Deposition of sediments during a flood event on seasonally flooded forests of the lower Orinoco River and two of its black-water tributaries, Venezuela

Deposition of suspended sediments andtheir associated nutrients were estimated during theflood event of 1995 in the seasonally flooded forestsof the Mapire and Caura Rivers, two black-watertributaries of lower Orinoco, and on two islands ofthis white-water river. The deposition spanned a widerange from 0.07 kg m^–2 in the depositional barforests of the Mapire River to 73.60 kg m^–2 onthe flooded forests of the Orinoco Island site calledJarizo. This variation is associated with the dynamicnature of sediment mobilization, transport anddeposition, as well as with the different geomorphicenvironments and erosion processes upstream from thestudy sites. The deposited sediment in all the studyareas was highly quartzitic with a relatively highcontent of kaolinite and goethite. Only in thesediment of the Orinoco Islands was mica (illite)identified in a relatively high proportion. Thesemineralogical results reflect the intense weatheringprocesses in the catchment areas of the study rivers.The chemical composition of the deposited sedimentsshowed a great variability among the different studyareas, which is in part related to the mineralcomposition of the sediments and their particle sizedistribution. The highest concentrations of K, Caand Mg were found on the clay sediments of the Orinocoagricultural island. The total amount of depositednutrients varied over a wide range, which isinfluenced by the amount of deposited sediments. Inthe Jarizo Island site of lower Orinoco were depositedthe largest amount of nutrients. In the floodedforests of the Mapire River, the nutrient contributionby the deposited sediments to the nutrient cycling isrelatively low in the depositional-bar forests andpractically nonexistent in the forests sites onterraces.     

Effects of periodic flooding on the water chemistry and primary production of the Mapire systems (Venezuela)

The Mapire river mouth forms a complex floodplain system, where the river behaves as a river during the dry season, but changes to a transient lake which partially covers the inundation forest during the rainy season. Thus, we expected changes in water chemistry and a gradual increase of primary production during high waters. The system was sampled monthly for one year; two floodplain lakes were also studied for comparative purposes. Variations in the concentration of macro- and micronutrients occurred in a pulse-like manner and seemed to relate to mechanisms at work in the transient lake. Dissolved oxygen showed a stratification with low values at the bottom, but never reached anoxia. Net and gross primary production and respiration did not show any clear spatial pattern, reflecting a mosaic of different biochemical states within the transient lake. Heterotrophy tended to prevail in the transient lake, while autotrophy dominated floodplain lakes.     

Aquatic vegetation of the Orinoco River Delta (Venezuela). An overview

The Orinoco River Delta is a complex of relatively unknown ecosystems made up of aquatic and semiaquatic habitats. The region includes a Mariusa National Park and the Orinoco Delta River Biosphere Reserve. The 23 sites studied included lentic habitats (lagoons and creeks) and lotic habitats (streams of variable breadth and current) which varied range from black to white waters. A collection of aquatic vascular plants was made and the physical and chemical variables were measured. A total of 100 species were identified, 48% of which are new records for the Delta territory. A Canonical Correspondence Analysis divided the species and communities into two groups: The lentic habitats of lakes and lagoons, which show a greater species richness and the lotic habitats of the main river courses. This study forms part of an ongoing research project on the floristic and abiotic characteristics of the aquatic communities in the Orinoco River Delta.     

Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation

Abstract The three living species of manatees, West Indian (Trichechus manatus), Amazonian (Trichechus inunguis) and West African (Trichechus senegalensis), are distributed across the shallow tropical and subtropical waters of America and the western coast of Africa. We have sequenced the mitochondrial DNA control region in 330 Trichechus to compare their phylogeographic patterns. In T. manatus we observed a marked population structure with the identification of three haplotype clusters showing a distinct spatial distribution. A geographic barrier represented by the continuity of the Lesser Antilles to Trinidad Island, near the mouth of the Orinoco River in Venezuela, appears to have restricted the gene flow historically in T. manatus. However, for T. inunguis we observed a single expanding population cluster, with a high diversity of very closely related haplotypes. A marked geographic population structure is likely present in T. senegalensis with at least two distinct clusters. Phylogenetic analyses with the mtDNA cytochrome b gene suggest a clade of the marine Trichechus species, with T. inunguis as the most basal trichechid. This is in agreement with previous morphological analyses. Mitochondrial DNA, autosomal microsatellites and cytogenetic analyses revealed the presence of hybrids between the T. manatus and T. inunguis species at the mouth of the Amazon River in Brazil, extending to the Guyanas and probably as far as the mouth of the Orinoco River. Future conservation strategies should consider the distinct population structure of manatee species, as well as the historical barriers to gene flow and the likely occurrence of interspecific hybridization.     

