The ecology of the two-spined blackfish Gadopsis Bispinosus (Pisces: Gadopsidae)

The Gadopsidae is an endemic mono-generic freshwater fish family of south-eastern Australia. The family was thought to be mono-specific, containing the River Blackfish Gadopsis marmoratus, until 1984 when a second species, the Two-spined Blackfish G. bispinosus was described (Sanger 1984). Due its relatively recent description, little information was available on the ecology or conservation status of G. bispinosus in NSW and the ACT. The distribution and abundance of G. bispinosus in southern NSW and the ACT was investigated with the species recorded at 16 of 119 sites surveyed. At most sites where they were recorded, G. bispinosus was abundant, and was invariably found in association with one of the trout species. G. bispinosus was found to be restricted to cool, clear upland streams with rocky, cobble bottoms and relatively intact forest vegetation. It was hypothesised that the presence of the species in the upper Murrumbidgee drainage was due to stream capture, in which the headwater streams from the Murray drainage have been captured by the Murrumbidgee drainage. Interpretation of historical reports of blackfish distribution in NSW indicated that G. bispinosus had suffered declines in some rivers with the species now apparently absent from the Yarrangobilly River and the Murrumbidgee, Naas, and Paddys rivers in the ACT. The decline is thought to have been due to habitat degradation, particularly sediment addition, which has reduced the cover available by filling the interstitial spaces in the cobble substrate favoured by G. bispinosus. The invariable association of G. bispinosus with introduced trout species and habitats with abundant cover, suggests that trout may have played some part in the current distribution of G bispinosus by excluding them from sub-optimal habitats. The movements of G. bispinosus was found to be very restricted with a home range of approximately 15 metres estimated for adult fish. Recapture rates were high, particularly in adult fish, in comparison with other studies of freshwater fish, indicating that adult G. bispinosus are particularly sedentary. The home ranges of G. bispinosus were found to be stable from year to year with fish able to maintain their position in the stream over the high flow periods of winter and spring. On the basis of aquarium observations of pugnacious and aggressive behaviour between adult G. bispinosus, it was considered that these home ranges may be considered territories under the definition of (Gerking 1953) who defined a territory as "any defended area". The diet of G. bispinosus was investigated with distinct seasonal and ontogenetic differences apparent in the diet. Juvenile fish consumed predominantly smaller items such as early instar ephemeropterans and chironomid larvae with some trichopterans present in the diet. The proportion of trichopterans in the diet increased with increasing fish size, with the importance of ephemeropterans and dipterans inversely related to fish size. terrestrial items were not present at all in the stomachs of juvenile fish, were of minor importance to immature fish, but were a major dietary item of adults. Terrestrial items were most abundant in the diet of both immature and adult fish in summer and autumn. The diet of Rainbow Trout 0. mykiss was also examined, with significant dietary overlap apparent between 0. mykiss and G. bispinosus. As with G. bispinosus, the diet of 0. mykiss was dominated by ephemeropterans, trichopterans and terrestrial items. Dietary overlap was greatest between similar size classes of both species, with some seasonal pattern evident. Significant overlap occurred between the non-adult G. bispinosus and juvenile 0. mykiss all seasons except autumn. Overlap was greatest between mature blackfish and non-juvenile trout with significant dietary overlap recorded in all seasons. It was considered that the consistent significant overlap values indicate the dietary competition is likely between these two fish species. The reproductive ecology of G. bispinosus was found to be similar to that recorded for G. marmoratus by Jackson (1978a). Both blackfish species deposit large, yolky, adhesive, demersal eggs in late spring/early summer when water temperatures exceed 16-17 °C. Fecundity in G. bispinosus is low with less than 300 eggs carried by most females. The natural spawning site was not located but is thought to be in the interstitial spaces between cobble and boulders on the river bed. Artificial P.V.C. spawning tubes proved successful with a total of 15 egg masses deposited in them over the course of the study. The numbers of eggs in each egg mass were within the fecundity estimates of individual fish, and all eggs within a mass were at the same stage of development , indicating that a single fish is probably responsible for each egg mass. A large adult male was present with each egg mass. Eggs hatched after approximately 15-17 days, with the embryo emerging from the chorion but the yolk sac remaining inside, effectively tethering the young to the spawning substrate. Parental care by the male continued for approximately 3-4 weeks after hatching by which time the yolk sac was almost fully utilised and young blackfish could swim well

