Spawning Migration Research Articles

Reproductive Condition in the Caspian Anadromous Shad Alosa kessleri kessleri (Alosidae) during Spawning Migration in the Volga River

Reproductive Condition in the Caspian Anadromous Shad Alosa kessleri kessleri (Alosidae) during Spawning Migration in the Volga River

Regional differences in oceanic migratory behavior of Japanese silver eel in waters with different vertical temperature gradients

BackgroundThe Japanese eel Anguilla japonica has a single spawning area on the west coast of the Mariana Islands, and the larvae disperse widely via the North Equatorial Current and the Kuroshio Current to freshwater and coastal areas of East Asia for nursery and growth habitats. Spawning adults reared in their respective habitats begin their migration to spawn from September to February, but little is known about regional differences in migration routes, their contribution to spawning populations, or their migratory behavior. To better understand the spawning migrations of Japanese eels, we tracked adult migratory stage eels (silver eels) captured in coastal areas of three regions (Tokai region, Sea of Japan coastline, and Tohoku region) from October 2019 to February 2020 using pop-up satellite archival tags.ResultsTwenty-three tagged eels were released in each coastal area, and data were collected on 15 eels for a maximum of 59 days. Eels released in the Tokai region migrated southeast along the Kuroshio Current. On the other hand, eels on the Sea of Japan coastline and in the Tohoku region tended to migrate westward and southward against the ocean current, respectively, but no eels from either region reached waters near the Kuroshio Current. In addition, the present study found region-specific vertical movement patterns among the eels. Eels from the Tokai region showed typical diurnal vertical movements, while an eel from the Sea of Japan coastline repeated non-diurnal vertical movements, which was attributed to regional differences in bathymetry and water mass structure. Except for one eel suspected of being preyed upon, all other eels did not venture into depth zones with temperatures below 4 ^{circ }textrm{C}, thus suggesting that the maximum depth of vertical movement is limited by water temperature.ConclusionsThis study provided new insights into the migratory behavior of Japanese silver eel from the Sea of Japan coastline and the Tohoku region, but further long-term tracking is required to reveal the fate of the spawning adults from the coast of Japan.

Reproductive Condition in the Caspian Anadromous Shad Alosa kessleri kessleri (Alosidae) during Spawning Migration in the Volga River

This paper describes the state of the gonads of Caspian anadromous shad, Alosa kessleri kessleri (Grimm, 1887), migrating for spawning in the Akhtuba River. In May of 2021, the peak of spawning was recorded at a water temperature of 17–18°C. Females and males had gonads at the developing and spawning-capable phases. The fork length (FL) of females averaged 254.1 mm, and their body weight was 178.9 g; for males, this was 209.9 mm and 87.5 g, respectively. Most females were over three years old, while males were between one and three years old. The gonadosomatic index (GSI) in females and males averaged 8.71 and 3.67%, respectively. Among the asynchronously developing secondary growth oocytes in the spawning capable gonads, three different-sized groups were distinguished for intending to spawn the same number of oocyte batches. The number of primary growth oocytes (26.7–59.4% of germ cells on sections) allows for considering these fish as iteroparous. The diameter of the tertiary vitellogenic oocyte was about 800 µm.

Arctic cod (Boreogadus saida) in fjord and glacial habitats: a collaborative study with Uummannap Kangerlua fishers

Arctic cod ( Boreogadus saida) (Lepechin, 1774) is often found in front of glaciers, which is the least studied of the species’ habitats. Uummannap Kangerlua and Sullorsuaq in West Greenland provide a unique opportunity to study Arctic cod in the glacial habitat, as they are among the few places with a directed Arctic cod fishery. Inuit fishers from these fjords regularly catch Arctic cod as fresh bait for the Greenland halibut ( Reinhardtius hippoglossoides) (Walbaum, 1792) longline fishery, the main economic activity in the region. We collaborated with the fishers to learn about Arctic cod through interviews and collection of fish samples. Ten informants provided information on fishing areas, fishing methods, interannual variability in the catches, relationships with temperature and sea ice, and reported a spawning area near Saattut. One of the two samples collected contained only 21% males, which were longer, heavier, older, and had a higher gonadosomatic index than females. This skewed sex ratio may result from size-selective predation or spawning migration. Collaboration with fishers provided important baseline information on Arctic cod in fjord and glacial habitats. Continued efforts could bring a better understanding of key aspects of Arctic cod that are relevant for all Arctic communities located near glacial fjords.

