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Context Movements of purebred and hybrid complexes of species show the interactions that facilitate hybridisation and genetic introgression. Aims This study combines genetic analysis of Acanthopagrus spp. and acoustic tracking to understand the spatial ecology of this species complex. Methods Acanthopagrus australis (yellowfin bream) and the Acanthopagrus hybrid complex of A. australis and Acanthopagrus butcheri (black bream) were tracked using acoustic telemetry within a south-eastern Australian estuary. Key results Movements between A. australis and Acanthopagrus hybrids showed similarities, fish displayed high levels of residency and site fidelity, with peak distributions occurring 15 and 32 km upstream of the river entrance. Offshore movements were recorded for 43% of A. australis and 38% of Acanthopagrus spp. hybrids where fish did not return to the study estuary. Estuarine movement patterns in A. australis and A. spp. hybrids were significantly related to conductivity, freshwater flow, temperature, genetic classification, and capture location. Repetitive spawning migrations were not observed for either A. australis or A. spp. hybrids. Overlap in distributions throughout the spawning period did occur. Conclusions This study highlighted the complexity of estuarine movement patterns in A. australis and Acanthopagrus hybrids because they appear to be dependent on freshwater flow, temperature, and ancestry. Implications A. australis and A. spp. hybrids may be capable of spawning within estuaries, and adult offshore movements may play a role in the genetic mixing of populations.

Understanding the impacts of extreme events is essential to effective fisheries management. During the summer of 2018–19 millions of native fish died in Lower Darling–Baaka River adjacent to Menindee, New South Wales, Australia. Hypoxia during a period of protracted low flow, triggered by climatic events, was responsible for the fish kills. From June 2019 to March 2020, further broader-scale fish kills occurred throughout ~600 km of the Darling–Baaka River as disconnected refuge pools contracted and water quality deteriorated. This study examined the status of the remnant fish populations, compared the fish assemblage of the Menindee fish death reach with an unaffected reach and monitored change of the fish community over 18 months after the initial fish kills. Significantly lower abundances of Murray cod (Maccullochella peelii), bony herring (Nematalosa erebi), carp gudgeon (Hypseleotris spp.) and freshwater prawn (Macrobrachium australiense) were captured within the Menindee fish death reach compared with the unaffected reach. Varied responses were observed in species abundances within the affected reach in the 18 months after the initial fish kills, attributed to the various life-history traits and reproductive strategies. The results presented highlight a fish community in continued stress. Continued monitoring will guide and track the effectiveness of recovery management interventions in the region.

This study examines the complex diadromous movements in pinkeye mullet (Trachystoma petardi) of south-eastern Australia. The techniques used to study these movements included LA-ICP-MS single line ablation transects and microchemical imaging as well as preliminary acoustic telemetry results which were used to aid in interpretation of chemical signatures related to complex movement patterns across salinity gradients. Ba:Ca and Sr:Ca from single ablation transects and microchemical images revealed differences between the otolith core and outer regions. Otolith Ba:Ca and Sr:Ca patterns were more easily distinguished in images compared to transects and these revealed that T. petardi spend their early life in saline waters. Movement patterns for adults varied, with a range of movements identified between fresh and saline waters. Telemetry data assisted in explaining the likely cause of the ambiguity in otolith microchemistry data, including identification of multiple rapid movements across salinity gradients. However, many movements through salinity gradients appear too brief to result in any clear Sr:Ca or Ba:Ca saline or mesohaline signature within the chemistry of the otolith. The combination of otolith chemistry and telemetry proved useful in providing information on this poorly understood species suggesting that T. petardi display a catadromous life history.

