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Spawning migrations of fishes are common case studies for examining the magnitude of resource subsidies; however, no studies have evaluated this phenomenon in iteroparous migrations of the Catostomid (i.e. suckers) genus Moxostoma (i.e. redhorses). Fish resource subsidies are usually represented as nitrogen (N) and phosphorus (P), and migratory redhorses can deliver these nutrients via excretion and eggs. We evaluated whether redhorses deliver N and P subsidies to Brasstown Creek—a fourth‐order stream in the Southeastern US—during their spawning migrations. We measured individual‐level nutrient contributions from excretion and eggs and extrapolated those values to estimate nutrient contributions based on daily abundances of migratory redhorses. We compared daily nutrient inputs to daily nutrient exports to determine the potential for resource subsidies. We estimated 71.6 kg of N and 4.4 kg of P were delivered to Brasstown Creek over a 98‐day migration period. N input exceeded N export on 15 of the 98 days, but phosphorus input never exceeded P export. Eggs accounted for the majority of N and P input at 51% and 100% respectively. Redhorse N inputs peaked in the spring during a period of low N exports, suggesting that redhorse subsidies were delivered during times of elevated nutrient demand and relatively low nutrient availability. Suckers receive little management attention, and several species of redhorses are imperilled. Given our conclusion that redhorses provide a temporally critical N subsidy that is likely available to multiple consumers in freshwater food webs, this study provides compelling motivation for increased conservation of these species and their migrations. [ABSTRACT FROM AUTHOR]

Spawning phenology and associated migrations of fishes are often regulated by factors such as temperature and stream discharge, but flow regulation of mainstem rivers coupled with climate change might disrupt these cues and affect fitness. Flannelmouth sucker (Catostomus latipinnis) persisting in heavily modified river networks are known to spawn in tributaries that might provide better spawning habitat than neighboring mainstem rivers subject to habitat degradation (e.g., embedded sediments, altered thermal regimes, and disconnected floodplains). PIT tag data and radio telemetry were used to quantify the timing and duration of flannelmouth sucker tributary spawning migrations in relation to environmental cues in McElmo Creek, a tributary of the San Juan River in the American Southwest. We also tested the extent of the tributary migration and assessed mainstem movements prior to and after tributary migrations. Additionally, multiyear data sets of PIT detections from other tributaries in the Colorado River basin were used to quantify interannual and cross‐site variation in the timing of flannelmouth sucker spawning migrations in relation to environmental cues. The arrival and residence times of fish spawning in McElmo Creek varied among years, with earlier migration and a 3‐week increase in residence time in relatively wet years compared to drier years. Classification tree analysis suggested a combination of discharge‐ and temperature‐determined arrival timing. Of fish PIT tagged in the fall, 56% tagged within 10 km of McElmo Creek spawned in the tributary the following spring, as did 60% of radio‐tagged fish, with a decline in its use corresponding to increased distance of tagging location. A broader analysis of four tributaries in the Colorado River basin, including McElmo Creek, found photoperiod and temperature of tributary and mainstem rivers were the most important variables in determining migration timing, but tributary and mainstem discharge also aided in classification success. The largest tributary, the Little Colorado River, had more residential fish or fish that stayed for longer periods (median = 30 days), whereas McElmo Creek fish stayed an average of just 10 days in 2022. Our results generally suggest that higher discharge, across years or across sites, results in extended use of tributaries by flannelmouth suckers. Conservation actions that limit water extraction and maintain natural flow regimes in tributaries, while maintaining open connection with mainstem rivers, may benefit migratory species, including flannelmouth suckers. [ABSTRACT FROM AUTHOR]

During spawning migrations, adult Pacific salmon (Oncorhynchus spp.) must undergo a suite of morphological and physiological changes to prepare for spawning. Modern genomics approaches can be used to conduct nonlethal assessments of physiology and infectious agent presence in migrating salmon. We investigated gene expression changes and shifts in the prevalence and load of 18 infectious agents in the gill tissue of adult sockeye salmon (Oncorhynchus nerka) during the final 50 km of their freshwater migration. We found 77% of fish successfully migrated to spawning grounds. Fish exhibited a decrease in thermal stress gene expression following lake migration, consistent with the hypothesized benefits of thermal refugia during spawning migrations. We also found evidence of cooler water selection (∼1.5 °C) during lake migration for fish with higher infection burden, suggesting behavioural changes for fish suffering higher infection burdens and potential benefits of thermal refuges for reducing the negative impacts of infection for migrating salmon. Collectively, our findings provide further evidence that fish behaviourally regulate exposure to stressful conditions such as high temperature that may undermine survival. [ABSTRACT FROM AUTHOR]

Earlier spring warming and anadromous fish migrations prompted by climate change are linked to shorter freshwater residency. Impacts of phenological change on anadromous fish populations are poorly understood with limited studies focused on iteroparous non-salmonids. We assessed freshwater residence time and reproductive success in an iteroparous clupeid, alewife (Alosa pseudoharengus) using a pedigree analysis and otolith-based spawning dates from captured juveniles. The primary objectives were to (1) estimate adult spawning duration in a freshwater pond (freshwater residence time) and (2) evaluate adult freshwater residence time, arrival date, length, sex, and reproductive success across 2 years in one system. Estimated freshwater residence times varied widely (1–64 days), and longer residence times were associated with earlier arrival dates, higher reproductive success, and more mating events. Longer freshwater residence times may allow alewife to spawn with more mates, produce more gametes, and experience a range of spawning and nursery conditions. Plasticity in alewife freshwater residence time could support earlier and shorter migration periods but may result in lower reproductive output if adults spend less time in freshwater ponds. [ABSTRACT FROM AUTHOR]

The ability for migratory fishes to move commonly limiting resources such as nitrogen (N) and phosphorus (P) between discrete environments can have pronounced effects on recipient ecosystems. To further understand the geographic and taxonomic scope of migratory fish resource subsidies, we quantified N and P subsidies delivered by adfluvial suckers (Smallmouth Buffalo, Ictiobus bubalus) via excretion, eggs and carcasses to a small oligotrophic stream during their annual spawning migration. We also compared nutrient inputs from migrant buffalo with watershed nutrient export to assess the likelihood that delivered nutrients were ecologically important. We estimated that approximately 67,000 buffalo delivered 730 kg of N and 80 kg of P to Citico Creek as a result of excretion and egg subsidies across three migration waves. We estimated that carcasses delivered negligible amounts of N and P due to extremely low retention. The ratio of migrant inputs (Mw) to system export (Ew; Mw/Ew) varied amongst three migration waves and compounds (i.e. dissolved inorganic nitrogen, ammonium and soluble reactive phosphorus), with values for Mw/Ew ranging from 0.25 to 5.10, reflecting the potential of nutrient subsidies to exceed nutrients exported from the system under certain conditions. Our findings suggest that suckers have the potential to deliver large resource subsidies to their spawning habitats and that these subsidies may be ecologically important, thus warranting additional consideration of the functional relevance of nongame fishes and their migrations. [ABSTRACT FROM AUTHOR]