Methods to maximise recovery of environmental DNA from water samples

<div><p>The environmental DNA (eDNA) method is a detection technique that is rapidly gaining credibility as a sensitive tool useful in the surveillance and monitoring of invasive and threatened species. Because eDNA analysis often deals with small quantities of short and degraded DNA fragments, methods that maximize eDNA recovery are required to increase detectability. In this study, we performed experiments at different stages of the eDNA analysis to show which combinations of methods give the best recovery rate for eDNA. Using Oriental weatherloach (<i>Misgurnus anguillicaudatus</i>) as a study species, we show that various combinations of DNA capture, preservation and extraction methods can significantly affect DNA yield. Filtration using cellulose nitrate filter paper preserved in ethanol or stored in a -20°C freezer and extracted with the Qiagen DNeasy kit outperformed other combinations in terms of cost and efficiency of DNA recovery. Our results support the recommendation to filter water samples within 24hours but if this is not possible, our results suggest that refrigeration may be a better option than freezing for short-term storage (i.e., 3–5 days). This information is useful in designing eDNA detection of low-density invasive or threatened species, where small variations in DNA recovery can signify the difference between detection success or failure.</p></div

Monitoring riverine fish communities through eDNA metabarcoding:Determining optimal sampling strategies along an altitudinal and biodiversity gradient

Monitoring aquatic biodiversity through DNA extracted from environmental samples (eDNA) combined with high-throughput sequencing, commonly referred to as eDNA metabarcoding, is increasing in popularity within the scientific community. However, sampling strategies, laboratory protocols and analytical pipelines can influence the results of eDNA metabarcoding surveys. While the impact of laboratory protocols and analytical pipelines have been extensively studied, the importance of sampling strategies on eDNA metabarcoding surveys has not received the same attention. To avoid underestimating local biodiversity, adequate sampling strategies (i.e. sampling intensity and spatial sampling replication) need to be implemented. This study evaluated the impact of sampling strategies along an altitudinal and biodiversity gradient in the upper section of the Murrumbidgee River (Murray-Darling Basin, Australia). An eDNA metabarcoding survey was used to determine the local fish biodiversity and evaluate the influence of sampling intensity and spatial sampling replication on the biodiversity estimates. The results show that optimal eDNA sampling strategies varied between sites and indicate that river morphology, species richness and species abundance affect the optimal sampling intensity and spatial sampling replication needed to accurately assess the fish biodiversity. While the generality of the patterns will need to be confirmed through future studies, these findings provide a basis to guide future eDNA metabarcoding surveys in river systems

Distributed under Creative Commons CC-BY 4.0 OPEN ACCESS Who&apos;s your mama? Riverine hybridisation of threatened freshwater Trout Cod and Murray Cod

ABSTRACT Rates of hybridization and introgression are increasing dramatically worldwide because of translocations, restocking of organisms and habitat modifications; thus, determining whether hybridization is occuring after reintroducing extirpated congeneric species is commensurately important for conservation. Restocking programs are sometimes criticized because of the genetic consequences of hatchery-bred fish breeding with wild populations. These concerns are important to conservation restocking programs, including those from the Australian freshwater fish family, Percichthyidae. Two of the better known Australian Percichthyidae are the Murray Cod, Maccullochella peelii and Trout Cod, Maccullochella macquariensis which were formerly widespread over the Murray Darling Basin. In much of the Murrumbidgee River, Trout Cod and Murray Cod were sympatric until the late 1970s when Trout Cod were extirpated. Here we use genetic single nucleotide polymorphism (SNP) data together with mitochondrial sequences to examine hybridization and introgression between Murray Cod and Trout Cod in the upper Murrumbidgee River and consider implications for restocking programs. We have confirmed restocked riverine Trout Cod reproducing, but only as inter-specific matings, in the wild. We detected hybrid Trout Cod-Murray Cod in the Upper Murrumbidgee, recording the first hybrid larvae in the wild. Although hybrid larvae, juveniles and adults have been recorded in hatcheries and impoundments, and hybrid adults have been recorded in rivers previously, this is the first time fertile F1 have been recorded in a wild riverine population. The F1 backcrosses with Murray cod have also been found to be fertile. All backcrosses noted were with pure Murray Cod. Such introgression has not been recorded previously in these two species, and the imbalance in hybridization direction may have important implications for restocking programs

Alternative conservation outcomes from aquatic fauna translocations: Losing and saving the Running River rainbowfish

1. The translocation of species outside their natural range is a threat to aquatic biodiversity globally, especially freshwater fishes, as most are not only susceptible to predation and competition but readily hybridize with congeners. 2. Running River rainbowfish (RRR, Melanotaenia sp.) is a narrow-ranged, small-bodied freshwater fish that recently became threatened and was subsequently listed as Critically Endangered, owing to introgressive hybridization and competition following the translocation of a congeneric species, the eastern rainbowfish (Melanotaenia splendida). 3. To conserve RRR, wild fish were taken into captivity, genetically confirmed as pure representatives, and successfully bred. As the threat of introgression with translocated eastern rainbowfish could not be mitigated, a plan was devised to translocate captive raised RRR into unoccupied habitats within their native catchment, upstream of natural barriers. The translocation plan involved careful site selection and habitat assessment, predator training (exposure to predators prior to release), soft release (with a gradual transition from captivity to nature), and post-release monitoring, and this approach was ultimately successful. 4. Two populations of RRR were established in two previously unoccupied streams above waterfalls with a combined stream length of 18 km. Post-release monitoring was affected by floods and low sample sizes, but suggested that predation and time of release are important factors to consider in similar conservation recovery programmes for small-bodied, short-lived fishes

