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The biomass of organisms of different sizes is increasingly being used to explore macroscale variation in food-web and community structure. Here we examine how invasive species and river flow regulation affect native fish biomass and fish community [log.sub.10] biomass--body mass scaling relationships in Australia's largest river system, the Murray-Darling. The [log.sub.10] biomass--body mass scaling exponent (scaling B) of invasive fishes (95% CI: -0.14 to -0.18) was less negative than for native fishes (95% CI: -0.20 to -0.25), meaning that invasive species attained a higher biomass in larger size-classes compared to native species. Flow alteration and invasive common carp (Cyprinus carpio) biomass were correlated with severe reductions in native fish biomass ranging from -47% to -68% (95% CI). Our study provides novel evidence suggesting that invasive and native communities have different biomass--body mass scaling patterns, which likely depend on differences in their trophic ecology and body size distributions. Our results suggest that restoration efforts using environmental flows and common carp control has potential to boost native fish biomass to more than double the current level.La biomasse d'organismes de differentes tailles est de plus en plus utilisee pour etudier les variations a echelle macroscopique de la structure des reseaux trophiques et des communautes. Nous examinons l'incidence d'especes envahissantes et de la regularisation du debit des rivieres sur la biomasse de poissons indigenes et les relations [log.sub.10] biomasse--masse corporelle pour les communautes de poissons dans le plus grand reseau hydrographique d'Australie, celui de Murray- Darling. L'exposant de la relation [log.sub.10] biomasse--masse corporelle (<>) de poissons envahissants (IC de 95 % : -0,14 a -0,18) est moins negatif que pour les poissons indigenes (IC de 95 %: -0,20 a -0,25), ce qui signifie que les especes envahissantes atteignent une plus grande biomasse dans les classes de plus grande taille que les especes indigenes. La modification du debit et la biomasse de carpes communes (Cyprinus carpio) envahissantes sont correlees a des baisses importantes de la biomasse de poissons indigenes allant de -47 % a -68 % (CI de 95 %). Notre etude fournit de nouvelles donnees qui donnent a penser que les communautes d'especes envahissantes et indigenes presentent differents motifs de relations entre la biomasse et la masse corporelle, qui dependent vraisemblablement de differences de leur ecologie trophique et de leurs repartitions des tailles du corps. Nos resultats indiqueraient que les efforts de restauration faisant appel aux debits environnementaux et au controle des carpes communes pourraient permettre de plus que doubler la biomasse de poissons indigenes. [Traduit par la Redaction], IntroductionEcological communities are size-structured (Hildrew et al. 2007) whereby large-bodied predators generally consume smaller prey and there are disproportionately more smaller organisms, with a higher total biomass, than large ones [...]

Rapid increases in native riverine fish populations associated with trophic upsurge immediately following reservoir construction are well documented. Repeated upsurge periods and extended benefits to populations are, however, less understood. We used sclerochronology to investigate fish growth and netting surveys to estimate recruitment and abundance of a lacustrine population of an Australian riverine fish, the Macquarie perch (Macquaria australasica) in Lake Dartmouth. Record low inflows from 1997 to 2008 caused the reservoir to shrink to its lowest volume since construction. Refilling began in 2008, reaching 99% capacity in 2013. We hypothesized that fish growth, recruitment, and abundance would increase in response to the refilling of the lake, reproducing a similar response to the initial filling period. Our findings supported this hypothesis. Macquarie perch growth, recruitment, and abundance were enhanced during the refilling of Lake Dartmouth. Growth, best explained by the effects of dam height, change in dam height, temperature (and their interactions), and recruitment, were highest during the first years of refilling when lake levels and temperatures were low. We propose one or a combination of varying levels of intraspecific competition (low during initial filling and high following population expansion) and improved riverine conditions for reproductive success as the most plausible explanation. Our results suggest extended periods of low lake levels followed by rapid inundation events are likely to enhance recruitment and population growth opportunities for this species. While reservoir construction in general impacts negatively on native fish populations, the potential to offset these impacts for conservation management purposes should be considered. Les augmentations rapides de populations de poissons de riviere indigenes associees a la poussee trophique qui suit immediatement la construction d'un reservoir sont bien documentees. La comprehension de periodes de poussee trophique successives et de leurs avantages pour les populations demeure toutefois plus limitee. Nous avons utilise la sclerochronologie pour etudier la croissance des poissons et des releves au filet pour estimer le recrutement et l'abondance d'une population lacustre d'un poisson de riviere australien, la perche de Macquarie (Macquaria australasica) dans le lac Dartmouth. Des debits entrants d'une faiblesse record de 1997 a 2008 ont fait diminuer le volume du reservoir jusqu'au point le plus bas enregistre depuis sa construction. Le nouveau remplissage a debute en 2008, pour atteindre 99% de la capacite du reservoir en 2013. Nous avons postule que la croissance, le recrutement et l'abondance des poissons augmenteraient en reponse a ce nouveau remplissage du lac, une reaction semblable a celle observee durant le remplissage initial. Nos constatations appuient cette hypothese. La croissance, le recrutement et l'abondance des perches de Macquarie ont augmente durant le nouveau remplissage du lac Dartmouth. La croissance, qu'expliquent le mieux les effets de la hauteur du barrage, des changements de cette hauteur et de la temperature (et leurs interactions), ainsi que le recrutement etaient a leur plus fort durant les premieres annees du nouveau remplissage, quand les niveaux et les temperatures du lac etaient faibles. Nous proposons que les variations du degre de concurrence intraspecifique (faible durant le remplissage initial, plus eleve apres l'expansion de la population) et (ou) l'amelioration des conditions fluviales necessaires au succes de reproduction constituent l'explication la plus plausible. Nos resultats donnent a penser que de longues periodes de faibles niveaux du lac suivies par des inondations rapides sont susceptibles d'accroitre les possibilites de recrutement et de croissance de la population pour cette espece. Si, en general, la construction de reservoirs a une incidence negative sur les populations de poissons indigenes, la compensation possible de ces impacts aux fins de gestion et de conservation devrait etre prise en consideration. [Traduit par la Redaction], Introduction The construction of large dams and subsequent creation of reservoirs has been a major driver of reductions in the range and abundance of native riverine fishes globally. The detrimental [...]

