Forest conversion adversely affects native Macrobrachium shrimp assemblages in tropical Malaysian streams

1. Commodity-driven forest conversion represents one of the most severe threats to freshwater biodiversity in Southeast Asia, notably causing population declines and the extinction of freshwater fish species.
2. Although a variety of freshwater taxa are likely to be adversely affected by forest conversion, little is known about the impact on ecologically and economically important invertebrates such as decapod crustaceans.
3. This study evaluated the impact of forest conversion and land-use change on freshwater Macrobrachium shrimp species, using species richness, abundance, and environmental data collected from 20 streams across southern Peninsular Malaysia. Streams were located in three types of landscape: forest; oil palm plantation; and mixed land use, comprising young secondary forest, small-scale plantations, patches of open and sparsely vegetated areas, and agricultural fields and clearings.
4. Generalized linear models showed that even incomplete change from forest habitats to mixed land use and oil palm plantation resulted in significantly lower Macrobrachium native species richness and higher non-native species abundance. Native species richness was positively correlated with canopy cover, leaf litter, substrate size, and dissolved oxygen, and was negatively correlated with water temperature and conductivity. Native species richness was also negatively correlated with non-native species abundance, with non-native species abundance increasing along the human disturbance gradient.
5. These results highlight the need for riparian habitat protection to conserve native Macrobrachium and limit the spread of non-native species. A management priority should be to maintain or restore optimum instream habitat conditions for shrimps, which would also benefit fish and other benthic macroinvertebrates. Suitable riparian management requires substantial support and funding from multiple stakeholders, but it can be aligned with other catchment-based strategies to optimize the use of limited resources available for freshwater biodiversity conservation.

     

Different longitudinal distribution patterns of native white-spotted charr and non-native brown trout in Monbetsu stream, Hokkaido, northern Japan

Abstract  This study focused on longitudinal distribution patterns of native white-spotted charr and non-native brown trout in a mountainous stream in Hokkaido, Japan. Brown trout ratio, which is the proportion of brown trout in the catch of salmonids, was decreasing from downstream to upstream. Brown trout ratio correlated negatively with water temperature. Thus, our results suggested that temperature may influence the possible competition between native white-spotted charr and non-native brown trout.     

Invasions of rainbow trout and brown trout in Japan: A comparison of invasiveness and impact on native species

Many species of salmonids have been stocked into waters outside of their native range. The invasiveness and impact of these species on native species varies depending on their biological traits, and on environmental conditions, such as climate. In Japan, rainbow trout and brown trout, both listed in 100 of the world's worst invasive alien species by the International Union for Conservation of Nature, occur as non-native species. The invasiveness of these two species is thought to be related to seasonal flooding, given flood waters can physically damage fry and prevent population establishment. Rainbow trout have successfully invaded waters in Hokkaido, northern Japan, where the likelihood of flooding is low between June and July, when their fry emerge, but successful invasions are rare in regions south of Hokkaido. Brown trout, however, have successfully invaded waters not only in Hokkaido, but also other regions. Since brown trout have a similar life history to the native white-spotted charr and masu salmon, with fry emerging before the flood season, they are more suited to the Japanese climate than Rainbow trout. Rainbow and brown trout interact with native species in various ways, but a common outcome of these interactions is the displacement of native charr species. Legal regulations of non-native salmonids should be based on understandings of the ecological traits of each invasive species and regional impacts on native species. Given the ongoing nature of climate change, the nature and extent of the effects of rainbow and brown trout on native species might also change.     

Complex influences of low-head dams and artificial wetlands on fishes in a Colorado River tributary system

Abstract  Low-head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low-head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non-native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacepède). Downstream, fish assemblages were dominated by non-native species. Upstream spawning migrations by non-native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non-native fishes and a sink habitat for native fishes. Two non-native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non-native fishes.     

