Effects of coastal development on sawfish movements and the need for marine animal crossing solutions.

Although human-made barriers to animal movement are ubiquitous across many types of ecosystems, the science behind these barriers and how to ameliorate their effects lags far behind in marine environments compared with terrestrial and freshwater realms. Using juvenile sawfish in an Australian nursery habitat as a model system, we aimed to assess the effects of a major anthropogenic development on the movement behavior of coastal species. We compared catch rates and movement behavior (via acoustic telemetry) of juvenile green sawfish (Pristis zijsron) before and after a major coastal structure was built in an important nursery habitat. Acoustic tracking and catch data showed that the development did not affect levels of sawfish recruitment in the nursery, but it did constrain movements of juveniles moving throughout the nursery, demonstrating the reluctance of shoreline-associated species to travel around large or unfamiliar coastal structures. Given the current lack of information on human-made movement barriers in the marine environment, these findings highlight the need for further research in this area, and we propose the development of and experimentation with marine animal crossings as an important area of emerging research.

Efectos del desarrollo costero sobre los movimientos del pez sierra y la necesidad de soluciones para el cruce de animales marinos Resumen Mientras que las barreras construidas por humanos que limitan el movimiento de animales son ubicuas en muchos tipos de ecosistemas, la ciencia que sustenta estas barreras y la reducción de sus impactos está muy retrasada en ambientes marinos en comparación con medios terrestres y dulceacuícolas. Utilizando peces sierra juveniles en un hábitat de vivero australiano como sistema modelo, intentamos evaluar los efectos de un importante desarrollo antropogénico sobre el comportamiento de especies costeras. Comparamos las tasas de captura y el comportamiento de movimiento (mediante telemetría acústica) de peces sierra verdes juveniles (Pristis zijsron) antes y después de que se construyera infraestructura costera en un importante hábitat de vivero. El seguimiento acústico y los datos de captura mostraron que el desarrollo no afectó los niveles de reclutamiento de pez sierra en el vivero, pero sí restringió los movimientos de los juveniles desplazándose por el vivero, lo cual demuestra la renuencia de las especies asociadas a la costa a viajar alrededor de estructuras costeras grandes o desconocidas. Dada la actual falta de información sobre las barreras de movimiento creadas por el hombre en el medio marino, estos hallazgos destacan la necesidad de realizar más investigaciones en esta campo, y proponemos el desarrollo y la experimentación con cruces para animales marinos como un área importante de investigación emergente.

Temporal niche partitioning as a novel mechanism promoting co-existence of sympatric predators in marine systems.

Niche partitioning of time, space or resources is considered the key to allowing the coexistence of competitor species, and particularly guilds of predators. However, the extent to which these processes occur in marine systems is poorly understood due to the difficulty in studying fine-scale movements and activity patterns in mobile underwater species. Here, we used acceleration data-loggers to investigate temporal partitioning in a guild of marine predators. Six species of co-occurring large coastal sharks demonstrated distinct diel patterns of activity, providing evidence of strong temporal partitioning of foraging times. This is the first instance of diel temporal niche partitioning described in a marine predator guild, and is probably driven by a combination of physiological constraints in diel timing of activity (e.g. sensory adaptations) and interference competition (hierarchical predation within the guild), which may force less dominant predators to suboptimal foraging times to avoid agonistic interactions. Temporal partitioning is often thought to be rare compared to other partitioning mechanisms, but the occurrence of temporal partitioning here and similar characteristics in many other marine ecosystems (multiple predators simultaneously present in the same space with dietary overlap) introduces the question of whether this is a common mechanism of resource division in marine systems.

Accounting for body mass effects in the estimation of field metabolic rates from body acceleration.

Dynamic body acceleration (DBA), measured through animal-attached tags, has emerged as a powerful method for estimating field metabolic rates of free-ranging individuals. Following respirometry to calibrate oxygen consumption rate (MO2) with DBA under controlled conditions, predictive models can be applied to DBA data collected from free-ranging individuals. However, laboratory calibrations are generally performed on a relatively narrow size range of animals, which may introduce biases if predictive models are applied to differently sized individuals in the field. Here, we tested the mass dependence of the MO2-DBA relationship to develop an experimental framework for the estimation of field metabolic rates when organisms differ in size. We performed respirometry experiments with individuals spanning one order of magnitude in body mass (1.74-17.15 kg) and used a two-stage modelling process to assess the intraspecific scale dependence of the MO2-DBA relationship and incorporate such dependencies into the coefficients of MO2 predictive models. The final predictive model showed scale dependence; the slope of the MO2-DBA relationship was strongly allometric (M1.55), whereas the intercept term scaled closer to isometry (M1.08). Using bootstrapping and simulations, we evaluated the performance of this coefficient-corrected model against commonly used methods of accounting for mass effects on the MO2-DBA relationship and found the lowest error and bias in the coefficient-corrected approach. The strong scale dependence of the MO2-DBA relationship indicates that caution must be exercised when models developed using one size class are applied to individuals of different sizes.

