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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]

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]

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]

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]

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]

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]

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]

Chinook salmon, Oncorhynchus tshawytscha (Walbaum), is an important biological and cultural resource in Alaska, but knowledge about Chinook salmon ecology is limited in many regions. From 2009 to 2012, spawning distribution and abundance of a northern Chinook salmon population on the Togiak River in south-west Alaska were assessed. Chinook salmon preferred deeper mainstem channel spawning habitat, with 12% (14 of 118 tags in 2009) to 21% (22 of 106 tags in 2012) of radio-tagged fish spawning in smaller order tributaries. Tributary spawners tended to have earlier run timing than mainstem spawners. Chinook salmon exhibited extended holding and backout (entering freshwater but returning to saltwater before completing anadromous migration) behaviours near the mouth of Togiak River, potentially prolonging their exposure to fishery harvest. Mark-recapture total annual run estimates (2010-2012) ranged from 11 240 (2011) to 18 299 (2012) fish. Exploitation of Chinook salmon ranged from 36% (2012) to 55% (2011) during the study period, with incidental fishery catches near the mouth of the river comprising the largest source of harvest. [ABSTRACT FROM AUTHOR]

This paper summarises materials from various sources and the author’s research on the biology of the Siberian sturgeon in the Ob basin. The paper evaluates the significance of various parts of this river system for habitation and formation of sturgeon stock. It has been possible to distinguish semi-diadromous sturgeon and four local (indigenous) schools, according to the difference in morphological characteristics and peculiarities of the Ob basin ecology. Semi-diadromous sturgeon spends most of their life in the lower reach of the Ob and in the Gulf of Ob and migrates to spawn to the upper Ob. These spawning migrations cover a distance of 2500 km or more. Spawners from local schools do not make such long spawning migrations. It is noted that at least two isolated schools have been formed higher up the dams of the hydroelectric power stations on the Ob and the Irtysh. Today, the stock of semi-diadromous sturgeon is extremely low, but this school used to be the most abundant. The population of young fish in the middle-Ob school is of high density. But it has an extremely high mortality rate. The Chulym school of Ob sturgeon is in the best condition. Its population increases from the waters of two sturgeon and nelma reserves.+ [ABSTRACT FROM PUBLISHER]

Pop-up satellite archival tags identified differences in oceanic migration of Atlantic salmon ( Salmo salar) kelts from three distinct Canadian populations. Kelts from two endangered populations were restricted to coastal areas near home rivers, whereas kelts from a persisting nearby population migrated to the Labrador Sea and towards the Flemish Cap. Kelts spent most time near the surface (0-5 m), but coastal migrants undertook repeated daytime dives (10-40 m), associated with feeding, upon marine entry and progress was slow (8-23 km·day−1). Distant migrants moved rapidly along the continental shelf (10-50 km·day−1) against prevailing ocean currents, remaining near the surface, except for deep dives (100-1000 m) when crossing ocean channels and at the shelf edge. Home range water temperatures (0-15 °C) indicated that kelts avoided warmer adjacent areas in summer. Kelts did not avoid cold coastal habitat (0-5 °C) in winter, but avoided the surface layers. Kelt migration mimicked that of postsmolts of similar origins, with water temperature acting as a directive or controlling factor. Containment of kelts from endangered populations in coastal habitat was probably responsible for the disappearance of repeat spawners. [ABSTRACT FROM AUTHOR]

Walleye ( Sander vitreus) in Lake Erie is a valuable and migratory species that spawns in tributaries. We used hydroacoustic sampling, gill net sampling, and Bayesian state-space modeling to estimate the spawning stock abundance, characterize size and sex structure, and explore environmental factors cuing migration of walleye in the Maumee River for 2011 and 2012. We estimated the spawning stock abundance to be between 431 000 and 1 446 000 individuals in 2011 and between 386 400 and 857 200 individuals in 2012 (95% Bayesian credible intervals). A back-calculation from a concurrent larval fish study produced an estimate of 78 000 to 237 000 spawners for 2011. The sex ratio was skewed towards males early in the spawning season but approached 1:1 later, and larger individuals entered the river earlier in the season than smaller individuals. Walleye migration was greater during low river discharge and intermediate temperatures. Our approach to estimating absolute abundance and uncertainty as well as characterization of the spawning stock could improve assessment and management of this species, and our methodology is applicable to other diadromous populations. [ABSTRACT FROM AUTHOR]

