Seasonal changes in the dissolved free amino acid and DOC concentrations in a hypertrophic African reservoir and its inflowing rivers

Dissolved free amino acid (DFAA) concentration and composition and dissolved organic carbon (DOC) concentration were measured over 16 months at three depths in hypertrophic Hartbeespoort Dam, South Africa and in its two perenially inflowing rivers. The range of DFAA concentrations in the reservoir and both rivers were similar with dominant DFAA consisting of serine, glycine, alanine and ornithine in all three systems. The range of DOC concentrations in the rivers was 1.5–11.1 mg l^–1, the major river (Crocodile) having about twice the DOC concentration of the Magalies River. The DFAA/DOC ratios ranged between 0.02–1.1% in the Crocodile River and 0.13–3.7% in the Magalies River. DFAA and DOC concentrations were positively correlated to the Magalies River flow, but for the Crocodile River, which received domestic and industrial effluents, DOC was inversely correlated to flow. The source of DFAA in both rivers was mainly terrestrial, in contrast to the main DOC source in the Crocodile River which was the effluents. The DFAA load of the Crocodile River ranged between 0.22 and 208 kg C d^–1.DOC (5.0–24.8mg l^–1) in Hartbeespoort Dam generally decreased with depth but DFAA (15–4800 nmol l^–1) concentration showed no clear trend. The DFAA/DOC ratios varied between 0.02 and 2.9%. DFAA concentrations were correlated (r = 0.3, n = 30, p = 0.04) with bacterial numbers at 0 and 10 m only while no significant correlations were found with bacterial production, chlorophyll a concentration and phytoplankton primary and EDOC (extracellular DOC) production at any depth. The rate of bacterial utilization of DFAA was low compared with data from other lakes. Diurnal phytoplankton production of DFAA in the euphotic zone of the whole lake was calculated to vary between 268 and 30 780 t C d^–1 indicating autochthonous DFAA sources were dominant to allochthonous DFAA sources. The autochthonous production of DFAA was > 2 × gross bacterial production of the euphotic zone indicating that although DFAA concentrations were frequently < 10 g C l^–1, the rate of DFAA production exceeded bacterial requirements.     

Invertebrate Food Supplies and Diet of Blue Duck on Rivers in 2 Regions of the North Island, New Zealand

Benthic invertebrates and samples of blue duck faeces were collected in September 1988 from sites along Manganuiateao River, central North Island, and in November 1988 from seven rivers and streams on the East Cape. The occurrence of invertebrate taxa in the faeces varied within and between rivers, and within pairs of birds and family groups on the East Cape. In both regions, most blue duck had been consuming large proportions of cased caddisfly larvae. These are thought to have been mainly species of Helicopsyche and Pycnocentrodes at the East Cape sites and Beraeoptera roria at the Manganuiateao sites. Plecoptera larvae were also relatively abundant in blue duck faeces from most Manganuiateao sites in September. Overall, blue duck consumed proportionately more cased caddisfly larvae than occurred in the benthos (especially at the East Cape sites), but fewer Chironomidae, Coloburiscus humeralis and leptophlebiid mayfly (mainly Deleatidium spp.) larvae. Factors that affect the type of invertebrate foods available to blue duck at a particular site could include habitat heterogeneity, chance encounter, frequency and magnitude of floods, and geographic differences in the pool of invertebrate colonists. Apparent selectivity or avoidance of some benthic invertebrate groups by blue duck may partly reflect predator evasion by fast-moving invertebrate species, and differences in activity and distribution on upper stone surfaces where invertebrates should be more susceptible to predation by blue duck.     