Summary Temperature strongly regulates the distribution and fitness of ectotherms, and many studies have measured the temperature dependence of physiological performance in controlled laboratory settings. In contrast, little is known about how temperature influences ectotherm performance in the wild, so the ecological significance of physiological performance as measured in the laboratory is unclear. Our aim was to measure the temperature dependence of performance in the wild for several species of fishes and to explore how temperatures that maximize performance in the wild (ToptE) are related to species biogeographies. We gathered body activity and growth data from the wild for nine tropical and temperate fish species, and by fitting thermal performance curves to these data, compared ToptE to species-specific warm range boundary temperatures (the average temperature of the warmest month at equatorward range limits). To explore the degree to which trends in the wild reflect trends in physiological performance measured in the laboratory, we also compiled published data on the temperature dependence of aerobic metabolic scope in fishes and compared these to our wild fish data. We found ToptE in the wild was strongly correlated with warm range boundary temperatures, and that the difference between these two temperatures (the ‘environmental heating tolerance’) was smaller for more-tropical species. Comparison with laboratory data revealed that ToptE approaches warm boundary temperatures in the wild at the same rate that the optimal temperature for aerobic scope (ToptAS) approaches upper critical temperatures (upper Tcrit) for aerobic scope in the laboratory, meaning that environmental heating tolerances in wild fishes closely mirror physiological heating tolerance (i.e. upper Tcrit − ToptAS) in captive fishes. Our comparison of field- and laboratory-derived data highlights the ecological significance of aerobic metabolic scope in fishes and suggests wild fish species tend to perform best near the highest temperatures encountered in their range while maintaining a safety margin from the deleterious effects of upper critical temperatures.

Space use and movement patterns are largely influenced by an animal’s size, habitat connectivity, reproductive mode, and foraging behaviours; and are important in defining the broader population biology and ecology of an organism. Acoustic telemetry was used to investigate the home range, habitat use and relative movement patterns of an estuarine dependant sparid (Acanthopagrus australis, Gunther). Ten fish were internally tagged with acoustic transmitters and manually tracked in a riverine estuary for four, 3-day periods. Positional data was converted into a relative index of fish movement (Minimum Activity Index, MAI), and also used to estimate kernel density distributions which approximated areas of core and total space use for each fish. Space use for A. australis was not related to fish size; although movement of each fish (MAI) increased with fish length and a reduction in water conductivity. The distance between tagged fish and mangrove habitat was correlated with time-of-day and tide level with yellowfin bream moving closer to mangroves during the daytime and on high tides. Fish movements, residency and site fidelity revealed the nature of decision-making for fish, and the conservation value of small patches of estuarine habitats.

Contamination in urbanised estuaries presents a risk to human health, and to the viability of populations of exploited species. Assessing animal movements in relation to contaminated areas may help to explain patterns in bioaccumulation, and assist in the effective management of health risks associated with consumption of exploited species. Using polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/Fs) contamination in Sydney Harbour estuary as a case study, we present a study that links movement patterns resolved using acoustic telemetry to the accumulation of contaminants in mobile fish on a multi-species basis. Fifty-four individuals across six exploited species (Sea Mullet Mugil cephalus; Luderick Girella tricuspidata; Yellowfin Bream Acanthopagrus australis; Silver Trevally Pseudocaranx georgianus; Mulloway Argyrosomus japonicus; Yellowtail Kingfish Seriola lalandi) were tagged with acoustic transmitters, and their movements tracked for up to 3 years. There was substantial inter-specific variation in fish distribution along the estuary. The proportion of distribution that overlapped with contaminated areas explained 84–98% of the inter-specific variation in lipid-standardised biota PCDD/F concentration. There was some seasonal variation in distribution along the estuary, but movement patterns indicated that Sea Mullet, Yellowfin Bream, Silver Trevally, and Mulloway were likely to be exposed to contaminated areas during the period of gonadal maturation. Acoustic telemetry allows examination of spatial and temporal patterns in exposure to contamination. When used alongside biota sampling and testing, this offers a powerful approach to assess exposure, bioaccumulation, and potential risks faced by different species, as well as human health risks associated with their consumption.

