Influences of low-head dams on the fish assemblages in the headwater streams of the Qingyi watershed, China

The influences of low-head dams on the fish assemblages were examined in this study, using fish data collected in six treatment and five reference sites at three low-head dams in the headwater streams of the Qingyi watershed, China. Comparing with those in the reference sites, local habitat variables were significantly altered by low-head dams in the treatment sites, involving wider channel (only in the impoundment area), deeper water and slower flow. Fish species richness varied significantly across seasons, not across site categories, suggesting that these low-head dams did not alter species richness. However, significant decreases in fish abundance and density were observed in the impoundment areas immediately upstream of dams, but not in the plunge areas downstream. Fish assemblage structures kept relative stability across seasons, and their significant difference between-site was only observed between the impoundment areas and the sites far from dams upstream. This variation in assemblage structures was due to the differing relative abundance of some co-occurring species; more lentic but less lotic fish was observed in the impoundment areas. The spatial and temporal patterns of fish assemblages were correlated with local habitat in this study area. Wetted width had negative correlation with fish species richness, abundance and density, respectively. Water temperature also positively affected species richness. In addition, wetted width, water depth, current velocity and substrate were the important habitat variables influencing assemblage structures. Our results suggested that, by modifying local habitat characteristics, low-head dams altered fish abundance and density in the impoundment areas immediately upstream of dam, not in the plunge areas immediately downstream, and thereby influenced fish assemblage structures in these stream segments.     

Does flooding affect spatiotemporal variation of fish assemblages in temperate floodplain wetlands?

1. Floodplain wetlands are productive components of lowland rivers and are thought to be important habitat and nurseries for many fish species. Fish assemblages inhabiting floodplain wetlands vary considerably through space and time and are largely shaped by wetting/drying cycles, although there is little understanding how many aspects of flooding (e.g. magnitude, timing, duration, frequency) influence the fish assemblages. As a consequence, decisions on flooding of wetlands by managers aimed at restoring native fish assemblages are often based on limited knowledge. 2. This study examined the importance of total duration of flooding on the temporal and spatial dynamics of wetland fish assemblages in the Murray River, in south‐eastern Australia. The study examined: (i) how the abundance of 0+ and 1+ fish varied with wetland, season and the duration of wetland filling; (ii) how environmental parameters, including food production changed in relation to the duration of wetland filling; (iii) changes in condition indices for the most abundant species and (iv) changes in species richness and total abundance over time. 3. The 0+ fish assemblage varied more through space and time than the 1+ assemblage. Longer cumulative river–wetland filling was associated with greater total abundances of newly recruited (0+) fish; this was particularly true for common carp (Cyprinus carpio, alien) and carp gudgeon (Hypseleotris spp., native). The body condition of carp gudgeon also increased with the duration of filling, even though static measures of food production declined. The small flooding events that occurred as part of this study did not translate into measurable improvements in the fish assemblage over the longer term (3 years), but did prevent wetlands from drying and thus maintained these habitats as refuges.     

Spatial Variation in Fish Assemblages across small Mediterranean Drainages: Effects of Habitat and Landscape Context

Much debate about assemblage organization in stream fish may stem from analysing the effects of both local and large-scale processes on assemblage attributes over whole geographic regions. This study addresses this issue, by examining the contribution of local habitat attributes and landscape context to fish assemblage variation across small Mediterranean drainages in southern Portugal. Fish abundance and species composition was estimated in 28 sites, across 10 drainages, in both a dry year (1999) and a wet year (2001), and related to two sets of variables reflecting habitat and landscape characteristics. Fish showed responses to both sets of variables with variance partitioning indicating that landscape context had important effects on species richness whereas habitat attributes were the primary determinants of local fish abundance. In general, high species richness was associated with larger drainage area and higher rainfall variability, whereas variation in species abundances mostly reflected the influence of width, depth, conductivity, current velocity, substrate size and emergent vegetation. The relative contributions of both landscape context and habitat attributes to species richness and abundance were generally lower in 1999 than in 2001, with much less diversified species–habitat relationships being found in the former dry year. These results point to the dynamic nature of assemblage organization, emphasizing the importance of innovative, multi-scale approaches in advancing our knowledge of fish assemblage structure in Mediterranean streams.     

