use of chemical cues in the upstream migration of coho salmon, Oncorhynchus kisutch Walbaum

The migratory behaviour of coho salmon was studied in the field. Coho salmon, Oncorhynchus kisutch , exposed to synthetic odours in a hatchery and released into Lake Michigan as juveniles, were recaptured as migrating adults 18 months later. The movements of 43 individuals were followed in experiments examining the role of imprinted chemical cues in the homing migration. Movements in relation to controlled distributions of the imprinting odours revealed that chemical cues are used by the salmon in their upstream migration. Acting with the rheotactic response, fish were guided upstream by imprinting odours simulating their home stream. Coho salmon, in the absence of their imprinting odour, respond negatively to the current. Differential responses to current appear to serve in segregating fish imprinted to odours of different home streams.     

Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (<Emphasis Type="Italic">Gobiomorphus cotidianus</Emphasis>) – implications for incipient speciation in island freshwater fish species

Background  

Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.     

And the Last Shall Be First: Heterochrony and Compensatory Marine Growth in Sea Trout (Salmo trutta)

Early juvenile growth is a good indicator of growth later in life in many species because larger than average juveniles tend to have a competitive advantage. However, for migratory species the relationship between juvenile and adult growth remains obscure. We used scale analysis to reconstruct growth trajectories of migratory sea trout (Salmo trutta) from six neighbouring populations, and compared the size individuals attained in freshwater (before migration) with their subsequent growth at sea (after migration). We also calculated the coefficient of variation (CV) to examine how much body size varied across populations and life stages. Specifically, we tested the hypothesis that the CV on body size would differ between freshwater and marine environment, perhaps reflecting different trade-offs during ontogeny. Neighbouring sea trout populations differed significantly in time spent at sea and in age-adjusted size of returning adults, but not on size of seaward migration, which was surprisingly uniform and may be indicative of strong selection pressures. The CV on body size decreased significantly over time and was highest during the first 8 months of life (when juvenile mortality is highest) and lowest during the marine phase. Size attained in freshwater was negatively related to growth during the first marine growing season, suggesting the existence of compensatory growth, whereby individuals that grow poorly in freshwater are able to catch up later at sea. Analysis of 61 datasets indicates that negative or no associations between pre- and post-migratory growth are common amongst migratory salmonids. We suggest that despite a widespread selective advantage of large body size in freshwater, freshwater growth is a poor predictor of final body size amongst migratory fish because selection may favour growth heterochrony during transitions to a novel environment, and marine compensatory growth may negate any initial size advantage acquired in freshwater.     

Post-settlement migratory behaviour and growth-related costs in two diadromous fish species, Galaxias maculatus and Galaxias brevipinnis

The physiological challenges incurred during the transition from sea to fresh water and the constraints they place on the rate at which the common galaxiid Galaxias maculatus and the climbing galaxiid Galaxias brevipinnis can migrate from marine to freshwater habitats were examined. The duration of the marine to freshwater transition, the relationship between post-settlement age (PSA) and standard length ( L _S) as a proxy for energetic costs incurred during settlement and the potential effects of estuary geomorphology on migratory behaviour was investigated. Rate of upstream migration after settlement was not uniform. Upstream migration rate was slowest directly after settlement and increased with increasing PSA and distance from the river mouth, indicating a delay in upstream migration by newly recruited galaxiids. L _s did not increase with age, at least within the first 21 days post settlement. These patterns were consistent for both species, in spite of differences in their life histories, across the recruitment season, despite seasonal variation in recruit size, and among estuaries with different properties. The results suggest that the timing and speed of migratory behaviour primarily reflect physiological constraints. Given the duration of residency of these species in estuaries, this study indicates that estuaries are critical transitional habitats for diadromous fishes during their migration from marine to freshwater habitats.     

Sequential fishways reconnect a coastal river reflecting restored migratory pathways for an entire fish community

River regulation infrastructure has been implicated in worldwide aquatic biodiversity loss. In‐stream barriers such as weirs prevent fish migration and the impact can be particularly severe for diadromous species. Fishways are frequently installed on in‐stream barriers to reconnect migratory pathways and rehabilitate diadromous fish populations. Sequential fishways may be necessary in rivers where multiple barriers prevent migration. We monitored a coastal fish community's response to fish passage restoration at 10 predominantly low‐level weirs in the freshwater reaches of the Nepean River in southeastern Australia. Few studies have simultaneously assessed fish community passage at successive fishways within a river system. Prior to the installation of the fishways, there was a gradient of reduced species diversity in an upstream direction including the absence of many diadromous species, despite the regular inundation frequency of most weirs. Following the installation of the fishways, species diversity was still greater in the downstream monitoring sites; however, there was evidence of a positive change in fish community structure in middle and upstream sites. Most notably, three diadromous species rapidly expanded their distribution upstream and one amphidromous species expanded its downstream distribution. This study demonstrates appropriately designed successive fishways can successfully reconnect river systems for an entire fish community, encompassing species with a broad range of swimming abilities and diverse life histories.     

