Native Fish Abundance Research Articles

Habitat variation and invasive species as factors influencing the distribution of native fishes in the lower Fraser River Valley, British Columbia, with an emphasis on brassy minnow (Hybognathus hankinsoni)

Brassy minnow (Hybognathus hankinsoni Hubbs, 1929) have disjunct distributions in western Canada, making them a species of conservation concern. We assessed changes in the distribution of invasive species as factors influencing the distribution of brassy minnow and other native species by comparing historical and current distributions in the lower Fraser River in British Columbia. We tested effects of physical habitat parameters on local distributions of brassy minnow and for evidence of negative interactions between brassy minnow and invasive brown bullhead (Ameiurus nebulosus (Lesueur, 1819)). Comparison of contemporary and historical (1956 and 1959) fish distributions indicated significant declines in native cypriniform (minnows and suckers) species, including brassy minnow, but no change in the number of invasive species, although there was some faunal turnover. Logistic regression suggested that conductivity, turbidity, and water temperature were important predictors of brassy minnow presence. Appearances of adult-sized brown bullhead at one site corresponded with reduced abundance of native fishes. In growth experiments with brassy minnow, brown bullhead, and redside shiner (Richardsonius balteatus (Richardson, 1836)), brassy minnow exhibited mass loss and mortalities, suggesting that they were poor competitors. Our results contribute to a better understanding of abiotic and biotic factors affecting distribution and persistence of brassy minnow.

Abundance of larval native and nonnative fishes in floodplain habitats of the lower Waikato River, New Zealand

The floodplains of many large rivers worldwide are important spawning and nursery habitats for multiple fish species. We investigated the potential importance of different floodplain habitats for fish larvae. Samples were collected from 14 sites along the Waikato River, northern New Zealand, from September to October 2010. Larval fishes were identified using traditional morphological identification and DNA analyses. Our results revealed high densities of invasive koi carp and goldfish larvae in flooded terrestrial habitats compared to other habitat types. Species richness was highest in the wetland habitat. Redundancy analysis revealed that koi carp and goldfish abundances were strongly positively correlated with chlorophyll a concentrations and zooplankton densities. Floodplain habitats seem to be important habitat for larvae of both native and introduced fish species in the lower Waikato River. Because introduced larval fish out-numbered native fishes in floodplain habitats managers should consider implementing measures that at key times provide controlled access to floodplain habitats for native species and also limit access of introduced fishes.

Managed and natural inundation: benefits for conservation of native fish in a semi‐arid wetland system

ABSTRACT Floodplain wetlands are areas of high biodiversity and conservation value, including those in semi‐arid regions. River regulation has resulted in disconnection from the main river channel of several ephemeral wetland systems, with profound modifications to their natural wetting/drying cycles that have contributed to the decline in diversity, distribution and abundance of native fish. From 2005 to 2011, a series of managed inundation events through pumping followed by natural inundation allowed assessment and comparison of the fish assemblage developing in Hattah Lakes, a semi‐arid wetland system of the regulated Murray River (Victoria, Australia). As a result of one‐way pumping from the main channel to Hattah Lakes, a ‘filtered’ fish assemblage consisting mainly of small‐bodied native species and very low numbers of non‐native species fully developed within 2 years. After disconnection from the main river channel in the absence of pumping, within‐system recruitment also occurred, but later drying of all water bodies caused the entire fish assemblage to perish. Conversely, following two‐way flooding by natural inundation a more diverse fish assemblage developed, including large‐bodied native species but also non‐native species, some of which were previously unrecorded. Managed inundation through pumping in Hattah Lakes represents a viable option for the creation of fish habitat, for promoting recruitment, and as a measure of rehabilitation. However, the absence of connectivity back to the main river channel means that future measures should be implemented to maintain a refuge water pool until the next inundation event. Long‐term monitoring is a key component of the integrated wetland conservation framework adopted by the Ramsar Wetland Convention, and this is especially relevant to the conservation of semi‐arid wetlands world‐wide including Hattah Lakes. Copyright © 2012 John Wiley & Sons, Ltd.

