Showing papers on "Fish migration published in 2023"

Tracking anadromous fish over successive freshwater migrations reveals the influence of tagging effect, previous success and abiotic factors on upstream passage over barriers

Abstract: Predicting and mitigating the impact of anthropogenic barriers on migratory fish requires an understanding of the individual and environmental factors that influence barrier passage. Here, the upstream spawning migrations of iteroparous twaite shad Alosa fallax were investigated over three successive spawning migrations in a highly fragmented river basin using passive acoustic telemetry (n=184). More fish approached and passed barriers in the lower river reaches than further upstream, with the median cumulative weir passage time (IQR) of 4.6 (1.8 - 9.2) days representing 18% of their time in river. Returning fish in their second year had significantly higher weir passage rates than in their tagging year, with passage rates also positively influenced by previous passage success. Higher water temperature and river level also had positive impacts on passage rates. Lower weir passage rates by newly tagged individuals suggests that reliance on within-year passage estimates in telemetry-based barrier impact assessments could result in conservative results, while higher passage rates of previously successful versus unsuccessful individuals suggests a conserved motivation and/or inherent ability to pass barriers.

Local variation in the timing of reproduction and recruitment in a widely distributed diadromous fish

Abstract: Īnanga (Galaxias maculatus) is a widespread freshwater fish, found around coastal New Zealand, Chatham Islands, southern Australia and southern South America, exhibiting both diadromous and land-locked life history patterns. We assessed population size structure, size at maturity, timing of reproduction, and post-reproductive survival in the Waikouaiti and Kakanui rivers, two regionally important G. maculatus populations in southern New Zealand. Size at maturity varied between rivers and sexes, with males generally maturing at smaller sizes than females. The timing of reproduction and recruitment was observed to vary across a relatively small spatial scale. Population length-frequencies indicated that both populations exhibited annual population dynamics, with most individuals spawning in their first year, then apparently dying soon afterwards (as indicated by a marked drop in post-spawning abundance). However, a few individuals with recently spent or resting gonads were present over the winter months, indicating some post-spawning survival. There was a lower frequency of exceptionally large (putatively 1+) individuals than reported for other populations around New Zealand and elsewhere, suggesting over-winter survival following spawning varies. Based on the variation in life history characters over small spatial scales, we suggest that management of regionally important G. maculatus populations should be based on catchment level information.

The decline of the ecosystem services generated by anadromous fish in the Iberian Peninsula

Abstract: Abstract This work aims to present an historical review of the ecosystem services provided by anadromous fish (i.e., species that migrate from the sea to the river to spawn) throughout Human time, as well as of the main related threats, focusing on the Iberian Peninsula region. Anadromous fish provide important provision, cultural, regulatory and supporting ecosystem services across their distribution range and have been extensively exploited by humans since prehistoric times. In the Iberian Peninsula, sea lamprey, allis and twaite shads, sea trout, Atlantic salmon and European sturgeon were once abundantly present in several river basins covering what is now Portuguese and Spanish territory. These species have suffered a severe decline across their distribution range, mainly due to habitat loss and overexploitation. Considered regal delicacies, these fishes were once a statement on the tables of the highest social classes, a much appreciated bounty for the poorer population and are still an important part of the local gastronomy and economy. Such high economic and cultural interest encouraged intensive fishing. Currently, management efforts are being implemented, pairing habitat rehabilitation (e.g., construction of fish passes in obstacles to migration such as weirs and dams) with sustainable fisheries. Considering the present climate change scenario, these species are bound to endure increased pressures, demanding novel management approaches to ensure population numbers that are able to secure their sustainable exploitation.

White perch health relative to urbanization and habitat degradation in Chesapeake Bay tributaries. II. Hepatic and splenic macrophage aggregates.