Variation in river flow is a strong behavioural determinant for the movement of many freshwater fish species and often is linked to key aspects of their life cycle. The alteration of natural flow regimes to meet human water demands can result in changes to this variability, and cause declines in water‐dependent biota. Environmental flows are used as a remediation tool in some regulated rivers with the intention of restoring aspects of the natural flow regime to benefit riverine species, although empirical data are required to inform the efficacy of these interventions.Using acoustic telemetry, we quantified the movement responses of two large‐bodied native fish species (freshwater catfish, Tandanus tandanus and Murray cod, Maccullochella peelii) to variations in river flow over 4 years in two intermittent regulated rivers in the northern Murray–Darling Basin, Australia. Both rivers received periodic environmental flow releases and also there were several large natural flow events during the study period.Both species displayed a range of intra‐specific movement behaviours. Analysis of individuals' movements revealed five distinct functional groups, which were represented in both species. We found that periods of environmental flow delivery played an important role in the movement behaviour of both species. Murray cod were more likely to move during periods of environmental flow releases, whereas freshwater catfish were less likely to move on an environmental release following higher antecedent flows.No large‐scale philopatric movements were observed, yet Murray cod were more likely to move during the breeding period, indicative of nest site selection. We also found that the likelihood of movement in both species was higher in the smaller of the two rivers for a given magnitude of flow.Our results suggest that environmental flows may benefit certain fish species by facilitating, rather than cueing breeding behaviours, allowing individuals improved access to, and provision of, higher‐quality nesting habitats.These findings will aid water managers in creating economical and targeted environmental flow releases, timing larger flow pulses for the species with flow‐cued reproductive strategies, and providing a continuity of smaller baseflows for species whose reproduction is not dependent on flow cues but may be enhanced by greater connectivity. [ABSTRACT FROM AUTHOR]

Evaluating wetland vegetation responses to flow regimes is challenging because of the inherently complex, variable and dynamic nature of wetland vegetation in space and time.Wepropose four principles to guide the development of management objectives and evaluation approaches to support adaptive management of wetland vegetation in flowmanaged systems. First, we assert a need for more explicit, direct and defensible alignment of management objectives, targets and indicators to reflect broader ecological, sociocultural and economic values, and the underlying ecosystem functions that support them. Second, we propose a framework for indicator selection across multiple spatiotemporal scales and levels of ecological organisation, from individuals to landscape mosaics (vegscapes). Third, we emphasise the need to evaluate vegetation condition and responses to environmental flows in relation to a more nuanced understanding of temporal flow dynamics. Finally, we discuss the importance of considering the effects of non-flow variables that can modify vegetation responses to environmental flows. We highlight key knowledge needs required to support the implementation of these principles, particularly the urgency of improving our understanding of ecological, sociocultural and economic values of wetland vegetation and the attributes and functions that support these values. [ABSTRACT FROM AUTHOR]

Globally, urban expansion and climate change interact to threaten stream ecosystems and are accelerating the loss of aquatic biodiversity. Waterway managers urgently need tools to understand the potential combined impacts of urbanization and climate change and to identify effective mitigating management interventions for protecting freshwater biota. We address this challenge using the semi‐aquatic mammal the platypus (Ornithorhynchus anatinus) as a focal species. We developed high‐resolution environmental spatial data for stream networks and spatially explicit habitat suitability models (HSMs) to explore the impact of threats and to identify the combination of management actions most likely to maintain or improve habitat suitability over the next 50 years in greater Melbourne, Australia. We developed and evaluated platypus HSMs (males‐and‐females and females‐only) including validation using an independent environmental DNA data set. Platypus occurred more commonly in larger, cooler streams with greater catchment‐weighted discharge, following periods of greater stream flow. They were positively associated with near‐stream forest cover and negatively associated with annual air temperature and urban stormwater runoff. Extensive reductions in suitable platypus habitat are predicted to occur under urbanization and climate change scenarios, with the greatest threat expected from reduced streamflows. This emphasizes the importance of maintaining flow regimes as part of conserving platypus in the region; however, substantial additional benefit is predicted by concurrent riparian revegetation and urban stormwater management efforts (that also have the potential to contribute to the streamflow objectives). Provision of adequate streamflows in a future with increasing water demands and water security requirements will likely require creative integrated water management solutions. Our high‐resolution stream network and HSMs have allowed predictions of potential range‐shifts due to urban expansion and climate change impacts at management‐relevant scales and at the whole‐of‐landscape scale. This has enabled systematic strategic planning, priority action planning and target setting in strategic policy development. [ABSTRACT FROM AUTHOR]