Browsing by Author "Block, Barbara A."

Now showing 1 - 7 of 7
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    Analysing detection gaps in acoustic telemetry data to infer differential movement patterns in fish
    Williamson, Michael J.; Tebbs, Emma J.; Dawson, Terence P.; Curnick, David J.; Ferretti, Francesco; Carlisle, Aaron B.; Chapple, Taylor K.; Schallert, Robert J.; Tickler, David M.; Harrison, Xavier A.; Block, Barbara A.; Jacoby, David M. P. (2021-03)
    A wide array of technologies are available for gaining insight into the movement of wild aquatic animals. Although acoustic telemetry can lack the fine-scale spatial resolution of some satellite tracking technologies, the substantially longer battery life can yield important long-term data on individual behavior and movement for low per-unit cost. Typically, however, receiver arrays are designed to maximize spatial coverage at the cost of positional accuracy leading to potentially longer detection gaps as individuals move out of range between monitored locations. This is particularly true when these technologies are deployed to monitor species in hard-to-access locations. Here, we develop a novel approach to analyzing acoustic telemetry data, using the timing and duration of gaps between animal detections to infer different behaviors. Using the durations between detections at the same and different receiver locations (i.e., detection gaps), we classify behaviors into "restricted" or potential wider "out-of-range" movements synonymous with longer distance dispersal. We apply this method to investigate spatial and temporal segregation of inferred movement patterns in two sympatric species of reef shark within a large, remote, marine protected area (MPA). Response variables were generated using network analysis, and drivers of these movements were identified using generalized linear mixed models and multimodel inference. Species, diel period, and season were significant predictors of "out-of-range" movements. Silvertip sharks were overall more likely to undertake "out-of-range" movements, compared with gray reef sharks, indicating spatial segregation, and corroborating previous stable isotope work between these two species. High individual variability in "out-of-range" movements in both species was also identified. We present a novel gap analysis of telemetry data to help infer differential movement and space use patterns where acoustic coverage is imperfect and other tracking methods are impractical at scale. In remote locations, inference may be the best available tool and this approach shows that acoustic telemetry gap analysis can be used for comparative studies in fish ecology, or combined with other research techniques to better understand functional mechanisms driving behavior.
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    Detecting Mediterranean White Sharks with Environmental DNA
    Jenrette, Jeremy F.; Jenrette, Jennifer L.; Truelove, N. Kobun; Moro, Stefano; Dunn, Nick I.; Chapple, Taylor K.; Gallagher, Austin J.; Gambardella, Chiara; Schallert, Robert; Shea, Brendan D.; Curnick, David J.; Block, Barbara A.; Ferretti, Francesco (The Oceanography Society, 2023-01)
    The white shark (Carcharodon carcharias) is a globally distributed, ecologically important top predator whose biology and population dynamics are challenging to study. Basic biological parameters remain virtually unknown in the Mediterranean Sea due to its historically low population density, dwindling population size, and lack of substantial sightings. White sharks are considered Critically Endangered in the Mediterranean Sea, and recent analyses suggest that the population has declined by 52% to 96% from historical levels in different Mediterranean sectors (Moro et al., 2020). Thus, white shark sightings dating back to 1860 are being used to estimate population trajectories throughout the entire region. Though the population size is unknown, remaining individuals are thought to be primarily restricted to a handful of hotspots deemed important for their reproduction and foraging. One of these hypothesized hotspots is the Sicilian Channel, which accounts for 19% of total historical sightings.
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    Environmental stress reduces shark residency to coral reefs
    Williamson, Michael J.; Tebbs, Emma J.; Curnick, David J.; Ferretti, Francesco; Carlisle, Aaron B.; Chapple, Taylor K.; Schallert, Robert J.; Tickler, David M.; Block, Barbara A.; Jacoby, David M. P. (Nature Portfolio, 2024-09-09)
    Coral reef ecosystems are highly threatened and can be extremely sensitive to the effects of climate change. Multiple shark species rely on coral reefs as important habitat and, as such, play a number of significant ecological roles in these ecosystems. How environmental stress impacts routine, site-attached reef shark behavior, remains relatively unexplored. Here, we combine 8 years of acoustic tracking data (2013-2020) from grey reef sharks resident to the remote coral reefs of the Chagos Archipelago in the Central Indian Ocean, with a satellite-based index of coral reef environmental stress exposure. We show that on average across the region, increased stress on the reefs significantly reduces grey reef shark residency, promoting more diffuse space use and increasing time away from shallow forereefs. Importantly, this impact has a lagged effect for up to 16 months. This may have important physiological and conservation consequences for reef sharks, as well as broader implications for reef ecosystem functioning. As climate change is predicted to increase environmental stress on coral reef ecosystems, understanding how site-attached predators respond to stress will be crucial for forecasting the functional significance of altering predator behavior and the potential impacts on conservation for both reef sharks and coral reefs themselves.