Net design for selective control of the "plague minnow" Gambusia holbrooki that minimises impact on native Australian fishes.

Gambusia holbrooki is one of the world's most environmentally damaging introduced species, being notoriously difficult to control once established. A composite double-winged fyke net comprising four vertically stacked compartments was developed to determine the potential to control G. holbrooki, while reducing negative interactions of this aggressive species with small threatened fishes. The stacked fyke net captured three times as many G. holbrooki as a conventional fyke net while maintaining consistent catches of native fishes relative to that from a conventional fyke net, and detected species-specific vertical distributions. This stratified net design represents a valuable management option for controlling this agonistic species or for limiting antagonistic interactions between G. holbrooki and native species during typical fyke sampling of native ecosystems.

Divergent field metabolic rates highlight the challenges of increasing temperatures and energy limitation in aquatic ectotherms.

Environments where extreme temperatures and low productivity occur introduce energetically challenging circumstances that may be exacerbated by climate change. Despite the strong link between metabolism and temperature in ectotherms, there is a paucity of data regarding how the metabolic ecology of species affects growth and fitness under such circumstances. Here, we integrated data describing field metabolic rates and body condition of two sympatric species of ectotherms with divergent lifestyles, the benthic freshwater (or largetooth) sawfish (Pristis pristis) and the epipelagic bull shark (Carcharhinus leucas) occurring in the Fitzroy River, Western Australia, to test the implications of their differing metabolic ecologies for vulnerability to rising temperatures. Over a temperature range of 18-34 °C, sawfish had lower field metabolic rates (63-187 mg O2 kg-0.86 h-1) and lower temperature sensitivity of metabolic rates [activation energy (EA) = 0.35 eV] than bull sharks (187-506 mg O2 kg-0.86 h-1; EA = 0.48 eV). Both species lost body mass throughout the dry season, although bull sharks significantly more (0.17% mass loss day-1) than sawfish (0.07% mass loss day-1). Subsequent bioenergetics modelling showed that under future climate change scenarios, both species would reach potentially lethal levels of mass loss during dry season periods before the end of the century. These results suggest that ectotherms with low metabolic rates may be better suited to extreme environmental conditions, and that even small increases in temperature due to climate change could have substantial impacts on the ability of ectotherms to grow and survive in harsh conditions, including high temperatures and energy-limiting circumstances.

Respirometer in a box: development and use of a portable field respirometer for estimating oxygen consumption of large-bodied fishes.

This study developed a portable, low-cost field respirometer for measuring oxygen consumption rates of large-bodied fishes. The respirometer performed well in laboratory tests and was used to measure the oxygen consumption rates ( M ˙ O2 ) of bull sharks Carcharhinus leucas (mean: 249.21 ± 58.10 mg O2 kg-1 h-1 at 27.05°C). Interspecific comparisons and assessments of oxygen degradation curves indicated that the respirometer provided reliable measurements of M ˙ O2 . This system presents a field-based alternative to laboratory respirometers, opening opportunities for studies on species in remote localities, increasing the ability to validate physiological field studies.

Thermal performance responses in free-ranging elasmobranchs depend on habitat use and body size.