海南岛宽额鳢(Channa gachua)群体遗传变异与生物地理过程

为了解海南岛宽额鳢(Channa gachua)的群体遗传分化和亲缘生物地理过程,采集了云南元江和海南岛5个水系(昌化江、陵水河、藤桥河、万泉河及南渡江)共6个种群168个宽额鳢个体,基于线粒体细胞色素b(Cyt b)基因全序列(1142 bp)对其遗传多样性和遗传分化程度进行了评估,并探讨了地质和气候等因素如何塑造了这一物种的亲缘地理结构及演化历史。基于Cyt b序列构建的系统树结果将所有个体分成两个主要谱系(A和B),谱系A包括海南岛所有种群,其中,部分昌化江个体形成独立的亚支(A2),其余个体聚为另一亚支(A1),谱系B为云南元江的全部个体,各谱系间的遗传分化指数均较高。种群历史动态分析表明,各谱系均没有发生种群扩张,但A1亚支与谱系B曾在约1万年前发生过有效种群数量减小的事件。根据研究结果推测,更新世冰期期间,北部湾因海平面下降而暴露,大陆和海南岛的水系发生接触,越南北部水系(包括元江/红河)通过一条联系雷州半岛和海南岛的古河道流入南海,因而冰期期间宽额鳢有机会从元江(红河)扩散至海南岛西南部,随后在海南岛内部,宽额鳢进一步扩散,并以五指山为种群间基因交流的重要地理障碍,各水系间种群发生基因交流和遗传分化。     

Long-term changes in the population size and geographical distribution of Pennella sp. (Copepoda) on the saury,Cololabis saira,in the western North Pacific Ocean and adjacent seas

Changes in the population size and geographical distribution of the mesoparasitic copepod Pennella sp. (Siphonostomatoida: Pennellidae) on the saury, Cololabis saira, were studied for a period of six years (1981–86) in the western North Pacific Ocean and adjacent seas. The parasite was first recorded in the western North Pacific in 1981. Its population size increased rapidly in 1982–83 and declined slightly in 1984. During these years, infected fish were widely distributed in the western and central North Pacific and also found in the Sea of Okhotsk and the Sea of Japan. However, the population declined dramatically in 1985 and its distributional range was reduced. The parasite disappeared in 1986. The observed frequency distributions of parasites on the host population were the Poisson in 1981 and 1985, but those during 1982–1984 were over-dispersed and fitted the negative binomial.Parasites of the saury, Cololabis saira (Brevoort)-IV.     

Morphological characteristics of an introduced threespine stickleback,Gasterosteus aculeatus,from Hasse Lake,Alberta: a first occurrence in the interior plains of North America

Synopsis Threespine stickleback, Gasterosteus aculeatus, are thought to have been introduced into Hasse Lake, Alberta, where they were discovered in 1980. The population has grown in numbers since 1980 and by 1981 was more abundant than the native brook stickleback, Culaea inconstans. This population is the first to be found in the interior plains of North America, and it occurs at a higher elevation than any other Canadian population. The source of this introduced population is unknown. Significant differences among four years were found in several meristic and morphometric characters but no significant trends during 1980–1983 were found. Most characters were well within the range of other populations of the species.     

Clonal Diversity in Introduced Populations of An Asian Sea Anemone in North America

Previous reports hypothesized that introduced populations of the Asian sea anemone Diadumene lineata (Verill, 1870 (Presented 1869) Communications of the Essex Institution 6: 51–104), which reproduces by fission, are often monoclonal or to be composed of few clones. To test this hypothesis, sea anemones were collected from thirteen sites in three non-native regions and one native region: Chesapeake Bay, New England, central California, and Japan. The internal transcribed spacer (ITS) region separating nuclear ribosomal RNA genes was amplified from each individual using PCR and surveyed for DNA sequence variation using single strand conformational polymorphism analysis (SSCP). Fifty-six distinct electrophoretic banding patterns were found in 268 anemones, and each pattern was considered a different genotype. The number of genotypes in a population ranged from one to thirteen. Only one sample (York River, Chesapeake Bay, n = 10) was monoclonal, although six populations were dominated (>50%) by single genotype. Only four genotypes were found in more than one population, and these were confined to single regions. Walker Creek, California was sampled in 1995 and 1997 and no genotypes were found in both years, suggesting rapid shifts in genotype frequency. We conclude that multiple genotypes of D. lineata have invaded North America and that the primary importance of clonal growth for introduced populations is the production of colonizing propagules.     

Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula)

The mottled duck (Anas fulvigula) is a year-round endemicresident of the Gulf Coast and one of two non-migratory dabbling ducksthat inhabit North America. To investigate population genetic structureof allopatric mottled duck populations, we collected 5' control regionsequences (bp 78–774) from the mitochondria of 219 mottled duckssampled at 11 widely spaced geographic localities in Texas, Louisiana,and Florida and compared them to each other and to homologous sequencesfrom 4 Mexican ducks (A. diazi), 13 American black ducks(A. rubripes), and 10 mallards (A. platyrhynchos). Weidentified 57 unique haplotypes composed of 665 or 666 nucleotides inthe 246 control region sequences. Of the 665 homologous positions,8.3% (n = 55) vary among haplotypes, and98.2% (n = 54) of these occur within the first351 nucleotides from the 5' end of the outgroup sequence.Neighbor-joining analysis shows a large distal clade (52.5% ofmottled ducks sampled in our study) composed of two reciprocallymonophyletic clades of mottled duck haplotypes, one of which is endemicto Texas and Louisiana and the other endemic to Florida. No mottledducks sampled in Florida occur in the clade composed of mottled ducksfrom Texas and Louisiana or vice versa, suggesting that (1) an enduringgeographic split has existed for many years between east and west, and(2) gene flow currently is non-existent (or at least undetectable)across the central Gulf Coast. The remaining 47.5% of mottledducks sampled in our study branch basally from this derived clade, showsubstantially less hierarchical structure, and fall into various lineagegroups of mixed species composition with no geographic orspecies-specific pattern. Pairwise F _ST valuescorroborate the pattern of strong differentiation observed betweenTexas/Louisiana and Florida. Our findings are consistent with apattern of partial lineage sorting from a polymorphic ancestral genepool reshuffled by hybridizing mallards. Control region data andpatterns of divergence in mallard-like species worldwide, furthermore,suggest that mottled ducks are close relatives of Mexican ducks, and inturn nested within black ducks. Genetic similarities to nominatemallards are less likely to be the product of common ancestry, but theresult of past hybridization with a dichromatic mallard ancestor thatinvaded North America from Asia many generations ago. Our findings haveseveral important consequences for the conservation biology of mottledducks across the Gulf Coast and our understanding of the phylogeographyof mallard-like species worldwide.     

Chlorophyll content of seston in a regulated Rocky Mountain river,Idaho, USA

The chlorophyll content of seston at four sites in a regulated mid-order Rocky Mountain river, Henry's Fork of the Snake River, Idaho, USA, was examined. Spectrometry was used to determine the amount of chlorophyll a, b, c and in seston and potential organic matter sources including macrophytes, algae, plankton, and terrestial plant litter. The amount of chlorophyll in seston varied among size fractions, sites, and seasons. Coarse seston (6–1 mm) contained the most chlorophyll a (2.3 mg g^–1 ashfree dry mass [AFDM]) followed by ultra fine seston (53–0.3 µm; 1.9 mg g^–1 AFDM), very coarse seston (> 6 mm, 1.8 mg g^–1 AFDM), very fine seston (250–53 µm; 1.3 mg g^–1 AFDM), and fine seston (1–0.25 mm; 0.7 mg g^–1 AFDM). Chlorophyll content of coarse seston was similar at all sites reflecting a common source, aquatic macrophyte debris. Chlorophyll content of coarse and fine seston were highest in fall reflecting the importance of phenology of aquatic plants on sestonic pigment levels. Very fine seston from below a reservoir contained more chlorophyll than seston from downstream and tributary sites suggesting a reservoir source. Terrestial plant litter was chlorophyll depleted compared to autochthonous materials and seston. Most seston was autochthonously-derived from a variety of macrophyte, algal, and planktonic sources. The chlorophyll content of Henry's Fork seston was higher than that reported for similar rivers. Island Park Dam moderates river temperature and flow, enhances autotrophy, and accounts for the consistently high sestonic chlorophyll levels.     

