Combining limnological and palaeolimnological approaches in assessing degradation of Lake Pskov

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were captured. Electronic supplementary material  Supplementary material is available for this article at and accessible for authorized user     

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.     

Pre-spawning migration of adult Pacific lamprey, <Emphasis Type="BoldItalic">Entosphenus tridentatus</Emphasis>, in the Willamette River,Oregon, U.S.A.

We describe the migration distances and timing of the adult Pacific lamprey, Entosphenus tridentatus, in the Willamette River Basin (Oregon, U.S.A.). We conducted aerial surveys to track radio-tagged fish upstream of a major waterfall and hydropower complex en route to spawning areas. We detected 24 out of the 43 fish that passed the waterfall-hydropower complex. Of the detected fish, 17 were detected multiple times. Their maximum migration distance upstream in the mainstem Willamette approximated a normal distribution. The maximum distance migrated upstream did not significantly correlate with total body length (r = −0.186, P = 0.385) or date that the fish passed Willamette Falls (r = −0.118, P = 0.582). Fish migrated primarily during the spring to early summer period before stopping during the summer, when peak river temperatures (≥20°C). However, at least three fish continued to migrate upstream after September. Behavior ranged from relatively slow migration, followed by holding; to rapid migration, followed by slow migration further up in the basin. This study provides a basis for informing more detailed research on Pacific lamprey in the future.     

Evidence of changing migratory patterns of wild Atlantic salmon Salmo salar smolts in the River Bush,Northern Ireland,and possible associations with climate change

The migration patterns, timing and biological characteristics of wild Atlantic salmon Salmo salar smolts in the River Bush, Northern Ireland, were examined over the period 1978–2008. A distinct change in the timing of the smolt run was detected with progressively earlier emigration periods evident across the time series. The shift in run timing ranged from 3·6 to 4·8 days 10 years^?1 for a range of standard migratory audit points. The timing of smolt emigration has been linked to ambient river temperature patterns. Distinct seasonal patterns were evident for biological characteristics of River Bush smolts with mean age and fork length decreasing throughout the emigration period. Marine survival patterns in 1 sea winter River Bush S. salar were strongly influenced by the run timing of the preceding smolt year such that later emigrating cohorts demonstrated increased survival. Possible mechanisms for this relationship based on local climatic variation have been explored, including the effect of potential thermal mismatch between freshwater and marine environments.     

The Influence of Discharge on Duration,Ascent Distance,and Fidelity of the Spawning Migration for Paddlefish of the Yellowstone-Sakakawea Stock,Montana and North Dakota,USA

Paddlefish, Polyodon spathula, of the Yellowstone-Sakakawea stock, Missouri and Yellowstone Rivers, Montana and North Dakota, were radio-tagged to assess the influence of spring discharge on duration of river residency, ascent distance, and site-fidelity during spawning migrations of 1999–2002. Contrary to expectations and reported results from other paddlefish populations, fish remained in the river for similar periods of time and ascended to similar reaches in years of higher, more sustained discharge and in years of lower, more fluctuating discharge. In all years, 65 of the 74 migrants (88%) restricted their ascent to reaches below Yellowstone River kilometer (YRkm) 55; only six migrants were found to further ascend to upriver reaches within 20 river kilometers (rkm) of the Intake Diversion Dam (YRkm 114). The lack of detectable annual differences in ascent distance over the study period despite annual differences in Yellowstone River spring flow regimes may have been partially attributed to the apparent site-fidelity demonstrated by the tagged fish over the study period. Ten of the 22 paddlefish contacted in more than one spring migration repeatedly limited their upriver movement to sites that were within 10 rkm of each other. In addition, similar to the reproductive homing tendencies documented in other large-river migratory fishes, site-fidelity occurred in different reaches of the river system. Results from this study suggest that, in years of moderate discharge, site-fidelity may be as influential as the spring flow regime in determining the reaches to which migratory paddlefish ascend. Further research is needed to investigate potential differential spawning success in fish that return to different reaches of the lower Yellowstone River.     