Abstract: Macrophage aggregate (MA) abundance in fish is a useful general biomarker of contaminant exposures and environmental stress. Hepatic and splenic MAs were evaluated in semi-anadromous white perch Morone americana (Gmelin, 1789) from the urbanized Severn River (S) and the more rural Choptank River (C), Chesapeake Bay. Fish were collected from different sites in the annual migratory circuit in each river that corresponded to active spawning in late winter-early spring, summer regenerating, autumn developing, and winter spawning-capable phases. An age-associated progressive increase in the total volume of MAs (MAV) was evident in the liver and spleen. Mean hepatic MAV (range in seasonal means, C: 6.4-23.1 mm3; S: 15.7-48.7 mm3) and mean splenic MAV (C: 7.3-12.6 mm3; S: 16.0-33.0 mm3) differed significantly among seasons and were significantly greater in females and in Severn River fish. Age and river were the most influential factors, suggesting that increased MAV in Severn River fish resulted from chronic exposures to higher concentrations of environmental contaminants. Hepatic MAV was directly related to the relative volume of copper granules in the liver. Less influential factors on splenic MAV included fish condition, trematode infections, and granulomas, indicating possible functional differences in MAs by organ. While organ volumes were strongly linked to gonadosomatic index (GSI) and reproductive phase, the reason for seasonal differences in MAV was less clear. Water temperature, salinity, and dissolved oxygen were not significantly related to MAV, and indicators of reproductive phase (hepatosomatic index and GSI) were significant but less important in explaining variation in MAV.

Shrinking body size and climate warming: Many freshwater salmonids do not follow the rule

Abstract: Declining body size is believed to be a universal response to climate warming and has been documented in numerous studies of marine and anadromous fishes. The Salmonidae are a family of coldwater fishes considered to be among the most sensitive species to climate warming; however, whether the shrinking body size response holds true for freshwater salmonids has yet to be examined at a broad spatial scale. We compiled observations of individual fish lengths from long‐term surveys across the Northern Hemisphere for 12 species of freshwater salmonids and used linear mixed models to test for spatial and temporal trends in body size (fish length) spanning recent decades. Contrary to expectations, we found a significant increase in length overall but with high variability in trends among populations and species. More than two‐thirds of the populations we examined increased in length over time. Secondary regressions revealed larger‐bodied populations are experiencing greater increases in length than smaller‐bodied populations. Mean water temperature was weakly predictive of changes in body length but overall minimal influences of environmental variables suggest that it is difficult to predict an organism's response to changing temperatures by solely looking at climatic factors. Our results suggest that declining body size is not universal, and the response of fishes to climate change may be largely influenced by local factors. It is important to know that we cannot assume the effects of climate change are predictable and negative at a large spatial scale.

Using acoustic tracking of an anadromous lamprey in a heavily fragmented river to assess current and historic passage opportunities and prioritise remediation

Abstract: Anthropogenic structures extensively fragment riverine systems, reducing longitudinal connectivity, inhibiting migration and leading to severe declines in many fish populations, especially for diadromous species. This study investigated the upstream spawning migration of anadromous river lamprey (Lampetra fluviatilis) in a heavily fragmented tributary of the Humber Estuary, the location of one of the largest UK river lamprey populations. Overall, this study quantified river lamprey migration, spawning habitat distribution and historic river levels to develop a novel empirical index to understand the impact of man‐made barriers and prioritise their remediation. Passage at all weirs only occurred during episodic high river levels, often after prolonged delays with no lamprey passing below average levels for the time of year or utilising the fish pass at the first weir (T1) at the tidal limit. Barrier passage opportunities at the first four weirs were only possible for 30.3%, 38.7%, 52.1% and 6.7% of the migration period, but were lower and severely limited in 15 of the last 21 years. In addition, more lamprey (60%, n = 18) were last detected in reaches with no spawning habitat than in spawning habitat (40%, n = 12). Given the impassibility of, and lack of retreat from, T1 to other Humber tributaries, the River Trent is currently considered an ecological trap for a large proportion of lamprey that enter from the Humber Estuary. This passage should be urgently remediated, per the prioritisation index presented here, to aid river lamprey conservation, especially given their status as a designated feature of the Humber SAC.