Lake Tana is one of the largest freshwater bodies in East Africa, with its 18 Labeobarbus species being the world's last remaining Cyprinid species flock. Many of them feed and grow in Lake Tana and migrate to the tributaries of the lake to reproduce. The construction of irrigation structures is increasing in the tributary rivers, however, without due attention being given to the spawning migration routes and critical spawning habitats. The present study examined the impacts of the Gilgel Abay Weir on the spawning migration of these species and discusses possible interactions with other human‐related impacts and potential mitigation measures. Fish samples were taken twice monthly from July to November 2019, both below and above the weir with gillnets. No spawning migration to the upstream of the weir has occurred since its construction, with the weir being a barrier to their spawning migration route of Lake Tana fisheries. Of the 11 species caught, only Labeobarbus intermedius (a habitat generalist) was observed above the weir, with the species diversity being significantly higher below the weir (p < 0.05) than above it. The total number of species observed during the present study was also lower, compared with previous reports. The fisheries impacts may also have been exacerbated by other contributing factors such as habitat destruction, river system degradation, destructive fishing practices and weed infestation, a situation which may lead to the collapse of Lake Tana fisheries and ultimately the lake's ecology. Reversing this situation is crucial, noting the implementation of such measures as habitat restoration and improvement, replacing the weir with environmentally friendly technologies, prohibition of illegal fishing, and construction of fish ladders could definitely alleviate the observed negative impacts of the Gilgel Abay Weir on the fisheries. [ABSTRACT FROM AUTHOR]

Simple Summary: Endocrine regulation has been thought to play a major role in the onset of migration. Anguillid eels provide a good model for studying the onset mechanisms of migrations to breeding areas, because the process of the onset of migration occurs in inland waters. In this review, we summarize information about the silvering process in anguillid eels and the dynamics of mRNA expression of neurohormones and pituitary hormones, thyroid hormones, and sex steroids associated with the onset of the spawning migration. We also provide new results. Because 11-KT drastically increases during silvering, the role of 11-KT in the onset of spawning migration was discussed in detail. Anguillid eels are the iconic example of catadromous fishes, because of their long-distance offshore spawning migrations. They are also a good model for research on the onset mechanisms of migrations to breeding areas, because the migrations begin in inland waters. When eels transform from yellow eels to silver eels, it is called silvering. Silver eels show various synchronous external and internal changes during silvering, that include coloration changes, eye-size increases, and gonadal development, which appear to be pre-adaptations to the oceanic environment and for reproductive maturation. A strong gonadotropic axis activation occurs during silvering, whereas somatotropic and thyrotropic axes are not activated. Among various hormones, 11-ketotestosterone (11-KT) drastically increases during spawning migration onset. Gradual water temperature decreases simulating the autumn migratory season, inducing 11-KT increases. Administration of 11-KT appeared to cause changes related to silvering, such as early-stage oocyte growth and eye enlargement. Moreover, 11-KT may be an endogenous factor that elevates the migratory drive needed for the spawning migration onset. These findings suggested that water temperature decreases cause 11-KT to increase in autumn and this induces silvering and increases migratory drive. In addition, we newly report that 11-KT is associated with a corticotropin-releasing hormone that influences migratory behavior of salmonids. This evidence that 11-KT might be among the most important factors in the spawning migration onset of anguillid eels can help provide useful knowledge for understanding endocrinological mechanisms of the initiation of spawning migrations. [ABSTRACT FROM AUTHOR]

The involvement of the preoptico- or hypothalamo-hypophysial neurosecretory system (HHNS) in the initiation of migration processes in fish has been discovered, based on the results of ecologo-histophysiological studies using light microscopy, immunohistochemistry, electron microscopy and morphometry, thus confirming the hypothesis proposed by N.L. Gerbilsky and A.L. Polenov about the nature of the migratory impulse in fish. It has been demonstrated for the first time that in genetically distant but ecologically similar anadromous migratory fish species with different breeding seasons (spring-spawning Russian sturgeon, stellate sturgeon, and fall-spawning pink salmon), the synthesis of neurosecretory products is activated in neurosecretory cells at the beginning of the migration process, followed by their transport and accumulation in the neurohypophysis. At the same time, neurosecretory products have been shown to be secreted into the cerebrospinal liquid of the 3rd ventricle. Thus, the HHNS has a complex synchronous effect, which includes: (1) the neurotropic action of nonapeptide neurohormones on behavior centers of the central nervous system (CNS), causing a dominant state of CNS excitation originally called the "migratory impulse", (2) osmoregulatory imbalance during the marine "fattening" period, and (3) the cessation of the known antigonadotropic action of nonapeptide neurohormones, thus promoting the switching of the organism to an energy-intensive type of energy metabolism. A comparative analysis of our own and literature data confirms the communality of this metabolic mechanism in fish, thus allowing it to be considered as the most important phylogenetic adaptation (aromorphosis) aimed at achieving biological progress of species. A leading role in the subsequent navigational mechanisms of homing, widely covered in the world literature, is played by the luliberinergic centers of the hypothalamus. The ecological diversity of these mechanisms at the population level and the presence of straying in fish allow considering them as microevolutionary specializations. Further analysis of HHNS functions during fish migrations and spawning will help establish the basic principle of integration of these processes at the given ontogenetic stage, which is of prime importance for the existence of species. [ABSTRACT FROM AUTHOR]

Non-physical deterrence and guidance technologies are sought after for management of invasive fish, but they have rarely been tested in the field during natural fish migrations. We tested the efficacy of a semi-portable deterrence and guidance system (DGS) that used vertical electrodes producing low-voltage electric field to deter the upstream spawning migration of common carp (Cyprinus carpio Linnaeus, 1758) and direct them into a trap (5 m by 25 m enclosure with a net) in a natural stream. The behavior of carp was monitored using Passive Integrated Transponder (PIT) tags and antennas. The migration began on 7 April 2019, when water temperature was 5 °C and lasted through May 2019. Performance of the DGS was evaluated during three separate periods, between which the DGS was briefly deactivated. During the first period (4/7-4/19), 559 unique carp challenged the DGS. Of those, 10 were able to cross the DGS (98.2% efficacy), 234 (41.8%) were directed into the trap and 54 were captured. The mean number of days each carp was detected at the DGS was 2.6. During the second period (4/25-5/7), 562 unique PIT carp challenged the DGS. Of those, 24 were able to cross it (95.8% efficacy), 241 (42.9%) were directed into the trap and 148 were captured. Mean time at the DGS was 5.6 days. During the third period (5/7-5/15), 147 PIT carp challenged the DGS and 2 were able to cross it (98.6% efficiency). The mean time at the DGS was 5.5 days. Due to decreasing numbers of carp during the third period, we did not attempt to direct them into the trap for removal. Stream discharge during our test exceeded the 11-year average by 2-3 times; the floodplain was periodically flooded, and it is possible that some carp migrated around the DGS rather than through it. Overall, our results suggest that DGS that generate mild, electric field can be useful in deterring seasonal migrations of common carp and facilitating new removal strategies. The semi-portable nature of the system and low site-engineering requirements allow for rapid deployments and targeted applications during seasonal migrations. [ABSTRACT FROM AUTHOR]