Invasion success and impact of an invasive fish, round goby, in Great Lakes tributaries

AbstractAimEnvironmental and biological characteristics interact in complex ways to determine ecosystem susceptibility to invasive species, and a greater understanding of their relative roles in invader spread and impact is needed. We evaluated relationships between environmental characteristics, biodiversity of indigenous species, and the abundance and ecological impact of an invasive fish, round goby (Neogobius melanostomus).LocationTributaries to Lake Michigan, WI, USA.MethodsWe assessed the distribution and abundance of round gobies and native fishes in tributaries via electrofishing. We compared fish community composition and diversity in streams with (n = 30) and without (n = 52) round gobies and examined how trends in round goby abundance from 2007 to 2010 correlated with changes in abundance of five native benthic fishes. We used redundancy analysis to determine how indigenous stream communities related to environmental characteristics and round goby abundance.ResultsRound goby abundance was best explained by environmental characteristics, with watershed area and temperature explaining 22.4% of the variation. Species richness and Shannon diversity only explained 6.9% of the variation in round goby abundance and only an additional 2.3% after considering environmental characteristics. Round goby abundance was not a significant predictor of fish community composition, which was best explained by seven environmental variables (30.3% of the variation). Invaded communities had significantly higher indigenous species richness than uninvaded communities (8.38 vs. 6.54). Round goby abundance was low compared with estimates from other studies, but showed an increasing trend in many tributaries (average 10.8‐fold increase from 2007 to 2010). Surprisingly, there were no temporal trends in native benthic fish abundance despite increases in round goby abundance.Main conclusionsEnvironmental characteristics favouring high fish diversity (e.g. resource availability and warm water temperature) were positively associated with round goby abundance. However, round goby density and impact are relatively low in most tributaries at present, emphasizing the importance of considering heterogeneity in an invader's abundance when assessing invasion success.

Size and quantity of woody debris affects fish assemblages in a sediment-disturbed lowland river

Responses by fish assemblages to individual restoration actions among a suite of channel modifications are not well understood. We investigated whether increasing woody debris abundance, without significant change to channel morphology, would increase native fish abundance and species richness in a sediment-disturbed river channel (Glenelg River, Victoria, Australia). We conducted a Before–After, Control-Impact design experiment at twelve locations containing either a high (n=6) or low (n=6) quantity of large woody debris (LWD). We added small woody debris (SWD) to half (n=6: 3 high, 3 low LWD densities) of the locations to increase woody debris complexity without the impacts on channel morphology associated with LWD manipulations. Fish species richness and abundance was quantified using electrofishing surveys before (4 sampling trips) and after (3 sampling trips) SWD addition. Fish species richness was not associated with high or low quantities of LWD or with types of woody debris (LWD or SWD). Addition of SWD altered fish assemblage composition but the effect depended on LWD quantity. SWD additions to locations with low LWD quantities increased abundance of two, wood-affiliated species: Philypnodon grandiceps and Gadopsis marmoratus. SWD additions to locations with high LWD quantities increased abundance of P. grandiceps and Galaxias olidus. Fish body size was important in detecting a response to added SWD because for two species, only certain size classes responded: adults of P. grandiceps (>50mm TL) and juveniles of G. marmoratus (<123mm TL). Fish assemblages responded positively to increased density of SWD through local increases in abundance, despite channel sedimentation. Unlike LWD, SWD is relatively cheap to place in rivers because it does not require heavy machinery and can be obtained without tree mortality. The use of SWD to assist in habitat restoration, especially for small species of native fish and juvenile fish, should be considered as a strategy in river restoration.

Estimating recruitment dynamics and movement of rainbow trout (Oncorhynchus mykiss) in the Colorado River in Grand Canyon using an integrated assessment model

We used an integrated assessment model to examine effects of flow from Glen Canyon Dam, Arizona, USA, on recruitment of nonnative rainbow trout ( Oncorhynchus mykiss ) in the Colorado River and to estimate downstream migration from Glen Canyon to Marble Canyon, a reach used by endangered native fish. Over a 20-year period, recruitment of rainbow trout in Glen Canyon increased with the annual flow volume and when hourly flow variation was reduced and after two of three controlled floods. The model predicted that approximately 16 000 trout·year–1emigrated to Marble Canyon and that the majority of trout in this reach originate from Glen Canyon. For most models that were examined, over 70% of the variation in emigration rates was explained by variation in recruitment in Glen Canyon, suggesting that flow from the dam controls in large part the extent of potential negative interactions between rainbow trout and native fish. Controlled floods and steadier flows, which were originally aimed at partially restoring conditions before the dam (greater native fish abundance and larger sand bars), appear to have been more beneficial to nonnative rainbow trout than to native fish.