Effect of flooding on fish assemblages in small streams in South Korea

The impact of Typhoon-Rusa-generated flood on fish assemblages was investigated in small streams in the northeastern part of South Korea. As a result of high precipitation (870 mm day⁻¹) during the typhoon, stream morphology and substrate composition changed. Stream depth and width decreased and slightly enlarged, respectively. Substantial amounts of mud and silt flowed into the streams and modified substrate composition to a simple state. Although the total number of individual fish significantly decreased after the flood, the dominant species remained the same relative to before the typhoon, and their relative abundance subsequently increased. However, the rank order of fish assemblages before and after the flood changed. Three years after the flood, fish assemblage recovered, but the number of individuals per site was still lower than prior to the flood. Flooding affects fish assemblages both directly and indirectly. Indirect impacts, such as habitat alteration, more critically affected the change in local fish assemblage and delayed recovery time. Nonetheless, fish assemblages persisted at sites where floods occurred.     

Spatial and vertical patterns in the tidepool fish assemblage on the island of O`ahu

The microtides, wave regimes, and relative isolation of the Hawaiian archipelago may provide unique environmental and biogeographic effects that shape the structure of tidepool fishes. We sampled fishes across a narrow gradient at low tide from 6 sites on the island of O`ahu. We tested predictions of the hypotheses that environmental conditions (pool depth, volume, macroalgal cover, temperature, and salinity) would result in a vertically structured tidepool fish assemblage unique to basalt or limestone rocky shores. 343 fish were recorded from 40 pools, and 19 species from 10 families were identified. Tidepool fish diversity (H’: O`ahu = 2.4; Sites Average = 0.0–0.9) was typical for tropical islands, with members from Gobiidae (5 species), Blenniidae (4 species), Pomacentridae (3 species), Acanthuridae (2 species) and Kuhliidae (2 species) among the most common. Endemism (32%) was higher than other well studied assemblages yet similar to Hawaiian reef fishes (25%). Assemblage abundance varied among shores with basalt or limestone substrate, among sites, and vertically among high, mid, and low pools. In general, blenniids occurred at higher proportions on limestone shores and gobiids were more common on basalt shores. High pools were characterized by an abundance of a small sized (29.0 mm median standard length) blenniid Istiblennius zebra, while the blenniid Entomacrodus marmoratus and wrasses Thalassoma spp. were more common in low pools. Temperature was the best environmental predictor of assemblages and this relationship warrants further investigation. Our findings indicate that assemblages can vary across a narrow geographical range and intertidal shore.     

Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems. Handling editor: J. Trexler     

活跃性和社会性对中华倒刺鲃集群行为的影响

为考察群体中不同的个性组成对鱼类集群行为的影响及其内在机制,选取中华倒刺鲃(Spinibarbus sinensis)幼鱼为实验对象,依次测定其活跃性和社会性,随后分别根据活跃性和社会性的高低分为高、低和混合活跃性(或社会性)鱼群,考察鱼群中不同个性组成对集群时的整体运动特征以及每尾鱼的个体运动特征的影响。研究发现：(1)中华倒刺鲃的个性特征稳定且个体间变异较大;(2)高活跃性鱼群的运动时间比和速度同步性均大于低活跃性鱼群,而混合鱼群位于二者之间且与两个同质性鱼群均无显著差异;高社会性鱼群速度同步性显著小于低社会性和混合社会性鱼群,而后两者之间没有显著差异。(3)活跃性特征与集群运动时每尾鱼的运动特征(速度及其同步性等)相关,社会性特征不仅与上述运动特征关联,还与凝聚力大小(距鱼群质心距离)相关。研究表明：(1)鱼群的活跃性和社会性组成均对集群行为产生重要影响,但其内在机制截然不同。主要表现为：就活跃性而言,群体的运动状态是由群体中所有成员共同决定(平均决定机制);就社会性而言,少数低社会性成员对鱼群的运动水平表现有着主导作用(少数决定机制);(2)实验鱼的活跃性在集群行为中得到了较大...     

Temporal and spatial patterns in littoral-zone fish assemblages of a reservoir (Lake Texoma,Oklahoma-Texas,U.S.A.)

