Oceanographic conditions associated with white shark (Carcharodon carcharias) habitat use along eastern Australia

Management of species with wide-ranging migrations is a complex issue, made more challenging when the species is both protected and poses a risk to humans. Understanding the oceanic conditions associated with shark habitat use can help develop mitigation strategies or warning systems that meet both conservation and human safety objectives. Using satellite tracks from 77 juvenile and sub-adult white sharks tagged over 10 yr, we modelled individual movement patterns using hidden Markov models and applied generalised additive (mixed) models to explore correlations between movement patterns (presence−absence, habitat selection and behavioural state) and oceanographic and bathymetric variables. White sharks used the whole of the continental shelf, down to depths of 350 m on the continental slope. Sharks were present over a wide range of sea surface temperatures (SSTs; 10−27°C), with the highest probability of occurring at ~20°C. However, the number of average daily tag positions was greatest when SST was between 14 and 18°C, and sharks were more likely to exhibit area-restricted movement when SST was between ~19 and 23°C. Sharks were more likely to be present and selected habitats in productive areas with moderate to high surface chl a concentrations as well as thermal and productivity fronts. Although mesoscale eddies did not influence the likelihood of individuals being present in an area, there was a higher density of sharks in cold-core eddies compared to warm-core eddies. This study indicates that white shark presence and dispersal may be linked, perhaps via prey distribution, to oceanic conditions, potentially assisting development of suitable shark bite mitigation strategies

Habitat selection, facilitation, and biotic settlement cues affect distribution and performance of coral recruits in French Polynesia

Habitat selection can determine the distribution and performance of individuals if the precision with which sites are chosen corresponds with exposure to risks or resources. Contrastingly, facilitation can allow persistence of individuals arriving by chance and potentially maladapted to local abiotic conditions. For marine organisms, selection of a permanent attachment site at the end of their larval stage or the presence of a facilitator can be a critical determinant of recruitment success. In coral reef ecosystems, it is well known that settling planula larvae of reef-building corals use coarse environmental cues (i.e., light) for habitat selection. Although laboratory studies suggest that larvae can also use precise biotic cues produced by crustose coralline algae (CCA) to select attachment sites, the ecological consequences of biotic cues for corals are poorly understood in situ. In a field experiment exploring the relative importance of biotic cues and variability in habitat quality to recruitment of hard corals, pocilloporid and acroporid corals recruited more frequently to one species of CCA, Titanoderma prototypum, and significantly less so to other species of CCA; these results are consistent with laboratory assays from other studies. The provision of the biotic cue accurately predicted coral recruitment rates across habitats of varying quality. At the scale of CCA, corals attached to the “preferred” CCA experienced increased survivorship while recruits attached elsewhere had lower colony growth and survivorship. For reef-building corals, the behavioral selection of habitat using chemical cues both reduces the risk of incidental mortality and indicates the presence of a facilitator

Continental-scale acoustic telemetry and network analysis reveal new insights into stock structure

Delineation of population structure (i.e. stocks) is crucial to successfully manage exploited species and to address conservation concerns for threatened species. Fish migration and associated movements are key mechanisms through which discrete populations mix and are thus important determinants of population structure. Detailed information on fish migration and movements is becoming more accessible through advances in telemetry and analysis methods however such information is not yet used systematically in stock structure assessment. Here, we described how detections of acoustically tagged fish across a continental-scale array of underwater acoustic receivers were used to assess stock structure and connectivity in seven teleost and seven shark species and compared to findings from genetic and conventional tagging. Network analysis revealed previously unknown population connections in some species, and in others bolstered support for existing stock discrimination by identifying nodes and routes important for connectivity. Species with less variability in their movements required smaller sample sizes (45–50 individuals) to reveal useful stock structure information. Our study shows the power of continental-scale acoustic telemetry networks to detect movements among fishery jurisdictions. We highlight methodological issues that need to be considered in the design of acoustic telemetry studies for investigating stock structure and the interpretation of the resulting data. The advent of broad-scale acoustic telemetry networks across the globe provides new avenues to understand how movement informs population structure and can lead to improved management