Effect of landscape factors on fish distribution in arctic Alaskan lakes

1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction. 2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables). 3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied with species. Extinction variables were most important for lake trout (Salvelinus namaycush) and slimy sculpin (Cottus cognatus), a mixture of extinction and colonisation variables was important for arctic char (Salvelinus alpinus), and colonisation variables were most important for arctic grayling (Thymallus arcticus) and round whitefish (Prosopium cylindraceum). 4. Ecological differences among species account for much of the difference in relative importance of colonisation versus extinction variables. In addition, stream piracy events have occurred over geologic time scales, which have resulted in lakes that are currently inaccessible but support relict fish populations. 5. Climate warming, currently occurring in the arctic, is likely to alter further the stream network, which could have dramatic effects on fish distributions by affecting access to isolated lakes or isolating lakes that are currently accessible.     

禁捕初期鄱阳湖鱼类群落的结构特征

为掌握禁捕初期鄱阳湖鱼类群落的结构特征, 研究于2020年4月(春季)、7月(夏季)、10月(秋季)和2021年1月(冬季)在鄱阳湖21个采样点开展了渔获物调查。全年共采集到57种鱼类, 隶属于8目12科43属。优势种有贝氏?(Hemiculter bleekeri)、短颌鲚(Coilia brachygnathus)、蛇(Saurogobio dabryi)、和似鳊(Pseudobrama simoni)等4种鱼类。江湖洄游型、江海洄游型和河流型鱼类物种数共占比45.61%, 平均体重<20 g的物种的丰度占所有渔获物丰度的88.47%。在空间结构上, 基于鱼类丰度的非度量多维排序分析将鄱阳湖分为通江水道和主湖区两个大的空间类群, 方差分析表明通江水道鱼类丰度显著低于主湖区, 但多样性高于主湖区。在季节变化方面, 不同季节渔获物丰度、生物量和多样性的差异极其显著, 高水位时期(夏、秋季)的多样性高于低水位时期(春、冬季)。2020年10月在鄱阳湖主湖区中部的S9和通江水道的S20两个采样点发现了鄱阳湖历史文献中没有记录的广盐性近海鱼类——鲻(Mugil cephalus), 可能得益于长江禁捕, 由于消除了捕捞压力, 促使了该鱼类的资源恢复和上溯, 也不排除其他人为因素的可能, 因而需要更长时间序列的跟踪和监测。研究为全面评估鄱阳湖禁捕的生态效果提供了基础数据, 也为制定鄱阳湖鱼类资源的保护政策提供了参考。     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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Fish community structure in lowland drainage channels

Land drainage channels constitute a vast network of aquatic habitat utilized by fish. Surveys of these channels (dykes) in Broadland in eastern England reveal similar fish communities whether the dykes drain grazing marsh, fenland or arable land, though there are indications of poor recruitment in the recently deeply drained dykes of arable land. The species encountered most predictably were pike, roach, eel and tench. In terms of biomass, pike ranked top, followed by tench, bream and roach. Eels could not be sampled quantitatively but they must rank in the top five species in terms of biomass. Ordination and other analyses of community structure revealed several physicochemical and biotic factors that correlate with fish distribution and abundance. In particular, the presence of a floating plant mat in summer was associated with low oxygen concentrations at night and the absence of roach. The composition of fish communities in dykes contrasts in a number of ways with those recorded in local rivers and lakes (broads).     

FISH ASSEMBLAGE RESPONSES TO DIFFERENT SECONDARY CHANNEL DESIGNS IN THE LOWER MISSISSIPPI RIVER,U.S.A.:A TEMPLATE FOR RIVER RESTORATION

The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.     

Some observations on the geomorphological impact of hippopotamus (Hippopotamus amphibius L.) in the Okavango Delta, Botswana

The Okavango Delta is a large wetland system situated in northern Botswana. The hippopotamus forms an integral part of this dynamic ecosystem, as it exerts a catalytic effect on geomorphological change. In the distal reaches of the wetland, regular movement of hippos to feeding grounds results in the development of incised channels, which are kept clear of vegetation and act as nodes for swamp expansion. Hippos maintain pathways in backswamp areas, which lead to the development of new channel systems during channel avulsion. They create breaches in the vegetation levees which flank channels in the permanent swamps, causing diversion of water and sediment to backswamp areas. Their paths often lead to lakes in the permanent swamps. During channel avulsion, diversion of a channel into lakes may occur via these paths, which can result in lake closure.     

