Evaluation of physical fish habitat quality enhancement designs in urban streams using a 2D hydrodynamic model

Creating a habitat for a variety of forms of life, such as riparian plants and various fish, is a necessity for stressed river ecosystems. In this study, the hydraulic characteristics of a fish habitat in an urban channel were analyzed using River2D, which is a two-dimensional (2D) depth-averaged finite element hydrodynamic model, to improve the habitat of two target fish in the Daejeon Stream, Korea. These species are Pseudopungtungia nigra, which is an endangered species in the Daejeon Stream, and Zacco platypus, which is a dominant species. In addition, changes in the weighted usable area (WUA) were compared and reviewed as boulders were placed in the stream. The best method for improving the P. nigra's habitat is proposed. A simulation analysis was performed on urban rivers for fish habitats. As a result, a straight and monotonous urban river flow was found to be an appropriate habitat environment for Z. platypus. The WUA for Z. platypus was about 20 times greater than that for P. nigra. Three different fish habitat enhancement methods were evaluated by calculating the WUA for the target fish in the study channel. By calculating the WUA to create fish habitats, the V-type riffle method was found to increase the usable area of the habitat environment for P. nigra by 360%, and the step stone method and single boulder method did so by 60% and 8%, respectively. For the single boulder method, boulders were placed in the channel bed at 3.5-m intervals, which significantly increased habitat availability. Moreover, centralizing the flow pattern in the channel among several types of boulder placements greatly expanded the habitat for P. nigra. Thus, an appropriate placement interval and boulder location that considers the characteristics of the riverbed and target fish species should be researched and implemented.     

Scale-dependence of fish habitat associations in a North American river system

1. Determining the appropriate measurement scale to assess habitat variables is critical for ecologists assessing biological or ecological conditions. Depth, velocity, substrate, woody debris and other fish cover variables occur on both reach and microhabitat scales, and fish habitat associations with these variables may be scale-dependent. The aim of this work was to better understand the importance of scale for fish–habitat associations with these variables in a framework consistent with environmental filtering and to test the hypothesis that habitat variable importance is scale-dependent.
2. I used prepositioned areal electrofishing in wadeable streams of the Delaware River basin to evaluate the associations of fish with the same variables summarised on different reach and microhabitat scales. The importance of scale for fish–habitat associations was assessed using two approaches that approximate an environmental filtering framework: variance partitioning with (1) ordination and (2) generalised linear mixed models.
3. Variables on both the reach and microhabitat scales explained a significant fraction of the total variation in fish community composition (p < 0.05). Variation decomposition of reach- and microhabitat-scale effects revealed 20.2% and 2.0% of all variation were due uniquely to reach and microhabitat scales, respectively. Measures of coarseness, embeddedness, amount of riffle and areal coverage of five fish cover variables were significant explanatory variables of community composition at the reach scale only (p < 0.05). Velocity and mesohabitat (amount or presence of riffle) were the only two habitat features that were significant explanatory variables of fish community composition at both the reach and microhabitat scales (p < 0.05). Individual models of species occurrence revealed similar patterns as seen with analyses of community composition.
4. For many fishes, habitat features quantified at the reach scale were more explanatory than at the microhabitat scale. Longnose dace (Rhinichthys cataractae) were more dependent upon microhabitat variables than reach-scale variables, relative to other fishes. Mean velocity at the reach scale was the most important explanatory variable for explaining fish community composition and indicated support for the concept of environmental filtering at the reach and microhabitat scales.
5. Few studies of fish occurrence have incorporated a study design and analytical framework that approximates the hierarchical nature of habitat. This study identifies important scales and predictors, demonstrates the importance of a multiscale approach, and provides support for the environmental filtering concept at the reach and microhabitat scales. These findings will allow ecologists to better account for scale-dependent habitat associations and justify the use of fish habitat associations on reach and microhabitat scales for assessing biotic integrity, restoration and conservation of fishes.