Temperature is one of the most influential drivers of physiological performance and behaviour in ectotherms, determining how these animals relate to their ecosystems and their ability to succeed in particular habitats. Here, we analysed the largest set of acceleration data compiled to date for elasmobranchs to examine the relationship between volitional activity and temperature in 252 individuals from 8 species. We calculated activation energies for the thermal performance response in each species and estimated optimum temperatures using an Arrhenius breakpoint analysis, subsequently fitting thermal performance curves to the activity data. Juveniles living in confined nursery habitats not only spent substantially more time above their optimum temperature and at the upper limits of their performance breadths compared to larger, less site-restricted animals, but also showed lower activation energies and broader performance curves. Species or life stages occupying confined habitats featured more generalist behavioural responses to temperature change, whereas wider ranging elasmobranchs were characterised by more specialist behavioural responses. The relationships between the estimated performance regimes and environmental temperature limits suggest that animals in confined habitats, including many juvenile elasmobranchs within nursery habitats, are likely to experience a reduction of performance under a warming climate, although their flatter thermal response will likely dampen this impact. The effect of warming on less site-restricted species is difficult to forecast since three of four species studied here did not reach their optimum temperature in the wild, although their specialist performance characteristics may indicate a more rapid decline should optimum temperatures be exceeded.

Metabolic rates and the energetic cost of external tag attachment in juvenile blacktip sharks Carcharhinus limbatus.

This study reports on the metabolic rate of the blacktip shark Carcharhinus limbatus and the energetic costs of external tag attachment. Metabolic rates, swimming speed and tail-beat (BT ) frequency were measured in a static respirometer with untagged animals and animals equipped with a small data logger. Tagged sharks showed significantly higher routine oxygen consumption and lower swimming speeds than untagged animals, indicating that tagging significantly affected the swimming efficiency and energetic requirements in these small sharks, and that these effects must be accounted for when interpreting telemetry data from free-ranging individuals.

Correlations of metabolic rate and body acceleration in three species of coastal sharks under contrasting temperature regimes.

The ability to produce estimates of the metabolic rate of free-ranging animals is fundamental to the study of their ecology. However, measuring the energy expenditure of animals in the field has proved difficult, especially for aquatic taxa. Accelerometry presents a means of translating metabolic rates measured in the laboratory to individuals studied in the field, pending appropriate laboratory calibrations. Such calibrations have only been performed on a few fish species to date, and only one where the effects of temperature were accounted for. Here, we present calibrations between activity, measured as overall dynamic body acceleration (ODBA), and metabolic rate, measured through respirometry, for nurse sharks (Ginglymostoma cirratum), lemon sharks (Negaprion brevirostris) and blacktip sharks (Carcharhinus limbatus). Calibrations were made at a range of volitional swimming speeds and experimental temperatures. Linear mixed models were used to determine a predictive equation for metabolic rate based on measured ODBA values, with the optimal model using ODBA in combination with activity state and temperature to predict metabolic rate in lemon and nurse sharks, and ODBA and temperature to predict metabolic rate in blacktip sharks. This study lays the groundwork for calculating the metabolic rate of these species in the wild using acceleration data.

Ectoparasites of the Critically Endangered Giant Shovelnose Ray Glaucostegus typus in the Eastern Indian Ocean, with a Summary of the Known Metazoan Parasites.

PURPOSE: This study examined the metazoan ectoparasites of the Critically Endangered giant shovelnose ray, Glaucostegus typus, in the eastern Indian Ocean. METHODS: We screened 186 G. typus for ectoparasites in four coastal regions of Western Australia between 2020 and 2022: the Pilbara Region, Exmouth Gulf, Ningaloo Coast and Shark Bay. RESULTS: Five parasite taxa were encountered on 186 G. typus: Caligus furcisetifer (Copepoda: Caligidae), Dermopristis cairae (Monopisthocotyla: Microbothriidae), Branchellion plicobranchus and Stibarobdella macrothela (Hirudinida: Piscicolidae), and praniza larvae of unidentified gnathiid isopod/s (Isopoda: Gnathiidae). Two of these species, B. plicobranchus and S. macrothela, are reported for the first time on G. typus. Only C. furcisetifer and S. macrothela were relatively common, encountered on 31% and 40% of G. typus, respectively. Gnathiids were observed infrequently, encountered on 13% of G. typus, and D. cairae and B. plicobranchus were scarce, encountered on 1% and 2% of G. typus, respectively. Intensity of infection for C. furcisetifer and gnathiids increased with host length. Likelihood of infection varied seasonally for C. furcisetifer, being considerably lower in summer, and regionally for gnathiids, being greatest at Shark Bay. Intensity and likelihood of infection for S. macrothela increased with host length and varied regionally, being greatest at Shark Bay. CONCLUSION: These findings improve our understanding of the downstream impacts for dependent parasites that might arise should populations of G. typus continue to decline.

Ectoparasites of the Critically Endangered green sawfish Pristis zijsron and sympatric elasmobranchs in Western Australia.