Life histories of closely related amphidromous and non‐migratory fish species: a trade‐off between egg size and fecundity

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Olfactory navigation during spawning migrations: a review and introduction of the Hierarchical Navigation Hypothesis

Migrations are characterized by periods of movement that typically rely on orientation towards directional cues. Anadromous fish undergo several different forms of oriented movement during their spawning migration and provide some of the most well‐studied examples of migratory behaviour. During the freshwater phase of the migration, fish locate their spawning grounds via olfactory cues. In this review, we synthesize research that explores the role of olfaction during the spawning migration of anadromous fish, most of which focuses on two families: Salmonidae (salmonids) and Petromyzontidae (lampreys). We draw attention to limitations in this research, and highlight potential areas of investigation that will help fill in current knowledge gaps. We also use the information assembled from our review to formulate a new hypothesis for natal homing in salmonids. Our hypothesis posits that migrating adults rely on three types of cues in a hierarchical fashion: imprinted cues (primary), conspecific cues (secondary), and non‐olfactory environmental cues (tertiary). We provide evidence from previous studies that support this hypothesis. We also discuss future directions of research that can test the hypothesis and further our understanding of the spawning migration.     

Response of seaward-migrating European eel (Anguilla anguilla) to manipulated flow fields

Anthropogenic structures (e.g. weirs and dams) fragment river networks and restrict the movement of migratory fish. Poor understanding of behavioural response to hydrodynamic cues at structures currently limits the development of effective barrier mitigation measures. This study aimed to assess the effect of flow constriction and associated flow patterns on eel behaviour during downstream migration. In a field experiment, we tracked the movements of 40 tagged adult European eels (Anguilla anguilla) through the forebay of a redundant hydropower intake under two manipulated hydrodynamic treatments. Interrogation of fish trajectories in relation to measured and modelled water velocities provided new insights into behaviour, fundamental for developing passage technologies for this endangered species. Eels rarely followed direct routes through the site. Initially, fish aligned with streamlines near the channel banks and approached the intake semi-passively. A switch to more energetically costly avoidance behaviours occurred on encountering constricted flow, prior to physical contact with structures. Under high water velocity gradients, fish then tended to escape rapidly back upstream, whereas exploratory ‘search’ behaviour was common when acceleration was low. This study highlights the importance of hydrodynamics in informing eel behaviour. This offers potential to develop behavioural guidance, improve fish passage solutions and enhance traditional physical screening.     

Use of water flow direction to provide spatial information in a small-scale orientation task

Experiments were designed to investigate whether three-spined sticklebacks Gasterosteus aculeatus can use direction of water flow as an orientation cue. The fish had to learn the location of a food patch in a channel where water flow direction was the only reliable indicator of the food patch position. Fish from two ponds and two rivers were trained and tested in the spatial task to determine whether river three-spined sticklebacks are more adept at using water flow as a spatial cue than fish from ponds. All fish were able to use water flow to locate the food patch but one of the two river groups was significantly faster at learning the patch location. When the task was reversed so that fish that had formerly been trained to swim downstream now had to learn to swim upstream and vice versa both river groups learned the reversed task faster than the two pond groups. In a second experiment, to investigate whether fish from ponds or rivers vary in the type of spatial cue that they prefer to use, fish from one pond and one river were given a choice between two different types of spatial cue: flow direction or visual landmarks. A test trial in which these two cues were put into conflict revealed that the river population showed a strong preference for flow direction whilst the pond population preferred to use visual landmarks.     

Spawning migrations in landlocked Atlantic salmon: time series modelling of river discharge and water temperature effects

River discharge and water temperature are frequently cited as controlling the upstream migration of adult salmonids to their spawning areas. The results of earlier studies on the effect of these environmental factors were examined. The statistical methods employed in some of these studies failed to consider the serial correlation often found in migration time series. To assess the effects of discharge and temperature on the migratory activity of the landlocked Atlantic salmon (ouananiche, Salmo salar ), 12 years of data on spawning migrations in the Mistassini R., Quebec, Canada, were analysed and the results obtained by ordinary least squares regression and time series regression were compared. In six of the 12 years, upstream migratory movement was related negatively to changes in river flow, suggesting that fish favour falling water phases for ascent. Water temperature appeared to have little effect on migratory movement. The mean body size of migrating fish decreased significantly throughout the summer; early migrants were on average 11.4% larger (mean fork length 522mm) than late migrants (469 mm). Larger, 3-lake-year salmon migrated 7.2 days earlier than 2-lake-year salmon. Because the residuals from ordinary regression exhibited strong autocorrelation, time series regression was more appropriate than ordinary regression for the analysis of migration time Series.     