Effects of the invasive swim bladder parasite Anguillicola crassus on health and condition indicators in the European eel.

Parasites negatively affect biological processes within their hosts, which may alter for example health, growth, and reproductive ability. Non-native invasive parasites, in particular, may have large effects on the endemic hosts, given that the hosts lack evolved specific defences against such parasites. The swim bladder nematode Anguillicola crassus, an invasive parasite originating from Asia, is found in the European eel (Anguilla anguilla, L. 1758), since the 1980s. We investigated whether A. crassus affected several indicators related to health of the European eel (spleen- and liver size, body fat content and relative condition). Our results indicate that during the continental residency of the eels, infection by A. crassus had no major negative impacts on the investigated health indicators at the generally low infection intensities present in this study (median 2-3 visible parasites). Given that many of the adult eels were found to have swim bladder damage, concerns about their spawning migration through deeper oceanic environments can still be raised. To allow further investigations, we suggest that quantification of swim bladder damage should be implemented in eel-monitoring programs. Compared to other parasite pressure parameters, swim bladder damage provides additional information about past infections and future problems.

Proteins journey-from marine to freshwater ecosystem: blood plasma proteomic profiles of pink salmon Oncorhynchus gorbuscha Walbaum, 1792 during spawning migration.

The pink salmon (Oncorhynchus gorbuscha) is a commercial anadromous fish species of the family Salmonidae. This species has a 2-year life cycle that distinguishes it from other salmonids. It includes the spawning migration from marine to freshwater environments, accompanied by significant physiological and biochemical adaptive changes in the body. This study reveals and describes variability in the blood plasma proteomes of female and male pink salmon collected from three biotopes-marine, estuarine and riverine-that the fish pass through in spawning migration. Identification and comparative analysis of blood plasma protein profiles were performed using proteomics and bioinformatic approaches. The blood proteomes of female and male spawners collected from different biotopes were qualitatively and quantitatively distinguished. Females differed primarily in proteins associated with reproductive system development (certain vitellogenin and choriogenin), lipid transport (fatty acid binding protein) and energy production (fructose 1,6-bisphosphatase), and males in proteins involved in blood coagulation (fibrinogen), immune response (lectins) and reproductive processes (vitellogenin). Differentially expressed sex-specific proteins were implicated in proteolysis (aminopeptidases), platelet activation (β- and γ-chain fibrinogen), cell growth and differentiation (a protein containing the TGF_BETA_2 domain) and lipid transport processes (vitellogenin and apolipoprotein). The results are of both fundamental and practical importance, adding to existing knowledge of the biochemical adaptations to spawning of pink salmon, a representative of economically important migratory fish species.

Seasonal migration, site fidelity, and population structure of European seabass (Dicentrarchus labrax)

Abstract Large-scale electronic tagging is a very powerful tool to study how fish movements and migrations shape the internal dynamics of populations. This knowledge, crucial for improving fishery management, was still limited for the European seabass, whose stocks in the Northeast Atlantic have declined drastically over the last decade. To better understand the species ecology and the spatio-temporal structure of the population, we tagged seabass in the North Sea, the English Channel, and the Bay of Biscay, from 2014 to 2016. Out of 1220 deployed DSTs, 482 have been recovered by November 2022. Approximately half of them included a period of potential spawning migration. Reconstructed trajectories confirmed seabass to be a partial migratory species, as individuals exhibited either long-distance migrations or residence. Most migrants exhibited fidelity to summer feeding areas and winter spawning areas. Our dataset enriches the knowledge of seabass biological traits (e.g. temperature and depth ranges, vulnerability to predation and fishing). Our results suggest a spatial structure of the Atlantic population that differs from the stock structure currently considered for assessment and management. The consequences should be explored at both the European level and by regional managers involved in conservation outcomes.