Effects of dynamic landscape elements on fish dispersal: the example of creek chub (Semotilus atromaculatus)

Barriers along a watercourse and interconnections between drainage systems are dynamic landscape elements that are expected to play major roles in the dispersal and genetic structure of fish species. The objective of this study was to assess the role of these elements using creek chub ( Semotilus atromaculatus ) in the Mastigouche Wildlife Reserve (Québec, Canada) as model. Numerous impassable waterfalls and interconnections among drainage systems were inferred with geographic information systems and confirmed de visu . The analysis of 32 populations using seven nuclear microsatellites revealed the presence of three genetically distinct groups. Some groups were found upstream of impassable barriers and in adjacent portions of distinct drainage systems. Admixture among groups was also detected in some populations. Constraining phylogenetic procedures as well as Mantel correlation tests confirmed that the genetic structure is more likely to result from interconnections between the drainage systems than from the permanent network. This study indicates that landscape elements such as interconnections are of major importance for circumventing impassable barriers and colonizing lakes that are otherwise inaccessible. Such an approach could be relevant for determining the origins of fish species (i.e. native vs. introduced) in the context of conservation.     

Abundance – distribution relationships in fish assembly of the Amazonas floodplain lakes

This study shows that patterns in some community assemblages are not mainly governed by local factors but also by regional ones. Using field data from 36 floodplain forest lakes in the Amazon basin, we present transect count data on the richness, abundance and distribution of floodplain lake fish species. A total of 194 fish species were collected, of which 43 were classified as short-distance migrants. A positive relation was found for local migratory and sedentary species abundances with distribution at a regional scale. The study also suggests that the probability of the presence of a migratory species is more affected by aspects of river-lake connectivity than sedentary species. Our results seem to indicate that migratory species play an important role in local dynamics of floodplain lakes.     

Spatial distribution of four freshwater fish species in different types of artificial European water bodies

Spatial distribution of young-of-the-year (YOY) and older roach, rudd, perch and ruffe was compared in two artificial lakes with macrophytes present and absent, and a valley reservoir, using gillnets. Almost all species of interest and both age categories preferred benthic habitats. The depth distribution in benthic habitats was relatively consistent across water bodies with the highest fish densities found in the shallowest depths. In the macrophyte-rich lake, YOY roach and perch utilize the 3–6 m benthic layer the most, whereas the fish preferred the 0–3 m benthic layer in the macrophyte-poor lake and reservoir. No differences were found in the depth distribution in pelagic habitats sampled by pelagic gillnets for YOY fish between the water bodies. Older fish usually utilized the surface water layer. Macrophytes influenced the depth distribution of YOY fish in benthic habitats, where their density maximum shifted deeper in the macrophyte-rich lake when fewer macrophytes were present in the shallowest benthic depth. In lakes, YOY fish utilized a wider depth spectrum due to the deeper thermocline when compared to the reservoir. Oxygen and temperature stratification are the main factors influencing fish distribution, whereas macrophyte presence particularly influences the depth distribution of YOY fish in benthic habitats.     

Salt Marsh Tidal Channel Morphometry: Applications for Wetland Creation and Restoration

The morphometry of tidal channels in a back-barrier salt marsh in New Jersey was investigated. Characteristics of the tidal channel drainage network plan form (order, bifurcation ratio, length, sinuosity) and cross section channel form (width:depth ratio, hydraulic geometry) are compared with data from other studies. Drainage patterns follow Horton’s Law of Stream Numbers and Law of Stream Lengths. Mitigation sites should be designed in accordance with these laws. The degree to which site-specific substrate, vegetation, and flow conditions constrain or facilitate the development of sinuous, meandering channel reaches should be estimated to provide information for the design of tidal channel geometries and dimensions that will accommodate predicted discharges. Drainage networks in created and restored wetlands should reflect the spatial distribution of width and depth properties (width:depth ratios, cross-sectional areas, longitudinal slopes, hydraulic geometry) found in similar natural systems. Reproducing these characteristics will lessen the practice of oversizing channels. Hydraulic geometry relationships can facilitate the sizing of channels at Atlantic coast salt marsh mitigation sites. Recommendations are given to promote the development of drainage networks that function like the coastal back-barrier Avalon/Stone Harbor marsh in New Jersey.     