Preventing and controlling nonnative species invasions to bend the curve of global freshwater biodiversity loss

The Emergency Recovery Plan for freshwater biodiversity recognizes that addressing nonnative species is one of six principal actions needed to bend the curve in freshwater biodiversity loss. This is because introduction rates of nonnative species continue to accelerate globally and where these species develop invasive populations, they can have severe impacts on freshwater biodiversity. The most effective management measure to protect freshwater biodiversity is to prevent introductions of nonnative species. Should a nonnative species be introduced, however, then its early detection and the implementation of rapid reaction measures can avoid it establishing and dispersing. If these measures are unsuccessful and the species becomes invasive, then control and containment measures can minimize its further spread and impact. Minimizing further spread and impact includes control methods to reduce invader abundance and containment methods such as screening of invaded sites and strict biosecurity to avoid the invader dispersing to neighbouring basins. Thesemanagement actions have benefitted from developments in invasion risk assessment that can prioritize species according to their invasion risk and, for species already invasive, ensure that management actions are commensurate with assessed risk. The successful management of freshwater nonnative species still requires the overcoming of some implementation challenges, including nonnative species often being a symptom of degraded habitats rather than the main driver of ecological change, and eradication methods often being non-species specific. Given the multiple anthropogenic stressors in freshwaters, nonnative species management must work with other restoration strategies if it is to deliver the Emergency Recovery Plan for freshwater biodiversity

Modelling the spatial extent of post-fire sedimentation threat to estimate the impacts of fire on waterways and aquatic species

Aim: Fires can severely impact aquatic fauna, especially when attributes of soil, topography, fire severity and post-fire rainfall interact to cause substantial sedimentation. Such events can cause immediate mortality and longer-term changes in food resources and habitat structure. Approaches for estimating fire impacts on terrestrial species (e.g. intersecting fire extent with species distributions) are inappropriate for aquatic species as sedimentation can carry well downstream of the fire extent, and occur long after fire. Here, we develop an approach for estimating the spatial extent of fire impacts for aquatic systems, across multiple catchments. Location: Southern Australian bioregions affected by the fires in 2019–2020 that burned >10 million ha of temperate and subtropical forests. Methods: We integrated an existing soil erosion model with fire severity mapping and rainfall data to estimate the spatial extent of post-fire sedimentation threat in waterways and in basins and the potential exposure of aquatic species to this threat. We validated the model against field observations of sedimentation events after the 2019–20 fires. Results: While fires overlapped with ~27,643 km of waterways, post-fire sedimentation events potentially occurred across ~40,449 km. In total, 55% (n = 85) of 154 basins in the study region may have experienced substantial post-fire sedimentation. Ten species—including six Critically Endangered—were threatened by post-fire sedimentation events across 100% of their range. The model increased the estimates for potential impact, compared to considering fire extent alone, for >80% of aquatic species. Some species had distributions that did not overlap with the fire extent, but that were entirely exposed to post-fire sedimentation threat. Conclusions: Compared with estimating the overlap of fire extent with species' ranges, our model improves estimates of fire-related threats to aquatic fauna by capturing the complexities of fire impacts on hydrological systems. The model provides a method for quickly estimating post-fire sedimentation threat after future fires in any fire-prone region, thus potentially improving conservation assessments and informing emergency management interventions

A national-scale dataset for threats impacting Australia's imperiled flora and fauna

Australia is in the midst of an extinction crisis, having already lost 10% of terrestrial mammal fauna since European settlement and with hundreds of other species at high risk of extinction. The decline of the nation's biota is a result of an array of threatening processes; however, a comprehensive taxon-specific understanding of threats and their relative impacts remains undocumented nationally. Using expert consultation, we compile the first complete, validated, and consistent taxon-specific threat and impact dataset for all nationally listed threatened taxa in Australia. We confined our analysis to 1,795 terrestrial and aquatic taxa listed as threatened (Vulnerable, Endangered, or Critically Endangered) under Australian Commonwealth law. We engaged taxonomic experts to generate taxon-specific threat and threat impact information to consistently apply the IUCN Threat Classification Scheme and Threat Impact Scoring System, as well as eight broad-level threats and 51 subcategory threats, for all 1,795 threatened terrestrial and aquatic threatened taxa. This compilation produced 4,877 unique taxon–threat–impact combinations with the most frequently listed threats being Habitat loss, fragmentation, and degradation (n = 1,210 taxa), and Invasive species and disease (n = 966 taxa). Yet when only high-impact threats or medium-impact threats are considered, Invasive species and disease become the most prevalent threats. This dataset provides critical information for conservation action planning, national legislation and policy, and prioritizing investments in threatened species management and recovery