Low water temperature and increased discharge trigger downstream spawning migration of ayu Plecoglossus altivelis

Low water temperature and increased discharge trigger downstream spawning migration of ayu Plecoglossus altivelis

Effect of the trap net emptying method on release mortality of Atlantic salmon estimated by a Bayesian system model

AbstractWe evaluated the effect of emptying techniques of a pontoon trap on mortality of Atlantic salmon on their spawning migration along the Finnish coast of the northern Baltic Sea by tagging and releasing fish from commercial trap nets. Two methods currently used, a traditional emptying chute and a lifting bag, were compared. The lifting bag has been developed primarily for minimising injuries for fish during emptying. A custom‐built Bayesian system model was used for mortality estimation. We also explored external injuries of salmon and compared the probability of getting an injury between the emptying methods. The mean probability of salmon dying due to release from a trap with an emptying chute was 24% (90% HDI 3%–43%), whereas that for salmon released from a trap with a lifting bag was 13% (90% HDI 1%–24%). Results showed a higher probability of injuries and longer air exposure time in salmon caught with a trap with an emptying chute, which may explain the observed difference in mortality. Manual handling of a lifting bag appears to pose a clear work safety risk for fishers. It is noteworthy that the role of release mortality for northern Baltic salmon stocks is small because the number of salmon released in coastal fishery is currently low.

Changes in infectious agent profiles and host gene expression during spawning migrations of adult sockeye salmon (Oncorhynchus nerka)

During spawning migrations, adult Pacific salmon ( Onco rhynchus 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.

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

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

Handling of wild Atlantic salmon smolts reduced marine survival more than hydropower turbine passage

AbstractAtlantic salmon smolts are sensitive to disturbance during their migration and negative effects experienced in freshwater may carry over into the marine environment. In this study, smolts were PIT‐tagged and detected during their subsequent spawning migration. A generalized linear model fitted to the return data predicted a return probability of 0.091 ± 0.0061 (±SE) for smolt that was released downstream of a hydropower dam. The additional effect of migrating through a Kaplan turbine associated with hydroelectric generation did not significantly reduce return rates, while the additional effect of being handled twice in a trap was significant and lowered the predicted return probability to 0.057 ± 0.0079 (±SE; model predictions from logistic regression). Catch‐mark‐recapture methods such as those using physical recapture of fish should be applied with great care to avoid multiple handling stress that may lead to reduced marine survival and biasing estimates intended to help monitor population statuses. Moreover, similar return rates in turbine and bypass migrating smolts emphasize that more knowledge is needed when evaluating mitigation actions for migratory fish at hydropower plants.

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

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

Strain-dependent spawning migration of stocked brown trout (Salmo trutta) to a northern Finnish river, in relation to rearing site and release area

The supportive stocking programs that aim to promote fisheries may increase straying among sympatric but genetically diverged populations and compromise local adaptations. We employed recapture sample data on coded wire tagged brown trout (Salmo trutta m. lacustris) from three hatchery-reared strains to study in which proportions they were represented as running spawners in the area of River Juutuanjoki, northern Finland. More specifically, we analysed how the migration tendency to the study river varied among the strains in relation to their different hatchery sites (local vs. non-local) and release areas (native river mouths vs. lake), manifesting in homing or straying behaviour. The strain native to River Juutuanjoki (JUU) and another strain originating from the adjacent River Siuttajoki (SIU) were maintained in a local hatchery using water of the studied river. The JUU strain was also reared in a non-local hatchery on the other side of the catchment area, together with the third strain originating from River Ivalojoki (IVA). The fish from each strain were released at ages 3 and 4 at the mouths of their original rivers and in the common feeding area of the Lake Inari. The JUU trout from the non-local hatchery were only released in the lake area. Release area did not affect the incidence of spawner samples in any of the strains. However, the JUU trout were significantly more likely represented than the SIU trout (3–4-fold difference), regardless of their common rearing site. When the JUU trout were reared in the non-local hatchery and thus lacked previous contact with their home river, their mean recapture probability among the spawner samples was significantly higher compared to the similarly treated IVA trout, and even slightly higher compared to the SIU trout. Irrespective of their release area, the IVA trout had significantly the lowest likelihood to become captured as spawners in the study river. The observed strain-dependent differences among lake-released fish suggest that JUU trout possessed a stronger genetic tendency to return to their native river for spawning than did the non-native strains, giving support for a hierarchical navigation hypothesis. We can also conclude that lake stockings from the local hatchery unlikely compromises the homing ability of JUU trout, in relation to their releases at the river mouth, and neither increases the undesirable incidence of spawners from the non-native strains.