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    First satellite track of a juvenile shortfin mako shark (Isurus oxyrinchus) in the Mediterranean Sea
    Shea, Brendan D.; Chapple, Taylor K.; Echwikhi, Khaled; Gambardella, Chiara; Jenrette, Jeremy F.; Moro, Stefano; Schallert, Robert J.; Block, Barbara A.; Ferretti, Francesco (Frontiers, 2024-12-09)
    The shortfin mako shark (Isurus oxyrinchus) is a highly mobile, coastal littoral, and epipelagic oceanic species broadly distributed in tropical, subtropical, and temperate seas worldwide (Rigby et al., 2019). In recent years, there has been growing recognition of the impacts of overfishing on shortfin mako populations, and the species is now listed as Endangered by the International Union for the Conservation of Nature (IUCN) (Rigby et al., 2019). The species is listed as Critically Endangered in the Mediterranean Sea due to long-term and continuing exploitation coupled with inadequate management (Walls and Soldo, 2016). Of particular concern is the ongoing capture of juvenile mako sharks in the Central Mediterranean and the Strait of Sicily, which have been identified as potential nursery areas (Walls and Soldo, 2016; Cattano et al., 2023; Mancusi et al., 2023). Even with significant declines in pelagic sharks regionally (Ferretti et al., 2008), sharks continue to be occasionally targeted in the Mediterranean Sea, though the most critical risk to shark populations in the region is bycatch in other fisheries (Bradai et al., 2018; Carpentieri et al., 2021). In the Mediterranean, most fishers typically retain their shark bycatch, with some estimates of shark discard rates as low as 1% (Megalofonou et al., 2005) even for protected species, though discard rates are likely to vary by season and gear (Carpentieri et al., 2021). Despite their imperiled status, shortfin mako sharks remain one of the region’s commonly encountered sharks for fishers, especially for longlines (Carpentieri et al., 2021), and sharks are typically retained despite falling under regional protections such as the Bern Convention, Bonn Convention, and Barcelona Convention (Serena et al., 2014). Of additional concern is the relatively unmonitored recreational fishery, which may additionally encounter high numbers of shortfin mako sharks, many of Frontiers in which are retained, but the scale of this fishery is not well known (Udovičić et al., 2019; Panayiotou et al., 2020). Concerningly, young-of-the-year (YOY) and juvenile specimens comprise the bulk of captured individuals reported in the Mediterranean (Saidi et al., 2019; Udovičić et al., 2019; Panayiotou et al., 2020; Cattano et al., 2023; Mancusi et al., 2023; Scacco et al., 2023). Given the life history of shortfin mako sharks, particularly their advanced age at maturity (Natanson et al., 2020), this frequent and ongoing capture of juvenile sharks represents a severe threat to regional populations, as many sharks will never reach maturity, let alone successfully reproduce. These losses highlight the need for more detailed information regarding the movement patterns and space use of juvenile shortfin mako sharks, for which little is known in the Mediterranean. In recent years, a proliferation of telemetry studies has drastically improved our understanding of themovements and space use of large marine predators like shortfin mako sharks around the globe (Queiroz et al., 2019); however, virtually no study has focused on Mediterranean populations, especially sharks. Here, we report the satellite track from a pop-off archival tag (PAT) deployed on a juvenile shortfin mako shark in the Mediterranean Sea in May 2023. To our knowledge, this track represents the first satellite tag deployed on a shortfin mako shark in the Mediterranean Sea. We describe the horizontal and vertical movements the study shark performed over 54 days at liberty (DAL), discussing potential drivers for the observed movements and the implications of the track for the conservation of shortfin mako sharks regionally.
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    The importance of migratory connectivity for global ocean policy
    Dunn, Daniel C.; Harrison, Autumn-Lynn; Curtice, Corrie; DeLand, Sarah; Donnelly, Ben; Fujioka, Ei; Heywood, Eleanor; Kot, Connie Y.; Poulin, Sarah; Whitten, Meredith; Akesson, Susanne; Alberini, Amalia; Appeltans, Ward; Manuel Arcos, Jos; Bailey, Helen; Ballance, Lisa T.; Block, Barbara A.; Blondin, Hannah; Boustany, Andre M.; Brenner, Jorge; Catry, Paulo; Cejudo, Daniel; Cleary, Jesse; Corkeron, Peter; Costa, Daniel P.; Coyne, Michael; Crespo, Guillermo Ortuno; Davies, Tammy E.; Dias, Maria P.; Douvere, Fanny; Ferretti, Francesco; Formia, Angela; Freestone, David; Friedlaender, Ari S.; Frisch-Nwakanma, Heidrun; Frojan, Christopher Barrio; Gjerde, Kristina M.; Glowka, Lyle; Godley, Brendan J.; Gonzalez-Solis, Jacob; Granadeiro, Jose Pedro; Gunn, Vikki; Hashimoto, Yuriko; Hawkes, Lucy M.; Hays, Graeme C.; Hazin, Carolina; Jimenez, Jorge; Johnson, David E.; Luschi, Paolo; Maxwell, Sara M.; McClellan, Catherine; Modest, Michelle; di Sciara, Giuseppe Notarbartolo; Palacio, Alejandro Herrero; Palacios, Daniel M.; Pauly, Andrea; Rayner, Matt; Rees, Alan F.; Salazar, Erick Ross; Secor, David; Sequeira, Ana MM M.; Spalding, Mark; Spina, Fernando; Van Parijs, Sofie; Wallace, Bryan; Varo-Cruz, Nuria; Virtue, Melanie; Weimerskirch, Henri; Wilson, Laurie; Woodward, Bill; Halpin, Patrick N. (Royal Society, 2019-09-18)
    The distributions of migratory species in the ocean span local, national and international jurisdictions. Across these ecologically interconnected regions, migratory marine species interact with anthropogenic stressors throughout their lives. Migratory connectivity, the geographical linking of individuals and populations throughout their migratory cycles, influences how spatial and temporal dynamics of stressors affect migratory animals and scale up to influence population abundance, distribution and species persistence. Population declines of many migratory marine species have led to calls for connectivity knowledge, especially insights from animal tracking studies, to be more systematically and synthetically incorporated into decision-making. Inclusion of migratory connectivity in the design of conservation and management measures is critical to ensure they are appropriate for the level of risk associated with various degrees of connectivity. Three mechanisms exist to incorporate migratory connectivity into international marine policy which guides conservation implementation: site-selection criteria, network design criteria and policy recommendations. Here, we review the concept of migratory connectivity and its use in international policy, and describe the Migratory Connectivity in the Ocean system, a migratory connectivity evidence-base for the ocean. We propose that without such collaboration focused on migratory connectivity, efforts to effectively conserve these critical species across jurisdictions will have limited effect.