Life history events, from mating and voltinism to migration and emergence, are governed by external and historically predictable environmental factors. The ways humans have altered natural environments during the Anthropocene have created myriad and compounding changes to these historically predictable environmental cues. Over the past few decades, there has been an increased interest in the control temperature exerts on life history events as concern over climate change has increased. However, temperature is not the only life history cue that humans have altered. In stream ecosystems, flow and light serve as important life history cues in addition to temperature. The timing and magnitude of peak flows can trigger migrations, decreases in stream temperature may cause a stream insect to enter diapause, and photoperiod appears to prompt spawning in some species of fish. Two or more of these cues may interact with one another in complex and sometimes unpredictable ways. Large dams and increasing impervious cover in urban ecosystems have modified flows and altered the timing of spawning and migration in fish. Precipitation draining hot impervious surfaces increases stream temperature and adds variability to the general pattern of stream warming from climate change. The addition of artificial light in urban and suburban areas is bright enough to eliminate or dampen the photoperiod signal and has resulted in caddisfly emergence becoming acyclical. The resulting changes in the timing of life history events also have the potential to influence the evolutionary trajectory of an organism and its interactions with other species. This paper offers a review and conceptual framework for future research into how flow, temperature, and light interact to drive life history events of stream organisms and how humans have changed these cues. We then present some of the potential evolutionary and ecological consequences of altered life history events, and conclude by highlighting what we perceive to be the most pressing research needs. [ABSTRACT FROM AUTHOR]

Choosing whether or not to migrate is an important life history decision for many fishes. Here we combine data from physical captures and detections on autonomous passive integrated transponder (PIT) tag antennas to study migration in an endangered fish, the humpback chub (Gila cypha). We develop hidden Markov mark–recapture models with and without antenna detections and find that the model fit without antenna detections misses a large proportion of fish and underestimates migration and survival probabilities. We then assess survival and growth differences associated with life history strategy and migration for different demographic groups (small male, small female, large male, large female). We find large differences in survival according to life history strategy, where residents had much lower overwinter survival than migrants. However, within the migratory life history strategy, survival and growth were similar for active migrants and skipped migrants for all demographic groups. We discuss some common challenges to incorporating detections from autonomous antennas into population models and demonstrate how these data can provide insight about fish movement and life history strategies. [ABSTRACT FROM AUTHOR]

Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations. [ABSTRACT FROM AUTHOR]

The majority of Columbia River summer-run steelhead encounter high river temperatures (near or > 20°C) during their spawning migration. While some steelhead pass through the mid-Columbia River in a matter of days, others use tributary habitats as temperature refuges for periods that can last months. Using PIT tag detection data from adult return years 2004–2016, we fit 3-component mixture models to differentiate between "fast", "slow", and "overwintering" migration behaviors in five aggregated population groups. Fast fish migrated straight through the reach on average in ~7–9 days while slow fish delayed their migration for weeks to months, and overwintering fish generally took ~150–250 days. We then fit covariate models to examine what factors contributed to the probability of migration delay during summer months (slow or overwintering behaviors), and to explore how migration delay related to mortality. Finally, to account for the impact of extended residence times in the reach for fish that delayed, we compared patterns in estimated average daily rates of mortality between migration behaviors and across population groups. Results suggest that migration delay was primarily triggered by high river temperatures but temperature thresholds for delay were lowest just before the seasonal peak in river temperatures. While all populations groups demonstrated these general patterns, we documented substantial variability in temperature thresholds and length of average delays across population groups. Although migration delay was related to higher reach mortality, it was also related to lower average daily mortality rates due to the proportional increase in reach passage duration being larger than the associated increase in mortality. Lower daily mortality rates suggest that migration delay could help mitigate the impacts of harsh migration conditions, presumably through the use of thermal refuges, despite prolonged exposure to local fisheries. Future studies tracking individual populations from their migration through reproduction could help illuminate the full extent of the tradeoffs between different migration behaviors. [ABSTRACT FROM AUTHOR]

Dredging is considered a major threat/impedance to anadromous fish migrating to spawning habitat. Due to the perceived threat caused by dredging, environmental windows that restrict dredge operations are enforced within many rivers along the east coast. However, it is generally unknown how anadromous fish react to encountering an active dredge during spawning migrations. Atlantic sturgeon (ATS) are an endangered, anadromous species along the Atlantic slope of North America. To determine if and how an active dredge may affect ATS spawning migration, a Vemco Positioning System array was deployed around an active hydraulic-cutterhead dredge that adult ATS must traverse to reach spawning habitat in the James River, VA. Telemetry data showed that all ATS that entered the study area survived. ATS that migrated upstream during dredge operations (N = 103) traversed the dredge area and continued upstream to spawning habitat. Many ATS made multiple trips through the study area during dredge operations. There was no noticeable difference in swim behavior regardless of whether the dredge was absent or working within the study area. We suggest that dredging in the lower James River does not create a barrier for adult ATS migrating to spawning habitat or cause adults to significantly modify swim behavior. This is the first study to utilize fine-scale telemetry data to describe how an organism moves in relation to an active dredge. This methodology could be used to describe dredge-sturgeon interactions on different life stages and in other locations and could be expanded to other aquatic organisms of concern. [ABSTRACT FROM AUTHOR]

Climate change is expected to affect the flow regime, cause loss of habitat, change community composition and behavioural habits of fish. This study assessed the impact of climate change on ecologically relevant streamflow conditions for fish migration and spawning in the Vistula and the Odra river basins. Streamflow simulations obtained with the Soil and Water Assessment Tool (SWAT) for the historical period and two future horizons were driven by nine bias‐corrected EURO‐CORDEX Regional Climate Models under two greenhouse gas concentration trajectories. This study identified a subset of Indicators of Hydrological Alteration (IHA) that are relevant for pike, Esox lucius L., chub, Squalius cephalus (L.), and Atlantic salmon, Salmo salar L. IHA indicators were calculated and compared for different scenarios. An index‐based framework identified that all considered species will be impacted by climate change, with Atlantic salmon facing the largest impact. The model's uncertainty was addressed through an aggregation method that assessed inconsistencies in the model's response. [ABSTRACT FROM AUTHOR]

Understanding migratory behavior, mortality, and physiology is essential for conservation of many species, particularly anadromous fish. In this study, freshwater and marine migrations of the endangered salmonid North Sea houting (Coregonus oxyrinchus (Linnaeus, 1758)) were investigated using telemetry. Furthermore, physiological samples were collected from North Sea houting and from resident and anadromous populations of the closely related European whitefish (Coregonus lavaretus (Linnaeus, 1758)) to compare hypo-osmotic tolerances. On average, North Sea houting spent 193 days at sea where the mortality was 36%. Most fish returned from sea in the autumn, and river entry correlated inversely with river temperature and positively with discharge. Fish spent an average of 49 days in the estuarine area. Artificial lakes negatively affected migration speeds. Migration speeds did not differ consistently between individuals (i.e., not a repeatable trait) but correlated positively with water temperature. Fish arrived at spawning areas in November. In the post-spawning state, Na+/K+-ATPase activities were elevated in North Sea houting and anadromous whitefish compared with resident whitefish, while osmolality was elevated only in North Sea houting. Our study provides important information for conservation planning related to the Habitat Directive of the European Union that lists the North Sea houting as critically endangered. [ABSTRACT FROM AUTHOR]

