RT info:eu-repo/semantics/doctoralThesis
T1 Acoustic studies of social coordination, trophic
ecology and habitat characterization of deepdiving cetaceans in the Canary islands
T2 Estudios acústicos de coordinación social, ecología trófica y caracterización del hábitat de cetáceos de buceo profundo en Canarias
A1 Alcázar Treviño, Jesús
A2 Grupo de Investigación BIOECOMACDepartamento de Biología Animal, Edafología y Geología. Universidad de La Laguna.
K1 beaked whales
K1 collective behaviour
K1 acoustic interference
K1 eavesdropping
K1 cooperative foraging
AB Sound is key for deep-diving cetaceans foraging at the twilight zone of great oceanic depths.Here, these predators use both their own active acoustic signals and passive monitoring toprobe their surroundings and to mediate biological functions from courtship to predator/prey detection. Thus, studying the bioacoustics of these soniferous animals and their acoustic environment can reveal relevant aspects of their biology and behaviour that cannot be directly observed, from the individual to the group and to their relation with their habitat. This thesis contributes knowledge about the behavioural ecology of deep diving whales and the acoustic characteristics of their deep-water habitat. This information is essential to understand theirlife requirements and thus basic to design measures towards the conservation management of their populations. This, in turn, repercutes in the conservation of the deep-water ecosystem, as deep diving odontoceti act as top-down regulators in oceanic trophic webs. Most biologging studies of deep-diving whales have described the behaviour of individuals, this thesis moves from the one to the group and to the habitat, addressing four main hypotheses and objectives: i) Group-living beaked whales are obligated vocalisers to forage by echolocation at depth. These sounds can attract acoustic guided predators such as killer whales. Beaked whales are defenceless if found as their small social units are not fitted for group defence from predators. Then, beaked whales should aim to reduce their detectability by killer whales. This was tested analysing animal-borne biologging data rendering observations of highly synchronized diving and vocal behaviour of groups of beaked whales and we modelled how this synchronization unavoidably reduces predation risk from orcas;ii) Synchronized vocalizations can generate interferences with conspecifics vocalising at thesame time, as well as render foraging benefits to individuals eavesdropping on the success ofother group members. We used beaked whales as model organisms to study cost-benefitbalance in acoustic social foragers, quantifying vocal rates of Blainville’s and Cuvier’s beaked whales while foraging, and the possible effects of group size on these rates. Results have inferences on evolutionary limitations to group size in beaked whales. Also, results areapplicable to improve the reliability of estimations of density of beaked whales from passive acoustic monitoring (PAM); iii) Deep-diving whales relate with other species in addition to their own. Species may compete, collaborate or ignore each other, and this will be dictated by their niche overlap and their behavioural characteristics. We studied foraging habitat overlap of five deep-diving odontoceti in the water column from epi- to meso-, bathy- and bentho- pelagic habitats; their foraging niche width (use of these layers) and its diel variation, and related the results with observations of agonistic encounters or spatial coexistence among studied species. In the last chapter the thesis moves from the whales to their habitat: iv) the mesopelagic realm and the migration of the Deep Scattering Layer (DSL) from meso- toepipelagic waters were found to be highly important for the five studied deep-diving species.Biomass estimations of mesopelagic fauna still differ within orders of magnitude and it wouldbe timely to improve these estimations towards ecosystem-based management of emergentproposals of fishing the DSL considering non-human predators. The thesis used PAM toinvestigate a potential acoustic signature of the migrating DSL indicated by an eveningchorus coincident with this migration. This was related with simultaneous active acousticdata in order to explore the possibility of estimating density of migrating DSL organismsfrom chorusing levels.The main methodological contributions of this thesis are the following:I. To gather and use biologging data from DTAGs (digital tags) deployments toquantify the coordination of dive profiles and acoustic behaviour of beaked whales living insocial groups and how this would reduce the probability of being detected by acoustic-guided predators such as orcas.II. To combine biologging data from DTAGs deployed singly and in pairs of whales within the same group and to analyse click and buzz