Percorrer por autor "Visser, Fleur"
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- Context-driven communication during deep-sea foraging in a social toothed whalePublication . Hessing, Sanne; Risser, Nolwenn Morgane; Pichot, Loanne; Oudejans, Machiel G; Guilpin, Marie; Barcelos, Luis M. D.; Curé, Charlotte; Visser, FleurSocial deep-diving odontocetes face the challenge of balancing near-surface proximity to oxygen and group members with foraging in the deep sea. Individuals rely on conspecifics for critical life functions, such as predator defence, but disperse during foraging to feed individually. To understand the role of social acoustic mediation during foraging in deep-diving toothed whales, we investigated the context of social burst-pulse call production in Risso’s dolphin (Grampus griseus) using biologgers. Dolphins produced context-specific burst pulses predominantly during daytime foraging, preceding or following foraging dives and in the early descent of daytime deep dives. Individuals applied differential short and long burst-pulse calls intended for either near-surface receivers (horizontal transmission) or deep-foraging receivers (vertical transmission). Our results show that deep-diving toothed whales are reliant on acoustic communication during certain foraging contexts, to relay information including foraging conditions or an individual’s location. Moreover, they accentuate the importance of maintaining acoustic contact with conspecifics, specifically when dispersed during deeper foraging. It also signifies that our oceanic top predators may be specifically vulnerable to the current strong increase in anthropogenic noise. Potential masking of the signals from group members communicating at a distance could undermine their social cohesion, and hence their capacity to maintain vital life functions.
- The Deep-Sea Preyscapes of Mammalian Top PredatorsPublication . Merten, Véronique; Guilpin, Marie; Parker, Julia; Oudejans, Machiel; Dolan, Shannon; Baumann-Pickering, Simone; Hazen, Elliott; Barcelos, Luís; Guerreiro, Miguel Fernandes; Porteiro, Filipe; Franzenburg, Sören; Bayer, Till; Hoving, Henk-Jan; Visser, FleurPrey richness, accessibility, and density shape predator foraging strategies. Deep-sea preyscapes, however, remain largely unknown, limiting our understanding of how prey presence and distribution shape predator movement, energy budget, and ecological role. Using combined eDNA metabarcoding and hydroacoustics, we investigated the deep-sea cephalopod and fish preyscapes of three co-occurring cetacean predators (Risso's dolphins (Grampus griseus), Sowerby's beaked whales (Mesoplodon bidens), and goose-beaked whales (Ziphius cavirostris)) across an inshore-offshore gradient. We tested whether (i) prey acoustic backscatter (a metric for density) and taxonomic richness decreased with distance from shore; (ii) predators exploit localized peaks in prey density and richness; and (iii) prey composition and density varied across adjacent foraging habitats along the inshore-offshore gradient. Across 117 samples, we detected 37 cephalopod and 66 fish taxa, including other top predators (sharks). Acoustic backscatter was concentrated within the deep scattering layer (DSL). Yet, peak taxonomic richness occurred above and below it, suggesting that the local DSL holds relatively limited fish and cephalopod richness. The offshore DSLs were vertically shallower and more stable, while the inshore DSL was deeper and bifurcated, possibly due to predator avoidance. Contrary to expectation, acoustic backscatter offshore was up to fivefold higher than inshore, and taxonomic richness did not decrease with distance from shore. Fish communities varied primarily with depth, whereas cephalopod communities varied along the inshore-offshore gradient. Bathypelagic offshore foraging zones of goose-beaked whales contained overall low acoustic backscatter but high taxonomic richness. This suggests that goose-beaked whales may target large, energy-rich cephalopods and prioritize prey quality over density. Our results reveal vertical and horizontal habitat complexity in an oceanic ecosystem that may shape predator–prey interactions and habitat partitioning among cetacean species.
- Temporal residency patterns of Risso's dolphins, Grampus griseus, off Pico Island, AzoresPublication . Hartman, Karin L.; Geelhoed, Steve C. V.; Visser, Fleur; Azevedo, José M. N.Temporal residency patterns of Risso's dolphins, Grampus griseus, occurring off Pico Island, Azores archipelago, were studied by conducting photoidentification surveys during 25 sampling months (May 2004-January 2007). A total of 1102 dolphins was identified, of which a restricted population (n= 996) was further analyzed. Temporal residency patterns were classified using year, season and monthly presence, and defined in three groups: non resident, partial resident and resident. Risso's dolphins were present in the research area in all seasons and all years. The seasonally parameter (4 seasons sighted) resulted in the highest percentage of residents (17%, n = 173). Age-classes and sexes showed different temporal residency patterns. Residents consisted largely of adult males and sub-adults, and were present in the research area throughout the sampling period. Partial and resident females were less frequently sighted, but showed a resident pattern when calving and nursing. The presence and number of old resident females strongly decreased. A calving peak was found in summer. Together with the existence of a resident population, this indicates that Pico is functioning as a critical habitat for Risso's dolphins occurring off Pico Island, was set up in 2000 by the Nova Atlantis Foundation. The aim of the present study was to obtain information on the residency pattern of Risso’s dolphins around Pico Island.