Movement of radio-tagged anadromous sea lamprey during the spawning migration in the River Mondego (Portugal)

The available spawning habitat for the anadromous sea lamprey, Petromyzon marinus L., population that enters the River Mondego has been drastically reduced in the last 20 years. The installation of a fish passage in the first impassable dam, the Açude-Ponte, would enable sea lamprey to recolonise the 34.6-km river stretch between the Açude-Ponte and Raiva dams. In order to assess the suitability of the upstream river stretches for this species, 10 radio-tagged sea lamprey were released upstream of the Açude-Ponte dam and tracked continuously throughout the entire migratory path. Lamprey were unable to pass over intact weirs that had been built for recreational purposes. Sea lamprey movements were more frequent during dusk and night than other periods. Increased river discharge at night, resulting from the operation of the Raiva power station, stimulated lamprey movements but reduced ground speeds recorded. After reaching a certain location, some of the animals maintained their position for several weeks, before undergoing a new movement. Two of the main tributaries of this river stretch were used by some sea lamprey, indicating that the animals were able to find these historical spawning grounds.     

Characteristics of the spawning stock of chinook salmon <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis> from the Apuka River (northeastern Kamchatka)

Biological features of chinook salmon Oncorhynchus tshawytscha from the Apuka River, the largest river of the northeastern Kamchatka inflowing Olyutorskii Bay of the Bering Sea, are studied. Chinook salmon from the Apuka River spend mainly a year in the river before downstream migration to the sea. The fish live in the sea for 1–4 years. The spawning migration of chinook salmon into the Apuka River begins in late May just after ice melting, and it continues until early August. The main part of the spawners enters the river during June. A hypothesis on the occurrence of two seasonal races in the Apuka River is proposed.     

Behavioural patterns of sea lampreys' spawning migration through difficult passage areas, studied by electromyogram telemetry

Electromyogram telemetry (EMG) was used to study the behaviour of sea lamprey Petromyzon marinus during migration through difficult passage areas. When swimming on stretches free from obstacles, the EMG values of sea lampreys showed a constant pattern of activity. Conversely, when negotiating difficult passage areas their behaviour were characterized by alternating between short bursts of intense activity ( i.e . burst movements) and periods of motionless rest during which sea lampreys attached to convenient structures by means of the oral sucker. During blockstone weirs negotiation, tagged sea lampreys spent on average 23% of the time swimming rapidly by means of multiple bouts of burst movements of 31 s duration. To recover from each burst movement, the sea lampreys spent on average 2 min 25 s resting. Sea lampreys seemed affected by increasing fatigue, which probably resulted from initiating a new burst movement without fully recovering physiologically from the previous efforts.     

Factors affecting the within-river spawning migration of Atlantic salmon,with emphasis on human impacts

We review factors affecting the within-river spawning migration of Atlantic salmon. With populations declining across the entire distribution range, it is important that spawners survive in the last phase of the spawning migration. Knowledge on the factors affecting migration is essential for the protection of populations, and to increase the success of reintroduction programmes. A number of studies have documented that the upstream migration may be delayed for many weeks at man-made obstacles such as power station outlets, residual flow stretches, dams, weirs and fishways. The fish may also be delayed at natural migration barriers. Often, the magnitude of delay is not predictable; fish may be considerably delayed at barriers that appear to humans to be easily passable, or they may quickly pass barriers that appear difficult. Stressful events like catch-and-release angling may affect upstream migration. Impacts of human activities may also cause altered migration patterns, affect the within-river distribution of the spawning population, and severe barriers may result in displacement of the spawning population to other rivers. Factors documented to affect within-river migration include previous experience, water discharge, water temperature, water velocity, required jump heights, fish size, fish acclimatisation, light, water quality/pollution, time of the season, and catch and handling stress. How each of these factors affects the upstream migration is to a varying extent understood; however, the effects may differ among different river sections and sites. There are likely a number of additional important factors, and the relationship between different factors is complex. The understanding of general mechanisms stimulating fish within-river migration are still lacking, and it cannot be reliably predicted under which conditions a fish will pass a given migration barrier or which conditions are needed to stimulate migration at different sites. The strong focus on the effects of water discharge in past work may have hampered consideration of other factors. Exploration of the influence of these other factors in future studies could improve our understanding of what controls the upstream migration.     