(inferred from week-long trends in underwater noise and local maritime records) was associated with a reduction in activity levels and increased depth distributions of mulloway. Stomach content data from a nearby estuary revealed a far-lower feeding rate and altered diet composition on weekends (when boating activity is greatest) compared to weekdays for this species, and an inferred foraging success rate almost one-third that of weekdays. These data suggest the behaviour and foraging intensity of mulloway is significantly influenced by anthropogenic disturbance. The overall fitness costs of the reduction in foraging success will depend on how readily mulloway can reallocate foraging to less disturbed conditions, and the extent of stressrelated responses to disturbance in this species. This study supports earlier predictions that anthropogenic disturbances like noise could have significant impacts on the behaviour and fitness of aquatic animals.

This study examined whether differences existed in the depth distributions and reproductive strategies of the co-occurring Sillago robusta and S. flindersi in coastal waters off eastern Australia. Marked spatial and temporal dissimilarities in demography and reproduction were observed between the 2 species, with S. robusta being more abundant in the shallow (15�30 m) strata and S. flindersi in the mid (31�60 m) strata, with neither species being consis- tently abundant in the deep (61�90 m) strata. The size composition of S. robusta was similar across depths, but smaller and immature S. flindersi predominantly occurred in the shallow strata, with larger and mature individuals occurring deeper. These data indicate partitioning of habitat resources, which may aid species coexistence. Both species potentially spawned year-round, which is probably an adaptation to the region's dynamic coastal environment. However, a greater proportion of S. robusta was in spawning condition between September and March, whereas S. flindersi displayed no such temporal pattern. Maturity ogives differed significantly between sexes and locations for both species. Both species displayed similar ovarian development, with females having multiple concurrent oocyte stages, indicating potential multiple spawning events as evidenced in other Sillaginidae. For both species, estimated batch fecundity increased with fish length, but S. robusta had a greater fecundity at any given length than S. flindersi. In contrast, S. flindersi potentially produced larger-sized eggs and invested greater energy into gonad devel- opment than S. robusta, indicating the 2 species have evolved slightly different reproductive strategies. Despite this, both species are subjected to substantial trawl fisheries, which may have already impacted their reproductive ecologies.

© 2014, Japanese Society of Fisheries Science. This study investigated variability in the growth, length, and age compositions and the rates of mortality of Flinders’ sillago Sillago flindersi exploited in a demersal trawl fishery in eastern Australia. Sampling was done over 2 years across three depth strata at two locations approximately 400 km apart. Ageing of sectioned sagittal otoliths indicated that the observed maximum age of females was 6 years and that of males 5 years, that growth was variable and that the von Bertalanffy growth parameters significantly differed according to gender and location. Females attained a greater L∞ than males, but males displayed greater k values. The L∞ values of both sexes and the mean length-at-age for fish aged 3–5 years were greater at the location of highest latitude. Length and age compositions differed according to depth, with smaller (31 m) strata. S. flindersi appear to use the shallow strata as a juvenile habitat, moving to deeper waters as they grow. This depth stratification between cohorts may reduce intraspecific competition and could potentially be used as a spatial management tool to reduce any fishing-associated impacts on juveniles. Fish between 1 and 3 years old dominated the age compositions of populations combined across all depths, with estimated total mortality ranging between 2.24 and 2.40. Fishing mortality ranged between 1.54 and 1.70 and was more than twice the derived natural mortality. Exploitation rates were approximately 0.70, indicating that the species was heavily fished.

