Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries

Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Markov models and network analysis reveal sex-specific differences in the space-use of a coastal apex predator

Understanding the links between external variables such as habitat and interactions with conspecifics and animal space-use is fundamental to developing effective management measures. In the marine realm, automated acoustic tracking has become a widely used method for monitoring the movement of free-ranging animals, yet researchers generally lack robust methods for analysing the resulting spatial-usage data. In this study, acoustic tracking data from male and female broadnose sevengill sharks Notorynchus cepedianus, collected in a system of coastal embayments in southeast Tasmania were analyzed to examine sex-specific differences in the sharks\u27 coastal space-use and test novel methods for the analysis of acoustic telemetry data. Sex-specific space-use of the broadnose sevengill shark from acoustic telemetry data was analysed in two ways: The recently proposed spatial network analysis of between-receiver movements was employed to identify sex-specific space-use patterns. To include the full breadth of temporal information held in the data, movements between receivers were furthermore considered as transitions between states of a Markov chain, with the resulting transition probability matrix allowing the ranking of the relative importance of different parts of the study area. Both spatial network and Markov chain analysis revealed sex-specific preferences of different sites within the study area. The identification of priority areas differed for the methods, due to the fact that in contrast to network analysis, our Markov chain approach preserves the chronological sequence of detections and accounts for both residency periods and movements. In addition to adding to our knowledge of the ecology of a globally distributed apex predator, this study presents a promising new step towards condensing the vast amounts of information collected with acoustic tracking technology into straightforward results which are directly applicable to the management and conservation of any species that meet the assumptions of our model

Intraspecific differences in movement, dive behaviour and vertical habitat preferences of a key marine apex predator

Understanding the patterns of large-scale movements of highly mobile marine predators is essential to understanding the impacts of anthropogenic pressures on the animals and the ecosystems they frequent. The broadnose sevengill shark Notorynchus cepedianus is one of the most important apex predators in temperate coastal areas around the world, yet little is known of its seasonal large-scale movements. Five male and five female sevengill sharks were equipped with pop-up satellite archival tags (PSATs) in a coastal embayment in southern Tasmania, that collected depth and temperature data during winter, when the animals leave the coastal embayment, resulting in a dataset covering a total of 818 d. Animal tracks indicated that males moved northwards into warmer waters, whereas females remained in southern waters. Three of the females stayed in the Tasmanian coastal areas while the other two left, with one of them moving into deeper waters of up to 360 m depth at the southern edge of the Tasmanian shelf before returning to the Tasmanian coast. These sex-specific differences in large-scale movement could potentially lead to the differential exploitation of the sexes when the sharks leave the protected areas where they were tagged. Both males and females switched between diel vertical migration and reverse diel vertical migration over the course of their tracks and displayed oscillatory vertical movements, probably linked to foraging. These vertical movements persisted throughout the tracks, suggesting that sevengill sharks foraged continuously during their migration rather than switching between transiting and foraging modes

Examining trends in abundance of an overexploited elasmobranch species in a nursery area closure

Determining the dynamics of ecological communities following periods of anthropogenic change is critical to assessing the effectiveness of management strategies. Several coastal areas in south-eastern Australia were proclaimed shark refuge areas (SRAs) following overfishing of the school shark (Galeorhinus galeus) during the 1940s and 1950s. In conjunction with catch reduction measures, these areas provide spatial protection for juvenile G. galeus. In the present study, we compared recent (2012–14) and historic (1991–97) longline catch rates to determine whether young-of-year (YOY) and juvenile G. galeus continue to use these nursery areas (42°47′60.00″S, 147°30′0.00″E). Our data suggest that YOY abundances in the SRAs may have increased, or at least have remained stable, since the 1990s. Data from research fishing conducted from 1947 to 1956 showed that YOY abundance in the SRA correlated well with overall stock abundance in the past. If this relationship still holds, our longline data indicate that the stock may be showing signs of recovery. However, the present-day importance of the SRA to overall stock recruitment, as well as the relationship between YOY abundance in the SRA and stock health, need to be resolved before monitoring of YOY abundance in the SRA can be used as a fisheries-independent stock-assessment tool

Preparing to launch: biologging reveals the dynamics of white shark breaching behaviour

Preparing to launch: biologging reveals the dynamics of white shark breaching behaviou

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

Mapping fisheries for marine spatial planning: Gear-specific vessel monitoring system (VMS), marine conservation and offshore renewable energy

Vessel Monitoring System (VMS) data from 2005 to 2008 in ICES Divisions VIIe-h were used to assess the distribution and intensity of fishing activity in and around the western English Channel, one of the most intensively used marine areas on the planet. The distribution of the UK fleet of large (>15. m length) fishing vessels was analysed and clear gear-specific temporal and spatial differences in activity were found. Mobile demersal gears had the highest intensity and widest distribution of activity in the study area, and so might be expected to have the most widespread ecosystem-level impacts. The potential effects of two proposed fisheries closures; a planned wave energy testing facility (Wave Hub) and a candidate offshore Marine Protected Area (Haig Fras) are described. Maps indicate that mobile demersal gear fleets would be little affected if they were excluded from these proposed closures, but if the static gear fleets were excluded this would likely result in displacement of certain vessels, increasing fishing pressure on other rocky grounds and other fishers. Predictions concerning the effects of fisheries displacement can be improved through the use of high-resolution gear-specific activity data. This study shows that VMS can provide an invaluable source of such data, provided that gear information is made available to fisheries managers and scientists