Effects of invasive macrophytes on freshwater fish and macroinvertebrate communities: the role of invasive plant traits

Biological invasions of aquatic plants (i.e., macrophytes) are a worldwide phenomenon, and within the last 15 years researchers have started to focus on the influence of these species on aquatic communities and ecosystem dynamics. We reviewed current literature to identify how invasive macrophyte species impact fishes and macroinvertebrates, explore how these mechanisms deviate (or not) from the accepted model of plant–fish interactions, and assess how traits that enable macrophytes to invade are linked to effects on fish and macroinvertebrate communities. We found that in certain instances, invasive macrophytes increased habitat complexity, hypoxia, allelopathic chemicals, facilitation of other exotic species, and inferior food quality leading to a decrease in abundance of native fish and macroinvertebrate species. However, mechanisms underlying invasive macrophyte impacts on fish and macroinvertebrate communities (i.e., biomass production, photosynthesis, decomposition, and substrate stabilization) were not fundamentally different than those of native macrophytes. We identified three invasive traits largely responsible for negative effects on fish and macroinvertebrate communities: increased growth rate, allelopathic chemical production, and phenotypic plasticity allowing for greater adaptation to environmental conditions than native species. We suggest that information on invasive macrophytes (including invasive traits) along with environmental data could be used to create models to better predict impacts of macrophyte invasion. However, effects of invasive macrophytes on trophic dynamics are less well-known and more research is essential to define system level processes.

Response by fish assemblages to an environmental flow release in a temperate coastal Australian river: A paired catchment analysis

AbstractDefining appropriate environmental flow regimes and criteria for the use of environmental water allocations requires experimental data on the ecological impacts of flow regime change and responses to environmental water allocation. Fish assemblages in one regulated and one unregulated tributary paired in each of two sub‐catchments of the Hunter River, coastal New South Wales, Australia, were sampled monthly between August 2006 and June 2007. It was predicted that altered flow regime due to flow regulation would reduce species richness and abundance of native fish, and assemblage composition would differ between paired regulated and unregulated tributaries. Despite significant changes in richness, abundance and assemblage composition through time, differences between regulated and unregulated tributaries were not consistent. In February 2007, an environmental flow release (‘artificial flood’) of 1400 ML was experimentally released down the regulated tributary of one of the two catchments over 6 days. The flow release resulted in no significant changes in fish species abundances or assemblage composition when compared to nearby unregulated and regulated tributaries. Flow regulation in this region has reduced flow variability and eliminated natural low‐flow periods, although large floods occurred at similar frequencies between regulated–unregulated tributaries prior to and during 2006–2007, resulting in only moderate changes to regulated flow regimes. Barriers to dispersal within catchments also compound the effects of flow regulation, and findings from this study indicate that the location of migratory barriers potentially confounded detection of the effects of flow regime change. Further experimental comparisons of fish assemblages in regulated rivers will refine river‐specific response thresholds to flow regime change and facilitate the sustainable use of water in coastal rivers. Copyright © 2010 John Wiley &amp; Sons, Ltd.

DNA barcoding of fishes of Laguna de Bay, Philippines

Laguna de Bay, the largest lake in the Philippines, is an important part of the country's fisheries industry. It is also home to a number of endemic fishes including Gobiopterus lacustris (Herre 1927) of family Gobiidae, Leiopotherapon plumbeus (Kner 1864) of family Terapontidae, Zenarchopterus philippinus (Peters 1868) of family Hemiramphidae and Arius manillensis Valenciennes 1840 of family Ariidae. Over the years, a steady decline has been observed in the abundance and diversity of native fishes in the lake due to anthropogenic disturbances. In this study, a total of 71 specimens of 18 different species belonging to 18 genera, 16 families, and seven orders were DNA barcoded using the mitochondrial cytochrome c oxidase subunit I (COI) gene. All of the fish species were discriminated by their COI sequences and one endemic species G. lacustris, showing deep genetic divergence, was highlighted for further taxonomic investigation. Average Kimura 2-parameter genetic distances within species, family, and order were 1.33%, 18.91%, and 24.22%, respectively. These values show that COI divergence increases as taxa become less exclusive. All of the COI sequences obtained were grouped together according to their species designation in the Neighbor-joining tree that was constructed. This study demonstrated that DNA barcoding has great potential as a tool for fast and accurate species identification and also for highlighting species that warrant further taxonomic investigation.