Parasite fauna of bream Abramis brama and roach Rutilus rutilus from a man-made waterway and a freshwater habitat in northern Germany

Fifty specimens each of bream Abramis brama and roach Rutilus rutilus were examined for metazoan parasite fauna and trichodinid ciliates; 25 specimens of each species were collected from the Kiel Canal, a man-made waterway, and a nearby freshwater lake, the Dieksee. This is the first detailed parasitological examination of A. brama and R. rutilus at these locations: 30 parasite species were found, comprising 4 protozoans, 4 myxozoans, 5 digeneans, 3 monogeneans, 2 cestodes, 6 nematodes, 2 acanthocephalans, 3 crustaceans and 1 hirudinean. The crustacean Caligus lacustris occurred in both habitats while 2 other crustacean species, 2 acanthocephalans and 1 hirudinean were recorded exclusively for the lake habitat. Larval as well as adult stages of the different parasite species were found, indicating that both fish species act as intermediate and final hosts in both habitats. The Kiel Canal (total of 17 parasite species) showed a lower parasite species richness for A. brama and R. rutilus (14 and 10 parasite species, respectively) than the lake (25 parasite species). A. brama had a higher parasite richness (22 species) than R. rutilus (16 species) in the lake habitat. Most parasites collected were of freshwater origin. Consequently, the observed infection pattern of both fish species in the waterway is mainly influenced by the limited salinity tolerance of freshwater parasites, which are negatively affected even by a salinity of 2.3 to 4.5. In the central Kiel Canal, neither fish species was infected with marine parasites of low host specifity. These parasites are either limited by the low salinity at this sampling site (<4.5 to 6.0) or they cannot enter the canal due to the environmental conditions prevailing in this artificial brackish water habitat. Thus, the canal may comprise a natural barrier preventing the distribution of North Sea parasites into the Baltic Sea. However, the brackish water Baltic Sea nematodes Paracuaria adunca and Cosmocephalus obvelatus were found in R. rutilus from the canal, demonstrating the ability of some parasite species to invade and extend their range of distribution through this man-made shipping route from the Baltic to the North Sea.     

Mitochondrial and Allozyme Genetics of Incipient Speciation in a Landlocked Population of Galaxias Truttaceus (Pisces: Galaxiidae)

Galaxias truttaceus is found in coastal rivers and streams in south-eastern Australia. It spawns at the head of estuaries in autumn and the larvae spend 3 months of winter at sea before returning to fresh water. In Tasmania there are landlocked populations of G. truttaceus in a cluster of geologically young lakes on the recently glaciated Central Plateau. These populations have no marine larval stage and spawn in the lakes in spring. Speciation due to land locking is thought to be a frequent occurrence within Galaxias. To investigate the nature of the speciation event which may be occurring within lake populations of G. truttaceus we studied the mitochondrial DNA (mtDNA) and allozyme diversity of both lake and stream populations. Using the presence or absence of restriction sites recognized by 13 six-base restriction endonucleases, we found 58 mtDNA haplotypes among 150 fish collected from 13 Tasmanian and one south-east Australian mainland stream populations. The most parsimonious network relating the haplotypes by site loss or gain was starlike in shape. We argue that this arrangement is best explained by selection upon slightly beneficial mutations within the mitochondrial genome. Gene diversity analysis under Wright's island model showed that the populations in each drainage were not genetically subdivided. Only two of these stream haplotypes were found among the 66 fish analyzed from four lake populations. Despite the extreme lack of mtDNA diversity in lake populations, the observed nuclear DNA heterozygosity of 40 lake fish (0.10355) was only slightly less than that of 82 stream fish (0.11635). In the short time (3000-7000 years) that the lake fish have been landlocked, random genetic drift in a finite, stable-sized population was probably not responsible for the lack of mtDNA diversity in the lake populations. We infer the lake populations have probably experienced at least one, severe, but transitory bottleneck possibly induced by natural selection for life-history characters essential for survival in the lacustrine habitat. If speciation is occurring in the landlocked populations of G. truttaceus, then it may be driven by genetic transilience.     