- Programmes of habitat restoration usually assume that the targeted populations will readily colonise the newly provided habitat. However, this assumption may not always hold, and the success of restoration may be impaired if the individuals are driven to aggregate in areas of the habitat already available instead of spreading to new ones. We investigated how weirs situated along a river could drive Atlantic salmon ( Salmo salar) to aggregate their redds and tested whether aggregation intensified at low fish density. For this, we applied spatial point pattern analysis to a data set consisting on the distribution of salmon redds in a small river over 15 years (1992-2006). Within the habitat suitable for spawning, redds were significantly aggregated, especially in the first 15 morphodynamic units below weirs. Our results suggest that the constraint imposed by obstacles on redd distribution should be considered when conducting habitat restoration. [ABSTRACT FROM AUTHOR]

Abstract: Parasites were inventoried on and in 470 Atlantic cod (Gadus morhua) collected from the southern Gulf of St. Lawrence, NAFO (North Atlantic Fisheries Organization) division 4T, and Cape Breton Shelf (NAFO subdivision 4Vn) in September of 2004 and 2005, and August 2006, respectively. Forward stepwise discriminant function analysis (DFA) of the 4T samples indicated that the nematodes, Hysterothylacium aduncum, and Pseudoterranova decipiens and the acanthocephalans Echinorhynchus gadi and Corynosoma strumosum were significant in the classification of cod to eastern or western 4T. Cross-validation yielded a classification efficiency of 74% overall, thereby supporting the findings of earlier mark-recapture studies which have indicated that 4T cod are comprised of discrete eastern and western spawning groups. Further analyses indicated that western 4T cod was distinct not only from eastern 4T cod, but also differed from cod from the Smokey Channel and Cape Breton Shelf slopewaters (4Vn), with rates of misclassification ranging from 6% to 9%. Hence, “parasite tags” may prove useful for monitoring the exploitation of cod from western 4T during their annual migration through the Cabot Strait and while over-wintering along the edge of the Cape Breton Shelf where mixing with eastern 4T and 4Vn cod may occur. Similar results could be achieved with migrant cod from eastern 4T through analyses of parasite markers together with host meristic or morphometric parameters. [ABSTRACT FROM AUTHOR]

Anadromous alewives (Alosa pseudoharengus) have the potential to alter the nutrient budgets of coastal lakes as they migrate into freshwater as adults and to sea as juveniles. Alewife runs are generally a source of nutrients to the freshwater lakes in which they spawn, but juveniles may export more nutrients than adults import in newly restored populations. A healthy run of alewives in Connecticut imports substantial quantities of phosphorus; mortality of alewives contributes 0.68 g P·fish–1, while surviving fish add 0.18 g P, 67% of which is excretion. Currently, alewives contribute 23% of the annual phosphorus load to Bride Lake, but this input was much greater historically, with larger runs of bigger fish contributing 2.5 times more phosphorus in the 1960s. A mesocosm experiment in a nearby lake showed that juvenile alewife growth is strongly density dependent, but early survival may be too low for juvenile outmigration to balance adult inputs. In eutrophic systems where nutrients are a concern, managers can limit nutrient loading by capping adult returns at a level where juvenile populations would not be suppressed. [ABSTRACT FROM AUTHOR]

Abstract: Tagging of more than 2000 turbot in the eastern Gotland basin in the central Baltic Sea revealed strong spawning site fidelity. Only 4 out of 653 recaptures were made outside the Gotland area and 95% of recaptures, 1–4 years after tagging, were found less than 30km from the original tagging site. Within the summer spawning season turbot were almost stationary and 95% of them were recaptured less than 16km from the tagging site. During the spawning they dwelled close to shore at a mean depth of only 5m while migration to deeper areas was evident in the feeding season. Indications of differences in the spawning behavior between sexes were found together with a positive correlation between recapture probability and body length. The revealed spawning site fidelity has implications for management practices of turbot in the Baltic Sea. [Copyright &y& Elsevier]