Invasive pike establishment in Cook Inlet Basin lakes, Alaska: diet, native fish abundance and lake environment

Northern pike (Esox lucius) were introduced to the northern Susitna Basin of south-central Alaska in the 1950’s, and have since spread throughout the upper Cook Inlet Basin. Extirpations of several native fish populations have been documented in this area. It is hypothesized here that invasive pike remodel the ecology of lakes by removing vulnerable prey types and that these changes are reflected in the diet of invasive pike. Trends in pike diet suggest that pike switch to less desirable but more abundant macroinvertebrate prey as preferred fish prey are eliminated. The impacts of pike introduction were studied in detail for one species of resident fish, the threespine stickleback (Gasterosteus aculeatus). Stickleback abundance decreases as pike invasion progresses. Conductivity is a significant environmental predictor of stickleback abundance, with higher conductivity apparently mitigating population reduction. Higher conductivity water may lessen the physiological costs of developing more robust armor, which reduces vulnerability to predation. Maximum lake depth also appears to predict stickleback abundance, though this trend was only marginally significant. Deeper lakes may provide an open-water refuge from pike predation by allowing stickleback to exist outside of the pike inhabited littoral zone. These findings indicate the importance of diverse habitat types and certain chemical and physical characteristics to the outcome of invasion by fish predators.

REMOVAL OF AQUATIC WEEDS GREATLY ENHANCES FISH COMMUNITY RICHNESS AND DIVERSITY: AN EXAMPLE FROM THE BURDEKIN RIVER FLOODPLAIN, TROPICAL AUSTRALIA

ABSTRACTHydrological changes associated with irrigation, in conjunction with increased nutrient concentrations and aquatic plant densities, have greatly impacted fish habitat values on the Burdekin River floodplain. The two most significant weeds in the Burdekin floodplain are water hyacinth (Eichhornia crassipes) and para grass (Urochloa mutica). Water hyacinth creates a base for the para grass (and then other weeds) to grow out into deeper water, creating weed mats that can then only be removed by mechanical means or floods of the largest magnitude. We attempted to rehabilitate floodplain lagoons by the mechanical removal of floating weed mats and monitored the result by measuring the subsequent effects on fish habitats and fish communities. Prior to weed removal, fish habitats were generally of poor quality, and fish community structure was skewed away from rich native assemblages to depauperate communities dominated in some instances by alien species. Poor water quality arising from floating weed mats is considered to be the main determinant of reduced fish abundance and diversity. After mechanical weed removal, recovery of water quality and physical habitat led to the re‐establishment of many native fish species. Key refuge habitats within the distribution channels were a critical source of recruits for fishes dispersing during times of elevated seasonal flows into the newly rehabilitated reaches. This study demonstrates that floating alien weed mats have significant negative effects upon aquatic communities and that mechanical removal of these weed mats (as opposed to chemical removal) results in dramatic improvements in native fish species richness and abundance. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Nonnative Fish Control in the Colorado River in Grand Canyon, Arizona: An Effective Program or Serendipitous Timing?

AbstractThe federally endangered humpback chub Gila cypha in the Colorado River within Grand Canyon is currently the focus of a multiyear program of ecosystem‐level experimentation designed to improve native fish survival and promote population recovery as part of the Glen Canyon Dam Adaptive Management Program. A key element of this experiment was a 4‐year effort to remove nonnative fishes from critical humpback chub habitat, thereby reducing potentially negative interactions between native and nonnative fishes. Over 36,500 fish from 15 species were captured in the mechanical removal reach during 2003–2006. The majority (64%) of the catch consisted of nonnative fish, including rainbow trout Oncorhynchus mykiss (19,020), fathead minnow Pimephales promelas (2,569), common carp Cyprinus carpio (802), and brown trout Salmo trutta (479). Native fish (13,268) constituted 36% of the total catch and included flannelmouth suckers Catostomus latipinnis (7,347), humpback chub (2,606), bluehead suckers Catostomus discobolus (2,243), and speckled dace Rhinichthys osculus (1,072). The contribution of rainbow trout to the overall species composition fell steadily throughout the study period from a high of approximately 90% in January 2003 to less than 10% in August 2006. Overall, the catch of nonnative fish exceeded 95% in January 2003 and fell to less than 50% after July 2005. Our results suggest that removal efforts were successful in rapidly shifting the fish community from one dominated numerically by nonnative species to one dominated by native species. Additionally, increases in juvenile native fish abundance within the removal reach suggest that removal efforts may have promoted greater survival and recruitment. However, drought‐induced increases in river water temperature and a systemwide decrease in rainbow trout abundance concurrent with our experiment made it difficult to determine the cause of the apparent increase in juvenile native fish survival and recruitment. Experimental efforts continue and may be able to distinguish among these factors and to better inform future management actions.