Flow and thermal regimes altered by a dam caused failure of fish recruitment in the upper Mekong River

Abstract: Riverine fishes have been increasingly threatened by the global proliferation of both small dams and large hydropower projects to meet the soaring water, energy and food demands from growing human populations and urbanisation. However, empirical evidence of the direct effects on a specific species before and after dam construction and operation is rare. Causes of population decline vary among species and, although little known, they are of great importance for successful environmental flow regulation. We monitored the hydroenvironment and population dynamics of a Schizothoracinae fish (Schizothorax lissolabiatus) for 9 years before and after dam (i.e., Dahuaqiao) construction in the upper Mekong River to understand fish response processes and the underlying mechanisms. Optimal hydroenvironmental conditions for key reproduction stages (e.g., pre-spawning, hatching and post-hatching) were reconstructed using daily increment analysis of larval otoliths and hydroenvironmental data. The flow regime was substantially disrupted by the dam, and water temperature was only slightly changed. The disappearance of young of the year from downstream after dam operation indicates that the changed hydroenvironment caused recruitment failure in S. lissolabiatus. By matching optimal hydroenvironmental conditions for S. lissolabiatus reproduction with the monitored hydroenvironmental data series before and after dam operation, we found that changes in thermal regime alone caused narrowing of the reproduction window by an average of 41%, whereas flow-regime change alone narrowed it by 96% and it was narrowed by 98% for thermal and flow changes combined. This study shows that the altered flow regime, but not the thermal regime, was the primary driver of the recruitment failure of S. lissolabiatus. The findings highlight the importance of prioritising flow-regime management to improve recruitment success for S. lissolabiatus and to favour the persistence of other imperilled Schizothoracinae fishes and native species in dammed rivers.

Does the loss of diadromy imply the loss of salinity tolerance? A gene expression study with replicate nondiadromous populations of Galaxias maculatus

Abstract: The recurrent colonization of freshwater habitats and subsequent loss of diadromy is a major ecological transition that has been reported in many ancestrally diadromous fishes. Such residency is often accompanied by a loss of tolerance to seawater. The amphidromous Galaxias maculatus has repeatedly colonized freshwater streams with evidence that freshwater‐resident populations exhibit stark differences in their tolerance to higher salinities. Here, we used transcriptomics to gain insight into the mechanisms contributing to reduced tolerance to higher salinities in freshwater resident populations. We conducted an acute salinity challenge (0 ppt to 23–25 ppt) and measured osmoregulatory ability (muscle water content) over 48 h in three populations: diadromous, saltwater intolerant resident (Toltén), and saltwater tolerant resident (Valdivia). RNA sequencing of the gills identified genes that were differentially expressed in association with the salinity change and associated with the loss of saltwater tolerance in the Toltén population. Key genes associated with saltwater acclimation were characterized in diadromous G. maculatus individuals, some of which were also expressed in the saltwater tolerant resident population (Valdivia). We found that some of these “saltwater acclimation” genes, including the cystic fibrosis transmembrane conductance regulator gene (CFTR), were not significantly upregulated in the saltwater intolerant resident population (Toltén), suggesting a potential mechanism for the loss of tolerance to higher salinities. As the suite of differentially expressed genes in the diadromous‐resident comparison differed between freshwater populations, we hypothesize that diadromy loss results in unique evolutionary trajectories due to drift, so the loss of diadromy does not necessarily lead to a loss in upper salinity tolerance.

Downstream fish passage at small-scale hydropower plants: Turbine or bypass?