     

长江口中华鲟自然保护区底层鱼类的群落结构特征

根据2004年8月、11月和2005年2月(Ⅰ年度)、2005年8月、11月和2006年2月、5月(Ⅱ年度)、2007年8月、11月和2008年2月和5月(Ⅲ年度)对长江口中华鲟自然保护区15个站位点的底拖网调查数据,对该水域的底层鱼类群落结构特征及时间和空间变化规律进行了分析。结果表明,调查中捕获底层鱼类42种,隶属于13目24科39属。底层鱼类的种类组成和群落结构进行聚类分析,15个站位聚合成两大类群,类群A位于南支北港和北港北沙近东滩水域,共出现20种底层鱼类,主要以淡水性和河口性鱼类为主;类群B位于北支和北港北沙近外海水域,共出现鱼类39种,主要以河口性和海洋性鱼类为主。ANOSIM和SIMPER分析表明底层鱼类群落结构不同季节间差异显著,造成这种趋势的主要原因可能是与棘头梅童鱼(Collichthys lucidus)和凤鲚(Coilia mystus)的繁殖和索饵洄游有关。     

Changes in fish assemblage structure with variability of flow in two different channel types

Despite the fact that flow and channel morphology are two critical factors that need to be taken into account when considering the conservation or restoration of river environments, there are no reports on the response of fish assemblages to changes involving both variables in combination. This study examined the response of fish assemblages to artificially induced changes in flow discharge in an experimental stream that had simple (a glide reach) and complex (pool–riffle reach) morphologies. When the flow of the glide reach was increased, the fish assemblage structure changed from one dominated by the demersal species Misgurnus anguillicaudatus and Cobitis sp. to one dominated by the water-column species Zacco platypus and Gnathopogon elongatus. In the pool–riffle reach, the fish assemblage structure changed from one dominated by Cobitis sp. and Z. platypus to one dominated by Plecoglossus altivelis altivelis. When the flow discharge was low, the fish assemblages of both reach types resembled each other in being dominated largely by demersal species, but when flow was increased these similarities faded and distinct assemblages emerged. In the glide reach, increasing the flow volume caused a linear increase in both water depth and velocity and a gradual increase in the diversity of water-column species, their relative abundance, and size. The number of Z. platypus increased fivefold whereas the number of M. anguillicaudatus decreased to less than a quarter of their original number. In the pool–riffle reach, the number of P. altivelis altivelis grew conspicuously although increased flow produced no clear increase in depth or velocity. Calculation of the availability of physical habitat environments suitable for Z. platypus and P. altivelis altivelis in each reach type indicated that preferable habitat for both species was more available in the glide reach. The lower abundance of P. altivelis altivelis in the glide reach was attributed to the relatively low availability of algal food resource due to the sand-predominated substrate whereas pebbles predominated in the pool–riffle reach providing good conditions for algal growth. Our findings suggest the need for a framework for considering environmental flow that takes into account variables such as channel morphology and food resource conditions.     

Impacts of hydropeaking and thermopeaking on the downstream habitat in the Dal River,Korea

Dams located upstream only release water during the period of hydropower generation. This induces short-term fluctuations of water discharge in the downstream reach, which is called hydropeaking. As occurs quite often, if the temperature of the water released form the upstream dam is different from the water that is flowing in the downstream reach, the water temperature also tends to show short-term fluctuations, which is called thermopeaking. This study investigates the impacts of both hydropeaking and thermopeaking on the downstream habitat. The study area is a 2.3 km long reach located downstream from the Goesan Dam in the Dal River, Korea. To assess such impacts, this study conducted physical habitat simulations. The CMS-Flow model was used for the computation of the flow and water temperature, and the GEP model for the habitat simulation. Three physical habitat variables, flow depth, velocity, and water temperature, were used. The Zacco platypus was selected as the target fish in the study area. Simulation results indicated that the hydropeaking flows significantly reduced both the CSI and the WUA when compared with the natural flow regime. In addition, the use of the water temperature in the physical habitat simulations further decreased both CSI and WUA, indicating that thermopeaking is as important as hydropeaking in this type of assessment.     