Migratory behaviour of adult pikeperch (Stizostedion lucioperca) in a lowland river

The behaviour of radio-tagged adult pikeperch (Stizostedion lucioperca (L.)) from two areas in the Danish River Gudenaa were recorded prior to, and during the spawning period. Eight of 13 tagged fish in the lower reaches of the river were located throughout the whole study. Five of these fish moved upstream to various sites in the river prior to spawning, which occurred from late April to June. The three remaining fish moved to the fjord. These movements were interpreted as a spawning migration, and it is suggested that the lower reaches of the River Gudenaa constitute an over-wintering area for pikeperch, which use different spawning areas. Ten pikeperch caught just downstream of an impassable hydropower plant were radio-tagged and translocated upstream of the dam to a reservoir. Within a week, half of the fish moved to a lake situated more than 30 km upstream the reservoir. This behaviour is hypothesised to be a homing response. The study reveals that the pikeperch is a highly mobile species with a complicated migration pattern, even in relatively small river systems.     

Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys

1.  Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2.  Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3.  Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4.  In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.     

Previously spawned Atlantic salmon ascend a large subarctic river earlier than their maiden counterparts

Spawning migration timing of maiden Atlantic salmon Salmo salar and previous spawners was analysed in the catches in 1989–2004 in the large subarctic River Teno in the northernmost parts of Finland and Norway. The hypothesis was that the migration timing of previous spawners and their maiden counterparts is similar, with the migration timing similar between sexes. In most cases, however, previous spawners were observed to migrate into the River Teno and its tributaries earlier than their maiden counterparts. The difference in run timing was especially evident between maiden one-sea-winter (1SW) Atlantic salmon and the corresponding group of previous spawners [1S1, 1 year at sea (1) followed by first spawning (S) and reconditioning period of 1 year (1) at sea and second spawning run] for both sexes in the River Teno and in its two tributaries. The same was also evident between 2SW maiden and 2S1 previous spawning female Atlantic salmon in the River Teno. Females showed earlier spawning migration than males both in previous spawners and maiden Atlantic salmon. Different maiden sea-age classes also showed differences in run timing as multi-sea-winter fish (2–4SW) ascended earlier than 1SW fish but the timing of 1S1 and 2S1 previous spawning females coincided. The results suggest that run timing of Atlantic salmon may not be strictly genetically fixed as previous spawners ascend earlier than they did on their first spawning migration as maiden fish, and indicated that the closeness of the reconditioning area of postspawners to the river of origin resulted in an early ascent. Run timing of different sea-age groups has major management implications if the populations are heavily exploited with numerous fishing methods in different periods of the fishing season, as in the River Teno system.     

Variability in migration timing of adult Pacific lamprey (<Emphasis Type="Italic">Lampetra tridentata</Emphasis>) in the Columbia River,U.S.A.

We examined the effects of river environment on the timing of spawning migrations by anadromous Pacific lamprey, Lampetra tridentata, in the Columbia River (U.S.A.). In a 41-year time series of adult lamprey counts, migration timing was earliest in warm, low-discharge years and latest in cold, high-flow years. Threshold temperatures associated with run timing were similar throughout the dataset despite significant impoundment-related warming, suggesting that temperature-dependent migration cues have been temporally stable. Within each year, migration rates of PIT-tagged lampreys were positively correlated with temperature and negatively correlated with discharge through multiple river reaches, offering additional evidence for environmental control of upstream movement. Both visual count and PIT-tag data indicated that there may be population-based differences in migration timing within the aggregate Columbia River lamprey run. These life history and behavioral results have potentially far-reaching implications for management of lamprey species.     