Anthropic exploitation of soil, forests, and water bodies contributes to the modification of river flow regimes and sediment transport dynamics, thus affecting fish habitats and water quality. In the last decades, the increasing awareness of the consequences of such modifications on natural contexts has stimulated researchers and practitioners to provide more innovative solutions aiming at enhancing river biodiversity. Recently developed eco-friendly approaches for river restoration evidenced the necessity of more careful planning and management of natural resources, including the maintenance and enhancement of fish species' habitats. The present study aims at assessing the interaction of different types of wood- and rock-made instream structures with river flow regimes and habitat requirements of many freshwater fish species, accounting for the influence of downstream scour potholes to facilitate fish species migration and spawning. Experimental tests showed that instream structures cause deep scour holes characterized by low flow velocity zones, thus decreasing the required fish swimming power and potentially providing suitable conditions for the migration of freshwater fish species. Using dimensional analysis, empirical relationships were derived to optimize the longitudinal distance between subsequent instream structures, accounting for the effects of various structure geometries and fish biological characteristics. Nevertheless, further investigation is needed to validate the proposed relationships at prototype scale. This study ultimately contributes at providing tools to design river instream structures favorable to fish migration. • The effects of different types of instream structures on fish swimming hydrodynamics have been investigated. • The analysis was conducted at model scale under identical fish Froude numbers F f. • Results showed that instream structures facilitate the migration of freshwater fish species. • Fish white muscles weight increases with the fish weight resulting in an increase of the available fish power. [ABSTRACT FROM AUTHOR]

Many commercially important groupers (Epinephelidae) form fish spawning aggregations (FSA) at specific sites where the spawning stock is concentrated to spawn within a couple of months each year. The concentrated nature and short duration of these FSAs render these species susceptible to fishing pressure leading to their disappearance or decrease in the number of spawning fish. As a result of directed fishing during FSAs many large-bodied groupers are now International Union for Conservation of Nature (IUCN) Red-listed. Puerto Rico within the US Caribbean is where protective measures have been designated for the recovery of grouper species that aggregate to spawn, in particular the threatened (Endangered Species Act) Nassau grouper (Epinephelus striatus) and sustainability of the red hind (Epinephelus guttatus). The regulations at three marine managed areas (MMAs) off the west coast of Puerto Rico, have been focused on reproductive seasons, through seasonal closures. However, these management zone boundaries may fail to fully encompass fish migration paths and temporal variability in FSAs, exposing threatened species like the Nassau grouper to incidental fishing and poaching. In addition to traditional methods used to study FSAs, passive acoustics represent a relatively new approach to assess the presence and spatio-temporal distribution of aggregating species. Sound production is common among many fishes, including the Nassau and red hind groupers, and is most often associated with courtship and spawning behavior. In this study, we present the results from the deployment of an autonomous surface vehicle equipped with a passive acoustic monitoring system along the insular shelf break that surveyed the MMAs during their peak spawning season. Our observations suggest that known FSA sites are critical habitat for both species and the existence of potential, previously unknown FSAs for multiple grouper species as well, highlighting the importance of spatial and temporal expansion of existing regulations. [ABSTRACT FROM AUTHOR]

This review summarizes what is known about the influence of water temperature and velocity on the migration and spawning success of an inland population of Chinook salmon Oncorhynchus tshawytscha. Models are then developed and used to illustrate how migration and spawning success might change if temperatures and velocities increase under a future climate. The illustration shows the potential for moderate increases in temperature and velocity to reduce homing and increase energy expenditure. Those two outcomes would reduce the abundance, productivity, and diversity of the population studied. Under the future scenario illustrated, it would become difficult for fish management actions alone to recover conservation-reliant populations of inland Chinook salmon. [ABSTRACT FROM AUTHOR]

Atlantic salmon populations appear to fluctuate stochastically through time. It is suspected that both density‐dependent and density‐independent factors cause these fluctuations but the relative importance of each, and the life stages at which they operate, is not well known. In this study, a long‐term data set on Atlantic salmon migrants returning to the Foyle catchment, Ireland, was used to determine the role of density‐dependent and life stage‐specific environmental factors regulating population size. A Ricker density‐dependent model showed that spawning adult population size significantly predicted variation in the resultant filial generation; however, a large amount of variation (ca. 68%) remained unexplained. It was shown that environmental factors were significant in explaining some of the remaining variance and that these influences were linked to specific life stages. Three life stages—spawning and incubation, fry emergence and marine survival—were shown to have significant environmental effects that resulted in changes in the returning cohort strength. It is concluded that these life stage‐specific environmental effects are likely to contribute to the stochastic variation in population size resulting from the application of traditional stock–recruitment models. The identification and quantification of these effects should allow improved model accuracy. [ABSTRACT FROM AUTHOR]

Otolith strontium and multi-year mark-recapture information were used to characterize associations between migration patterns and spawning frequencies in an anadromous Dolly Varden (Salvelinus malma) population (Rat River, Northwest Territories, Canada) that undertakes a long migration between freshwater spawning/overwintering (Fish Creek; a tributary to Rat River) and marine feeding habitats (Beaufort Sea) (~800 km round trip). Reconstructions of lifetime annual migration histories among otolith annuli was matched to information on reproductive status (current-year ‘spawner’ or ‘non-spawner’) that was known in two different, sometimes successive, years for each fish. Two migratory life histories were observed: fish either migrated annually after smoltification or periodically skipped an annual ocean migration to remain in freshwater and spawn. Different spawning frequencies were detected where fish not migrating annually tended to spawn in alternate years (84.6%) more often than those migrating annually (50%). Additionally, annually migrating fish had lower longevity (≤9 years vs. ≤13 years). The evaluation of differences in spawning frequency between sexes, independent of migration tactic, revealed males (84.6%) skipped spawning more often than females (51.2%) suggesting fitness trade-offs between life histories differ between sexes. Further, some fish returned from the sea considerably earlier than the majority of other current-year migrants. Our findings demonstrate intrapopulation diversity in migration behaviour and reproductive frequency. [ABSTRACT FROM AUTHOR]

Repeat spawners of anadromous salmonids may contribute significantly to population resilience by providing multiple cohorts to both seawater and freshwater life stages. In this study, winter survival of sea trout (Salmo trutta Linnaeus, 1758) post spawners (kelts) was 89%. Sea survival increased linearly with female length with a return probability between 30% and 50%, whereas males attained a maximum return probability of 60% at 520 mm. Of the returning sea trout, 40% skipped spawning and they had significantly lower condition factor as kelts compared with those who returned after one summer. These results suggest that sex-specific differences in individual post-spawning growth–survival trade-off exist and that energetic status of descending kelts may influence the probability to skip spawning. We discuss to what extent hydropower may reduce post-spawning survival due to blocking of river descent opportunities, potentially altering the fitness landscape and favouring new life-history adaptations. From a management perspective, it is concluded that it is crucial to maintain connectivity in regulated rivers, allowing fish to complete repetitive spawning and feeding migrations, thus contributing to population productivity. [ABSTRACT FROM AUTHOR]