Effects of non-native brook trout (Salvelinus fontinalis) on threatened juvenile Chinook salmon (Oncorhynchus tshawytscha) in an Idaho stream

Macneale KH, Sanderson BL, Courbois J-YP, Kiffney PM. Effects of non-native brook trout ( Salvelinus fontinalis ) on threatened juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in an Idaho stream.
Ecology of Freshwater Fish 2010: 19: 139–152. © 2009 John Wiley & Sons A/S
Abstract –  Non-native fishes have been implicated in the decline of native species, yet the mechanisms responsible are rarely apparent. To examine how non-native brook trout may affect threatened juvenile Chinook salmon, we compared feeding behaviours and aggressive encounters between these sympatric fish in Summit Creek, Idaho. Snorkelers observed 278 focal fish and examined diets from 27 fish in late summer 2003. Differences in feeding behaviours and diets suggest that there was minimal current competition for prey, although individual Chinook feeding activity declined as their encounter rate with other fish increased. While difference in size between fish generally determined the outcome of encounters (larger fish 'winning'), it was surprising that in some interspecific encounters aggressive Chinook displaced slightly larger brook trout (≤20 mm longer). We suggest that in late summer, frequent intraspecific interactions may be more important than interspecific interactions in potentially limiting Chinook growth in Summit Creek and perhaps in other oligotrophic streams where they co-occur.     

Contrasting changes in freshwater fish assemblages and food webs follow modification of tropical waterways

Fresh waters are increasingly threatened by flow modification. Knowledge about the impacts of flow modification is incomplete, especially in the tropics where ecological studies are only starting to emerge in recent years. Using presence/absence data dated approximately four decades apart (~1966 to ~2010) from 10 tropical rivers, we assessed the changes in freshwater fish assemblage and food web after flow modification. The sites were surveyed with methods best suited to habitat conditions (e.g., tray/push netting for low‐order forest streams, visual surveys for canalised rivers and net casting for impounded rivers). With the presence/absence data, we derived and compared six measures of fish assemblage and food web structure: species richness, proportion of native species, overall functional diversity, native functional diversity, food web complexity and maximum trophic level. We found that changes in community assemblage and food web structure were not generalisable across modification regimes. In canalised sites, species richness and maximum trophic levels were lower in the second time period while the opposite was true for impounded sites. However, proportion of native species was consistently lower in the second time period across modification regimes. Changes in fish assemblages and food webs appear to be driven by species turnover. We recorded 79 cases of site‐specific extirpation and 117 cases of site‐specific establishment. Our data further suggest that turnover in assemblage is again contingent on flow‐modification regime. While the process was stochastic in canalised rivers, benthopelagic species were more likely to be extirpated from impounded rivers where species lost were replaced by predominantly alien fish taxa.     

Mitigating the impacts of stream and lake regulation in the flathead river catchment,Montana, USA: An ecosystem perspective

1. Seventy-two per cent of the Flathead River catchment (22 241 km²) is federally designated and protected as wilderness or national park. Thus, the catchment remains one of the more pristine areas of its size in the temperate latitudes of the world. 2. Discharge in the downstream reaches of the river system outside the protected areas is regulated by three dams for flood control and hydropower production. These dams have blocked natural migration of native fish from Flathead Lake (496 km²) and isolated populations in sub-catchments. Temperature and erratic flow fluctuations have altered phenologies of river zoobenthos and fish, and in dam tailwaters aquatic biodiversity is drastically reduced in comparison to unregulated segments. 3. Ecological problems caused by changing water quality conditions, altered land-use patterns and introductions of non-native biota are interactive with the impacts of stream and lake level regulation, thereby emphasizing the complexity of this river–lake ecosystem. 4. Mitigation of the effects of regulation is compromised by differing management priorities and regulatory mandates of County, State, Tribal, and Federal agencies responsible for natural resource management within the catchment. Moreover, economic and ecological interests outside the Flathead influence the way flows are regulated within the catchment. 5. The most pervasive influences of stream and lake regulation can be ameliorated by retrofitting the hypolimnial release dam with a selective depth outlet structure to allow temperature control, and by controlling changes in flow rates to create a more natural hydrograph in the tailwaters of the large dams. Allowing fish passage by construction of fish ladders is problematic because upstream passage will commingle native species that were isolated upstream by construction of the dams with non-native species that were introduced subsequently below the dams. Cascading food web interactions elicited by invasions of non-native biota may offset any advantage to native stocks gained by passage and/or augmentation with hatchery stocks. 6. Mitigation must be adaptive in the sense that unanticipated effects and interactions with other management objectives can be documented and alternative action can be implemented. 7. This case history of the effects of stream and lake level regulation, and the approaches to management reviewed in this paper, should serve as a lesson in river conservation.     