Development of blooms of <Emphasis Type="Italic">Cyclotella meneghiniana</Emphasis> and <Emphasis Type="Italic">Nitzschia</Emphasis> spp. (Bacillariophyceae) in a shallow river and estimation of effective suppression flows

Diatom blooms in the middle reaches of the shallow, freshwater, Hunter River, Australia, are a frequent nuisance to river users. During a 4-year study, blooms of Cyclotella meneghiniana and Nitzschia spp. coincided with water temperatures above 23°C and flows below 400 Ml d⁻¹ that lasted for more than 12 days. Redundancy analysis showed that water temperature was positively related, and antecedent flow was negatively related, to the abundance of both taxa. Addition experiments indicated that nutrients are seldom limiting to growth. It is suggested that a combination of faster growth rates at higher temperatures and longer retention times at low flows allows bloom populations to develop. Simulation modelling showed that flow regulation and water extraction have decreased flows in the river during summer, and consequently have probably increased the number of diatom blooms. Environmental flows have been provided to the river, but are not sufficient to prevent blooms. Discharges required for bloom suppression are described.     

Annual variability in upstream migration of glass eels in a southern USA coastal watershed

We investigated the environmental factors that affected temporal variability of eel recruitment and upstream migration in a freshwater coastal river along the southeastern US. Glass eels Anguilla rostrata were collected through ichthyoplankton sampling in the lower Roanoke River, North Carolina. Monthly samples were taken from fixed stations from May 2001 through June 2003. There was no evidence of consistent seasonal migration patterns for glass eels in Roanoke River. From May through December in 2001, glass eels were captured only during August. In 2002, glass eels arrived in February and remained in ichthyoplankton samples through October, with the exception of samples from September. Peak catch occurred in March at 4.02 ± 1.2 and declined through June to 0.18 ± 0.07 (#/1,000 m³). By August, the mean density increased to 0.96 ± 0.82 and to 3.59 ± 2.77 by October. In 2003 from January through June, glass eels were captured only during February and March. Glass eels were routinely collected when river discharge rates were <150 m³ s⁻¹. River discharge rates >650 m⁻³ s⁻¹ resulted in no glass eels in our samples. Upstream migration during 2002 was not correlated with water temperature or related to lunar phase. Glass eel freshwater upstream migration was initiated when water temperatures exceeded a threshold range of 10°C to 15°C; however, glass eels continued to migrate when water temperatures approached 30°C. The overall negative effect of river discharge suggests that changes in the water release schedules of upstream hydroelectric facilities during glass eel migration could strongly influence their recruitment success.     

Alternative migration and host parasitism strategies and their long-term stability in river lampreys from the River Endrick, Scotland

The stability of a discrete body size dimorphism of sexually mature river lamprey Lampetra fluviatilis from the River Endrick, Scotland, was examined over a 21 year period. Stable isotope analysis was used to test the hypothesis that the two size forms comprise individuals with differing migration and parasitic foraging strategies. Maturing river lamprey and the brook lamprey Lampetra planeri were trapped over 3 months each year in the periods 1983–1984 and 2004–2005. Brook lamprey catches and catches of both species combined showed no significant trend in catch rate with time. The catch rate of small body size river lamprey declined between 1983–1984 and 2004–2005 (although the difference did not reach statistical significance; P = 0·055). In contrast, there was a significant increase in the catch rate of the large body size river lamprey and as a consequence, a significant change in the relative proportion of each of the two river lamprey morphs over the study period. Analysis of the stable isotopes of C and N in muscle tissue showed that brook lamprey tissue derived its carbon from a freshwater source and had a δ¹³C more consistent with that of the River Endrick than with Loch Lomond. δ¹⁵N values for this species showed it to be feeding at the base of the food chain, consistent with filter feeding as an ammocoete. The large body size and the small body size river lamprey adults differed substantially in their δ¹³C values, with the small body size δ¹³C signature indicative of a freshwater carbon source and the large body size morph of a marine source. The small body size morph had a δ¹³C signature that was consistent with that of Loch Lomond powan Coregonus lavaretus suggesting that they share a common carbon source. The large body size morph was clearly feeding at a higher trophic level than the small body size morph. A single small body size river lamprey individual with typical morphology for that group, however, had C and N signatures that clustered with those of the large body size morphs. This individual had either migrated to sea to forage, as is typical for the species, or had been feeding on an anadromous fish with a strong marine C signature in fresh water. It is concluded that the body size dimorphism is indicative of a differential migration and foraging strategy in the parasitic phase of the life cycle of river lamprey at this site.     

