David A. Crook

Climate change and its implications for Australia's freshwater fish

Freshwater environments and their fishes are particularly vulnerable to climate change because the persistence and quality of aquatic habitat depend heavily on climatic and hydrologic regimes. In Australia, projections indicate that the rate and magnitude of climate change will vary across the continent. We review the likely effects of these changes on Australian freshwater fishes across geographic regions encompassing a diversity of habitats and climatic variability. Commonalities in the predicted implications of climate change on fish included habitat loss and fragmentation, surpassing of physiological tolerances and spread of alien species. Existing anthropogenic stressors in more developed regions are likely to compound these impacts because of the already reduced resilience of fish assemblages. Many Australian freshwater fish species are adapted to variable or unpredictable flow conditions and, in some cases, this evolutionary history may confer resistance or resilience to the impacts of climate change. However, the rate and magnitude of projected change will outpace the adaptive capacities of many species. Climate change therefore seriously threatens the persistence of many of Australia’s freshwater fish species, especially of those with limited ranges or specific habitat requirements, or of those that are already occurring close to physiological tolerance limits. Human responses to climate change should be proactive and focus on maintaining population resilience through the protection of habitat, mitigation of current anthropogenic stressors, adequate planning and provisioning of environmental flows and the consideration of more interventionist options such as managed translocations.

The influence of spatial scale and habitat arrangement on diel patterns of habitat use by two lowland river fishes

There is growing awareness that patterns of habitat use by animals cannot be isolated from issues of scale. Recently, techniques have been devised which allow empirical testing of hypotheses related to the effects of spatial scale on habitat use. We used spatially explicit statistical procedures to examine the roles of scale and habitat arrangement in determining fish distribution patterns in a reach of an Australian lowland river. Native golden perch and introduced common carp were tracked day and night using radiotelemetry over a 10 day period and their distributions compared with mapped habitat variables. Golden perch were significantly associated with depth, current velocity, substratum and cover at larger scales of analysis both day and night, and at smaller scales during the day. At night, however, associations between golden perch and habitat variables were generally much weaker at small scales. Common carp were generally not significantly associated with habitat variables at larger scales of analysis, whereas at smaller scales they were associated with depth, current velocity, substrate and cover. Associations were generally stronger during the day than at night. Our study emphasises the need to consider scale-dependence in studies of fish-habitat associations. Management and restoration of fish habitat in lowland rivers should be based on an understanding of habitat use at scales relevant for the fish rather than at scales arbitrarily defined by humans.

Human effects on ecological connectivity in aquatic ecosystems: Integrating scientific approaches to support management and mitigation

Understanding the drivers and implications of anthropogenic disturbance of ecological connectivity is a key concern for the conservation of biodiversity and ecosystem processes. Here, we review human activities that affect the movements and dispersal of aquatic organisms, including damming of rivers, river regulation, habitat loss and alteration, human-assisted dispersal of organisms and climate change. Using a series of case studies, we show that the insight needed to understand the nature and implications of connectivity, and to underpin conservation and management, is best achieved via data synthesis from multiple analytical approaches. We identify four key knowledge requirements for progressing our understanding of the effects of anthropogenic impacts on ecological connectivity: autecology; population structure; movement characteristics; and environmental tolerance/phenotypic plasticity. Structuring empirical research around these four broad data requirements, and using this information to parameterise appropriate models and develop management approaches, will allow for mitigation of the effects of anthropogenic disturbance on ecological connectivity in aquatic ecosystems.

Development and Evaluation of Methods for Osmotic Induction Marking of Golden Perch Macquaria ambigua with Calcein and Alizarin Red S

Abstract We conducted a series of osmotic induction procedures for marking golden perch Macquaria ambigua with calcein and alizarin red S (ARS), evaluated the factors that influenced mark quality, and tested for any effects on fish growth and mortality. Three aspects of the marking protocols were considered: immersion time in a 5% salt solution (0, 5, or 10 min), immersion time in the fluorescent dye (5 or 10 min), and concentration of the dye (low or high). Quantitative estimates of mark intensity using photographs of marked fish were made with image analysis software. Although there were some significant interactions between factors, salt immersion was generally the primary determinant of mark intensity, followed by dye concentration and dye immersion time. Fish marked with calcein did not have higher mortality rates than unmarked fish and had significantly higher growth rates. The highest-exposure ARS treatments resulted in higher mortality and lower growth rates than for unmarked fish. Following this ...

Transgenerational marking of freshwater fishes with enriched stable isotopes: a tool for fisheries management and research

A promising new method of marking larval freshwater fishes with enriched stable isotopes by means of injecting the maternal parent with the marking agent was investigated. The (138)Ba:(137)Ba ratios in the otoliths of larval golden perch Macquaria ambigua were compared to determine the effect of injecting female broodstock with different dosages of enriched (137)Ba at various times before spawning. There was 100% mark success in the progeny of fish injected with 20 microg g(-1) of enriched (137)Ba 24 h before inducing spawning with hormones and 40 microg g(-1) administered at the same time as inducement of spawning. Injection of 40 microg g(-1) enriched (137)Ba 21 days before spawning resulted in only 81% mark success and suggests rapid elimination of barium in M. ambigua. Injection with enriched (137)Ba did not significantly affect the fertilization rate, number of fertilized eggs or hatching rate compared with long-term hatchery records. These results suggest that transgenerational marking is an effective and affordable means of mass-marking larval fishes. Thousands of larval fishes can be permanently marked with a unique artificial isotopic mark via a single injection into the maternal parent, thus avoiding the handling of individual fishes or having to deal with chemical baths. Because no single mark or tagging method is suitable for all situations, transgenerational marking with enriched stable isotopes provides another method for researchers and managers to discriminate both hatchery-reared and wild fishes.