A marine reserve’s effectiveness for sustaining transient spawning reef fish populations is dependent on inclusion of fish spawning aggregations and consideration of the natural spatial boundaries of the populations themselves. Seasonal migrations of Mutton Snapper Lutjanus analis between protected nearshore areas and spawning grounds on Riley’s Hump in Dry Tortugas, Florida, were assessed from 2008 to 2012 by acoustic telemetry. Individual fish showed synchronized reproductive migrations (up to 5 trips fish −1  yr −1 ) from resident habitats to spawning grounds swimming at an estimated 63 ± 18 cm s −1 (mean ± SD) over minimum linear distances up to 35.2 km. Migrations occurred from April to August, corresponding with the lunar cycle and an increase in water temperature from 25 to 30 °C. Fish arrived on spawning grounds on the full moon and stayed for 7 ± 2 d (mean ± SD). Observations of multiple spawning events made one to five days after the full moon in the late afternoon confirm these movements as spawning migrations. Functional migration areas (109.59 ± 61.01 km 2 ; mean ± SD), which included estimates of staging/courtship/spawning area (4.51 ± 1.84 km 2 [mean ± SD]) and home site area (2.50 ± 1.31 km 2 [mean ± SD]), were combined to estimate the minimum catchment area of the population studied (291.3 km 2 ). Although this study focuses on movements and habitat use of a single fish species in the Tortugas, the results are relevant to the design of marine reserve networks intended to protect and manage fishes that undergo transient spawning migrations in other locations as well. [ABSTRACT FROM AUTHOR]

The risk of mortality associated with a long-distance migration will depend on an animal's physiological state, as well as the prevailing ecological conditions. Here, we assess whether juvenile telomere length, which in endotherms has been shown to be a biomarker of physiological state and expected life span, predicts whether wild Atlantic salmon Salmo salar successfully complete their marine migration., Over 1,800 juvenile fish were trapped, measured, passive integrated transponder tagged and a tissue biopsy taken when migrating as juveniles down-river towards the sea. Survivors of the marine phase of the life cycle were then re-trapped and re-sampled when returning to the river to spawn as sexually mature adults, 1.5-2.5 years later. Most individuals experienced a reduction in telomere length during the marine migratory phase of their life cycle. While the relative rate of telomere loss was greater in males than females, telomere loss was unrelated to growth at sea., Contrary to expectations, salmon that had the shortest telomeres at the time of the outward migration had the greatest probability of surviving through to the return migration. This effect, independent of body size, may indicate a trade-off between investment in readiness for marine life (which favours high glucocorticoid levels, known to increase telomere attrition in other vertebrate species) and investment in telomere maintenance. Survival was also significantly influenced by the seasonal timing of outward migration, with the fish migrating downstream earliest in the spring having the highest probability of return., This study reveals that telomere length is associated with survival, although in ways that contrast with patterns seen in endotherms. This illustrates that while telomeres may be universally important for chromosome protection, the potential for telomere dynamics to predict performance may vary across taxa., A is available for this article. [ABSTRACT FROM AUTHOR]

Atlantic herring ( Clupea harengus) migrates from offshore to coastal areas to spawn and their eggs and larvae may substantially increase prey resources for resident predators. We combined an in situ predator exclusion experiment using eggs naturally spawned on submerged aquatic vegetation and field observations of predator abundance to estimate the magnitude of predation mortality of herring eggs. During our predator exclusion experiment, performed in an important spawning ground in the southwest Baltic Sea, 20% of the herring eggs were consumed resulting in an extrapolated predation of 42% of all eggs between spawning and hatch. Abundance and stomach content analyses indicated that one predator (threespine stickleback, Gasterosteus aculeatus) was responsible for the majority of the predation impact. Predation mortality estimates from this in situ study were more than 10-fold higher than those of an empirical egg predation model for the same predator in the same region. Our findings highlight the potential of resident predators to regulate the survival of early life stages of ocean-going fishes that rely on the nursery functions of inshore transitional waters. [ABSTRACT FROM AUTHOR]

Climate oscillations exert direct control over the environment in which they occur and may influence the physical condition of migratory marine species, such as tuna, as reported by several authors. The main aim of this study was to explore the association between the potential effects of the North Atlantic Oscillation (NAO) on the fitness condition of bullet tuna ( Auxis rochei ) migrating to the Spanish Mediterranean Sea. A total of 2357 length-weight pairs of data obtained from individuals collected on the Spanish Mediterranean coast were analysed. A non-parametric Spearman test was used to investigate correlations between the atmospheric oscillation indexes and two physical condition indexes. The results suggest that, in general, positive phases of the NAO index improve the physical condition of fish migrating to spawning grounds in the Mediterranean Sea. These results could be explained by changes in the dominant winds, which could favour pre-spawning migration, and by nutrients availability, which guarantees their recovery after the spawning period. [ABSTRACT FROM AUTHOR]

A telemetry study analysing the diel and seasonal behaviour of asp was performed weekly in the Elbe River, Czech Republic, over 12 months. Asp diel movements and home range size varied across seasons, reaching maxima in summer and autumn with diurnal and/or crepuscular peaks of activity. On the contrary, no peaks of activity occurred during spring and winter, when the diel movements were low and the home range was small. Asp occurred predominantly within their home range. The probability of displaying migratory behaviour peaked during spring spawning and autumn wintering migrations (both triggered by temperatures from 4 to 8 °C). Three spawning grounds were detected within the studied river stretch. Most of the spawners utilised the first suitable spawning ground below the weir, which was not passed by any of the tagged specimens. Our results suggest a strong impact of weirs, even equipped with modern fish passes, on migratory behaviour and thus population dynamics of river-dwelling asp. [ABSTRACT FROM AUTHOR]

Movement patterns of marine fishes can have considerable impacts on their population dynamics. A thorough understanding of fish movements is therefore required for informing stock identification, stock assessment, and fishery management. This study investigated the seasonal movements and connectivity of a spring-spawning component of Atlantic cod (Gadus morhua) in the western Gulf of Maine. From 2010 through 2013, spawning cod were sampled within an inshore spawning closure and tagged with conventional tags (n = 2368), acoustic transmitters (n = 106), and archival data storage tags (n = 266). Acoustic receivers were deployed on three inshore spawning sites to test for connectivity among sites. Data from archival tags were used to describe seasonal habitat occupancy and movement patterns via geolocation to statistical areas. Tagging data indicated that cod were primarily residential in the western Gulf of Maine, moving inshore to spawn during the spring (April-July), followed by an offshore migration to their feeding grounds for summer and fall. Cod generally inhabited waters from 45 to 175 m, with the deep offshore basins (>150 m) serving as overwintering habitat. Occupied water temperatures ranged from 4.0 to 13.3 °C, with the coldest temperatures experienced from March through July and the warmest temperatures experienced from September through January. Results provided evidence of spawning site fidelity and connectivity among spawning sites, with some fish visiting multiple spawning sites within or between years. The movements observed during and after the spring-spawning season serve as important mechanisms influencing metapopulation dynamics in the Gulf of Maine region, including both fine- and broad-scale population structure. The improved understanding of cod movement patterns will assist fishery managers in developing management plans, including spawning protection measures, and help to address remaining uncertainties with respect to cod population structure in the Gulf of Maine and other regions. [ABSTRACT FROM AUTHOR]

The article presents a study of the association of water temperature and daytime and migration intensity, as wel as the effect of water turbidity, light and obstacles on the spawning migration of the Caspian lamprey or Caspiomyzon wagneri. It highlights the importance of temperature and light during the spawning migration of the Caspian lamprey and the challenges of the propagation of lampreys in the Shirud River, India.