Vertical distribution of Pleuromamma (Copepoda: Metridinidae) across the eastern North Pacific Ocean

Vertical distributions of six species of Pleuromamma at ten stations across the eastern North Pacific Ocean from Honolulu to San Diego were determined from oblique Longhurst-Hardy Plankton Recorder tows to 650 m (350–450 m in the California Current). Vertical resolution was 20 m below 200 m and 5–10 m above. There was considerable overlap in surface layer distributions at night among all co-occurring species; daytime distributions showed less overlap. All species generally occurred deeper both day and night as distance offshore increased. The proportion of a species' population that remained at daytime depths during the night decreased with distance offshore. Warm water species penetrated into the California Current and nearshore region to a much greater extent than cool water species entered central gyre waters.     

Molecular genetic structure and evolution in native and colonized populations of the Chinese mitten crab, Eriocheir sinensis

Chinese mitten crab (Eriocheir sinensis), a native species in China, has populated Continental Europe and North America since 1912. In this paper, the nucleotide variation in the fragments of mitochondrial COII (693 bp), Cytb (766 bp), and nucleotide ITS (706 bp) was analyzed in native (Yantgze, Yellow, and Liaohe Rivers in China) and colonized (Elbe, Rhine, and Thames Rivers in Europe, and San Francisco Bay in North America) populations of the Chinese mitten crab. The major findings are as follows. First, the genetic variability in the native populations is higher than that in the colonized European and North American populations, with the exception of the Elbe River population, which possesses a similar level of variability with the native populations. Second, a remarkable loss of singletons has been associated with the colonization of Chinese mitten crabs. Third, the AMOVA and F _ST results demonstrate that there are no significant genetic differentiations among the populations from the three continents, but there is a significant differentiation between pairwise populations within and among continents. Fourth, it is found that expansion-drift and gene flow pattern are involved in the European populations. The neutrality test and R ₂ statistics suggest that a moderate founder population exists in the colonized populations, and only the Yangtze River population has undergone a recent population expansion. Finally, the results demonstrate that the European populations originate from multiple rivers in China on multiple occasions. The San Francisco population originates from both the native Chinese populations and the colonized European populations, most likely the Thames population.     

Migrating ducks in inland North America ignore major rivers as leading lines

A recently developed radar‐based technique permitted empirical re‐evaluation of the established but poorly supported theory that migrating North American waterfowl (Anatidae) use landscape features such as rivers as leading lines. Ducks departing the Illinois River Valley in the autumn of each of 15 years travelled SSE with a mean track that was 68° different from the 220° course of the Illinois River (P ≤ 0.001). We conclude that leading lines were unimportant navigation aids for ducks leaving this major stopover site in autumn and suggest that rivers have less effect on the spatial course of duck migration than previously thought. Timing of departures was examined in a representative subset of 8 years and found to be consistent, with a mean start time of 44 min after civil sunset.     

A comparison of zygote survival of native and non-native walleye stocks in two Georgian Bay rivers

Synopsis Poor natural recruitment of a Georgian Bay walleye stock that spawns in the Shawanaga River has been attributed to poor survivorship of early life stages. I investigated whether low zygote survival was part of the problem by conducting an in-situ incubation experiment with artificially fertilized eggs from the Shawanaga and the nearby Magnetawan River stocks. Both rivers have low buffering capacity (5–6.5 mg·l^–1 alkalinity), but moderately low pH (5.5) had only been recorded in the Shawanaga. Zygotes were reared in both rivers. Minimum pH during incubation was 6.2 in the Shawanaga and 6.8 in the Magnetawan River. Mean survival rate to hatching strongly favoured the native stock in both rivers (86 vs. 25 % in the Shawanaga River and 80 vs. 40% in the Magnetawan River), and these differences were statistically significant. The results suggest that viability of Shawanaga zygotes is not a problem, but a low pH effect on zygote survival could not be inferred from the relatively high pH of Shawanaga water in the spring of 1990. The large difference in hatching success between native and non-native stocks was unexpected, and may have been the result of stock-specific adaptation to differing cation: anion and/or metal concentrations in the two rivers, or to some other factor.     