Relationships among invasive common carp, native fishes and physicochemical characteristics in upper Midwest (USA) lakes

Abstract – Common carp Cyprinus carpio is a widespread invasive species that, in high abundance, can impose numerous deleterious effects in aquatic ecosystems. Common carp increase turbidity and nutrient availability while reducing invertebrate prey resources and aquatic macrophytes, transforming shallow lakes from the clear‐ to turbid‐water state. However, potential effects of common carp on native fish communities have received limited attention. We evaluated the relationships among relative abundances of nine native fishes and common carp for 81 lakes in eastern South Dakota and their associated physicochemical characteristics. Inverse threshold relationships among relative abundances of native fishes and common carp were identified for black bullhead Ameiurus melas, black crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, white bass Morone chrysops and northern pike Esox lucius, while marginally significant relationships were detected for largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu. Lakes where common carp relative abundance exceeded 0.6 fish per net night had low abundance of native fishes, whereas lower abundance of common carp resulted in variable abundance of native fishes. Lakes with abundance of common carp surpassing 0.6 fish per net night were also characterised by larger surface areas and watersheds and impaired water quality (higher dissolved solids and chlorophyll a concentrations and lower secchi depth). Our results are consistent with the biotic‐abiotic constraining hypothesis that proposes biotic factors can regulate fish populations regardless of abiotic conditions. Thus, common carp abundance may need to be reduced and sustained below ecological thresholds to improve water quality and increase abundance of native fishes.

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 &amp; Sons A/SAbstract – 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.

Floodplain degradation and restoration in Northern Queensland: The response of the Alien Fish Pest Gambusia holbrooki

The Burdekin River basin is one of Queensland’s most important areas in terms of primary production, with sugar cane production dominating the delta region. Extensive clearing – as well as extensive irrigation which has altered the hydrology from naturally intermittent to artificially perennial – has greatly changed fish habitats on the delta (Perna 2003). Changes in hydrology have greatly benefited aquatic weeds, which in turn has greatly reduced dissolved oxygen content in the waterbodies (Perna 2003; Perna & Burrows 2005). Large-scale physical removal of aquatic weed infestations by floating harvester and excavator has been shown to greatly improve water quality, fish habitat and the diversity and abundance of native fishes in two lagoons and a 15 km reach of Sheep Station Creek, a typical floodplain creek system on the delta (Perna 2003, 2004; Perna & Burrows 2005).

Resilience of fishes and invertebrates to prolonged drought in two California streams

Long‐term data are needed to assess spatial and temporal variability of communities and their resilience to natural and anthropogenic disturbances, particularly in climatic regions marked by high interannual variability (e.g. mediterranean‐climate). A long‐term study at four sites on two streams in mediterranean‐climate California (annual sampling over 20 yr) allowed us to quantify the influence of a 5‐yr prolonged drought on stream invertebrate and fish communities. Invertebrate community composition did not show recovery following drought. The primary environmental factors influencing community composition, identified through principle components and multiple correspondence analyses were precipitation and flow permanence. Invertebrate taxon richness and abundance exhibited few responses (some site specific) and recovered quickly. Native fish abundance was lowest during the drought period and highest during the wet years that occurred at the end of the study period. Importantly, the prolonged drought facilitated the establishment and success of the invasive green sunfish (Centrarchidae: Lepomis cyanellus) that was then resilient to subsequent large flow events. There was high spatial synchrony in the temporal changes among all four sites, and three distinct periods were identified: early drought, late drought, and post‐drought years. However, we still found differences among sites along the flow permanence gradient from temporary to perennial in the response to drought of both invertebrate and fish assemblages likely as a result of changes in substrate, vegetation, and other habitat characteristics. The observed lack of resilience and negative impacts to biodiversity due to prolonged drought associated with long‐term habitat changes is important because hydroclimatic extremes are predicted to increase in frequency and magnitude with global climate change.