Theoretical and laboratory studies generally show ectotherm performance increases with temperature to an optimum, and subsequently declines. Several physiological mechanisms likely shape thermal performance curves, but responses of free-ranging animals to temperature variation will represent a compromise between these mechanisms and ecological constraints. Thermal performance data from wild animals balancing physiology and ecology is rare, and this represents a hindrance for predicting population impacts of future temperature change. We used internally-implanted accelerometers near the middle of a species' geographical distribution and gill-net catch data near the species' latitudinal extremes to quantify temperature-related activity levels of a wild predatory fish (Platycephalus fuscus). We examined our data in the context of established models of thermal performance, and the relationship between thermal performance thresholds and biogeography. Acceleration data approximated a thermal performance curve, with activity peaking at 23°C, but declining rapidly at higher temperatures. Gill-net catch data displayed a similar trend, with a temperature-associated increase and decrease in catch rates in temperate and tropical regions, respectively. Extrapolated estimates of zero activity (CTmin and CTmax) from the accelerometers were similar to the minimum and maximum mean monthly water temperatures experienced at the southern and northern (respectively) limits of the species distribution, consistent with performance-limited biogeography in this species. These data highlight the fundamental influence of temperature on ectotherm performance, and how thermal performance limits may shape biogeography. Biologging approaches are rarely used to examine thermal performance curves in free-ranging animals, but these may be central to understanding the trade-offs between physiology and ecology that constrain species' biogeographies and determine the susceptibility of ectotherms to future increases in temperature.

Determining the links among estuarine hydrography, habitat and spawning of estuarine-dependent fish is essential for understanding reproductive dynamics, recruitment processes and directing conservation efforts. Acoustic tracking was used to evaluate fine-scale spatial and temporal patterns in spawning activity of Percalates colonorum (estuary perch) within the Shoalhaven River, south-eastern Australia. Plankton tows were used to determine the timing of spawning events. Tagged P. colonorum exhibited movements restricted to areas of structurally complex large wooden debris and a concrete ferry landing. Egg counts confirmed that spawning events coincided with adult aggregations, whereas egg abundances peaked at night during the first 2 h of the run-out tide. We postulate that spawning and recruitment success of P. colonorum is attributable to its selective spawning habitats that are (1) structurally complex to provide refuge and protection from predation, as well as congregate prey items, (2) adjacent to deep water of high velocities to maximise egg dispersal and (3) in close proximity to river entrance to facilitate coastal dispersal of eggs and inter-estuarine connectivity of larvae.

Activity rhythms are ubiquitous in nature, and generally synchronized with the day–night cycle. Several taxa have been shown to switch between nocturnal and diurnal activity in response to environmental variability, and these relatively uncommon switches provide a basis for greater understanding of the mechanisms and adaptive significance of circadian (approx. 24 h) rhythms. Plasticity of activity rhythms has been identified in association with a variety of factors, from changes in predation pressure to an altered nutritional or social status. Here, we report a switch in activity rhythm that is associated with rainfall. Outside periods of rain, the estuarine-associated teleost Acanthopagrus australis was most active and in shallower depths during the day, but this activity and depth pattern was reversed in the days following rain, with diurnality restored as estuarine conductivity and turbidity levels returned to pre-rain levels. Although representing the first example of a rain-induced reversal of activity rhythm in an aquatic animal of which we are aware, our results are consistent with established models on the trade-offs between predation risk and foraging efficiency.

Temperate basses and perches (family Percichthyidae) worldwide have declined in distribution and abundance during the past few decades due to anthropogenic impacts such as fishing, habitat degradation and alteration to river flows. This study examined differences in the age, growth and longevity of Macquaria colonorum among three south-eastern Australian coastal rivers. Estimates of ages were made by counting opaque zones in sectioned otoliths. Ages were validated by using marginal increment analysis, staining fish otoliths with oxytetracycline and sampling young-of-the-year fish. Length-at-age data from 1644 fish indicated that growth of M. colonorum is rapid in the first 3 to 4 years, after which it slows considerably. Females grew faster and reached larger asymptotic lengths than males. The species was found to be long lived, with the oldest fish estimated at 41 years. Population age structures indicated variable year-class strengths in all three rivers and there was an absence of larger, older (>10 years) individuals in the populations from the two rivers with a history of commercial fishing. These results indicate that M. colonorum populations, similar to other global percichthyid and estuarine-dependent fishes, have been subjected to episodic recruitment and age truncation and that these are likely influenced by environmental flows and fishing pressure.