Synopsis We sampled the littoral-zone fish fauna of Lake Texoma reservoir by electrofishing from January through December 1986 to examine species abundance, species associations and assemblage structure. Although total fish abundance differed significantly across seasons, only one common species (Dorosoma cepedianum) exhibited significant seasonal movement into or out of the littoral zone. Overall littoral-zone assemblage structure (based on rank order of species abundance) was concordant across seasons and habitat types, (vegetation, wood, open). However, within individual seasons and habitat types, assemblage structure was likely influenced by temporal and spatial differences in habitat availability and physicochemical conditions. Associations characteristic of species in natural aquatic environments were not well developed among species in this partly artificial, evolutionarily short-lived reservoir assemblage. Conditions related to water-level fluctuation appeared to deter the formation of persistent species associations and assemblage structure, especially in vegetation and open littoral zone habitats of this multi-purpose reservoir.Senior author     

Reef habitats and associated sessile-benthic and fish assemblages across a euphotic–mesophotic depth gradient in Isla Desecheo, Puerto Rico

Quantitative surveys of sessile benthos and fish populations associated with reef habitats across a 15–50 m depth gradient were performed by direct diver observations using rebreathers at Isla Desecheo, Puerto Rico. Statistically significant differences between depths were found for total live coral, total coral species, total benthic algae, total sponges and abiotic cover. Live coral cover was higher at the mid-shelf (20 m) and shelf-edge (25 m) stations, whereas benthic algae and sponges were the dominant sessile-benthic assemblage at mesophotic stations below 25 m. Marked shifts in the community structure of corals and benthic algae were observed across the depth gradient. A total of 119 diurnal, non-cryptic fish species were observed across the depth gradient, including 80 species distributed among 7,841 individuals counted within belt-transects. Fish species richness was positively correlated with live coral cover. However, the relationship between total fish abundance and live coral was weak. Abundance of several numerically dominant fish species varied independently from live coral cover and appeared to be more influenced by depth and/or habitat type. Statistically significant differences in the rank order of abundance of fish species at euphotic vs mesophotic stations were detected. A small assemblage of reef fishes that included the cherubfish, Centropyge argi, sunshine chromis, Chromis insolata, greenblotch parrotfish, Sparisoma atomarium, yellowcheek wrasse, Halichoeres cyanocephalus, sargassum triggerfish, Xanthichthys ringens, and the longsnout butterflyfish, Chaetodon aculeatus was most abundant or only present from stations deeper than 30 m, and thus appear to be indicator species of mesophotic habitats.     

Does seasonal flooding give a native species an edge over a global invader?

1. The factors that promote coexistence of global invaders and native species are poorly understood. The role of abiotic factors in determining the dominance of invasive species is also an area of increasing interest. Gambusia holbrooki (Eastern Mosquitofish) is an important global invader, displacing endemic fish and frogs on four continents. However, Gambusia co‐occurs with a similar‐sized fish (Hypseleotris spp.) in dynamic floodplain wetland pools of south‐eastern Australia. 2. We examined the relative abundance of Gambusia and Hypseleotris in regularly flooded and irregularly flooded pools to determine whether seasonal hydrological disturbance may be advantageous to the native species. We aimed to determine whether Gambusia and Hypseleotris populations respond differently to regular seasonal flooding and whether this could reduce the ability of Gambusia to dominate numerically the native species. We tested this by sampling fish bi‐monthly in 15 floodplain pools over 2.5 years. 3. We found that the relative abundance of the two species differed between regularly and irregularly flooded pools, while both pool types persisted (over a period of a year). Hypseleotris were numerically dominant in regularly flooded pools from spring through to autumn, following a major spring flood. In contrast, Gambusia were more abundant than Hypseleotris in irregularly flooded pools from summer until pools dried completely. 4. Due to the higher reproductive response of Hypseleotris to a spring flood, and the timing of its breeding season, we suggest that Hypseleotris may have a reproductive advantage over Gambusia during productive post‐flood spring/summer conditions. While the abundances of both species were usually within a similar range, variation in hydrologic habitats and the inter‐play between life‐history traits and hydrologic disturbance may nonetheless give the native fish an edge.     

