Gadopsis Bispinosus Research Articles

Two wild carnivores selectively forage for prey but not amino acids

In nutritional ecology the intake target is the diet that maximises consumer fitness. A key hypothesis of nutritional ecology is that natural selection has acted upon the behavioural and physiological traits of consumers to result in them Selectively Consuming prey to match the Intake Target (SCIT). SCIT has been documented in some herbivores and omnivores, which experience strong heterogeneity in the nutritional quality of available foods. Although carnivores experience a prey community with a much more homogeneous nutrient composition, SCIT by carnivores has nevertheless been deemed highly likely by some researchers. Here we test for SCIT for micronutrients (amino acids) in two freshwater carnivores: the river blackfish and the two-spined blackfish. Although both blackfishes exhibited non-random consumption of prey from the environment, this resulted in non-random consumption of amino acids in only one species, the river blackfish. Non-random consumption of amino acids by river blackfish was not SCIT, but instead an artefact of habitat-specific foraging. We present hypotheses to explain why wild populations of freshwater carnivores may not exhibit SCIT for amino acids. Our work highlights the need for careful, critical tests of the hypotheses and assumptions of nutritional ecology and its application to wild populations.

Differential impacts of a wildfire and post-fire sedimentation event on platypus and fish populations in a Victorian upland river

Context Wildfire can affect freshwater ecosystems in many ways, notably when post-fire rainfall washes ash and sediment into waterways. Aims We investigated species-specific effects of bushfire and subsequent channel sedimentation on the abundance of platypus and fish populations in the upper Buffalo River, Australia. Methods Pre- and post-fire population surveys were conducted using fyke nets. Key results There was no evidence that fish numbers declined because of direct fire effects. However, native two-spined blackfish and Macquarie perch numbers dropped dramatically following post-fire sedimentation, whereas non-native redfin perch increased, most likely as a result of migration from a nearby lake. Platypus captures were consistently recorded at all survey sites both before and after the fire and sediment inflows occurred, with many juveniles being recorded in the first post-fire breeding season. Conclusions The platypus’s greater resilience to post-fire sediment inflows than that of native fish presumably reflects its reliance on lungs rather than gills and its ability to take refuge in burrows. It also has a broad diet, flexible foraging behaviour, is highly vagile and typically stores enough fat to support fasting for up to 2–3 weeks. Implications Management of fire-affected aquatic ecosystems must consider species-specific responses of freshwater vertebrates to fire.

Effects of current and future climates on the growth dynamics and distributions of two riverine fishes

Abstract To facilitate conservation planning, there is a need for improved confidence in forecasts of climate change impacts on species distributions. Towards that end, there have been calls for the development of process‐based models to test hypotheses concerning the mechanisms by which temperature shapes distribution and to corroborate forecasts of correlative models. Models of temperature‐dependent growth (TDG) were developed for two Australian riverine blackfishes with disjunct longitudinal distributions: Gadopsis marmoratus (occupies lower, warmer elevations) and Gadopsis bispinosus (occupies higher, cooler elevations). The models were used to (a) predict blackfish monthly and annual growth dynamics under current and future climate scenarios within different elevation bands of their current distribution, and (b) test the hypothesis that, under the current climate, the distributions of each species would be positively correlated with predicted TDG. Increases in mean annual growth were forecast for both species under all warming scenarios, across all elevation bands. Both species currently occupy annual habitat temperatures below those optimal for growth. Under certain warming scenarios, the predicted increases in annual growth belie forecasts of within‐year dynamics that may interact with the phenology of blackfish to impair recruitment. There was not a significant positive linear relationship between predicted TDG and observed abundance among river segments for either species. Both species were strongly under‐represented where annual growth rates were forecast to be optimal and over‐represented where growth rates were forecast to be intermediate. Confidence in forecasts of climate change impacts based on correlative models will increase when those forecasts are consistent with a mechanistic understanding of how specific drivers (e.g. water temperature) affect processes (e.g. growth). This process‐based study revealed surprises concerning how future climates may affect fish growth dynamics, showing that although the blackfish distributions are correlated with temperature the temperature‐dependent mechanisms underpinning that correlation require further investigation.

