In the face of accelerating climate change, conservation strategies will need to consider how marine animals deal with forecast environmental change as well as ongoing threats. We used 10 yr (2009-2018) of data from commercial fisheries and a bather protection program along the coast of New South Wales (NSW), southeastern Australia, to investigate (1) spatial and temporal patterns of occurrence in bull sharks and (2) environmental factors affecting bull shark occurrence along the coast of NSW. Predicted future distribution for this species was modelled for the forecast strengthening East Australian Current. Bull sharks were mostly harvested in small to larger estuaries, with average depth and rainfall responsible for contrasting patterns for each of the fisheries. There was an increase in the occurrence of bull sharks over the last decade, particularly among coastal setline fisheries, associated with seasonal availability of thermal gradients >22°C and both westward and southward coastal currents stronger than 0.15 and 0.60 m s-1, respectively, during the austral summer. Our model predicts a 3 mo increase in the availability of favourable water temperatures along the entire coast of NSW for bull sharks by 2030. This coastline provides a uniquely favourable topography for range expansion in the face of a southerly shift of warmer waters, and habitat is unlikely to be a limiting factor for bull sharks in the future. Such a southerly shift in distribution has implications for the management of bull sharks both in commercial fisheries and for mitigation of shark-human interactions.

The present study aims at inferring linkages between the abundance of potentially dangerous sharks (PDSs) and shark hazard, so as to derive information about the underlying processes of shark peril off Recife, Brazil. Fishery-independent longline and drumline data collected from May 2004 through December 2014 for Carcharhinus leucas and Galeocerdo cuvier measuring ≥109cm were considered for analysis. Generalised additive models showed that the frequency of shark bites was directly proportional to and followed the same seasonal trends as PDS abundance, meeting the hypothesis that higher shark abundance may result in an increased chance of a shark bite. However, the species-specific seasonality of bull and tiger sharks seemed to follow distinct patterns. This method was helpful in comparing the abundance dynamics of the PDSs caught by the local shark hazard-mitigation program with the distribution of shark bites, so as to infer whether the species involved in the incidents were being effectively captured. Also, it provided some information about each species’ contribution to the overall dynamics in local shark hazard. However, despite being a potentially useful risk-management tool, its predictive efficacy for shark-peril mitigation may depend on the availability of abundant data spanning across wide temporal ranges.

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Acoustic telemetry enables spatial ecologists to collect movement data from a variety of aquatic species. In estuaries and rivers, accounting for the complex shape of water bodies is challenging. Current methods for analysing utilization distributions (UDs) are restricted to using the locations of receivers where animals have been detected, which limits the information available to estimate movement paths. We present a new r package (RSP—Refined Shortest Paths) for analysing the movements of animals tracked with acoustic transmitters in environments constrained by landmasses. The method estimates the shortest in water locations of monitored animals between pairs of detections using least‐cost path analysis. It then applies dynamic Brownian Bridge Movement Models to calculate UD areas. Intra‐ and interspecific overlaps in space and time are calculated and can be used, for example, to investigate potential influencing environmental factors. Tracks refined with RSP follow the estuary shape, yielding substantially longer, but more realistic travel distances. Showcased examples demonstrate how RSP can be used to analyse intra‐ and interspecific movement patterns; determine similarities in habitat use; identify the environmental conditions responsible for influencing the size of the space use areas; and assess levels of spatial overlap between different species. The RSP toolkit generates more realistic movements of tracked animals than those derived using receiver locations alone. An incidental benefit is its ability to deal with receiver loss, a common problem in acoustic telemetry studies. The analysis can be readily customized to suit different study species, array configurations and habitat shapes.

Globally, marine animal distributions are shifting in response to a changing climate. These shifts are usually considered at the species level, but individuals are likely to differ in how they respond to the changing conditions. Here, we investigate how movement behaviour and, therefore, redistribution, would differ by sex and maturation class in a wide-ranging marine predator. We tracked 115 tiger sharks (Galeocerdo cuvier) from 2002 to 2020 and forecast class-specific distributions through to 2030, including environmental factors and predicted occurrence of potential prey. Generalised Linear and Additive Models revealed that water temperature change, particularly at higher latitudes, was the factor most associated with shark movements. Females dispersed southwards during periods of warming temperatures, and while juvenile females preferred a narrow thermal range between 22 and 23 °C, adult female and juvenile male presence was correlated with either lower (< 22 °C) or higher (> 23 °C) temperatures. During La Niña, sharks moved towards higher latitudes and used shallower isobaths. Inclusion of predicted distribution of their putative prey significantly improved projections of suitable habitats for all shark classes, compared to simpler models using temperature alone. Tiger shark range off the east coast of Australia is predicted to extend ~ 3.5° south towards the east coast of Tasmania, particularly for juvenile males. Our framework highlights the importance of combining long-term movement data with multi-factor habitat projections to identify heterogeneity within species when predicting consequences of climate change. Recognising intraspecific variability will improve conservation and management strategies and help anticipate broader ecosystem consequences of species redistribution due to ocean warming.

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Spawning is a key life history event for aquatic species that can be triggered by environmental signals. For estuarine-dependent species, the timing of such triggers can be important for determining future patterns in recruitment. Here, we used acoustic telemetry to identify the potential drivers of spawning migration in female Giant Mud Crabs (Scylla serrata). Eighty-nine mature female crabs were tagged in two subtropical south-east Australian estuaries, the Clarence River (~ 29.4°S) and Kalang River (~ 30.5°S), during the summer spawning season (November–June) over two years (2018/19 and 2020/21), and their movements were monitored for up to 68 d, alongside high-resolution environmental data. Crabs were considered to have ‘successfully’ migrated if they were detected at the mouth of the estuary, a behaviour exhibited by 52% of tagged crabs. The highest probability of migration was associated with relatively low temperatures (< 22 °C) and when conductivity rapidly declined (< -10 mS cm−1 d−1) following heavy rainfall. Furthermore, migration coincided with larger tides associated with the new and full moon, and following heavy rainfall, which may aid rapid downstream migration. Oceanic detections of 14 crabs (30% of ‘successful’ migrators) showed that once crabs left estuaries they migrated north. These patterns show that variability in environmental triggers for spawning migrations may contribute to interannual variation in spawning patterns, which may in turn impact fisheries productivity in this region.

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