Infection Status of Zoonotic Trematode Metacercariae in Fishes from Vientiane Municipality and Champasak Province in Lao PDR

The infection status of fishborne zoonotic trematode (FZT) metacercariae was investigated in fishes from 2 localities of Lao PDR. Total 157 freshwater fishes (17 species) were collected in local markets of Vientiane Municipality and Champasak Province in December 2010 and July 2011, and each fish was examined by the artificial digestion method. Total 6 species of FZT metacercariae, i.e., Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium, were detected in fishes from Vientiane Municipality. The metacercariae of O. viverrini were detected in 50 (49.5%) out of 101 fishes (6 species), and their average number was 154 per fish infected. The remaining 5 species of heterophyid metacercariae were detected in 36.8%, 65.8%, 9.4%, 23.9%, and 5.1% fishes examined, and their average densities were 12, 1,038, 4, 15, and 13 per infected fish, respectively. In fishes from Champasak Province, 3 species of FZT metacercariae, i.e., O. viverrini, H. taichui, and H. yokogawai, were detected. Only 2 O. viverrini metacercariae were found in only 1 Barbonymus schwanefeldi. The metacercariae of H. taichui and H. yokogawai were detected in 60.0% and 50.0% of fishes examined, and their average densities were 47 and 28 per fish infected. By the present study, it has been confirmed that several species of FZT metacercariae are prevalent in fishes from Vientiane Municipality, with P. varium being a new member of FZT in Lao PDR. In comparison, FZT metacercariae are less prevalent in fishes from Champasak Province.     

马鞍列岛岩礁生境鱼类群落结构时空格局

基于2009年马鞍列岛潮下带岩礁生境的多网目三层组合刺网逐月调查数据,对鱼类群落月相和季度间的变化、区域尺度上的空间差异和群落的稳态进行了探讨,应用优势种相对丰度和生物量、定居性鱼类和洄游种的季节动态、非度量多维标度(nMDS)和生物量丰度曲线(ABC)分析方法对群落时空格局进行了分析。结果显示:季节性洄游种集中出现在夏秋季,但对岩礁生境的利用表现出不同区域的强度差异;小黄鱼Larimichthys polyactis和黄姑鱼Nibea albiflora周年利用岩礁生境,但强度有别,尤其在冬季;定居性鱼类褐菖鲉Sebastiscus marmoratus、斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii在春末夏初的种群密度最高,同样表现出某些或大部分月份的区域差异;而河口种中国花鲈Lateolabrax maculatus则更多地选择秋冬季出现在岩礁生境。多元分析结果揭示了当地岩礁生境鱼类群落格局上显著的季节和区域差异,这是定居性鱼类对岩礁生境利用的阶段性变化和区域差异、结合洄游种季节迁移和选择性分布等因素作用下共同形成的格局。ABC分析进一步发现,丰富的鱼类生态类型形成了夏季岩礁生境更为稳定的群落状态,而冬季相反;同时各季度A区的群落干扰明显强过B区。研究表明,产卵季节海域西北部的岩礁生境很可能起着主要的产卵场功能,而东南部区域各季度皆侧重于幼鱼育肥场的功能表达。丰富的种类区系加之优势种的季节性交替出现,共同塑造了岩礁生境极具动态的鱼类群落格局,对维持岛礁海域鱼类多样性以及局部区域生态系统的稳定性起着非常重要的作用。     

High Endemicity with Clonorchis sinensis Metacercariae in Fish from Yongjeon-cheon (Stream) in Cheongsong-gun,Gyeongsangbuk-do,Korea

The infection status with Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fishes from Yongjeon-cheon (a branch of Nakdong-gang) located in Cheongsong-gun, Gyeongsangbuk-do, the Republic of Korea (Korea). A total of 750 fishes in 19 species were examined by the artificial digestion method for 2 years (2019 and 2020). CsMc were detected in 378 (51.4%) out of 735 fishes in 14 species (73.7%), and the infection intensity was 666 per fish infected. In 2019, CsMc were found in 172 (68.0%) out of 253 fishes in 10 species, and the infection intensity was 565 per fish infected. In 2020, CsMc were detected in 206 (62.2%) out of 331 fishes in 10 species, and the infection intensity was 751 per fish infected. The other zoonotic trematode, ie. Metagonimus spp., Centrocestus armatus, Echinostoma spp. and Clinostomum complanatum, metacercariae were also detected in fishes from the survey streams, but their endemicities were relatively low. Conclusively, it was first confirmed that CsMc are highly endemic in fishes from Yongjeon-cheon in Cheongsong-gun, Gyeongsangbuk-do, Korea.     

Utilization of the exotic cladoceran Daphnia lumholtzi by juvenile fishes in an Illinois River floodplain lake

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid‐ to late‐summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm L_T juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid‐ to late‐summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.     