On coho salmon <i>Oncorhynchus kisutch</i> from Iturup Island

Results of biological analysis are presented for 162 specimens of coho salmon caught at the coast and in the rivers of Iturup Island (southern Kuril Islands) during their spawning migration in August-October, 2021. Almost all females and males close to puberty in the current year spent one year in the sea and were aged 1.1+ (66.7 %) and 2.1+ (30.0 %). The fish that spent two years in the sea were single – 1 specimen aged 1.2+ and 3 specimens aged 2.2+ (2.5 %). Taking into account the age of puberty and the body weight (2.63 kg for females and 2.44 kg for males, on average) the spawners reproduction in short streams is assumed. The high value of the gonad-somatic index (up to 20–22 % for some females) is other evidence that all these fish cannot run to other spawning areas but at least a part of them should spawn in the water bodies of Iturup Island. Indeed, some coho salmon were captured directly in the rivers. Beside the spawning fish, two actively feeding coho females aged 0.0+ (0.55 kg) and 1.0+ (1.11 kg) were caught with fixed nets.

Detection and distribution of the North Atlantic capelin (Mallotus villosus) using environmental DNA—comparison with data from the main fishery management survey

AbstractCapelin (Mallotus villosus) is both an important commercial and ecological resource of the North Atlantic subpolar region. Two decades ago, the stock distribution around Iceland drastically changed. During autumn, which corresponds to the main feeding period, the capelin stock was previously located between the North of Iceland and the Jan Mayen area. Since the beginning of 2000s, the feeding aggregation has been located at the east coast of Greenland, inducing slight changes in the timing and route of the capelin spawning migration along the Icelandic shelf, and therefore in the catches. Changes in the distribution of capelin around Iceland made it both more difficult and expensive to assess the distribution of the stock with current survey methods. Here, we compare environmental DNA (eDNA) data to the acoustic data collected during the autumn monitoring survey, which leads to a preliminary estimation of the stock size. eDNA samples were collected at five different depths and were analyzed both horizontally across latitudes and longitudes and vertically across depth profiles. We detected eDNA in most of the locations where acoustic data detected capelin. Generalized linear models suggested that eDNA concentrations can be used as a proxy for the detection and quantification of capelin. The horizontal distribution of eDNA observed during both years corresponds with the horizontal distribution of capelin registered with the acoustic approach, while the vertical distribution indicated both effects of oceanic currents and diel vertical migration on eDNA detection and quantification.