Nutritional status of adult sea lamprey (Petromyzon marinus Linnaeus, 1758) during spawning migration in the Minho River,NW Iberian Peninsula

The anadromous sea lamprey (Petromyzon marinus) stop feeding during spawning migration; following the migration effort, the energy reserves of their tissues are expected to be mobilised and depleted. The present work aimed at testing if mobilisation of nutrients occurred in sea lampreys during the 2011 spawning run in the Minho River. Professional fishermen at three sampling sites captured the individuals used: two at the beginning of the freshwater spawning migration (one at the river mouth and one upstream the estuary) and one near the spawning grounds (35 km upstream the estuary limit). The total lipids (Folch extraction), protein (nitrogen conversion), energy content (direct calorimetry) and fatty acids (GC/EI‐MS‐SIM) were determined in the carcass (n = 19) and female liver (n = 8) and gonads (n = 8). The results indicated that a reduction of carcass dry matter during migration was mainly caused by a lipid decrease (51.0 ± 2.46% downstream and 38.0 ± 2.92% upstream, LSmean ± SE). In females, a decrease in the measured amounts of liver lipids was also observed (4.28 ± 2.637 g downstream and 0.64 ± 2.206 g upstream, LSmean ± SE) and the monounsaturated fatty acids consistently composed the larger fraction of lipids in all tissues (ranging between 42.9 ± 4.20% and 54.9 ± 3.43% of total fatty acids, LSMean ± SE). The results suggest a dynamic nutrient mobilisation and the major importance of liver fatty acids (such as 14:1n‐5 and 16:1n‐7) as possible energy sources for embryonic development or combustion during spawning migration. The P. marinus individuals captured at the intermediate sampling site (approximately 35 km upstream river mouth) in the middle of the season seemed as ready to spawn as the upstream sea lampreys.     

Migrating silver eels return from the sea to the river of origin after a false start

The European eel''s singular spawning migration from European waters towards the Sargasso Sea remains elusive, including the early phase of migration at sea. During spawning migration, the movement of freshwater resident eels from river to sea has been thought to be irreversible. We report the first recorded incidents of eels returning to the river of origin after spending up to a year in the marine environment. After migrating to the Baltic Sea, 21% of the silver eels, tagged with acoustic transmitters, returned to the Narva River. Half returned 11–12 months after moving to the sea, with 15 km being the longest upstream movement. The returned eels spent up to 33 days in the river and migrated to the sea again. The fastest specimen migrated to the outlet of the Baltic Sea in 68 days after the second start—roughly 1300 km. The surprising occurrence of returning migrants has implications for sustainable management and protection of this critically endangered species.     

Spawning migration behaviour of sea trout (Salmo trutta L.) in a boreal river system: effects of flow conditions and obstacles on migratory activity

In this study, radio telemetry was used to examine the upstream spawning migration behaviour of anadromous brown trout (sea trout), Salmo trutta L., in a boreal river system, the River Isojoki, western Finland. The aim was to study the movement activity and migration characteristics of trout during the upstream spawning migration, as well as to locate the important spawning habitats and study the spawning characteristics. Furthermore, the authors analysed how flow conditions and a hydropower dam, with adjacent fishways, affected the upstream spawning migration. Tagged trout spawned in both the main stem and four tributaries, with spawning taking place from early October to November. The movement activity of radio-tagged trout was influenced by a hydropower dam (Perus dam), with spring migrators spending prolonged periods at the dam area, postponing the migration upstream. Flow conditions affected the total time spent at the dam area, as well as the movement activity in the free-flowing sections above the dam, with increasing flow stimulating activity. In addition, time of river ascent and location of spawning area had a significant effect on the movement activity of tagged trout. These results are further evidence that synergistic effects of flow and migratory obstacles can negatively influence migrations of anadromous fish, regardless of constructed fishways. The management of flow regimes and the efficiency of fishways are vital, as climate change will likely influence the flow and increase the water temperature of boreal river systems, further aggravating issues caused by obstacles.     

Effect of vasotocin on plasma free fatty acid level in the migrating anadromous sea lamprey.