Home range,movements, and density of the central stoneroller,Campostoma anomalum,in a small Ohio stream

Synopsis A population of central stonerollers, Campostoma anomalum, in Harker's Run, Butler County, Ohio U.S.A., was examined during autumn, 1980, to determine the species' movements, density, and home range size. During the study period, 170 fish were marked by fin clips and released into the specific pool or riffle where they were captured within the 187 m study section. Eighty percent of the recaptured, marked fish (20) were recaptured in their initial capture area (specific pool or riffle). No fish moved more than 135 m from its original capture area. Density estimates of C. anomalum for each pool and riffle within the study section ranged from 0.10–3.91 fish m⁻² (mean = 1.25 fish m⁻²). Home range size was estimated to be 35.2 ± 14.1 m (mean ± 95% CI) of stream length. Campostoma anomalum in Harker's Run occurred at densities similar to those reported for the species in other streams, and their home ranges in this system were of similar size to those of other small, stream-dwelling fishes.     

An evaluation of the use of branching fire-corals (Millepora spp.) as refuge by reef fish in the Abrolhos Bank, eastern Brazil

Branching scleractinians provide fish with critical refuge against predation. While in the Caribbean and Indo-Pacific regions they are conspicuous elements of the reef community, in the tropical Southwestern Atlantic (Brazil) branching corals are lacking and massive forms dominate. The only branching forms that occur in Brazil are stinging fire-corals of genus Millepora (Hydrozoa). Preliminary observations showed that several fish species seek refuge within fire-corals in Brazil, suggesting that they may replace the functional role played by scleractinians in other regions. Here, the association of fishes to individual fire-coral colonies (Millepora alcicornis and M. brasiliensis) and the relationship between fire-coral cover and fish abundance was studied in eastern Brazil. A total of 38 fish species from 18 families (37?% of the regional species pool) were recorded within fire-corals. Most records were of relatively small-bodied fishes and juveniles of large-bodied fishes. Comparative observations between day and night indicated that fire-corals are used as sleeping sites by a few species. Volume of colonies was positively correlated with fish abundance and species richness. Over a large spatial scale (tens of kilometers) fire-coral cover had a positive and significant influence on the abundance of three fish species only (Abudefduf saxatilis, Acanthurus coeruleus and Microspatodon chrysurus). Although physical attributes of colonies and fire-coral cover may help to account for some of the spatial variability in fish abundance, fire-corals may be considered as an alternative instead of a critical microhabitat for fish. The advantages and drawbacks of living in a branching and stinging environment are discussed.     

Fish predation affects the structure of a benthic community

1. We conducted an experimental study of predation by benthivorous fish on a natural community of stream invertebrates using a reach‐scale approach. Over a 2‐year period (experimental phase), the benthic invertebrate community of a stretch containing two species of benthivorous fish was compared with a fishless stretch. Thereafter, all fish were removed and benthic community structure was analysed again to account for natural differences between the two stretches (reference phase). 2. Benthivorous fish at the moderate densities investigated did not affect total benthic biomass or density, but did alter species composition. In addition, the fish effect differed between pool and riffle habitats, with larger effects in the pools indicating a habitat‐specific predation effect. In the reference phase, when all fish were removed from the stream, the difference between the two stretches was reduced. 3. The benthivorous fish reduced the densities of four taxa (Pisidium sp., Dugesia gonocephala, Gammarus pulex, Limoniidae), representing 29% of total biomass. It is possible that density reductions of other species were masked by prey migration despite the relatively large spatial scale. Indeed, higher drift activity in the upstream fishless stretch could have increased the density of Baetis rhodani in the fish stretch, as indicated by the results of a drift model. 4. Our results provide insights into stream food web ecology because fish predation showed effects even in a natural system where habitat complexity was high, environmental factors were highly variable and many predator and prey species interacted and because benthivorous fish were the focus, whereas the majority of previous predation experiments in streams have used drift‐feeding trout.     