Effects of Flow Restoration and Exotic Species Removal on Recovery of Native Fish: Lessons from a Dam Decommissioning

Flow diversion and invasive species are two major threats to freshwater ecosystems, threats that restoration efforts attempt to redress. Yet, few restoration projects monitor whether removal of these threats improve target characteristics of the ecosystem. Fewer still have an appropriate experimental design from which causal inferences can be drawn as to the relative merits of removing exotic fish, restoring flow, or both. We used a dam decommissioning in Fossil Creek, Arizona, to compare responses of native fish to exotic fish removal and flow restoration, using a before-after-control-impact design with three impact treatments: flow restoration alone where exotics had not been present, flow restoration and exotic fish removal, and flow restoration where exotics remain and a control reach that was unaffected by restoration actions. We show that removal of exotic fish dramatically increased native fish abundance. Flow restoration also increased native fish abundance, but the effect was smaller than that from removing exotics. Flow restoration had no effect where exotic fish remained, although it may have had other benefits to the ecosystem. The cost to restore flow ($12 million) was considerably higher than that to eradicate exotics ($1.1 million). The long-term influence of flow restoration could increase, as travertine dams grow and re-shape the creek increasing habitat for native fish. But in the 2-year period considered here, the return on investment for extirpating exotics far exceeded that from flow restoration. Projects aimed to restore native fish by restoring flow should also consider the additional investment required to eradicate exotic fish.

Aquaculture, non‐native salmonid invasions and associated declines of native fishes in Northern Patagonian lakes

Summary1. Even though intensive aquaculture production of salmonids in lakes occurs in many locations around the world published studies on the survival and reproductive success of escaped cultured salmonids in freshwater ecosystems are not common. A recent expansion of aquaculture in Chile has led it to become the world’s second largest producer of cultured salmonids.2. We document the recent history of escaped and self‐sustaining salmonid populations over a wide spatial scale and a long temporal scale in Chilean Patagonian lakes. Our hypotheses are that salmonid density in lakes will be higher where there is intensive aquaculture, due to greater numbers of potential escapees. Secondly, if non‐native salmonids have adverse impacts on native fishes, increases in the abundance of non‐native species should be associated with decreases in relative abundance of native species. Finally, if the first two hypotheses are correct we anticipate that diets of salmonids may show evidence of predation on native fishes, diet overlap with native species, and evidence of the influence of feed from aquaculture operations in the diets of salmonids and native fishes.3. We sampled six lakes with gill nets from 1992 to 2001. Our results show that the relative abundance of free‐living salmonids is closely related to the level of fish farming production. Salmonids are the top predators and in lakes with fish farming the main prey item is native fishes. The relative abundance of native fishes has decreased, most likely due to predation by salmonids.4. Our study contributes to the understanding of the effects of non‐native salmonids in oligotrophic lakes, and it provides a starting point to judge the establishment of new fish farming sites in lakes around the world.

Breeding Season Diets of Egrets in Southeast Australia: Implications for Future Population Viability

Abstract Populations of egrets and other waterbirds in the Murray-Darling Basin of eastern Australia are declining. River regulation and increasing frequency of droughts are considered to be mainly responsible by reducing the frequency and extent of flooding to temporary wetlands. However, other changes have occurred to wetlands, such as the introduction of non-native fish, widespread severe declines in the abundance of native fish, increased salinity, sediment and nutrient concentrations, and removal of aquatic vegetation by livestock grazing. Current knowledge of the diets of egrets is inadequate for an assessment of any ecological implications arising from these changes. In this study the breeding season diets of Eastern Great Egret Ardea modesta and Intermediate Egret A. intermedia were quantified at a colony in the Murray Basin. Eastern Great Egrets depended mainly on introduced Common Carp Cyprinus carpio (94% of diet biomass), a species regarded as a severe pest of river systems and wetlands within...

A Threatened Fish Species (Aphanius dispar) in Saudi Arabia, A Case Study

The present study showed that the population density of a native fish (A. dispar) in the freshwater environments of Saudi Arabia is declining. It is concluded from the present investigations that A. dispar is not threatened by a single isolated factor, but instead faces numerous stressors that jeopardize multiple stages of their life cycle. Reduced availability of food, habitat degradation, chemical contamination, introduction of exotic species and exploitation have contributed to the decline of such native fish's abundance. Protecting fishes will help to protect aquatic biodiversity and in conservation of biological heritage of the country.