Distribution and Seasonal Abundance of Trematode Parasites (Trematoda: Allocreadiidae: <Emphasis Type="Italic">Crepidostomum</Emphasis> spp.) in burrowing-mayfly nymphs (Ephemeroptera: Ephemeridae: <Emphasis Type="Italic">Hexagenia</Emphasis> spp.) from Connecting Rivers of the Laurentian Great Lakes

Burrowing-mayfly nymphs such as Hexagenia spp. have been used extensively in North America and Europe as a biomonitoring tool to indicate mesotrophic water quality, yet infestation by associated parasites has not been well documented. We performed laboratory analysis of archived samples of Hexagenia spp. nymphs collected in 1985 and 1986 to provide base-line data on the distribution (1985) and seasonal infestation (1986) of the trematode parasite Crepidostomum spp. in Hexagenia spp. nymphs in connecting rivers between Lakes Superior and Erie of the Laurentian Great Lakes. In May and June 1985, frequency of occurrence of metacercariae was widely distributed throughout the connecting rivers (63% of 203 stations with nymphs), except in areas where nymph densities were relatively low (i.e.,≤69 nymphs/m²). Distribution was probably underestimated in the present study because of low probability (mean = 31%, range = 0–57%) of detecting infestation in a small number of collected nymphs ( ≤10) at nymph densities ≤69/m². In 1986, seasonal infestation between April and October occurred in 3.3% (627) of 18696 nymphs. Overall prevalence, mean intensity, and mean abundance of parasites at one station in the St. Marys River indicate parasite transmission occurred between June and September. This period of transmission is dependent on the life-cycle of the parasite. In addition, the life-cycle of Hexagenia spp. determines which annual cohort of nymphs is infested and therefore, the duration of infestation. Although, no impacts of infestation on Hexagenia spp. nymphs were observed in the present study, infestation intensities were high enough (≥25 metacercariae per nymph) at one station in the St. Marys River to potentially cause tissue damage in a high proportion (53%) of infested nymphs.     

Basin-scale Patterns in the Drift of Embryonic and Larval Fishes and Lamprey Ammocoetes in two Coastal Rivers

We studied the distribution and abundance of drifting embryonic and larval fishes and lampreys in the Smith and Van Duzen rivers of northern California, U.S.A. We collected seven fish species in four families and at least one lamprey species in the drift. All taxa drifted almost exclusively at night. Sculpins, Cottus aleuticus and C. asper, outnumbered all other taxa, comprising 63% of the catch in the Van Duzen River and 90% of the catch in the Smith River. We estimated that sculpin drift reached 3×10⁷ individualsh^–1 during the relatively high flow period from late winter through early summer. Most sculpin in these two rivers appeared to drift to the estuaries; we estimated 2.5×10⁹ sculpin embryos and larvae reached the Smith River estuary in 1995. In contrast to the sculpins, the patterns in the drift of other taxa suggest limited transport to the estuaries. Suckers, Catostomus occidentalis in the Van Duzen River, C. rimiculus in the Smith River, threespine stickleback, Gasterosteus aculeatus, and lamprey, Lampetra tridentata and possibly L. richardsoni, drifted at much lower rates and later in the year than sculpins. In the Van Duzen River, drift appeared to serve as a dispersal mechanism for only one of three introduced cyprinids. California roach, Lavinia symmetricus, drifted at low rates throughout the summer while we captured only seven Sacramento pikeminnow, Ptychocheilus grandis, and no speckled dace, Rhynichthys osculus. The information gathered on the drift of early life history phases is germane to both the conservation of native fishes and management of non-indigenous species in coastal rivers.     