rates, heading and depth data from acoustic recordings and orientation sensors (i.e., magnetometers and accelerometers) toinvestigate potential trade-offs of sociality for extreme deep-diving Blainville`s and Cuvier’sbeaked whales i.e., acoustic interference and eavesdropping, cooperative foraging orcompetition for prey. III. To estimate the vertical foraging habitat overlap and segregation between fivespecies of deep diving odontocetes by combining biologging data, i.e., the analysis offoraging depth and altitude above the seafloor, with stomach content data from the bibliography and adapting foraging niche index equations to study the foraging habitat, i.e., Levin’s and Pianka’s indexes of foraging niche width and overlap, respectively.IV. The simultaneous use of active and passive acoustic instruments to sample the water column in the open ocean to characterize an evening chorus and relate it to the dielvertical migration of part of the DSL. The main scientific contributions of this thesis are:I. Analysing biologging data from Blainville’s and Cuvier’s beaked whales (14 and12 tagged whales, respectively), we showed that these animals overlap foraging times by98% with group members and perform a coordinated and silent ascent after foraging at great depths, in unpredictable direction and covering a mean of 1 km from their last vocal position. The highly synchronised and stereotypical diving and acoustic behaviour of groups of beaked whales can be explained by the evolution of behaviour in a soundscape of fear of predation.However, this successful predator-abatement strategy has turned partly maladaptive in theAnthropocene, when naval sonar induced extreme responses lead to mass strandings ofbeaked whales.II. DTAG data from deployments on 16 Blainville’s and 10 Cuvier’s beaked whalesoff the Canary Islands and Ligurian Sea shows that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. Thisenables whales to coordinate their mean travel direction despite differing individual instantaneous headings as they pursue prey on a minute-by-minute basis. While beakedwhales coordinate their echolocation-based foraging periods tightly, individual click andbuzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.III. This thesis analysed 81 DTAG deployments in subtropical to warm temperate waters on adult whales of five deep-diving species: 16 Blainville’s (Md) and 10 Cuvier’s (Zc) beaked whales, 27 short-finned pilot whales (Gm), 12 Risso’s dolphins (Gg) and 16 sperm (Pm) whales. Pianka’s Index values of niche overlap varied for all pairs of species between day and night due to differences in the adaptations of each species to the nictemeral migration of the DSL. Values were high (>0.9) during the day among Md, Zc, Gm and Pm because they all foraged mainly within the mesopelagic realm (between 200-1000 m depth).Values were lower (0.5 to 0.8) during the night as Zc shifted to the bathypelagic. Gg had lowoverlap with all the others but overlapped with Gm only at night, when both exploited theupwards migration of the DSL to forage in the epipelagic (0-200 m). This did not occur forany of the other species. All the species preyed on benthopelagic resources (at < 100 m ofthe seafloor), but this was less important for Gm (6 & 0% for day and night, respectively)than for the others (5-31% overall). Niche overlap can contribute to explain observations of agonistic behaviours of Gm and Gg towards Pm. These species can be territorial thanks totheir numerous groups. In contrast, Md and Zc can coexist in the same area in spite of highniche overlap, probably because their small groups do not support territorial confrontationswith other species. Thus, bevioural ecology can help to understand the distribution of thesedeep-diving apex predators. The reliance of all species on meso- and benthopelagic resourcesindicates that bottom-trawling, deep-sea mining and DSL fisheries can pose threats to these protected apex predators of the deep ocean.IV. The report for the first time in the Atlantic Ocean of an evening chorus similar tofindings in the Pacific and Indian oceans. The chorus occurs concurrently with the upwardsmigration of the DSL at dusk. Moreover, the maximum received level of the chorus ispositively correlated with the acoustic backscatter of DSL organisms that migrate from mesopelagic to epipelagic depths at dusk. We conclude that mesopelagic fish are most likely responsible for the chorusing event by degasification during the ascent. Measures of chorus levels could provide estimates of the abundance of mesopelagic organisms, some of them targeted by apex predators such as deep-diving cetaceans.
YR 2021
FD 2021
LK http://riull.ull.es/xmlui/handle/915/34689
UL http://riull.ull.es/xmlui/handle/915/34689
LA en
NO Tesis Doctoral, Jesús Alcázar Treviño
DS Repositorio institucional de la Universidad de La Laguna
RD 15-may-2024