High temporal species turnover enhances the complexity of fish assemblages in Amazonian Terra firme streams

Abstract –  The objective of this study was to quantify fish species diversity in Terra firme streams of the Río Amazonas drainage. Fish diversity was quantified as the number of species collected or species richness in two sites of Yahuarcaca stream, a typical, first order tributary of the central Río Amazonas near Leticia (Colombia). The extremely high species richness recorded, 131 and 133 for the two study sites for a total of 171 species, was primarily due to species of low abundance (rare species) mostly with adults <5 cm in total length. The nonasymptotic tendencies of accumulated species richness over time for the 1999 samples at the two study sites and for the combined samples of 1999, 2001 and 2005 at site 2 suggested that the real number of fish species may be still greater. These findings emphasise the importance of long-term sampling designs to quantify species richness in these systems. Terra firme streams actually sustain greater fish richness than previously reported for similar sized streams that in turn, represent a substantial per cent of the total species richness reported for vast areas of the main stem of Río Amazonas including tributaries and lakes. Terra firme streams should be considered critical hotspots for conservation and management efforts which are urgently needed given the rapid development of ornamental fisheries on small streams throughout Río Amazonas drainage.     

Quantifying fish species richness and abundance in Amazonian streams: assessment of a multiple gear method suitable for Terra firme stream fish assemblages

A multigear sampling method to quantify fish richness and abundance in Amazonian Terra firme streams was assessed. This method is based on the four‐pass removal method using the combined application of different nets. The efficiency of the method was explored over 10 replicated sites along three streams over day, night and seasons. Use of four successive passes allowed both abundant and rare species to be collected and the abundance of common species to be estimated. On average, a high proportion (41%) of rare species was collected per sample (only one or two individuals) after four fishing passes. The efficiency of the sampling method to detect species richness per sample between successive passes was estimated using an autosimilarity approach. Although species richness and abundance increased with successive passes, no major differences were obtained between the third and fourth pass. A single pass considerably underestimated the richness and abundance of species in these type of streams, and night sampling also increased beta‐diversity by at least 20%. Abundance estimates demonstrated high efficiency with an overall sampling error of only 8 and 11% for samples and single species, respectively. Capture efficiency differed among fish species exhibiting different ecological traits and showed significant differences among seasons for total samples. Results supported the robustness of the method and its suitability to quantify fish richness and abundance in small, wadeable Amazonian Terra firme streams inhabited by highly diverse fish assemblages.     

A riverscape perspective of Pacific salmonids and aquatic habitats prior to large‐scale dam removal in the Elwha River,Washington, USA

Abstract Dam removal has been increasingly proposed as a river restoration technique. In 2011, two large hydroelectric dams will be removed from Washington State’s Elwha River. Ten anadromous fish populations are expected to recolonise historical habitats after dam removal. A key to understanding watershed recolonisation is the collection of spatially continuous information on fish and aquatic habitats. A riverscape approach with an emphasis on biological data has rarely been applied in mid‐sized, wilderness rivers, particularly in consecutive years prior to dam removal. Concurrent snorkel and habitat surveys were conducted from the headwaters to the mouth (rkm 65–0) of the Elwha River in 2007 and 2008. This riverscape approach characterised the spatial extent, assemblage structure and patterns of relative density of Pacific salmonids. The presence of dams influenced the longitudinal patterns of fish assemblages, and species richness was the highest downstream of the dams, where anadromous salmonids still have access. The percent composition of salmonids was similar in both years for rainbow trout, Oncorhynchus mykiss (Walbaum), coastal cutthroat trout, Oncorhynchus clarkii clarkii (Richardson) (89%; 88%), Chinook salmon, Oncorhynchus tshawytscha (Walbaum) (8%; 9%), and bull trout, Salvelinus confluentus (Suckley) (3% in both years). Spatial patterns of abundance for rainbow and cutthroat trout (r = 0.76) and bull trout (r = 0.70) were also consistent between years. Multivariate and univariate methods detected differences in habitat structure along the river profile caused by natural and anthropogenic factors. The riverscape view highlighted species‐specific biological hotspots and revealed that 60–69% of federally threatened bull trout occurred near or below the dams. Spatially continuous surveys will be vital in evaluating the effectiveness of upcoming dam removal projects at restoring anadromous salmonids.     