Most Pacific salmon Oncorhynchus spp. migrate to their natal sites to spawn. Some, however, stray into nonnatal habitats and interact (e.g., reproduce) with individuals from other populations. Pacific salmon straying has been heavily studied for several decades, particularly from the perspective of the populations that donate the stray migrants. Conservation consequences are experienced primarily by the populations that receive strays, though, and there is recent evidence of significant levels of genetic introgression in small recipient populations, which could contribute to the loss of local adaptations. Straying may also provide the benefit of a demographic rescue effect that could save declining recipient populations from extirpation. We highlight the influence of population abundances on the magnitude of straying into recipient populations and demonstrate this using evidence we collected from a small population of Sockeye Salmon O. nerka in British Columbia, Canada. We also review potential factors that might promote higher donor stray rates and therefore recipient straying. Evidence of factors that affect straying is limited and we identify several knowledge gaps, as well as anthropogenic activities that could promote straying. We encourage further discussion and research on the potential effects of recipient straying and the factors that affect straying rates. [ABSTRACT FROM AUTHOR]

Many fish species migrate to form fish spawning aggregations. The temporal and spatial predictability of these migrations and spawning aggregation locations makes species vulnerable to overfishing, as the majority of an adult population within a large region may be harvested quickly with minimal effort. Historically, the Nassau grouper, Epinephelus striatus (Bloch, 1792), was an important fishery species throughout its range, but due to spawning aggregation overfishing, it is now rare in many reef ecosystems. In The Bahamas, stocks continue to decline despite the implementation of spawning aggregation protections. W h i l e more Nassau grouper spawning aggregations have been reported in The Bahamas than any other country, very few have been validated, and the dynamics of spawning migrations to and from these sites is poorly understood. Here, we used acoustic telemetry to describe, for the first time, Nassau grouper migrations along Andros Island, The 3ahamas, which is bordered by one of the longest barrier reefs in the world. We report the likely extirpation of a historically important spawning aggregation and suggest Nassau grouper are migrating to a previously undocumented spawning location. Fish migrated in groups during the January 2015 full moon along the barrier reef shelf edge traveling roundtrip distances of 7 1 . 5 - 2 6 0 . 3 km [x = 164.5 (SD 65.7) km, n = 9]. These results are critical to assess the efficacy of current management strategies in The Bahamas. Thus far, all known spaning aggregations have been reported to the scientific community by fishers. Data from our study, however, suggest the presence of a potential spawning aggregation informed by passive telemetry and warrants further investigation. [ABSTRACT FROM AUTHOR]

The conservation and management of heavily exploited fish stocks require reliable data on various aspects of reproduction. In particular, information about spawning migration and spawning period of both sexes is essential for protecting important spawning habitats. However, studies that focus on male spawning ecology are very limited. We elucidated the male spawning migration, core duration of reproduction, and seasonal changes in the maturity of the barfin flounder Verasper moseri , an important target flatfish for stock enhancement programs in Japan. We conducted histological observations of the testes and utilized the sperm duct volume index to facilitate accurate determination of the male spawning period. Fish before spermiation were mainly observed off Hokkaido and partially off northern Tohoku (40.2–43.4°N) during August–December. However, fish undergoing spermiation and sperm release were not found near these areas and were observed only off southernmost Tohoku (35.8–37.5°N approximately 300 m deep) from late January to April. Very few spent fish were caught off southern Tohoku, but were frequently observed off Hokkaido during May–June. These results demonstrate that male V. moseri repeat widespread spawning migrations over 700 km between feeding grounds off Hokkaido and spawning grounds off southern Tohoku. Moreover, a combined analysis related to seasonal variations in the sperm duct volume and the proportion of spawning adults identified that the core duration of male reproduction was during March. Until now, reproduction of the next generation in the wild has not been confirmed, despite the continual release of seedlings and local fishery restrictions around Hokkaido. Our results underscore the necessity of a more widespread fishery management plan for V. moseri that encompasses the waters off Hokkaido and Tohoku to more effectively enhance reproduction. [ABSTRACT FROM AUTHOR]

In the past decade improved acoustic hard- and software have enabled estimations of abundance and distribution patterns of aquatic organism, including non-intrusive monitoring of fish migrations and behaviour. In this study, a high frequency acoustic camera (DIDSON-LR, 1.2 MHz, 0.7 MHz) and a portable split-beam scientific echo sounder (Simrad EY60, 200 kHz) collected acoustic data on 192 and 157 individuals within 24 hr (19-20 April 2011) in the Mituo reach of the Yangtze River, China. Mean fish length estimated from the acoustic camera data was 18.7 ± 5.6 cm, with an average swimming speed of 0.19 ± 0.13 m s−1. The mean fish target strength (TS) produced by the echo sounder was −43.8 ± 4.4 dB, which corresponded to 5.7-119.9 cm fish length when converted by three different TS-length equations. Average swimming speed was 0.11 ± 0.06 m s−1 from the echo sounder. Compared with the actual fish catch by the three layers of drift gill net in the survey area, the target length indicated by DIDSON was more accurate than the EY60 results, which were highly affected by the choice of TS length equations. It was determined that the two devices used synchronously could estimate fish length effectively to investigate their behaviour and distribution. [ABSTRACT FROM AUTHOR]

Anadromous fishes often use various survival tactics while migrating through main stem rivers to successfully reach spawning grounds and reproduce. Mixed-stock assemblages of anadromous adult summer steelhead Oncorhynchus mykiss re-enter the Columbia River from late spring through fall including the period of peak summer water temperatures, and previous studies suggest that stocks alter migratory behaviour in response to warm temperatures by seeking cool water refuges. We combined parentage-based tagging with mixed stock analyses to test whether steelhead use a non-natal tributary (Deschutes River, OR, USA) as a thermal refuge and if this migratory behaviour is associated with stock-specific run-timing. Results collected over two migration years indicated that out-of-basin fish in the Deschutes River were disproportionately from specific stocks in the Snake River (Salmon and Grande Ronde) that had migrated through the main stem Columbia River when water temperatures exceeded 21 °C. Stocks migrating through the main stem river during cooler temperature periods were either less frequent (Clearwater River), or not encountered (lower Snake River) in the Deschutes River. This study facilitates an improved understanding of stock-specific migratory characteristics associated with environmental conditions in this system. Results potentially affect fisheries management, hatchery protocols, cool-water refuge maintenance, and conservation of wild Deschutes River populations. [ABSTRACT FROM AUTHOR]

