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Projeto de investigação
Understanding behavioural rules in movements of marine megafauna
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Residency and space use estimation methods based on passive acoustic telemetry data
Publication . Kraft, Sebastian; Gandra, Miguel; Lennox, R. J.; Mourier, J.; Winkler, Alexander; Abecasis, David
Acoustic telemetry has helped overcome many of the challenges faced when studying the movement ecology of aquatic species, allowing to obtain unprecedented amounts of data. This has made it into one of the most widely used methods nowadays. Many ways to analyse acoustic telemetry data have been made available and deciding on how to analyse the data requires considering the type of research objectives, relevant properties of the data (e.g., resolution, study design, equipment), habits of the study species, researcher experience, among others. To ease this decision process, here we showcase (1) some of the methods used to estimate pseudo-positions and positions from raw acoustic telemetry data, (2) methods to estimate residency and (3) methods to estimate two-dimensional home and occurrence range using geometric or hull-based methods and density-distribution methods, a network-based approach, and three-dimensional methods. We provide examples of some of these were tested using a sample of real data. With this we intend to provide the necessary background for the selection of the method(s) that better fit specific research objectives when using acoustic telemetry.
Movement patterns and connectivity of argyrosomus regius along the southwest coast of Portugal using network analysis
Publication . Fanna, Samuele; Gandra, Miguel; Kraft, Sebastian; Martínez Ramírez, Lucas; Vilas, Cesar; Winkler, Alexander; Abecasis, David
The meagre (Argyrosomus regius) is a large teleost inhabiting the coastal waters of the East Atlantic Ocean and the Mediterranean Sea. Along the Iberian Peninsula, it is frequently targeted by both commercial and recreational fisheries. Despite its relevance, information on its population structure and movement ecology has been scarce until recently. While these studies have provided a foundation, information on the main migratory corridors along the coast is still missing. The current study aimed to identify primary migratory routes, aggregations, and residency sites along the Southwest coast of Portugal. Forty-nine adult meagres were captured and tagged with acoustic transmitters between 2018 and 2023. Their movement was monitored from 122 acoustic receivers, grouped into 25 arrays, which were deployed throughout the Gulf of C´adiz and along the Southwest coast of Portugal. A spatial network approach was applied to analyse these data. The locations near the tagging site and along the Southwest coast displayed high values of eigenvector and betweenness centralities, indicating their crucial role in facilitating the connectivity of adult meagre between the two regions. Furthermore, co-occurrences outside the spawning season highlight their role as potential feeding grounds. The number of detections and co-occurrences near the Guadiana Estuary provides further evidence that the location may serve as a spawning ground, although additional data are needed to confirm this. Our findings expand previous research, identifying key passages and aggregation sites for meagre along the coast. These results can inform management and conservation efforts, particularly in the context of marine spatial planning.
Long-distance migrations and seasonal movements of meagre (Argyrosomus regius), a large coastal predator, along the Iberian Peninsula coast
Publication . Gandra, Miguel; Winkler, Alexander; Afonso, Pedro; Abecasis, David
Background The meagre, Argyrosomus regius, is a large coastal predatory fish inhabiting waters from the north-eastern Atlantic and Mediterranean Sea, where it is targeted by commercial and recreational fisheries. Previous genetic studies have found an unexpectedly high population differentiation not only between the Atlantic and the Mediterranean, but also along the Atlantic coast. However, the reasons underpinning this genetic barrier remained unclear. Likewise, even though the species is amongst the world’s largest marine teleosts, knowledge about its movement ecology and migratory behaviour remains notably scarce, and primarily reliant on fisheries-dependent data. Methods In this study, we used a combination of acoustic telemetry and pop-up satellite archival tags to investigate the movements of 22 adult meagre (70–143 cm total length) along the Southwestern coast of the Iberian Peninsula. Results Our results strongly suggest that the previously reported genetic differentiation is not maintained by limited adult dispersal/movement, as hypothesized. On the contrary, we documented some of the longest individual annual migrations ever recorded for a coastal teleost, up to >2000 km, with frequent back-and-forth movements between the West and Southern Iberian coasts. Moreover, their detected regional movement patterns support the existence of a marked seasonal behavioural shift, with individuals being less active and moving to deeper waters during winter, and are consistent with spawning philopatry associated to their summer reproductive movements. Finally, we identified putative aggregation areas that may harbour important feeding/overwintering grounds. Conclusions These findings shed new light on the movement and behaviour patterns of meagre that may be of particular importance for the conservation and spatial management of this species throughout its range, and open the door to further research on functional connectivity.
Long-term multitracking reveals contrasting yet highly resident movement ecologies of two sympatric and endangered deep-sea sharks
Publication . Gandra, Miguel; Fontes, Jorge; Macena, Bruno C.L.; Meyer, Carl G.; Afonso, Pedro
Studying shark movement ecology is vital for understanding their ecological roles and supporting sustainable management and conservation strategies. However, such information remains scarce for deep-sea sharks. We used biotelemetry to investigate the spatial behaviour and movements of two endangered deep-sea predators, the kitefin (Dalatias licha) and bluntnose sixgill (Hexanchus griseus) sharks, in the Azores, northern Mid-Atlantic Ridge. We tagged a total of 21 kitefin sharks with acoustic transmitters (some including depth sensors) and seven sixgill sharks with different tag configurations: three were fitted exclusively with acoustic transmitters, two were double-tagged with both acoustic transmitters and pop-up satellite archival tags (PSATs), and two were tagged exclusively with PSATs deployed via a speargun-equipped submersible. Both species exhibited diel vertical migrations and unexpected high site fidelity (up to 4 years), using habitats that inter-connect seamounts, slopes, and island shelves. Sixgill sharks exhibited more extensive and diverse individual home ranges and vertical diel activity patterns than kitefin sharks. Sexual segregation was evident in kitefin sharks, with males and females displaying distinct differences in depth distribution and habitat use, supporting earlier hypotheses based on fisheries data. These behavioural patterns suggest that sixgill sharks function as wide-ranging, deep-sea opportunistic foragers and predators, traversing interconnected habitats in search of prey – including kitefin sharks, which occupy a more slope-associated mesopredator niche. Our novel findings support ecological theory suggesting that deep-sea sharks exhibit far more contrasting spatial ecologies than previously thought, driven by their life histories. These differences may have implications for their high vulnerability to fisheries and climate change-induced habitat degradation.
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UI/BD/151309/2021