Metabarcoding demonstrates dietary niche partitioning in two coexisting blackfish species

A problem for fisheries ecologists who carry out dietary analysis on their specimens is dealing with contents that are difficult to identify, particularly when the contents comprise digested prey. We used a DNA metabarcoding approach to determine the diets of two co-occurring black fish species (Gadopsis bispinosus and Gadopsis marmoratus) to circumvent any issues with trying to apply microscopic methods to identify diets. We examined the frequency of occurrence of taxa across all specimens and the proportion that taxa contributed to total diet. In this way we hoped to demonstrate that a DNA-based method could resolve dietary differences of coexisting taxa. We showed that 10 macroinvertebrate taxa dominated the diets of both species and, of these, 7 occurred in all specimens of both taxa, indicating they were an important component of the diet of both species. Twelve taxa were present only in the G. bispinosus diet and four of those were terrestrial invertebrates; six taxa were found only in G. marmoratus. Our DNA-based approach to examine the taxa in the guts of two co-existing Gadopsis species provided sufficient resolution to show a significant degree of dietary partitioning.

Contrasting fundamental and realized niches: two fishes with similar thermal performance curves occupy different thermal habitats

AbstractHuman alteration of thermal regimes of freshwater ecosystems is creating an urgent need to understand how freshwater ectotherms will fare under different thermal futures. Two key questions are: 1) how well do the fundamental thermal niches of ectotherms map to their realized thermal niches, and 2) which axes of the fundamental thermal niche must be modeled to predict temperature-dependent fitness in real ecosystems? The first question is particularly challenging in riverine systems, where gradients in temperature are strongly confounded by gradients in other biotic and abiotic drivers. To address these questions, we compared the realized and fundamental thermal niches of 2 congeneric riverine fish: Gadopsis marmoratus and Gadopsis bispinosus. We characterized their realized thermal niches by examining their distributions in relation to environmental temperature at multiple scales. We characterized their fundamental thermal niches by doing laboratory experiments on the thermal sensitivity of swimmi...

Assessing the impacts of reservoir expansion using a population model for a threatened riverine fish

Increasing demand for water and a desire for greater human water security has facilitated the global expansion of dams, with river regulation acknowledged as the leading cause of biodiversity decline in rivers. Native biota within these stressed systems are also impacted by reductions in habitat availability, decreased hydraulic diversity, increased sedimentation, movement barriers, invasive species and altered flows that may profoundly change the character and functioning of rivers. Construction or enlargement of reservoirs is continuing, and whilst downstream impacts are often considered, upstream impacts receive far less attention. We develop a population model to examine the impacts of reservoir expansion on a threatened riverine species in South Eastern Australia: the two-spined blackfish. We examined two processes, loss of breeding habitat and increased predation, directly linked to reservoir expansion as well as a broader threat of recruitment failure due to sedimentation. These threatening processes were assessed using the expected minimum population size as an indicator of risk. As is often the case for threatened species, limited data were used to parameterise the model and sensitivity analysis performed to assess the appropriateness of the model parameterisation. The outcomes indicate that the two-spined blackfish population is vulnerable to the loss of breeding habitat particularly if two-spined blackfish are unable to spawn in the larger dam, although this vulnerability is ameliorated if the whole river is accounted for. Including possible impacts from the resident trout population for the whole river, indicates the two-spined blackfish to be vulnerable to low level predation particularly if the trout population have a high growth rate. Population modelling has rarely been used to predict the consequences of dam construction on aquatic species/communities. The example here shows it to be a powerful tool to visualise and quantify potential biodiversity outcomes.