This study reports the metazoan ectoparasite fauna of juvenile Critically Endangered green sawfish, Pristis zijsron, and sympatric elasmobranchs in Western Australia. Five parasite taxa were found on 76 screened P. zijsron: Caligus furcisetifer (Copepoda: Caligidae), Dermopristis pterophila (Monogenea: Microbothriidae), Branchellion plicobranchus and Stibarobdella macrothela (Hirudinea: Piscicolidae), and praniza larvae of an unidentified gnathiid isopod. Only C. furcisetifer and D. pterophila were common, exhibiting discrepant site-specificity, with C. furcisetifer occurring mostly on the head and rostrum, and D. pterophila around the pectoral and pelvic fins. Intensity of infection for C. furcisetifer and D. pterophila increased with host total length and was influenced by host sex, but in opposite directions; intensity of C. furcisetifer was greater on female P. zijsron, whereas intensity of D. pterophila was greater on males. In the Ashburton River, likelihood of infection for C. furcisetifer and D. pterophila on P. zijsron increased with time since substantial freshwater discharge events, suggesting decreased salinity impacts both taxa. In addition to P. zijsron, five other sympatric elasmobranch species were opportunistically screened for ectoparasites in the study area: the giant shovelnose ray, Glaucostegus typus, the eyebrow wedgefish, Rhynchobatus palpebratus, the nervous shark, Carcharhinus cautus, the lemon shark, Negaprion acutidens, and the graceful shark, Carcharhinus amblyrhynchoides. Caligus furcisetifer was found on R. palpebratus; no other parasites of P. zijsron were found on other sympatric elasmobranch species. Conversely, Perissopus dentatus (Copepoda: Pandaridae) was found on all three carcharhinids but not on batoid rays (P. zijsron, G. typus or R. palpebratus).

A new microbothriid monogenean Dermopristis pterophilus n. sp. from the skin of the Critically Endangered green sawfish Pristis zijsron Bleeker, 1851 (Batoidea: Pristidae) in Western Australia.

A new microbothriid monogenean Dermopristis pterophilus n. sp. is described from the skin of the Critically Endangered green sawfish Pristis zijsron Bleeker, 1851 in the Ashburton River delta, northern Western Australia. Analyses of the 28S ribosomal DNA marker and the molecular barcoding markers Histone 3 and Elongation Factor 1 α confirmed position among the Microbothriidae, with close affinity to the only other sequenced representative of Dermopristis Kearn, Whittington and Evans-Groing, 2010. The new species is morphologically consistent with the concept of Dermopristis; it has two testes, lacks a male copulatory organ and has a simple haptor. It is smaller than its two congeners D. paradoxus Kearn, Whittington and Evans-Gowing, 2010 and D. cairae Whittington and Kearn, 2011 and is most similar to the former, distinguished only in that it lacks the strong, transverse, parallel ridges on the ventral body surface that characterise that species. It is more easily distinguished from D. cairae, differing in body shape, possession of a seminal receptacle, and relative position and size of the haptor. It may further differ from both species by fine details of the gut diverticula, although these details are difficult to ascertain. Spermatophores were observed in the new species, similar to those previously reported for D. cairae. The new species exhibits site attachment preference: infections were greatest on and immediately adjacent to the host pelvic fins (including male reproductive organs, i.e. claspers), moderate in proximity to the dorsal and pectoral fins, few on the caudal fin and peduncle, and infrequently, isolated worms occurred elsewhere on the dorsal and ventral surfaces of the body. There was no incidence of infection on the head (including rostrum). We presume D. pterophilus is restricted to P. zijsron and thus likely faces the same threat of extinction.

Wet season flood magnitude drives resilience to dry season drought of a euryhaline elasmobranch in a dry-land river.

The increase in severity and occurrence of drought from environmental change poses a significant threat to freshwater ecosystems. However, many of the mechanisms by which periodic drought affects aquatic animals are poorly understood. Here we integrated physical, physiological, and behavioural measurements made in the field over a twelve-year period to provide a comprehensive understanding of the factors affecting the loss of body condition of fish in arid rivers, using the Critically Endangered freshwater sawfish (Pristis pristis) in the dryland Fitzroy River, Western Australia, as a model species. Sawfish lost condition throughout the long dry season in all years and had significantly poorer body condition throughout years characterized by low volumes of wet season flooding and little occurrence of overbank flooding. A mechanistic examination of factors leading to this loss of condition using measurements of body temperature, field energetics, and habitat use from telemetry techniques showed that the loss of condition throughout the season was likely due to substantial habitat compression and low productivity in drier years, while high rates of competition were more likely to drive this pattern in wetter years. This information can be used to forecast how climate change and water abstraction will affect aquatic fauna experiencing intermittent drought and can inform management decisions to help mitigate these threats.