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

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

Swimbladder Function in the European Eel Anguilla anguilla

Eels use the swimbladder for buoyancy control. The ductus pneumaticus connecting the esophagus with the swimbladder is closed soon after initial opening of the swimbladder in the glass eel stage, so that eels are functionally physoclist. Subsequent filling of the swimbladder is achieved by activity of gas gland cells in the swimbladder epithelium and countercurrent concentration in the rete mirabile. Gas gland cells produce and release lactic acid and CO2. In blood, acidification induces a release of oxygen from the hemoglobin (Root effect). The resulting increases in PO2 and PCO2 provide diffusion gradients for the diffusion of oxygen and CO2 into the swimbladder, the main gases secreted into the swimbladder. In addition, the partial pressure of these two gases remains elevated in venous blood leaving the swimbladder epithelium and returning to the rete mirabile. Back-diffusion from venous to arterial capillaries in the rete results in countercurrent concentration, allowing for the generation of high gas partial pressures, required for filling the swimbladder under elevated hydrostatic pressure. The transition of the yellow eel to the silver eel stage (silvering) is accompanied by a significant improvement in swimbladder function, but swimbladder volume cannot be kept constant during the daily vertical migrations silver eels perform during their spawning migration back to the spawning grounds in the Sargasso Sea. Infection of the swimbladder with the nematode Anguillicola crassus significantly impairs the function of the swimbladder as a buoyancy organ.

Understanding the impact of barriers to onward migration; a novel approach using translocated fish

River catchments worldwide are heavily fragmented by anthropogenic barriers, reducing their longitudinal connectivity and contributing to the decline of migratory fish populations. Direct impacts of individual barriers on migratory fish are well-established, but barrier impacts on onward migration are poorly understood, despite their relevance to evidence-based, catchment-scale, management of threatened species. This study investigated the upstream spawning migration of 352 acoustic tagged river lamprey (Lampetra fluviatilis), translocated upstream of two key barriers (R2: n = 60 & 59; R3: n = 59 & 52) compared to a control group (R1: n = 61 & 59), across two contrasting (dry and wet, n = 180 and 172) years in the River Yorkshire Ouse, England, to reveal the impact of barriers on the onward migration of upstream migrating fish. Release further upstream increased the degree of catchment penetration, with median distance upstream of R1 56.1% and 68.6% greater for lamprey released at R2 and R3 respectively. Median delays at the two downstream-most main river barriers by the control group were 23.8 and 5.4 days (2018/19) and 9.3 and 11.4 days (2019/20). However, impacts of delay were only observed on the time to reach spawning habitat, time to reach final assumed spawning location and speed of movement in one upper catchment tributary during 2019/20 whilst they were only observed on time to reach spawning habitat during 2018/19 and on assumed spawning location distance during 2019/20 in the other. Ultimately, limited impacts of delay at barriers on onward fish migration post-passage were observed but median catchment penetration was increased with consecutive release upstream. This study demonstrated the importance of a true understanding of barrier impacts to inform catchment-wide planning, evidence vital for management worldwide. Although the findings of this study do support the use of trap and transport as a measure to remediate barrier impacts on migration, fish passage engineering improvements or barrier removal, at structures shown to be the most inhibiting to fish migration should be considered the best and most sustainable option to improve barrier passage.

Characterization of the Iraqi Artisanal Marine Fisheries, Northwest of the Arabian Gulf

The study described the characteristics of the Iraqi artisanal marine fisheries in the northwest Arabian Gulf between January 2020 and December 2021. The study aimed to update knowledge on the fish landings of the artisanal marine fisheries in the study area. A total of 19,877 t of fish were landed in 2020 and 13,784 t in 2021. A Student’s t-test showed a significant difference between the species’ landings over the two years. The main species exploited were mullets (10.5%), threadfin bream (10.4%) and spotted leatherskin (8.4%) in 2020, whereas threadfin bream (14.2%), mullets (9.6%) and tigertooth croaker (8.3%) were mainly landed in 2021. Unfortunately, the contribution of river shad catches has dropped to lower levels over recent years, comprising 3.6-5.8% of the total landings during 2020-2021. Shrimps contributed 15.6 and 16.1% of the total landings during 2020 and 2021, respectively, and mixed fish contributed 11.8 and 15.3%, respectively. The trends of the landings of the main fish groups increased substantially from 2011 to 2021. Unfortunately, the contribution of river shad (T. ilisha) catches has dropped to lower levels over recent years, in contrast with the contributions of other species. Therefore, the study recommends the following management measures for the river shad stock: to protect the brood stock during the breeding season no fishing should be allowed in the Shatt Al-Arab River during the main spawning migration from May to June and small T. ilisha (<23.0 cm) should not be caught.