Regionalisation of freshwater fish assemblages in the Murray–Darling Basin, Australia

Regionalisations based on species assemblages are a useful framework for characterising ecological communities and revealing patterns in the environment. In the present study, multivariate analyses are used to discern large-scale patterns in fish assemblages in the Murray–Darling Basin, based on information from the Murray–Darling Basin Authority’s first Sustainable Rivers Audit (SRA), conducted in 2004–2007. The Basin is classified into nine regions with similar historical fish assemblages (i.e. without major human intervention), using data that combine expert opinion, museum collections and historical records. These regions are (1) Darling Basin Plains, (2) Northern Uplands, (3) Murray Basin Plains, (4) Northern Alps, (5) Central East, (6) Avoca Lowland, (7) Southern Slopes, (8) Southern Alps and (9) South-Western Slopes. Associations between assemblages and physical variables (catchment area, elevation, hydrology, precipitation, temperature) are identified and used to reinforce the definitions of regions. Sustainable Rivers Audit data are compared with the historical assemblages, highlighting species whose range and abundance have changed since the early 19th century. Notable changes include declines in native species such as silver perch, river blackfish, mountain galaxias, Macquarie perch, trout cod and freshwater catfish, and the advent of alien species including common carp, eastern gambusia, goldfish, redfin perch, brown trout and rainbow trout. Less significant declines are evident for native carp gudgeons, golden perch, two-spined blackfish, bony herring and flathead gudgeon. Changes are evident even in regions where habitats have been little disturbed in the past 200 years.

An accurate tool for ageing Two‐spined Blackfish for use in determining timing of spawning in upland streams in the Brindabella ranges, ACT, Australia

SummaryTo manage populations of threatened fish species in modified habitats and regulated rivers requires an understanding of their reproductive biology and spawning cues. In particular, accurate information about early life stages in these species can be used to facilitate programmes that maximise recruitment and breeding success. This study aimed to develop methods to accurately age early juvenile freshwater native fish, Two‐spined Blackfish, (Gadopsis bispinosus), to allow the determination of spawning date. This was accomplished through the examination of otolith microstructure in early juveniles. The age at which the first ring was deposited and the relationship between days and number of rings were determined using both field and aquarium trials. Field trials of marked juvenile otoliths revealed daily deposition of rings (1.02 ± 0.02 rings per day for fish sacrificed six days postmarking). The strength of this relationship lessened slightly as juveniles aged (0.92 ± 0.02 rings per day for fish sacrificed 13 days postmarking). The first otolith ring was deposited 7.50 ± 1.09 days after spawning. The enumeration of daily rings combined with knowledge of the commencement of ring deposition enabled accurate estimation of spawning date. The current study is the first to examine otolith microstructure in juvenile Two‐spined Blackfish allowing accurate determination of spawning date. While more research is required to accurately age older juveniles, this technique has the potential to precisely correlate spawning with environmental cues, facilitating better management of temperature and flow during breeding periods, potentially increasing spawning and recruitment of this endangered species.

Ensemble algorithms for ecological niche modeling from presence‐background and presence‐only data

Ecological niche modeling is central to many problems in population dynamics, conservation biology, biogeography, and evolutionary ecology. Recently, methodological advances have been achieved by adopting modeling principles from statistical and machine learning. One such principle that has not been explored is that voted ensembles of weakly tuned (underfit) models often exhibit similar bias and lower variance than individual well‐tuned models. A further contribution of machine learning is the one class support vector machine. One class support vector machines may be more suited to ecological niche modeling than classification algorithms because the “boundary estimation” property of this class of models better represents the conception of the niche as the set of environments in which populations of a species persist. This paper brings together these approaches and applies them to a data set on the distribution two‐spined blackfish (Gadopsis bispinosus) in southeastern Australia with the aim of improving performance and enriching the repertoire of methods for ecological niche modeling. First, a study of low‐bias bagging (LOBAG) applied to conventional two‐class support vector machines, an approach to presence‐background modeling, found this method to be comparable to another widely used method, MAXENT. Next, I introduce a variant of LOBAG for one class classification, LOBAG‐OC, to be used for ecological niche modeling with presence‐only data. This method performed better than other presence‐only methods (DOMAIN and BIOCLIM) and nearly as well as LOBAG and MAXENT, despite the fact that the presence‐only problem is considerably more difficult than the corresponding presence‐background problem. Results of these analyses suggest that LOBAG and LOBAG‐OC may provide robust, high‐performing solutions to the presence‐background and presence‐only modeling problems and point to ways in which ecological niche modeling may be simultaneously both improved and automated.

