Why landscape connectivity matters to fish populations.

One of the objectives of providing fish passage is to improve fish populations. Connectivity at large scales is difficult to implement, especially given the costs and time-frames involved. Indeed, the need for fish passage over multiple barriers and large scales is often questioned. With limited evidence available to indicate improvement to populations, this can be a hard proposition to prosecute. Golden perch is a wide-ranging, mobile fish species of thee Murray-Darling Basin (MDB) in south-eastern Australia. It has migratory movements of both adults and juveniles, in addition to drifting eggs and larvae. It is a popular angling species, but like most native MDB fishes, it must compete for both water and habitat access with irrigation needs and infrastructure. This species is distributed across the MDB (almost 1 M km2) and this paper utilises new knowledge of the movements of this species through its inclusion in a metapopulation model to illustrate how actions in any location have the ability to alter populations in other regions of its range. Reinstatement of key flow components, together with connectivity, both of which greatly affect movements, are vital to the management of golden perch populations. Predictions from population modelling provide theoretical indications of the need for landscape-scale connectivity, and the potential benefits to golden perch populations. This approach may be applicable to prosecuting the case for fish passage for many other species

Priority management actions for alien freshwater fish species in Australia

In Australia, alien freshwater fish are continuing to steadily increase in number of species (reported in this paper to be 43), abundance, and distribution. In general however, their impacts are not well quantified in either environmental or economic terms and current management to reduce their impacts is limited and lacking direction. Although carp Cyprinus carpio have received some attention, very little is known about the impacts and even the distribution of most species. There is a lack of recognition of the problem, inconsistency in legislation, policy, and approaches across jurisdictions, and no nationally coordinated on?the?ground management actions. Where legislation and policy is available it is not always used to good effect. This paper provides a synthesis of existing knowledge of alien fishes in Australia, suggests a new management approach, and recommends priority management actions

Will they stay or will they go? Movement and recruitment dynamics of an iconic Australian freshwater fish in a cold-water impacted River

The construction of large water storages and subsequent alteration of flow regimes and thermal pollution have had devastating impacts on native freshwater fish populations globally. Native fish populations in the lower reaches of the Mitta Mitta River have declined substantially since the construction (in the 1970’s) and operation of Dartmouth Dam. Self-sustaining populations of Trout cod and Murray cod were reported to have substantially declined or become locally extinct in the river by the early 1990’s, attributed largely to the largely annual release of cold water during spring and summer. In more recent times, recreational fishing reports and fish surveys have detected Murray cod again occupying this reach of river. This prompted managers to reconsider the general view that the reach is unsuitable for native fish populations. Here we present outcomes of a research project aimed at improving the knowledge of the Murray cod population in the lower Mitta Mitta River with the aim of guiding improved river operations and management. We investigate patterns of recruitment dynamics, movement and hydrological records to understand the role of water operations in influencing population dynamics of Murray cod in the lower reaches of the River. We then use this information in a population modelling framework to explore long-term trajectories of the population under a variety of management scenarios

Deformation-induced and reaction-enhanced permeability in metabasic gneisses, Iona, Scotland: controls and scales of retrograde fluid movement

The spatial distribution of greenschist-facies retrograde reaction products in metabasic gneisses from Iona, western Scotland, has been investigated. The retrograde products may be broadly accounted for by a single reaction, but their different spatial and temporal development indicates that a series of reactions occur with significantly different scales of metasomatic transfer. After initial fluid influx linked to deformation-induced high permeability, reaction-enhanced permeability, coupled to cycling of fluid pressure during faulting, strongly controls the pervasive retrogression. Ca-plagioclase and pyroxene in the gneisses are replaced by albite and chlorite in pseudomorphic textures, and this is followed by localized epidotization of the albite. Two main generations of epidote are formed in the gneisses. Epidosite formation is associated with prominent zones of cataclasite indicating a strong link between faulting and fluid influx. In contrast, complete alteration of albite to epidote in the host metabasic gneisses is spatially complex, and areas of pervasive alteration may be constrained by both epidote-rich veins and cataclasites. In other instances, reaction fronts are unrelated to structural features. Volume changes associated with individual stages of the reaction history strongly control the localized distribution of epidote and the earlier more widespread development of chlorite and albite. Such behaviour contrasts with adjacent granitic gneisses where epidotization is restricted to local structural conduits. Many small-scale mineralized fractures with evidence of having previously contained fluids do not enhance the pervasive retrogression of the metabasic gneisses and represent conduits of fluid removal. Retrogression of these basement gneisses is dominated by a complex combination of reaction-enhanced and reaction-restricted permeability, kinetic controls on the nucleation of reaction products, changes in fluid composition buffered by the reactions, and periodic local migration of fluids associated with fault movements. This combination generates spatially complex patterns of epidotization that are limited by cation supply rather than fluid availability and alternations between focused and pervasive types of retrogression