Common Distribution Patterns of Marsupials Related to Physiographical Diversity in Venezuela

The aim of this study is to identify significant biotic regions (groups of areas with similar biotas) and biotic elements (groups of taxa with similar distributions) for the marsupial fauna in a part of northern South America using physiographical areas as Operational Geographical Units (OGUs). We considered Venezuela a good model to elucidate this issue because of its high diversity in landscapes and the relatively vast amount of information available on the geographical distribution of marsupial species. Based on the presence-absence of 33 species in 15 physiographical sub-regions (OGUs) we identified Operational Biogeographical Units (OBUs) and chorotypes using a quantitative analysis that tested statistical significance of the resulting groups. Altitudinal and/or climatic trends in the OBUs and chorotypes were studied using a redundancy analysis. The classification method revealed four OBUs. Strong biotic boundaries separated: i) the xerophytic zone of the Continental coast (OBU I); ii) the sub-regions north of the Orinoco River (OBU III and IV); and those south to the river (OBU II). Eleven chorotypes were identified, four of which included a single species with a restricted geographic distribution. As for the other chorotypes, three main common distribution patterns have been inferred: i) species from the Llanos and/or distributed south of the Orinoco River; ii) species exclusively from the Andes; and iii) species that either occur exclusively north of the Orinoco River or that show a wide distribution throughout Venezuela. Mean altitude, evapotranspiration and precipitation of the driest month, and temperature range allowed us to characterize environmentally most of the OBUs and chorotypes obtained.     

Fish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basins

Aim The aim of this study was to determine whether the Casiquiare River functions as a free dispersal corridor or as a partial barrier (i.e. filter) for the interchange of fish species of the Orinoco and Negro/Amazon basins using species assemblage patterns according to geographical location and environmental features. Location The Casiquiare, Upper Orinoco and Upper Negro rivers in southern Venezuela, South America. Methods Our study was based on an analysis of species presence/absence data and environmental information (11 habitat characteristics) collected by the authors and colleagues between the years 1984 and 1999. The data set consisted of 269 sampled sites and 452 fish species (> 50,000 specimens). A wide range of habitat types was included in the samples, and the collection sites were located at various points along the entire length of the Casiquiare main channel, at multiple sites on its tributary streams, as well as at various nearby sites outside the Casiquiare drainage, within the Upper Orinoco and Upper Rio Negro river systems. Most specimens and field data used in this analysis are archived in the Museo de Ciencias Naturales in Guanare, Venezuela. We performed canonical correspondence analysis (CCA) based on species presence/absence using two versions of the data set: one that eliminated sites having < 5 species and species occurring at < 5 sites; and another that eliminated sites having < 10 species and species occurring at < 10 sites. Cluster analysis was performed on sites based on species assemblage similarity, and a separate analysis was performed on species based on CCA loadings. Results The CCA results for the two versions of the data set were qualitatively the same. The dominant environmental axis contrasted assemblages and sites associated with blackwater vs. clearwater conditions. Longitudinal position on the Casiquiare River was correlated (r² = 0.33) with CCA axis‐1 scores, reflecting clearwater conditions nearer to its origin (bifurcation of the Orinoco) and blackwater conditions nearer to its mouth (junction with the Rio Negro). The second CCA axis was most strongly associated with habitat size and structural complexity. Species associations derived from the unweighted pair‐group average clustering method and pair‐wise squared Euclidean distances calculated from species loadings on CCA axes 1 and 2 showed seven ecological groupings. Cluster analysis of species assemblages according to watershed revealed a stronger influence of local environmental conditions than of geographical proximity. Main conclusions Fish assemblage composition is more consistently associated with local environmental conditions than with geographical position within the river drainages. Nonetheless, the results support the hypothesis that the mainstem Casiquiare represents a hydrochemical gradient between clearwaters at its origin and blackwaters at its mouth, and as such appears to function as a semi‐permeable barrier (environmental filter) to dispersal and faunal exchanges between the partially vicariant fish faunas of the Upper Orinoco and Upper Negro rivers.     