Abstract: Trace elemental signatures of otolith nuclei and edges were analysed by LA-ICP-MS in 514 specimens of the highly migratory oceanic fish southern blue whiting, Micromesistius australis australis, that were caught in their two distant spawning grounds located in the Southwest Atlantic (Patagonian Shelf around the Falkland Islands) and Southeast Pacific (shelf and slope of the southern Chile). The elemental fingerprints in the otolith edges, accumulated during the adult life of M. a. australis were spawning-site specific. Using just four elements (Li, Mg, Sr and Ba), the correct allocation of fish to their sampling areas situated in either Chilean or Falkland spawning grounds was about 90%, meaning the adult fish have a close affinity to their respective spawning grounds. Despite this, chemical concentrations in their otolith cores revealed two clusters of signatures, with the majority of Chilean fish (more than 80%) grouped into Cluster 1, which is characterized by lower Sr concentrations, and about 80% of Patagonian fish grouped into Cluster 2, which is characterized by higher Sr concentration. This most likely indicates that the Chilean spawning population consists of about four fifths of the native fish plus about one fifth of migrants from the Atlantic, and vice versa. Possible ways of the population interchange and migrations of Chilean and Patagonian fish were discussed contributing to identification of their stock status. [Copyright &y& Elsevier]

Changes in the behaviour of cyprinids belonging to different ecology groups were observed below a weir that was restricting their upstream migrations during the spawning period May–July. Positions of chub Leuciscus cephalus (L.), Prussian carp Carrasius auratus gibelio (Bloch 1783), bream Abramis brama (L.) and white bream Blicca bjoerkna (L.) were recorded every 12 min over a 24-h period using an automatic data logger (ALS) in the upper Elbe River, Czech Republic. For all observed species, two activity peaks occurred; however, the interspecies timing of these peaks differed. Peak times for chub, bream and white bream occurred at night and during daylight, whereas Prussian carp was active mostly at night. Specimens belonging to the rheophilous group suggested more efficient behavioural tactics in passing the weir, staying below the obstacle one month longer than did eurytopic species. [ABSTRACT FROM AUTHOR]

Population genetic structures of the mackerel (Scomber scombrus) and chub mackerel ( Scomber japonicus) were studied in the Mediterranean Sea. Fragments of 272 bp ( S. scomber) and 387 bp ( S. japonicus) of the 5′-end of the mitochondrial control region were sequenced from spawning individuals collected off the coasts of Greece, Italy, Spain, and Portugal. High levels of mitochondrial control region haplotypic diversity (> 0.98) were found for both Scomber species. Nucleotide diversity was higher in the mackerel (0.022) than in the chub mackerel (0.017). Global FST values were also higher and significant in the mackerel (0.024, P<0.0001) as opposed to the chub mackerel (0.003, P>0.05). Molecular variance analyses showed differential genetic structuring for these two closely related species. There is extensive gene flow between Mediterranean Sea and Atlantic Ocean populations of chub mackerel, which are organized into a larger panmictic unit. In contrast, Mediterranean Sea populations of mackerel show some degree of genetic differentiation and are structured along an east–west axis. The analysed eastern Mediterranean Sea mackerel populations (Greece, Italy) are clearly separated from that of the western Mediterranean Sea (Barcelona), which forms a panmictic unit with eastern Atlantic Ocean populations. The genetic structures of both species showed asymmetric migration patterns and indicated population expansion. [ABSTRACT FROM AUTHOR]

Anadromous fishes migrate to sea, apparently to take advantage of growing conditions, and return to fresh water to spawn. Migration is an energetically demanding part of the life cycle, and animals tend to evolve physiological and behavioral traits that suit the environmental conditions they experience during migration. We hypothesized that this premature migration is a consequence of the fish having to avoid stressful summer temperatures in order to access certain suitable areas for spawning in the fall. We tested this idea in sockeye salmon, Oncorhynchus nerka, by compiling data on the timing of migration and spawning and the freshwater temperature regime along the migration route in populations throughout the species North American range. The timing of migration varied among populations and was primarily related to temperature regime during migration and the timing of spawning. When temperatures were moderate, sockeye salmon tended to migrate to the vicinity of the spawning grounds about 1 month prior to spawning, regardless of the length of the freshwater migration. A long delay between migration and spawning seems to be an adaptation to avoid migration when temperatures are high. The results supported the hypotheses that the mean and variance of delay among populations from warm areas would be greater than those for populations from cold areas. At the southern end of the North American range of sockeye salmon, populations in Washington State and southern British Columbia experience higher water temperatures than other populations, and may also have evolved greater tolerance of warm water than northern populations. In summary, patterns of migratory timing among populations reflect both passage conditions and spawning time for adults.