The effect of injections of arginine vasotocin (AVT) on plasma free fatty acid (FFA) levels was studied in anadromous sea lampreys collected in the St. John River, New Brunswick, during their upstream spawning migration. Plasma FFA was significantly higher in lampreys injected with a single dose of 1 000 mU vasotocin/kg body weight than in those receiving only the vehicle solution, the difference being the greater at 90 than at 30 min post-injection. The significance of AVT in migration is discussed.     

Influence of aperiodic summer droughts on leaf litter breakdown and macroinvertebrate assemblages: testing the <Emphasis Type="Italic">drying memory</Emphasis> in a Central Apennines River (Aterno River,Italy)

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.     

Swimming behaviour of upriver migrating sea lamprey assessed by electromyogram telemetry

The main subject of this study was the swimming behaviour of upriver migrating sea lamprey, Petromyzon marinus , with particular focus on identification of their swim strategies to overcome areas of difficult passage. A biotelemetry technique (electromyogram telemetry) was used to register muscle activity of the tagged animals. In the 2005 spawning season, five adult sea lampreys were surgically tagged and released in the field. Before release, electromyogram (EMG) records were calibrated with the P. marinus swimming speed in a swim tunnel. Differences between ground speed and swimming speed in the wild suggest that the calibrated CEMG (coded electromyogram) transmitter output corresponds to an activity index, and cannot be properly related to actual swimming speed. This study notes the need to confirm the laboratory calibration curves, to ascertain their use in determining swimming speed of tagged fish in the wild. In 2006, in order to confirm the field results seven adult sea lampreys were tagged, calibrated in the laboratory and released in a 30-m long experimental outdoor canal. The results were similar: observed swimming speed was generally higher when compared with the swimming speed obtained with the EMG signal. In the river, when swimming through slow-flow stretches, sea lampreys maintained a constant pattern of activity, attaining an average ground speed of 0.76 BL s⁻¹ (2.5 km h⁻¹). When sea lampreys encountered rapid flow reaches they alternated between short movements ( c. 67 s) and periods of rest ( c. 99 s). In each swim bout they progressed approximately 14 m; to overcome more difficult obstacles sea lampreys increased their number of burst movements instead of longer or more violent swimming events. About 43% of the time negotiating difficult passage areas was spent in resting by attaching motionless to the substrate with their oral disk.     

Migration and spawning energetics of the anadromous sea lamprey,Petromyzon marinus

Synopsis Energy expended in migration and reproduction was determined from measurements of caloric concentration and body and gonodal weight for nontrophic sea lampreys collected from different sites along the St. John River, New Brunswick. The estimated cost of locomotion in swimming the 140 km which separates the estuary from the spawning redds was 300 and 260 kcal for males and females respectively. Acutal distance which lampreys swam as well as mean swimming speed were estimated from a linear regression equation relating energy expenditure for locomotion and body weight. Energy expenditure for breeding was considerably greater than that catabolized throughout the upstream migration.     

Polymorphism of spawners of the resident form of European river lamprey <Emphasis Type="Italic">Lampetra fluviatilis</Emphasis> (Petromyzontidae)

Data on polymorphism (plastic and meristic characters) are obtained for spawners of resident nonparasitic form of European river lamprey Lampetra fluviatilis from the Serebristaya River. The new data verify the diagnosis of this species and contribute to the formulation of a hypothesis on the presence of several phenotypic groups: dwarf, small-sized, and common. Analysis of plastic characters and of the number of trunk myomeres demonstrated that the values of these characters reliably depend on position of lampreys in a certain discerned group. Some aspects of biology of this species are discussed: spawning and interaction between resident nonparasitic river and migrating parasitic lampreys.     

