Defining the home range of vulnerable species is critical for designing effective spatial management strategies. However, animal home ranges often change with ontogeny, and quantifying the associated temporal and spatial changes is particularly challenging for mobile marine species. Here, we investigated how the space use of a top predatory reef-associated fish (giant trevally Caranx ignobilis ) scales with body size. Fish were tagged with acoustic transmitters and passively tracked for >3 yr at a tropical island and atoll in the Republic of Seychelles. A sheltered atoll environment was critical for juvenile fish (<60 cm fork length, FL) that exhibited a shift in home range location and area as they matured into adults. Small (60-100 cm FL) and large (>100 cm FL) adult fish appeared to favour shallow coral reefs and associated reef drop offs whilst sharing a similar core home range location. Large adult fish utilized a greater diversity of habitat types and had significantly (p < 0.05) greater annual dispersal distances (mean = 35.29 km, max = 91.32 km) than small adults (mean = 13.72 km, max = 21.55 km). Additionally, the home range of large adults (mean = 209.74 km 2 ) was significantly (p < 0.05) larger than that of juveniles (mean = 38.73 km 2 ) and small adults (77.32 km 2 ) and there was a significant (p = 0.02) relationship between fish length and home range size. Furthermore, tagged fish took up to 34 mo (mean = 18.54 mo) to utilize the full extent of their home range. The habitat shift and expansion in home range size throughout ontogeny should be taken into account when designing effective spatial management plans for C. ignobilis .

A drone was used to study the richness and behaviour of scavengers attracted to the carcass of a sperm whale (Physeter microcephalus) in Seychelles, Western Indian Ocean. Over 30 sharks of 3 species (tiger shark Galeocerdo cuvier, bull shark Carcharhinus leucas and tawny nurse shark Nebrius ferrugineus) were recorded scavenging on the carcass. Tiger sharks dominated the scavenging, but with no evidence of agonistic behaviours or hierarchy, and may have facilitated scavenging by other species. Drone use allowed the analysis of such behaviours without observer influence, providing new insights into communal scavenging events.

A large, pregnant, female bull shark Carcharhinus leucas was tracked migrating from Seychelles across open ocean to south-east Madagascar, c. 2000 km away, and back again. In Madagascar, the shark spent a prolonged period shallower than 5 m, consistent with entering estuarine habitat to pup, and upon return to Seychelles the shark was slender and no longer gravid. This represents an unprecedented return migration across the open ocean for a C. leucas and highlights the need for international collaboration to manage the regional C. leucas population sustainably.

There is a lack of studies on how provisioning may influence shark numbers and behaviour. The effects of long-term provisioning were investigated at a Red Sea reef, where both grey reef shark (Carcharhinus amblyrhynchos) and silky shark (Carcharhinus falciformis) occurred. Initially, grey reef sharks outnumbered silky sharks, but over 6 years, silky shark numbers increased almost 20-fold, whereas grey-reef sightings decreased >90%. Following this, silky-shark sightings also declined considerably (>80%). It is suggested that these declines could relate to local overfishing. Many silky sharks were identified individually through distinctive markings or conventional tagging. Some individual silky sharks were recorded regularly over 2 years or more, but most appeared to be transient visitors. Sighting records indicated that provisioning extended the residency of transient individuals. If visiting silky sharks were drawn from a larger regional population, this would explain both their initial accumulation and why, to begin with, sightings were sustained despite local fishing pressure. Conversely, the site fidelity typical of grey reef sharks would have made them more susceptible to local depletion. Silky sharks were recorded as behaving more boldly when present in greater numbers, but the decline in grey reef sharks appears to be unrelated to the initial increase in the numbers of silky shark.

Many shark populations are experiencing critical declines from overfishing, triggering potentially detrimental cascade effects on marine ecosystems. Silky sharks, Carcharhinus falciformis, have experienced some of the most severe declines, yet little information exists on their behavioural ecology to inform management decisions. In the present study, the movement patterns of a sexually segregated subpopulation of female silky sharks on reefs in the Central Red Sea were investigated using acoustic telemetry to characterise habitat-use and residency patterns. Frequent baiting of sharks at a particular reef-site significantly increased time spent in the vicinity, although no increases in use of other reef areas 5–10 and 50–60 km away were recorded, and regular use of all three reef areas persisted in the absence of bait. Observed residency patterns varied considerably, from being present almost year-round to visiting only intermittently. The sharks spent significantly longer times at study reefs during daylight hours, even within bait-free regions, suggesting the diel bias is normal. This pattern became less distinct nearer the full moon when there is more ambient light. The regular, perennial use of these reefs by mature and near-mature female silky sharks highlights the importance of this habitat in the Red Sea for recruitment into the local shark population.