Upstream migration rates of radio‐tagged adult Chinook salmon in riverine habitats of the Columbia River basin

Upstream migration rates were assessed for 1801 radio‐tagged adult spring–summer Chinook salmon Oncorhynchus tshawytscha through 12 unimpounded river reaches in the Columbia River basin from 1997 to 2002. Reaches were 36 to 241 km long (mean = 130 km) and included sections of the large Columbia and Snake Rivers and smaller free‐flowing tributaries. Median Chinook salmon migration rates ranged from <10 km day⁻¹ in the Deschutes and Clearwater Rivers to >35 km day⁻¹ in the Columbia and Snake Rivers. Using multivariate analyses, migration date explained the most variance in Chinook salmon migration rates while river discharge, migration year and migration reach were secondary. Both within and between years, Chinook salmon migrated more rapidly as migration date increased and more slowly when discharge was high. Arrival at high elevation spawning grounds at appropriate times and increased metabolic activity and reproductive maturation may explain the greater power of migration date, relative to river discharge, in predicting migration rates of Columbia basin spring–summer Chinook salmon.     

Foraging activity patterns in the goosander (Mergus merganser) and the red-breasted merganser (M. serrator) in relation to patterns of activity in their major prey species

Summary Diel and seasonal foraging activity patterns of goosanders (Mergus merganser L.) and red-breasted mergansers (M. serrator L.) were studied during the breeding season on the Rickleå River in northern Sweden (64°05N). In addition, the locomotor activity patterns of their most important prey species, the river lamprey (Lampetra fluviatilis (L.)) and the three-spined stickleback (Gasterosteus aculeatus L.), were recorded.During spring, as mergansers arrived in the breeding area, both species exhibited a bimodal, diurnal pattern of activity with morning and evening peaks. By June (the spawning period for the river lamprey and the migratory period for the three-spined stickleback), goosander activity had shifted to late in the evening. This new activity peak correlated well with the main activity period in the river lamprey. Red-breasted mergansers remained predominantly diurnal throughout the observation period. Their diurnal activity correlated with the activity of their major prey, the three-spined stickleback.Both merganser species utilize a specialized foraging technique, i.e. probing the river-bottom with the bill, to catch hiding fish more or less at random. This behaviour probably helps them to forage during the relatively bright summer nights and thus prey upon the abundant nocturnal river lamprey. The goosander preys upon the river lamprey to a greater extent than does the red-breasted merganser, thus leading to a temporal segregation in food resource utilization between the two duck species.     

Seasonal changes in zooplankton abundance in the lower Rhine during 1987–1991

Zooplankton in the River Rhine was surveyed for five years at the Dutch sampling stations, Lobith (German/Dutch border) and Maassluis (at the point of discharge of the river into the North Sea). The zooplankton abundance showed an apparent seasonal pattern at both stations, characterized by low densities during the winter period, and higher densities during the summer period, with a spring peak. Zooplankton was dominated by rotifers at both stations, although during the winter periods the contribution of copepods was considerable. The rotifers were dominated byBrachionus angularis, B. calyciflorus, Keratella cochlearis andK. quadrata; the copepods by cyclopoid nauplii; the cladocerans by small-sized species mainly belonging toBosmina. At Maassluis the relative contribution of copepods was higher than at Lobith. Furthermore, the zooplankton at Maassluis included the speciesEurytemora affinis, characteristic for estuarine conditions. In spring, the rotifer density and water temperature and rotifer density and chlorophylla concentration were positively correlated. Furthermore, both rotifer density and chlorophylla were inversely correlated with discharge. The possible role of environmental factors (water temperature, chlorophyll content, discharge and biotic factors) controlling the river zooplankton dynamics is indicated.     

Evidence for the genetic basis and epistatic interactions underlying ocean‐ and river‐maturing ecotypes of Pacific Lamprey (Entosphenus tridentatus) returning to the Klamath River,California

Surveys of genomic variation have improved our understanding of the relationship between fitness‐related phenotypes and their underlying genetic basis. In some cases, single large‐effect genes have been found to underlie important traits; however, complex traits are expected to be under polygenic control and elucidation of multiple gene interactions may be required to fully understand the genetic basis of the trait. In this study, we investigated the genetic basis of the ocean‐ and river‐maturing ecotypes in anadromous Pacific lamprey (Entosphenus tridentatus). In Pacific lamprey, the ocean‐maturing ecotype is distinguished by advanced maturity of females (e.g., large egg mass) at the onset of freshwater migration relative to immature females of the river‐maturing ecotype. We examined a total of 219 adult Pacific lamprey that were collected at‐entry to the Klamath River over a 12‐month period. Each individual was genotyped at 308 SNPs representing known neutral and adaptive loci and measured at morphological traits, including egg mass as an indicator of ocean‐ and river‐maturing ecotype for females. The two ecotypes did not exhibit genetic structure at 148 neutral loci, indicating that ecotypic diversity exists within a single population. In contrast, we identified the genetic basis of maturation ecotypes in Pacific lamprey as polygenic, involving two unlinked gene regions that have a complex epistatic relationship. Importantly, these gene regions appear to show stronger effects when considered in gene interaction models than if just considered additive, illustrating the importance of considering epistatic effects and gene networks when researching the genetic basis of complex traits in Pacific lamprey and other species.     