Abstract: Introduction: Hydropower plants are frequently equipped with physical and behavioral fish protection barriers to prevent downstream moving fish from harmful turbine passage and to guide them to alternative bypasses. As not only diadromous but also potamodromous fish species migrate and inevitably have to pass hydropower plants, knowledge on corridor usage for a wide range of species is important to identify potential deficits and to improve bypass efficiency. Methods: In this study, the corridor usage of downstream moving fish (6,646 individuals from 42 species) was investigated at four small-scale hydropower plants with different concepts to prevent turbine entrainment and to bypass fish. Results: Despite existing bypasses and fine screens with 15 mm and 20 mm bar spacing to prevent turbine entrainment, a large proportion of fish (35%–88%) still passed the turbines. The mainly poor efficiency of the investigated bypasses was probably due to low discharge and unfavorable bypass location or detectability. The various bypass types were used by a different range of fish species and sizes due to species-specific behavior and differing fish communities between sites. The effectiveness of the investigated downstream corridors was positively correlated with the share of discharge. Discussion: To reduce the negative ecological impacts of hydropower plants on downstream moving fish, well-performing bypasses are required that consider not only current requirements regarding design, dimensioning and location, but also the site-specific fish community. Thus, bypasses should function for the widest possible range of species, which can be achieved through less selective bypass types such as full-depth bypasses, or a combination of different bypass systems. Moreover, less harmful turbine technologies and more effective fish protection systems need to be implemented, since fine screens with 15 mm and 20 mm bar spacing cannot prevent small-bodied fish species and juvenile fish <20 cm from turbine entrainment.

Differences in the Natural Swimming Behavior of Schizothorax prenanti Individual and Schooling in Spatially Heterogeneous Turbulent Flows

Abstract: Simple Summary Exploring the behavioral strategies of fish in response to complex hydrodynamic environments is an important scientific focus in fish habitat enrichment research. The results of this research indicated that (1) the swimming speed of fish schooling (three fish) was significantly lower than that of individual fish, (2) fish schools performed obvious slow-speed exploration behavior during upstream migration, and (3) fish mainly tended to occupy low and medium flow velocity areas. The results of this research enrich the knowledge of fish behavioral responses to spatially heterogeneous turbulent flows, which is an important aspect for developing reliable and accurate estimates of fish passage facilities and husbandry environments. Abstract Spatially heterogeneous turbulent flow refers to nonuniform flow with coexisting multiple flow velocities, which is widely distributed in fish natural or husbandry environments, and its hydraulic parameters affect fish swimming behavior. In this study, a complex hydrodynamic environment with three flow velocity regions (low, medium, and high) coexisting in an open-channel flume was designed to explore volitional swimming ability, the spatial-temporal distribution of fish swimming trajectories, and the range of preferred hydrodynamic parameters of Schizothorax prenanti individual and schooling (three fish). The results showed that the swimming speed of individual fish during upstream migration was significantly higher than that of fish schools (p < 0.05). The swimming trajectories of fish schooling showed that they spent more time synchronously exploring the flow environment during upstream migration compared with individual fish. By superimposing the fish swimming trajectories on the environmental flow field, the range of hydrodynamic environments preferred by fish in complex flow fields was quantified. This research provides a novel approach for investigating the natural swimming behavior of fish species, and a theoretical reference for the restoration of fish natural habitats or flow enrichment of husbandry environments.

Unravelling the life history patterns and habitat preferences of Japanese eel (Anguilla japonica) in the Pearl River China.

Abstract: Eels have fascinated biologists for centuries, due to their amazing long-distance migrations between freshwater habitats and very distant ocean spawning areas. The migratory life histories of the Japanese eel, Anguilla japonica, in the waters of south China are not very clear, despite its ecological importance, and the need for fishery regulation and management. In this study, strontium (Sr) and calcium (Ca) microchemical profiles of the otoliths of sliver eels were measured by X-ray electron probe microanalysis (EPMA) based on data collected from different habitats (including freshwater and brackish habitats), in the large subtropical Pearl River. The corresponding habitat preference characteristics were further analyzed using redundancy analysis (RDA). A total of 195 Japanese eels were collected over six years. The collected individuals ranged from 180 to 771 mm in total length and from 8 to 612 g in body weight. Two-dimensional pictures of the Sr:Ca concentrations in otoliths revealed that the A. japonica in the Pearl River are almost entirely river eels, spending the majority of their lives in freshwater without exposure to salt water. While the catadromous migration time has delayed about one month in the Pearl River estuary in the past 20 years. RDA analysis further indicated that juveniles and adults preferred water with high salinity and high tide levels. Youth preferred habitats with high river fractals. Our findings contribute to a growing body of evidence, and showing that the eels extremely scarce currently and conservation measures against them are imminent, including the protection of brackish and freshwater areas where they live in south China.