胶州湾海域鱼类群落种类组成及多样性

为了解胶州湾海域鱼类群落结构特征,根据2016—2017年间对胶州湾海域进行的4个航次底拖网调查数据,采用相对重要性指数、生态多样性指数和典范对应分析(canonical correspondence analysis,CCA)、非线性多维标度排序(non-metric multidimensional scaling,NMDS)等方法分析了胶州湾海域鱼类群落的种类组成和多样性特征。结果表明:调查共采集到鱼类46种,隶属2纲10目30科41属,以硬骨鱼纲鱼类为主(45种,97.83%)。其中,鲈形目(Perciformes)最多(22种,47.83%),其次是鲉形目(Scorpaeniformes),占15.22%。种类数季节变化明显,以夏季最高,23种;秋季最低,16种。优势种组成以赤鼻棱鳀(Thryssa kammalensis)、褐菖鲉(Sebastiscus marmoratus)、褐牙鲆(Paralichthys olivaceus)、大泷六线鱼(Hexagrammos otakii)、许氏平鮋(Sebastes schlegeli)和矛尾鰕虎鱼(Chaeturichthys stigmatias)等鱼类为主。多样性分析显示,鱼类物种多样性存在明显的季节差异。多样性指数(H′)季节变化范围为1.668—2.453,以夏季最高,春季最低;均匀度指数(J′)季节变化范围为0.577—0.808,以秋季最高,春季最低;丰富度指数(D′)季节变化范围为2.431—3.123,以冬季最高,秋季最低。典范对应分析表明,水温、盐度、水深和pH是影响胶州湾海域鱼类群落物种组成的主要环境因子,且水温和pH是影响鱼类群落结构及多样性时空变化的主要因子。与历史调查资料相比,由于人类活动对胶州湾生态系统的干扰,鱼类群落结构发生了较大变化,优势种组成更替明显,多样性水平降低,鱼类群落结构趋向简单化。     

Community Structure of Coastal Fishes in Relation to Heavily Impacted Human Modified Habitats

Diversity and community structure of coastal fishes were compared between reforested mangrove and reclaimed sandy habitats at Pasir Ris, in the eastern part of Singapore. Both habitats supported a total of 91 species, but a single species, Ambassis kopsii dominated in abundance. Mean fish density was significantly higher at the reclaimed sandy shore than the reforested mangrove, but the reforested mangrove habitat yielded higher diversity. Apart from A. kopsii, abundant species in the mangroves included Ambassis interrupta, Thryssa hamiltonii, Acentrogobius sp., Scatophagus argus and Arius sagor. Anodontostoma chacunda, Acentrogobius sp., Leiognathus decorus, Sillago sihama and Stolephorus sp. were abundant in the reclaimed sandy habitat. Both habitats exhibited a higher mean density and average species richness during high tide. Several species from the family Gobiidae dominated the catch during low tide while pelagic fishes were most abundant during high tide. Diel variation showed significantly higher density during the day than at night, a result that contrasts to similar studies elsewhere. However, species richness showed no significant variation between day and night catches. Interaction between combined factors of time of the day and tidal height on fish density and average species richness was significantly different. The results indicated both habitat types to be important fish nurseries.     

Food partitioning among carnivores within feeding guild structure of fishes inhabiting a mudflat ecosystem of Indian Sundarbans

The present study was aimed to determine dietary composition and feeding guild structure of the fishes inhabiting mudflat habitat of Indian Sundarbans. In addition, partitioning of food resources by the fish species belonging to the carnivorous feeding guild was also performed to understand the survival strategies of fish in a mudflat estuarine habitat. Seventeen prey categories were isolated from the stomachs of 31 studied fish species. Overall, five feeding guilds (viz. plankti-benthivore: 12 species, herbivore: one species, detritivore: three species, omnivore: one species and carnivore: 14 species) were identified on the basis of the prey abundance within their stomachs, considering 64 % Bray–Curtis similarity. Among the carnivorous, maximum trophic richness was obtained for Uroconger lepturus followed by Ophichthus apicalis. Teleost and decapods were the main animal prey items preferred by majority of the carnivorous fishes. However, O. apicalis and Terapon jarbua showed their preference toward maximum number of prey categories among carnivores, which was also ratified by the high values for standardized niche breadth presented by them. The maximum degree of interspecific dietary overlap was found between Uropterygius marmoratus and Pseudapocryptes elongatus as both of them were recognized as cranci-piscivore. The lowest was observed between Hyporhamphus limbatus and Coilia neglecta. As food resources are not limiting in the mudflats of Indian Sundarbans, the general patterns of resource partitioning and niche differentiation in resident ecological communities will improve the understanding of the mechanisms underlying species coexistence and community structure.     