Large-scale spheroidal redoximorphic features around plinthite nuclei in Orinoco River sediments reflect mean seasonal fluctuation in river stage and ENSO-related anomalies

In sediments emerging on the scarp of Lower Orinoco River, Venezuela, we have discovered and studied large (0.5 m) features formed by a plinthite nucleus surrounded by evenly spaced concentric spheroidal structures of iron oxides separated by depletion zones. These features are located in sediments subjected to the mean annual river fluctuation (approx. 14 m) and hence are submerged for several months each year. To the best of our knowledge, structures like these have never been reported or studied. The nuclei and concentric ring formations found in the Orinoco sediments represent an extreme case of regular currently alternating redox conditions. Here we show that the concentric ferric rings surrounding the nuclei could be the result of repeated cycles of diffusion of ferrous ions during flood and subsequent precipitation as ferric oxide during the dry period, thus reflecting the seasonal fluctuation in river level. Our results are consistent with a simple proposed model of ferrous iron diffusion/oxidation according to the flood/dry intervals imposed by river dynamics. This paper is a contribution toward understanding these redoximorphic features (RFs) by: (1) describing their composition and mineralogy; (2) suggesting a possible mode of their formation using the switch to reducing conditions and diffusion of soluble Fe during flood, and its subsequent oxidation and hence immobilization and partial crystallization once exposed to the air; (3) by confirming how this theoretical approach fits the actual pattern of river hydrology in Orinoco, both under average conditions, and as modified by climatic extreme conditions influenced by the El Niño/La Niña Southern Oscillation (ENSO) affecting the ratio of flood/emergence.     

Transport of major solutes and the relationship between solute concentrations and discharge in the Apure River,Venezuela

The Apure River is a major white-water tributary of the Orinoco River in Venezuela. The Apure is rich in solutes; its contribution to dissolved inorganic solids in the Orinoco (24%) is proportionately much greater than its contribution to discharge (6%). About 40% of the calcium and bicarbonate at the mouth of the Orinoco originate in the Apure drainage. The relationship between discharge and the concentrations of major solutes in the Apure was characterized with a two-compartment hyperbolic mixing model. Previous applications of the two-compartment model have been based on separate determinations of the model parameter , which is a constant describing watershed hydrology, for each solute from data on concentrations. The use of a weighted mean for all solutes is proposed as a means of assessing the importance of processes other than mixing. The model, when used on the Apure data, shows that a strong dilution effect prevails for sodium, calcium, magnesium, sulfate, and bicarbonate, and that a strong purging effect (increase of concentration with increasing discharge) is characteristic of soluble silicon. Biological immobilization of soluble silicon by diatoms during the season of low discharge is sufficiently large to account for the positive relationship between discharge and the concentration of soluble silicon. Specific transport rates of solutes from the basin are generally higher than global averages. In contrast, specific transport of chloride is low. Atmospheric sources control chloride transport in the Apure watershed; the low transport rates of chloride are probably explained by the great distance between the Apure watershed and the oceanic sources of atmospheric chloride.     

Review of Colombian Conchostraca (Crustacea) — ecological aspects and life cycles — families Lynceidae,Limnadiidae, Leptestheriidae and Metalimnadiidae

This study gives an overview of our current knowledge of the ecology and distribution patterns of Colombian conchostracans. Colombian euphyllopods are generally restricted to the warm tropical lowlands. OnlyCyclestheria hislopi can be found year-round in larger semipermanent waters and living sympatrically with abundant predators, such as planktivorous fish. The other conchostracans are restricted to the typical habitat of temporary waters.Eulimnadia magadalenensis is especially adapted to very short-term temporary ponds in relatively arid zones andE. colombiensis prefers somewhat cooler ponds of a longer duration. The two species can be found sympatrically in intermediate climatic conditions. A third form,Eulimnadia cf. geayi cohabits with the two other species in the lower Magdalena Valley, its ecological role is not clear.Limnadia orinoquiensis is the selvatic substitute of the open savannah conchostracan fauna (mainlyEulimnadia forms) living in pools in forest clearings in the vicinity of the Upper Orinoco.Four species of Lynceidae were found, twoLynceus and twoParalimnetis. Their distribution patterns are not yet clear, they prefer smaller temporary ponds of moderated temperatures. Two undescribed species ofLeptestheria were found, one restricted to the banks of the Orinoco and the other to one locality in the upper Magdalena Valley, living in ponds with a muddy bottom.Metalimnadia serratura was found in special rock pools of the Guiana Shield in the vicinity of the Orinoco, cohabiting with several other conchostracan species, with differential adaptations to very high water temperatures.     