Maladaptive behavior reinforces a recruitment bottleneck in newly settled fishes

Settlement from the plankton ends the major dispersive stage of life for many marine organisms and exposes them to intense predation pressure in juvenile habitats. This predation mortality represents a life-history bottleneck that can determine recruitment success. At the level of individual predator–prey interactions, prey survival depends upon behavior, specifically how behavior affects prey conspicuousness and evasive ability. We conducted an experiment to identify behavioral traits and performance levels that are important determinants of which individuals survive or die soon after settlement. We measured a suite of behavioral traits on late stage, pre-settlement Ward's damsel (Pomacentrus wardi) collected using light traps. These behavioral traits included two measures of routine swimming (indicators of conspicuousness) and eight measures of escape performance to a visual startle stimulus. Fish were then released onto individual patch reefs, where divers measured an additional behavioral trait (boldness). We censused each patch reef until approximately 50% of the fish were missing (~24 h), which we assumed to be a result of predation. We used classification tree analysis to discriminate survivors from fish presumed dead based on poor behavioral performance. The classification tree revealed that individuals displaying the maladaptive combination of low escape response speed, low boldness on the reef, and high routine swimming speed were highly susceptible to predation (92.4% with this combination died within 24 h). This accounted for 55.2% of all fish that died. Several combinations of behavioral traits predicted likely survival over 24 h, but there was greater uncertainty about that prediction than there was for fish that were predicted to die. Thus maladaptive behavioral traits were easier to identify than adaptive traits.     

Setting Goals and Measuring Success: Linking Patterns and Processes in Stream Restoration

The influences of productivity, vegetation coverage, and benthivorous fish abundance on macroinvertebrate abundance and mean size were examined in Midwestern USA impoundments. While impoundment productivity was not strongly related to total abundance and mean size of macroinvertebrates, it was related to specific taxa. As productivity increased, Ephemeroptera and Odonata abundance decreased and Diptera abundance increased. Despite the shift in taxonomic composition, mean individual size of the macroinvertebrate community varied little with changes in impoundment productivity. Relationships between macroinvertebrates and benthivorous fish were mixed. Macroinvertebrate abundance, especially Diptera, increased with increases in bluegill Lepomis macrochirus Rafinesque abundance and decreased with increases in channel catfish Ictalurus punctatus (Rafinesque) (which are stocked annually) abundance. Fish were not related to the mean size of macroinvertebrates. Macrophyte coverage was not related to macroinvertebrate abundance or mean size. Overall, macroinvertebrate abundance was mostly related to productivity and benthivorous fish in these impoundments. Mean size of macroinvertebrates did not differ with productivity, fish abundance, or macrophyte coverage.     

Effects of a Severe Flood on the Movements of Japanese Fluvial Sculpin

I studied the movements of adult Japanese fluvial sculpin, Cottus pollux, in a Japanese mountain stream. An exceptionally severe flood in late September had negative impacts on refuge abundance, condition and population density of the sculpin. The mean distance moved monthly correlated positively with water discharge, but not with water temperature or with population density. Overall, the mean distance sculpins moved after the flood was significantly greater than before the flood, and sculpins tended to move into riffle-raceways after the flood. Comparisons of refuge-site limitation for adults and water depths between habitats indicated that the flood affected riffle-raceways less than pools. Fish in poorer conditions were likely to move extensively, and the condition of fish captured initially in pools deteriorated more significantly than that of sculpins captured in riffle-raceways. Movement bias into riffle-raceways by the sculpins after the flood suggests they sought suitable habitat with available refuges. The results suggest vulnerability to flood disturbance of the sculpins inhabiting the interstitial spaces of the substrate.     

The influence of flood cycle and fish predation on invertebrate production on a restored California floodplain