Effect of origin, sex and sea age of Atlantic salmon on their recapture rate after river ascent

The recapture rate of Atlantic salmon (Salmo salar L.) after river ascent was examined by the trapping and tagging of ascending spawners in the lower reaches of the Simojoki River, which flows into the northern Baltic Sea. In 1997 and 1998, altogether 825 Carlin‐tagged salmon were released to continue their upstream migration. Of these, 800 could be sexed and categorized as reared (91%) or wild (9%) salmon. In 1997, most of the ascending salmon were multi‐sea‐winter (MSW) fish, whereas in 1998 almost all were one‐sea‐winter (1SW) male grilse due to the late trapping season. About 10% of all tagged fish were recaptured, two‐thirds of which were caught in the river before their descent to the sea. There was no difference in the recapture rate between salmon of wild (8.5%) or reared (9.5%) origin, or between females (11.6%) and males (9.3%). Generalized linear models for data from 1997 showed that the recapture rate increased with length and age of females, but that the opposite was true for males. River fishing did not seem to remove proportionally more early ascending salmon than fish that ascended later.     

Neuroendocrine and behavioral responses to weak electric fields in adult sea lampreys (Petromyzon marinus)

We characterized the behavioral and neuroendocrine responses of adult sea lampreys (Petromyzon marinus) to weak electric fields. Adult sea lampreys, captured during upstream spawning migration, exhibited limited active behaviors during exposure to weak electric fields and spent the most time attached to the wall of the testing arena near the cathode (−). For adult male sea lampreys, exposure to weak electric fields resulted in increased lamprey (l) GnRH-I mRNA expression but decreased lGnRH-I immunoreactivities in the forebrain, and decreased Jun (a neuronal activation marker) mRNA levels in the brain stem. Similar effects were not observed in the brains of female sea lampreys after weak electric field stimulation. The influence of electroreception on forebrain lGnRH suggests that electroreception may modulate the reproductive systems in adult male sea lampreys. The changes in Jun expression may be associated with swimming inhibition during weak electric field stimulation. The results for adult sea lampreys are the opposite of those obtained using parasitic-stage sea lampreys, which displayed increased activity during and after cathodal stimulation. Our results demonstrate that adult sea lampreys are sensitive to weak electric fields, which may play a role in reproduction. They also suggest that electrical stimuli mediate different behaviors in feeding-stage and spawning-stage sea lampreys.     

The post‐spawning movements of migratory brown trout Salmo trutta L.

The post spawning behaviour of sea trout Salmo trutta was studied over a 2 year period in the river and estuary of the River Fowey, south‐west England. Forty‐five sea trout kelts were trapped immediately after spawning in December and intraperitoneally tagged with miniature acoustic transmitters. The subsequent emigration into coastal waters was monitored using acoustic receivers deployed throughout the river catchment. The levels of gill Na⁺K⁺ATPase activity in sea trout kelts sampled at the same time as the tagged fish were within the range of 2·5 to 4·5 μmol Pi per mg protein per h indicating that the post‐spawning fish were not physiologically adapted to salt water. The tagged kelts were resident in fresh water between 4 and 70 days before entering the estuary. Sixty two per cent of the tagged kelts subsequently migrated successfully into coastal waters, with a higher success rate for male fish (75%) than females (58%). There was a significant size related difference in the run‐timing of the kelts with the larger fish moving more quickly into coastal waters after spawning than smaller fish. Seaward migration within fresh water was predominantly nocturnal and generally occurred in conjunction with increasing river discharge and rising water temperature. Migration through the estuary continued to be predominantly nocturnal and occurred during an ebbing tide. Residency within the estuary varied amongst individuals although it was invariably short, with most fish moving out into coastal waters within one to two tidal cycles. Five tagged kelts returned from the coastal zone and re‐entered fresh water during April and June. Marine residence time varied between 89 and 145 days (mean 118 days) and the minimum estimated marine survival was c. 18%. One of these sea trout was subsequently recaptured after successfully spawning in the vicinity where it had been previously tagged demonstrating a degree of spawning site fidelity.     

Freshwater and coastal migration patterns in the silver‐stage eel Anguilla anguilla

The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north‐west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver‐stage A. anguilla (total length, L_T, range: 332–520 mm) were trapped 152 km upstream from a coastal marine sea‐lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater (FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea‐lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea‐lough, so this suggests high levels of mortality during sea‐lough migration, or less likely, long‐term sea‐lough residence by silver A. anguilla emigrants. This has important implications for eel management plans.