Metacercariae of new trematode species of the genus Diplostomum (Trematoda,Diplostomidae) from fishes of Lake Tana,Ethiopia

Four new species of trematodes of the genus Diplostomum are described from metacercariae found in fishes from Lake Tana in Ethiopia: Diplostomum garrae sp. n. from the lens of Garra dembecha, D. longicollis sp. n. from the lens of Barbus humilis, D. montanum sp. n. from the lens of Barbus humilis, and D. tilapiae sp. n. from the vitreous body of Oreochromis niloticus. The metacercariae of the new species considerably differ in morphology and size from those of all known Holarctic species. It is the first African record of metacercariae of the genus Diplostomum in fish.     

Survey of Zoonotic Trematode Metacercariae in Fish from Irrigation Canal of Togyo-jeosuji (Reservoir) in Cheorwon-gun,Gangwon-do,Republic of Korea

The infection status of zoonotic trematode metacercariae (ZTM) was investigated in total 568 freshwater fishes (19 species) from the irrigation canal of Togyo-jeosuji (Reservoir) in Cheorwon-gun, Gangwon-do, the Republic of Korea for 3 years (2018–2020). All fishes were examined using the artificial digestion method. The metacercariae of Clonorchis sinensis (CsMc) were detected in 180 (43.8%) out of 411 fish of positive species, and their infection intensity was 38 per fish infected (PFI). Especially, in 2 fish species, i.e., Pseudorasbora parva and Puntungia herzi, the prevalence was 82.1% and 31.3%, and the infection intensity with CsMc was 88 and 290 PFI, respectively. Metagonimus spp. metacercariae (MsMc) were found in 403 (74.1%) out of 544 fish of positive species, and their infection intensity was 62 PFI. In the pale chub, Zacco platypus, the prevalence of MsMc was 98.6%, and their infection intensity was 144 PFI. Centrocestus armatus metacercariae were detected in 171 (38.9%) out of 440 fish of positive species, and their infection intensity was 1,844 PFI. Echinostoma spp. metacercariae were found in 94 (19.6%) out of 479 fish of positive species, and their infection intensity was 3 PFI. Metorchis orientalis metacercariae were detected in 43 (29.3%) out of 147 fish of positive species, and their infection intensity was 4 PFI. By the present study, it has been confirmed that some species of ZTM, including CsMc and MsMc, are prevalent in fishes from the irrigation canal of Togyo-jeosuji in Cheorwon-gun, Gangwon-do, Korea.     

Conflicting effects of woody debris on stream fish populations: implications for management

1. Coarse woody debris (CWD) in stream channels causes changes in flow, sedimentation and ratios of pool to riffle areas. There is a consensus among fishery managers and scientists that CWD is beneficial to stream fish communities because of its enhancement of habitat diversity, invertebrate production and cover. Our hypothesis was that CWD accumulation or introduction would not increase in‐stream habitat capacity for all species and their ontogenic stages at reach and stream scales. 2. The study used a system of gravel‐bed streams with naturally dynamic CWD accumulations and a fish community consisting of Salmo trutta, Cotttus gobio, Phoxinus phoxinus, Lampetra cf planeri, Nemacheilus barbatulus and Anguilla anguilla. Cotttus gobio and L. cf planeri are protected by an EU Directive and S. trutta is exploited for angling. Riffles, pools and CWD matrices, considered as the basic habitat/spatial units of channel structure, were sampled separately and abundance of each fish species quantified seasonally at each spatial scale. 3. Multiple‐pass electric fishing techniques were used. Capture efficiencies were calculated for species, habitat and season. Areal densities (number m^?2) were compared for habitat types and season using nonparametric anova . Canonical analysis and stepwise multiple regression were used to show the most influential physical variables on fish density. Densities were also compared by unit volume (numbers m^?3) for pools and CWD matrices to investigate direct three‐dimensional use for cover. Reach‐scale densities for each fish species in relation to habitat composition were made using Spearman rank correlation of habitat‐scale densities with proportionate areas of the different habitat units in the reach. 4. Habitat‐scale densities of bullheads and age 0+ trout were negatively correlated with depth and CWD areas for some seasons. Densities of lampreys, older trout, eels and minnows were positively correlated with depth in some seasons. Water depth had the most consistent influence on fish abundance at the habitat unit scale. Three‐dimensional comparisons of pools and CWD matrices indicated that only trout older than 1+ may use CWD habitats as cover. 5. Reach‐scale densities of 0+ trout and bullheads were significantly correlated with proportion of riffle area and negatively with CWD and combined CWD‐pool habitat area in the reach. Densities of older trout, large eels and lampreys were positively correlated with CWD area and combined CWD‐pool area in some seasons. Inundation of riffles caused by impoundment upstream of CWD accumulations reduced spawning habitat for trout, bullheads, brook lampreys, minnows and stone loach. A trade‐off was an increase in refugia for older trout, minnows and eels. 6. Coarse woody debris accumulation in streams is not beneficial to all species or ontogenic stages in a mixed species population and could severely limit essential habitat areas for some species. Thus, physical manipulation of channels should be implemented only after a thorough study of the habitat relationships of all species present, especially where protected species coexist with target species. The relative importance of in‐stream morphological changes depends on the spatial and temporal scale of the species life histories.     