A multigene molecular assessment of cryptic biodiversity in the iconic freshwater blackfishes (Teleostei: Percichthyidae:Gadopsis) of south-eastern Australia

Freshwater biodiversity is under ever increasing threat from human activities, and its conservation and management require a sound knowledge of species-level taxonomy. Cryptic biodiversity is a common feature for aquatic systems, particularly in Australia, where recent genetic assessments suggest that the actual number of freshwater fish species may be considerably higher than currently listed. The freshwater blackfishes (genus Gadopsis) are an iconic group in south-eastern Australia and, in combination with their broad, naturally divided distribution and biological attributes that might limit dispersal, as well as ongoing taxonomic uncertainty, they comprise an ideal study group for assessing cryptic biodiversity. We used a multigene molecular assessment including both nuclear (51 allozyme loci; two S7 introns) and matrilineal markers (cytb) to assess species boundaries and broad genetic substructure within freshwater blackfishes. Range-wide examination demonstrates the presence of at least six candidate species across two nominal taxa, Gadopsis marmoratus and Gadopsis bispinosus. Phylogeographical patterns often aligned to purported biogeographical provinces but occasionally reflected more restricted and unexpected relationships. We highlight key issues with taxonomy, conservation, and management for a species group in a highly modified region. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 521–540.

Spatial ecology and habitat use of two-spined blackfish Gadopsis bispinosus in an upland reservoir

The scale and patterns of movement and habitat use are primary considerations in the conservation and management of threatened species. Movement, activity and habitat use of the threatened two-spined blackfish Gadopsis bispinosus were assessed in a small upland reservoir in south-eastern Australia using manual and remote radio-telemetry. Movements and activity of two-spined blackfish (n = 19) were studied over a 28-day period and exhibited proportionately large directional crepuscular movement and activity with heightened activity continuing throughout the night (although movement was subdued). Two daily movement strategies were observed: movements from diurnal home-shelter habitats (predominantly rock) to macrophytes at night (14 individuals), and occupation of macrophytes during the entire diel period and restricted movement (five individuals). Daily movement strategies were fixed (not plastic) among all individuals, with one exception, for the duration of the study period. Rock, fallen timber and macrophytes were the most commonly used daytime shelter habitat (in order of preference). Although some information exists on movements and habitat use of this species and the congeneric river blackfish G. Marmoratus in lotic environments, we present the first study of movements and habitat use for either species in lentic environments. Given the occupation of lentic environments by this threatened species, the data presented in this study provide insight into the habitat requirements for this species, and offer opportunities for habitat enhancement in existing reservoirs within the species' geographic range.

Managing potential impacts of reservoir enlargement on threatened Macquaria australasica and Gadopsis bispinosus in southeastern Australia

Enlargement of a domestic water supply reservoir on the Cotter River in southeastern Australia (4 to 78 Gl) includes an inundation zone that contains 2 threatened fish species, Mac- quarie perch Macquaria australasica and two-spined blackfish Gadopsis bispinosus. The enlarged reservoir will be 50 m deeper and impound an additional 4.5 km of river and thus poses a number of potential threats to these fish species. The majority of threats relate to the inundation zone or upstream environments, as downstream environments have been degraded by significant flow alterations from the existing Cotter Dam and 2 upstream dams. Threats include the loss of refuge habitat and associated increased predation, loss of preferred food sources, invasion and expansion of alien fish populations, loss of spawning habitat (or access to it), and the introduction of disease. To minimise or mitigate these threats, a collaborative and comprehensive research and manage- ment program is underway involving participation from the water utility and various universities and government agencies. Funding by the water utility of an independent senior fisheries scien- tist, establishment of a stakeholder steering group, independent peer review processes, and ded- icated staff within the design and construction alliance are intended to ensure fish requirements are considered in dam design, construction, and operation. The establishment of an independent, collaborative science-driven process, coupled with the establishment of a long-term monitoring program in an adaptive management framework is a model for other infrastructure projects world- wide, particularly those that threaten riverine fish.