Ecological factors influencing group sizes of river dolphins (Inia geoffrensis and Sotalia fluviatilis)

Living in groups is usually driven by predation and competition for resources. River dolphins do not have natural predators but inhabit dynamic systems with predictable seasonal shifts. These ecological features may provide some insight into the forces driving group formation and help us to answer questions such as why river dolphins have some of the smallest group sizes of cetaceans, and why group sizes vary with time and place. We analyzed observations of group size for Inia and Sotalia over a 9 yr period. In the Amazon, largest group sizes occurred in main rivers and lakes, particularly during the low water season when resources are concentrated; smaller group sizes occurred in constricted waters (channels, tributaries, and confluences) that receive an influx of blackwaters that are poor in nutrients and sediments. In the Orinoco, the largest group sizes occurred during the transitional water season when the aquatic productivity increases. The largest group size of Inia occurred in the Orinoco location that contains the influx of two highly productive whitewater rivers. Flood pulses govern productivity and major biological factors of these river basins. Any threats to flood pulses will likely have an effect on the functionality of these ecosystems and the species living in them.     

Changes in photosynthesis and fluorescence in response to flooding in emerged and submerged leaves of Pouteria orinocoensis

In the seasonally flooded forest of the Mapire River, a tributary of the Orinoco, seedlings remain totally covered by flood water for over six months. In order to characterize the physiological response to flooding and submergence, seedlings of the tree Pouteria orinocoensis, an important component of the forest vegetation, were subjected experimentally to flooding. Flooding was imposed gradually, the maximum level of flood including submerged and emerged leaves. After 45 d a severe reduction of net photosynthetic rate (P _N) and stomatal conductance (g _s) was observed in emerged leaves, whereas leaf water potential remained constant. The decrease in P _N of emerged leaves was associated to an increase in both relative stomatal and non-stomatal limitations, and the maintenance of the internal/air CO₂ concentration (C _i/C _a) for at least 20 d of flooding. After this time, both P _N and g _s became almost zero. The decrease in photosynthetic capacity of emerged leaves with flooding was also evidenced by a decrease in carboxylation efficiency; photon-saturated photosynthetic rate, and apparent quantum yield of CO₂ fixation. Oxygen evolution rate of submerged leaves measured after three days of treatment was 7 % of the photosynthetic rate of emerged leaves. Submersion determined a chronic photoinhibition of leaves, viewed as a reduction in maximum quantum yield in dark-adapted leaves, whereas the chlorophyll fluorescence analysis of emerged leaves pointed out at the occurrence of dynamic, rather than chronic, photoinhibition. This was evidenced by the absence of photochemical damage, i.e. the maintenance of maximum quantum yield in dark-adapted leaves. Nevertheless, the observed lack of complementarity between photochemical and non-photochemical quenching after 12 d of flooding implies that the capacity for photochemical quenching decreased in a non-co-ordinate manner with the increase in non-photochemical quenching.     

Do metacommunity theories explain spatial variation in fish assemblage structure in a pristine tropical river?

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Distribution of the cyanophyte Trichodesmium (Oscillatoriaceae) in the eastern Caribbean Sea: influence of the Orinoco River

Orinoco River influence in the Caribbean Sea, characterized by high nutrient input, causes a decrease of Trichodesmium populations. The Caribbean Time Series (CaTS) station, south of Puerto Rico (17 degrees 36'N 67 degrees 00'W), was monitored for 25 months in order to observe the Trichodesmium abundance pattern and the presence of the river plume. In general, mean Trichodesmium abundance was higher at the surface and decreased with depth. The mean upper water column (surface to 20 m) abundance was 54.1 +/- 32.6 col/m3. Within the sampling period, abundance was highly variable (1-700 col/m3). Correlation between Trichodesmium abundance and wind speed (p=0.002), chlorophyll a concentration (p=0.001), nitrate (p=0.02) and silicate (p=0.003) concentrations were statistically significant. However, Trichodesmium abundance was not correlated with salinity (p=0.70), temperature (p=0.16) and seawater density (p=0.71) variations at CaTS. Eastern Caribbean regions highly influenced by the Orinoco River discharge were devoid of Trichodesmium colonies.     