Life-history divergence in Chinook salmon: historic contingency and parallel evolution

By jointly considering patterns of genetic and life-history diversity in over 100 populations of Chinook salmon from California to British Columbia, we demonstrate the importance of two different mechanisms for life-history evolution. Mapping adult run timing (the life-history trait most commonly used to characterize salmon populations) onto a tree based on the genetic data shows that the same run-time phenotypes exist in many different genetic lineages. In a hierarchical gene diversity analysis, differences among major geographic and ecological provinces explained the majority (62%) of the overall G(ST), whereas run-time differences explained only 10%. Collectively, these results indicate that run-timing diversity has developed independently by a process of parallel evolution in many different coastal areas. However, genetic differences between coastal populations with different run timing from the same basin are very modest (G(ST) < 0.02), indicating that evolutionary divergence of this trait linked to reproductive isolation has not led to parallel speciation, probably because of ongoing gene flow. A strikingly different pattern is seen in the interior Columbia River Basin, where run timing and other correlated life-history traits map cleanly onto two divergent genetic lineages (G(ST) approximately 0.15), indicating that some patterns of life-history diversity have a much older origin. Indeed, genetic data indicate that in the interior Columbia Basin, the two divergent lineages behave essentially as separate biological species, showing little evidence of genetic contact in spite of the fact that they comigrate through large areas of the river and ocean and in some locations spawn in nearly adjacent areas.     

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.     

Parasitic Attachments by Overwintering Silver Lampreys, Ichthyomyzon unicuspis, and Chestnut Lampreys, Ichthyomyzon castaneus

We present evidence that at least some parasitic-phase silver lampreys, Ichthyomyzon unicuspis, and chestnut lampreys, I. castaneus, remain attached to host fish during the winter. Lake sturgeon, Acipenser fulvescens, harvested through the ice by spearfishers in the Lake Winnebago system in Wisconsin may bear silver lampreys or fresh lamprey wounds, and sturgeon with lamprey marks were significantly larger than sturgeon without them. Silver lampreys collected on paddlefish, Polyodon spathula, in the Wisconsin River in March were not significantly longer than silver lampreys collected previously in late October, but they were significantly heavier, an indication that they were feeding to at least some extent during the intervening period. Other large fish species, including northern pike, Esox lucius, and flathead catfish, Pylodictus olivaris, have been collected or observed during the winter with silver or chestnut lampreys attached. Although energy and nutrient intake by parasitic lampreys may be reduced during the winter, lampreys attached to hosts may also benefit from the hosts' mobility and ability to avoid potentially harmful situations.     

Genetic diversity,endemism and phylogeny of lampreys within the genus Lampetra sensu stricto (Petromyzontiformes: Petromyzontidae) in western North America

Phylogenetic structure of four Lampetra species from the Pacific drainage of North America (western brook lamprey Lampetra richardsoni, Pacific brook lamprey Lampetra pacifica, river lamprey Lampetra ayresii and Kern brook lamprey Lampetra hubbsi) and unidentified Lampetra specimens (referred to as Lampetra sp.) from 36 locations was estimated using the mitochondrial cytochrome b gene. Maximum parsimony and Bayesian inferences did not correspond with any taxonomic scheme proposed to date. Rather, although L. richardsoni (from Alaska to California) and L. ayresii (from British Columbia to California) together constituted a well‐supported clade distinct from several genetically divergent Lampetra populations in Oregon and California, these two species were not reciprocally monophyletic. The genetically divergent populations included L. pacifica (from the Columbia River basin) and L. hubbsi (from the Kern River basin) and four Lampetra sp. populations in Oregon (Siuslaw River and Fourmile Creek) and California (Kelsey and Mark West Creeks). These four Lampetra sp. populations showed genetic divergence between 2·3 and 5·7% from any known species (and up to 8·0% from each other), and may represent morphologically cryptic and thus previously undescribed species. A fifth population (from Paynes Creek, California) may represent a range extension of L. hubbsi into the Upper Sacramento River.     