Connecting post-release mortality to the physiological stress response of large coastal sharks in a commercial longline fishery.

Bycatch mortality is a major factor contributing to shark population declines. Post-release mortality (PRM) is particularly difficult to quantify, limiting the accuracy of stock assessments. We paired blood-stress physiology with animal-borne accelerometers to quantify PRM rates of sharks caught in a commercial bottom longline fishery. Blood was sampled from the same individuals that were tagged, providing direct correlation between stress physiology and animal fate for sandbar (Carcharhinus plumbeus, N = 130), blacktip (C. limbatus, N = 105), tiger (Galeocerdo cuvier, N = 52), spinner (C. brevipinna, N = 14), and bull sharks (C. leucas, N = 14). PRM rates ranged from 2% and 3% PRM in tiger and sandbar sharks to 42% and 71% PRM in blacktip and spinner sharks, respectively. Decision trees based on blood values predicted mortality with >67% accuracy in blacktip and spinner sharks, and >99% accuracy in sandbar sharks. Ninety percent of PRM occurred within 5 h after release and 59% within 2 h. Blood physiology indicated that PRM was primarily associated with acidosis and increases in plasma potassium levels. Total fishing mortality reached 62% for blacktip and 89% for spinner sharks, which may be under-estimates given that some soak times were shortened to focus on PRM. Our findings suggest that no-take regulations may be beneficial for sandbar, tiger, and bull sharks, but less effective for more susceptible species such as blacktip and spinner sharks.

Depth-dependent dive kinematics suggest cost-efficient foraging strategies by tiger sharks.

Tiger sharks, Galeocerdo cuvier, are a keystone, top-order predator that are assumed to engage in cost-efficient movement and foraging patterns. To investigate the extent to which oscillatory diving by tiger sharks conform to these patterns, we used a biologging approach to model their cost of transport. High-resolution biologging tags with tri-axial sensors were deployed on 21 tiger sharks at Ningaloo Reef for durations of 5-48 h. Using overall dynamic body acceleration as a proxy for energy expenditure, we modelled the cost of transport of oscillatory movements of varying geometries in both horizontal and vertical planes for tiger sharks. The cost of horizontal transport was minimized by descending at the smallest possible angle and ascending at an angle of 5-14°, meaning that vertical oscillations conserved energy compared to swimming at a level depth. The reduction of vertical travel costs occurred at steeper angles. The absolute dive angles of tiger sharks increased between inshore and offshore zones, presumably to reduce the cost of transport while continuously hunting for prey in both benthic and surface habitats. Oscillatory movements of tiger sharks conform to strategies of cost-efficient foraging, and shallow inshore habitats appear to be an important habitat for both hunting prey and conserving energy while travelling.

Recruitment of a critically endangered sawfish into a riverine nursery depends on natural flow regimes.

The freshwater sawfish (Pristis pristis) was recently listed as the most Evolutionarily Distinct and Globally Endangered (EDGE) animal. The Fitzroy River in the remote Kimberley region of north-western Australia represents a significant stronghold for the species, which uses the freshwater reaches of the river as a nursery. There is also mounting pressure to develop the water resources of the region for agriculture that may substantially affect life history dynamics of sawfish in this system. However, the relationship between hydrology and population dynamics of freshwater sawfish was unknown. We used standardized catch data collected over 17 years to determine how wet season volume influences recruitment of freshwater sawfish into their riverine nursery. Negligible recruitment occurred in years with few days of high flood levels (above 98th percentile of cease-to-flow stage height), and relatively high recruitment occurred in years with 14 or more days of high flood levels. This relationship is indicative of a distinct boom-or-bust cycle, whereby freshwater sawfish rely almost entirely on the few years with large wet season floods, and the brief periods of highest water levels within these years, to replenish juvenile populations in the Fitzroy River nursery. This has direct implications for sustainable water resource management for the Fitzroy River basin in order to preserve one of the last known intact nursery habitats for this globally threatened species.