Although floodplains are known to be tightly controlled by the flood cycle, we know comparatively little about how flooding influences predators and their consumption of secondary production, particularly in highly seasonal floodplains typical of Mediterranean climates. In this study, we investigate how the seasonal dynamics of a central California floodplain influence the timing and magnitude of fish predation and the abundance and composition of invertebrates. For 3 years (2000–2002), we compared changes in abundances and size distributions of invertebrates through the flood season (January–June) with seasonal changes in the abundance of larval and juvenile fishes. Using diet analysis of fishes and manipulative feeding experiments with fishes in field enclosures, we link specific changes in invertebrate populations directly to feeding preferences of seasonally abundant fish. Early in the flood season prior to March, we found little influence of fish predation, consistent with the near absence of larval and juvenile fishes during this period. Coinciding with the midseason increase in the abundance of larval and juvenile fishes in April, we found significant declines in zooplankton abundance as well as declines in the size of zooplankton consistent with fish feeding preferences. Our results were consistent with results from feeding enclosure experiments that showed that fish rapidly depressed populations of larger cladocerans with much less effect on smaller cladocerans and calanoid copepods. At the end of the flood season, zooplankton abundances rapidly increased, consistent with a switch in the feeding of juvenile fish to aquatic insects and subsequent fish mortality. We also found that zooplankton biomass on the floodplain reached a maximum 2–3 weeks after disconnection with the river. We suggest that floodplain restoration in this region should consider management strategies that would ensure repeated flooding every 2–3 weeks during periods that would best match the peaks in abundance of native fishes. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Macroecological analysis of the fish fauna inhabiting Cymodocea nodosa seagrass meadows

In this study, patterns in the taxonomic richness and composition of the fish fauna inhabiting Cymodocea nodosa seagrass meadows were described across their entire distribution range in the Mediterranean Sea and adjacent Atlantic Ocean. Specifically, the study tested whether there are differences in the composition of fish assemblages between those ecoregions encompassed by the distribution range of C. nodosa, and whether these differences in composition are connected with differences in bioclimatic affinities of the fish faunas. A literature review resulted in a total of 19 studies, containing 22 fish assemblages at 18 locations. The ichthyofauna associated with C. nodosa seagrass meadows comprises 59 families and 188 species. The western Mediterranean (WM) Sea has the highest species richness (87 species). Fish assemblages from the Macaronesia–Canary Islands, the Sahelian Upwelling, South European Atlantic Shelf and the WM differ, in terms of assemblage composition, relative to other ecoregions. In contrast, the composition of the fish fauna from the central and eastern Mediterranean overlaps. There is a significant serial correlation in fish assemblage composition between adjacent ecoregions along the distribution range of C. nodosa. Dissimilarities in assemblage composition are connected with the geographical separation between locations, and the mean minimum annual seawater temperature is the environmental factor that explains most variation in fish assemblage composition.     

基于栖息地斑块尺度的青弋江河源溪流鱼类群落的时空格局

确定鱼类的栖息地利用格局是研究物种与环境关系的基础, 也是鱼类多样性保护和管理的必要前提。目前, 有关溪流鱼类群落的栖息地斑块利用格局尚存在争议。基于2012年9月至2013年8月对青弋江河源溪流的逐月调查数据, 初步研究了鱼类群落的栖息地斑块利用格局, 着重在栖息地斑块尺度上解析了鱼类群落的时空变化规律。主要研究结果显示, 深潭和急滩2类斑块间的底质、流速、水深、溶氧栖息地因子显著差异, 且深潭斑块的环境稳定性高于急滩。研究共采集鱼类15种, 其中鲤科鱼类8种, 占采集物种数50%以上。基于鱼类物种存在与否的不连续变量的分析结果显示, 鱼类物种组成的斑块间和月份间变化均不具显著性。但是, 基于鱼类物种多度的连续变量的分析结果显示, 鱼类群落结构存在有显著的斑块间变化和时间动态; 就斑块间变化而言, 原缨口鳅(Vanmanenia stenosoma)在急滩斑块中的多度更高, 而宽鳍 (Zacco platypus)、光唇鱼(Acrossocheilus fasciatus)和尖头 (Phoxinus oxycephalus)等其他关键物种则在深潭中具有更高多度。深潭斑块的鱼类物种数显著高于急滩, 但2类斑块间的个体数无显著差异。深潭斑块的鱼类物种数较稳定, 而个体数月变化显著, 可能与鱼类繁殖和群体补充以及越冬死亡等有关; 急滩鱼类物种数和个体数的月变化均显著, 除了与鱼类群体补充和越冬死亡有关以外, 还可能受越冬时栖息地斑块选择变化的影响。上述结果表明, 在栖息地斑块空间尺度上, 由于研究区域内大多数物种在栖息地斑块选择上无明显的特化性, 深潭和急滩斑块间鱼类的物种组成分布不符合前人所报道的生境-共位群格局, 但区域内常见种多度的变化可引起鱼类群落结构的斑块间差异和季节动态。       

Consumer trait variation influences tritrophic interactions in salt marsh communities