基于G-SSR和EST-SSR标记的鲫6个群体遗传结构分析

研究同时利用非编码区和编码区微卫星标记(G-SSR和EST-SSR)分析黑龙江、长江、奉化江及淮河水系共6个野生鲫(Carassius auratus)群体的遗传多样性及遗传结构, 并比较2类不同来源SSR用于鲫群体遗传多样性分析的差异。8个G-SSR标记在6个鲫群体中检测到173个等位基因, 平均N_a、N_e、H_o、H_e以及PIC分别为22、12.9、0.769、0.893和0.879, 群体间F_st值介于0.008—0.085, 其中来自黑龙江水系的2个群体与其余水系的所有群体均达到或接近于中等程度的遗传分化, 而长江、奉化江和淮河水系4个群体间的遗传分化程度不明显。Nei’s遗传距离介于0.203—0.701; 根据遗传距离所绘制的UPGMA聚类图将6个鲫群体划分为2个大分支, 其中来自黑龙江水系的2个群体聚为一枝, 其余水系群体聚为另一枝。贝叶斯分析也支持这一结果, 将6个鲫群体划分为2个最佳理论群。利用8个EST-SSR标记在6个鲫群体中共检测到155个等位基因, 平均N_a、N_e、H_o、H_e以及PIC分别为19、9.5、0.728、0.870和0.855; 群体间F_st值和Nei’s遗传距离分别介于0.005—0.084和0.117—0.683; 基于EST-SSR标记的UPGMA聚类分析和贝叶斯分析也将6个鲫群体划为两大类群: 黑龙江水系群体; 长江、奉化江和淮河水系群体。G-SSR和EST-SSR标记检测6个鲫群体的平均多态信息含量(PIC)分别为0.786—0.864和0.761—0.833。研究结果显示: 6个野生鲫群体均具有较高的遗传多样性, 但黑龙江水系群体多样性低于其他水系群体; 尽管EST-SSR标记的多态性略小于G-SSR标记, 但是2类微卫星标记均揭示了相似的鲫群体遗传结构和分化格局。研究结果对鲫种质资源的保护和EST-SSR标记在鱼类群体遗传学研究价值的评价提供了新的信息。     

Iron and copper in Plagioscion squamosissimus (Piscis: Sciaenidae) from the Orinoco river, Venezuela

Bauxite explotation of the Orinoco River in recent years is an important source of heavy metals discharge in the ecosystem, changing the natural biochemical flow of these elements and their concentrations in water, sediment and organisms. Iron and copper concentrations were measured in the fish Plagioscion squamosissimus in the Orinoco river, by sampling the fish population for three months (September-November 1998) in the main channel of the middle Orinoco (07 degrees 38' 21.2" N; 66 degrees 19' 10.9" W) and in Castillero lagoon (7 degrees 39' 09" N; 66 degrees 09' 00" W) with 2 and 4 cm mesh sizes. The internal organs of 30 fishes per month and site were stove-dried at 80 degrees C, pulverized and dried in disecator for 30 min to use as indicators with the acid digestion method for predicting the effect of heavy metals. We found relatively high values of iron and copper concentrations in fishes of the lagoon, and high seasonal variations in the iron concentration.     

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

SUMMARY. 1. The composition of surface waters of the Boro River, Okavango Delta, Botswana, was determined on five occasions during 1989–1990. The waters could be characterized as caicium—sodium—bicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mg1-⁻¹, were: Ca²⁺ 4.8, Mg²⁺ 1.3, Na⁺ 3.9, K⁺ 2.7, HCO₃⁻ 27, Cl⁻ 1.0 and SiO₂ 38; pH c. 7.
2. The relative ionic composition of the waters changed gradually from the inlet in Seronga to the outlet at Boro/Thamalakane junction. There was a gradient of increasing concentrations of solutes resulting from the evaporative concentration of the waters in this semi-arid region with an almost permanent water deficit, and the total dissolved solutes increased from c. 30 to 95 mg 1-⁻¹
3. There were seasonal differences in solute concentrations, connected with the rainfall pattern and climatic cycle and an ill-defined relation with discharge. The chemical spectrum of the Boro, and the freshness of its waters, can be attributed to the major influence of precipitation within the basin and selective removal of solutes.
4. Chemical equilibrium models indicate that amorphous silica and sepiolite are likely to precipitate from the Boro waters. Carbonate and silicate systems are responsible for the selective removal of solutes in the swamps, islands, or flood plains, as proposed by others in recent studies, but not in the Boro River waters.     