Response of two-spined blackfish Gadopsis bispinosus to short-term flow fluctuations in an upland Australian stream

Environmental flows are applied to regulated rivers, predominantly with the aim of benefiting native fauna. However, the outcomes for biodiversity and the mechanisms that underpin changes due to these manipulations are poorly understood. We examined the effects of elevated water release, of the magnitude used for riffle maintenance, on the movement and habitat use of the locally-threatened two-spined blackfish, Gadopsis bispinosus, in the Cotter River, a regulated upland stream in south-eastern Australia. We compared the behaviour of radio-tagged individuals during baseline flow conditions (0.12 m3 s−1) and during elevated flow releases (1.74 m3 s−1). Eight individuals (196 ± 8 mm TL) were radio-tracked at one site over 22 days, and six individuals (180 ± 5 mm TL) were monitored by fixed telemetry stations at a second site for 1 month. At both the sites, two-spined blackfish were nocturnal and occupied small linear ranges (23 ± 6 m). They preferentially used pools, but also used runs and riffles. Elevated discharge did not significantly affect movement, activity or dispersal of two-spined blackfish. Two individuals utilised inundated vegetation during high flow. Despite a small number of behavioural changes, there was no response to elevated flow at the population level. It is likely that the benthic nature of this species precludes its behaviour being affected by a 15-fold increase in-stream discharge. However, the indirect effects of flows of this magnitude on two-spined blackfish, and their responses to discharges of greater magnitude, remain to be investigated.

Radio-tagging flexible-bodied fish: temporary confinement enhances radio-tag retention

Animals that occupy holes or squeeze into interstitial spaces often have particularly flexible bodies and can be difficult to tag effectively. The present study evaluated three methods for radio-tagging the cryptic, eel-like fish Gadopsis bispinosus, a species that inhabits interstitial spaces among cobbles and boulders in streams. The three methods were an externally attached radio-tag with a whip antenna, an internally implanted coil radio-tag (internal coil) and an internally implanted radio-tag with an externally exited whip antenna (internal–external). Successful radio-tagging was determined in aquaria trials based on a combination of four indicators: (1) survival; (2) retention of the radio-tag; (3) healing of the surgical incision; and (4) rapid resumption of feeding. Externally attached radio-tags were shed and proved to be unsuitable (100%). Three of nine individuals with internal–external tagging completed the study with regular feeding, healed incisions and retained radio-tags. Conversely, five of nine individuals with internal coils were successful. This included two of three individuals held in either a simple environment for 3 days or for the duration of the trial and one of three individuals held in a complex environment. Temporary confinement following implantation with coil radio-tags offers a viable means of radio-tagging G. bispinosus. Temporary confinement following radio-tagging may also be useful for reducing radio-tag rejection and mortality for other fish species with similar body morphs and habitat use (e.g. eel species and sculpin).

In-stream behaviour of threatened fishes and their food organisms based on remote video monitoring

Can remote underwater video be used to investigate the in-stream behaviour of small fishes and decapods? Diel activity of two threatened freshwater fishes (Macquaria australasica and Gadopsis bispinosus), a palaemonid prawn and an atyid shrimp, was established from remote underwater video in a pool of an upland stream in the current study. Decapods and large fishes (>5 cm TL) were nocturnal, whereas, small fishes (<5 cm TL) were diurnal. The suitability of using underwater video to quantify short-term (seconds) behavioural interaction among individuals was also demonstrated, with early-juvenile-phase Gadopsis bispinosus exhibiting interference competition on 35% of occasions when two or more individuals were observed. This study demonstrates that remote underwater video is useful for observing the in-stream behaviour of threatened freshwater fauna where other techniques are not viable, and presents sub-sampling of video as a means of reducing video processing time in assessing fish diel activity patterns.

Spawning Season and Site Location of Gadopsis Bispinosus Sanger (Pisces: Gadopsidae) in a Montane Stream of Southeastern Australia

SummaryThe spawning status of a population of G. bispinosus from Buffalo Creek in north-eastern Victoria was monitored over two consecutive spawning seasons. Spawning occurred in December of both years and coincided with increasing water temperature. Eggs were found deposited in artificial spawning tubes placed in the creek and in the stream substrate, under small, generally flat, boulders, confirming previous authors’ assumptions. The implications of this reproductive strategy include the susceptibility of the species to increased sedimentation and cold water pollution.