Habitat associations of fish assemblages in the Cache River, Illinois

Fish and habitat were sampled by state agencies at 48 stations throughout the Cache River watershed, Illinois between 1992 and 2009. Two distinct fish assemblages were identified, one primarily found in the lower mainstem Cache River and a second found throughout tributaries and the upper mainstem Cache River. Using a canonical correspondence analysis, the distribution of fish species was largely explained by substrate, land use, drainage area and local habitat features. Creek chub, central stoneroller, fringed darter and fantail darter are species found to be positively associated with gravel substrate and forest. In contrast, black buffalo, gizzard shad, smallmouth buffalo, freshwater drum and bigmouth buffalo were positively associated with drainage area, silt, channel width and row crops. Cobble appears to be rare habitat associated with fringed darter, freckled madtom and fantail darter. Results suggest that substrate, land use and local habitat features influence fish assemblages within the Cache River watershed. This information contributes to both understanding aquatic community structure in a highly altered yet diverse watershed as well as management activities within the Cache River watershed.     

Relationships between fish assemblages, macrophytes and environmental gradients in the Amazon River floodplain

During the flood season of 1992–1993, 139 species of fishes were collected from a floodplain lake system in the central Amazon Basin. Fish species distribution was examined relative to abiotic variables in seven vegetation strata on Marchantaria Island, Solimões River. Both environmental variables and species distributions were influenced by a river channel to floodplain-interior gradient. Species diversity was significantly higher in vegetated areas than in unvegetated areas, with deeper water Paspalum repens stands harbouring the highest diversity. As a result, species richness and catches were positively related to habitat complexity, while catch was also negatively related to dissolved oxygen (DO) and water depth. Low DO and shallow waters appeared to act as a refuge from predation. Fish assemblages were related to water chemistry, but species richness was not. Canonical correspondence analysis provided evidence that floodplain fish assemblages formed by the 76 most common species were influenced by physical variables, macrophyte coverage and habitat complexity, which jointly accounted for 67% of the variance of fish species assemblages. Omnivores showed no pattern relative to the river channel to floodplain-interior gradient while detritivores were more likely to be found at interior floodplain sites and piscivores closer to the river. Piscivores could be further separated into three groups, one with seven species associated with free-floating macrophytes in deep water, a second with five species found in shallow waters with rooted grasses and a third with six open water orientated species. The results suggest that fish assemblages in the Amazon floodplain are not random associations of species.     

牛山湖两种不同生境小型鱼类的种类组成、多样性和密度

研究了2003年春季浅水草型湖泊牛山湖小型鱼类空间分布（种类组成、多样性和密度等）与生境异质性之间的关系.根据水生植被状况、离岸距离和水深,选择了两种差异较大且有代表性的生境类型,即近岸沉水植物茂密的生境A和远岸沉水植物稀疏的生境B.使用围网（180 m²）在这两种生境中进行小型鱼类的采样,采用多次标志回捕法和Zippin去除法估算了围网内小型鱼类的密度.结果表明,两种不同生境中小型鱼类的种类组成、多样性度量值和密度估算值均存在一定程度的差异：1）生境A中的渔获物由5科14种小型鱼类组成,优势种类为生活在中、下水层的高体鳑鲏、彩副鱊和麦穗鱼;生境B中的渔获物由3科9种小型鱼类组成,优势种类为生活在湖底的子陵吻鰕虎鱼和小黄黝鱼.2）生境A和生境B小型鱼类群落间的Bray-Curtis指数为0.222,结构相似性较低;但二者的物种等级丰度分布则无显著差异,均属于对数级数分布.3）生境A中高体鳑鲏、彩副鱊、麦穗鱼等9种小型鱼类的总密度值为8.71 ind·m^-2,生境B中子陵吻鰕虎鱼、小黄黝鱼等5种小型鱼类的总密度值只有3.54 ind·m^-2.小型鱼类在这两种不同生境中的空间分布差异可能与其逃避捕食、觅食和繁殖等生态习性的生境需求有关,因此,水生植被生境对小型鱼类资源合理开发和多样性保护具有重要意义.     

Quality and status of fish stocks in lakes: gillnetting,seining, trawling and hydroacoustics as sampling methods