Particulate organic carbon, sterols, fatty acids and pigments in the Amazon River system

Water samples were collected from the Amazon River system during a high flood period, in June 1989, and lipids associated with particles retained on GF/F filters were examined. Particles showed a highly variable organic carbon content (1.8–29.0%). Corresponding organic carbon concentrations varied from 0.36 to 1.13 mg/l. The flood conditions encountered during the sampling period may feed exceptional inputs of soil organic matter into the tributaries and the Amazon River. Composition and concentration of sterols, fatty acids and pigments were determined to estimate the relative portion of terrigenous and autochthonous fraction of this complex organic matter. Sterol distribution patterns were similar to other equatorial rivers, in the Orinoco (Venezuela) and Solo (Indonesia). In comparison with the dominant profile of the Amazon system, distinct patterns were found in the Trombetas River (29^5,22 27⁵ 29⁵ 28⁵, 28^5,22) and in the Tapajos River (27^5,22 > 27⁵ 29⁵, 28⁵, 28^5,22). These fingerprints reflect different vegetation types of drainage basins and distinct planktonic pools. The distribution of even-carbon numbered saturated fatty acids in the carbon range of 24–36 revealed low inputs of constituents associated with cuticular waxes of vascular plants in Black waters and in the Tapajos River (200 ng/l), higher in White waters (328–483 ng/l) and highest in the Trombetas River (704 ng/l) and in stagnant waters of a small lake close to the Amazon (1088 ng/l). Pigment concentrations showed that in the main river and most tributaries vegetal carbon did not represent more than 2%, except for the Tapajos River (6.2%) and in relatively stagnant waters sampled along the main river (9.2%). Based on relative abundance of Chl b, Chl c, fucoxanthin, peridinin, alloxanthin, and zeaxanthin, various phytoplanktonic assemblages were evidenced in the Amazon River system. Branched fatty acids in the carbon range of 15–17 gave insight into bacterial signatures. They showed low microbial contribution to the fatty acid pool, with slightest higher contribution in a swamp of stagnant waters and in the White waters of the Solimoes River.     

Spatial population structure of the Neotropical tiger catfish Pseudoplatystoma metaense: skull and otolith shape variation

Using geometric morphometrics, the skull and otolith of tiger catfish Pseudoplatystoma metaense were analysed to identify population structure in tributaries of the Apure River (i.e. the Sarare, Caparo, Guanare, Portuguesa and San Carlos Rivers) in the Orinoco basin, Venezuela. The analyses show uniformity in skull and otolith shapes of P. metaense within and among four tributaries, with only the Caparo River showing significant differences. Within the Apure basin, the stock of P. metaense was differentiated through spawning, refuge and nursery areas. This study concludes that populations of P. metaense from each major tributary in the Orinoco basin should be considered as part of a metapopulation system for management purposes. Human disturbances in the catchment have directly reduced the spawning areas available to this species, decreased the total biomass and changed the spatial distribution of spawning areas.     

Genetics, recruitment, and migration patterns of Arctic cisco (Coregonus autumnalis) in the Colville River, Alaska, and Mackenzie River, Canada

Arctic cisco Coregonus autumnalis have a complex anadromous life history, many aspects of which remain poorly understood. Some life history traits of Arctic cisco from the Colville River, Alaska, and Mackenzie River basin, Canada, were investigated using molecular genetics, harvest data, and otolith microchemistry. The Mackenzie hypothesis, which suggests that Arctic cisco found in Alaskan waters originate from the Mackenzie River system, was tested using 11 microsatellite loci and a single mitochondrial DNA gene. No genetic differentiation was found among sample collections from the Colville River and the Mackenzie River system using molecular markers (P > 0.19 in all comparisons). Model-based clustering methods also supported genetic admixture between sample collections from the Colville River and Mackenzie River basin. A reanalysis of recruitment patterns to Alaska, which included data from recent warm periods and suspected changes in atmospheric circulation patterns, still finds that recruitment is correlated to wind conditions. Otolith microchemistry (Sr/Ca ratios) confirmed repeated, annual movements of Arctic cisco between low-salinity habitats in winter and marine waters in summer.