Modern data on the biology of the Pacific rainbow smelt Osmerus dentex (Osmeridae) of the estuarine zone of the Nyukhcha River, Onega Bay of the White Sea

Abstract: Pacific rainbow smelt Osmerus dentex Steindachner et Kner, 1870 is ubiquitous in the coastal areas of the White Sea, found mainly in desalinated bays. This is a semi-anadromous pelagic species. The paper presents biological data on the Pacific rainbow smelt from the estuarine part of the Nyukhcha River, collected in the period from 2004 to 2018. In the study area, its maximum length (according to Smitt) is 35.3 cm, weight is 398 g, the maximum recorded age is 10 years. It reaches maturity at the age of three years, less often in the second year of life. Spawning occurs mainly in May, less often in late April and early June. Eggs are laid on the bottom; average absolute fertility is 46.5 thousand eggs. It feeds mainly on crustaceans and small fish.

Fish Injury from Movements across Hydraulic Structures: A Review

Abstract: Fish migration is essential to maintain healthy aquatic ecosystems, but hydraulic structures across rivers have impeded natural fish migration worldwide. While efforts have been made to allow fish to pass some hydraulic structures, there is limited understanding of hydrodynamic effects that cause fish injury in different hydraulic systems, such as spillways and stilling basins as well as hydropower systems. This study reviewed available literature on this topic to identify the current knowledge of fish injury thresholds in laboratory- and field-based studies of hydraulic systems. Often, the hydraulic effects that lead to fish injury have been described with time-averaged simplified parameters including shear stress, pressure changes, acceleration, vortical motions, aeration, collision, and strike, while these hydrodynamic effects often occur simultaneously in the turbulent flows across hydraulic structures, making it difficult to link specific fish injuries to a particular hydrodynamic effect. Strong variations of injury may occur, depending on the type and the intensity of hydrodynamic effects, as well as the fish species and fish sizes. Modelling can provide information of stressors, but real-world tests are needed to accurately assess fish injury and mortality. Fish injury mechanisms at hydropower turbines are well understood, however, clear understanding at other sites is lacking. Future studies should aim to report holistic hydrodynamic thresholds with associated fish injury rates. Multidisciplinary systematic research is required, including laboratory and field studies, using passive tracer sensor packages and state-of-the art instrumentation in conjunction with live fish. This can quantify stressors with meaningful parameters, aiming to improve fish safety with more sustainable design of water infrastructure that reduces fish injury when passing across hydraulic structures.

Postrelease exploration and stress tolerance of landlocked and anadromous Atlantic salmon and their hybrids

Abstract: Threatened fish populations worldwide are relying on stock supplementation by hatchery‐reared fish. Although stocking with non‐native fish may lead to hybridization, thereby disrupting local adaptations, it could also improve the adaptive potential of small populations by increasing variability in essential behavioral traits. In this study, we crossbred the critically endangered Finnish landlocked salmon with a geographically close Baltic anadromous salmon population to compare boldness‐related behavioral traits among the crossing groups. We studied postrelease exploration in seminatural streams and tested stress tolerance of the fish, as reflected by their response during swimming trials and commencement of feeding after the trials. In the stress tolerance experiments, we compared fish with different rearing backgrounds to gain insight into environmentally induced variability in stress tolerance. When compared with the anadromous salmon, the landlocked salmon showed more active postrelease exploration and higher stress tolerance. The hybrids displayed intermediate behaviors compared with the purebred salmon, indicating heritability of these traits. The landlocked salmon showed less variable exploration than the hybrids with anadromous salmon as the maternal strain, but we did not find rearing‐dependent responses in stress tolerance. In summary, our findings suggest that hybridization could help in reversing likely domestication‐related negative behavioral traits in the landlocked salmon.

