Colton Perna

Development of a robust classifier of freshwater residence in barramundi (Lates calcarifer) life histories using elemental ratios in scales and boosted regression trees

Field and experimental studies showed that solution-based analysis of scales could be used to discriminate the long-term freshwater residents in the coastal fishery for catadromous barramundi. A new, robust classification technique was developed using boosted regression trees (MART) and its performance was compared with traditional linear discriminant analysis (LDA). The non-parametric MART had errors 33–81% less than LDA, and could account for non-linear relationships and interactions among elemental ratios. The best model used Sr : Ca, Ba : Ca, Fe : Ca and Mn : Ca in scales as predictors of salinity regime. Analysis of scales collected repeatedly from sub-adult fish of known environmental history showed the MART classifier could identify fish of freshwater origin until at least 10 months residence in seawater, and possibly several years, but scale growth rate could affect the temporal stability of the classifier after that time. The experiment indicated an approximate fourfold rise in Sr : Ba ratios in new scale margins, which were strongly classified by the MART as coming from saltwater fish, but inner scale sections of the same scales were still correctly classified as coming from freshwater fish. We conclude that solution-based elemental analyses of whole scales, and also annuli within scales, could offer a cost-effective, non-destructive technique to help understand the mechanisms causing enhanced year-class strength following high freshwater outflows.

Temporal dynamics of fish assemblages in small seasonal streams in the Queensland tropics

The structure and dynamics of fish assemblages were studied in two small coastal streams in the seasonal tropics of northern Queensland. The study encompassed two consecutive wet seasons of contrasting flood magnitudes. Flooding had substantial effects on physical habitats by shifting sediments and removing aquatic macrophytes, and short-term changes in the fish assemblages reflected these habitat changes. Changes were of higher magnitude following a one-in-eighteen-year flood than a one-in-one-year flood; however, in both cases return to prior assemblage structure occurred as the dry season progressed, but with more rapid recovery after the smaller event. The stream fish assemblages showed high resilience to the flood disturbance at magnitudes seen in this study.

Is the elusive Gymnothorax polyuranodon really a freshwater moray

Analysis of 36 records of the rarely encountered moray Gymnothorax polyuranodon indicate that juveniles and adults inhabit fresh and mildly brackish habitats (salinity < 5) in streams of the Australian Wet Tropics Eighty-one per cent of these records were from freshwater streams and collectively demonstrate that this species inhabits fresh water throughout all seasons. A survey of fish researchers, each with at least 100 h of field experience in Australias Wet Tropics, revealed that 33% of researchers working in fresh waters (nine of 27 researchers) had encountered the species and 15% of researchers with substantial experience working in estuaries (two of 13 researchers) had encountered the species. The species was not sampled or observed in the nearshore marine environment. The only record of an elver of this species was, however, found in an estuary at a salinity of 33·4. This preliminary evidence suggests adult G. polyuranodon occupy freshwater habitats, but further research is required to understand the complete life cycle, including movements, habitat use and reproductive ecology of the species.

Freshwater fishes of northern Australia

Northern Australia is biologically diverse and of national and global conservation signicance. Its ancient landscape contains the worlds largest area of savannah ecosystem in good ecological condition and its rivers are largely free-flowing. Agriculture, previously confined largely to open range-land grazing, is set to expand in extent and to focus much more on irrigated cropping and horticulture. Demands on the water resources of the region are thus, inevitably increasing. Reliable information is required to guide and inform development and help plan for a sustainable future for the region which includes healthy rivers that contain diverse fish assemblages. Based on a range of information sources, including the outcomes of recent and extensive new field surveys, this study maps the distribution of the 111 freshwater fishes (excluding elasmobranches) and 42 estuarine vagrants recorded from freshwater habitats of the region. We classify the habitat use and migratory biology of each species. This study provides a comprehensive assessment of the diversity and distribution of fishes of the region within a standardised nomenclatural framework. In addition, we summarise the outcomes of recent phylogeographic and phylogenetic research using molecular technologies to identify where issues of taxonomy may need further scrutiny. The study provides an informed basis for further research on the spatial arrangement of biodiversity and its relationship to environmental factors (e.g. hydrology), conservation planning and phylogentic variation within individual taxa.

Contrasting and complex evolutionary histories within the terapontid grunter genus Hephaestus revealed by nuclear and mitochondrial genes

Contrasting evolutionary histories may be revealed by mitochondrial and nuclear information. Divergent New Guinean and eastern and western Australian lineages of Hephaestus fuliginosus (sooty grunter) were detected using mitochondrial data, with the extent of divergence consistent with cryptic speciation events. However, this phylogeographic pattern was not supported by nuclear gene data, and evidence for cryptic speciation appears driven almost entirely by introgression between H. fuliginosus and congeners on the periphery of its distribution (e.g. with H. tulliensis, H. jenkinsi or H. roemeri). Hephaestus fuliginosus is a single species with a complex evolutionary history. Introgression on the eastern coast is consistent with transfer of the mitochondrial genome of the resident species (H. tulliensis) to the invading species (H. fuliginosus) and may have provided the metabolic capacity for H. fuliginosus to spread into the cooler rainforest environment of the Wet Tropics region. Mitochondrial and nuclear analyses both identified the genus Hephaestus as polyphyletic with H. carbo and H. habbemai placed in a clade with Leiopotherapon unicolor and Amniataba percoides. The present study demonstrated the need to consider a variety of genetic information when assessing species identity in a widespread species and the need for a systematic revision of the genus and family as a whole.