The importance of intraspecific variation has emerged as a key question in community ecology, helping to bridge the gap between ecology and evolution. Although much of this work has focused on plant species, recent syntheses have highlighted the prevalence and potential importance of morphological, behavioral, and life history variation within animals for ecological and evolutionary processes. Many small‐bodied consumers live on the plant that they consume, often resulting in host plant‐associated trait variation within and across consumer species. Given the central position of consumer species within tritrophic food webs, such consumer trait variation may play a particularly important role in mediating trophic dynamics, including trophic cascades. In this study, we used a series of field surveys and laboratory experiments to document intraspecific trait variation in a key consumer species, the marsh periwinkle Littoraria irrorata, based on its host plant species (Spartina alterniflora or Juncus roemerianus) in a mixed species assemblage. We then conducted a 12‐week mesocosm experiment to examine the effects of Littoraria trait variation on plant community structure and dynamics in a tritrophic salt marsh food web. Littoraria from different host plant species varied across a suite of morphological and behavioral traits. These consumer trait differences interacted with plant community composition and predator presence to affect overall plant stem height, as well as differentially alter the density and biomass of the two key plant species in this system. Whether due to genetic differences or phenotypic plasticity, trait differences between consumer types had significant ecological consequences for the tritrophic marsh food web over seasonal time scales. By altering the cascading effects of the top predator on plant community structure and dynamics, consumer differences may generate a feedback over longer time scales, which in turn influences the degree of trait divergence in subsequent consumer populations.     

Cascading effects of predatory fish on the composition of benthic algae in high‐altitude streams

Cascading effects of predators can affect ecosystem properties by changing plant biomass, distribution and assemblage composition. Using data from field surveys and whole‐stream experiments we tested the hypothesis that predatory trout change assemblage composition of benthic algae in high‐elevation streams mediated by grazer behavior. Field surveys revealed that the taxonomic composition of algal assemblages differed significantly between streams that contained trout and those that were fishless; but comparisons of palatable versus unpalatable algal taxa between fish and fishless streams were equivocal because of high natural variability. Therefore, we tested for a behavioral (non‐consumptive) trophic cascade experimentally by adding brook trout chemical cues to six naturally fishless streams for 25 days and compared responses of grazers and algae to six reference streams without fish cues added. Algal response variables included rates of change in the abundance of three physiognomic categories, from most palatable (attached erect and prostrate diatoms) to least palatable (non‐diatoms), as determined from food selectivity analyses of the most common grazers (mayflies and caddisflies). Fish cues did not affect the mean densities or changes in densities of total grazers or any individual grazer species. However, in streams where fish cues were added, rates of accrual of attached erect diatoms, which was the preferred algal type for the grazer most vulnerable to trout predation (Baetis), were higher and their densities increased significantly faster with increasing densities of this grazer species than in reference streams. Results of his experiment support the hypothesis that predator induced suppression of grazer foraging behavior, rather than cascading effects of top predators on grazer density, may contribute to variation in the composition of algal assemblages among streams by allowing proliferation of most palatable algal species.     

Responses of Fish to Experimental Introduction of Structural Woody Habitat in Riffles and Pools

The declining condition of river systems associated with rapid development of human societies has led to substantial declines in fish diversity. One cause of decline is the loss of in‐stream Structural Woody Habitat (SWH), an important component of stream ecosystems, particularly as fish habitat. As a result there has been an increase in the number of rehabilitation programs that introduce SWH into rivers. This paper assesses fish responses to SWH introduction in riffles and pools in the Hunter River, eastern Australia, using a Multiple‐Before‐After‐Control‐Impact (MBACI) experimental and analytical design. In the riffle experiment, species richness was comparable among all control and treatment riffles across the entire study period. However, there were significant differences in assemblage structure, fish abundance, and biomass between control and treated riffles. The introduction of SWH (bank embedded deflector jams) appeared to create additional habitat which was utilized by one native fish species (Retropinna semoni—Australian smelt) and one alien species (Gambusia holbrooki—mosquito fish). In pools there were no significant changes in fish species richness, abundance, or biomass following introduction of SWH (pool jams). These findings have important practical and cost implications in terms of the design and implementation of rehabilitation strategies using SWH to restore fish assemblages in degraded streams.