Visser Fleur

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Visser
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Fleur
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  • Article
    Dynamic biosonar adjustment strategies in deep-diving Risso's dolphins driven partly by prey evasion
    (Company of Biologists, 2019-12-10) Jensen, Frants H. ; Keller, Onno A. ; Tyack, Peter L. ; Visser, Fleur
    Toothed whales have evolved flexible biosonar systems to find, track and capture prey in diverse habitats. Delphinids, phocoenids and iniids adjust inter-click intervals and source levels gradually while approaching prey. In contrast, deep-diving beaked and sperm whales maintain relatively constant inter-click intervals and apparent output levels during the approach followed by a rapid transition into the foraging buzz, presumably to maintain a long-range acoustic scene in a multi-target environment. However, it remains unknown whether this rapid biosonar adjustment strategy is shared by delphinids foraging in deep waters. To test this, we investigated biosonar adjustments of a deep-diving delphinid, the Risso's dolphin (Grampus griseus). We analyzed inter-click interval and apparent output level adjustments recorded from sound recording tags to quantify in situ sensory adjustment during prey capture attempts. Risso's dolphins did not follow typical (20logR) biosonar adjustment patterns seen in shallow-water species, but instead maintained stable repetition rates and output levels up to the foraging buzz. Our results suggest that maintaining a long-range acoustic scene to exploit complex, multi-target prey layers is a common strategy amongst deep-diving toothed whales. Risso's dolphins transitioned rapidly into the foraging buzz just like beaked whales during most foraging attempts, but employed a more gradual biosonar adjustment in a subset (19%) of prey approaches. These were characterized by higher speeds and minimum specific acceleration, indicating higher prey capture efforts associated with evasive prey. Thus, tracking and capturing evasive prey using biosonar may require a more gradual switch between multi-target echolocation and single-target tracking.
  • Article
    Co-designing a multidisciplinary deep-ocean observing programme at the Mid-Atlantic Ridge in the Azores region: a blueprint for synergy in deep ocean research and conservation
    (Oxford University Press, 2022-11-02) Pachiadaki, Maria G. ; Janssen, Felix ; Carreiro-Silva, Marina ; Morato, Telmo ; Carreira, Gilberto P ; Frazão, Helena C ; Heimbach, Patrick ; Iglesias, Isabel ; Muller-Karger, Frank E ; Santos, Miguel M ; Smith, Leslie M ; Vardaro, Michael F ; Visser, Fleur ; Waniek, Joanna J ; Zinkann, Ann-Christine ; Colaço, Ana
    Under the umbrella of the Deep Ocean Observing Strategy (DOOS) and the All-Atlantic Ocean Observing System (AtlantOS), researchers at the Okeanos—University of the Azores, local stakeholders and authorities, and the deep ocean science community are adopting a co-design approach [which, as highlighted by the Global Ocean Observing System (GOOS), the co-design concept aims to combine the knowledge of diverse experts and stakeholders to create innovative approaches to meet stakeholder needs in ways beyond what could be achieved by any one of those involved working alone] to create a deep-ocean observation project to strengthen deep ocean observing capacities in accordance with users’ and societal needs. The demonstration project discussed below builds on decades of co-design in collaborative efforts in the Azores Archipelago between science, private entities, governmental institutions, and local authorities for science-based management (Santos et al., 1995). Already in the 1980s, several Marine Protected Areas (MPAs) that impose fishing limitations to promote the sustainable use of marine resources were established by this collaborative effort (Santos et al., 1995). During the 2000s, the joint effort between the Regional Government of the Azores and the University of the Azores resulted in the inclusion of 11 sites in the Oslo Paris Convention for the Protection of the North Atlantic (OSPAR; https://www.ospar.org/) MPAs’ network. This made Portugal, and particularly the Azores, a pioneer in the protection of marine biodiversity at an international level (Ribeiro, 2010), and an important progressive player in the ground-breaking OSPAR high-seas MPAs process (Abecasis et al., 2015).