Mark Allen

Adverse fire regimes threaten biodiversity, potentially leading to population declines and increased extinction risk. Understanding how varying fire regimes affect threatened species is essential for effective ecosystem management, including in Western Australia where diverse ecosystems are exposed to wildfires, Indigenous burning, and prescribed fire. We compiled and synthesised data on the threat of adverse fire regimes to threatened animal taxa in Western Australia. Using a threat classification scheme, we ranked adverse fire regimes as having either no, low, medium, high, or unknown impact on each taxon. A total of 212 taxa were reviewed, 153 (72%) of which are considered fire-threatened: 29 high, 67 medium, 43 low, and 14 unknown impact. This includes 100% of threatened amphibians (3 taxa), 91% of threatened mammals (29), 71% of threatened invertebrates (85), 67% of threatened fish (6), 63% of threatened reptiles (10) and 61% of threatened birds (20). Only some bird (6), mammal (5), and invertebrate (18) taxa received a ranking of ‘high’. Across all fire-threatened taxa, we synthesised 330 fire response cases from 169 studies. Most taxa (75%) are considered fire-threatened due to small ranges and limited dispersal (primarily invertebrates and island taxa), with much smaller numbers reliant on long-unburnt vegetation (>10–40 years; 7%) or habitat features that take decades to form (e.g. tree hollows; 7%). Many taxa should be considered putatively fire-threatened until further information on their fire responses and the nature of fire regimes within their ranges is collected. We identify key research priorities to inform fire management and threatened species conservation.

Context
The south-western corner of Australia is a biodiversity hotspot that includes a freshwater fauna with a high proportion of endemic species. The temperate perches comprise nearly half of the obligate freshwater fishes of the region, representing important components of local ecosystems and are of significant conservation concern.

Aims
Provide a spatially comprehensive molecular genetic assessment of species boundaries and major substructure for all local members of the family to better understand the interplay of ecology and environment across a common landscape.

Methods
Nuclear markers (allozymes) and matrilineal (cytb) datasets were generated to infer genetic groupings and any instances of hybridisation or introgression in relation to the current taxonomy, regional geography and ecological understanding.

Key results
There were contrasting patterns of diversification across genera, with Nannoperca housing four likely species-level splits, Nannatherina having three distinct geographically and ecologically separated subpopulations, and Bostockia comprising several refugial subpopulations that appear partially introgressed. Repeated genetic patterns were identified across particular biogeographic features, most notably the Margaret River and Shannon River.

Conclusions
This study highlighted the value of comparative range-wide molecular studies to inform taxonomy, ecology and conservation planning.

Implications
These analyses pave the way for taxonomic revision, management of key habitat refuges, and other conservation actions.

Context In this study, single-nucleotide polymorphisms (SNPs) were used to investigate kinship for the green sawfish (Pristis zijsron). Aims To examine the relatedness of P. zijsron across an expansive coastline in Western Australia. Methods Sampling was conducted between the Fitzroy River estuary and Bay of Rest in the eastern Indian Ocean (north-western Australia) between 2003 and 2022. SNPs were generated from tissues collected from 137 live and 1 recently deceased P. zijsron. Key results Overall, 62 individual P. zijsron were assigned to 25 litters of full siblings, with litter sizes ranging from 2 to 5 pups, and 76 P. zijsron individuals were assigned to 96 half sibling pairwise relationships. Four pairs of half siblings were captured more than 500 km and born at least 6 years apart, including one pair of neonates captured ~870 km and 8 years apart, in the Ashburton River estuary (Pilbara) and Cable Beach (Broome). Furthermore, a pair of full-sibling pups (i.e. young of the year) caught at Cape Keraudren (Pilbara) in 2008 were half siblings of a pup caught in the Ashburton River in 2014. Conclusions This study provides evidence of long-distance, likely parental, movement of P. zijsron. Implications Dispersal of P. zijsron over large spatial scales indicates that populations could be replenished from elsewhere should they experience a decline, thereby reducing the risk of localised extinction for this species.

Gambusia holbrooki is arguably the most widely introduced and ecologically damaging freshwater fish in the world. Although aspects of its aggressive behaviour have been studied in lentic environments and ex situ experiments, the physical damage to native freshwater fishes in riverine systems caused by this behaviour remains relatively unknown.

This study quantified the spatial and temporal patterns of abundance of G. holbrooki and the prevalence of fin-nipping damage on freshwater fishes in river systems of south-western Australia, a globally endemic hotspot with a high proportion of threatened species. It then determined the environmental factors influencing the abundance of G. holbrooki and the prevalence of fin-nipping damage on native fishes.

Caudal fin damage differed significantly among four endemic native fishes, with damage being most prevalent in the percichthyid Nannoperca vittata, which has a similar size and ecological niche to G. holbrooki. Fin-nipping damage of native species also showed significant seasonal variation; occurring most commonly during summer and autumn when many rivers in this region cease to flow and contract to refuge pools, probably increasing interactions between G. holbrooki and the native fishes. Moreover, the environmental variables that best explained both the density of G. holbrooki and the prevalence of fin-nipping were broadly similar and were characteristic of more degraded habitats.

We anticipate that habitat degradation, river regulation and severe declines in surface flows resulting from climate change will benefit G. holbrooki to the detriment of native fishes. Restoration of riverine environments along with public education campaigns to prevent the further spread of G. holbrooki or the introduction of additional species is crucial to mitigate their effects on aquatic ecosystems.

1. Small‐bodied freshwater fishes are commonly overlooked in threatened species management despite being highly imperilled. Before this study, the newly described little pygmy perch (Nannoperca pygmaea ) was known from only 0.06 km2 of habitat in a single catchment in south‐western Australia and a lack of knowledge prevented an understanding of its conservation status and priority actions.