Iteroparity (repeat spawning) is a life history attribute with significant conservation value for at-risk populations of steelhead trout (Oncorhynchus mykiss). However, stock-specific rates of iteroparity and abundance of post-spawned steelhead "kelts" can be difficult to monitor in large river systems where multiple populations are commonly encountered as aggregated mixtures. We used genetic mixed-stock analysis (MSA) to determine steelhead origins and tested for stock-specific differences in the prevalence of an iterparous reproductive strategy. Steelhead from the Snake River, USA were sampled as "returns" migrating upstream to spawn and as emigrating post-spawned "kelts". Fish were assigned between two regions that are characterized by predominant run-type. We observed a larger overall proportion of kelts from region-1 (putative-A run; 82%) compared to kelts from region-2 (putative B-run; 18%), but returns from region-2 (30%) were nearly twice as abundant as kelts. Female kelts were predominant throughout the basin, occurring in similar proportions between regions (72% region-1, 77% region-2). The inferred ocean age distribution of kelts was distinct between regions, and regional differences in body size and emigration timing were significant (P<0.0001). Although the ocean age-classes for kelts and returns within the same region were similarly distributed, kelts were significantly smaller in average body size compared to returns, and the results were temporally consistent. The association between body size and post-spawn survival suggests that strategies to improve overall recovery of steelhead, such as artificial reconditioning, may achieve greater success by targeting smaller kelts. Moreover, monitoring of post-spawn survival, and repeat spawning potential will likely benefit from MSA to augment demographic information and improve the accuracy of differentiating among specific stocks or regions. [ABSTRACT FROM AUTHOR]

From late April until mid-June Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758), migrates along the western coast of Sardinia to reach spawning grounds of the Mediterranean. Despite the substantial information on the reproductive biology of the species, the tracking of its reproductive parameters along the migratory pathways is far to be completed. This study provides some reproductive parameters for adult bluefin tuna collected from the last trap fishery Tonnara of the Mediterranean. The following points summarize our results: (i) gonadosomatic index (GI) was positively correlated with fork length (FL) and varied significantly between sexes, having higher values in males; (ii) ovaries contained a mixture of oocyte stages with primary growth oocytes representing 72%, cortical alveoli 16%, primary and secondary vitellogenic stages 4.6% and 6% respectively, only a small proportion of late vitellogenic oocytes and atretic follicles; (iii) batch fecundity was 95–125 oocytes per gram of body mass and varied from 1.6 million for a female of 105 cm FL, to 29.5 million eggs for a 233 cm FL specimen; (iv) sex ratio differed significantly from 1:1, with males being predominant both for the size classes and years analyzed. These findings suggest that bluefin tuna from western Sardinia exhibits intermediate reproductive characteristics between specimens migrating through the Strait of Gibraltar and those from the spawning grounds of the Balearic Islands. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

The relative contribution of Sepioteuthis sp. 1 and Sepioteuthis sp. 2 to oval squid fishery stocks in western Japan was examined using microsatellite DNA and partial sequences of mitochondrial cytochrome oxidase subunit I. A total of 1718 Sepioteuthis spp. individuals from 19 populations were identified to determine the proportion of each species in fishery stocks. Samples from Tanegashima and Yakushima Islands in southwestern Japan were also examined to determine depth distributions. DNA was used to refer 233 (17.3 %) individuals to Sepioteuthis sp. 1 and 1421 (82.7 %) individuals to Sepioteuthis sp. 2. Sepioteuthis sp. 1 was found on the Pacific side of mainland Japan, but was predominant in Tanegashima (77.1 %) and Yakushima Islands (100 %), suggesting its distribution was limited by the warmer waters of the Kuroshio Current. In contrast, Sepioteuthis sp. 2 was most commonly found around mainland Japan. Whereas Sepioteuthis sp.1 was caught in 10 to 53 m depth, Sepioteuthis sp. 2 was caught in 2 to 30 m depth. Differences in the spatial and bathymetric distributions of these two species might reflect differences in temperature preference, spawning depth, and migration patterns. Our results would be useful for managing the fishery stocks and spawning grounds of both species. [ABSTRACT FROM AUTHOR]

In this study, animal-borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter-specialist diel-migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12-14° C) optimal for hunting and feeding during non-reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non-reproductive periods, respectively, active selection was limited to selection for 4-6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night-time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal-habitat selection was a good predictor of night-time habitat occupancy in a diel-migrating species. Together, these results show that thermal-habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized. [ABSTRACT FROM AUTHOR]

Management of multiple exploited stocks of anadromous salmonids in large catchments requires understanding of movement and catchment use by the migrating fish and of their harvesting. The spawning migration of sea trout ( Salmo trutta) and Atlantic salmon ( Salmo salar) was studied in the River Tweed, UK, using acoustic telemetry to complement exploitation rate data and to quantify catchment penetration. Salmon ( n = 79) and sea trout ( n = 65) were tagged in the tidal-influenced Tweed in summer-autumn. No tagged salmon left the river before spawning, but 3% (2010) and 8% (2011) of pre-spawning sea trout dropped out. Combined tag regurgitation/fish mortality in salmon was 12.5%, while trout mortality was 6% (2010) and 0% (2011). The estimated spawning positions of salmon and sea trout differed; tagged salmon were mostly in the main channel while trout occurred mostly in the upper Tweed and tributaries. Early fish migrated upstream slower than later fish, but sea trout moved through the lower-middle river more quickly than salmon, partly supporting the hypothesis that the lower exploitation rate in autumn of trout (1 vs 3.3% for salmon) there is generated by differences in migration behaviour. [ABSTRACT FROM AUTHOR]

Many relevant aspects of the breeding ecology of South American migratory fishes remain obscure. We conducted kinship analyses and parental reconstruction based on microsatellite genotypes of 41 Salminus brasiliensis larvae sampled from a single natural spawning event. Polygynandry involving 25 (12:13) potential parents was suggested, supporting ecological observations of aggregation during spawning. Some parents contributed up to five half-sibling larvae genotypes, implying a skewed contribution of genes to the progeny. This study contributed to preliminary insights into the S. brasiliensis genetic mating system. [ABSTRACT FROM AUTHOR]

Argentine shortfin squid Illex argentinus (Ommastrephidae) is one of the most abundant cephalopods in the Southwest Atlantic, with total annual catch exceeding 1 mln t in some years. During its annual life cycle, I. argentinus perform long distance migrations, from their subtropical spawning grounds in Uruguay and southern Brazil to temperate feeding grounds on the Patagonian Shelf and back. Oceanography and squid distribution were studied during a research survey carried out in the south-eastern part of the Patagonian Shelf to reveal environmental cues that determine pathways of shelf to continental slope pre-spawning migrations. It was found that the outflows of less dense Patagonian Shelf Waters (PSW) over the slope may act as proxies determining the locations of I. argentinus migrations from the shelf to the slope. During maturation I. argentinus did not significantly change their buoyancy with females becoming slightly more buoyant with depth. Subsequent movement of mature I. argentinus to denser Sub-Antarctic Superficial waters (SASW) located at deeper depths (600–700 m) enable them to approach near-neutral buoyancy and therefore facilitate the distant pre-spawning migrations. [ABSTRACT FROM AUTHOR]