Identifying the influence of channel morphology on physical habitat availability for native fish: application to the two-spined blackfish (Gadopsis bispinosus) in the Cotter River, Australia

The impact of channel morphology and flow on physical habitat availability for the two-spined blackfish (Gadopsis bispinosus) was assessed in the Cotter River, ACT, Australia. Physical habitat requirements for three life stages were identified based on previous field sampling in the Cotter River. Two sites were selected with contrasting channel morphology: Spur Hole, with a moderate gradient and runs and glides, and Vanity’s Crossing, with a steeper gradient, rapids, and fast-flowing pools. Physical Habitat Simulation System (PHABSIM) was used to simulate the flow v. physical habitat availability relationship for each life stage at both sites. Clear differences were apparent between sites, with Spur Hole characterised by increasing habitat with increasing flow and Vanity’s Crossing showing the opposite relationship. The nature of the channel morphology determined this difference, with Spur Hole characterised by marginal zones becoming inundated at higher flows and providing additional suitable physical habitat as discharge increases. Vanity’s Crossing does not contain similar marginal zones. Further analysis demonstrated that high water velocity was the most important factor limiting physical habitat availability at both sites. This approach demonstrates the importance of channel morphology in determining physical habitat availability and an alternative use of PHABSIM to highlight limiting factors for target species.

The role of introduced trout in the decline of the spotted tree frog ( Litoria Spenceri) in south-eastern Australia

The spotted tree frog ( Litoria spenceri) is one of numerous amphibian species in Australia that have suffered population declines in recent years, and is currently listed nationally as critically endangered. It occurs in upland streams in south-eastern Australia, along with two other lotic frog species: Lesueur's frog ( Litoria lesueuri) and the leaf-green tree frog ( Litoria phyllochroa). L. phyllochroa is uncommon along upland streams and may also have declined. In contrast L. lesueuri remains common in upland streams and has not declined. Brown trout ( Salmo trutta) and rainbow trout ( Onchorhynchus mykiss) have been introduced throughout the range of L. spenceri. The geographic pattern of decline of L. spenceri suggests that trout may have contributed to population declines. To assess this hypothesis, predation of tadpoles of L. spenceri and sympatric frog species by trout was experimentally evaluated. Experiments were conducted to compare the relative susceptibility of tadpoles of L. spenceri, L. phyllochroa and L. lesueuri to predation by two native fish species, mountain galaxias ( Galaxias olidus) and two-spined blackfish ( Gadopsis bispinosus), and S. trutta. Trout predation upon tadpoles was also investigated within a natural stream enclosure. Native fish species ate none or only few tadpoles of the riverine species, despite preying heavily upon tadpoles of a non-riverine species. In contrast, trout preyed upon all species to varying degrees. Fingerling trout preyed heavily upon hatchling tadpoles of L. spenceri and L. phyllochroa, but predation levels on tadpoles of L. lesueuri were much lower. L. lesueuri is the species that remains common in upland streams in the region. Trout were able to significantly reduce survivorship of tadpoles of L. spenceri and L. phyllochroa over short time periods within a stream pool enclosure where alternative prey and tadpole refugia were available. These findings indicate that introduced trout may have played a major role in the decline of L. spenceri.

Mitochondrial DNA variation suggests river capture as a source of vicariance in Gadopsis bispinosus (Pisces: Gadopsidae)

Gadopsis bispinosus from the Australian Capital Territory (ACT) were genetically similar to a population in north‐east Victoria, but highly divergent from another population in central Victoria. Upper tributary populations from the Murray and Murrumbidgee Rivers were similar probably due to river capture.

Mitochondrial DNA variation suggests river capture as a source of vicariance in Gadopsis bispinosus (Pisces: Gadopsidae)

Mitochondrial DNA variation suggests river capture as a source of vicariance in Gadopsis bispinosus (Pisces: Gadopsidae)