A moving target—incorporating knowledge of the spatial ecology of fish into the assessment and management of freshwater fish populations

Freshwater fish move vertically and horizontally through the aquatic landscape for a variety of reasons, such as to find and exploit patchy resources or to locate essential habitats (e.g., for spawning). Inherent challenges exist with the assessment of fish populations because they are moving targets. We submit that quantifying and describing the spatial ecology of fish and their habitat is an important component of freshwater fishery assessment and management. With a growing number of tools available for studying the spatial ecology of fishes (e.g., telemetry, population genetics, hydroacoustics, otolith microchemistry, stable isotope analysis), new knowledge can now be generated and incorporated into biological assessment and fishery management. For example, knowing when, where, and how to deploy assessment gears is essential to inform, refine, or calibrate assessment protocols. Such information is also useful for quantifying or avoiding bycatch of imperiled species. Knowledge of habitat connectivity and usage can identify critically important migration corridors and habitats and can be used to improve our understanding of variables that influence spatial structuring of fish populations. Similarly, demographic processes are partly driven by the behavior of fish and mediated by environmental drivers. Information on these processes is critical to the development and application of realistic population dynamics models. Collectively, biological assessment, when informed by knowledge of spatial ecology, can provide managers with the ability to understand how and when fish and their habitats may be exposed to different threats. Naturally, this knowledge helps to better evaluate or develop strategies to protect the long-term viability of fishery production. Failure to understand the spatial ecology of fishes and to incorporate spatiotemporal data can bias population assessments and forecasts and potentially lead to ineffective or counterproductive management actions.

Nuptial coloration varies with ambient light environment in a freshwater fish

Visual signals play a vital role in many animal communication systems. Signal design, however, often varies within species, raising evolutionarily important questions concerning the maintenance of phenotypic diversity. We analysed nuptial colour variation within and among nine populations of southern pygmy perch (Nannoperca australis Günther) along an environmental light gradient. Within populations, larger males were redder and blacker, and better‐condition males were blacker. Among populations, red colour was positively correlated with the amount of orange‐red light present, suggesting that males are likely optimizing signal conspicuousness by producing proportionally larger and redder patches in broad spectrum environments with more orange‐red light. Signal contrast, in this regard, is maximized when red colour, appearing bright because of the prevalence of red wavelengths, is viewed against the water‐column background. Together, our results are concordant with the sensory drive hypothesis; selection favours signal adaptations or signal plasticity to ensure communication efficacy is maximized in different light environments.

A Method for Improving the Estimation of Natal Chemical Signatures in Otoliths

Abstract Laser ablation-inductively coupled plasma mass spectrometry has been widely used in studies aimed at identifying the natal sites of fish through analysis of the otolith core region. It is critical, then, that measurements of chemistry at the core accurately represent the natal chemical environment, rather than reflecting potential physiological and ontogenetic influences on elemental incorporation during the embryonic and early larval phases. We analyzed sagittal otoliths from 840 age-0 and age-1 Australian smelt Retropinna semoni using a 193-nm Ar-F excimer laser system with a fast response two-volume sample cell to demonstrate a rapid depth-profiling method that enables more accurate estimations of the natal chemistry by sampling a target region of the otolith that excludes the primordium. The method involves (1) examination of validated daily growth increments to identify the target region; (2) measurement of the amount of otolith material removed by each laser pulse; and (3) use of elevated 5...

Production of External Fluorescent Marks on Golden Perch Fingerlings through Osmotic Induction Marking with Alizarin Red S

Abstract Osmotic induction marking trials with alizarin red S (ARS) were conducted on golden perch Macquaria ambigua to evaluate the use of ARS as a lower-cost alternative to osmotic induction marking with calcein for producing external fluorescent marks on hatchery-produced fish. After a 10-min immersion in a 5% solution of salt, experimental groups of golden perch were rinsed for 5 s in freshwater and immersed for 10 min in either a 0.1% or 0.5% solution of ARS, whereas control groups were either left untreated or immersed in a 0.1% solution of ARS for 10 min without prior immersion in the salt solution. All fish treated in the 0.5% solution of ARS died within 5 min of immersion, but no mortalities were observed in any of the controls or fish treated with the 0.1% solution of ARS. External fluorescent marks were observed on both the osmotic induction-marked fish and the direct ARS immersion-marked fish 100 d after treatment, but the osmotic induction-marked fish possessed more intense marks. Clear marks...

Evidence of diadromous movements in a coastal population of southern smelts (Retropinninae: Retropinna) from Victoria, Australia

Understanding the migratory behaviour of fishes is critical to the conservation and management of fish assemblages in coastal rivers. We analysed the otolith chemical signatures of smelt, Retropinna sp., from inland and coastal populations in mainland south-eastern Australia to determine whether individuals within coastal populations of the species were diadromous. Assessments of otolith chemical composition combined with water chemistry data were used to make inferences about the migration histories of individual fish. A proportion of the smelt collected from the freshwater reaches of a coastal river exhibited diadromous movements, with the majority of fish analysed showing evidence of estuarine or marine occupation as larvae/juveniles and a minority inhabiting freshwater throughout their life histories. A broad range in the daily ages of upstream migration into freshwater (15-106 days) and the timing of these migrations suggest that spawning and migration occur over several months during the summer/autumn period. The results of this study suggest that southern smelts are an ecologically variable taxonomic group and that conservation and management actions should take into account the range of migratory behaviours exhibited both within populations and across regions.