The objective of this study was to advance the use of pop-up satellite archival tags to track the migrations of Atlantic bluefin tuna ( Thunnus thynnus) to their spawning grounds. Deployment of tags occurred in the Gulf of St. Lawrence, Canada, during fall months from 2007 to 2013. Pop-up satellite archival tags ( n = 135) were attached to 125 Atlantic bluefin tuna (curved fork length (CFL) = 268 ± 20 cm (mean ± SD)) with the objective of keeping tags on until visitation to a spawning area or longer. A dataset of 18 800 days was acquired, which included 5800 days of time-series data from 19 recovered satellite tags. Many Atlantic bluefin tuna visited the Gulf of Mexico spawning grounds (74%), the mean size of which was 275 ± 14 cm (CFL ± SD, n = 49), with a measured CFL of 243 to 302 cm. These fish had a mean entry date into the Gulf of Mexico of 14 January ± 42 days (SD). The mean residency period for fish that had tracks with entrance and exit from the Gulf of Mexico was 123 ± 49 days (SD) ( n = 22). Atlantic bluefin tuna that moved into the Gulf of Mexico during the spawning season remained west of the 45°W meridian for the duration of the track. Electronic tagging datasets from two fish were obtained before, during, and after the Deepwater Horizon oil spill. Both fish utilized habitat in the vicinity of the Macondo Well on 20 April 2010 when the Deepwater Horizon oil drilling rig accident occurred. Spawning hotspots are identified in the Gulf of Mexico using kernel density analyses and compared with the newly established closed areas. [ABSTRACT FROM AUTHOR]

We investigated maternal body size and environmental effects on the oocyte size of the Atlantic sardine, Sardina pilchardus, a marine pelagophil, using a novel, oocyte stage-specific approach which takes into account the spawning lag. In particular, we focused on anatomical constraints imposed by the maternal body cavity to the growth of the ovary and its oocytes during the course of vitellogenesis (VIT) and oocyte maturation (OM). We analyzed variability in oocyte size in VIT and OM ovaries as a factor of maternal size, ambient temperature (SST) and preservation medium (formalin vs. ethanol) using the spawning lag of recent and imminent spawners, respectively, as a covariate. We showed that oocyte size correlates with maternal size in OM ovaries but not in VIT ovaries. More specifically, 10 cm difference in maternal body length corresponds to 0.112 mm (or 12 %) difference in the cross section of fully hydrated oocytes just previous to ovulation. On the other hand there was no inverse relationship between OM oocyte size at spawning and batch fecundity. Ambient SST was not an important determinant of hydrated oocyte size since the same 12 % difference in oocyte size was estimated for the entire SST range of the study. We suggest that these stage-specific differences in the effect of maternal size on oocyte size are due to a functional relationship between the abdominal volume and ovarian size. [ABSTRACT FROM AUTHOR]

The sex-specific daily spawning seaward migration of striped mullet Mugil cephalus was analysed in Palaiopotamos Lagoon (western Greek coast, eastern Mediterranean Sea) in an 86 day time series. The data set included the daily number of M. cephalus catches in barrier traps, as well as a time series of some weather variables. The analysis revealed an important linkage of the daily migration rate as well as a sex-specific response of the species to the lunar cycle and the short-term fluctuation of weather variables. The daily migration pattern of females was more persistent than that of males, indicating a possible female leadership role during the spawning migration. Multiregression models described quite accurately the sex-specific daily migration rates of the species, thus providing a potentially powerful tool regarding the lagoon fishery management of M. cephalus, especially in the context of climate change. [ABSTRACT FROM AUTHOR]

Body condition and reproduction data are broadly used to assess the health status of fish because of its implications for recruitment and ecosystem structure. Sardina pilchardus is a small pelagic distributed throughout both Mediterranean and Eastern Atlantic. Seasonal trend analysis of energy storage and reproduction was carried out in sardines from two areas along the Atlantic-Mediterranean transition: Southern Portugal-Gulf of Cádiz (POR-GC) (Atlantic Ocean) and Alboran Sea (Alb) (Mediterranean Sea) from 2019 to 2021. Energetic condition was estimated using tissue and mesenteric fat content, hepatosomatic index (HSI), and the relative condition factor (Kn). Sex, reproductive developmental stage, and gonadosomatic index (GSI) were also obtained. In addition, the oceanographic and meteorological characteristics of the areas were analysed. Results showed that seasonal Kn, tissue and mesenteric fat content, and HSI values of POR-GC specimens exceeded Alb's with summer arrival, period in which sardine acquires reserves to allocate them to reproduction. These differences could be associated to greater productivity of the former area mainly due to rivers discharges and trade winds intensification during summer (from July to September). Furthermore, gonad maturation of POR-GC stock occurred before the Alb. However, no spawning capable individuals were identified until February in POR-GC. In contrast, in Alb it was observed a remarkable fraction of spawning capable and active spawner individuals in October. We hypothesized the migration of mature individuals from POR-GC to the spawning areas located in the Alb. Seasonal genetic population studies are required to untangle it and reliably evaluate the environmental effect on the stocks. • Atlantic sardines show better somatic condition than Alboran individuals at storage period. • Productivity in the Atlantic area is greater than in the Alboran Sea. • Rivers discharges and summer's trade winds intensification could be its main cause. • Results suggest the migration of mature fish from the Atlantic towards the Alboran. • Seasonal genetic population studies are required. [ABSTRACT FROM AUTHOR]

Understanding dispersal capacities for migratory species is crucial for their management. By coupling otolith microchemistry and microsatellite genetic analyses, we provided information on snapshot and long-term dispersal capacity of Allis shad ( Alosa alosa), an anadromous clupeid in decline throughout its distribution range. The allocation of natal origin was obtained from water chemistry and signatures in otoliths of juveniles and spawners within a Bayesian model. The majority of adults were assigned to a source river with high degrees of confidence; only 4% were undetermined. Otolith natal origins were used to define a population baseline by grouping individuals from the same natal river and not from the same sampling location as usually done. While A. alosa exhibited a high level of natal site fidelity, this species showed weak genetic structure, which supported the evidence of a substantial flow of strayers between river basins in the vicinity or at longer distances. However, long distance straying was probable but not frequent. In a context of global change, straying would be a key mechanism to drive dispersal and allow resilience of Allis shad populations. [ABSTRACT FROM AUTHOR]

Understanding the location and duration of habitat use by young fish is important for management and restoration efforts, but is largely unknown in anadromous species. We used otolith microchemistry and ambient water concentrations of Ca, Ba, Mn, and Sr to identify habitat use in the first year of growth for 131 returning adult blueback herring ( Alosa aestivalis) collected in seven spawning runs along the coast of Maine, USA. Ambient Sr:Ca ratios were correlated with salinity and were used as primary indicators of habitat use. Results revealed variable individual migration histories with several discrete migratory patterns; some fish migrated into seawater well before the end of the first year, while the majority exhibited longer residency in freshwater or low salinity habitat. Total area of available habitats ranged from approximately 213 to 6053 ha fresh water and 204 to 3395 ha estuary. Residency in freshwater or low salinity habitats was positively correlated with extent of freshwater habitat ( r = 0.37, P < 0.001). Results emphasize the importance of conserving a variety of habitat types to maintain variation in life histories and ensure plasticity in migratory behavior of diadromous species. [ABSTRACT FROM AUTHOR]