Comparative phylogeography of bagrid catfishes in Taiwan

A phylogeographic analysis of two bagrid catfishes in Taiwan was conducted using sequence data from a portion of the mitochondrial DNA (mtDNA) control region. For Pseudobagrus brevianalis, which is most probably endemic to Taiwan, a total of eight haplotypes were detected in 189 specimens from nine river systems covering its entire distribution range, from northern to central western areas of the island. Obvious genetic differentiation was observed among its populations (average F _ST = 0.753); in particular, the northernmost Tamsui River population was fixed for a single endemic haplotype. Nested clade phylogeographic analysis (NCPA) indicated that the dispersal center of mtDNA was the area around the Touchien River and Holong River, north to the Miaoli Plateau, in northwestern Taiwan, suggesting both northward and southward dispersal in this species. There was no evidence for the validity of P. taiwanensis, the nominal species described from Taiwan, morphologically similar to P. brevianalis. We confirmed that P. adiposalis was distributed discontinuously in three river systems; analysis of 42 specimens from the rivers indicated a total of four haplotypes and population differentiation (average F _ST = 0.876). Fixation into a largely differentiated haplotype in the northernmost Tamsui River population was also found in this species, but different processes for this phylogeographic pattern were implied for the two species. Comparison with P. ussuriensis, a widespread continental species morphologically similar to P. adiposalis, suggested the possibility that P. adiposalis is a group of local populations of P. ussuriensis in Taiwan. Two migration routes vs. random fixation scenarios for the population structure of P. adiposalis are discussed with information on other fishes and the geological history of the island.     

Habitat use of juvenile white sturgeon in the Kootenai River, Idaho and British Columbia

Ultrasonic telemetry was used to assess habitat features utilized by 36 endangered juvenile white sturgeon, Acipenser transmontanus, in the lower 120 km of the Kootenai River of Idaho, USA and British Columbia, Canada during the summer and early fall of 1999 and 2000. All 36 fish were initially captured in pools using gillnets and released there, but most of the subsequent telemetry contacts were in glides, indicating these fish moved freely between the two macro-habitats. The low electivity indices indicated little preference between glides and pools. Most contacts were in glides, in the outside bend of the river channel (50), and in or near a visually defined thalweg. Contacts were most often associated with sand substrates and no cover. Physical habitat characteristics (nose [bottom] water velocity, depth, substrate, and cover) were recorded at 168 contact locations. The combination of significantly greater velocities and depths at contact sites vs. non-contact sites (p < 0.01) indicated these fish actively found and used areas of higher velocity and greater depth within the Kootenai River. There was little cover found for fish in the river other than large sand dunes and depth. The combination of depth and nose velocity data supported the idea that large sand dunes are providing refugia in the form of velocity breaks.     

Fragmentation by weirs in a riverine system: A study of genetic variation in time and space among populations of European grayling (Thymallus thymallus) in a Danish river system

Human induced habitat alterations affect the genetic structure of many fish populations. Weirs in particular have caused fragmented populations previously connected by gene-flow. We studied the effects of weirs on the distribution of genetic variation within European grayling (Thymallus thymallus) populations from the Skjern River, Denmark. We compared microsatellite data from DNA extracted from historic scale samples collected 60 years ago with data from contemporary samples. Pairwise multilocus F _ST estimates between all contemporary population samples were significant as well as exact tests for population differentiation. Assignment tests of individuals to a set of baseline samples showed correct assignment to the population of origin of between 54 and 79%. Assignment of individuals from recent samples to the historic population samples showed highly variable results (3–83%) of correct assignment suggesting different population histories. Pairwise multilocus F _ST estimates were significantly correlated with the number of intervening weirs but not with waterway distance. A simulation procedure was used to estimate differences in relative population sizes, which indicated that the main river population was approximately three times larger than those of the tributaries. There were no signs of any loss of genetic variation for the river system as a whole during these 60 years. The results show that weirs can be an important factor for creating the current distribution patterns of genetic variation among grayling populations, most likely by only allowing passive downstream drift of fry and obstructing active upstream migration. This revised version was published online in July 2006 with corrections to the Cover Date.