Effects of small dam condition and drainage on stream fish community structure

Low‐head dams are ubiquitous in eastern North America, and small dam removal projects seek to improve habitat conditions for resident and migratory fishes. Effects of small dams of varying status on local fish communities are poorly documented, and recent work suggests benefits of maintaining fragmentation. We sampled fish at 25 dams (9 breached, 7 relict, 9 intact) in three river basins in North Carolina, USA. Fishes were sampled at three reaches/dam from 2010 to 2011. Study reaches were located upstream (free‐flowing reaches), downstream (tailrace) and >500 m downstream of dams (n = 75 reaches). Analyses revealed significantly elevated fish CPUE, taxa richness and percentage intolerant taxa in intact dam tailraces suggesting small dams may improve conditions for resident taxa. Breached dam tailrace reaches exhibited lower fish CPUE, taxa richness and percentage intolerant taxa relative to upstream reference reaches. Relict dams exhibited no between‐reach differences in fish community metrics. Nonmetric multidimensional scaling revealed drainage‐specific stream fish responses across study drainages. Tar and Roanoke drainage streams with intact and relict dams supported fish assemblages indicative of natural communities, whereas Neuse Drainage streams with intact and breached dams contained disturbed habitats and communities. These data demonstrate fish community responses to dam condition are drainage specific but communities in streams with intact and relict dams are largely similar. Additionally, breached dams may warrant higher removal priorities than intact dams because they negatively influence fish communities. The variability in response to some dams indicates managers, regardless of region or country, should consider holistic approaches to dam removals on a case‐by‐case basis.     

Predation relationships between introduced salmonids and the native fish fauna in lakes and reservoirs in northern Patagonia

Abstract– A few native and exotic fish species are caught frequently in Andean lakes and reservoirs of northwestern Patagonia. Puyen ( Galaxias maculatus ) prey on zooplankton and benthos. Percichthys trucha has a wide range of prey, mainly benthos, while P. colhuapiensis become piscivorous when grown. Pejerrey ( Odonthestes hatcheri ) is omnivorous and large size individuals can be piscivorous. A siluroid, Diplomystes viedmensis , preys on benthos, insects, and fishes. Introduced salmonids are potential piscivorous. The puyen is the major prey category among fishes. Salmonids and perchichtids seem to partially overlap their diets but predation on Diplomystes appears to be restricted to salmonids. Present abundance of puyen, pejerrey and Percichthys spp. does not indicate a strong salmonid effect. However, the low abundance of D. viedmensis does. We studied present predation relationships among native and introduced fishes and postulated possible effects upon native fish fauna.     

Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed,the Qingyi Stream,China

Abstract – Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first‐order through third‐order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C‐link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.     

Trophic plasticity of invasive juvenile largemouth bass Micropterus salmoides in Iberian streams

Biological invasions are a major factor for biodiversity loss, particularly in freshwater environments. Largemouth bass Micropterus salmoides is native to North America and is invasive on the Iberian Peninsula, primarily to provide angling opportunities in reservoirs. However, this species is a threat to the endemic Iberian fauna via predation and competition. Currently, there is little information on largemouth bass in European streams. Thus, we assessed the trophic plasticity and body condition of young largemouth bass in both invasive (the regulated Bullaque River) and native (Murray Creek) streams. Abundance of juvenile largemouth bass, percentage of full stomachs and body condition were higher in Bullaque River. Largemouth bass preyed on benthic invertebrates much more heavily in the Bullaque River, whereas fishes were the most important prey in Murray Creek. Prey richness, diet diversity and trophic niche breadth were higher in the Bullaque River population. Largemouth bass preferred water-column fishes as prey and avoided consuming benthic fishes in Murray Creek, whereas water-column fishes were avoided in Bullaque River. These results demonstrate that largemouth bass display substantial trophic plasticity which possibly facilitates its success as invasive species. Regulated Iberian streams may provide both suitable food and habitat resources with minimal predation pressure, and hence may serve as recruitment sources for this invasive fish.     

Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context

Pires DF, Pires AM, Collares-Pereira MJ, Magalhães MF. Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context. Ecology of Freshwater Fish 2010: 19: 74–86. © 2009 John Wiley & Sons A/S
Abstract –  Knowledge of patterns of refuge use by fish is critical for maintaining biodiversity in drought-prone streams. In this study, the fish assemblages of 21 dry-season pools in a Mediterranean stream were characterised and related to three sets of factors reflecting pool morphology, physicochemistry and spatial context. Fish were associated with the three sets of variables, with variation partitioning indicating that overall species richness and abundance were primarily related to pool morphology but relative species abundances were mainly associated with physicochemical contexts. In general, species richness was the highest but overall fish abundance was the lowest in large pools. Pools well shaded by riparian canopy held the highest richness and abundance of native fish, but relative species abundances and assembly structure varied among pools contingent on canopy cover, substrate composition and spatial location. These results suggested that conservation of fish diversity in Mediterranean streams requires networks of pools with diverse sizes and physicochemical contexts.     