Dramatic orientation shift of white-crowned sparrows displaced across longitudes in the high Arctic

Advanced spatial-learning adaptations have been shown for migratory songbirds, but it is not well known how the simple genetic program encoding migratory distance and direction in young birds translates to a navigation mechanism used by adults. A number of convenient cues are available to define latitude on the basis of geomagnetic and celestial information, but very few are useful to defining longitude. To investigate the effects of displacements across longitudes on orientation, we recorded orientation of adult and juvenile migratory white-crowned sparrows, Zonotrichia leucophrys gambelii, after passive longitudinal displacements, by ship, of 266-2862 km across high-arctic North America. After eastward displacement to the magnetic North Pole and then across the 0 degrees declination line, adults and juveniles abruptly shifted their orientation from the migratory direction to a direction that would lead back to the breeding area or to the normal migratory route, suggesting that the birds began compensating for the displacement by using geomagnetic cues alone or together with solar cues. In contrast to predictions by a simple genetic migration program, our experiments suggest that both adults and juveniles possess a navigation system based on a combination of celestial and geomagnetic information, possibly declination, to correct for eastward longitudinal displacements.     

Endangered Golden mahseer <Emphasis Type="Italic">Tor putitora</Emphasis> Hamilton: a review of natural history

Golden mahseer, Tor putitora Hamilton, one of the largest freshwater fish of the Indian sub-continent, inhabits mainly Himalayan rivers in the foothills. Among numerous freshwater fishes of the sub-continent, Golden mahseer is the most striking due to its large size, attractive golden colour, sustenance and sporting values. Tor putitora is known by various common names such as king mahseer, mighty mahseer and the tiger of water. Being a migratory fish, Golden mahseer undertakes periodic upstream migration during pre-monsoon and monsoon seasons from large rivers and higher order streams in the foothills to lower order streams for spawning. In recent years, conservationists, anglers and commercial fishermen have expressed concern over the declining populations of Golden mahseer due to indiscriminate fishing of brooders and juveniles besides the adverse effects of dams. Despite its ecological and economic importance, specific conservation measures by way of protective legal provisos are lacking for Golden mahseer in India. In view of its physical features, ecology and vulnerable conservation status, there is an exigent need to promote the Golden mahseer as a flagship conservation species of the Himalayan rivers. In view of the recent reports of unprecedented river regulation projects on the Himalayan rivers and need to draw global attention of conservationists, we review various aspects of ecology, life history, interesting features, traits and threats associated with the reduced chances of survival of Golden mahseer.     

The nature and role of learning in the orientation and migratory behavior of fishes

Synopsis Fish migration may be viewed as the product of two processes; the selection and tracking of optimal environmental conditions through time and space, and the use of predictive information about environmental structure to bias movements towards a goal. The establishment and maintenance of directional bias is based on the interaction of experience and instinct. The preoccupation of much fish orientation research with innate fixed patterns of behavior on one hand and hydrodynamics on the other has led us to underestimate the possibility that orientation is a flexible process relying on developmental sequences, calibration of the motor-sensory interaction based on experience and the learning of environmental pattern. Evidence illustrating how experience and learning may influence the direction of movement and how the goal is recognized is presented according to two general categories: (a) imprinting and early experience and (b), spatial learning, including the social transmission of migratory routes and directions. In the first category, the olfactory hypothesis of salmon homing is briefly reviewed and new data presented describing olfactory imprinting in Atlantic salmon,Salmo salar. In the second category, evidence is presented demonstrating the modifiability of sun-compass orientation and the ability of some fish species to learn the spatial distribution of landmarks. The role of social transmission in the migration of coral reef fishes is reviewed. The possible role of these learning phenomena in the formation of familiar area maps, route-based and location-based navigation and the critical distance factor is considered. The relationship between life history and the nature of learning in migratory orientation is discussed     

Annual dynamics variation of a landlocked Galaxias maculatus (Jenyns 1842) population in a Northern Patagonian river: occurrence of juvenile upstream migration