2. The present study determined the distribution, biology, and movement patterns of N. pygmaea and compared these with other small, sympatric percihthyids to assess its conservation status and likely resilience to threatening processes.

3. The current ‘extent of occurrence' of N. pygmaea was determined to be 3,420 km2 and the ‘area of occupancy' was 10 km2. Nannoperca pygmaea inhabited permanent refuge pools in the main stem of an ephemeral, secondarily salinized catchment where salinities remained <6 ppt during summer.

4. During winter N. pygmaea undertook a short upstream migration into a seasonally flowing freshwater tributary to serially spawn. The timing of reproduction was partitioned among three sympatric pygmy perches within the austral winter/spring period.

5. The species qualifies as ‘Endangered' under the IUCN Red List assessment criteria. Its restriction to freshwater refugia within salinized rivers suggests that N. pygmaea may have a limited salinity tolerance similar to the sympatric, threatened Nannatherina balstoni , and that the species is susceptible to prolonged drought, drying of critical baseflow refuges, increasing salinization, and introductions of alien species.

6. The study serves as an example that small‐bodied freshwater fishes need greater research attention to understand the biological and environmental mechanisms underpinning their decline.

An anomalous El Niño-associated sea surface temperature stress event was predicted to affect tropical Australian reefs, including those in North Western Australia in the summer of 2015/2016. Thermal stress events are well known to result in widespread hard coral mortality events, but other symbiotic organisms such as soft corals, giant clams and sponges can also be affected. Here, we examine whether the 2016 thermal stress event deleteriously impacted coral reef communities in the remote Bonaparte Archipelago, central inshore Kimberley bioregion, North West Australia. Our results confirm the region experienced a thermal stress event of similar magnitude to other regional localities (i.e., southern Kimberley and Scott Reef), but contrary to those locations that experienced widespread bleaching events, we find no evidence to suggest widespread mortality events occurred among photosymbiotic organisms in the Bonaparte Archipelago. Photosymbiotic organisms in this region are assumed to be well adapted to fluctuating environmental conditions; however, in this instance, a greater magnitude of night-time cooling may have driven variability in regional susceptibility to thermal stress. The Bonaparte Archipelago is emerging as a globally significant ecological refuge for photosymbiotic benthic fauna that are threatened by cumulative anthropogenic and climate stressors in other parts of their distribution.

Goldfish (Carassius auratus) was one of the first fishes to be domesticated and has been widely introduced across the globe, but is now considered one of the world's worst invasive aquatic species. Surprisingly, there is a dearth of information on its spatial and temporal movement patterns, which hampers the development of effective control programmes. We examined the movement patterns of an introduced population of C. auratus in a south-western Australian river using passive acoustic telemetry. The study population had a high residency index within the array (i.e. proportion of all days at liberty that, on average, each fish was detected by a receiver) with fish being detected on 64% of days. The individuals were also reasonably mobile, travelling a mean of 0.30 km (linear river kilometres).day-1 within the array, and one fish moved 231.3 km over the 365-day study period (including 5.4 km in a 24 hr period). Importantly, C. auratus displayed significant seasonal movement patterns including a clear shift in habitats during its breeding period with most mature individuals being detected in an off-channel wetland during that time. The results of this study strongly suggest that C. auratus undertook a spawning migration into a lentic habitat. These results have important implications for developing control programmes for the species, such as targeting connections to off-channel lentic systems during its breeding period.

The largest of the sawfishes is the Critically Endangered green sawfish Pristis zijsron, a species believed to have undergone a major decline (38%) in extent of occurrence. Conservation efforts are hampered by the lack of information on the habitat requirements of this species. We used passive acoustic telemetry to document the movement patterns of 37 juvenile P. zijsron (<3000 mm total length) in a recently discovered nursery area in a remote estuary and adjacent mangrove creeks in the Pilbara region of Western Australia. All age classes had a high site fidelity near the mouth of the Ashburton River (<700 m upstream) or in the adjacent tidal mangrove creeks. Neonates stayed close to the river mouth for several months, with movement in creasing with growth. For larger individuals, movement between the river mouth or creeks and nearshore coastal habitats was largely tidally driven, with nearshore coastal habitats used during low tide and protected tidal waters (mangrove creeks) used during high tide. Emigration from the river estuary appeared to be influenced by increases in freshwater discharge and high turbidity brought on by cyclonic rainfall events. The high relative abundance and site fidelity of multiple age classes of P. zijsron over multiple years confirms that the study area provides important nursery habitats for the species. Additionally, the localised movements of juveniles suggest that this population may be sensitive to disturbances within these habitats. Given the significance of this region for P. zijsron, it is imperative to focus conservation efforts here to ensure that the population remains in a relatively healthy condition.

Climate change is projected to alter river discharge in every populated basin in the world. In some parts of the world, dam removal now outpaces their construction and the diminishing cost efficiency of dams in drying regions is likely to further increase the rate of removals. However, the potential influence of climate change on the impact of dam removals has received almost no consideration. Most dams have major biological and ecological impacts and their removal would greatly benefit riverine ecosystems. However, using model regions in the Southern Hemisphere, we highlight that artificial lentic habitats created by dams can act as refuges for increasingly imperiled freshwater fishes, and dams may also prevent the upstream spread of invasive alien species in rivers. We argue that, in these and other regions where the major impact of climate change will be to reduce streamflow and aquatic refuge availability, a shifting balance between the negative and positive environmental impacts of dams requires policy makers to include climate change predictions in prioritisation processes for dam removal