Metapopulation analysis indicates native and non‐native fishes respond differently to effects of wildfire on desert streams

Ash flows and flooding associated with wildfires represent important but understudied sources of disturbance for fish populations. Knowledge concerning these disturbances is especially limited for larger streams where warm water species dominate. Fire‐related disturbances have been hypothesised to differentially affect native and non‐native fishes, although this hypothesis has only been tested for salmonids. The objective of our research was to contrast effects of uncharacteristically large wildfires followed by flooding on metapopulations of native and non‐native fishes in the Gila River of southwest New Mexico. Probabilities of occupancy, colonisation and local extinction of fishes were calculated across sites before and during disturbance and were also measured across a broader spatial scale during disturbance to identify potential refuge locations. Occupancy was higher for native fishes than non‐natives, but multiple wildfire and flood events increased extinction probabilities of native species. Responses of non‐native species to wildfires were mixed; extinction of non‐native salmonids increased during disturbance, while extinction of several warm water species remained unchanged or decreased. Several undisturbed sites were poor refugia for natives as they were impacted by non‐native piscivores, dewatering, and fragmentation. However, despite exposure to multiple disturbances, sites located in large tributary and valley reaches were consistently occupied by native species, suggesting these habitats provided refugia. We suggest that management actions (forest thinning; prescribed burning) that restore a more natural disturbance regime of small and less severe fires coupled with habitat remediation activities (non‐native removal; decreased water withdrawal; improved connectivity) might diminish extinction risk for native fishes exposed to wildfire disturbance.     

Development and evaluation of a fish‐based index to assess biological integrity of Mediterranean streams

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Association of brook trout and Oncorhynchus spp. with large wood jams in a Lake Superior tributary in a northern old‐growth watershed

Wood in streams functions as fish habitat, but relationships between fish abundance (or size) and large wood in streams are not consistent. One possible reason for variable relationships between fish and wood in streams is that the association of fish with wood habitat may depend on ecological context such as large‐scale geomorphology. We studied the relationship between salmonid assemblages and large wood jams (LWJ) in four settings that differed geomorphically at the scale of the stream corridor along a tributary to Lake Superior in old‐growth conifer–hardwood forest in northern Michigan. The focal fish species of this study were brook trout (Salvelinus fontinalis), which were wild in the stream. Relocation efforts for coaster brook trout (an adfluvial life history variant of brook trout) were ongoing in the study stream. We measured fish abundance and length in pairs of pools of similar size and substrate, but varying in the presence of LWJ; this allowed us to evaluate associations of fish simply with the presence of LWJ rather than with other channel or flow‐shaping functions of LWJ. The length of Oncorhynchus spp. and young introduced brook trout was not strongly correlated with LWJ presence; however, the presence of LWJ in pools was positively correlated with larger wild brook trout. We also found that the correspondence of LWJ with the abundance of salmonids appears to be moderated by the presence of alternative habitat in this relatively natural, old‐growth forest stream.     

Taxonomic versus functional diversity metrics: how do fish communities respond to anthropogenic stressors in reservoirs?

Biological indicators are frequently used to assess the effects of anthropogenic stressors on freshwater ecosystems. The structure of fish communities and their response to stressors have been commonly described by taxonomic richness, diversity and evenness. More recently, functional structure of communities has also been suggested to be a reliable indicator of disturbance. This article aimed at testing whether taxonomic and functional diversity metrics can provide comparable or complementary information on the response of fish communities to eutrophication and abundance of non‐native species in reservoirs. Comparison of the responses of taxonomic and functional diversities to biogeography, habitat and stressors was made in 112 French reservoirs. Widely observed effects of biogeographic and habitat variables on taxonomic and functional diversities were identified. Taxonomic and functional richness metrics notably increased with lake area and temperature respectively. Taxonomic diversity metrics did not respond to any stressor, while all functional diversity metrics were found to be impacted by non‐native species. Eutrophication was further found to decrease the impact of non‐native species on two functional diversity metrics: evenness and divergence. Our study therefore reveals that functional metrics are more sensitive than taxonomic metrics to anthropogenic stressors in the studied reservoirs. Still, the multiple linear regressions tested had overall low explanatory power. Further refinements will thus be needed to use this type of metrics in an impact assessment scheme.