All sampling methods give selective or biased estimates of fish species abundance, distribution and size structure. This creates problems, e.g. in regard to the Water Framework Directive of the European Union, which demands evaluation of the quality and status of fish stocks in lakes. We compared fish sampling by means of Nordic multimesh gillnets, seining, trawling and hydroacoustics in two Finnish lakes in summer 2007 and 2008. Sampling methods were used ‘as such’, i.e. no special design was implemented for method comparison. In the shallow eutrophicated lake the species’ composition of gillnet sampling and seining were very different. The biomass-% of percids dropped from gillnet (61%) to seining (9%) and that of cyprinids grew from 39 to 90%, respectively. In the deep pelagic area of the oligotrophic lake, vendace and smelt predominated in trawl catches. The number of fish caught by gillnetting in that area was too small to make any conclusions about the species composition. In the eutrophicated lake, the combined length distribution for all fish species differed significantly between gillnetting and seining. In the oligotrophic lake, the gillnet catches were too small for any comparison of fish size. The difference in the length distribution of fish between trawl and echosounding was significant in most analysed depth layers. In upper depth layers acoustics sampled larger fish than trawling, and in deeper layers smaller fish. Using a combined acoustic-trawl method, the pelagic fish biomass was estimated to be approx. 17 kg ha⁻¹ in the deep and oligotrophic lake. We conclude that in large and deep-water areas, the use of active gear is enough in fish sampling to evaluate the quality and status of fish stocks. Gillnetting together with seining is an appropriate method to work out the quality and status of fish stocks in shallow and littoral areas of large lakes. Variation in the catch selectivity of fish sampling gear requires a discrete ecological classification for each type of gear.     

Aspects of the reproductive biology of Hippopotamyms pictus from Lake Kainji, with notes on four other mormyrid species

A method is described for the assessment of fecundity in mormyrid fish. In all species examined a tri-modal egg size distribution was found in the mature pre-spawning ovary. These modes represented one oocyte and two ova components. The significance of the presence of two sizes of ovum is discussed in relation to breeding periodicity in Hippopotamyrus pictus . Size and age at first maturity are estimated for this species. The probable effects of the formation of the lake on the breeding behaviour of mormyrids is discussed.     

Fish distribution and benthic invertebrate biomass relative to depth in an Ontario lake

Synopsis A survey of fish distribution relative to depth in Lake Opinicon, Ontario, using the strip count method showed 80–90% of the biomass to be concentrated along the lake margins at a depth of up to 2.5 m. This figure applied throughout the summer, and to both day and night. Invertebrate diversity and biomass was also biassed towards the margins but slightly less so (mean summer figure 68% of biomass at depth of 2.5 m or less) for the segment of the lake studied. The central parts of the lake have good populations of 1–2 cm Chironomus spp. not predated by fish.There is a close link between the distribution of the specific prey organisms of fish species and the fish themselves. In their predominantly marginal distribution both are concentrated into the area of maximum productivity.     

Physical structure of habitat network differently affects migration patterns of native and invasive fishes in Lake Biwa and its tributary lagoons: stable isotope approach

A good understanding of how migratory animals use their habitat network is expected to provide important insights for the prediction of population dynamics at both local and regional scales. We focused on how the physical structure of a habitat network could affect fish migration between Lake Biwa and its tributary lagoons. Although the lagoons provide suitable breeding and nursery grounds for native fishes, it is a matter of concern that they can also be a hotbed of invasive exotic fishes. Here, we assessed the migration patterns of native crucian carps (Carassius spp.) and exotic largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) using their carbon and nitrogen stable isotopes as migration tracers. As there were marked differences in the carbon isotope ratios of basal food webs between the main lake and its tributary lagoons, stable isotopic signatures of individual fishes collected from each lagoon enabled us to judge whether they were residents of the lagoon or recent immigrants from the main lake. The analysis revealed that native and invasive fishes showed different migration patterns across a variety of lagoons. Exotic fishes frequently immigrated from the main lake to the lagoon as the distance of the channel connecting these two habitats was short. For native crucian carps, in contrast, their migrations were unaffected by the channel distance but were promoted by narrow channels. Physical barriers of weirs and dense vegetation within the channel obstructed their migrations. Such ecological information on migration behavior will be vital to plan designs for habitat restoration to conserve native fishes.     

Fish diversity and its relationships with environmental variables in a West African basin

Fish distribution in relation with environmental variables was investigated in the Boubo River, a coastal river in Ivory Coast. Fourty freshwater fish species belonging to 17 families and 26 genera were captured. Five brackish water species, two introduced species and one hybrid complete the list. Seven species are reported for the first time in this river. A significant correlation between species distribution and environmental variables was found. Rocky and leaves-dead wood substrates, oxygen, canopy closure, width, depth and velocity were the main environmental variables influencing fish distribution. Our findings are opposed to the tendency for species composition to increase from the source to the mouth of the river, which is probably due to two major human activities (dam construction and discharge of waste of palm oils and motor oils in the main channel). These activities could constitute in the future a real threat for the fish population and other aquatic organisms.