Early detection and recovery of river herring spawning habitat use in response to a mainstem dam removal

Abstract: Historical loss of river and stream habitats due to impassable dams has contributed to the severe decline of many fish species. Anadromous fishes that migrate from the sea to freshwater streams to spawn have been especially impacted as dams restrict these fish from accessing ancestral spawning grounds. In 2018, Bloede Dam was removed from the Patapsco River near Baltimore, Maryland, restoring approximately 100 km of potential habitat for migratory fish. We assessed the response of anadromous river herring, alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), to this dam removal by monitoring environmental DNA (eDNA) and eggs from 2015 to 2021 at locations upstream and downstream of the dam site during their spawning migrations. We additionally assessed the presence of fish by collecting electrofishing samples and tracked the movements of individual adult fish within the river using passive integrated transponder (PIT) tags. No adult river herring, eDNA, or eggs were detected upstream of Bloede Dam in the four years prior to its removal despite the presence of a fish ladder. Our results suggest initial habitat use recovery by spawning river herring in the first year post-removal, although a relatively small proportion of the population in the river used the newly accessible habitat. In the three years post-removal, the likelihood of detecting river herring eDNA upstream of the former dam site increased to 5% for alewife and 13% for blueback herring. Two adult fish were also collected in electrofishing samples upstream of the dam site in 2021. We found no evidence of changes in egg abundance and no tagged fish were detected upstream of the dam site post-removal. While long term monitoring is needed to assess population changes, this study highlights the value of integrating methods for comprehensive understanding of habitat use following dam removal.

Reservoirs facilitate colonization of river catchments by a native invasive fish through provision of pelagic larval rearing habitat

Abstract: Abstract Dams on rivers are known to facilitate the colonisation and spread of aquatic alien and native invasive species, but the actual mechanisms involved are poorly understood. Since the construction of the Solina Dam on the upper San River system in Poland, European perch ( Perca fluviatilis ) have expanded their distribution into the headwaters of this river system, becoming a native invader. In this study, we assessed the spread of perch in detail over time upstream of the Solina Reservoir, and used otolith trace element microchemistry to determine the spawning and larval rearing locations of perch in the catchment upstream of the dam. Extensive sampling over several years across the catchment upstream of the Solina Reservoir confirmed the widespread occurrence of perch into the headwaters of the tributary river systems, with smaller size classes dominating locations closer to the Solina Reservoir. Despite perch being widely distributed upstream of the Solina Reservoir, otolith microchemical analysis indicated the populations from various reservoir tributaries mostly shared the same spawning and larval rearing habitat, most likely the Solina Reservoir. Our results suggest that reservoirs can facilitate the colonisation of river systems by providing a critical habitat element that would be otherwise missing from riverine landscapes, i.e., an extensive and productive pelagic larval rearing environment. This research shows that the impacts of large dams can extend many kilometers upstream from the river reaches directly affected by the resulting impoundment.

Joint temporal trends in river discharge and temperature over the past 57 years in a large European basin: implications for diadromous fish