Food habits of sika deer in the Shiranuka Hills,eastern Hokkaido: a northern example from the north–south variations in food habits in sika deer

Seasonal changes in the composition of the diet of the sika deer population in the Shiranuka Hills, eastern Hokkaido, in 1998 were determined by fecal analyses. The deer were dependent on Sasa nipponica, a dwarf bamboo, throughout the year, particularly in winter when it accounted for as much as 77.7% of the diet. It accounted for 33.1% and 45.6% in spring and summer, respectively, and this decreased to 12.2% in autumn. Besides S. nipponica, all the graminoid categories accounted for large amounts (66–96.7%), while dicotyledonous plants accounted for little (3–8%) except in autumn when they accounted for 31%. The strong dependence of the Shiranuka population on graminoids was different from other Hokkaido deer populations, for example the population from Ashoro/Onbetsu and the extremely high density population on Nakanoshima Island. In spite of these differences, food for all Hokkaido sika deer was poor in winter. Along the north–south geographical cline in the food composition of sika deer along the Japanese archipelago, the Shiranuka population was positioned as a grazer type, in contrast to the southern populations. However, it is important to note that variations are great among local populations in Hokkaido.     

Genetic diversity and divergence of the endangered freshwater goby Rhinogobius sp. BB in Okinawa Island

The genetic diversity and population structure of Rhinogobius sp. BB, the fluvial landlocked endangered goby, were investigated and were compared with those of the closely related amphidromous Rhinogobius sp. MO at 11 microsatellite loci. Specimens of Rhinogobius sp. BB were collected from the Genka and Takae-A rivers, and those of Rhinogobius sp. MO were collected from the Genka and Suginda rivers in Okinawa Island. At 11 microsatellite loci, the two populations of Rhinogobius sp. BB showed lower variation than the two Rhinogobius sp. MO populations: the average number of alleles was 3.6 and 2.0 vs. 8.6 and 7.6, respectively; and the observed heterozygosity was 0.263 and 0.281 vs. 0.440 and 0.545, respectively. Pairwise F_st tests showed significant differences (P < 0.001) among the populations: F_st was 0.525 between the two Rhinogobius sp. BB populations, 0.079 between the two Rhinogobius sp. MO populations, and varied from 0.456 to 0.462 for comparisons among Rhinogobius sp. BB and MO. Nei’s genetic distance between the two Rhinogobius sp. BB populations is extremely large (0.604) compared with that between the two Rhinogobius sp. MO populations (0.126). The two populations of Rhinogobius sp. BB are genetically divergent, and they have extremely low genetic diversity. Therefore, the conservation of Rhinogobius sp. BB in Okinawa Island requires the assessment of each river’s population.     

Distribution and dispersal capacity of the Ponto-Caspian tubificid oligochaete Potamothrix moldaviensis Vejdovský et Mrázek, 1903 in the Baltic Sea Region

Over the last few centuries, several Ponto-Caspian tubificid oligochaetes have gradually dispersed from the Black Sea – Caspian Sea region to the north-west and west over Europe. The present world distribution comprising also the Great Lakes of North America clearly demonstrates that anthropochorous vectors of dispersal are involved. Passive transportation in the ballast water of ships has radically changed the possibilities of dispersal for many invertebrate species and has even made dispersal between continents possible. The construction of navigable canals has furthermore facilitated the crossing of watersheds and continents. Other likely vectors of longway dispersal for oligochaetes, as well as for other small-size aquatic invertebrates, are birds and mammals. The dispersal of the Potamothrixspecies is likely to have taken place in successive waves (three) with front-lines still on the move from the east to the west over the Baltic States and Scandinavia. The rheophilous species Potamothrix moldaviensishas presently reached – apart from the large rivers of Russia and many Central-European water bodies – also the Baltic States and south-eastern Sweden. Trajectories of dispersal demonstrate routes across the Baltic Sea – via the ballast water of ships. In the largest rivers of the Eastern Baltic Region (Neva, Daugava, Nemunas), downstream dispersal is the most likely way of transportation. P. moldaviensis together with P. heuscheri(second wave) and P. vejdovskyi(third wave) are presently forming front-lines running obliquely from the north-east to the south-west over south Sweden. In mesotrophic-eutrophic basins of eastern Lake Mälaren, the abundance as well as the species diversity of oligochaetes is particularly high wherever Ponto-Caspian Potamothrixspecies – often several species together – are involved.     