Comparison between community structures of fishes in <Emphasis Type="Italic">Enhalus acoroides</Emphasis>- and <Emphasis Type="Italic">Thalassia hemprichii</Emphasis>-dominated seagrass beds on fringing coral reefs in the Ryukyu Islands,Japan

To clarify differences in community structures and habitat utilization patterns of fishes in Enhalus acoroides- and Thalassia hemprichii-dominated seagrass beds on fringing coral reefs, visual censuses were conducted at Iriomote and Ishigaki islands, southern Japan. The numbers of fish species and individuals were significantly higher in the E. acoroides bed than in the T. hemprichii bed, although the 15 most dominant fishes in each seagrass bed were similar. Cluster and ordination analyses based on the number of individuals of each fish species also demonstrated that fish community structures were similar in the two seagrass beds. Species and individual numbers of coral reef fishes which utilized the seagrass beds numbered less than about 15% of whole coral reef fish numbers, although they comprised about half of the seagrass bed fishes. Of the 15 most dominant species, 5 occurred only in the two seagrass beds, including seagrass feeders. Ten other species were reef species, their habitat utilization patterns not differing greatly between the two seagrass beds. Some reef species, such as Lethrinus atkinsoni and L. obsoletus, showed ontogenetic habitat shifts with growth, from the seagrass beds to the coral areas. These results indicate that community structures and habitat utilization patterns of fishes were similar between E. acoroides- and T. hemprichii-dominated seagrass beds, whereas many coral reef fishes hardly utilized the seagrass beds.     

Distribution patterns of fishes in a canyon-shaped reservoir

In August 2004 and 2005, an extensive study of the fish community was carried out in the largest water supply reservoir in the Czech Republic and Central Europe, the canyon‐shaped ?elivka Reservoir, using a fleet of Nordic multimesh gillnets. Fishes were sampled at eight locations along the longitudinal profile of the reservoir and at five benthic depth layers covering depths from the surface down to 18 m (benthic gillnet 1·5 m high), and at three pelagic depth layers down to the depth of 5 m above the bottom (pelagic gillnets 4·5 m high). Catches of both juvenile (age 0+ year) and adult (fishes >1 year) fishes were highest in the upper layers of the water column (i.e. in the epilimnion down to 5 m, and down to 10 m in the benthic habitats). Along the tributary–dam axis in the pelagic habitats, both juvenile and adult fishes preferred the upper part of the reservoir, where the maximum number of species and also the greatest abundance of zooplankton were found. In the benthic habitats, fishes selected location according to factors other than trophic status. More juvenile fishes were recorded in the benthic habitats than in the pelagic habitats. Depth had the largest explanatory power for predicting fish community composition, followed by the affiliation with benthic and pelagic habitats, and location on the longitudinal axis of the reservoir. The fish community was represented mainly by cyprinids and consisted of two distinct groups of species, with bleak Alburnus alburnus, rudd Scardinius erythrophthalmus and asp Aspius aspius dominating the offshore group while perch Perca fluviatilis and ruffe Gymnocephalus cernuus were affiliated with the inshore group of the adult fish community. Roach Rutilus rutilus, bream Abramis brama and pikeperch Sander lucioperca occurred in important proportions in both the inshore and the offshore zones. All species, with the exceptions of adult perch (1+ year and older), 0+ year perch and 0+ year roach, preferred the most eutrophic tributary part of the reservoir. The fish community was relatively stable between the 2 years sampled.