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    Shark fin trade bans and sustainable shark fisheries
    Ferretti, Francesco; Jacoby, David M. P.; Pfleger, Mariah O.; White, Timothy D.; Dent, Felix; Micheli, Fiorenza; Rosenberg, Andrew A.; Crowder, Larry B.; Block, Barbara A. (2020)
    The U.S. Congress is currently discussing the Shark Fin Sales Elimination Act to eliminate shark fin trade at the federal level. This bill was introduced in 2017 and has been proceeding very slowly in Congress because of mixed reviews from the scientific community. Debate exists on whether shark conservation and management are effectively addressed with tightened trade controls for imported shark products or blanket bans that outright end U.S. participation in the shark fin trade. Here we contribute to this debate with a review and analysis of economic, nutritional, ethical, and legal arguments, as well as of the shark fisheries status and shark fin trade. We show that the United States has a limited commercial interest in shark fisheries and contributes to the shark fin trade mainly as a facilitator. A fin trade ban has few tangible economic drawbacks but would have a considerable conservation impact. While making all shark fisheries sustainable is the ultimate goal, in practice this objective is far from achievable everywhere in the world. Conversely, banning shark fin trade is an interim measure that nations like the United States can take with negligible cost and can truly impact the biggest driver of shark exploitation globally.
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    Shark movement strategies influence poaching risk and can guide enforcement decisions in a large, remote marine protected area
    Jacoby, David M. P.; Ferretti, Francesco; Freeman, Robin; Carlisle, Aaron B.; Chapple, Taylor K.; Curnick, David J.; Dale, Jonathan J.; Schallert, Robert J.; Tickler, David; Block, Barbara A. (British Ecological Society, 2020-05-12)
    Large, remote marine protected areas (MPAs) containing both reef and pelagic habitats, have been shown to offer considerable refuge to populations of reef‐associated sharks. Many large MPAs are, however, impacted by illegal fishing activity conducted by unlicensed vessels. While enforcement of these reserves is often expensive, it would likely benefit from the integration of ecological data on the mobile animals they are designed to protect. Consequently, shark populations in some protected areas continue to decline, as they remain a prime target for illegal fishers. To understand shark movements and their vulnerability to illegal fishing, 3 years of acoustic tracking data, from 101 reef‐associated sharks, were analysed as movement networks to explore the predictability of movement patterns and identify key movement corridors within the British Indian Ocean Territory (BIOT) MPA. We examined how space use and connectivity overlap with spatially explicit risk of illegal fishing, through data obtained from the management consultancy enforcing the MPA. Using individual‐based models, the movement networks of two sympatric shark species were efficiently predicted with distance‐decay functions (>95% movements accurately predicted). Model outliers were used to highlight the locations with unexpectedly high movement rates where MPA enforcement patrols might most efficiently mitigate predator removal. Activity space estimates and network metrics illustrate that silvertip sharks were more dynamic, less resident and link larger components of the MPA than grey reef sharks. However, we show that this behaviour potentially enhances their exposure to illegal fishing activity. Synthesis and applications. Marine protected area (MPA) enforcement strategies are often limited by resources. The British Indian Ocean Territory MPA, one of the world's largest ‘no take’ MPAs, has a single patrol vessel to enforce 640,000 km2 of open ocean, atoll and reef ecosystems. We argue that to optimize the patrol vessel search strategy and thus enhance their protective capacity, ecological data on the space use and movements of desirable species, such as large‐bodied reef predators, must be incorporated into management plans. Here, we use electronic tracking data to evaluate how shark movement dynamics influence species mortality trajectories in exploited reef ecosystems. In doing so we discuss how network analyses of such data might be applied for protected area enforcement.