Galaxias maculatus, broadly distributed in the southern hemisphere, presents both diadromic and landlocked populations. The upstream migration of larvae and juveniles from the sea to freshwater habitats is a characteristic phenomenon of diadromous populations, but upstream migration has never been reported in those that are landlocked. The objective of this study was to establish the population dynamics of a peculiar riverine landlocked population that presents an upstream migration at the larvae–juvenile transition from the Piedra del Águila Reservoir to the Caleufú River (Argentina). A spawning season from September to November and the arrival of shoals of metamorphic larvae and juveniles from February to April to the adult habitat were coincidental with lacustrine landlocked populations, but not with diadromous populations. Growth rate and age at migration, 147 ± 22.6 days, were also similar to other landlocked and diadromous populations. The arrival of these shoals produced a 20‐fold increase in fish density while the two cohorts of G. maculatus overlapped in time and space. No significant differences in morphology or vertebrae number were detected when riverine and reservoir adults were compared. The great life history plasticity of G. maculatus, shown to be even greater in our results, could be the key to explain the wide distribution of this species in the southern hemisphere. Likewise, discovering this juvenile potamodromous behaviour in a landlocked population will provide a new view for the analysis of the ways of this species’ dispersion in continental waters.     

Species-specific attraction of migratory banded kokopu juveniles to adult pheromones

Juvenile migratory Galaxias fasciatus juveniles or whitebait were attracted to odours produced by adults. The attraction was dependent on concentration with an upstream movement and attraction to the odour chamber at intermediate level concentrations. At a high concentration the migratory response of whitebait was retarded with the majority of fish not moving upstream but remaining in the lower section of the apparatus. There was no response to odours from adults of other galaxiid species, the inanga G. maculatus or koaro G. brevipinnis at any concentration. These results demonstrate G. fasciatus whitebait have the ability to discriminate species-specific pheromones during their migratory phase, providing evidence of a pheromonal attraction in migratory amphidromous fish which could possibly provide a basis for effective habitat selection.     

Migration of Sakhalin taimen (<Emphasis Type="Italic">Parahucho perryi</Emphasis>): evidence of freshwater resident life history types

Sakhalin taimen (Parahucho perryi) range from the Russian Far East mainland along the Sea of Japan coast, and Sakhalin, Kuril, and Hokkaido Islands and are considered to primarily be an anadromous species. We used otolith strontium-to-calcium ratios (Sr/Ca) to determine the chronology of migration between freshwater and saltwater and identify migratory contingents of taimen collected from the Koppi River, Russia. In addition, we examined taimen from the Sarufutsu River, Japan and Tumnin River, Russia that were captured in marine waters. Transects of otolith Sr/Ca for the Sarufutsu River fish were consistent with patterns observed in anadromous salmonids. Two fish from the Tumnin River appeared to be recent migrants to saltwater and one fish was characterized by an otolith Sr/Ca transect consistent with marine migration. Using these transects as benchmarks, all Koppi River taimen were classified as freshwater residents. These findings suggest more work is needed to assess life history variability among locations and the role of freshwater productivity in controlling migratory behavior in taimen.     

An accurate tool for ageing Two‐spined Blackfish for use in determining timing of spawning in upland streams in the Brindabella ranges,ACT, Australia

To manage populations of threatened fish species in modified habitats and regulated rivers requires an understanding of their reproductive biology and spawning cues. In particular, accurate information about early life stages in these species can be used to facilitate programmes that maximise recruitment and breeding success. This study aimed to develop methods to accurately age early juvenile freshwater native fish, Two‐spined Blackfish, (Gadopsis bispinosus), to allow the determination of spawning date. This was accomplished through the examination of otolith microstructure in early juveniles. The age at which the first ring was deposited and the relationship between days and number of rings were determined using both field and aquarium trials. Field trials of marked juvenile otoliths revealed daily deposition of rings (1.02 ± 0.02 rings per day for fish sacrificed six days postmarking). The strength of this relationship lessened slightly as juveniles aged (0.92 ± 0.02 rings per day for fish sacrificed 13 days postmarking). The first otolith ring was deposited 7.50 ± 1.09 days after spawning. The enumeration of daily rings combined with knowledge of the commencement of ring deposition enabled accurate estimation of spawning date. The current study is the first to examine otolith microstructure in juvenile Two‐spined Blackfish allowing accurate determination of spawning date. While more research is required to accurately age older juveniles, this technique has the potential to precisely correlate spawning with environmental cues, facilitating better management of temperature and flow during breeding periods, potentially increasing spawning and recruitment of this endangered species.     

Field studies of avian nocturnal migratory orientation I. interaction of sun,wind and stars as directional cues

Tracking radar and visual observation techniques were used to observe the orientation of free-flying passerine nocturnal migrants in situations in which potentially usable directional cues were absent or gave conflicting information. When migrants had seen the sun near the time of sunset and/or the stars, they oriented in appropriate migratory directions even when winds were opposed. Under solid overcast skies that prevented a view of both sun and stars, the birds headed downwind in opposing winds and thus moved in seasonally inappropriate directions. The data point to the primacy of visual cues over wind direction, with either sun or stars being sufficient to allow the birds to determine the appropriate migration direction.