Abstract: Stream temperature and discharge are two fundamental triggers of key periods of the life cycle of aquatic organisms such as the migration of diadromous fish. However, the increase in stream temperature, more frequent and severe droughts, and asynchronous evolution of stream temperature and discharge due to climate change can modify the duration and frequency of favorable temperature-flow associations for the realization of species&#8217; ecological processes.In this study, we investigated the influence of changes in favorable temperature-flow velocity associations for the upstream migration of Atlantic salmon, Alis shad and Sea lamprey at the scale of the Loire River basin (&#160;km&#178;). First, we used a physically-based thermal model (T-NET), coupled with a semi-distributed hydrological model (EROS) to reconstruct continuous daily times series over the 1963-2019 period (Seyedhashemi et al., 2022). Current velocity (V) was estimated using discharge through a hydraulic geometry model (Morel et al., 2020). We identified suitable water temperature-flow velocity associations for the migration of the three studied species based on (1) the literature and (2) observed migration recorded at fish passage stations. Using the &#8220;Choc method&#8221; (Arevalo et al., 2020), we then quantified the changes in frequency of occurrence of these suitable environmental windows over the past six decades across the hydrographic network of the Loire River basin.Our results showed that the greatest increases in stream temperature were associated with the greatest decreases in flow velocity over the past six decades. We also found that the frequency of suitable temperature-velocity associations for upstream migration of Atlantic salmon has significantly reduced, mainly in the southern part of the basin. In contrary, the frequency of suitable associations for upstream migration of the two other species has mainly increased.These results highlighted strong disparities in the consequence of global changes on fish migratory processes among species and in space. This work provides operational results for the management of these threatened diadromous species and the prioritization of management measures in a context of climate change.Key words: climate change, hydrological change, water temperature, temporal trends, fish migration, long-term, large scale, Loire basin&#160;Seyedhashemi, H., Vidal, J.P., Diamond, J.S., Thi&#233;ry, D., Monteil, C., Hendrickx, F., Maire, A. and Moatar, F., 2022. Regional, multi-decadal analysis on the Loire River basin reveals that stream temperature increases faster than air temperature. Hydrology and Earth System Sciences, 26(9), pp.2583-2603.Morel, M., Booker, D.J., Gob, F. and Lamouroux, N., 2020. Intercontinental predictions of river hydraulic geometry from catchment physical characteristics. Journal of Hydrology, 582, p.124292.Arevalo, E., Lassalle, G., T&#233;tard, S., Maire, A., Sauquet, E., Lambert, P., Paumier, A., Villeneuve, B. and Drouineau, H., 2020. An innovative bivariate approach to detect joint temporal trends in environmental conditions: Application to large French rivers and diadromous fish. Science of the Total Environment, 748, p.141260.

Otolith-inferred patterns of marine migration frequency in Nunavik Arctic charr.

Abstract: Alternative migratory tactics in salmonids reflect the large observed inter-individual variation in spatial behaviour which may range from strict freshwater residency to uninterrupted anadromy. In Salvelinus, sea migrations are performed during the ice-free period as freshwater over-wintering is thought to be obligatory due to physiological constraints. As a result, individuals can either perform a migration the next spring or remain in freshwater, as anadromy is generally considered facultative. In Arctic charr (S. alpinus), skipped migrations are known to occur but limited data are available about their frequencies within and among populations. Here, we used an otolith microchemistry approach relying on Strontium (88 Sr) to infer movements between freshwater and marine habitats, and annual oscillations in Zinc (64 Zn) to help with age identification. We determined the age-at-first-migration and the occurrence of subsequent annual migrations in two Nunavik Arctic charr populations sampled in Deception Bay (Salluit) and, river systems linked to Hopes Advance Bay (Aupaluk), northern Québec, Canada. The mode for age-at-first-migration was 4+ for both populations, although it exhibited large variation (range: 0+ to 8+). Skipped migrations constituted a rare event, as 97.7% and 95.6% of the examined Arctic charr at Salluit (n = 43, mean age = 10.3 ± 2.0 years) and Aupaluk (n = 45, mean age = 6.0 ± 1.9 years), respectively, were found to have performed uninterrupted annual migrations after initiation of the behaviour. The consistency of the annual migrations suggests that the tactic is sufficiently fitness-rewarding to be maintained under current environmental conditions. From a fisheries management perspective, these repeated migrations combined with low site fidelity may lead to large interannual variations in abundance at the local scale, which may represent a challenge for monitoring Arctic charr demographics on a river-by-river basis. This article is protected by copyright. All rights reserved.