E-Thesis 208 views 56 downloads
Bimodality in depth use by sharks reflects bimodality in behaviour - a case study with Whale Sharks (Rhincodon typus) / SIENA MCQUADE
Swansea University Author: SIENA MCQUADE
Abstract
Movement (body translocation) is a fundamental aspect of life for many animals and tends to have a clear purpose that enhances lifetime reproductive success. Obligate ram-ventilated sharks must move continuously to respire, making their patterns of movement less defined by clear behaviours. Among ot...
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Swansea, Wales, UK
2023
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MRes |
| Supervisor: | Wilson, Rory P. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa63273 |
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| Abstract: |
Movement (body translocation) is a fundamental aspect of life for many animals and tends to have a clear purpose that enhances lifetime reproductive success. Obligate ram-ventilated sharks must move continuously to respire, making their patterns of movement less defined by clear behaviours. Among other functions, sharks must feed and behaviourally regulate their body temperature, and their position in the water column can play a key role in both. Sharks display bimodality in their use of depth, either ‘surface swimming’ or ‘diving’ (term used to encompass all behaviour below the surface), and this study aims to examine how these modes differ in functionality and costs for whale sharks (Rhincodon typus). Analysis of data from animal-attached tags recording acceleration, heading, temperature and depth from 20 animals indicated that the two modes were distinct in energetic costs and amount of time allocated to them. Surface swimming was more tortuous and required significantly more energy than diving, and diving accounted for a greater proportion of time (on average 65%) and feeding events. The allocation of time to each mode varied between day and night, with personality thought to play a role since individuals differed significantly. This study refutes the common assumption that surface swimming is entirely a thermoregulatory behaviour since depth and temperature were not correlated, yet bimodality was still shown. It also highlights a gap in our understanding of whale shark behaviour, since they perform energy expensive, tortuous movements even when not feeding – a behaviour that is not often discussed in the literature. Although surface swimming and diving have broadly similar functions in whale sharks, systematic differences in behaviour metrics imply that there are subtle behaviour differences between the two modes. We also highlight the need for a novel focus on the behavioural plasticity between individuals and different populations, considering the factors that contribute to behavioural variations. |
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| Keywords: |
Tortuosity, Energy efficiency, Feeding, Biologging, Vertical velocity |
| College: |
Faculty of Science and Engineering |