Phosphate requirement of Anabaena oscillarioides and its ecological implications

Anabaena oscillarioides (pure culture isolated from Waikato River, lat. 38°S, long. 176°E, North Island, New Zealand) was shown to be phosphorous deficient with low internal cellular phosphours content and high induced alkaline phosphatase activity when it was grown in membrane-filtered river water in batch cultures under defined laboratory conditions. The calculated relatively high Ks (half-saturation substrate constant) for inorganic phosphate is 67 µg 1^–1, which is above usual river level for the nutrient. This explains the low density of the algae in the river where maximum growth is limited by low phosphorus concentration and the algae survive at suboptimal growth rate. Growth rate of the algae is proportional to phosphate concentration up to 100 µg 1^–1 beyond which increases in phosphate concentration only affects final yield. When the river was supplemented with 100 µg 1^–1 phosphate, the deficiency symptoms disappeared and the doubling time was reduced from two days to half a day.     

Dynamics of phytoplankton growth in the Waikato River,North Island,New Zealand

The Waikato River (latitude 38°S, longitude 176°E, North Island, New Zealand) is overwhelming y dominated by diatoms (mainly Melosira species) while blue-green and green algae are of minor importance. Both laboratory and in situ nutrient enrichment experiments showed enhanced growth of natural and index blue-green and green algae by addition of phosphate and nitrate. These algae were also shown to require higher temperature and light intensity than the diatoms. On the other hand, Waikato River with its higher silica content, moderate range of temperature and running water habitat was more favourable an environment for diatoms.     

The contribution of newly established populations to the dynamics of range expansion in a one-dimensional fluvial-estuarine system: rainbow trout (Oncorhynchus mykiss) in Eastern Quebec

Aim Rainbow trout (Oncorhynchus mykiss, Walbaum 1792) is an exotic salmonid invading eastern Canada. First introduced for recreational fishing in Ontario, Quebec and the Maritime provinces, the species is now spreading in salmon rivers located in Eastern Quebec, where its stocking is strictly forbidden. Newly established populations have been found along the St Lawrence Estuary. To effectively mitigate the potential threat the invasion poses to native salmonids, we aimed to document the invasion’s origin and progress in the St Lawrence River and estuary. We first determined genetic origins among several potential wild and cultured source populations, found at the upstream and downstream extremities of the St Lawrence system. Thereafter, we studied the range expansion, predicting that the invasion process conforms to a one‐dimensional stepping‐stone dispersion model. Location Recently invaded salmon rivers that flow into the Estuary and Gulf of St Lawrence in Quebec, and watercourses supporting naturalized populations (Lake Ontario, Lake Memphremagog and Prince‐Edward‐Island rivers). Methods Rainbow trout from 10 potential source populations (wild and domestic strains) and 243 specimens captured in salmon rivers were genotyped at 10 microsatellite loci. Genetic origins of specimens and relationship between colonies were assessed using assignment analyses based on individuals and clusters. Results Invasion of rainbow trout in Eastern Quebec is directed downstream, driven by migrants from upstream naturalized populations, found in the Ganaraska River (Lake Ontario), and, to a lesser extent, in Lake Memphremagog. Populations from the Maritime provinces and domestic strains do not contribute to the colonisation process. A recently established population in Charlevoix (Eastern Quebec) supplies other downstream colonies. Main conclusions Rainbow trout is spreading from Lake Ontario downstream to Eastern Quebec using the St Lawrence River system as an invasion corridor. Range expansion in a downstream direction is driven by a more complex stepping‐stone dispersion model than predicted. Management options to protect native salmonids include reducing the effective size of the Charlevoix population, impeding reproduction in recently colonized rivers, halting the upstream migration of anadromous spawners, and curtailing stocking events inside the stocking area.